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in The Impact of Large Scale Near - IR surveys
... The Two Micron All Sky Survey (2MASS; Skrutskie et al. 1997 ) and Sloan Digital Sky Survey (SDSS; York et al. 2000) are fertile grounds for identifying rare stellar objects with unusual colors , such as brown dwarfs (Kirkpatrick et al. 1999; Strauss et al. 1999; Burgasser et al. 1999), carbon stars (Margon et al. 2002), RR Lyrae stars (Ivezi´cIvezi´c et al. 2005), and white dwarf/M dwarf pairs (Raymond et al. 2003; Smolči´Smolči´c et al. 2004; Silvestri et al. 2006 ). Relatively little attention has been devoted to understanding and documenting the detailed characteristics of 'normal' main-sequence stars detected in these surveys, despite the fact that they represent an important source of contamination in the search for any set of rare objects. ...
... The SDSS camera (Gunn et al. 1998), populated by six CCDs in each of five filters (u, g, r, i, z; Fukugita et al. 1996) observes in time delay and integrate (TDI) mode to generate near-simultaneous photometry along a strip 2.5 degrees in width; a second scan, slightly offset from the first, fills in the areas on the sky that fall in the gaps between CCDs. The survey's photometric calibration strategy (Hogg et al. 2001; Smith et al. 2002; Tucker et al. 2006) produces a final catalog which is 95% complete to a depth of r ∼ 22.2, and accurate to 0.02 mags (both absolute and RMS error) for sources not limited by Poisson statistics (Ivezi´cIvezi´c et al. 2004). Sources with r < 20.5 have astrometric errors less than 0.1 ′′ per coordinate (rms ; Pier et al. 2003), and robust star/galaxy separation is achieved above r ∼ 21.5 (Lupton et al. 2001). ...
... The Two Micron All Sky Survey used two 1.3 m telescopes to survey the entire sky in near–infrared light 8 (Skrutskie et al. 1997; Cutri et al. 2003 ). Each telescope's camera was equipped with three 256 × 256 arrays of HgCdTe detectors with 2 ′′ pixels and observed simultaneously in the J (1.25 µm), H (1.65 µm), and K s (2.17 µm) bands. ...
The Sloan Digital Sky Survey (SDSS) and Two Micron All Sky Survey (2MASS) are rich resources for studying stellar astrophysics and the structure and formation history of the Galaxy. As new surveys and instruments adopt similar filter sets, it is increasingly important to understand the properties of the ugrizJHKs stellar locus, both to inform studies of "normal" main-sequence stars and enable robust searches for point sources with unusual colors. Using a sample of ~600,000 point sources detected by SDSS and 2MASS, we tabulate the position and width of the ugrizJHKs stellar locus as a function of g - i color, and provide accurate polynomial fits. We map the Morgan-Keenan spectral type sequence to the median stellar locus by using synthetic photometry of spectral standards and by analyzing 3000 SDSS stellar spectra with a custom spectral typing pipeline, described in the Appendix to this paper. We develop an algorithm to calculate a point source's minimum separation from the stellar locus in a seven-dimensional color space, and use it to robustly identify objects with unusual colors, as well as spurious SDSS/2MASS matches. Analysis of a final catalog of 2117 color outliers identifies 370 white-dwarf/M dwarf (WDMD) pairs, 93 QSOs, and 90 M giant/carbon star candidates, and demonstrates that WDMD pairs and QSOs can be distinguished on the basis of their J - Ks and r - z colors. We also identify a group of objects with correlated offsets in the u - g versus g - r and g - r versus r - i color-color spaces, but subsequent follow-up is required to reveal the nature of these objects. Future applications of this algorithm to a matched SDSS-UKIDSS catalog may well identify additional classes of objects with unusual colors by probing new areas of color-magnitude space.
... SDSS footprint is discussed below). The IR flux in the J, H, and K band is measured from images of 2MASS ( Skrutskie et al. 1997;Jarrett et al. 2000) using a circular aperture with a radius equal to the 90% light radius in r-band. When available, we substitute the 2MASS images with UKIDSS images ( Lawrence et al. 2007;Hambly et al. 2008) since the latter provide a better signal to noise ratio. ...
... • , with p ∼ 1 (Mineshige & Shields 1990;Siemiginowska & Elvis 1997). The increased waittime and longer flare duration reduce the rate of detected AGN flares from massive black holes, potentially explaining the lack of TDF candidates at high mass. ...
The tidal disruption of a star by a massive black hole is expected to yield a luminous flare of thermal emission. About two dozen of these stellar tidal disruption flares (TDFs) may have been detected in optical transient surveys. However, explaining the observed properties of these events within the tidal disruption paradigm is not yet possible. This theoretical ambiguity has led some authors to suggest that optical TDFs are due to a different process, such as a nuclear supernova or accretion disk instabilities. Here we present a test of a fundamental prediction of the tidal disruption event scenario: a suppression of the flare rate due to the direct capture of stars by the black hole. Using a recently compiled sample of candidate TDFs with black hole mass measurements, plus a careful treatment of selection effects in this flux-limited sample, we confirm that the dearth of observed TDFs from high-mass black holes is statistically significant. All the TDF impostor models we consider fail to explain the observed mass function; the only scenario that fits the data is a suppression of the rate due to direct captures. We find that this suppression can explain the low volumetric rate of the luminous TDF candidate ASASSN-15lh, thus providing new evidence that this flare belongs to the TDF family. Our work is the first to present the optical TDF luminosity function. A steep power-law is required to explain the observed rest-frame g-band luminosity, $dN/dL \propto L^{-2.5}$. Integrating over this power-law yields a mean rate of about $1 \times 10^{-4}$ per galaxy per year, consistent with the theoretically expected tidal disruption rate.
... The DENIS mini-survey project (Delfosse et al. 1997; Delfosse, Tinney & Forveille 1997) has begun this search by observing brown dwarf candidates from the first ∼1% (230 • ) of the initial DENIS data. Infrared spectroscopy obtained on the 3.9m Anglo-Australian Telescope (AAT) confirmed that at least three of the mini-survey objects were as cool, or cooler than, GD 165B (Delfosse et al. 1997). Optical spectroscopy was obtained with the AAT on 1997 June 7-9 (UT), using the RGO Spectrograph with TEK 1K CCD#2. ...
... a Positions for the DENIS objects are from Delfosse et al. 1997 ...
... The discovery of the brown dwarf Gl 229B (Nakajima et al. 1995) heralded a stream of direct detections of sub-stellar objects. Field surveys such as the Two Micron All-Sky Survey (2MASS; Skrutskie et al. 1997), the Deep Near Infrared Survey (DENIS; Epchtein et al. 1997), and the Sloan Digital Sky Survey (SDSS; Gunn and Weinberg 1995) helped raise the number of brown dwarf identifications today to close to a thousand. But despite these advances, the search for brown dwarf companions at intermediate and narrow separations (say less than a few arcseconds) to main sequence stars remains difficult. ...
... In Section 5 we discuss how we may generate limiting – 8 – magnitudes and brown dwarf mass limits from these algorithm-generated noise maps. In cases where we positively identified a potential brown dwarf companion to a parent star, we next estimated its apparent K s magnitude, using the non-coronagraphed calibration images of the parent star and published 2MASS K-magnitudes (Skrutskie et al. 1997 ). Resulting magnitudes are displayed inTable 2. Once we established an apparent K s magnitude, we derived a corresponding absolute K s magnitude, assuming the candidate had a distance equal to the parent system. ...
In this first of a two-paper sequence, we report techniques and results of the Cornell High-Order Adaptive Optics Survey (CHAOS) for brown dwarf companions. At the time of this writing, this study represents the most sensitive published population survey of brown dwarf companions to main-sequence stars for separations akin to our own outer solar system. The survey, conducted using the Palomar 200 inch (5 m) Hale Telescope, consists of Ks coronagraphic observations of 80 main-sequence stars out to 22 pc. At 1" separation from a typical target system, the survey achieves median sensitivities 10 mag fainter than the parent star. In terms of companion mass, the survey achieves typical sensitivities of 25MJ (1 Gyr), 50MJ (solar age), and 60MJ (10 Gyr), using the evolutionary models of Baraffe and coworkers. Using common proper motion to distinguish companions from field stars, we find that no systems show positive evidence of a substellar companion (searchable separation ~1"-15" projected separation ~10-155 AU at the median target distance). In the second paper of the series we will present our Monte Carlo population simulations.
... By far the largest near-IR survey to date is the Two Micron All Sky Survey (2MASS, Skrutskie et al. 1997 ). There have already been several studies of the different AGN populations within 2MASS. ...
... Cutri et al. (2002) have shown that 2MASS sources with extremely red near-IR colors (J − K s > 2) are mostly an unusual type of Type-1 AGN (Smith et al. 2002; Wilkes et al. 2002 ). K s is a filter similar to K but cutting off at a shorter red wavelength to minimize thermal emission (Skrutskie et al. 1997). Barkhouse & Hall (2001) have studied the 2MASS colors of QSOs identified at other wavelengths, and Gregg et al. (2002) identified some very unusual and dusty QSOs by cross-correlating the 2MASS database with a radio sample. ...
We present an unbiased near-IR-selected AGN sample, covering 12.56 deg2 down to Ks~15.5, selected from the Two Micron All Sky Survey (2MASS). Our only selection effect is a moderate color cut (J-Ks>1.2) designed to reduce contamination from Galactic stars. We observed both pointlike and extended sources. Using the brute-force capabilities of the Two Degree Field multifiber spectrograph on the Anglo-Australian Telescope, we obtained spectra of 65% of the target list: an unbiased subsample of 1526 sources. Eighty percent of the 2MASS sources in our fields are galaxies, with a median redshift of 0.15. The remainder are K and M dwarf stars. We find tentative evidence that Seyfert 2 nuclei are more common in our IR-selected survey than in blue-selected galaxy surveys. We estimate that 5.1+/-0.7% of the galaxies have Seyfert 2 nuclei with Halpha equivalent widths greater than 0.4 nm, measured over a spectroscopic aperture of radius ~2.5 kpc. Blue-selected galaxy samples only find Seyfert 2 nuclei meeting these criteria in ~1.5% of galaxies. We find that 1.2+/-0.3% of our sources are broadline (type 1) AGNs, giving a surface density of 1.0+/-0.3 deg2, down to Ks
... To strengthen the continuum reddening determinations in §4, we complement the SDSS spectra with data from the 2 Micron All Sky Survey (2MASS; Skrutskie et al. 1997). These IR data provide a longer baseline for the reddening determinations. ...
We conduct a spectroscopic search of quasars observed by the Sloan Digital
Sky Survey (SDSS) with broad absorption line (BAL) troughs due to Mg II and
troughs due to Fe II that simultaneously exhibit strong Balmer narrow emission
lines (NELs). We find that in a redshift range of 0.4 less than or equal to z
less than or equal to 0.9 approximately 23 of the 70 Mg II BALs and 4 of a
subset of 15 Fe II BALs exhibit strong Balmer emission. We also find
significant fractions of Mg II BALs (approximately 23%) and those Mg II BALs
with Fe II troughs (approximately 27%) have strong continuum reddening, E(B -
V) greater than or equal to 0.1. From measurements of the Balmer decrement in
three objects, we find similarly significant reddening of the NEL region in
three of the four objects; the NELs in the fourth object are not measurable. We
also include one object in this study not taken from the SDSS sample that shows
Fe II absorption and strong narrow emission, but due to measurement uncertainty
and low continuum reddening the comparison is consistent but inconclusive. We
find a trend in both the Mg II and Fe II BAL samples between the NEL reddening
and continuum reddening. Because the narrow line reddening is consistent with
the continuum reddening in every object in the two SDSS samples, it suggests
that the reddening sources in these objects likely exist at larger radial
distances than the narrow line regions from the central nucleus.
... Thanks to the Two Micron All Sky Survey (2MASS; Skrutskie et al. 1997) the astronomical community now has J, H, and K s magnitudes for almost all the brighter stars of the Magellanic Clouds and a number of nearby galaxies, since their [signal-to-noise ratio (S/N) of 10] magnitude limits are, respectively, 16.3, 15.3, and 14.7. These observations are particularly suitable to investigate the red giant branch and asymptotic giant branch (AGB) populations of nearby galaxies. ...
We matched spectroscopically identified C stars (from low-resolution objective prism surveys) in the Magellanic Clouds with Two Micron All Sky Survey (2MASS) sources. We confirm that C stars show a large spread in absolute magnitudes, even in the Ks band. We show that the I and Ks magnitude distributions of a population of C stars (in the LMC) have a similar narrow dispersion if the C stars are selected in a well-defined color range. Using magnitude and color criteria, we employ the 2MASS data to identify 26 C stars in the Fornax dwarf spheroidal galaxy. The mean Ks magnitude and the mean bolometric magnitude of C stars are found to be slightly brighter in the LMC and SMC when compared with those of the Fornax dwarf spheroidal galaxy. The difference could be explained by ages and/or abundance differences.
... The Two-Micron All Sky Survey (2MASS, Skrutskie et al. 1997) has scanned the regions of the sky containing six of the objects inTable 2, including the M dwarf. The corresponding 2MASS objects and their J, H and K s magnitudes are listed inTable 4. ...
This paper describes the discovery of seven dwarf objects of spectral type `L' (objects cooler than the latest M dwarfs) in commissioning imaging data taken by the Sloan Digital Sky Survey (SDSS). Low-resolution spectroscopy shows that these objects have spectral types from L0 to L8. Comparison of the SDSS and 2MASS photometry for several of these objects indicates the presence of significant opacity at optical wavelengths, perhaps due to atmospheric dust. This comparison also demonstrates the high astrometric accuracy (better than 1'' for these faint sources) of both surveys. The L dwarfs are shown to occupy a distinctive region of color-color space as measured in the SDSS filters, which should enable their identification in a straightforward way. This should lead eventually to a complete sample of many hundreds of these low mass objects, or about one per 15 square degrees to i'~20, in the complete SDSS data set. Comment: 22 Pages Latex with embedded figures, submitted to AJ. Also available at http://www.astro.princeton.edu/~strauss/sdss/ldwarf.ps (with high-resolution figures)
... The spectroscopic catalogs are complete in the near-infrared to absolute magnitude M Ks = −22.7+5logh using photometry from 2MASS, the Two-Micron All-Sky Survey (Skrutskie et al. 1997). This limit is approximately one magnitude fainter than M * Ks , the characteristic magnitude of the luminosity function averaged over all environments (Cole et al. 2001; Rines et al. 2004). ...
We investigate the environmental dependence of star formation in cluster virial regions and infall regions as part of the Cluster and Infall Region Nearby Survey (CAIRNS), a large spectroscopic survey of the infall regions surrounding nine nearby rich clusters of galaxies. We use complete, homogeneous spectroscopic surveys of Ks-limited samples in eight of the CAIRNS clusters. Our long-slit spectroscopy yields estimates of star formation rates in environments from cluster cores to the general large-scale structure. Galaxies in infall regions probe whether processes affecting star formation are effective over scales larger than cluster virial regions. The fraction of galaxies with current star formation in their inner disks as traced by Halpha emission increases with distance from the cluster and converges to the ``field'' value only at 2-3 virial radii, in agreement with other investigations. However, among galaxies with significant current star formation (EW[Halpha]>=2 Å), there is no difference in the distribution of EW[Halpha] inside and outside the virial radius. This surprising result, first seen by Carter and coworkers, suggests that (1) star formation is truncated either on very short timescales or only at moderate and high redshifts or (2) that projection effects contaminate the measurement. We quantify the possible impact of mechanisms that only affect the outer parts of galaxies and thus might not be detected in this survey or any fiber-based survey. The number density profiles of star-forming and non-star-forming galaxies indicate that, among galaxies projected inside the virial radius, at least half the former and 20% of the latter are ``infall interlopers,'' galaxies in the infall region but outside the virial region. We show that the kinematics of star-forming galaxies in the infall region closely match those of absorption-dominated galaxies. This result shows that the star-forming galaxies in the infall regions are not interlopers from the field and excludes one model of the backsplash scenario of galaxy transformation. Finally, we quantify systematic uncertainties in estimating the global star formation in galaxies from their inner disks.
... Recent past has seen several NIR surveys, i.e. DENIS(Epchtein et a1 1997), 2MASS (Skrutskie et a1 1997), etc, which, however, either lack depth or suffer from confusion due to high source densities in these regions. Also, the J band data in DENIS is undersampled in this region of high extinction. ...
Inner 300 pc of the Galactic Center region is surveyed with the SIR-IUS camera mounted on the InfraRed Survey Facility (IRSF) telescope of the SAAO, during June-July 2002, resulting in the deepest near infrared view of the Milky Way Nuclear Bulge Region. Here we present first results from this survey underlining the capabilities of the SIRIUS camera and the photometric procedures adopted in this work involving highly crowded star fields.
... The procedure used to derive T eff estimates for HE 2148À1247 is fully explained in xx 4–6 of Cohen et al. (2002). Very briefly, T eff is derived from broadband colors, taking the mean estimates deduced from the dereddened VÀK and VÀJ colors, where the infrared colors are from 2MASS (Skrutskie et al. 1997). Measurements on both the 1.5 m telescope at Palomar Mountain and on the Swope Telescope at the Las Campanas Observatory yield B ¼ 15:233 AE 0:015, V ¼ 14:780 AE 0:023 mag for HE 2148À 1247. ...
Abundances for 27 elements in the very metal-poor dwarf star HE 2148-1247 are presented, including many of the neutron capture elements. We establish that HE 2148-1247 is a very highly s-process-enhanced star with anomalously high Eu as well, Eu/H ~ half-solar, demonstrating the large addition of heavy nuclei at [Fe/H] = -2.3 dex. Ba and La are enhanced by a somewhat larger factor and reach the solar abundance, while Pb significantly exceeds it, thus demonstrating the addition of substantial s-process material. Ba/Eu is 10 times the solar r-process ratio but much less than that of the s-process, indicating a substantial r-process addition as well. C and N are also very highly enhanced. We have found that HE 2148-1247 is a radial velocity variable; it is probably a small-amplitude long-period binary. The C, N, and the s-process element enhancements were thus presumably produced through mass transfer from a former asymptotic giant branch (AGB) binary companion. The large enhancement of heavy r-nuclides also requires an additional source as this is far above any inventory in the interstellar medium at such low [Fe/H]. We consider that the s-process material was added by mass transfer of a more massive companion during its thermally pulsating AGB phase and ending up as a white dwarf. We further hypothesize that accretion onto the white dwarf from the envelope of the star caused accretion-induced collapse of the white dwarf, forming a neutron star, which then produced heavy r-nuclides and again contaminated its companion. This mechanism in a binary system can thus enhance the envelope of the lower mass star in s- and r-process material sequentially. Through analysis of the neutron capture element abundances taken from the literature for a large sample of very metal-poor stars, we demonstrate, as exemplified by HE 2148-1247, that mass transfer in a suitable binary can be very efficient in enhancing the heavy elements in a star; it appears to be capable of enhancing the s-process elements in very metal-poor stars to near the solar abundance but not substantially above it. The yield of Pb relative to Ba appears to vary among very metal-poor stars. Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.
... In fact, however, distinguishing the later-type dwarfs from the much more numerous giants of similar colors is straightforward. As shown by Gould & Morgan (2003), they can easily be identified on a reduced proper motion (RPM) diagram constructed using data from USNO-A (Monet 1996Monet , 1998) and 2MASS (Skrutskie et al. 1997). With USNO-B (Monet et al. 2002) it should be possible to extend coverage to fainter magnitudes and to achieve higher precision as well. ...
Photon-limited transit surveys in the V band are in principle about 20 times more sensitive to planets of fixed size in the habitable zone around M stars than G stars. In the I band the ratio is about 400. The advantages of a closer habitable zone and smaller stars (together with the numerical superiority of M stars) more than compensate for the reduced signal because of the lower luminosity of the later-type stars. That is, M stars can yield reliable transit detections at much fainter apparent magnitudes than G stars. However, to achieve this greater sensitivity, the later-type stars must be monitored to these correspondingly fainter magnitudes, which can engender several practical problems. We show that with modest modifications, the Kepler mission could extend its effective sensitivity from its current MV=6 to 9. This would not capture the whole M dwarf peak but would roughly triple its sensitivity to Earth-like planets in the habitable zone. To take advantage of the huge bump in the sensitivity function at MV=12 would require major changes in Kepler. However, the reduced photometric-precision requirements at MV=12 makes a search for these transits possible from the ground. Photometric stability requirements are much less severe for M stars than G stars. To detect Earth-mass planets in the habitable zone around G stars, the variability on transit timescales must be less than 2×10-5, but for middle M stars the limit is 1.2×10-3.
... Ground-based observations at those wavelengths have to cope with strong absorption features due to water and CO 2 in the terrestial atmosphere, but broadband photometry through the atmospheric windows at 1.25µm (J), 1.6µm (H), 2.2µm (K) and 3.5 µm (L) has been available for M dwarfs for over three decades. Recent large-scale surveys, notably 2MASS (Skrutskie et al., 1997), provide extensive JHK data for the even cooler L and T dwarfs. Narrowband spectrophotometry from 1 to 2.5µm, extending through terrestial water bands, was obtained for a handful of M dwarfs by Reid & Gilmore (1984), and extended to 3.5µm for a subset of those stars by Berriman & Reid (1987). ...
We present narrowband M photometry of nine low-mass dwarfs with spectral types ranging from M2.5 to L0.5. Combining the (L'-M') colors derived from our observations with data from the literature, we find colors consistent with a Rayleigh-Jeans flux distribution for spectral types earlier than M5, but enhanced F3.8/F4.7 flux ratios (negative [L'-M'] colors) at later spectral types. This probably reflects increased absorption at M' due to the CO fundamental band. We compare our results against recent model predictions and briefly discuss the implications.
... The Two Micron All Sky Survey (2MASS, Strutskie et al. 1997) began imaging the sky in 1997 using two 1.3 meter telescopes at Mt. Hopkins, Az, and CTIO, Chile. The final release has covered 95% of the sky in three near-infrared wavebands: J(1.25µm), H(1.65µm), and K s (2.17µm). ...
We have constructed a sample of bright near-infrared sources which are
detected at radio wavelengths but undetected on the POSS I plates in order to
search for a population of dust-obscured quasars. Optical and infrared
spectroscopic followup of the sample has led to the discovery of seventeen
heavily reddened quasars (B-K>6.5), fourteen of which are reported here for the
first time. This has allowed us to define a region in the R-K, J-K color plane
in which 50% of the radio-selected objects are highly reddened quasars. We
compare the surface density of this previously overlooked population to that of
UVX- radio-selected quasars, finding that they make up ~20% of the total quasar
population for K < 15.5.
... B. Vandame et al. (2006, in preparation) estimated the seeing for the frames to range from 0.31 ′′ to 0.66 ′′ , with a median value of 0.46 ′′ . Zero points for the individual ISAAC frames were derived by matching photometry of ∼50 stars on each frame with the shallower SOFI (Arnouts et al. 2001 ) and Two Micron All Sky Survey (2MASS; Skrutskie et al. 1997 ) im- ages. As a check on the zero points, we performed photometry on the ∼ 20 z ∼ 0.4 − 1.0 E/S0s in each ISAAC frame (ACS BV iz + ISAAC JK s bands) and then fit a spectral energy distribution (SED) to the six opticalinfrared fluxes. ...
We have detected 506 i-dropouts (z~6 galaxies) in deep, wide-area HST ACS fields: HUDF, enhanced GOODS, and HUDF parallel ACS fields (HUDF-Ps). The contamination levels are ~92% are at z~6). With these samples, we present the most comprehensive, quantitative analyses of z~6 galaxies yet and provide optimal measures of the UV luminosity function (LF) and luminosity density at z~6, and their evolution to z~3. We redetermine the size and color evolution from z~6 to z~3. Field-to-field variations (cosmic variance), completeness, flux, and contamination corrections are modeled systematically and quantitatively. After corrections, we derive a rest-frame continuum UV (~1350 Å) LF at z~6 that extends to M1350,AB~-17.5 (0.04L*z=3). There is strong evidence for evolution of the LF between z~6 and z~3, most likely through a brightening (0.6+/-0.2 mag) of M* (at 99.7% confidence), although the degree depends on the faint-end slope. As expected from hierarchical models, the most luminous galaxies are deficient at z~6. Density evolution (phi*) is ruled out at >99.99% confidence. Despite large changes in the LF, the luminosity density at z~6 is similar to (0.82+/-0.21 times) that at z~3. Changes in the mean UV color of galaxies from z~6 to z~3 suggest an evolution in dust content, indicating that the true evolution is substantially larger: at z~6 the star formation rate density is just ~30% of the z~3 value. Our UV LF is consistent with z~6 galaxies providing the necessary UV flux to reionize the universe. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program 9803. Observations have been carried out using the Very Large Telescope at the European Southern Observatory (ESO) Paranal Observatory, under program ID LP168.A-0485.
... Recent studies by), Laurikainen, Salo, & Rautiainen (2002,, and Block et al. (2002) have provided the first attempts to derive the maximum force ratios for significant samples of galaxies. However, in these cases, the samples were either ill-defined statistically, based entirely on relatively short exposure Two Micron All-Sky Survey (2MASS, Skrutskie et al. 1997) near-infrared images, or used deprojected images that did not allow for the typically rounder shapes of bulges or the most reliable estimates of vertical scaleheights. ...
The maximum value of the ratio of the tangential force to the mean background radial force is a useful quantitative measure of the strength of nonaxisymmetric perturbations in disk galaxies. Here we consider the distribution of this ratio, called Qg, for a statistically well-defined sample of 180 spiral galaxies from the Ohio State University Bright Galaxy Survey and the Two Micron All Sky Survey. The ratio Qg can be interpreted as the maximum gravitational torque per unit mass per unit square of the circular speed and is derived from gravitational potentials inferred from near-infrared images under the assumptions of a constant mass-to-light ratio and an exponential vertical density law. In order to derive the most reliable maximum relative torques, orientation parameters based on blue-light isophotes are used to deproject the galaxies, and the more spherical shapes of bulges are taken into account using two-dimensional decompositions that allow for analytical fits to bulges, disks, and bars. Also, vertical scale heights hz are derived by scaling the radial scale lengths hR from the two-dimensional decompositions, allowing for the type dependence of hR/hz indicated by optical and near-infrared studies of edge-on spiral galaxies. The impact of dark matter is assessed using a ``universal rotation curve'' parameterization and is found to be relatively insignificant for our sample. In agreement with a previous study by Block et al., the distribution of maximum relative gravitational torques is asymmetric toward large values and shows a deficiency of low-Qg galaxies. However, because of the above refinements, our distribution shows more low-Qg galaxies than that of Block et al. We also find a significant type dependence in maximum relative gravitational torques, in the sense that Qg is lower on average in early-type spirals than in late-type spirals. The effect persists even when the sample is separated into bar-dominated and spiral-dominated subsamples and also when near-infrared types are used, as opposed to optical types.
... Towards the ellucidation of the frequency of occurrence of main-sequence circumstellar dust, particularly of exozodiacal type, we present the results of a survey employing a novel technique: we used the 2-Micron All-Sky Survey (2MASS, Skrutskie et al. 1997) to obtain near-infrared SEDs of stars, and IRAS 12 pm photometry to thus search for 12 pm excesses, presumably from exozodiacal dust. ...
... With T eff e2900 K (Leggett et al. 2000), the coolest subdwarfs known have masses just above the hydrogen burning minimum mass (HBMM), 8 which ranges from 0.072 M for solar composition (Z ¼ Z ) to 0.092 M for Z ¼ 0 (Chabrier & Baraffe 1997; Burrows et al. 2001). In contrast, hundreds of significantly cooler Population I, or disk, dwarfs have been identified, 9 predominately in the wide-field optical and near-infrared (NIR) surveys Deep Near Infrared Survey of the Southern Sky (DENIS; Epchtein et al. 1997), the Two Micron All Sky Survey (2MASS; Skrutskie et al. 1997), and the Sloan Digital Sky Survey (SDSS; York et al. 2000). These discoveries include many dozens of substellar objects and extend well beyond the M spectral class into the L (Kirkpatrick et al. 1999; Martín et al. 1999) and the T (Burgasser et al. 2002; Geballe et al. 2002 ) classes. ...
We present the discovery of the first L-type subdwarf, 2MASS J05325346+8246465. This object exhibits enhanced collision-induced H2 absorption, resulting in blue near-infrared (NIR) colors (JKs ¼ 0:26 � 0:16). In addition, strong hydride bands in the red optical and NIR, weak TiO absorption, and an optical/ J-band spectral morphology similar to the L7 DENIS 0205� 1159AB imply a cool, metal-deficient atmosphere. We find that 2MASS 0532+8246 has both a high proper motion, l ¼ 2>60 � 0>15 yr� 1, and a substantial radial velocity, vrad ¼� 195 � 11 km s� 1, and its probable proximity to the Sun (d ¼ 10 30 pc) is consistent with halo membership. Comparison to subsolar-metallicity evolutionary models strongly suggests that 2MASS 0532+8246 is substellar, with a mass of 0:077dMd0:085 Mfor ages 10-15 Gyr and metallic- ities Z ¼ 0:1 0:01 Z� . The discovery of this object clearly indicates that star formation occurred below the hydrogen burning mass limit at early times, consistent with prior results indicating a flat or slightly rising mass function for the lowest mass stellar subdwarfs. Furthermore, 2MASS 0532+8246 serves as a prototype for a new spectral class of subdwarfs, additional examples of which could be found in NIR proper-motion surveys. Subject headings: infrared: stars — solar neighborhood — stars: chemically peculiar — stars: individual (2MASS J05325346+8246465) — stars: low-mass, brown dwarfs — subdwarfs
... Despite this, of the discovered brown dwarf population, companion or otherwise, T dwarfs are especially rare, most likely due to selection effects – they are also the faintest dwarfs due to their cool temperatures. Recent massive sky surveys have detected hundreds of brown dwarfs in the field, including the Deep Near-Infrared Survey (DENIS) (Tinney, Delfosse, and Forveille 1997), 2 µm All-Sky Survey (2MASS; Skrutskie et al. 1997), and the Sloan Digital Sky Survey (Strauss et al. 1999; Tsvetanov et al. 2000). Of these, only about 20 have been classified as methane brown dwarfs, including the L/T transition objects. ...
... They estimated the number of members in the cluster at 25. Based on Pavani et al. (2001) and Dias et al. (2002), van den Bergh (2006) gives a value of 2.61 pc for the diameter of the cluster. Pavani & Bica (2007) reanalysed Two Micron All Sky Survey (2MASS; Skrutskie et al. 1997) photometry and UCAC2 proper motions to confirm NGC 1252 as a 2.8 Gyr old loose OCR located at a distance of 790 pc from the Sun and 610 pc below the disc. Ahumada & Lapasset (2007) ratified their 1995 results using data from Dias et al. (2002). ...
If stars form in clusters but most stars belong to the field, understanding
the details of the transition from the former to the latter is imperative to
explain the observational properties of the field. Aging open clusters are one
of the sources of field stars. The disruption rate of open clusters slows down
with age but, as an object gets older, the distinction between the remaining
cluster or open cluster remnant (OCR) and the surrounding field becomes less
and less obvious. As a result, finding good OCR candidates or confirming the
OCR nature of some of the best candidates still remains elusive. One of these
objects is NGC 1252, a scattered group of about 20 stars in Horologium. Here we
use new wide-field photometry in the UBVI pass-bands, proper motions from the
Yale/San Juan SPM 4.0 catalogue and high resolution spectroscopy concurrently
with results from N-body simulations to decipher NGC 1252's enigmatic
character. Spectroscopy shows that most of the brightest stars in the studied
area are chemically, kinematically and spatially unrelated to each other.
However, after analysing proper motions, we find one relevant kinematic group.
This sparse object is relatively close (about 1 kpc), metal poor and is
probably not only one of the oldest clusters (3 Gyr) within 1.5 kpc from the
Sun but also one of the clusters located farthest from the disc, at an altitude
of nearly -900 pc. That makes NGC 1252 the first open cluster that can be truly
considered a high Galactic altitude OCR: an unusual object that may hint at a
star formation event induced on a high Galactic altitude gas cloud. TW Hor and
HD 20286 are unlikely to be part of NGC 1252. NGC 1252 17 is identified as an
unrelated, Population II cannonball star moving at about 400 km/s.
... Several approaches can be used: a detailed investigation of the CIMF (Portegies Zwart et al. 2007, Dowell et al. 2008, Stolte et al. 2005 ); an accurate estimation of the disruption effects (Lamers et al. 2005); and finally a study to find out if the cluster mass distribution is really independent of the star formation history (Portegies Zwart et al. 2006). More than 2000 infrared " hidden " star cluster candidates have been discovered in the last 5-6 years from allsky IR surveys such as the 2 MASS (Skrutskie et al. 1997) and the Spitzer Space Telescope Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE, Benjamin et al. 2003) and can be used to test the recent star formation in the Galaxy. This work is a part of a larger program aimed at characterizing the hidden current star population in the Galaxy (Ivanov et al. 2002 Borissova et al. 2003 Borissova et al. , 2005 Borissova et al. , 2006 Kurtev el al. 2007). ...
Context: Recent near- and mid-infrared surveys have brought evidence that the Milky Way continues to form massive clusters.
Aims: We carry out a program to determine the basic physical properties of the new massive cluster candidate [DBS2003] 179.
Methods: Medium-resolution K-band spectra and deep near-infrared images of [DBS2003] 179 were used to derive the spectral types of eight member stars, and to estimate the distance and reddening to the cluster.
Results: Seven of ten stars with spectra show emission lines. Comparison with template spectra indicated that they are early O-type stars. The mean radial velocity of the cluster is V_rad=-77 ± 6 km s-1. Knowing the spectral types of the members and the color excesses, we determined extinction AV ˜ 16.6 and distance modulus (m-M)0 ˜ 14.5 mag (D˜7.9 Kpc). The presence of early O-stars and a lack of red supergiants suggests a cluster age of 2-5 Myr. The total cluster mass is approximated to 0.7 × 10 ^4~Msun and it is not yet dynamically relaxed.
Conclusions: The candidate [DBS2003] 179 further increases the family of the massive young clusters in the Galaxy, although it appears less massive than the prototypical starburst clusters.
Based on observations collected with the Very Large Telescope of the European Southern Observatory within the Observing Program 79.D-0149(A).This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.
... Rigopoulou et al. 1999; Soifer et al. 1999 Soifer et al. , 2001), and the peak may not be spatially coincident with the radio nucleus. However we can exclude this possibility because we find excellent positional agreement between the radio nucleus (above) and a K-band image of the nucleus obtained from the astrometrically accurate 2MASS survey (Skrutskie et al. 1997). Since the position of the near-IR nucleus and the radio nucleus correspond, we can safely assume that obscuration is not a factor in determining the position of the AGN core at wavelengths longward of 2 µm.Figure 4 displays the 3.5 cm radio map superimposed on images made at 15 µm with ISOCAM (Fig. 4a), and at 2.2 µm with UKIRT (Fig. 4b , an image based on near- IR data from Appleton & Marcum 1993). ...
We describe Infrared Space Observatory (ISO) and BIMA observations of the z = 0.04 Seyfert 1 ring galaxy NGC 985 which suggest close parallels with some quasar host galaxies. NGC 985 contains two closely spaced nuclei embedded in an R1/4-law stellar bulge and an outer ring, evidence of an ongoing merger. The system contains ~1.8 × 1010 M☉ of highly disturbed molecular gas which lies in an asymmetric barlike structure with the peak in observed CO column densities significantly offset from the compact double nucleus. In contrast to this, the ISO observations show strong dust emission centered on the active galactic nucleus (AGN), located in one of the two nuclei. Fainter CO, mid-infrared (MIR), and radio continuum emission provides a glimpse of the complexities of star formation in the outer ring. An analysis of the kinematics of the main CO emission reveals evidence for two dynamically distinct molecular components within NGC 985. The first is a set of isolated supergiant molecular clouds (SGMCs) which are concentrated within 9-10 kpc of the active nucleus. Although randomly distributed about the center, the clouds may form part of a clumpy highly disturbed disk which may be either just forming around double nucleus (the making of an ultraluminous infrared galaxy [ULIRG]) or alternatively in the process of being disrupted, perhaps as a result of a powerful nuclear outflow (the breaking of a ULIRG). A second major concentration of CO lies offset from the double nucleus in a dynamically coherent ridge of emission in which powerful star formation is occurring. We tentatively associate CO emission with two out of six UV absorption lines seen in the blue wing of the very broad Lyα emission. Such an association would imply a complex interrelationship between the nuclear CO cloud population in colliding systems and AGN-driven winds.
... We identified the X-ray sources in the optical, NIR, and MIR bands using the Naval Observatory Merged Astrometric Dataset (NOMAD) 10 , the Two-Micron All- Sky Survey (2MASS; Skrutskie et al. 1997), SIRIUS, and GLIMPSE. GLIMPSE is a Legacy Program of the Spitzer Space Telescope to survey a ∼220 deg 2 region of the Galactic Plane at four MIR bands ([3.6], [4.5], [5.8], and [8.0] µm) with a 1. 6–1. 9 resolution using IRAC (Fazio et al. 2004). ...
We present the results of a high-resolution X-ray imaging study of the stellar population in the Galactic massive star-forming region RCW 49 and its central OB association Westerlund 2. We obtained a ~40 ks X-ray image of a ~17' × 17' field using the Chandra X-Ray Observatory and deep NIR images using the Infrared Survey Facility in a concentric ~8.3' × 8.3' region. We detected 468 X-ray sources and identified optical, NIR, and Spitzer MIR counterparts for 379 of them. The unprecedented spatial resolution and sensitivity of the X-ray image, enhanced by optical and infrared imaging data, yielded the following results: (1) The central OB association Westerlund 2 is resolved for the first time in the X-ray band. X-ray emission is detected from all spectroscopically identified early-type stars in this region. (2) Most (~86%) X-ray sources with optical or infrared identifications are cluster members in comparison with a control field in the Galactic plane. (3) A loose constraint (2-5 kpc) for the distance to RCW 49 is derived from the mean X-ray luminosity of T Tauri stars. (4) The cluster X-ray population consists of low-mass pre-main-sequence and early-type stars as obtained from X-ray and NIR photometry. About 30 new OB star candidates are identified. (5) We estimate a cluster radius of 6'-7' based on the X-ray surface number density profiles. (6) A large fraction (~90%) of cluster members are identified individually using complimentary X-ray and MIR excess emission. (7) The brightest five X-ray sources, two Wolf-Rayet stars and three O stars, have hard thermal spectra.
... Bertin & Arnouts (1996) show that this magnitude underestimates the flux in galaxies by ∼6%. We do not correct for this effect as almost all local galaxy surveys adopt similarly biased Kron or Petrosian magnitudes (e.g., Blanton et al. 2003b; Skrutskie et al. 1997 ). The spectral shapes for R-band detected objects were measured by performing seeing-adaptive, weighted aperture photometry in all 17 frames at the position of the R-band detected object using the package MPIAPHOT (Röser & Meisenheimer 1991, Meisenheimer et al., in preparation). ...
We present the rest-frame colors and luminosities of ~25,000 mR 24 galaxies in the redshift range 0.2 < z ≤ 1.1 drawn from 0.78 deg2 of the COMBO-17 survey (Classifying Objects by Medium-Band Observations in 17 Filters). We find that the rest-frame color distribution of these galaxies is bimodal at all redshifts out to z ~ 1. This bimodality permits a model-independent definition of red early-type galaxies and blue late-type galaxies at any given redshift. The colors of the blue peak become redder toward the present day, and the number density of blue luminous galaxies has dropped strongly since z ~ 1. Focusing on the red galaxies, we find that they populate a color-magnitude relation. Such red sequences have been identified in galaxy cluster environments, but our data show that such a sequence exists over this redshift range even when averaging over all environments. The mean color of the red galaxy sequence evolves with redshift in a way that is consistent with the aging of an ancient stellar population. The rest-frame B-band luminosity density in red galaxies evolves only mildly with redshift in a Λ-dominated cold dark matter universe. When we account for the change in stellar mass-to-light ratio implied by the redshift evolution in red galaxy colors, the COMBO-17 data indicate an increase in stellar mass on the red sequence by a factor of 2 since z ~ 1. The largest source of uncertainty is large-scale structure, implying that considerably larger surveys are necessary to further refine this result. We explore mechanisms that may drive this evolution in the red galaxy population, finding that both galaxy merging and truncation of star formation in some fraction of the blue star-forming population are required to fully explain the properties of these galaxies.
... Errors in the BV RI magnitudes are typically on the order of 0.01– 0.02 magnitudes. Near infrared JHK photometry was, again with the exception of HD 122563, provided by the Two Micron All Sky Survey (2MASS) Point Source Catalog (Skrutskie et al. 1997). Estimates of the interstellar reddening, E(B − V ), for each object were obtained from the Schlegel, Finkbeiner, & Davis (1998) map; the extinction of each band was obtained from the reddening relation provided in their Table 6. ...
Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among which 16 are newly analyzed in the present work, were selected from candidate metal-poor stars identified in the HK survey of Beers and colleagues. The metallicity range covered by our sample is -3.1 ~< [Fe/H] ~< -2.4. The abundances of carbon, alpha-elements, and iron-peak elements determined for these stars confirm the trends found by previous work. One exception is the large over-abundance of Mg, Al and Sc found in BS16934--002, a giant with [Fe/H] = -2.8. By combining our new results with those of previous studies, we investigate the distribution of neutron-capture elements in very metal-poor stars, focusing on the production of the light neutron-capture elements (e.g., Sr, Y, and Zr).
... After eluding undisputed detection for many years, numerous brown dwarfs – objects with sub-stellar mass – are now known. While some candidates were discovered in small-scale surveys of young nearby clusters, such as the Pleiades and Hyades, or as companions to low-mass stars, the biggest breakthrough has come as a result of large-scale surveys such as the Deep Near-Infrared Sky (DENIS) survey (Delfosse et al. 1997), 2MASS, the 2-Micron All-Sky Survey (Skrutskie et al. 1997, Kirkpatrick et al. 1999) and the Sloan Digital Sky Survey (SDSS) (Strauss et al. 1999). Recently, using optical (CCD) spectroscopy, Kirkpatrick et al. (1999) have defined a new spectral class, L-dwarfs, in which the metallic oxides (such as TiO and VO) found in M stars lose their dominance to metallic hydrides (such as FeH and CrH). ...
Near-infrared spectroscopic observations of a sample of very cool, low-mass objects are presented with higher spectral resolution than in any previous studies. Six of the objects are L dwarfs, ranging in spectral class from L2 to L8/9, and the seventh is a methane or T dwarf. These new observations were obtained during commissioning of the near-infrared spectrometer (NIRSPEC), the first high-resolution near-infrared cryogenic spectrograph for the Keck II 10 m telescope on Mauna Kea, Hawaii. Spectra with a resolving power of R ≈ 2500 from 1.135 to 1.360 μm (approximately J band) are presented for each source. At this resolution, a rich spectral structure is revealed, much of which is due to blending of unresolved molecular transitions. Strong lines due to neutral potassium (K I) and bands due to iron hydride (FeH) and steam (H2O) change significantly throughout the L sequence. Iron hydride disappears between L5 and L8, the steam bands deepen, and the K I lines gradually become weaker but wider because of pressure broadening. An unidentified feature occurs at 1.22 μm that has a temperature dependence like FeH but has no counterpart in the available FeH opacity data. Because these objects are 3-6 mag brighter in the near-infrared compared with the I band, spectral classification is efficient. One of the objects studied (2MASSW J1523+3014) is the coolest L dwarf discovered so far by the 2 Micron All-Sky Survey (2MASS), but its spectrum is still significantly different from the methane-dominated objects such as Gl 229B or SDSS 1624+0029.
... We present here a robust and efficient method of starlight removal in the optical and the near-infrared band. Briefly, PCA is first applied to the optical spectra of STELIB (Le Borgne et al. 2003), a newly available stellar library in the wavelength coverage of 3500-9500Å, and the near-infrared photometric data at J, H, and K s bands collected from the 2 Micron All Sky Survey (2MASS; Skrutskie et al. 1997), supplemented by the stellar library presented by Pickles (1998) ( §3). The stellar eigen-spectra in the visible range are then used to model a homogeneous library of 1016 galactic spectra picked up from the Sloan Digital Sky Survey Data Release One (SDSS DR1; Abazajian et al. 2003). ...
An empirical method of modeling the stellar spectrum of galaxies is proposed, based on two successive applications of principal component analysis (PCA). PCA is first applied to the newly available stellar library STELIB, supplemented by the J, H, and Ks magnitudes taken mainly from the Two Micron All Sky Survey. Next, the resulting eigenspectra are used to fit the observed spectra of a sample of 1016 galaxies selected from the Sloan Digital Sky Survey Data Release 1 (SDSS DR1). PCA is again applied to the fitted spectra to construct the eigenspectra of galaxies with zero velocity dispersion. The first nine galactic eigenspectra so obtained are then used to model the stellar spectrum of the galaxies in SDSS DR1 and synchronously to estimate the stellar velocity dispersion, the spectral type, the near-infrared spectral energy distribution, and the average reddening. Extensive tests show that the spectra of different types of galaxies can be modeled quite accurately using these eigenspectra. The method can yield stellar velocity dispersion with accuracies better than 10% for the spectra of typical signal-to-noise ratios in SDSS DR1.
... The Two Micron All Sky Survey (2MASS ; Skrutskie et al. 1997) is surveying the entire sky in near-infrared light.37 The observations are done simultaneously in the J (1.25 km), H (1.65 km), and (2.17 km) bands. ...
We discuss measurements of the properties of ~13,000 asteroids detected in 500 deg² of sky in the Sloan Digital Sky Survey (SDSS) commissioning data. The moving objects are detected in the magnitude range 14 < r* < 21.5, with a baseline of ~5 minutes, resulting in typical velocity errors of ~3%. Extensive tests show that the sample is at least 98% complete, with a contamination rate of less than 3%. We find that the size distribution of asteroids resembles a broken power law, independent of the heliocentric distance: D-2.3 for 0.4 km D 5 km, and D⁻⁴ for 5 km D 40 km. As a consequence of this break, the number of asteroids with r* < 21.5 is 10 times smaller than predicted by extrapolating the power-law relation observed for brighter asteroids (r* 18). The observed counts imply that there are about 670,000 objects with D > 1 km in the asteroid belt, or up to 3 times less than previous estimates. The revised best estimate for the impact rate of the so-called "killer" asteroids (D > 1 km) is about 1 every 500,000 yr, uncertain to within a factor of 2. We predict that by its completion SDSS will obtain about 100,000 near simultaneous five-band measurements for a subset drawn from 340,000 asteroids brighter than r* < 21.5 at opposition. Only about a third of these asteroids have been previously observed, and usually in just one band. The distribution of main-belt asteroids in the four-dimensional SDSS color space is bimodal, and the two groups can be associated with S- (rocky) and C- (carbonaceous) type asteroids. A strong bimodality is also seen in the heliocentric distribution of asteroids: the inner belt is dominated by S-type asteroids centered at R ~ 2.8 AU, while C-type asteroids, centered at R ~ 3.2 AU, dominate the outer belt. The median color of each class becomes bluer by about 0.03 mag AU⁻¹ as the heliocentric distance increases. The observed number ratio of S and C asteroids in a sample with r* < 21.5 is 1.5 : 1, while in a sample limited by absolute magnitude it changes from 4 : 1 at 2 AU, to 1 : 3 at 3.5 AU. In a size-limited sample with D > 1 km, the number ratio of S and C asteroids in the entire main belt is 1 : 2.3.
The colors of Hungarias, Mars crossers, and near-Earth objects, selected by their velocity vectors, are more similar to the C-type than to S-type asteroids. In about 100 deg² of sky along the celestial equator observed twice 2 days apart, we find one plausible Kuiper belt object (KBO) candidate, in agreement with the expected KBO surface density. The colors of the KBO candidate are significantly redder than the asteroid colors, in agreement with colors of known KBOs. We explore the possibility that SDSS data can be used to search for very red, previously uncataloged asteroids observed by 2MASS, by extracting objects without SDSS counterparts. We do not find evidence for a significant population of such objects; their contribution is no more than 10% of the asteroid population.
... These objects are of interest because they occupy the mass range between that of stars and giant planets; because many of them are likely to have the intrinsic properties of giant planets, which at present cannot be directly observed; and because they allow the investigation of the initial mass function to substellar masses. Field L and T dwarfs have been discovered in large numbers in recent sky surveys: the Deep – 3 – Near Infrared Survey (DENIS, Epchtein 1997); the Two Micron All Sky Survey (2MASS, Skrutskie et al. 1997; Beichman et al. 1998), and the optical Sloan Digital Sky Survey SDSS (York et al. 2000). Including objects described in the present paper, there are now about 280 L dwarfs and 58 T dwarf systems published (e.g. ...
We present new JHK photometry on the MKO-NIR system and JHK spectroscopy for a large sample of L and T dwarfs. Photometry has been obtained for 71 dwarfs, and spectroscopy for 56. The sample comprises newly identified very red objects from the Sloan Digital Sky Survey (SDSS) and known dwarfs from the SDSS and the Two Micron All Sky Survey (2MASS). Spectral classification has been carried out using four previously defined indices from Geballe et al. that measure the strengths of the near infrared water and methane bands. We identify nine new L8–9.5 dwarfs and 14 new T dwarfs from SDSS, including the latest yet found by SDSS, the T7 dwarf SDSS J175805.46+463311.9. We classify 2MASS J04151954-0935066 as T9, the latest and coolest dwarf found to date. We combine the new results with our previously published data to produce a sample of 59 L dwarfs and 42 T dwarfs with imaging data on a single photometric system and with uniform spectroscopic classification. We compare the near-infrared colors and absolute magnitudes of brown dwarfs near the L–T transition with predictions made by models of the distribution and evolution of photospheric condensates. There is some scatter in the Geballe et al. spectral indices for L dwarfs, suggesting that these indices are probing different levels of the atmosphere and are affected by the location of the condensate cloud layer. The near-infrared colors of the L dwarfs also show scatter within a given spectral type, which is likely due to variations in the altitudes, spatial distributions, and thicknesses of the clouds. We have identified a small group of late-L dwarfs that are relatively blue for their spectral type and that have enhanced FeH, H2O, and K I absorption, possibly due to an unusually small amount of condensates. The scatter seen in the H-K color for late-T dwarfs can be reproduced by models with a range in surface gravity. The variation is probably due to the effect on the K-band flux of pressure-induced H2 opacity. The correlation of H-K color with gravity is supported by the observed strengths of the J-band K I doublet. Gravity is closely related to mass for field T dwarfs with ages greater than108 yr and the gravities implied by the H-K colors indicate that the T dwarfs in our sample have masses in the range 15–75MJupiter. One of the SDSS dwarfs, SDSS J111010.01+011613.1, is possibly a very low mass object, with log g ~ 4.2–4.5 and mass ~ 10–15MJupiter.
... With effective temperatures T ef f < 4000K, these stars and brown dwarfs emit the bulk of their radiative flux at near-infrared wavelengths. We are therefore using JHK S photometry provided by the 2-Micron All Sky Survey (2MASS - Skrutskie et al., 1997), both in isolation and in combination with other surveys, to search for previously unrecognised M and L dwarfs within 20 parsecs of the Sun. ...
We present low-resolution optical spectroscopy and BVRI photometry of 453 candidate nearby stars drawn from the NLTT proper-motion catalog. The stars were selected based on optical/near-infrared colors, derived by combining the NLTT photographic data with photometry from the 2MASS Second Incremental Data Release. Based on the derived photometric and spectroscopic parallaxes, we identify 111 stars as lying within 20 pc of the Sun, including nine stars with formal distance estimates of less than 10 pc. A further 53 stars have distance estimates within 1 σ of our 20 pc limit. Almost all of those stars are additions to the nearby-star census. In total, our NLTT-based survey has so far identified 496 stars likely to be within 20 pc, of which 195 are additions to nearby-star catalogs. Most of the newly identified nearby stars have spectral types between M4 and M8.
... In Cohen, Behr, & Briley (2001, we demonstrated that the Kurucz and MARCS predicted colors are essentially identical, at least for the specific colors used here. The optical photometry we adopt is from Stetson et al. (1989), and the infrared photometry is from 2MASS (Skrutskie et al. 1997). The reddening is low; we adopt EðBÀV Þ ¼ 0:02 mag and a distance of 19.1 kpc from the on-line database of Harris (1996); the all-sky maps of Schlegel, Finkbeiner, & Davis (1998) yield a slightly larger E(BÀV ) of 0.036 mag. ...
We present a detailed abundance analysis for 21 elements based on high-dispersion, high spectral resolution Keck spectra for four members of the outer halo "young" Galactic globular cluster Palomar 12. All four stars show identical abundance distributions with no credible indication of any star-to-star scatter. However, the abundance ratios of the Pal 12 stars are very peculiar. There is no detected enhancement of the α-elements; the mean of [Si/Fe], [Ca/Fe], and [Ti/Fe] is -0.07 ± 0.05 dex, O/Fe is also solar, while Na is very deficient. The distribution among the heavy elements shows anomalies as well. These are inconsistent with those of almost all Galactic globular clusters or of field stars in the Galaxy. The peculiarities shown by the Pal 12 stars are, however, in good general agreement with the trends established by Smecker-Hane & McWilliam and by Bonifacio et al. for stars in the Sagittarius dwarf spheroidal (dSph) galaxy evaluated at the [Fe/H] of Pal 12. This reinforces earlier suggestions that Pal 12 originally was a cluster in the Sgr dSph galaxy that during the process of accretion of this galaxy by our own was tidally stripped from the Sgr galaxy to become part of the extended Sgr stream.
... The ordinary matter, i.e. the baryonic matter, accounts for only a small fraction (∼ 15% of the non-relativistic matter). With these favorable cosmological parameters plus some other reasonable parameters for the Hubble constant and for the primordial density fluctuations, the CDM model can match most of the current observations, including the cosmic microwave background, the intergalactic medium at high redshift, the abundance of rich clusters, and the large-scale distributions of galaxies in the Two Degree Field Galaxy Redshift Survey (2dFGRS, Colless et al. 2001), in the 2-Micron All Sky Survey (2MASS, Skrutskie et al. 1997), and in the Sloan Digital Sky Survey (SDSS, York et al. 2000) (e.g. Peacock et al. 2001; Maller et al. 2003; Tegmark et al. 2004). ...
We model the galaxy formation in a series of high-resolution N-body simulations using the semianalytical approach. Unlike many earlier investigations based on semianalytical models, we make use of the subhalos resolved in the N-body simulations to follow the mergers of galaxies in dark halos, and we show that this is pivotal in modeling correctly the galaxy luminosity function at the bright end and the bimodal nature of galaxy color distribution. Mergers of galaxies based on subhalos also result in many more bright red galaxies at high z. The semianalytical model we adopt is similar to those used in earlier semianalytical studies, except that we consider the effect of a prolonged cooling in small halos and that we explicitly follow the chemical enrichment in the interstellar medium. We use our model to make predictions for the properties of the galaxy population at low redshift and compare them with various current observations. We find that our model predictions can match the luminosity functions of galaxies in various wavebands redder than the u band. The shape of the luminosity function at the bright end is well reproduced if galaxy mergers are modeled with the merger trees of subhalos, and the steep faint-end slope can be moderated if the gas cooling time in low-mass halos is comparable to the age of the universe. The model with subhalos resolved can reproduce the main features in the observed color bimodal distribution, although it still predicts too many bright blue galaxies. The same model can also match the color-magnitude relation for elliptical galaxies in clusters, the metallicity-luminosity relation and metallicity-rotation velocity relation of spiral galaxies, and the gas fraction in present-day spiral galaxies. We also identify areas where further improvements of the model are required.
... Large sky surveys have proven to be fertile ground for identifying extremely late-type stellar and substellar objects (Reid & Hawley 2000). In the past decade, the accumulation of sizable samples of low mass stars and brown dwarfs has been largely the result of near-infrared surveys such as the Deep Near-Infrared Survey (DENIS) (Delfosse et al. 1997) and the Two-Micron All Sky Survey (2MASS) (Skrutskie et al. 1997). These discoveries culminated in the definition of the L spectral class (Kirkpatrick et al. 1999; Martin et al. 1999; Kirkpatrick et al. 2000; Basri et al. 2000). ...
An extensive sample of M, L, and T dwarfs identified in the Sloan Digital Sky Survey (SDSS) has been compiled. The sample of 718 dwarfs includes 677 new objects (629 M dwarfs and 48 L dwarfs), together with 41 that have been previously published. All new objects and some of the previously published ones have new optical spectra obtained either with the SDSS spectrographs or with the Apache Point Observatory 3.5 m ARC telescope. Spectral types and SDSS colors are available for all objects; approximately 35% also have near-infrared magnitudes measured by 2MASS (Two Micron All Sky Survey) or on the Mauna Kea system. We use this sample to characterize the color–spectral type and color-color relations of late-type dwarfs in the SDSS filters and to derive spectroscopic and photometric parallax relations for use in future studies of the luminosity and mass functions based on SDSS data. We find that the i* - z* and i* - J colors provide good spectral type and absolute magnitude (Mi*) estimates for M and L dwarfs. Our distance estimates for the current sample indicate that SDSS is finding early M dwarfs out to ~1.5 kpc, L dwarfs to ~100 pc, and T dwarfs to ~20 pc. The T dwarf photometric data show large scatter and are therefore less reliable for spectral type and distance estimation.
The next decade promises an explosion of information about the infrared sky from wavelengths from 1 μ m to 1,000 μ m, in the continuum and in spectral lines. Measurements of objects ranging from comets in the Kuiper Belt to newly-forming galaxies will be useful for almost every branch of astrophysics. The number of catalogued infrared sources will increase a thousand-fold from the 600,000 presently known from IRAS. This talk addresses the compelling scientific interest of the infrared and describes why, years from now, astronomers will view this decade as a golden era for the exploration of the infrared sky.
The existence of substellar-mass, star-like objects was first considered seriously by Kumar [K11] (Section 3.3), who outlined their essential properties: no central energy source due to hydrogen fusion, degeneracy and short luminous lifetimes. Like low-mass M dwarfs, these objects — renamed ‘brown dwarfs’ by Tarter [T1] — are ideal baryonic dark matter candidates, and have been the targets of a wide variety of surveys over the last three decades. As with any search for a newly-hypothesised object, the first task is to determine whether any exist. In answering this question, one can utilise all available techniques, without regard to the complications of biases and selection effects. However, once the issue of existence has been answered in the affirmative, the emphasis of observational programmes must change, moving from simple discovery searches to addressing specific issues through statistically well-controlled surveys. With the near-contemporaneous discoveries of Gl 229 B and the planet orbiting 51 Peg, both brown-dwarf and planet surveys have moved from the first to the second stage. Early results from the DENIS, 2MASS and SLOAN sky surveys are providing the data necessary for a transition from phenomenology to statistics.
We present new nonlinear, time-dependent convective hydrodynamical models of
RR Lyrae stars computed assuming a constant helium-to-metal enrichment ratio
and a broad range in metal abundances (Z=0.0001--0.02). The stellar masses and
luminosities adopted to construct the pulsation models were fixed according to
detailed central He burning Horizontal Branch evolutionary models. The
pulsation models cover a broad range in stellar luminosity and effective
temperatures and the modal stability is investigated for both fundamental and
first overtones. We predict the topology of the instability strip as a function
of the metal content and new analytical relations for the edges of the
instability strip in the observational plane. Moreover, a new analytical
relation to constrain the pulsation mass of double pulsators as a function of
the period ratio and the metal content is provided. We derive new
Period-Radius-Metallicity relations for fundamental and first-overtone
pulsators. They agree quite well with similar empirical and theoretical
relations in the literature. From the predicted bolometric light curves,
transformed into optical (UBVRI) and near-infrared (JHK) bands, we compute the
intensity-averaged mean magnitudes along the entire pulsation cycle and, in
turn, new and homogenous metal-dependent (RIJHK) Period-Luminosity relations.
Moreover, we compute new dual and triple band optical, optical--NIR and NIR
Period-Wesenheit-Metallicity relations. Interestingly, we find that the optical
Period-W(V,B-V) is independent of the metal content and that the accuracy of
individual distances is a balance between the adopted diagnostics and the
precision of photometric and spectroscopic datasets.
This paper is based on 2MASS photometry (J H Ks magnitudes) of 1172 Be stars. The observed mean intrinsic colours have been derived with aid of two-colour diagrams for Be stars of luminosity classes Ie-IIe, IIIe and IVe-Ve. The obtained results are the first determinations of their intrinsic colours in the astronomical literature. The smoothed infrared colours are compared with those obtained for “normal” B stars. Several two-colour diagrams and plots of observed and smoothed intrinsic colour versus spectral type of luminosity classes Ie-IIe, IIIe and IVe-Ve are presented. Generally the determined infrared intrinsic colours of Be stars (V – J)0, (V – H)0, and (V – Ks)o differ substantially from those of “normal” B stars. It is found that the intrinsic colours of B stars are generally bluer than Be stars of corresponding spectral type and luminosity class. The mean absolute visual magnitude Mv of 528 Be stars for luminosity classes Iae, Ibe-Iabe, IIe, IIIe and IVe-Ve is derived from HIPPARCOS parallaxes. The Mv calibration is compared with the existing ones. The Be stars are generally brighter than “normal” B stars of corresponding spectral types. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
We present a three-dimensional extinction map in the r band. The map has a spatial angular resolution, depending on latitude, between 3 and 9 arcmin and covers the entire Xuyi
Schmidt Telescope Photometric Survey of the Galactic Anticentre (XSTPS-GAC) survey area of over 6000 deg2 for Galactic longitude 140 < l < 240 deg and latitude −60 < b < 40 deg. By cross-matching the photometric catalogue of the
XSTPS-GAC with those of 2MASS and WISE, we have built a multiband photometric stellar sample of about 30 million stars and applied spectral energy distribution
(SED) fitting to the sample. By combining photometric data from the optical to the near-infrared, we are able to break the
degeneracy between the intrinsic stellar colours and the amounts of extinction by dust grains for stars with high photometric
accuracy, and trace the extinction as a function of distance for low Galactic latitude and thus highly extincted regions.
This has allowed us to derive the best-fitting extinction and distance information of more than 13 million stars, which are
used to construct the three-dimensional extinction map. We have also applied a Rayleigh–Jeans colour excess (RJCE) method
to the data using the 2MASS and WISE colour (H − W2). The resulting RJCE extinction map is consistent with the integrated two-dimensional map deduced using the best-fitting
SED algorithm. However for individual stars, the amounts of extinction yielded by the RJCE method suffer from larger errors
than those given by the best-fitting SED algorithm.
In this paper, we present a catalogue of dense molecular clumps located within the W51 giant molecular cloud (GMC). This work
is based on Heterodyne Array Receiver Programme 13CO J = 3–2 observations of the W51 GMC and uses the automated CLUMPFIND algorithm to decompose the region into a total of 1575 clumps of which 1130 are associated with the W51 GMC. We clearly see
the distinct structures of the W51 complex and the high-velocity stream previously reported. We find the clumps have characteristic
diameters of 1.4 pc, excitation temperatures of 12 K, densities of 5.6 × 1021 cm−2, surface densities 0.02 g cm−2 and masses of 90 M⊙. We find a total mass of dense clumps within the GMC of 1.5 × 105 M⊙, with only 1 per cent of the clumps detected by number and 4 per cent by mass found to be supercritical. We find a clump-forming
efficiency of 14 ± 1 per cent for the W51 GMC and a supercritical clump-forming efficiency of per cent. Looking at the clump mass distribution, we find it is described by a single power law with a slope of above ∼100 M⊙. By comparing locations of supercritical clumps and young clusters, we see that any future star formation is likely to be
located away from the currently active W51A region.
This review addresses the infrared emission from the most important classes of carbon-rich objects: the N- and R-type carbon stars, the carbon dwarfs and the CH-stars. Examples of carbon rich objects in the Galactic halo and the Magellanic Clouds are discussed. Discrimination of carbon-rich objects against red oxygen-rich objects is investigated. The detectibility of N-type carbon Miras in the DENIS and 2MASS near-infrared surveys is discussed.
We present the discovery of a bright (J=13.94+/-0.03) T dwarf, 2MASS 1503+2525, identified in a new, wide-field search for T dwarfs using the recently completed Two Micron All Sky Survey (2MASS). The 1-2.5 mum spectrum of this object exhibits the strong H2O and CH4 bands characteristic of mid- and late-type T dwarfs, and we derive a spectral type of T5.5 using both the Burgasser et al. and the Geballe et al. classification schemes. Based on its spectral type and the absolute magnitudes of known T dwarfs, we estimate the distance of this object as 8+/-3 pc if it is single, likely within 10 pc of the Sun. Our new 2MASS search, which covers 74% of the sky and greatly expands on earlier color constraints, should identify 15-25 new T dwarfs with J
The next decade promises an explosion of information about the infrared sky from wavelengths from 1 μm to 1,000 μm, in the continuum and in spectral lines. Measurements of objects ranging from comets in the Kuiper Belt to newly-forming galaxies will be useful for almost every branch of astrophysics. The number of catalogued infrared sources will increase a thousand-fold from the 600,000 presently known from IRAS. This talk addresses the compelling scientific interest of the infrared and describes why, years from now, astronomers will view this decade as a golden era for the exploration of the infrared sky.
In recent years, new astronomical instruments have reversed three decades
of fruitless searching for brown dwarfs, the failed stars that are too small
to burn nuclear fuel. These discoveries have confirmed predictions about the
importance of methane and dust in the atmospheres of brown dwarfs. But they
also demonstrate that, contrary to expectation, brown dwarfs do not contribute
significantly to our Galaxy's dark matter.
We present the HI observations of 94 flat spiral galaxies from RFGC (Revised Flat Galaxy Catalog) and 14 galaxies from 2MFGC (the 2MASS selected Flat Galaxy Catalog) performed with the 100-m radio telescope in Effelsberg (Germany). HI fluxes, heliocentric radial velocities, and HI line
widths are given for 65 detected galaxies. We present a mosaic of HI profiles. We calculated some of the global parameters
of the galaxies and analyzed the linear correlations between them. The ratios of the total (indicative) masses of the galaxies
to their luminosities lie within the range 0.4–8.2 with a mean of 3.8 (M
⊙/L
⊙), and the mean mass fraction of neutral hydrogen is 13%. Upper limits are given for the radio fluxes from 43 undetected galaxies.
We present a new catalogue, the Imperial IRAS-FSC Redshift Catalogue (IIFSCz), of 60 303 galaxies selected at 60 μm from the IRAS Faint Source Catalogue (FSC). The IIFSCz consists of accurate position, optical, near-infrared and/or radio identifications, spectroscopic redshift
(if available) or photometric redshift (if possible), predicted far-infrared (FIR) and submillimetre (submm) fluxes ranging
from 12 to 1380 μm based upon the best-fitting infrared template. About 55 per cent of the galaxies in the IIFSCz have spectroscopic
redshifts, and a further 20 per cent have photometric redshifts obtained through either the training set or the template-fitting
method. For S(60) > 0.36 Jy, the 90 per cent completeness limit of the FSC, 90 per cent of the sources have either spectroscopic
or photometric redshifts. Scientific applications of the IIFSCz include validation of current and forthcoming infrared and
submm/mm surveys such as AKARI, Planck and Herschel, follow-up studies of rare source populations, large-scale structure and galaxy bias, local multiwavelength luminosity functions
and source counts. The catalogue is publicly available at http://astro.imperial.ac.uk/~mrr/fss/.
The absolute visual magnitudes, MV, of A-M stars are based on calculated Hipparcos trigonometric parallaxes. The sample used consists of 30986 unreddened and reddened A-M stars in luminosity classes Ia, Iab, Ib, II, III, IV and V. The colour excesses of the reddened stars were calculated using the mean colour indices, according to the SIMBAD data base and the intrinsic B - V values calibrated for the given spectral types and luminosity classes by Schmidt-Kaler. The values of the total-to-selective extinction, RV = AV/E(B - V), for all the reddened stars were calculated from previously published near-infrared photometric measurements. The calculated visual magnitudes, MV, of A-M stars compare with the earlier determinations of Schmidt-Kaler. The mean absolute magnitudes published by Schmidt-Kaler are generally brighter (except for the stars in luminosity classes V and IV) than those determined in this paper.
Before the 2-Micron All-Sky Survey (2MASS) began, only six objects were known with spectral types later than M9.5 V. In the first 371 deg^2 of actual 2MASS survey data, we have identified another 20 such objects spectroscopically confirmed using the Low Resolution Imaging Spectrograph (LRIS) at the W. M. Keck Observatory. Because the TiO and VO bands, which dominate the far-optical portions of late-M spectra, disappear in these cooler dwarfs, we define a new spectral class ``L'' in which metallic oxides are replaced by metallic hydrides and neutral alkali metals as the major spectroscopic signatures. We establish classification indices and type all 25 L dwarfs. The 26th ``post-M9.5'' object-Gl 229B-is the prototype of a methane-dominated spectral class, which we propose as class ``T.'' At least five of the 20 2MASS L dwarfs show the 6708 Å lithium doublet at low resolution, the strongest having an equivalent width of 18.5 Å. For objects this cool, the presence of lithium proves that they are substellar. Two other 2MASS objects appear to have lithium lines at the limit of our detectability, which if verified means that at least one-third of our L dwarfs are bona fide brown dwarfs. All of the 2MASS brown dwarfs discovered so far have J-K_s>1.30. We have not yet, despite deliberately searching for them, found any brown dwarfs with colors resembling Gl 229B (J-K_s~-0.1).
We present (12) CO J = 1-0 and 2-1 observations of 14 S-stars, and
report 6 new detections. Two stars were observed in the (13) CO J = 1-0
and 2-1 lines, and one tentative 2-1 detection is reported. A
compilation is presented of all CO observations of S-stars. The stars in
this sample are separated into ``intrinsic'' and ``extrinsic'' S-stars,
based on direct observation of the Technetium line, or infrared
properties. The dust mass loss rate per unit distance is derived from
IRAS 60 mu m data taking into the fact that for small mass loss rates
the observed flux is an overestimate of the excess emission due to dust.
The gas mass loss rate per unit distance is derived from CO data.
Distances and luminosities are estimated, partly from hipparcos parallax
data. The largest mass loss rate derived is that for W Aql with
(0.8-2.0) x 10(-5) {Msun} yr(-1) , and the lowest is that for
o Ori with <1.2 x 10(-9) {Msun} yr(-1) . The S-stars
without Tc have smaller mass loss rates, than those with Tc. Diagrams
showing mass loss rate, dust-to-gas ratio and expansion velocity versus
pulsation period are presented, and compared to similar data for carbon-
and oxygen-rich Miras. The S-Miras stand not out in any way from the C-
or O-Miras in these diagrams. In the diagram with expansion velocity
versus pulsation period, the S-SRs span the same range in velocity as
the S-Miras, but they have periods which are about a factor of 2.5
shorter. This was previously noted for O-rich SRs. As in that case, the
most straightforward explanantion is that the SRs among the S-stars
pulsate in a higher order pulsation mode. Based on data from the ESA
hipparcos astrometry satellite.
Using the Florida Multi-object Imaging Near-IR Grism Observational Spectrometer (FLAMINGOS), we have conducted the FLAMINGOS Extragalactic Survey (FLAMEX), a deep imaging survey covering 7.1 deg2 within the 18.6 deg2 NOAO Deep Wide-Field Survey (NDWFS) regions. FLAMEX is the first deep, wide-area, near-infrared survey to image in both the J and Ks filters, and is larger than any previous NIR survey of comparable depth. The intent of FLAMEX is to facilitate the study of galaxy and galaxy cluster evolution at 1 < z < 2 by providing rest-frame optical photometry for the massive galaxy population at this epoch. This effort is designed to yield a public data set that complements and augments the suite of existing surveys in the NDWFS fields. We present an overview of FLAMEX and initial results based on ~150,000 Ks-selected sources in the Boötes field. We describe the observations and reductions, quantify the data quality, and verify that the number counts are consistent with results from previous surveys. Finally, we comment on the utility of this sample for detailed study of the ERO population, and present one of the first spectroscopically confirmed z > 1 galaxy clusters detected using the joint FLAMEX, NDWFS, and Spitzer IRAC Shallow Survey data sets.
The progenitor of Type II-P (P = plateau) supernova SN 2004dj is identified with a supergiant in a compact star cluster known as "Sandage's star 96" (S96) in the nearby spiral galaxy NGC 2403, which was fortuitously imaged as part of the Beijing-Arizona-Taiwan-Connecticut (BATC) Multicolor Sky Survey from 1995 February to 2003 December prior to SN 2004dj. The superior photometry of BATC images for S96, taken with 14 intermediate-band filters covering 3000-10000 Å, unambiguously establishes the star cluster nature of S96, with an age of ~20 Myr, a reddening of E(B - V) ~ 0.35 mag, and a total mass of ~96,000 M☉. The compact star cluster nature of S96 is also consistent with the lack of light variations in the past decade. The SN progenitor is estimated to have a main-sequence mass of ~12 M☉. The comparison of our intermediate-band data of S96 with the postoutburst photometry obtained as the SN significantly dims with time may hopefully conclusively establish the nature of the progenitor.
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