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-NIR color-magnitude diagram for all sources observed toward NGC 2068/71 (dots) and all members (squares). The dashed line is the 2 Myr isochrone from Siess et al. (2000) at the distance of NGC 2068/71. The solid line is a reddening vector extending from a 2 Myr M0 star at the distance of NGC 2068/71, with every 5 A V marked with an plus sign.
Source publication
We study the disk and accretion properties of young stars in the NGC 2068 and NGC 2071 clusters. Using low-resolution optical spectra, we define a membership sample and determine an age for the region of ~2 Myr. Using high-resolution spectra of the H-alpha line we study the accretion activity of these likely members and also examine the disk proper...
Context in source publication
Context 1
... we define our members based on optical spectra, we cannot survey the deeply embedded population. Figure 3 shows a J vs. J-H color-magnitude diagram, similar to Figure 2, with a reddening vector extending from a 3 Myr old M0 star at 400 pc. Our sample is limited to A V < 5 although many sources further along the reddening vector have excess emission at 3.6-24µm consistent with circumstellar disks and hence are probably embedded cluster members. ...
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Citations
... Source 5 also contains two nearby protostellar sources found through the VISTA survey (Spezzi et al. 2015). The upper source, 054607.227-001134.91, is approximately 15″ away from our detection, and is labeled as a Class II source (Spezzi et al. 2015), and was previously found by Flaherty & Muzerolle (2008) and Fang et al. (2009). The lower source, 054607.884-001156.83, is approximately 9″ away from our detection, and is labeled as a potential Class III source (Spezzi et al. 2015). ...
We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 3 observations of 73 starless and protostellar cores in the Orion B North molecular cloud. We detect a total of 34 continuum sources at 106 GHz, and after comparisons with other data, four of these sources appear to be starless. Three of the four sources are located near groupings of protostellar sources, while one source is an isolated detection. We use synthetic observations of a simulation modeling a collapsing turbulent, magnetized core to compute the expected number of starless cores that should be detectable with our ALMA observations and find at least two (1.52) starless cores should be detectable (at 5σ), consistent with our data. We run a simple virial analysis of the cores to put the Orion B North observations into context with similar previous ALMA surveys of cores in Chamaeleon I and Ophiuchus. We conclude that the Chamaeleon I starless core population is characteristically less bounded than the other two populations, along with external pressure contributions dominating the binding energy of the cores. These differences may explain why the Chamaeleon I cores do not follow turbulent model predictions, while the Ophiuchus and Orion B North cores are consistent with the model.
... The fact that the source is detected in only one of the eight bins of the light curve allows us to draw some conclusions on the frequency of flares of this object, and therefore on their energy. Several stars in the neighbourhood were identified as T Tauri stars using IR analysis (Flaherty & Muzerolle 2008 ;Gibb 2008 ;Skinner et al. 2009 ;Spezzi et al. 2015 ). At least N = 58 stars classified as T Tauri at any stage of evolution are found within the second Fermi catalogue's error ellipse. ...
NGC 2071 is a star-forming region that overlaps with three $\gamma$-ray sources detected by the Fermi Space Telescope. We propose that strong flare activity in T Tauri stars could produce $\gamma$-ray emission in a way that makes them a counterpart to some unidentified sources detected by the Large Area Telescope aboard the Fermi satellite. We have performed a spectral and temporal analysis for two Fermi data sets: the first 2 yr and the entire 14 yr of observations. We have found that the $\gamma$-ray source is detectable at 3.2$\sigma$ above the background at energies above 100 GeV during the first 2 yr of observation. The analysis of the expected frequency of the highest energy flares occurring in T Tauri stars is consistent with our estimate. In addition, we have determined the minimum energy of the flare that would produce $\gamma$-ray emission, which is $\sim 5 \times 10^{37}$ erg. This agreement becomes a hard observational constraint supporting previous hypotheses about rare flares as the origin of unidentified $\gamma$-ray sources in star-forming regions.
... The fact that the source is detected in only one of the eight bins of the light curve allows us to draw some conclusions on the frequency of flares of this object, and therefore on their energy. Several stars in the neighbourhood were identified as T Tauri stars using IR analysis (Flaherty & Muzerolle 2008 ;Gibb 2008 ;Skinner et al. 2009 ;Spezzi et al. 2015 ). At least N = 58 stars classified as T Tauri at any stage of evolution are found within the second Fermi catalogue's error ellipse. ...
NGC 2071 is a star-forming region that overlaps with three γ-ray sources detected by the Fermi Space Telescope. We propose that strong flare activity in T Tauri stars could produce γ-ray emission in a way that makes them a counterpart to some unidentified sources detected by the Large Area Telescope aboard the Fermi satellite. We have performed a spectral and temporal analysis for two Fermi data sets: the first 2 yr and the entire 14 yr of observations. We have found that the γ-ray source is detectable at 3.2σ above the background at energies above 100 GeV during the first 2 yr of observation. The analysis of the expected frequency of the highest energy flares occurring in T Tauri stars is consistent with our estimate. In addition, we have determined the minimum energy of the flare that would produce γ-ray emission, which is ∼5 × 1037 erg. This agreement becomes a hard observational constraint supporting previous hypotheses about rare flares as the origin of unidentified γ-ray sources in star-forming regions.
... Since accretion is fed by disks, the sample of YSOs identified by accretion lines should be identical to the sample of young stars with dusty disks found by Spitzer (Winston et al. 2009). Around 15% of stars, however, show mismatches in their classifica-tions by spectroscopic and mid-IR criteria; this may be due to the presence of disks without strong Hα, the presence of chromospheric Hα lines toward active stars without disks, or perhaps the inability to detect disks due to nebulosity or weak mid-IR emission (Flaherty & Muzerolle 2008;Kounkel et al. 2017a). In particular, chromospheric emission lines may provide a new and currently under-utilized means for identifying young stars without disks (Herbig & Dahm 2002;Karnath et al. 2019). ...
We review the use of young low mass stars and protostars, or young stellar objects (YSOs), as tracers of star formation. Observations of molecular clouds at visible, infrared, radio and X-ray wavelengths can identify and characterize the YSOs populating these clouds, with the ability to detect deeply embedded objects and all evolutionary stages. Surveys with the Spitzer, Herschel, XMM-Newton and Chandra space telescopes have measured the spatial distribution of YSOs within a number of nearby (< 2.5 kpc) molecular clouds, showing surface densities varying by more than three orders of magnitude. These surveys have been used to measure the spatially varying star formation rates and efficiencies within clouds, and when combined with maps of the molecular gas, have led to the discovery of star-forming relations within clouds. YSO surveys can also characterize the structures, ages, and star formation histories of embedded clusters, and they illuminate the relationship of the clusters to the networks of filaments, hubs and ridges in the molecular clouds from which they form. Measurements of the proper motions and radial velocities of YSOs trace the evolving kinematics of clusters from the deeply embedded phases through gas dispersal, providing insights into the factors that shape the formation of bound clusters. On 100 pc scales that encompass entire star-forming complexes, Gaia is mapping the young associations of stars that have dispersed their natal gas and exist alongside molecular clouds. These surveys reveal the complex structures and motions in associations, and show evidence for supernova driven expansions. Remnants of these associations have now been identified by Gaia, showing that traces of star-forming structures can persist for a few hundred million years.
... The current epoch of star formation is confined to the Orion A and B molecular clouds, which contain massive clusters such as the Orion Nebula Cluster (ONC), NGC 2024, and NGC 2068. The stars in these clouds have typical ages of ∼1-3 Myr ( Levine et al. 2006;Flaherty & Muzerolle 2008;Muench et al. 2008;Da Rio et al. 2010). Several other populations of young stars that have already dissipated their molecular gas and dust can also be identified. ...
... Each one has its own advantages and limitations, pertaining to the ability to reject nonclustered field sources that are not part of any group (such as foreground or background stars); ability to separate populations that are closer to each other than their respective sizes; ability to identify structures of different sizes, shapes, and densities; and dependence on the initial assumptions pertaining to the structure within the data. A review of various methodologies is presented by Everitt et al. (2011) andFeigelson & Babu (2012). We chose "average linkage" hierarchical clustering that gives structures Table 2 Astrometric Solutions from Gaia Utilized in the Analysis ...
We present an analysis of spectroscopic and astrometric data from APOGEE-2 and Gaia DR2 to identify structures toward the Orion Complex. By applying a hierarchical clustering algorithm to the six-dimensional stellar data, we identify spatially and/or kinematically distinct groups of young stellar objects with ages ranging from 1 to 12 Myr. We also investigate the star-forming history within the Orion Complex and identify peculiar subclusters. With this method we reconstruct the older populations in the regions that are currently largely devoid of molecular gas, such as Orion C (which includes the σ Ori cluster) and Orion D (the population that traces Ori OB1a, OB1b, and Orion X). We report on the distances, kinematics, and ages of the groups within the Complex. The Orion D group is in the process of expanding. On the other hand, Orion B is still in the process of contraction. In λ Ori the proper motions are consistent with a radial expansion due to an explosion from a supernova; the traceback age from the expansion exceeds the age of the youngest stars formed near the outer edges of the region, and their formation would have been triggered when they were halfway from the cluster center to their current positions. We also present a comparison between the parallax and proper-motion solutions obtained by Gaia DR2 and those obtained toward star-forming regions by the Very Long Baseline Array. © 2018. The American Astronomical Society. All rights reserved.
... For NGC 2024, we find a maximum age of 3.7 Myr, for NGC 2068, a maximumage of 2.3 Myr and NGC 2071, a maximum age of 2.1 Myr. These are consistent with the isochronal ages found for these regions (Levine et al. 2006, Flaherty & Muzerolle 2008. ...
... Observations of Orion and other associations paint a picture where stars in the molecular clouds have ages ≤ 2 Myr (Jeffries 2007, Flaherty & Muzerolle 2008, while stars in the association have ages ranging up to 10 Myr (Briceno 2008). This requires some method for creating and destroying clouds on ∼ 2 Myr timescales, while sustaining star formation within the OB association for a 10 Myr period. ...
We analyze the spatial distribution of dusty young stellar objects (YSOs)
identified in the Spitzer Survey of the Orion Molecular clouds, augmenting
these data with Chandra X-ray observations to correct for incompleteness in
dense clustered regions. We also devise a scheme to correct for spatially
varying incompleteness when X-ray data are not available. The local surface
densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with
protostars tending to be in higher density regions. This range of densities is
similar to other surveyed molecular clouds with clusters, but broader than
clouds without clusters. By identifying clusters and groups as continuous
regions with surface densities $\ge10$ pc$^{-2}$, we find that 59% of the YSOs
are in the largest cluster, the Orion Nebular Cluster (ONC), while 13% of the
YSOs are found in a distributed population. A lower fraction of protostars in
the distributed population is evidence that it is somewhat older than the
groups and clusters. An examination of the structural properties of the
clusters and groups show that the peak surface densities of the clusters
increase approximately linearly with the number of members. Furthermore, all
clusters with more than 70 members exhibit asymmetric and/or highly elongated
structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc,
suggesting that the cluster is only $\sim 2$ Myr in age. We find the star
formation efficiency (SFE) of the Orion B cloud is unusually low, and that the
SFEs of individual groups and clusters are an order of magnitude higher than
those of the clouds. Finally, we discuss the relationship between the young low
mass stars in the Orion clouds and the Orion OB 1 association, and we determine
upper limits to the fraction of disks that may be affected by UV radiation from
OB stars or by dynamical interactions in dense, clustered regions.
... The Orion B cloud contains the NGC 2024 H ii region as well as the NGC 2023, 2068, and 2071 reflection nebulae. All of these regions also contain clusters or groups of young stars (Lada et al. 1991;Chen & Tokunaga 1994;Allen & Davis 2008;Peterson & Megeath 2008;Meyer et al. 2008;Flaherty & Muzerolle 2008). Directly to the north of the Orion B cloud is the Lynds 1622 cloud. ...
We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments on board Spitzer. In total, five distinct fields were mapped, covering 9 deg{sup 2} in five mid-IR bands spanning 3-24 {mu}m. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630, and 1622 dark clouds, and the NGC 2023, 2024, 2068, and 2071 nebulae. These data are merged with the Two Micron All Sky Survey point source catalog to generate a catalog of eight-band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main-sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in two to three epochs over six months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5 {mu}m bands. We find that 50% of the dusty YSOs show variability. The variations are typically small ({approx}0.2 mag) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8, and 8 {mu}m variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots.
... NGC 2068/2071 is another young SFR in Ori OB association. Flaherty & Muzerolle (2008) presented Spitzer data, spectral type, and stellar paremeters of 69 likely members. Among 69 likely members, 48 stars are low-mass stars (Sp = K7 – M4), and 26 out of 48 stars are classified as CTTS. ...
We have performed mid-IR photometry of the young open cluster NGC 2264 using the images obtained with the Spitzer Space Telescope IRAC and MIPS instruments and present a normalized classification scheme of young stellar objects in various color-color diagrams to make full use of the information from multicolor photometry. These results are compared with the classification scheme based on the slope of the spectral energy distribution (SED). From the spatial distributions of Class I and II stars, we have identified two subclusterings of Class I objects in the CONE region of Sung et al. The disked stars in the other star forming region S MON are mostly Class II objects. These three regions show a distinct difference in the fractional distribution of SED slopes as well as the mean value of SED slopes. The fraction of stars with primordial disks is nearly flat between log m = 0.2 -- -0.5, and that of transition disks is very high for solar mass stars. In addition, we have derived a somewhat higher value of the primordial disk fraction for NGC 2264 members located below the main pre-main sequence locus (so-called BMS stars). This result supports the idea that BMS stars are young stars with nearly edge-on disks. We have also found that the fraction of primordial disks is very low near the most massive star S Mon and increases with distance from S Mon. Comment: 38 pages, 21 figures, 5 tables (AJ accepted)
We review the use of young low mass stars and protostars, or young stellar objects (YSOs), as tracers of star formation. Observations of molecular clouds at visible, infrared, radio and X-ray wavelengths can identify and characterize the YSOs populating these clouds, with the ability to detect deeply embedded objects at all evolutionary stages. Surveys with the Spitzer, Herschel, XMM-Newton and Chandra space telescopes have measured the spatial distribution of YSOs within a number of nearby (<2.5 kpc) molecular clouds, showing surface densities varying by more than three orders of magnitude. These surveys have been used to measure the spatially varying star formation rates and efficiencies within clouds, and when combined with maps of the molecular gas, have led to the discovery of star-forming relations within clouds. YSO surveys can also characterize the structures, ages, and star formation histories of embedded clusters, and they illuminate the relationship of the clusters to the networks of filaments, hubs and ridges in the molecular clouds from which they form. Measurements of the proper motions and radial velocities of YSOs trace the evolving kinematics of clusters from the deeply embedded phases through gas dispersal, providing insights into the factors that shape the formation of bound clusters. On 100 pc scales that encompass entire star-forming complexes, Gaia is mapping the young associations of stars that have dispersed their natal gas and exist alongside molecular clouds. These surveys reveal the complex structures and motions in associations, and show evidence for supernova driven expansions. Remnants of these associations have now been identified by Gaia, showing that traces of star-forming structures can persist for a few hundred million years.
Context. Planets form in circumstellar disks around pre-main-sequence stars. A key question is, how do the formation and evolution of protoplanetary disks depend on stellar mass? Studies of circumstellar disks at infrared and submillimeter wavelengths around intermediate-mass Herbig Ae/Be stars have revealed disk structures such as cavities, gaps, and spiral arms. The Herbig Ae/Be stars represent an older population of intermediate-mass pre-main-sequence stars. Since these evolve toward the main sequence on timescales comparable to those of typical disk dissipation, a full picture of disk dispersal in intermediate-mass pre-main-sequence stars must include the intermediate-mass T Tauri (IMTT) stars.
Aims. We seek to find the precursors of the Herbig Ae/Be stars in the solar vicinity within 500 pc from the Sun. We do this by creating an optically selected sample of IMTT stars from the literature, here defined as stars of masses 1.5 M ⊙ ≤ M * ≤ 5 M ⊙ and with a spectral type between F and K3.
Methods. We used literature optical photometry (0.4–1.25 μm) and distances determined from Gaia DR2 parallax measurements together with Kurucz stellar model spectra to place the stars in a HR diagram. We employed Siess evolutionary tracks to identify IMTT stars from the literature and derived masses and ages. We used Spitzer spectra to classify the disks around the stars into Meeus Group I and Group II disks based on their [F 30 /F 13.5 ] spectral index. We also examined the 10 μm silicate dust grain emission and identified emission from polycyclic aromatic hydrocarbons (PAH). From this, we built a qualitative picture of the disks around the IMTT stars and compared this with available spatially resolved images at infrared and submillimeter wavelengths to confirm our classification.
Results. We find 49 IMTT stars with infrared excess. The identified disks are similar to the older Herbig Ae/Be stars in disk geometries and silicate dust grain population. The detection frequency of PAHs is higher than from disks around lower mass T Tauri stars but less frequent than from Herbig Ae/Be disks. Spatially resolved images at infrared and submillimeter wavelengths suggest gaps, and spirals are also present around the younger precursors to the Herbig Ae/Be stars.
Conclusions. Comparing the timescale of stellar evolution toward the main sequence and current models of protoplanetary disk evolution, the similarity between Herbig Ae/Be stars and the IMTT stars points toward an evolution of Group I and Group II disks that are disconnected and represent two different evolutionary paths.
