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Discovery of a Nova-Like Cataclysmic Variable in the Kepler Mission Field
Abstract
We announce the identification of a new cataclysmic variable (CV) star in the field of the Kepler Mission, KIC J192410.81+445934.9. This system was identified during a search for compact pulsators in the Kepler field. High-speed photometry reveals coherent large-amplitude variability with a period of 2.94 hr. Rapid, large-amplitude quasi-periodic variations are also detected on time scales of 1200 s and 650 s. Time-resolved spectroscopy covering one half photometric period shows shallow, broad Balmer and He I absorption lines with bright emission cores as well as strong He II and Bowen blend emission. Radial velocity variations are also observed in the Balmer and He I emission lines that are consistent with the photometric period. We therefore conclude that KIC J192410.81+445934.9 is a nova-like (NL) variable of the UX UMa class in or near the period gap, and it may belong to the rapidly growing subclass of SW Sex systems. Based on Two Micron All Sky Survey photometry and companion star models, we place a lower limit on the distance to the system of ~500 pc. Due to limitations of our discovery data, additional observations including spectroscopy and polarimetry are needed to confirm the nature of this object. Such data will enable further understanding of the behavior of NL variables in the critical period range of 3-4 hr, where standard CV evolutionary theory finds major problems. The presence of this system in the Kepler Mission field of view also presents a unique opportunity to obtain a continuous photometric data stream of unparalleled length and precision on a CV system.
Superhumps are among the abundant variable phenomena observed in the light curves of cataclysmic variables (CVs). They come in two flavours as positive and negative superhumps, distinguished by periods slightly longer or shorter, respectively, than the orbital periods of these interacting binary systems. Positive superhumps are ubiquitous in superoutbursting short period dwarf novae of the SU UMa type but are less common in longer period systems with accretion disks in a permanent bright state such as novalike variables and most old novae. Negative superhumps do not seem not to have a preference for a particular type of CV. Here, I take advantage of the long high cadence light curves provided by TESS for huge number of stars, selecting all old novae and novalike variables with past reported superhumps for which TESS light curves are available and have not yet been analysed in previous publications in order to study their superhump behaviour. In combination with information taken from the literature the results enable to compile the most complete census of superhumps in these stars so far. As a corollary, for the eclipsing systems in the present sample of objects eclipse epochs derived from the TESS light curves and in some cases from archival light curves are listed and used to update orbital ephemeris and to discuss period changes.
Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during the 2017 season, and characterized these objects. WZ Sge-type stars identified in this study are PT And, ASASSN-17ei, ASASSN-17el, ASASSN-17es, ASASSN-17fn, ASASSN-17fz, ASASSN-17hw, ASASSN-17kd, ASASSN-17la, PNV J20205397$+$2508145, and TCP J00332502$-$3518565. We obtained new mass ratios for seven objects using growing superhumps (stage A). ASASSN-17gf is an EI Psc-type object below the period minimum. CRTS J080941.3$+$171528 and DDE 51 are objects in the period gap, and both showed a long-lasting phase of stage A superhumps. We also summarize the recent advances in understanding of SU UMa-type and WZ Sge-type dwarf novae.
We present an analysis of all available time-resolved photometry from the literature and new light curves obtained in 2013-2014 for the old nova RR Pictoris. The well-known hump light curve phased with the orbital period reveals significant variations over the last 42 years in shape, amplitude and other details which apparently are caused by long-term variations in the disc structure. In addition we found evidence for the presence of superhumps in 2007, with the same period (~9% longer than the orbital period), as reported earlier by other authors from observations in 2005. Possibly, superhumps arise quickly in RR Pic, but are sporadic events, because in all the other observing runs analysed no significant superhump signal was detected. We also determined an actual version of the Stolz--Schoembs relation between superhump period and orbital period, analysing separately dwarf novae, classical novae and nova-like stars, and conclude that this relation is of general validity for all superhumpers among the cataclysmic variables (CVs), in spite of small but significant differences among the sub-types mentioned above. We emphasize the importance of such a study in context with the still open question of the interrelation between the different sub-classes of CVs, crucial for our understanding of the long-term CV evolution.
We report on the detection of the linear rms–flux relation in two accreting white dwarf binary systems: V1504 Cyg and KIC
8751494. The rms–flux relation relates the absolute root-mean-square (rms) variability of the light curve to its mean flux.
The light curves analysed were obtained with the Kepler satellite at a 58.8 s cadence. The rms–flux relation was previously detected in only one other cataclysmic variable (CV),
MV Lyr. This result reinforces the ubiquity of the linear rms–flux relation as a characteristic property of accretion-induced
variability, since it has been observed in several black hole binaries, neutron star binaries and active galactic nuclei.
Moreover, its detection in V1504 Cyg is the first time the rms–flux relation has been detected in a dwarf nova-type CV during
quiescence. This result, together with previous studies, hence points towards a common physical origin of accretion-induced
variability, independent of the size, mass or type of the central accreting compact object.
We analyzed a Kepler light curve of KIC 8751494, a recently recognized
novalike cataclysmic variable in the Kepler field. We detected a stable
periodicity of 0.114379(1) d, which we identified as being the binary's orbital
period. The stronger photometric period around 0.12245 d, which had been
detected from the ground-based observation, was found to be variable, and we
identified this period as being the positive superhump period. This superhump
period showed short-term (10-20 d) and strong variations in period most
unexpectedly when the object entered a slightly faint state. The fractional
superhump excess varied as large as ~30%. The variation of the period very well
traced the variation of the brightness of the system. The time-scales of this
variation of the superhump period was too slow to be interpreted as the
variation caused by the change in the disk radius due to the thermal disk
instability. We interpreted that the period variation was caused by the varying
pressure effect on the period of positive superhumps. This finding suggests
that the pressure effect, in at least novalike systems, plays a very important
(up to ~30% in the precession rate) role in producing the period of the
positive superhumps. We also described a possible detection of the negative
superhumps with a varying period of 0.1071-0.1081 d in the Q14 run of the
Kepler data. We also found that the phase of the velocity variation of the
emission lines reported in the earlier study is compatible with the SW Sex-type
classification. Further, we introduced a new two-dimentional period analysis
using least absolute shrinkage and selection operator (Lasso) and showed
superior advantage of this method.
The NASA {\it Kepler} mission has been in science operation since May 2009
and is providing high precision, high cadence light curves of over 150,000
targets. Prior to launch, nine cataclysmic variables were known to lie within
{\it Kepler's} field of view. We present spectroscopy for seven systems, four
of which were newly discovered since launch. All of the stars presented herein
have been observed by, or are currently being observed by, the {\it Kepler}
space telescope. Three historic systems and one new candidate could not be
detected at their sky position and two candidates are called into question as
to their true identity.
This paper describes the first data release of the Kepler-INT Survey (KIS),
that covers a 116 deg2 region of the Cygnus and Lyra constellations. The Kepler
field is the target of the most intensive search for transiting planets to
date. Despite the fact that the Kepler mission provides superior time series
photometry, with an enormous impact on all areas of stellar variability, its
field lacks optical photometry complete to the confusion limit of the Kepler
instrument necessary for selecting various classes of targets. For this reason,
we follow the observing strategy and data reduction method used in the IPHAS
and UVEX galactic plane surveys in order to produce a deep optical survey of
the Kepler field. This initial release concerns data taken between May and
August 2011, using the Isaac Newton Telescope on the island of La Palma. Four
broadband filters were used, U, g, r, i, as well as one narrowband one, Halpha,
reaching down to a 10-sigma limit of around 20th mag in the Vega system.
Observations covering around 50 deg2, thus about half of the field, passed our
quality control thresholds and constitute this first data release. We derive a
global photometric calibration by placing the KIS magnitudes as close as
possible to the Kepler Input Catalog (KIC) photometry. The initial data release
catalogue containing around 6 million sources from all the good photometric
fields is available for download from the KIS webpage, as well as via MAST.
We present results from the first two quarters of a survey to search for pulsations in compact stellar objects with the Kepler spacecraft. The survey sample and the various methods applied in its compilation are described, and spectroscopic observations are presented to separate the objects into accurate classes. From the Kepler photometry we clearly identify nine compact pulsators, and a number of interesting binary stars. Of the pulsators, one shows the strong, rapid pulsations typical for a V361 Hya type sdB variable (sdBV), seven show long-period pulsations characteristic of V1093 Her type sdBVs, and one shows low-amplitude pulsations with both short and long periods. We derive effective temperatures and surface gravities for all the subdwarf B stars in the sample and demonstrate that below the boundary region where hybrid sdB pulsators are found, all our targets are pulsating. For the stars hotter than this boundary temperature a low fraction of strong pulsators (<10 per cent) is confirmed. Interestingly, the short-period pulsator also shows a low-amplitude mode in the long-period region, and several of the V1093 Her pulsators show low amplitude modes in the short-period region, indicating that hybrid behaviour may be common in these stars, also outside the boundary temperature region where hybrid pulsators have hitherto been found. Comment: Accepted for publication in MNRAS
The timing capabilities and sensitivity of Kepler, NASA's observatory to find Earth-sized planets within the habitable zone of stars, are well matched to the timescales and amplitudes of accretion disk variability in cataclysmic variables. This instrumental combination provides an unprecedented opportunity to test and refine stellar accretion paradigms with high-precision, uniform data, containing none of the diurnal or season gaps that limit ground-based observations. We present a 3-month, 1 minute cadence Kepler light curve of V344 Lyr, a faint, little-studied dwarf nova within the Kepler field. The light curve samples V344 Lyr during five full normal outbursts and one superoutburst. Surprisingly, the superhumps found during superoutburst continue to be detected during the following quiescent state and normal outburst. The fractional excess of superhump period over the presumed orbital period suggests a relatively high binary mass ratio in a system where the radius of the accretion disk must vary by less than 2% in order to maintain tidal precession throughout the extended episode of superhumping. Disk radius is less restricted if the quiescent signal identified tentatively as the orbital period is a negative superhump, generated by a retrograde-precessing accretion disk, tilted with respect to the binary orbital plane. Comment: ApJL, in press, 5 pages, 3 figures
The disrupted magnetic braking theory for the period gap of cataclysmic
variable systems is used to study the binary evolution of low-mass
main-sequence-like stars with white dwarf companions. The model is able
to reproduce the observed location and width of the gap provided that
the average mass transfer rates above the upper edge of the gap are
greater than about 1.9 x 10 to the -9th solar masses/yr. For the case of
angular momentum loss by magnetic braking, the slope of the mass
transfer rate with respect to orbital period is shown to range from 3.4
to 3.7. For the evolutionary sequences considered, the He-3 abundance at
the surface of the secondary exceeds 0.0015 after the complete mixing
phase, resulting in modifications in the nuclear burning development of
nova explosions.
We present optical photometry and spectroscopy of the nova-like variable
V795 Her. The emission lines exhibit an extremely complex structure
consisting of several time-variable emission and absorption components.
We confirm the spectroscopic modulation of 0.1082d which we attribute to
the orbital period of the system. The equivalent widths (EWs) of all the
emission lines are strongly modulated on this period, showing a
pronounced minimum around phase 0.5. We associate this minimum with the
transit of an absorption feature which drives dramatic line changes,
seen as transient double peaks and PCygni type profiles. The absorption
depth grows with the excitation level in Balmer and HeI lines, but both
the HeII lambda4686 and the metallic lines (e.g. CII lambda4267 and the
Bowen blend) are entirely in emission. The centroid of the Hα
emission (which is contaminated very little by the absorption feature)
is delayed by 83 deg with respect to the high-excitation lines. We
assume that the latter trace the orbital motion of the primary, enabling
us to define an absolute zero-phase. High-velocity S-waves are clearly
observed in all Balmer lines, with amplitudes of about 1750 km s^-1 and
maximum redshift at about phase 0. However, our high-resolution spectra
suggest that these can be separated into two phased components, with
gamma-velocities of ~+/-750 km s^-1 and K~1000 km s^-1, probably formed
in accretion columns on the white dwarf. In addition, the HI cores
exhibit the presence of low-velocity (K=268 km s^-1) S-waves, roughly
phased with their high-amplitude partners. On the other hand, our R-band
photometry is dominated by flickering with no evidence for modulation
with the orbital period nor the previously reported 0.1165-d
periodicity. Based on the spectral properties, we propose that V795 Her
is a new SW Sex star, observed at intermediate inclination. The complex
behaviour of V795 Her can be qualitatively explained invoking an
intermediate polar scenario with a synchronously rotating white dwarf.
An overview of the detector requirements for WET photometry is given,
including discussion of why CCD usage has not been attractive for WET
until comparatively recently. Initial CCD usage by WET is described
along with a comparison of results from CCD photometry programs applied
to the same data. It was found that a CCD on a 0.75 m telescope provided
data which were almost as good as a photomultiplier tube results on a
1.9 m telescope. Aperture photometry was generally found to be in
agreement with theoretical expectation, as well as being more precise
than point spread function fitting. This latter result is surprising and
not understood, though it is possible that coding problems are
responsible.
An observational review on H I in the Galaxy is presented. Attention is given to observations of interstellar atomic hydrogen from Lyman-alpha and the 21-cm line through indirect tracers such as dust and gamma rays; to what can be learned from such observations; to what the H I sky looks like; and to the state of knowledge in this area and the future prospects. Consideration is also given to results from recent H I investigations that bear on two important areas: the spatial organization of interstellar H I and its vertical distribution in the Galaxy.
We report the discovery of 11 new variable DA white dwarf (ZZ Ceti) stars. Candidates were selected by deriving temperatures from model fits to spectra obtained from the Sloan Digital Sky Survey (SDSS). We also find objects whose temperatures and gravities indicate they lie within the instability strip for pulsation but were not observed to vary. Although the temperatures are based on relatively low signal-to-noise ratio spectra, an impure strip is unexpected, which if confirmed, has implications for DA asteroseismology. This work brings the total number of published variable DA white dwarf stars to 82.
We present limits on planetary companions to pulsating white dwarf stars. A subset of these stars exhibit extreme stability in the period and phase of some of their pulsation modes; a planet can be detected around such a star by searching for periodic variations in the arrival time of these pulsations. We present limits on companions greater than a few Jupiter masses around a sample of 15 white dwarf stars as part of an ongoing survey. One star shows a variation in arrival time consistent with a 2MJ planet in a 4.5 yr orbit. We discuss other possible explanations for the observed signal and conclude that a planet is the most plausible explanation based on the data available.
The observational data for the 124 cataclysmic and low-mass X-ray binaries of known orbital period are compiled. It is found that the eruption properties are very well correlated with the orbital periods, in a manner that suggests that the mass transfer is the all-important determinant of evolution and of the eruptive behavior. Transfer rates of 10 to the -11th to 10 to the -7th solar mass/year are found, which are well correlated with orbital period. It is concluded that the mechanism which drives these systems is the magnetic braking of the secondary's rotation by its own stellar wind, coupled with the enforcement of synchronous rotation by tidal friction. This permits CVs to lose sufficient angular momentum to begin mass transfer in a reasonable time and drives the mass transfer at a high rate once it begins. An account of the long-lived phases of CV evolution is given.
We report the detection of modulated circular polarization in V795 Her. The degree of polarization increases with wavelength and is modulated with a period of 19.54 min, which is very close to the reported optical QPO period. The modulation has a peak-to-peak amplitude of 0.12% in the U-band. The estimated magnetic field intensity is in the range 2-7 MG.
We report on the discovery of variable circular polarization in the SW Sex star LS Pegasi. The observed modulation has an amplitude of ~0.3 % and a period of 29.6 minutes, which we assume as the spin period of the magnetic white dwarf. We also detected periodic flaring in the blue wing of Hbeta, with a period of 33.5 minutes. The difference between both frequencies is just the orbital frequency, so we relate the 33.5-min modulation to the beat between the orbital and spin period. We propose a new accretion scenario in SW Sex stars, based on the shock of the disk-overflown gas stream against the white dwarf's magnetosphere, which extends to the corotation radius. From this geometry, we estimate a magnetic field strength of B(1) ~ 5-15 MG. Our results indicate that magnetic accretion plays an important role in SW Sex stars and we suggest that these systems are probably Intermediate Polars with the highest mass accretion rates. Comment: Accepted by ApJ Letters. LaTeX, 14 pages, 3 PostScript figures
We report on time-resolved optical spectroscopy of 10 non-eclipsing nova-like cataclysmic variables in the orbital period range between 3 and 4 h. The main objective of this long-term programme is to search for the characteristic SW Sextantis behaviour and to eventually quantify the impact of the SW Sex phenomenon on nova-likes at the upper boundary of the orbital period gap.
Of the 10 systems observed so far, HL Aqr, BO Cet, AH Men, V380 Oph, AH Pic and LN UMa are identified as new members of the SW Sex class. We present improved orbital period measurements for HL Aqr (Porb= 3.254 ± 0.001 h) and V380 Oph (Porb= 3.69857 ± 0.00002 h). BO Cet and V380 Oph exhibit emission-line flaring with periodicities of 20 and 47 min, respectively. The Hα line of HL Aqr shows significant blueshifted absorption modulated at the orbital period. Similarly to the emission S-wave of the high-inclination SW Sex stars, this absorptionS-wave has its maximum blue velocity at orbital phase ∼0.5. We estimate an orbital inclination for HL Aqr in the range 19° < i < 27°, which is much lower than that of the emission-dominated, non-eclipsing SW Sex stars (i∼ 60°–70°). This gives rise to the interesting possibility of many low-inclination nova-likes actually being SW Sex stars, but with a very different spectroscopic appearance as they show significant absorption. The increasing blueshifted absorption with decreasing inclination points to the existence of a mass outflow with significant vertical motion.
These six new additions to the SW Sex class increase the presence of non-eclipsing systems to about one-third of the whole SW Sex population, which therefore makes the requirement of eclipses as a defining criterion for SW Sex membership no longer valid. The statistics of the cataclysmic variable population in the vicinity of the upper period gap are also discussed.
The study of cataclysmic variables - interacting binary stars containing a white dwarf accreting from an orbiting companion - is undergoing an exciting renaissance, as it embraces observations at all wavelengths. Cataclysmic variables allow, in particular, the direct and detailed study of equilibrium and non-equilibrium accretion discs; in turn these developments also help in our understanding of X-ray binaries, black holes and active galactic nuclei. This timely volume provides the first comprehensive survey of cataclysmic variable stars, integrating theory and observation into a single, synthesised text. An introductory chapter gives the historical background of studies of cataclysmic variables. The author then goes on to give an up-to-date review of both the observations (at all wavelengths, and over all time-scales), the theories, the models of the structures and accretion processes believed to be involved. A very detailed bibliography is also provided to guide the reader to pertinent primary literature.
We present time-resolved spectroscopy and circular spectropolarimetry of the SW Sex star RX J1643.7+3402. We find significant
polarization levels exhibiting a variability at a period of 19.38 ± 0.39 min. In addition, emission-line flaring is found
predominantly at twice the polarimetric period. These two findings are strong evidences in favour of the presence of a magnetic
white dwarf in the system. We interpret the measured periodicities in the context of our magnetic accretion model for SW Sex
stars. In contrast with LS Pegasi – the first SW Sex star discovered to have modulated circular polarization – the polarization
in RX J1643.7+3402 is suggested to vary at 2(ω−Ω), while the emission lines flare at (ω−Ω). However, a 2ω/ω interpretation
cannot be ruled out. Together with LS Peg and V795 Her, RX J1643.7+3402 is the third SW Sex star known to exhibit modulated
circular polarization.
Emission-line profiles of several cataclysmic variables have been
observed through eclipse, and they do not show strong evidence for the
rotational signature that is characteristic of an accretion disk. The
lines appear to be formed in material that has some rotation with
respect to the white dwarf, but that also has a substantial velocity
directed radially with respect to the degenerate dwarf. The data are
suggestive that the emission lines of many novae and novalike variables
may not originate in disks, but in rotating polar accretion columns, and
that the existence of a strong magnetic field may be an important
parameter for the nova phenomenon.
I obtained radial-velocity spectra of PG 0834 + 488, PG 1003 + 678 = CH
UMa, and PG 1711 + 336 = V795 Her to determine their orbital periods. PG
0834 + 488 has an apparently normal dwarf-nova type spectrum, and its
orbital period is here found to be 6.4 hr with no cycle-count ambigu-
ity. The present data show no visible absorption from a secondary star.
PG 1003 + 678 = CH UMa most likely has a period of 8.3 hr, which is an
alias of the preliminary period of 12.5 hr announced by Thorstensen
(1985); the 12.5 hr period remains possible. It shows absorption
features in its spectrum characteristic of a late-type secondary star,
and these features appear to have velocities in antiphase to the
emission lines. The velocity amplitude is small and the lines narrow,
suggesting a low inclination. PG 1711 + 336 = V795 Her has a most likely
period of 14.8 hr, unusually long for a cataclysmic binary; because of
the weakness of the emission lines, some doubt remains about the period.
The 2.75 hr photometric period determined by Baidak et al. (1985) is not
indicated in the velocities. The emission lines are weak and the flux
distribution very blue. The object is evidently a nova-like variable in
a perpetual high state. if the photometric and spectroscopic periods are
both correct, it may be a very slow DQ Her star as well.
We present a full-sky 100 μm map that is a reprocessed composite of the COBE/DIRBE and IRAS/ISSA maps, with the zodiacal foreground and confirmed point sources removed. Before using the ISSA maps, we remove the remaining artifacts from the IRAS scan pattern. Using the DIRBE 100 and 240 μm data, we have constructed a map of the dust temperature so that the 100 μm map may be converted to a map proportional to dust column density. The dust temperature varies from 17 to 21 K, which is modest but does modify the estimate of the dust column by a factor of 5. The result of these manipulations is a map with DIRBE quality calibration and IRAS resolution. A wealth of filamentary detail is apparent on many different scales at all Galactic latitudes. In high-latitude regions, the dust map correlates well with maps of H I emission, but deviations are coherent in the sky and are especially conspicuous in regions of saturation of H I emission toward denser clouds and of formation of H2 in molecular clouds. In contrast, high-velocity H I clouds are deficient in dust emission, as expected.
I outline some of the plans for following up transiting-planet candidates identified by NASA's Kepler mission. An initial spectroscopic reconnaissance will be used to sort out most of the candidates that involve eclipsing binaries instead of transiting planets. Very precise radial velocities will then be obtained for the survivors, with the goal of deriving spectroscopic orbits and planetary masses. When combined with the planetary radii derived from the transit light curves, this will provide critical information for the characterization of the planets discovered with Kepler.
We present high-time-resolution spectroscopy of the non-eclipsing old nova V533 Herculis (N Her 1963). It is the second nova remnant affected by the ‘SW Sex syndrome’. A modulation of the equivalent width of the emission lines with a period of 23.33 min has been detected. This, together with the strong He iiλ4686 emission characteristic of magnetic systems, leads us to link this period to the spin of a magnetic white dwarf. Similar flaring activity has been recorded in other SW Sex stars, namely, the old nova BT Mon, LS Peg and DW UMa, supporting the idea of these systems being magnetic accretors. Stationary emission features are also observed in the Balmer lines, which we attribute to the ejected nova shell.
We carefully consider observational and theoretical constraints on the global properties of secondary stars in cataclysmic variable stars (CVs). We then use these constraints to construct and test a complete, semi-empirical donor sequence for CVs with orbital periods Porb≤ 6 h. All key physical and photometric parameters of CV secondaries (along with their spectral types) are given as a function of Porb along this sequence. This provides a benchmark for observational and theoretical studies of CV donors and evolution.
The main observational basis for our donor sequence is an empirical mass–radius relationship for CV secondaries. Patterson and co-workers have recently shown that this can be derived from superhumping and/or eclipsing CVs. We independently revisit all of the key steps in this derivation, including the calibration of the period excess–mass ratio relation for superhumpers and the use of a single representative primary mass for most CVs. We also present an optimal technique for estimating the parameters of the mass–radius relation that simultaneously ensures consistency with the observed locations of the period gap and the period minimum. We present new determinations of these periods, finding Pgap,+= 3.18 ± 0.04 h (upper edge), Pgap,−= 2.15 ± 0.03 h (lower edge) and Pmin= 76.2 ± 1.0 min (period minimum).
We test the donor sequence by comparing observed and predicted spectral types (SpTs) as a function of orbital period. To this end, we update the SpT compilation of Beuermann and co-workers and show explicitly that CV donors have later SpTs than main-sequence (MS) stars at all orbital periods. This extends the conclusion of the earlier study to the short-period regime (Porb < 3 h). We then compare our donor sequence to the CV data, and find that it does an excellent job of matching the observed SpTs. Thus the empirical mass–radius relation yields just the right amount of radius expansion to account for the later-than-MS spectral types of CV donors. There is remarkably little intrinsic scatter in both the mass–radius and SpT–Porb relations, which confirms that most CVs follow a unique evolution track.
The donor sequence exhibits a fairly sharp drop in temperature, luminosity and optical/infrared flux well before the minimum period. This may help to explain why the detection of brown dwarf secondaries in CVs has proven to be extremely difficult.
We finally apply the donor sequence to the problem of distance estimation. Based on a sample of 22 CVs with trigonometric parallaxes and reliable 2MASS data, we show that the donor sequence correctly traces the upper envelope of the observed MJHK–Porb distribution. Thus robust lower limits on distances can be obtained from single-epoch infrared observations. However, for our sample, these limits are typically about a factor of 2 below the true distances.
We present time-series optical photometry of five new cataclysmic variables (CVs) identified by the Hamburg Quasar Survey (HQS). The deep eclipses observed in HS 0129+2933 (= TT Tri), HS 0220+0603 and HS 0455+8315 provided very accurate orbital periods of 3.35129827(65), 3.58098501(34) and 3.56937674(26) h, respectively. HS 0805+3822 shows grazing eclipses and has a likely orbital period of 3.2169(2) h. Time-resolved optical spectroscopy of the new CVs (with the exception of HS 0805+3822) is also presented. Radial velocity studies of the Balmer emission lines provided an orbital period of 3.55 h for HS 1813+6122, which allowed us to identify the observed photometric signal at 3.39 h as a negative superhump wave. The spectroscopic behaviour exhibited by all the systems clearly identifies them as new SW Sextantis (SW Sex) stars. HS 0220+0603 shows unusual N ii and Si ii emission lines suggesting that the donor star may have experienced nuclear evolution via the CNO cycle.
These five new additions to the class increase the number of known SW Sex stars to 35. Almost 40 per cent of the total SW Sex population do not show eclipses, invalidating the requirement of eclipses as a defining characteristic of the class and the models based on a high orbital inclination geometry alone. On the other hand, as more SW Sex stars are identified, the predominance of orbital periods in the narrow 3–4.5 h range is becoming more pronounced. In fact, almost half the CVs which populate the 3–4.5 h period interval are definite members of the class. The dominance of SW Sex stars is even stronger in the 2–3 h period gap, where they make up 55 per cent of all known gap CVs. These statistics are confirmed by our results from the HQS CVs. Remarkably, 54 per cent of the Hamburg nova-like variables have been identified as SW Sex stars with orbital periods in the 3–4.5 h range. The observation of this pile-up of systems close to the upper boundary of the period gap is difficult to reconcile with the standard theory of CV evolution, as the SW Sex stars are believed to have the highest mass-transfer rates among CVs.
Finally, we review the full range of common properties that the SW Sex stars exhibit. Only a comprehensive study of this rich phenomenology will prompt to a full understanding of the phenomenon and its impact on the evolution of CVs and the accretion processes in compact binaries in general.
This paper reports extensive optical observations on the PG0027 + 260 binary, carried out on August 1984 with the 1.3 McGraw-Hill telescope and Mark II spectrometer at Michigan-Dartmouth-MIT Observatory on Kitt Peak. It is shown that this object is an eclipsing novalike variable with an orbital period of 3.51 hr. The PG0027 + 260 displays several unexplained phenomena which are remarkably similar to those of the SW Sex, DW UMa, and V1315 Aql, which are eclipsing novalike stars with periods between 3 and 4 hrs. The eclipse of the PG0027 + 260 is modeled, and it is shown that, while the mean eclipse light curve is easy to match, there is no simple explanation for the variable depth.
In this article we present the preliminary results of an observational search
for subdwarf B and white dwarf pulsators in the Kepler field of view, performed
using the DOLORES camera attached to the 3.6m Telescopio Nazionale Galileo
(TNG).
We review the most decisive currently available measurements of the surface effective temperatures, Teff, of white dwarf (WD) primaries in cataclysmic variables (CVs) during accretion quiescence, and use these as a diagnostic for their time averaged accretion rate, . Using time-dependent calculations of the WD envelope, we investigate the sensitivity of the quiescent Teff to long term variations in the accretion rate. We find that the quiescent Teff provides one of the best available tests of predictions for the angular momentum loss and resultant mass transfer rates which govern the evolution of CVs. While gravitational radiation is sufficient to explain the of strongly magnetic CVs at all Porb, faster angular momentum loss is required by the temperatures of dwarf nova primaries (non-magnetic systems). This provides evidence that a normal stellar magnetic field structure near the secondary is essential for the enhanced braking mechanism to work, supporting the well-known stellar wind braking hypothesis. The contrast in is most prominent for orbital periods Porb > 3 hours, above the period gap, but a modest enhancement is also present at shorter Porb. The averaging time which reflects is as much as 10^5 years for low- systems and as little as 10^3 years for high- systems. We discuss the security of conclusions drawn about the CV population in light of these time scales and our necessarily incomplete sample of systems. Measurements for non-magnetic systems above the period gap fall below predictions from traditional stellar wind braking prescriptions, but above more recent predictions with somewhat weaker angular momentum loss. We also discuss the apparently high Teff's found in the VY Scl stars. (abridged)
We critically examine the basic paradigm for the origin of the 2-3 hr period
gap in cataclysmic variables (CVs). We carry out an extensive population
synthesis study of CVs starting from ~ 3 x 10^6 primordial binaries, and
evolving some ~ 2 x 10^4 surviving systems through their CV phase. In
particular we study current-epoch distributions of CVs in the $\dot M-P_{orb}$,
R_{2}-P_{orb}, M_{2}-P_{orb}, q-P_{orb}, T_{eff}-P_{orb}, and L_{2}-P_{orb}
planes, where $\dot M$ is the mass transfer rate, q is the mass ratio M_2/M_1,
and M_2, R_2, T_{eff}, and L_2 are the donor star mass, radius, effective
temperature, and luminosity, respectively. This work presents a new perspective
on theoretical studies of the long-term evolution of CVs. In particular, we
show that if the current paradigm is correct, the secondary masses in CVs just
above the period gap should be as much as ~ 50% lower than would be inferred if
one assumes a main-sequence radius-mass relation for the donor star.
We present an analysis of the first far-ultraviolet observations of the SW Sextantis-type cataclysmic variable DW Ursae Majoris, obtained in November 2001 with the Far Ultraviolet Spectroscopic Explorer. The time-averaged spectrum of DW UMa shows a rich assortment of emission lines (plus some contamination from interstellar absorption lines including molecular hydrogen). Accretion disk model spectra do not provide an adequate fit to the far-ultraviolet spectrum of DW UMa. We constructed a light curve by summing far-ultraviolet spectra extracted in 60-sec bins; this shows a modulation on the orbital period, with a maximum near photometric phase 0.93 and a minimum half an orbit later. No other periodic variability was found in the light curve data. We also extracted spectra in bins spanning 0.1 in orbital phase; these show substantial variation in the profile shapes and velocity shifts of the emission lines during an orbital cycle of DW UMa. Finally, we discuss possible physical models that can qualitatively account for the observed far-ultraviolet behavior of DW UMa, in the context of recent observational evidence for the presence of a self-occulting disk in DW UMa and the possibility that the SW Sex stars may be the intermediate polars with the highest mass transfer rates and/or weakest magnetic fields. Comment: accepted by the Astronomical Journal; 36 pages, including 12 figures and 4 tables
We describe a high speed time-series CCD photometer for the prime focus of the 82-in (2.1 m) telescope at McDonald Observatory, and summarize the observational results we have obtained since it was placed into regular use in February, 2002. We compare this instrument with the three-channel time-series photometers we have previously used in the asteroseismological study of pulsating white dwarf stars, which used photomultiplier tubes (PMT) as the detectors. We find the CCD instrument is about 9 times more sensitive than the PMT instruments used on the same telescope for the same exposure time. We can therefore find and measure variable white dwarf stars some 2.4 magnitudes fainter than before, significantly increasing the number of such objects available for study. Comment: 13 pages, 7 figures, instrument paper submitted to PASP
We present spectrophotometry of the eclipsing old nova BT Mon (Nova Mon 1939). By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be K_R = 205+/-5 km/s and its rotational velocity to be vsin i = 138+/-5 km/s. We also measure the radial velocity semi-amplitude of the primary star to be K_R = 170+/-10 km/s. From these parameters we obtain a mass of 1.04+/-0.06 M_sun for the white dwarf primary star and a mass of 0.87+/-0.06 M_sun for the G8V secondary star. The inclination of the system is found to be 82.2+/-3.2 deg and we estimate that the system lies at a distance of 1700+/-300pc. The high mass of the white dwarf and our finding that BT Mon was probably a fast nova together constitute a new piece of evidence in favour of the thermonuclear runaway model of classical nova outbursts. The emission lines are single peaked throughout the orbital cycle, showing absorption around phase 0.5, high velocity S-wave components and large phase offsets in their radial velocity curves. In each of these respects, BT Mon is similar to the SW Sex stars. We also find quasi-periodic flaring in the trailed spectra, which makes BT Mon a candidate intermediate polar. Comment: 19 pages, LaTeX, 15 figures, accepted by MNRAS, 11 Sept 1997
We review optical observations and theoretical models of the non-magnetic
nova-like variables (UX UMa, VY Scl and SW Sex stars). A brief discussion of
the classification scheme is followed by a statistical overview of the observed
properties. The most important features of each of the sub-classes are then
reviewed, concluding with a summary of the theoretical models invoked to
understand these systems.
We present the complete set of 34 ASCA observations of non-magnetic cataclysmic variables. Timing analysis reveals large X-ray flux variations in dwarf novae in outburst (Z Cam, SS Cyg and SU UMa) and orbital modulation in high inclination systems (including OY Car, HT Cas, U Gem, T Leo). We also found episodes of unusually low accretion rate during quiescence (VW Hyi and SS Cyg). Spectral analysis reveals broad temperature distributions in individual systems, with emission weighted to lower temperatures in dwarf novae in outburst. Absorption in excess of interstellar values is required in dwarf novae in outburst, but not in quiescence. We also find evidence for subsolar abundances and X-ray reflection in the brightest systems.
LS Peg, V426 Oph and EI UMa have X-ray spectra that are distinct from the rest of the sample and all three exhibit candidate X-ray periodicities. We argue that they should be reclassified as intermediate polars.
In the case of V345 Pav we found that the X-ray source had been previously misidentified.
Our previous theoretical study of the impact of an accreting envelope on the thermal state of an underlying white dwarf (WD) has yielded equilibrium core temperatures, classical nova ignition masses and thermal luminosities for WDs accreting at time averaged rates of = 10^-11 - 10^-8 Msun/yr. These 's are appropriate to WDs in cataclysmic variables (CVs) of P_orb <~ 7 hr, many of which accrete sporadically as Dwarf Novae. Approximately thirty nonmagnetic Dwarf Novae have been observed in quiescence, when the accretion rate is low enough for spectral detection of the WD photosphere, and a measurement of T_eff. We use our theoretical work to translate the measured T_eff's into local time-averaged accretion rates, confirming the factor of ten drop in predicted for CV's as they transit the period gap. For DN below the period gap, we show that if is that given by gravitational radiation losses alone, then the WD masses are > 0.8 Msun. An alternative conclusion is that the masses are closer to 0.6 Msun and is 3-4 times larger than that expected from gravitational radiation losses. In either case, it is very plausible that a subset of CVs with P_orb < 2 hours will have T_eff's low enough for them to become non-radial pulsators, as discovered by van Zyl and collaborators in GW Lib. Comment: 4 pages, 3 figures; uses emulateapj; Accepted by the Astrophysical Journal Letters
- D J Schlegel
- D P Finkbeiner
- M Davis
Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ, 500,
525
- R E Nather
- A S Mukadam
Nather, R. E., & Mukadam, A. S. 2004, ApJ, 605, 846
- C Knigge
Knigge. C. 2006, MNRAS, 373, 484
- P Rodríguez-Gil
- J Casares
- I G Martínez-Pais
- P Hakala
- D Steeghs
Rodríguez-Gil, P., Casares, J., Martínez-Pais, I. G., Hakala, P., &
Steeghs, D. 2001, ApJ, 548, L49
- P Rodríguez-Gil
Rodríguez-Gil, P., et al. 2007a, MNRAS, 377, 1747
- F Mullally
- S E Thompson
- B G Castanheira
- D E Winget
- S O Kepler
- D J Eisenstein
- S J Kleinman
- Nitta
Mullally, F., Thompson, S. E., Castanheira, B. G., Winget, D. E.,
Kepler, S. O., Eisenstein, D. J., Kleinman, S. J., & Nitta, A.
2005, ApJ, 625, 966
- U Munari
- T Zwitter
Munari, U., & Zwitter, T. 1997, A&A, 318, 269
- S B Howell
- L A Nelson
- S Rappaport
Howell, S. B., Nelson, L. A., & Rappaport, S. 2001, ApJ, 550, 897
- P Rodríguez-Gil
- I G Martínez-Pais
Rodríguez-Gil, P., & Martínez-Pais, I. G. 2002, MNRAS, 337, 209