arXiv subjects

Paula Szkody

Publications and source records attributed to Paula Szkody.

At least 127 records · Page 7Linked to original sources

arXiv2005

SDSS J210014.12+004446.0: A New Dwarf Nova with Quiescent Superhumps?

We report follow-up observations of the Sloan Digital Sky Survey Cataclysmic Variable SDSS J210014.12+004446.0 (hereafter SDSS J2100). We obtained photometry and spectroscopy in both outburst and quiescent states, providing the first quiescent spectrum of this source. In both states, non-sinusoidal photometric modulations are apparent, suggestive of superhumps, placing SDSS J2100 in the SU UMa subclass of dwarf novae. However, the periods during outburst and quiescence differ significantly, being 2.099 plus or minus 0.002 hr and 1.96 plus or minus 0.02 hr respectively. Our phase-resolved spectroscopy during outburst yielded an estimate of about 2 hr for the orbital period, consistent with the photometry. The presence of the shorter period modulation at quiescence is unusual, but not unique. Another atypical feature is the relative weakness of the Balmer emission lines in quiescence. Overall, we find a close similarity between SDSS J2100 and the well-studied superhump cataclysmic Variable V503 Cygni. By analogy, we suggest that the quiescent modulation is due to a tilted accretion disk -- producing negative superhumps -- and the modulation in outburst is due to positive superhumps from the precession of an elliptical disk.

astro-ph↗

arXiv2004

XMM-Newton and optical follow-up observations of three new polars from the Sloan Digital Sky Survey

We report follow-up XMM-Newton and optical observations of three new polars found in the Sloan Digital Sky Survey. Simple modeling of the X-ray spectra, and consideration of the details of the X-ray and optical lightcurves corroborate the polar nature of these three systems and provide further insights into their accretion characteristics. During the XMM-Newton observation of SDSS J072910.68+365838.3, X-rays are undetected apart from a probable flare event, during which we find both the typical hard X-ray bremsstrahlung component and a very strong line O VII (E=0.57 keV), but no evidence of a soft blackbody contribution. In SDSS J075240.45+362823.2 we identify an X-ray eclipse at the beginning of the observation, roughly in phase with the primary minimum of the optical broad band curve. The X-ray spectra require the presence of both hard and soft X-ray components, with their luminosity ratio consistent with that found in other recent XMM-Newton results on polars. Lastly, SDSS J170053.30+400357.6 appears optically as a very typical polar, however its large amplitude optical modulation is 180 degrees out of phase with the variation in our short X-ray lightcurve.

astro-ph↗

arXiv2004

Quiescent observations of the WZ Sge type dwarf nova PQ Andromedae

We have obtained time series optical spectra of the cataclysmic variable PQ And in quiescence. The spectra show a white dwarf continuum with narrow Balmer emission superimposed over strong Balmer absorption. The emission lines have blue and red components whose strength changes with time. An analysis of the H$α$ emission line implies a short orbital period below the period gap. Given its lack of accretion disk features, its large and infrequent outbursts, and an orbital period below the period gap, PQ And is probably a low accretion rate object similar to WZ Sge. In addition, white dwarf model fits imply that PQ And is an excellent ZZ Cet candidate.

astro-ph↗

arXiv2004

Time-Resolved Ultraviolet Spectroscopy of the SW Sex Star DW UMa: Confirmation of a Hidden White Dwarf and the UV Counterpart to Phase 0.5 Absorption Events

We present time-resolved, ultraviolet (UV) spectroscopy of the SW Sex star DW UMa in the high state. We confirm that, shortward of 1500 Å, the high-state, UV continuum level is lower than the white dwarf (WD)-dominated low-state level. We also do not see the WD contact phases in the high state eclipse light curves. These results confirm our earlier finding that the WD in this system is hidden from view in the high state. Based on this, we caution that eclipse mapping of high-inclination SW Sex stars in the high state may yield incorrect or misleading results. In the context of DW UMa, we demonstrate explicitly that distance estimates obtained by recent eclipse mapping studies cannot be reconciled with the WD-dominated low-state spectrum. We also show that the fluxes of the UV emission lines in the high state drop near orbital phase 0.5. This is the first detection of a UV counterpart to the class-defining phase 0.5 absorption seen in the optical emission lines of SW Sex stars.

astro-ph↗

arXiv2004

Unravelling the Puzzle of the Eclipsing Polar SDSSJ 015543.40+002807.2 with XMM and Optical Photometry/Spectropolarimetry

The cataclysmic variable SDSSJ 015543.40+002807.2 is confirmed to be a magnetic system of the AM Herculis type. With an orbital period of 87.13 min, it is also the shortest-period eclipsing Polar known. Monitoring with XMM-Newton finds a high-state light curve dominated by a single X-ray emitting accretion pole located slightly prograde of the secondary star. The hard X-ray spectrum is typical of radial shocks on magnetic white dwarfs (kT ~ 10keV), and there is evidence for a soft X-ray component consistent with reprocessing from the stellar surface. The optical circular polarization is weak (v < 3%) when the accretion rate is high (mV ~ 15.5), due to optically-thick cyclotron emission and the apparent competition between two accreting poles. However, in low states (mV ~ 18), the polarization increases smoothly to the blue, reaching 20% at 4200A, and the flux spectrum displays a rich set of thermally-broadened cyclotron harmonics that indicate a polar field of 29MG. The phase interval preceding the 6.5 min eclipse depicts the development of P-Cygni components followed by complete absorption reversals in the emission lines. This phenomenon is not unexpected for a strongly accreting magnetic system viewed through the cool base of the funnel, and high-quality spectroscopy through this interval will likely lead to new insights into the dynamics of magnetic coupling and gas flow onto the white dwarf.

astro-ph↗

arXiv2004

FUSE Spectroscopy of the Transitional Magnetic Cataclysmic Variable V405 Aurigae

We present Far Ultraviolet Spectroscopic Explorer observations of the magnetic cataclysmic variable V405 Aurigae. Together with four other DQ Her type binaries, V405 Aur forms a small subclass of intermediate polars which are likely to evolve into low magnetic field strength polars, similar to AM Her. Our co-added FUSE spectrum exhibits broad O VI and C III emission-lines as well as a narrow O VI emission-line component which likely forms near the white dwarf surface. The O VI 1032/1038 narrow emission line flux ratio is near 2.0 throughout the orbit, indicative of its formation in an optically thin gas. Radial velocity measurements of the narrow O VI emission-lines restrict any orbital modulation to a very low amplitude (Kwd = 2.5+/- 0.5 km/s) indicating, along with other single peaked broad disk emission lines in the UV and optical, that the binary system is at low inclination.

astro-ph↗

arXiv2004

Phase-Resolved Infrared H- and K-band Spectroscopy of EF Eridani

We present new phase-resolved H and K-band spectroscopy of the ultra-short period magnetic cataclysmic variable EF Eri in its current, prolonged ``low'' state obtained using NIRI on Gemini-North, and NIRSPEC on Keck II. These new data show that the H-band spectrum of EF Eri appears to be dominated by cyclotron emission during the entire orbital cycle. The {\it K}-band spectrum of EF Eri is likewise dominated by cyclotron emission during most of an orbital period, but near binary phase 0.0, the secondary star spectrum may be visible. We conclude that strong, and highly variable cyclotron emission is responsible for the photometric variation previously reported for EF Eri. The nature of this cyclotron emission is complex: the H-band spectra show that the dominant cyclotron harmonic at phase 0.5 peaks at 1.65 $μ$m, but at phase 0.0, the harmonic peaks near 1.72 $μ$m. At phase 0.5, there is another cyclotron feature present that peaks in between the H and K bands (near 1.93 $μ$m), but at phase 0.0, no such feature is present. These data suggest that cyclotron emission from both poles is occurring.

astro-ph↗

arXiv2004

XMM-Newton Observations of the Extremely Low Accretion Rate Polars SDSSJ15531.12+551614.5 and SDSSJ132411.57+032050.5

XMM-Newton observations of the polar SDSSJ155331.12+551614.5 reveal that all the X-ray flux emerges at energies less than 2 keV. The best fit to the spectrum is with a thermal plasma with kT=0.8 keV plus a 20-90 ev black body, yielding a thermal X-ray luminosity of 8-9.5E28 ergs/s. The low temperature and X-ray luminosity, together with the lack of variation of the X-ray flux during the observations, are all consistent with an extremely low accretion rate that puts the system in the bombardment regime of accretion, rather than accretion involving a standoff shock. It is likely that the observed X-rays originate from the M dwarf secondary star, thus providing a base activity level for late main sequence stars in close binaries. SDSSJ132411.57+032050.5 is detected by XMM-Newton at the faint EPIC pn count rate of 0.0012 c/s, giving an upper limit to the X-ray luminosity of 7E28 ergs/s for a distance of 300 pc, which is also consistent with the above scenario.

astro-ph↗

arXiv2004

Chandra HETG Spectra of SS Cyg and U Gem in Quiescence and Outburst

Chandra HETG spectra of the prototypical dwarf novae SS Cyg and U Gem in quiescence and outburst are presented and discussed. When SS Cyg goes into outburst, it becomes dimmer in hard X-rays and displays a dramatic shift in its relative line strengths, whereas when U Gem goes into outburst, it becomes brighter in hard X-rays and displays only a minor shift in its relative line strengths. In both systems, the emission lines become significantly broader in outburst, signaling the presence of high velocity gas either in Keplerian orbits around the white dwarf or flowing outward from the system.

astro-ph↗

arXiv2004

Cataclysmic Variables from SDSS III. The Third Year

This paper continues the series that identifies new cataclysmic variables found in the Sloan Digital Sky Survey. We present 36 cataclysmic variables and one possible symbiotic star from Sloan spectra obtained during 2002, of which 34 are new discoveries, 2 are known dwarf novae (BC UMa, KS UMa) and one is a known CV identified from the 2dF survey. The positions, colors and spectra of all 37 systems are presented, along with follow-up spectroscopic/photometric observations of 10 systems. As in the past 2 years of data, the new SDSS systems show a large variety of characteristics based on their inclination and magnetic fields, including 3 eclipsing systems, 4 with prominent He II emission, and 15 systems showing features of the underlying stars.

astro-ph↗

arXiv2004

Far Ultraviolet Observations of the Dwarf Nova VW Hyi in Quiescence

We present a 904-1183 A spectrum of the dwarf nova VW Hydri taken with the Far Ultraviolet Spectroscopic Explorer during quiescence, eleven days after a normal outburst, when the underlying white dwarf accreter is clearly exposed in the far ultraviolet. However, model fitting show that a uniform temperature white dwarf does not reproduce the overall spectrum, especially at the shortest wavelengths. A better approximation to the spectrum is obtained with a model consisting of a white dwarf and a rapidly rotating ``accretion belt''. The white dwarf component accounts for 83% of the total flux, has a temperature of 23,000K, a v sin i = 400 km/s, and a low carbon abundance. The best-fit accretion belt component accounts for 17% of the total flux, has a temperature of about 48,000-50,000K, and a rotation rate Vrot sin i around 3,000-4,000 km/s. The requirement of two components in the modeling of the spectrum of VW Hyi in quiescence helps to resolve some of the differences in interpretation of ultraviolet spectra of VW Hyi in quiescence. However, the physical existence of a second component (and its exact nature) in VW Hyi itself is still relatively uncertain, given the lack of better models for spectra of the inner disk in a quiescent dwarf nova.

astro-ph↗

arXiv2004

Chandra Observation of V426 Oph: Weighing the Evidence for a Magnetic White Dwarf

We report the results of a 45 ks Chandra observation of the cataclysmic variable V426 Ophiuchus. The high resolution spectrum from the high-energy transmission grating spectrometer is most consistent with a cooling flow model, placing V426 Oph among the group of CVs including U Gem and EX Hya. An uninterrupted lightcurve was also constructed, in which we detect a significant 4.2 hr modulation together with its first harmonic at 2.1 hrs. Reanalysis of archival Ginga, and ROSAT X-ray lightcurves also reveals modulations at periods consistent with 4.2 and/or 2.1 hrs. Furthermore, optical photometry in V, simultaneous with the Chandra observation, indicates a modulation anti-correlated with the X-ray, and later more extensive R band photometry finds a signal at ~2.1 hrs. The earlier reported X-ray periods at ~0.5 and 1 hrs appear to be only transient and quasi-periodic in nature. In contrast, the 4.2 hr period or its harmonic are stable and persistent in X-ray/optical data from 1988 to 2003. This periodicity is clearly distinct from the 6.85 hr orbit, and could be due to the spin of the white dwarf. If this is the case, V426 Oph would be the first long period intermediate polar with a ratio P_spin/P_orb of 0.6. However, this interpretation requires unreasonable values of magnetic field strength and mass accretion rate.

astro-ph↗

arXiv2004

A Catalog of Spectroscopically Identified White Dwarf Stars in the First Data Release of the Sloan Digital Sky Survey

We present the full spectroscopic white dwarf and hot subdwarf sample from the SDSS first data release, DR1. We find 2551 white dwarf stars of various types, 240 hot subdwarf stars, and an additional 144 objects we have identified as uncertain white dwarf stars. Of the white dwarf stars, 1888 are non-magnetic DA types and 171, non-magnetic DBs. The remaining (492) objects consist of all different types of white dwarf stars: DO, DQ, DC, DH, DZ, hybrid stars like DAB, etc., and those with non-degenerate companions. We fit the DA and DB spectra with a grid of models to determine the Teff and log(g) for each object. For all objects, we provide coordinates, proper motions, SDSS photometric magnitudes, and enough information to retrieve the spectrum/image from the SDSS public database. This catalog nearly doubles the known sample of spectroscopically-identified white dwarf stars. In the DR1 imaged area of the sky, we increase the known sample of white dwarf stars by a factor of 8.5. We also comment on several particularly interesting objects in this sample.

astro-ph↗

arXiv2003

Keck IR Spectroscopy of WZ Sge: Detection of Molecular Emission from the Accretion Disk

Time-resolved IR spectroscopy of WZ Sge was obtained using NIRSPEC on Keck II. We detect CO and H$_{\rm 2}$ emission from the accretion disk placing WZ Sge into a rarefied class of astronomical objects including YSOs and high luminosity early-type stars. During the eclipse phase, the molecular emission greatly weakens but no firm evidence for the secondary star is seen allowing new limits on its luminosity to be determined. The detection of molecular emission provides physical properties within the outer disk of T=3000K and N$_H$$>10^{10}$ cm$^{-3}$. Such a cool, dense region, not associated with areas of H I and He I emission, provides the first observational confirmation of predictions made by accretion disk models.

astro-ph↗

arXiv2003

WZ Sge: HST Spectroscopy of the Cooling of the White Dwarf after the 2001 Outburst

Following an outburst in 2001 July, the UV flux of WZ Sge has declined slowly toward pre-outburst levels. Here, we describe new 1150-1710 Angstrom HST/STIS spectra of WZ Sge obtained between 2002 April and 2003 March to follow the decline. A combined analysis of these and spectra obtained in the fall of 2001 show that if log g=8.5, then the white dwarf temperature decreased from 23,400 K in 2001 October, shortly after the steady decline of the system began, to 15,900 K 17 months later. The UV flux in 2003 March was still 2.4 times higher than measured prior to the outburst and so the system was still recovering from the outburst. During this period, the shape of the spectrum and the flux from the system are consistent with a log g=8.5, 0.9 solar mass white dwarf at the astrometrically-determined distance to WZ Sge. Although the spectrum from 2001 September resembles that of a white dwarf with a temperature of 28,200 K, the implied radius is smaller than in the remainder of the observations. If the entire white dwarf was visible in 2001 September, then either a second component, such as the disk emission, was distorting the spectrum, or more likely, the temperature on the white dwarf photosphere was not uniform then. The metal lines in the spectra of WZ Sge have weakened with time. Model fits that allow for material along the line of sight to the white dwarf photosphere are substantial improvements over models which assume all the lines arise from the photosphere. This obviates the need to explain very unusual abundance ratios in the photosphere and complicates the determination of the rotation rate of the white dwarf.

astro-ph↗

arXiv2003

Cataclysmic Variables from SDSS II. The Second Year

The first full year of operation following the commissioning year of the Sloan Digital Sky Survey has revealed a wide variety of newly discovered cataclysmic variables. We show the SDSS spectra of forty-two cataclysmic variables observed in 2002, of which thirty-five are new classifications, four are known dwarf novae (CT Hya, RZ Leo, T Leo and BZ UMa), one is a known CV identified from a previous quasar survey (Aqr1) and two are known ROSAT or FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS positions, colors and spectra of all forty-two systems are presented. In addition, the results of follow-up studies of several of these objects identify the orbital periods, velocity curves and polarization that provide the system geometry and accretion properties. While most of the SDSS discovered systems are faint (>18th mag) with low accretion rates (as implied from their spectral characteristics), there are also a few bright objects which may have escaped previous surveys due to changes in the mass transfer rate.

astro-ph↗

arXiv2003

Observations of the SW Sextantis star DW Ursae Majoris with the Far Ultraviolet Spectroscopic Explorer

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.

astro-ph↗

arXiv2003

Investigating the Sloan Digital Sky Survey Cataclysmic Variable SSDS J132723.39+652854.2

Photometric and spectroscopic observations reveal the Sloan Digital Sky Survey cataclysmic variable SDSS J132723.39+652854.2 to be a likely SW Sex star with an orbital period of P = 3.28 hours. The Sloan Digital Sky Survey spectrum shows strong HeI, HeII and Balmer emission lines. Time resolved spectra acquired at Apache Point Observatory reveal absorption-line structure within the emission lines near phase 0.5. Photometric data obtained at Manastash Ridge Observatory using Harris V and B filters reveal a high inclination system (i = 80 degrees) with deep (~ 2 mag.) eclipses. The orbital period and the spectral variations favor an SW Sex interpretation.

astro-ph↗