INFRARED PHOTOMETRY AND SPECTROSCOPY OF VY Aqr AND EI Psc: TWO SHORT-PERIOD CATACLYSMIC VARIABLES WITH CURIOUS SECONDARY STARS (original) (raw)

The X-Ray Spectra of VY Sculptoris Stars Are Not Blackbodies

Using ASCA data, we find, contrary to other researchers using ROSAT data, that the X-ray spectra of the VY Sculptoris stars TT Arietis and KR Aurigae are poorly fitted by an absorbed blackbody model but are well fitted by an absorbed thermal plasma model. The different conclusions about the nature of the X-ray spectrum of KR Aur may be due to differences in the accretion rate since this star was in a high optical state during the ROSAT observation but in an intermediate optical state during the ASCA observation. TT Ari, on the other hand, was in a high optical state during both observations and so directly contradicts the hypothesis that the X-ray spectra of VY Scl stars in their high optical states are blackbodies. Instead, based on theoretical expectations and the ASCA, Chandra, and XMM spectra of other nonmagnetic cataclysmic variables, we believe that the X-ray spectra of VY Scl stars in their low and high optical states are due to hot thermal plasma in the boundary layer between the accretion disk and the surface of the white dwarf, and we appeal to the acquisition of Chandra and XMM grating spectra to test this prediction.

GSC 4560–02157: a new long-period eclipsing cataclysmic variable star

Research in Astronomy and Astrophysics, 2015

We study the newly discovered variable star GSC 4560-02157. CCD photometry was performed in 2013-2014, and a spectrum was obtained with the 6-m telescope in June, 2014. GSC 4560-02157 is demonstrated to be a short-period (P = 0.265359 d) eclipsing variable star. All its flat-bottom primary minima are approximately at the same brightness level, while the star's out-of-eclipse brightness and brightness at secondary minimum varies considerably (by up to 0.6 m) from cycle to cycle. Besides, there are short-term (time scale of 0.03-0.04 days) small-amplitude brightness variations out of eclipse. This behavior suggests cataclysmic nature of the star, confirmed with a spectrum taken on June 5, 2014. The spectrum shows numerous emissions of the hydrogen Balmer series, HeI, HeII.

Simultaneous optical and near-IR photometry of 4U1957+115 - a missing secondary star

Monthly Notices of the Royal Astronomical Society, 2014

We report the results of quasi-simultaneous optical and NIR photometry of the lowmass X-ray binary, 4U 1957+115. Our observations cover B, V, R, I, J, H and K-bands and additional time-series NIR photometry. We measure a spectral energy distribution, which can be modelled using a standard multi-temperature accretion disc, where the disc temperature and radius follow a power-law relation. Standard accretion disc theory predicts the power law exponent to be -3/4, and this yields, perhaps surprisingly, acceptable fits to our SED. Given that the source is a persistent X-ray source, it is however likely that the accretion disc temperature distribution is produced by X-ray heating, regardless of its radial dependence. Furthermore, we find no evidence for any emission from the secondary star at any wavelength. However, adding a secondary component to our model allows us to derive a 99% lower limit of 14 or 15 kpc based on Monte Carlo simulations and using either an evolved K2 or G2V secondary star respectively. In >60% of cases the distance is >80kpc. Such large distances favor models with a massive (>15 M ⊙ ) black hole primary. Our quasi-simultaneous J and V-band time-series photometry, together with the SED, reveals that the optical/NIR emission must originate in the same region i.e. the accretion disc. The likely extreme mass ratio supports suggestions that the accretion disc must be precessing which, depending on the length of the precession period, could play a major part in explaining the variety of optical light curve shapes obtained over the last two decades.

ACTIVITY ON THE M STAR OF QS Vir

The Astronomical Journal, 2010

We report analysis of VRIJH photometry, and phase-resolved optical spectroscopy of the eclipsing DA white dwarf plus dMe dwarf binary QS Vir. Modeling of the photometric data yields an inclination of i = 74.9±0.6 and a mass ratio of q = M 2 /M 1 = 0.50±0.05. Our Doppler maps indicate the presence of material in the Roche lobe of the white dwarf, at a location near the M star, likely due to accretion from the stellar wind of the M star (as opposed to Roche-lobe overflow accretion). We also constructed images of the brightness distribution of the M star at different epochs which reveal the location of two stable active regions.

Young solar type active stars: the TYC 2627-638-1 system

Astronomy and Astrophysics, 2010

We present BV(RI) C and JHKs photometry and low-and high-resolution spectroscopy of the 11th mag G-type star TYC 2627-638-1. Our investigation reveals that the target is separated into two young, early-G-type main-sequence (or late pre-main-sequence) stars, which are most probably bound and form a wide binary system. A substellar body orbits the brighter component as implied by radial velocity variations. The brighter component possibly also has a faint, later type stellar companion.

The nature of G52.381-0.849 and G56.240-0.345: young stellar objects associated with extended mid-infrared emission?

Monthly Notices of the Royal Astronomical Society, 2010

We report the results of visual spectroscopy, mid-infrared (MIR) mapping and photometry, and near infrared (NIR) photometry of two candidate symbiotic stars (IPHAS J193108.67+164950.5 and IPHAS J193709.65+202655.7) associated with extended MIR emission. Our analysis of the continua of these sources shows that they are likely to represent Class I-II young stellar objects (YSOs) in which most of the IR emission arises from circumstellar disks, and for which the physical characteristics (stellar temperatures, radii, masses and luminosities) are similar. The extended emission is characterised by a substantial increase in fluxes and dimensions to longer MIR wavelengths. This is likely to arise as a result of emission by polycyclic aromatic hydrocarbons (PAHs) within extended photodissociation regimes (PDRs), centred upon more compact ionized regions responsible for much of the shorter wave emission. Such dual emission structures are characteristic of those observed in many compact HII regions. Finally, we note that the clouds have asymmetrical structures and windswept morphologies, conceivably indicative of shock interaction with external winds. Where this is the case, then it is possible that the YSOs are located in regions of triggered star-formation.

PACS and SPIRE spectroscopy of the red supergiant VY CMa

Astronomy and Astrophysics, 2010

With a luminosity > 10 5 L ⊙ and a mass-loss rate of ∼ 2.10 −4 M ⊙ yr −1 , the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55 -672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as ∼1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope.

On the secondary star of the cataclysmic variable 1RXS?J094432.1+035738

Astronomy and Astrophysics, 2002

We present V and Rc-band photometry and optical near-infrared spectroscopy of the cataclysmic variable 1RXS J094432.1+035738. We detected features of a cool secondary star, which can be modeled with a red dwarf of spectral type M2 +0.5 −1.0 V at a distance of 433 ± 100 pc.

VLT/FORS spectroscopy of faint cataclysmic variables discovered by the Sloan Digital Sky Survey

Monthly Notices of the Royal Astronomical Society, 2006

We present medium-resolution VLT/FORS2 spectroscopy of six cataclysmic variables discovered by the Sloan Digital Sky Survey. We determine orbital periods for SDSS J023322.61+005059.5 (96.08 ± 0.09 min), SDSS J091127.36+084140.7 (295.74 ± 0.22 min), SDSS J103533.02+055158.3 (82.10 ± 0.09 min), and SDSS J121607.03+052013.9 (most likely 98.82 ± 0.16 min, but the one-day aliases at 92 min and 107 min are also possible) using radial velocities measured from their Hα and Hβ emission lines. Three of the four orbital periods measured here are close to the observed 75-80 min minimum period for cataclysmic variables, indicating that the properties of the population of these objects discovered by the SDSS are substantially different to those of the cataclysmic variables found by other means. Additional photometry of SDSS J023322.61+005059.5 reveals a periodicity of approximately 60 min which we interpret as the spin period of the white dwarf, suggesting that this system is an intermediate polar with a low accretion rate. SDSS J103533.02+055158.3 has a period right at the observed minimum value, a spectrum dominated by the cool white dwarf primary star and exhibits deep eclipses, so is an excellent candidate for an accurate determination of the parameters of the system. The spectroscopic orbit of SDSS J121607.03+052013.9 has a velocity amplitude of only 13.8 ± 1.6 km s −1 , implying that this system has an extreme mass ratio. From several physical constraints we find that this object must contain either a high-mass white dwarf or a brown-dwarf-mass secondary component or both.

Two Long-period Cataclysmic Variable Stars: ASASSN-14ho and V1062 Cyg

We report spectroscopy and photometry of the cataclysmic variable stars ASASSN-14ho and V1062 Cyg. Both are dwarf novae with spectra dominated by their secondary stars, which we classify approximately as K4 and M0.5, respectively. Their orbital periods, determined mostly from the secondary stars' radial velocities, proved to be nearly identical, respectively 350.14 ± 0.15 and 348.25 ± 0.60 min. The Hα emission line in V1062 Cyg displays a relatively sharp emission component that tracks the secondary's motion, which may arise on the irradiated face of the secondary; this is not often seen and may indicate an unusually strong flux of ionizing radiation. Both systems exhibit double-peaked orbital modulation consistent with ellipsoidal variation from the changing aspect of the secondary. We model these variations to constrain the orbital inclination i, and estimate approximate component masses based on i and the secondary velocity amplitude K 2 .