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Register a new userA subtle IR excess associated with a young White Dwarf in the Edinburgh-Cape Blue Object Survey
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We report the discovery of a subtle infrared excess associated with the young white dwarf EC,05365--4749 at 3.35 and 4.6,$mu$m. Follow-up spectroscopic observations are consistent with a hydrogen atmosphere white dwarf of effective temperature 22,800,K and log [emph{g} (,cm,s$^{-2}$) ] = 8.19. High resolution spectroscopy reveals atmospheric metal pollution with logarithmic abundances of [Mg/H] = --5.36 and [Ca/H] = --5.75, confirming the white dwarf is actively accreting from a metal-rich source with an intriguing abundance pattern. We find that the infrared excess is well modeled by a flat, opaque debris disk, though disk parameters are not well constrained by the small number of infrared excess points. We further demonstrate that relaxing the assumption of a circular dusty debris disk to include elliptical disks expands the widths of acceptable disks, adding an alternative interpretation to the subtle infrared excesses commonly observed around young white dwarfs.
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We present a simple method for identifying candidate white dwarf systems with dusty exoplanetary debris based on a single temperature blackbody model fit to the infrared excess. We apply this technique to a sample of Southern Hemisphere white dwarfs from the recently completed Edinburgh-Cape Blue Object Survey and identify four new promising dusty debris disk candidates. We demonstrate the efficacy of our selection method by recovering three of the four $textit{Spitzer}$ confirmed dusty debris disk systems in our sample. Further investigation using archival high resolution imaging shows $textit{Spitzer}$ data of the un-recovered fourth object is likely contaminated by a line-of-sight object that either led to a mis-classification as a dusty disk in the literature or is confounding our method. Finally, in our diagnostic plot we show that dusty white dwarfs which also host gaseous debris lie along a boundary of our dusty debris disk region, providing clues to the origin and evolution of these especially interesting systems.
We give an update of the results of a campaign to obtain orbital solutions of subdwarf B stars from the Edinburgh-Cape survey (Stobie et al. 1997). To date we have obtained blue spectra of 40 subdwarf B stars from the Edinburgh-Cape catalogue using the grating spectrograph at the 1.9m Radcliffe telescope at the South African Astronomical Observatory. We find that 17 out of these 40 are certain binaries with a few other objects showing radial velocity variations of small amplitude. The binary fraction found in our sample, after correcting for our binary detection efficiency, is 48%. We have secured the orbital parameters for 4 of the 17 systems and narrowed down the orbits of another 7 to a small range of periods.
We present the first results of a campaign to obtain orbital solutions of subdwarf B (sdB) stars from the Edinburgh-Cape survey. We have obtained blue spectra of 35 sdBs, 20 of which have been observed in more than two epochs. 15 out of the 35 are certain binaries with a few other objects showing radial velocity variations with small amplitude, possibly long period sdB binaries. We have secured the orbital parameters for 2 of the 15 systems and narrowed down the orbits of another one to a small range of periods. These preliminary results only use data taken up to December 2003.
1SWASP,J162117.36$+$441254.2 was originally classified as an EW-type binary with a period of 0.20785,days. However, it was detected to have undergone a stellar outburst on June 3, 2016. Although the system was latter classified as a cataclysmic variable (CV) and the event was attributed as a dwarf-nova outburst, the physical reason is still unknown. This binary has been monitored photometrically since April 19, 2016 and many light curves were obtained before, during and after the outburst. Those light and color curves observed before the outburst indicate that the system is a special CV. The white dwarf is not accreting material from the secondary and there are no accretion disks surrounding the white dwarf. By comparing the light curves obtained from April 19 to September 14, 2016, it was found that magnetic activity of the secondary is associated with the outburst. We show strong evidence that the $L_1$ region on the secondary was heavily spotted before and after the outburst and thus quench the mass transfer, while the outburst is produced by a sudden mass accretion of the white dwarf. These results suggest that J162117 is a good astrophysical laboratory to study stellar magnetic activity and its influences on CV mass transfer and mass accretion.
The number of spatially unresolved white dwarf plus main-sequence star binaries has increased rapidly in the last decade, jumping from only ~30 in 2003 to over 3000. However, in the majority of known systems the companion to the white dwarf is a low mass M dwarf, since these are relatively easy to identify from optical colours and spectra. White dwarfs with more massive FGK type companions have remained elusive due to the large difference in optical brightness between the two stars. In this paper we identify 934 main-sequence FGK stars from the Radial Velocity Experiment (RAVE) survey in the southern hemisphere and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey in the northern hemisphere, that show excess flux at ultraviolet wavelengths which we interpret as the likely presence of a white dwarf companion. We obtained Hubble Space Telescope ultraviolet spectra for nine systems which confirmed that the excess is indeed caused, in all cases, by a hot compact companion, eight being white dwarfs and one a hot subdwarf or pre-helium white dwarf, demonstrating that this sample is very clean. We also address the potential of this sample to test binary evolution models and type Ia supernovae formation channels.
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