Compact white-dwarf binaries in the combined SRG/eROSITA/SDSS eFEDS survey
arxiv(2024)
摘要
Aims. Compact white-dwarf binaries are selected from spectra obtained in the
early SDSS-V plate program. A dedicated set of SDSS plate observations were
carried out in the eFEDS field, providing spectroscopic classifications for a
significant fraction of the optically bright end (r < 22.5) of the X-ray
sample. The identification and subclassification rests on visual inspections of
the SDSS spectra, spectral variability, color-magnitude and color-color
diagrams involving optical and X-ray fluxes, optical variability and literature
work. Results. Upon visual inspection of SDSS spectra and various auxiliary
data products we have identified 26 accreting compact white-dwarf binaries
(aCWDBs) in eFEDS, of which 24 are proven X-ray emitters. Among those 26
objects are 12 dwarf novae, three WZ Sge-like disk-accreting non-magnetic CVs
with low accretion rates, five likely non-magnetic high accretion rate novalike
CVs, two magnetic CVs of the polar subcategory, and three double degenerates
(AM CVn objects). Period bouncing candidates and magnetic systems are rarer
than expected in this sample, but it is too small for a thorough statistical
analysis. Fourteen of the systems are new discoveries, of which five are
fainter than the Gaia magnitude limit. Thirteen aCWDBs have measured or
estimated orbital periods, of which five were presented here. Through a Zeeman
analysis we revise the magnetic field estimate of the polar system J0926+0105,
which is likely a low-field polar at B = 16 MG. We quantify the success of
X-ray versus optical/UV selection of compact white-dwarf binaries which will be
relevant for the full SDSS-V survey. We also identify six white-dwarf
main-sequence (WDMS) systems, among them one confirmed pre-CV at an orbital
period of 17.6 hours and another pre-CV candidate.
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