V532 Oph Is a New R Coronae Borealis Star
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abstract
V532 Oph has been found to be a member of the rare, hydrogen-deficient R
Coronae Borealis (RCB) stars from new photometric and spectroscopic data
reported in this paper. The lightcurve of V532 Oph shows the sudden, deep,
irregularly spaced declines characteristic of RCB stars. Its optical spectrum
is typical of a warm (T(eff)~7000 K) RCB star, showing weak or absent hydrogen
lines, the C2 Swan bands, and no evidence for 13C. In addition, the star shows
small pulsations typical of an RCB star and an infrared excess due to circum-
stellar dust. It also appears to be significantly reddened by foreground dust.
The distance to V532 Oph is estimated to be 5.5-8.7 kpc. These new data show
that this star was misclassified as an eclipsing binary in the General Catalog
of Variable Stars. The new data presented here for V532 Oph reveal the power of
high-quality, high-cadence all-sky photometric surveys, such as ASAS-3, to
identify new RCB candidates on the basis of lightcurve data alone, now that
they have been collecting data for durations sufficiently long to reveal
multiple declines. Despite their small numbers, RCB stars may be of great
importance in understanding the late stages of stellar evolution. In
particular, their measured isotopic abundances imply that many, if not most,
RCB stars are produced by WD mergers, which may be the low-mass counterparts of
the more massive mergers thought to produce type Ia supernovae. Therefore,
establishing the population of RCB stars in the Galaxy will help constrain the
frequency of these WD mergers.
