GALEX J201337.6+092801: The lowest gravity subdwarf B pulsator
We present the recent discovery of a new subdwarf B variable (sdBV), with an exceptionally low surface gravity. Our spectroscopy places it at T eff = 32,100 ± 1000, log g = 5.15 ± 0.20, and log(NHe/NH)=-2.8 ± 0.2. With a magnitude of B=12.0, it is the second brightest V361 Hya star ever found. Photometry from three different observatories reveals a temporal spectrum with 11 clearly detected periods in the range 376-566 s, and at least five more close to our detection limit. These periods are unusually long for the V361Hya class of short-period sdBV pulsators, but not unreasonable for p- and g-modes close to the radial fundamental, given its low surface gravity. Of the ∼50 short-period sdB pulsators known to date, only a single one has been found to have comparable spectroscopic parameters to GALEX J201337.6+092801(J20136+0928, for short). This is the enigmatic high-amplitude pulsator V338Ser, and we conclude that J20136+0928 is the second example of this rare subclass of sdB pulsators located well above the canonical extreme horizontal branch in the H-R diagram.
Physics, Astronomy, and Materials Science
stars: early-type, stars: variables: general, subdwarfs
Østensen, Roy H., Peter I. Pápics, Raquel Oreiro, M. D. Reed, A. C. Quint, J. T. Gilker, L. L. Hicks et al. "GALEX J201337. 6+ 092801: The lowest gravity subdwarf B pulsator." The Astrophysical Journal Letters 731, no. 1 (2011): L13.
Astrophysical Journal Letters