Paper: astro-ph/0507520
Date: Thu, 21 Jul 2005 20:08:28 GMT (80kb)

Title: The Hypervelocity Star SDSS J090745.0+024507 is a Short-Period Variable

Authors: Cesar I. Fuentes, K. Z. Stanek, B. Scott Gaudi, Brian A. McLeod,
Slavko B. Bogdanov, Joel D. Hartman, Ryan C. Hickox, Matthew J. Holman
Comments: ApJL, submitted, 4 pages, 4 figures
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We present high-precision photometry of the hypervelocity star SDSS
J090745.0+024507 (HVS), which has a Galactic rest-frame radial velocity of
v=709 km/s, and so has likely been ejected from the supermassive black hole in
the Galactic center. Our data were obtained on two nights using the MMT 6.5m
telescope, and is supplemented by lower precision photometry obtained on four
nights using the FLWO 1.2m telescope. The high-precision photometry indicates
that the HVS is a short-period, low-amplitude variable, with period P=0.2-2
days and amplitude A = 2-10%. Together with the known effective temperature of
T_eff ~ 10,500 K (spectral type B9), this variability implies that the HVS is a
member of the class of slowly pulsating B-type main sequence stars, thus
resolving the previously-reported two-fold degeneracy in the luminosity and
distance of the star. The HVS has a heliocentric distance of 71 kpc, and an age
of ~0.35 Gyr. The time of ejection from the center of the Galaxy is < 100 Myr,
and thus the existence of the OS constitutes observational evidence of a
population of young stars in the proximity of the central supermassive black
hole ~0.1 Gyr ago. It is possible that the HVS was a member of a binary that
was tidally disrupted by the central black hole; we discuss constraints on the
properties of the companion's orbit.

\\ ( http://arXiv.org/abs/astro-ph/0507520 , 80kb)