THE RØMER DELAY AND MASS RATIO OF THE sdB+dM BINARY 2M 1938+4603 FROM KEPLER ECLIPSE TIMINGS

• Published in: The Astrophysical journal Vol. 753; no. 2; pp. 1 - 7
• Main Authors: BARLOW, Brad N, WADE, Richard A, LISS, Sandra E
• Format: Journal Article
• Language: English
• Published: Bristol IOP 10.07.2012
• Subjects: ASTRONOMY; ASTROPHYSICS; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Asymptotic properties; BINARY STARS; Delay; DIAGRAMS; DWARF STARS; Earth, ocean, space; Eccentricity; ECLIPSE; Eclipses; Exact sciences and technology; MASS; Mass ratios; Mathematical models; ORBITS; PHOTOMETRY; Red dwarf stars; REFLECTION; STARS; TIME DELAY; VISIBLE RADIATION; Eclipsing binary stars; binaries: eclipsing; B stars; Circular orbit; Eccentricity; techniques: photometric; Light curves; binaries: close; Subdwarf; Hot star; Mass ratio; Close binary stars; subdwarfs; stars: individual (2M 1938+4603); Models; Modelling; Time delay; Timing; Photometry
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/753/2/101

The eclipsing binary system 2M 1938+4603 consists of a pulsating hot subdwarf B star and a cool M dwarf companion in an effectively circular three-hour orbit. The light curve shows both primary and secondary eclipses, along with a strong reflection effect from the cool companion. Here, we present constraints on the component masses and eccentricity derived from the Romer delay of the secondary eclipse. Using six months of publicly available Kepler photometry obtained in short-cadence mode, we fit model profiles to the primary and secondary eclipses to measure their centroid values. We find that the secondary eclipse arrives on average 2.06 + or - 0.12 s after the midpoint between primary eclipses. Under the assumption of a circular orbit, we calculate from this time delay a mass ratio of q = 0.2691 + or - 0.0018 and individual masses of M sub(sd) = 0.372 + or - 0.024 M sub([middot in circle]) and M sub(c) = 0.1002 + or - 0.0065 M sub([middot in circle]) for the sdB and M dwarf, respectively. These results differ slightly from those of a previously published light-curve modeling solution; this difference, however, may be reconciled with a very small eccentricity, e cos omega [asymptotically =] 0.00004. We also report a decrease in the orbital period of P = (-1.23 + or - 0.07) x 10 super(-10).