HD 15082

HD 15082 (also known as WASP-33) is a star located 378 light years away^[1] in the constellation of Andromeda.^[2] The star is a Delta Scuti variable, and also a planetary transit variable. It is the first Delta Scuti variable known to host a planet.^[3] A hot Jupiter type extrasolar planet orbits this star with an orbital period of 1.22 days.

Spectral type

In common with many stars of spectral type A, the spectrum of HD 15082 is complex. The hydrogen lines and effective temperature of the star are similar to spectral type A8, however the calcium II K line resembles that of an A5 star, and the metallic lines are more similar to an F4 star. The spectral type is thus written kA5 hA8 mF4.^[1]

Planet

In 2010, the SuperWASP project announced the discovery of an extrasolar planet, designated HD 15082 b, orbiting the star. The discovery was made by detecting the transit of the planet as it passes in front of its star, an event which occurs every 1.22 days. As the planet crosses the star's disc, it causes the rotational broadening signature in the star's spectrum to change, enabling the determination of the sky-projected angle between the star's equator and the orbital plane of the planet to be determined. (This differs from the Rossiter-McLaughlin effect which is observed for radial velocity measurements). For HD 15082 b, this angle is about 250 degrees, indicating that it is in a retrograde orbit. Limits from radial velocity measurements imply it has less than 4.1 times the mass of Jupiter.^[1]

Non-Keplerian features of motion for HD 15082 b

In view of the high rotational speed of its parent star, the orbital motion of HD 15082 b may be affected in a measurable way by non-Keplerian effects like, e.g., the huge oblateness of the star and the general relativistic gravitomagnetic field. More precisely, the gravitational field of the distorted star is different from that coming from the usual Newtonian inverse-square law. The same holds also for the terms arising from general relativity, yielding the well-known frame-dragging precession. As a consequence, the orbital trajectory of HD 15082 b is shifted with respect to the purely Keplerian ellipse.

Notes

1. ^ Parameters from the photometric + radial velocity solution in table 3 of Cameron et al. (2010). Different analysis methods result in slightly different parameters, see Cameron et al. (2010) for details.

References