Sunday, July 5, 2015

Giant Planet around Aldebaran

Aldebaran is an orange giant star located approximately 65 light years away in the constellation Taurus. It is the brightest star in the constellation Taurus and is also one of the brightest stars in the night sky. Aldebaran is currently in an advance stage of stellar evolution and has expanded to 44.2 times the Sun’s diameter. The surface temperature of Aldebaran is about 4,000 K and the star shines with ~500 times the Sun’s luminosity.

Figure 1: Artist’s impression of a giant planet.

Using new radial velocity measurements combined with data from observations stretching back 30 years, Hatzes et al. (2015) present the detection of a giant planet around Aldebaran. The amplitude of the radial velocity curve of Aldebaran indicates how much back and forth motion the star is experiencing due to the gravitational tugging from a companion planet. This enables the mass of the planetary companion around Aldebaran to be determined. Assuming Aldebaran has 1.13 ± 0.11 times the Sun’s mass, its planetary companion is estimated to have at least 6.47 ± 0.53 times the mass of Jupiter. With such a mass, the planetary companion is a giant planet. It orbits Aldebaran at a distance of 1.46 ± 0.27 AU, and has an orbital period of 628.96 ± 0.9 days.

Aldebaran is a giant star and long-lived features on the star’s surface may create radial velocity signatures that can mimic the presence of a planet. These surface features can last for up to several years. As a result, three decades of radial velocity data is needed to show that the period of 628.96 ± 0.9 days in the radial velocity curve is consistent enough to be attributed to a giant planet. This newly discovered giant planet around Aldebaran resembles the giant planets found around other giant stars. These planets tend to have between 3 to 14 times the mass of Jupiter and have orbital radii of roughly 2 AU.

Figure 2: Radial velocity measurements for Aldebaran from 7 data sets spanning three decades. Hatzes et al. (2015).

Figure 3: Radial velocity measurements for Aldebaran from 7 data sets phased to the orbital period of the giant planet. Hatzes et al. (2015).

Hatzes et al. (2015), “Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity”, arXiv:1505.03454 [astro-ph.SR]