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]