Fundación Galileo Galilei - INAF Telescopio Nazionale Galileo 28°45'14.4N 17°53'20.6W 2387.2m A.S.L.

Three elder suns with planets

Wouldn't it be great to see what our Solar System would look like in a billion years from now? What will happen to the planets we know? How their orbits will be modified by an aging Sun? We would like to know it but given we do not live enough to watch it we have to explore the consequences of age observing other stars. The project TAPAS (Tracking Advanced Planetary Systems with Harps-N) is looking for planets orbiting older sisters of our Sun, evolved stars of exactly solar mass.

The older sisters of our Sun are red giants, huge, cool, and tricky stars that can play with us and mimic planets using dark spots on their surfaces. To distinguish between a planet and a spot we need long-term observations lasting several rotation periods of the stars and given that the stars are giants they rotate very slowly. TAPAS discovered three new planets around such old systems: the red giant stars HD 4760, HD 96992 and TYC 434-4538-1. The most extreme case of the problem is HD 4760 b, a massive (13.9 mJ) planet in 1.14 au orbit around a huge, 43 R☉ star with a massive deficit of metals relative to our Sun [Fe/H=-0.91]. The star was observed for about 9 years to distinguish between a spot and a planet. On the contrary, HD 96992 b is a planet very similar to our Jupiter (1.14 mJ) revolving in an orbit of only 1.24 au, its sun, a star only 7 times larges than ours (observed for 14 years!). TYC 434-4538-1 has its 6.1mJ planet in a tight, nearly circular (e=0,08) orbit of only 0.66 au, which means that the planet may be engulfed by its host quite soon (in astronomical time-scale).

These three newly discovered planetary system join six previously discovered by the TAPAS collaboration around elder suns.

TAPAS is a project devoted to search with Harps-N at TNG for exoplanets around targets selected with the Hobby-Eberly Telescope. The project is led by Eva Villaver (Centro de Astrobiología, CSIC-INTA), Andrzej Niedzielski (Nicolaus Copernicus University in Toruń, Poland), and Alex Wolszczan (Pennsylvania State University, USA).

The paper is accepted by Astronomy and Astrophysics.

Figure 1. The keplerian model of HD 4760 b fitted to 9 year long observing run with,
initially, Hobby-Eberly Telescope and, later on with Harps-N at TNG.