Investigation of the Key Parameters in the Process of Extrasolar Planet Formation around Intermediate-Mass G-K Giant Stars

• Applicant: Professor Dr. Artie P. Hatzes
• Subject Area: Astrophysics and Astronomy
• Term: from 2011 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 181884489

• Final Report Year: 2017

Final Report Abstract

The main results of our program are summarized as follows: 1. Our program K-giant stars have a median mass of 1.3 M⨀ and a median metallicity of [Fe/H] = -0.1. 2. Approximately 15 % of our samples have stellar companions. 3. One star in our sample has a brown dwarf companion with minimum mass, m sin i = 42 MJup. The frequency of brown dwarfs companions in our sample is ≈ 1 %. 4. Approximately 20 % of our samples have candidate giant planet companions. 5. The planet candidates of our sample have an average mass of about 6 MJup, an average period ≈ 500 d, and a mean eccentricity of 0.20. If these are all planet candidates, then planets around K giant stars tend to be massive and on eccentric orbits. 6. Our program has discovered two giant planets of K giant stars in the shortest period orbits, HD 32518 (P = 157.5) and HD 94084 (P = 111 d). 7. We have discovered long-period RV variations in 3 K giant stars which initially mimicked the variations due to a planet. These were later shown to have amplitude variations suggesting a stellar origin. This is a new phenomenon in K giant stars, most likely caused by stellar oscillations. If true, the occurrence rate for planets around K giant stars may have to be revised downwards.

Publications

• "Exoplanets around G-K Giants" 2011, in Planetary Systems Beyond the Main Sequence: Proceedings of the International Conference. AIP Conference Proceedings, Volume 1331, pp. 79-87
  M.P. Döllinger, A.P. Hatzes, L. Pasquini, E.W. Guenther, M. Hartmann, J. Setiwan, L. Girardi, J.R. de Medeiros, L. da Silva
  
• "Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity" 2015, Astronomy & Astrophysics, 580, 31
  A.P. Hatzes, W.D. Cochran, M. Endl, E.W. Guenther, P. MacQueen, M. Hartmann, M. Zechmeister, I. Han, B.-C. Lee, G.A.H. Walker, S. Yang, A. Larson, K.-M. Kim, D. E. Mkrtichian, M. Döllinger, A.E. Simon, L. Girardi
  
• "Mass of WASP-33b", 2015, Astronomy & Astrophysics, 578, 4
  H. Lehmann, E. Guenther, D. Sebastian, M. Döllinger, M. Hartmann, D.E. Mkrtichian
  
• "Spectroscopic and Interferometric Measurements of Nine K Giant Stars" 2016, Astronomical Journal, 152, 66
  E. K. Baines, M.P. Döllinger, E.W. Guenther, A.P. Hatzes, M. Hrudkova, G.T. van Belle