Charakterisierung und Interpretation der Planetenpopulation um Sterne mittlerer Masse

• Antragstellerin: Privatdozentin Dr. Sabine Reffert
• Fachliche Zuordnung: Astrophysik und Astronomie
• Förderung: Förderung von 2017 bis 2021
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 362466951

• Erstellungsjahr: 2021

Zusammenfassung der Projektergebnisse

The goal of this project was a better understanding of the planet population around giant stars, in particular in comparison with the planet populations around main-sequence and subgiant stars. As a first step, we therefore combined various planet search samples consisting of giant stars for better statistics, and derived the planet occurrence rates as a function of stellar metallicity and stellar mass. As in previous studies, we found that planet occurrence rises until a stellar mass of about 1.7 solar masses, while for even larger stellar masses giant planet occurrence on orbits up to a few years drops again. Furthermore, planet occurrence steeply rises with stellar metallicity, though not quite as steep as previously suspected. Having established the planet occurrence rate around a large evolved stellar samples, we then set out to compare the planet occurrence rates and properties of the planets to those found around main-sequence stellar hosts. As it turns out, the evolved samples contain fewer close-in planets, and also a notable pile-up at intermediate periods. We were specifically interested in whether stellar evolution was capable of changing the orbital parameters of the observed planets around giant stars such that they would be in line with having developed out of the known planet populations around main-sequence stars. In order to answer that question, we carried out simulations of known planetary systems around giant stars and turned back time, in order to derive their properties once the stars were located on the zero-age main-sequence. However, the answer is that stellar evolution is most likely not to blame for the differing planet properties around main-sequence and evolved stellar hosts, since stellar evolution actually changed very little on the planet properties. In essence, the only drastic changes are expected once the stars with masses less than 1.9 solar undergo a helium flash, but most of the horizontal branch stars are too massive, and the red giant branch stars are not old enough to have experienced the helium flash already. Consequently, other mechanisms possibly related to the original planet formation process must be responsible for the different planet properties around main-sequence and evolved stellar hosts. Finally, we planned to increase the statistics of known planetary systems orbiting giant stars through a continued Doppler survey, using our own Waltz Telescope and Spectrograph in Heidelberg for this task. A major redesign of the frontend of the telescope and a significant improvement of the telescope infrastructure were realized during this project, and the Waltz will be ready for scientific observations in the near future.

Projektbezogene Publikationen (Auswahl)

• (2019). Orbital relaxation and excitation of planets tidally interacting with white dwarfs. MNRAS 486.3, 3831
  Veras, D., Efroimsky, M., Makarov, V. V., Boué, G., Wolthoff, V., Reffert, S., Quirrenbach, A., Tremblay, P.-E. & Gänsicke, B. T.
  
• (2019). Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b. A&A 625, A22
  Reichert, K., Reffert, S., Stock, S., Trifonov, T. & Quirrenbach, A.
  
• (2019). Precise radial velocities of giant stars. XIII. A second Jupiter orbiting in 4:3 resonance in the 7 CMa system. A&A 631, A136
  Luque, R., Trifonov, T., Reffert, S., Quirrenbach, A., Lee, M. H., Albrecht, S., Fredslund Andersen, M., Antoci, V., Grundahl, F., Schwab, C. & Wolthoff, V.
  
• (2019). TESS Asteroseismology of the Known Red-giant Host Stars HD 212771 and HD 203949. ApJ 885.1, 31
  Campante, T. L., Corsaro, E., Lund, M. N., Mosser, B., Serenelli, A., Veras, D., Adibekyan, V., Antia, H. M., Ball, W., Basu, S., Bedding, T. R., Bossini, D., Davies, G. R., Delgado Mena, E., García, R. A., Handberg, R., Hon, M., Kane, S. R., Kawaler, S. D., Kuszlewicz, J. S., Lucas, M., Mathur, S., Nardetto, N., Nielsen, M. B., Pinsonneault, M. H., Reffert, S., Silva Aguirre, V., Stassun, K. G., Stello, D., Stock, S., Vrard, M., Yildiz, M., Chaplin, W. J., Huber, D., Bean, J. L., Çelik Orhan, Z., Cunha, M. S., Christensen-Dalsgaard, J., Kjeldsen, H., Metcalfe, T. S., Miglio, A., Monteiro, M. J. P. F. G., Nsamba, B., Örtel, S., Pereira, F., Sousa, S. G., Tsantaki, M. & Turnbull, M. C.
  
• (2019). Two Jovian Planets around the Giant Star HD 202696: A Growing Population of Packed Massive Planetary Pairs around Massive Stars? AJ 157.3, 93
  Trifonov, T., Stock, S., Henning, T., Reffert, S., Kürster, M., Lee, M. H., Bitsch, B., Butler, R. P. & Vogt, S. S.
  
• (2020). Precise radial velocities of giant stars. XIV. Evidence of planetary companions around HD 25723, 17 Sco, 3 Cnc, and 44 UMa. A&A 644, A1
  Tala Pinto, M., Reffert, S., Quirrenbach, A., Stock, S., Trifonov, T. & Mitchell, D. S.