Abstract
Context. We carried out a long-term campaign spanning 17 years to obtain high-precision radial velocities (RVs) with the HARPS spectrograph for a large sample of evolved stars in open clusters.
Aims. The aim of this work is to search for planets around evolved stars, with a special focus on stars more massive than 2 M⊙ in light of previous findings that show a drop in planet occurrence around stars above this mass.
Methods. We used kima —a package for Bayesian modelling of RV and activity data with Gaussian process capability and Nested sampling for model comparison— to find the Keplerian orbits most capable of explaining the periodic signals observed in RV data, which have semiamplitudes of between 75 and 500 m s−1 . We also studied the variation of stellar activity indicators and photometry in order to discard stellar signals mimicking the presence of planets.
Results. We present a planet candidate in the open cluster NGC3680 that orbits the 1.64 M⊙ star No. 41. The planet has a minimum mass of 5.13MJ and a period of 1155 days. We also present periodic and large-amplitude RV signals of probable stellar origin in two more massive stars (5.84 and 3.05 M⊙ in the clusters NGC2345 and NGC3532). Finally, using new data, we revise the RV signals of the three stars analysed in our previous paper. We confirm the stellar origin of the signals observed in NGC2423 No. 3 and NGC4349 No. 127. On the other hand, the new data collected for IC4651 No. 9122 (1.79 M⊙) seem to support the presence of a bona fide planet of 6.22MJ at a period of 744 days, although more data will be needed to discard a possible correlation with the CCF-FWHM.
Conclusions. The targets presented in this work showcase the difficulties in interpreting RV data for evolved massive stars. The use of several activity indicators (CCF-FWHM, CCF-BIS, Hα), photometry, and long-term observations (covering several orbital and stellar rotational periods) is required to discern the true nature of the signals. However, in some cases, all this information is insufficient, and the inclusion of additional data —such as the determination of magnetic field variability or RV points in the near-infrared— will be necessary to identify the nature of the discovered signals.
Aims. The aim of this work is to search for planets around evolved stars, with a special focus on stars more massive than 2 M⊙ in light of previous findings that show a drop in planet occurrence around stars above this mass.
Methods. We used kima —a package for Bayesian modelling of RV and activity data with Gaussian process capability and Nested sampling for model comparison— to find the Keplerian orbits most capable of explaining the periodic signals observed in RV data, which have semiamplitudes of between 75 and 500 m s−1 . We also studied the variation of stellar activity indicators and photometry in order to discard stellar signals mimicking the presence of planets.
Results. We present a planet candidate in the open cluster NGC3680 that orbits the 1.64 M⊙ star No. 41. The planet has a minimum mass of 5.13MJ and a period of 1155 days. We also present periodic and large-amplitude RV signals of probable stellar origin in two more massive stars (5.84 and 3.05 M⊙ in the clusters NGC2345 and NGC3532). Finally, using new data, we revise the RV signals of the three stars analysed in our previous paper. We confirm the stellar origin of the signals observed in NGC2423 No. 3 and NGC4349 No. 127. On the other hand, the new data collected for IC4651 No. 9122 (1.79 M⊙) seem to support the presence of a bona fide planet of 6.22MJ at a period of 744 days, although more data will be needed to discard a possible correlation with the CCF-FWHM.
Conclusions. The targets presented in this work showcase the difficulties in interpreting RV data for evolved massive stars. The use of several activity indicators (CCF-FWHM, CCF-BIS, Hα), photometry, and long-term observations (covering several orbital and stellar rotational periods) is required to discern the true nature of the signals. However, in some cases, all this information is insufficient, and the inclusion of additional data —such as the determination of magnetic field variability or RV points in the near-infrared— will be necessary to identify the nature of the discovered signals.
| Original language | English |
|---|---|
| Article number | A94 |
| Number of pages | 21 |
| Journal | Astronomy and Astrophysics |
| Volume | 679 |
| DOIs | |
| Publication status | Published - 16 Nov 2023 |
Bibliographical note
We thank François Bouchy and Xavier Dumusque for coordinating the shared observations with HARPS and all the observers who helped collecting the data. We thank the referee for their careful review that helped to improve this paper. E.D.M., J.G.S, J.P.F., N.C.S., J.H.M., S.G.S. acknowledge the support from Fundação para a Ciência e a Tec-nologia (FCT) through national funds and from FEDER through COM-PETE2020 by the following grants: UIDB/04434/2020 & UIDP/04434/2020 and 2022.04416.PTDC. E.D.M. acknowledges the support from FCT through Stimulus FCT contract 2021.01294.CEECIND and Investigador FCT contract IF/00849/2015/CP1273/CT0003 and in the form of an exploratory project with the same reference. S.G.S acknowledges the support from FCT through Investigador FCT contract CEECIND/00826/2018 and POPH/FSE (EC). This research has been Co-funded by the European Union (ERC, FIERCE, 101052347). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. This research has made use of The Extrasolar Planets Encyclopaedia, SIMBAD and WEBDA databases. This work has also made use of the IRAF facility. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.Keywords
- stars: individual: NGC3680MMU41, NGC2345MMU50, NGC3532MMU670, IC4651MMU9122, NGC2423MMU3, NGC4349MMU127
- stars: planetary systems
- stars: evolution
- planets and satellites: physical evolution
- Galaxy: open clusters and associations