Issue |
A&A
Volume 673, May 2023
|
|
---|---|---|
Article Number | A43 | |
Number of page(s) | 16 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202244394 | |
Published online | 03 May 2023 |
Convective blueshift strengths for 242 evolved stars★
1
Max Planck Institute for Solar System Research,
Justus-von-Liebig-Weg 3,
37077
Göttingen,
Germany
e-mail: liebing@mps.mpg.de
2
Institut für Astrophysik und Geophysik (IAG), Universität Göttingen,
Friedrich-Hund-Platz 1,
37077
Göttingen,
Germany
Received:
1
July
2022
Accepted:
30
January
2023
Context. With the advent of extreme precision radial velocity (RV) surveys, seeking to detect planets at RV semi-amplitudes of 10 cm s−1, intrinsic stellar variability is the biggest challenge to detecting small exoplanets. To overcome the challenge we must first thoroughly understand all facets of stellar variability. Among those, convective blueshift caused by stellar granulation and its suppression through magnetic activity plays a significant role in covering planetary signals in stellar jitter.
Aims. Previously we found that for main sequence stars, convective blueshift as an observational proxy for the strength of convection near the stellar surface strongly depends on effective temperature. In this work we investigate 242 post main sequence stars, covering the subgiant, red giant, and asymptotic giant phases and empirically determine the changes in convective blueshift with advancing stellar evolution.
Methods. We used the third signature scaling approach to fit a solar model for the convective blueshift to absorption-line shift measurements from a sample of coadded HARPS spectra, ranging in temperature from 3750 K to 6150 K. We compare the results to main sequence stars of comparable temperatures but with a higher surface gravity.
Results. We show that convective blueshift becomes significantly stronger for evolved stars compared to main sequence stars of a similar temperature. The difference increases as the star becomes more evolved, reaching a 5× increase below 4300 K for the most evolved stars. The large number of stars in the sample, for the first time, allowed for us to empirically show that convective blueshift remains almost constant among the entire evolved star sample at roughly solar convection strength with a slight increase from the red giant phase onward. We discover that the convective blueshift shows a local minimum for subgiant stars, presenting a sweet spot for exoplanet searches around higher mass stars, by taking advantage of their spin-down during the subgiant transition.
Key words: convection / techniques: radial velocities / Sun: granulation / stars: activity
Table C.1 and full Table C.2 are available at the CDS via anonymous cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/673/A43
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model.
Open Access funding provided by Max Planck Society.
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