J/A+A/673/A43 Convective blueshifts for evolved stars (Liebing+, 2023)
Convective blueshift strengths for 242 evolved stars.
Liebing F., Jeffers S.V., Zechmeister M., Reiners A.
<Astron. Astrophys. 673, A43 (2023)>
=2023A&A...673A..43L 2023A&A...673A..43L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Line Profiles ; Radial velocities ; Optical
Keywords: convection - techniques: radial velocities - Sun: granulation -
stars: activity
Abstract:
With the advent of extreme precision radial velocity (RV) surveys,
seeking to detect planets at RV semi-amplitudes of 10cm/s, 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.
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.
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 3750K
to 6150K. We compare the results to main sequence stars of
comparable temperatures but with a higher surface gravity.
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 5x increase below 4300K 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.
Description:
We calculated the convective blueshift strength for 241 evolved stars
observed by HARPS relative to a solar template. For each star we
provide the important parameters, details on the coadded spectrum and
line-by-line fit as well as the magnitude and uncertainty of the solar
relative convection strength. We further provide interpolated results
for CBS strength over a range of temperatures and corresponding RV
values from our model.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 17 20 Modeled CBS reference values
tablec2.dat 93 242 Stellar parameters and results
indices for each galaxy
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/636/A74 : HARPS radial velocity database (Trifonov+, 2020)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 K Teff [4100/6000] Effective Temperature
6- 10 F5.3 --- Scale [0.76/1.53] Solar-relative CBS scale factor
12- 17 F6.1 m/s ConvBS [-546.8/-275.5] Convective blueshift
velocity (1)
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Note (1): Assuming a representative median line absorption depth of 0.7.
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- Name Name of the star
16- 34 I19 --- GaiaDR2 Gaia DR2 star ID (1)
36- 39 I4 K Teff [3797/6105] Effective temperature (1)
41- 45 F5.2 mag GMAG [-8.54/3.85] Absolute Gaia G magnitude (2)
47- 50 F4.2 [cm/s2] logg [0.05/4.01] Surface gravity (4)
52- 55 A4 --- Evo Evolutionary Phase (4)
57- 61 F5.2 m/s vsini [0.00/6.79]? Projected rotational velocity (3)
63- 65 I3 --- Ncoadd [1/724] Number of coadded spectra
67- 70 I4 --- S/N [36/5651] Signal-to-Noise ratio
72- 75 I4 --- Nlines [897/1223] Number of fitted lines
77- 82 F6.2 --- chi2P [0.01/652.34] Pearson Chi-square of fit
84- 88 F5.2 --- Scale [-0.15/3.49] Solar-relative CBS scale factor
90- 93 F4.2 --- e_Scale [0.02/0.24] Error on CBS scale factor
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Note (1): From GAIA DR2 (2018yCat.1345....0G 2018yCat.1345....0G, Cat. I/345),
Note (2): From GAIA DR2 (2018yCat.1345....0G 2018yCat.1345....0G, Cat. I/345),
using GAIA DR2 parallaxes,
Note (3): Taken from SIMBAD and Glebocki & Gnacinski (2005yCat.3244....0G 2005yCat.3244....0G,
Cat. III/244))
Note (4): From fitted MIST evolution grids and synthetic photometry,
Dotter (2016ApJS..222....8D 2016ApJS..222....8D); Choi et al. (2016ApJ...823..102C 2016ApJ...823..102C);
Paxton et al. (2011ApJS..192....3P 2011ApJS..192....3P, 2013ApJS..208....4P 2013ApJS..208....4P,
2015ApJS..220...15P 2015ApJS..220...15P).
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Acknowledgements:
Florian Liebing, Liebing(at)mps.mpg.de
(End) Patricia Vannier [CDS] 08-Mar-2023