J/A+A/654/A168 Convective blueshifts for solar-type stars (Liebing+, 2021)
Convective blueshift strengths of 810 F to M solar-type stars.
Liebing F., Jeffers S.V., Reiners A., Zechmeister M.
<Astron. Astrophys. 654, A168 (2021)>
=2021A&A...654A.168L 2021A&A...654A.168L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, dwarfs ; Line Profiles ; Radial velocities
Keywords: convection - techniques: radial velocities - Sun: granulation -
stars: activity
Abstract:
The detection of earth-mass exoplanets in the habitable zone around
solar-mass stars using the radial velocity technique requires
extremely high- precision of the order of 10cm/s. This puts the
required noise floor below the intrinsic variability of even
relatively inactive stars, like the Sun. One such variable is
convective blueshift varying temporally, spatially and between
spectral lines.
We develop a novel approach to measure convective blueshift and
determine the strength of convective blueshift for 810 stars observed
by the HARPS spectrograph, spanning spectral types from late-F, G, K
to early-M. We derive a model to infer blueshift velocity for lines of
any depth in later-type stars of any effective temperature.
Using a custom list of spectral lines, covering a wide range of
absorption depths, we create a model for the line-core shift as a
function of line depth, commonly known as the third signature of
granulation. For this we utilize an extremely high-resolution solar
spectrum (R∼1.000.000) to empirically account for the non-linear
nature of the third signature. The solar third signature is then
scaled to all 810 stars. Through this we obtain a measure of the
convective blueshift relative to the Sun as a function of stellar
effective temperature.
We confirm the general correlation of increasing convective blueshift
with effective temperature and establish a tight, cubic relation
between the two that strongly increases for stars above ∼5800K. For
stars between ∼4100K and ∼4700K we show for the first time a plateau
in convective shift and a possible onset of a plateau for stars above
6000K. Stars below ∼4000K show neither blue or red shift. We provide
a table listing expected blueshift velocities for each spectral
subtype in the data set to quickly access the intrinsic noise floor
through convective blueshift for the RV technique.
Description:
We calculated the convective blueshift strength for 810 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 strength and uncertainty of the solar relative
convection strength. We further provide interpolated results for CBS
strength over a range of spectral types 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
tablee1.dat 21 29 Modeled CBS reference values
tablee2.dat 104 810 Stellar parameters and results
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See also:
J/A+A/636/A74 : HARPS radial velocity database (Trifonov+, 2020)
Byte-by-byte Description of file: tablee1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- SpType Spectral Type
4- 7 I4 K Teff [4000/7220] Effective Temperature
9- 13 F5.3 --- Scale [0.21/6.02] Solar-relative CBS scale factor
15- 21 F7.1 m/s ConvBS [-2163.1/-77.8] Convective blueshift velocity (1)
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Note (1): Assuming a median solar line has absorption depth 0.7 with -350m/s
CBS.
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Byte-by-byte Description of file: tablee2.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 [3296/6393] Effective Temperature (1)
41- 42 A2 --- SpType Spectral Type (2)
44- 48 F5.2 mag Gmag [3.13/13.46] GAIA G Magnitude (1)
50- 54 F5.2 m/s vsini ? Projected Rotational Velocity (3)
56- 60 F5.1 d Prot [9.4/58.4]? Rotation Period (4)
62- 66 F5.2 --- logR'HK [-5.55/-3.68]? CaII H/K activity indicator (5)
68- 71 I4 --- Ncoadd [3/9735] Number of coadded spectra
73- 77 I5 --- S/N [28/18823]? Signal-to-Noise ratio
79- 82 I4 --- Nlines [712/1226] Number of lines fitted lines
84- 92 F9.2 --- chi2P Pearson Chi-square of 3rd signature fit
94- 99 F6.2 --- Scale [-38.01/24.19] Solar-relative CBS scale factor
101-104 F4.2 --- e_Scale [0.01/3.19] 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): Interpolation from SDSS (g-i) color, converted from GAIA (BP-RP) (See
Note 1, https://gea.esac.esa.int/archive/documentation/GDR2/Data_
processing/chapcu5pho/seccu5phocalibr/sseccu5pho_
PhotTransf.html), following Covey et al. (2007AJ....134.2398C 2007AJ....134.2398C)
Note (3): Taken from SIMBAD and Glebocki & Gnacinski (2005yCat.3244....0G 2005yCat.3244....0G,
Cat. III/244)
Note (4): Lovis et al. (2011arXiv1107.5325L 2011arXiv1107.5325L)
Note (5): Boro Saikia et al. (2018A&A...616A.108B 2018A&A...616A.108B) and
Marvin et al. (2016, submitted)
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Acknowledgements:
Florian Liebing, Florian.Liebing(at)uni-goettingen.de
(End) Patricia Vannier [CDS] 06-Aug-2021