J/A+A/695/A89 lambda And PEPSI and STELLA RVs (Adebali+, 2025)
First Doppler image and starspot-corrected orbit for lambda Andromedae.
A multifaceted activity analysis.
Adebali O., Strassmeier K.G., Ilyin I.V., Weber M., Gruner D., Kovari Zs.
<Astron. Astrophys. 695, A89 (2025)>
=2025A&A...695A..89A 2025A&A...695A..89A (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, spectroscopic ; Radial velocities ; Optical
Keywords: techniques: radial velocities - techniques: spectroscopic -
stars: activity - stars: magnetic field - stars: rotation - starspots
Abstract:
Starspots on a rotating stellar surface impact the measured radial
velocities and thereby limit the determination of precise
orbital elements as well as astrophysical stellar parameters and even
jeopardize the detection and characterization of (exo)planets.
We quantify the effect of starspots for the orbital elements of the
spotted RS CVn binary λ And and present an empirical
correction. The aim is a more precise orbital solution that can be
used to better study the system's severe orbital-rotational
asynchronism.
Phase-resolved high-resolution optical spectra were recorded over the
course of 522 days in 2021-2022. We employed two
facilities with medium and high resolution spectroscopy for the
multiple activity analyses. Doppler imaging is used to reconstruct
λ And's starspots with high resolution (R=250000) and high
signal-to-noise ratio spectra. Optimized cross-correlation functions
are used to measure precise radial velocities at a few ten's of m/s
level.
The spot-corrected radial velocities enable on average a three-fold
increase of precision of the individual orbital elements. The residual
velocity jitter with a full range of 500m/s is modulated by the
rotation period of λ And of 54.4±0.3d. Our logarithmic
gravity from spectrum synthesis of 2.8±0.2 together with the
interferometrically determined stellar radius suggest a most-likely
mass of the primary of ∼1.4M☉. The small orbital mass function
then implies a secondary mass of just ∼0.1M☉, appropriate for an
L-class brown dwarf. The Doppler image reconstructs a dominating cool
spot with an umbral temperature difference of ∼1000K with respect
to the photosphere of 4660K and is likely surrounded by a moat-like
velocity field. Three more but weaker spots add to the total surface
spottedness of up to 25% of the visible surface. Seven optical
chromospheric tracers show rotational modulation of their emission
line fluxes in phase with the cool spots. This surface configuration
appeared to have been stable for the 522d of our observations. We
also redetermine the carbon isotope ratio to 12C/13C=30±5 and
measure a contemporaneous disk-integrated mean longitudinal magnetic
field of polarity Plus/Minus up to 2.70±0.35G from Stokes-V line
profiles.
Description:
Radial velocity data of the target lambda Andromedae.
Objects:
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RA (2000) DE Designation(s)
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23 37 33.84 +46 27 29.3 lambda And = HR 8961
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stellarv.dat 117 184 STELLA radial velocities (table A1)
pepsirv.dat 117 81 PEPSI radial velocities (table A2)
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Byte-by-byte Description of file: stellarv.dat pepsirv.dat
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Bytes Format Units Label Explanations
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1- 23 A23 "date" Obs.Date Coordinated Universal Time of observation
25- 39 F15.7 d BJD Barycenteric Julian Date of observation
41- 47 F7.4 km/s RV Radial velocity
49- 64 F16.11 m/s RVres Residual of radial velocity
66- 69 F4.1 m/s e_RV Error of radial velocity
71- 83 F13.11 --- Phaseorb Orbital phase of the star
85- 97 F13.11 --- Phaserot Rotational phase of the star
99-117 F19.16 km/s RVc Activity corrected radial velocity
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Acknowledgements:
Ozgun Adebali, oadebali(at)aip.de
(End) Patricia Vannier [CDS] 11-Feb-2025