J/A+A/593/A123 STELLA-SES Radial Velocities of HD 208472 (Ozdarcan+, 2016)
Time series Doppler imaging of the red giant HD 208472.
Active longitudes and differential rotation.
Ozdarcan O., Carroll T.A., Kunstler A., Strassmeier K.G., Evren S.,
Weber M., Granzer T.
<Astron. Astrophys. 593, A123 (2016)>
=2016A&A...593A.123O 2016A&A...593A.123O (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Radial velocities
Keywords: stars: activity - stars: imaging - starspots -
stars: individual: HD 208472
Abstract:
HD 208472 is among the most active RS CVn binaries with cool
starspots. Decade-long photometry had shown that the spots seem to
change their longitudinal appearance with a period of about six years,
coherent with brightness variations.
Our aim is to spatially resolve the stellar surface of HD 208472 and
related the photometric results to the true longitudinal and
latitudinal spot appearance. Furthermore, we investigate surface
differential rotation pattern of the star.
We employ three years of high resolution, high S/N spectroscopic data
from the STELLA robotic observatory and determine new and more precise
stellar physical parameters. Pre-calculated synthetic spectra are fit
to each of these spectra and new spot-corrected orbital elements are
given. A sample of 34 absorption lines per spectrum is used to
calculate mean line profiles with a S/N of several hundred. A total of
13 temperature Doppler images are reconstructed from these line
profiles with the inversion code iMap. Differential rotation is
investigated by cross-correlating successive Doppler images in each
observing season.
Spots on HD 208472 are distributed preferably at high latitudes and
less occasionally around mid-to-low latitudes. No polar-cap like
structure is seen at any epoch. We observed a flip-flop event between
2009 and 2010, manifested as a flip of the spot activity from phase
0.0 to phase 0.5, while the overall brightness of the star continued
to increase and reached an all-time maximum in 2014. Cross-correlation
of successive Doppler images suggests a solar-like differential
rotation which is ∼15 times weaker in strength compared to the Sun.
Description:
Precise radial velocity measurement of HD 208472 based on 229 high
resolution Stella Echelle Spectrograph (SES) spectra obtained at
STELLA robotic observatory on Tenerife, Spain from March 22, 2009 to
July 20, 2011 are presented. High precision radial velocities allow
one to trace spot jitter effect on measured radial velocities via
residuals from spectroscopic orbit solution. In case of HD 208472,
removing spot jitter effect from measured velocities, precision on
calculated orbital parameters were improved by factor of 4 without
changing the actual value of parameters.
Objects:
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RA (2000) DE Designation(s)
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21 55 14.46 +44 25 06.9 HD 208472 = V* V2075 Cyg
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
rv.dat 27 229 Measured radial velocities
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Byte-by-byte Description of file: rv.dat
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Bytes Format Units Label Explanations
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1- 12 F12.4 d HJD Heliocentric Julian Date of observation
15- 20 F6.3 km/s RV Radial velocity
23- 27 F5.3 km/s e_RV Uncertainty of radial velocity
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Acknowledgements:
Orkun Ozdarcan, orkun.ozdarcan(at)ege.edu.tr
(End) Orkun Ozdarcan [AIP, Ege University], Patricia Vannier [CDS] 13-Jul-2016