The GAPS Programme with HARPSN at TNG. XVII. Line profile indicators and kernel regression as diagnostics of radialvelocity variations due to stellar activity in solarlike stars
Abstract
Aims: Stellar activity is the ultimate source of radialvelocity (hereinafter RV) noise in the search for Earthmass planets orbiting latetype mainsequence stars. We analyse the performance of four different indicators and the chromospheric index log R^{'}_{HK} in detecting RV variations induced by stellar activity in 15 slowly rotating (υ sin i ≤ 5 km s^{1}), weakly active (log R^{'}_{HK} ≤ 4.95) solarlike stars observed with the highresolution spectrograph High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPSN).
Methods: We consider indicators of the asymmetry of the crosscorrelation function (CCF) between the stellar spectrum and the binary weighted line mask used to compute the RV, that is the bisector inverse span (BIS), ∆V, and a new indicator V_{asy(mod)} together with the full width at half maximum (FWHM) of the CCF. We present methods to evaluate the uncertainties of the CCF indicators and apply a kernel regression (KR) between the RV, the time, and each of the indicators to study their capability of reproducing the RV variations induced by stellar activity.
Results: The considered indicators together with the KR prove to be useful to detect activityinduced RV variations in 47 ± 18 percent of the stars over a twoyear time span when a significance (twosided pvalue) threshold of one percent is adopted. In those cases, KR reduces the standard deviation of the RV time series by a factor of approximately two. The BIS, the FWHM, and the newly introduced V_{asy(mod)} are the best indicators, being useful in 27 ± 13, 13 ± 9, and 13 ± 9 percent of the cases, respectively. The relatively limited performances of the activity indicators are related to the very low activity level and υ sin i of the considered stars. For the application of our approach to sunlike stars, a spectral resolution allowing λ/∆λ ≥ 10^{5} and highly stabilized spectrographs are recommended.
Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.The IDL macro to compute the line profile indicators is also available at the CDS via anonymous ftp to http://cdsarc.ustrasbg.fr (ftp://130.79.128.5) or via http://cdsarc.ustrasbg.fr/vizbin/qcat?J/A+A/616/A155
 Publication:

Astronomy and Astrophysics
 Pub Date:
 September 2018
 DOI:
 10.1051/00046361/201731010
 arXiv:
 arXiv:1804.07039
 Bibcode:
 2018A&A...616A.155L
 Keywords:

 planetary systems;
 stars: activity;
 stars: latetype;
 starspots;
 stars: atmospheres;
 techniques: radial velocities;
 Astrophysics  Earth and Planetary Astrophysics;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 15 pages, 6 figures, 5 tables, one Appendix, accepted to Astronomy and Astrophysics