Line bisector analysis of stars with companions in the SARG survey at the TNG

¹ Fundación Galileo Galilei – INAF, Rbla. José Ana Fdez. Pérez 7, 38712 Breña Baja (TF), Spain
² INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
³ Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123, Italy
⁴ McDonald Observatory, The University of Texas at Austin, Austin, TX 78712, USA

Abstract

We present an analysis of how bisectors of spectral lines vary, for a few stars observed during the high-accuracy 
radial-velocity planet survey ongoing at the Telescopio Nazionale Galileo (TNG) using the Galileo High Resolution Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG), and discuss their relation with differential radial velocities. The iodine cell lines employed in the radial velocity measurements were used to improve the wavelength calibration and then removed before bisector analysis. The line bisectors were then computed from average absorption profiles obtained by cross-correlation of the stellar spectra with a mask made from suitable lines of a solar catalog. Bisector velocity spans were determined and the run of bisector velocity span against radial velocity was studied to search for correlations between line asymmetries and radial velocity variations. We present an analysis of spectra of HD 216122B that show a slight contamination likely to be due to a stellar companion, and an analysis of spectra of HD 76036A, a case where the line bisectors are useful for improving the RV measurements. These systems are part of a survey sample being observed with adaptive optics (AdOpt at the TNG since 2006) in an attempt to visually resolve stellar companions.