Line bisectors and radial velocity jitter from SARG spectra

¹ Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: fiorenzano@pd.astro.it
² INAF – Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
³ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, Catania, Italy
⁴ INAF – Centro Galileo Galilei, Calle Alvarez de Abreu 70, 38700 Santa Cruz de La Palma (TF), Spain
⁵ McDonald Observatory, The University of Texas at Austin, Austin, TX 78712, USA

Received: 16 February 2005
Accepted: 11 July 2005

Abstract

We present an analysis of spectral line bisector variations for a few stars observed in the SARG high precision radial velocity planet survey, and discuss their relationship with differential radial velocities. The spectra we consider are the same used for determining radial velocities. The iodine cell lines employed in the measurement of radial velocities were 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 then determined: errors in these quantities compare well with theoretical expectations based on resolution, S/N and line shape. The plot of bisector velocity span against radial velocity was studied to search for correlations between line asymmetries and radial velocity variations. A correlation was seen for HD 166435 due to stellar activity, and for HD 8071B due to spectral contamination by the companion. No correlation was seen for 51 Peg and ρ CrB, stars hosting planets. We conclude that this technique may be useful to separate radial velocity variations due to barycenter motion from spurious signals in spectra acquired with the iodine cell.