An estimation of the radial velocity jitter
R. Martínez-Arnáiz1, J. Maldonado2, D. Montes1, C. Eiroa2 and B. Montesinos3
Universidad Complutense de Madrid,
Facultad de Ciencias Físicas, Dpt. Astrofísica, av.
Complutense s/n. 28040 Madrid, Spain e-mail: email@example.com
2 Universidad Autónoma de Madrid, Departamento de Física Teórica, Módulo 15, 28049 Cantoblanco, Madrid, Spain
3 LAEX, CAB (CSIC-INTA), ESAC Campus, PO BOX 78, 28691 Villanueva de la Cañada, Madrid, Spain
Accepted: 27 January 2010
Context. Chromospheric activity produces both photometric and spectroscopic variations that can be mistaken as planets. Large spots crossing the stellar disc can produce planet-like periodic variations in the light curve of a star. These spots clearly affect the spectral line profiles, and their perturbations alter the line centroids creating a radial velocity jitter that might “contaminate” the variations induced by a planet. Precise chromospheric activity measurements are needed to estimate the activity-induced noise that should be expected for a given star.
Aims. We obtain precise chromospheric activity measurements and projected rotational velocities for nearby (d ≤ 25 pc) cool (spectral types F to K) stars, to estimate their expected activity-related jitter. As a complementary objective, we attempt to obtain relationships between fluxes in different activity indicator lines, that permit a transformation of traditional activity indicators, i.e., Ca ii H & K lines, to others that hold noteworthy advantages.
Methods. We used high resolution (~50 000) echelle optical spectra. Standard data reduction was performed using the IRAF echelle package. To determine the chromospheric emission of the stars in the sample, we used the spectral subtraction technique. We measured the equivalent widths of the chromospheric emission lines in the subtracted spectrum and transformed them into fluxes by applying empirical equivalent width and flux relationships. Rotational velocities were determined using the cross-correlation technique. To infer activity-related radial velocity (RV) jitter, we used empirical relationships between this jitter and the index.
Results. We measured chromospheric activity, as given by different indicators throughout the optical spectra, and projected rotational velocities for 371 nearby cool stars. We have built empirical relationships among the most important chromospheric emission lines. Finally, we used the measured chromospheric activity to estimate the expected RV jitter for the active stars in the sample.
Key words: solar neighbourhood / stars: late-type / stars: activity / stars: chromospheres / stars: rotation / planetary systems
Based on observations made with the 2.2 m telescope at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto (Spain) and the Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Istituto Nazionale de Astrofisica Italiano (INAF), in the Spanish Observatorio del Roque de los Muchachos. This research has been supported by the Programa de Acceso a Infraestructuras Científicas y Tecnológicas Singulares (ICTS).
Tables A1 to A4 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/520/A79
© ESO, 2010