Bisectors of the HARPS Cross-Correlation-Function. The dependence on stellar atmospheric parameters

Abstract

Bisectors of the HARPS cross-correlation function (CCF) can discern between planetary radial-velocity (RV) signals and spurious RV signals from stellar magnetic activity variations. However, little is known about the effects of the stellar atmosphere on CCF bisectors or how these effects vary with spectral type and luminosity class. Here we investigate the variations in the shapes of HARPS CCF bisectors across the HR diagram in order to relate these to the basic stellar parameters, surface gravity and temperature. We use archive spectra of 67 well studied stars observed with HARPS and extract mean CCF bisectors. We derive previously defined bisector measures (BIS, v_bot, c_b) and we define and derive a new measure called the CCF Bisector Span (CBS) from the minimum radius of curvature on direct fits to the CCF bisector. We show that the bisector measures correlate differently, and non-linearly with log g and T_eff. The resulting correlations allow for the estimation of log g and T_eff from the bisector measures. We compare our results with 3D stellar atmosphere models and show that we can reproduce the shape of the CCF bisector for the Sun.

13 pages, 20 figures. Accepted by A&A

References in corpus (8)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes
• Basic physical parameters of a selected sample of evolved stars
• Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters
• Precise radial velocities of giant stars. III. Spectroscopic stellar parameters
• Bisectors of the cross-correlation function applied to stellar spectra. Discriminating stellar activity, oscillations and planets
• 3D LTE spectral line formation with scattering in red giant stars
• Line bisectors and radial velocity jitter from SARG spectra

Cited by in corpus (9)

• Stellar Activity Masquerading as Planets in the Habitable Zone of the M dwarf Gliese 581
• A Grid of 3D Stellar Atmosphere Models of Solar Metallicity: I. General Properties, Granulation and Atmospheric Expansion
• Stellar activity mimics a habitable-zone planet around Kapteyn's star
• Modelling the photosphere of active stars for planet detection and characterization
• Spatially resolved spectroscopy across stellar surfaces. I. Using exoplanet transits to analyze 3-D stellar atmospheres
• MARVELS-1: A face-on double-lined binary star masquerading as a resonant planetary system; and consideration of rare false positives in radial velocity planet searches
• SOAP-GPU: Efficient Spectral Modelling of Stellar Activity Using Graphical Processing Units
• The conjectured S-type retrograde planet in nu Octantis: more evidence including four years of iodine-cell radial velocities
• Searching double-peaked emission line profiles in the spectra of galaxies through the symmetry of the cross-correlation function