New analytical expressions of the RossiterMcLaughlin effect adapted to different observation techniques
Abstract
The RossiterMcLaughlin (hereafter RM) effect is a key tool for measuring the projected spinorbit angle between stellar spin axes and orbits of transiting planets. However, the measured radial velocity (RV) anomalies produced by this effect are not intrinsic and depend on both instrumental resolution and data reduction routines. Using inappropriate formulas to model the RM effect introduces biases, at least in the projected velocity Vsini_{⋆} compared to the spectroscopic value. Currently, only the iodine cell technique has been modeled, which corresponds to observations done by, e.g., the HIRES spectrograph of the Keck telescope. In this paper, we provide a simple expression of the RM effect specially designed to model observations done by the Gaussian fit of a crosscorrelation function (CCF) as in the routines performed by the HARPS team. We derived a new analytical formulation of the RV anomaly associated to the iodine cell technique. For both formulas, we modeled the subplanet mean velocity v_{p} and dispersion β_{p} accurately taking the rotational broadening on the subplanet profile into account. We compare our formulas adapted to the CCF technique with simulated data generated with the numerical software SOAPT and find good agreement up to Vsini_{⋆} ≲ 20 km s^{1}. In contrast, the analytical models simulating the two different observation techniques can disagree by about 10σ in Vsini_{⋆} for large spinorbit misalignments. It is thus important to apply the adapted model when fitting data.
A public code implementing the expressions derived in this paper is available at http://www.astro.up.pt/resources/arome. A copy of the code is also available at the CDS via anonymous ftp to cdsarc.ustrasbg.fr (130.79.128.5) or via http://cdsarc.ustrasbg.fr/vizbin/qcat?J/A+A/550/A53
 Publication:

Astronomy and Astrophysics
 Pub Date:
 February 2013
 DOI:
 10.1051/00046361/201220146
 arXiv:
 arXiv:1211.3310
 Bibcode:
 2013A&A...550A..53B
 Keywords:

 techniques: spectroscopic;
 instrumentation: spectrographs;
 planetary systems;
 methods: analytical;
 methods: data analysis;
 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 16 pages, 11, figures, accepted in Astronomy and Astrophysics. Public code available at http://www.astro.up.pt/resources/arome