Search for exoplanets with the radial-velocity technique : quantitative diagnostics of stellar activity

By M. Desort, Anne-Marie Lagrange, F. Galland, S. Udry, M. Mayor. 2007

182 citations recorded by the source corpus.

Aims. It is known that stellar activity may complicate the analysis of high-precision radial-velocity spectroscopic data when looking for exoplanets signatures. We aim at quantifying the impact of stellar spots on stars with various spectral types and rotational velocities and comparing the simulations with data obtained with the HARPS spectrograph. Methods. We have developed detailed simulations of stellar spots and estimated their effects on a number of observables commonly used in the analysis of radial-velocity data when looking for extrasolar planets, such as radial-velocity curves, cross-correlation functions, bisector velocity spans, and photometric curves. Stellar and spot properties are taken into account, as well as the characteristics of the spectrograph used (generally HARPS). The computed stellar spectra are then analyzed in the same way as when searching for exoplanets. Results. 1) A first grid of simulation results (radial-velocity amplitudes, bisector velocity-span amplitudes and shapes, and photometry) is built for F-K type stars, with different stellar and spot properties. 2) It is shown quantitatively that star spots with typical sizes of 1% can mimic both radial-velocity curves and the bisector behavior of short-period giant planets around G-K type stars with a v sini lower than the spectrograph resolution. For stars with intermediate v sini, smaller spots may produce similar features. Such spots may complicate the search for low-mass planets on short-period orbits. In these cases, additional observables (e.g., photometry, spectroscopic diagnostics) are mandatory to confirm the presence of short-period planets. We discuss these possibilities and show that, in some cases, photometric variations may not be enough to clearly rule out spots as explanations of the observed radial-velocity variations. This is particularly important when searching for super-Earth planets. 3) It is also stressed that quantitative values obtained for radial-velocity and bisector velocity-span amplitudes depend strongly on the detailed star properties, on the spectrograph used, on the line or set of lines used, and on the way they are measured. High-resolution spectrographs will help in distinguishing between spots and planets.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/579915bb7536b73daed305ceea44e59aaf327066

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Citations in the corpus

Disentangling between stellar activity and planetary signals (2010, background): “Second, it can only be used if the vsini of the star is sufficient to resolve the effect of spots on the bisector (Desort et al. 2007; Bonfils et al. 2007).”
SOAP 2.0: A TOOL TO ESTIMATE THE PHOTOMETRIC AND RADIAL VELOCITY VARIATIONS INDUCED BY STELLAR SPOTS AND PLAGES (2014, methodology): “As already demonstrated by other authors (Boisse et al. 2012; Desort et al. 2007), a high resolution will therefore strengthen the correlation between the RV and the BIS SPAN or the FWHM variations.”
WASP-19b: THE SHORTEST PERIOD TRANSITING EXOPLANET YET DISCOVERED (2010, background): “Starspots can cause periodic low-amplitude RV variations (e.g., Huélamo et al. 2008; Desort et al. 2007) but not photometric transits as well; thus, a single star blended with a fainter stellar eclipsing binary (EB) is the preferred false positive scenario for transiting planets.”
State of the Field: Extreme Precision Radial Velocities (2016, background): “However, when looking at slow rotators like the Sun, it is more difficult to resolve the tiny variations in the bisector and FWHM, making these ineffective diagnostics of stellar activity (Desort et al. 2007; Dumusque et al. 2014; Santos et al. 2014).”
Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators (2017, background): “3 and is predicted with spot simulations (Desort et al. 2007; Reiners et al. 2010).”
Extrasolar planets and brown dwarfs around A-F type stars. VI. High precision RV survey of early type dwarfs with HARPS (2008, background): “Indeed, the bisector and bisectors’ velocity span are very good diagnostics of stellar activity (spots, pulsations) provided 1) they can be measured (see below), and 2) the star projected rotational velocity is higher than the instrumental resolution (see Desort et al. 2007).”
DETECTING PLANETS AROUND VERY LOW MASS STARS WITH THE RADIAL VELOCITY METHOD (2009, methodology): “Desort et al. (2007) modeled the effect of a cool spot for observations of sun-like stars at optical wavelengths.”
Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system (2013, background): “The smaller impact of the surface brightness inhomogeneities on the RV variations could be due to the small v sin i of the star (Bruntt et al. 2010), because the amplitude of these variations scales approximately with v sin i (Desort et al. 2007).”
DETERMINING THE MASS OF KEPLER-78b WITH NONPARAMETRIC GAUSSIAN PROCESS ESTIMATION (2015, result): “Additionally, the value of a is broadly consistent with the results of Desort et al. (2007), who illustrate that the expected radial velocity contribution from starspots on a K dwarf is larger at shorter wavelengths, resulting in a larger signal in HIRES than in HARPS-N, as HARPSN has significant…”