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Giant planets and brown dwarfs around A-F type stars: a Harps survey
Simon Borgniet, Anne-Marie Lagrange, Franck Galland, NadХge Meunier
Institut de PlanИtologie et d'Astrophysique de Grenoble (France)

Email : Simon.Borgniet@obs.ujf-grenoble.fr

Abstract:
Since 1995, the radial velocity technique has allowed to detect nearly 600 planets and has widely contributed to the dramatical improvement of our knowledge of exoplanets. However, past radial velocity surveys mainly focused on solar-type stars, and there are still many open questions. In particular, the impact of the host star mass on the planetary properties remains largely unknown, while formation models predict different behaviors according to the stellar mass. In this context, we undertook two radial velocity surveys dedicated to search for substellar and planetary companions around more massive, early-type (A-F) Main-Sequence stars (one with HARPS/La Silla for the Southern stars and the other with SOPHIE/OHP for the Northern stars). We introduce here the first results of the HARPS Southern survey.

Method : high-precision RV for A-F type stars Sample
Observations : HARPS / La Silla (3800-6900 е) Timescale : 2005 ­ 2011. 30-50 spectra / star in average. Data Reduction : Early-type stars : few spectral lines, rotation-broadened. Not adapted for classical correlation with a binary mask
B-V vsini

109 early-type Main-Sequence stars Selection : -Spectral type : B8 to F7 -Distance : nearby stars A type : < 67 pc F type : < 33 pc -removing : known spectroscopic and close visual binaries pulsators ( Scu, Dor) Ap, Am variable stars
Stellar mass (Mo)

+

=
Ref. CCF

Build a reference spectrum (sum of spectra) Correlation of each spectrum with this reference Accurate relative radial velocities (SAFIR software, Galland et al 2005)

Detections and candidates
Two giant planets around the F6V dwarf HD60532 (M=1.44Mo): m1sini = 1.03 Mjup @ 0.76 AU m2sini = 2.46 Mjup @ 1.58 AU (Desort et al 2008)

Typical detection limits
F3V dwarf, M=1.3 Mo, vsini = 12 km/s down to 0.2 Mjup @ 0.03 AU 1 Mjup @ 1 AU A3V dwarf, M=1.7 Mo, vsini = 95 km/s down to 0.9 Mjup @ 0.03 AU 5 Mjup @ 1 AU

Example of planetary candidate: F5V dwarf, M=1.2 Mo, vsini = 28 km/s m1sini = 4.8 Mjup @ 1.8 AU (raw estimate)

Mass (Mjup)

Semi-major axis (AU)

References
Galland et al. 2005, A&A 443, 337 Desort et al. 2008, A&A 491, 883 Lagrange et al. 2009, A&A 495, 335 Lagrange et al. 2012, A&A 542, 18 Borgniet et al. 2014, A&A 561, 65

Next steps : statistical study
Data analysis : work in progress Combine Harps results for this A-F sample with SOPHIE "twin" survey of Northern stars Statistical study of detected planetary and/or substellar companions Contribution to planetary formation and evolution models