extrasolar planets and brown dwarfs around a-凯发官网入口

arxiv:astro-ph/0602592v1 27 feb 2006astronomy & astrophysics manuscript no. 4079 february 5, 2008(doi: will be inserted by hand later)extrasolar planets and brown dwarfs around a-f type stars⋆iv. a candidate brown dwarf around the a9v pulsating star hd180777.f. galland 1,2 , a.-m. lagrange 1 , s. udry 2 , j.-l. beuzit 1 , f. pepe 2 , and m. mayor 21laboratoire d’astrophysique de l’observatoire de grenoble, université joseph fourier, bp 53, 38041 grenoble, france2observatoire de genève, 51 ch. des maillettes, 1290 sauverny, switzerlandreceived august 22, 2005 / accepted february 06, 2006abstract.we present here the detection of a brown dwarf orbiting the a9v star hd180777. the radial velocity measurements, obtainedwith the elodie echelle spectrograph at the haute-provence observatory, show a main variation with a period of 28.4 days.assuming a primary mass of 1.7 m ⊙ , the best keplerian f i t to the data leads to a minimum mass of 25 m jup for the companion(the true mass could be signif i cantly higher). we also show that, after substraction of the keplerian solution from the radialvelocity measurements, the residual radial velocities are related to phenomena intrinsic to the star, namely pulsations withtypical periods of γ dor stars. these results show that in some cases, it is possible to disentangle radial velocity variations dueto a low mass companion from variations intrinsic to the observed star.key words. techniques: radial velocities - stars: early-type - stars: brown dwarfs - stars: variable - stars: individual: hd1807771. introductionradial velocity surveys have lead to the detection of morethan 160 planets during the past decade1 . we are perform-ing a radial velocity survey dedicated to the search for extraso-lar planets and brown dwarfs around a volume-limited sampleof more massive stars than currently done, namely a-f main-sequence stars (i) with the elodie f i ber-fed echelle spectro-graph (baranne et al. 1996) mounted on the 1.93-m telescopeat the observatoire de haute-provence (cnrs, france) in thenorthern hemisphere, and (ii) with the harps spectrograph(pepe et al. 2002) installed on the 3.6-m eso telescope at lasilla observatory (eso, chile) in the southern hemisphere.finding planets and brown dwarfs around massive stars is im-portant, as this will allow us to test planetary formation andevolution processes around a wider variety of objects.as a-f main-sequencestars exhibit a small numberof stel-lar lines, usually broadened and blended by stellar rotation, wedeveloped a new radial velocity method that is described ingalland et al., 2005a (paperi), together with the detection lim-its we achieved and the estimates of the minimum detectablemasses. the f i rst results of the survey are (i) discovering withsend of f print requests to: f. galland,e-mail: franck.galland@obs.ujf-grenoble.fr⋆based on observations made withtheelodiespectrograph attheobservatoire de haute-provence (cnrs, france).1a comprehensive list of known exoplanets is available athttp://www.obspm.fr/encycl/cat1.htmlelodie a planet around an f6v star (galland et al., 2005b,paperii), and (ii) f i nding the limits to the presence of an in-ner giant planet around β pictoris, with harps and coralie(galland et al., 2006a, paperiii); in this last case, the observedradial velocity variations are attributed to δ scuti type pulsa-tions.we present here the detection of a brown dwarf around oneof the objects surveyed with elodie , hd180777. section 2provides the stellar properties of this star. section 3 explainsthe measurement of the radial velocities, and the keplerian so-lution associated to the main radial velocity variations is de-rived in sect. 4. in sect. 5, we rule out other possible origins ofthese main radial velocity variations. the large radial velocityresiduals around the orbital solution are interpreted in terms ofpulsations in sect. 6.2. stellar propertieshd180777 (hip94083, hr7312) is located at 27.3 pc fromthe sun (esa 1997). its projected rotational velocity, calcu-lated using auto-correlation, is vsini=50kms −1 ; if the truerotational velocity of this star meets the mean rotational ve-locity of a9v type stars, namely 125kms −1 (gray 2005),the value of sini would be 0.4. the ef f ective tempera-ture t ef f =7250k and the surface gravity logg=4.34 aretaken from king et al. (2003). the stellar properties are sum-marized in table1. note that the mk spectral type ofhd180777 varies from a9v to f2v depending on the au-