arXiv:0812.0599v1 [astro-ph] 3 Dec 2008 t;eg iri ta.20) liaeyamda nigEa finding at aimed ultimately planets. 2008), size p super-Earth al. (4 or et space Aigrain from e.g. transits planet ets; 2008). targeting al. f is et survey Search CoRoT Anderson Area addition, XO Wide e.g. the planets; the Network and 15 2008), 2007), (SuperWASP; Telescope al. Planets al. et Automated Burke et e.g. Trans- Shporer Hungarian planets; (5 e.g. the the Mandushev planets; e.g. 2008), ), 9 (HATNet; planets; 2007 al. 4 al. et (TrES; et Udalski Survey e.g. Exoplanet th Atlantic planets; as Experi such Lens 7 Gravitational successful, (OGLE-III; Optical very the are of campaigns surveys transit these of Several way. exoplanet transiting makes value. This scientific 2008). great al. et Tinett Snellen 2002; 2007; al. tra et atmospheric Charbonneau and 20 (e.g. 2007), spectroscopy al. al. mission et Knutson et 2005; al. Charbonneau et (e.g. Deming thro observations probed be eclipse can me secondary and atmospheres radius, their mass, Furthermore, planet density. as such o parameters, measurements fundamental direct allow planets extrasolar Transiting Introduction 1. edo Send oebr5 2018 5, November srnm Astrophysics & Astronomy nle I.A.G. Snellen aypooercmntrn uvy r urnl under- currently are surveys monitoring photometric Many GE-RLb neolnttastn atrttn 3s F3 fast-rotating a transiting exoplanet An OGLE2-TR-L9b: 6 5 4 3 2 1 u ob neclettastn lntcandidate. planet transiting excellent an be to out h i odtrietetastprmtr thg precisio high at parameters transit the determine to aim the Results. Methods. Aims. Context. rmispeitdtm.Tepiayojc safs rotatin fast a is object primary The time. predicted its from n [Fe and public made been recently have among campaign objects this of curves light eetr one nteMPI the on mounted detector, e words. agreem Key excellent the 2) and spectrosc photometry, the the between from consistency determined the scenar 1) re blend of stellar The combination A date. the data. uncer to photometric discovered the multi-color , planets the rotating other of fast most a for than to larger found planet first the tr n odtrietems ftetastn betthro object transiting the of mass the determine to and star, banduigtefie-e FLAMES fiber-fed the using obtained ff rn eussto requests print nvreCutr ehiceUniversit¨at M¨unchen, Technische Bolt Cluster, Universe ot fia srnmclOsraoy ..Bx9 Observ 9, Box P.O. Observatory, Astronomical African South ntttfu srpyi,Georg-August-Universit¨at G¨ f¨ur Astrophysik, Institut a-lnkIsiu ¨retaersrsh hsk Gie Physik, f¨ur extraterrestrische Max-Planck-Institut Germany Universit¨ats-Sternwarte M¨unchen, Munich, ednOsraoy ednUiest,Psbs91,2300 9513, Postbus University, Leiden Observatory, Leiden nti ae erpr norivsiaino h renatur true the of investigation our on report we paper this In / H] h htmti rni,nwmr hn7yasatrtelast the after 7 than more now transit, photometric The htmti bevtosfrteOL-Imcoesmonito microlens OGLE-II the for observations Photometric ihpeiinpooercosrain aebe obtaine been have observations photometric precision High = tr:paeaysses-tcnqe:pooerc-techn - photometric techniques: - systems planetary : 1 − opnofrJ. Koppenhoefer , ∼ 0.05 50 tr ntreCrn ed oad h aatcdisk. galactic the towards fields three in stars 15700 [email protected] : ± .0 h rniigojc sa xrslrpae ihM with planet extrasolar an is object transiting The 0.20. aucitn.aa˙uvesplan no. manuscript / S .mtlsoea aSla ih pcso high-dispers of epochs Eight Silla. La at telescope 2.2m ESO 2 , / 3 VSEhlesetorp,mutdo S’ eyLreTele Large Very ESO’s on mounted spectrograph, Echelle UVES a e ugR.F.J. Burg der van , Kr¨uhler T. 3 tign rerc-udPaz1 77 G¨ottingen, Germ 37077 1, Friedrich-Hund-Platz ottingen, , snahtas,D878Grhn,Germany Garching, D-85748 ssenbachstrasse, 6 alaR.P. Saglia , oo neryFsa ihafitelpigbnr ytmi ex is system binary eclipsing faint a with star F early an of io their f tal. et i 3sa,with star, F3 g mnsrß ,D878 acig Germany Garching, D-85748, 2, zmannstraße ,adb pcrsoi bevtos oetmt h prope the estimate to observations, spectroscopic by and n, anisi h ailvlct esrmnsadi h plan the in and measurements velocity radial the in tainties g ailvlct measurements. velocity radial ugh ment pcprmtr ftesa n h endniyo h transi the of density mean the and star the of parameters opic ABSTRACT lan- of s ugh eto fpsil ln cnro a ae naquantitat a on based was scenarios blend possible of jection n ewe h rni inla bevda ordi four at observed as signal transit the between ent 05; ns- rth an In or A edn h Netherlands The Leiden, RA, u nlsso hs aahsrvae 3lwapiuetr low-amplitude 13 revealed has data these of analysis Our . e tr 95 ot Africa South 7935, atory 1 rilrS. Dreizler , fOL2T-9 yr-bevn h htmti rni w transit photometric the re-observing by OGLE2-TR-L9, of e GE-RL .Tesse a nIbn antd of magnitude I-band an has system I The b. OGLE2-TR-L9 il.Tepriua ol fteeosrain r h re the are o observations and parameters these transit improved of transit, the goals of discovery particular The Silla. iswr icvrdaogtelgtcre of curves light the tran amplitude among low discovered The were 1997). al. sits mi- et of finding Udalski phase (OGLE-I at 2005; 2000 Szymanski second aimed and 1997 primarily the between conducted campaign of events, Th crolensing a database S07). project, online (2007; OGLE the al. the of from et sample drawn Snellen a by were from candidate presented planetary objects prime thirteen The the date. was wh to detected system around been sit star has planet sequence) extrasolar (main orbiting an hottest and rotating fastest aec hnuulfrtastsres ih1 di with a have surveys, data transit curve for light usual the than that cadence Note plane. galactic ih13.0 with onstknprngt oaln 500 totalling night, per taken points ntuetmutdo h MPI the GROND on the with mounted taken instrument OGLE2-TR-L9, of photometry transit low to pl sensitive extrasolar indeed transiting is yield set can data and a transits, amplitude such that shows work This in d = qe:rda velocity radial iques: 39,ada ria eidof period orbital an and 13.97, igcmag aebe ae ntepro 1997 period the in taken been have campaign ring nti ae epeetanwtastn xrslrplanet, extrasolar transiting new a present we paper this In nscin2o hspprw rsn h nlsso new of analysis the present we paper this of 2 section In 3 GEI bevtos a edsoee only re-discovered was observations, OGLE-II g v ujj F.N. Vuijsje , ′ sin n fteeojcs GE-RL (P OGLE2-TR-L9 objects, these of One , r ′ i , = < i p 39.33 ′ 4 = and , I rie J. Greiner , < 4.5 60 oae ntreCrn ed oad the towards fields Carina three in located 16.0, ± ± z . M 1.5 .8km 0.38 ′ adsmlaeul,uigtenwGROND new the using simultaneously, band 1 Jup 3 / o pcrsoi bevtoswere observations spectroscopic ion ,T s, n R and eHo M.D.J. Hoon de , = 6933 p = cp tParanal. at scope 1.61 ∼ ± / . as h otsa sthe is star host The days. 2.5 S .mtlsoea La at telescope 2.2m ESO 8K o g log K, 58 − ± 0.04R 0 pcsoe years. 4 over epochs 600 ff any rn wavelengths. erent ∼ . as,turned days), 2.5 Jup te ftehost the of rties 1 tr asare mass etary usrT.O. Husser , ldd u to due cluded, ic hsis this Since . = e betas object ted v analysis ive ∼ − − 4.25 minutes 8 photometric 2 00 All 2000.

∼ c ansiting 50 stars, 15700 tar ± S 2018 ESO 0.01, anets. ith ⋆ ff rbital erent tran- 5 ich , ey I; - - - 2 Snellen et al.: An extrasolar planet transiting a fast-rotating F3 star

OGLE2−TR−L9 in Munich1. After the initial bias and flatfield corrections, cos-

1.005 1.005 mic rays and bad pixels were masked and the images resampled oo o o o to a common grid. The frames did not suffer from detectable o o o o oo o o o o ooooo o oo o o o o o ooo o ooo o o o o oo o ooo oo fringing, even in z-band. Aperture photometry was performed 1.000 oo ooo o o o o o 1.000 ooo o o o oooooo o ooo oo oo o o o o o o o o oo o o o o oo on OGLE2-TR-L9 and eight to ten interactively selected refer- o o oo o o o o o o o o ooo o 0.995 ooo 0.995 ence stars, after which light curves were created for each of the Fg o o ooo Fr o o o o oo o 4 bands. The aperture radius was chosen to be 12 pixels, corre- oo o o oooo o o o o o oo oo o o o o o 0.990 o o oo ooo o o 0.990 o o o o oo o o o sponding to 1.9 arcseconds, with a seeing of typically 1.1 arc- ooo oo o o ooo o o o o o o o oo o ooo ooo o o o o o ooo o o o o o o o seconds during the observations. The sky was determined in an 0.985 o 0.985 annulus between 20 and 30 pixels from the object positions. The 1.005 o 1.005 o o o o o o o rms in the individual light curves of the reference stars was in all o o o o o oo o o o o o o o oo o ooooo o o oo o cases better than 0.3%. This resulted in typical precisions of the o o oo o o o 1.000 o o o o o oo oo o 1.000 o o o ooo ooo oo o o o oo o o o o o o o o o oo o o o o relative fluxes better than 0.2%. oo o o o o o o o oo o o o o o o o o o oo oo 0.995 o o o 0.995 o o Fi o oo Fz o o o o o o o o o o ooo o 2.2. Fitting the transit light curves o o oo o o o o oo o o o o 0.990 o o o o o o o o o o 0.990 o o o oo oo ooo o oo o o o o o o o o o oo o o o o oo o o ooo ′ ′ ′ ′ o o o o o oo o oo The lightcurves in g ,r , i ,andz , were fitted with analytic mod- o o o o o 0.985 o o o o 0.985 els as given by Mandel & Agol (2002). We use quadratic limb- 2.75 2.80 2.85 2.75 2.80 2.85 darkening coefficients taken from Claret (2004), for a star with [Fe/H]=0.0, log g=4.5, and effective HJD − 2454490d temperature Teff=7000K (very close to the spectroscopic param- eters of the star as determined below). The values of the limb- Fig. 1. Transit lightcurves of OGLE-TR-L9 in g′, r′, i′ and z′ darkening coefficients are given in Table 1. Using a simultaneous observed simultaneously with the GROND instrument, mounted fit to all 4 lightcurves we derived the mean stellar density, M on the MPI/ESO 2.2m telescope. The line shows the best model star / R3 in solar units, the radius ratio R / R , the impact fit for the combined light curves, as discussed in the text. star planet star parameter βimpact in units of Rstar, and the timing of the central transit. Together with a scaling factor for each band, there were Table 1. Limb-darkening coefficients used for the transit fit- eight free parameters to fit. ting, taken from Claret (2004) for a star with metallicity The light curves and the model fits are shown in Fig. 1., and [Fe/H]=0.0, surface gravity log g=4.5, and effective tempera- the resulting parameters are listed in Table 2. All lightcurves ture Te f f =7000K. fit well to the model except for the g-band lightcurve, which is attributed to the significantly more noisy light curve, and the filter γ γ 1 2 poorly determined baseline, particularly before ingress. g′ 0.3395 0.3772 r′ 0.2071 0.3956 i′ 0.1421 0.3792 z′ 0.0934 0.3682 3. Spectroscopic Observations with UVES/FLAMES We observed OGLE2-TR-L9 with the UV-Visual Echelle ephemeris. In section 3 the spectroscopic observations with the Spectrograph (UVES; Dekker et al. 2000), mounted at the FLAMES/UVES multi-fiber spectrograph on ESO’s Very Large Nasmyth B focus of UT2 of ESO’s Very Large Telescope (VLT) Telescope are described, including a description of the analysis at Paranal, Chile. The aims of these observations were to esti- of the variations, of the bisector span, and the mate the spectroscopic parameters of the host star, and to deter- spectroscopic parameters of the host star. In section 4 and 5 the mine the radial velocity variations. The observations were per- stellar and planetary parameters with their uncertainties are de- formed in fiber mode, with UVES connected to the FLAMES termined, and arguments against a stellar blend scenario laid out. fiber facility (Pasquini et al. 2002),with 7 science fibers and with The results are discussed in section 6. simultaneous thorium-argon wavelength calibration (UVES7 mode). Apart from our main target, fibers were allocated to two other OGLE-II transit candidates from S07 (OGLE2-TR- 2. Transit photometry with GROND L7 and OGLE2-TR-L12), and three random stars within the 25′ FLAMES field. In addition, one fiber was positioned on empty 2.1. Data acquisition and analysis sky. A setup with a central wavelength of 580 nm was used, We observed one full transit of OGLE-TR-L9 with GROND resulting in a wavelength coverage of 4785−6817Å over two (Greiner et al. 2008), which is a gamma ray burst follow-up CCDs, at a resolving power of R=47000. Since the upper CCD instrument mounted on the MPI/ESO 2.2m telescope at the La turned out to cover only a small number of strong stellar ab- Silla observatory. GROND is a 7-channel imager that allows to sorption lines, in addition to suffering from significant telluric take 4 optical (g′r′i′z′) and 3 near infrared (JHK) exposures si- contamination, only the lower CCD (4785−5729Å)was used for multaneously.On January 27, 2008,a total of 104 imagesin each further analysis. optical band and 1248 images in each near infrared band were Eight observations were taken in Director’s Discretionary taken. The JHK-images turned out to have insufficient signal to Time, in service mode in the course of December 2007 and noise to detect the transit, and will not be considered further. January 2008,spread in such a way that the data would be evenly Using exposure times of 66 seconds and a cycle rate of 2.5 min- distributed in orbital phase of our main target (see table 3). utes, we covered a period of about 4 hours centered on the pre- The data were analysed using the midas-based UVES/FLAMES dicted transit time. All optical images have been reduced with the mupipe software developed at the University Observatory 1 http://www.usm.lmu.de/∼arri/mupipe/ Snellen et al.: An extrasolar planet transiting a fast-rotating F3 star 3

Table 3. Spectroscopic observations of OGLE2-TR-L9 taken with UVES/FLAMES. The first three columns give the Heliocentric Julian Date, the planet’s orbital phase at the time of observation, and the signal-to-noise ratio of the spectra per res- olution element in the center of the middle order. Column 4 and 5 give the radial velocity and the bisector span measurements.

HJD Orbital SNR RV BiS -2450000 Phase km s−1 km s−1 4465.8421 0.157 19.0 1.090±0.224 -0.076±0.482 4466.8583 0.566 16.6 1.204±0.276 0.173±0.380 4468.7219 0.316 11.2 0.842±0.212 -0.233±0.683 4472.7447 0.934 14.7 1.105±0.231 -0.492±0.460 4489.6749 0.746 9.0 2.345±0.376 0.123±1.101 4490.8382 0.214 15.3 0.472±0.318 0.235±0.339 4493.7697 0.393 19.9 1.187±0.187 -0.150±0.432 4496.7703 0.601 19.0 1.190±0.272 0.418±0.545 Fig. 2. The central part of one order of the combined UVES spectrum of OGLE2-TR-L9, with overplotted a synthetic spec- trum with T=6900 K, g=4.5, [Fe/H]=0, and vsini = 39.33 3.1. Determination of stellar spectroscopic parameters km/sec. The spectroscopic parameters of the star, vsini, surface temper- ature, surface gravity, and metallicity, were determined from the Table 2. The transit, host star, and planetary companion param- SNR-weighted, radial velocity shifted combination of the eight eters as determined from our photometric and spectroscopic ob- epochs taken with UVES. This combined spectrum has a signal- servations. to-noise ratio of ∼42 in the central areas of the orders. Detailed synthetic spectra were computed using the interactive data lan- Transit: guage (IDL) interface SYNPLOT (I. Hubeny, private communi- ρs = 0.4260±0.0091 ρsun cation) to the spectrum synthesis program SYNSPEC (Hubeny Rp/Rs = 0.10847±0.00098 et al. 1995), utilising Kurucz model atmospheres2. These were βimpact = 0.7699±0.0085 least-squares fitted to each individual order of the combined t = 2 454 492.79765±0.00039 HJD 0 UVES spectrum. The final atmospheric parameters were taken P = 2.4855335±7×10−7 d Host star: as the average values across the available orders. The uncertain- Coord. (J2000) = 11h 07m 55.29s −61◦ 08′ 46.3′′ ties in the fitted parameters estimated using a χ-square analysis I mag = 13.974 and from the scatter between the orders, give similar results, of I−J mag = 0.466±0.032 which the latter are adopted. J−K mag = 0.391±0.049 The best fitting parameters and their uncertainties are given T = 6933±58 K in table 2. One order of the combined UVES spectrum is shown log g = 4.47±0.13∗ in figure 2, showing the Mg 5170Å complex, with the syn- ∗∗ b log g = 4.25±0.01 thetic spectrum with T=6900 K, log g=4.5, [Fe/H]=0, and vsini [Fe/H] = −0.05±0.20 = 39.33 km/sec, overplotted. vsini = 39.33±0.38 km/s Rs = 1.53±0.04 Rsun Ms = 1.52±0.08 Msun 3.2. Radial velocity measurements Age < 0.66 Gyr Planetary Companion: The orders of the eight spectra were first cosine-tapered to re- K = 510±170 m/s duce edge effects. Cross-correlations were performed using the i = 79.8±0.3◦ best-fitted velocity-broadenedsynthetic spectrum, as determined a = 0.0308±0.0005 AU above, as a reference. The spectrum of the sky-fiber indicated Rp = 1.61±0.04 Rjup that the sky contribution was typically of the order of ∼0.5%. = ± Mp 4.5 1.5 Mjup However, for the observation at 0.74 orbital phase ( 5), ∗Determined from the spectroscopic analysis ∗∗Determined from mean stellar density combined with the the relative sky levels were an order of magnitude larger, due to evolutionary tracks a combination of bad seeing and full moon. We therefore sub- tracted the sky spectrum from all target spectra before cross- correlation. The resulting radial velocity data are listed in table 3, cor- rected to heliocentric values. The uncertainties are estimated from the variation of the radial velocity fits between the different pipeline as provided by ESO, which results in fully reduced, orders. The final radial velocity data as function of orbital phase wavelength calibrated spectra. Since we were concerned about (the latter determined from the transit photometry), are shown in the wavelength calibration of the fifth epoch (see below), we also figure 3. The data were fitted with a sine functionwith the ampli- analysed the data using purpose-build IDL routines. No signif- tude of the radial velocity variations, K, and a zero-point, V0, as icant differences in the wavelength solutions were found. The free parameters. The radial velocity amplitude was determined resulting signal-to-noise per resolution element, in the central at K= 510 ± 170 m/s, with V0=+0.2 km/s. part of the orders, varies between ∼10 and 20 over the different epochs (see table 3). 2 http://kurucz.harvard.edu/grids.html 4 Snellen et al.: An extrasolar planet transiting a fast-rotating F3 star

Fig. 3. The radial velocity measurements of OGLE2-TR-L9 as function of orbital phase from the ephemeris of the transit pho- tometry.

We also determined the variations of the bisector span (fol- lowing Queloz et al. 2001) as function of radial velocity and or- bital phase. These are shown in figure 4. We least-squares fitted Fig. 4. Bisector variations as function of orbital phase (top the bisector span measurements as function of orbital phase with panel) and radial velocity value (bottom panel). The solid line a sinusoid, but no significant variations at a level of −0.01±0.140 and dashed lines in the top panel indicate the least-squares fit- km s−1 are found. Although this means that there is no indica- ted sinusoidal variation in the bisector span and its uncertainty − ± −1 tion that the measured radial velocity variations are due to line at 0.01 0.140 km s . shape variations, caused by either stellar activity or blends of more than one star, the errors are very large, making any claim marginally larger, although its mean density is similar to that of based on the bisector span rather uncertain. . Even so, OGLE2-TR-L9b is significantly larger than ex- pected for an irradiated ∼4.5 MJup planet (Fressin et al. 2007). 4. Estimation of the stellar and planetary parameters 5. Rejection of blended eclipsing binary scenarios 4.1. , radius, and age Large photometric transit surveys are prone to produce a signif- icant fraction of false interlopers among genuine transiting ex- The transit photometry provides an estimate of the mean den- trasolar planets. If the light from a short-period eclipsing stel- sity of the host star, while the spectroscopic observations yield lar binary is blended with that from a third, brighter star, the its surface temperature, surface gravity, and metallicity. The stel- combined photometric signal can mimic a transiting exoplanet. lar evolutionary tracks of Siess et al. (2000) were subsequently Although the radial velocity variations induced by an eclipsing used to estimate the star’s mass, radius, and age, resulting in binary should be orders of magnitude larger than those caused Ms=1.52±0.08 Msun, Rs=1.53±0.04 Rsun, and an age of <0.66 by a planet, the blending of the spectral lines with those from Gyr. These parameters correspond to a surface gravity of log g the brighter, third star could produce variations in the overal = 4.25±0.01, which is in reasonable agreement, but about 1.7σ cross-correlation profile that have significantly smaller ampli- lower than the spectroscopic value. It should be realised that it tudes, possibly as small as expected for giant planets. Since this is notoriously difficult to obtain reliable log g values from rela- would be accompanied with significant line-shape variations, bi- tively low signal to noise spectra. sector span analyses are often used to reject a blended eclipsing binary scenario. 4.2. Planetary Mass and Radius Although no significant variations in the bisector span are observed in OGLE2-TR-L9, it could be argued that this is due Using the values obtained from the transit fit to the GROND to the lack of signal-to-noise. We show however that a blended light curves, the radial velocity fit, and the stellar parameters as eclipsing binary scenario can be rejected anyway, because of the derived above, we obtain a planetary mass of Mp = 4.5±1.5Mjup following observations: and a planetary radius of Rp = 1.61±0.04 Rjup. The semi-major axis of the orbit is at a=0.0308±0.0005 AU. The mean density 1 Transit light curves from g′ to z′ band: As can be seen in of the planet is 1.44±0.49 g cm−3. Fig. 1, there is an excellent agreement between the light This means that OGLE2-TR-L9b is one of the largest curves from g to z band. This means that if the transit was known transiting hot , only TrES-4b and WASP-12b are actually caused by a background eclipsing binary blended Snellen et al.: An extrasolar planet transiting a fast-rotating F3 star 5

sistent with an early F star. Using the argument above, this means that if this is a blend, then both the foreground star and the eclipsed binary star should be early F stars.

However, if we now assume that a significant fraction of the light comes from a foreground star, and we remove this contribution from the light curve, the transit can no longer be fitted by an early F star, but only by a star of significantly higher mean den- sity, implying a cooler, less massive star, which is again in con- tradiction with point 1). This means that the early F star is the transited object, and that a blended eclipsing binary scenario can be rejected. To further explore the possible role of additional light from a blended star, we performed a quantitative analysis, simulating background eclipsing binary systems with their light diluted by that from a third star. We first used the stellar evolutionary tracks of Siess et al. (2000)to determine the full range of stellar param- eters that can be present in eclipsing binaries, of which only the stellar surface temperature, Tecl, and the mean stellar density, ρecl of the eclipsed star are of interest for the simulations. Note that the evolutionary status of the third star is not important, since we do not restrict ourselves to physical triple systems, but also include chance-alignments of back- and foreground stars. As is indicated in the top panel of figure 5, where the stellar evolu- tionary tracks are shown, there is a maximum possible mean- stellar density for a given surface temperature. This was used as a boundary condition in the simulations. In our simulations we varied two parameters, 1) the differ- ence between the surface temperature of the eclipsed star and that of the third star, ∆T(−1000 K<∆T<+1000 K), and 2) the fraction of light coming from the third (possibly unrelated) star, F3rd (0

Udalski, A., et al. 2008, A&A, 482, 299