Spectral types of planetary host star candidates from OGLE III

0.42 MB·English

by  S. Dreizler

Astronomy&Astrophysicsmanuscriptno.dreizler˙4362 (cid:13)c ESO2008
February5,2008
Spectral types of planetary host star candidates from OGLE III
1 1 1
S.Dreizler ,S.Schuh ,D.Homeier
Institutfu¨rAstrophysik,Georg-August-Universita¨tGo¨ttingen,Friedrich-Hund-Platz1,D–37077Go¨ttingen,Germany
received;accepted
7 ABSTRACT
0
0 Context.The Optical Gravitational Lensing Experiment project has recently provided the OGLEIII list of low-luminosity object
2 transitsfromcampaigns#3and#4,reporting40newobjectsexhibitingthelow-amplitudephotometriceclipsesexpectedforexoplan-
ets.ComparedtopreviousOGLEtargets,theseOGLEIIIcandidateshavebeenmorerestrictivelyselectedandmaycontainlow-mass
n planets.
a Aims. Wehave secured follow-up low-resolution spectroscopy for 28 candidates out of this list (and one from the OGLE Carina
J
fields)toobtainanindependentcharacterizationoftheprimarystarsbyspectralclassificationandthusbetterconstraintheparameters

5 oftheircompanions.
2 Methods.Wefedtheconstraintsfromtheseresultsbackintoanimprovedlightcurvesolution.Togetherwiththeradiusratiosfrom
thetransitmeasurements,wederivedtheradiiofthelow-luminositycompanions.Thisallowsustoexaminethepossiblesub-stellar

1 natureoftheseobjects.
v Results.Sixteenof thecompanions can beclearly identified aslow-mass starsorbiting amain sequence primary, while10 more
8 objects are likely to have red giant primaries and therefore also host a stellar companion; 3 possibly have a sub-stellar nature
1 (R≤0.15R⊙).
7 Conclusions.Theplanetarynatureoftheseobjectsshouldthereforebeconfirmedbydynamicalmassdeterminations.
1
Keywords.binaries:eclipsing-stars:low-mass-stars:browndwarfs-stars:planetarysystems
0
7
0
/ 1. Introduction ets’ atmospheres (Charbonneauetal. 2002; Vidal-Madjaretal.
h
2004).
p
The detection of planets outside our solar system has been
-
o a longstanding goal of astronomy. After the first detections
r (Wolszczan&Frail 1992; Mayor&Queloz1995), an intensive This potentially large scientific output motivated the ini-
st search with variousmethodsbegan(see Schneider 2001for an tiation of several photometric monitoring projects to de-
a overview). Out of the more than 200 currently known planets, tect planetary transits. Currently, OGLE (Optical Gravitational
v: mosthavebeendetectedwithDoppler-velocitymeasurementsof Lensing Experiment, e.g. Udalskietal. 2002a,b,c, 2003) is
i the planets’ (late type main sequence)hoststars. With increas- the most successful one with five of the fourteen confirmed
X ing precision, the application of the Doppler-method could be transit planets out of 137 candidates. Additional 40 transit-
r extendedtoNeptune-massplanets(e.g.Santosetal.2004). ing planetary/low-luminosity companions were announced by
a Meanwhile, planet detections using alternatives to the OGLE (Udalskietal. 2004), increasing their total number of
Doppler method have also been successfully applied. The candidatesto177.Theseobjectswereextractedfromasampleof
first four microlensing planets have been detected (Bondetal. starsobservedduringtwocampaignsofseveralweeksofphoto-
2004; Udalskietal. 2005; Beaulieuetal. 2006; Gouldetal. metric monitoring between February and July 2003 (and some
2006), possible first direct images of extra-solar planets additional observations in 2004). In a sub-sample of 230000
were published (Chauvinetal. 2004, 2005a,b; Neuha¨useretal. starswithaphotometricaccuracybetterthan1.5%,these40can-
2005; Billeretal. 2006), and the number of detections due didatesexhibitshallow(≤0.05mag),flat-bottomedeclipsesin
to transit searches increased to fourteen (Satoetal. 2005; their light curves, indicating the presence of a transiting low-
Bouchyetal.2005b;McCulloughetal.2006;Bakosetal.2006; luminositycompanion.Theradiiofthevisibleprimariesandof
O’Donovanetal.2006;CollierCameron2006). the invisiblesecondarieswere derivedfromthe analysesof the
The transit method is of special interest, since it permits lightcurves.ComparedtopreviousOGLEcandidates,theseare
thederivationofadditionalplanetaryparametersliketheradius more restrictively selected. The candidate list contains several
either indirectly via the radius determination of the host star (relatively) brighttargets and several targets with very shallow
or directly via detection of the secondary eclipse as observed transits.PreliminaryanalysesofthelightcurvesbyUdalskietal.
with the Spitzer Space Telescope (Charbonneauetal. 2005; (2004)indicatepossibleplanetsdowntoNeptunesize.Thepri-
Demingetal.2005).Ifcombinedwitharadialvelocityvariation maryandcompanionradiusestimates,derivedfromtheeclipse
measurement, the mass and mean density can be determined, duration and the orbital period by adopting a main sequence
allowing us to obtain constraints for the planetary structure. mass-radius relation, are based on the assumption of a central
Furthermore,transitingsystemsallowustoinvestigatetheplan- passage.Thiscanonlybeconfirmedfromlightcurvestudiesby
detailedanalysisofthetransitshape(Seager&Malle´n-Ornelas
Send offprint requests to: Dreizler, [email protected] 2003; Tingley&Sackett 2005), which is difficultwith the cur-
goettingen.de rentlyavailablephotometricdata.
2 Dreizleretal.:SpectraltypesofOGLEIIIplanetarycandidates
Fig.1. Optical spectra of the early type target stars down to spectral type F9 together with template spectra (in grey) from
Silva&Cornell(1992)andthederivedreddening.Seetextfordetails.
Transit searchesare a very promising methodfor detecting Heinze&Hinz(2005)haveidentifiedpossiblegiantstarsamong
planets,evenfromground-basedtelescopes(Gillonetal.2005). thecandidatesOGLE-TR-134throughOGLE-TR-137.
The success of all ongoingand future transit searches depends
Up to now, no spectroscopic information of the primaries
ontherejectionoffalse positivescausedbylow-massmainse-
from the latest OGLE-list (Udalskietal. 2004) has been pub-
quencecompanions,blends,andgrazingeclipses.Thenecessity
lished.Theaimofthisprojectthereforeistoprovidethisinfor-
for such a pre-selection can be seen from the large fraction of
mation and to decide about the nature of these low-luminosity
blends in the sample of Konackietal. (2003b, 4 likely blends
companions.Thespectraltypeprovidesaconstraintforthepri-
out of 5 candidates). Based on OGLE candidate lists, several
maryradiuswhich,togetherwiththetransitlightcurve,permits
selection techniques have been used to reduce the amount of
amoreaccuratedeterminationoftheradiusoftheunseencom-
high-resolution spectroscopy for a final dynamical mass deter-
panion. Using data from the SAAO 1.9m+SpCCD, we previ-
mination.Gallardoetal.(2005)uselowresolutionspectroscopy
ouslyweededoutmanyA+M-starpairsfromthefirstOGLElist
incombinationwithIRphotometryinordertoexcludegiantpri-
withthisprocedure(Dreizleretal.2002).Theremainingobjects
marystarsandprovideaccurateeffectivetemperaturesandradii
withradiisuitableforsub-stellarobjectscanthenbeconsidered
of the OGLE-candidates. From low resolution spectroscopy,
for further follow-upto obtain a dynamicalmass measurement
fortheunseencompanionfromradialvelocityvariations.
Dreizleretal.:SpectraltypesofOGLEIIIplanetarycandidates 3
Fig.2. Optical spectra of our late type target stars together with template spectra (in grey) from Silva&Cornell (1992) and the
derivedreddening.Dependingonthebrightnessoftheobjectaswellasontheobservingconditions,spectracouldonlybeextracted
inalimitedspectrarange.Seetextfordetails.
We describe the observations,data reductionand the deter- Spectrograph equipped with a 266×1798 SITe chip. The grat-
mination of the spectral types of the primaries in Sect.2, and ing7 in combinationwith a slit width of 1.5” provideda spec-
presentimprovedlightcurvesolutions.Theresultsarediscussed tral resolution of 5A˚, and exposure times ranged from 1800s
inSect.3. to7200sdependingontheobservingconditionsandthebright-
ness of the objects. Standard data reduction of these long-slit
spectrawasperformedusingIDLandincludedbiassubtraction,
2. Observations,datareduction,andspectral flat-fieldcorrection,aswellaswavelengthcalibration.Fluxcal-
typesofthe primarystars ibrationwasdoneusingspectrafromthestandardstarsEG274
andLTT4364.Duetothevaryingweathercondition,thesignal-
2.1. Spectra to-noiseratio of the spectravariesform10 (OGLE-TR-168)to
about200(OGLE-TR-139).Mostspectrahaveasignal-to-noise
We selected 28 candidates from the OGLE III list of
ratiobetween30and50.
Udalskietal.(2004),withobjectstakenfrombothcampaign#3
(fields at RA=11h) and campaign #4 (fields at RA=13h). All The spectra were compared to the spectral library of
objectswithmI <16.35wereobserved.Starswithentriesinthe Silva&Cornell(1992) withoutinterpolationwithinthe library.
ESODataArchiveforhigh-resolutionspectraweregivenalow Both observed and template spectra were normalized prior to
priority.FollowingthesuggestionofPontetal.(2005b),wealso comparisonwithapolynomialfittothecontinuum.Thequality
addedOGLE-TR-82tothetargetlist(seeTable1). of the matchbetweenobservedandtemplate spectrumwasde-
ThespectrawereobtainedattheSAAO1.9mtelescopebe- terminedwithanχ2test(withareducedχ2rangingfrom0.99to
tween 2005/04/26 and 2005/05/02 using the spCCD Grating 1.2forthebestfits)allowingusaclassificationbetterthanhalfa
4 Dreizleretal.:SpectraltypesofOGLEIIIplanetarycandidates
Table1.Resultsforourprogramstars:Derivedspectraltypesandradiioftheprimarystar(columns2,3).Thetransitdepthfrom
theOGLElightcurveprovidesthecompanionradiusRc (columns4 to5)followedbytheellipsoidalvariationδIe.Thelefthand
valueis derivedfromthe OGLE lightcurve(“< 0.5” denotescaseswhere a formalfit resultsin amplitudesbetween0.1and 0.5
mmag),while the righthandvalueis froma Nightfallsimulationofthe correspondingsystem assuminga stellar companion
(onlyvaluesnotinaccordancewithamplitudesintheobservedlightcurvesaregiven).Nightfallfitsaregivenincolumns7to
12followedbyourfinalassessment.Seetextfordetails.
# type Rs/R⊙ Rc/Rs Rc/R⊙ δIe Rs/R⊙ Rc/R⊙ i Rc/R⊙ 3rdlight Rc/R⊙ cat.
[mmag] [deg] [%]
spectraltype OGLE Nightfallfit Nightfallfit Nightfallfit
82 F8F9 1.16−0.1 0.18 0.20−.01 0.68 5.52 0.71±.09 0.10±.03 <80 0.20±.01 70±10 0.29±.02 S
+0.9 +.16
138 G9K0 0.86−0.1 0.12 0.10−.01 0.85±.08 0.10±.05 86±1 0.10±.01 50±10 0.14±.01
+0.3 +.03
138 K5 0.72−0.1 0.12 0.09−.01 0 0.67±.04 0.09±.03 89±1 0.09±.01 25± 5 0.10±.01 SP
+0.1 +.01
139 A2 2.12−0.5 0.17 0.35−.08 <.5 1.28 1.70±.22 0.26±.10 80±1 0.41±.05 80±10 0.73±.20 S
+1.7 +.28
140 F8F9 1.16−0.1 0.20 0.23−.01 1.13 0.17 0.84±.08 0.17±.05 83±1 0.42±.02 80±10 0.85±.40 S
+1.7 +.33
141 A8 1.58−0.1 0.13 0.21−.01 <.5 1.47±.50 0.18±.05 83±4 0.44±.24 15±15 0.20±.01 S
+1.7 +.22
142 A2 2.12−0.5 0.18 0.37−.08 0 0.88 1.30±.24 0.18±.05 80±1 0.51±.06 90± 5 0.87±.13 S
+1.7 +.30
143 K4 0.75−0.1 0.07 0.06−.01 <.5 0.54±.02 0.06±.04 87±1 0.08±.01 10±10 0.07±.01 G
+0.1 +.01
145 A9F0 1.52−0.1 0.13 0.20−.01 <.5 1.79±.12 0.21±.05 89±1 0.20±.02 5± 5 0.20±.02 S
+1.7 +.22
147 A9F0 1.52−0.1 0.17 0.25−.01 0 1.57±.35 0.22±.08 82±5 0.40±.17 70±20 0.57±.23 S
+1.7 +.27
149 F8F9 1.16−0.1 0.15 0.18−.01 0.87 0 1.00±.07 0.16±.02 85±2 0.24±.06 55±35 0.40±.23 S
+0.9 +.14
150 A2 2.12−0.5 0.07 0.14−.03 <.5 1.98±.07 0.13±.10 83±2 0.13±.01 70±20 0.28±.11 S
+1.7 +.11
151 G9K0 0.86−0.1 0.14 0.12−.01 0 0.93±.05 0.11±.02 87±3 0.13±.02 45±25 0.18±.06 G
+0.3 +.04
152 F8F9 1.16−0.1 0.13 0.15−.01 0 1.52±.13 0.18±.05 86±3 0.19±.05 60±10 0.28±.08 S
+0.9 +.12
153 A8 1.58−0.1 0.17 0.26−.02 0.76 0.18 1.04±.07 0.17±.04 81±4 0.54±.27 50±45 0.51±.30 S
+1.7 +.28
154 G1G2 1.05−0.1 0.11 0.11−.01 <.5 1.23±.08 0.13±.04 84±3 0.15±.01 35±35 0.20±.08 G
+0.6 +.06
155 A6 1.66−0.1 0.09 0.14−.01 1.43±.27 0.13±.06 82±3 0.28±.10 45±45 0.36±.22
+1.7 +.15
155 A8 1.58−0.1 0.09 0.14−.01 <.5 1.53±.11 0.13±.06 84±5 0.23±.10 50±40 0.35±.22 S
+1.7 +.15
156 A9F0 1.52−0.1 0.18 0.27−.01 0 0.84±.08 0.15±.02 80±3 0.40±.05 80±10 0.60±.25 S
+1.7 +.29
158 K4 0.75−0.1 0.13 0.11−.01 0 0.39±.02 0.06±.01 87±1 0.15±.02 15± 5 0.10±.01 SP:
+0.1 +.01
160 F6F7 1.24−0.1 0.09 0.11−.01 1.39±.21 0.12±.05 84±3 0.17±.05 50±20 0.21±.08
+1.3 +.11
160 F8F9 1.16−0.1 0.09 0.10−.01 <.5 1.12±.09 0.10±.05 85±2 0.14±.03 25±20 0.15±.04 SP:
+0.9 +.08
161 G9K0 0.86−0.1 0.07 0.06−.01 1.54±.08 0.14±.04 90±0 0.10±.01 10±10 0.11±.01
+0.3 +.02
161 K5 0.72−0.1 0.07 0.05−.01 0 1.09±.14 0.10±.05 89±1 0.06±.01 10±10 0.07±.01 G
+0.1 +.01
162 A9F0 1.52−0.1 0.10 0.15−.01 0 1.12±.17 0.10±.04 81±4 0.20±.05 50±40 0.31±.17 S
+1.7 +.17
163 G7 0.89−0.1 0.18 0.16−.01 0.77±.06 0.12±.01 81±1 0.15±.01 80±10 0.34±.11
+0.4 +.06
163 G9K0 0.86−0.1 0.18 0.15−.01 0.5 2.22 0.73±.04 0.11±.01 81±1 0.15±.01 70± 5 0.24±.01 S
+0.3 +.05
166 G9K0 0.86−0.1 0.10 0.09−.01 1.09±.06 0.11±.03 90±0 0.10±.01 25±25 0.13±.02
+0.3 +.03
166 K5 0.72−0.1 0.10 0.07−.01 0 0.97±.03 0.10±.04 90±0 0.07±.01 25±25 0.09±.01 G
+.01 +.01
167 G9K0 0.86−0.1 0.14 0.12−.01 0.83 0 0.81±.04 0.11±.03 88±1 0.14±.02 40±35 0.18±.06 G
+.03 +.04
168 K4 0.75−0.1 0.11 0.08−.01 0 0.80±.03 0.10±.03 90±0 0.09±.01 40±30 0.13±.03 G
+0.1 +.04
172 G9K0 0.86−0.1 0.07 0.06−.01 0.99±.05 0.08±.04 87±2 0.09±.01 50± 5 0.12±.02
+0.3 +.02
172 K5 0.72−0.1 0.07 0.05−.01 0.57 0.3 0.90±.04 0.07±.03 89±1 0.06±.01 55±25 0.09±.03 G
+0.1 +.01
173 G7 0.89−0.1 0.13 0.12−.01 0 0.69±.07 0.09±.03 83±2 0.19±.06 35±35 0.13±.07 G
+0.4 +.05
174 G1F2 1.05−0.1 0.12 0.13−.01 <.5 0.79±.19 0.08±.05 83±2 0.19±.04 70±20 0.29±.10 G
+0.9 +.13
176 F8F9 1.16−0.1 0.14 0.16−.01 <.5 1.26±.14 0.16±.02 84±3 0.22±.06 35±35 0.28±.10 S
+0.9 +.16
spectralclass,sufficientforourfurtheranalysis.Fortargetstars discriminationbetweenlateGandmidKwasdifficultsothatwe
withmultiplespectraweobtainedspectralclassificationswithin listthesolutionsforbothpossibleclassifications.
thiserrorlimit.Duetotheabsenceofsufficientlystrongfeatures
for our spectral resolution and due to the low signal-to-noisea Inafirststep,werestrictedthetheclassificationtoluminos-
ityclassV,becauseadiscriminationbetweendifferentluminos-
ityclassesistoouncertainfromourspectra.Wealsodetermined
Dreizleretal.:SpectraltypesofOGLEIIIplanetarycandidates 5
the interstellar reddening assuming RV=3.1 with the IDL rou- step, we keptthe primaryradiusfixedat the spectroscopically-
tine ccm unred. This spectral classifications of all objects and derived values and fitted the orbital inclination, as well as the
the derived reddenings are displayed in Figs.1 and 2 with the secondaryradius(columns9,10).Results generallyagreewith
inversepolynomialfunctionthatweusedtonormalizethetem- ourspectroscopically-derivedvalues(Table1).Finally,we also
platespectrumofthecorrespondingspectraltypeappliedtothe investigated the possible presence of third light contribution
observed spectrum. The presence of the companion could not (columns11,12);however,theconstraintsfromthelightcurves
bedetectedfromourdata,neitherfromdoublelinedspectranor are not very stringent in that case. The solution for the most
fromthefluxdistribution. promisingcandidates,i.e.withradiiequalorbelow0.15R ,are
⊙
In a second step we checked our restriction to luminosity- shown together with the OGLE light curvesin Fig.3 using the
class V with a procedure adapted from Gallardoetal. (2005). valuesfromcolumns3and5inTable1.
The interstellar extinction was modeled according to a sim- We also investigated the ellipsoidal variation of the light
ple homogeneous exponential disc for distances from 0 to 1.5 curveoutoftheeclipses(Table1,column6).Weestimatedthe
kpc using k0 = 0.70 and k0 = 1.05 . While Gallardoetal. 1σ detection significance level to be about 0.3 mmag. OGLE-
(2005) used IR photometry, we took the I magnitudes from TR-140showsthelargestamplitudeof1.13mmag.Inthiscase,
Udalskietal.(2004),de-reddenedwiththemodeledextinction, the ellipsoidal variation can only be explained with a shorter
and intrinsic colors corresponding to the derived spectral type orbital period. Inspection of the original light curve indeed in-
takenfromRam´ırez(2005).Wecouldthendeterminethelimb- dicated a period of 1.69665 days rather than 3.3933 days of
darkened angular diameter of the stars using the results of Udalskietal.(2004).FromourNightfallsimulationforthe
Kervellaetal.(2004).Thestrongcorrelationofmassandlumi- OGLE-TR-140systemwitha1.69665daysorbitalperiodwede-
nosity,aswellasmassandradiusonthemainsequence,allowed rivedanellipsoidalvariationwithanamplitudeof1.16mmag,in
us to derive an effective temperature as a function of distance agreementwiththeobservation,whiletheoriginalperiodwould
(Eq.10ofGallardoetal.2005).Theeffectivetemperaturesand result in about a tenth of the observed amplitude. OGLE-TR-
thereddeningsderivedfromthespectrashouldthereforebecon- 149, OGLE-TR-153, OGLE-TR-167, and OGLE-TR-172 also
sistentwith thiscurve.Thisis notthecase forobjectswith ex- show lower amplitude in the simulations. As for OGLE-TR-
treme reddening even if we take uncertainties in the brigtness, 140, a shorter period might also be acceptable from the light
spectral class, and flux calibration with conservative error bars curve. For OGLE-TR-82, OGLE-TR-139, OGLE-TR-142, and
into account. These stars are likely to be giants, marked with OGLE-TR-163, the amplitude from the simulated light curves
G in the last column of Table1. For the further evaluation, we is clearly larger than from the observed one. For OGLE-TR-
howeverassumeamain-sequenceprimaryforallsystems. 139 and OGLE-TR-142, twice the orbital period would bring
thesimulationsinagreementwithobservations.ForOGLE-TR-
82,anatleastafactorofthreelongerperiodisrequiredinorder
2.2. Lightcurves
reduce the ellipsoidal variation to the observed amplitude.The
We then used the derived spectral classes to estimate the stel- significancefortheperiodofOGLE-TR-163isveryhighdueto
lar radii of the primary stars (Table 1, column 3) by interpo- 23 transit events. If we fix the period and adjust the secondary
lating the tabulated values from Cox (2000). The uncertainty massinordertofittheellipsoidalvariation,abrown-dwarfcom-
range,alsoindicatedinTable1,iscalculatedfromzero-ageand panionof20-40Jupitermassesfitsbest.
terminal-agemain-sequencemodelsfromSchalleretal. (1992)
and Charbonneletal. (1999) with solar metallicity. This re- 3. Discussion
flects the spread of interferometric radius determinations from
e.g. Kervellaetal. (2004) for αCenA and τ Ceti, where the Dependingonthecompanionradiiobtainedfromourinvestiga-
former is 20% larger, the latter 10% smaller compared to the tions,wedefinedthreecategories.(1)The16objects(including
interpolated radius using the values from Cox (2000) for a OGLE-TR-82)incategoryShavecompanionsofstellarsize,i.e.
G2V or G8V star, respectively.The photometricmonitoringof aradiuslargerthan0.15R⊙ foralldeterminedvalues(columns
Udalskietal. (2004) provides the brightness variation during 5,8,10,and12inTable1).(2)Regardlessoftheanalysisofthe
eclipses. Assuming a negligible radiation from the secondary, light curve, G classifies binaries that are likely to have a giant
a central passage in front of the primary, and no third light primarystarasderivedfromthespectralanalysisandtherefore
contribution,thisbrightnessvariationisdirectlyproportionalto also have a main sequence companion.(3) SP are objects with
the radius ratio squared. When multiplied by the primary ra- radii compatiblewith either small M stars or youngsub-stellar
dius it yields the radius of the secondary (Table 1, column 5). objects,i.e.aradiusbetween0.1and0.15R⊙ (3objects).Those
Not indicated in Table 1 are the masses for the primary star, with one of the values above the limit of 0.15R⊙ are marked
which we derived from the tabulated values from Cox (2000), witha“:”.Therearenoclearplanetarycandidates,i.e.withradii
Schalleretal.(1992),andCharbonneletal.(1999)correspond- belowthestellarlimit(0.1R⊙).
ingtotheradii,andforthesecondaryobject,whichwerederived Morefollow-upobservationsenablingadynamicalmassde-
from evolutionary models for low-mass stars of Baraffeetal. terminationcanfinallyconfirmthenatureoftheseobjects.While
(1998), Chabrieretal. (2002), and Baraffeetal. (2002) assum- objectsfromcategorySandGcanbeexcludedfromfutureob-
ingalow-massstarcompanion. servations aiming at planet detections, three deserve closer in-
Using the derived radii and masses as initial start parame- spection: OGLE-TR-138, OGLE-TR-158, OGLE-TR-160, and
ters,wefittedtheOGLElightcurveswiththeclosebinarypro- possibly OGLE-TR-163, which either have very small stellar
gram Nightfall1 written by Rainer Wichmann. Best values companions like OGLE-TR-122b (Pontetal. 2005a) or sub-
anduncertaintieswerederivedfromχ2-contoursbyvaryingthe stellarcompanionswithlargeradiilikeHD209458b.
parameters. First, we fixed the inclination to 90◦ and fitted the Severaloftheobjectsanalyzedherearenowsubjecttohigh-
radii of both components(Table 1, columns 7, 8). In a second resolutionstudiesaccordingtotheESODataArchive.Thenear
futurewillthereforeshedmorelightonthenatureofseveralof
1 http://www.lsw.uni-heidelberg.de/∼rwichman/Nightfall.html ourprogramstars.
6 Dreizleretal.:SpectraltypesofOGLEIIIplanetarycandidates
Fig.3.OGLElightcurvesfortheplanetarycompanioncandidatesamongourtargetstarswithournewlightcurvesolutionsassuming
aplanetwithoneJupitermassandaninclinationof90◦.Solidline:Primaryandcompanionradiifromcolumns3and5ofTable1,
dashedlines:Loweranduppervaluesfortheradiiasindicatedincolumns3and5.
Acknowledgements. This paper uses observations made at the Pont,F.,Melo,C.H.F.,Bouchy,F.,etal.2005a,A&A,433,L21
South African Astronomical Observatory (SAAO, Run No. 163), Pont,F.,Bouchy,F.,Melo,C.,etal.2005b,A&A,438,1123
kindly supported by D. Kilkenny. S.S. acknowledges a travel Ram´ırez,I.,Mele´ndez,J.,2005,ApJ,626,465
grant from the Deutsche Forschungsgemeinschaft (DR-281/21-1). Santos,N.C.,BouchyF.,MayorM.,etal.2004,A&A,426,L19
We acknowledge the use of the Nightfall program for the light Sato,B.,Fischer,D.A.,Henry,G.W.,etal.2005,ApJ,633,465
curve synthesis of eclipsing binaries written by Rainer Wichmann Schaller,G.,Schaerer,D.,Meynet,G.,&Maeder,A.1992,A&AS,96,269
(http://www.lsw.uni-heidelberg.de/∼rwichman/Nightfall.html). Schneider,J.2001,Encyclopedia ofAstron.&Astrophys.,ed.P.Murdin,IoP
Publishing,BristolandNaturePublishingGroup,London
Seager,S.&Malle´n-Ornelas,G.2003,ApJ,585,1038
Silva,D.R.,Cornell,M.E.1992,ApJS,81,865
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