Long-term EXOTIME photometry and follow-up spectroscopy of the sdB pulsator HS 0702+6043

0.04 MB·English

by  R. Lutz

o
Comm.in Asteroseismology,N 159, 2009
ProceedingsoftheJENAM2008SymposiumNo 4: AsteroseismologyandStellarEvolution
Long-term EXOTIME photometry and follow-up spectroscopy of the
sdB pulsator HS0702+6043
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0 R.Lutz1,2,S.Schuh1,R.Silvotti3,R.Kruspe1,andS.Dreizler1
2
1Institutfu¨rAstrophysik,Friedrich-Hund-Platz1,37077Go¨ttingen,Germany
n 2Max-Planck-Institutfu¨rSonnensystemforschung,Max-Planck-Straße2,
a 37191Katlenburg-Lindau,Germany
J 3INAF-OsservatorioAstronomicodiCapodimonte,viaMoiariello16,
80131Napoli,Italy
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2

]
R Abstract
S
Pulsating subdwarf B(sdB) stars oscillate inshort-period p-modes orlong-period g-modes.
.
h HS0702+6043 (DW Lyn) isone of a few objects to show characteristics of both types and
p is hence classified as hybrid pulsator. It is one of our targets in the EXOTIME program to
- search for planetary companions around extreme horizontal branch objects. In addition to
o the standard exercise in asteroseismology to probe the instantaneous inner structure of a
r star,measuredchangesinthepulsationfrequencies asderivedfromanO–Cdiagramcanbe
t
s comparedtotheoretical evolutionarytimescales. Basedonthephotometric dataavailableso
a far, we are able to derive a high-resolution frequency spectrum and to report on our efforts
[ to construct a multi-season O–C diagram. Additionally, we have gathered time-resolved

spectroscopic datainordertoconstrainstellarparametersandtoderivemodeparametersas
1
wellasradialandrotational velocities.
v
4 IndividualObjects: HS0702+6043,HS2201+2610,HWVir
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5
Timing Method and the EXOTIME program
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.
1 The O–Canalysis(Observed minus Calculated) is a tool to measure the phasevariations of a periodic
0 function. Theobservedtimesofthepulsationmaximaofsinglerunsarecomparedtothecalculatedmean
ephemeris ofthewholedataset. Sincealow-masscompanion,duetoitsgravitationalinfluence,would
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cause cyclically advanced and delayed timingsof an oscillatingsdB’s pulsationmaxima (due to motion
0 aroundthecommonbarycenter),thismethodcanbeusedtosearchforexoplanets. Asinusoidalcomponent
: inanO–Cdiagramisthereforeasignatureforacompanion. Inaddition,thismethodcanbeusedtoderive
v evolutionarytimescalesbymeasuringlinearchangesinthepulsationperiods. Thesignaturewouldinthis
i casebeaparabolicshapeintheO–Cdiagram. Usingthistimingmethod,Silvottietal.(2007)detected
X agiantplanetcompaniontothepulsatingsubdwarfBstarHS2201+2610(V391Peg)andrecentlyLee
etal.(2008)reportedtwoplanetsaroundtheeclipsingsdB+MbinarysystemHWVir,alsorevealedbyan
r
a O–Cdiagramanalysisbymeasuringthetimingsoftheeclipseminima.
TheEXOplanetsearchwiththeTImingMEthod(EXOTIME)programisaninternationallycoordinated
efforttoexaminepulsatingsdBstarsintermsofplanetarycompanionsandevolutionaryaspects. Closely
relatedtothepuzzlingevolutionofsdBstarsisthelate-stageorpost-RGevolutionofplanetarysystems
and the question if planets could beresponsiblefor the extreme masslossof the sdBprogenitors (e.g.
Soker1998). EXOTIMEperformsground-basedtime-seriesphotometryfromvarioussiteswithtelescopes
inthe0.5mto3.6mrange.
2 Long-termEXOTIMEphotometryandfollow-upspectroscopyofthesdBpulsatorHS0702+6043
Table1: OurcurrentphotometricdataarchiveforHS0702+6043. Sites: CalarAlto2.2m/1.2m(CA2/1),
NOT2.56m(N),Go¨ttingen 0.5m(G), Tu¨bingen0.8m(T),Steward Bok2.2m(SB), Loiano1.5m(L),
Mt.Bigelow1.55m(MB),Konkoly1m(K).
Date Site Length Date Site Length
[h] [h]
December1999 CA1 8.4 Nov07-Mar08 MB 424.0
October2000 N 0.7 March2008 G 0.6
February 2004 T 7.3 March2008 L 8.0
February 2004 SB 12.0 March2008 K 11.5
January2005 CA2 56.0 May2008 G 4.1
December2007 T 31.8 September 2008 G 3.3
December2007 G 12.0 October 2008 K 2.6
February 2008 T 20.1 October 2008 CA2 4.2
February 2008 G 32.2 November2008 CA2 8.7
Long-term Photometry
HS0702+6043 was first identified as a variable by Dreizler et al. (2002). It is placed at the common
boundaryofthe p-and g-modeinstabilityregions ina logg-Teff diagram. The two strongestp-mode
pulsationsat363.11sand383.73s(amplitudesof30and6mmag,respectively)willbeusedtoconstruct
multi-seasonalO–Cdiagrams,forwhichatimebaseofseveralyearsisneeded. ForderivingasingleO–C
point,atleastthreetofourconsecutivenightsofobservationsareneededtoprovideasufficientfrequency
resolution. WeaimforaminimumofsixO–Cpointsperyear. OurdataarchiveforHS0702+6043dates
backto1999,unfortunatelywithlargegapsinbetween. Table1listsourcurrentphotometricdataarchive,
notyetsufficienttopresentameaningfulO–Cdiagramduetothelargegapbetweentheobservationsin
1999and2004.
Follow-up Spectroscopy
The772timeresolvedhigh-resolutionEchellespectra(20seach)ofHS0702+6043takenattheHobby
Eberly Telescope will provide rotational and in particular pulsational radial velocities. The pulsational
amplitudes are expected to be larger for HS0702+6043 than for HS2201+2610 since the photometric
amplitudesarelarger. An analysisof thetime-resolved spectroscopy ofHS2201+2610can befoundin
Schuhetal.(2008).
Acknowledgments. TheauthorsthankallobserverswhocontributedobservationstotheHS0702+6043
data archive: B.Beeck, Z.Bognar, E.M.Green and collaborators, M.Hundertmark, T.Nagel, R.Østensen,
M.Paparo, P.Papics, T.Stahn. Partly based on observations collected in service mode by L.Montoya,
M.AlisesandU.ThieleforourprogramH08-2.2-009attheCentroAstrono´micoHispanoAlem´an(CAHA)
atCalarAlto,operatedjointlybytheMax-PlanckInstitutfu¨rAstronomieandtheInstitutodeAstrof´ısicade
Andaluc´ıa(CSIC).TheauthorsalsothanktheAstronomischeGesellschaftaswellastheconferencesponsors
andinparticularHELAS(EuropeanHelio-andAsteroseismologyNetwork,anEuropeaninitiativefunded
bytheEuropeanCommissionsinceApril1st,2006,asa”Co-ordinationAction”underitsSixthFramework
ProgrammeFP6)forfinanciallysupportingtheposterpresentationatJENAM2008MinisymposiumN◦4
throughtravelgrantstoR.L.andS.S.
References
Dreizler,S.,Schuh,S.,Deetjen,J.L.,etal.2002,A&A,386,249
Lee,J.W.,Kim,S.-L.,Kim,C.-H.,etal.2008,arXiv,0811.3807
Schuh,S.,Kruspe,R.,Lutz,R.,&Silvotti,R.2008,theseproceedings
Silvotti,R.,Schuh,S.,Janulis,R.,etal.2007,Nature,449,189
Soker,N.1998,AJ,116,1308