Properties and nature of Be stars XXIII. Long-term variations and physical properties of kappa Dra

0.78 MB·English

by  S. M. Saad

Astronomy&Astrophysicsmanuscriptno.0241 February2,2008
(DOI:willbeinsertedbyhandlater)
⋆
Properties and nature of Be stars
XXIII. Long-term variations and physical properties of κ Dra
S.M.Saad1,2,J.Kuba´t1,P.Koubsky´1,P.Harmanec3,1,P.Sˇkoda1,D.Korcˇa´kova´1,J.Krticˇka4,1,M.Sˇlechta1,
H.Bozˇic´5,H.Ak6,P.Hadrava1,andV.Votruba4,1
4
0 1 Astronomicky´ u´stav,AkademieveˇdCˇeske´republiky,CZ-25165Ondˇrejov,CzechRepublic
0
2 NationalResearchInstituteofAstronomyandGeophysics,11421Helwan,Cairo,Egypt
2
3 Astronomicky´ u´stavUK,VHolesˇovicˇka´ch2,CZ-18000Praha8,CzechRepublic

n 4 U´stavteoreticke´fyzikyaastrofyzikyPˇrFMU,Kotla´ˇrska´2,CZ-61137Brno,CzechRepublic
a 5 OpservatorijHvar,Geodetskifakultet,SveucˇilisˇteZagreb,10000Zagreb,Croatia
J
6 AnkaraUniversity,ScienceFaculty,AstronomyandSpaceScienceDept.,Tandog˘an,Ankara,06100Turkey
3
2
Received1September2003/Accepted7January2004

1
v Abstract. Wepresent ananalysis of new spectroscopic observations of thebright Bestar κDraobtained atthe Ondˇrejov
1 observatoryduring1992–2003andUBV photometricobservationssecuredatseveralobservatories.Generalcharacteristics
9 andalineidentificationofthespectrumofκDraareobtainedintheregions3730–5650A˚ and5850–7800A˚ byacomparison
4 withthetheoreticalspectrum.ThefundamentalstellarparametershavebeenobtainedfromacomparisonwithagridofNLTE
1 model atmospheres. The best fit was found for Teff = 14000K, logg = 3.5, and vsini = 170km s−1. These values
0 togetherwithaHipparcosparallaxleadtoastellarmassM =4.8±0.8M⊙andradiusR=6.4±0.5R⊙.Itisencouraging
4
toseethatthesevaluesagreewellwiththeexpectedevolutionary massandradiusfortheeffectivetemperaturewederived.
0
Long-termvariationsofκDrawereanalysedusingmeasurementsofequivalentwidths,centralintensities,peakintensitiesof
/
h emissionlinesandemissionpeakvelocitydifferencesforHα,Hβ,Hγ,Hδ,andsomehelium,silicon,andironlines.Itturned
p outthatthepreviouslyreportedperiodof23yearsinthevariationoftheemissionstrengthisprobablyacyclic,notastrictly
- periodicphenomenon. Anattempt tofindout aperiodfromallavailablerecordsof theHβ emissionstrengthledtoavalue
o
r of(8044±167) days(22.0years)butthephaseplotsshow thateachcyclehasadifferentshapeandlength.Themaximum
t strengthoftheemissionlagsbehindthebrightnessmaximum.Thisisabehaviourusuallyobservedforlong-termchangesofBe
s
a starswithapositivecorrelationbetweenthebrightnessandemissionstrength.Sincethereareobviouslynopublishedspeckle
: observations of thestar,wesuggest theseshould be carriedout. Theycould helptodeny or confirmthepossibility thatthe
v
emissionepisodes aretriggered byaperiastronpassage of aputativebinary companion moving inaneccentricorbit witha
i
X 8044-dperiod,asitseemstobethecaseforsomeBebinaries.Forthemoment,thenatureandoriginofthediskaroundκDra
r stillremainsunknown.Fromthecomparisonoftheelectronicspectraobtainedatdifferentphasesofthelong-termcycleand
a syntheticspectraitappearsthattherearenodetectablechangesinthephotosphericpartoftheBalmerlinesrelatedtovariations
intheBalmeremissionstrengthwhichcouldbeattributedtoanextendedphotospherecorrespondingtoinnerpartsofthedisk,
opticallythickincontinuum.
Keywords.Stars:emission-line,Be–stars:individual:κDra–line:profiles
1. Introduction manycontroversialreportsonthetimescalesandcharacterof
its variability in various observables. This made it one of the
κDra(5Dra,HD109387,HR4787,BD+70◦703,MWC222,
mostchallengingobjectsforfurtherstudies.Adetailedhistory
HIP61281) is one of the brightest variable (V = 3m. 75 –
ofitsinvestigationissummarizedinpapersbyJuzaetal.(1991,
3m. 95) Northern Hemisphere Be stars, for which the bright
1994)andHirata(1995)andneednotberepeatedhere.
HαlinehadalreadybeenreportedbyCampbell(1895).Since
that,κDrahasbeenasubjectofnumerousinvestigations,with The most importantresults of several more recent studies
canbesummarizedasfollows:
Sendoffprintrequeststo:J.Kuba´t,
e-mail:[email protected]
⋆ Tables 2 to 4 are only available in electronic form at CDS 1. PeriodicvariationsoftheHβ emissionstrengthwithape-
(http://cdsweb.u-strasbg.fr/cats/J.A+A.htx)andat riod of 23 years, discovered by Jessup (1932), have been
http://www.edpsciences.org. confirmed and detected also in photometry and contin-
2 S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra
uumpolarimetry.Theirperiodwasimprovedto8406days spectrographHEROS(HeidelbergExtendedRangeOptical
(23.01years;Juzaetal.1994). Spectrograph)attached to the Cassegrain focus. See, e.g.,
2. The maximumbrightness in the long-termcycle precedes Stahl et al. (1995), Sˇtefl & Rivinius (2000) or Sˇkoda &
the maximum of the emission strength for a few years Sˇlechta(2002)formoredetailsaboutHEROS.
(Juza etal.1994). Themaximumof theemissionstrength – 31 spectra were obtained with a CCD camera attached to
coincides with the maximum of continuum polarization the coude´ focus;24 of them near Hα, 6 near Hβ and one
(Arsenijevic´ etal.1994).Thesefactsseemtoindicatethat aroundHγ.
the brightening of the object is related to temporarily ex-
tended photosphere which can be satisfactorily modelled
byrotatingmodelphotospheres(Hirata1995). A complete reduction of Reticon spectra, i.e. wavelength
3. κDra is the primary component of a single-line spectro- calibration, rectification, and intensity and equivalent-width
scopic binary in a circular orbit with an orbital period of (W) measurements were all carried out using the program
61d.55andasemi-amplitudeofK ∼7−8kms−1.Thisor- SPEFO written by Dr.J.Horn (see Horn et al. 1992, Sˇkoda
bitalradial-velocity(RVhereafter)variationscouldbede- 1996 for details). All initial reduction of HEROS and CCD
tected in virtually all published RVs. They are accompa- spectra (biassubtraction,flat-fieldingandwavelengthcalibra-
niedbyparallelphase-lockedV/Rvariationsofthedouble tion)werecarriedoutusingmodifiedMIDASandIRAFpack-
Balmeremissionlines(Juzaetal.1991). ages,respectively.Theunrectified,wavelength-calibratedspec-
4. Acontroversialperiodofrapidvariationsof0d.890384orits trawerethenexportedintoSPEFOwheretherectificationand
variousaliasescouldbefoundinallavailableRVdatasets, alllineparametermeasurementsweredone.
lineasymmetryandpolarizationanditsvaluecorresponds
well to the expected rotational period of the Be primary
2.2. Photometry
(Juzaetal.1991).
5. The rapid variations in the form of line width and asym-
A rich collection of UBV photometric observations was ob-
metry and also travelling sub-features, seen in a series of
tained at Hvar and Skalnate´ Pleso, and complementedby ob-
electronic spectra,can best be reconciledwith a periodof
servations collected from the astronomical literature, by Juza
0d.545 (one of the aliases of the 0d.89 period according to
et al. (1994). In addition to these observations, we obtained
Juza et al. 1991) and can be interpreted as signatures of
newUBV photometryofκDraattwoobservatories:10obser-
nonradialpulsations(Hill1991).
vations at Hvar and 47 observationsat Tubitak. All these ob-
Itisclearthatunderstandingthelong-termvariabilityisone servationswerecorrectedfordifferentialextinctionandtrans-
ofthemostimportantcluestounderstandingthenatureofthe formed into a standard UBV system (based on the mean val-
stillmysteriousBe phenomenon.Sucha taskrequires,among ues given by Johnson et al. 1966) via non-linear transforma-
otherthings,averypatientcollectionofobservationaldataand tionformulæusingHEC22/VYPARphotometricsoftware(see
their careful reduction. Since κDra has been on our observ- Harmanec&Horn1998andHarmanecetal.1994forthede-
ing program both at Ondˇrejov (spectroscopy with electronic tails and copies of the programs). We also extracted 115 H
p
detectors),andatHvar,andrecentlyalsoatTubitak(UBV pho- photometricobservationshavingphotometricflag0or1 from
tometry)formorethanadecade,itwasdeemedusefultopub- theHipparcosarchive(Perrymanetal.1997)andtransformed
lishtheseuniquedatasetsinextenso,withrelevantanalyses,to themintoJohnsonV magnitudeusingHarmanec’s(1998a)for-
enablefurthercomparisonswithcurrentandfuturetheoretical mula.Finally,wereadout96V magnitudedifferencesfroma
modelsoftheBephenomenon.Wealsooffersomeinterpreta- graphpublishedinaposterpaperbyCroxalletal.(2001)and
tions and deriveimprovedbasic physicalpropertiesof the Be shiftedthemproperlytogetthemonascaleofotherdatausing
star based on detailed comparisonwith synthetic line profiles thenightswherethisdatasetoverlapswithourcalibrateddata.
overalargerangeofwavelengths.
Afewcommentsarerelevant:
2. Observationsanddatareduction
1. To ensure the best homogeneity of Hvar data, we only
2.1. Spectroscopy used differentialphotometryof κDra obtainedrelative to
HR4687 = HD107193 for which the following all-sky
Electronic spectra of κDra were secured from June 1992 to
UBV valueswere adoptedon the basis of recentdata ho-
April 2003 in the coude´ and Cassegrain foci of the Ondˇrejov
mogenizationV = 5m. 489, B−V = +0m. 038, U−B =
2m telescope. The details of observations are summarized in
+0m. 079. The check star HR5018 = HD115612 (V =
Table1.
6m. 215, B−V = −0m. 056, U−B = −0m. 137) was ob-
– Mostofthespectra(102)wereobtainedinthecoude´focus servedasfrequentlyasthevariable.
with a Reticon RL-1872F/30 detector at a reciprocal dis- 2. Thesamecomparisonswerealsousedatthe0.4-mreflector
persionof17A˚/mm;93ofthemcovertheHαregion,6of atTubitak.
themcontainHβ and3theHγ line. 3. AllolderHvarandSkalnate´PlesoUBV observations,pub-
– Since January 2001 to March 2003, 30 spectra were ob- lishedbyJuzaetal.(1994),werealsore-reducedrelativeto
tainedattheredandbluechannelsofthefibre-fedechelle theabovevaluesforthecomparison.
S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra 3
Table1.TheobservationaljournalofκDraattheOndˇrejovObservatory.
Epoch No.of Spectrograph Detector Resolving Spectral
[HJD−2400000] spectra power range[A˚]
48000–51714 93 coude´ ReticonRL-1872F/30 10000 6300–6740
49021–49026 3 coude´ ReticonRL-1872F/30 10000 4310–4520
49079–49116 6 coude´ ReticonRL-1872F/30 10000 4750–4960
52321–52321 1 coude´ CCDSITe005800×2000 10000 4300–4554
52323–52323 2 coude´ CCDSITe005800×2000 10000 6256–6769
51900–52727 30 HEROS CCDEEV2000×800 20000 3450–5650
CCDEEV1152×770 20000 5850–8620
52742–52754 6 coude´ CCDSITe005800×2000 10000 4753–5005
52734–52754 22 coude´ CCDSITe005800×2000 10000 6256–6769
3. Theopticalspectrumofκ Dra modelatmosphereanalysisgiveonlyanapproximateestimate
oftheeffectivetemperatureandgravity.
Thevastmajorityofthenewspectracoverthewavelengthre-
We calculated a small grid of NLTE plane-parallel
gionfromabout6300to 6700A˚, whichincludesthe Hαline.
hydrogen-helium model atmospheres for all combinations of
Thisspectralregionischaracterizedbyapermanentpresence
three values of T (13000K,14000K,15000K) and logg
ofemissioninHαandFeII 6456A˚ lines,whilethelinesSiII (3.0,3.5,4.0) usinegffa computer code developed by one of us
6347A˚, SiII 6371A˚, and HeI 6678A˚ are seen in absorption. (see, e.g., Kuba´t 2003, and referencestherein). The hydrogen
In a much wider spectral range 3450 – 8620A˚, covered only
modelatomconsistsof15levelsofHIand1levelofHII,the
bythe HEROSspectra,the Balmer linesupto H15 aswell as
helium model atom consists of 29 levels of HeI and 1 level
someinfraredlinesareseen.
ofHeII.Theatomicdata(transitionprobabilities,photoioniza-
Thegeneraltimebehaviourdocumentedbythespectralre- tioncross-sections,collisionalstrengths)werethesameasde-
gionaroundHαseemstobeconfirmedbytherestofthevisible scribedinKuba´t(1999).Bysimplecomparisonoftheobserved
spectrum.Asusually,theBalmeremissionisstrongestforHα spectrum of higher Balmer lines to the model one, one finds
anddecreasestowardhighermembersoftheseries.Anumber thatthe modelatmospherewith T = 14000Kand logg =
eff
of FeII emission lines are present in the whole optical spec- 3.5 leads to quite a satisfactory agreement with the observed
trum,whereasboththetripletandsingletHeI linesarein ab- spectrumforarotationalvelocityofvsini=170kms−1.
sorption.Linesofotherions,likeMgII,CII,OI areallinab- Rotationofthe modelspectrumwastaken intoaccountin
sorption,withanotableexceptionoftheinfraredoxygentriplet anapproximatewayusingtheconvolutionoftherotationpro-
OI 7772,7774,7775A˚.Notethatcertainpartsoftheredand filewiththelineprofilefollowingGray(1976).
infraredspectrumarestronglycontaminatedbythetelluricab- One can admit that the comparison of the observed and
sorptionlinesandbands. model spectrum should also take into account the radiation
of the secondary component of the binary. However, Juza
et al. (1991) presented rather convincing arguments that the
3.1. Comparisonwith a theoreticalspectrum
secondary to κDra is not a Roche-lobe filling giant but a
Determinationof basic parametersof stellar atmospheres(the smallcompactobjectwithamassprobablysmallerthansome
effective temperature T and the surface gravity g) is a rel- 0.9M⊙.Inthewholeopticalspectrum,theluminosityofsuch
eff
atively straightforward procedure for normal, main sequence anobjectwouldbenegligibleincomparisontotheBegiantand
stars, where simplifying assumptionsof local thermodynamic weconcludethatonecansafelyneglectthecontributionofthe
equilibrium(LTE)inastaticatmosphereandplane-parallelge- secondary to the observed spectrum in the investigated range
ometryarefulfilledwithasufficientaccuracy. ofwavelengths.ThevaluesofTeff andlogg wefoundarenot
However,thisisnotthecaseforBestars.Theverypresence toodifferentfromthosepresentedbyChauvilleetal.(2001)in
oftheemissionlinesindicatestheviolationoftheassumptions theirTable1,namelyTeff = 13900Kandlogg = 3.84,based
ofaplane-parallelgeometryandastaticatmosphere.Yet,one ontheBCDclassificationsystem(Chalonge&Divan1952).
can try to derive approximate values based on standard mod- Thevalue ofvsini is in a goodagreementwith the value
els, keeping their limited applicability in mind. This should 180km s−1 determined by Stoeckley & Buscombe (1987).
work rather well in circumstances when the star in question Higher valuesof the projectionrotationalvelocity seem to be
istemporarilywithoutanyobservablesignaturesoftheBeen- unrealistic.
velopeandhasapureabsorptionspectrum.Indeed,verysatis- The observed and theoretical spectrum is compared in
factoryresultsfortwootherBe stars, 4Her(HD142926)and Figures1and2,whichcorrespondtowavelengthregionscov-
60Cyg(HD200310),wereobtainedthisway–cf.Koubsky´ et eredbytheblueandredchanneloftheHEROSspectrograph,
al.(1997)andKoubsky´ etal.(2000),respectively. respectively.Both partsof the spectrumwere obtainedsimul-
Veryregrettably,κDrahasneverbeenobservedtolooseits taneouslyatHJD51924.5409.
Onecanseethatthereisageneralagreementbetweenthe
emission lines completely.Therefore,the followingresults of
synFig relative intensity relative intensity relative intensity relative intensity relative intensity 4
T=14000Klogg=3.5efftheticNLTEspectrum,(fullline)..1.LineidentificationandcomparisonofthespectrumofDraobtainedusingthebluechanneloftheHEROSspectrograph(dots)andtheκ (Å)l 5250 5300 5350 5400 5450 5500 5550 5600 5650 0 0.2FFeeF SSeIIII III55III 44 0.45550644226237 932++F MMMFFFFFFFFFFePS 0.6eeeeeeeeee gggI I IIIIIIIIIIII IIIIIIIIIIIIIII5III 555555555555455545422233335212442237781468365606660064603750?427 0.8 1 (Å)l 4900 4950 5000 5050 5100 5150 5200 5250 0 0.2Fe II 0.45199FFHSOFeeMFFFFFFFFeiHHSSS e SS 0.6I IIeeeeeeeegIIIIIee Iiii I 4454IIIIIIIIII IIIII5IIIIIIIIIIIIIIIII9909 15555555555555555522527202222110100201214265811123606194104862 24775019888611648? 0.8 1 (Å)l 4500 4550 4600 4650 4700 4750 4800 4850 0 0.2S II 4 0.4H5b52 + FFFFFFFSHSNSSSS 0.6eeeeeeeie i IIIIIIIIIIII IIIIIIIIIIIIIIIIII 444444444444444588855555567665212201245821235564685396493213 0.8 1 (Å)l 4150 4200 4250 4300 4350 4400 4450 4500 0 0.2 Hg 0.4HMFeHHHSS egMIeeeii CF4I IIIgFFFFFFIIIIIIIHH4 eOS 0.64444444IIeeeeee7IIee 3311114 I144IIIIIII II5824238IIIIIIIIIII32 2814811444444444448614112344144576177309361237393318950 0.8 1 (Å)l 3750 3800 3850 3900 3950 4000 4050 4100 0Ca II 39C8 0.2H + He I 38896 I8IH 1312111093HHHHHHHede9 1IHH 9 0.43ee 9+ C6IIHHHHH SSSS C543aeeeeeiiii08 II IIII22IIIIIIIIIII 60 0.634443333333901098888892020367556279134823631 0.8 1 S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarDraκ
725synFig relative intensity relative intensity relative intensity relative intensity relative intensity
07590A,andA.˚˚T=efftheticNLTEspectrum.2.Lineidentificationandcom 7400 7450 0 0.2 0.4 FF 0.6ee IIII 77444692 0.8 1 7000 7050 0 0.2 0.4 He 0.6 I 7065 0.8telluric lines 1 6650 0 0.2 0.4 He 0.6 I 6678 0.8 1 6250 6300 0 0.2Fe II 6 0.4238 +F AS 0.6eli IIIIII 666222443839 0.8telluric lines 1 5850 5900 0 0.2 0.4 He 0.6 I 5876 0.8 1 S.M
14000Klogg,parisonofthesp 7500 Fe II 7513 7100 6700 6350 SFi IeI 6II3 643718 5950 Si II 5979 .Saadetal.:Lon
=3.5(fuectrumof 7550 7150 6750 Si II 6371 6000 Fe II 5991 ? g-termvar
llline)Draκ 6400 iations
.NotethepresenceoftelluriclinesandobtainedusingtheredchanneloftheHE (Å)l 7600 7650 7700 telluric lines (Å)l 7200 7250 7300 telluric lines He I 7281 (Å)l 6800 6850 6900 telluric lines (Å)l 6450 6500 FOe IIII 66443536 ++ FFFFFeeeee IIIIIIIIII 66666554441113568736 telluric lines (Å)l 6050 6100 6150 Fe II 6148 + FFeeO I IIII 666011854469 andphysicalpropertiesoftheBestarκ
bR Fe II 7712 D
andsOSs 6550 ra
628nearpectrogra 7750 7350 telluric lines 6950 HaCC IIII 66557883 6200
0p
A˚h
Hα,,(dots) OOO III 777777777245 6600
6870A,˚andthe 7800 7400 7000 6250 Fe II 6238 +F ASeli IIIIII 666222443839 5
6 S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra
observed and model spectrum in the wings of Balmer lines
Ha − k Dra
(withtheexceptionofHα),whiletheBalmerlinecoresareaf-
fectedbythe emission.Quitesatisfactory agreementwas also
achievedfortheHeIlinesandfortheMgII4481A˚ line.Apart
fromHαwings,whicharesubjecttohighvariability,theratio
betweenMgII4481A˚ andHeI4471A˚ isoneofthebestclassi-
ficationcriteriaforspectraltypesB7–B8(Steeleetal.1999).
However,thesyntheticSiII 6347and6371A˚ linesaredeeper
thantheobservedoneswhichprobablyindicatesthattheyare
filledbyaweakemission.Apronounceddifferenceisseenfor
HJD 2400000+
theinfraredOI7772,7774,7775triplet,whichisobservedas
adouble-peakemission.
52754.4157
The FeII linesstudied by Hanuschik(1987) – namelythe
triplet4924A˚,5018A˚,5169A˚,andsomewhatweaker4549A˚,
52734.3215
4584A˚,and5316A˚ lines–arealsoobservedtohaveemission.
On the other hand,there is no observableFeII 6384A˚ line in
52683.5671
thespectraofκDra,similarlyasforαColfromHanuschik’s
sample.
51924.5409
A casual inspection of the observed spectrum could lead
to a conclusion that FeII 4924A˚ line has a P Cygni profile. y
Note,however,thatthisfeatureisinfactablendofHeI4922A˚ nsit 51714.3660
e
absorption and FeII 4924A˚ double peak emission. Similarly, e int 51669.3846
theobservedasymmetryoftheemissionpeaksofFeII5018A˚ ativ
lineisalsocausedbyblendingwithanabsorptionHeI lineat rel
5016A˚. 51433.3457
To see if there are any secular changes in the seemingly
51238.5568
photosphericpartsoftheobservedspectrallineswealsocom-
pared the theoretical spectrum with the most recent spectrum
ofκDracorrespondingtoanotherphaseoflong-termchanges. 50518.4640
Itturnedoutthattheonlychangesareseeninthecoresofthe
emissionlines,especiallyoflowerBalmerlines,andFeIIlines. 50160.4200
Thefit to theouterwingsofhigherlinesofthe Balmer series
remainsunchanged.Thisseemstoindicatethatanypartsofthe 49862.3758
emission-lineenvelopearenotcontributingsignificantlytothe
observedcontinuumradiationorthattheircontributionwasthe 49463.3293
sameonbothoccasions.
49133.3452
2
4. Measurements 100% 49018.5747
To investigate long-term variations of κDra, we focused on 48883.5010
1
Hα, Hβ, Hγ,Hδ,SiII 6347A˚,SiII 6371A˚,HeI 6678A˚,and
−20 −15 −10 −5 0 5 10 15 20 25
FeII6456A˚ lines.WemeasuredequivalentwidthW,peakin- Dl (Å)
tensitiesofthedoubleemissionlines,andthecentralintensity
of the absorption reversals relative to the adjacent continuum Fig.3.Evolutionof theHαintensityprofileobserved inκDraover
thelast11years.Allspectraarenormalizedtothelocalcontinuum.
(I ,I andI ,respectively)andalsothe peakseparationbe-
V R c
tweenvioletandredpeaks(∆ν ).NotethatW istakenwitha
p
negativesignfortheemissionlineprofile. 4.1. Balmerlines
Both W and all intensities were measured in the original
4.1.1. Equivalentwidth(W)
spectrum,i.e. withoutanysubtractionofa syntheticspectrum
(asitissometimesdoneinsimilarstudies)sincethiswouldim- Hαlinehasalwaysbeenobservedasadouble-peakedemission
plyan implicitassumptionofan opticallythinenvelope.This with a variable shape and strength (see Fig.3). Fig.4d shows
neednotbethecase,especiallyinthecoresofBalmerlines. the time variations of the Hα equivalent width W during the
Only W and I were measured,of course,forthe absorp- past 30 years. Data prior to HJD2448802.43819 were taken
c
tion lines of He and Si. All measurements are collected to- fromAlvarezetal.(1990),Juzaetal.(1994),andMoujtahidet
getherwithheliocentricJuliandatesofmid-exposures(HJDs) al.(2000).NumericalvaluesofW,shownonlyinagraphical
inTables2,3,and4. forminFig.1ofMoujtahidetal.(2000)paperwerekindlypro-
S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra 7
1974 1980 1986 1992 1998 2004 1974 1980 1986 1992 1998 2004
3.8
3.6 1.15 Juza et al.
(a) Ondrejov
3.4
1.1
3.2
3 1.05
Iv 2.8
2.6 1
2.4 C
2.2 E/ 0.95
2 Ondrejov
0.9
1.8
40000 42000 44000 46000 48000 50000 52000 54000
0.85
1974 1980 1986 1992 1998 2004
3.8 0.8
3.6
(b) 0.75
3.4
40000 42000 44000 46000 48000 50000 52000 54000
3.2
HJD -2400000
3
Ir 2.8 Fig.5.Long-termvariationsoftheE/C Hβemissionstrengthbased
2.6
onboth,datafromJuzaetal.andnewobservations.
2.4
2.2
2 Ondrejov
1.4
1.8
40000 42000 44000 46000 48000 50000 52000 54000 1.6 H b
1974 1980 1986 1992 1998 2004
3.8 1.8
3.6
(c) 2
3.4
3.2
2.2
3 Å)
Ic 22..68 W( 2.4
2.4 2.6
2.2
2 Banerjee 2.8
1.8 Ondrejov
1.6 3
40000 42000 44000 46000 48000 50000 52000 54000
3.2
1974 1980 1986 1992 1998 2004 51800 52000 52200 52400 52600 52800
−25
A−M Hubert HJD −2400000
Juza et al.
−20 Banerjee 1.16
Ondrejov
1.14 Hb
−15
Å)
W ( 1.12
−10
1.1
−5
1.08
(d)
0 Ic 1.06
40000 42000 44000 46000 48000 50000 52000 54000
1.04
1974 1980 1986 1992 1998 2004
220 1.02
200 (e) A−M Hubert
180 Ondrejov 1
s] 160 0.98
m/ 140
[kp 120 51800 52000 52200 52400 52600 52800
100 HJD -2400000
Dn
80
Fig.6.VariationsofHβequivalentwidth(upperpanel)andintensity
60
40 (lowerpanel).
40000 42000 44000 46000 48000 50000 52000 54000
HJD −2400000
Fig.4.Correlationbetweenlong-termvariationsoftheHαemission videdtousbyDr.A.-M.Hubert.Onemeasurementwastaken
line.(a)and(b):Therelativeintensityoftheviolet(IV)andred(IR) fromBanerjeeetal.(2000).Werecallagainthatthemoreneg-
peaks, (c): relative central intensity of the line (Ic), (d): equivalent ative valuesof the equivalentwidth the stronger the emission
widthoftheHαline,(e):peak-separation∆νp(Hα). line.
Theobservationspublishedearlierlocateoneminimumof
theemissionstrength(thearithmeticmaximumofW)intothe
8 S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra
1994 1997 2000 2003 1994 1997 2000 2003
1.12 300
Dn (Ha )
Dn p(Hb )
1.1 Dn p(Hg)
p
250
1.08
1.06
s] 200
R) 1.04 m/
(V/ 1.02 [kp 150
Dn
1
0.98 100
0.96
50
0.94
48000 49000 50000 51000 52000 53000 54000 48000 49000 50000 51000 52000 53000 54000
HJD -2400000 HJD -2400000
Fig.7. A timeplot of theV/Rchanges of Hαemission lineduring Fig.8.ComparisonofthepeakseparationofHα,Hβ,andHγlines.
thelast11years.Nolong-termvariationsareobserved.
trasttomanyotherBestars–thereisnoclearevidenceofpar-
allellong-termV/RvariationsasFig.7shows.
interval between HJD2443200 and 2443800, when WHα ∼ As shownalreadybyJuza et al. (1991), thisratio exhibits
−3A˚.Theother,recentminimumissharplydefinedbyourdata phase-lockedvariations with phase of the 61d.55 binary orbit.
at HJD2451380, when WHα reached the value of −7.17A˚. We postpone investigation of orbital changes of κDra into a
Withsomescatter,theavailabledatalocatethetimeofthemax- follow-upstudy.
imumemissionaroundHJD2447000withavalueofW be-
Hα
tween−20A˚ and−21A˚. Themostrecentdataagainindicate
4.1.3. Peakseparation(∆ν )
valuesnearW =−21A˚ orlower. p
Hα
AvailableequivalentwidthsofaHβlinesbasicallyconfirm Usually the double-peak structure is one of the characteris-
thetrenddefinedbyHα,thoughwithanincreasedscatter.This ticfeaturesoftheemissionlinesinBestars.Peak-separations
isillustratedbytheupperpanelofaFig.6. (∆ν ) were measured for Balmer lines whenever they were
p
available in ourκDra spectra,the mostprominentoneswere
inHα,Hβ,andHγ lines.
4.1.2. Central(I ) andpeak(E/C) line intensities
c The∆ν ofHαunderwentveryclearlong-termvariations
p
The central intensity I of the emission line we define as the overtheintervalcoveredbyourdata.AfterHJD48802.43819
c
intensityofthecentralpartofthelinerelativetothecontinuum (in 1992) it started a gradual increase until it reached a max-
level.Fortheparticularcaseofourstar(κDra)wemeasureit imum of 142km s−1 at HJD 51378.5441 (in 1999). This
atthepositionofthecentralabsorption.Ontheotherhand,we was followed by a steep decrease to its minimum value of
can expressthe peakintensity by the ratio E/C, whichis the 53kms−1onHJD52684.5418(in2003).NotethatArsenijevic´
meanintensityofbothredandvioletpeaks,i.e.(I +I )/2. etal(1994)reportedthemaximumvalueofthepeakseparation
WemeasuredthecentralintensitiesI foreachlinVe.ForRcom- of 206km s−1 (in the years 1961–1962and 1985–1986)and
parison with the data of Juza et al. (c1994) we measured the theminimumof69kms−1 in1980.Fig.4edisplaysthelong-
intensity of Hβ in terms of (I + I )/2 as well. Our mea- term behaviour of Hα peak separation based on the new and
V R
surements of the central intensity of Hα were complemented compiled data. The first part of the ∆νp long-term behaviour
by one observation published by Banerjee et al. (2000). The is mainly based on data from Moujtahid et al. (2000), kindly
centralintensity I showsparallelbehaviorwith red (I ) and providedtousbyDr.A.-M.Hubert.Theygofromearly70’sto
c R
violet(I ) peakintensities, andalso with W , as illustrated 1995.
V Hα
bythefirstfourpanelsofFig.4. WealsomeasuredthepeakseparationforHβandHγlines
inallspectrograms,wheretheselineswereavailable.Fig.8il-
Fig.5representstheintensityvariationofHβemissionover
lustratesthecomparisonbetweenthepeakseparationvaluesof
the last 30 years. Data prior to HJD2451924.5409have been
Hα, Hβ and Hγ. The measurements of ∆ν (Hγ) have large
adaptedfromJuzaetal.(1994).Onecanseeacontinuingcyclic p
uncertainties because of weakness of the emission. Note that
variationoverwhichasecularincreaseintheemissionstrength
the values of ∆ν (Hβ) are significantly higher than those of
seemstobeoverlapped. p
Hα,andsmallerthan∆ν (Hγ).Inparticular,∆ν (Hγ)ranges
ThecentralintensitiesofHγandHδlineshavebeenslowly p p
from 220 to 250km s−1, ∆ν (Hβ) from 144 to 190km s−1
increasingwithtimefrom0.62to0.66,andfrom0.53to0.56, p
and ∆ν (Hα) from 53 to 108km s−1 for the time interval
respectively,overtheperiodcoveredbyournewdata,showing p
where data for all three lines overlap.We observe that at any
againchangesparalleltothoseseeninHα.
timetherelation
Parallelchangesof the intensityof theemission peaksI
V
andI havebeenfoundforHα.Note,however,that–incon- ∆ν (Hα)<∆ν (Hβ)<∆ν (Hγ) (1)
R p p p
S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra 9
holds. This reflects differentregionsof the formationof indi-
HeI 6678 − k Dra
vidual Balmer emission lines. The opacity in lower members
ofBalmerseriesislarger.Consequently,thelinesareoptically
thickintheradialdirectiontoa relativelylargedistance.This
distancedecreaseswiththeincreasingprincipalquantumnum-
beroftheuppertransitionlevel.Highermembersoftheseries HJD 2400000+
originateatregionsclosertothestellarsurface,havinghigher
Keplerianvelocity,andthereforelarger∆ν . 52754.4157
p
Averaging the ratios ∆ν (Hγ)/∆ν (Hα),
p p
∆ν (Hγ)/∆ν (Hβ), and ∆ν (Hβ)/∆ν (Hα) over all 52734.3215
p p p p
commonepochswecanconcludethat
52683.5671
∆ν (Hγ)
p =1.37±0.15 (2a)
∆νp(Hα) 51924.5409
∆νp(Hγ) =2.98±0.76 (2b) 2 51714.3660
∆ν (Hβ)
p
51669.3846
∆ν (Hβ)
p =2.16±0.32 (2c)
∆νp(Hα) 51433.3457
y
Withintheerrors,theseratiosareclosetothemeanvalueses- nsit
timatedbyHanuschiketal.(1988)andDachsetal.(1992): nte 51238.5568
e i
v
∆νp(Hβ) ≈1.8±0.5 (3a) relati 50518.4640
∆ν (Hα)
p
50160.4200
∆ν (Hγ)≈1.2∆ν (Hβ)≈2.2∆ν (Hα), (3b)
p p p
49862.3758
forBestarshavingsymmetricdouble-peakprofiles.
49463.3293
4.2. Otherlines
49133.3452
The lines of SiII 6347A˚, SiII 6371A˚, FeII 6456A˚, and HeI
6678A˚ are all relatively weak in comparison to the Balmer 49018.5747
lines but in most cases their measurements were reliable
enough.ThesiliconlinesSiII6347A˚ andSiII6371A˚,andthe 10% 48883.5010
heliumlineHeI6678A˚ havebeeninabsorption,whiletheFeII 1
6456A˚ linehasappearedasadouble-peakedemissionprofile
during all 11 years of observations. The line profiles of HeI
6678A˚ and FeII 6456A˚ are shownin Figs. 9 and 10,respec-
tively.Notethatatcertaintimesitwasquitedifficulttomeasure
theseweaklinesbecauseofaheavyblendingwithneighbour-
ingtelluriclines.
−20 −15 −10 −5 0 5 10 15 20
HeI 6678A˚ isthestrongestabsorptionlinebesidesHαin Dl (Å)
the red part of the spectrum. It appears as a shallow absorp-
Fig.9. Evolution of the HeI 6678A˚ intensity profile observed in
tionlinewithanintensity0.04relativetothecontinuumlevel κDraover thelast11years. Allspectraarenormalizedtothelocal
(see Fig.9).Itsequivalentwidthvariesfrom0.12A˚ to 0.22A˚
continuum.
fromtheearly1992to1999andthendecreases,withlargefluc-
tuations, to 0.1A˚ (see lower panel of Fig. 11). In spite of the
scatter,onecansee thatHeI 6678A˚ equivalentwidthfollows varyingbetween0.98and1.06andback,inparalleltothevari-
thesametrendastheemissionlinesofHαandFeII6456A˚. ationsoftheBalmerlines;Theequivalentwidthofthislinein-
BothSiII6347A˚ andSiII6371A˚ linesexhibitvariationsin creases(withfluctuations)fromthe valueof−0.17A˚ in1992
theirequivalentwidthfrom0.04A˚ to0.1A˚ atmost,asshown to−0.05A˚ in1999(seeFig.12).Between2000and2003the
in the upper and middle panels of Fig. 11. In spite of a con- emissionstrengthensrapidlysothattheequivalentwidtharith-
siderablescatter,onecanrecognizeamonotonousdecreaseof meticallydecreases,reachingitslowestvalueof−0.5A˚ during
theirequivalentwidthwithtime. themostrecentobservations.TheepochswhentheFeII6456A˚
LineprofileofFeII6456A˚ appearspermanentlyasadou- line is either veryfaintor completelymissing, correlateswell
ble emission(see Fig.10).ItscentralintensityI isgradually withphasesofweakestHαemission.
c
10 S.M.Saadetal.:Long-termvariationsandphysicalpropertiesoftheBestarκDra
FeII 6456 − k Dra 1994 1997 2000 2003
0.18
SiII 6347 (Å)
0.16
HJD 2400000+ 0.14
0.12
Å) 0.1
52754.4157 W( 0.08
0.06
52734.3215
0.04
52683.5671 0.02
0
51924.5409 48000 49000 50000 51000 52000 53000 54000
HJD −2400000
51714.3660 1994 1997 2000 2003
2 0.16
SiII 6371 (Å)
51669.3846 0.14
0.12
51433.3457
sity 0.1
n
e inte 51238.5568 W(Å) 0.08
v
elati 50518.4640 0.06
r
0.04
50160.4200
0.02
49862.3758 0
48000 49000 50000 51000 52000 53000 54000
HJD −2400000
49463.3293
1994 1997 2000 2003
49133.3452 0.25 HeI 6678 (Å)
49018.5747
0.2
10%
48883.5010
1 Å)
W( 0.15
0.1
−20 −15 −10 −5 0 5 10 15 20 48000 49000 50000 51000 52000 53000 54000
Dl (Å) HJD −2400000
Fig.10. Evolution of the FeII 6456A˚ intensity profile observed in Fig.11.Long-termvariationsoftheequivalentwidthofSiII6347A˚
κDraoverthelast11years. Allspectraarenormalizedtothelocal line(upper panel),SiII6371A˚ line(middlepanel),andHeI 6678A˚
continuum. (lowerpanel).
d normals.One can see thatthe brightnessin the V passband
Central intensities of HeI 6678A˚ line, and of both SiII clearlycorrelateswiththelong-termspectralchanges.
6347A˚ and 6371A˚ lines are subjectto a largescatter andare
Besides, it is clear that occasionalsmaller brighteningsor
notdisplayed.
fadingsoccuronamuchshortertimescalethanthelong-term
ones.Whileitisconceivablethatasinglecaseofsuchabehav-
4.3. Photometry ior could be blamed for larger observational errors, we want
topointoutthat,e.g.,thesuddenbrighteningobservedatHvar
Long-term variations of the V magnitude and of both B−V on HJD 2451377.4, is undoubtedly a real phenomenon. This
and U−B indices are shown in the Fig. 13 in the form of 1- normalpointisbasedonthreeobservationsgivingasmallrms