The X-ray spectrum of delta Orionis observed by LETGS aboard Chandra

0.64 MB·English

by  A. J. J. Raassen

Astronomy&Astrophysicsmanuscriptno.18544 c ESO2013
(cid:13)
January10,2013
δ
The X-ray spectrum of Orionis observed by LETGS aboard
Chandra
A.J.J.Raassen1,2 andA.M.T.Pollock3
1 SRONNetherlandsInstituteforSpaceResearch,Sorbonnelaan2,3584CAUtrecht,TheNetherlands
2 AstronomicalInstitute”AntonPannekoek”,SciencePark904,1098XHAmsterdam,UniversityofAmsterdam,TheNetherlands
3 EuropeanSpaceAgencyXMM-NewtonScienceOperationsCentre,EuropeanSpaceAstronomyCentre,Apartado78,Villanueva
delaCan˜ada,28691Madrid,Spain
26November2012
3
1
ABSTRACT
0
2
Aims.Weanalyzethehigh-resolutionX-rayspectrumofthesupergiantO-starδOrionis(O9.5II)withlineratiosofHe-likeionsand

n athermalplasmamodel,andweexamineitsvariability.
a Methods.TheO-supergiantδOriwasobservedinthewavelengthrange5–175ÅbytheX-raydetectorHRC-Sincombinationwith
J thegratingLETGaboardChandra.WestudiedtheHe-likeionsincombinationwiththeUV-radiationfieldtodeterminelocalplasma
9 temperaturesandtoestablishthedistanceoftheX-rayemittingionstothestellarsurface.Wemeasuredindividuallinesbymeansof
Gaussianprofiles,foldedthroughtheresponsematrix,toobtainwavelengths,linefluxes,halfwidthsathalfmaximum(HWHM)and
] lineshiftstocharacterizetheplasma.Weconsidermultitemperaturemodelsincollisionalionizationequilibrium(CIE)todetermine
R temperatures,emissionmeasures,andabundances.
S Results. AnalysisoftheHe-liketripletsextendedtoNviandCvimpliesionizationstratificationwiththehottestplasmatobefound
withinafewstellarradii3R (Mgxi)andthecoolestfartherout,farbeyondtheaccelerationzone,upto49R (Nvi)and75R (Cv).
.
h Theobservedtemperaturesc∗overarangefromabout0.1to0.7keV,i.e.,1–8MK.TheX-rayluminosity(L )∗is 1.5 1032e∗rg/sin
p therangefrom0.07to3keVcoveredbyLETGS.Velocitywidthsofabout1040kms 1havebeendeterminexd. ∼ ×
−
-
o Keywords.techniques:spectroscopic–stars:individual:δOri–stars:stellarwindstars:early-type–missions:Chandra
r
t
s
a
1. Introduction shouldprovidenewconstraintsontheory,it hasbeenproposed
[
torecordthespectrumofδOri,thesoftestoftheX-raybrightest

1 Since the launch of the first X-ray observatories, it has been O-starsobservedwith ROSAT.ThispaperdiscussestheLETGS
v knownthatO-typestarsandearlyB-typestarsareX-raysources. dataobtainedinthecontextofindividuallinediagnosticstoob-
7 Harndenetal.(1979),Sewardetal.(1979),andCassinellietal. tainplasmacharacteristics,aswellasoverallthermalmodels.
4 (1981)describedthefirstobservationswithEinstein.Theinves-
TheO-star δ Ori(HD 36486)is the western starin the belt
8 tigationswerecontinuedwithASCA(Corcoranetal.1994)and
of Orion, named Mintaka, with a parallax of 4.71(0.58) mas,
1
ROSAT(Haberl&White1993,Bergho¨feretal.1996).Although
. i.e., at a distance of 212 pc (SIMBAD: Van Leeuwen 2007)
1 the origin of the emission was initially a matter of debate, it 1. The position in J2000 coordinates is RA=053200.400 and
0 is now generallybelievedthatinstabilities and clumpingin the Dec= 001756.74.ItisabrightX-raysourceandsufferslower
3 strongline-drivenstellarwindisthemechanismthatheatssmall −
interstellarabsorptionthanζOri.Itispartofatriplestarsystem,
1 parts of the wind (e.g., Lucy & Solomon 1970;Lucy & White
containingofδOriA,δOriB,andδOriC.Herewefocusonthe
:
v 1980;Lucy1982;Owockietal.1988;Dessart&Owocki2005). “single star” δ OriA, which in itself is also a triple star system
i ThelaunchesofChandraandXMM-Newtonin1999withhigh- (Aa1,Aa2,andAb).Thetertiarystar(Ab)istoofarawaytoplay
X
resolution instruments aboard have offered the possibility to
aroleinourobservation.Theprimary(Aa1),asupergiant,isof
r study the X-ray spectra in more detail, resulting in, e.g., esti-
a spectral type O9.5II, with a temperature of 33000K. The sec-
mates of line ratios, line profiles, temperatures, emission mea-
ondary(Aa2)is of spectraltype B0.5III,with a temperature of
sures,andabundances(Waldron&Cassinelli2001,2007;Cohen
27000K(Voelsetal.1989andTarasovetal.1995).Theyforma
et al. 2006; Kahn et al. 2001; Raassen et al. 2008). Generally,
binarysystemwithaperiodof5.7325days(Harveyetal.1987).
theoverallspectrahavebeendescribedbymeansofcollisional Different stellar mass values are given in the literature. Harvin
ionization equilibrium (CIE) models with several temperature etal.(2002)giveM =10.3M asaveragewithR =11R and
p p
components,oftencomplementedbyanalysisofindividualline forthesecondarystar M = 5.2⊙M andR = 4R ,whileM⊙ayer
s s
profiles,linefluxes,andlinefluxratiosofHe-likeions.Basedon etal.(2010)suggestvaluesofM ⊙=25M withR⊙ =16 17R .
p s
RGSobservationsof ζ Ori,Pollock(2007)suggestsan alterna- Theprimaryandsecondarystarsaresepa⊙ratedby33R ,−equiva⊙-
tivemechanismduetothenon-equilibriumion-ioninteractions lentto3R .ThepropertiesofδOri,whichwehaveap⊙plied,are
p
faroutinthewind.Sinceextendingthehigh-resolutioncoverage
giveninTable1.
to the longer wavelengths available with the Chandra LETGS
The spectrum of δ Ori was studied in X-rays with earlier
satellitesbyCassinelli&Swank(1983),Haberl&White(1993),
Sendoffprintrequeststo:A.J.J.Raassen,
e-mail:[email protected] 1 http://simbad.u-strasbg.fr/simbad/sim-fid
1
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Table1.AdoptedpropertiesofδOri.
Property δOri
DistancefromEarth(pc) 212a
Spectraltype O9.5IIb
Radius(R ) 11b
Mass(M ⊙) 10.3b
T (K)⊙ 33000c
eff
Terminalwindvelocity(kms 1) 2000d
−
M˙(M yr 1) 1.07 10 6d
− −
⊙ ×
Notes:
a:VanLeeuwen(2007)
b:Milleretal.(2002),takenfromHarvinetal.(2002).
c:Milleretal.(2002),takenfromVoelsetal.(1989).
d:Milleretal.(2002),takenfromLamers&Leitherer(1993).
andCorcoranetal.(1994)andmostrecentlyathighresolution Fig.1. The zeroth-order lightcurve of δ Ori, observed with
byWaldron&Cassinelli(2007)andMilleretal.(2002)withthe LETGS,andrebinnedtotimebinsof15700seconds.Thecurve
ChandraHETGS.Theyfocusedonlineprofilesandlinewidths, indicatesa minimumat the beginningof the observationand a
togetherwith ratios of forbiddenand intercombinationlines in flatteningoftheincreaseattheendoftheobservation.
He-likeions.
The set up of this paper is as follows. The emphasis of
the paper is on determining the location of the X-ray emitting countsinthiszeroth-orderimageis26350counts.Noperiodicity
plasmaanditstemperatureinrelationtothestellarsurfaceand couldbeestablishedinthelightcurve,asthisobservationistoo
theUV-radiationfield.Thereforeweneedindividuallinefluxes. short to cover several stellar revolutions. However, after rebin-
In Sect. 2 the observationand the lightcurveare discussed. We ningtotimebinsofabout16ksthelightcurveshowssomevari-
showindividuallinefluxes,linewavelengths,andlinebroaden- ation in count rate from 0.264(0.004)to 0.278(0.004)counts/s
ings in Sect. 3. Based on the individual line fluxes of He-like during this observation. This is a change of about 5%. During
ions, the location relative to the stellar surface, as well as the the observation the phase of the binary system was 0.83-0.02,
temperatureoftheplasma,isderived.TheyaregiveninSect.4. derivedfromHarvinetal.(2002),or0.87-0.07,asderivedfrom
We discuss a multitemperature model fit to the total spectrum Mayeret al. (2010).This implies thatthe secondaryis in front
with a CIE-model in Sect. 5. As suggested by the light curve, oftheprimaryduringtheobservation.Inlatersectionsweinves-
wealsomakeatimesplit,dividingthetotalobservationof98ks tigateapossiblerelationbetweenthebehaviorofthelightcurve
intothefirstpartof49ksandthesecondpartof49ks. andtheobservedspectrumbycuttingtheobservationintoafirst
partfrom0to49ksandasecondpartfrom49to98ks.
2. Observationandlightcurve
3. Individuallinefluxes
2.1.Dataandpipelining
TheindividuallinefluxesoftheLETGSspectrumofδOriwere
The X-ray spectrum of δ Ori was obtained by means of HRC- measured.ForeachobservedlineaGaussianprofilewasfolded
S in combination with the Low-Energy-Transmission-Grating through the response matrix and fit to the observed line pro-
(LETG) on board Chandra on November9, 2007 during97 ks file, establishing the line positions, line fluxes, as well as the
(JD=54413.92705-54415.05066).The log of the observationis linewidths. A powerlaw was added to describe the continuum
showninTable2. near the line features. The line profiles are symmetric. This is
The data were pipelined with CIAO3.4 with CALDB ver- showninFig.2fortheOVIIIandCVIlines.Thisagreeswith
sion 3.4.1and preparedforSPEX by the programs extract and observations of δ Ori by Miller et al. (2002), when applying
creledevelopedatSRON.Thespectrumderivedfromthisobser- HETGS. Seeming asymmetriesin the data are due to asymme-
vationisthesumofthe+1and-1order.Thebackground,which triesintheinstrumentallinespreadfunction(LSF).Italsoinflu-
isquitedominantinthehigherwavelengthareaof LETGspec- encestheobservedwidthsofthelines.Thesituationinζ Oriis
tra,hasbeensubtracted.Thespectrumcontains31500countsin different.Inthatstarthelinesareasymmetricandbroadenedby
thespectralrangefrom5to175Å. themselvesasshownbyPollock(2007).
The measured wavelengths (Å) and line fluxes (in units
10 4 photons cm 2s 1 and in units 10 13 ergs cm 2s 1) are
2.2.Zeroth-orderlightcurve − − − − − −
collected in Table 3, together with the theoretical wavelengths
Inotherwavelengthranges(opticalandIUE)fluctuationsdueto from laboratory measurements collected by Kelly (1987) and
eclipsing have been observed in the lightcurve of δ Ori. These the NIST4 database 2. The stronger lines have a low value for
changesareabout.12mfortheprimaryeclipseand.07mforthe the(1σ)uncertainty.TheiruncertaintiesareafewmÅ.
secondaryeclipse(Harvinetal.2002).Thiscorrespondstoade- There are very few line features above 50 Å, and they
creaseofabout11%duringtheprimaryeclipseandofabout6% are often dueto higher-orderlines, especially third-orderlines,
during the secondary eclipse. Based on the zeroth-orderimage which have their strong first-order componentbetween 10 and
a lightcurve has been constructed. Figure 1 shows the zeroth-
orderlightcurveofthisobservationofδOri.Thetotalnumberof 2 http://www.nist.gov/pml/data/asd.cfm
2
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Table2.ObservationlogofthedataofδOri.
ObsID Instrument Grating StartDate EndDate Duration(ks) Wavelengthrangea
7416 HRC-S LETG 2007-11-09T10:14:57 2007-11-10T13:12:57 97.08 5-175Å
JD54413.92705 JD54415.05066
Notes:
a:Rangealsousedduringthefittingprocedure.
iconandiron,andtheiroptimalionizationtemperatureisaround
0.1keV.
Some stronger lines are collected in Table 5 and shown in
Fig.3.Thistableshowsthelineshiftsandthelinebroadenings.
Thelineshiftsshowvelocitiesbetween-160and+160kms 1.
−
The earth’s orbitalvelocity in the direction of δ Ori duringthe
observation and the velocity of δ Ori itself (Wilson 1963) are
both about 16 km s 1, but they have opposite signs and are
−
canceling. The obtained velocities are comparable with those
givenbyMilleretal.(2002),basedonobservationsbyHETGS.
The HWHMs of the strong lines result in a velocity of about
840 km s 1, below the terminal velocity of 2000 km s 1. Our
− −
value is higher than the values given by Miller et al. (2002),
based on HETGS. This might be due to an inconsistency be-
tween the instrumentalLSFs of LETGSandHETGS. However,
our value agrees with Wojdowski & Schulz (2005), who also
usedHETGS.Theultimatevelocityattheendofthewing,cor-
rected for the instrumental width are also given. These values
are about1850km s 1 with an uncertaintyof 200km s 1. The
− −
linesin the separatedspectraobtainedfromthe two time inter-
vals (0-49 ks and 49-98 ks) were measured, and no significant
differences between the line measurements of the two time in-
tervalshavebeenestablished.
4. He-likelineratios
TheindividuallinefluxesofthelinetripletsintheHe-likeions,
consisting of a resonance line (r), an intercombinationline (i),
and a forbidden line (f), are tools for density and temperature
diagnostics(GabrielandJordan 1969),becausethe upperlevel
oftheforbiddenline (1s2s3S ) isdepopulatedbycollisionsin
1
favoroftheupperleveloftheintercombinationline(1s2p3P ).
1
Ontheotherhand,thesameeffectofdepopulationcanbecaused
byastrongUVradiationfield(Blumenthaletal.1972).Thelat-
ter gives the size of the UV field flux and therewith an indica-
Fig.2.LineshapesoftheOviiilineat18.97ÅandtheCviline tionofthedistancetothestellarsurfacewheretheX-rayemit-
at 33.74 Å in the spectrum of δ Ori. Data are in red/gray, the tingionsareformed.Whileforlatetypestarsthecollisionsand
fittedGaussianmodellinefoldedthroughtheresponsematrixis therewith the electron density are the dominant processes, for
giveninblack.Therestwavelengthisalsoshown.Keepinmind hot, early type stars the strong UV radiation field (the location
thatthewidthisalsoinfluencedbytheinstrumentallinespread relativetothestellarsurface)ismostimportant.Thishasbecome
function. awell-provendiagnostictoolforestablishingtheradiallocation
of the X-ray source in the stellar wind of hot stars (Miller et
al.2002;Leuteneggeretal.2006;Waldron&Cassinelli2007).
The appropriatefeaturesin the He-like ions of Cv, Nvi, Ovii,
35 Å. The second-order lines of Fexvii at 16.777, 17.054, Neix,Mgxi,andSixiiilieintherangefrom5to45Å,whichis
and 17.097 Å contribute a bit to the wings of the Cvi line at coveredbyLETGS.
33.736 Å. The third-order Nex resonance line at 12.134 Å is Thelinefluxesofthesespecialcaseshavebeenmeasureda
blendedbytheSxiitransitionat36.500Å,andthesecond-order slightlydifferentwayfromtheotherlinesgiveninTable3.After
OviiiresonancelinecontributestothewingoftheSxiandSixiii the final overall multitemperature CIE-model fit (see Sect. 5),
featureat37.787Å.Somefreeunblendedhigher-orderlines are limitedwavelengthrangeswereselectedjustaroundtherelevant
giveninTable4.Thehigherorderlinesareimplementedinthe line features of the He-like ions. Then the lines from the ions
model fits of Sects. 5.1 and 5.2. First-order lines in the wave- under investigation were ignored from the model. In this way
lengthrangeabove50Åbelongtolowerionizationstagesofsil- thecontinuumisbasedonthemultitemperaturefitandpossible
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A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Table3.LinepositionsandlinefluxesinδOri. ion λa λb fluxc fluxd
0 obs
[Å] [Å]
ion λa λb fluxc fluxd Cvi 33.736 33.728(.008) 4.88(.39) 2.88
[Å0] [Åob]s Caxi 35.212 35.175(.078) 0.53(.18) 0.30
Sxv 5.038+.0664.977(.103)f 0.27(.15) 1.07 Caxi 35.576 35.580(.054) 0.62(.18) 0.35
Sixiv 6.182 6.168(.029) 0.05(.03) 0.14 Sxii 36.563+.398 36.500(.036) 0.74(.20) 0.40
Sixiii 6.648 6.635(.007) 0.14(.03) 0.43 Sixiii+Sxi 37.786+.773 37.787(.040) 0.83(.23) 0.43
Sixiii 6.688+.704 6.698(.011) 0.08(.03) 0.24 Sxi 39.240+.323 39.234(.036) 1.43(.29) 0.72
Sixiii 6.740 6.751(—) 0.01(.01) 0.03 Cv 40.268 40.240(.020) 2.74(.74) 1.35
Mgxii 8.422 8.423(.009) 0.09(.03) 0.21 Cv 40.729 40.730e 1.96(.53) 0.97
Mgxi 9.168 9.165(.008) 0.18(.04) 0.39 Cv 41.472 41.474(.024) 0.66(.32) 0.32
Mgxi 9.231 9.229(.010) 0.12(.04) 0.25 Mgx+Sixii 44.050+.020 44.031(.022) 0.85(.13) 0.39
Mgxi 9.314 9.315(.011) 0.08(.03) 0.17 Siix+xii 44.249+.165 44.265(.017) 0.92(.13) 0.41
Nex 9.710 9.716(.019) 0.08(.04) 0.17 Sixii 45.520+.680 45.533(.033) 0.20(.09) 0.09
Nex 10.24010.238(.012) 0.08(.03) 0.15 Sixi 46.300+.410 46.308(.062) 0.42(.11) 0.18
Fexix 10.64010.647(.008) 0.11(.04) 0.21 Mgx+Six 47.280+.500 47.410(.050) 0.58(.12) 0.24
Fexvii 11.13011.136(.019) 0.05(.03) 0.09 Arix+Sixi 49.180+.220 49.165(.025) 1.10(.16) 0.44
Fexvii 11.25111.274(.016) 0.09(.04) 0.16 Six 50.254+.305 50.284(.015) 1.07(.21) 0.42
Fexviii 11.53011.552(.009) 0.16(.04) 0.28 Six 50.524+.691 50.545(.031) 1.21(.20) 0.48
Nex 12.13412.131(.003) 1.00(.08) 1.66 Six 52.1784+.248 52.232(.038) 0.72(.22) 0.28
Fexxi 12.28612.271(.008) 0.28(.05) 0.45 Fexv+Siix 52.911+.834 52.838(.044) 1.04(.24) 0.39
Nixix 12.43012.437(.015) 0.08(.04) 0.13 Fexvi 54.710 54.700(.045) 0.72(.19) 0.26
Nixix 12.65412.662(.022) 0.07(.04) 0.11 Siix 55.356+.272 55.340(.028) 1.50(.22) 0.54
Fexx 12.818+.84712.845(.009) 0.25(.05) 0.39 Fexv 59.404 59.350(.103) 0.38(.15) 0.13
Fexx 12.946+.97812.973(.014) 0.12(.04) 0.18 ??? — 60.003(.078) 0.40(.15) 0.13
Siix+xiii 61.050-.8461.416(.087)f 1.90(.14) 0.61
??? —13.257(.016) 0.10(.04) 0.16
Neix 13.44713.450(.006) 1.45(.15) 2.15 Siix+xii 68.148+.548 68.328(.081) 0.70(.22) 0.20
Neix 13.55313.542(.007) 1.10(.14) 1.61 Siviii 69.825 69.812(.055) 0.81(.21) 0.23
Neix 13.70013.723(.011) 0.27(.05) 0.39
Notes:
Fexvii 13.82313.824(.009) 0.42(.06) 0.60
a:λ arethetheoreticalwavelengthvaluesfromKelly(1987).
Nixix 14.040+.08114.052(.008) 0.31(.05) 0.43 0
b:λ istheobservedwavelengthwiththestatistical1σerrorin
Fexviii 14.202+.25514.209(.005) 0.76(.11) 1.06 obs
parentheses.
Fexviii 14.344+.36114.364(.008) 0.34(.05) 0.48
c:inunits10 4photonscm 2s 1
Fexvii 15.01515.011(.002) 2.54(.11) 3.36 − − −
d:inunits10 13ergscm 2s 1
Oviii 15.17615.175(.012) 0.50(.10) 0.64 − − −
e:wavelengthfixedattheoreticalvalues
Fexvii 15.26015.264(.008) 1.03(.11) 1.34
f:broadline
??? —15.844(.013) 0.20(.12) 0.24
Oviii 16.00716.002(.006) 0.89(.11) 1.11
Fexvii 16.07316.092(.014) 0.34(.09) 0.42
Fexvii 16.229 16.220(—) <0.07 0.08
Table4.Higher-orderlinesandtheirlinefluxesinthespectrum
Fexix 16.28416.296(.020) 0.∼06(.03) 0.07
ofδOri.
Fexvii 16.77716.775(.003) 1.39(.09) 1.62
Fexvii 17.054 17.054e 2.48(.18) 2.89
ion λa λb λ /order fluxc
Fexvii 17.097 17.097e 1.02(.16) 1.18 0 obs obs
Ovii 17.76817.763(.012) 0.16(.05) 0.18 [Å] [Å] [Å]
Ovii 18.62718.628(.008) 0.58(.07) 0.62 Fexvii 15.015 30.020(.012) 15.010(.006) 0.27(.09)
Oviii 18.96918.968(.002) 6.60(.18) 6.91 Neix 13.447+.553 40.545(—-) 13.515(—-) 1.12(—-)
Nvii 20.910 20.894(—) 0.06(—) 0.05 Fexvii 15.015 45.004(.026) 15.001(.009) 0.47(.10)
Ovii 21.60221.614(.003) 6.29(.24) 5.81 Fexvii17.054+.097 51.204(.067) 17.068(.022) 0.50(.17)
Ovii 21.80421.793(.003) 5.57(.23) 5.07 Oviii 18.969 56.936(.030) 18.978(.010) 1.79(.24)
Ovii 22.101 22.101e 0.25(.09) 0.22 Ovii 21.602+.804 65.171(.165) 21.724(.055) 1.86(.52)
Caxiv+Sxiv24.133+.28524.167(.056) 0.26(.11) 0.21 Cvi 33.736101.222(.348) 33.741(.116) 2.02(.88)
Nvii 24.78124.788(.011) 1.38(.15) 1.11
Notes:
Arvii 25.68425.705(.030) 0.46(.12) 0.36
a:λ arethetheoreticalwavelengthvaluesfromKelly(1987).
Cvi 26.357 26.356(—) 0.26(—) 0.20 0
b:λ higher-orderobservedwavelengthwiththestatistical1σerror
Cvi 26.99026.990(.047) 0.30(.13) 0.23 obs
inparentheses.
Cvi 28.46628.462(.017) 0.57(.15) 0.40
c:inunits10 4photonscm 2s 1.
Nvi 28.78728.763(.028) 1.27(.20) 0.88 − − −
Nvi 29.08429.065(.037) 0.86(.18) 0.58
Nvi 29.53429.475(.060) 0.36(.14) 0.24
blendsaretakenintoaccount.Fromthatpointonthesamepro-
cedure was used as in Sect. 4: a Gaussian was folded through ThelinefluxratiosarecomparedwiththosegivenbyMilleretal.
theresponsematrixandfittedtothelineprofilesofeachionline (2002)usingHETGS. Theirvaluesandoursarein goodagree-
individually. The line flux ratios (f/i) obtained in this way are ment.TheratioshavebeenappliedtoaPlanckUV-radiationfield
collectedinTable6.Theymightdifferfromratiosderivedfrom of33000Katthewavelengthsofthe1s2s3S–1s2p3Ptransitions
Table 3, as in that table total feature fluxes, polluted by blends ofthecorrespondingions,incombinationwithscaledformulas
andsatellite linesare givenwith theirdominantidentifications. given by Blumenthal et al (1972). This UV radiation field de-
4
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Table6.He-likeandH-likeoverHe-likelinefluxratiosandcor- The influence of the UV radiation field on the population
respondingdistancesinR andtemperatures.Valuesobtainedby ofthe 1s2s3S and1s2p 3P levelsis reflectedinthe f/iratio,
1 1
Milleretal(2002)areals∗ogiven. hence in the distance to the stellar surface as shown in Fig. 4.
Theshapesofthecurvesare thesameasthosegivenbyMiller
thiswork Milleretal.2002 etal.(2002)forMgxi,Neix,andOvii. Thecurvesof Nviand
ion f/i distance(R ) f/i Cvarenewandestablishedasaresultofourinvestigation.The
Cv 0.31(.10) 75(14) ∗ —- boldintervalsonthetrajectoryshowtheaveragedistancefrom
Nvi 0.38(.17) 49(13) —- the stellar surface (includingthe 1σ statistical error)where the
Ovii 0.052(.016) 9.0(1.5) <0.2 ion is formed. From this figure it is clear that the hotter ions
Neix 0.10(.06) 3.4(1.1) <∼0.1 (MgxiandNeix)areformedclosertothestellarsurfacethanthe
Mgxi 0.73(.48) 3.2(1.4) 0∼.5(.4) coolerones(CvandNvi).Intheshortwavelengthsourresults
Sixiii <0.6 — 2.2(1.5) are in goodagreementwith Fig. 4 in the paperby Miller et al.
ion ∼(f +i)/r T(MK) f +i/r (2002) and with the values of Mgxi and Ovii by Waldron &
Cv 0.96(.34) 1.0 —- Cassinelli(2007),basedonHETGSobservations.Atthelonger
Nvi 0.86(.23) 1.6 —-
wavelengths,NviandCv(outsidetheHETGSrange)showthat
Ovii 0.93(.06) 1.7 0.78(0.35)
theX-raysareformedmuchfartheroutinthewindthanthewind
Neix 0.94(.14) 2.3 1.09(0.44)
accelerationzone,whichstopsatabout10R .TheNviislocated
Mgxi 1.08(.37) 2.1 0.54(0.28)
Mgxia 0.81(.23) 4.4 —- at 49(13)R and Cv at 75(14)R with temp∗eratures of 1.6 MK
Sixiii 0.69(.27) 8.0 0.84(0.34) and1.0MK∗ respectively(seeTa∗ble6).
Sixiiia 0.77(.22) 6.4 —- Only an upper value has been determined for Sixiii. This
ion rb/(r+i+ f)T(MK) feature is better imaged by HETGS, and therefore the distance
H
Cvi/v 0.91(.18) 1.18(0.07) ofitsplasmatothestellarsurfaceisexcludedfromTable6and
Nvii/vi 0.55(.09) 1.64(0.08) Fig. 4. Also included in Table 6 are the temperature indicators
Oviii/vii 0.55(.02) 2.44(0.02) G = (f + i)/r of the He-like ions, as well as the ratios of the
Nex/ix 0.35(.04) 3.8(0.1)
H-likeresonancelinesandtheHe-likelinetriplets. Theyresult
Mgxii/xi 0.24(.09) 6.0(0.5)
intemperaturesfortheX-rayemittingplasma,relatedtothelo-
Sixiv/xiii0.22(.14) 9.4(1.3)
cationofthespecificionsintheplasma.
Notes:
a:AverageofourvalueandtheHETGSvalueobtainedbyMilleretal.
(2002) 5. Multitemperaturefitting
b:r isthelinefluxfortheH-likeresonancelinedoublet
H
Along with the individual line analysis we investigated the
LETG-spectrum of δ Ori using a multithermal model for opti-
callythinplasmainCIEasimplementedinSPEX(Kaastraetal.
creaseswith distancefromthe stellarsurfacebya dilution fac- 1996a)incombinationwithMEKAL(Meweetal.1985,1995;
tor: Kaastraetal. 1996b)3. Itprovidesa calculationwiththousands
oflinesandamodelelectroncontinuum.Theionizationequilib-
1 R 2 1/2 rium is based on calculations by Arnaud & Rothenflug (1985)
W(r)= 1 1 ∗ . (1)
2  − −(cid:18) r (cid:19) !  aAnpdplAicrantaioundo&f aRanyomnoenqdui(li1b9r9iu2m), itohneizlaatttieornemspoedceialldlyidfonrotiriomn-.
As a result of the radial dependence of the radiation field, the provethedescriptionofthespectrum.
observed f/iratiocanbeusedtoderivetheradiallocationofthe The fits were applied using the C-statistics approach. For
He-likeionsthatareproducingtheobserved firlines. the transition probabilities of the model line features, an un-
certainty of 15% was assumed, a value that accords with the
NISTdatabase4.Thefirstcalculationwasfittedtothedata,tak-
ingtheerrorsonthedatacountrateintoaccount.Inthe follow
up of the fitting procedure the errors on the model count rate
were applied to avoid over-influences of incidental low count
ratebins.
5.1.A3-Tmodel
We started the fitting procedure with more fixed temperature
components, out of which only three components were signif-
icant. From that point on a three temperature (3-T) fit was ap-
plied for the CIE-model. The values of the fit are collected in
Table7.ThistableshowstheinterstellarcolumndensityN ,the
H
obtainedtemperatures,the emission measures,the luminosities
ofthedifferenttemperaturebins,absorptioncolumndensitiesfor
thethreetemperaturecomponentsinthewind,abundances,line
shifts(z),andlinebroadening(vmic).
Fig.4.The f/iratioversusthedistancetothestellarsurfacein 3 http://www.sron.nl/SPEX
stellarradii(R*). 4 http://www.nist.gov/pml/data/asd.cfm
5
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Table 7.The3-T fitto the LETGSspectrumof δ Ori, applying
aCIE-modeltothetotal(time)spectrum.Thedistanceisputat
212pc(VanLeeuwen2007).
Parameters
model
logN [cm 2] 20.18(.03)
H −
z(Redshift) -2.3(.5)e-4
v 1039(21)
mic
T [keV] 0.098(.005)
1
T [keV] 0.228(.008)
2
T [keV] 0.647(.010)
3
EM [1054cm 3] 2.05(.20)
1 −
EM [1054cm 3] 2.27(.09)
2 −
EM [1054cm 3] 0.88(.04)
3 −
L [1031erg/s]a 7.10
1
L [1031erg/s] 5.14
2
L3[1031erg/s] 2.59 Fig.5.ThespectrumofδOri(red/gray),togetherwiththemodel
LTot[1031erg/s] 14.83 (black) derived from the multitemperature fit applying the pa-
Nh [1020cm 2] 0.21(.16)
1 − rametersgiveninTable7.
Nh [1020cm 2] 1.52(.37)
2 −
Nh [1020cm 2] 26.7(4.0)
3 −
C 1.080(.016)
TheInterStellarMedium(ISM)N was fittedandfoundto
H
N 1.046(.020) be1.5 1020cm 2. Threeadditionalwindabsorptionparameters
O 0.859(.009) × −
wereappliedusingthehotmoduleinSPEX.Itdescribesawarm
Ne 1.243(.015)
plasma,astheCIE-model,whilecalculatingthecontinuumab-
Mg 1.650(.022)
Si 0.913(.012) sorption,aswellasthelineabsorption.Emissionlineswiththe
Fe 1.000(fix) highest oscillator strength are mostly influenced.The tempera-
C stat/d.o.f. 2836/1609 turesofthishotplasmawerecoupledtothetemperaturesofthe
−
C stat 1.76 components in the CIE-model. The hottest component, which
− red
is formed deeper in the wind (see Sect. 4), results in the high-
a:Intherangefrom0.07to3keV.(LETGSband). estabsorptioncolumndensity.Noabsorptionforthecoolwind
(33000 K) could be determined. This implies that the overall
coolstellarwindabsorptionisnottakenintoaccountandmight
Threestatisticallywell-determinedtemperaturecomponents havebeentakenoverpartlybythefittedISM-parameterNH.
at 0.10, 0.23, and 0.65 keV have been established. The two A slight shift in λ ( -2.3e-4) was applied to optimize the
≈
coolestcomponentscorrespondtothelinesoftheHe-likeions, fitted wavelengths. A line broadening parameter vmic of 1039
discussedinSect.4.Accordingtoconclusionsfromthatsection, km/s was added and fitted to the overall spectrum to take into
the hottestcomponent(0.65keV), thatis responsibleforSixiv accountthebroadeningofthelinefeatures.TheHWHMofaline
andS xvisformeddeeperinthewind. isrelatedtothevmic bythefollowingformula(seealsoSect.3):
Theresultsofthetotal3-Tfittothespectrumareshownin
Fig.5.Thelinesandcontinuafromthethreeindividualtempera- HWHM/λ = √ln2vmic. (5)
turecomponentsareshowninthethreetoppanelsofFig.6.The obs c
bottom panel shows the data with the calculated continuum as
sumofthethreecontinuaofthesecomponents. The X-ray luminosities of the three individual temperature
Thetabulatedemissionmeasureisdefinedas componentsaregivenovertheLETGenergyrangefrom0.07to
3.0keV.Fortheluminositiesnoindividualstatisticalerrorshave
EM =nenHV, (2) been determined. Their uncertainties are supposed to have the
samerelativevaluesasthosefortheemissionmeasuresbecause
inwhichn =0.85 n .
H e
× the luminosity is mostly determined by the emission measures
Knowledge of the electron density offers the possibility to
in this temperature range, and therefore L EM. The total
calculatetheX-rayemittingvolume.Theelectrondensityforhot X
∝
luminosities (summed over the three temperature components)
starswitha sphericallysymmetricstellarwindcanbeobtained
in other energy bands (0.5-4 keV, 0.1-2.4 keV, and 0.4-4 keV)
viathefollowingcontinuityequation:
for Einstein, ROSAT, ASCA given in the papers by Cassinelli
M˙ =4πR2ρ(R)V(R). (3) & Swank (1983), Haberl & White (1993), and Corcoran et al.
(1994),respectively,do agreewith ourvalueswhentaking dif-
Inthisformula M˙ isthemasslossrate(1.07 10−6M /year ferencesininterstellarabsorptionordistanceintoaccount.
(Lamers&Leitherer1993))forδOri,Risthedis×tancefr⊙omthe The abundances are relative to solar photospheric values
stellarsurface,ρ(R)thedensityatdistanceR,andV(R)thewind (Loddersetal.2009).Theabsolutevaluesoftheabundancesare
velocityatdistanceR,relatedtotheterminalvelocity(V )by stronglyinfluencedbytheobtainedvaluesoftheemissionmea-
∞
V(R)=V (1 R /R)β, (4) sures. The productofabundancesandemission measures(A ×
∞× − ∗ EM),however,istherobustquantityforthelinespectrum,there-
inwhichβisacoefficientbetween0.85forsubgiantsand1.1for fore,abundance-ratiosareoftengivenrelativetoanabundantel-
supergiants.Weuseavalueof1.0forβ. ementinthestellaratmosphere.Heretheabundanceofironwas
6
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
fixedatitssolarphotosphericvalue.Theabundancevaluesagree to 10 R , respectively. This is in accordance with observations
withthevalueof 0.9thatSimo´n-D´ıaz(2010)findsforoxygen by Wald∗ron & Cassinelli (2007) and Miller et al. (2002)using
≈
andsiliconabundancesintheOrionstar-formingregion. HETGS. Using LETGS that extendsto longerwavelengths, the
A fit to the spectrum taken by HETGS applying the same coolerions Nvi and Cv have been observedas part of this in-
setofparametersneedsalowervalueforv (seealsoSect.3). vestigation.TheX-raysfromtheseionsareformedonaverageat
mic
ThismightbeduetoinconsistencybetweentheLSFsoftheused 50R and75R ,respectively,muchfartheroutinthewindthan
instruments.AlsothedescriptionoftheSixiiiandSixivlinefea- thea∗cceleration∗zone,wherethefinalvelocityhasbeenreached.
turesisnotsatisfactory.Thismightbebecausethesefeaturesare Here the wind is expected to be steady. However, small devia-
neartheendofthecalibratedareaforbothinstruments. tionsinvelocity(weakshocks)willbeabletoproducethecooler
Toinvestigatethetimedependenceofthespectrum,assug- ions.
gestedbythelightcurve(seeFig1)wesplittheobservationinto ThespectrumisdescribedwellbyaCIEmodel.Threewell-
twotimeintervals,0-49ksand49-98ks.Theemissionmeasure distinguished temperature components have been determined:
ofthehottestcomponent(formedclosesttothestellarsurface)is 0.10, 0.23, and 0.65 keV. The first two are in good agreement
about10%lowerinthefirsttimeintervalthaninthelast49ks. with the two temperatures found by Haberl & White (1993).
Thismightagreewithsomeeclipsingbythecompanionstar. Theydidnotdetermineathirdtemperaturecomponent.Thetwo
lowertemperaturecomponents(0.098and0.228keV)describe
the line-forming regions of the cooler ions, Nvi and Cv, and
5.2.DEMmodeling
themoderatelyionizedspeciesMgxi,Neix,Ovii,andOviii,re-
To show the smooth connection between the separated tem- spectively,while thehottestcomponentis supposedto produce
perature bins, we performed a continuous DEM-modeling for evenhotterionsdeeperinthewindandahotcontinuum.
the spectrum of δ Ori by applying the regularization method Threeemission measuresare established, related to the ob-
(Kaastraetal.1996b)intheSPEX-code.Thismethodusesdirect tained temperatures. Knowledge of the electron density offers
matrix inversionwith the additionalconstraintthat the second- thepossibilitytocalculatetheX-rayemittingvolume.Applying
orderderivativeof the solution with respectto the temperature thedistances(seeTable6andFig.4)andthewindvelocityand
isassmoothaspossible.InthisDEMmodelingtheabundances densityformulas4and5,giveninSect.5.1,wehavecalculated
giveninTable7havebeenused.TheresultsareshowninFig.7. theelectrondensitiesfortheregionswherethespecificionspro-
Theresultsofthefits,collectedinTable7andFig.7,arein duceX-rayradiation.
good agreement. The peak of our DEM agrees with the peaks BecausethedistancesgiveninTable6andFig.4areaverage
foundbyMilleretal. (2002)andWojdowski&Schulz(2005). valueswiththestatisticalerroronthisaverageandnotthe lim-
However, our DEM extends more to lower temperatures and its of the X-ray emitting distance, it is difficultto calculate the
their values extend further to higher temperatures as a conse- total wind volume in which the conditions are optimal for the
quenceofusingtwodifferentinstruments.Thepeakvaluegiven corresponding He-like ion emission. By assuming a wind vol-
byWojdowski&Schulz(2005)ishigher. umefromhalftotwicetheobtainedaveragedistancewegetthe
percentageofthewindthatcontributestothation.Theemitting
As forthe CIE-fit we also performeda DEM-modelingfor
the partial spectra of 0-49 ks and 49-98 ks, again applying the volumesareabout1%ofthewindvolumeforthecoolerplasma
regularizationmethod.ThesetwoDEM-modelingsareshownin andlessforthehotterions.
Fig. 8. Although the hottest component is again a bit stronger TheNH oftheISMismainlybasedonthelongwavelength
for the last 49 ks, no significant difference can be established partofthespectrum.Itsvalueof1.51(.06) 1020cm−2 isingood
betweenfitstothepartialspectra. agreementwiththevalueof1.56 1020cm−×2foundbyJenkinset
×
al.(1999)basedon57IUEobservations,andslightlylowerthan
thevaluefoundbyHaberl&White(1993)fortheirT=0.1keV
6. Discussionandconclusions component. Additional wind absorption column densities have
been determined(see Table 7). They are related to the temper-
The X-ray spectrum of the O-star δ Ori obtained with LETGS ature components of 0.10, 0.23, and 0.65 keV, with distances
isrichinlinesbelongingtoH-likeandHe-likeionsofC,N,O, to the stellarsurfaceof about60R , 6R , and2R , respectively,
Ne, Mg, and Si. A weak He-like (Sxv) triplet is also present. wheretheplasmaisformedonaver∗age.I∗ncombin∗ationwithfor-
Otherpossibleweakfeaturespresentbelow5Åfalloutsidethe mula 4 we calculated that about7% of the wind contributesto
calibratedbandwidthoftheLETGS.IronL-shelllinesaredomi- thehotwindabsorption.Noabsorptionoftheoverallcoolstel-
nant.TheNe-liketransitions,betweenelectronconfigurationsof lar wind could be determined. This means that this absorption
aninertnoblegas,arefavoredforiron(FeXVII)aswellasfor componentisnotexplicitlytakenintoaccountduringthefitting
calcium(CaXI),andnickel(NiXIX). procedure. However, the effect might have been taken over by
Above 50 Å a few new line features were identified, some theotherabsorptionparameters.
of whichare third-orderlinesassociated with strongfirst-order The X-ray luminosities of the three temperature compo-
featureslocatedbetween15and35Å.Nolinesofcoolionswere nentsinthetotalLETGSband(0.07-3keV)are7.10,5.14,and
detectedatwavelengthshigherthan70Å.Themainreasonsfor 2.59 1031erg/s. Two partial spectra were derived: one from the
theabsenceoftheselinefeaturesistheabsenceofanoticeable first49ksandanotherfromthelast49ksoftheobservation.This
volumeofcool(0.05keV)plasmaandtheinterstellarabsorption. divisionwassuggestedbythelightcurve(seeFig1).Nosignif-
Basedontheforbiddenlineoverintercombinationlineratio icant differences between the spectra, their temperature struc-
inHe-likeionstheaveragedistanceoftheX-rayemittingplasma tures,theirlineshapes,orlinefluxeshavebeenestablished.
tothestellarsurfacehasbeendetermined.Dependingontheion The obtained abundancesare relative to solar photospheric
(temperature),theplasmaemittingregionisbetween2and80R values (Lodders et al. 2009). They were fit by fixing the iron
forionsfromMgxitoCv.Thecoolerplasma(lowerionization∗ abundanceatitssolarphotosphericvalueandleavingthecarbon,
stages)islocatedfartheroutinthewind.Forthehotions,Mgxi, nitrogen,oxygen,neon,magnesium,andsiliconabundancesfree
Neix, and Ovii, the average X-ray emitting plasma is from 2 to vary.Fixingtheironabundancewasdonebecausethe abun-
7
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
dancesandemissionmeasuresarestronglyanticorrelated,espe- Leutenegger,M.A.,Paerels,F.B.S.,Kahn,S.M.,&Cohen,D.H.2006,ApJ,650,
ciallyinspectrawithaweakcontinuumtoestablishtheemission 1096
measure.Theobtainedvaluesforoxygenandsiliconareingood Lodders, K., Palme, H., & Gail, H.-P., 2009, Landolt-Bornstein, New
Series, Astronomy and Astrophysics, Springer Verlag, Berlin (eprint
agreementwithvaluesfoundbySimo´n-D´ıaz(2010)intheOrion
arXiv:0901.1149)
star-formingregion. Lucy,L.B.1982,ApJ,255,286
The lines are symmetric and their HWHMs are about Lucy,L.B.,&White,R.1980,ApJ,241,300
840 km s 1, far below the terminal velocity of 2000 km s 1, Lucy,L.B.,&Solomon,P.M.1970,ApJ,159,879
− − Mayer,P.,Harmanec,P.,Wolf,M.,Bozˇic,H.,&Sˇlechta,M.2010,A&A,520,
but higher than the values found by Miller et al. (2002) using
A89
HETGS.Thismightbeduetoinconsistenciesbetweentheinstru-
Mewe,R.,Gronenschild,E.H.B.M.,&vandenOord,G.H.J.1985,A&AS,62,
mental line spread functions in the calibration files of HETGS 1(mekal)
andLETGS.Theultimatevelocities,measuredattheendofthe Mewe,R.,Kaastra,J.S.,&Liedahl,D.A.1995,Legacy6,16
wings,areabout1850kms 1withanuncertaintyof200kms 1. Miller,N.A.,Cassinelli, J.P.,Waldron,W.L.,MacFarlane, J.J.,&Cohen,D.H.
− − 2002,ApJ,577,951
The measuredline shiftsgivenin Table 5, as well as the z-
Oskinova,L.M.,Feldmeier,A.,&Hamann,W.-R.2006,MNRAS,372,313
valuegiveninTable7,indicatethatthevelocityoftheradiative Owocki,S.P.,&Cohen,D.H.2006,ApJ,648,565
plasmainthedirectionfromortotheobserverislow.Thisiswell Owocki,S.P.,Castor,J.I.,&Rybicki,G.B.1988,ApJ,335,914
known for OB stars, especially among giants and supergiants Pollock,A.M.T.,2007,A&A,463,1111
Raassen, A.J.J., van der Hucht, K.A., Miller, N.A., & Cassinelli, J.P., 2008,
(Waldron&Cassinelli2007).
A&A,478,513
The conclusion should be that the radiation we observe is
Seward,F.D.,Forman,W.R.,Giacconi,R.,etal.1979,ApJ,234,L55
producedin plasma that has a very low velocity or movesper- Simo´n-D´ıaz,S.2010,A&A,510,A22
pendicularto thelineof sight.Theremightbeseveralexplana- Tarasov,A.E.,Harmanec,P.,Horn,J.,etal.1995,A&AS,110,59
tions.Theclumps,whichcollidewiththewindandproducethe VanLeeuwen,F.2007,A&A,474,653
Voels, S.A.,Bohannan, B., Abbott, D.C.,& Hummer, D.G.. 1989, ApJ, 340,
X-rayradiation,havelowvelocities.Inthatcasetherelativeve-
1073
locity of the clumps to the wind is highest far out in the wind Waldron,W.L.,&Cassinelli,J.P.2001,ApJ,548,L45
at terminalwind velocity. As a consequencethe higheststages Waldron,W.L.,&Cassinelli,J.P.2007,ApJ,668,456
ofionizationareproducedfaroutinthewind,whichcontradicts Wilson, R.E. 1963, General Catalogue Of Stellar Radial Velocities, Carnegie
InstitutionofWashingtonpublication601
ourobservationbasedontheforbidden-to-intercombinationline
Wojdowski,P.S.,&Schulz,N.S.2005,ApJ,627,953
ratiosinHe-likeions(seeFig.4).Additionally,afterthe accel-
eration phase one does not expect velocity differences that are
too high. The secondary star and its wind play importantroles
in the explanation of the δ Ori spectrum. However, this is dis-
cussedbyMilleretal.(2002)andrejected.Athirdoptionisthat
the clumps screen their own X-ray radiation when they are in
between the star and the observer. Only when the wind-clump
collision is almost perpendicular to the line of sight is the ra-
diation observable and spread over a narrow velocity range as
derivedfromtheHWHM.Theeffectsofclumpingandporosity
onX-Rayemission-lineprofilesfromhot-starwindshavebeen
describedextensivelybyOwocki&Cohen(2006)andOskinova
etal.(2006).
Acknowledgements. TheSRON National Institute forSpace Research is sup-
portedfinanciallybyNWO.
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8
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Fig.7. DEM-modeling of δ Ori, based on the regularization
method (Kaastra et al. 1996b) (see text). The EM is given in
unitsof1054cm 3.
−
Fig.8. DEM-modeling of δ Ori, based on the regularization
method.ThetwoDEMsshowamodelingofthespectrumover
thetimeinterval0-49ks(red/gray)and49-98ks(black).
Fig.6.ThespectrumofδOri(red/gray),togetherwiththethree
individualtemperaturecontributionstothemodel(black),apply-
ingtheparametersgiveninTable7.Theyimplythelineandcon-
tinuum radiation from the individual components. The bottom
panelshowsthemodelelectroncontinuum(black).Thisimplies
thesumofthethreecontinua.
9
A.J.J.Raassen&A.M.T.Pollock:TheLETGSX-rayspectrumofδOrionis
Fig.3.PartofthespectrumofδOri.Themostdominantlinesareindicated.Dataareinred(gray),theCIE-modelinblack)
Table5.Wavelengthshiftsandhalfwidthathalfmaximum(HWHM)valuesforsomestrongisolatedlinesinthespectrumofδOri
ThevalueshavebeencomparedwiththosefromMilleretal.2002.
ion λa λ ∆λ shift shift(Miller) HWHM HWHM(Miller)bluewing redwing
0 obs
[Å] [Å] [Å] inkms 1 inkms 1 inkms 1 inkms 1 inkms 1 inkms 1
− − − − − −
Nex 12.134 12.1305(.0030) -0.0035(.0030) -87(74) -150(100) 653(123) 420(170) -1168 1246
Fexvii15.015 15.0100(.0023) -0.0050(.0023) -100(46) -50(100) 840(80) 510(220) -1734 1915
Fexvii16.777 16.7745(.0034) -0.0025(.0034) -45(57) 100(150) 853(89) 420(250) -1804 1783
Oviii 18.969 18.9684(.0015) -0.0006(.0015) -9(24) 60(100) 854(30) 700(100) -2009 2067
Ovii 21.602 21.6148(.0038) 0.0128(.0038) 178(53) ——- 792(47) ——– -1808 1826
Ovii 21.804 21.7930(.0041) -0.0110(.0041) -151(56) ——- 812(61) ——– -1915 2066
Nvii 24.781 24.7866(.0100) 0.0056(.0100) 68(121) 120(400) 750(169) 420(870) -1704 1669
Cvi 33.736 33.7252(.0050) -0.0108(.0050) -96(44) ——- 835(55) ——– -1834 1751
Notes:
a:λ arethetheoreticalwavelengthvaluesfromKelly(1987).
0
10