Line identification in soft X-ray spectra of stellar coronae by comparison with the hottest white dwarf's photosphere: Procyon, alpha Cen A+B, and H1504+65

0.09 MB·English

by  K. Werner

Astronomy&Astrophysicsmanuscriptno.2057 February2,2008
(DOI:willbeinsertedbyhandlater)
Line identification in soft X-ray spectra of stellar coronae by
comparison with the hottest white dwarf’s photosphere:
α +
Procyon, Cen A+B, and H1504 65
K.Werner1 andJ.J.Drake2
5
0 1 Institutfu¨rAstronomieundAstrophysik,Universita¨tTu¨bingen,Sand1,72076Tu¨bingen,Germany
0 2 Harvard-SmithsonianCenterforAstrophysics,MS3,60GardenStreet,Cambridge,MA02138,USA
2

n Receivedxxx/Acceptedxxx
a
J
Abstract.H1504+65isayoungwhitedwarfwithaneffectivetemperatureof200000Kandisthehottestpost-AGBstarever
3 analysed withdetailed model atmospheres. Chandra LETG+HRC-Sspectra have revealed the richest X-ray absorption line
1
spectrumrecordedfromastellarphotospheretodate.Thelineformingregionsinthisextremelyhotphotosphereproducemany

transitionsinabsorptionthatarealsoobservedinemissionincoolstarcoronae.Wehaveperformedadetailedcomparisonof
1
ChandraspectraofH1504+65withthoseofProcyonandαCenAandB.Stateoftheartnon-LTEmodelspectraforthehot
v
whitedwarfhaveenabledustoidentifyawealthofabsorptionlinesfromhighlyionizedO,NeandMg.Inturn,thesefeatures
8
4 haveallowedustoidentifycoronallineswhoseoriginswerehithertounknown.
2
1 Keywords. stars:atmospheres–stars:coronae–X-rays:stars–stars:individualProcyon–stars:individualαCen–stars:
0 individualH1504+65
5
0
/
h 1. Introduction fraction of the forestof weaker featuresremainsunidentified.
p Identificationofthesefeaturesisdesirablebecausetheycould
- High-resolution X-ray spectroscopy performedwith Chandra beusedasspectroscopicdiagnostics,becausetheypotentially
o
and XMM-Newton allows very detailed studies of coronae
r contribute to the flux of diagnostic lines currently employed,
st about cool stars. While many individual emission lines were andbecausetheycontributetotheoverallplasmaradiativeloss.
a detected for the first time in stellar spectra by the Extreme
: Ultraviolet Explorer Satellite (EUVE; see, e.g., Drake etal. Two nearby stars that have illuminated the forest of lines
v
i 1995),theresolvingpowerofλ/∆λ ∼ 200oftheEUVEspec- in the 30-170 Å range are αCen (G2V+K1V) and Procyon
X (F5IV). All three stars exhibitclassical solar-like X-ray emit-
trographs was a quite modest compared with that of present
r day X-ray observatories. In particular, the unprecedentedres- ting coronae. Indeed, analogues of the relatively X-ray faint
a Sun are difficultto observebecause theybecomeunreachable
olution capabilities of the Chandra X-ray Observatory Low
withcurrentinstrumentationbeyondafewparsecs,andαCen
EnergyTransmissionGratingSpectrograph(LETG)inthe30-
170Årange(λ/∆λ∼1000)thatoverlapswiththeEUVEShort andProcyonrepresentthenearestandbrightestcoronalsources
with solar-likeactivity.Onlya smallfractionof the multitude
Wavelength spectrometer (70-170 Å), have revealed many
oflinesbetween30-170ÅseenintheirChandraLETGspec-
moreweakspectrallines.
tra could be identified based on current radiative loss models
The 25-70 Å region is a relatively uncharted part of the
(Raassen etal. 2002, 2003). Drake etal. (in prep.) have esti-
soft X-ray spectrum. Prior to Chandra, only a small handful
matedthatthesemodelsunderestimatethetruelinefluxinthe
of astrophysical observations had been made at anything ap-
range30-70Åinthesestarsbyfactorsofupto5orso.
proachinghighspectralresolutioninthisrange:thesewereof
thesolarcoronausingphotographicspectrometers(Widing& The “missing lines” are predominantly transitions involv-
Sandlin1968;Freeman&Jones1970;Schweizer&Schmidtke ing n = 2 ground states in abundant elements such as Ne,
1971;Behringetal.1972;Actonetal.1985)achannelelectron Mg,Si,SandAr—theanalogoustransitionstotheFe“L-shell”
photomultiplier (Malinovsky & Heroux 1973) and a Geiger- linesbetween∼8-18Å,togetherwithFen=3(the“M-shell”)
Mu¨llercounter(Manson1972).Whiletheseworksresultedin transitions(Drake1996,Drakeetal.1997,Jordan1996).Some
identifications for many of the bright spectral lines, a large of these lines have been identified based on Electron Beam
Ion Trap experiments (Beiersdorfer etal. 1999, Lepson etal.
Sendoffprintrequeststo:K.Werner 2002, 2003). In the present paper we approach this problem
Correspondenceto:[email protected] from a new perspective, namely through a Chandra observa-
2 K.Werner&J.J.Drake:LineidentificationinsoftX-rayspectraofstellarcoronae
7
tionofthephotosphereofthehottestwhitedwarf(WD)known,
H1504+65,andits quantitativeanalysisbymeansofdetailed
photosphere model
non-LTEmodelatmospheres.
NeVII
H1504+65hasaneffectivetemperatureof200000K.Itbe- MgVII MgVII
6
longs to the PG1159 spectral class, which are hot, hydrogen-
deficient(pre-)white dwarfs.Theirsurfacechemistry(typical
abundances: He=33%, C=48%, O=17%, Ne=2%, mass frac-
tions)suggeststhattheyexhibitmatterfromthehelium-buffer
layer between the H- and He-burningshells in the progenitor 5
AGB star (Werner 2001). This is likely because the PG1159
stars have suffered a late He-shell flash, a phenomenon that
drives the fast evolutionary rates of such famous stars like st
n
FGSge and Sakurai’s object. H1504+65 is in fact a peculiar co4
memberofthisclass,becauseitisalsohelium-deficient.Itsat- +
s
mosphereismainlycomposedofcarbonandoxygenplusneon nt
u
and magnesium (C=48%, O=48%, Ne=2%, Mg=2%, mass co H1504+65
Tfreaffctainodnsc)h.eHm1ic5a0l4s+u6rf5aciseacoumnpiqouseitioobnj,eacnt,dcwoneshidaevreinspgeictsulhaitgedh elative 3 & dmeogdraedled
that it represents the naked C/O core of a former red giant r
(Werneretal.2004,W04).
MgVII
ChandraLETG+HRC-SspectrafromH1504+65havere- SiVI
2
vealed the richest X-ray absorption line spectrum recorded
fromastellarphotospheretodate.Wehaverecentlyperformed
NeVII
adetailedanalysisofthisspectrum(W04)andweuseinthepa-
perinhandthephotosphericspectrumofH1504+65together
1
with an appropriate model atmosphere to identify a number
of emission lines in the coronae of αCenA, αCenB, and
Procyon. The difference in particle densities in the WD pho-
Procyon
tosphere and in the coronae amounts to many orders of mag-
nitude (roughly n =1013 − 1018 and 1010cm−3, respectively), 0
e 83.5 84.0 84.5
however, the temperature in the line forming regions of the λ / Ao
WD (up to 300000K) is comparable to the low-temperature
Fig.1. Comparison of Chandra X-ray spectra of H1504+65 and
componentofmulti-temperaturefitstocoronae,requiredtoac-
Procyon.LinesfromMgandNeareinabsorptioninH1504+65
countforthelinesoflow-ionizationstages(e.g.630000Kfor
andinemissioninProcyon.Top:photospheremodelforH1504+65
Procyon; Raassen etal. 2002). As a consequence, numerous
with line identifications for Mg and Ne. Middle: Degraded
lines from O, Ne- and Mg- are visible in the soft
model spectrum (i.e. folded with a 0.05 Å FWHM Gaussian) plot-
X-rayspectraofboth,the coolstar coronae(inemission)and ted over H1504+65 observation. Bottom: Procyon spectrum with
thehotWDphotosphere(inabsorption).Linesfromhigherion- lineidentificationsfromRaassenetal.(2002).Chandraspectrawere
izationstagesareformedinthehigh-temperatureregionsofthe smoothedwitha0.03Åboxcar.
coronae(Toftheorder1–2.5millionKforthestarsstudiedin
thispaper),hence,theirrespectiveabsorptionlinecounterparts
cannotbeformedintheWDphotosphere. tectednear110Å.Between105Åand100Åthefluxdropsbe-
Inthefollowing,wefirstintroducebrieflythecharacteris- causeofphotosphericabsorptionfromtheOedgecausedby
tics of the objectsstudiedhere. We describeour modelatmo- thefirstexcitedatomiclevel.Theedgeisnotsharpbecauseof
spherecalculationforthehotWD,concentratingontheatomic aconverginglineseriesandpressureionization.Below100Å
dataemployed.Wethenperformadetailedcomparisonofthe the flux decreases, representing the Wien tail of the photo-
absorptionandemission linespectraandsuggesta numberof sphericfluxdistribution.Thecompletespectrumwithdetailed
newlineidentificationsforthecoolstarcoronae. lineidentificationswaspresentedinW04.
TheαCenAandBobservationhasbeendescribedindetail
byRaassenetal. (2002)andwedescribeithereonlyinbrief.
2. Observations
αCenwasobservedwiththeLETG+HRC-SonDecember25,
H1504+65wasobservedwiththeChandraLETG+HRC-Son 1999 with an exposure time of 81.5ks, including dead time
September27,2000,withanintegrationtimeofapproximately correctionstoaccountfortelemetrysaturationduringintervals
25ks. Flux was detectedin the range 60 Å–160Å. The spec- of high background. The observation was designed such that
trum is that of a hot photosphere, characterized by a contin- thetwostarsweremaximallyseparatedinthecross-dispersion
uumwithalargenumberofabsorptionlinesfromhighlyion- axis, with the dispersion axis positioned nearly perpendicular
izedspecies:O-,Ne-,andMg-.Itrollsoffatlong totheaxisofthebinary.Atthetimeoftheobservation,thestars
wavelengthsduetoISMabsorption.Themaximumfluxisde- were separatedby16′′ onthe sky.Thespectrawere extracted
K.Werner&J.J.Drake:LineidentificationinsoftX-rayspectraofstellarcoronae 3
MgVIII MgVII
7
NeVII NeVIII
6 photosphere model
st5
n
o
c
+
s
nt4
u
o H1504+65
e c & degraded model
v
ati3
el
r
2
αCenA
1
Procyon
0
86.5 87.0 87.5 88.0 88.5
λ / Ao
Fig.2.ComparisonofChandraX-rayspectraofH1504+65withProcyonandαCenA,similartoFig.1.Allshownlinesfromhighlyionized
NeandMgareidentifiedforthefirsttimeinthecoolstarcorona,exceptforMg86.85/87.02 ÅandtheNedoubletat88.1Å,which
wereidentifiedbyRaassenetal.(2002,2003).ChandraspectraofH1504+65andthecoronaeweresmoothedwith0.03Åand0.05Åboxcars,
respectively.
withthestandardCIAObow-tieregion,thoughthecentraltwo nesium. They comprise 88 and 122 NLTE levels, connected
backgroundregionsinterferedwiththestellarspectraandonly with312and310radiativelinetransitions,respectively,inthe
theouterregionswereusedforbackgroundsubtraction. ionizationstages -.Thefinalsyntheticspectrumwascom-
The two Procyonobservationsstudied herewere obtained puted considering fine structure splitting of levels and multi-
with the LETG+HRC-S as part of the Chandra on-orbit cal- pletsassumingrelativeLTEpopulationsforlevelswithinapar-
ibration programmeand Emission Line Project. The observa- ticular term. We have tried to use the best available data for
tions were executed contiguously beginning on November 6, levelenergiesandlinewavelengths,compilingthemfromsev-
1999 at 21:11:32UT. The second observationbegan on 1999 eral sources. For the lines discussed here (Table 1), we used
November16:59:48UT.Theeffectiveexposuretimesforthese thefollowingdatabases:
observationswere69,643sand69,729s,respectively,including (i)NationalInstituteofStandardsandTechnology(NIST)1,
deadtimecorrections. (ii)Cdatabase(Youngetal.2003)2,
ReductionoftheHRC-Seventlistsforalltheobservations (iii)KellyAtomicLineDatabase3.
wasinitiallybasedonstandardpipelineproducts.Eventswere However,inordertoassemblethecompletemodelatoms,other
furtherfiltered inpulse heightin orderto removebackground sourceswereessential,too:
events. The final reduced first orderspectra were co-addedin (iv)OpacityProject(OP,Seatonetal.1994)TOPbase4,
orderto maximise the signal. In the case of Procyon,we also (v)UniversityofKentuckyAtomicLineList5.
co-addedthetwoseparateobservations.
4. ComparisonofH1504+65withαCenA,αCenB,
3. PhotosphericmodelforH1504+65 andProcyon
We use here a photospheric spectrum from a line blanketed We have performed a detailed comparison of the H1504+65
non-LTE model atmosphere constructed for H1504+65 by photosphericabsorptionline spectrum with the coronalemis-
W04.Modelparametersare:T =200000K,logg=8[cms−2], sion line spectra of αCenA, αCenB, and Procyon. We have
eff
and C=48%, O=48%, Ne=2%, Mg=2%, (mass fractions). 1 http://physics.nist.gov/
Details of model assumptions and calculations can be found 2 http://wwwsolar.nrl.navy.mil/chianti.html
inthatreferenceandwerestrictourselvesheretothosecharac- 3 http://cfa-www.harvard.edu/amdata/ampdata/kelly/kelly.html
teristicswhichareofimmediaterelevanceinourcontext.This 4 http://legacy.gsfc.nasa.gov/topbase/home.html
primarilyconcernstheNLTEmodelatomsforneonandmag- 5 http://www.pa.uky.edu/∼peter/atomic/
4 K.Werner&J.J.Drake:LineidentificationinsoftX-rayspectraofstellarcoronae
Table1.ListofX-raymultipletsinthewavelengthregion69–151ÅobservedinboththeH1504+65photosphereoritsmodelandinthecoronae
ofeitherαCenA(“A”),αCenB(“B”),orProcyon(“P”),assuggestedinthispaper.Inthelastcolumn,wenoteearlierlineidentificationsin
eithersolarspectra(SA=Actonetal.1985; SB=Behringetal.1972; SF=Freeman&Jones1970; SM=Manson1972; SMH=Malinovsky&
Heroux1973;SW=Widing&Sandlin1968)orstellarspectra(D=Drakeetal.1995;R=Raassenetal.2002,2003).Theletter“u”isappended
inthecaseofthefeaturehavingbeenobservedbutnotidentified.“N”denotesanewidentificationsuggestedinthispaper.“N”incombination
withotherlettersmeansthatatleastonecomponentofthemultipletisnewlyidentifiedhere.Expressionsinbracketsdenotedoubtfulcases.
Thecolumn“Source”givesthereferencetothelevelenergiesofthetransition.Aftereachtransitionwehavemarked,ifthelowerlevelisa
groundstate(“G”)orametastablestate(“M”).
λ/Å(H1504+65model) Seenin Ion Transition Source Remark
69.41,.47,.57 A,B,P Mg 2p 2Po –3p 2D G N N,SMu,blendwithbluewingof
– Si69.63Å
74.27,.32,.34,.37,.41,.43 A,B,P Mg 2p24P –3d 4Do M N N,SAu,SMu,broademissionfeature
74.78,.81,.87 A,B Ne 2p 3Po –4p3D M N N,SAu,SBu,SMu,blendwithMg74.86Å
74.86,75.03,.04 A,B,P Mg 2p 2Po –3d 2D G N SA,SB,SF,SM,SMH,SW,R,blendwith
– Fe74.85notedbyR,andNe74.87Å
(78.34),78.41,78.52 A,B,P Mg 2p33P –3p 3Po G Kelly N,SAu,SMu
80.23,.25 A,B,P Mg 2p22D –3d 2Do N SMu,R
80.95,81.02,.14 A,(B,P) Mg 2p33P –3p 3So G Kelly N,SAu,SMu
81.37 (A),B,P Ne 2p 1Po –4p1P Kelly N
81.73,.79,.84,.87,.94,.98 A,B,P Mg 2p24P –3s 4Po M N N,SFu,SMu,broademission,blendwith
– Si81.89ÅnotedbyR
82.17,.20,.27 A,B,(P) Ne 2p 3Po –4d3D M Kelly N
(82.60),.82 A,B,P Mg 2p 2Po –3s 2S G N (SBu,SFu),SM,R,blendwithFe82.84Å
– notedbyR
83.51,.56,.59,.64,.71,.76 A,B,P Mg 2p33P –3d 3Po G Kelly N,SBu,SF,SW,SM,D,R,broademission
– feature;poss.SiVIcontributionnotedbyR
83.91,.96,.99,84.02,.09,.11 A,B,P Mg 2p33P –3d 3Do G Kelly N,SB,SF,SM,SMH,R,broad
– emissionfeature
(84.19,.23,).30 A Ne 2p 3Po –4s3S M Bashkin SMu,R
85.41 (A,B,P) Mg 2p21D –3d 1Fo M Kelly N,SBu,SMu,blendwithFe85.46Å
– notedbyR
86.82 A,B,P Ne 2p21D –4d1Fo M Kelly N,SBu,SFu,SMu,blendwithFe86.77,
– Mg86.84ÅnotedbyR
86.84,.85,87.02 A,B,P Mg 2p22D –3s 2Po N N,SBu,SFu,SMu,R
87.46 A Ne 2s21S –3s1Po G N N
87.72 A Mg 2p21D –3d 1Do M Kelly N
88.08,88.12 A,B,P Ne 2s 2S –3p2Po M N SA,SB,SF,SM,SMH,D,R
88.68 (A),B,P Mg 2p21S –3d 1Po M Kelly N,SMu
89.64,.65 A,(P) Mg 2p32Po –4s 2P M Kelly N,SBu
91.56 P Ne 2p 1Po –4s1S Kelly SMu,R
92.13,.32 A,B,P Mg 2p22S –3s 2Po N N,SMu,SBu,R
92.85 P Ne 2p21S –4d1Po M Kelly SMu,R
(93.89),94.07,.10,(.27) A,B,P Mg 2p 2P –3s 2Po N N,(SAu,SBu),SMu,blendwith
– Fe94.012Å,Mg94.04Å
94.04,(.17,.24) A,B,P Mg 2p35So –3s 5P M Kelly N,SMu,SFu,blendwithFe94.012Å
– notedbyR,andMg94.07Å
alsousedthemodelspectrumofH1504+65forthispurpose.It truminadditiontotheH1504+65spectrumhelpsconsiderably
turnsoutthatnotalllinespredictedbythemodel,particularly toidentifylinesinthecoronalspectra.
theweakerones,arereadilyidentifiedinH1504+65,whichis
atleastinpartduetotheS/NoftheChandraspectrum.Another Table 1 summarizes the results of our comparison. Lines
from 65 multipletsof O, Ne-, and Mg- are iden-
reason is heavy blending by lines from iron group elements,
tified in both,H1504+65(oritsmodel)andin atleast oneof
whicharenotconsideredinthemodelusedhere.Itwasshown
that identification of weak lines suffers from iron and nickel theconsideredcoronae.Manyofthesehadalreadybeenidenti-
fiedinearliersolarwork(Widing&Sandlin1968;Freeman&
lineblends,whichisaproblembecausetheaccuratepositions
Jones1970;Behringetal.1972;Manson1972;Malinovsky&
ofthemajorityoflinesfromFe-groupelementsinthesoftX-
Heroux1973;Acton et al. 1985)and by Raassen etal. (2002,
raydomainisunknown(W04).Theuseofoursyntheticspec-
2003),butthemajorityrepresentsnewidentifications.Table1
also denotes lines or features seen in earlier solar spectra but
K.Werner&J.J.Drake:LineidentificationinsoftX-rayspectraofstellarcoronae 5
Table1.continued
λ/Å(H1504+65model) Seenin Ion Transition Source Remark
94.26,.27,.30,.31,.36,.39 B Ne 2p 3Po – 3p3P M Bashkin N,SMu
95.03,.04 B Mg 2p33Do – 3s’3D Kelly N
95.26,.38,.42,.49,.56,.65 (A,B,P) Mg 2p33P – 3s 3Po G Kelly N,SBu,SFu,SMu,blendwithFe95.338Å
– notedbyR;Mg95.42Å
(95.38,.42,.48) (A,B,P) Mg 2p34So – 3d 4P G Kelly SBu,SFu,SMu,R,blendwith
– Mg95.26–.65Å
95.75,.81,.89,.90,.91,96.0 A,B,P Ne 2p 3Po – 3p3D M Bashkin N,SMu,broademission,blendwith
– Si96.02ÅnotedbyR
96.08,.09 (A,B,P) Mg 2p32Po – 3d”2D M Kelly N,SBu,SMu,blendwithFe96.12Å
– notedbyR
97.50 A,B,P Ne 2s21S – 3p1Po G Kelly SM,SW,SMH,R
98.11,.26 A,B,P Ne 2p 2Po – 3d2D N SB,SM,SMH,SW,D,R
98.50,.51 B Mg 2p32Po – 3d’2S M Kelly N,SBu,SMu
99.69 B O 2s – 6p G Kelly N,SMu
100.70,.90 A Mg 2p32Do – 3d2F M Kelly N,SBu
101.49,.55 B Mg 2p32Do – 3d2P M Kelly N,SBu,SMu
102.91,103.08 A,B,P Ne 2p 2Po – 3s2S N SM,SMH,SW,D,R
103.09 (A,B,P) Ne 2p 1Po – 3p1D Kelly N,SBu,blendwithNe103.08Å
104.81 B,P O 2s – 5p G Kelly SMu,R
105.17 A,(B) Mg 2p31Do – 3s’1D Kelly N,SMu,blendwithFe105.21ÅnotedbyR
106.03,.08,.19 P Ne 2p 3Po – 3d3D M Kelly N,SM,SW,D,R
(111.10,.16),.26 A,B,P Ne 2p 2Po – 3p2D G Kelly N,SBu,SMu,blendwithCa111.20
– poss.MgcontributionnotedbyR
111.15 (A),B,P Ne 2p21D – 3d1Po M Kelly N,blendwithCa111.20,Ne111.16Å
– poss.MgcontributionnotedbyR
111.55,.75,.86 B,(A,P) Mg 2p34So – 3s 4P G Kelly SB,R
(115.33),.39,(.52) A,B,P Ne 2p 3Po – 3s3S M Kelly R
115.82,.83 B O 2s – 4p G Kelly SB,SMu,Ru
115.96 B Ne 2p21D – 3d1Do M Kelly N
(116.35),.42 B O 2p– 5d Kelly N
116.69 B Ne 2p 1Po – 3d1D Kelly SMu,R
116.97,117.22 A Mg 2p32Do – 3s’2P M Kelly N,SMu,poss.MgcontributionnotedbyR
(117.33),.40 B O 2p– 5s Kelly N
(117.43),.66,(.78) P Mg 2p33So – 3s 3P Kelly N,Ru
(117.52),.64,(.81) P Mg 2p33Po – 3p 3P Kelly N,Ru
120.20,.27,.33,.35,.42,.48 P Ne 2p23P – 3s3Po Kelly N,blendwithO120.33ÅnotebyR
122.49,.69 B,P Ne 2p 2Po – 3d2D G Kelly N,SBu,SMu,SMH,D,R
123.59 P Mg 2p42D – 3siv2Do Kelly N,SMu,Ru
127.67 B,P Ne 2p 1Po – 3s1S Kelly SMu,R
129.78,.87 A,B,P O 2p– 4d Kelly SMH,SB,R
130.31,.64 B Mg 2p42P – 3sv2Po Kelly N
130.94,131.09,.30 A,B,P Mg 2p33So – 3p 3P Kelly N,SBu,blendwithFe130.94,131.24Å
– notedbyR
132.22,.31 A,B O 2p– 4s Kelly N
150.09,.12 B,P O 2s – 3p G Kelly SMH,SB,D,R
whichwereunidentifiedintheearlierwork.Theidentifications Procyon. They are also clearly seen as absorption features in
presented here can then also be applied (either wholly or in theH1504+65spectrum.Overthis,wehaveplottedthemodel
part,allowingforblends)tothesesolarspectra.Many,butnot spectrum,degradedto theChandraspectralresolution,which
all, of the tabulated lines have lower levels which are either can qualitatively reproducethe observed line features. Placed
ionic ground states or metastable states (labeled G or M, re- at the top of this Figure we show the original, non-degraded
spectively).Asanexamplehowthespectracompare,weshow model spectrum, showing the diverse structure of the multi-
inFig.1thespectraofProcyonandH1504+65inawavelength plets,whosecomponentsarenotentirelyresolvedinChandra
regionwherea bunchoflinesfromtwo MgandoneNe spectra,neitherofH1504+65norofProcyon.
multipletislocated.Allthreemultiplets,oratleastsomecom-
ponents of them, were identified by Raassen etal. (2002) in Figure 2 shows a detail from the spectra of Procyon and
αCenAcomparedtoH1504+65inanotherwavelengthinter-
6 K.Werner&J.J.Drake:LineidentificationinsoftX-rayspectraofstellarcoronae
val. It displays some new line identifications in the coronal Freeman,F.F.&Jones,B.B.1970,Sol.Phys.,15,288
spectra, see for example the 87.46Å resonance line of Ne Jordan, C. 1996, in Astrophysics in the Extreme Ultraviolet,
inαCenA.ThestrongestemissionsinαCenAstemfromtwo IAU Coll.152, ed. S.Bowyer, R.F.Malina, Dordrecht: Kluwer
NeandMgdoublets,identifiedalreadyinRaassenetal. AcademicPubl.,p.81
(2003).ButnotethattheMg86.84Åcomponentisblended Lepson, J. K., Beiersdorfer, P., Brown, G. V., etal. 2002, ApJ, 578,
withthepossiblystronger,newlyidentifiedNe86.82Åline. 648
Lepson,J.K.,Beiersdorfer,P.,Behar,E.,&Kahn,S.M.2003,ApJ,
Some of the newly identified lines do blend with other
590,604
linesusedforcoronaldiagnostics.TheemissivityoftheFe
Malinovsky,L.&Heroux,M.1973,ApJ,181,1009
lines at 130.94Å and 132.24Å in Procyonwas computedby
Manson,J.E.1972,Sol.Phys.,27,107
Raassen etal. (2002) using a three-temperature model. They Raassen,A.J.J.,Mewe,R.,Audard,M.,etal.2002,A&A389,228
stressthattheselinestrengthsarestronglyunderestimated,by Raassen,A.J.J.,Ness,J.-U.,Mewe,R.,etal.2003,A&A400,671
factors 6 and 4 compared to the observation. The result of Seaton,M.J.,Yan,Y.,Mihalas,D.,&Pradhan,A.K.1994,MNRAS,
their differential emission measure (DEM) model underesti- 266,805
mates the emissivity even more (factors9 and 6). This can at Schweizer,W.&Schmidtke,G.1971,ApJL,169,27
leastpartiallybeexplainedbythefactthattwocomponentsof Werner, K. 2001, in Low Mass Wolf-Rayet Stars: Origin and
a Mg triplet (at 130.94 Å and 131.30 Å) can contribute to Evolution,ed.T.Blo¨cker,L.B.F.M.Waters,A.A.Zijlstra,Ap&SS,
theFelineemissivities.Asimilarexplanationmayholdfor 275,27
Werner, K., Rauch, T., Barstow, M. A., & Kruk, J. W. 2004, A&A,
theFe105.20Åline,whichalsoappearedtooweakintheir
421,1169
model.ItisblendedwithaMgsingletat105.17Å.
Widing,K.G.&Sandlin,G.D.1968,ApJ,152,545
Another example is the Mg 74.86 Å line observed in
Young,P.R.,DelZanna,G.,Landi,E.,etal.2003,ApJS,144,135
αCenA and αCenB. Raassen etal. (2003) find that the line
fluxesfromtheirmodelsaretoosmallbyabout40%.Wethink
thatthemissingfluxiscontributedbyablendwithanewneon
line located at almost the same wavelength, Ne 74.87 Å.
Detailed emission measure modeling, which is beyond the
scope of this paper, is needed to quantify these suggestions.
Other blends with previously identified emission lines in the
coronaeofProcyonandαCenareindicatedinTable1.
5. Summary
We have performed a detailed comparison of Chandra soft
X-ray spectra from the photosphere of the hottest known
white dwarf, H1504+65,with the corona spectra of αCenA,
αCenB,andProcyon.Withthehelpofadetailedmodelspec-
trumforH1504+65wehavefoundthatalargenumberoflines
frommultipletsofO,Ne,andMgarepresentinboththepho-
tospheric absorption line spectrum and the coronal emission
line spectra. In the coronal spectra we have newly identified
linesfromabout40multipletsofO,Ne-,andMg-.
Some of these lines are blends with previously known lines,
which are in use for diagnostic purposes, hence, their contri-
bution to the line flux must be consideredin detailed spectral
analyses.
Acknowledgements. AnalysisofX-raydatainTu¨bingenissupported
by the DLR under grant 50OR0201. JJD was supported by NASA
contractNAS8-39073totheChandraX-rayCenter.
References
Acton,L.W.,Bruner,M.E.,Brown,W.A.,etal.1985,ApJ,291,865
Behring,W.E.,Cohen,L.,&Feldman,U.1972,ApJ,175,493
Beiersdorfer,P.,Lepson,J.K.,Brown,G.V.,etal.1999,ApJL,519,
185
Drake,J.J.1996,inCoolStars;StellarSystems;andtheSun:9,ed.
R.Pallavicini,A.K.Dupree,ASPConferenceSeries,109,203
Drake,J.J.,Laming,J.M.,&Widing,K.G.1995,ApJ,443,393
Drake,J.J.,Laming,J.M.,&Widing,K.G.1997,ApJ,478,403