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