arXiv:1105.5276v1 [astro-ph.SR] 26 May 2011 .5 C 0.85, – h soito fUieste o eerhi Astronomy, in NAS5-26666. Research contract NASA for Universities is of which Institute, Association Science the Telescope Space the NASA NAS5-32 at the obtained contract with NASA for observations under on operated University Based Hopkins was Johns the FUSE by Explorer. Spectroscopic Ultraviolet log e ,adO ihrte ies bnac atrs(He patterns abundance diverse rather with composed O, mainly are and envelopes C, Their He, flash. He-shell late a of tr eua n ht wrs( dwarfs p white of stars and post-AGB central hottest nebulae the deficient etary comprising diagram region Hertzsprung-Russell a the cover In they hot 2006). Herwig are & (Werner stars 1159 PG Introduction 1. eaudnepiosplain Qiine l 07.Anot 2007). al. et (Quirion pulsations poisons abundance He n tas eaetepooyeo h WVrsas which 1979) stars, al. the Vir et GW Besides (McGraw the pulsators. variable of 1159 g-mode PG prototype multimode is the non-radial became are the also it that and found Subsequent was 1985). al. et it (Wesemael survey Green Palomar the fzy,bcueterdadbu de ftesrpdpn on depend strip the of edges st blue instability He and the the red of the location The because “fuzzy”, 1984). al. et (Starrfield O PG non-variable contains also stars. li it “pure” that not meaning is strip, them Ceti mechanism, by ZZ driving occupied strip question the instability key concerns the the cause pulsators of these One to 2008). related al. et (Costa methods oseismic uy3,2018 31, July ⋆ Astrophysics & Astronomy ae nosrain aewt h AACE-S Far NASA-CNES-CSA the with made observations on Based h rttp G1159 PG prototype The h rmr usto rvri ylcinsto fCand C of ionisation cyclic is driver pulsation primary The g rnaudnei h rttp G15 tr WVrpulsator Vir GW star, 1159 PG prototype the in abundance Iron fteP 19seta ls n h WVrplaos n ft of and pulsators, Vir GW the and class spectral 1159 PG the of eeto fFe of detection within epromda rnaudnedtriaino h o,hyd hot, the of determination abundance iron an performed We eevd3 ac 2011 March 31 Received 3 2 1 ht dwarfs White – G15 tr ( stars 1159 PG e words. Key notions. previous to contrast in deficient, iron = / C avr-mtsna etrfrAtohsc,6 adnSt Garden 60 USA Astrophysics, 20771, for MD Center Greenbelt, Harvard-Smithsonian Center, Flight Space Goddard NASA nttt o srnm n srpyis elrCne fo Center e-mail: T¨ubingen, Kepler Germany, 72076 Astrophysics, 1, Sand and Astronomy for Institute . ) hi ecec sms rbbyteresult the probably most is deficiency H Their 8). – 5.5 − / = bnac ai ntediigrgo;tohg an high too region; driving the in ratio abundance O 3 spoal h trta sbs tde ihaster- with studied best is that star the probably is 035 T .3–06,O 0.60, – 0.13 e ff = 1 0 5 0 ,w n oa rnaudne hsrsl a result This abundance. iron solar a find we K, 000 150 – 000 110 tr:idvda:P 1159 PG individual: Stars: T viii e ff = ie nselrpoopee.I nte G15 tr G14 PG star, 1159 PG another In . stellar in lines 5 0 0 0 )ta xii Fe exhibit that K) 000 200 – 000 150 = − / 3 ( 035 .2–02,ms fractions). mass 0.20, – 0.02 aucitn.16992 no. manuscript cetd1 a 2011 May 13 Accepted G1159 PG = / .Werner K. S ubeSaeTelescope, Space Hubble ESA T WVr a icvrdin discovered was Vir) GW e ff = − 3 tr:audne tr:amshrs–Sas evolut Stars: – atmospheres Stars: – abundances Stars: – 035 500–2000K, 000 200 – 000 75 1 [email protected] − .Rauch T. , 3,adrltdobjects related and 035, prtdby operated n. under Inc., = NASA ethe ke x i is rip 1159 1 0.30 ABSTRACT 985. lan- ie.O h hl,w n htteP 19sasaentsigni not are stars 1159 PG the that find we whole, the On lines. ..Kruk J.W. , be- her of et abig,M 23,USA 02138, MA Cambridge, reet, ly s sr n atcePyis bradKrsUniversit¨at T Karls Eberhard Physics, Particle and Astro r oe ecetps-G trP 1159 PG star post-AGB deficient rogen , , orltdojcs(G1520 (PG objects related wo iiigFe hibiting eemnto fP 1159 PG of determination 5 0 ,log K, 000 150 strip. instability the therefore narrow would iron, abundance is iron driving solar pulsation supports that species olrojc G1424 PG object cooler Fe detect to able be should UEadHTsetao G1159 PG of spectra HST and FUSE h o-eeto fteelnswudma edfiinyof deficiency Fe a mean would lines these of non-detection the iul neetdFe undetected viously sato o eemnn h rnaudne lsn h gap the closing abundance, iron the ( ser coolest determining They the for twin. between its tool and a prototype as the including stars, 1159 PG ersetocpcti,tennplao G1520 PG non-pulsator the twin, spectroscopic near edfiinywsbsdo o eetn Fe or detecting weak not mentione on rather previously based The be e was stars. deficiency high to 1159 Fe PG the predicted in of are undetectable even Because lines nebulae. these ce planetary Fe temperatures, hydrogen-rich ultraviolet of hot were of stars observations tool tral from main known the well Hitherto, lines, assess. to ficult of claims were 2007). there al. Fo twins, et abundance. (Jahn the deficiency iron including iron tw the stars, is these 1159 PG question of some open composition remaining and One gravity, stars. temperature, derive to composition chemical e envelope Considerable their similar. provided strip, Vir GW UEsetao he eimht( medium-hot three of spectra FUSE rmhge oiainsae fio eeukonutlre- until unknown were iron Fe of when stages cently, ionisation higher from rnaudnewsderived. was abundance iron ( T e ff G1159 PG pcrsoial,teio bnac nP 19sasi di is stars 1159 PG in abundance iron the Spectroscopically, nti ae,w nonetedtcino Fe of detection the announce we paper, this In ≥ 2 5 0 )P 19sas(enre l 00.Asolar A 2010). al. et (Werner stars 1159 PG K) 000 150 n ..Kurucz R.L. and , re ihorrcn bnac nlsso h hottest the of analysis abundance recent our with grees 24 x − o h rttm,w rsn nio abundance iron an present we time, first the For . + 3 ( 035 3,w eetFe detect we 535, g x = ie eedtce nfieo h eyhottest very the of five in detected were lines T .) oetal enstebu deo the of edge blue the defines potentially 7.5), e ff T + + e vii = ff ff 2,P 1144 PG 525, 3 ( 535 r a u nosetocpcanalyses spectroscopic into put was ort ∼ < 4 0 ,log K, 000 140 − ie.Ti erhi xeddt the to extended is search This lines. 3 4 0 )P 19sas hr we where stars, 1159 PG K) 000 140 3.W aeul eass archival re-assess carefully We 035. vii T o tr:ABadpost-AGB and AGB Stars: – ion ⋆ e n h eyhtetojcsex- objects hottest very the and , vii ff − = 3,wihi h prototype the is which 035, ie.I l orsas each stars, four all In lines. 1 0 ,log K, 000 110 − + T 3 olo o ek pre- weak, for look to 035 0) ae ntefirst the on based 005), e ff = g 4 0 5 0 K) 000 150 – 000 140 = ) oehrwt a with together 7), vii ie.U lines UV lines.

c g ¨ubingen, ficantly + = viii S 2018 ESO 2 ( 525 ) where 7), ie in lines sub- a , ff ective T e ff vii ve n- in is f- = d r 2 K. Werner et al.: Iron abundance in PG 1159−035 and related objects

1.2 o o o o Fe VIII 1006.09 A Fe VIII 1062.44 A Fe VIII 1125.49 A Fe VIII 1148.22 A

1.0 ? SiVI? ?H i.s. relative flux 0.8 2 ? OVI H2 i.s. OVI

0.6 FeII i.s. FeII i.s. 1005 1006 1007 1061 1062 1063 1064 1124 1125 1126 1127 1147 1148 1149 1150 o wavelength / A

Fig. 1. Fe viii lines detected in PG1159−035. Overplotted is the final model with solar iron abundance (model parameters: Teff = 140000K, log g = 7, He/C/O/Ne = 0.32/0.48/0.17/0.02; mass fractions).

o o Fe VIII 1148.22 A Fe VIII 1148.22 A

PG1159-035 140 000/7.0 PG0038+199 140 000/7.5 5

PG1159 DO

PG1520+525 150 000/7.5 PG1034+001 120 000/7.5

4 PG1159 DO

PG1144+005 150 000/6.5 NGC 7293

PG1159 H-rich CSPN 3

relative flux Abell 43 110 000/5.7 LSS 1362

PG1159-hybrid H-rich CSPN

2 NGC 7094 110 000/5.7 NGC 1360

PG1159-hybrid H-rich CSPN

Abell 78 110 000/5.5 NGC 6853 1

[WC]-PG1159 H-rich CSPN ??

1148 1149 1148 1149 o wavelength / A Fig. 2. The Fe viii λ 1148.22Å line in PG1159 stars and other objects. Left panel, from top: three PG1159 stars, two PG1159- hybrids, and a [WC]–PG1159 transition object. Right panel: two hot DOs and four H-rich central stars. Depicted numbers denote temperature and gravity of the overplotted (red) models. They have solar iron abundance except for the two DOs where Fe is ten times solar. one dex (Reiff etal. 2008).We also report on Fe viii lines in other lines in FUSE spectra of PG1159 stars. All four Fe viii lines are hot H deficient and H rich post-AGB stars. present in the prototype PG1159−035 (Fig. 1). We find Fe viii In the following section, we present the detection of Fe viii lines in two more PG1159 stars and in several other hot (pre-) lines in PG1159−035 and other objects (Sect.2). Then we de- white dwarfs as well. From these objects we display the region scribe our model atmospheres (Sect.3) and the spectroscopic around Fe viii λ 1148.22Å in Fig.2. iron abundance analysis of four PG1159 stars (Sect.4), and we conclude in Sect.5. The two other PG 1159 stars have slightly higher tem- peratures than the prototype (PG1520+525: Teff = 150000K, log g = 7.5; PG1144+005: Teff = 150000K, log g = 6.5). 2. Observations and line identifications Different PG1159 stars from which FUSE spectra exist are ob- viously too hot or too cool to exhibit Fe viii lines. In particu- Recently, Landi & Young (2010) have been able to identify four lar, these are the hottest ones exhibiting Fe x lines mentioned Fe viii coronal emission lines in the λ 1000 – 1200Å region of in the introduction (Teff ≥ 150000K), and the cooler object the quiet Sun, in spectra obtained with the SOHO/SUMER in- PG 1424+535 (Teff = 110000K) that will be discussed below strument. This prompted us to look for accordingly photospheric (Sect. 4.2). K. Werner et al.: Iron abundance in PG 1159−035 and related objects 3

2 S 2 So 2 P 2 Po 2 D 2 Do 2 F 2 Fo 2 G 2 Go 2 H 2 Ho 2 I 4 S 4 So 4 P 4 Po 4 D 4 Do 4 F 4 Fo 4 G 4 Go 4 H 4 Ho 4 I

1 -1

o

o 1062, 1125 A 1006, 1148 A energy / 1 000 000 cm

Iron VIII 0 ionization energy 1 261 380 cm-1 Fig. 3. Grotrian diagram of Fe viii. For clarity, it is drawn from Opacity Project (OP) data that represent a small subset of the Kurucz dataset utilised in our computations. The OP level energies differ from Kurucz values. The transitions giving rise to the observed lines are indicated.

Teff variation at log g = 7 g variation at 140 000 K Fe abundance variation 1.0

-1.0 dex 0.9 -0.5 dex 160 000 K 150 000 K log g = 7.3 relative flux 130 000 K 0.8 log g = 6.7 solar 140 000 K log g = 7.0

Fe = solar Fe = solar Teff = 140 000 K log g = 7.0 0.7 1148.0 1148.2 1148.4 1148.0 1148.2 1148.4 1148.0 1148.2 1148.4 o wavelength / A Fig. 4. Effects of model parameter variations on the Fe viii λ 1148.22Å line profile. The line strength is maximum at the parameters of PG1159−035 (Teff = 140000K, log g = 7); other abundances are He/C/O/Ne = 0.32/0.48/0.17/0.02.

The central stars Abell 43 and NGC7094 are hybrid- Table 1. Wavelengths and oscillator strengths fi j of Fe viii lines. PG1159 stars (i.e. exhibiting H-Balmer lines), and Abell 78 is a [WC]–PG 1159 transition object. They all have low surface grav- viii ity, and the extraordinary wide profiles indicate that the Fe Line λKurucz/Å λLandi/Å fij lines are strongly affected by a . The low surface 4s 2S − 3d2 2Po 1006.087 1006.015 0.0169 gravity also favours the appearance of Fe viii although Teff of 1/2 1/2 2 − 2 o (1) these stars is relatively low (≈ 110000K). 4s S1/2 4p P3/2 1062.440 1062.463 0.401 2 − 2 o Two of the hottest known DO white dwarfs, PG0038+199 4s S1/2 4p P1/2 1125.492 1125.546 0.216 2 2 2 o 4s S / − 3d P 1148.224 1148.223 0.0828 with Teff = 115000K and PG1034+001with 100000K (Dreizler 1 2 3/2 & Werner 1996), display Fe viii lines. Comparison with prelim- (1) mean value from two measurements inary model calculations indicates a necessary upward revision of the temperatures by ≈ 20000K in order to reproduce these lines. We detect Fe viii in neither KPD0005+5106, the hottest DO (200000K; Wassermann etal. 2010), nor in cooler DOs like formation iterations for the iron population densities were com- RE J0503−289 (70000K, Dreizler & Werner 1996). puted on these model structures, i.e., keeping fixed temperature We also find Fe viii lines in several hydrogen-rich central and density structure. For details on the used iron model atom, stars. Four very prominent examples are displayed in Fig.2: see Wassermann etal. (2010). We employ new versions of iron 1 NGC7293 (Teff = 120000K, log g = 6.3), LSS1362 (Teff = datasets (Kurucz 2009) . They include many more levels and viii 114000K, log g = 5.7), NGC1360 (Teff = 97000K, log g = lines, in particular the four Fe lines discussed in this paper. viii 5.3), NGC6853 (Teff = 126000K, log g = 6.5); the parameters Properties of the newly detected Fe lines are listed in are from Hoffmann etal. (2005). Table 1. They all arise from the same lower level. We specify the Kurucz wavelengths, as well as those measured by Landi & Young (2010). The differences are all smaller than 0.1Å. The 3. Model atmospheres and synthetic spectra largest deviation (0.072Å) is shown by the 1006Å line. The Kurucz wavelengths should be more accurate than the measured For our analysis we use a grid of line-blanketed non-LTE model wavelengths since the energy levels involved were determined atmospheres, which is described in detail in Werner etal. (2004). from more than one line. We also list the f-values from the In essence, the models include the main photospheric con- stituents, namely He, C, O, Ne, and occasionally H. NLTE line 1 http://kurucz.harvard.edu/atoms.html 4 K. Werner et al.: Iron abundance in PG 1159−035 and related objects

1.2 o o o o Fe VII 1073.95 A Fe VII 1095.34 A Fe VII 1117.58 A Fe VII 1141.43 A

1.0

0.8 SiV CIV FVI FeII i.s. FeII i.s. 0.6 1073 1074 1075 1094 1095 1096 1097 1116 1117 1118 1119 1140 1141 1142 1143

1.2 o o o o Fe VII 1154.99 A Fe VII 1163.87 A Fe VII 1166.17 A Fe VII 1180.82 A

1.0

relative flux 0.8 ??

0.6 1154 1155 1156 1162 1163 1164 1165 1165 1166 1167 11681179 1180 1181 1182

1.2 o o o o Fe VII 1208.37 A Fe VII 1226.65 A Fe VII 1239.69 A Fe VII 1332.38 A

1.0

0.8 SiVI NV

0.6 1207 1208 1209 1210 1225 1226 1227 1228 1238 1239 1240 1241 1331 1332 1333 1334 o wavelength / A Fig. 5. Fe vii lines in PG1159−035. Overplotted is the final model with solar iron abundance (model parameters like in Fig.1). FUSE data are used for λ< 1200Å and HST data otherwise.

1.2 o o o o Fe VII 1095.34 A Fe VII 1117.58 A Fe VII 1141.43 A Fe VII 1154.99 A

1.0

relative flux 0.8 FeII i.s. FeII i.s. PV FVI 0.6 SVI 1094 1095 1096 1097 1116 1117 1118 1119 1140 1141 1142 1143 1154 1155 1156 o wavelength / A

Fig. 6. Fe vii lines in PG1424+535. Overplotted is a model with solar iron abundance (model parameters: Teff = 110000K, log g = 7, He/C/O/Ne = 0.49/0.43/0.06/0.02).

Kurucz data. A simplified Grotrian diagram indicating the ob- In contrast, we previously decided there is an iron deficiency served line transitions is shown in Fig. 3. of > 0.7 dex from not detecting Fe vii lines (Jahn etal. 2007), so We computed a small model grid in order to study the de- we need to address this question again here. A close inspection vii pendence of the Fe viii lines on Teff , log g , and Fe abundance. of the FUSE and HST spectra reveals a number of weak Fe The result for λ 1148Å is displayed in Fig.4, and the other lines lines (Fig.5), which are fitted by our solar Fe abundance model. behave similarly. It turns out that effective temperature and grav- The reason we rejected the Fe vii detection in our previous ity of PG1159−035 are the most favourable for the detection of work was the apparent absence of the two strong predicted lines Fe viii. It also explains why Fe viii lines are not seen in objects at λλ 1154.99 and 1180.82Å in the FUSE data. The cause of that are much cooler or hotter. the non-detection remains unclear. In particular, we carefully re- addressed the wavelength calibration. We are confident that the accuracy of the wavelengths is at least 0.02Å. We also think 4. Iron abundance analysis that the oscillator strengths of these lines are correct because, to- gether with other Fe vii lines, they are rather prominent in spec- 4.1. PG1159−035 tra of H-rich central stars of planetary nebulae (e.g. Rauch etal. Figure 1 shows Fe viii lines profiles computed from a solar Fe 2007). Either way, the simultaneous fit of the detected Fe vii abundance model for PG1159−035 compared to the observa- and Fe viii lines independently confirms the validity of Teff and tion. The fit is satisfactory, and a comparison with the Fe varia- log g derived in earlier work. tion shown in the right panel of Fig.4 clearly rules out a signifi- In Table 2 we list the iron lines newly detected in cant iron deficiency. PG 1159−035, together with lines from an Ne vi multiplet K. Werner et al.: Iron abundance in PG 1159−035 and related objects 5

Table 2. New Fe vii, Fe viii, and Ne vi lines detected in Table 3. Parameters of PG1159−035. PG 1159−035. Parameter Result Abundances Ref. Wavelength / Å Ion Transition (solar units) viii 2 2 2 o 1006.09 Fe 4s S1/2 − 3d P1/2 Teff / K 140 000 ± 5000 (1), (2) viii 2 2 o −2 1062.44 Fe 4s S1/2 − 4p P3/2 log g / cm s 7.0 ± 0.5 (1),(2) 1073.95 Fe vii 4s 1D − 4p 1Po H ≤ 0.02 ≤ 0.027 (2) vii 3 3 o 1095.34 Fe 4s D3 − 4p P2 He 0.33 1.3 (2) 1117.58 Fe vii 4s 1D − 4p 1Fo C 0.48 203 (2) viii 2 2 o 1125.49 Fe 4s S1/2 − 4p P1/2 N 0.001 1.4 (2) vii 3 3 o 1141.43 Fe 4s D3 − 4p F4 O 0.17 30 (2) viii 2 2 2 o −6 1148.22 Fe 4s S1/2 − 3d P3/2 F 3.2 · 10 6.3 (2) vii 3 3 o Ne 0.02 16 (2) 1154.99 Fe 4s D2 − 4p F3 vii 3 3 o Si 3.6 · 10−4 0.54 (2) 1163.88 Fe 4s D2 − 4p D3 vii 3 3 o P ≤ 6.4 · 10−6 ≤ 1.1 (2) 1166.17 Fe 4s D1 − 4p F2 vii 3 3 o S 5.0 · 10−6 0.016 (2) 1180.82 Fe 4s D3 − 4p D3 vii 3 3 o Fe 1.3 · 10−3 1.0 (1) 1226.65 Fe 4s D3 − 4p D2 vii 3 3 o +0.068 1239.69 Fe 4s D1 − 4p D1 M/M⊙ 0.536 (1) 1 1 o −0.010 1332.38 Fe vii 4s D − 4p D +0.29 4 o 4 log L/L⊙ 2.58−0.29 (1) 1645.06 Ne vi 3s P − 3p P3/2 1/2 +0.334 4 o 4 vi d/kpc 0.750−0.585 (1) 1645.59 Ne 3s P3/2 − 3p P5/2 vi 4 o 4 1654.01 Ne 3s P1/2 − 3p P1/2 Element abundances are given in mass fractions (2nd column) and rel- vi 4 o 4 1657.16 Ne 3s P3/2 − 3p P3/2 ative to solar abundances (Asplund et al. 2009 values; 3rd column). vi 4 o 4 References: (1) this work, (2) Jahn et al. (2007) and references therein, 1666.24 Ne 3s P3/2 − 3p P1/2 vi 4 o 4 (3) Miller Bertolami & Althaus (2006). 1667.82 Ne 3s P5/2 − 3p P5/2 vi 4 o 4 1679.67 Ne 3s P5/2 − 3p P3/2 This table augments the UV line list of Jahn et al. (2007), their Table 2. 5. Summary and conclusions Our analysis of Fe vii and Fe viii lines in the FUSE spectra of four PG1159 stars results in solar iron abundances. Recent (NIST2 wavelengths) that we have discovered in the HST/STIS work on five hotter PG 1159 stars exhibiting Fe x lines (Werner spectrum during the present analysis. This table complements etal. 2010) arrived at the same result. This set of nine stars the UV line list presented by Jahn etal. (2007). comprises four objects, which previously were supposedly iron deficient: PG1159−035, PG1520+525, PG1424+535, K1-16 In Table 3 we summarise the photospheric parameters of (Miksa etal. 2002, Jahn etal. 2007). The reason for this contrary PG 1159−035 from spectroscopic analyses and derived quanti- result is twofold: an underestimation of T in the case of K1- ties. In comparisonto Jahn etal. (2007),the table is improved for eff 16 (Werner etal. 2010) and problems with the identification of both the Fe abundance and the re-determination of mass, lumi- the inherently weak lines from Fe vii as described in the present nosity, and distance based on more realistic evolutionary tracks work. Fe vii was the only relevant ionisation stage with accu- of Miller Bertolami & Althaus (2006). rately known line positions at that time when earlier analyses were performed. 4.2. PG1144+005, PG1520+525, PG1424+535 There are still two objects left with seemingly strong iron de- ficiency. These are the hybrid-PG1159 star NGC 7094 and the The two other PG1159 stars in which we found Fe viii lines are [WC]–PG1159 transition object Abell 78 (Miksa etal. 2002). PG 1144+005 (Teff = 150000K, log g = 6.5) and PG1520+525 In both stars we have discovered strong Fe viii lines (Fig.1). (Teff = 150000K, log g = 7.5). The lines are fitted with pro- They are much broader than predicted from our static models. files from models with solar iron abundance (Fig.2). We do not The reason is most probably that the lines form in the stellar detect Fe vii lines in these stars, because they are hotter than wind of these low-gravity (i.e. high-luminosity) central stars. PG 1159−035 so that we expect weaker lines, and because the The same mechanism could hamper the detection of weak Fe vii S/N of the available FUSE spectra is worse. The abundances of lines, whose apparent absence the assertion of Fe deficiency was the modelsshown in Fig.2 are He/C/O/Ne = 0.43/0.38/0.17/0.02 based on. Because of the prominent Fe viii lines, we may specu- for PG1520+525 and 0.38/0.58/0.02/0.02for PG1144+005. late that the iron abundance in these objects is about solar, too, The fourth PG1159 star considered in the present study, but a detailed analysis with expanding model atmospheres is re- PG 1424+535,is too coolto exhibitFe viii lines. The star is inter- quired. Our results ease the problem of explaining the previously esting because an iron deficiency of at least 1 dex was concluded believed extreme iron deficiency with models, from the claimed absence of Fe vii (Reiff etal. 2008). Similar to which do not predict such large Fe depletions by neutron cap- the case of PG1159−035, we again addressed this question and tures in the intershell region of AGB stars. found that Fe vii lines are present after all. In Fig.6 we show a Two of the objects investigated in this study (PG 1159−035 selection of Fe vii lines from the FUSE spectrum compared to a and PG1520+525) have rather similar parameters and they can solar iron abundance model. The match is very good. be regarded as a fixed point for the blue edge of the GW Vir , at least for a particular chemical envelope com- position. Within error limits, they have the same atmospheric 2 http://physics.nist.gov/pml/data/asd.cfm abundance pattern (in particular the Fe abundance) and, thus, 6 K. Werner et al.: Iron abundance in PG 1159−035 and related objects differences in the pulsation driving behaviour should only result from differences in Teff and log g . Our correct match of the Fe vii/Fe viii ionisation balance cor- roborates the previously determined parameters for the pulsator PG 1159−035: Teff = 140000K, log g = 7.0. The non-pulsator PG 1520+525 has Teff = 150000K, log g = 7.5. These parame- ters are confirmed by an analysis of its Chandra X-ray spectrum (Adamczak et al., in prep.).

Acknowledgements. T.R. is supported by the German Aerospace Centre (DLR) under grant 05 OR 0806. Some of the data presented in this paper were ob- tained from the Multimission Archive at the Space Telescope Science Institute (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts.

References Asplund, M., Grevesse, N., Sauval, A. J., & Scott, P. 2009, ARA&A, 47, 481 Costa, J. E. S., Kepler, S. O., Winget, D. E., et al. , 2008, A&A, 477, 627 Dreizler, S., & Werner, K. 1996, A&A, 314, 217 Hoffmann, A. I. D., Traulsen, I., Werner, K., Rauch, T., Dreizler, S., & Kruk, J. W. 2005, ASP Conf. Ser., 334, 321 Jahn, D., Rauch, T., Reiff, E., et al. 2007, A&A, 462, 281 Kurucz, R. L. 2009, in Recent Directions in Astrophysical Quantitative Spectroscopy and Radiation Hydrodynamics, eds. I. Hubeny, et al., AIP Conf. Proc., 1171, 43 Landi, E., & Young, P. R. 2010, ApJ, 713, 205 McGraw, J. T., Starrfield, S. G., Liebert, J., & Green, R. 1979, in White Dwarfs and Variable Degenerate Stars, IAU Coll. 53, eds. H. M. van Horn, V. Weidemann, Rochester, p. 377 Miksa, S., Deetjen, J.L., Dreizler, S., Kruk, J., Rauch, T., & Werner, K. 2002, A&A, 389, 953 Miller Bertolami, M. M., & Althaus, L. G. 2006, A&A, 454, 845 Quirion, P.-O., Fontaine, G., & Brassard, P. 2007, ApJS, 171, 219 Rauch, T., Ziegler, M., Werner, K., et al. 2007, A&A, 470, 317 Reiff, E., Werner, K., Rauch, T., Koesterke, L., & Kruk, J. W. 2008, in Hydrogen- Deficient Stars, eds. K. Werner, T. Rauch, ASP Conf. Ser., 391, 121 Starrfield S., Cox A. N., Kidman R. B., & Pesnell W. D. 1984, ApJ 281, 800 Wassermann, D., Werner, K., Rauch, T., & Kruk, J. W. 2010, A&A, 524, A9 Werner, K., & Herwig, F. 2006, PASP, 118, 183 Werner, K., Rauch, T., Reiff, E., Kruk, J. W., & Napiwotzki, R. 2004, A&A, 427, 685 Werner, K., Rauch, T., & Kruk, J. W. 2010, ApJ, 719, L32 Wesemael, F., Green, R. F., & Liebert, J. 1985, ApJS, 58, 379