The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018Stellar atmospheres are prime laboratories to determine
atomic properties of highly ionized species.
Reliable opacities are crucial ingredients for the
calculation of stellar atmospheres of white dwarfs
and subdwarfs. A detailed investigation on the
precision of many iron-group oscillator strengths
is still outstanding. To make progress, we used
the Hubble Space Telescope Imaging Spectrograph
to measure high-resolution spectra of three hot
subdwarfs that exhibit extremely high iron-group
abundances. The predicted relative strengths of
the identified lines are compared with the observations
to judge the quality of Kurucz’s line data
and to determine correction factors for abundance
determinations of the respective elements.Astronom

Landstorfer, A.

Löbling, L.

Quinet, P.

Rauch, T.

Werner, K.

English

Texas ScholarWorks

21st European Workshop on White DwarfsCastanheira, Campos, Montgomery, eds.July 23–27, 2018, Austin, Texas, USAHigh-Precision Atomic Physics Laboratories in Space:White Dwarfs and SubdwarfsA. Landstorfer1, L. Lo¨bling1,2, T. Rauch1, K. Werner1, P. Quinet3,41Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University,Sand 1, 72076 Tu¨bingen, Germany, email: landstorfer@astro.uni-tuebingen.de2European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany3Physique Atomique et Astrophysique, Universite´ de Mons – UMONS, 7000 Mons, Belgium4IPNAS, Universite´ de Lie`ge, Sart Tilman, 4000 Lie`ge, BelgiumAbstractStellar atmospheres are prime laboratories to de-termine atomic properties of highly ionized species.Reliable opacities are crucial ingredients for thecalculation of stellar atmospheres of white dwarfsand subdwarfs. A detailed investigation on theprecision of many iron-group oscillator strengthsis still outstanding. To make progress, we usedthe Hubble Space Telescope Imaging Spectrographto measure high-resolution spectra of three hotsubdwarfs that exhibit extremely high iron-groupabundances. The predicted relative strengths ofthe identified lines are compared with the obser-vations to judge the quality of Kurucz’s line dataand to determine correction factors for abundancedeterminations of the respective elements.1 Introduction“Rubbish in, rubbish out” ultimately describes the resultsof any astrophysical code, as sophisticated as it maybe if the input is inaccurate, rudimental, or approxi-mate. In case of non-local thermodynamical equilib-rium (NLTE) stellar atmosphere modeling, the crucialingredient is the atomic data. Since the occupationnumbers of all atomic levels treated in NLTE have tobe calculated in detail via the rate equations (Werner& Dreizler, 1999), e.g., reliable transition probabili-ties are required, not only for those few lines that areidentified in an observation but for the complete modelatoms that are considered in the model-atmospherecalculations.Sources for atomic data are beside standard databases like, e.g., the atomic spectra database1 of the Na-tional Institut for Standards and Technologies (NIST),the extended line lists provided by Kurucz2 (Kurucz,1https://www.nist.gov/pml/atomic-spectra-database2http://kurucz.harvard.edu/atoms.html1991, 2011) or the Opacity Project3 (Seaton et al.,1994). These databases, however, are far from beingcomplete.When Werner et al. (2012b) newly discov-ered lines of ten trans-iron elements, namely Ga,Ge, As, Se, Kr, Mo, Sn, Te, I, and Xe inthe far-ultraviolet spectrum of the hot, helium-rich, DO-type white dwarf RE0503 289 (eﬀectivetemperature Te↵ =70 000± 2000K, surface gravitylog (g / cm s 2) = 7.5±0.1, Rauch et al., 2016b), it wasonly possible to measure the Kr and Xe abundances be-cause oscillators strengths for the ionization stages ￿￿ -￿￿￿ were only available for these species. This initiateda campaign to calculate transition probabilities andoscillators strengths for trans-iron elements (Table 1).The newly calculated data is provided by our TübingenOscillator Strengths Service (TOSS).So far, the quality of the oscillator strengths of the el-ements with atomic numbers Z   20 is only evaluatedin part, e.g., for Sc ￿￿￿ - ￿￿￿￿ (Massacrier & Artru, 2012),Xe ￿￿ (Rauch et al., 2015b), and Mo ￿-￿￿ (Rauch et al.,2016a). A critical evaluation of lines of the iron-group(IG, namely Ca - Ni) elements ist still outstanding.To make progress, we use high-resolution and highsignal-to-noise (S/N) ultraviolet (UV) spectra of twosuper metal-rich sd(O)B-type stars (Edelmann, 2003),namely EC11481 2303 and PG0909+276 (Wild &Jeﬀery, 2017), and of the He-sdO Feige 110 (Rauchet al., 2014b) which is a primary flux standard of theHubble Space Telescope (HST). The diﬀerence of about18 000K in Te↵ between these stars (Table 2) allowsus to investigate on ionization stages ￿￿￿-￿￿ of the iron-group elements.Although UV spectra obtained with the InternationalUltraviolet Explorer (IUE) and the Far Ultraviolet Spec-troscopic Explorer (FUSE) of these stars are available,their low S/N and insuﬃcient resolution as well as thehigh number of IG lines and the strong contaminationby interstellar line absorption hampers the identifica-3http://cdsweb.u-strasbg.fr/topbase/TheOP.htmlV nderbosch, M ntgomery, eds.Evolutionary and pulsational properties of ultra-massive whitedwarfs. The role of oxygen-neon phase separation.F. C. De Ge o´nimo,1,2, M. E. Camis ssa1,2, A. H. Co´ sico1,2, L. G. Althaus,1,2Facultad de Cie cias Astrono´micas y Geofı´sicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, (1900) La Plata, Ar-gentina; fdegeronimo@fcaglp.unlp.edu.arInstituto de Astrofı´sica La Plata, CONICET-UNLPAbstractUltra-massive hydrogen-rich white dwarfs (WDs)ar expected to harbor oxygen/ne n c s result-ing from semi-degenerate carbon burning wh nthe progenitor t r evolves through the superasymptotic giant branch (SAGB) phase. Th se starre expected to be crystallized by the time theyrea h the ZZ Ceti domain. We show that crystal-lization leads to a phase separation of oxyg n anneon in the core of ultra-massive WDs, which im-pacts markedly the pulsational properties, thus f-fering unique opportunity to study t e processesof crystallization and to infer the core chemicalcomposition in WD stars.1 Meth d logy & input physicsWe computed the evolution (Camisassa et al., 2018)and pulsation properties (De Gerónimo et al., 2018)of ultra-massive DA (hydrogen-rich) WD sequenceswith stellar masses M? = 1.10, 1.16, 1.22, and 1.29M (Fig. 1) resulting from the complete evolution of theprogenitor stars through the SAGB phase (Siess, 2010).Prior evolution provides us with realistic core chemicalprofiles, envelope stratification and helium mass. Intabl 1 we show the He mass of our models, toge herwith the eﬀective temp rature and surface gravity atthe onset of crystallization, and the frac of crystal-lized mass at the blue and red edge of the ZZ Cetiinstability strip. The c res are composed mostly of 16Oand 20Ne, and smaller amounts f 12C, 23Na and 24Mg.The H con ent is set to MH ⇠ 10 6M?.Nonradial g-mode (gravity mode) pulsations of ourcomplet set of ultra-m ssive ONe-core DA WD mod-els were computed using th adiab tic versi n of theLP-PUL pulsati n code (Córsico et al., 2005). The pul-sation code is based on the general Newton-Raphsontechnique that solves the full fourth order set ofequations and boundary conditions governing linear,spheroidal, adiabatic, non-radial stellar pulsations fol-lowing the dimensionless formulation of Dziembowski(1971). To account for the eﬀects of crystallization onthe pulsation spectrum of g mod s, we adopted the“hard sphere” bound ry conditions, which assume thatthe amplitude of the eigenfunctions of g modes is dras-tically reduc d below the solid/liquid i terface due toth non-zer sh ar modulus of the solid, as comparedwith the amplitude in the fluid region (see Montgomery& Winget, 1999).The DA WD evolutionary models developed in thiswork were computed with the amply used LPCODE evo-lutionary code (Althaus et al., 2005). This code consid-ers all the physical ingredients involved in WD, includ-ing element diﬀusion. In this work we included, for thefirst time, both energy release and chemical abundancechanges caused by the process of phase separation dur-ing crystallization. We considered the phase diagramof Medin & Cumming (2010), suitable for the denseplasma of oxygen/neon mixtures appropriate for ultra-massive WDs. We computed an additional sequence ofCO-core WDs with M? = 1.10M , for which crystal-lization was considered following the phase diagramof Horowitz et al. ( 0). Phase diagrams provide uswith the temperature at which crystallization occ rsand the resulting abundances of the solid phase. Toour knowledge, this is the first evolutionary and pul-sational a alysis of ultra-massive DA WD models thatincludes phase separation processes in ONe cores.2 ResultsIn Fig. 1 we show th log g   Te↵ plane of our WDseque ces, computed for this work. In additi n, we plotthe isochrones of 0.1, 0.5, 1, 2 and 5 Gyr (blue lines)toge er with th sample of ultra-massive DA WDsknown to date (black plus symbols) and ultra-massiveZZ Ceti stars (red squares). I can be seen a ch nge ofslope f the isochrones, reflecting the dependence ofcooli g times on the mass of the WD: at early stages,evolution proceeds slower in more mas ive WDs, whilethe opposite trend is found at advanced stages.We found that phase separation during crystalliza-tion strongly modifies the core chemical profiles of our2 High-precision Atomic Physics Laboratories in SpaceCrIVNiVIScIVCoVCrIVTiIVFeVCrIVFeVCoVNiVFeVINiV CoVICoVCoVCoVNiVINiVICoVCoVCoVNiVFeVINiIVNiV CoVFeVICrIVScVNiVNiV CoVFeVCrVIICoVCoVCoVNiV CoVCrIVNiIVCoVCoVNiV CoIVFeVFeVCoVCoVNiV ScVCoVV IVCrIVCrIVNiV CoVFeVNiVNiV CoVICoVNiVNiV CrIVV IVNiVNiV CoVNiVNiIVFeV-11.6-11.4-11.2-11.0-10.8EC 11481-2303SWP48112HLlog (f λ / ergcm-2s-1Ao-1)OI isSiII is-11.6-11.4-11.2-11.01301 1302 1303 1304 1305 wavelength / AoFigure 1: Top panel: Theoretical spectra for EC 11481 2303 calculated with Kurucz’s so-called POS lines (observed, POSitivelyidentified, Kurucz, 2011) in a small wavelength interval close to the maximum sensitivity of STIS with E140M convolvedwith Gaussians to match the resolving power of STIS (R =  /   = 45 800; red, thick line) and IUE (R = 10 000; blue, thin).The marks indicate all POS lines, those with log gf values   0.01 are identified; Bottom: High-resolution IUE observation(SWP48112HL), “is” denotes interstellar lines. The poor S/N hampers line identifications.1231200 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 wavelength / Ao relative fluxFigure 2: STIS spectra of EC11481 2303 (red), Feige 110 (black), and PG0909+276 (blue), smoothed with a Gaussian of1Å (FWHM) and shifted for clarity. Ly↵1215Å and He ￿￿  1640Å are prominent, besides presumably thousands of IG lines.tion of isolated IG lines (Figure 1). Therefore we usedthe Space Telescope Imaging Spectrograph (STIS) aboardHST in the wavelength range of 1140 1709Å to ob-tain high-resolution spectra (grating E140M) with anS/N of about 30 50 that is necessary for our purpose.The three spectra are shown in Figure 2, each one isexpected to feature   2000 IG absorption lines.2 Spectral analysis and prelimi-nary resultsTo calculate synthetic spectra for our three programmestars, we employ the Tübingen Model-Atmosphere Pack-age (TMAP, Werner et al., 2012a; Rauch & Deetjen,2003) that can calculate plane-parallel NLTE modelatmospheres in radiative and hydrostatic equilibrium.NLTE modeling is mandatory due to the high Te↵ ofour stars (Table 2).Unlike few thousands of lines from light metals, theIG elements have of hundreds of thousands of levelsand hundreds of millions of lines. The reason for therapid increase in line number is the electron configu-ration of the IG elements, where the 3d and 4s shellsare partly filled. To include all lines but still not to ex-ceed the maximum number of NLTE levels (that TMAPis capable to consider), a statistical approach usingthe Iron Opacity and Interface Code (IrOnIc Rauch &Deetjen, 2003) combines all atomic levels of an ion toLandstorfer et al. 3FUSE B0540901IUE SWP 48111 LLno Ca - Ni opacities[Ca, ..., Ni] > 1-11.6-11.4-11.2-11.0-10.8-10.61000 1100 1200 1300 1400 1500 1600 1700 1800 1900 wavelength / Ao log (f λ / ergcm-2s-1Ao-1)Figure 3: Observed UV spectrum of EC11481 2303 compared with a model considering HHeCNO (blue) and HHeCNO+IGelements with IG abundances   10⇥ solar abundances (red, Ringat & Rauch, 2012).Table 1: Recently calculated transition probabilities.Element Ions ReferenceZn ￿￿ - ￿ Rauch et al. (2014a)Ga ￿￿ - ￿￿ Rauch et al. (2015a)Ge ￿ - ￿￿ Rauch et al. (2012)Se ￿ Rauch et al. (2017b)Kr ￿￿ - ￿￿￿ Rauch et al. (2016b)Sr ￿￿ - ￿￿￿ Rauch et al. (2017b)Zr ￿￿ - ￿￿￿ Rauch et al. (2017a)Tc ￿￿ - ￿￿ Werner et al. (2015)Mo ￿￿ - ￿￿￿ Rauch et al. (2016a)Te ￿￿ Rauch et al. (2017b)I ￿￿ Rauch et al. (2017b)Xe ￿￿ - ￿￿￿ Rauch et al. (2015b, 2017a)Ba ￿ - ￿￿￿ Rauch et al. (2014c)(typically) seven superlevels and the respective lines tosuperlines. This strongly reduces the number of NLTElevels. IrOnIc uses Kurucz’s line lists as an input, con-sidering so-called LIN and POS lines. While POS lineshave been measured experimentally and can be usedfor line identification, the LIN lines include quantummechanically calculated lines in addition and are usedfor model-atmosphere calculations only.The element abundances of EC 11481-2303 have al-ready been determined by Ringat & Rauch (2012), butwith the new high-resolution STIS spectrum, we areable to precisely adjust these abundances. We calcu-lated individual atmosphere models for each IG ele-ment. Each model consists of the elements HHeCNO,and in addition one IG element. The abundancesthat we determined confirm the results of Ringat &Rauch (2012), showing very low C and O abundances,and remarkably high Fe, Co, and Ni abundances of⇡ 10  1000⇥ the solar values (Table 3). Although weFeVFeIIIFeIVFeIIIFeVFeIVFeVFeIVFeVFeVFeIVFeVFeIIIFeVFeVFeIVFeIIIFeIVFeIII241460 1462 1464 1466 wavelength / Ao relative fluxFigure 4: Part of the STIS spectrum of EC11481 2303(grey), compared with a HHeCNOFe TMAP spectrum (red).The blue line shows Fe lines only, with identification marksat top. The synthetic spectra are convolved with a rotationalprofile (vrot = 25 km/s) and a Gaussian (FWHM of 0.05Å)to account for STIS’s resolution.still can find only upper limits for some elements, otherelements clearly show hundreds of absorption lines. Itseems that Fe, Co, and Ni are primarily responsible forthe depressed UV flux, and therefore can be used tomodel the spectrum very well. In Figure 4, we show apart the of EC11481 2303 spectrum compared witha TMAP spectrum. Most of the Fe lines fit the spectrumwell, while the gaps will probably be filled by the otherIG elements.Our analysis is still ongoing. However, with the high-quality spectra of STIS, we will be able to identify lineper line, element per element, and we will provide acorrection table for the oscillator strengths of the IGelements to improve model-atmosphere calculationsand abundance analyses.4 High-precision Atomic Physics Laboratories in SpaceTable 2: Parameters of our three program stars.Te↵ / K log(g / g/cm2) He/H mass ratio distance / pcdEC11481 2303a 55 000±5 000 5.8±0.3 0.01±0.01 291±7Feige 110b 47 250±2 000 6.0±0.2 0.11±0.05 268±6PG0909+276c 37 290± 640 6.1±0.2 0.87±0.04 267±8a Ringat & Rauch (2012). b Rauch et al. (2014b). c Wild & Jeﬀery (2017).d calculated with parallaxes from Gaia DR2 (https://gea.esac.esa.int/archive).Table 3: Photospheric abundances of EC11481 2303. [X]denotes log(abundance/solar abundance) of element X. Theabundance uncertainty is ±0.2dex.Element Mass Fraction [X]H 9.45⇥ 10 1 0.11He 9.38⇥ 10 3  1.42C < 4.64⇥ 10 8 <  4.71N 4.40⇥ 10 4  0.20O < 5.60⇥ 10 6 <  3.01Ca < 2.78⇥ 10 2 < 2.66Sc < 2.65⇥ 10 3 < 4.75Ti < 5.62⇥ 10 3 < 3.28V < 2.50⇥ 10 3 < 3.94Cr 5.09⇥ 10 3 2.51Mn 1.84⇥ 10 4 1.24Fe 4.52⇥ 10 2 1.57Co 6.91⇥ 10 3 3.28Ni 2.81⇥ 10 2 2.62ReferencesEdelmann H., 2003, Dissertation, University Erlangen-Nuremberg, GermanyKurucz R. L., 1991, in Crivellari L., Hubeny I., Hum-mer D. G., eds, NATO ASIC Proc. 341: Stellar Atmo-spheres - Beyond Classical Models. p. 441Kurucz R. L., 2011, Canadian Journal of Physics, 89,417Massacrier G., Artru M.-C., 2012, A&A, 538, A52Rauch T., Deetjen J. L., 2003, in Hubeny I., MihalasD., Werner K., eds, Astronomical Society of the Pa-cific Conference Series Vol. 288, Stellar AtmosphereModeling. p. 103 (arXiv:astro-ph/0403239)Rauch T., Werner K., Biémont É., Quinet P., Kruk J. W.,2012, A&A, 546, A55Rauch T., Werner K., Quinet P., Kruk J. W., 2014a, A&A,564, A41Rauch T., Rudkowski A., Kampka D., Werner K., KrukJ. W., Moehler S., 2014b, A&A, 566, A3Rauch T., Werner K., Quinet P., Kruk J. W., 2014c, A&A,566, A10Rauch T., Werner K., Quinet P., Kruk J. W., 2015a, A&A,577, A6Rauch T., Hoyer D., Quinet P., Gallardo M., Raineri M.,2015b, A&A, 577, A88Rauch T., Quinet P., Hoyer D., Werner K., DemleitnerM., Kruk J. W., 2016a, A&A, 587, A39Rauch T., Quinet P., Hoyer D., Werner K., Richter P.,Kruk J. W., Demleitner M., 2016b, A&A, 590, A128Rauch T., Gamrath S., Quinet P., Löbling L., Hoyer D.,Werner K., Kruk J. W., Demleitner M., 2017a, A&A,599, A142Rauch T., Quinet P., Knörzer M., Hoyer D., Werner K.,Kruk J. W., Demleitner M., 2017b, A&A, 606, A105Ringat E., Rauch T., 2012, in Kilkenny D., JeﬀeryC. S., Koen C., eds, Astronomical Society of thePacific Conference Series Vol. 452, Fifth Meetingon Hot Subdwarf Stars and Related Objects. p. 71(arXiv:1111.0555)Seaton M. J., Yan Y., Mihalas D., Pradhan A. K., 1994,MNRAS, 266, 805Werner K., Dreizler S., 1999, Journal of Computationaland Applied Mathematics, 109, 65Werner K., Dreizler S., Rauch T., 2012a, TMAP: Tübin-gen NLTE Model-Atmosphere Package, AstrophysicsSource Code Library (ascl:1212.015)Werner K., Rauch T., Ringat E., Kruk J. W., 2012b, ApJ,753, L7Werner K., Rauch T., Kučas S., Kruk J. W., 2015, A&A,574, A29Wild J., Jeﬀery C. S., 2017, Open Astronomy, 26, 246AcknowledgementsAL is supported by the German Aerospace Center (DLR,grant 50OR1704) and LL by the German ResearchFoundation (DFG, grant WE1312/49-1) and by the Stu-dentship Programme of the European Southern Obser-vatory. Financial support from the Belgian FRS-FNRS isalso acknowledged. PQ is research director of this orga-nization. The TOSS (http://astro-uni-tuebingen.de/~TOSS) service was constructed as part of the Tübin-gen project of the German Astrophysical Virtual Obser-vatory (GAVO, http://www.g-vo.org). This researchhas made use of NASA’s Astrophysics Data System andthe SIMBAD database, operated at CDS, Strasbourg,France.

High-precision Atomic Physics Laboratories in Space: White Dwarfs and Subdwarfs

Quinet, Pascal

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High-precision atomic physics laboratories in space : white dwarfs and subdwarfs

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High-precision Atomic Physics Laboratories in Space: White Dwarfs and Subdwarfs

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