Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland1 Light and heavy metal abundances in hot central stars Klaus Werner University of Tübingen, Germany Collaborators: A. Hoffmann, T. Rauch, E. Reiff, I. Traulsen (Tübingen) J.W. Kruk (JHU, USA)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland2 Outline Results from UV spectral analysis of: Some of the hottest known hydrogen-rich central stars - New T eff and log g determinations - Abundance determinations of CNO and iron Hydrogen-deficient PG1159 (central) stars Abundance determinations of neon, fluorine, iron

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland3 Analysis of hottest H-rich CSPN Observations: HST/STIS UV-spectra of 7 central stars NGC 1360, NGC 4361, NGC 6853, NGC 7293, Abell 36, LSS 1362, LS V (= Sh2-216) Selection criteria: Extremely hot (T eff around 100,000 K) UV-bright (aimed at high resolution and high-S/N) Further observations for some of these objects: FUSE far-UV spectra new optical spectra taken at CA 3.5m, SSO 2.3m, HET 9.2m

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland4 Analysis of hottest H-rich CSPN Why UV spectroscopy? The only way to determine metal abundances. Metals are highly ionized, most metals have no spectral lines in the optical The only reliable way for precise T eff determination. Many metals show lines from at least 2 ionisation stages. Problems in the optical: - He I / He II ionisation balance not available (no He I lines) - Balmer line problem still unsolved for T eff > 100,000 K (no unique model fit to all Balmer lines possible; higher Balmer series members require higher T eff )

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland5 Example: Fixing T eff of NGC 7293 by using the lines from O IV, O V, O VI

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland6 Analysis of hottest H-rich CSPN In this way, using several CNO ions, we revised T eff previously determined from optical spectra alone. Largest correction found for NGC “Evolved” from coolest to hottest object in our sample: T eff = 82,000 → 126,000 K

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland7 Analysis of hottest H-rich CSPN Stellar masses: 0.55 – 0.65 M  Traulsen et al. (2005)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland8 Summary of abundance analysis of hottest H-rich CSPN 5 out of 7 stars have essentially solar CNO abundances (weak 3rd dredge-up because of low mass? M f =0.65 M   M i =3 M  ) Two exceptions: LS V (=Sh2-216): CNO and He 1-2 dex subsolar T eff =93,000K log g=6.9 → gravitational settling NGC 4361 This is a halo PN (Torres-Peimbert 1990) Fe lines very weak, N is subsolar by factor 10, Si by factor 20 but: O is solar and – very surprising – C is 20* oversolar Similar to K 648, the CSPN in the globular cluster M15 (Rauch et al. 2002) Possible: 12 C dredged up from C/O core

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland9 Analysis of hottest H-rich CSPN Analysis of iron (group) lines is still on-going (Fe, Ni, Cr, Mn) Many objects display Fe V and/or Fe VI and Fe VII lines → further check of T eff possible; abundances. Example: Fit to Fe VI lines in LS V +4621

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland10 New results on H-deficient PG1159 (central) stars Recall: PG1159 stars represent the transition phase from Wolf- Rayet type central stars to non-DA white dwarfs They are extremely hot: T eff = 75,000 – 200,000 K Their atmospheres are dominated by He, C, and O: e.g. prototype PG : He=33%, C=48%, O=17% (mass fractions) H-envelope ingested and burnt after a late He-shell flash Surface chemistry = material between H and He burning shells in precursor AGB-star (intershell abundances)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland11 Prominent born-again stars: FG Sge and Sakurai’s star

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland12 AGB star structure +CO core material (dredged up) From Lattanzio (2003) M  M 

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland13 Wolf-Rayet central stars PG1159 stars non-DA white dwarfs

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland14 FUSE spectroscopy, immediate aim: identification abundance determination of trace metals PG1159 stars enable to study composition of intershell matter; usually hidden under thick H-mantle Abundances reveal nuclear reaction chains and mixing processes in stellar interior  testing stellar evolution theory Important: intershell chemistry also affects efficiency of s-process (e.g. through 12 C abundance dredged up from C/O core) H-deficient PG1159 (central) stars

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland15 s-process in AGB stars Neutron sources are 2 reactions starting from 12 C and 22 Ne nuclei (from 3α-burning shell): 12 C(p,  ) 13 N(  + ) 13 C(α,n) 16 O protons mixed down from H envelope 22 Ne(α,n) 25 Mg  depth H-burning He-burning Lattanzio 1998 s-process in 13 C pocket

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland16 H-deficient PG1159 (central) stars FUSE spectra reveal an underabundance of iron in PG1159 stars (1-2 dex); Miksa et al. (2002) Explanation: Neutron captures completely destroy iron in the 13 C pocket Accumulation of Fe-deficient matter in the intershell after each thermal pulse (pulse-driven convection) Exhibition of this matter on surface after late He-flash

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland17 H-deficient PG1159 (central) stars FUSE spectra reveal a overabundance of neon in PG1159 stars, 2% by mass = 20 times solar (Werner et al. 2004) Explanation: 22 Ne is produced in He-burning shell by alpha captures on (CNO-cycled) 14 N 22 Ne is accumulated in intershell during thermal pulses Exhibition of Ne-enriched matter on surface after late He- flash. Model predictions: Ne=2%

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland18 Ne VII Å line in FUSE spectra detectable even at solar neon abundance level: Only possibility to identify neon in hot hydrogen-rich (i.e. “normal”) central stars. PG1159 central star Ne 20 times solar (=2%) H-rich central star Ne solar Ne VII Å. For the very first time identified in astrophysical source

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland19 H-deficient PG1159 (central) stars FUSE spectra allow for the first identification of fluorine in post- AGB stars, F is solar in some PG1159 stars, but we find a strong overabundance of fluorine in other PG1159 stars, up to 200 times solar! (Werner et al. 2005) Explanation: 19 F is produced in s-processing 13 C pocket and can be accumulated in intershell during thermal pulses Exhibition of F-enriched matter on surface after late He-flash

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland20 s-process in AGB stars Neutron sources are 2 reactions starting from 12 C and 22 Ne nuclei (from 3α-burning shell): 12 C(p,  ) 13 N(  + ) 13 C(α,n) 16 O protons mixed down from H envelope 22 Ne(α,n) 25 Mg  depth H-burning He-burning Lattanzio F production in 13 C pocket

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland21 Fluorine production Nucleosynthesis path : 14 N(α,  ) 18 F(  + ) 18 O(p,α) 15 N(α,  ) 19 F Protons are provided by 14 N(n,p) 14 C with neutrons liberated from 13 C(α,n)O N and 13 C can result from H-burning by CNO cycling, but not enough to produce significant amounts of F Additional p injection from H-envelope necessary: “partial mixing” (this also activates the usual s-process)

Institute for Astronomy and Astrophysics, University of Tübingen, Germany June 29, 2005Planetary Nebulae as Astronomical Tools, Gdansk, Poland22 First discovery of fluorine in hot post-AGB stars: F VI Å fluorine abundance in PG1159 stars up to 200 times solar