Hydrogen-deficient central of planetary nebulæ

Helge Todt W.-R. Hamann, G. Gr¨afener, M. Pe˜na, A. Liermann, U. R¨uhling, A. Barniske, J. Z¨uhlke, . . .

Institut f¨ur Physik und Astronomie Universit¨at Potsdam

07. May 2011

Quantitative Stellar Spectroscopy as a Key Tool of Astrophysical Research Planetary and its central

NGC 6369 Evolution of a low-mass star in the HRD

Teff in kK 200 100 50 20 10 5 2 5

4 t AGB

3 )

2 ZAMS

log (L/L M = 2 M

1

0 M = 1 M Herwig 2001

-1 5.5 5.0 4.5 4.0 3.5

log Teff WR stars with hydrogen atmospheres?

Keeler, J. 1898, ApJ 8 BD+30◦ 3639: a low mass WR star Wolf-Rayet stars: massive WC vs. low-mass [WC]

[WC] CS: strong, broad emission lines of C, He, O 7 6 NGC 6369 5 (neb.) β C IV

4 He II H [OIII] (neb.) O VI He II O V C IV C IV 3

2 Normalized flux

1

0 Hubble/NASA 4200 4400 4600 4800 5000 5200 5400 5600 5800 o λ [A] Massive WC: strong, broad emission lines of C, He, O 7 6 WR 52 5 C IV

4 He II O VI He II O V C IV C IV 3

Normalized flux 2

1

0 ESO/R/MAMA+SERC/J/DSS1 4200 4400 4600 4800 5000 5200 5400 5600 5800 o λ [A] Central stars: H-normal vs. [WC] – Spectra

[WC] CS: strong, broad emission lines of C, He, O 7 6 NGC 6369 5 (neb.) β C IV

4 He II H [OIII] (neb.) O VI He II O V C IV C IV 3

2 Normalized flux

1

0 Hubble/NASA 4200 4400 4600 4800 5000 5200 5400 5600 5800 o λ [A] H-normal CS: weak absorption lines of H, He 7 6 Abell 20 5

4 δ γ β H H He II 4686 H He II 5412 3

Normalized flux 2

1

0 4200 4400 4600 4800 5000 5200 5400 5600 5800 o Schwarz et al. 1992 λ [A] Classification of [WC] stars - subtypes

Subtype classification of [WC] stars via spectra lines of different ionization stages:

[WC] subtype observed Ions T /kK early / [WCE] C IV O VI, O V He II 75 . . . 200

late / [WCL] C II ,C III, C IV He I 20. . . 75 PoWR Previous work Previous [WC] analyses I

[WCL] (unblanketed models): Leuenhagen & Hamann (1994): V 348 Sgr, T ≤ 25 kK, He:C:H=41:56:4 Leuenhagen et al. (1996), Leuenhagen & Hamann (1998) Marcolino et al. (2007), including iron line blanketing

He C O 40% 50% 10% Previous [WC] analyses II

[WCE] (unblanketed models): Koesterke & Hamann (1997a,b):

He C O 60% 30% 10%

Crowther et al. (2003), Marcolino et al. (2007), including iron line blanketing:

He C O 45% 45% 10% V348 Sgr [WC12] IRAS 21282... [WC11] H K 2-16 [WC11] He 2-113 [WC11] He M 4-18 [WC11] C CPD-56o 8032 [WC11] PM 1-188 [WC11] O SwSt 1 [WC11] BD+30o 3639 [WC9] He 2-99 [WC9] M 2-43 [WC8] He 2-459 [WC8] NGC 40 [WC8] [WCL] LMC-SMP61 [WC4] NGC 6369 [WC4] [WCE] IC 1747 [WC4] He 2-55 [WC3] NGC 7026 [WC3] NGC 1501 [WC4] NGC 6751 [WC4] NGC 5189 [WC2] PB 6 [WC2] Sand 3 [WC3] NGC 2867 [WC2] NGC 2452 [WC2] NGC 6905 [WC2] A 78 wels A 30 wels NGC 7094 PG PN K 1-16 PG NGC 246 PG RX J2117... PG 0 20 40 60 80 Mass fraction [%] Theoretical scenarios: formation of H-deficient CS

AFTP 4.0 AGB final AFTP thermal pulse LTP AGB 3.5 Planetary nebulae (Herwig 2001)

3.0

) LTP Late thermal 2.5 VLTP pulse (Bl¨ocker log (L/L

2.0 White dwarfs 1995)

1.5 VLTP Very late 1.0 thermal pulse

5.0 4.5 4.0 3.5 (Herwig 2001)

log Teff Expected abundance pattern for [WC] stars

Models for simultaneous mixing and burning (upper panel: Herwig 2001; lower panel: Althaus et al. 2005), calculated surface compositions after occurence of

H He C O N AFTP (1)

AFTP (2)

LTP

VLTP (Her.) mass fraction 0 10 20 30 40 50 60 70 80 90 100% VLTP (Alt.) Ne Recent analyses [WCE]: The He:C ratio and the diagnostic line pair

3.0 He II 7 - 4 C IV 10 - 7 2.0

1.0 C : He = 56 : 28 Wλ (C)/Wλ (He) = 3 0.0

3.0 He II 7 - 4 C IV 10 - 7 2.0

1.0 Normalized flux C : He = 48 : 36 Wλ (C)/Wλ (He) = 2 0.0

3.0 He II 7 - 4 C IV 10 - 7 2.0

1.0 C : He = 30 : 60 Wλ (C)/Wλ (He) = 1 0.0 5400 5450 5500 5550 o λ / A [WCE]: The He:C ratio and the diagnostic line pair

3.0 2.0

He II 7 - 4 C IV 10 - 7 3.0 2.0 1.0 2.0 1.0 1.7 C : He = 56 : 28 Wλ (C)/Wλ (He) = 3 1.5 0.0 ) 1.5 1.3 1.3

R 0.5 3.0 1.3 1.0 / t

R 1.3 He II 7 - 4 C IV 10 - 7 2.0 1.3 log ( 1.0 1.0 Normalized flux C : He = 48 : 36 Wλ (C)/Wλ (He) = 2 0.0 0.0

3.0 He II 7 - 4 C IV 10 - 7 2.0 1.0 -0.5 1.0

1.0 4.8 4.9 5.0 5.1 5.2 5.3 C : He = 30 : 60 Wλ (C)/Wλ (He) = 1 log (T / kK) 0.0 * 5400 5450 5500 5550 o λ / A Contour lines with equal Wλ(C)/Wλ(He) [WCE] results

We reanalyzed [WCE] stars with improved models (e.g. iron line blanketing) and new high-resolution spectra, optical (M. Pe˜na) and FUSE Ne detected, but exact value unclear N overabundant with 1 . . . 2%, in concordance with VLTP He C O N Ne mass fraction 0 10 20 30 40 50 60 70 80 90 100% VLTP (Alt.)

AFTP (2) H

low carbon abundances of typically 30% for [WCE] points to AFTP Weak emission line stars

among 130 emission line stars listed by Acker & Neiner (2003), about 50 so called wels, e.g.:

7 6 NGC 6572 5

4 δ γ β H H He II 4686 H He II 5412 C IV 3

Normalized flux 2

1

0 4200 4400 4600 4800 5000 5200 5400 5600 5800 o λ [A] wels → collective name so far no systematic spectral analyses Are wels identical with intermediate [WC] stars, i.e. between [WCE] and [WCL]? A special wels: PB8

classified as: Of-WR(H) (M´endenz 1991); wels (Tylenda et al. 1992); [WC4-6] (Acker & Neiner 2003) A special wels: PB8

classified as: Of-WR(H) (M´endenz 1991); wels (Tylenda et al. 1992); [WC4-6] (Acker & Neiner 2003) 2 /

2.4 1

o

S o o o O O S S P P o 2 S P 1 P 3 3 1 P P P 1 P 3 1 1 2 2 2 (neb.) (neb.) 2 2 S - o - 3s S 3 D D - '3p - '3p - 3s 2 - 3s 1 P 1 1 / o o O 1 O 3 D - '3s D P P - '3s - - S - 5p S - 3p P D - 3p D - 3p P P 3 1 1 1 1 2 2 2 2.0 3 1 2 1 2 P P - 3s 3 3 o P D - 2p 1 1 β He II 9 - 4 N V 3p N III 3d C III 3p He II 4 - 3 N IV 6 - 5 He II 8 - 4 H [OIII] [OIII] C IV 6s O V 3p N IV '3p O III '3d He II 7 - 4 O III '3p C III 3d N IV '3d C IV 3s He I α

1.6 C IV 10 - 7 N IV 2s4s - 2s4p He II 16 - 5 N IV 3p He II 15 - 5 He II 14 - 5 He II 6 - 4 H He I 3d He II 13 - 5

1.2 Normalized flux

10x 0.8 4500 4800 5100 5400 5700 6000 6300 6600 o λ /A Observation (–) vs. model (–) PB 8: results

[WCE]

PB 8 H He CON

mass fraction 0 10 20 30 40 50 60 70 80 90 100% PB 8: results

[WCE]

PB 8 H He CON WN mass fraction 0 10 20 30 40 50 60 70 80 90 100%

→ the first identified [WN/C] star! suggested formation via diffusion-induced CNO-flash (Miller Bertolami et al. 2011) more [WN/C] stars? Evolution of hydrogen-deficient PNe

Collaboration with Leibniz-Institut f¨ur Astrophysik Potsdam (AIP):

NEBEL (Steffen, Sch¨onberner, Sandin, Stellar atmospheres NEBEL Jacob): models of evolving PNe PoWR calculations of thermal conduction synthetic X-ray spectra + X-ray observations X-rays + stellar evolution models Open questions Do [WC] stars form an evolutionary sequence? T *

[WO] 10 [WC]

5 Number of objects

0 1 2 3 4 4 5-67-8 8 8-9 9 10 11 Subtypes [WCE] [WCL] From which scenario(s) do [WC] stars originate?

AFTP 4.0 AGB final AFTP thermal pulse LTP AGB 3.5 Planetary nebulae (Herwig 2001)

3.0

) LTP Late thermal 2.5 VLTP pulse (Bl¨ocker log (L/L

2.0 White dwarfs 1995)

1.5 VLTP Very late 1.0 thermal pulse

5.0 4.5 4.0 3.5 (Herwig 2001)

log Teff How does an H-deficent star become a WR star?

I.e. why do they have so strong winds? For massive WNL stars: proximity to Eddington limit, i.e. high L/M ratio ≈ 15 000 − 30 000 (in solar units): Gr¨afener & Hamann (2008) For CSPNe: L/M ≈ 3 000 − 30 000 in avarage but for most CSPN distances unknown → L and M unknown

our wind models with fixed L = 6000 L⊙ and M = 0.6 M⊙, −7 always η < 1 (D = 10, M˙ ≈ 10 M⊙/yr) hydrodynamically consistent model (Gr¨afener et al. 2008) for NGC 6905 → needs D = 100 (!) possible explanation: enrichment with s-process elements (not in our models, atomic data not available) NGC 6751