The UV Spectra of the WELS
Wagner L. F. Marcolino(1,2)
Francisco Xavier de Araujo(2)
Helson B. M. Junior (2,3)
Eduardo S. Duarte (3)
(1) Laboratoire d'Astrophysique de Marseille (LAM) - France
(2) Observatorio Nacional (ON/MCT) - Brazil
(3) Centro Federal de Educacao Tecnologica (CEFET) - Brazil
Tübingen, September 2007
Introduction:
Central stars of planetary nebulae that are H-deficient (neglecting O(He),RCB stars, etc):
[WR] – Wolf-Rayets
PG 1159 Stars
[WC]-PG 1159 Stars
Broad, strong emissions of He, C, O(Crowther et al. 1998; Acker & Neiner 2003)
Mainly C IV and He II absorptions(Wesemael et al. 1985;Werner et al. 1997)(about 15 have PN associated)
Mixed spectrum (abs+ems)(Werner & Herwig 2006)
Tübingen, September 2007
~ 75 objects
~ 40 objects
~ 2-5 objects!
late-type [WR] => early-type [WR] => [WC]-PG1159 => PG 1159 => non DA white dwarfs(e.g. Acker et al. 1996; Pena et al. 2001; Werner et al. 1992; Hamann 1997)
(other sequences are possible/needed !)
The “weak emission line central stars” - WELS:
- First mention to WELS : Aller & Keyes (1985)
Tübingen, September 2007
- The definition : Tylenda et al. (1993)
- 77 objects were studied: 39 classified as [WR] and 38 as WELS
Weak emissions (compared to [WR] stars)
emission at 4650A(N III + C III + C IV)
C IV 5805(weak emission or absent)
C III 5696A(weak emission or absent)
DEFINITION:
The “weak emission line central stars” - example:
Tübingen, September 2007
Informations, questions and confusions about the WELS:
Tübingen, September 2007
- What is their evolutionary status ?
- Parthasarathy et al. (1998) : WELS are [WC]-PG 1159 stars !
- There are about 50 WELS known (Tylenda et al. 1993; Parthasarathy et al. 1998; Gorny et al. 2004)
- Most works were done in the optical part of the spectrum: We do not know their UV !
- Their physical parameters (e.g. Teff
, vinf
, Mdot) and chemical abundances remain unknown.
[WCL] => [WCE] => WELS => PG 1159 => non DA
- Pena et al. (2001;2003): WELS are not descendants of the [WR] stars (v_exp)
- PNe analysis: Some WELS could be progenitors of [WO] stars (Gesick et al. 2006)
- Other recent works (e. g. Girard et al. 2007)
Tübingen, September 2007
The UV Spectra of the WELS
The Ultraviolet Spectra of the WELS:
Tübingen, September 2007
- We retrieved all the data available from the IUE database: 20 WELS (42 spectra selected)
- line identifications and measurements of W
λ and
fluxes for all lines (stellar and/or nebular)
- measured terminal velocities for all objects presenting P-Cygni profiles
- compared the results obtained to the two prototypes [WC]-PG1159 stars: A30 and A78
The Ultraviolet Spectra of the WELS:
Tübingen, September 2007
Group (1): Presence of a strong P-Cygni profile of C IV 1549
average Wλ(CIV) ~ 6
The Ultraviolet Spectra of the WELS:
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Group (2): Presence of a weak C IV 1549 in P-Cygni
average Wλ(CIV) ~ 1
The Ultraviolet Spectra of the WELS:
Tübingen, September 2007
Group (3): Absence of P-Cygni's
Wλ(CIV) ≥ 100
The UV of the [WC]-PG 1159 stars:
Tübingen, September 2007Typical UV of most of the WELS with P-Cygni's
Considered the prototypes of the [WC]-PG 1159 class (Werner & Herwig 2006)Note the simultaneous presence of N V 1238, O V 1371 and C IV 1549
The three exceptions : NGC 6543, NGC 6567 and NGC 6572
Tübingen, September 2007
WELS in fact resembling the [WC]-PG 1159 stars
Note: NGC 6567 was already considered a [WC]-PG 1159 star (Hamann 1996)
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Terminal Velocities
Calibration provided by Prinja (1994):
“Determining hot star wind terminal velocities from low-resolution IUE data” (A&A, 289, 221)
a1 = 883, a
2 = 259, a
3 = 3 for C IV 1549
a1 = 2723, a
2 = 621, a
3 = 18 for N V 1238
`
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Results:
values concentrated in ~1000-1500 km/s
much higher values: ~3000 km/s (C IV)
`
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Results:
Bin width is 500 km/s. Data for [WR] and PG 11 59 stars are from Koesterke (2001).
Terminal velocities distribution of H deficient CSPN
`
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Results:
Central stars temperature distribution – Gesicki et al. (2006)
`
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Conclusions from the UV analysis:
1) We found that the WELS can be divided in three groups
- A 30 and A 78 show intense and simultaneous P-Cygni's in N V 1238, O V 1371 and C IV 1549
- The WELS present weak or no O V 1371 (the same is true for N V in a few cases)
- The situation is ambiguous for NGC 6543, NGC 6567 and NGC 6572
2) The WELS are distinct from A 30 and A 78 ([WC]-PG1159 stars)
The question remains: What is their evolutionary status ?
- Terminal velocities considerably lower than in [WC]-PG1159 stars
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Quantitative analysis of WELS
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CMFGEN models for the WELS:
Optical : ESO 1.52m Telescope(resolution of ~2Å)
IUE satellite(resolution ~6Å)
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Preliminary results for Hen 2-12:
- Very low mass-loss (about 10-9 solar mass/year)
- Regarding the 4650Å feature: N V absorptions on its side ! N III lines could not be reproduced
- Teff
lower (< 100kK) than in A 30 and A 78 and in [WO] stars
- More work under way...
yeah, right!Hey, I know what the WELS are !
THANKS !
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