The UV Spectra of the WELS

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)


~ 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)


- 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:


Informations, questions and confusions about the WELS:


- 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)


The UV Spectra of the WELS

The Ultraviolet Spectra of the WELS:


- 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



Group (1): Presence of a strong P-Cygni profile of C IV 1549

average Wλ(CIV) ~ 6



Group (2): Presence of a weak C IV 1549 in P-Cygni

average Wλ(CIV) ~ 1



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


WELS in fact resembling the [WC]-PG 1159 stars

Note: NGC 6567 was already considered a [WC]-PG 1159 star (Hamann 1996)


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

`


Results:

values concentrated in ~1000-1500 km/s

much higher values: ~3000 km/s (C IV)

`


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

`


Results:

Central stars temperature distribution – Gesicki et al. (2006)

`


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


Quantitative analysis of WELS

`


CMFGEN models for the WELS:

Optical : ESO 1.52m Telescope(resolution of ~2Å)

IUE satellite(resolution ~6Å)

`


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 !

The UV Spectra of the WELS

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