A comprehensive variability study of the enigmatic WN8 stars: final results

Марченко, С. В.; Moffat, A. F. J.; Eversberg, Thomas; Hill, Graham; Tovmassian, G.; Morel, Thierry; Seggewiß, W.

doi:10.1111/j.1365-8711.1998.01174.x

Cited by 39 publications

(38 citation statements)

References 23 publications

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“…Again, this mechanism could be related to the observed pulsations (see e.g. Marchenko et al 1998;Lefèvre et al 2005) or rotational driving. Note that also the non-detection of X-ray emission from WN 8 subtypes might be a hint to a different wind driving mechanism (see Oskinova 2005).…”

Section: Are Wr Winds Generally Driven By Radiation?mentioning

confidence: 86%

Mass loss from late-type WN stars and itsZ-dependence

Gräfener¹,

Hamann²

2008

A&A

244

319

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Context. The mass loss from Wolf-Rayet (WR) stars is of fundamental importance for the final fate of massive stars and their chemical yields. Its Z-dependence is discussed in relation to the formation of long-duration Gamma Ray Bursts (GRBs) and the yields from early stellar generations. However, the mechanism of formation of WR-type stellar winds is still under debate. Aims. We present the first fully self-consistent atmosphere/wind models for late-type WN stars. We investigate the mechanisms leading to their strong mass loss, and examine the dependence on stellar parameters, in particular on the metallicity Z. Methods. We perform a systematic parameter study of the mass loss from WNL stars, utilizing a new generation of hydrodynamic non-LTE model atmospheres. The models include a self-consistent treatment of the wind hydrodynamics, and take Fe-group lineblanketing and clumping into account. They thus allow a realistic modelling of the expanding atmospheres of WR stars. The results are verified by comparison with observed WNL spectra. Results. We identify WNL stars as very massive stars close to the Eddington limit, potentially still in the phase of central H-burning. Due to their high L/M ratios, these stars develop optically thick, radiatively driven winds. These winds show qualitatively different properties than the thin winds of OB stars. The resultant mass loss depends strongly on Z, but also on the Eddington factor Γ e , and the stellar temperature T . We combine our results in a parametrized mass loss recipe for WNL stars. Conclusions. According to our present model computations, stars close to the Eddington limit tend to form strong WR-type winds, even at very low Z. Our models thus predict an efficient mass loss mechanism for low metallicity stars. For extremely metal-poor stars, we find that the self-enrichment with primary nitrogen can drive WR-type mass loss. These first WN stars might play an important role in the enrichment of the early ISM with freshly produced nitrogen.

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Section: Are Wr Winds Generally Driven By Radiation?mentioning

confidence: 86%

Mass loss from late-type WN stars and itsZ-dependence

Gräfener¹,

Hamann²

2008

A&A

244

319

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“…Abbott & Conti 1987). Among the WR stars, the subtype WN8 stars are currently thought of being direct evolutionary descendants of massive and luminous Of stars Marchenko et al (1998) and show various spectroscopic and light variations on a variety of time scales. Some of the variations were suspected to be caused by stellar pulsations, and periodic variations had been searched for in WN8 stars (Marchenko et al 1998, and references therein).…”

Section: Introductionmentioning

confidence: 99%

A MOST probable explanation of the pulsation of WR 123

Dorfi¹,

Gautschy

Saio

2006

A&A

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Aims. Resorting to the observed period of the cyclic part of WR 123's photometric variability we constrain its stellar parameters. Methods. Radiation hydrodynamic simulations were performed on selected stellar envelope models for which also linear stability analyses were computed. Results. Pulsations of massive hydrogen-rich stellar envelopes subject to sufficiently high luminosity-to-mass ratios are excited with periods that conform with the observed one by MOST in WR123.

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“…Considering that the star shows a consistent level of photometric variability that practically never exceeds ∼0.15 mag long-term (daysmonth: e.g. Marchenko et al 1998;Lefèvre et al 2005, our study) and rarely exceeds ∼0.05 mag during any particular night of ground-based observations (e.g., Fig. 1), such a level of lpv cannot be a consequence of the continuum variations alone.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, all photometric, polarimetric and spectroscopic monitoring campaigns of WN8 stars have consistently shown the highest level of intrinsic variability among all WR stars (e.g. ; Moffat & Shara 1986;Lamontagne & Moffat 1987;Drissen et al 1987;Balona et al 1989;Robert et al 1989;Robert 1992;Antokhin et al 1995;Marchenko et al 1998). However, despite the claims of multiple photometric periods ranging from hours to days, there is no period that could A&A 530, A151 (2011) be labeled as unique to all the campaigns for any given WN8 star.…”

Section: Introductionmentioning

confidence: 99%

“…Discovery of any stable periodicity pattern in a WN8 star would help to establish whether the star is a binary or a single rotator with an inhomogeneous wind or, alternatively, to refine the rather controversial pulsation models of WR stars. All of the above applies specifically to our target, WR 123 (see Marchenko et al 1998, for references), which shows an extremely complex, rapidly evolving light curve, along with seemingly aperiodic polarimetric (St-Louis et al 1988) and high-amplitude line-profile variability (Massey & Conti 1980;Lamontagne et al 1983;Marchenko et al 1998). All searches for periodic signals provided rather inconsistent results until 2004, when an intense, long-term, broad-band photometry campaign of WR 123 (Lefèvre et al 2005) was performed by the MOST (Microvariability and Oscillations of STars) satellite.…”

Section: Introductionmentioning

confidence: 99%

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A 10-h period revealed in optical spectra of the highly variable WN8 Wolf-Rayet star WR 123

Chené

Foellmi²,

Марченко

et al. 2011

A&A

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Aims. What is the origin of the large-amplitude variability in Wolf-Rayet WN8 stars in general and WR123 in particular? A dedicated spectroscopic campaign targets the ten-hour period previously found in the high-precision photometric data obtained by the MOST satellite. Methods. In June-August 2003 we obtained a series of high signal-to-noise, mid-resolution spectra from several sites in the λλ 4000−6940 Å domain. We also followed the star with occasional broadband (Johnson V) photometry. The acquired spectroscopy allowed a detailed study of spectral variability on timescales from ∼5 min to months. Results. We find that all observed spectral lines of a given chemical element tend to show similar variations and that there is a good correlation between the lines of different elements, without any significant time delays, save the strong absor ption components of the Hei lines, which tend to vary differently from the emission parts. We find a single sustained periodicity, P ∼ 9.8 h, which is likely related to the relatively stable pulsations found in MOST photometry obtained one year later. In addition, seemingly stochastic, large-amplitude variations are also seen in all spectral lines on timescales of several hours to several days.

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A comprehensive variability study of the enigmatic WN8 stars: final results

Cited by 39 publications

References 23 publications

Mass loss from late-type WN stars and itsZ-dependence

Mass loss from late-type WN stars and itsZ-dependence

A MOST probable explanation of the pulsation of WR 123

A 10-h period revealed in optical spectra of the highly variable WN8 Wolf-Rayet star WR 123

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