An outflow from the nebula around the LBV candidate S 119

Abstract

Abstract.We present an analysis of the kinematic and morphological structure of the nebula around the LMC LBV candidate S 119. On HST images, we find a predominantly spherical nebula which, however, seems to be much better confined in its eastern hemisphere than in the western one. The filamentary western part of the nebula is indicative of matter flowing out of the nebula's main body. This outflow is evidenced by our long-slit echelle spectra. They show that, while most of the nebula has an expansion velocity of 25.5 km s −1 , the outflowing material reaches velocities of almost 140 km s −1 , relative to the systemic one. A ROSAT HRI image shows no trace of S 119 and thus no indications of hot or shocked material.Key words. stars: evolution -stars: individual: S 119 -stars: mass-loss -ISM: bubbles -ISM: jets and outflows IntroductionStars with masses in the range of 50−100 M and luminosities of 10 5 −10 6 L populate the upper left end of the Hertzsprung-Russell Diagram (HRD). During their short lives of < ∼ 10 7 yrs they evolve from hot O stars on the main sequence towards cooler temperatures, first at almost constant luminosities. They soon enter a phase of very strong mass loss of up to 10 −4 M yr −1 . This influences their further evolution dramatically: They do not evolve further towards lower temperatures, i.e., towards the red supergiant state, but rather turn in the HRD and become hotter again, albeit later less luminous (e.g., Schaller et al. 1992;Langer et al. 1994).The region in the HRD where this turn occurs is known to be the domain of the Luminous Blue Variables (LBVs). There exists an empirical limit that separates a region in the HRD into which the most massive stars do not evolve, the so-called Humphreys-Davidson Limit (Humphreys & Davidson 1979. Here the stars not only exhibit large continuous mass loss, but at least some of them undergo giant eruptions. Both, the continuous wind and the eruptions lead to a peeling off of the outer parts of the stellar envelope and to the formation of circumstellar LBV nebulae (LBVN; e.g., Nota et al. 1995). Humphreys & Davidson (1994) Bohannan & Walborn (1989). Since the early eighties, there was already the suspicion of a close relation between Ofpe/WN9 stars and LBVs when R127, located again in the LMC and previously classified as Ofpe/WN9 underwent an LBV outburst (Stahl et al. 1983). The evidence for a connection between the two stellar classes has become even stronger since then, as longtime spectroscopic monitoring of LBVs and Ofpe/WN9 stars became available (see, e.g., Stahl & Wolf 1986;Wolf et al. 1988;Bohannan & Walborn 1989;Nota et al. 1996;Pasquali et al. 1996).After discovering a nebula around S 119, Nota et al. (1994) classified the star as an LBV candidate. Their ESO New Technology Telescope (NTT) image shows a nebula of 7 × 9 size (corresponding to 1.9 pc × 2.1 pc for an assumed distance of the LMC of 51.2 kpc), with a brighter lobe. Their NTT/EMMI spectra indicate an expansion velocity of the S 119 nebula of ∼25 km s −1 , and a ratio of H α /N ...

On the structure and kinematics of nebulae around LBVs and LBV candidates in the LMC

“…Such an outflow might results, e.g., from Rayleigh-Taylor instabilities in the nebula, density gradients in the ambient medium or the onset of an asymmetric faster stellar wind. Finally, note that the location of S 119 in the disk of the LMC is still under debate since the star's radial velocity is much slower than expected (Nota et al 1994;Danforth & Chu 2001;Weis et al 2003). Hence, the nebula's size might be different, giving a possibly shorter distance.…”

“…The nebula expands with roughly 14 km s −1 . Several analysis and studies of this object (Weis et al 1995(Weis et al , 1997bWeis & Duschl 2002) let us suspect that this object is an LBV candidate due to its brightness, UV spectra (see Smith Neubig & Bruhweiler 1999), and the large nebula, which is especially strong in the [N ] lines. The [N ]λ6583 Å/H α ratio of 0.7 is comparable to those of other LBV nebulae (e.g., AG Car: [N ]λ6583 Å/H α ∼ 0.5, de Freitas Pacheco et al 1992).…”

“…The following objects have been observed with the HST (see Table 1) and analyzed in this paper: R 127, R 143, S 61, R 71, S Dor, R 99. For S 119, see Weis et al (2003). For R 110, R 84, HDE 269582, and Sk−69 • 279, no HST observations exist so far.…”

“…Nota et al (1994) were the first to resolve a 7 × 9 large nebula (1.9 pc× 2.1 pc) associated with S 119. We analysed this nebula (Weis et al 2003) using HST imaging and 4 m long-slit highresolution spectra, in the same set-up as descibed in this work. The images show that the nebula is nearly spherical with a diameter of 7.…”

Nebulae around Luminous Blue Variables – large bipolar variety

“…A large fraction of nebulae are bipolar. Bipolarity is seen either as an hourglass shape like in η Car (Weis 2001) and HR Car (Weis et al 1997), or bipolar attachments-caps-as in WRA 751 (Weis 2000) or R 127 (Weis 2003). At least η Car and P Cyg show several distinct nebula parts, the outer ejecta, Homunculus, and Little Homunculus for η Car and the inner and outer shell of P Cyg.…”