A Newly Discovered Open Cluster Surrounding the Wolf‐Rayet Stars WR 38 and WR 38a

Shorlin, S. L. S.; Turner, D. G.; Pedreros, Mario H.

doi:10.1086/382554

Cited by 12 publications

(45 citation statements)

References 25 publications

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“…We dispute, however, the proposal that these stars form a star cluster as suggested by Shorlin (1998), whose conclusion was possibly the result of the small FOV covered by their photometry. Our wider area coverage clearly enables us to see that are looking at a population of field stars of same reddening and age, but located at different position inside the Carina arm.…”

Section: Group Acontrasting

confidence: 63%

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Searching for spiral features in the outer Galactic disk

Carraro

Costa

2008

A&A

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Context. The detailed spiral structure of the outer Galactic disk remains poorly constrained, and for several line of sights in the Galaxy we depend on model extrapolations. Aims. One of these regions is the fourth Galactic quadrant, between Vela and Carina (270, where, apart from the conspicuous Carina branch of the Carina Sagittarius arm, no spiral arms have been detected so far in the optical beyond l ∼ 270• . Methods. By means of deep UBVI photometry, we search for spiral features in known low absorption windows. Although observationally demanding, U photometry constitutes a powerful tool for detecting and characterizing distant aggregates of young stars, and allows firmer distance estimates to be derived. We study a direction close to the tangent (l ∼ 290• ) of the Carina arm, in an attempt to detect optical spiral tracers far beyond the Carina branch, where radio observations and model predictions appear to indicate the presence of an extension of the Perseus and Norma-Cygnus spiral arms in the fourth quadrant. Results. Along this line of sight, we detect three distinct groups of young stars. Two of them, at distances of ∼2.5 and ∼6.0 kpc, belong to the Carina spiral arm, which is traversed twice in this particular direction. Interestingly, the latter is detected for the first time. The third group, at a distance of ∼12.7 kpc, is probably related to the Perseus arm which lies beyond the Carina arm, and constitutes the first optical detection of this arm in the fourth Galactic quadrant. The position of this feature is consistent with both HI observations and model predictions. We also present evidence that this extremely distant group, formerly assumed to be a star cluster (Shorlin 1), is a diffuse, young population, typically found in spiral galaxies. In addition, our data-set does not support, as claimed in the literature, the possible presence of the Monoceros Ring in this direction Conclusions. This study highlights how multicolor optical studies can be effective in probing the spiral structure of the outer Galactic disk. More fields need to be studied in this region of the Galaxy to constrain the spiral structure in the fourth Galactic quadrant more accurately, in particular, the shape and extent of the Perseus arm, and, possibly, to detect the even more distant Norma-Cygnus arm.

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Section: Group Acontrasting

confidence: 63%

“…We investigate the field towards the Wolf-Rayet (WR) stars WR38 and WR38a (RA = 11 h 06 m , Dec = −61 • 14 , Shorlin et al 2004, hereafter Sh04; Wallace et al 2005, hereafter Wa05), which attracted our attention for several reasons.…”

Section: Introductionmentioning

confidence: 99%

Searching for spiral features in the outer Galactic disk

Carraro

Costa

2008

A&A

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“…Our fit is not very consistent, possibly indicating that the lines are diluted by a companion's continuum. From a weak cluster around WR 38, Shorlin et al (2004) When we analyze its line spectrum assuming that the star is single, the obtained parameters place the star distinctly above the sequence of single WC stars in the log T * -log R tplane (see Fig. 6).…”

Section: Discussionmentioning

confidence: 99%

The Galactic WC stars

Sander

Hamann

Todt

2012

A&A

238

405

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Context. The life cycles of massive stars from the main sequence to their explosion as supernovae or gamma ray bursts are not yet fully clear, and the empirical results from spectral analyses are partly in conflict with current evolutionary models. The spectral analysis of Wolf-Rayet stars requires the detailed modeling of expanding stellar atmospheres in non-LTE. The Galactic WN stars have been comprehensively analyzed with such models of the latest stage of sophistication, while a similarly comprehensive study of the Galactic WC sample remains undone. Aims. We aim to establish the stellar parameters and mass-loss rates of the Galactic WC stars. These data provide the empirical basis of studies of (i) the role of WC stars in the evolution of massive stars, (ii) the wind-driving mechanisms, and (iii) the feedback of WC stars as input to models of the chemical and dynamical evolution of galaxies. Methods. We analyze the nearly complete sample of un-obscured Galactic WC stars, using optical spectra as well as ultraviolet spectra when available. The observations are fitted with theoretical spectra, using the Potsdam Wolf-Rayet (PoWR) model atmosphere code. A large grid of line-blanked models has been established for the range of WC subtypes WC4 -WC8, and smaller grids for the WC9 parameter domain. Both WO stars and WN/WC transit types are also analyzed using special models. Results. Stellar and atmospheric parameters are derived for more than 50 Galactic WC and two WO stars, covering almost the whole Galactic WC population as far as the stars are single, and un-obscured in the visual. In the Hertzsprung-Russell diagram, the WC stars reside between the hydrogen and the helium zero-age main sequences, having luminosities L from 10 4.9 to 10 5.6 L . The mass-loss rates scale very tightly with L 0.8 . The two WO stars in our sample turn out to be outstandingly hot (≈200 kK) and do not fit into the WC scheme. Conclusions. By comparing the empirical WC positions in the Hertzsprung-Russell diagram with evolutionary models, and from recent supernova statistics, we conclude that WC stars have evolved from initial masses between 20 solar masses and 45 M . In contrast to previous assumptions, it seems that WC stars in general do not descend from the most massive stars. Only the WO stars might stem from progenitors that have been initially more massive than 45 M .

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“…It is also true that the use of the PSF technique allows a clean removal of the star-light contribution from neighbors leading to larger magnitudes and, therefore, negative mean differences in all colors and magnitudes. On the other hand, since Shorlin et al (2004) have pointed out that the METHACROME chip at UTSO actually generates a small non-linear Balmer discontinuity effect in the U band of stars near the Balmer maximum, i.e. late B-type and A-type stars, there is a chance for part of the differences and standard …”

Section: Observations and Data Reductionmentioning

confidence: 99%

Revisiting the area of the open cluster Stock 16

Vazquez

Baume

Feinstein

et al. 2005

A&A

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Abstract. Deep CCD UBV(RI) C photometry has been carried out in the area of the open cluster Stock 16. The different photometric diagrams indicate the presence of three superimposed stellar groups, all composed of early type stars. The first of them, the cluster Stock 16, suffers from slightly variable reddening with a mean color excess E B−V = 0.51 . The second group, reddened by E B−V = 0.84 , includes the Wolf-Rayet star WR 50 (a WC7+OB), and the third one, with a mean E B−V = 1.18 , also includes another Wolf-Rayet star, WR 51 (a WN4+OB?). Our results confirm the distance and reddening already stated for Stock 16 but include new members. Concerning the other two highly reddened groups, we show that the first one -located at a distance of 3600 pc -is probably related to an anonymous OB association behind Cen OB1 also at 3600 pc already mentioned in the literature; the other seems to be a distant OB association -at more than 9000 pc -which may belong to the Scutum-Crux spiral arm. In these two groups we find evidence that the absorption law, A V /E B−V = R amounts to 4.0 approximately. The ages of the different star populations in the zone range from 5 × 10 6 yr to 6.4 × 10 6 yr for Stock 16, 8 × 10 6 for the second most reddened group and 5 × 10 6 for the probable association in Scutum-Crux. A determination of the IMF slope of Stock 16 was also carried out for stars in the mass range 1.8 < M < 14 M , giving a normal value x = 1.3. IntroductionThe very young open cluster Stock 16 lies close to the east border of the Coal Sack in Crux (l = 306.11, b = +0.14) where it appears projected against the H region RCW 75 (Rodgers et al. 1960), probably excited by the UV radiation field from the O7.5 V ((f)) star HD 115455 (Walborn 1973). A few photometric studies of the brightest members of Stock 16 have been carried out in the past, e.g. Lyngå (1970), Crampton (1971 and Lundström & Stenholm (1984). Later on, Turner (1985; hereafter T85) performed a detailed analysis in Stock 16 and the surrounding area by means of UBV photometry for 33 stars finding a color excess E B−V = 0.49 and a distance of 1.90 ± 0.08 kpc which coincides with the distance estimation, also quoted by T85, of Cen OBI and Cen Rl (1.88 ± 0.24 kpc). Since the age computed for Stock 16, 5 × 10 6 yr, is comparable to the ages of Cen OBI and the R association (Herbst 1975) Cen R1 (from 10 6 to 8 × 10 6 yr) and the distances of all Based on observations collected at the University of Toronto Southern Observatory (UTSO), Las Campanas, Chile. Feinstein et al. (2003), who have studied several moderately bright stars, has allowed determination of the properties of the ISM toward the cluster finding a mean polarization percentage P ≈ 2.5%.The present photometric investigation is aimed at performing a deeper study of the region including the open cluster Stock 16 and the surrounding area. We will try to confirm the earlier assumption of T85 who proposed that the star formation process in the area has taken place along the axis joining the elephant trunk stru...

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A Newly Discovered Open Cluster Surrounding the Wolf‐Rayet Stars WR 38 and WR 38a

Cited by 12 publications

References 25 publications

Searching for spiral features in the outer Galactic disk

Searching for spiral features in the outer Galactic disk

The Galactic WC stars

Revisiting the area of the open cluster Stock 16

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