S Dor-Type Variables in Other Galaxies

Sharov, A. S.

doi:10.1007/978-94-010-9934-9_38

Cited by 15 publications

(9 citation statements)

References 16 publications

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“…The historical light curve of Var B was described, among others by Hubble & Sandage (1953), Rosino & Bianchini (1973), and Sharov (1973, 1975. The star underwent ample secular light variation between ∼17 and ∼14.5 (photographic magnitudes).…”

Section: Discussionmentioning

confidence: 90%

The present status of four luminous variables in M 33

Viotti¹,

Rossi

Polcaro³

et al. 2006

A&A

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Context. Understanding the origin of the instabilities of LBVs is important for shedding light on the late evolutionary stages of massive stars and on the chemical evolution of galaxies. Aims. To investigate the physical nature of variable stars in the upper H-R diagram, we performed a spectrophotometric study of the Romano's star GR 290 and the Hubble-Sandage variables A, B, and C in the close galaxy M 33. Methods. New spectroscopic and photometric data were employed in conjunction with already published data of these stars in order to derive spectral types, energy distribution and bolometric luminosities. Results. The yellow hypergiant Var A is still at minimum, with a ∼G-type spectrum and strong Hα emission (W eq −35 Å). Var B is in a low luminosity hot state (V = 17.5, B − V = −0.15) with very strong Hα emission (W eq = −310 Å). Its absolute bolometric luminosity is 0.6 × 10 6 L . Var C, at V = 16.4, is fainter than in the mid 1980s, but its spectrum shows the typical features of LBVs at maximum, a spectrum that is very rich in Fe ii emission lines. Its L bol is about 0.7 × 10 6 L . The Romano's star GR 290 has a rich hot emission-line spectrum and is very bright with L bol = 3 × 10 6 L . During 2004 the star brightened by ∼half magnitude in each of the BVR filters. Conclusions. Our observations confirm that Var A probably is an intermediate type hypergiant star surrounded by an expanding envelope with a collisionally excited hydrogen emission, largely obscured by dusty disk and nebula. In recent years, Var B has undergone a blueward transition in the H-R diagram, probably at constant bolometric luminosity, while Var C is in a post-maximum phase with an η Car-type spectrum. GR 290 is notable for its spectrum and luminosity, and it is likely to develop ample spectral variations in the near future, similar to those observed in AG Car.

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Section: Discussionmentioning

confidence: 90%

The present status of four luminous variables in M 33

Viotti¹,

Rossi

Polcaro³

et al. 2006

A&A

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“…The first two of the three stars were already known as variable objects in the 16th century, but it was not until the 1970s when their similarities and their possible connection to a certain stage in the massive star evolution was discussed (see e.g. Humphreys 1975Humphreys , 1978Sharov 1975;Humphreys & Davidson 1979;Wolf et al 1980).…”

Section: Late Wn Stars As Lbv Candidatesmentioning

confidence: 99%

The Wolf-Rayet stars in M 31

Sander

Todt

Hainich

et al. 2014

A&A

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Context. Comprehensive studies of Wolf-Rayet stars were performed in the past for the Galactic and the LMC population. The results revealed significant differences, but also unexpected similarities between the WR populations of these different galaxies. Analyzing the WR stars in M 31 will extend our understanding of these objects in different galactic environments. Aims. The present study aims at the late-type WN stars in M 31. The stellar and wind parameters will tell about the formation of WR stars in other galaxies with different metallicity and star formation histories. The obtained parameters will provide constraints to the evolution of massive stars in the environment of M 31. Methods. We used the latest version of the Potsdam Wolf-Rayet model atmosphere code to analyze the stars via fitting optical spectra and photometric data. To account for the relatively low temperatures of the late WN10 and WN11 subtypes, our WN models have been extended into this temperature regime. Results. Stellar and atmospheric parameters are derived for all known late-type WN stars in M 31 with available spectra. All of these stars still have hydrogen in their outer envelopes, some of them up to 50% by mass. The stars are located on the cool side of the zero age main sequence in the Hertzsprung-Russell diagram, while their luminosities range from 10 5 to 10 6 L . It is remarkable that no star exceeds 10 6 L . Conclusions. If formed via single-star evolution, the late-type WN stars in M 31 stem from an initial mass range between 20 and 60 M . From the very late-type WN9-11 stars, only one star is located in the S Doradus instability strip. We do not find any late-type WN stars with the high luminosities known in the Milky Way.

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“…Once known variable stars and the blended star I-18 were excluded, from this stage there emerged 1,722 stars which had satisfactory (σ < 0.10 mag) measurements in each of B and V from at least two different studies. These stars should now represent just about the best reference list that we can achieve-a gold standard-for determining and removing systematic photometric offsets from the remaining six datasets, which did not previously have fully independent calibrations: the Sandage (1962) photographic data, and the Sharov (1965), Cannon (1968), McClure & Twarog (1977), Caputo et al (1990), and Dinescu et al (1996) results. There is no need to impose a selection on the U, R, and I filters at this point, since none of these studies presented U, R, or I data.…”

Section: Examination Ofmentioning

confidence: 99%

A Star Catalog for the Open Cluster NGC 188

Stetson¹,

McClure²,

VandenBerg³

2004

PUBL ASTRON SOC PAC

102

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We present new BVRI broad-band photometry for the old open cluster NGC 188 based upon analysis of 299 CCD images either obtained by us, donated by colleagues, or retrieved from public archives. We compare our results on a star-by-star basis with data from eleven previous photometric datasets for the cluster. We homogenize and merge the data from all the photometric studies, and also merge membership probabilities from four previous proper-motion studies of the cluster field. Fiducial cluster sequences in the BV (Johnson) RI (Cousins) photometric system of Landolt (1992, AJ, 104, 340) represent the principal result of this paper. These have been compared to reference samples defined by (a) Landolt's standard stars, (b) the old open clusters M 67 and NGC 6791, and (c) stars within 25 pc having modern photometry and precise Hipparcos parallaxes. In a companion paper we show that our derived cluster results agree well with the predictions of modern stellar-interior and -evolution theory, given reasonable estimates of the cluster chemical abundances and foreground reddening.The individual and combined datasets for NGC 188 have been made available through our web site.

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S Dor-Type Variables in Other Galaxies

Cited by 15 publications

References 16 publications

The present status of four luminous variables in M 33

The present status of four luminous variables in M 33

The Wolf-Rayet stars in M 31

A Star Catalog for the Open Cluster NGC 188

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