Stars In LMC Research Articles

The Spectrum of HD 51585 in the Blue and in the Ultraviolet

New visible and ultraviolet spectra of the peculiar emission line star HD 51585 are described. Interstellar lines and the λ 2200 feature are rather weak. A colour excess E(B-V) = 0.33 is derived. The extinction curve resembles the one obtained from LMC stars.

R81: P Cygni of the LMC

Extensive photometric UBV observations and spectroscopic high dispersion (20 Å/mm and 38 Å/mm) coudé observations of the very luminous (Mv = −8.2) B2.5 eq supergiant R81 of the LMC were carried out between 1970 and 1980 at ESO, La Silla. In addition the IUE satellite was used to obtain a high resolution (0.2 Å) spectrogram in the ultraviolet wavelength range 1200 < λ < 1950 Å. The most prominent features of the visual spectrum are P Cygni profiles of the Balmer lines, indicating a shell with an expansion velocity of about 140 km s−1. The ultraviolet spectrum of R 81 is dominated by blue-shifted absorption resonance lines (Si II, Si IV, C II, C IV, Al III etc.) and Fe III absorption lines originating from metastable lower levels. From the UV resonance lines a very high mass loss rate (M = 5 10−5 M⊙ yr−1) was estimated. The early Balmer lines show very broad shallow emission wings (total width 40 to 50 Å), attributed to electron scattering. The mass loss is highly variable and presumably occurs in the form of sudden ejections of discrete shells. Irregular brightness variations of a few tenths of a magnitude in V on timescales of weeks were found. An absolute bolometric magnitude Mbol ≈ −10 and a photospheric radius R ≈ 70 R⊙ were estimated. A comparison with theoretical evolutionary tracks indicates a stellar mass M > 50 M⊙. The observed spectroscopic properties lead us to suggest that the LMC star R 81 is a close counterpart of the galactic star P Cyg, representing a short lived transient stage in the evolution of the most massive stars.

Ultraviolet studies of the Magellanic Clouds - I. Interstellar lines in the spectra of FD 70 and SK-71-45

High dispersion ultraviolet spectra of the two LMC members, HD 38282 (FD 70) and HD 269676 (SK-71-45), have been obtained with IUE. Velocity profiles have been presented of the numerous interstellar lines observed in the spectra of these stars and associated with the absorption in both the Galaxy and the LMC. In both lines-of-sight well defined interstellar components are observed at heliocentric velocity shifts of 0, +70, +150 and 200–300 km s−1, similar to those values reported for the interstellar Ca IIk lines observed in the spectrum of the LMC star HD 38268 in 30 Doradus by Blades & Meaburn. The extended blue asymmetric absorption observed in the LMC interstellar Ca IIk line absorption is also observed in both ultraviolet interstellar line profiles in FD 70 and SK-71-45, although the latter star is far removed from the 30 Doradus region. This result favors an origin for these features associated with gas in a halo around the LMC as proposed by de Boer and Savage.

Calcium abundances of F supergiants in the Magellanic Clouds

Low-dispersion image tube spectra have been obtained for six supergiant stars in the Large Magellanic Cloud and for four supergiants in the Small Magellanic Cloud. These stars are of spectral type F, though differences from galactic MK standards make precise classification difficult. The observed calcium K-line and Balmer-line strengths have been compared with simple synthetic spectra based on the model atmospheres of Kurucz. For the LMC stars, (Ca/H)=-0.2 +- 0.1; for the SMC stars, (Ca/H)=-0.6 +- 0.1. Better model atmospheres and synthetic spectra for supergiant stars are desirable to improve these values.

Interstellar extinction in the Large Magellanic Cloud

Recent UV observations together with complementary visible data of several reddened and comparison stars of similar spectral types in the Large Magellanic Cloud have been used to study the interstellar extinction in that galaxy. Most of the reddened stars studied here are located within 2° of 30 Doradus and show remarkably high extinction in the far UV, suggesting a large abundance of small particles. From the optical wavelength to 2,600 A the normalised extinction curves of the LMC stars are similar to the mean galactic extinction law.

The Eclipsing Binary System LB3459

The extremely blue foreground LMC star LB3459 (= HDE 269696) was reported by Kilkenny, Hilditch and Penfold (1978) to be an eclipsing binary system with a period of 6h17m. Preliminary analysis of uvby photometry and data obtained with the University of Cape Town highspeed photometer (Nather 1973) indicated that the system was composed of two degenerate stars, probably 0-type subdwarfs.

A comparison of galactic and Large Magellanic Cloud G-type supergiants by a method of spectrum synthesis

view Abstract Citations (24) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A comparison of galactic and Large Magellanic Cloud G-type supergiants by a method of spectrum synthesis. Fry, M. A. ; Aller, L. H. Abstract The spectra of two G4 Ia supergiants - HR 8752 and R 59, in the Perseus spiral arm and Large Magellanic Cloud, respectively - are analyzed by a method of spectrum synthesis, heretofore applied mostly to the sun. Evidence is presented that both of these stars are reddened by local dust clouds. Consequently, selection of appropriate model atmospheres must depend heavily on line spectrum data. A self-consistent spectrum synthesis analysis suggests that these stars are similar in composition to the sun, although there is evidence that metals are definitely underabundant in the LMC star as compared with the sun. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1975 DOI: 10.1086/190332 Bibcode: 1975ApJS...29...55F Keywords: G Stars; Line Spectra; Magellanic Clouds; Spectrum Analysis; Stellar Spectra; Supergiant Stars; Abundance; Atmospheric Models; Dust; Late Stars; Stellar Atmospheres; Tables (Data); Astrophysics full text sources ADS | data products SIMBAD (5)

Spectral and UBV Data for 583 Stars (Supergiants and Foreground Stars) in the Direction of the Large Magellanic Cloud

The stars observed are mainly from the Catalogue by Fehrenbach and Duflot. Some other stars – overexposed on the objective-prism plates, faint blue stars in H ii regions, stars with overlapping objective-prism spectra – have been added.The photoelectric UBV photometry was done with the 1-m telescope at La Silla. The UBV filters have always been those recommended by Johnson. Normally 3 measurements or more on different nights have been made for each star. For a single observation of a program star the internal standard deviations are The spectra have been taken with a Cassegrain spectrograph mounted on the 1.52-m telescope at La Silla. The dispersion is 73 Å mm−1, the spectral range 3250-5000 Å, and the limiting resolution 1.3 Å.As a result of our observations, we present 409 stars as members of the LMC, 42 as possible members and 132 as galactic foreground stars (19 of these having high radial velocity). Remarkable features regarding velocities, spectra, magnitudes and colors are noted and commented.All stars down to B = 11.5 have been observed spectrographically as well as photometrically. This is also the case for the majority of the high-velocity stars down to B = 12.0. For fainter objects the photometry is quite representative, whereas the spectroscopy is more scarce. The limiting magnitude is B = 14.0.As radial velocities were used as membership criterion, our data do not suffer from any spectral type selection effects.It was easy to apply the MK criteria to our dispersion using the Yerkes atlas and the Bidelman list of supergiants. A continuous series of supergiant standards in the LMC has been established from 06 to G2. Comparison with Radcliffe data and with recent results of Divan gives a dispersion in spectral type of less than one tenth of a spectral class. Also the luminosity classification shows good agreement.In the classification several difficulties were met:(1) The LMC stars are very luminous objects. In the Galaxy we do not have many corresponding stars. This is especially so for later spectral types.(2) With the dispersion used, the differences between IaO and la are not very pronounced, especially not for F-G type stars.(3) Many of the LMC supergiants are P Cygni stars. They show very sharp, often asymmetric line profiles with a sharp rise to the long wavelength side. This might cause erroneous classification, and also affect radial velocities.(4) The presence of an extended atmosphere, causing dilution effects, can give spurious spectral classification.We have found 8 A type high-velocity stars. The UBV results confirm their classification. 11 G-K type stars have been found to be high-velocity stars, among which are two subdwarfs earlier discussed by Fehrenbach and Thackeray. The number of late type high-velocity stars is quite high.Full accounts have been given in Astron. Astrophys. Suppl.6 (1972), 249.