Galactic Counterparts Research Articles

Extremely energetic planetary nebulae in the Large Magellanic Cloud

view Abstract Citations (37) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extremely energetic planetary nebulae in the Large Magellanic Cloud. Dopita, M. A. ; Ford, H. C. ; Webster, B. L. Abstract Highly energetic planetary nebulae have been identified in the Large Magellanic Clouds. These have higher expansion velocities than any of their galactic counterparts and appear to show directed expansion flows rather than having a spherically symmetric expanding shell. Comparison of their properties with similar, but less extreme, galactic planetaries suggests that these objects are highly luminous bipolar type I planetaries in which the central star is undergoing continued energetic mass loss, but which is nevertheless insufficient to supply the energy and momentum of the nebula. This class of objects is expected to represent the upper end of the mass range of precursor stars which are able to evolve to the planetary nebula phase, and circumstantial evidence connecting them with the symbiotic stars is presented. Publication: The Astrophysical Journal Pub Date: October 1985 DOI: 10.1086/163555 Bibcode: 1985ApJ...297..593D Keywords: Astronomical Spectroscopy; Magellanic Clouds; Planetary Nebulae; Electron Energy; Stellar Luminosity; Stellar Temperature; Astrophysics full text sources ADS | data products SIMBAD (8) NED (3)

Extreme Be stars in the Magellanic Clouds

view Abstract Citations (23) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Extreme Be stars in the Magellanic Clouds. Garmany, C. D. ; Humphreys, R. M. Abstract In the course of a spectroscopic investigation of the O-type stars in the Magellanic Clouds, a population of luminous Be stars was serendipitously encountered. They are here referred to as extreme Be stars, following the terminology used by Schild (1966) for a population of Be stars in the region of h and Chi Persei which lie significantly above the main sequence. As members of the Clouds, their luminosities and intrinsic colors can be determined directly. A comparison of these new high-luminosity Be stars with known H-beta-emission-line supergiants in the Clouds is made in both the optical and UV spectral regions. The Galactic counterparts of these Be stars are also discussed. Although these Be stars are an average of several magnitudes brighter than those in the Galaxy, this may in part be a selection effect. Publication: The Astronomical Journal Pub Date: October 1985 DOI: 10.1086/113906 Bibcode: 1985AJ.....90.2009G Keywords: B Stars; Magellanic Clouds; O Stars; Stellar Luminosity; Variable Stars; Astronomical Spectroscopy; Emission; Line Spectra; Astrophysics full text sources ADS | data products SIMBAD (52) NED (1)

Stellar winds from hot stars in the Magellanic Clouds

O and B stars in the LMC and SMC have been observed with the IUE in order to compare their winds and mass loss rates with those of their galactic counterparts. It is found that while the wind terminal velocities are generally about 20 percent lower than in galactic stars of the same spectral type, it is not clear that the mass loss rates are significantly lower. This conclusion differs from the conclusions of other studies, and the reasons are discussed. The most important reason is that a less luminous set of stars with new spectral types determined from slit spectra is being examined. The discussion of stellar winds rests heavily on a comparison of relevant wind parameters observed in O stars using both high and low dispersion IUE spectra.

Recent optical identifications of HEAO-1 X-ray sources

The HEAO-1 satellite has produced the most complete, all-sky, X-ray survey. The sources extend to levels as faint as 1/2 Uhuru Flux Unit (UFU), with uncertain completeness below 1.25 UFU. Approximately 350 out of 840 sources have certain or highly probable optical counterparts. The identifications are necessary for estimating distances to the objects, so that properties are measured intrinsic to the source, and for establishing the classifications of the astronomical systems. There is also the opportunity to obtain TENMA and EXOSAT observations of X-ray spectra and time variability, since in general almost nothing is known of the X-ray characteristics of these weaker sources. Methods are here reviewed and the new active galactic nuclei X-ray counterparts are discussed.

SIT-VIDICON Surface Photometry of Globular Clusters in the Magellanic Clouds

The globular clusters in the Large Magellanic Cloud offer an unique possibility for the study of their spatial structures. Their ages show a very wide range from 6·107 to >5·109 years which is unknown for their galactic counterparts. The latter ones are all very old and therefore dynamically relaxed systems, whereas the young globular clusters of the Magellanic Clouds (age <108 years) have still preserved the dynamical state with which they were formed (Geyer et al. 1979). Furthermore, these young globulars show in their Hertzsprung-Russell diagram morphology the massive and luminous stars still on the main sequence with only a few evolved red supergiants. As in general the luminosity of the individual stars depends on their evolutionary state, the total mass to total luminosity ratio of a stellar cluster represents also its evolutionary state.

Spectrophotometry of Early-Type Supergiants in the LMC

Measures of the equivalent widths of major stellar features in the visible and UV regions of a sample of the LMC supergiants whose types range from 05 to A1 have been derived. Their low resolution UV spectra were obtained with the IUE and complemented in the visual with spectra from ESO 3.6 m and SAAO 1.95 m telescopes. The methods used are entirely numerical and as far as possible free from subjective estimates. The data for the LMC members have been compared with those obtained for their Galactic counterparts. The variation of CIV 1550 Å and Si IV 1400 Å absorptions with spectral type has been investigated. It may be that the intensity of HeI lines is smaller for the middle and late B supergiant members of the LMC as compared with those Galactic standards, otherwise there is no systematic difference within the observational errors between the Galactic and LMC supergiants in the strengths of the principal stellar features observed in the visible as a function of spectral type. Galactic 0 and early B supergiants have greater equivalent widths of Si IV λ 1400 and C IV λ 1550 absorptions than the LMC supergiants of similar spectral types, confirming earlier observations of Hutchings.

The X-ray Properties of Supernova Remnants in the Large Magellanic Cloud

There are at least 25 supernova remnants (SNR) in the Large Magellanic Cloud (LMC) with X-ray luminosities exceeding 2 × 1035 erg s−1. As many as 25 other SNR may be contained in the X-ray survey conducted with the Einstein Observatory of the LMC. The X-ray spectra of the 6 SNR observed with the Solid State Spectrometer (SSS) resemble their galactic counterparts; two SNR, N157B and 0540–69.3, may emit X-rays primarily by synchrotron radiation. The density of the medium in which SNR are expanding inferred from the X-ray data appears to decrease with SNR diameter; the density of the ISM inferred from the Balmer lines of 4 new SNR in the LMC is much lower than that inferred from X-ray observations. The apparent thermal energy content of LMC SNR evolves with diameter, peaking at ∼5 × 1050 ergs. The ratio of the densities of the X-ray and [SII] emitting plasmas is consistent with their being in pressure equilibrium. The SN rate in the LMC is ∼1 per 100–200 years. This is the number of SN expected from other considerations. The number diameter relation of LMC SNR is consistent with free expansion. The X-ray data are difficult to understand in terms of traditional Sedov models on SNR evolution; probably ejecta and multiphase ISM are required to explain the X-ray properties of LMC SNR.

Optical identification of serendipitous Einstein X-ray sources - Luminosity and redshift relations in the X-ray and optical emission from active galaxies and quasars

view Abstract Citations (82) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical identification of serendipitous Einstein sources : luminosity and redshift relations in the X-ray and optical emission from active galaxies and quasars. Reichert, G. A. ; Mason, K. O. ; Thorstensen, J. R. ; Bowyer, S. Abstract We have optically identified 40 objects from a sample of 139 serendipitous Einstein X-ray sources. Thirteen of the sources are identified with galactic counterparts, and 27 are identified with extragalactic counterparts. The galactic counterparts include normal bright (V< 10) stars, emission line stars, RS CVn stars, and cataclysmic variables; these are similar in their X-ray properties to other galactic objects observed at X-ray wavelengths. All but one of the extragalactic counterparts are active galactic nuclei (AGNs). The optical spectra of the X-ray selected AGNs are indistinguishable from those of AGNs discovered by their radio or optical emission. We have combined our sample of X-ray selected AGNs with other samples of X-ray selected and previously cataloged AGNs in order to investigate correlations between their optical and X-ray properties. No significant correlations between emission line luminosities and X-ray luminosity are found, when the separate correlations with optical luminosity are taken into account. Previously reported correlations of the ratio of the luminosities in Hβ and in [O III], and of the widths of the Hβ emission lines, with continuum luminosities are shown to be artifacts due to systematic differences between narrow line and broad line objects. The ratio of X-ray luminosity to optical luminosity is observed to decrease with increasing optical luminosity. Regression analysis shows that Lx/L0 cannot be constant, but must decrease by at least a factor of 1.6 for every factor 10 increase in L0, and may decrease by more if Lx/L0 also increases with increasing redshift. The data do not allow Lx/L0 to decrease with increasing redshift. The observed variation in Lx/L0 with L0 is sufficient to explain the deficit of intermediate and high redshift (z > 0.5) AGNs in the X-ray selected sample, and it is therefore not necessary to propose constraints on the luminosity evolution of AGNs, or systematic differences in X-ray emission between X-ray selected and optically selected AGNs. The expected contribution to the extragalactic X-ray background from AGNs depends critically upon the assumed relationship between Lx and L0, ranging (for objects brighter than B=20) from 20% of the observed background for weak variation in Lx/L0 to 50% for a strong variation in Lx/L0. Publication: The Astrophysical Journal Pub Date: September 1982 DOI: 10.1086/160267 Bibcode: 1982ApJ...260..437R Keywords: Active Galaxies; Astronomical Spectroscopy; Galactic Nuclei; Optical Emission Spectroscopy; Quasars; Red Shift; X Ray Sources; Binary Stars; Emission Spectra; Extraterrestrial Radiation; Graphs (Charts); Light Emission; Line Spectra; Spectral Line Width; Stellar Luminosity; Astronomy full text sources ADS | data products NED (36) SIMBAD (1)

Ring nebulae associated with Wolf-Rayet stars in the Large Magellanic Cloud. II - Kinematics of DEM 45, 137, 165, 174, and 208

view Abstract Citations (11) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ring nebulae associated with Wolf-Rayet stars in the Large Magellanic Cloud. II - Kinematics of DEM 45, 137, 165, 174, and 208 Chu, Y. -H. Abstract The velocity fields of five ring nebulae associated with Wolf-Rayet stars in the Large Magellanic Cloud are investigated in order to distinguish among possible origins. Velocities were mapped by the use of the CTIO pressure-scanned Fabry-Perot interferometer at the forbidden O III line, and the high-resolution line profiles obtained were used to determine the dynamical ages of the nebulae. Comparison of ring dynamical ages with the age of the Wolf-Rayet star confirms DEM 174 as an amorphous H II region illuminated by the star. DEM 45 and 165 have internal motion less than 10 km/sec, while DEM 137 and 208 are shells expanding at about 15 to 20 km/sec with dynamical ages of several million years. These last four are structured H II regions, and are 10 to 20 times larger than their Galactic counterparts. It is suggested that the two largest rings, DEM 137 and 208, were formed by stellar associations, while DEM 45 and 165 are part of a molecular cloud-H II region complex. Publication: The Astrophysical Journal Pub Date: April 1982 DOI: 10.1086/159805 Bibcode: 1982ApJ...255...79C Keywords: Hydrogen Ions; Magellanic Clouds; Nebulae; Wolf-Rayet Stars; Amorphous Materials; Fabry-Perot Interferometers; Forbidden Transitions; H Ii Regions; High Resolution; Astronomy full text sources ADS | data products NED (1)

DISCOVERY OF THE FIRST S STAR IN THE SMALL MAGELLANIC CLOUD.

ABSTRACT A pure S-type star found in the SMC is described. The extreme rarity of such stars relative to C and M giants is shown by Magellanic Clouds surveys for red giants. For the S star, the bolometric magnitude is -5.1 + or - 0.1, a value in fair agreement with that found for the few known galactic counterparts with reliable distance moduli; and one near the faint limit expected theoretically.

IUE ultraviolet spectroscopy of stars in the Magellanic Clouds

view Abstract Citations (35) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS IUE ultraviolet spectroscopy of stars in the Magellanic Clouds. Hutchings, J. B. Abstract Low dispersion IUE spectra of seven hot supergiants in the Large Magellanic Cloud and one in the Small Magellanic Cloud are presented. Stellar winds are present in all the stars, but the resonance lines have weak or no emission and probably have lower terminal velocities than galactic counterparts. Spectral energy distributions are used to derive effective temperature, luminosities, and interstellar extinction values. These are in reasonable agreement with ground-based estimates. Some peculiarities are noted and compared with galactic stars. Line features in the spectra are discussed, including several unusual emission lines. The peculiar star R99 appears to be very luminous (bolometric magnitude of about -11.4) and reddened. Publication: The Astrophysical Journal Pub Date: April 1980 DOI: 10.1086/157868 Bibcode: 1980ApJ...237..285H Keywords: Hot Stars; Iue; Magellanic Clouds; Supergiant Stars; Ultraviolet Spectroscopy; Interstellar Extinction; Line Spectra; Spectral Energy Distribution; Spectrum Analysis; Stellar Luminosity; Stellar Temperature; Stellar Winds; Astrophysics full text sources ADS | data products SIMBAD (9) MAST (1)

Evolved stars in open clusters.

radial-velocity observations and MK classifications have been used to study evolved stars in 25 open clusters. Published data on stars in 72 additional clusters are rediscussed and combined with the observations made in this investigation to yield positions in the Hertzsprung-Russell diagram for 559 evolved stars in 97 clusters. Ages for the parent clusters were estimated from the main-sequence turnoff points, earliest spectral types, est stars in the clusters themselves. The evolved stars were sorted into six age groups ranging from 4 x 10/sup 6/ yr to 4 x 10/sup 8/ yr, and the composit H-R diagram for each age group was then used to study the evolutionary tracks for stars of various masses. The observational results were found to be in reasonably good agreement with recent theoretical computations. The composite color-magnitude diagrams were found to be strikingly different from those of the rich open clusters in the Magellanic Clouds. At a given age the red giants in the Small Magellanic Cloud and the Large Magellanic Cloud clusters are brighter and bluer than their galactic counterparts. It is suggested that these effects may be accounted for by differences in metal abundance. (AIP)

The Cluster System in the Small Magellanic Cloud

Visual examination of 330 star clusters in the SMC on UBV plates taken with the UK 48-in. Schmidt telescope allows clusters to be classified by colour and structure into six types. A distinct pattern in the spatial distribution of clusters reported by Hodge is confirmed, though the effective size of the cluster system is the same as that defined by integrated star light. Cluster sizes, excluding red globulars, are on the whole larger than their galactic counterparts.

Photoelectric Observations of Magellanic Cloud Cepheids

Two-colour photoelectric light-curves have been obtained for 27 cepheids in the Magellanic Clouds. Eight of these have periods shorter than 20 days, and 6 periods longer than 50 days. The shorter-period SMC cepheids are intrinsically about 0.2 mag bluer than their galactic counterparts. The SMC period-luminosity relation is found to be |$\langle V \rangle=17.85-2.97\enspace \text{log} P$| with a slope agreeing closely with that found by Woolley & others for the LMC cepheids. Assuming that galactic, SMC and LMC cepheids obey a common period-luminosity relation, the apparent modulus of the SMC is 19.1, and of the LMC 18.65. Their distances are 61 and 50 kpcs respectively.