目录
图像
上传图像
DSS Images Other Images
相关文章
Wra 751, a luminous blue variable developing an S Doradus cycle
Aims. The object Wra 751 is a luminous blue variable that latelyexhibits strong changes in light and color. We summarise the availablephotometry of Wra 751, present new photometric observations, and discussthese data with special attention on the systematic differences betweenthe various data sources. In addition, we establish an empiricalrelationship between b-y and B-V for this class of stars. Methods: Wra751 is a strong-active member of the S Dor class, and it exhibitsvery-long term S Doradus phases with an amplitude of about twomagnitudes in V and a cycle length of several decades. The associatedB-V colour-index amplitude is about 0.4 mag. At this moment this LBV,which is the reddest member of the class, is going through the bright(and red) stage of a long-term S Dor cycle. Results: The S Dorbehaviour of this system shows some resemblence to the temporalcharacteristics of the Galactic LBV AG Car, because the time scales andamplitudes of light and colour variability are very similar.Individual photometric measurements (Tables 2-4) are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/484/463
| On the structure and kinematics of nebulae around LBVs and LBV candidates in the LMC
We present a detailed analysis of the morphology and kinematics ofnebulae around LBVs and LBV candidates in the Large Magellanic Cloud.HST images and high-resolution Echelle Spectra were used to determinethe size, shape, brightness, and expansion velocities of the LBV nebulaearound R 127, R 143, and S 61. For S Dor, R 71, R 99, and R 84 wediscuss the possible presence of nebular emission, and derive upperlimits for the size and lower limits on the expansion velocities ofpossible nebulae. Including earlier results for the LBV candidates S 119and Sk-69o279 we find that in general the nebulae around LBVsin the LMC are comparable in size to those found in the Milky Way. Theexpansion velocities of the LMC nebulae, however, are significantlylower - by about a factor of 3 to 4 - than those of galactic nebulae ofcomparable size. Galactic and LMC nebulae show about the same diversityof morphologies, but only in the LMC do we find nebulae with outflow.Bipolarity - at least to some degree - is found in nebulae in the LMC aswell as in the Milky Way, and manifests a much more general featureamong LBV nebulae than previously known.
| S Doradus variables in the Galaxy and the Magellanic Clouds
The goal in writing this paper is five fold: (1) to summarize thescientific achievements in the 20th century on S Dor variables (orLBVs); (2) to present an inventory of these variables in the Galaxy andthe Magellanic Clouds with a description of their physical state andinstability properties; (3) to emphasize the photometric achievements ofthe various types of instabilities. Generally this seems to be aneglected item resulting in a number of misunderstandings continuouslywandering through literature; (4) to investigate the structure of the SDor-area on the HR-diagram; (5) to estimate the total numbers of S Dorvariables in the three stellar systems. The position of the strongactive S Dor variables in minimum brightness obey the following linearrelation on the HR-diagram:log L/Lsun = 1.37 log T_eff -0.03. The relatively small dispersion of less active and supposed ex-and dormant S Dor variables with respect to this relation is twice aslarge at the blue side than at the red side. This might be caused byevolution to the WR stage and/or to high rotation. S Dor variables canbe subject to five types of instabilities: the very rare genuineeruptive episodes (the ``SD-eruptions''), two different brighteningphases caused by slow pulsations (the ``SD-phases''): one on a timescale of years, the other on a time scale of decades at a more or lessconstant luminosity and two types of microvariations: one on a timescale of weeks, the other on a time scale of about 100 d. So far, noperiodicities of light curve characteristics of any of theseinstabilities have ever been found. The durations of active andnon-active stages are estimated for about half of the sample based onscattered magnitude estimations such as from historical records, and onmodern monitoring campaigns. It would be a misunderstanding to believethat all S Dor variables should be always spectacular. It is estimatedthat most of them will not be spectacular at all for at least 70% oftheir lifetime as an S Dor variable. Tables 1 to 6 and 8 to 17 are onlyavailable in electronic form at http://www.edpsciences.org, Table 7 isonly available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/366/508. Figures 2--10,12, 14, 15, 17--19 are only available in electronic form athttp://www.edpsciences.org, see Note added in proof
| UBV photometry of Galactic foreground and LMC member stars - III. LMC member stars - a new data base
New UBV photometry for 878 luminous member stars of the Large MagellanicCloud (LMC) and 13 stars of uncertain membership is presented. The datawill be available at Centre de Données astronomiques deStrasbourg. Including former observations now UBV data are available foraltogether 2470 luminous LMC stars and 2106 foreground stars plus 65stars of uncertain membership. The observations have been used alreadyfor several investigations dealing e.g. with interstellar reddeninglines and intrinsic colours, the dust distribution and the calibrationof charge-coupled device exposures.
| VBLUW photometry of fifteen alpha CYG variables (including LBVs) in the Galaxy, the LMC and the SMC
VBLUW photometry (Walraven system) of 15 alpha Cyg-type variables,(luminous massive stars), including 10 LBVs and one suspected LBV arepresented. Formulae are given to transform the V and V-B of the Walravensystem to V and B-V of the Johnson UBV system.
| Light variations of massive stars (alpha Cyg variables). XV. The LMC supergiants R99 (LBV), R103, R123 (LBV) and R128
VBLUW photometry (Walraven system) of the four variable LMC supergiantsR99, R103, R123 and R128 is analysed, searched for periods anddiscussed. Based on former and present photometry we conclude that twoof the three emission-line objects are undoubtedly active LBVs (R99 andR123), although not so spectacular. R123, like AG Car near minimumbrightness, shows a low amplitude S Dor activity with superimposed alphaCyg-type variations. Based on observations obtained at the EuropeanSouthern Observatory at La Silla, Chile
| The HIPPARCOS proper motion of the Magellanic Clouds
The proper motion of the Large (LMC) and Small (SMC) Magellanic Cloudusing data acquired with the Hipparcos satellite is presented. Hipparcosmeasured 36 stars in the LMC and 11 stars in the SMC. A correctlyweighted mean of the data yields the presently available most accuratevalues, mu_alpha cos(delta) = 1.94 +/- 0.29 mas/yr, mu_delta = - 0.14+/- 0.36 mas/yr for the LMC. For the SMC, mu_alpha cos(delta) = 1.23 +/-0.84 mas/yr, mu_delta = - 1.21 +/- 0.75 mas/yr is obtained, whereby careis taken to exclude likely tidal motions induced by the LMC. Bothgalaxies are moving approximately parallel to each other on the sky,with the Magellanic Stream trailing behind. The Hipparcos proper motionsare in agreement with previous measurements using PPM catalogue data byKroupa et al. (1994), and by Jones et al. (1994) using backgroundgalaxies in a far-outlying field of the LMC. For the LMC the Hipparcosdata suggest a weak rotation signal in a clockwise direction on the sky.Comparison of the Hipparcos proper motion with the proper motion of thefield used by Jones et al. (1994), which is about 7.3 kpc distant fromthe center of the LMC, also suggests clockwise rotation. Combining thethree independent measurements of the proper motion of the LMC and thetwo independent measurements of the proper motion of the SMC improvesthe estimate of the proper motion of the LMC and SMC. The correspondinggalactocentric space motion vectors are computed. Within theuncertainties, the LMC and SMC are found to be on parallel trajectories.Recent theoretical work concerning the origin of the Magellanic Systemis briefly reviewed, but a unique model of the Magellanic Stream, forthe origin of the Magellanic Clouds, and for the mass distribution inthe Galaxy cannot yet be decided upon. Future astrometric space missionsare necessary to significantly improve our present knowledge of thespace motion of the two most conspicuous galactic neighbours of theMilky Way.
| A comparison of near-infrared spectra of the galactic center compact He I emission-line sources and early-type mass-losing stars
We present R approximately = 570 resolution K band spectra of eightsources in the Galactic center, including four sources within the IRS 16cluster, IRS 13, IRS 1 W, and the compact He I emission-line sources AF(also known as AHH) and AHH NW. We also present R approximately = 570 Hand K band spectra of the AF source and nine galactic and largemagellanic cloud (LMC) early-type mass-losing stars, including Ofpe/WN9,WN, and LBV stars. The spectra of both the Galactic center sources andthe comparison stars show a wide range of behavior in the He I (1.70micrometer, 2.06 micrometer, 2.11 micrometer) and H I (Brackettseries)lines. While the Galactic center and companion star spectra showsome morphological similarities, we find significantly larger He Iequivalent widths in the AF source and two galactic early-typemass-losing stars than in any of the LMC stars. Several of the Galacticcenter He I sources are found to have higher He I velocity widths thanany of the galactic or LMC early-type mass-losing stars. At least onesource, IRS 13, shows significant emission to the red of the He I 2.06micrometer line emission, which may be a red wing to this line or ablend of other unidentified lines. We also rule the Galactic center He Isources normal OB giant/supergiants, WC, or WN7-8 stars based oncomparison of our spectra to published spectra of these types. Weestimate the BCK = Mbol - MK for theGalactic center sources as a function of effective temperature frompublished data on LBV, WN9, and Ofpe/WN9 stars, and use limits on theeffective temperature to place the Galactic center sources in the H-Rdiagram.
| Ultraviolet interstellar absorption lines in the LMC: Searching for hidden SNRs
Strong x-ray emission detected in Large Magellanic Cloud (LMC)superbubbles has been explained as the result of interior supernovaremnants (SNRs) hitting the dense superbubble shell. Such SNRs cannot befound using conventional criteria. We thus investigate the possibilityof using the interstellar absorption properties in the ultraviolet (UV)as a diagnostic of hidden SNR shocks. The International UltravioletExplorer (IUE) archives provide the database for this pilot study. Theycontain high-dispersion spectra of several stars in x-ray brightsuperbubbles. To distinguish the effects of SNR shocks from those oflocal stellar winds and a global hot halo around the LMC, we includedcontrol objects in different environments. We find that almost allinterstellar absorption properties can be explained by the interstellarenvironment associated with the objects. Summarizing the two mostimportant results of this study: (1) a large velocity shift between thehigh-ionization species (C IV and Si IV) and the low-ionization species(S II, Si II, and C II*) is a diagnostic of hidden SNR shocks; however,the absence of a velocity shift does not preclude the existence of SNRshocks; (2) there is no evidence that the LMC is uniformly surrounded byhot gas; hot gas is preferentially found associated with largeinterstellar structures like superbubbles and supergiant shells, whichmay extend to large distances from the plane.
| Redshifts of high-luminosity stars - The K effect, the Trumpler effect and mass-loss corrections
The Trumpler effect is demonstrated in B and A supergiants in h + ChiPersei, as well as in other associations of young luminous stars. TheK-Trumpler effect is also shown in O, B, and A supergiants in theMagellanic Clouds, as well as in nearby galaxies such as NGC 1569 and2777 and in blue irregular variables in M31 and M33. Mass outflow inluminous stars is shown to require an average correction of about 20km/s and to increase the excess redshifts of the stars in the MagellanicClouds to a significance level of 6 sigma. Completely empirical andindependent measurements show that mass-loss corrections of this sizeare required on average for supergiants in both the SMC and LMC and alsoin the Milky Way.
| Recent Variability in the S Doradus - Type Star AG Carinae [errata: 1993MNSSA..52....2C]
Not Available
| Observations of long-period variables in the Large Magellanic Cloud.
Eight hundred and seventy-nine observations of seventy-nine redvariables in the Large Magellanic Cloud are reported. K andmbol light curves are given for each.
| SN 1961V - an extragalactic ETA Carinae analog
Spectra of the site of the unique type V supernova SN 1961V in NGC 1058and of two nearby H II regions have been obtained. Broad H-alphaemission with a luminosity of 2 x 10 to the 36th ergs/s is detected atthe position, so that SN 1961V becomes the first historicalextragalactic object classified as a supernova to be opticallyrecovered. The characteristics and origin of the high-excitation H IIregions of the site are discussed. It is argued that SN 1961V was not asupernova, but an exaggerated Eta Carinae-type outburst of a verymassive, evolved star near the end of core hydrogen burning.
| Effects of SN 1987A on the interstellar medium around it
It is shown that the interstellar spectrum from SN 1987A in the LMCshows a rather strong component in C IV and Si IV, and possibly a weakcomponent in N V, at a velocity of about 300 + or - 10 Km/s. In thespectra of the neighboring stars HD38268 and R123, a component at thisvelocity is only seen in low-ionization lines, not in the C IV, or N Vlines. The possibility is studied that SN 1987A ionized a measurablefraction of this 300 Km/s cloud within less than one day since the SiIV, C IV, and possibly, N V interstellar lines are seen only about oneday after the first light from the supernova explosion was detected.This may be the case, but only if the supernova temperature at outburstwas larger than 50,000 K, depending on the density assumed for theinterstellar cloud. Also, H and He must have been preionized once.
| A Provisory Catalogue of S-Doradus Candidate Stars in the Magellanic Clouds
Not Available
| CO overtone emission from Magellanic Cloud supergiants
A sample of 63 high-luminosity LMC supergiants has been searched forfirst-overtone CO emission at 2.3 microns. Six new CO emission starshave been found, showing that CO first-overtone emission is a commoncharacteristic of luminous stars with dense circumstellar envelopes andhaving a wide range of stellar temperatures. Of the non-CO emissionstars, eight have strong He I emission. Nine stars show CO absorption at2.3 microns from late-type companions. CO emission was not found in anyof the three LMC S Doradus variables, and the stars which do show COemission are not known to be photometrically variable.
| The galactic and LMC extreme line supergiants compared: IUE observations of the Henize-Carlson and Zoo star samples of massive supergiants
The Henize-Carlson sample of galactic massive supergiants, and acomparison between the Galactic and LMC samples are discussed. Severalof the stars, notably He3-395 and S 127/LMC, have very similar shellcharacteristics. There appears to be little difference, other thanluminosity, between the LMC and Galactic samples. One star, He3-1482,was detected with the Very Large Array at 6 cm. The UV data is combinedwith IRAS and optical information.
| Astrometry of SN 1987A and SK -69.202 deg
Two sets of astrometric plates (epochs 1987.2 and 1973.0) and asecondary reference system comprised of LMC members were used todetermine the position of SN 1987A relative to about 30 Perth 70 stars.The positional coincidence of the SN and Star 1 of Sanduleak -69 deg 202is confirmed to within an uncertainty of + or - 0.13 arcsec in eachcoordinate. The relative brightness of the two major components of Sk-69 deg 202 was assessed by fitting the density profiles of the blendedimages.
| The peculiar emission-line supergiant HD 37836
The luminous emission-line star HD 37836 of the LMC has been studiedusing high-dispersion spectra in the UV and in the optical. In addition,IUE low-dispersion spectra and UBVRIJHKL photometry have been used tostudy the energy distribution. The emission-line spectrum of the star isvery peculiar. Its UV absorption-line spectrum is more normal andindicates that HD 37836 is a late O type supergiant. Specifically,strong stellar-wind lines with an edge velocity of ?2400 kms-1 have been found. The most likely explanation for thevariety of velocities which are found appears to be a disk surroundingthe star. It is shown that the continuum energy distribution is inagreement with the presence of a disk. The two LMC stars HDE 269445 andHen S131 have similar energy distributions and emission-line spectra andmay thus represent other cases of luminous, hot supergiants surroundedby gaseous disks.
| A compact nebulosity surrounding the peculiar blue emission-line supergiant HD 37836 of the LMC.
Not Available
| Identification of LMC Clusters and Emission Line Objects in the HD and HDE Catalogues
Not Available
| Circumstellar shells around luminous emission-line stars in the Large Magellanic Cloud
High-resolution echelle spectrograms obtained with CASPEC of sevenluminous emission-line stars in the LMC are discussed. The authors findnarrow nebular emission lines in all stars of this sample. The emissionlines are clearly resolved in all cases. The three S Dor variables R 71,S Dor and R 127 show velocity-doubled [N II] 6548, 6583 lines. Theauthors consider the presence of the nebular emission lines as evidencefor the presence of supergiant planetary nebulae around the centralstars. The density of the nebulae exceeds 105cm-3in several cases. The authors discuss the origin of the expandingshells. It seems most likely that they have been ejected during previousS Dor episodes of the central stars. This implies that a major fractionof the most luminous emission-line stars undergoes S Dor-like outbursts.
| Atlas of high-dispersion spectra of peculiar emission-line stars in the Magellanic Clouds
The authors present an atlas of high-dispersion spectra of 24 of thebrightest peculiar emission-line stars in the Magellanic Clouds. Radialvelocity measurements of the Balmer lines are also listed. Furthermore,UBVRIJHKLM photometric data of these stars and additional MC bluesupergiants are given. The photometric and spectroscopic variability ofthe program stars is discussed. On the basis of these data the authorspropose to distinguish three subgroups: the classical P Cygni stars, theOfpe/WN9 stars and the stars with dust shells.
| Variable blue supergiants in the Large Magellanic Cloud - R 84, R 85, and R 99
During a search for luminous blue variables in the LMC the threeemission-line stars R 84 (OIafpe), R 85 (B5Iae), and R 99 (OBf:pe) havebeen found to show significant brightness and colour variations.Photometric and spectroscopic data from the UV to the IR have been usedto discuss the nature of these variables. It is argued that they areclosely related to the S Dor variables. The implications of this findingfor the interpretation of the Ofpe/WN9 stars and the S Dor variables arediscussed. Photometric data for 11 additional suspected variables aregiven.
| The early-type strong emission-line supergiants of the Magellanic Clouds - A spectroscopic zoology
The results of a spectroscopic survey of 21 early-type extreme emissionline supergiants of the Large and Small Magellanic Clouds using IUE andoptical spectra are presented. The combined observations are discussedand the literature on each star in the sample is summarized. Theclassification procedures and the methods by which effectivetemperatures, bolometric magnitudes, and reddenings were assigned arediscussed. The derived reddening values are given along with someresults concerning anomalous reddening among the sample stars. Thederived mass, luminosity, and radius for each star are presented, andthe ultraviolet emission lines are described. Mass-loss rates arederived and discussed, and the implications of these observations forthe evolution of the most massive stars in the Local Group areaddressed.
| On the photometric differences between luminous OBA type stars in the LMC with and without P Cygni characteristics
A comparison is presented of the photometric characteristics of O to A0stars of high luminosity in the Large Magellanic Cloud which exhibit ordo not exhibit P Cygni characteristics. VBLUW observations were made of29 OBA stars and 15 OBA stars with P Cygni characteristics (OBA/PC/stars). Examination of the three two-color diagrams in the systemindicates that the OBA(PC) stars are slightly bluer than the OBA stars,which may be explained by a higher luminosity for the OBA(PC) stars at agiven temperature. Computations of the free-free emission from theextended envelopes of OBA(PC) stars show the contribution of suchemission to the spectral energy distribution to be negligible in theabsence of extreme conditions in the shell. Comparison of observed withtheoretical colors reveals the reddening in OBA(PC) stars to be on theaverage 0.07 magnitudes greater than in OBA stars. Results suggest thatOBA supergiants start to exhibit P Cygni characteristics when the massloss rate becomes greater than or equal to 2 x 10 to the -6th solarmass/year.
| Radial velocities from objective-prism plates in the direction of the Large Magellanic Cloud
A catalog is presented of 711 Large Magellanic Cloud (LMC) stars, withattention to the radial velocities of 418 of these. Also given are theradial velocities of 1127 galactic stars in the direction of the LMC, aswell as discussions of the precision of these measurements and of radialvelocity dispersion in different fields.
| The peculiar, luminous early-type emission line stars of the Magellanic clouds: A preliminary taxonomy
A sample of some 20 early type emission supergiants in the Magellanicclouds was observed with both the SWP and LWR low resolution mode ofIUE. All stars have strong H-emission, some showing P-Cygni structure aswell with HeI, HeII, FeII and other ions also showing strong emission.It is found that the stars fall into three distinct groups on the basisof the HeII/HeI and HeI/HI strengths: (1) HeII strong, HeI, HI; (2) HeIIabsent, HeI, HI strong; (3) HeI absent, HI, FeII, FeII, strong inaddition to low excitation ions. The two most extreme emission linestars found in the Clouds S 134/LMC and S 18/SMC are discussed. Resultsfor the 2200A feature in these supergiants, and evidence for shellsaround the most luminous stars in the clouds are also described.
| A Note on Interstellar Absorption in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1980PASP...92..592H
| Stellar winds from hot stars in the Magellanic Clouds
Spectrographic data have been obtained of O and B supergiants in theMagellanic Clouds at dispersions 12 and 25 A/mm in the blue and 25 and50 A/mm in the red. Mass loss phenomena, line radial velocities, andline intensities have been measured on them and are compared withsimilar data on galactic stars. There appear to be some differencesbetween the SMC, LMC, and the Galaxy in all these respects. Mass loss isclearly occurring in the Magellanic Cloud stars, and the SMC stars haveparticularly discrepant line intensities.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
INHABITED SKY
