내용
사진
사진 업로드
DSS Images Other Images
관련 글
HD 331319: A Post-AGB F Supergiant with He I Lines
Not Available
| Checking the yellow evolutionary void. Three evolutionary critical Hypergiants: HD 33579, HR 8752 & IRC +10420
We have checked the reality of the yellow evolutionary void (which is anarea in the Hertzsprung-Russell diagram where atmospheres of bluewardevolving super- and hypergiants are moderately unstable), by comparingone star inside the void: HD 33579 (= R76), and two at thelow-temperature border of it: HR 8752 (= HD 217476, V509 Cas) andIRC+10420. We found that the first star has a large mass and a fairlystable behaviour over time. These aspects suggest, together withabundance determinations by others, that it is a fairly young, stillredward-evolving supergiant. For such a star the void is not forbidden.The two other stars, HR 8752 resp. IRC+10420, have low masses whichplaces them in the post-red blueward loop. They show indications of theexpected bouncing effect for blueward returning red supergiants: whenapproaching the void they eject mass, resulting in a sudden reduction ofT_eff and a decrease of the atmospheric acceleration to g_eff =~ zero.Thereafter T_eff and g_eff increase again. For HR 8752 two such recent`bounces' have been identified. The photometric variations of HR 8752and of HD 33579 are due to high-l gravity-wave pulsations. Based onobservations at the La Palma Observatory and the ESO Observatory inChili.
| 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). XVI. The LMC supergiants R 85 (LBV) and R 110 (LBV) and the SMC supergiants R 42 and R 45
Multi-colour photometry of four variable supergiants in the LMC and SMC,viz. R 85, R 110, R 42 and R 45, is searched for periods, studied anddiscussed. The suspected LBV R 85 is undoubtedly an active LBV, thoughnot as spectacular as R 110. Their microvariations superimposed on the SDor-activity are analyzed as well as those exhibited by R 42 and R 45.Often, a period search is difficult because of the very complicatedmicro-variability. We suggest that this is caused by an intricatemulti-cyclic behaviour combined with stochastic processes. The length ofthe strongest cyclicity in the power spectrum of R 42 (128 d) is of theorder of the rotation periods of BA-type supergiants. In connection withour findings described in the present paper and the previous ones, wediscuss various competing theoretical models on the instability of alphaCyg variables, including the LBVs. Based on observations obtained at theEuropean Southern Observatory at La Silla, Chile (observing proposals55D-0317, 56D-0249, 57D-0133 and 58D-0118)
| HIPPARCOS photometry of 24 variable massive stars (alpha Cygni variables)
The photometric variability of 24 alpha Cyg variables, i.e. variablesuper-and hypergiants, observed by the Hipparcos satellite is described.Three of the selected stars are situated in the SMC, 12 in the LMC andthe remaining 9 in the Galactic plane. Four of them are hot S Dor-typevariables, or LBVs (luminous blue variables) and two are possiblemembers of this class. Light curves are presented for all stars. Forfive stars, among which one LBV, the variability was discovered from theHipparcos photometric data. Results of period searches are presentedand, when relevant, folded light curves are shown. The linear ephemerisof two variables was revised. For most of the program stars theHipparcos magnitude scale (Hp) differs from the V of the UBV system byla 0fm1 . For all variables temperatures and M_bol are given. Galacticforeground reddening for the objects in the Magellanic Clouds are givenbased on IRAS maps.
| The yellow hypergiants
We list the main stellar data of known hypergiants and similarlyluminous stars, and then concentrate on a review of the yellowhypergiants. These stars are post-red supergiants evolving alongblueward loops in the Hertzsprung-Russell diagram. Their properties,their location in the Hertzsprung-Russell diagram and their occasionalmass ejections are related to a region of atmospheric instability in theH-R diagram, the Yellow Void. The `bouncing against the border of theVoid' of three objects: ρ Cas, HR8752 and IRC+10420, is described.The apparent atmospheric instability of yellow hypergiants is related tothe atmospheric pulsations. There are indications that the approach tothe Void is associated with an increased amplitude of the pulsation andwith enhanced mass loss. The observed small-scale motion field is onlyapparently strongly supersonic; the observed large stochastic velocitiesare the quasi-stochastically varying thermal motions in the many hotsheets that occur in the wakes of many small shocks, while the realhydrodynamic velocity component is small and subsonic. This shock-wavefield is also responsible for the observed rate of mass loss and foremission in the wings of Hα . Most yellow hypergiants haveenvelopes containing gas and dust, but a thick extended envelope,presumably dissipating and showing bipolar outflow, is only known aroundIRC+10420. At the interface of the bipolar wind and the interstellarmedium one or more stationary shocks may develop as is observed in thecase of IRC+10420 and suspected with ρ Cas.
| An obstacle to the late evolution of massive stars
During their evolution, massive stars first swell and thus become redsupergiants, after which they shrink again to evolve to the bluesupergiant phase. When, during this blueward loop, the effectivephotospheric temperature T_eff has increased to values of about 7000 K,the main part of the photosphere becomes moderately unstable.Observations of the yellow hypergiant star HD 217476=HR 8752 show thatthe approach to this instability region may lead to phases of enhancedmass loss and consequent reduced surface temperature, after which T_effslowly increases until it again `bounces' against the atmosphericinstability region. Two such bounces have been observed in the last 30yr and a third seems imminent; frequent observations of this star aretherefore useful. Other `yellow hypergiants', like rhoCas and IRC+10420,seem to show the same behaviour. Repeated observations of these starsmay help us to understand how massive stars pass the instability regionduring their evolution towards the blue supergiant phase.
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Spectroscopic study of the outflowing disk winds of B[e] supergiants in the Magellanic Clouds.
We report on UV high resolution spectroscopic observations of R50 in theSmall Magellanic Cloud, and R82 and HenS22 in the Large Magellanic Cloudobtained with the International Ultraviolet Explorer. The observed starsare supposed to represent edge-on cases of B[e] supergiants for which atwo-component stellar wind model has previously been suggested. Thespectra are characterized by P Cygni-type lines of FeII. Theobservations show that the three stars have very slowly expanding windswith terminal velocities derived from the blue absorption edges of 75,100, and 120km/s, respectively. Fits of the FeII lines of Hen S22 andR82 using the SEI method lead to even slower velocities of about 60 to80km/s, respectively. This is about a factor of ten slower than theterminal velocity of normal B-type supergiants. The results areconsistent with the assumption that the observed stars are viewededge-on. We derived optical depths of the absorption components of theFeII resonance lines of Hen S22 and R82 of larger than about 5, yieldinglower limits for the disk mass-loss rates of the order of 6x10^-7^ and5x10^-7^Msun_/yr, respectively. The very low terminalvelocity of the disk can be explained by the fact that the disks of theB[e] supergiants are on the low-velocity side of the bi-stability jumpof radiation driven winds (which reduces vinfinity_/v_esc_)and a rotational velocity of about 0.75 of the critical rotationvelocity (which reduces the effective v_esc_). The effective gravityderived from vinfinity_ and vinfinity_/v_esc_=1.3is very low. It is on the order of logg_eff_=0.2 to 0.7.
| Stellar Abundances and Winds of A-Type Supergiant Stars in M33: First Results from the Keck HIRES Spectrograph
In this Letter, we report the first results of detailed analyses ofA-type supergiants in M33 from high-quality Keck HIRES echelle spectra.The two stars, designated 117-A and B-324, now constitute the mostdistant stars for which detailed abundances have been measured. We find117-A is metal-poor (roughly 1/10 solar), resembling an early Asupergiant in the SMC. B-324 has P Cygni--like profiles for most of themetal lines, but fitting only the photospheric component yields metalabundances similar to solar. These two stars are located at distinctlydifferent galactocentric distances in M33; comparing their abundancesshows that the metallicity gradient of this galaxy, previously reportedonly from H II--region surveys, is also qualitatively apparent in thesestars. Estimates of the stellar-wind parameters for these stars yieldmass-loss rates of ~2.5 x 10-8 Mȯ yr-1 for 117-A and ~1.2 x 10-5Mȯ yr-1 for B-324 from the H alpha line profiles. When we examinethe location of these stars in the wind momentum--luminosity plane, wefind that they are in excellent agreement with the loci of luminous bluestars in the Galaxy, LMC, and SMC, taking into account differences inmetallicity.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| R 40: The first luminous blue variable in the Small Magellanic Cloud
During the past decade R 40 in the Small Magellanic Cloud (SMC) hasbrightened in the visual range by about 0.5 magnitudes. Correlated withthe brightening the spectral type has changed from B8Ia to A3Ia-O. Thisbehavior shows R 40 to be a luminous blue variable (LBV) the first onediscovered in the SMC. During the past eight years we obtained extensiveStroemgren photometry. R 40 was also observed in the IR range in theJHKL filter system. High resolution spectra were observed in Dec. 1991and Jan. 1993 in the optical range at European Southern Observatory(ESO) with CASPEC at the 3.6 m telescope and with our fiber-linkedechelle spectrograph at the 2.2 m telescope. In addition one highresolution LWP-IUE spectrum and one SWP and LWP low resolution spectrumwere secured during the present outburst phase of R 40. For comparisonIUE archive data were consulted; R 40 had been exposed in the lowresolution SWP and LWP mode in 1987. Apart from the secular brighteningat a timescale of years R 40 exhibits photometric pulsation-likemicrovariations with a quasi-period of 120 days which is also typicalfor LBVs. From the continuum energy distribution (from the satellite UVto the IR range) and from the CASPEC spectrum we derived stellarparameters of R 40 during the outburst phase in 1991 by making use ofKurucz model atmospheres: Teff = 8700 K, log g = 0.75 andwith a distance module of 18.85 for the SMC Mbol = -9.4 and R= 280 solar radii and M = 16 solar mass. The mass-loss rate was derivedfrom the P Cygni type H-alpha profile to 8 x 10-6 solarmass/yr which is small but not exceptional for an LBV (cf. e.g. R110 ofthe Large Magellanic Cloud (LMC)). Comparison of the present spectralenergy distribution with the one of 1987 shows that the brightening inthe visual is accompanied by a corresponding decrease of the satelliteUV continuum; i.e. as expected for LBVs the outburst occurs under thecondition of Mbol = const. Since the metallicity is down by0.6 dex in the SMC, R 40 demonstrates that low metallicity does notpreclude LBV outbursts.
| Luminosities of yellow supergiants from near-infrared spectra - Calibration through Magellanic Cloud stars
The possibility of using medium resolution spectrograms in the nearinfrared region to determine luminosities of A-G supergiants has beenexplored. A sample of 49 of these stars has been observed in the twoMagellanic Clouds, and using the intensities of the O I 7774 triplet andan index (CP), which is a combination of the Ca II triplet and Paschenlines intensities, a preliminary luminosity calibration, based on LMCstars, has been obtained. Such a calibration predicts reliableluminosities for Galactic supergiants, and offers the advantage of beingcompletely reddening independent. The reddening free CP index combinedwith BVRI color indices has also been used to estimate the interstellarreddenings of Magellanic Cloud stars.
| 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.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Stellar wind properties of A-type hypergiants
The visually bright objects from the Magellanic Clouds are examined interms of observed properties that indicate properties relevant to thestellar wind. IUE observations are accomplished in the long-wavelengthprimary echelle mode in the optical wavelength near H-alpha of theobjects HD 33579 and HD 7583. The Fe-II lines are found to have widthsthat are dependent upon log gf and the excitation potential; thesedependencies relate to an accelerated wind that is directed outwards.The terminal velocity is found to be approximately equal to 200 km/s forboth stars as evinced by the strong Fe-II lines. A flat velocity law isdetermined and a mass-loss rate of 2 x 10 exp 6 solar mass/yr is givenfor both of the stars. The wind properties of the A-types are concludedto relate to a uniform acceleration mechanism.
| Positional reference stars in the Magellanic Clouds
The equatorial coordinates are determined of 926 stars (mainly ofgalactic origin) in the direction of the Magellanic Clouds at the meanepoch T = 1978.4 with an overall accuracy characterized by the meanvalues of the O-C coordinates, Sa = 0.35 arcsec and Sd = 0.38 arcsec,calculated from the coordinates of the Perth reference stars. Thesevalues are larger than the accuracy expected for primary standard stars.They allow the new positions to be considered as those of reliablesecondary standard stars. The published positions correspond to anunquestionable improvement of the quality of the coordinates provided inthe current catalogs. This study represents an 'astrometric step' in thestarting of a 'Durchmusterung' of the Magellanic Clouds organized by deBoer (1988, 1989).
| The stellar temperature scale for stars of spectral types from O8 to F6 and the standard deviation of the MK spectral classification
Empirical effective temperature of 211 early-type stars found in aprevious investigation (Kontizas and Theodossiou, 1980; Theodossiou,1985) are combined with the effective temperatures of 313 early-typestars from the literature. From these effective temperatures of a totalnumber of 524 early-type stars of spectral types from O8 to F6 a newstellar temperature scale is developed along with the standard deviationof the MK spectral classification.
| The anomalous A-type supergiants in the Magellanic Clouds - Evidence for post-red supergiant evolution
Non-LTE model atmospheres are used to show that the strength of thehydrogen lines and the Balmer jump in a group of A-type supergiants inthe Large and Small Magellanic Clouds can best be explained by enhancedhelium in the atmospheres of these supergiants. On the HR diagram thesestars are found between M(Bol) is approximately equal to -6 to -8 mag,corresponding to an initial mass of 10 to 20 solar masses. Given theirlocation on the HR diagram, their spectral and color anomalies which canbe explained by enhanced helium, and the existence of spectroscopicallynormal A supergiants in the same luminosity range, it is suggested thatthese anomalous A-type supergiants are He-burning postred supergiantsand that they are excellent candidates for the predecessor of the kindof star that became SN 1987a.
| Structure of the interstellar medium in the Magellanic Clouds
Using optical and UV observations, the internal gas structure ofMagellanic Clouds (MCs) was examined for clues to the recent evolutionof the Magellanic System and further signs of this collision event.Results indicate that the intermediate velocity clouds (IVCs) havedifferent origins. Thus, the '60-km/s' IVC is clearly of Galacticorigin. The '130-km/s' IVC is probably also Galactic and is not directlyassociated with the MCs. The '170 km/s' IVC is quite clearly associatedwith the LMC and seems to be the front of the LMC. The overall gasstructure in the MCs indicates that there is a distance-velocityassociation except in two regions: one to the south-west of the SMC (andis enigmatic), and the other to the south of 30 Doradus and appears tobe smoothly linked with the H I bridge, indicating that both featureshave a common overall cause such as the recent tidal collision.
| The catalogue of equivalent line widths in the spectra of A- and F-stars.
Not Available
| Abundances of the heavy elements in the Magellanic Clouds. I - Metal abundances of F-type supergiants
Metal abundances of eight F-type supergiants in each of the MagellanicClouds were determined using the results of high-resolution spectroscopyanalysis of these stars, together with new Stromgren uvby and Cousins(1980) BVRI photometry. It was found that the mean Fe abundance (Fe/H)for the SMC is -0.65 + or - 0.2 dex, and the mean Fe abundance for theLMC is -0.30 + or - 0.2 dex. The abundances of stars in both the SMC andLMC appear relatively uniform, and the abundances of the elementsrelative to Fe are very similar in both Magellanic Clouds and in Canopus(the carbon-to-iron abundances are the same for all three). It was alsofound that Nd and Sm are overabundant in both clouds, supporting thetrends found by Spite et al. (1988) for the three SMC stars theystudied.
| BVR photoelectric photometry of late-type stars and a compilation of other data in the Small Magellanic Cloud
The basic data used in a discussion of the structure and morphology ofthe SMC Martin et al., (1989) are presented. New BVR photoelectric dataacquired at ESO, 88 SMC K-M type supergiants and three foreground Mstars; for all these stars, high-accuracy Coravel radial velocities hadbeen obtained. Taking into account all available data, a list of mean Vmagnitudes is obtained for 307 stars in the direction of the SMC withknown radial velocities. Also established is a list of mean weightedradial velocities on the IAU standard system for the 307 stars (amongwhich only two are probably foreground Galactic stars).
| The structure of the Small Magellanic Cloud
The structure of the SMC is investigated using previous H-I data,accurate radial velocities of 307 young stars and 35 H-II regions, andhigh-spectral-resolution profiles of interstellar absorption lines. Itis found that 224 stars and 30 H-II regions of the main body of the SMCare associated with four H-I components, and that 54 of the objects arenot associated with H I. Two main complexes of gas, stars, and H-IIregions are found, one with a velocity of about -28 km/s and the otherwith a velocity of about +9 km/s. Most of the young stars are shown tolie within a depth smaller than 10 kpc, in agreement with recentMagellanic Cepheid data.
| Sequential star formation in the Magellanic Clouds
Joint stellar and nebular studies were carried out for a few adjacentstellar associations in the Magellanic Clouds. The spread in ages of WRstars of different subtypes as deduced from their different environmentsis analyzed. A similar study is briefly sketched for S Dor type stars.It is shown how a starburst propagates in the interstellar medium at ascale of 100-300 pc in about 10 to the 7th yr for three regions of theMagellanic Clouds, using both new observational data and published ones.In view of the results provided by such detailed studies, several trapsin the methods were pointed out based on integrated properties of starclusters and their associated nebulae, or their brightest stars.Finally, the moderately old age found (from their environment) for S Dortype stars and their tendency to enter into multiple systems are pointedout.
| Small Magellanic Cloud: H-gamma-line equivalent widths and luminosity classes of the brightest blue star members
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...69..421A&db_key=AST
| Studies of massive stars in the Magellanic Clouds. II - New spectral classification of OB stars in the SMC
Abstract image available at:http://adsabs.harvard.edu/abs/1987AJ.....93.1070G
| Radial velocities of southern stars obtained with the photoelectric scanner CORAVEL. VI - 233 F to M type stars in and near the Small Magellanic Cloud - Comparison with 80 spectrographic radial velocities of O to K type stars in this galaxy
Abstract image available at:http://adsabs.harvard.edu/abs/1987A&AS...67..423M
| Photometric Studies of Magellanic Cloud Supergiants. II. Variability
Abstract image available at:http://adsabs.harvard.edu/abs/1986ApJS...62..451G
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
