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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
| SN 2005 gj: evidence for LBV supernovae progenitors?
There is mounting observational evidence in favour of Luminous BlueVariables (LBVs) being the direct progenitors of supernovae. Here wepresent possibly the most convincing evidence yet for such progenitors.We find multiple absorption component P-Cygni profiles of hydrogen andhelium in the spectrum of SN 2005gj, which we interpret as being animprint of the progenitor's mass-loss history. Such profiles havepreviously only been detected in Luminous Blue Variables. This strikingresemblance of the profiles, along with wind velocities and periodsconsistent with those of LBVs leads us to connect SN 2005gj to an LBVprogenitor.Based on observations at the European Southern Observatory with UVES onthe VLT in programme 276.D-5020A and 078.D-0720.
| Estimating the Structure and Geometry of Winds from Luminous Blue Variables via Fitting the Continuum Energy Distributions
By combining the UV spectra from IUE with photometric data in theoptical band, we present a quantitative study on the continuum energydistributions of LBVs to determine the structure and geometry of LBVwinds. It is shown that the shape of continuum energy distributionsaround the Balmer jump is sensitive to the velocity law of LBV winds. Asimple, spherically symmetric wind model including free-bound andfree-free radiation is constructed to compute the continuum energydistributions of LBVs. By matching theoretical ones to the observedcontinuum energy distributions around the Balmer jump, we have obtainedvalue of the exponent of the velocity law β in both minimum andmaximum state for five LBVs, i.e., AG Car, HR Car, R40, S Dor, and R127.We have found that β is about 0.5-0.7 in the minimum state andlarger than 1.5 in the maximum state. Transitions in the ionizationstates of metals between the minimum and maximum state of LBVs, whichlead to changes in the radiative acceleration due to spectral lines, aremost likely responsible for such effect on the velocity law. We havealso determined the geometry of the wind and found that a sphericallysymmetric wind model can well reproduce the observed continuum energydistributions of the five LBVs. Based on these results we suggest thatthe wind of LBVs be basically quasi-spherical, maybe with some clumpystructure in the spherical wind to produce some observed asphericalfeatures.
| Spectral atlas of massive stars around He I 10 830 Å
We present a digital atlas of peculiar, high-luminosity massive stars inthe near-infrared region (10 470-11 000 Å) at medium resolution(R≃7000). The spectra are centered around He I 10 830 Å,which is formed in the wind of those stars, and is a crucial line toobtain their physical parameters. The instrumental configuration alsosampled a rich variety of emission lines of Fe II, Mg II, C I, N I, andPa γ. Secure identifications for most spectral lines are given,based on synthetic atmosphere models calculated by our group. We alsopropose that two unidentified absorption features have interstellarand/or circumstellar origin. For the strongest one (10 780 Å) anempirical calibration between E(B-V) and equivalent width is provided.The atlas displays the spectra of massive stars organized in fourcategories, namely Be stars, OBA Iape (or luminous blue variables, LBVcandidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars.For comparison, the photospheric spectra of non emission-line stars arepresented. Selected LBVs were observed in different epochs from 2001 to2004, and their spectral variability reveals that some stars, such asη Car, AG Car and HR Car, suffered dramatic spectroscopic changesduring this time interval.Based on observations made at Observatório do Pico dos Dias/LNA(Brazil). Figures 5 to 18 are only available in electronic form athttp://www.aanda.org Electronic version of the spectra (fichiers FITS)is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/993
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Asphericity and clumpiness in the winds of Luminous Blue Variables
We present the first systematic spectropolarimetric study of LuminousBlue Variables (LBVs) in the Galaxy and the Magellanic Clouds, in orderto investigate the geometries of their winds. We find that at least halfof our sample show changes in polarization across the strong Hαemission line, indicating that the light from the stars is intrinsicallypolarized and therefore that asphericity already exists at the base ofthe wind. Multi-epoch spectropolarimetry on four targets revealsvariability in their intrinsic polarization. Three of these, AG Car, HRCar and P Cyg, show a position angle (PA) of polarization which appearsrandom with time. Such behaviour can be explained by the presence ofstrong wind-inhomogeneities, or “clumps” within the wind.Only one star, R 127, shows variability at a constant PA, and henceevidence for axi-symmetry as well as clumpiness. However, if viewed atlow inclination, and at limited temporal sampling, such a wind wouldproduce a seemingly random polarization of the type observed in theother three stars. Time-resolved spectropolarimetric monitoring of LBVsis therefore required to determine if LBV winds are axi-symmetric ingeneral. The high fraction of LBVs (>50%) showing intrinsicpolarization is to be compared with the lower ~20-25% for similarstudies of their evolutionary neighbours, O supergiants and Wolf-Rayetstars. We anticipate that this higher incidence is due to the lowereffective gravities of the LBVs, coupled with their variabletemperatures within the bi-stability jump regime. This is alsoconsistent with the higher incidence of wind asphericity that we find inLBVs with strong Hα emission and recent (last ~10 years) strongvariability.
| On the population of galactic Luminous Blue Variables
We report the first results of a long term infrared monitoring campaignof known and candidate galactic Luminous Blue Variables (LBVs). Inparticular, we are able to confirm the LBV nature ofG24.73+0.69, a luminous mid-B supergiant associatedwith a dusty ejection nebula. We find that prior to 2003 SeptemberG24.73+0.69 exhibited low amplitude (Δ JHK 0.4 mag) variability, but in the ~200 day period between 2003September-2004 April it abruptly brightened by ~0.7 mag in the broadbandJ filter. Subsequently, a further ~0.4 mag increase was observed between2004 April-October, resulting in an overall difference of ~1.1 magbetween (current) photometric mimimum and maximum; similar variabilityalso being observed in the H and K bands. In light of the numerousrecent IR studies of the galactic hot star population we also compile anupdated census of confirmed and candidate galactic LBVs, reporting 12and 23 members respectively for each class. Finally, we utilise this newcensus to construct an H-R diagram for the galactic LBV population,resulting in a striking confirmation of the LBV-minimum light strip.
| Infrared Observations of the Candidate LBV 1806-20 and Nearby Cluster Stars1,
We report near-infrared photometry, spectroscopy, and speckle imaging ofthe hot, luminous star we identify as candidate LBV 1806-20. We alsopresent photometry and spectroscopy of three nearby stars, which aremembers of the same star cluster containing LBV 1806-20 and SGR 1806-20.The spectroscopy and photometry show that LBV 1806-20 is similar in manyrespects to the luminous ``Pistol star,'' albeit with some importantdifferences. They also provide estimates of the effective temperatureand reddening of LBV 1806-20 and confirm distance estimates, leading toa best estimate for the luminosity of this star of greater than5×106Lsolar. The nearby cluster stars havespectral types and inferred absolute magnitudes that confirm thedistance (and thus luminosity) estimate for LBV 1806-20. If we dropkinematic measurements of the distance(15.1+1.8-1.3 kpc), we have a lower limit on thedistance of greater than 9.5 kpc and on the luminosity of greater than2×106Lsolar, based on the cluster stars. Ifwe drop both the kinematic and cluster star indicators for distance, anammonia absorption feature sets yet another lower limit to the distanceof greater than 5.7 kpc, with a corresponding luminosity estimate ofgreater than 7×105 Lsolar for the candidateLBV 1806-20. Furthermore, on the absis of very high angular resolutionspeckle images, we determine that LBV 1806-20 is not a cluster of starsbut is rather a single star or binary system. Simple arguments based onthe Eddington luminosity lead to an estimate of the total mass of LBV1806-20 (single or binary) exceeding 190Msolar. We discussthe possible uncertainties in these results and their implications forthe star formation history of this cluster.Based on data obtained at the Palomar Observatory 200 inch telescope,which is operated by the California Institute of Technology, the JetPropulsion Laboratory, and Cornell University.This publication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation.
| HD 183143: A Hypergiant
We present spectroscopic evidence that the luminosity of HD 183143 ishigher by one magnitude than thought previously. The star is yet anotherB6-8 Ia-0 white hypergiant of the Galaxy. Its absolute visual magnitudeis close to -8 mag, and its distance is close to 2 kpc. We describespectroscopic manifestations of the nonstationary behavior of itsatmosphere and wind.
| A newly identified Luminous Blue Variable in the galactic starburst cluster Westerlund 1
We present observations of the massive transitional starW243 in Westerlund 1. We find anapparent spectral type of early-mid A from our data, in contrast to anearlier classification of B2I, made from data obtained in 1981. Theconcurrent development of a rich emission line spectrum suggests a veryhigh mass loss rate; the continued presence of He I emission suggestingthat the underlying star remains significantly hotter than implied byits apparent spectral type. We suggest that W243 is a Luminous BlueVariable undergoing an eruptive phase, leading to an extreme mass lossrate and the formation of a pseudo photosphere.Based on observations collected at the European Southern Observatory, LaSilla, Chile (ESO 67.D-0211, 69.D-0039, 71.D-0151 & 271.D-5045).
| Discovery of Highly Dynamic Matter Enhancements along the Polar Axis and Equatorial Plane in the Luminous Blue Variable Binary HD 5980
HD 5980 is a W-R+O eclipsing binary in the Small Magellanic Cloud thathas attracted considerable attention since it underwent a luminous bluevariable (LBV)-type outburst in 1994. Since then, intense spectroscopicand photometric monitoring have revealed the presence of periodicvariability on a timescale of 6-7 hr that cannot be explained by ourcurrent understanding of the system. In this paper, we present the firstresults from our polarimetric observations around secondary eclipse whenthe assumed Wolf-Rayet (W-R) star passes in front of the assumed LBVcomponent (phase φ=0.36). These data confirm the presence ofstochastic polarimetric variability on a typical timescale of ~30minutes, reaching a very high amplitude of almost 1% on our last of fivenights. At that time, we also found that the mass loss, which isresponsible for the polarimetric variability, presented fluctuations inaxial symmetry ranging from very rapid density enhancements along theorbital plane to polar ejections. We propose that either a fast rotatormodel for the W-R star or the presence of a close orbiting neutron starcould qualitatively explain the observed polarimetric, spectroscopic,and photometric behavior. The evidence presented in this paper iscrucial for an understanding of the erratic behavior of this importantbinary and should be taken into account in any consistent model of thesystem.
| Long-term spectroscopic monitoring of the Luminous Blue Variable HD 160529
We have spectroscopically monitored the galactic Luminous Blue VariableHD 160529 and obtained an extensive high-resolution data set that coversthe years 1991 to 2002. During this period, the star evolved from anextended photometric minimum phase towards a new visual maximum. Inseveral observing seasons, we covered up to four months with almostdaily spectra. Our spectra typically cover most of the visual spectralrange with a high spectral resolution (lambda /Delta lambda ~ 20 000 ormore). This allows us to investigate the variability in many lines andon many time scales from days to years. We find a correlation betweenthe photospheric HeI lines and the brightness of the star, both on atime scale of months and on a time scale of years. The short-termvariations are smaller and do not follow the long-term trend, stronglysuggesting different physical mechanisms. Metal lines also show bothshort-term and long-term variations in strength and also a long-termtrend in radial velocity. Most of the line-profile variations can beattributed to changing strengths of lines. Propagating features in theline profiles are rarely observed. We find that the mass-loss rate of HD160529 is almost independent of temperature, i.e. visual brightness.Based on observations collected at the European Southern Observatory atLa Silla, Chile (proposals 69.D-0378, 269.D-5038).
| An atlas of spectra of B6-A2 hypergiants and supergiants from 4800 to 6700 Å
We present an atlas of spectra of 5 emission-line stars: thelow-luminosity luminous blue variables (LBVs) HD 168625 and HD 160529,the white hypergiants (and LBV candidates) HD 168607 and AS 314, and thesupergiant HD 183143. The spectra were obtained with 2 echellespectrometers at the 6-m telescope of the Russian Academy of Sciences inthe spectral range 4800 to 6700 Å, with a resolution of 0.4Å. We have identified 380 spectral lines and diffuse interstellarbands within the spectra. Specific spectral features of the objects aredescribed.The complete atlas and Table 2 are only available in electronic form atthe CDS via anonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/1035
| MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation
The galaxies of the Local Group serve as important laboratories forunderstanding the physics of massive stars. Here I discuss what isinvolved in identifying various kinds of massive stars in nearbygalaxies: the hydrogen-burning O-type stars and their evolved He-burningevolutionary descendants, the luminous blue variables, red supergiants,and Wolf-Rayet stars. Primarily I review what our knowledge of themassive star population in nearby galaxies has taught us about stellarevolution and star formation. I show that the current generation ofstellar evolutionary models do well at matching some of the observedfeatures and provide a look at the sort of new observational data thatwill provide a benchmark against which new models can be evaluated.
| Infrared [FeII] emission in the circumstellar nebulae of luminous blue variables
After a serendipitous discovery of bright [FeII]λ16435 emissionin nebulae around η Carinae and P Cygni, infrared spectra of otherluminous blue variables (LBV) and LBV candidates were obtained. Brightinfrared [FeII] emission appears to be a common property among LBVs withprominent nebulae; this is an interesting discovery because strong[FeII]λ16435 is typically seen in shock-excited objects likesupernova remnants and outflows from newly formed massive stars, as wellas in active galactic nuclei (AGN), where the excitation mechanism isuncertain. This paper presents spectra in the H-band (1.5 to 1.75 μm)for the central stars and nebulae of η Car, AG Car, P Cyg, Wra 751,HR Car, HD 168625, HD 160529, R 127 and S Doradus. Seven of nine targetsshow bright [FeII]λ16435 in their nebulae, while it is absent inall central stars except the LBV candidate Wra 751. The two objects (SDor and HD 160529) without prominent [FeII]λ16435 are not yetknown to have nebulae detected in optical images, and both lack brightthermal infrared emission from dust. The possible excitation mechanismsfor this line and the implications of its discovery in LBV nebulae arediscussed; there are good reasons to expect shock excitation in someobjects, but other mechanisms cannot be ruled out.
| Outflow from and asymmetries in the nebula around the LBV candidate Sk-69o279
We present and discuss new long-slit Echelle spectra of the LMC LBVcandidate Sk-69o279 and put them in context with previousimages and spectra. While at first glance it resembles a simplespherically expanding symmetric shell, we find a considerably morecomplex morphology and kinematics. The spectra indicate thatmorphologically identified deviations from sphericity are outflows offaster material out of the main body of Sk-69o279. Themorphological as well as the kinematic similarity with other LBV nebulaemakes it likely that Sk-69o279 is an LBV candidate and posesthe question: in how far are outflows out of expanding LBV nebulae ageneral property of such nebulae - at least during some phases of theirevolutions.
| The enigmatic WR46: A binary or a pulsator in disguise. III. Interpretation
Photometric and spectroscopic monitoring campaigns of WR46 (WN3p), as presented in Veen et al. (2002a,b; hereafterPapers I and II, respectively), yield the following results. The light-and colour variations reveal a dominant single-wave period ofPsw89=0.1412 d in 1989, andPsw91 =0.1363 d in 1991. Because of a smalldifference in the minima, this periodicity may be a double-wavephenomenon (Pdw). The line fluxes vary in concert with themagnitudes. The significant difference of the periods can be either dueto the occurence of two distinct periods, or due to a gradual change ofthe periodicity. A gradual brightening of the system of 0.12m appearedto accompany the period change. In addition, the light variations in1989 show strong evidence for an additional period Px=0.2304d. Generally, the radial velocities show a cyclic variability on a timescale of the photometric double-wave. However, often they do not vary atall. The observed variability confirms the Population I WR nature of thelight source, as noted independently by Marchenko et al. (2000). In thepresent paper, we first show how the photometric double-wave variabilitycan be interpreted as a rotating ellipsoidal density distribution in thestellar wind. Subsequently, we discuss what mechanisms could drive sucha configuration. First, stellar rotation of a single star is discardedas a likely cause. Second, the obvious interpretation of the double-wavephotometry, i.e., a close binary system, is investigated. Howeverunlikely, we discuss how the observed period change might be reconciledwithin a model of a strongly interacting binary. Third, aninterpretation of a non-radial multi-mode pulsator is investigated. Theobserved period change and the multi-frequency behaviour do support thisinterpretation. We propose that the pulsational mode l=1 and |m|=1 maymimic a ``binary'' light- and radial-velocity curve. However, thephasing of the radial velocity and the light curve may be inconsistent.The possibility l=2 and |m|=0 is also discussed. Finally, we suggest howthe enigma of the variability of WR 46 may be solved.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Outflow-induced Dynamical and Radiative Instability in Stellar Envelopes with an Application to Luminous Blue Variables and Wolf-Rayet Stars
Theoretical models of the remnants of massive stars in a very hot,post-red-supergiant phase display no obvious instability if standardassumptions are made. However, the brightest observed classical luminousblue variables (LBVs) may well belong to such a phase. A simpletime-dependent theory of moving stellar envelopes is developed in orderto treat deep hydrodynamical disturbances caused by surface mass lossand to test the moving envelopes for dynamical instability. In the caseof steady state outflow, the theory reduces to the equivalent of theCastor, Abbott, & Klein formulation for optically thick winds atdistances well above the sonic point. The time-dependent versionindicates that the brightest and hottest LBVs are both dynamically andradiatively unstable, as a result of the substantial lowering of thegeneralized Eddington luminosity limit by the mass-loss acceleration. Itis suggested that dynamical instability, by triggering secular cycles ofmass loss, is primarily what differentiates LBVs from the purelyradiatively unstable Wolf-Rayet stars. Furthermore, when accuratemain-sequence mass-loss rates are used to calculate the evolutionarytracks, the predicted surface hydrogen and nitrogen abundances of theblue remnants agree much better with observations of the brightest LBVsthan before.
| HD 331319: A Post-AGB F Supergiant with He I Lines
Not Available
| Multiwavelength monitoring of QS Tel
Multiwavelength monitoring observations of the AM Her system, QS Tel,are presented, the centrepiece being a coordinated campaign with theASCA, EUVE and HST satellites and optical observations on 1996 September28-29. The star was initially observed in an intermediate brightness,single pole state in 1996 April by ROSAT. However two EUVE snapshots ofthe system in August found it in a deep low state, the light curvesappearing to retain a bright and faint phase morphology although thebright interval showed significant phase drifts compared with theearlier ROSAT data. At this time, the system appeared optically bright,while polarimetry pointed to one active pole. A modest recovery ofintensity, albeit accompanied by an apparently chaotic extremeultraviolet (EUV) light curve, was subsequently recorded during thecoordinated run in late September. This brightening was confirmed by asecond ROSAT pointing in early October, although the EUV brightening ismatched by a marked decay in its optical output. These observations, allof which found the system in a fainter EUV state than seen in 1993, addto the catalogue of accretion mode behaviour in QS Tel. However, as yet,the data base of observations does not allow us to establish whether theaccretion mode is dictated by accretion-rate dependent penetration ofthe magnetosphere or asynchronous rotation. The ASCA spectrum obtainedduring the coordinated observation is adequately described by a thermalspectrum with a temperature of about 4.4keV and an absorbing columndensity of less than 8×1020cm-2. At the sametime, the 1150-2600Å UV HST spectrum shows a strong, broadLyα absorption profile which we attribute to the white dwarf. Weinfer an effective temperature of 16000-19000K and a mass between 0.5and 0.93Msolar for the white dwarf, at least some of theuncertainty arising because the profile is very probably contaminatedand broadened by Zeeman features. The orbital variation seen by HST canbe matched by a blackbody-like spectrum with a temperature above 24000K.The near UV part of the spectrum contains evidence of phase-variablecyclotron harmonics.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Simultaneous Hα and photometric observations of P Cygni
For the first time an extensive set of (quasi-) simultaneous photometric(UBV) and spectroscopic (Hα line profiles) observations of PCygni, covering a period from May, 1990 to June, 1994 was analyzed interms of time variability. It is found that the Hα equivalentwidth (EW) exhibits two different patterns of variability: a slower one,called Long-Term (LT) variability, with an amplitude of about 30Åand a characteristic duration of about 600 days and a faster one,called Short-Term (ST) variability, with an amplitude up to 10Åand duration of 40 to 60 days. Suggestive evidence for EWvariation on a longer time scale (about few years) also exists. Thevariations in the Hα luminosity are not solely due to changes inthe underlying continuum but also reflect variations in the physicalproperties of the wind. We find, in terms of a simplifiedspherically-symmetric wind model, that the LT variation of the line canbe successfully explained in terms of a 26% alteration of the mass-lossrate, possibly accompanied by variations in the velocity field. From theanalysis of the photometric behaviour of the star we find evidence for avery slow variation in the stellar brightness with an amplitude of about0.13 mag and a duration of about 2600 days, i.e. about 7 years. Duringthis variation, i.e. when the star brightens, the effective temperaturedecreases (by about 10%) and the radius increases (by about 7%). Theproperties of this Very Long Term (VLT) variation suggest that P Cygnihas probably experienced a normal S Dor-type variation with a minimumphase around 1988 and a maximum phase in 1992. Some hints for a positivecorrelation between mass loss variations and changes in the stellarradius, due to the normal SD variability, do exist implying that thebehaviour of P Cygni is more likely similar to that of R71 and S Dor butdifferent from e.g. AG Car, R127 and HD 160529. Superimposed on the VLTcomponent in the photometric variability of P Cygni, we observe STbrightness variations with an amplitude between 0.1 and 0.2 mag whichappears to recur on a time scale of three to four months. The colourbehaviour of these microvariations, at least of those which appear nearthe maximum phase of the VLT variation, is redder in B-V and bluer inU-B when the star brightens in V. The properties of this ST photometricvariability are similar to the properties of the so-called ``100 d-typemicro-variations'', recognized in other LBVs by van Genderen et al.(\cite{van97a},b). Based on time-scale evidences we suggest that themicrovariabilities observed are rather due to ``relaxationoscillations'' (Stothers & Chin \cite{Stothers95}) than tostrange-mode oscillations in the stellar interior. Evidence for a closerelationship between ST variations in Hα and changes in thestellar brightness and temperature is found. From other results about PCygni's spectral variations (Markova \cite{Markova2000a}), we concludethat the ST variability of the wind is most likely connected withprocesses in the stellar photosphere.
| 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
| AS 314: A dusty A-type hypergiant
We present the results of our observations of the poorly-studiedemission-line star AS 314 which include high-resolution spectroscopy,obtained at the 6 -meter telescope of the Russian Academy of Sciences,multicolor optical and near-infrared photometry. The strong Hαline, Hβ and Hγ of moderate strength and a number of weak Feii lines were detected in emission. The Balmer lines and most of the Feii lines show narrow P Cyg-type profiles which implies a very lowterminal velocity of the stellar wind. Very weak signs of emission arefound in Hdelta . Photospheric lines detected for the first time allowedus to determine the object's spectral type, A0. The luminosity, M_bol ~-8.0 mag was estimated using several methods and implies that AS 314 isa hypergiant, which is located at about 10 kpc from the Sun and has aninitial mass of ~ 20; Msun . Modeling of the Balmer lineprofiles resulted in the following parameters of the stellar wind: dot{M} = 2\ 10-5;Msun yr-1, v_infty =75;km s-1. The star is located within the LBV strip in theHRD. Its noticeable far-IR excess is due to the circumstellar dustemission and is likely evidence of an LBV-type outburst in the past.Table 5 is only available in electronic form in the online edition ofthe present issue.
| P Cygni: An Extraordinary Luminous Blue Variable
P Cygni is a prototype for understanding mass loss from massive stars.This textbook star is known first of all because of two great eruptionsin the 17th century. In the first half of this century it has given itsname to a class of stars which are characterized by spectral linesconsisting of nearly undisplaced emissions accompanied by ablue-displaced absorption component. This characteristic P Cygni-typeprofile betrays the presence of a stellar wind, but P Cygni's wind isquite unlike that of other hot supergiants. P Cygni was the first starthat showed the effects of stellar evoluton from a study of itsphotometric history. It shares some common properties with the so-calledLuminous Blue Variables. However, P Cygni is a unique object. Thisreview deals with P Cygni's photometric properties, its circumstellarenvironment - including infrared and radio observations - and itsoptical and ultraviolet spectrum. Smaller sections deal with P Cygni'swind structure and evolution.
| Light variations of the blue hypergiants HD 168607 and HD 168625 (1973-1999)
Strömgren differential photometry of HD 168607 and HD 168625collected during the previous 27 years is analysed. We bring to an endour quarter of a century monitoring of these objects and conclude thatHD 168607 shows typical variability of an uneventful LBV, whereas HD168625 remains to be classified as a variable hypergiant, or amarginally-dormant LBV. The long-term light- and colour behaviour of HD168607 indicates the possible presence of a very slowly-developing S Dorphase - that is, a bright phase that coincides with redder colours.Besides the alpha Cygni-type microvariability, no other signs ofultrashort-periodic variability has been observed. Based on observationsobtained at the European Southern Observatory at La Silla, Chile(applications ESO 56D-0249, 58D-0118, 60D-0148, 61D-0128 and 62H-0110)
| A Semiempirical Test for Dynamical Instability in Luminous Blue Variables
By employing as input parameters only observationally determined stellarsurface quantities, detailed envelope models for six well-observedluminous blue variables at quiescence are constructed and tested formarginal dynamical instability. The best-observed of these objects, PCyg, proves to be exactly in a state of marginal dynamical instability,just as predicted. Within the larger observational errors estimated forthe five other objects, they too are probably in the same marginallyunstable state as P Cyg.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| The orientation within the Galaxy and the Large Magellanic Cloud of nebulae ejected by massive stars
The orientation of nebulae ejected by massive stars (Luminous BlueVariables, WR stars, SN1987A) is investigated with respect to thestructure of the galaxy to which they belong. In the Galaxy, we findthat the projected long axes of the nebulae most often align with thegalactic plane, and then also with the galactic magnetic field. Thisalignment is statistically significant. In addition, a few nebulae areapparently oriented perpendicular to the galactic plane. In the LargeMagellanic Cloud, the nebular axes are found to closely follow thespiral magnetic field. With different inclinations, the Galaxy and theLarge Magellanic Cloud probably offer complementary views of the samephenomenon. Although the sample studied thus far is small and thestatistics limited, these results suggest that the orientation ofmassive star ejecta depends on galactic magnetic fields. Since thenebular axes are apparently correlated to the symmetry axes of the starsthemselves, and since, in the early evolutionary stages, alignments ofaccretion disk axes with the interstellar magnetic field have beenreported, it is argued that the observed alignment effect results fromthe star formation process. Based in part on observations collected atthe European Southern Observatory (ESO, La Silla)
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Скорпион |
| Прямое восхождение: | 17h41m59.03s |
| Склонение: | -33°30'13.7" |
| Видимая звёздная величина: | 6.778 |
| Расстояние: | 1923.077 парсек |
| Собственное движение RA: | -1.3 |
| Собственное движение Dec: | 0.3 |
| B-T magnitude: | 8.11 |
| V-T magnitude: | 6.888 |
Каталоги и обозначения:
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