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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
| 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
| The Oxygen Abundance in the Inner H II Regions of M101: Implications for the Calibration of Strong-Line Metallicity Indicators
I present deep spectroscopy of four H II regions in the inner,metal-rich zone of the spiral galaxy M101 obtained with the LRISspectrograph at the Keck telescope. From the analysis of thecollisionally excited lines in two of the target H II regions, H1013 andH493, I have obtained oxygen abundances 12+log(O/H)=8.52 and12+log(O/H)=8.74, respectively. These measurements extend thedetermination of the oxygen abundance gradient of M101 via the directmethod to only 3 kpc from the center. The intensity of the C IIλ4267 line in H1013 leads to a carbon abundance 12+log(C/H)=8.66,corresponding to nearly twice the solar value. From a comparison of thecontinuum temperature derived from the Balmer discontinuity, T(Bac)=5000K, and the line temperature derived from [O III]λ4363/λ5007, T[O III]=7700 K, an average temperatureT0=5500 K and a mean square temperature fluctuationt2=0.06 have been derived. Accounting for the spatialinhomogeneity in temperature raises the oxygen abundance obtained fromthe oxygen auroral lines to 12+log(O/H)=8.93. These findings arediscussed in the context of the calibration of strong-line metallicityindicators, in particular of the upper branch of R23. Thereis no evidence for the strong abundance biases arising from temperaturegradients predicted theoretically for metal-rich H II regions.The data presented herein were obtained at the W. M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| Spectral Analysis of the Pre-WN Candidate HD 326823
We present a spectral analysis of the peculiar emission-line star HD326823. As has been reported in the literature, this object seems to bea rare, massive star entering the Wolf-Rayet (W-R) phase. In order toconfirm its evolutionary status, we used the radiative transfer codeCMFGEN to obtain its physical parameters and chemical abundances for thefirst time. By analyzing ultraviolet to optical observations of HD326823, we were able to obtain the following parameters:L=2×105 Lsolar, R*=30Rsolar, T*=22,280 K,M˙=5.2×10-6 Msolar yr-1, andv∞=200 km s-1. In addition, we demonstratedthat this star is severely hydrogen-depleted and helium-rich, withXH~3% and XHe~96% (mass fractions), confirmingprevious qualitative claims of a hydrogen deficiency. From the N IIλ5754 transition, we estimated an upper limit for the nitrogenabundance that is compatible with the idea that HD 326823 is a pre-WNstar (XN<~1%). Our models indicate that the Fe II linespresent in the optical spectrum are not formed in a sphericallysymmetric wind. We found that the iron ionization structure is dominatedby Fe III and Fe IV, and that these ions dominate the UV. By comparingour results with WNE and WNL stars in the H-R diagram, we suggest thatHD 326823 is a pre-WN8 star. The use of the transformedradius-temperature diagram also confirms a pre-WNL status. The idea thatstars may enter the W-R stage with a very low hydrogen mass fraction issupported by our results.
| The atypical emission-line star Hen3-209
We analyse observations, spanning 15 yr, dedicated to the extremeemission-line object Hen3-209. Our photometric data indicate that theluminosity of the star undergoes marked variations with a peak-to-peakamplitude of 0.65 mag. These variations are recurrent, with a period of16.093 +/-0.005 d. The spectrum of Hen3-209 is peculiar with manydifferent lines (HI, HeI, FeII, ...) showing P Cygni profiles. The lineprofiles are apparently changing in harmony with the photometry. Thespectrum also contains [OIII] lines that display a saddle profile toppedby three peaks, with a maximum separation of about 600 kms-1.Hen3-209 is most likely an evolved luminous object suffering from massejection events and maybe belonging to a binary system.Based on observations collected at the European Southern Observatory (LaSilla, Chile) and the Cerro-Tololo Observatory (Chile).Postdoctoral Researcher FNRS (Belgium). ‡E-mail: naze@astro.ulg.ac.be §Research Associate FNRS (Belgium). ¶Research Director FNRS (Belgium).
| The UV Scattering Halo of the Central Source Associated with η Carinae
We have made an extensive study of the UV spectrum of η Carinae andfind that we do not directly observe the star and its wind in the UV.Because of dust along our line of sight, the UV light that we observearises from bound-bound scattering at large impact parameters. We obtaina reasonable fit to the UV spectrum by using only the flux thatoriginates outside 0.033". This explains why we can still observe theprimary star in the UV despite the large optical extinction: it is dueto the presence of an intrinsic coronagraph in the η Car system andto the extension of the UV-emitting region. It is not due to peculiardust properties alone. We have computed the spectrum of the purportedcompanion star and show that it could only be directly detected in theUV spectrum, preferentially in the FUSE spectral region (912-1175Å). However, we find no direct evidence for a companion star, withthe properties indicated by X-ray studies and studies of the Weigeltblobs, in UV spectra. This might be due to reprocessing of thecompanion's light by the dense stellar wind of the primary. Broad Fe IIand [Fe II] emission lines, which form in the stellar wind, are detectedin spectra taken in the southeastern lobe, 0.2" from the central star.The wind spectrum shows some similarities to the spectra of the B and DWeigelt blobs but also shows some marked differences in that linespumped by Lyα are not seen. The detection of the broad lines lendssupport to our interpretation of the UV spectrum and to our model forη Car.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-2655.
| The Discovery of a P Cygni Analog in M31
We present spectroscopy and discuss the photometric history of apreviously obscure star in M31. The spectrum of the star is an extremelyclose match to that of P Cygni, one of the archetypes of luminous bluevariables (LBVs). The star has not shown much variability over the past40 years (<0.2 mag), although small-scale (0.05 mag) variations overa year appear to be real. Nevertheless, the presence of a subarcsecondextension around the star is indicative of a past outburst, and from thenebula's size (0.5 pc diameter) we estimate that the outburst took placeroughly 2000 years ago. P Cygni itself exhibits a similar photometricbehavior and has a similar nebula (0.2 pc diameter). We argue that thismay be more typical behavior for LBVs than commonly assumed. The star'slocation in the H-R diagram offers substantial support for stellarevolutionary models that include the effects of rotation, as the star isjust at a juncture in the evolutionary track of a 85 Msolarstar. The star is likely in a transition from an O star to a late-typeWN Wolf-Rayet star.Based in part on observations made with the NASA/ESA Hubble SpaceTelescope (HST), obtained from the Data Archive at the Space TelescopeScience Institute, which is operated by the Association for Universitiesfor Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
| MWC 930 - a new luminous blue variable candidate
We present the results of optical high-resolution and near-infraredlow-resolution spectroscopy and multicolour optical and near-infraredphotometry of the emission-line star MWC 930. The spectrum is rich withFeII emissions, most of which have P Cyg-type profiles. The emissionlines are strong and narrow, indicating a powerful stellar wind with alow terminal velocity (v&infy;~ 140kms-1). Thephotospheric absorption lines are broad and show splitting, which mightbe due to the object's binarity. MWC 930 is most probably located in theNorma spiral arm at a distance of D= 3-4kpc. This strong and slow windas well as the star's luminosity (logL/Lsolar~ 5.5) and theinfrared excess shape suggest that MWC 930 is an unusual B-typesupergiant, most likely undergoing the luminous blue variableevolutionary phase.
| 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.
| The Ultraviolet Spectrum of η Carinae: Investigation of the Ejecta Absorption
We have investigated the far- through mid-UV (1150-2360 Å)spectrum of η Carinae during the late stages of its broad maximumusing the Hubble Space Telescope (HST) Space Telescope ImagingSpectrograph (STIS) moderate dispersion echelle modes. The η Carspectrum is a mixture of absorption and emission lines from thesurrounding nebula superimposed on broad stellar wind features. Thispaper provides a description of the observed spectrum including the windfeatures, the interstellar absorption, and the emission spectrum fromthe surrounding nebula, but with the emphasis on the absorption spectrumformed in the foreground ejecta. The ejecta absorption spectrum has acomplicated velocity structure in which two velocity structures, at -146and -513 km s-1, are easily distinguished. These two velocitycomponents, formed in different regions of the η Car nebula, have inan earlier analysis been identified and demonstrated to have verydifferent spectral characteristics. The slower velocity component istime variable over the spectroscopic period and is characterized byspectral lines from mainly singly ionized iron-peak elements, while thefaster one shows transitions from neutral and singly ionized elements inaddition to molecular lines from the hydrogen Lyman bands. Thehigh-velocity H2 lines dominate great parts of the spectrumwith over 800 identified transitions from energy levels up to 30,000cm-1. The STIS MAMA data provide the tool for spatialinvestigations of the central parts of η Car. H I Lyα pumpedand semiforbidden emission lines are observed to be formed east of thecentral source toward Weigelt blobs B and C, located up to 0.2" from thecentral source. The complete spectrum, with nebular and interstellarline identifications, is available in the electronic edition of thepaper.Laboratory for Astronomy and Solar Physics, Code 681, Goddard SpaceFlight Center, Greenbelt, MD 20771.
| The Optical/Near-Infrared Counterpart of the INTEGRAL Obscured Source IGR J16318-4848: An sgB[e] in a High-Mass X-Ray Binary?
The X-ray source IGR J16318-4848 was the first source discovered byINTEGRAL on 2003 January 29. The high-energy spectrum exhibits such ahigh column density that the source is undetectable in X-rays below 2keV. On 2003 February 23-25, we triggered our Target of Opportunity(ToO) program using the EMMI and SOFI instruments on the New TechnologyTelescope of the European Southern Observatory (La Silla) to obtainoptical and near-infrared (NIR) observations. We confirm the alreadyproposed NIR counterpart and for the first time extended detection intooptical. We report here photometric measurements in the R, I, and Jbands, upper flux limits in the Bb and V bands, and lower flux limits inthe H and Ks bands. We also obtain NIR spectroscopy between0.95 and 2.52 μm, revealing a large number of emission lines,including forbidden iron lines and P Cygni profiles, and showing astrong similarity with CI Cam, another strongly absorbed source.Together with the spectral energy distribution (SED), these data pointto a high-luminosity, high-temperature source, with an intrinsicoptical/NIR absorption greater than the interstellar absorption but 2orders of magnitude below the X-ray absorption. We propose the followingpicture to match the data: the source is a high-mass X-ray binary (HMXB)at a distance between 0.9 and 6.2 kpc, and the optical/NIR counterpartcorresponds to the mass donor, which is an early-type star, maybe ansgB[e] star, surrounded by a dense and absorbing circumstellar material.This would make the second HMXB with an sgB[e] star as the mass donorafter CI Cam. Such sources may represent a different evolutionary stateof X-ray binaries previously undetected with the lower energy spacetelescopes; if so, a new class of strongly absorbed X-ray binaries isbeing unveiled by INTEGRAL.Based on observations collected at the European Southern Observatory,Chile (observing proposal ESO N 70.D-0340).
| A new approach to IRAS observations of Be stars
The IRAS associations for 193 Be stars are identified in this paper.From the infrared colors, the IRAS low-resolution spectra (LRS) and thespectral types, some physical properties and environment of the samplesare discussed. It can be concluded that not only free-free emission orfree-bound emission from the circumstellar ionized gas can beresponsible for the large IR excesses of Be stars as suggestedpreviously, but also, for some Be stars, thermal radiation from thecircumstellar dust and/or nebula around the star can produce large IRexcess as well. It is also found that the far IR excess of Be starsincreases with wavelengths.
| Near-Infrared Spectroscopy of MCNeil's Nebula Object
We present 0.8-5.2 μm spectroscopy of the compact source at the baseof a variable nebula (McNeil's Nebula Object) in the Lynds 1630 darkcloud that went into outburst in late 2003. The spectrum of this objectreveals an extremely red continuum, CO bands at 2.3-2.5 μm inemission, a deep 3.1 μm ice absorption feature, and a solid-state COabsorption feature at 4.7 μm. In addition, emission lines of H, CaII, Mg I, and Na I are present. The Paschen lines exhibit P Cygniprofiles, as do two lines of He I, although the emission features arevery weak in the latter. The Brackett lines, however, are seen to bepurely in emission. The P Cygni profiles clearly indicate that massoutflow is occurring in a wind with a velocity of ~400 kms-1. The H line ratios do not yield consistent estimates ofthe reddening, nor do they agree with the extinction estimated from theice feature (AV~11). We propose that these lines areoptically thick and are produced in a dense, ionized wind. Thenear-infrared spectrum does not appear similar to any known FUor or EXorobject. However, all evidence suggests that McNeil's Nebula Object is aheavily embedded low-mass Class I protostar, surrounded by a disk, whosebrightening is due to a recent accretion event.Based on observations made with the NASA Infrared Telescope Facility.
| The abundance distributions of Galactic bulge and disc planetary nebulae
We present an abundance analysis of a sample of Galactic bulge planetarynebulae (GBPNe). The observational data set consists of spectra of 88nebulae obtained with the FLAIR II multiobject spectrograph on the UKSchmidt Telescope, together with spectra of 42 nebulae obtained with theRGO Spectrograph on the Anglo-Australian Telescope. After selectingthose for which reliable nebular electron temperatures could be derived,collisionally excited line abundances were derived for 45 GBPNe.These were then compared with similarly derived abundances for 54Galactic disc PNe (GDPNe), taken from the work of Kingsburgh &Barlow. We find that within the errors the abundances have the sameaverage values, essentially the same distributions - including that forthe mass-sensitive N/O ratio - and show the same relationships. Thewidth of the nitrogen distribution exceeds that arising from errors,which could be a consequence of the range of precursor masses. The ratioof Type-I to non-Type-I PNe in the bulge and disc samples is similar, 18and 25 per cent respectively. For the GDPNe, we find larger N/H and N/Oratios for the small number of those with He/H > 0.14, compared withthose with He/H < 0.14.For neither disc nor bulge sample is there any strong evidence for adepletion of oxygen for the higher-mass precursor stars (Type I PNe). Wefind no correlation between O/H and N/O or He/H. On the N/O to He/Hplane, the bulge and disc PNe show a distribution whereby the low N/Ovalues only occur for low He/H values, but at N/O > 0.25 the wholerange of He/H values were sampled. The theoretical tracks to which wecompare our data do not explain the PNe with low He/H abundance and highN/O ratio.Realistic uncertainties in collisionally excited lines (CEL) abundancesfor individual PNe are quite large, of the order of 40 per cent foroxygen. Large samples are therefore required to get good statisticalaccuracy. This is usually achieved by combining many studies, and so wehave compared the results of a number of published studies with our own,to search for any systematic differences. The average abundances arefound to be the same within the errors except for cases where theabundance derivation methods are dissimilar, where systematicdifferences can occur. The N/O ratio is especially sensitive to thedetails of the abundance derivations.Our bulge PN sample shows no evidence for either very-low-metallicityobjects or for super-metal-rich objects - the implied mass and agedistributions of the bulge PN precursor stars are indistinguishablewithin the observational errors from those in the local Galactic disc.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Dusty ring nebulae around new candidate Luminous Blue Variables
We report on the discovery of a further two ring nebulae in theMidcourse Space Experiment (MSX) Galactic Plane Survey;G24.73+0.69 and G26.47+0.02.Morphologically, both appear similar to the nebulae found around theLuminous Blue Variable (LBV) candidates G79.29+0.46and Wra 17-96. A central, unresolved point source wasidentified in both cases - positional coincidence with the starStRS 237 was found forG26.47+0.02, while no optical counterpart could beidentified for G24.73+0.69. However, subsequent nearIR broadband imaging of the G24.73+0.69 fieldidentified a very red - (J-K) ~ 2 mag - stellar counterpart to thecentral object. Near-IR spectroscopy of both objects reveal richemission line spectra dominated by H I, He I and low excitation metals,suggesting classification as luminous B supergiants and revealing astriking superficial similarity to the other MSX ring sources and knownLBVs. We utilised a NLTE model atomsphere code to model the K bandspectra and near-IR spectral energy distributions of the central starsin order to determine their physical parameters. Adopting a distance, d=5.2 kpc to G24.73+0.69 yields a temperature, T= 12kK, luminosity, log (L/Lsun) = 5.6 and mass loss rate, dot{M}=1x 10-5 Msun yr-1.G26.47+0.02 appears to be a more extreme object;adopting d= 6.5 kpc results in T= 17 kK, log (L/Lsun) = 6.0and dot {M}=9x 10-5 Msun yr-1, placingit at the Humphreys-Davidson limit for massive stellar objects. Analysisof the spatially resolved mid-IR fluxes of both objects reveal extendedperiods of enhanced mass loss, resulting in comparatively low massnebulae, with chemistries dominated by O-rich dust (with a population ofsmall Fe grains existing co-spatially with the silicate dust).Comparison to the other MSX ring nebulae sources reveals a homogeneousgroup of objects, with both stellar and nebular properties consistentwith known LBVs. With both spectroscopic and/or photometric variabilityobserved for those sources with multiepoch observations, we propose aclose affinity between both classes of object and suggest that long termmonitoring of the MSX sources will reveal them to be bona fide LBVs.
| Using spectroscopic analysis of unclassified supergiants to investigate massive stars in transition. II. The superluminous HD 327083
New optical high-resolution (R~50 000) spectra of the star HD 327083 arereported in this paper. The Balmer and Fe II lines show P Cygni profileswhile He I lines are all in pure absorption, resembling the spectra ofthe Luminous Blue Variable HR Carinae. However, the blue absorptioncomponents of the Balmer lines are more pronounced and the Fe II linesare less numerous and less intense in HD 327083. A spectroscopicanalysis of the Balmer lines (Hα , Hβ , Hγ and Hdelta) with a non-LTE wind model has been performed. The derived stellarparameters for HD 327083 are: log (Lstar/Lsun) =6.0, Tstar = 11 500 K, dot M = 8.0 x 10-5Msun/yr and He/H = 0.2 (by number). From these results weconcluded that HD 327083 is a superluminous object in an evolved phaseof an evolutive track of MZAMS ~ 60 Msun. It islikely to be about to enter in a Luminous Blue Variable phase.Based on observations made with the 1.52 m telescope at the EuropeanSouthern Observatory (La Silla, Chile) under the agreement with theObservatório Nacional, Brazil.
| Confirmation of the Luminous Blue Variable nature of AFGL 2298
We present new photometric and spectroscopic observations of the stellarsource AFGL 2298 (= IRAS18576+0341) that has recently been proposed as a candidateLuminous Blue Variable (LBV). Our data confirm that the star is a highlyluminous B supergiant which is both spectroscopically andphotometrically variable. Assuming a distance of 10 kpc, comparison ofthe 2001 June data to synthetic spectra suggest stellar parameters ofT=12.5 kK, log(L/Lsun)=6.2 and dot M=5*E-5Msun yr-1. Data obtained in 2002 August indicatean increase in both temperature (=15 kK) and mass loss rate(=1.2*E-4 Msun yr-1) at constantbolometric luminosity. These physical parameters place AFGL2298 at the Humphreys-Davidson limit for the most luminousstars known. We conclude that the position of AFG2298 in the HR diagram, the significant variability observedbetween 1999-2002 and presence of a massive ejection nebula areconsistent with a classification of AFGL 2298 as abona fide LBV.
| The Origin of Fe II and [Fe II] Emission Lines in the 4000-10000 Å Range in the BD Weigelt Blobs of η Carinae
We present numerical simulations that reproduce the salient features ofthe amazingly strong [Fe II] and Fe II emission spectra in the B and DWeigelt blobs of η Carinae. For our studies we have used spectraobtained during the 1998 epoch observations with the Hubble SpaceTelescope (HST). The spectrum of the B and D Weigelt blobs dominates in[Fe II] and Fe II emission lines. The same observations show no Fe I orFe III. We have compared our measurements of the strongest (>=200)[Fe II] and Fe II lines and blends in the spectrum with theoreticalpredictions. Our predictions are based on non-LTE modeling of the Fe IIatom, which includes the lowest 371 energy levels (all levels up to 11.6eV). We have investigated the dependence of the spectrum on electrondensity, pumping by the blackbody-like stellar continuum, and intenseLyα emission. We find that radiative pumping is essential inexplaining the observed spectrum. We have identified the main pumpingroutes responsible for the observed Fe II emission. Comparison betweenthe model and observations reveals details of the radiation field.Pumping by the blackbody-like stellar radiation field from η Carinaeexplains the numerous strong [Fe II] and Fe II lines in the range of4000-6500 Å. The strongest Fe II lines in a range of 8000-10000Å are pumped by intense Lyα radiation. Based on observationsmade with the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
| Properties of galactic B[e] supergiants. I. CI Camelopardalis
We present a study of the high-resolution (R=60 000) optical spectrum ofthe B[e] supergiant CI Cam obtained 4 years after its all-wavelengthoutburst. The profiles of most of the emission lines show atriple-peaked structure, an effect previously not observed. The Na ID-lines clearly have 2 interstellar absorption components, suggestingthat the system is most probably located within the Perseus arm at adistance of le 3 kpc. Uncertainties of the distance toward the object,its luminosity, and physical parameters of the circumstellar disk arediscussed. Simple observational tests are suggested to clarify theseissues.
| An Infrared Ring Nebula around MSX5C G358.5391+00.1305: The True Nature of Suspected Planetary Nebula Wray 17-96 Determined via Direct Imaging and Spectroscopy
The Midcourse Space Experiment (MSX) Galactic plane survey discovered anearly perfectly circular ring nebula around the suspected planetarynebula Wray 17-96. Using near-IR spectral typing and modeling of themid-IR nebula, we find that Wray 17-96 is more likely a candidate to bea luminous blue variable (LBV) surrounded by a large spherical ejectashell. It is very similar to the G79.29+0.46 LBV candidate in Cygnus andthe Pistol Star. The K-band spectrum and the mid-IR data indicate astellar temperature of 13,000 K. The most likely distance to the sourceis 4.5 kpc, leading to a luminosity of 1.8×106Lsolar. We suggest that the nebula consists of multipleshells and that an evolution from oxygen-rich to carbon-rich chemistrymay be indicated.
| A Spectral Atlas of the Pre-WN Candidate HD 326823
HD 326823 is a peculiar emission line object. In the literature it wasconsidered as a pre-WN candidate. Based mainly on high-resolution data,obtained with the FEROS spectrograph, we made an atlas covering3800-9200 Å region. This atlas confirms the presence of severalstrong He I lines and numerous nitrogen lines. There is also adeficiency of hydrogen, indicating that this object is indeed in anevolved stage. In addition, with low-resolution spectra, we obtainedintensities of several lines. Based on observations mainly done with the1.52 m telescope at the European Southern Observatory (La Silla, Chile),under the agreement with the Observatório Nacional-MCT (Brazil)and also with the 1.6 m telescope at the Laboratório Nacional deAstrofísica (Brasópolis, Brazil).
| Astrophysics in 2000
It was a year in which some topics selected themselves as importantthrough the sheer numbers of papers published. These include theconnection(s) between galaxies with active central engines and galaxieswith starbursts, the transition from asymptotic giant branch stars towhite dwarfs, gamma-ray bursters, solar data from three major satellitemissions, and the cosmological parameters, including dark matter andvery large scale structure. Several sections are oriented aroundprocesses-accretion, collimation, mergers, and disruptions-shared by anumber of kinds of stars and galaxies. And, of course, there are theusual frivolities of errors, omissions, exceptions, and inventories.
| Spectroscopic verification of suspected planetary nebulae. IV.
Verification of 7 objects as PNe (Table 1/A) as well asmisclassification of 5 objects as PNe (Table 1/C) are discussedaccording to our CCD spectra; the status of 4 objects (Table 1/B)remains uncertain. In Table we give the estimates of line-strengths andthe measured intensities of emission lines as well as the derived hel.radial velocities and their standard deviations.
| On the Nature of the Central Source in η Carinae
Long-slit spectroscopic observations of η Carinae and its Homunculushave recently been obtained using STIS on the Hubble Space Telescope(HST). We have extracted the spectrum of the central source using a0.1"×0.13" aperture. As expected, the spectrum is very differentfrom ground-based spectra obtained under normal seeing conditions (i.e.,1")-the HST observed spectrum exhibits primarily broad permittedemission lines (vFWHM~500 km s-1), whileground-based spectra show strong narrow (vFWHM~40 kms-1) permitted and forbidden lines (primarily [Fe II], Fe II,and H I) superimposed on a broad emission-line spectrum. In the optical,the spectrum shows strong H I, He I, and Fe II emission lines, manyexhibiting P Cygni absorption components. Emission features due to N I,Si II, Na I, Mg II, Ca II, and Al II can also be identified. Only a fewweak broad lines of [Fe II] are seen. The spectrum is qualitativelysimilar to a much less luminous object, the extreme P Cygni star HDE316285. We have performed a detailed analysis of the spectrum using thenon-LTE line blanketed wind code of Hillier & Miller. Despite thecomplexity of η Carinae, we are able to obtain a good fit to theoptical emission line spectrum using a model with a mass-loss rate of10-3 Msolar yr-1 . The weakness of theelectron-scattering wings indicates that the wind is clumped, with avolume filling factor of approximately 0.1. Because of the parameterrange and the extremely dense wind associated with the central star, ourbest-fit model is not unique. As is the case for HDE 316285, there is astrong coupling between the derived mass-loss rate and the derivedN(H)/N(He) abundance ratio. In addition, the wind is so dense that thestar's surface cannot be observed. Consequently, the effectivetemperature of the underlying star is not well determined. Because ofthe rich emission-line spectrum we are able to place limits on manyabundances: Mass fractions of species such as Fe and Mg (and perhaps Ca,Si, and Al) are solar to within a factor of 2. In accord with standardevolutionary scenarios, Na is slightly enhanced, the N mass fraction isat least a factor of 10 over solar, while C and O show substantialdepletions. The adopted luminosity of 5×106Lsolar is based on the observed IR flux and an assumeddistance of 2.3 kpc. Thus, based on the Eddington limit, the minimummass of the system is approximately 120 (L/5×106Lsolar) Msolar [for N(H)/N(He)=5]. While ηCarinae may be a binary, recent evidence suggests that the purportedsecondary star has a mass less than 30 Msolar. Thus theprimary star is currently more massive than 90 Msolar, andthe initial mass of the star should conservatively have been in excessof 150 (L/5×106) Msolar. Based onobservations with the NASA/ESA Hubble Space Telescope obtained at theSpace Telescope Science Institute, which is operated by AURA, Inc.,under NASA contract NAS 5-26555.
| 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
| Physical Parameters of Erupting Luminous Blue Variables: NGC 2363-V1 Caught in the Act
A quantitative study of the luminous blue variable NGC 2363-V1 in theMagellanic galaxy NGC 2366 (D=3.44 Mpc) is presented, based onultraviolet and optical Hubble Space Telescope STIS spectroscopy.Contemporary WFPC2 and William Herschel Telescope imaging reveals amodest V-band brightness increase of ~0.2 mag per year between 1996January-1997 November, reaching V=17.4 mag, corresponding toMV=-10.4 mag. Subsequently, V1 underwent a similar decreasein V-band brightness, together with a UV brightening of 0.35 mag from1997 November to 1999 November. The optical spectrum of V1 is dominatedby H emission lines, with Fe II, He I and Na I also detected. In theultraviolet, a forest of Fe absorption features and numerous absorptionlines typical of mid-B supergiants (such as Si II, Si III, Si IV, C III,C IV) are observed. From a spectral analysis with the non-LTE,line-blanketed code of Hillier & Miller, we derive stellarparameters of T*=11 kK, R*=420 Rsolar,log (L/Lsolar)=6.35 during 1997 November, andT*=13 kK, R*=315 Rsolar, log(L/Lsolar)=6.4 for 1999 July. The wind properties of V1 arealso exceptional, with M~=4.4×10-4Msolaryr-1 and v&infy;~=300 km s-1, allowingfor a clumped wind (filling factor=0.3) and assuming H/He~4 by number.The presence of Fe lines in the UV and optical spectrum of V1 permits anestimate of the heavy elemental abundance of NGC 2363 from our spectralsynthesis. Although some deficiencies remain, allowance for chargeexchange reactions in our calculations supports a SMC-like metallicity,that has previously been determined for NGC 2363 from nebular oxygendiagnostics. Considering a variety of possible progenitor stars, V1 hasdefinitely undergone a giant eruption, with a substantial increase instellar luminosity, radius, and almost certainly mass-loss rate, suchthat its stellar radius increased at an average rate of ~4 kms-1 during 1992 October-1995 February. The stellar propertiesof V1 are compared to other LBVs, including η Car and HD 5980 duringits brief eruption in 1994 September, the latter newly analyzed here.The mass-loss rate of the HD 5980 eruptor compares closely with V1, butits bolometric luminosity was a factor ~6 times larger. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by AURA, Inc.,under NASA contract NAS 5-26555.
| Spectroscopy and photometry of the emission-line B-type stars AS 78 and MWC 657
We present the results of low- and high-resolution spectroscopic andmulticolour photometric observations of two early-type emission-linestars, AS 78 and MWC 657. Theywere identified by Dong & Hu (\cite{dong}) with the IRAS sources03549+5602 and 22407+6008, respectively, among many other sourcesdisplaying a very strong infrared excess, V-[25] >= 8 mag AS 78 isrecognized as a photometric variable for the first time. A large near-IRexcess radiation is detected in AS 78 and confirmed by new,higher-quality, data for MWC 657. Significant variations in the Balmerline profiles are detected for both objects. Modelling of the Balmerline profiles of AS 78 obtained in 1994 yields the following parametersof the star and its wind: Teff ~ 17 000 K, logLbol/Lsun ~ 4.0, dot M ~ 10-6Msun yr-1. The photometric and new spectroscopicdata indicate that the star's Teff increases with time, whilethe stellar wind changes its structure. Distances towards both objectsare estimated on the basis of their radial velocities and the galacticrotation curve. Consideration of different options about the nature andevolutionary state of both objects leads us to suggest that they arebinary systems containing a B-type intermediate-luminosity star and agaseous disk around the less luminous component. Table 9 is onlyavailable in electronic form at the CDS via anonymous ftp (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html
| Spectroscopy of the candidate luminous blue variable at the center of the ring nebula G79.29+0.46
We report optical and near-infrared spectra of the central star of theradio source G79.29+0.46, a candidate luminous blue variable. Thespectra contain numerous narrow (FWHM < 100 km s-1)emission lines of which the low-lying hydrogen lines are the strongest,and resemble spectra of other LBVc's and B[e] supergiants. A fewprominent infrared lines are unidentified. The terminal wind speed isdetermined from Hα to be 110 km s-1. The strength ofHα implies the presence of a very dense wind. Extended emissionfrom Hα and [N ii] was detected but appears to be associated withthe Cygnus X region rather than the radio source. Both diffuseinterstellar bands and interstellar absorption lines are present in theoptical spectrum of the central star, suggesting that there are bothdiffuse and molecular cloud components to the extinction and implying aminimum distance of 1 kpc and minimum luminosity of ~ 105Lsun for the star. The new spectra and their analysisindicate a low excitation, dense, and slowly expanding wind and supportthe LBVc classification.
| Massive stars in the galactic center
The relatively brief history of infrared observations and quantitativeanalysis of massive stars in the Galactic Center is reviewed. Currentobservational and the theoretical status is also reported: A newgeneration of NLTE wind blanketed models, together with high S/N spectraof the hot star population are allowing one, for the first time, toperform metal abundance determinations (Fe, Si, Mg, Na, etc).Metallicity studies of hot stars in the IR will provide majorconstraints not only on the theory of evolution of massive stars butalso on our efforts to solve the puzzle of the central parsecs of theGalaxy. Preliminary results are presented.
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Osservazione e dati astrometrici
| Costellazione: | Sagittario |
| Ascensione retta: | 17h48m14.03s |
| Declinazione: | -28°00'53.1" |
| Magnitudine apparente: | 9.202 |
| Moto proprio RA: | -5.2 |
| Moto proprio Dec: | -5.2 |
| B-T magnitude: | 11.074 |
| V-T magnitude: | 9.357 |
Cataloghi e designazioni:
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