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Variability in red supergiant stars: pulsations, long secondary periods and convection noise
We study the brightness variations of galactic red supergiant starsusing long-term visual light curves collected by the AmericanAssociation of Variable Star Observers over the last century. The fullsample contains 48 red semiregular or irregular variable stars, with amean time-span of observations of 61 yr. We determine periods and periodvariability from analyses of power density spectra and time-frequencydistributions. We find two significant periods in 18 stars. Most ofthese periods fall into two distinct groups, ranging from a few hundredto a few thousand days. Theoretical models imply fundamental, first andpossibly second overtone mode pulsations for the shorter periods.Periods greater than 1000 d form a parallel period-luminosity relationthat is similar to the long secondary periods of the asymptotic giantbranch stars. A number of individual power spectra shows a single moderesolved into multiple peaks under a Lorentzian envelope, which weinterpret as evidence for stochastic oscillations, presumably caused bythe interplay of convection and pulsations. We find a strong 1/f noisecomponent in the power spectra that is remarkably similar in almost allstars of the sample. This behaviour fits the picture of irregularphotometric variability caused by large convection cells, analogous tothe granulation background seen in the Sun.
| A census of the Carina Nebula - I. Cumulative energy input from massive stars
The Carina Nebula (NGC 3372) is our richest nearby laboratory in whichto study feedback through ultraviolet radiation and stellar winds fromvery massive stars during the formation of an OB association, at anearly phase in the evolution of the surrounding proto-superbubble beforesupernova explosions have influenced the environment. This feedback istriggering successive generations of new star formation around theperiphery of the nebula, while simultaneously evaporating the gas anddust reservoirs out of which young stars are trying to accrete material.This paper takes inventory of the combined effect from all the knownmassive stars that power the Carina Nebula through their total ionizingflux and integrated mechanical energy from their stellar winds. Carinais close enough and accessible enough that spectral types for individualstars are available, and many close binary and multiple systems haverecently been spatially resolved, so that one can simply add them.Adopting values from the literature for corresponding spectral types,the present-day total ionizing photon luminosity produced by the 65 Ostars and three WNL stars in Carina is QH~=1051s-1, the total bolometric luminosity of allstars earlier than B2 is 2.5 × 107Lsolar,and the total mechanical luminosity of stellar winds is LSW~=105Lsolar. The total QH was about 25per cent higher when η Carinae was on the main sequence, before itand its companion were surrounded by its obscuring dust shell; for thefirst 3Myr, the net ionizing flux of the 70 O stars in Carina was about150 times greater than in the Orion Nebula. About400-500Msolar has been contributed to the HII region bystellar wind mass-loss during the past 3Myr. Values for QHand LSW are also given for the individual clusters Tr14, 15and 16, and Bo10 and 11, which are more relevant on smaller spatialscales than the total values for the whole nebula.
| The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCSstellar atmosphere models to determine the effective temperatures of 74Galactic red supergiants (RSGs). The stars are mostly members of OBassociations or clusters with known distances, allowing a criticalcomparison with modern stellar evolutionary tracks. We find we canachieve excellent matches between the observations and the reddenedmodel fluxes and molecular transitions, although the atomic lines Ca Iλ4226 and Ca II H and K are found to be unrealistically strong inthe models. Our new effective temperature scale is significantly warmerthan those in the literature, with the differences amounting to 400 Kfor the latest type M supergiants (i.e., M5 I). We show that the newlyderived temperatures and bolometric corrections give much betteragreement with stellar evolutionary tracks. This agreement provides acompletely independent verification of our new temperature scale. Thecombination of effective temperature and bolometric luminosities allowsus to calculate stellar radii; the coolest and most luminous stars (KWSgr, Case 75, KY Cyg, HD 206936=μ Cep) have radii of roughly 1500Rsolar (7 AU), in excellent accordance with the largeststellar radii predicted from current evolutionary theory, althoughsmaller than that found by others for the binary VV Cep and for thepeculiar star VY CMa. We find that similar results are obtained for theeffective temperatures and bolometric luminosities using only thedereddened V-K colors, providing a powerful demonstration of theself-consistency of the MARCS models.
| Guilt by Association: The 13 Micron Dust Emission Feature and Its Correlation to Other Gas and Dust Features
A study of all full-scan spectra of optically thin oxygen-richcircumstellar dust shells in the database produced by the ShortWavelength Spectrometer on ISO reveals that the strength of severalinfrared spectral features correlates with the strength of the 13 μmdust feature. These correlated features include dust features at 19.8and 28.1 μm and the bands produced by warm carbon dioxide molecules(the strongest of which are at 13.9, 15.0, and 16.2 μm). The databasedoes not provide any evidence for a correlation of the 13 μm featurewith a dust feature at 32 μm, and it is more likely that a weakemission feature at 16.8 μm arises from carbon dioxide gas ratherthan dust. The correlated dust features at 13, 20, and 28 μm tend tobe stronger with respect to the total dust emission in semiregular andirregular variables associated with the asymptotic giant branch than inMira variables or supergiants. This family of dust features also tendsto be stronger in systems with lower infrared excesses and thus lowermass-loss rates. We hypothesize that the dust features arise fromcrystalline forms of alumina (13 μm) and silicates (20 and 28 μm).Based on observations with the ISO, a European Space Agency (ESA)project with instruments funded by ESA member states (especially thePrincipal Investigator countries: France, Germany, the Netherlands, andthe United Kingdom) and with the participation of the Institute of Spaceand Astronautical Science (ISAS) and the National Aeronautics and SpaceAdministration (NASA).
| Imaging study of NGC 3372, the Carina nebula - I. UBVRIJHK photometry of Tr 14, Tr 15, Tr 16 and Car I
We present the results of a large-scale imaging photometric study of thestellar population in the northern part of NGC 3372 in the UBVRIJHKbands with a wavelength coverage from 0.33 to 2.5 μm. Theobservations were made at Las Campanas Observatory. The optical CCDmosaics cover an area approximately of 32 × 22 arcmin2centred between the Tr 14 and Tr 16 clusters. The survey was extended tocover 12 × 12 arcmin2 at the location of Tr 15.Near-infrared NICMOS3 mosaics covering the areas occupied by theseclusters were obtained in the JHK photometric bands. By means of starcounts in V, the centres and sizes of each cluster were redeterminedyielding: Tr 14 (r= 264 arcsec), Tr 15 (r= 320 arcsec) and Tr 16 (r= 320arcsec). It was confirmed that Cr 232 is not a true cluster. Multicolouroptical photometry was obtained for 4152 stars. Two colour andcolour-magnitude diagrams are presented and analysed for each individualcluster and compared to those of the field. We confirm the widespreadvariations in the dust density and also in the dust size distributionleading to widely different values of AV and reddening lawstowards Tr 14 and Tr 16. No spatial patterns were found for thesevariations. Spectroscopic parallaxes were computed and the results areconsistent with all three clusters being at a similar distance from theSun (= 2.7 kpc) but the data have shown very large scatter inboth AV and d. Analyses of the extinction-correctedcolour-magnitude diagrams suggest ages between 3 and 60 million yearsfor the stars in Tr 15 and between less than 1 and 6 million years forTr 14 and Tr 16. A small number of infrared-excess stars were found inTr 16 and Tr 14 but not in Tr 15. The distribution of stars in Tr 14seen in the near-infrared suggests that this cluster is partiallyembedded in a molecular cloud. This molecular cloud extends towards thewest reaching its highest density, marked by a CO peak emission, somethree arcmin to the south-west of the nucleus of Tr 14. The richultraviolet field created by the Tr 14 stars ionizes most of the visibleHII region in its vicinity and most of the radio HII region Car I.Evidence is found of ionization fronts leading into the molecular cloud,which appears to be `wrapping' the Tr 14 cluster. Deep JHK images of theCar I region reveal the presence of an embedded stellar populationilluminating a large infrared reflection nebula. It includes at leastone O9-B0 star associated with an ultracompact HII region. Nebulous 2.2μm emission from three of the mid-infrared sources in the Tr 14region is also found.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/397/997
| 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.
| A Catalog and Atlas of Cataclysmic Variables: The Living Edition
The Catalog and Atlas of Cataclysmic Variables (Edition 1: Downes &Shara; Edition 2: Downes, Webbink, & Shara) has been a valuablesource of information for the cataclysmic variable community. However,the goal of having a central location for all objects is slowly beinglost as each new edition is generated. There can also be a long timedelay between new information becoming available on an object and itspublication in the catalog. To eliminate these concerns, as well as tomake the catalog more accessible, we have created a Web site which willcontain a ``living'' edition of the catalog. We have also added orbitalperiod information, as well as finding charts for novae, to thecatalog.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Observational investigation of mass loss of M supergiants
We present the analysis of infrared photometry and millimeterspectroscopy of a sample of 74 late-type supergiants. These observationsare particularly suitable to study the mass loss and the circumstellarenvelopes of evolved massive stars. In particular, we quantify thecircumstellar infrared excess, the relation of mass loss with stellarproperties, using the K-[12] colour index as mass-loss indicator. We donot find any clear correlation between mass loss rate and luminosity. Wealso show that the K-band magnitude is a simple luminosity indicator,because of the relative constancy of the K-band bolometric correction.Based on observations collected at the European Southern Observatory, LaSilla, Chile within program ESO 54.E-0914, and on observations collectedwith the IRAM 30m telescope. Tables A1 to A3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| A Catalog and Atlas of Cataclysmic Variables-Second Edition
We present a catalog of all 1020 known cataclysmic variables (CVs). Thispaper is a major update of the first edition of the catalog (Downes andShara 1993, PASP, 105, 127), which contained coordinates (measured inthe reference frame of the Hubble Space Telescope Guide Star Survey forthe non-novae, and obtained from the literature for the novae), thevariability type, the magnitude range, and references to both findingcharts and spectroscopy. Also included in the catalog were findingcharts for all dwarf novae, novalike variables, and objects classifiedonly as cataclysmic variables known as of 1993; a similar catalog andatlas for novae has been published by Duerbeck (1978a). This updatededition includes 195 new objects (172 CVs and 23 non-CVs), revisedidentifications for 57 objects, and revised information (classificationand spectral references) when available. We also now include plateidentification information for the coordinate measurements, a referenceto the classification, proper motion information where appropriate, anda table showing the CVs observed by space-based observatories. Thissecond edition is inclusive of the first edition, although only new orupdated charts are presented. (SECTION: Special Issue on CataclysmicVariable Stars)
| ISO-SWS Observations of Stars with Unusual IRAS LRS Characteristics
Observations of 5 stellar sources with unusual characteristics of IRASLow Resolution Spectra were made with the SWS on ISO. Observed stars are4 late-type stars with silicate bands and one planetary nebula. TheirIRAS LRS contain somewhat unusual features in respect of the 10/18µm intensity ratio or narrow emission feature from unknownmolecular bands. Some narrow unusual features are confirmed by ISO SWS01spectra but the broad features were turned out to be false.
| Really Cool Stars at the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1988B&db_key=AST
| ROSAT Observations of Symbiotic Binaries and Related Objects
Not Available
| Infrared Measurements of Faint Symbiotic Stars
Not Available
| A catalog and atlas of cataclysmic variables
The General Catalogue of Variable Stars contains information necessaryfor obtaining observations of variable stars, and in particular,cataclysmic variables. However, the coordinates presented are notaccurate enough for observatories such as the Hubble Space Telescope,and the references to finding charts are often to journals not easilyaccessible to some astronomers. We have therefore created a catalog ofall cataclysmic variables (known to us as of February 1992) whichcontains coordinates (measured in the reference frame of the HubbleSpace Telescope Guide Star Survey for the nonnovae, and obtained fromthe literature for the novae), the variability type, the magnituderange, and references to both finding charts and spectroscopy. The atlascontains finding charts for the dwarf novae, novalike variables, andobjects classified only as cataclysmic variables, for which we couldobtain valid identifications; a similar catalog and atlas for novae hasbeen published by Duerbeck (1987).
| Intracluster dust polarization in the Carina Nebula
New UBVRI polarimetric observation of 25 Carina Nebula-embedded stars,together with BV polarimetric observations of 60 additional stars fromthat nebula, are presently used in conjunction with polarimetricobservations from the literature to model and subtract the foregrounddust contribution in the color excess and the visual polarization. Theintracluster dust component thus obtained is found to have apolarization efficiency lower than the maximum observed for theinterstellar medium. This result is consistent with the anomalousextinction for this region.
| Third list of corrections to the identifications of IRAS sources in Astron. & Astrophys Suppl. 65, 607 and Astron. J. 98, 931
Not Available
| The Perkins catalog of revised MK types for the cooler stars
A catalog is presented listing the spectral types of the G, K, M, and Sstars that have been classified at the Perkins Observatory in therevised MK system. Extensive comparisons have been made to ensureconsistency between the MK spectral types of stars in the Northern andSouthern Hemispheres. Different classification spectrograms have beengradually improved in spite of some inherent limitations. In thecatalog, the full subclasses used are the following: G0, G5, G8, K0, K1,K2, K3, K4, K5, M0, M1, M2, M3, M4, M5, M6, M7, and M8. Theirregularities are the price paid for keeping the general scheme of theoriginal Henry Draper classification.
| New LRS spectra for 356 bright IRAS sources
The low-resolution spectra of all IRAS point sources with F(nu) (12microns) greater than 40 Jy that were not included in the Atlas ofLow-Resolution Spectra are presented. These have been classified intoeight groups based upon the spectral morphology. Silicate emissionspectra and red-continuum spectra associated with H II region sourcesform about 60 percent of this sample. All types of spectra in the LRSAtlas are represented in the sample except for emission-line sources.The sample is used to test a recent classification scheme for IRASsources based on broadband colors. The spectra is used to test a recentclassification scheme for IRAS sources based on broadband colors. Thespectra are consistent with the classifications from the colors in mostcases.
| Infrared circumstellar shells - Origins, and clues to the evolution of massive stars
The infrared fluxes, spatial and spectral characteristics for a sampleof 111 supergiant stars of spectral types F0 through M5 are tabulated,and correlations examined with respect to the nature of theircircumstellar envelopes. One-fourth of these objects were spatialyresolved by IRAS at 60 microns and possess extended circumstellar shellmaterial, with implied expansion ages of about 10 to the 5th yr.Inferences about the production of dust, mass loss, and the relation ofthese characteristics of the evolution of massive stars, are discussed.
| Spectral morphology in the open clusters Trumpler 14 and Trumpler 15
A total of 21 and 14 stars in the fields of the open clusters Tr 15 andTr 14, respectively, have been observed in order to provide spectraltypes derived through the MK process. The spectroscopic parallaxes forthose groups have also been obtained, finding that Tr 15 is almost atthe same distance from the sun as Tr 16 but that Tr 14 is possibly moredistant. This cluster, with its high concentration of O-type stars, isalso the youngest of both groups studied in this work and may be youngerthan Tr 16.
| The interstellar extinction in the open clusters TR 14, TR 15, TR 16/Cr 232 and CR 228 in NGC 3372 - New near-infrared photometry
Near-infrared JHKL photometry of more than 200 stars, members of theopen clusters Tr 14, Tr 15, Tr 16, Cr 228 and Cr 232 in the CarinaNebula are presented. From comparing these results with the availablevisual photometry and spectroscopy, it is found that, except in Tr 15,the intracluster reddening is characterized by a 'normal' extinction lawat lambda of greater than 0.5 microns but is highly anomalous andvariable in the U-bands and B-bands. This behavior may be explained bythe presence of intracluster interstellar grains 'processed' by shockwaves presumably associated with the explosive history of Eta Carinae.All clusters are found to be at the same distance from the sun at d =2.4 + or - 0.2 kpc. The total amount of reddening, though, differssignificantly from cluster to cluster.
| Near-infrared spectral classification of symbiotic stars
Near-infrared spectra of 16 symbiotic stars and 29 G, K and M standardstars are presented. The spectrograms are used to classify the coolcomponents in symbiotic stars. The equivalent width of the CN bandfeature at (7916 + 7941) A is demonstrated to be a quantitativeluminosity indicator for classes III to I in the (single) M0 to M3standard stars. Six of the observed symbiotic stars have temperatureclasses within this range and the criterium is applied to theirspectrograms. Accordingly, four of the late-type components are normalgiants, while the nature of two systems remains ambiguous. The resultsare discussed in the light of presently proposed interacting binarymodels for symbiotic stars.
| Valinhos 2.2 micron survey of the southern galactic plane. II - Near-IR photometry, IRAS identifications and nature of the sources
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...71...39E&db_key=AST
| RT Carinae; a late type supergiant within an elongated dusty nebula
Observations of an elongated dusty nebula surrounding the luminoussupergiant star RT Carinae are reported. The observations were carriedout in the infrared using the Schmidt telescope at CTIO. The nebula wasdetected on a near infrared plate (emulsion: IV-N) using ahypersensitized filter. The exposure time of the plates was about 60minutes. A densitometric record of the infrared plate(lambdaef = 0.79 microns) at different density levels wasobtained using a PDS scanner having a slit width of 15-micron and1-micron steps. The features of the nebula sourrounding RT Carinae arein agreement, at least qualitatively, with the predictions of Blandfordet al. (1983) on the tail formation mechanism of the collimated jet inthe Grab Nebula. Photographic examples of the infrared plates areprovided.
| M supergiants in the Milky Way and the Magellanic Clouds Colors, spectral types, and luminosities
The differences in metal abundances between the Milky Way, LargeMagellanic Cloud (LMC), and Small Magellanic Cloud (SMC) affect most ofthe observable properties of the M supergiants in these galaxies; thosein the SMC (which has the lowest metal abundance) have the earliest meanspectral type, while those of the Milky Way exhibit the latest meanspectral type. This is presently interpreted as a combination of twoeffects of differing metal abundance on the supergiant atmospheres:first, lower abundance stars of a given effective temperature haveearlier MK spectral types due to reduced TiO abundance; second, theHayashi track is shifted to hotter effective temperature at reducedmetal abundance, thereby shifting the mean spectral type still earlier.The fact that the 10-micron excess decreases linearly with metalabundance suggests that mass loss rates are roughly the same for starsin all three galaxies, with the dust-to-gas ratio proportional to metalabundance.
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| Сазвежђа: | Прамац |
| Ректацензија: | 10h44m47.15s |
| Deклинација: | -59°24'48.2" |
| Apparent магнитуда: | 8.603 |
| Даљина: | 671.141 parsecs |
| Proper motion RA: | -7.7 |
| Proper motion Dec: | 1.9 |
| B-T magnitude: | 11.363 |
| V-T magnitude: | 8.831 |
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INHABITED SKY
