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Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
For a complete 12 μm flux-limited sample of 207 IRAS sources(F12>=150 Jy, |b|>=5deg), the majority ofwhich are AGB stars (~87%), we have extracted light curves in seveninfrared bands between 1.25 and 60 μm using the database of theDiffuse Infrared Background Experiment (DIRBE) instrument on the CosmicBackground Explorer (COBE) satellite. Using previous infrared surveys,we filtered these light curves to remove data points affected by nearbycompanions and obtained time-averaged flux densities and infraredcolors, as well as estimates of their variability at each wavelength. Inthe time-averaged DIRBE color-color plots, we find clear segregation ofsemiregulars, Mira variables, carbon stars, OH/IR stars, and red giantswithout circumstellar dust (i.e., V-[12]<5) and with little or novisual variation (ΔV<0.1 mag). The DIRBE 1.25-25 μm colorsbecome progressively redder and the variability in the DIRBE databaseincreases along the oxygen-rich sequence nondusty slightly varying redgiants-->SRb/Lb-->SRa-->Mira-->OH/IR and the carbon-richSRb/Lb-->Mira sequence. This supports previous assertions that theseare evolutionary sequences involving the continued production andejection of dust. The carbon stars are redder than their oxygen-richcounterparts for the same variability type, except in theF12/F25 ratio, where they are bluer. Of the 28sources in the sample not previous noted to be variable, 18 are clearlyvariable in the DIRBE data, with amplitudes of variation of ~0.9 mag at4.9 μm and ~0.6 mag at 12 μm, consistent with them being verydusty Mira-like variables. We also present individual DIRBE light curvesof a few selected stars. The DIRBE light curves of the semiregularvariable L2 Pup are particularly remarkable. The maxima at1.25, 2.2, and 3.5 μm occur 10-20 days before those at 4.9 and 12μm, and, at 4.9 and 12 μm, another maximum is seen between the twonear-infrared maxima.
| 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.
| 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.
| Hipparcos Versus GCVS Amplitudes of Non-Mira M-Type Giants
A recent paper by Dumm and Schild deals with the determination of radiiand masses for Hipparcos stars with non-Mira giant M-type spectra. Theirlist contains 350 stars, of which 205 are either verified or suspectedvariables, including 53 SR (semiregular) and 51 Lb (irregular)variables. The authors determined that the masses and radii of thenon-variable stars show a clear correlation, whereas thevariable starsdeviate from this relation roughly according to their amplitudes. Incomparing the Hipparcos amplitudes with the amplitudes in the GCVS andNSV I found numerous conspicuous discordances, ranging well over a wholemagnitude. I therefore hoped that the older amplitudes, based in generalupon data more specifically obtained for period determination, mightimprove the scatter in the Dumm and Schold diagram, but this is not thecase. In the course of the investigation, numerous stars wereencountered that merit further observations. Two were found of especialinterest: V370 And, discovered by Hipparcos, and () Dra,with a reputed period of 1100 days.
| Distance Determination of Mass-Losing Stars
Based on the Principal Component Analysis on IRAS colors and the radiodata, the distances to 183 mass-losing red giant stars were determinedusing the radial velocity and Oort's galactic rotation model for azero-point calibration in the distance modulus. Also, based on therequirement of higher accuracy of the distance determination, themass-losing red giant stars were divided into two groups by means of thefirst-principal component representing an intrinsic photometric propertyof the expanding shell; then, the distances were estimated to be log{d(kpc)}=0.458 p_2+0.09+/-0.13 for group 1 and log {d(kpc)}=0.325p_2+0.45+/-0.15 for group 2, where p_2 is the principal componentcorresponding to the distance, as obtained from the IRAS flux, which wasassumed to be inversely proportional to the square of the distance.Thus,these two groups differ from each other not only by theirphotometric properties, but also by their average distances, by a factorof about 2. Systematic differences exist between the two groups in theirpopulation characteristics and in their evolutionary stages.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Stellar radii of M giants
We determine the stellar radii of the M giant stars in the Hipparcoscatalogue that have a parallax measured to better than 20% accuracy.This is done with the help of a relation between a visual surfacebrightness parameter and the Cousins (V - I) colour index, which wecalibrate with M giants with published angular diameters.The radii of(non-Mira) M giants increase from a median value of 50 R_Sun at spectraltype M0 III to 170 R_Sun at M7/8 III. Typical intermediate giant radiiare 65 R_Sun for M1/M2, 90 R_Sun for M3, 100 R_Sun for M4, 120 R_Sun forM5 and 150 R_Sun for M6. There is a large intrinsic spread for a givenspectral type. This variance in stellar radius increases with latertypes but in relative terms, it remains constant.We determineluminosities and, from evolutionary tracks, stellar masses for oursample stars. The M giants in the solar neighbourhood have masses in therange 0.8-4 M_Sun. For a given spectral type, there is a close relationbetween stellar radius and stellar mass. We also find a linear relationbetween the mass and radius of non-variable M giants. With increasingamplitude of variability we have larger stellar radii for a given mass.
| 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 Renewed Search for Water Maser Emission from Mira Variables.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1602L&db_key=AST
| Aluminum Oxide and the Opacity of Oxygen-rich Circumstellar Dust in the 12--17 Micron Range
Amorphous alumina (Al2O3) was produced by a sol-gel technique in orderto make available its optical constants for possible astrophysicalapplications. Gradual annealing showed that the X-ray amorphousness ofalumina ended somewhere between 723 and 873 K. Above this transitionpoint, the structure changes into disordered gamma -Al2O3. At T >1273 K, crystalline alpha -Al2O3 (corundum) is formed. Mie calculationsshow that amorphous alumina exhibits a wide Al-O vibrational band,peaking at 11.5--11.8 mu m and having a steep "blue" and an extended"red" wing. It may be an important contributor to the continuous opacitybetween the silicate bands in oxygen-rich circumstellar envelopes,whereas it is ruled out for the explanation of the 13 mu m band. Anaverage 13 mu m band profile was derived from 51 IRAS low-resolutionspectra of bright Mira stars and semiregular variables. Its shape, whichis satisfactorily represented by a Lorentz profile, can be reproduced byMie calculations with the data of alpha -Al2O3, but not with those ofgamma -Al2O3. The calculations show that the 13 mu m band profile ofalpha -Al2O3 is sensitive to grain shape. If alpha -Al2O3 is theabsorber, a second band should be present at 21 mu m. A closecorrelation was found between the strengths of the 13 mu m band and the10 mu m silicate band. It suggests that the 13 mu m band carrier couldalso be somehow connected with silicate dust. Experimental argumentssupporting this attribution are presented.
| 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
| High Mass Agb-Stars in the South Galactic CAP
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.267..711W&db_key=AST
| CO and HCN observations of circumstellar envelopes. A catalogue - Mass loss rates and distributions
We have searched the literature for all observations of the (C-12)O(1-0), (C-12)O (2-1), and HCN (1-0) lines in circumstellar envelopes oflate type stars published between January 1985 and September 1992. Wereport data for 1361 observations (stellar velocity, expansion velocity,peak intensity, integrated area, noise level). This CO-HCN sample nowcontains 444 sources; 184 are identified as O-rich, 205 as C-rich, andthere are 9 S stars. About 85 percent of the sources are AGB stars.There are 32 planetary nebulae and about thirty post-AGB starscandidates. Besides results of mm-observations, we also listidentifications, coordinates, IRAS data, and chemical and spectral typesfor every source. For AGB stars, we have estimated (or compiled)bolometric fluxes and distances for 349 sources, and mass loss ratesdeduced from CO results for 324 sources, taking into account theinfluence of the CO photodissociation radius. We also list mass lossrates derived from detailed models of CO emission in the literature.
| 1612 MHz OH survey of IRAS point sources. I - Observations made at Dwingeloo, Effelsberg and Parkes
The data from a large sky survey are presented including a northernpilot study and a detailed southern study in which detections are biasedtoward the most evolved sources and distant sources. Both areinvestigated at the 1612-MHz transition of OH to take advantage of thestrongest line for AGB stars with optically thick dust shells. The IRASsources are chosen by considering their IR colors related to fluxes at12, 25, and 60 microns. Observations are reported for 2703 IRAS pointsources at the 1612-MHz transition, and 738 OH/IR stars are detected.The survey identifies 597 of the sources as previously unidentified, and95 percent of the OH profiles observed have twin-peak masercharacteristics which are related to emission from expandingcircumstellar shells. The other 5 percent of the sources are concludedto be transition objects between OH/IR stars and planetary nebulae.
| Galactic bulge M giants. IV - 0.5-2.5 micron spectrophotometry and abundances for stars in Baade's Window
Spectrophotometric observations of bulge and local M giants from 0.45 to2.5 microns at a resolution of about 1000 are presented. From ananalysis of strong atomic lines of Na I and Ca I in the K band, a meanmetallicity of the M giants in Baade's Window is derived. It isdemonstrated that J-K is a good temperature indicator for both the fieldand bulge nonvariable M giants, and that the relationship between thetwo quantities is the same for both types of stars. In addition, thereis no difference in the surface gravity between bulge and field giantsof the same J-K color (i.e., temperature). A major difference in theoverall spectral energy distributions of bulge and local M giants isthat the classical H-band bump attributed to the opacity minimum of theH(-) ion near 1.6 microns is considerably reduced in many of the bulgestars.
| A survey for infrared excesses among high galactic latitude SAO stars
This project involves extending the previous analysis of infraredexcesses among a volume-limited sample of 134 nearby A-K main-sequencestars to a magnitude-limited sample of stars, culled from the SAOCatalog, with excesses determined from the IRAS Point Source Catalogflux density ratios. This new sample includes 5706 B-M type stars, 379of which have infrared excesses. The objective involved use of astatistically complete survey of objects in a standard catalog in orderto assess the frequency with which different physical processes canaffect the infrared output of stars. These processes include, but arenot limited to, orbiting cold particle clouds and the onset of rapidmass loss. It is concluded that cold disks are consistent with theinfrared excesses found among A-G dwarfs and G-K giants in the sample.
| Detection of 51 new 86 GHz SiO, V = 1, J = 2-1 masers associated with IRAS point sources
This paper reports the results of a search for southern stellar SiO, v =1, J = 2-1 masers in a survey of IRAS point sources. Out of the 116observed southern sources, 51 identified as new SiO, v = 1, J = 2-1masers, on the basis of their position in IRAS color-color plot. Ofthese, 42 masers have stellar identifications in IPSC, two arepreviously known non-IRAS IR objects, and six have no identification inIPSC.
| Galactic bulge M giants. III - Near-infrared spectra and implications for the stellar content of E and S0 galaxies
Spectra at 0.6-0.9 micron of 320 K and M giants in six low-absorptionfields along the minor axis of the galactic bulge and of an additional60 late-type giants and dwarfs in the solar neighborhood were obtained.Indices of the strength of molecular absorption are combined withprevious infrared and optical photometry to estimate the mean metalabundance of the bulge M giants and to constrain the relativecontribution of late giants and dwarfs to the integrated light of E andS0 galaxies.
| An OH survey of Mira-like objects from the IRAS point source catalog
An OH survey was performed of IRAS sources that present IR colorssimilar to Mira stars and for which an LRS observation was available. Atotal of 143 objects were observed in the 1612 and 1667 MHz lines: OHmasers were found in 36 objects. The aim of this work is to characterizea large number of evolved circumstellar envelopes from microwavespectra, and to explore the evolution of Asymptotic Giant Branchobjects. Special attention is given to the comparison of the objectsfound in the present study with the known Miras. The kinematics of theenvelopes that show peculiar OH spectra is discussed.
| A comparison between CO-, OH-, and IR-mass-loss rates of evolved stars
Mass rates of AGB stars with oxygen-rich circumstsellar shells arecompared with AGB stars with carbon-rich shells, using three methods toderive mass loss rates: interpretation of (thermal) CO(1 - 0), CO(2 - 1)line profiles; interpretation of OH(1612 MHz) maser line profiles; andIR model fits. Mass loss rates found from these methods are comparedwith each other in terms of the tau(s) value, which is the ratio betweenthe total momentum in the wind and the total momentum represented by thestellar luminosity. It is found that, for oxygen-rich shells, the valueof tau(s) exceeds unity for a large number of sources, while forcarbon-rich shells this happens only for a small number of sources. Itis proposed that, in oxygen-rich shells, the 9.7 micron silicate featureis responsible for high values of tau(s).
| Water maser emission from southern IRAS sources
A search for water maser emission in 112 bright, southern IRAS sourceswas conducted. Water maser emission was detected in 27 cases. Thesesources include M-type stars and previously unidentified IRAS objects.The detection rate is discussed with reference to IRAS low-resolutionspectral (LRS) class and the (60-25) micron color index. Water maseremission was detected in three sources which have LRS class 4n,indicating the presence of 11-micron SiC emission. The O/C-richness ofthe circumstellar envelopes of these sources is discussed, and it isconcluded that these sources are probably M-type stars whose LRS classis misassigned.
| The transition from oxygen-rich to carbon stars
Evolutionary tracks for the transition from oxygen-rich to carbon-richstars are calculated, using the model of Willems and de Jong (1988). Itis found that model spectra produce excellent fits to the observedenergy distributions of carbon stars. The mass-loss rate and the timesince shell detachment can be determined for each individual object bycomparing observed data with the models.
| Dust grains and gas in the circumstellar envelopes around luminous red giant stars
Far-infrared color-color diagrams have been constructed for over 100 ofthe brightest evolved stars in the IRAS Point Source Catalog. Thediagrams are used to deduce average values of the dust grain emissivityindex (p) between 12 and 100 microns. Grains in C-rich and O-richenvironments have similar values of p between 12 and 25 microns andbetween 60 and 100 microns, but between 25 and 60 microns p is larger byapproximately 0.4 for the O-rich stars. Dust grains in envelopes aroundS-type stars seem to have 25 to 60 micron emissivities more nearly likegrains in O-rich rather than C-rich environments. CO and HCN emissionsfrom various stars are used to reclassify several stars as oxygen orcarbon rich.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| Hyades and Sirius supercluster members brighter than magnitude (V) 7.1. II - Right ascension six to twelve hours
The present star sample is contained in the Bright Star Catalogue andits Supplement, augmented with a further supplement of 788 stars foundduring various observing programs over the past 40 years. Accurate,four-color and H-beta, or (RI), photometry is available for most of thesupercluster members. The criteria for membership are the comparisons ofthe proper motion, radial velocity, and luminosity obtained from thesupercluster parameters with the observed motions and the luminosityderived from the photometric parameters. New proper motions, based onall available catalogs, have been derived for the additional 788 starsdiscussed here, as well as all supercluster members.
| Infrared studies of southern AFGL sources. I - Limited ground-based survey
The authors have searched for the infrared emission from twenty-threeselected areas (4arcmin×4arcmin) around the unidentified southernAFGL sources. Sources with a significant signal-to-noise ratio have beenfound in almost all the selected areas; the total number of sourcesdetected is 42. JHKLM photometry has been carried out for the seventeensources detected at the highest confidence level. The analysis of theinfrared energy distribution of the reddest objects found in theauthors' survey, suggests the association of ten ground-based sourceswith the relative AFGL sources reported in the catalog of Price andWalker (1976). A brief discussion about the nature of these objects isreported.
| New Bright Southern Variable Stars
Not Available
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| קבוצת-כוכבים: | קנטאור |
| התרוממות ימנית: | 11h48m39.22s |
| סירוב: | -35°59'12.9" |
| גודל גלוי: | 7.055 |
| מרחק: | 200.401 פארסק |
| תנועה נכונה: | -10.6 |
| תנועה נכונה: | -7.6 |
| B-T magnitude: | 8.686 |
| V-T magnitude: | 7.19 |
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