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AKARI's infrared view on nearby stars. Using AKARI infrared camera all-sky survey, 2MASS, and Hipparcos catalogs
Context. The AKARI, a Japanese infrared space mission, has performed anAll-Sky Survey in six infrared-bands from 9 to 180 ?m with higherspatial resolutions and better sensitivities than IRAS. Aims: Weinvestigate the mid-infrared (9 and 18 ?m) point source catalog (PSC)obtained with the infrared camera (IRC) onboard AKARI, in order tounderstand the infrared nature of the known objects and to identifypreviously unknown objects. Methods: Color-color diagramsand a color-magnitude diagram were plotted with the AKARI-IRC PSCand other available all-sky survey catalogs. We combined the Hipparcosastrometric catalog and the 2MASS all-sky survey catalog with theAKARI-IRC PSC. We furthermore searched literature and SIMBADastronomical database for object types, spectral types, and luminosityclasses. We identified the locations of representative stars and objectson the color-magnitude and color-color diagram schemes. Theproperties of unclassified sources can be inferred from their locationson these diagrams. Results: We found that the (B-V) vs.(V-S9W) color-color diagram is useful for identifying thestars with infrared excess emerged from circumstellar envelopes ordisks. Be stars with infrared excess are separated well from other typesof stars in this diagram. Whereas (J-L18W) vs. (S9W-L18W)diagram is a powerful tool for classifying several object types.Carbon-rich asymptotic giant branch (AGB) stars and OH/IR stars formdistinct sequences in this color-color diagram. Young stellarobjects (YSOs), pre-main sequence (PMS) stars, post-AGB stars, andplanetary nebulae (PNe) have the largest mid-infrared color excess andcan be identified in the infrared catalog. Finally, we plot the L18W vs.(S9W-L18W) color-magnitude diagram, using the AKARI data togetherwith Hipparcos parallaxes. This diagram can be used to identify low-massYSOs and AGB stars. We found that this diagram is comparable to the [24]vs. ([8.0]-[24]) diagram of Large Magellanic Cloud sources usingthe Spitzer Space Telescope data. Our understanding of Galactic objectswill be used to interpret color-magnitude diagram of stellar populationsin the nearby galaxies that Spitzer Space Telescope observed. Conclusions: Our study of the AKARI color-color andcolor-magnitude diagrams will be used to explore properties ofunknown objects in the future. In addition, our analysis highlights afuture key project to understand stellar evolution with a circumstellarenvelope, once the forthcoming astronometrical data with GAIA areavailable.Catalog (full Tables 3 and 4) are only available in electronic form atthe 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/514/A2
| Newly Identified Silicate Carbon Stars from IRAS Low-Resolution Spectra
The discovery of silicate carbon star poses a challenge to the theory ofstellar evolution in the late stage, hence it is important to look formore silicate carbon stars. To this end we have carried outcross-identifications between the new IRAS Low-Resolution Spectrum (LRS)database and the new carbon star catalog, CGCS3. We have found nine newsilicate carbon stars with silicate features around 10? m and/or 18?m. These newly identified stars are located in the Regions IIIa andVII in the IRAS two-color diagram, which means they indeed have typicalfar infrared colors of silicate carbon stars. The infrared properties ofeach of these sources are discussed.
| 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
| Carbon-rich giants in the HR diagram and their luminosity function
The luminosity function (LF) of nearly 300 Galactic carbon giants isderived. Adding BaII giants and various related objects, about 370objects are located in the RGB and AGB portions of the theoretical HRdiagram. As intermediate steps, (1) bolometric corrections arecalibrated against selected intrinsic color indices; (2) the diagram ofphotometric coefficients 1/2 vs. astrometric trueparallaxes varpi are interpreted in terms of ranges of photosphericradii for every photometric group; (3) coefficients CR andCL for bias-free evaluation of mean photospheric radii andmean luminosities are computed. The LF of Galactic carbon giantsexhibits two maxima corresponding to the HC-stars of the thick disk andto the CV-stars of the old thin disk respectively. It is discussed andcompared to those of carbon stars in the Magellanic Clouds and Galacticbulge. The HC-part is similar to the LF of the Galactic bulge,reinforcing the idea that the Bulge and the thick disk are part of thesame dynamical component. The CV-part looks similar to the LF of theLarge Magellanic Cloud (LMC), but the former is wider due to thesubstantial errors on HIPPARCOS parallaxes. The obtained meanluminosities increase with increasing radii and decreasing effectivetemperatures, along the HC-CV sequence of photometric groups, except forHC0, the earliest one. This trend illustrates the RGB- and AGB-tracks oflow- and intermediate-mass stars for a range in metallicities. From acomparison with theoretical tracks in the HR diagram, the initial massesMi range from about 0.8 to 4.0 Msun for carbongiants, with possibly larger masses for a few extreme objects. A largerange of metallicities is likely, from metal-poor HC-stars classified asCH stars on the grounds of their spectra (a spheroidal component), tonear-solar compositions of many CV-stars. Technetium-rich carbon giantsare brighter than the lower limit Mbol =~ -3.6+/- 0.4 andcentered at =~-4.7+0.6-0.9 at about =~(2935+/-200) K or CV3-CV4 in our classification. Much like the resultsof Van Eck et al. (\cite{vaneck98}) for S stars, this confirms theTDU-model of those TP-AGB stars. This is not the case of the HC-stars inthe thick disk, with >~ 3400 K and>~ -3.4. The faint HC1 and HC2-stars( =~ -1.1+0.7-1.0) arefound slightly brighter than the BaII giants ( =~-0.3+/-1.3) on average. Most RCB variables and HdC stars range fromMbol =~ -1 to -4 against -0.2 to -2.4 for those of the threepopulation II Cepheids in the sample. The former stars show the largestluminosities ( <~ -4 at the highest effectivetemperatures (6500-7500 K), close to the Mbol =~ -5 value forthe hot LMC RCB-stars (W Men and HV 5637). A full discussion of theresults is postponed to a companion paper on pulsation modes andpulsation masses of carbon-rich long period variables (LPVs; Paper IV,present issue). This research has made use of the Simbad databaseoperated at CDS, Strasbourg, France. Partially based on data from theESA HIPPARCOS astrometry satellite. Table 2 is 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/390/967
| 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.
| The effective temperatures of carbon-rich stars
We evaluate effective temperatures of 390 carbon-rich stars. Theinterstellar extinction on their lines of sights was determined andcircumstellar contributions derived. The intrinsic (dereddened) spectralenergy distributions (SEDs) are classified into 14 photometric groups(HCi, CVj and SCV with i=0,5 and j=1,7). The newscale of effective temperatures proposed here is calibrated on the 54angular diameters (measured on 52 stars) available at present from lunaroccultations and interferometry. The brightness distribution on stellardiscs and its influence on diameter evaluations are discussed. Theeffective temperatures directly deduced from those diameters correlatewith the classification into photometric groups, despite the large errorbars on diameters. The main parameter of our photometric classificationis thus effective temperature. Our photometric < k right >1/2 coefficients are shown to be angular diameters on arelative scale for a given photometric group, (more precisely for agiven effective temperature). The angular diameters are consistent withthe photometric data previously shown to be consistent with the trueparallaxes from HIPPARCOS observations (Knapik, et al. \cite{knapik98},Sect. 6). Provisional effective temperatures, as constrained by asuccessful comparison of dereddened SEDs from observations to modelatmosphere predictions, are in good agreement with the values directlycalculated from the observed angular diameters and with those deducedfrom five selected intrinsic color indices. These three approaches wereused to calibrate a reference angular diameter Phi 0 and theassociated coefficient CT_eff. The effective temperatureproposed for each star is the arithmetic mean of two estimates, one(``bolometric'') from a reference integrated flux F0, theother (``spectral'') from calibrated color indices which arerepresentative of SED shapes. Effective temperatures for about 390carbon stars are provided on this new homogeneous scale, together withvalues for some stars classified with oxygen-type SEDs with a total of438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given.Objects with strong infrared excesses and optically thick circumstellardust shells are discussed separately. The new effective temperaturescale is shown to be compatible and (statistically) consistent with thesample of direct values from the observed angular diameters. Theeffective temperatures are confirmed to be higher than the mean colortemperatures (from 140 to 440 K). They are in good agreement with thepublished estimates from the infrared flux method forTeff>= 3170 K, while an increasing discrepancy is observedtoward lower temperatures. As an illustration of the efficiency of thephotometric classification and effective temperature scale, the C/Oratios and the Merrill-Sanford (M-S) band intensities are investigated.It is shown that the maximum value, mean value and dispersion of C/Oincrease along the photometric CV-sequence, i.e. with decreasingeffective temperature. The M-S bands of SiC2 are shown tohave a transition from ``none'' to ``strong'' at Teff =~(2800+/- 150right ) K. Simultaneously, with decreasing effectivetemperature, the mean C/O ratio increases from 1.04 to 1.36, thetransition in SiC2 strength occurring while 1.07<= C/O<= 1.18. This research has made use of the Simbad database operatedat CDS, Strasbourg, France. Table 10 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)}or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/178
| 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: The Stars
Not Available
| Dust extinction and intrinsic SEDs of carbon-rich stars. III. The Miras, CS, and SC stars
The present work is an extension of a recent study by Knapik &Bergeat (\cite{knapik97}), and Bergeat et al. (\cite{berge98b})henceforth called Papers I and II, respectively. The spectral energydistributions (SEDs) of about 440 carbon-rich stars and the interstellarextinction observed on their line of sights were analysed. The methodsoriginally developed for Semi-Regular (SR) and Irregular (L) variables(Paper I: our groups CV1 to CV6) were then extended (Paper II) to thehot carbon (HC) stars (our groups HC0 to HC5) and related objects (RCB,BaII and HdC stars). Shortly, this is a kind of a pair method making usesimultaneously of the whole SED from UV to IR. Our approach is appliedhere to the galactic cool carbon-rich variables which were notconsidered in Paper I, namely the carbon Miras and very cool non-Miras,and the CS and SC variables. The carbon Miras with infrared silicateemission are also studied. The photometric CV1 to CV6 classificationscheme of paper I is implemented, and we add here a later CV7-group anda specific SCV-group which corresponds to spectroscopic SC stars. Acontinuous S-SC-CS-C sequence is clearly supported by our results. Thecarbon stars with IR silicate emission included in our study do havecarbon-rich SEDs of the three consecutive groups HC5, CV1 and CV2. Theystand among the relatively hot carbon variables, in the 3600-3000 Krange in effective temperature. The carbon Miras are satisfactorilydescribed in this enlarged scheme. No specific extension is requiredsince non-Miras are also found in the CV7 and SCV-groups. The derivedgroup is however frequently phase-dependent in these large amplitudevariables. Additional selective extinction of circumstellar (CS) originis observed in variable amounts. The mean extinction law for theinterstellar diffuse medium as tabulated by Mathis (\cite{mathis}) isshown to be relevant. It applies to both interstellar and circumstellarextinction with a possible CS neutral extinction in addition which wouldremain undetected here. The corresponding colour excess E(B-V) is largerat minimum light or intermediate phases than what it is at maximum light(where it can amount to zero). It is associated to large IR excessesattributed to the emission from CS dust. Long-term variations onthousands of days may be interpreted in terms of varying CS dust opacityon the line of sight. The dust influence is discussed. It is shown thatscattering, if substantial on the line of sight in the observing lobe,has to be essentially wavelength-independent, i.e. due to large neutralscatterers, especially in high opacity objects like IRC +10216. Finally,with the HC0 to HC5 classification of HC stars (Paper II), we obtain afourteen groups sequence (HC0 to HC5 and then CV1 to CV7 from theearlier one to the latest one, and SCV for SC stars apart). The numberof studied stars amounts now to about 600 that is about 40 stars pergroup on the average when the oxygen-type SEDs are subtracted. Theeffective temperature calibration of this classification scheme iscurrently in preparation. This research has made use of the Simbaddatabase operated at CDS, Strasbourg, France.}\fnmsep\thanks{Partiallybased on data from the ESA HIPPARCOS astrometrysatellite}\fnmsep\thanks{Table~5 is only available in electronic form atthe CDS via anonymous ftp 130.79.128.5
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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 search for SiO, OH, CO and HCN radio emission from silicate-carbon stars
We report upper limits for radio emission of SiO at 86 and 43 GHz, of OHat 1612 and 1665/1667 MHz, of CO at 115 GHz and HCN at 88.6 GHz in thesilicate-carbon stars. These upper limits of SiO imply that oxygen-richmaterial has not been detected within 2Rstar of a centralstar even though the detected emission from silicate dust grains, H2Oand OH maser establishes the presence of oxygen-rich material from abouttens to thousands of AU of a central star. The upper limit of the SiOabundance is consistent with that found in oxygen-rich envelopes. Upperlimits of the mass loss rate (based on the CO data) are estimated to bebetween 10-6 to 10-7 solar mass/yr assuming adistance of 1.5 kpc for these stars. The absence of HCN microwaveemission implies that no carbon-rich material can be detected at largedistances (thousands of AU) from a central star. The lack of detectionsof SiO, CO, and HCN emission is most likely due to the large distancesof these stars. A number of C stars were detected in CO and HCN, butonly the M supergiant VX Sgr was detected in CO.
| Carbon stars with 10 micron silicate features
Twenty-three carbon stars with IRAS LRS 2n, 3n, and 6n are presented, ofwhich seven samples have been identified to have 10 microns silicatefeatures. It is determined that on the IRAS color-color diagram most ofthe samples are located in the M star region or in the overlappingregion of S-type stars and carbon stars. Thus the circumstellar shellsof the stars are either oxygen rich or are undergoing the stage oftransition from the oxygen rich to the carbon rich.
| Contribution to the interpretation of carbon stars associated with oxygen-rich circumstellar envelopes
Astrometric, spectroscopic, and photometric data on the five knownsouthern carbon stars associated with an oxygen-rich circumstellarenvelope are presented. CS2123 is shown to be incorrectly identifiedwith IRAS13442-6109. CS1633 is shown to have been incorrectly classifiedas a carbon-rich star (in fact, spectral type M7111). The 1-60-micronenergy distributions of the three remaining objects (CS1003, MC79-11,FJF270) are clearly bimodal. The observed energy distributions might bereproduced by the model of a detached oxygen-rich shell surrounding acarbon star, but with rather extreme parameters implying, for thecentral star, a short transition time from the oxygen-rich stage to thecarbon-rich stage (less than 100 years). On another hand, the data arenot in conflict with the binary star model for these three sources.
| SiO and CO emission from carbon stars with silicate features and southern IRAS sources
Forty-one southern IRAS sources have been observed in the CO J = 1-0 andSiO J = 2-1, v = 1 lines with the 15-m Swedish European SubmillimeterTelescope, and CO or SiO emission has been detected in 20 sources. Among41 sources, southern carbon stars with silicate features were observedbut no CO or SiO emission was detected except in IRAS 13442-6109 forwhich the identification with the carbon star C2123 is questionable.Nondetection of SiO masers in carbon stars with silicate features favorsthe transition-phase hypothesis for the origin of these stars. Some SiOemission has been detected in stars with IRAS LRS class 4n, confirmingthat silicate absorption can mimic SiC emission in the coldest 4nsources. The detection rate and chemistry of circumstellar envelopes arediscussed.
| Carbon stars with silicate dust shells. I - Carbon stars with enhanced C-13 (J stars)
New optical observations show that three southern carbon stars withsilicate dust shells are J stars, in addition to two already known fromthe Northern Hemisphere. Four more J stars have similar red IRAS colorsalthough infrared spectra are lacking. A review of published datasuggests that all the carbon stars with silicate shells may be J stars.These dust shells are all very red and must be optically thick, yet thecarbon stars are not conspicuously reddened at optical wavelengths. Theinfrared sources are not very variable, although the probability is highthat a companion of such red color would be a variable of largeamplitude. It is suggested that material expelled from the carbon star,starting while it still had an oxygen-rich envelope, has accumulated ina disk around a hypothetical companion. The properties of J stars withsilicate dust shells are consistent with this suggestion, while theunusual feature of the infrared sources are accounted for.
| Red giants with unusual dust shells. I - The database
A number of red giants are classified as type M (oxygen-rich) but aredefined in the IRAS LRS Catalog as having SiC emission (a characteristicof carbon-rich environments). It is shown that the NIR spectra arecharacteristic of oxygen-rich stars, but that at least some appear tohave C/O abundance ratios close to unity (in other words they should beclassified as S stars). It is suggested that, when C/O approaches unity,dust condensation theories assuming chemical and thermodynamicequilibrium may not be realistic. It is postulated that a number ofcarbon stars which have been found to have silicate dust features mayalso have C/O abundance ratios close to unity.
| 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.
| A general catalogue of cool carbon stars
Not Available
| 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.
| Rotation curves for spiral galaxies in clusters. II - Variations as a function of cluster position
Inner and outer velocity gradients, residuals from synthetic rotationcurves for field spirals, and M/L gradients are used to study therotation curves of spiral galaxies. A good correlation is found betweenthe outer gradient of the rotation curve and the galaxy's distance fromthe cluster center, with a similar effect noted in the residuals betweenthe observed and synthetic rotation curves. A correlation is also shownto exist between the M/L gradient across a galaxy and the galaxy'sposition in the cluster. The results suggest that the inner clusterenvironment may strip away some fraction of the mass in the outer haloof a spiral galaxy or may not allow the halo to form.
| Masers associated with two carbon stars - V778 Cygni and EU Andromedae
The authors present several observations of the 22.2 GHz H2Omaser line from two C stars, V778 Cyg and EU And, and the 1665/67 MHz OHmaser lines from V778 Cyg. For both sources the intensity of theH2O line has varied by more than a factor of 5 over severalmonths. The authors interpret the systems as being binaries, each withan M star component with a thick shell and a C star component.
| Water masers from carbon stars with silicate features
The authors have searched for water maser emission at 22.235 GHz in fivesouthern carbon stars which exhibit 10 and 20 micron silicate featuresin their IRAS low resolution spectra. Two stars, MC79-11 and C2123, havebeen found to show water maser emission. These detections, together withthe detection of water masers in two northern stars firmly establish thepresence of oxygen-rich circumstellar envelopes around some carbonstars. The high detection rate of 22 GHz water emission in the carbonstars with silicate features (four out of nine) supports the hypothesisthat these objects are in a transition phase of evolution betweenoxygen-rich and carbon-rich circumstellar envelopes.
| On the contribution of interstellar extinction to the 10 micron dust feature in OH/IR stars
The IRAS Low Resolution Spectra of 467 sources with the 10 micron dustfeature are analyzed. The strengths of the dust feature are determinedby the ratio of the flux at 9.7 micron to the fitted continuum level.Color temperatures are derived from the fluxes of the four IRASphotometric bands after correcting for the effect of the 10 micronfeature on the fluxes of the 12 micron band. A definite correlationbetween the strength of the feature and the color temperature of thecontinuum is found, implying that the 10 micron dust feature is largelycircumstellar in origin. A reexamination of the strength of the silicatefeature for seven of the OH/IR star used by Gehrs and colleagues in 1985has failed to reproduce the optical depth-distance relationship found bythese authors. It is concluded that interstellar extinction does notplay a major role in the formation of the 10 micron absorption feature.
| Carbon stars with oxygen-rich circumstellar dust shells Observational evidence for the onset of the carbon star phase
Results from the IRAS Low Resolution Spectrograph (LRS) are presentedwhich show that some carbon stars are surrounded by circumstellar shellscontaining oxygen-rich silicate-type dust rather than carbon-rich dust.This observation suggests that these stars have quite recently becomecarbon stars because they are still surrounded by the last remnant ofthe oxygen-rich M-type phase. It also suggests a direct transition fromM-type to C-type rather than through an intermediate S phase. Thetransition takes place in about 100 years. Using a simple statisticalargument, the typical duration of the carbon star phase is estimated tobe from 1000 to 10,000 years.
| 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.
| Photometry and Radial Velocities of Southern Carbon Stars
Not Available
| A general catalogue of cool carbon stars
Not Available
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