내용
사진
사진 업로드
DSS Images Other Images
관련 글
Analysis of ISO SWS01 spectra of S stars
The Infrared Space Observatory (ISO) Short-Wavelength Spectrometer(SWS01) plays an important role in studying properties of S stars. Wereduce and analyze the SWS01 spectra of 17 S stars, and identify thecandidate carriers of molecular absorption features. The ISO SpectralAnalysis Package (ISAP) developed by the LWS and SWS Instrument Teamsand Data Centers is used to process and analyze the SWS01 spectra of 17S stars. The ISO archives of 17 S stars are obtained from the ISOdatabase. Of 17 S stars, two stars are extrinsic S stars, the others areintrinsic S stars. The 15 intrinsic S stars can be divided into threegroups (6 stars for Group I, 7 stars for Group II, and 2 stars for GroupIII) according to their Infrared Astronomical Satellite (IRAS)low-resolution spectra (LRS) and dust mass-loss rate dot{M}_dust, wheredot{M}_dust increases from Group I to II and III gradually. 17 S starsshow the following properties: 1. two extrinsic S stars and 15 intrinsicS stars among different groups have different infrared properties; 2.two extrinsic S stars and 6 intrinsic S stars in Group I have similarISO SWS01 spectra and their continua can be approximately described by asingle blackbody representing the stellar photosphere, while someintrinsic S stars in Group I have 60 μm infrared excess; 3. forintrinsic S stars in Groups I, II, and III, their continua peak shiftstoward longer wavelength from Groups I to II to III; 4. S stars inGroups II and III show obvious dust emission features in which the 10μm dust features seem to display two different shapes. Moreover, twoS stars (IRAS 00192-2020 & IRAS 15492+4837) present the 13 μmfeature; 5. molecules H{2}O, CO, and CO{2} greatly affect the ISO SWS01spectra of S stars. It is noted that the absorption features ofmolecules CS and HCN usually thought to exist only in C stars may appearin the S stars.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries: France, Germany, TheNetherlands, and the United Kingdom) with the participation of ISAS andNASA.
| Two Micron All Sky Survey, Infrared Astronomical Satellite, and Midcourse Space Experiment Color Properties of Intrinsic and Extrinsic S Stars
We attempt to select new candidate intrinsic and extrinsic S stars inthe General Catalogue of Galactic S Stars (GCGSS) by combining data fromthe Two Micron All Sky Survey, the Infrared Astronomical Satellite, andthe Midcourse Space Experiment. Catalog entries are cross-identified,yielding 528 objects, out of which 29 are known extrinsic S stars and 31are known intrinsic S stars. Their color-color diagrams,(H-[12])-(K-[12]) and (K-[12])-(J-[25]), are drawn and used to identifya new sample of 147 extrinsic and 256 intrinsic S star candidates, whilethe nature of 65 stars remains identified. We infer that about 38%+/-10%of the GCGSS objects are of extrinsic type. Moreover, we think thatcolors such as J-[25] can be used to split off the two categories of Sstars, while single colors are not appropriate. The color-colordiagrams, such as (H-[12])-(K-[12]) and (K-[12])-(J-[25]), are proven tobe powerful tools for distinguishing the two kinds of S stars.
| 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
| Infrared investigation from earth and space on the evolutionary state of a sample of LPV
We selected a sample of highly reddened AGB stars among the sourcesobserved with the SWS instrument on the ISO satellite. These SWS dataallow us to compute the source's photometry in the mid-IR filters of thecamera TIRCAM at the TIRGO telescope. Our photometric data, supplementedwith other measurements taken from the literature, permit to select thecarbon-rich sources in the sample. For these stars, a linear relationholds between dust mass loss and the color index [8.8]-[12.5]. One maythen, from photometric data alone, evaluate the total mass loss (forwhich we used the estimate of \citet{loup}, based on radio data). Theoxygen-rich sources, on the other hand, are distributed in two branches,of which the upper one appears superimposed with carbon stars; the starsin this group have both high luminosity and high wind velocity andtherefore higher masses. Finally S stars lie between the carbon-starbranch and the low-mass oxygen-rich stars, in agreement with theirintermediate evolutionary status.
| The Henize sample of S stars. IV. New symbiotic stars
The properties of the few symbiotic stars detected among the 66 binary Sstars from the Henize sample are discussed. Two stars (Hen 18 and Hen121) exhibit both a strong blue-violet continuum and strongHalpha emission (FWHM of 70 km s-1), whereas Hen134 and 137 exhibit weak Halpha emission. TheHalpha profiles are typical of non-dusty symbiotic starsbelonging to class S-3 as defined by Van Winckel et al. (1993, A&AS102, 401). In that class as in the Henize symbiotic S stars, He I, [NII] or [S II] emission lines are absent, suggesting that the nebulardensity is high but the excitation rather low. The radial velocity ofthe centre of the Halpha emission is identical to that of thecompanion star (at least for Hen 121 where this can be checked from theavailable orbital elements), thus suggesting that the Halphaemission originates in gas moving with the companion star. For Hen 121,this is further confirmed by the disappearance of the ultraviolet Balmercontinuum when the companion is eclipsed by the S star. Hen 121 is thusthe second eclipsing binary star discovered among extrinsic S stars (thefirst one is HD 35155). A comparison of the available data on orbitalperiods and Halpha emission leads to the conclusion thatHalpha emission in s stars seems to be restricted to binarysystems with periods in the range 600-1000 d, in agreement with thesituation prevailing for red symbiotic stars (excluding symbioticnovae). Symbiotic S stars are found among the most evolved extrinsic Sstars. Based on observations carried out at the European SouthernObservatory (ESO, La Silla, Chile; program 60.E-0805) and at the Swiss70 cm telescope (La Silla, Chile).
| 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.
| The Henize sample of S stars. II. Data
This paper presents data collected on the Henize sample of 205 S stars:(i) CORAVEL radial-velocity data; (ii) photometric data in the UBV bandsof the Geneva photometric system; (iii) photometric data in the JHKLbands of the SAAO photometric system; (iv) IRAS fluxes; (v)low-resolution spectra of 158 S stars. Close visual companions have beenfound for Hen 47, 94, 105 and 155. Spectroscopic orbital elements areprovided for Hen 2, 108, 121, 137 and 147. The analysis of these data ispresented in a companion paper. Based on observations carried out at theEuropean Southern Observatory (ESO, La Silla, Chile), at the 70~cm Swisstelescope at ESO and at the South African Astronomical Observatory.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| CO observations and mass loss of MS- and S-stars
We present (12) CO J = 1-0 and 2-1 observations of 14 S-stars, andreport 6 new detections. Two stars were observed in the (13) CO J = 1-0and 2-1 lines, and one tentative 2-1 detection is reported. Acompilation is presented of all CO observations of S-stars. The stars inthis sample are separated into ``intrinsic'' and ``extrinsic'' S-stars,based on direct observation of the Technetium line, or infraredproperties. The dust mass loss rate per unit distance is derived fromIRAS 60 mu m data taking into the fact that for small mass loss ratesthe observed flux is an overestimate of the excess emission due to dust.The gas mass loss rate per unit distance is derived from CO data.Distances and luminosities are estimated, partly from hipparcos parallaxdata. The largest mass loss rate derived is that for W Aql with(0.8-2.0) x 10(-5) {Msun} yr(-1) , and the lowest is that foro Ori with <1.2 x 10(-9) {Msun} yr(-1) . The S-starswithout Tc have smaller mass loss rates, than those with Tc. Diagramsshowing mass loss rate, dust-to-gas ratio and expansion velocity versuspulsation period are presented, and compared to similar data for carbon-and oxygen-rich Miras. The S-Miras stand not out in any way from the C-or O-Miras in these diagrams. In the diagram with expansion velocityversus pulsation period, the S-SRs span the same range in velocity asthe S-Miras, but they have periods which are about a factor of 2.5shorter. This was previously noted for O-rich SRs. As in that case, themost straightforward explanantion is that the SRs among the S-starspulsate in a higher order pulsation mode. Based on data from the ESAhipparcos astrometry satellite.
| The HIPPARCOS Hertzsprung-Russell diagram of S stars: probing nucleosynthesis and dredge-up
HIPPARCOS trigonometrical parallaxes make it possible to compare thelocation of Tc-rich and Tc-poor S stars in the Hertzsprung-Russell (HR)diagram: Tc-rich S stars are found to be cooler and intrinsicallybrighter than Tc-poor S stars. The comparison with the Genevaevolutionary tracks reveals that the line marking the onset of thermalpulses on the asymptotic giant branch (AGB) matches well the observedlimit between Tc-poor and Tc-rich S stars. Tc-rich S stars are, asexpected, identified with thermally-pulsing AGB stars of low andintermediate masses, whereas Tc-poor S stars comprise mostly low-massstars (with the exception of 57 Peg) located either on the red giantbranch or on the early AGB. Like barium stars, Tc-poor S stars are knownto belong exclusively to binary systems, and their location in the HRdiagram is consistent with the average mass of 1.6+/-0.2 Msb ȯderived from their orbital mass-function distribution (Jorissen et al.1997, A&A, submitted). A comparison with the S stars identified inthe Magellanic Clouds and in the Fornax dwarf elliptical galaxy revealsthat they have luminosities similar to the galactic Tc-rich S stars.However, most of the surveys of S stars in the external systems did notreach the lower luminosities at which galactic Tc-poor S stars arefound. The deep Westerlund survey of carbon stars in the SMC uncovered afamily of faint carbon stars that may be the analogues of thelow-luminosity, galactic Tc-poor S stars. Based on data from theHIPPARCOS astrometry satellite
| 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 catalogue of associations between IRAS sources and S stars.
Cross identifications between the General Catalogue of Galactic S Stars(GCGSS), the IRAS Point Source Catalogue (PSC), and the Guide StarCatalogue (GSC) are presented. The purpose of the present catalogue isi) to provide a clean sample of S stars with far-IR data, and ii) toprovide accurate GSC positions for S stars, superseding those listed inthe GCGSS. The IRAS colour-colour diagram and the galactic distributionof S stars associated with an IRAS source are presented. Several S starshaving extended images in at least one IRAS band have also beenidentified.
| Circumstellar CO emission in S stars. I. Mass-loss with little or no dust.
47 S stars have been searched for circumstellar CO (J=1-0 and/or 2-1)emission, and 29 have been detected, including 4 which show no evidenceof dust in their IRAS LRS spectra, and one with possibly no Tc (andtherefore not an AGB star). Six stars show anomalous features in theirprofiles, showing the presence of more than one kinematic component inthe expanding outflow. Two stars may have detached-shell envelopes. Theexpansion velocity distribution for S stars envelopes is different thanthat for C-rich stars, with the former having a slightly lower meanexpansion velocity, and a significantly higher fraction of objects withvery low expansion velocities (<~5.5km/s). In most S stars, themass-loss rates are >2x10^-7^Msun_/yr and the gas-to-dustratios are >1000. Our detection of CO in S stars with little or nodetectable dust implies substantial mass-loss in these objects. Theexpansion velocities and mass-loss rates of the relatively dust-freestars show a much steeper dependence on the the far-infrared excess({DELTA}IR_e_), as compared to the more dusty stars. This suggests thatwhen the amount of dust becomes small, mass-loss may be partially drivenby a different mechanism than radiation pressure on grains, whichprobably dominates in the dusty envelopes.
| Circumstellar Properties of S Stars. I. Dust Features
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...416..769C&db_key=AST
| S stars: infrared colors, technetium, and binarity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..463J&db_key=AST
| Emission features in IRAS low-resolution spectra of MS, S and SC stars
A progression of emission features due to dust grains in the 8-22-micronregion of IRAS low-resolution spectra has been detected which parallelstheir increasing C:O ratio and s-process enhancement. Strong S starstypically have a 9-14-micron emission feature which peaks around 10.8microns, while mild S or MS stars reveal a variety of features such as athree-component feature and a 10-micron silicate emission. The infraredexcesses in the 8-22-micron region are found to correlate with theperiod of Mira S, MS, and SC variables and to increase sharply for Miravariables with periods of between 380 and 400 days.
| 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.
| A General Catalogue of Galactic S-Stars - ED.2
Not Available
| A general catalogue of S stars.
Not Available
| New Bright Southern Variable Stars
Not Available
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
