Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
An ISO/SWS study of the dust composition around S stars. A novel view of S-star dust
Aims: We investigate the composition of the solid-state materials in thewinds around S-type AGB stars. The S stars produce dust in their windthat bears a resemblance to the dust produced in some O-rich AGB stars.However, the reported resemblance is mostly based on IRAS/LRS spectrawith limited spectral resolution, sensitivity, and wavelength coverage.Methods: We investigate the dust composition around S stars usingISO/SWS data that surpass the previous studies in terms of spectralresolution and wavelength coverage. We selected the dust producing Sstars in the ISO/SWS archive with enough signal to perform a detaileddust analysis, and then compare the dust spectra from the 9 sources withthe O-rich AGB spectra and a subset of M super-giants. We constructedaverage dust emission spectra of the different categories. Results: We report the discovery of several previously unreported dustemission features in the S star spectra. The long wavelength spectra ofW Aql and π1 Gru exhibit the “30” μmfeature attributed to MgS. Two sources exhibit a series of emissionbands between 20 and 40 μm that we tentatively ascribe to Diopside.We show that the 10-20 μm spectra of the S stars are significantlydifferent from the O-rich AGB stars. The O-rich stars exhibit astructured emission feature that is believed to arise from amorphoussilicate and aluminium-oxide. The S stars lack the substructure found inthe O-rich stars. Instead they show a smooth peak with a varyingpeak-position from source to source. We suggest that this feature iscaused by a family of related materials, whose exact compositiondetermines the peak position. The observed trend mimics the laboratorytrend of non-stoichiometric silicates. In this scenario the degree ofnon-stoichiometry is related to the Mg to SiO4 ratio, in other words, tothe amount of free O available during the dust grain growth.based on observations obtained with ISO, an ESA project with instrumentsfunded by ESA Member states (especially the PI countries: France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA.
| Infrared photometry and evolution of mass-losing AGB stars. II. Luminosity and colors of MS and S stars
Context: Asymptotic giant branch (AGB) phases mark the end of theevolution for low- and intermediate-mass stars. Our understanding of themechanisms through which they eject the envelope and our assessment oftheir contribution to the mass return to the interstellar medium and tothe chemical evolution of Galaxies are hampered by poor knowledge oftheir luminosities and mass loss rates, both for C-rich and for O-richsources. Aims: We plan to establish criteria permitting a morequantitative determination of luminosities (and subsequently of massloss rates) for the various types of AGB stars on the basis of infraredfluxes. In this paper, in particular, we concentrate on O-rich ands-element-rich MS, S stars and include a small sample of SC stars. Methods: We reanalyze the absolute bolometric magnitudes and colors ofMS, S, SC stars on the basis of a sample of intrinsic (single) andextrinsic (binary) long period variables. We derive bolometriccorrections as a function of near- and mid-infrared colors, adopting asreferences a group of stars for which the spectral energy distributioncould be reconstructed in detail over a large wavelength range. Wedetermine the absolute HR diagrams, and compare luminosities and colorsof S-type giants with those, previously derived, of C-rich AGB stars.Luminosity estimates are also verified on the basis of existingperiod-luminosity relations valid for O-rich Miras. Results: S starbolometric luminosities are almost indistinguishable from those ofC-rich AGB stars. On the contrary, their circumstellar envelopes arethinner and less opaque. Despite this last property the IR wavelengthsremain dominant, with the bluest stars having their maximum emission inthe H or K(short) bands. Near-to-mid infrared color differences are inany case smaller than for C stars. Based on period-luminosity relationsfor O-rich Miras and on Magnitude-color relations for the same variableswe show how approximate distances (hence intrinsic parameters) forsources of so far unknown parallax can be inferred. We argue that mostof the sources have a rather small mass (<2 Mȯ);dredge-up might then be not effective enough to let the C/O ratio exceedunity.Tables [see full textsee full textsee full textsee full textsee fulltextsee full text]-[see full textsee full textsee full textsee fulltextsee full textsee full text] are only available in electronic form athttp://www.aanda.org Tables 11 and 12 are 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/488/675
| 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
| Near-infrared observations of candidate extrinsic S stars
Photometric observations in the near infrared for 161 S stars, including18 Tc-rich (intrinsic) stars, 19 Tc-deficient (extrinsic) ones and 124candidates for Tc-deficient S stars, are presented in this paper. Basedon some further investigations into the infrared properties of bothTc-rich and Tc-deficient S stars, 104 candidates are identified as verylikely Tc-deficient S stars. The large number of infrared-selectedTc-deficient S stars provides a convenient way to study the physicalproperties and the evolutionary status of this species of S 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.
| On the Variability of S Stars as Observed by the Hipparcos
The Hipparcos photometry of S type stars shows that they are allvariable. The intrinsic S stars show a larger range of amplitudes thando the extrinsic S stars.
| 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
| 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.
| 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
| On the Infrared Properties of S-Stars with and Without Technetium
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..180G&db_key=AST
| Companions to bright S and MS stars - Technetium deficiency and binarity
To test the popular hypothesis that technetium-deficient stars ofspectral types S and MS are mass-transfer binaries, we have searched forultraviolet light from the putative hot secondaries in spectra takenwith the SWP spectrograph of IUE. Although most S and MS stars areapparently thermally pulsing AGB (asymptotic giant branch) stars whosesurfaces have been enriched with s-process elements and carbon dredgedup from the interior, those stars whose spectra show enhanced s-processelements but no Tc are widely believed to be cooler analogs of the Ba IIstars, which apparently owe their unusual abundances to prior masstransfer, the Tc from which has decayed away. We report IUE observationsof 15 S and MS stars with the SWP, including the identification of sixhot companions. Assembling all the IUE observations made to date, wefind clear support for the mass-transfer hypothesis, confirming evidencefrom other lines of research. We further discuss the ages of thecompanions and the implications of these discoveries for stellarevolution.
| Occultations of stars by solar system objects. IX - Occultations of catalog stars by steroids, planets, and major satellites in 1992 and 1993
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1992AJ....103.2079W&db_key=AST
| Additional late-type stars with technetium
The results of a survey of 279 late-type giants and supergiants for thespectral lines of the radioactive element technetium (Tc I) at 4297,4262, and 4238 A are presented. The following conclusions are reached:(1) the presence of Tc correlates very strongly with the existence oflight variability; (2) evolutionary MS stars show Tc and spectroscopicMS stars do not show Tc; (3) single S stars show Tc; (4) SC stars showTc; (5) about 75 percent of the C stars show Tc; and (6) Ba II stars donot show Tc. The findings are compatible with predictions from stellarevolution theory.
| A General Catalogue of Galactic S-Stars - ED.2
Not Available
| A general catalogue of S stars.
Not Available
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Yay |
| Sað Açýklýk: | 18h09m17.18s |
| Yükselim: | -36°57'57.6" |
| Görünürdeki Parlaklýk: | 8.2 |
| Uzaklýk: | 4347.826 parsek |
| özdevim Sað Açýklýk: | 3.7 |
| özdevim Yükselim: | -4.7 |
| B-T magnitude: | 10.416 |
| V-T magnitude: | 8.383 |
Kataloglar ve belirtme:
|
INHABITED SKY
