Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
BIMA CO Observation of EP Aquarii: The Semiregular Pulsating Star with a Double-Component Line Profile
This paper reports the results of a Berkeley-Illinois-MarylandAssociation array interferometric observation of EP Aqr, a semiregularpulsating star with a double-component line profile in the CO J=1-0line. The broad component shows a flat-topped profile, and the narrowcomponent shows a spiky strong peak. Although previous single-dishobservations suggested that the CO J=2-1 line exhibits a Gaussian-likeprofile, the CO J=1-0 line does not. The spatial distributions of boththe narrow and the broad components appear to be roughly round with thesame peak positions. No significant velocity gradient is seen. Thespatial-kinetic properties of the molecular envelope of EP Aqr arereminiscent of a multiple-shell structure model rather than of a bipolarflow and disk model. A problem with this interpretation is that noevidence of interaction between the narrow- and broad-component regionsis seen. A Gaussian-like feature seen in the CO J=2-1 line might play akey role in understanding the spatiokinetic properties of the molecularenvelope of EP Aqr.
| High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument . Dusty environment spatially resolved
We present the results of N-band spectro-interferometric observations ofthe silicate carbon star IRAS08002-3803 with the MID-infraredInterferometric instrument (MIDI) at the Very Large TelescopeInterferometer (VLTI) of the European Southern Observatory (ESO). Theobservations were carried out using two unit telescopes (UT2 and UT3)with projected baseline lengths ranging from 39 to 47 m. Ourobservations of IRAS08002-3803 have spatially resolved the dustyenvironment of a silicate carbon star for the first time and revealed anunexpected wavelength dependence of the angular size in the N band: theuniform-disk diameter is found to be constant and 36 mas (72Rstar) between 8 and 10 μm, while it steeply increaseslongward of 10 μm to reach 53 mas (106 Rstar) at 13μm. Model calculations with our Monte Carlo radiative transfer codeshow that neither spherical shell models nor axisymmetric disk modelsconsisting of silicate grains alone can simultaneously explain theobserved wavelength dependence of the visibility and the spectral energydistribution (SED). We propose that the circumstellar environment ofIRAS08002-3803 may consist of two grain species coexisting in the disk:silicate and a second grain species, for which we consider amorphouscarbon, large silicate grains, and metallic iron grains. Comparison ofthe observed visibilities and SED with our models shows that such diskmodels can fairly - though not entirely satisfactorily - reproduce theobserved SED and N-band visibilities. Our MIDI observations and theradiative transfer calculations lend support to the picture whereoxygen-rich material around IRAS08002-3803 is stored in a circumbinarydisk surrounding the carbon-rich primary star and its putativelow-luminosity companion.
| BIMA Array Observations of the Highly Unusual SiO Maser Source with a Bipolar Nebulosity IRAS 19312+1950
We report the results of mapping observations of the bipolar nebula withSiO maser emission, IRAS 19312+1950, in the CO (J=1-0 and 2-1),13CO (J=1-0 and 2-1), C18O (J=1-0), CS (J=2-1), SO(JK=32-21), and HCO+ (J=3-2)lines with the Berkeley-Illinois-Maryland Association array. Theevolutional status of this source has been evoking a controversy sinceits discovery, although SiO maser sources are usually identified aslate-type stars with active mass loss. In line profiles, two kinematicalcomponents are found, as reported in previous single-dish observations:a broad pedestal component and a narrow component. Spatiokineticproperties of a broad-component region traced by 12CO linesare roughly explained by a simple spherical outflow model with anexpanding velocity typical of an AGB star, although some properties ofthe broad-component region still conflict with properties of a typicalAGB spherical outflow. A narrow-component region apparently exhibits abipolar flow. The angular size of the narrow-component region isspatially larger than that of the broad-component region. The intensitydistribution of the CS emission avoids the central region of the source,and that of the SO broad-component emission exhibits a small featurepeaked exactly at the mapping center. According to the present results,if the broad component really originates in a spherical outflow, anoxygen-rich evolved stellar object seems to be a natural interpretationfor the central star of IRAS 19312+1950.
| Integrated spectral analysis of 18 concentrated star clusters in the Small Magellanic Cloud
We present in this study flux-calibrated integrated spectra in the range(3600-6800) Å for 18 concentrated SMC clusters. Cluster reddeningvalues were estimated by interpolation between the extinction maps ofBurstein & Heiles (1982, AJ, 87, 1165) and Schlegel et al. (1998,ApJ, 500, 525). The cluster parameters were derived from the templatematching procedure by comparing the line strengths and continuumdistribution of the cluster spectra with those of template clusterspectra with known parameters and from the equivalent width (EW) method.In this case, new calibrations were used together with diagnosticdiagrams involving the sum of EWs of selected spectral lines. A verygood agreement between ages derived from both methods was found. Thefinal cluster ages obtained from the weighted average of values takenfrom the literature and the present measured ones range from 15 Mr (e.g.L 51) to 7 Gyr (K 3). Metal abundances have been derived for only 5clusters from the present sample, while metallicity values directlyaveraged from published values for other 4 clusters have been adopted.Combining the present cluster sample with 19 additional SMC clusterswhose ages and metal abundances were put onto a homogeneous scale, weanalyse the age and metallicity distributions in order to explore theSMC star formation history and its spatial extent. By considering thedistances of the clusters from the SMC centre instead of theirprojections onto the right ascension and declination axes, the presentage-position relation suggests that the SMC inner disk could have beenrelated to a cluster formation episode which reached the peak ~2.5 Gyrago. Evidence for an age gradient in the inner SMC disk is alsopresented.
| Forty Years of Spectroscopic Stellar Astrophysics in Japan
The development of Japanese spectroscopic stellar astrophysics in therecent 40 years is reviewed from an observational point of view. In thisarticle, the research activities are provisionally divided into fourfields: hot stars, hot emission-line (Be) stars, cool stars, and otherstars. Historical developments of the observational facilities atOkayama Astrophysical Observatory (spectrographs and detectors) are alsosummarized in connection with the progress in scientific researchactivities.
| Disklike Structure in the Semiregular Pulsating Star X Herculis
This paper reports the results of a Berkeley-Illinois-Maryland (BIMA)array interferometric observation of a semiregular pulsating star withan unusual narrow molecular line profile, X Her, in the CO J=1-0 line.In the CO spectrum, a double-component profile (including narrow andbroad components) is seen, as reported by previous observations. Thenarrow component consists of two spiky peaks. The spatial structure ofthe board component shows bipolar shape, and that of the narrowcomponent shows an elliptical/spherical shape. The two peaks in thenarrow component show a systematic difference in the integratedintensity map. The kinematical and geometrical properties of the narrowcomponent are reminiscent of a Keplerian rotating disk with a centralmass of 0.9 Msolar, although an interpretation as anexpansion disk seems to be more natural. A secondary bipolar flowinstead of the disk also cannot be fully excluded as an interpretationof the narrow line.
| High-Resolution Mid-Infrared Imaging of the Asymptotic Giant Branch Star RV Bootis with the Steward Observatory Adaptive Optics System
We present high-resolution (~0.1"), very high Strehl ratio (0.97+/-0.03)mid-IR adaptive optics (AO) images of the asymptotic giant branch (AGB)star RV Boo utilizing the MMT adaptive secondary AO system. RV Boo wasobserved at a number of wavelengths over two epochs (9.8 μm in 2003May and 8.8, 9.8, and 11.7 μm in 2004 February) and appeared slightlyextended at all wavelengths. While the extension is very slight at 8.8and 11.7 μm, the extension is somewhat more pronounced at 9.8 μm.With such high Strehl ratios, we can achieve superresolutions of 0.1" bydeconvolving RV Boo with a point-spread function (PSF) derived from anunresolved star. We tentatively resolve RV Boo into a 0.16" FWHMextension at a position angle of 120°. At a distance of390+250-100 pc, this corresponds to a FWHM of60+40-15 AU. We measure a total flux at 9.8 μmof 145+/-24 Jy for the disk and star. Based on a dust thermal emissionmodel for the observed IR spectral energy distribution and the 9.8 μmAO image, we derive a disk dust mass of 1.6×10-6Msolar and an inclination of 30°-45° from edge-on. Wediscuss whether the dust disk observed around RV Boo is an example ofthe early stages in the formation of asymmetric structure in planetarynebulae.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| On the Flux of Extrasolar Dust in Earth's Atmosphere
Micron-size extrasolar dust particles have been convincingly detected bysatellites. Larger extrasolar meteoroids (5-35 μm) have most likelybeen detected by ground-based radar at Arecibo and New Zealand. Wepresent estimates of the minimum detectable particle sizes and thecollecting areas for both radar systems. We show that particles largerthan ~10 μm can propagate for tens of parsecs through theinterstellar medium, opening up the possibility that ground-based radarsystems can detect AGB stars, young stellar objects such as T Tauristars, and debris disks around Vega-like stars. We provide analyticaland numerical estimates of the ejection velocity in the case of a debrisdisk interacting with a Jupiter-mass planet. We give rough estimates ofthe flux of large micrometeoroids from all three classes of sources.Current radar systems are unlikely to detect significant numbers ofmeteors from debris disks such as β Pictoris. However, we suggestimprovements to radar systems that should allow for the detection ofmultiple examples of all three classes.
| IRAS 08544-4431: A new post-AGB star in a binary system surrounded by a dusty disc
We present an analysis of our extensive data-set on IRAS 08544-4431. Itis the first object we discuss of our newly defined sample of stars,selected for their position in the ``RV Tauri'' box in the IRAS[12]-[25], [25]-[60] two-color diagram. Moreover, our selection criteriaincluded an observed excess in the L-band, indicative of a dusty disc.The SED of IRAS 08544-4431 shows a broad IR excess starting already atH. Our optical photometric data reveal some evidence for deep andshallow minima in the light curve and a pulsation time-scale of around100 days with a small amplitude (Delta V peak-to-peak = 0.17 mag). OurCORALIE radial velocity measurements show that IRAS 08544-4431 is abinary system with a period of 499 +/- 3 days and a mass function of0.02 Msun. Moreover, IRAS 08544-4431 is detected in both theCO (2-1) and (1-0) mm-wave emission lines. The triangular shape of theweak CO profile confirms that part of the circumstellar material is notfreely expanding but resides probably in a dusty circumbinary disc. Ourchemical abundance analysis of a high resolution spectrum of high S/Nreveals that a depletion process has modified the photosphericabundances to a moderate extent ([Zn/Fe]=+0.4). All these findingsconfirm that the F-type IRAS 08544-4431 is another good example of abinary Post-AGB star surrounded by a dusty disc. The Hα , P-Cygniprofile shows ongoing mass-loss with a very high outflow velocity, theorigin of which is not understood. The strength and velocity of theHα -absorption are modulated with the orbital motion; the maximaof both quantities ( ~ 400 \kms, 5 Å, respectively) occur atsuperior conjunction.Based on observations collected at the European Southern Observatory inChile (62.L-0508) and at SAAO. The radial velocity data was obtainedwith the Swiss 1.2 m Euler telescope at La Silla, Chile.
| Reprocessing the Hipparcos data of evolved stars. III. Revised Hipparcos period-luminosity relationship for galactic long-period variable stars
We analyze the K band luminosities of a sample of galactic long-periodvariables using parallaxes measured by the Hipparcos mission. Theparallaxes are in most cases re-computed from the Hipparcos IntermediateAstrometric Data using improved astrometric fits and chromaticitycorrections. The K band magnitudes are taken from the literature andfrom measurements by COBE, and are corrected for interstellar andcircumstellar extinction. The sample contains stars of several spectraltypes: M, S and C, and of several variability classes: Mira, semiregularSRa, and SRb. We find that the distribution of stars in theperiod-luminosity plane is independent of circumstellar chemistry, butthat the different variability types have different P-L distributions.Both the Mira variables and the SRb variables have reasonablywell-defined period-luminosity relationships, but with very differentslopes. The SRa variables are distributed between the two classes,suggesting that they are a mixture of Miras and SRb, rather than aseparate class of stars. New period-luminosity relationships are derivedbased on our revised Hipparcos parallaxes. The Miras show a similarperiod-luminosity relationship to that found for Large Magellanic CloudMiras by Feast et al. (\cite{Feast-1989:a}). The maximum absolute Kmagnitude of the sample is about -8.2 for both Miras and semi-regularstars, only slightly fainter than the expected AGB limit. We show thatthe stars with the longest periods (P>400 d) have high mass lossrates and are almost all Mira variables.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA \cite{Hipparcos}).Table \ref{Tab:data1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/993
| 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
| A New Look at the Evolution of Wolf-Rayet Central Stars of Planetary Nebulae
On the basis of recent observational evidence and new theoreticalresults, we construct a speculative scenario for the evolution ofWolf-Rayet central stars of planetary nebulae. Although single-starevolutionary calculations have succeeded recently in reproducing thecomposition of these objects, it is clear from the latest infraredobservations that a new perspective has to be adopted; the simultaneouspresence of carbon- and oxygen-rich dust (double-dust chemistry), whilebeing a rare phenomenon for H-rich central stars, is found around thevast majority of cool Wolf-Rayet central stars. This correlation betweenWolf-Rayet characteristics and double-dust chemistry points to a commonmechanism. Within the binary evolution framework established by Soker,two scenarios are proposed, responsible for the majority (80%-85%) andminority (15%-20%) of Wolf-Rayet central stars. In the first scenario,proposed here for the first time, a low-mass main-sequence star, browndwarf, or planet spirals into the asymptotic giant branch star, inducingextra mixing, hence a chemistry change, and terminating the asymptoticgiant branch evolution. In the second scenario, previously proposed, aclose binary companion is responsible for the formation of a disk aroundeither the binary or the companion. This long-lived disk harbors theO-rich dust. Both models are speculative, although they are supported byseveral observations and recent theoretical results.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is 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/386/492, and from theauthors on CD-Rom.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| 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
| Large Circumbinary Dust Grains around Evolved Giants?
We have detected continuum emission at 450 μm, 850 μm, and 1.35 mmfrom SS Lep (or 17 Lep), 3 Pup, and probably BM Gem, respectively, whichare likely or confirmed binary systems consisting of at least oneevolved giant. The observed submillimeter fluxes are probably emitted bygrains rather than ionized gas. The fluxes are larger than thoseexpected from a ``normal'' dusty wind; the dust temperature is <=70 Kwithin 6" of the stars. To explain why grains are so cold near the star,we suggest that the emission at λ>=450 μm is produced byparticles as large as 0.1 mm in radius and that these large particlesprobably have grown by coagulation in circumbinary orbiting disks withmasses >=5×1028 g.
| Binary (Post) AGB evolution
In this contribution the observational characteristics of F to G typepost-AGB stars, showing both O-rich and C-rich circumstellar chemistry,are reviewed. It turns out that binarity and the presence of a stablecircumbinary dusty disc are fundamental properties of these objects. Thepossible common origin of the mixed chemistry observed in these systemsand in IR-bright [WC] stars is discussed.
| General Catalog of Galactic Carbon Stars by C. B. Stephenson. Third Edition
The catalog is an updated and revised version of Stephenson's Catalogueof Galactic Cool Carbon Stars (2nd edition). It includes 6891 entries.For each star the following information is given: equatorial (2000.0)and galactic coordinates, blue, visual and infrared magnitudes, spectralclassification, references, designations in the most significantcatalogs and coordinate precision classes. The main catalog issupplemented by remarks containing information for which there was noplace in entries of the main part, as well as some occasional notesabout the peculiarities of specific stars.
| IRAS 12311-3509: a carbon star with SiC2 emission
The optical spectrum of the carbon star IRAS 12311-3509 is dominated bythe Merrill-Sanford emission bands of SiC2, by absorption andemission in the Swan system of C2, and by resonance emissionlines of neutral metals. The infrared energy distribution is flat from 1to 60μm. These observations are interpreted as arising from a starwith a cool dusty disc which is edge-on to the observer and obscuresdirect starlight. The infrared continuum is caused predominantly byabsorption of stellar light by dust in the disc and re-emission atlonger wavelengths. The optical stellar spectrum is seen by reflectionoff dusty material which lies out of the plane of the disc, and themolecular and atomic emission arises in the same geometry throughresonance fluorescence. The object has similarities to the J-silicatestars, but may have a carbon-rich rather than oxygen-rich disc. A fullspectroscopic assignment and discussion of the SiC2 bands andtheir intensities are given. Modelling of the rotational contours of the000 band yields a rotational temperature of 250K,indicating very cool gas.
| The origin of silicate carbon stars: ISO/SWS observation of V778 Cygni
The origin of silicate carbon stars has been a mystery ever since theirdiscovery. We discuss here a full grating spectrum between 2.4 and 45 mum of the silicate carbon star V778 Cyg obtained bythe ISO/SWS. The spectrum, taken about 14 years after the IRAS LRSobservation, confirms the complex nature of the object. The spectrum isclearly divided into a short wavelength (lambda < 6.5 mu m),carbon-rich part and long-wavelength, oxygen-rich part. No obviouschange of the 10 and 18 mu m silicate features is observed between IRASand ISO spectra, indicating that the silicate dust is in a steadystructure. The 2.7 mu m H2O band and the 15 mu mCO2 bands are tentatively detected. The near-infrared part ofthe spectrum indicates that the present-day mass-loss rate is very low.The silicate features can only be fitted by optically thin dust emissionfrom sub-micron size grains. The total oxygen-rich dust mass seen atinfrared wavelengths is 2-10x 10-6 Msun, of which3-50x 10-8 Msun is warm (300-600 K). If the dustis heated by radiation from the central star, the dust should be locatedas close as about 12 stellar radii from the star. We suggest that thedust responsible for the emission features is in a steady outflow fromthe system. We show that the dust cannot be located in a circum-binarydisk, but is stored in a disk around the companion star during theprevious O-rich mass-loss phase. The duration of silicate emission isestimated as ~ 104 yr. It is compatible with the fact thatnot all J-type carbon stars show silicate emission. The evolution of thecentral star and formation of the disk in AGB binary systems largelydepends on the orbital separation. V778 Cyg and other``IRAS discovered'' silicate carbon stars probably have wide orbits. Insuch a case, a disk is formed around the companion. Close-binary systemssuch as the Red Rectangle form massive equatorialO-rich disks, and the evolution of the central star is largelyinfluenced by the binarity. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, the Netherlands and the United Kingdom) withthe participation of ISAS and NASA. The SWS is a joint project of SRONand MPE.
| A systematic investigation of the mass loss mechanism in dust forming long-period variable stars
In order to investigate the relations between the mass loss frompulsating red giants and quantities which can be obtained fromobservations, we have explored the behavior of theoretical models whichtreat the time-dependent hydrodynamics of circumstellar outflows,including a detailed treatment of the dust formation process. Thisapproach, while ignoring effects such as a possible non-sphericity ofthe stellar atmospheres which are difficult to assess, accountscorrectly for factors such as the grain formation and destruction whichare crucial to the mass-loss mechanism. We built a grid of ~ 150 modelscovering a wide range of physical situations. This grid allows us tocharacterize the effects of different parameters, such as the stellarluminosity and temperature, the period and the amplitude of thepulsation, and the C/O element abundance ratio, on the behavior of AGBwinds and on the rates of mass loss. We find two regimes for the stellaroutflows. The first one (A) is characterized by stable winds with alayered structure of the circumstellar dust shell, outflow velocities inexcess of 5 km s-1, and a large rate of mass loss. Theseoutflows are dominated by radiation pressure on dust. For these modelswe find good correlations between near-infrared colors and the mass lossrates. In the second regime (B), the winds are slow and do not present alayered structure. The outflows displaying the second behavior come,e.g., from red giants with low luminosity, high temperature, or shortperiod. For them there is no correlation between color and mass lossrate. The mass loss rates are low and never exceed 3 10-7Msunyr-1. Radiation pressure on dust plays only aminor role in this regime. We have explored the effect of differentparameters on the behavior of the stellar winds. We find that, ingeneral, all other parameters been kept identical, there is a narrowrange of values for each parameter within which the models abruptlychange from B to A, and that once a model is stabilized in the A modethe changes in the values of each parameter have only a smooth effect onthe wind characteristics. Table~2 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| Quantitative Analysis of Carbon Isotope Ratios in N-, SC-, and J-type Carbon Stars
Not Available
| The Chemical Composition of Carbon Stars. II. The J-Type Stars
Abundances of lithium, heavy elements, and carbon isotope ratios havebeen measured in 12 J-type Galactic carbon stars. The abundance analysisshows that in these stars the abundances of s-process elements withrespect to the metallicity are nearly normal. Tc is not present in mostof them, although upper limits have been derived for WZ Cas and WX Cyg,perhaps two SC-type rather than J-type carbon stars. The Rb abundances,obtained from the resonance λ7800 Rb I line, are surprisinglylow, probably owing to strong non-LTE effects in the formation of thisline in cool carbon-rich stars. Lithium and 13C are found tobe enhanced in all the stars. These results together with the nitrogenabundances and oxygen isotope ratios measured by Lambert et al. andHarris et al. are used to discuss the origin of J stars. The luminosityand variability class of the stars studied would indicate that they arelow-mass (M<~2-3 Msolar), less evolved objects than thenormal carbon stars, although the presence of some luminous(Mbol<-5.5) J stars in our Galaxy (WZ Cas may be anexample) and in other galaxies, suggests the existence of at least twotypes of J stars, with different formation scenarios depending upon theinitial mass of the parent star. Standard evolutionary AGB models aredifficult to reconcile with all the observed chemical characteristics.In fact, they suggest the existence of an extra mixing mechanism thattransports material from the convective envelope down to hotter regionswhere some nuclear burning occurs. This mechanism would act preferablyon the early-AGB phase in low-mass stars. Mixing at the He-core flashand the binary system hypothesis are also discussed as alternatives tothe above scenario.
| Atomic Carbon in the Envelopes of Carbon-rich Post-Asymptotic Giant Branch Stars
Atomic carbon has been detected in the envelopes of three carbon-richevolved stars: HD 44179 (=AFGL 915, the ``Red Rectangle''), HD 56126,and, tentatively, the carbon star V Hya. This brings to seven the numberof evolved star envelopes in which C I has been detected. Upper limitswere found for several other stars, including R CrB. C I was notdetected in several oxygen-rich post-asymptotic giant branch (AGB) stars(OH 231.8+4.2, for example), although it is detected in theircarbon-rich analogs. Two trends are evident in the data. First,circumstellar envelopes with detectable C I are overwhelminglycarbon-rich, suggesting that much of the C I is produced by thedissociation of molecules other than CO. Second, the more evolved theenvelope away from the AGB, the higher the C I/CO ratio. The oxygen-richsupergiant star α Ori remains the only oxygen-rich star with awind containing detectable C I. These data suggest an evolutionarysequence for the C I/CO ratio in cool circumstellar envelopes. Thisratio is small (a few percent) while the star is on the AGB, and the C Iis located in the outer envelope and produced by photodissociation. Theratio increases to about 0.5 as the star evolves away from the AGBbecause of the dissociation of CO and other carbon-bearing molecules byshocks caused by the fast winds which appear at the end of evolution onthe AGB. Finally, the ratio becomes >>1 as the central starbecomes hot enough to photodissociate CO.
| The circumstellar CO emission of RV Bootis. Evidence for a Keplerian disk?
We report on high-resolution CO J=1-0 and J=2-1 interferometricobservations of the oxygen-rich semiregular variable RV Boo supplementedby single-dish multi-transition data of CO(J=1-0, 2-1, 3-2, 4-3).Detections of the thermal SiO(v=0, J=2-1, 3-2) transitions as well asthe vibrationally excited SiO(v=1, J=2-1) line are also reported. Theinterferometric CO J=2-1 observations, with a spatial resolution ofabout 1farcs 7, reveal a disk-like structure of size 4farcs 2x 3farcs 3around RV Boo. Furthermore, the position-velocity information along aline through the center of the source at a position angle of about150degr can be interpreted as a sign of Keplerian rotation. Sixsymmetrically placed features, possibly corresponding to three rings,around a central feature are seen. These observations may therefore, toour knowledge, present the first indications of a rotating disk aroundan AGB star. However, it cannot be fully excluded that the observedkinematical structure is caused by a bipolar outflow. From thesingle-dish CO observations we estimate the molecular mass of the sourceto be 3x 10-5 Msun .
| The chemical composition of the rare J-type carbon stars.
Abundances of lithium, heavy elements and carbon isotope ratios havebeen derived in 12 J-type galactic carbon stars. The abundance analysisshows that in these stars the abundances of s-process elements withrespect to the metallicity are nearly solar. Tc is not present in mostof them. The Rb abundances, obtained from the resonance 7800 {\AA} RbIline, are surprisingly low, probably due to stroong non-LTE effects.Lithium and $^{13}$C are found to be enhanced in all the stars. Theseresults are used to discuss the origin of J-stars.
| Orbiting Molecular Reservoirs around Evolved Red Giant Stars
We report molecular emission from the circumstellar envelopes of twocarbon-rich stars with oxygen-rich envelopes, EU And and BM Gem. We finda narrow (FWHM~5 km s^-1) CO (2-1) emission line from EU And and an evennarrower (FWHM ~ 1 km s^-1) ^13CO emission line from BM Gem. We alsoplace upper limits to the emission of HCN, SiO, SO, HCO^+, and CS fromBM Gem. We argue that the narrow CO emission lines are signatures oflong-lived reservoirs of orbiting gas and that standard models for COemission from red giant winds are not appropriate for these two stars.By including the Red Rectangle and AC Her, narrow CO emissioncharacteristic of gravitationally bound gas has been detected from fourpost-main-sequence systems, and we can begin to characterize theseapparently similar environments. Some common characteristics are thefollowing: (1) Their diameters are typically between ~100 and ~1000 AU.(2) The masses of CO are near 10^27 g. (3) Unlike the envelopes aroundmass-losing carbon stars where M_CO/M_dust~ 2, the circumstellarorbiting reservoirs often appear to have M_CO
| Oxygen-rich semiregular and irregular variables. A catalogue of circumstellar CO observations
Using the SEST, the Onsala 20 m telescope, the JCMT, and the IRAM 30 mtelescope we have carried out a survey of circumstellar CO(J=1-0, 2-1,3-2, and 4-3) emission on a large sample of oxygen-rich semiregular (SRaand SRb) and irregular variables (Lb). A total of 109 stars wereobserved in at least one CO line: 66 were shown to have circumstellar COline emission (7 SRa, 36 SRb, and 23 Lb variables), ~ 60% of thesemiregulars and all but one of the irregulars were detected for thefirst time. Most stars were observed in at least two transitions. Thereis a total of 138 detected CO lines. For twelve stars stronginterference from interstellar CO emission precluded detection. Wepresent here a catalogue of all observational data and the spectra ofall detections, as well as brief discussions on detection statistics(including its dependence on variability type, period, IRAS-colour, IRASLRS-class, and M-subclass), line profiles (including line shapeasymmetry, multi-component line shapes, and line intensity ratios), gasexpansion velocity distributions, and correlations between CO line andIR continuum fluxes (including implications for the mass-lossmechanism). Based on observations collected using at the EuropeanSouthern Observatory, La Silla, Chile, the Onsala Space Observatory,Chalmers Tekniska Högskola, Sweden, the James Clerk MaxwellTelescope, Hawaii and the IRAM 30~m telescope, Pico Veleta, Spain.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Близнецы |
| Прямое восхождение: | 07h20m59.01s |
| Склонение: | +24°59'58.1" |
| Видимая звёздная величина: | 8.407 |
| Расстояние: | 546.448 парсек |
| Собственное движение RA: | -2.4 |
| Собственное движение Dec: | -5 |
| B-T magnitude: | 12 |
| V-T magnitude: | 8.704 |
Каталоги и обозначения:
|
