Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
BAV-Results of Observations
This 67th compilation contains the results of visual and photographicobservations of BAV-members mostly from the years 2009 and 2010. Here wepublish altogether 468 minima and maxima of 152 eclipsing binaries andpulsating stars. The data were acquired by 13 observers.
| Mapping the 12CO J = 1-0 and J = 2-1 emission in AGB and early post-AGB circumstellar envelopes. I. The COSAS program, first sample
We present COSAS (CO Survey of late AGB Stars), a project to map andanalyze the 12CO J = 1-0 and J = 2-1 line emission in arepresentative sample of circumstellar envelopes around AGB and post-AGBstars. The survey was undertaken with the aim of investigating small-and large-scale morphological and kinematical properties of themolecular environment surrounding stars in the late AGB and earlypost-AGB phases. For this, COSAS combines the high sensitivity andspatial resolving power of the IRAM Plateau de Bure interferometer withthe better capability of the IRAM 30 m telescope to map extendedemission. The global sample encompasses 45 stars selected to span arange in chemical type, variability type, evolutionary state, andinitial mass. COSAS provides means to quantify variations in themass-loss rates, assess morphological and kinematical features, and toinvestigate the appearance of fast aspherical winds in the earlypost-AGB phase. This paper, which is the first of a series of COSASpapers, presents the results from the analyses of a first sample of 16selected sources. The envelopes around late AGB stars are found to bemostly spherical, often mingled with features such as concentric arcs (RCas and TX Cam), a broken spiral density pattern (TX Cam), molecularpatches testifying to aspherical mass-loss (WX Psc, IK Tau, V Cyg, and SCep), and also with well-defined axisymmetric morphologies andkinematical patterns (X Her and RX Boo). The sources span a wide rangeof angular sizes, from relatively compact (CRL 2362, OH 104.9+2.4 andCRL 2477) to very large (? Cyg and TX Cam) envelopes, sometimespartially obscured by self-absorption features, which particularly forIK Tau and ? Cyg testifies to the emergence of aspherical winds inthe innermost circumstellar regions. Strong axial structures with moreor less complex morphologies are detected in four early post-AGB stars(IRAS 20028+3910, IRAS 23321+6545, IRAS 19475+3119 and IRAS 21282+5050)of the sub-sample.Based on observations carried out with the IRAM Plateau de BureInterferometer and 30 m radio-telescope. IRAM is supported by INSU/CNRS(France), MPG (Germany) and IGN (Spain).Table 2 is only available inelectronic form at http://www.aanda.org
| 3.6 Years of DIRBE Near-infrared Stellar Light Curves
The weekly averaged near-infrared fluxes for 2652 stars were extractedfrom the cold and warm era all-sky maps of the Diffuse InfraredBackground Experiment (DIRBE). Since the DIRBE program only archived theindividual Calibrated Infrared Observations for the 10 month cold eramission, the weekly averaged fluxes were all that were available for thewarm era. The steps required to extract stellar fluxes are described asare the adjustments that were necessary to correct the results forseveral systematic effects. The observations are at a cadence of once aweek for 3.6 years (~1300 days), providing continuous sampling onvariable stars that span the entire period for the longest fundamentalpulsators. The stars are divided into three categories: those with largeamplitude of variability, smaller amplitude variables, and sources whosenear-infrared brightness do not vary according to our classificationcriteria. We show examples of the results and the value of the addedbaseline in determining the phase lag between the visible and infrared.
| 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
| Extinct 93Zr in Single Presolar SiC Grains from Low Mass Asymptotic Giant Branch Stars and Condensation from Zr-depleted Gas
Synchrotron X-ray fluorescence was used in this study for the first timeto measure trace element abundances in single presolar grains. Theabundances of Zr and Nb were determined in SiC grains of the KJFsize-separate. These grains are most likely from C-rich asymptotic giantbranch stars (mainstream grains). Comparison of the data with s-processcalculations suggests that the relatively short-lived isotope93Zr (t 1/2 = 1.5 × 106 yr)condensed into the grains. The Nb/Zr ratios of the majority of thegrains are higher than the s-process and CI chondrite ratios. This isprobably due to grains condensing from stellar gas that was depleted inZr, potentially because of earlier condensation of ZrC, but not depletedin Nb. However, grain contamination with solar system Nb is possible aswell. Upper limits on the initial 93Zr/Zr ratios in thegrains agree with the ratios observed in late-type S stars.
| Infrared photometry and evolution of mass-losing AGB stars. III. Mass loss rates of MS and S stars
Context. The asymptotic giant branch (AGB) phase marks the end of theevolution for low- and intermediate-mass stars, which are fundamentalcontributors to the mass return to the interstellar medium and to thechemical evolution of galaxies. The detailed understanding of mass lossprocesses is hampered by the poor knowledge of the luminosities anddistances of AGB stars. Aims: In a series of papers we are tryingto establish criteria permitting a more quantitative determination ofluminosities for the various types of AGB stars, using the infrared (IR)fluxes as a basis. An updated compilation of the mass loss rates is alsorequired, as it is crucial in our studies of the evolutionary propertiesof these stars. In this paper we concentrate our analysis on the studyof the mass loss rates for a sample of galactic S stars. Methods:We reanalyze the properties of the stellar winds for a sample ofgalactic MS, S, SC stars with reliable estimates of the distance on thebasis of criteria previously determined. We then compare the resultingmass loss rates with those previously obtained for a sample of C-richAGB stars. Results: Stellar winds in S stars are on average lessefficient than those of C-rich AGB stars of the same luminosity.Near-to-mid infrared colors appear to be crucial in our analysis. Theyshow a good correlation with mass loss rates in particular for the Mirastars. We suggest that the relations between the rates of the stellarwinds and both the near-to-mid infrared colors and the periods ofvariability improve the understanding of the late evolutionary stages oflow mass stars and could be the origin of the relation between the ratesof the stellar winds and the bolometric magnitudes.
| Circumstellar molecular line emission from S-type AGB stars: mass-loss rates and SiO abundances
Aims: The main aim is to derive reliable mass-loss rates andcircumstellar SiO abundances for a sample of 40 S-type AGB stars basedon new multi-transitional CO and SiO radio line observations. Inaddition, the results are compared to previous results for M-type AGBstars and carbon stars to look for trends with chemical type. Methods: The circumstellar envelopes are assumed to be sphericallysymmetric and formed by a constant mass-loss rate. The mass-loss ratesare estimated from fitting the CO observations using a non-local,non-LTE radiative transfer code based on the Monte Carlo method. In theexcitation analysis, the energy balance equation is solvedself-consistently simultaneously as the radiative transfer and thetemperature structure of the gas is derived. Effects of dust grains arealso included in the molecular excitation analysis. Once the physicalproperties of the circumstellar envelopes are determined, the sameradiative transfer code is used to model the observed SiO lines in orderto derive circumstellar abundances and the sizes of the SiOline-emitting regions. Results: We have estimated mass-loss ratesof 40 S-type AGB stars and find that the derived mass-loss rates have adistribution that resembles those previously derived for similar samplesof M-type AGB stars and carbon stars. The estimated mass-loss rates alsocorrelate well with the corresponding expansion velocity of theenvelope, in accordance with results for M-type AGB stars and carbonstars. In all, this indicates that the mass loss is driven by the samemechanism in all three chemical types of AGB stars. In addition, we haveestimated the circumstellar fractional abundance of SiO relative to H{2}in 26 of the sample S-type AGB stars. The derived SiO abundances are, onaverage, about an order of magnitude higher than predicted by stellaratmosphere thermal equilibrium chemistry, indicating thatnon-equilibrium chemical processes determines the abundance of SiO inthe circumstellar envelope. Moreover, a comparison with the results forM-type AGB stars and carbon stars show that for a certain mass-lossrate, the circumstellar SiO abundance seems independent (although with alarge scatter) of the C/O-ratio. Conclusions: In our comparisonof S-type AGB stars with carbon stars and M-type AGB stars, we find nolarge differences in circumstellar physical properties or SiO abundancesdepending on the chemical type of the star.Appendices are only available in electronic form at http://www.aanda.org
| 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
| AGB variables and the Mira period-luminosity relation
Published data for large-amplitude asymptotic giant branch variables inthe Large Magellanic Cloud (LMC) are re-analysed to establish theconstants for an infrared (K) period-luminosity relation of the formMK = ρ[logP - 2.38] + δ. A slope of ρ = -3.51+/- 0.20 and a zero-point of δ = -7.15 +/- 0.06 are found foroxygen-rich Miras (if a distance modulus of 18.39 +/- 0.05 is used forthe LMC). Assuming this slope is applicable to Galactic Miras we discussthe zero-point for these stars using the revised Hipparcos parallaxestogether with published very long baseline interferometry (VLBI)parallaxes for OH masers and Miras in globular clusters. These result ina mean zero-point of δ = -7.25 +/- 0.07 for O-rich Galactic Miras.The zero-point for Miras in the Galactic bulge is not significantlydifferent from this value.Carbon-rich stars are also discussed and provide results that areconsistent with the above numbers, but with higher uncertainties. Withinthe uncertainties there is no evidence for a significant differencebetween the period-luminosity relation zero-points for systems withdifferent metallicity.
| Infrared spectroscopic study of a selection of AGB and post-AGB stars
We present here near-infrared spectroscopy in the H and K bands of aselection of nearly 80 stars that belong to various asymptotic giantbranch (AGB) types, namely S type, M type and SR type. This sample alsoincludes 16 post-AGB (PAGB) stars. From these spectra, we seekcorrelations between the equivalent widths of some important spectralsignatures and the infrared colours that are indicative of mass-loss.Repeated spectroscopic observations were made on some PAGB stars to lookfor spectral variations. We also analyse archival Spitzer mid-infraredspectra on a few PAGB stars to identify spectral features due topolycyclic aromatic hydrocarbon (PAH) molecules providing confirmationof the advanced stage of their evolution. Further, we model the spectralenergy distributions (SEDs) of the stars (compiled from archival data)and compare circumstellar dust parameters and mass-loss rates indifferent types.Our near-infrared spectra show that in the case of M- and S type stars,the equivalent widths of the CO(3-0) band are moderately correlated withinfrared colours, suggesting a possible relationship with mass-lossprocesses. A few PAGB stars revealed short-term variability in theirspectra, indicating episodic mass-loss: the cooler stars showed in COfirst overtone bands and the hotter ones showed in HI Brackett lines.Our spectra on IRAS 19399+2312 suggest that it is a transition object.From the Spitzer spectra, there seems to be a dependence between thespectral type of the PAGB stars and the strength of the PAH features.Modelling of SEDs showed among the M and PAGB stars that the higher themass-loss rates, the higher the [K - 12] colour in our sample.
| The Correlations Between the Parameters of the Sharpness of the Light Curve and Period for Miras.
Not Available
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| Mass-loss properties of S-stars on the AGB
We have used a detailed non-LTE radiative transfer code to model newAPEX CO(J = 3 → 2) data, and existing CO radio line data, on asample of 40 AGB S-stars. The derived mass-loss-rate distribution has amedian value of 2 × 10-7~Mȯyr-1, and resembles values obtained for similar samples ofM-stars and carbon stars. Possibly, there is a scarcity ofhigh-mass-loss-rate (≥10-5~Mȯyr-1) S-stars. The distribution of envelope gas expansionvelocities is similar to that of the M-stars, the median is 7.5 kms-1, while the carbon stars, in general, have higher gasexpansion velocities. The mass-loss rate correlates well with the gasexpansion velocity, in accordance with results for M-stars and carbonstars.
| Secular Evolution in Mira Variable Pulsations
Stellar evolution theory predicts that asymptotic giant branch (AGB)stars undergo a series of short thermal pulses that significantly changetheir luminosity and mass on timescales of hundreds to thousands ofyears. These pulses are confirmed observationally by the existence ofthe short-lived radioisotope technetium in the spectra of some of thesestars, but other observational consequences of thermal pulses are subtleand may only be detected over many years of observations. Secularchanges in these stars resulting from thermal pulses can be detected asmeasurable changes in period if the star is undergoing Mira pulsations.It is known that a small fraction of Mira variables exhibit largesecular period changes, and the detection of these changes among alarger sample of stars could therefore be useful in evolutionary studiesof these stars. The American Association of Variable Star Observers(AAVSO) International Database currently contains visual data for over1500 Mira variables. Light curves for these stars span nearly a centuryin some cases, making it possible to study the secular evolution of thepulsation behavior on these timescales. In this paper we present theresults of our study of period change in 547 Mira variables using datafrom the AAVSO. We use wavelet analysis to measure the period changes inindividual Mira stars over the span of available data. By making linearfits to the period versus time measurements, we determine the averagerates of period change, dlnP/dt, for each of these stars. We findnonzero dlnP/dt at the 2 σ significance level in 57 of the 547stars, at the 3 σ level in 21 stars, and at the level of 6 σor greater in eight stars. The latter eight stars have been previouslynoted in the literature, and our derived rates of period change largelyagree with published values. The largest and most statisticallysignificant dlnP/dt are consistent with the rates of period changeexpected during thermal pulses on the AGB. A number of other starsexhibit nonmonotonic period change on decades-long timescales, the causeof which is not yet known. In the majority of stars, the periodvariations are smaller than our detection threshold, meaning theavailable data are not sufficient to unambiguously measure slowevolutionary changes in the pulsation period. It is unlikely that morestars with large period changes will be found among heretoforewell-observed Mira stars in the short term, but continued monitoring ofthese and other Mira stars may reveal new and serendipitous candidatesin the future.
| 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
| The analysis of indexed astronomical time series - IX. A period change test
A frequency domain test statistic is applied to the full time series ofbrightness maxima and minima in order to test for changes in the meanpulsation periods of 382 Mira stars. The test statistic depends on twoparameters that are related to the intrinsic cycle-to-cycle scatter inthe period, and to the measurement error, respectively. It is shown thatthe former is strongly related to the mean pulsation period of the star.
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| 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
| How many Hipparcos Variability-Induced Movers are genuine binaries?
Hipparcos observations of some variable stars, and especially oflong-period (e.g. Mira) variables, reveal a motion of the photocentercorrelated with the brightness variation (variability-induced mover -VIM), suggesting the presence of a binary companion. A re-analysis ofthe Hipparcos photometric and astrometric data does not confirm the VIMsolution for 62 among the 288 VIM objects (21%) in the Hipparcoscatalogue. Most of these 288 VIMs are long-period (e.g. Mira) variables(LPV). The effect of a revised chromaticity correction, which accountsfor the color variations along the light cycle, was then investigated.It is based on ``instantaneous'' V-I color indices derived fromHipparcos and Tycho-2 epoch photometry. Among the 188 LPVs flagged asVIM in the Hipparcos catalogue, 89 (47%) are not confirmed as VIM afterthis improved chromaticity correction is applied. This dramatic decreasein the number of VIM solutions is not surprising, since the chromaticitycorrection applied by the Hipparcos reduction consortia was based on afixed V-I color. Astrophysical considerations lead us to adopt a morestringent criterion for accepting a VIM solution (first-kind risk of0.27% instead of 10% as in the Hipparcos catalogue). With this moresevere criterion, only 27 LPV stars remain VIM, thus rejecting 161 ofthe 188 (86%) of the LPVs defined as VIMs in the Hipparcos catalogue.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).Table 1 is also available in electronic form at the CDS, via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1167
| 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.
| 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.
| Stellar and circumstellar evolution of long period variable stars
In a first paper, HIPPARCOS astrometric and kinematic data were used tocalibrate both infrared K and IRAS luminosities at the same time askinematic parameters of Long Period Variable stars (LPVs). Individualestimated absolute magnitudes and a probabilistic assignation togalactic populations were deduced from these calibrations for each LPVof our sample. Here we propose a scenario of simultaneous stellar andcircumstellar evolution according to the galactic populations. Thetransitory states of S and Tc stars allow us to confirm the location ofthe first dredge-up at Mbol=-3.5. There is also evidencesuggesting that a previous enrichment in s-elements from a more evolvedcompanion may accelerate the evolution along the AGB. The possibleevolution to OH LPVs is included in this scenario, and any of thesestars may have a mass at the limit of the capability for a C enrichmentup to C/O > 1. A list of bright massive LPVs with peculiar envelopeand luminosity properties is proposed as Hot Bottom Burning candidates.The He-shell flash star, R Cen, is found to be exceptionally bright andcould become, before leaving the AGB, a C-rich LPV brighter than theusual luminosity limit of carbon stars.
| Envelope tomography of long-period variable stars III. Line-doubling frequency among Mira stars
This paper presents statistics of the line-doubling phenomenon in asample of 81 long-period variable (LPV) stars of various periods,spectral types and brightness ranges. The set of observations consistsof 315 high-resolution optical spectra collected with the spectrographELODIE at the Haute-Provence Observatory, during 27 observing nights atone-month intervals and spanning two years. When correlated with a maskmimicking a K0III spectrum, 54% of the sample stars clearly showed adouble-peaked cross-correlation profile around maximum light, reflectingdouble absorption lines. Several pieces of evidence are presented thatpoint towards the double absorption lines as being caused by thepropagation of a shock wave through the photosphere. The observation ofthe Balmer lines appearing in emission around maximum light in thesestars corroborates the presence of a shock wave. The observed velocitydiscontinuities, ranging between 10 and 25 km s-1, are notcorrelated with the brightness ranges. A comparison with thecenter-of-mass (COM) velocity obtained from submm CO lines originatingin the circumstellar envelope reveals that the median velocity betweenthe red and blue peaks is blueshifted with respect to the COM velocity,as expected if the shock moves upwards. The LPVs clearly exhibitingline-doubling around maximum light with the K0III mask appear to be themost compact ones, the stellar radius being estimated from theireffective temperatures (via the spectral type) and luminosities (via theperiod-luminosity relationship). It is not entirely clear whether or notthis segregation between compact and extended LPVs is an artefact of theuse of the K0III mask. Warmer masks (F0V and G2V) applied to the mostextended and coolest LPVs yield asymmetric cross-correlation functionswhich suggest that line doubling is occurring in those stars as well.Although a firm conclusion on this point is hampered by the largecorrelation noise present in the CCFs of cool LPVs obtained with warmmasks, the occurrence of line doubling in those stars is confirmed bythe double CO Delta v = 3 lines observed around 1.6 mu m by Hinkle etal. (1984, ApJS, 56, 1). Moreover, the Hdelta line in emission, which isanother signature of the presence of shocks, is observed as well in themost extended stars, although with a somewhat narrower profile. This isan indication that the shock is weaker in extended than in compact LPVs,which may also contribute to the difficulty of detecting line doublingin cool, extended LPVs. Based on observations made at Observatoire deHaute Provence, operated by the Centre National de la RechercheScientifique, France. Table 3 is only available in electronic form athttp://www.edpsciences.org and 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/379/305
| Polarimetry of 167 Cool Variable Stars: Data
Multicolor photoelectric polarimetry is presented for 167 stars, most ofwhich are variable stars. The observations constitute a data set thatfor some stars covers a time span of 35 yr. Complex variations are foundover time and wavelength and in both the amount of polarization and itsposition angle, providing constraints for understanding the polarizingenvironments in and around these cool stars.
| 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).
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable 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/qcar?J/A+A/367/521
| 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.
| On the Relations between Infrared Colors and Mass Loss Rates for S Stars
A relation between the infrared color K-[12] and the mass loss rate,dM/dt, is found for the intrinsic S stars. This relation isqualitatively similar to the ones for carbon stars and oxygen-rich Mirastars, but quantitatively different. It could be useful in the contextof the near infrared surveys, DENIS and 2MASS, which are in progress.Correlations between J-K and [12]-[25] indices and dM/dt are found to beloose for S stars.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Ikizler |
| Sað Açýklýk: | 07h07m21.28s |
| Yükselim: | +22°42'12.7" |
| Görünürdeki Parlaklýk: | 8.318 |
| özdevim Sað Açýklýk: | 0 |
| özdevim Yükselim: | 0 |
| B-T magnitude: | 11.119 |
| V-T magnitude: | 8.55 |
Kataloglar ve belirtme:
|
INHABITED SKY
