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Публикации по объекту
The Distribution of SiO in the Circumstellar Envelope around IRC +10216
New interferometric observations of SiO J=5-->4 circumstellar lineemission around the carbon star IRC +10216 using the Submillimeter Arrayare presented. Complemented by multitransition single-dish observations,including infrared observations of rovibrational transitions, detailedradiative transfer modeling suggests that the fractional abundance ofSiO in the inner part of the envelope, between ~3 and 8 stellar radii,is as high as ~1.5×10-6. This is more than an order ofmagnitude higher than predicted by equilibrium stellar atmospherechemistry in a carbon-rich environment and indicative of the importanceof non-LTE chemical processes. In addition to the compact component, aspatially more extended (re~2.4×1016 cm) lowfractional abundance (f0~1.7×10-7) region isrequired to fit the observations. This suggests that the majority of theSiO molecules are effectively accreted onto dust grains in the innerwind, while the remaining gas-phase molecules are eventuallyphotodissociated at larger distances. Evidence of departure from asmooth wind is found in the observed visibilities, indicative of densityvariations of a factor 2-5 on an angular scale corresponding to atimescale of about 200 yr. In addition, constraints on the velocitystructure of the wind are obtained.
| Phase Lags in the Optical-Infrared Light Curves of Asymptotic Giant Branch Stars
To search for phase lags in the optical-infrared light curves ofasymptotic giant branch stars, we have compared infrared data from theCOBE DIRBE satellite with optical light curves from the AAVSO and othersources. We found 17 examples of phase lags between the times ofinfrared and optical maximum, and 4 stars with no observed lags. Thereis a clear difference between the Mira variables and the semiregularvariables in the sample, with the maximum in the optical preceding thatin the near-infrared in the Miras, while in most of the semiregularvariables no lags are observed. Comparison to published theoreticalmodels indicates that the phase lags in the Miras are due to strongtitanium oxide absorption in the visual at stellar maximum, and suggeststhat Miras pulsate in the fundamental mode, while at least somesemiregular variables are first-overtone pulsators. There is a clearoptical-near-infrared phase lag in the carbon-rich Mira V CrB; this islikely due to C2 and CN absorption variations in the optical.
| SiO in C-rich circumstellar envelopes of AGB stars: effects of non-LTE chemistry and grain adsorption
Aims.New SiO multi-transition millimetre line observations of a sampleof carbon stars, including J = 8→7 observations with the APEXtelescope, are used to probe the role of non-equilibrium chemistry andthe influence of grains in circumstellar envelopes of carbon stars. Methods: .A detailed radiative transfer modelling, including theeffect of dust emission in the excitation analysis, of the observed SiOline emission is performed. A combination of low- and high-energy linesare important in constraining the abundance distribution. Results:.It is found that the fractional abundance of SiO in these C-richenvironments can be several orders of magnitude higher than predicted byequilibrium stellar atmosphere chemistry. In fact, the SiO abundancedistribution of carbon stars closely mimic that of M-type (O-rich) AGBstars. A possible explanation for this behaviour is a shock-inducedchemistry, but also the influence of dust grains, both as a source fordepletion as well as production of SiO, needs to be furtherinvestigated. As observed for M-type AGB stars, a clear trend that theSiO fractional abundance decreases as the mass-loss rate of the starincreases is found for the carbon stars. This indicates that SiO isaccreted onto dust grains in the circumstellar envelopes.
| Oscillation mode lifetimes in ξ Hydrae: will strong mode damping limit asteroseismology of red giant stars?
We introduce a new method to measure frequency separations and modelifetimes of stochastically excited and damped oscillations, so-calledsolar-like oscillations. Our method shows that velocity data of the redgiant star ξ Hya (Frandsen et al. 2002) support a large frequencyseparation between modes of roughly 7~μHz. We also conclude that thedata are consistent with a mode lifetime of 2 days, which is so shortrelative to its pulsation period that none of the observed frequenciesare unambiguous. Hence, we argue that the maximum asteroseismic outputthat can be obtained from these data is an average large frequencyseparation, the oscillation amplitude and the average mode lifetime.However, the significant discrepancy between the theoreticalcalculations of the mode lifetime (Houdek & Gough 2002) and ourresult based on the observations of ξ Hya, implies that red giantstars can help us better understand the damping and driving mechanismsof solar-like p-modes by convection.
| The light curve of the semiregular variable L2 Puppis - II. Evidence for solar-like excitation of the oscillations
We analyse visual observations of the pulsations of the red giantvariable L2 Puppis (L2 Pup). The data cover 77 yrbetween 1927 and 2005, thus providing an extensive empirical base forcharacterizing properties of the oscillations. The power spectrum of thelight curve shows a single mode resolved into multiple peaks under anarrow envelope. We argue that this results from stochastic excitation,as seen in solar oscillations, with a mode lifetime of about 5 yr. Therandom fluctuations in phase also support this idea. A comparison with XCam, a true Mira star with the same pulsation period, and W Cyg, a truesemiregular star, illustrates the basic differences in phase behaviours.The Mira shows very stable phase, consistent with excitation by theκ-mechanism, whereas W Cyg shows large phase fluctuations thatimply stochastic excitation. We find L2 Pup to beintermediate, implying that both mechanisms play a role in itspulsation. Finally, we also checked the presence of low-dimensionalchaos and could safely exclude it.
| Dust cloud formation in stellar environments. II. Two-dimensional models for structure formation around AGB stars
This paper reports on computational evidence for the formation ofcloud-like dust structures around C-rich AGB stars. This spatio-temporalstructure formation process is caused by a radiative/thermal instabilityof dust-forming gases as identified by Woitke et al. (2000, A&A,358, 665). Our 2D (axisymmetric) models combine a time-dependentdescription of the dust formation process according to Gail &Sedlmayr (1988, A&A, 206, 153) with detailed, frequency-dependentcontinuum radiative transfer by means of a Monte Carlo method (Niccoliniet al. 2003, A&A, 399, 703) in an otherwise static medium (v = 0).These models show that the formation of dust behind already condensedregions, which shield the stellar radiation field, is strongly favoured.In the shadow of these clouds the temperature decreases by severalhundred Kelvin, which triggers the subsequent formation of dust andensures its thermal stability. Considering an initially dust-free gaswith small density inhomogeneities, we find that finger-like duststructures develop which are cooler than the surroundings and pointtowards the centre of the radiant emission, similar to the“cometary knots” observed in planetary nebulae and starformation regions. Compared to a spherical symmetric reference model,the clumpy dust distribution has little effect on the spectral energydistribution, but dominates the optical appearance in near IRmonochromatic images.
| A study of bright Southern long period variables
In this paper we present radial velocity curves of AGB variables thatexhibit various kinds of anomalies: semiregular variables (SRVs) withtypical mira periods, SRVs exceeding the mira 2.5 mag amplitude limit,miras with secondary maxima in their light curves, and a SRV with a longsecondary period. The stars with reliable Hipparcos parallaxes from thisand from previous studies are plotted in a log P-MK-diagram.Our objects nicely follow the log P-MK-relations determinedfor the LMC. This allows the pulsation mode to be identified. While allmiras fall on the fundamental mode sequence, the SRVs fall on both thefirst overtone and fundamental mode sequences. The SRVs on thefundamental mode sequence occur at both high and low luminosities, someof them being more luminous than larger amplitude miras. Thisdemonstrates observationally that some parameter other than luminosityaffects the stability of long period variables, probably mass. Firstovertone pulsators all show velocity amplitudes around 4 kms-1. For the fundamental mode pulsators, the velocityamplitude shows a correlation with light amplitude. The two miras R Cenand R Nor, known for their double-peaked light curves, have velocitycurves that are quite different. The R Nor velocity curve shows noevidence of the double peaks, meaning that the true pulsation period isthe time between alternate minima or maxima. There is slight evidencefor a double bump in the R Cen velocity curve. It is suggested thatthese stars are relatively massive (3-5 Mȯ).
| Variable Star Network: World Center for Transient Object Astronomy and Variable Stars
Variable Star Network (VSNET) is a global professional-amateur networkof researchers in variable stars and related objects, particularly intransient objects, such as cataclysmic variables, black-hole binaries,supernovae, and gamma-ray bursts. The VSNET has been playing apioneering role in establishing the field of transient object astronomy,by effectively incorporating modern advances in observational astronomyand global electronic networks, as well as collaborative progress intheoretical astronomy and astronomical computing. The VSNET is now oneof the best-featured global networks in this field of astronomy. Wereview the historical progress, design concept, associated technology,and a wealth of scientific achievements powered by VSNET.
| A W Roberts: the observations (paper 2).
Not Available
| Period-luminosity relation for M-type semiregular variables from Hipparcos parallaxes
We have studied the period-luminosity (P-L) relationships of oxygen-richsemiregular (SR) variables in several wavelength bands using Hipparcosparallaxes with an accuracy of better than 10 per cent. We have shownthat there is a clear dependence on period of absolute magnitude in theU,B,V,R,IC,J,H,K,L,M,N, [12], [25], [60] and [100] bands, andthat the slope of the linear Mλ- logP relation is asmooth function of wavelength. We point out that this relation can inprinciple be used to derive absolute bolometric magnitude as a functionof period.The behaviour of the second periods of SR variables in the P-L relationin the V and K bands is also discussed.
| Multiwavelength diameters of nearby Miras and semiregular variables
We have used optical interferometry to obtain multiwavelength visibilitycurves for eight red giants over the wavelength range 650-1000 nm. Theobservations consist of wavelength-dispersed fringes recorded withMAPPIT (Masked Aperture-Plane Interference Telescope) at the 3.9-mAnglo-Australian Telescope. We present results for four Miras (R Car, oCet, R Hya and R Leo) and four semiregular variables (R Dor, W Hya,L2 Pup and γ Cru). All stars except γ Cru showstrong variations of angular size with wavelength. A uniform-disc modelwas found to be a poor fit in most cases, with Gaussian (or other moretapered) profiles preferred. This, together with the fact that moststars showed a systematic increase in apparent size towards the blue anda larger-than-expected linear size, even in the red, all point towardssignificant scattering by dust in the inner circumstellar environment.Some stars showed evidence for asymmetric brightness profiles, whileL2 Pup required a two-component model, indicating anasymmetrical circumstellar dust shell.
| Probing the inner wind of AGB stars: Interferometric observations of SiO millimetre line emission from the oxygen-rich stars R Dor and L2Pup
High angular resolution Australia Telescope Compact Array (ATCA)observations of SiO ``thermal'' millimetre line emission towards the twooxygen-rich, low mass loss rate AGB stars R Dor andL2 Pup are presented. In both cases the emission isresolved with an overall spherical symmetry. Detailed radiative transfermodelling of the SiO line emission has been performed, and thecomparison between observations and models are conducted in thevisibility plane, maximizing the sensitivity. The excitation analysissuggests that the abundance of SiO is as high as 4×10-5 in the inner part of the wind, close to the predictedvalues from stellar atmosphere models. Beyond a radius of ≈ 1×1015 cm the SiO abundance is significantly lower, about3× 10-6, until it decreases strongly at a radius ofabout 3× 1015 cm. This is consistent with a scenariowhere SiO first freezes out onto dust grains, and then eventuallybecomes photodissociated by the interstellar UV-radiation field. Inthese low expansion velocity sources the turbulent broadening of thelines plays an important role in the line formation. Micro-turbulentvelocity widths in the range 1.1-1.5 km s-1 result in a verygood reproduction of the observed line shapes even if the gas expansionvelocity is kept constant. This, combined with the fact that the SiO andCO lines are well fitted using the same gas expansion velocity (towithin 5-10%), suggest that the envelope acceleration occurs close tothe stellar photosphere, within 20-30 stellar radii.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
For a complete 12 μm flux-limited sample of 207 IRAS sources(F12>=150 Jy, |b|>=5deg), the majority ofwhich are AGB stars (~87%), we have extracted light curves in seveninfrared bands between 1.25 and 60 μm using the database of theDiffuse Infrared Background Experiment (DIRBE) instrument on the CosmicBackground Explorer (COBE) satellite. Using previous infrared surveys,we filtered these light curves to remove data points affected by nearbycompanions and obtained time-averaged flux densities and infraredcolors, as well as estimates of their variability at each wavelength. Inthe time-averaged DIRBE color-color plots, we find clear segregation ofsemiregulars, Mira variables, carbon stars, OH/IR stars, and red giantswithout circumstellar dust (i.e., V-[12]<5) and with little or novisual variation (ΔV<0.1 mag). The DIRBE 1.25-25 μm colorsbecome progressively redder and the variability in the DIRBE databaseincreases along the oxygen-rich sequence nondusty slightly varying redgiants-->SRb/Lb-->SRa-->Mira-->OH/IR and the carbon-richSRb/Lb-->Mira sequence. This supports previous assertions that theseare evolutionary sequences involving the continued production andejection of dust. The carbon stars are redder than their oxygen-richcounterparts for the same variability type, except in theF12/F25 ratio, where they are bluer. Of the 28sources in the sample not previous noted to be variable, 18 are clearlyvariable in the DIRBE data, with amplitudes of variation of ~0.9 mag at4.9 μm and ~0.6 mag at 12 μm, consistent with them being verydusty Mira-like variables. We also present individual DIRBE light curvesof a few selected stars. The DIRBE light curves of the semiregularvariable L2 Pup are particularly remarkable. The maxima at1.25, 2.2, and 3.5 μm occur 10-20 days before those at 4.9 and 12μm, and, at 4.9 and 12 μm, another maximum is seen between the twonear-infrared maxima.
| ``Thermal'' SiO radio line emission towards M-type AGB stars: A probe of circumstellar dust formation and dynamics
An extensive radiative transfer analysis of circumstellar SiO``thermal'' radio line emission from a large sample of M-type AGB starshas been performed. The sample contains 18 irregulars of type Lb (IRV),7 and 34 semiregulars of type SRa and SRb (SRV), respectively, and 12Miras. New observational data, which contain spectra of several groundvibrational state SiO rotational lines, are presented. The detectionrate was about 60% (44% for the IRVs, and 68% for the SRVs). SiOfractional abundances have been determined through radiative transfermodelling. The abundance distribution of the IRV/SRV sample has a medianvalue of 6*E-6, and a minimum of 2*E-6 and amaximum of 5*E-5. The high mass-loss rate Miras have a muchlower median abundance, la 10-6. The derived SiO abundancesare in all cases well below the abundance expected from stellaratmosphere equilibrium chemistry, on average by a factor of ten. Inaddition, there is a trend of decreasing SiO abundance with increasingmass-loss rate. This is interpreted in terms of depletion of SiOmolecules by the formation of silicate grains in the circumstellarenvelopes, with an efficiency which is high already at low mass-lossrates and which increases with the mass-loss rate. The high mass-lossrate Miras appear to have a bimodal SiO abundance distribution, a lowabundance group (on average 4*E-7) and a high abundance group(on average 5*E-6). The estimated SiO envelope sizes agreewell with the estimated SiO photodissociation radii using an unshieldedphotodissociation rate of 2.5*E-10 s-1. The SiOand CO radio line profiles differ in shape. In general, the SiO lineprofiles are narrower than the CO line profiles, but they havelow-intensity wings which cover the full velocity range of the CO lineprofile. This is interpreted as partly an effect of selfabsorption inthe SiO lines, and partly (as has been done also by others) as due tothe influence of gas acceleration in the region which produces asignificant fraction of the SiO line emission. Finally, a number ofsources which have peculiar CO line profiles are discussed from thepoint of view of their SiO line properties.Based on observations using the SEST at La Silla, Chile, the 20 mtelescope at Onsala Space Observatory, Sweden, the JCMT on Hawaii, andthe IRAM 30 m telescope at Pico Veleta, Spain.
| Mass-loss from dusty, low outflow-velocity AGB stars. I. Wind structure and mass-loss rates
We present the first results of a CO(2-1), (1-0), and 86 GHz SiO masersurvey of AGB stars, selected by their weak near-infrared excess. Amongthe 65 sources of the present sample we find 10 objects with low COoutflow velocities, vexp <~ 5 km s-1.Typically, these sources show (much) wider SiO maser features.Additionally, we get 5 sources with composite CO line profiles, i.e. anarrow feature is superimposed on a broader one, where both componentsare centered at the same stellar velocity. The gas mass-loss rates,outflow velocities and velocity structures suggested by these lineprofiles are compared with the results of hydrodynamical modelcalculations for dust forming molecular winds of pulsating AGB stars.The observations presented here give support to our recent lowoutflow-velocity models, in which only small amounts of dust are formed.Therefore, the wind generation in these models is dominated by stellarpulsation. We interpret the composite line profiles in terms ofsuccessive winds with different characteristics. Our hydrodynamicalmodels, which show that the wind properties may be extremely sensitiveto the stellar parameters, support such a scenario.Based on observations obtained at the European Southern Observatory, LaSilla, Chile and at the IRAM, Pico Veleta, Spain.
| 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
| The light curve of the semiregular variable L2 Puppis - I. A recent dimming event from dust
The nearby Mira-like variable L2 Pup is shown to beundergoing an unprecedented dimming episode. The stability of the periodrules out intrinsic changes to the star, leaving dust formation alongthe line of sight as the most likely explanation. Episodic dustobscuration events are fairly common in carbon stars but have not beenseen in oxygen-rich stars. We also present a 10-μm spectrum, takenwith the Japanese Infrared Telescope in Space satellite, showing strongsilicate emission that can be fitted with a detached, thin dust shell,containing silicates and corundum.
| The Very Slow Wind from the Pulsating Semiregular Red Giant, L2 Puppis
We have obtained 11.7 and 17.9 μm images at the Keck I telescope ofthe circumstellar dust emission from L2 Pup, which is one ofthe nearest (D=61 pc) mass-losing, pulsating red giants that has asubstantial infrared excess. We propose that the star is losing mass ata rate of ~3×10-7 Msolar yr-1.Given its relatively low luminosity (~1500 Lsolar),relatively high effective temperature (near 3400 K), relatively shortperiod (~140 days), and inferred gas outflow speed of 3.5 kms-1, standard models for dust-driven mass loss do not apply.Instead, the wind may be driven by the stellar pulsations, withradiation pressure on dust being relatively unimportant, as described insome recent calculations. L2 Pup may serve as the prototypeof this phase of stellar evolution, in which a star could lose ~15% ofits initial main-sequence mass.
| Mass loss rates of a sample of irregular and semiregular M-type AGB-variables
We have determined mass loss rates and gas expansion velocities for asample of 69 M-type irregular (IRV 22 objects) and semiregular (SRV; 47objects) AGB-variables using a radiative transfer code to model theircircumstellar CO radio line emission. We believe that this sample isrepresentative for the mass losing stars of this type. The (molecularhydrogen) mass loss rate distribution has a median value of 2.0 x10-7 Msun yr-1, and a minimum of 2.0 x10-8 Msun yr-1 and a maximum of 8 x10-7 Msun yr-1. M-type IRVs and SRVswith a mass loss rate in excess of 5 x 10-7 Msunyr-1 must be very rare, and among these mass losing stars thenumber of sources with mass loss rates below a few 10-8Msun yr-1 must be small. We find no significantdifference between the IRVs and the SRVs in terms of their mass losscharacteristics. Among the SRVs the mass loss rate shows no dependenceon the period. Likewise the mass loss rate shows no correlation with thestellar temperature. The gas expansion velocity distribution has amedian of 7.0 km s-1, and a minimum of 2.2 km s-1and a maximum of 14.4 km s-1. No doubt, these objects samplethe low gas expansion velocity end of AGB winds. The fraction of objectswith low gas expansion velocities is very high, about 30% havevelocities lower than 5 km s-1, and there are objects withvelocities lower than 3 km s-1: V584 Aql,T Ari, BI Car, RXLac, and L2 Pup. The mass loss rate and thegas expansion velocity correlate well, a result in line with theoreticalpredictions for an optically thin, dust-driven wind. In general, themodel produces line profiles which acceptably fit the observed ones. Anexceptional case is R Dor, where the high-quality,observed line profiles are essentially flat-topped, while the model onesare sharply double-peaked. The sample contains four sources withdistinctly double-component CO line profiles, i.e., a narrow featurecentered on a broader feature: EP Aqr, RVBoo, X Her, and SV Psc.We have modelled the two components separately for each star and derivemass loss rates and gas expansion velocities. We have compared theresults of this M-star sample with a similar C-star sample analysed inthe same way. The mass loss rate characteristics are very similar forthe two samples. On the contrary, the gas expansion velocitydistributions are clearly different. In particular, the number oflow-velocity sources is much higher in the M-star sample. We found noexample of the sharply double-peaked CO line profile, which is evidenceof a large, detached CO-shell, among the M-stars. About 10% of theC-stars show this phenomenon.
| The hydrodynamical structure of circumstellar envelopes around low mass-loss rate, low outflow velocity AGB stars
Recent hydrodynamical models (Winters et al. 2000b) allow the existenceof pulsating, large velocity amplitude Asymptotic Giant Branch (AGB)stars with tenuous dusty circumstellar shells, which produce lowmass-loss rates and simultaneously low wind velocities. The Semi-regularlong-period variable L2 Pup shows a broad SiO maser featureat 86 GHz (v=1, J=2-1), indicating an outward velocity of the materialclose to the stellar photosphere of at least 10 km s-1 , andnarrow CO (J=2-1) and (1-0) line profiles indicating an outflow velocityof the material in the circumstellar shell of only about 3 kms-1 . This can be explained in terms of our hydrodynamicalmodels which provide large velocities in the shocked stellar atmosphereand low velocities of the circumstellar outflow. Based on observationsobtained at the European Southern Observatory, La Silla, Chile.
| Gas and dust emission in the Lupus globular filaments GF 17 and GF 20
We present large-scale millimeter molecular line observations as well asIRAS co-added images of the globular filaments GF 17 and GF 20 in thesouthern constellation of Lupus. A comparison is made of the extendedfar-infrared emission detected by IRAS at 60 and 100 mu m and theCO(1-0), 13CO(1-0), and C18O(1-0) emission in GF17 and GF 20. Based on the far-infrared emission estimates of the dusttemperature, optical depth and visual extinction are derived. We find acorrelation between the measured dispersion in our extinctiondeterminations and the extinction toward the clouds, which is verysimilar to that found for other clouds, and interpret this as evidencethat the cloud edges are characterized by a smooth density gradient. Wefind a remarkably good agreement between our 100 mu m optical depthimages and the 13CO integrated emission maps. The dust 100 mum optical depth is well correlated with the gas column densitysuggesting that the far-infrared emission must originate from asubstantial depth in the clouds. The dust temperature is found to beanticorrelated with the gas column density indicating that these cloudsare heated externally. Our calculated far-infrared luminosities of GF 17and GF 20 imply that the dominant source of dust heating is the ISRF dueto the nearby Sco OB2 association. Analysis of the gas velocitystructure within GF 17 and GF 20 reveals evidence for smooth large-scalestreaming motions along the filamentary structures with magnitude ~0.5km s-1 pc-1. Our results indicate that thevelocity gradients are likely due to the interaction of GF 17 and GF 20with the Upper-Scorpius and Upper-Centaurus-Lupus HI expanding shells,via propagating shock fronts. Based on observations at the EuropeanSouthern Observatory, La Silla, Chile.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| 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
| Hipparcos parallaxes for Mira-like long-period variables
This paper concerns the calibration of the K period-luminosity relationfor Mira variables using Hipparcos parallaxes. K magnitudes areavailable for 255 Mira-like variables which were observed by Hipparcos.Period-luminosity zero-points are evaluated for various subgroups ofdata. The best solution for oxygen-rich Miras, which uses 180 stars,omitting the short-period red group (which had different kinematics fromthe short-period blue stars) and the low-amplitude variables, provides azero-point of σ2σ2π +(0.4605)2π2PL(K)σ2K + σ2PL(K),0.84+/-0.14mag, which implies a distance modulus for the LargeMagellanic Cloud of σK = 0.3ΔK√N,18.64+/-0.14mag, or perhaps slightly greater if a metallicity correctionis required, in good agreement with the value derived from Cepheids. Thezero-point of the period-luminosity relation for carbon stars is brieflydiscussed. Linear diameters are derived for red variables with measuredangular diameters and parallaxes, and are used to examine thelong-standing question of the pulsation mode(s) of these stars. Evidenceis presented to suggest that most of them are pulsating in the same modeand, if published model atmospheres are correct, this is probably thefirst overtone. Some discussion is given of sequences in theperiod-luminosity and period-colour diagrams and their bearing on thepulsation mode problem.
| Infrared colours for Mira-like long-period variables found in the (Mȯ<~10-7 Msolar yr-1) Hipparcos Catalogue
Near-infrared, JHKL, photometry is presented for 193 Mira andsemi-regular variables that were observed by Hipparcos; periods,bolometric magnitudes and amplitudes are derived for 92 of them. Becauseof the way in which the Hipparcos targets were selected, this group ofstars provides a useful data base of Miras with low mass-loss rates(Mȯ<~10-7Msolaryr-1).Various period-colour relationships are discussed in detail. The colour,particularly BCK = 10.86 - 38.10 K (J - K)0 +64.16(J - K)20 - 50.72(J -K)30 + 19, K-L, at a given period is found todepend on the pulsation amplitude of the star. A comparison with modelssuggests that this is a consequence of atmospheric extension, in thesense that large-amplitude pulsators have very extended atmospheres andredder Mȯ<10-7Msolaryr-1, K-L and H-K but bluerJ-H than their lower amplitude counterparts. The stars with veryextended atmospheres also have higher values of K-[12] and hence highermass-loss rates. This finding provides further evidence for the causalconnection between pulsation and mass loss. Two sequences are identifiedin the Hp-K versus logP diagram (where Hp is the Hipparcos broad-bandmagnitude) at short periods (logP<2.35). At a given period these twogroups have, on average, the same pulsation amplitude, but differentJHKL colours and spectral types. The short-period stars in the bluersequence have similar near-infrared colours to the Miras found inglobular clusters. Long-term trends in the infrared light curves arediscussed for stars that have sufficient data.
| Mira kinematics from Hipparcos data: a Galactic bar to beyond the Solar circle
The space motions of Mira variables are derived from radial velocities,Hipparcos proper motions and a period-luminosity relation. Thepreviously known dependence of Mira kinematics on the period ofpulsation is confirmed and refined. In addition, it is found that Miraswith periods in the range 145-200d in the general Solar neighbourhoodhave a net radial outward motion from the Galactic Centre of75+/-18kms-1. This, together with a lag behind the circularvelocity of Galactic rotation of 98+/-19kms-1, is interpretedas evidence for an elongation of their orbits, with their major axesaligned at an angle of ~17° with the Sun-Galactic Centre line,towards positive Galactic longitudes. This concentration seems to be acontinuation to the Solar circle and beyond of the bar-like structure ofthe Galactic bulge, with the orbits of some local Miras probablypenetrating into the bulge. These conclusions are not sensitive to thedistance scale adopted. A further analysis is given of the short-period(SP) red group of Miras discussed in companion papers in this series. InAppendix A the mean radial velocities and other data for 842 oxygen-richMira-like variables are tabulated. These velocities were derived frompublished optical and radio observations.
| On the Variability of K5-M Stars
I investigate the Hipparcos Satellite photometry of K5-M stars to seethe pattern of activity of these stars. A few stars for which furtherstudy is desirable are identified.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Корма |
| Прямое восхождение: | 07h13m32.40s |
| Склонение: | -44°38'23.0" |
| Видимая звёздная величина: | 5.1 |
| Расстояние: | 60.753 парсек |
| Собственное движение RA: | 109.4 |
| Собственное движение Dec: | 325 |
| B-T magnitude: | 6.316 |
| V-T magnitude: | 4.767 |
Каталоги и обозначения:
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INHABITED SKY
