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Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be Stars
Using the three-telescope IOTA interferometer on Mount Hopkins, wereport results from the first near-infrared (λ=1.65 μm)closure-phase survey of young stellar objects (YSOs). These closurephases allow us to unambiguously detect departures from centrosymmetry(i.e., skew) in the emission pattern from YSO disks on the scale of ~4mas, expected from generic ``flared disk'' models. Six of 14 targetsshowed small, yet statistically significant nonzero closure phases, withlargest values from the young binary system MWC 361-A and the(pre-main-sequence?) Be star HD 45677. Our observations are quitesensitive to the vertical structure of the inner disk, and we confrontthe predictions of the ``puffed-up inner wall'' models of Dullemond,Dominik, & Natta (DDN). Our data support disk models with curvedinner rims because the expected emission appears symmetricallydistributed around the star over a wide range of inclination angles. Incontrast, our results are incompatible with the models possessingvertical inner walls because they predict extreme skewness (i.e., largeclosure phases) from the near-IR disk emission that is not seen in ourdata. In addition, we also present the discovery of mysterious H-band``halos'' (~5%-10% of light on scales 0.01"-0.50") around a few objects,a preliminary ``parametric imaging'' study for HD 45677, and the firstastrometric orbit for the young binary MWC 361-A.
| Bright Localized Near-Infrared Emission at 1-4 AU in the AB Aurigae Disk Revealed by IOTA Closure Phases
We report on the detection of localized off-center emission at 1-4 AU inthe circumstellar environment of the young stellar object AB Aurigae. Weused closure-phase measurements in the near-infrared that were made atthe long-baseline interferometer IOTA, the first obtained on a youngstellar object using this technique. When probing sub-AU scales, allclosure phases are close to zero degrees, as expected given thepreviously determined size of the AB Aurigae inner-dust disk. However, aclear closure-phase signal of -3.5d +/- 0.5d is detected on one trianglecontaining relatively short baselines, requiring a high degree ofnon-point symmetry from emission at larger (AU-sized) scales in thedisk. We have not identified any alternative explanation for theseclosure-phase results, and we demonstrate that a ``disk hot spot'' modelcan fit our data. We speculate that such detected asymmetricnear-infrared emission might arise as a result of localized viscousheating due to a gravitational instability in the AB Aurigae disk, or tothe presence of a close stellar companion or accreting substellarobject.
| Lithium abundances and rotational behavior for bright giant stars
Aims.We study the links possibly existing between the lithium content ofbright giant stars and their rotational velocity. Methods: .Weperformed a spectral analysis of 145 bright giant stars (luminosityclass II) spanning the spectral range from F3 to K5. All these starshave homogeneous rotational velocity measurements available in theliterature. Results: .For all the stars of the sample, we provideconsistent lithium abundances (A_Li), effective temperatures (T_eff),projected rotational velocity (v sin i), mean metallicity ([Fe/H]),stellar mass, and an indication of the stellar multiplicity. The gradualdecrease in lithium abundance with T_eff is confirmed for bright giantstars, and it points to a dilution factor that is at least assignificant as in giant stars. From the F to K spectral types, the A_Lispans at least three orders of magnitude, reflecting the effects ofstellar mass and evolution on dilution. Conclusions: .We find thatthe behavior of A_Li as a function of v sin i in bright giant starspresents the same trend as is observed in giants and subgiants: starswith high A_Li are moderate or fast rotators, while stars with low A_Lishow a wide range of v sin i values.
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} 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/430/165}
| Near-Infrared Interferometric Measurements of Herbig Ae/Be Stars
We have observed the Herbig Ae/Be sources AB Aur, VV Ser, V1685 Cyg (BD+40°4124), AS 442, and MWC 1080 with the Palomar TestbedInterferometer, obtaining the longest baseline near-IR interferometricobservations of this class of objects. All of the sources are resolvedat 2.2 μm with angular size scales generally <~5 mas, consistentwith the only previous near-IR interferometric measurements of HerbigAe/Be stars, by Millan-Gabet and collaborators. We determine the angularsize scales and orientations predicted by uniform-disk, Gaussian, ring,and accretion disk models. Although it is difficult to distinguishdifferent radial distributions, we are able to place firm constraints onthe inclinations of these models, and our measurements are the firstthat show evidence for significantly inclined morphologies. In addition,the derived angular sizes for the early-type Herbig Be stars in oursample, V1685 Cyg and MWC 1080, agree reasonably well with thosepredicted by the face-on accretion disk models used by Hillenbrand andcollaborators to explain observed spectral energy distributions. Incontrast, our data for the later-type sources AB Aur, VV Ser, and AS 442are somewhat inconsistent with these models and may be explained betterthrough the puffed-up inner disk models of Dullemond and collaborators.
| Sub-Astronomical Unit Structure of the Near-Infrared Emission from AB Aurigae
We present near-infrared, long-baseline, interferometric observations ofAB Aurigae, a well-known Herbig Ae/Be star, obtained with the InfraredOptical Telescope Array. The near-infrared emission from this source hasbeen spatially resolved for the first time, and the observationsindicate a characteristic diameter of 5 mas for the emission,corresponding to 0.7 AU at the distance of AB Aur. The data appear to bemost consistent with models in which the circumstellar material aroundAB Aurigae lies in a flattened structure with a central large hole oroptically thin region of radius about 0.3 AU.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Giants with infrared excess.
We have correlated optical and infrared catalogs in order to extract alarge sample of luminosity class III stars with known infrared fluxdensities. For a non-negligible fraction of G and K giants, afar-infrared excess emission was found, starting beyond 25μm. Anexplanation in terms of present-day mass loss thus becomes unlikely,since the dust should then be warmer and the excess emission less far inthe infrared. We believe that the far-infrared excesses of theseobjects, most likely first-ascent giants, are related to the Vegaphenomenon. The dusty disks around these stars, gradually cooled downduring their main-sequence phase, could be reheated once the star leavesthe main sequence and enters the luminous post-main-sequence phase. Thefairly large sample we constructed enables us to derive an estimationfor the occurrence of excesses. This fraction of G or K giants withfar-infrared excess appears to be distinctly smaller than amongmain-sequence stars. Since the higher radiation field of giants couldlead to a larger evaporation rate of the circumstellar debris, this factdoes not conflict with our hypothesis.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| Narrow-band photometry of late-type stars. II
This paper presents extensive narrow-band photometry in the Uppsalasystem supplementing earlier published mesurements so that data now areavailable for all late-type stars brighter than V = 6.05 and a number ofgalactic cluster members. Numerous UBV and BV measurements are alsopublished. The data are used to determine relations for the predictionof UBV intrinsic colors for late-type stars from the narrow-bandmeasurements. The main purpose of the data is to constitute the basisfor the determination of solar-neighborhood space densities of late-typestars, mainly giants of different kinds; these space densities will becombined with narrow-band data for fainter stars in the north Galacticpole region to yield the decrease of space density with distance fromthe galactic plane for many kinds of late-type stars.
| MK Spectral Types for 185 Bright Stars
Not Available
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Membro dei seguenti gruppi:
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Osservazione e dati astrometrici
| Costellazione: | Auriga |
| Ascensione retta: | 05h04m14.50s |
| Declinazione: | +30°29'41.0" |
| Magnitudine apparente: | 6.14 |
| Distanza: | 178.253 parsec |
| Moto proprio RA: | 10.5 |
| Moto proprio Dec: | -14.7 |
| B-T magnitude: | 7.678 |
| V-T magnitude: | 6.292 |
Cataloghi e designazioni:
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INHABITED SKY
