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Near-infrared speckle interferometry and radiative transfer modelling of the carbon star LP Andromedae
We present the near-infrared speckle interferometry for LPAnd in the H and K' bands with diffraction-limited resolutionsof 56 and 72 mas, new JHKLM photometry, and the results of our radiativetransfer modelling of this carbon star. The reconstructed visibilityreveals a spherically-symmetric envelope surrounding the central star.To determine the physical parameters of the latter and the properties ofits dusty envelope, we performed extensive radiative transfercalculations. The well-defined spectral energy distribution ofLP And in the entire range from the near-IR tomillimeter wavelengths (including the absorption feature visible in thestellar continuum at 3 μm and the shapes of the dust emission bandsat 11 and 27 μm), together with our H-band visibility can bereproduced by a spherical dust envelope with parameters that are verysimilar to those of CW Leo (IRC +10216), the best studied carbon star. For the newly estimatedpulsation period P = 617 ± 6 days and distance D = 740 ±100 pc, our model of LP And changes its luminosityLstar between 16 200 and 2900 Lȯ, itseffective temperature Tstar between 3550 and 2100 K, and itsradius Rstar between 340 and 410 Rȯ. Themodel estimates the star's mass-loss rate dot{M} ≈ 1.9 ×10-5 Mȯ yr- 1, assuming a constantoutflow velocity v = 14 km s-1. If the latter also applied tothe innermost parts of the dusty envelope, then presently the star wouldbe losing mass at a rate dot{M} ≈ 6.0 × 10-5Mȯ yr-1. However, we believe that the innerwind velocity must actually be closer to v ≈ 4 km s-1instead, as wind acceleration is expected in the dust-formation zone.The dusty envelope of LP And extends fromR1 ≈ 2 Rstar to distances of R2 ≈3 pc from the star. The total mass of the envelope lost by the centralstar is M = 3.2 Mȯ assuming a dust-to-gas mass ratio ofρ_d/ρ = 0.0039. The circumstellar optical depth towards the staris τV = 25 in the visual. The dust model contains smallsilicon carbide grains, inhomogeneous grains made of a mixture of SiCand incompletely amorphous carbon, and thin mantles made ofiron-magnesium sulfides. This dust mixture perfectly fits the infraredcontinuum and both the 11.3 μm and 27 μm emission bands. We findthat our K'-band visibility could not be fitted by our spherical model,so we discuss possible reasons for this interesting result. Moreobservations are required in order to determine what causes this effect.If slight deviations from spherical geometry in its envelope are thereason, then the object's evolutionary stage would be even more similarto that of CW Leo. It appears that LPAnd is a highly-evolved intermediate-mass star (initial massM^0star ≈ 4 Mȯ) at the end of its AGBphase.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 174: HD 14914, HR 2599, and HD 221422
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| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| BVRI photometry of spectroscopic binaries
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| 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.
| Mesures de vitesses radiales. VII. Accompagnement AU sol DU programme d'observation DU satellite Hipparcos. Radial velocities. VII. Ground based measurements for Hipparcos.
We publish 734 radial velocities of stars distributed in 28 fields of4x4deg. We continue the PPO series (Fehrenbach et al. 1987; Duflot etal. 1990 and 1992), using the Fehrenbach objective prism method.
| Spectroscopic binary orbits from photoelectric radial velocities. A synopsis of papers 1-100
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| Spectroscopic binaries - 15th complementary catalog
Published observational data on the orbital characteristics of 436spectroscopic binaries, covering the period 1982-1986, are compiled intables. The data sources and the organization of the catalog are brieflydiscussed, and notes are provided for each item.
| A spectroscopic orbit for HR 152
HR 152, one of the four reference stars used to standardizeradial-velocity observations made at Cambridge, has been shown bymeasurements made with the Dominion Astrophysical Observatoryradial-velocity spectrometer to be a spectroscopic binary. The effectsof its variabilty are traceable in the residuals of manyspectroscopic-binary orbits based on Cambridge data. The orbit has aperiod of 576 days and a semiamplitude of 0.69 + or - 0.08 km/s; this isthe first plausible orbit to be published with a semiamplitude smallerthan 1 km/s.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 57: HD 222018
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