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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.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
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Observation and Astrometry data
| Constellation: | Andromeda |
| Right ascension: | 23h32m31.05s |
| Declination: | +43°12'23.5" |
| Apparent magnitude: | 7.831 |
| Distance: | 207.039 parsecs |
| Proper motion RA: | -32.7 |
| Proper motion Dec: | -16.4 |
| B-T magnitude: | 9.101 |
| V-T magnitude: | 7.936 |
Catalogs and designations:
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INHABITED SKY
