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Posts: 131433
Date:
 Nearest Young Stars Permalink Title: The Sizes of the Nearest Young Stars Authors: Kyle A. McCarthy, Russel J. White We present moderate resolution (R ~ 3575) optical spectra of 19 known or suspected members of the AB Doradus and beta Pictoris Moving Groups, obtained with the DeVeny Spectrograph on the 72-inch Perkins telescope at Lowell Observatory. For 4 of 5 recently proposed members, signatures of youth such as Li\,I 6708 \AA\, absorption and H \alpha emission further strengthen the case for youth and membership. Effective temperatures are determined via line ratio analyses for the 11 F, G and early K stars observed, and via spectral comparisons for the 8 late-K and M stars observed. We assemble updated candidate membership lists for these Moving Groups that account for known binarity. We then use temperature, luminosity, and distance estimates to predict angular diameters for these stars; the motivation is to identify stars that can be spatially resolved with long-baseline optical/infrared interferometers in order to improve age estimates for these Groups and to constrain evolutionary models at young ages. Considering the portion of the sky accessible to northern hemisphere facilities (DEC > -30), 6 stars have diameters large enough to be spatially resolved (\theta > 0.4 mas) with the CHARA Array; this subsample includes the low mass M2.5 member of AB Dor, GJ 393, which is likely to still be pre-main sequence. For southern hemisphere facilities (DEC < +30), 18 stars have diameters larger than this limiting size, including the low mass debris disk star AU Mic (0.72 mas). However, the longest baselines of southern hemisphere interferometers (160-m) are only able to resolve the largest of these, the B6 star \alpha Gru (1.17 mas); proposed long-baseline stations may alleviate the current limitations. Read more (94kb, PDF) __________________

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Posts: 131433
Date:
 O-type stars Permalink Title: On the origin of field O-type starsAuthors: E. Schilbach, S. RoeserAims: We try to identify the origins of field O-stars in the nearest 2 to 3 kpc around the Sun using the best presently available kinematic data on O-stars and on young open clusters. We investigate the question if the present-day data are consistent with the assumption that O-stars have formed in groups (clusters, associations), or in isolation. Methods: We apply the epicycle theory for back-tracing the orbits of O-type stars and of candidate parent open clusters. Results: From the 370 O-stars in the Galactic O star catalogue v 2.0'' (GOSV2) we have investigated 93 stars classified as "field", and found the origin for 73 of them in 48 open clusters younger than 30 Myrs. Only for 32 stars or about 9% of all O-stars from this catalogue, the question of their origin in groups is not solved; some of them may have originated in isolation or may have disintegrated the group in which they formed. Fifty percent of the young open clusters (age < 30 Myr) in the Catalogue of Open Cluster Data'' (COCD) have O-stars as members, or have ejected at least one O-star in the first 10 Myrs of their life, or both. During this period the average mass loss from open clusters by ejecting O-stars is found to be 3 to 5 M_Sun per Myr. We prove that zeta Pup had its origin in the open cluster Trumpler 10 which it left about 2.5 Myrs ago, and that its present-day distance is 300 pc (compared to 440 pc before). The revised distance implies a significant revision of the stellar parameters (a radius of 14 R_Sun, a mass of 22.5 M_Sun, and a luminosity of log L/L_Sun of 5.74) i.e, zeta Pup is closer, less massive, and less luminous than previously thought. Our findings provide independent estimates of the present-day distances and absolute magnitudes of field O-stars. Read more (127kb, PDF) __________________

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Posts: 131433
Date:
 RE: Nearby stars Permalink Title: Astrobiologically Interesting Stars within 10 parsecs of the SunAuthors: G.F. Porto de Mello (1), E.F. del Peloso (1 and 2), L. Ghezzi (2) ((1) Observatorio do Valongo/UFRJ, Rio de Janeiro, Brazil, (2) Observatorio Nacional/MCT, Rio de Janeiro, Brazil)The existence of life based on carbon chemistry and water oceans relies upon planetary properties, chiefly climate stability, and stellar properties, such as mass, age, metallicity and Galactic orbits. The latter can be well constrained with present knowledge. Researchers present a detailed, up-to-date compilation of the atmospheric parameters, chemical composition, multiplicity and degree of chromospheric activity for the astrobiologically interesting solar-type stars within 10 parsecs of the Sun. They determine their state of evolution, masses, ages and space velocities, and produce an optimised list of candidates that merit serious scientific consideration by the future space-based interferometry probes aimed at directly detecting Earth-sized extrasolar planets and seeking spectroscopic infrared biomarkers as evidence of photosynthetic life. The initially selected stars number 33 solar-type within the population of 182 stars (excluding late M-dwarfs) closer than 10 pc. A comprehensive and detailed data compilation for these objects is still essentially lacking: a considerable amount of recent data has so far gone unexplored in this context. The researchers present 13 objects as the nearest "biostars", after eliminating multiple stars, young, chromospherically active, hard X-ray emitting stars, and low metallicity objects. Three of these "biostars", HD 1581, 109358 and 115617, closely reproduce most of the solar properties and are considered as premier targets. They show that approximately 7% of the nearby stars are optimally interesting targets for exobiology. Read More (PDF) __________________

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Posts: 131433
Date:
 Permalink Nearby stars from the LSPM-north Proper Motion Catalogue. I. Main Sequence Dwarfs and Giants Within 33 Parsecs of the SunAuthors: Sebastien LepineComments: 13 pages, accepted for publication in the Astronomical JournalA list of 4,131 dwarfs, sub giants, and giants located, or suspected to be located, within 33 parsecs of the Sun is presented. All the stars are drawn from the new LSPM-north catalogue of 61,976 stars with annual proper motions larger than 0.15 seconds of arc per year . Trigonometric parallax measurements are found in the literature for 1,676 of the stars in the sample; photometric and spectroscopic distance moduli are found for another 783 objects. The remaining 1,672 objects are reported here as nearby star candidates for the first time. Photometric distance moduli are calculated for the new stars based on the (M_V,V-J) relationship, calibrated with the sub sample of stars which have trigonometric parallaxes. The list of new candidates includes 539 stars which are suspected to be within 25 parsecs of the Sun, including 63 stars estimated to be within only 15 parsecs. The current completeness of the census of nearby stars in the northern sky is discussed in light of the new candidates presented here. It is estimated that 32% (18%) of nuclear burning stars within 33 parsecs (25 parsecs) of the Sun remain to be located. The missing systems are expected to have proper motions below the 0.15''/yr limit of the LSPM catalogue. Read More (762kb PDF)Sebastien Lepine is a research fellow in the Astrophysics Department at the American Museum of Natural History. He is a "cartographer of the Galaxy", much of his research efforts are in the search for nearby stars; his goal is to obtain a most complete and accurate map of the stars located within 100 parsecs (300 light-years) of the Sun. His most notable effort is the SUPERBLINK survey, an all-sky survey of stars with large proper motions.LSPM-NORTH catalogue: This catalogue is a comprehensive list of 61,977 stars north of the J2000 celestial equator, which have proper motions larger than 0.15 seconds of arc per year. The catalogue has been generated primarily as a result of a systematic search for high proper motion stars in the Digitized Sky Surveys.Download: (4.1mb)LSPM-SOUTH catalogue: currently in preparation, this catalogue will list stars south of the J2000 celestial equator and with annual proper motions exceeding 0.15 seconds of arc per year.-- Edited by Blobrana at 13:53, 2005-06-10 __________________
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