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Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| Can Life Develop in the Expanded Habitable Zones around Red Giant Stars?
We present some new ideas about the possibility of life developingaround subgiant and red giant stars. Our study concerns the temporalevolution of the habitable zone. The distance between the star and thehabitable zone, as well as its width, increases with time as aconsequence of stellar evolution. The habitable zone moves outward afterthe star leaves the main sequence, sweeping a wider range of distancesfrom the star until the star reaches the tip of the asymptotic giantbranch. Currently there is no clear evidence as to when life actuallyformed on the Earth, but recent isotopic data suggest life existed atleast as early as 7×108 yr after the Earth was formed.Thus, if life could form and evolve over time intervals from5×108 to 109 yr, then there could behabitable planets with life around red giant stars. For a 1Msolar star at the first stages of its post-main-sequenceevolution, the temporal transit of the habitable zone is estimated to beseveral times 109 yr at 2 AU and around 108 yr at9 AU. Under these circumstances life could develop at distances in therange 2-9 AU in the environment of subgiant or giant stars, and in thefar distant future in the environment of our own solar system. After astar completes its first ascent along the red giant branch and the Heflash takes place, there is an additional stable period of quiescent Hecore burning during which there is another opportunity for life todevelop. For a 1 Msolar star there is an additional109 yr with a stable habitable zone in the region from 7 to22 AU. Space astronomy missions, such as proposed for the TerrestrialPlanet Finder (TPF) and Darwin, that focus on searches for signatures oflife on extrasolar planets, should also consider the environments ofsubgiants and red giant stars as potentially interesting sites forunderstanding the development of life. We performed a preliminaryevaluation of the difficulty of interferometric observations of planetsaround red giant stars compared to a main-sequence star environment. Weshow that pathfinder missions for TPF and Darwin, such as Eclipse andFKSI, have sufficient angular resolution and sensitivity to search forhabitable planets around some of the closest evolved stars of thesubgiant and red giant class.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| 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.
| 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
| Statistical studies of visual double and multiple stars. II. A catalogue of nearby wide binary and multiple systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..28...43P&db_key=AST
| BVRI photometry of the Gliese Catalogue stars
Photoelectri BVRI photometry on the Cousins (Kron-Cape) system has beenobtained for many of the southern faint stars in the Gliese Catalog(1969). This extends the work of Cousins (1980) and provides a uniformset of data for the nearby stars. Several red dwarfs are noted, whichwere used to define the red end of the Cousins system.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Predicted infrared brightness of stars within 25 parsecs of the sun
Procedures are given for transforming selected optical data intoinfrared flux densities or irradiances. The results provide R, T(eff)blackbody approximations for about 2000 of the stars in Woolley et al.'sCatalog of Stars (1970) within 25 pc of the sun, and additional whitedwarfs, with infrared flux densities predicted for them at ninewavelengths from 2.2 to 101 microns including the Infrared AstronomySatellite bands.
| DDO Observations of Southern Stars
Not Available
| VRI photometry of nearby stars.
Not Available
| Fundamental data for southern stars (First list)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957MNRAS.117..534E&db_key=AST
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Observation and Astrometry data
| Constellation: | Μικροσκόπιον |
| Right ascension: | 21h27m01.32s |
| Declination: | -44°48'30.9" |
| Apparent magnitude: | 7.477 |
| Distance: | 23.518 parsecs |
| Proper motion RA: | 253.2 |
| Proper motion Dec: | 179.6 |
| B-T magnitude: | 8.606 |
| V-T magnitude: | 7.571 |
Catalogs and designations:
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