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Exoplanet Atmospheres
At the dawn of the first discovery of exoplanets orbiting Sun-like starsin the mid-1990s, few believed that observations of exoplanetatmospheres would ever be possible. After the 2002 Hubble SpaceTelescope detection of a transiting exoplanet atmosphere, many skepticsdiscounted it as a one-object, one-method success. Nevertheless, thefield is now firmly established, with over two dozen exoplanetatmospheres observed today. Hot Jupiters are the type of exoplanetcurrently most amenable to study. Highlights include: detection ofmolecular spectral features, observation of day-night temperaturegradients, and constraints on vertical atmospheric structure.Atmospheres of giant planets far from their host stars are also beingstudied with direct imaging. The ultimate exoplanet goal is to answerthe enigmatic and ancient question, “Are we alone?” viadetection of atmospheric biosignatures. Two exciting prospects are theimmediate focus on transiting super Earths orbiting in the habitablezone of M-dwarfs, and ultimately the spaceborne direct imaging of trueEarth analogs.
| Lucky Imaging survey for southern M dwarf binaries
Context. While M dwarfs are the most abundant stars in the Milky Way,there is still large uncertainty about their basic physical properties(mass, luminosity, radius, etc.) as well as their formation environment.Precise knowledge of multiplicity characteristics and how they change inthis transitional mass region, between Sun-like stars on the one sideand very low mass stars and brown dwarfs on the other, provideconstraints on low mass star and brown dwarf formation. Aims: Inthe largest M dwarf binary survey to date, we search for companions toactive, and thus preferentially young, M dwarfs in the solarneighbourhood. We study their binary/multiple properties, such as themultiplicity frequency and distributions of mass-ratio and separation,and identify short period visual binaries, for which orbital parametersand hence dynamical mass estimates can be derived in the near future. Methods: The observations are carried out in the SDSS i' and z'band using the Lucky Imaging camera AstraLux Sur at the ESO 3.5 m NewTechnology Telescope. Lucky Imaging is a very efficient way of observinga large sample of stars at an angular resolution close to thediffraction limit. Results: In the first part of the survey, weobserved 124 M dwarfs of integrated spectral types M 0-M 6 andidentified 34 new and 17 previously known companions to 44 stars. Wederived relative astrometry and component photometry for these binaryand multiple systems. More than half of the binaries have separationssmaller than 1” and would have been missed in a simplyseeing-limited survey. Correcting our sample for selection effectsyields a multiplicity fraction of 32±6% for 108 M dwarfs within52 pc and with angular separations of 0.1”-6.0”,corresponding to projected separations of 3-180 AU at median distance 30pc. Compared to early-type M dwarfs (M ? 0.3 M&sun;),later-type (and hence lower mass) M dwarf binaries appear to have closerseparations, and more similar masses.Based on observations made with ESO Telescopes at La Silla or ParanalObservatories under programme ID 082.C-0053.Tables 1 and 2 are onlyavailable in electronic form at http://www.aanda.org
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| Common Proper Motion Companions to Nearby Stars: Ages and Evolution
A set of 41 nearby stars (closer than 25 pc) is investigated which havevery wide binary and common proper motion (CPM) companions at projectedseparations between 1000 and 200,000 AU. These companions are identifiedby astrometric positions and proper motions from the NOMAD catalog.Based mainly on measures of chromospheric and X-ray activity, ageestimation is obtained for most of 85 identified companions.Color-absolute magnitude diagrams are constructed to test whether CPMcompanions are physically related to the primary nearby stars and havethe same age. Our carefully selected sample includes three remote whitedwarf companions to main-sequence stars and two systems (55 Cnc and GJ777A) of multiple planets and distant stellar companions. Ten new CPMcompanions, including three of extreme separations, are found. Multiplehierarchical systems are abundant; more than 25% of CPM components arespectroscopic or astrometric binaries or multiples themselves. Two newastrometric binaries are discovered among nearby CPM companions, GJ 264and HIP 59000, and preliminary orbital solutions are presented. TheHyades kinematic group (or stream) is presented broadly in the sample,but we find few possible thick-disk objects and no halo stars. Itfollows from our investigation that moderately young (age<~1 Gyr)thin-disk dwarfs are the dominating species in the near CPM systems, ingeneral agreement with the premises of the dynamical survival paradigm.
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| Search for associations containing young stars (SACY). I. Sample and searching method
We report results from a high-resolution optical spectroscopic surveyaimed to search for nearby young associations and young stars amongoptical counterparts of ROSAT All-Sky Survey X-ray sources in theSouthern Hemisphere. We selected 1953 late-type (B-V~≥~0.6),potentially young, optical counterparts out of a total of 9574 1RXSsources for follow-up observations. At least one high-resolutionspectrum was obtained for each of 1511 targets. This paper is the firstin a series presenting the results of the SACY survey. Here we describeour sample and our observations. We describe a convergence method in the(UVW) velocity space to find associations. As an example, we discuss thevalidity of this method in the framework of the β Pic Association.
| Identification of New M Dwarfs in the Solar Neighborhood
We present the results from a spectroscopic study of 1080 nearby activeM dwarfs, selected by correlating the Two Micron All Sky Survey andROSAT catalogs. We have derived the spectral types and estimateddistances for all of our stars. The spectral types range between K5 andM6. Nearly half of our stars lie within 50 pc. We have measured theequivalent width of the Hα emission line. Our targets show anincrease in chromospheric activity from early to midspectral types, witha peak in activity around M5. Using the count rate and hardness ratiosobtained from the ROSAT catalog, we have derived the X-ray luminosities.Our stars display a ``saturation-type'' relation between thechromospheric and coronal activity. The relation is such thatlogLX/Lbol remains ``saturated'' at a value ofapproximately -3 for varying Hα equivalent width. We have found568 matches in the USNO-B catalog and have derived the tangentialvelocities for these stars. There is a slight trend of decreasingchromospheric activity with age, such that the stars with highervtan have lower Hα equivalent widths. The coronalemission, however, remains saturated at a value oflogLX/Lbol~-3 for varying tangential velocities,suggesting that the coronal activity remains saturated with age. We donot find any break in the saturation-type relation at the spectral typeat which stars become fully convective (~M3.5). Most of the stars in oursample show more coronal emission than the dMe stars in the Hyades andPraesepe and have vtan<40 km s-1, suggesting ayoung population.
| New Hipparcos-based Parallaxes for 424 Faint Stars
We present a catalog of 424 common proper-motion companions to Hipparcosstars with good (>3 σ) parallaxes, thereby effectively providingnew parallaxes for these companions. Compared with typical stars in theHipparcos catalog, these stars are substantially dimmer. The catalogincludes 20 white dwarfs and an additional 29 stars withMV>14, the great majority of the latter being M dwarfs.
| 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.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Speckle Interferometry at the US Naval Observatory. VIII.
The results of 2044 speckle interferometric observations of doublestars, made with the 26 inch (66 cm) refractor of the US NavalObservatory, are presented. Each speckle interferometric observation ofa system represents a combination of over a thousand short-exposureimages. These observations are averaged into 1399 mean positions andrange in separation from 0.16" to 14.97", with a mean separation of2.51". This is the eighth in a series of papers presenting measuresobtained with this system and covers the period 2001 March 18 through2001 December 30.
| Meeting the Cool Neighbors. I. Nearby Stars in the NLTT Catalogue: Defining the Sample
We are currently undertaking a program aimed at identifying previouslyunrecognized late-type dwarfs within 20 pc of the Sun. As a first step,we have cross-referenced Luyten's NLTT proper-motion catalog against thesecond incremental release of the Two Micron All Sky Survey (2MASS)Point Source Catalog and use optical/infrared colors, derived bycombining Luyten's mr estimates with 2MASS data, to identifycandidate nearby stars. This paper describes the definition of areference sample of 1245 stars and presents a compilation of literaturedata for more than one-third of the sample. Only 274 stars havetrigonometric parallax measurements, but we have used data for nearbystars with well-determined trigonometric parallaxes to computecolor-magnitude relations in the (MV, V-K), (MV,V-I), and (MI, I-J) planes and use those relations todetermine photometric parallaxes for NLTT stars with optical photometry.Based on the 2MASS JHKs data alone, we have identified afurther 42 ultracool dwarfs (J-Ks>0.99) and useJ-Ks colors to estimate photometric parallaxes. Combiningthese various techniques, we identify 308 stars with formal distances ofless than 20 pc, while a further 46 have distance estimates within 1σ of our survey limit. Of these 354 stars, 75, including 39 of theultracool dwarfs, are new to nearby-star catalogs. Two stars with bothoptical and near-infrared photometry are potential additions to theimmediate solar neighborhood, with formal distance estimates of lessthan 10 pc.
| Kinematics of Hipparcos Visual Binaries. II. Stars with Ground-Based Orbital Solutions
This paper continues kinematical investigations of the Hipparcos visualbinaries with known orbits. A sample, consisting of 804 binary systemswith orbital elements determined from ground-based observations, isselected. The mean relative error of their parallaxes is about 12% andthe mean relative error of proper motions is about 4%. However, even 41%of the sample stars lack radial velocity measurements. The computedGalactic velocity components and other kinematical parameters are usedto divide the stars with known radial velocities into kinematical agegroups. The majority (92%) of binaries from the sample are thin diskstars, 7.6% have thick disk kinematics and only two binaries have halokinematics. Among them, the long-period variable Mira Ceti has a verydiscordant {Hipparcos} and ground-based parallax values. From the wholesample, 60 stars are ascribed to the thick disk and halo population.There is an urgent need to increase the number of the identified halobinaries with known orbits and substantially improve the situation withradial velocity data for stars with known orbits.
| Hipparcos astrometry for 257 stars using Tycho-2 data
We present improved Hipparcos astrometry for 257 Hipparcos stars,resolved into 342 components. For 64 of the stars no astrometry wasobtained in the Hipparcos Catalogue, while for the remaining starsadditional components have been added by this solution or the positionshave been revised considerably. We have used the published Hipparcostransit data for the new solutions, together with results from thesecond reduction of the Tycho data for defining better initial values.Based on observations made with the ESA Hipparcos astrometry satellite.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Mass determination of astrometric binaries with Hipparcos. II. Selection of candidates and results
In a previous paper (\cite{Mar97}) we have shown that for double starswith orbital periods smaller than about 25 years, it was possible todetermine from the Hipparcos data, the mass ratio B of the components orthe difference between the mass and intensity ratios, beta -B, providedthe orbital elements of the relative orbit are available. From anextensive literature search we have selected 145 potential systems, ofwhich 46 yielded eventually a satisfactory solution. For eight systemswith the largest separations, the peculiarities of the natural directionassociated to the Hipparcos observations, the 'hippacentre', have beenfully exploited to derive the mass ratio of the components without anyadditional assumption. For the remaining 38, the derivation of the massratio was possible only by taking the magnitude difference between thetwo components from other sources. The parallax determinedsimultaneously, is then used to produce the individual masses of thecomponents. The astrophysical relevance of the results is discussed andwhen possible (17 systems) the masses are compared to ground-basedvalues.
| Distribution and Corrlation of Age, Abundance, and Motion of Lower Main Sequence Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..466E&db_key=AST
| ICCD Speckle Observations of Binary Stars. XII. Measurements During 1984-1986 From the Perkins 1.8 M Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..393A&db_key=AST
| Pre-Main-Sequence Stars in the Pleiades Supercluster
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1749E&db_key=AST
| VRI photometry of late dwarf common proper motion pairs
VRI photometry and photometric distance moduli are presented for 266late dwarf common proper motion pairs. From the distance modulusdifferences between the components of each pair, it is inferred that atleast 56 percent of the pairs contain one or more additional stellarcomponents. The maximum separation of M dwarf binaries appears to be ofthe order 10,000-20,000 AU.
| H-alpha photometry of dwarf K and M stars - Chromospheric activity
H-alpha photometry of 118 K and M dwarfs are presented, with H-alphaequivalent width measures accurate to about 0.05 A. The data arecombined with the spectroscopic surveys of Stauffer and Hartmann (1986)and Fleming et al. (1988) to study the main features of thechromospheric activity versus mass relation for low-mass stars. An upperbound to the H-alpha equivalent width is found to be a function of themass relation (R-I). H-alpha luminosities and surface fluxes arecalculated for active stars, showing that both quantities generallydecline with R-I. The upper bound to the fraction of a star's bolometricluminosity, however, is independent of R-I. The results suggest that thechromospheres of most dMe stars with R-I less than 1.1 are in anactivity-saturated state. Also, H-alpha variability, probably due toflares, is detected in several stars.
| Micrometer observations of double stars and new pairs. XIII
From a program of double star observations which emphasizes orbital,neglected, and newly discovered pairs, results obtained from October1984 to January 1987 are presented. A total of 3030 visual and 550photographic measures are listed. The positions in WDS format andDurchmusterung numbers are shown for 117 pairs for which firstobservations appear in this paper. Magnitudes are estimated for some ofthe objects.
| Photographic Astrometry of Binary and Proper-Motion Stars - Part Two
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986AJ.....92..446H&db_key=AST
| Orbits of 20 visual binaries
Micrometer observations of 20 visual binaries, obtained at CTIO andSwarthmore during 1985, are reported and used to recompute the orbitalelements and ephemerides. Masses are determined whenever thedynamical-parallax precepts of Heintz (1978) are applicable. The dataand results are presented in tables and briefly characterized.
| Dwarf K and M stars of high proper motion found in a hemispheric survey
A recently completed visual/red spectral region objective-prism surveyof more than half the sky found some 2200 dwarf K and M stars ofnegligible proper motion (Stephenson, 1986). The present paper adds the1800-odd spectroscopically identified dwarfs that did prove to havesignificant proper motions. About half of these had previous spectralclassifications of some sort, especially by Vyssotsky (1952, 1956). Forthe great majority, the present coordinates are more accurate thanprevious data. The paper includes about 50 stars with unpublishedparallaxes, likely to have parallaxes of 0.05 arcsec or more. Combiningthe present data with the first paper suggests that the number oflow-proper-motion stars in that paper was not unreasonable.
| 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.
| Parallaxes and proper motions. X.
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80..711U
| Luminosities and temperatures of M dwarf stars from infrared photometry
Bolometric magnitudes for a large number of M type dwarf stars, obtainedby broadband infrared photometry at 1.65, 2.2, and 3.5 microns, arereviewed. The data obtained indicate that one parameter is sufficient todescribe the blanketing in all of the UBVRI bands for all types of Mdwarfs. In general, late M dwarfs seem to have lower effectivetemperatures than are predicted by theoretical models.
| Parallaxes of 21 stars determined from plates taken with the MC Cormick 26-inch refractor.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73...47L&db_key=AST
| Catalogue de 240 couples visuels d'étoiles naines rouges
Not Available
| Measures of 278 double stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..403W&db_key=AST
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