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Characterization of the hot Neptune GJ 436 b with Spitzer and ground-based observations
We present Spitzer Space Telescope infrared photometry of a secondaryeclipse of the hot Neptune GJ 436 b. The observations were obtainedusing the 8-μm band of the InfraRed Array Camera (IRAC). The dataspanning the predicted time of secondary eclipse show a clear fluxdecrement with the expected shape and duration. The observed eclipsedepth of 0.58 mmag allows us to estimate a blackbody brightnesstemperature of Tp = 717 ± 35 K at 8 μm. We comparethis infrared flux measurement to a model of the planetary thermalemission, and show that this model reproduces properly the observed fluxdecrement. The timing of the secondary eclipse confirms the non-zeroorbital eccentricity of the planet, while also increasing its precision(e = 0.14 ± 0.01). Additional new spectroscopic and photometricobservations allow us to estimate the rotational period of the star andto assess the potential presence of another planet.Our final secondary eclipse, photometric and Ca II H+K index time seriesare available 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/475/1125
| A New Planet around an M Dwarf: Revealing a Correlation between Exoplanets and Stellar Mass
We report precise Doppler measurements of GJ 317 (M3.5 V) that revealthe presence of a planet with a minimum mass MPsini=1.2MJup in an eccentric, 692.9 day orbit. GJ 317 is only thethird M dwarf with a Doppler-detected Jovian planet. The residuals to asingle-Keplerian fit show evidence of a possible second orbitalcompanion. The inclusion of a second Jupiter-mass planet (P~2700 days,MPsini=0.83 MJup) decreasessqrt(χ2ν) from 2.02 to 1.23, and reducesthe rms from 12.5 to 6.32 m s-1. A false-alarm test yields a1.1% probability that the curvature in the residuals of thesingle-planet fit is due to random fluctuations, lending additionalcredibility to the two-planet model. However, our data only marginallyconstrain a two-planet fit, and further monitoring is necessary to fullycharacterize the properties of the second companion. To study the effectof stellar mass on giant planet occurrence, we measure the fraction ofstars with planets in three mass bins comprised of our samples of MDwarfs, solar-mass stars, and intermediate-mass subgiants. We find apositive correlation between stellar mass and the occurrence rate ofJovian planets within 2.5 AU. Low-mass K and M stars have a 1.8%+/-1.0%planet occurrence rate compared to 4.2%+/-0.7% for solar-mass stars and8.9%+/-2.9% for the higher mass subgiants. This result indicates thatthe former F- and A-type stars with M*>=1.3Msolar in our sample are nearly 5 times more likely than theM dwarfs to harbor a giant planet. Our analysis shows that thecorrelation between Jovian planet occurrence and stellar mass existseven after correcting for the effects of stellar metallicity.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| The HARPS search for southern extra-solar planets. X. A m sin i = 11 M_⊕ planet around the nearby spotted M dwarf GJ 674
Context: How planet properties depend on stellar mass is a keydiagnostic of planetary formation mechanisms. Aims: This motivatesplanet searches around stars that are significantly more massive or lessmassive than the Sun, and in particular our radial velocity search forplanets around very low-mass stars. Methods: As part of that program,we obtained measurements of GJ 674, an M 2.5 dwarf atd = 4.5 pc. These measurements have dispersion much in excess of theirinternal errors. An intensive observing campaign demonstrates that theexcess dispersion is due to two superimposed coherent signals, withperiods of 4.69 and 35 days. Results: These data are described well bya 2-planet Keplerian model where each planet has a ~11 M_⊕ minimummass. A careful analysis of the (low-level) magnetic activity ofGJ 674, however, demonstrates that the 35-day periodcoincides with the stellar rotation period. This signal thereforeoriginates in a spot inhomogeneity modulated by stellar rotation. The4.69-day signal, on the other hand, is caused by a bona-fide planet,GJ 674b. Conclusions: Its detection adds to thegrowing number of Neptune-mass planets around M-dwarfs and reinforcesthe emerging conclusion that this mass domain is much more populatedthan the Jovian mass range. We discuss the metallicity distributions ofM dwarf with and without planets and find a low 11% probability thatthey are drawn from the same parent distribution. Moreover, we findtentative evidence that the host star metallicity correlates with thetotal mass of their planetary system.Based on observations made with the HARPS instrument on the ESO 3.6 mtelescope under the GTO program ID 072.C-0488 at Cerro La Silla (Chile).Radial-velocity, photometric and Ca II H+K index time series are onlyavailable in electronic format the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strabg.fr/cgi-bin/qcat?J/A+A/474/293
| Far-Infrared Properties of M Dwarfs
We report the mid- and far-infrared properties of nearby M dwarfs.Spitzer MIPS measurements were obtained for a sample of 62 stars at 24μm, with subsamples of 41 and 20 stars observed at 70 and 160 μm,respectively. We compare the results with current models of M starphotospheres and look for indications of circumstellar dust in the formof significant deviations of K-[24 μm] colors and 70 μm/24 μmflux ratios from the average M star values. At 24 μm, all 62 of thetargets were detected; 70 μm detections were achieved for 20 targetsin the subsample observed, and no detections were seen in the 160 μmsubsample. No clear far-infrared excesses were detected in our sample.The average far-infrared excess relative to the photospheric emission ofthe M stars is at least 4 times smaller than the similar average for asample of solar-type stars. However, this limit allows the averagefractional infrared luminosity in the M-star sample to be similar tothat for more massive stars. We have also set low limits(10-4 to 10-9 M⊕ depending onlocation) for the maximum mass of dust possible around our stars.
| Multiepoch Radial Velocity Observations of L Dwarfs
We report on the development of a technique for precise radial velocitymeasurements of cool stars and brown dwarfs in the near infrared. Ourtechnique is analogous to the iodine (I2) absorption cellmethod that has proven so successful in the optical regime. We rely ontelluric CH4 absorption features to serve as a wavelengthreference, relative to which we measure Doppler shifts of the CO andH2O features in the spectra of our targets. We apply thistechnique to high-resolution (R~50,000) spectra near 2.3 μm of nine Ldwarfs taken with the Phoenix instrument on Gemini South and demonstratea typical precision of 300 m s-1. We conduct simulations toestimate our expected precision and show that our performance iscurrently limited by the signal-to-noise ratio (S/N) of our data. Wepresent estimates of the rotational velocities and systemic velocitiesof our targets. With our current data we are sensitive to companionswith Msini>2 MJ in orbits with periods less than 3 days.We identify no companions in our current data set. Future observationswith improved S/N should result in radial velocity precision of 100 ms-1 for L dwarfs.
| The HARPS search for southern extra-solar planets. XI. Super-Earths (5 and 8 M{⊕}) in a 3-planet system
This Letter reports on the detection of two super-Earth planets in theGl 581 system, which is already known to harbour ahot Neptune. One of the planets has a mass of 5 M⊕ andresides at the “warm” edge of the habitable zone of thestar. It is thus the known exoplanet that most resembles our own Earth.The other planet has a 7.7 M⊕ mass and orbits at 0.25AU from the star, close to the “cold” edge of the habitablezone. These two new light planets around an M3 dwarf further confirm theformerly tentative statistical trend toward (i) many more very low-massplanets being found around M dwarfs than around solar-type stars and(ii) low-mass planets outnumbering Jovian planets around M dwarfs.Based on observations made with the HARPS instrument on the ESO 3.6 mtelescope at La Silla Observatory under the GTO programme ID 072.C-0488.Table of radial velocities is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/469/L43
| Moderate-Resolution Spitzer Infrared Spectrograph Observations of M, L, and T Dwarfs
We present 10-19 μm moderate-resolution spectra of 10 M dwarfs, one Ldwarf, and two T dwarf systems obtained with the Infrared Spectrograph(IRS) on board the Spitzer Space Telescope. The IRS allows us to examinemolecular spectroscopic features/lines at moderate spectral resolutionin a heretofore untapped wavelength regime. TheseR=λ/Δλ~600 spectra allow for a more detailedexamination of clouds and nonequilibrium chemistry, as well as themolecular features of H2O, NH3, and other tracemolecular species that are the hallmarks of these objects. A cloud-freemodel best fits our mid-infrared spectrum of the T1 dwarf ɛ IndiBa, and we find that the NH3 feature in ɛ Indi Bb isbest explained by a nonequilibrium abundance due to vertical transportin its atmosphere. We examined a set of objects (mostly M dwarfs) inmultiple systems to look for evidence of emission features, which mightindicate an atmospheric temperature inversion, as well as tracemolecular species; however, we found no evidence of either.
| A Spitzer Infrared Spectrograph Spectral Sequence of M, L, and T Dwarfs
We present a low-resolution (R≡λ/Δλ~90),5.5-38 μm spectral sequence of a sample of M, L, and T dwarfsobtained with the Infrared Spectrograph (IRS) on board the Spitzer SpaceTelescope. The spectra exhibit prominent absorption bands ofH2O at 6.27 μm, CH4 at 7.65 μm, andNH3 at 10.5 μm and are relatively featureless atλ>~15 μm. Three spectral indices that measure the strengthsof these bands are presented; H2O absorption features arepresent throughout the MLT sequence, while the CH4 andNH3 bands first appear at roughly the L/T transition.Although the spectra are, in general, qualitatively well matched bysynthetic spectra that include the formation of spatially homogeneoussilicate and iron condensate clouds, the spectra of the mid-type Ldwarfs show an unexpected flattening from roughly 9 to 11 μm. Wehypothesize that this may be a result of a population of small silicategrains that are not predicted in the cloud models. The spectrum of thepeculiar T6 dwarf 2MASS J0937+2931 is suppressed from 5.5 to 7.5 μmrelative to typical T6 dwarfs and may be a consequence of its mildlymetal-poor/high surface gravity atmosphere. Finally, we computebolometric luminosities of a subsample of the M, L, and T dwarfs bycombining the IRS spectra with previously published 0.6-4.1 μmspectra and find good agreement with the values of Golimowski et al.,who use L'- and M'-band photometry to account forthe flux emitted at λ>2.5 μm.
| 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.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| NEXXUS: A comprehensive ROSAT survey of coronal X-ray emission among nearby solar-like stars
We present a final summary of all ROSAT X-ray observations of nearbystars. All available ROSAT observations with the ROSAT PSPC, HRI and WFChave been matched with the CNS4 catalog of nearby stars and the resultsgathered in the Nearby X-ray and XUV-emitting Stars data base, availablevia www from the Home Page of the Hamburger Sternwarte at the URLhttp://www.hs.uni-hamburg.de/DE/For/Gal/Xgroup/nexxus. Newvolume-limited samples of F/G-stars (dlim = 14 pc), K-stars(dlim = 12 pc), and M-stars (dlim = 6 pc) areconstructed within which detection rates of more than 90% are obtained;only one star (GJ 1002) remains undetected in a pointed follow-upobservation. F/G-stars, K-stars and M-stars have indistinguishablesurface X-ray flux distributions, and the lower envelope of the observeddistribution at FX ≈ 104 erg/cm2/sis the X-ray flux level observed in solar coronal holes. Large amplitudevariations in X-ray flux are uncommon for solar-like stars, but maybemore common for stars near the bottom of the main sequence; a largeamplitude flare is reported for the M star LHS 288. Long term X-raylight curves are presented for α Cen A/B and Gl 86, showingvariations on time scales of weeks and demonstrating that α Cen Bis a flare star.Tables 1-3 are also available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/651
| Target Selection for SETI. II. Tycho-2 Dwarfs, Old Open Clusters, and the Nearest 100 Stars
We present the full target list and prioritization algorithm developedfor use by the microwave search for technological signals at the SETIInstitute. We have included the Catalog of Nearby Habitable StellarSystems (HabCat, described in Paper I), all of the nearest 100 stars and14 old open clusters. This is further augmented by a subset of theTycho-2 catalog based on reduced proper motions, and this larger catalogshould routinely provide at least three target stars within the largeprimary field of view of the Allen Telescope Array. The algorithm forprioritizing objects in the full target list includes scoring based onthe subset category of each target (i.e., HabCat, cluster, Tycho-2, ornearest 100), its distance (if known), and its proximity to the Sun onthe color-magnitude diagram.
| 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
| The radii and spectra of the nearest stars
We discuss direct measurements of the radii of 36 stars located closerthan 25 parsecs to the Sun. We present the data on 307 radii and 326spectral types and luminosity classes for the nearest stars locatedinside the sphere with a radius of 10 parsecs.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| Stellar encounters with the solar system
We continue our search, based on Hipparcos data, for stars which haveencountered or will encounter the solar system(García-Sánchez et al. \cite{Garcia}). Hipparcos parallaxand proper motion data are combined with ground-based radial velocitymeasurements to obtain the trajectories of stars relative to the solarsystem. We have integrated all trajectories using three different modelsof the galactic potential: a local potential model, a global potentialmodel, and a perturbative potential model. The agreement between themodels is generally very good. The time period over which our search forclose passages is valid is about +/-10 Myr. Based on the Hipparcos data,we find a frequency of stellar encounters within one parsec of the Sunof 2.3 +/- 0.2 per Myr. However, we also find that the Hipparcos data isobservationally incomplete. By comparing the Hipparcos observations withthe stellar luminosity function for star systems within 50 pc of theSun, we estimate that only about one-fifth of the stars or star systemswere detected by Hipparcos. Correcting for this incompleteness, weobtain a value of 11.7 +/- 1.3 stellar encounters per Myr within one pcof the Sun. We examine the ability of two future missions, FAME andGAIA, to extend the search for past and future stellar encounters withthe Sun.
| 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
| Nearby Microlensing Events: Identification of the Candidates for theSpace Interferometry Mission
The Space Interferometry Mission (SIM) is the instrument of choice whenit comes to observing astrometric microlensing events where nearby,usually high proper motion, stars (``lenses'') pass in front of moredistant stars (``sources''). Each such encounter produces a deflectionin the source's apparent position that, when observed by SIM, can leadto a precise mass determination of the nearby lens star. We search forlens-source encounters during the 2005-2015 period using Hipparcos, ACT,and NLTT to select lenses, and USNO-A2.0 to search for the correspondingsources, and rank these by the SIM time required for a 1% massmeasurement. For Hipparcos and ACT lenses, the lens distance andlens-source impact parameter are precisely determined so that the eventsare well characterized. We present 32 candidates beginning with a 61 CygA event in 2012 that requires only a few minutes of SIM time. ProximaCentauri and Barnard's star each generate several events. For NLTTlenses, the distance is known only to a factor of 3, and the impactparameter only to 1''. Together, these produce uncertaintiesof a factor ~10 in the amount of SIM time required. We present a list of146 NLTT candidates and show how single-epoch CCD photometry of thecandidates could reduce the uncertainty in SIM time to a factor of ~1.5.
| The ROSAT all-sky survey catalogue of the nearby stars
We present X-ray data for all entries of the Third Catalogue of NearbyStars \cite[(Gliese & Jahreiss 1991)]{gli91} that have been detectedas X-ray sources in the ROSAT all-sky survey. The catalogue contains1252 entries yielding an average detection rate of 32.9 percent. Inaddition to count rates, source detection parameters, hardness ratios,and X-ray fluxes we also list X-ray luminosities derived from Hipparcosparallaxes. Catalogue also available at CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Stellar Encounters with the Oort Cloud Based on HIPPARCOS Data
We have combined Hipparcos proper-motion and parallax data for nearbystars with ground-based radial velocity measurements to find stars thatmay have passed (or will pass) close enough to the Sun to perturb theOort cloud. Close stellar encounters could deflect large numbers ofcomets into the inner solar system, which would increase the impacthazard at Earth. We find that the rate of close approaches by starsystems (single or multiple stars) within a distance D (in parsecs) fromthe Sun is given by N= 3.5D^2.12 Myr^-1, less than the number predictedby a simple stellar dynamics model. However, this value is clearly alower limit because of observational incompleteness in the Hipparcosdata set. One star, Gliese 710, is estimated to have a closest approachof less than 0.4 pc 1.4 Myr in the future, and several stars come within1 pc during a +/-10 Myr interval. We have performed dynamicalsimulations that show that none of the passing stars perturb the Oortcloud sufficiently to create a substantial increase in the long-periodcomet flux at Earth's orbit.
| Astrometric positions of stars with high proper motions in the Southern Hemisphere
Several stars with large proper motions, cited by W.J. Luyten, wereincluded in the preliminary programme for the HIPPARCOS mission. Whenperforming preparatory measurements of plates, difficulties wereencountered in identifying certain of these stars when relying only onpublished coordinates. We have taken advantage of this work whichrelates to the southern sky in order to determine the astrometricposition of the greatest possible number of these objects, even forthose which were not included in the programme. Catalogue 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/Abstract.html
| A search for companions to nearby southern M dwarfs with near-infrared speckle interferometry.
We searched the 9 M-dwarf primaries nearer than 5pc and south ofdeclination δ=-30^o^ for companions with separations 1-10AU andfound none. Taken together with the 25 northern primaries studied byHenry and McCarthy (1990ApJ...350..334H) the fraction of binaries andtriples within the now complete sample of all M dwarfs within 5pc is9/34=26+/-9%, and the average number of companions per system is0.32+/-0.10. This is lower by 2σ than the observed multiplicityfraction of 43+/-5%, and companions per system of 0.49+/-0.05 in thesample of nearby solar-type main sequence stars. It is also much lowerthan the extrapolated binary fraction among young stars in Taurus. Wediscuss the implications of this finding.
| The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&db_key=AST
| The Cousins VRI System: A Consistency Test of Equatorial and Southern Standard Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....111.1338T
| 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
| Correlations of Coronal X-Ray Emission with Activity, Mass, and Age of the Nearby K and M Dwarfs
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...450..401F&db_key=AST
| The X-Ray View of the Low-Mass Stars in the Solar Neighborhood
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...450..392S&db_key=AST
| A volume-limited ROSAT survey of extreme ultraviolet emission from all nondegenerate stars within 10 parsecs
We report the results of a volume-limited ROSAT Wide Field Camera (WFC)survey of all nondegenerate stars within 10 pc. Of the 220 known starsystems within 10 pc, we find that 41 are positive detections in atleast one of the two WFC filter bandpasses (S1 and S2), while weconsider another 14 to be marginal detections. We compute X-rayluminosities for the WFC detections using Einstein Imaging ProportionalCounter (IPC) data, and these IPC luminosities are discussed along withthe WFC luminosities throughout the paper for purposes of comparison.Extreme ultraviolet (EUV) luminosity functions are computed for singlestars of different spectral types using both S1 and S2 luminosities, andthese luminosity functions are compared with X-ray luminosity functionsderived by previous authors using IPC data. We also analyze the S1 andS2 luminosity functions of the binary stars within 10 pc. We find thatmost stars in binary systems do not emit EUV radiation at levelsdifferent from those of single stars, but there may be a fewEUV-luminous multiple-star systems which emit excess EUV radiation dueto some effect of binarity. In general, the ratio of X-ray luminosity toEUV luminosity increases with increasing coronal emission, suggestingthat coronally active stars have higher coronal temperatures. We findthat our S1, S2, and IPC luminosities are well correlated withrotational velocity, and we compare activity-rotation relationsdetermined using these different luminosities. Late M stars are found tobe significantly less luminous in the EUV than other late-type stars.The most natural explanation for this results is the concept of coronalsaturation -- the idea that late-type stars can emit only a limitedfraction of their total luminosity in X-ray and EUV radiation, whichmeans stars with very low bolometric luminosities must have relativelylow X-ray and EUV luminosities as well. The maximum level of coronalemission from stars with earlier spectral types is studied also. Tounderstand the saturation levels for these stars, we have compiled alarge number of IPC luminosities for stars with a wide variety ofspectral types and luminosity classes. We show quantitatively that ifthe Sun were completely covered with X-ray-emitting coronal loops, itwould be near the saturation limit implied by this compilation,supporting the idea that stars near upper limits in coronal activity arecompletely covered with active regions.
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| Csillagkép: | Oltár |
| Rektaszcenzió: | 17h28m39.95s |
| Deklináció: | -46°53'42.7" |
| Vizuális fényesség: | 9.472 |
| Távolság: | 4.537 parszek |
| RA sajátmozgás: | 573.7 |
| Dec sajátmozgás: | -878.1 |
| B-T magnitude: | 11.381 |
| V-T magnitude: | 9.63 |
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