Contents
Images
Upload your image
DSS Images Other Images
Related articles
The HARPS search for southern extra-solar planets. XXXI. The M-dwarf sample
Context. Searching for planets around stars with different masses helpsus to assess the outcome of planetary formation for different initialconditions. The low-mass M dwarfs are also the most frequent stars inour Galaxy and potentially therefore, the most frequent planet hosts. Aims: We present observations of 102 southern nearby M dwarfs,using a fraction of our guaranteed time on the ESO/HARPS spectrograph.We observed for 460 h and gathered 1965 precise (~1-3 m/s) radialvelocities (RVs), spanning the period from Feb. 11, 2003 to Apr. 1,2009. Methods: For each star observed, we derive a time seriesand its precision as well as its variability. We apply systematicsearches for long-term trends, periodic signals, and Keplerian orbits(from one to four planets). We analyze the subset of stars with detectedsignals and apply several diagnostics to discriminate whether theobserved Doppler shifts are caused by either stellar surfaceinhomogeneities or the radial pull of orbiting planets. To prepare forthe statistical view of our survey, we also compute the limits onpossible unseen signals, and derive a first estimate of the frequency ofplanets orbiting M dwarfs. Results: We recover the planetarysignals of 9 planets announced by our group (Gl 176 b, Gl 581 b, c, d& e, Gl 674 b, Gl 433 b, Gl 667C b, and Gl 667C c). We presentradial velocities confirming that GJ 849 hosts a Jupiter-mass planet,plus a long-term radial-velocity variation. We also present RVs thatprecise the planetary mass and period of Gl 832b. We detect long-term RVchanges for Gl 367, Gl 680, and Gl 880, which are indicative of yetunknown long-period companions. We identify candidate signals in theradial-velocity time series of 11 other M dwarfs. Spectral diagnosticsand/or photometric observations demonstrate however that these signalsare most probably caused by stellar surface inhomogeneities. Finally, wefind that our survey is sensitive to a few Earth-mass planets forperiods up to several hundred days. We derive a first estimate of theoccurrence of M-dwarf planets as a function of their minimum mass andorbital period. In particular, we find that giant planets (msini = 100 -1000 M⊕) have a low frequency (e.g. f ≲ 1% for P =1 - 10 d and f = 0.02+0.03-0.01 for P = 10 - 100d), whereas super-Earths (msini = 1 - 10 M⊕) are likelyvery abundant (f = 0.36+0.25-0.10 for P = 1 - 10 dand f = 0.52+0.50-0.16 for P = 10 - 100 d). Wealso obtained η⊕ =0.41+0.54-0.13, which is the frequency ofhabitable planets orbiting M dwarfs (1 ≤ msini ≤ 10M⊕). For the first time, η⊕ is adirect measure and not a number extrapolated from the statistics of moremassive and/or shorter-period planets.Based on observations made with the HARPS instrument on the ESO 3.6-mtelescope at La Silla Observatory under programme ID072.C-0488(E).Figures 3, 13-19, Tables 3-9, and Appendix A are availablein electronic form at http://www.aanda.orgRadial velocity dataare only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A109
| The AstraLux Large M-dwarf Multiplicity Survey
We present the results of an extensive high-resolution imaging survey ofM-dwarf multiplicity using the Lucky Imaging technique. The survey madeuse of the AstraLux Norte camera at the Calar Alto 2.2 m telescope andthe AstraLux Sur camera at the ESO New Technology Telescope in order tocover nearly the full sky. In total, 761 stars were observed (701 M-typeand 60 late K-type), among which 182 new and 37 previously knowncompanions were detected in 205 systems. Most of the targets have beenobserved during two or more epochs, and could be confirmed as physicalcompanions through common proper motion, often with orbital motion beingconfirmed in addition. After accounting for various bias effects, wefind a total M-dwarf multiplicity fraction of 27% ± 3% within theAstraLux detection range of 0farcs08-6'' (semimajor axes of ~3-227 AU ata median distance of 30 pc). We examine various statistical multiplicityproperties within the sample, such as the trend of multiplicity fractionwith stellar mass and the semimajor axis distribution. The resultsindicate that M-dwarfs are largely consistent with constituting anintermediate step in a continuous distribution from higher-mass starsdown to brown dwarfs. Along with other observational results in theliterature, this provides further indications that stars and browndwarfs may share a common formation mechanism, rather than beingdistinct populations.Based on observations collected at the European Southern Observatory,Chile, under observing programs 081.C-0314(A), 082.C-0053(A), and084.C-0812(A), and on observations collected at the CentroAstronómico Hispano Alemán (CAHA) at Calar Alto, operatedjointly by the Max-Planck Institute for Astronomy and the Instituto deAstrofísica de Andalucía (CSIC).
| A Catalog of Rotation and Activity in Early-M Stars
We present a catalog of rotation and chromospheric activity in a sampleof 334 M dwarfs of spectral types M0-M4.5 populating the parameter spacearound the boundary to full convection. We obtain high-resolutionoptical spectra for 206 targets and determine projected rotationalvelocity, vsin i, and H? emission. The data are combined withmeasurements of vsin i in field stars of the same spectral type from theliterature. Our sample adds 157 new rotation measurements to theexisting literature and almost doubles the sample of available vsin i.The final sample provides a statistically meaningful picture of rotationand activity at the transition to full convection in the solarneighborhood. We confirm a steep rise in the fraction of active stars atthe transition to full convection known from earlier work. In addition,we see a clear rise in rotational velocity in the same stars. In veryfew stars, no chromospheric activity but a detection of rotationalbroadening is reported. We argue that all of them are probably spuriousdetections; we conclude that in our sample all significantly rotatingstars are active, and all active stars are significantly rotating. Therotation-activity relation is valid in partially and in fully convectivestars. Thus, we do not observe any evidence for a transition from arotationally dominated dynamo in partially convective stars to arotation-independent turbulent dynamo in fully convective stars;turbulent dynamos in fully convective stars of spectral types around M4are still driven by rotation. Finally, we compare projected rotationalvelocities of 33 stars to rotational periods derived from photometry inthe literature and determine inclinations for a few of them.
| Effect of different stellar galactic environments on planetary discs - I. The solar neighbourhood and the birth cloud of the Sun
We have computed trajectories, distances and times of closest approachesto the Sun by stars in the solar neighbourhood with known position,radial velocity and proper motions. For this purpose, we have used afull potential model of the Galaxy that reproduces the local z-force,the Oort constants, the local escape velocity and the rotation curve ofthe Galaxy. From our sample, we constructed initial conditions, withinobservational uncertainties, with a Monte Carlo scheme for the 12 mostsuspicious candidates because of their small tangential motion. We findthat the star Gliese 710 will have the closest approach to the Sun, witha distance of approximately 0.34 pc in 1.36 Myr in the future. We showthat the effect of a flyby with the characteristics of Gliese 710 on a100 au test particle disc representing the Solar system is negligible.However, since there is a lack of 6D data for a large percentage ofstars in the solar neighbourhood, closer approaches may exist. Wecalculate parameters of passing stars that would cause notable effectson the solar disc. Regarding the birth cloud of the Sun, we performedexperiments to reproduce roughly the observed orbital parameters such aseccentricities and inclinations of the Kuiper belt. It is now known thatin Galactic environments, such as stellar formation regions, the stellardensities of new born stars are high enough to produce close encounterswithin 200 au. Moreover, in these Galactic environments, the velocitydispersion is relatively low, typically ?˜ 1-3 kms-1. We find that with a velocity dispersion of ˜1 kms-1 and an approach distance of about 150 au, typical ofthese regions, we obtain approximately the eccentricities andinclinations seen in the current Solar system. Simple analyticalcalculations of stellar encounters effects on the Oort Cloud arepresented.
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Accurate Coordinates and 2MASS Cross Identifications for (Almost) All Gliese Catalog Star
We provide precise J2000, epoch 2000 coordinates, andcross-identifications to sources in the 2MASS Point Source Catalog fornearly all stars in the Gliese, Gliese-Jahreiss, and Woolley catalogs ofnearby stars. The only Gliese objects where we were not successful aretwo Gliese sources that are actually QSOs; two proposed companions tobrighter stars, which we believe do not exist; four stars included inone of the catalogs but identified there as only optical companions; oneprobable plate flaw; and two stars that simply remain unrecovered. Forthe 4251 recovered stars, 2693 have coordinates based on Hipparcospositions, 1549 have coordinates based on 2MASS data, and 9 havepositions from other astrometric sources. All positions have beencalculated at epoch 2000 using proper motions from the literature, whichare also given here.
| UBV(RI)C JHK observations of Hipparcos-selected nearby stars
We present homogeneous, standardized UBV(RI)C photometry forover 700 nearby stars selected on the basis of Hipparcos parallaxes.Additionally, we list JHK photometry for about half of these stars, aswell as L photometry for 86 of the brightest. A number of stars withpeculiar colours or anomalous locations in various colour-magnitudediagrams are discussed.
| 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.
| The effect of activity on stellar temperatures and radii
Context: Recent analyses of low-mass eclipsing binary stars haveunveiled a significant disagreement between the observations andpredictions of stellar structure models. Results show that theoreticalmodels underestimate the radii and overestimate the effectivetemperatures of low-mass stars but yield luminosities that accord withobservations. A hypothesis based upon the effects of stellar activitywas put forward to explain the discrepancies. Aims: In this paper westudy the existence of the same trend in single active stars and providea consistent scenario to explain systematic differences between activeand inactive stars in the H-R diagram reported earlier. Methods: Theanalysis is done using single field stars of spectral types late-K and Mand computing their bolometric magnitudes and temperatures throughinfrared colours and spectral indices. The properties of the stars insamples of active and inactive stars are compared statistically toreveal systematic differences. Results: After accounting for a numberof possible bias effects, active stars are shown to be cooler thaninactive stars of similar luminosity therefore implying a larger radiusas well, in proportions that are in excellent agreement with those foundfrom eclipsing binaries. Conclusions: The present results generalisethe existence of strong radius and temperature dependences on stellaractivity to the entire population of low-mass stars, regardless of theirmembership in close binary systems.Tables 1 and 2 are only 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/478/507
| Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHKphotometry for over 100 M stars selected from an earlier paper on thebasis of apparent photometric constancy. L photometry has been obtainedfor stars brighter than about L = 6. Most of the stars have asubstantial number of UBV(RI)C observations and, it is hoped,will prove useful as red supplementary standards. Additionally, we listJHK photometry for nearly 300 Hipparcos red stars not selected asstandards, as well as L photometry for the brightest stars.
| The Carina-Near Moving Group
We identify a group of ~20 comoving, mostly southern hemisphere, ~200Myr old stars near Earth. Of the stars likely to be members of thisCarina-Near moving group, in either its nucleus (~30 pc from Earth) orits surrounding stream, all but three are plausible members of amultiple star system. The nucleus is (coincidentally) located quiteclose to the nucleus of the AB Doradus moving group notwithstanding thatthe two groups have substantially different ages and Galactic spacemotions, UVW.
| 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.
| Confirmation of Variability of Bidelman-MacConnell Suspected Variables
Precise positions are given for the NSV stars originating from a paperby Bidelman and MacConnell (1973). Variability is confirmed and type andperiod are given for a number of these stars, base on ASAS3 and TASSsurvey data.
| 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
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
| 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.
| The Solar Neighborhood. VI. New Southern Nearby Stars Identified by Optical Spectroscopy
Broadband optical spectra are presented for 34 known and candidatenearby stars in the southern sky. Spectral types are determined using anew method that compares the entire spectrum with spectra of more than100 standard stars. We estimate distances to 13 candidate nearby starsusing our spectra and new or published photometry. Six of these starsare probably within 25 pc, and two are likely to be within the ResearchConsortium on Nearby Stars (RECONS) horizon of 10 pc.
| 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
| Catalogue and bibliography of the UV Cet-type flare stars and related objects in the solar vicinity
This new catalogue of flare stars includes 463 objects. It containsastrometric, spectral and photometric data as well as information on theinfrared, radio and X-ray properties and general stellar parameters.From the total reference list of about 3400 articles, partial listsselected by objects, authors, key words and by any pairs of thesecriteria can be obtained Tables 1, 2 and 3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.
| 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
| 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 general catalogue of trigonometric [stellar] paralaxes
Not Available
| Far infrared properties of late type dwarfs. Infrared fluxes of K & M dwarfs
IRAS fluxes/upper limits are presented for a large sample of K and Mdwarfs. Good agreement is found between the 12 micrometer fluxes andthose derived from the photospheric models of Mould (1976).Relationships between the optical and infrared colors are derived. Theactive dMe/dKe stars appear systematically brighter in the infraredcompared with the less active dM/dK stars, which could be attributed tomore efficient nonradiative heating in their atmosphere. Any systematicdifferences found in our results when compared with those obtained fromprevious studies are attributed to the different analysis packages used.
| The importance of surface inhomogeneities for K and M dwarf chromospheric fluxes
We present published and archived spectroscopic and spectrophotometricdata of H-alpha, Ca II, Mg II, and X-rays for a large sample of K and Mdwarfs. The data set points to the importance that surfaceinhomogeneities have in the flux luminosity diagrams in these late-typedwarfs, irrespective of whether the Balmer lines are in emission orabsorption. Although supporting the fact that cooler stars exhibitincreasing levels of surface activity, evident through an increasingincidence of Balmer emission, surface inhomogeneities, or variations inthe local temperature and density structure, at the chromospheric level,dominate the total Ca II and Mg II fluxes. We show that the flux-fluxand luminosity-luminosity relations indicate differing extents ofinhomogeneity from the chromosphere through to the corona. A goodcorrelation between Ca II and Mg II fluxes indicates that they areformed in overlapping regions of the chromosphere, so that thecontribution of surface inhomogeneities is not evident from thisparticular flux-flux diagram. In the region of the upper chromospherethrough to the transition and corona, the correlation between Ly-alphaand X-ray fluxes indicates regions with similar levels of arealinhomogeneity. This appears to be uncorrelated with that at thechromospheric level.
| Infrared colors of low-mass stars
A total of 322 red dwarf stars are studied in a review of IR IJHKphotometry to discern chromospheric activity and kinematic dataregarding metallicity effects in the IR color:color diagrams. Themetallicity variations are employed to assess changes in the H(-)continuum opacity and water-vapor characterizations. The stars areclassified in terms of metal-richness with five categories includingyoung disk, old disk, and halo types with attention given to the inverserelationship between metallicity and water-band absorption strength. Theresults include IR photometric parallax relations for each metallicitygroup and absolute magnitudes for single stars as well as temperatures,intrinsic colors, and spectral types. The body of data is useful forconstraining models of the interiors and atmospheres of this class ofstars.
| Chromospheric heating in late-type dwarfs - Acoustic or magnetic?
Mg II h and k fluxes for 69 K and 88 M dwarfs have been analyzed. Anempirical lower limit is found in the Mg II flux, extended down to thelatest spectral types. Based on the data presented here it is themagnetic component that dominates the emission from the atmosphere ofcool dwarfs, especially the M dwarfs. It, however, coexists with anacoustically heated component, which can only be identified in the starswith the lowest fluxes in the flux-color diagram, these stars possiblybeing the slowest rotators. Data for the dM(e) stars, i.e., those starswith zero H-alpha, show that these are divided into two classes: (1) aninactive M dwarf star with very weak chromospheric heating, perhaps onlyby acoustic waves; and (2) an intermediate chromospheric activity stardominated by magnetic heating.
| Chromospheric diagnostics in late-type stars
Moderate and low resolution spectroscopic observations of late typedwarfs covering a broad range of activity are presented. The strength ofthe TiO band in 4762 A is used for spectral classification. Calibratedfluxes for the Balmer and the Ca II H and K lines are derived. H-alphaequivalent widths are given for those stars where the line is inabsorption as well as those in emission. It is confirmed that stars withno detectable or very weak H-alpha do exist. It is also shown that starswith very weak or no detectable emission in Ca II H and K also exist,this occurring preferentially in late M dwarfs. Although this can beexplained in terms of reduced nonradiative heating in the chromosphere,the results cannot be conclusive due to the limited resolution of thedata.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Voiles |
| Right ascension: | 09h39m46.37s |
| Declination: | -41°04'03.2" |
| Apparent magnitude: | 10.699 |
| Distance: | 9.493 parsecs |
| Proper motion RA: | -527.8 |
| Proper motion Dec: | 355.4 |
| B-T magnitude: | 12.663 |
| V-T magnitude: | 10.862 |
Catalogs and designations:
|
