Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Chromospheric Activity of Southern Stars from the Magellan Planet Search Program
I present chromospheric-activity measurements of ~670 F, G, K, and Mmain-sequence stars in the Southern Hemisphere, from ~8000 archivalhigh-resolution echelle spectra taken at Las Campanas Observatory since2004. These stars were targets from the Old Magellan Planet Search, andare now potential targets for the New Magellan Planet Search that willlook for rocky and habitable planets. Activity indices (S values) arederived from Ca II H and K line cores and then converted to the MountWilson system. From these measurements, chromospheric (logR'HK) indices are derived, which are then used as indicatorsof the level of radial-velocity jitter, age, and rotation periods thesestars present.Based on observations obtained with the Magellan Telescopes, operated bythe Carnegie Institution, Harvard University, University of Michigan,University of Arizona, and the Massachusetts Institute of Technology.
| 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.
| Target selection for the SUNS and DEBRIS surveys for debris discs in the solar neighbourhood
Debris discs - analogous to the asteroid and Kuiper-Edgeworth belts inthe Solar system - have so far mostly been identified and studied inthermal emission shortward of 100?m. The Herschel space observatoryand the Submillimetre Common-User Bolometer Array-2 (SCUBA-2) camera onthe James Clerk Maxwell Telescope will allow efficient photometricsurveying at 70 to 850?m, which allows for the detection of coolerdiscs not yet discovered, and the measurement of disc masses andtemperatures when combined with shorter wavelength photometry. TheSCUBA-2 Unbiased Nearby Stars survey (SUNS) and the Disc Emission via aBias-free Reconnaissance in the Infrared/Submillimetre (DEBRIS) HerschelOpen Time Key Project are complementary legacy surveys observing samplesof ~500 nearby stellar systems. To maximize the legacy value of thesesurveys, great care has gone into the target selection process. Thispaper describes the target selection process and presents the targetlists of these two surveys.
| 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.
| Spectrophotometric properties of pre-main-sequence stars: the ?Chamaeleontis cluster
We present a study of flux-calibrated low-resolution opticalspectroscopy of 10 stars belonging to eight systems in the ~5-Myr-old?Chamaeleontis (?Cha) pre-main-sequence (PMS) starcluster. Using synthetic broad-band colours, narrow-band continuum,atomic and molecular lines derived from the spectra, we compare the?Cha stars to a slightly older PMS cluster, the ~8-Myr-old?Cha cluster and to main-sequence dwarfs. Using synthetic VRIcolours and other indices, we find that the relationship betweenbroad-band colours and spectroscopic temperature indicators for?Cha cluster members is indistinguishable from that of Gyr-olddwarfs. This result is identical to that found earlier in ?Cha.Gravity-sensitive line indices place the cluster between the giant anddwarf sequences, and there is clear evidence that ?Cha starshave lower surface gravity than ?Cha stars. This result isconsistent with ?Cha being the slightly younger PMS association,a few Myr younger according to the Hertzsprung-Russell (HR) diagramplacement of these two clusters and comparison with PMS evolutionarygrids. Late M-type ?Cha cluster members show a B-band fluxexcess of ~0.2mag compared to observations of standard dwarfs, whichmight be related to enhanced magnetic activity. A similar level ofexcess B-band emission appears to be a ubiquitous feature of low-massmembers of young stellar populations with ages less than a few hundredMyr, a very similar time-scale to the PMS phase of elevated relativeX-ray luminosity.
| M dwarfs: effective temperatures, radii and metallicities
We empirically determine effective temperatures and bolometricluminosities for a large sample of nearby M dwarfs, for which highaccuracy optical and infrared photometry is available. We introduce anew technique which exploits the flux ratio in different bands as aproxy of both effective temperature and metallicity. Our temperaturescale for late-type dwarfs extends well below 3000K (almost to the browndwarf limit) and is supported by interferometric angular diametermeasurements above 3000K. Our metallicities are in excellent agreement(usually within 0.2dex) with recent determinations via independenttechniques. A subsample of cool M dwarfs with metallicity estimatesbased on hotter Hipparcos common proper motion companions indicates ourmetallicities are also reliable below 3000K, a temperature rangeunexplored until now. The high quality of our data allows us to identifya striking feature in the bolometric luminosity versus temperatureplane, around the transition from K to M dwarfs. We have compared oursample of stars with theoretical models and conclude that thistransition is due to an increase in the radii of the M dwarfs, a featurewhich is not reproduced by theoretical models.
| 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
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| The component star masses in RW Tri
We use time-resolved spectra of the cataclysmic variable RW Tri in the Iand K bands to determine the orbital velocity of the secondary starusing skew-mapping and cross-correlation techniques respectively. Wefind radial velocity amplitudes of 250 +/- 47 km s-1 in the Iband, and 221 +/- 29 km s-1 in the K band. We also determinethe rotational velocity of the secondary star using the K-band data andfind a Vrot sin i of 120 +/- 20 km s-1. Acombination of these results coupled with an estimate of the effect ofheating on the secondary star suggests a mass ratioM2/M1 in the range 0.6-1.1 the mass ratio rangewith no correction for heating is 0.5-0.8. These lead to most likelyestimates of the primary and secondary star masses in the range 0.4-0.7and 0.3-0.4 Msolar respectively. Further refinement of thestellar masses is hampered by uncertain knowledge of the white dwarforbital velocity, and we discuss evidence that at least some estimatesof the white dwarf velocity are contaminated by non-orbital components.
| 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
| 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.
| The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History
We present high-resolution echelle spectroscopy of 676 nearby M dwarfs.Our measurements include radial velocities, equivalent widths ofimportant chromospheric emission lines, and rotational velocities forrapidly rotating stars. We identify several distinct groups by theirHα properties and investigate variations in chromospheric activityamong early (M0-M2.5) and mid (M3-M6) dwarfs. Using a volume-limitedsample together with a relationship between age and chromosphericactivity, we show that the rate of star formation in the immediate solarneighborhood has been relatively constant over the last 4 Gyr. Inparticular, our results are inconsistent with recent large bursts ofstar formation. We use the correlation between Hα activity and ageas a function of color to set constraints on the properties of L and Tdwarf secondary components in binary systems. We also identify a numberof interesting stars, including rapid rotators, radial velocityvariables, and spectroscopic binaries. Observations were made at the 60inch telescope at Palomar Mountain, which is jointly owned by theCalifornia Institute of Technology and the Carnegie Institution ofWashington.
| Meeting the Cool Neighbors. II. Photometry of Southern NLTT Stars
We present BVRI photometry of 180 bright, southern nearby-starcandidates. The stars were selected from the New Luyten Two-Tenthsproper-motion catalog based on optical/infrared colors, constructed bycombining Luyten's mr estimates with near-infrared photometryfrom the Two Micron All Sky Survey. Photometric parallaxes derived fromV-Ks, V-I, and I-J colors, combined with the limitedavailable astrometry, show that as many as 108 stars may lie within 20pc of the Sun. Of these, 53 are new to nearby-star catalogs, includingthree within 10 pc of the 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
| 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
| 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
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1838R&db_key=AST
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| The low mass Hyades and the evaporation of clusters
The 135 single stars and 85 binary systems, redder than R-I = +0.34 magand brighter than V = 17 mag, between alpha = 3.75 h and 5.0 h and delta= +5 deg and + 25 deg show a luminosity function that differsconsiderably from that of the general field stars within 20 pc of theSun. The ratio of double star components to single cluster membersincreases markedly with decreasing luminosity. Forty-three single starsand 16 binary systems that are members of the Hyades supercluster within20 pc of the Sun show the same luminosity function as the field stars inthat region. Fifty percent of the cluster members and 40 percent of thesupercluster members are components of binary stars. The equivalentwidths of H-alpha appear to support a range of ages (approximately 8 to16 x 108 yr) for the cluster stars and demonstrate that theoldest objects are in the supercluster. A list of cluster members, whichmay include the end of the stable main sequence, but for which accurate(R-I) photometry is not available, is included. The half-dozen knownparallax stars of the faintest luminosity contain at least onesupercluster member, TVLM 868-110639, which is probably beyond thestable, nuclear burning main sequence as a 'transitional' or 'brown'dwarf.
| 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.
| Color distributions in early type galaxies. III - Radial gradients in spectral features
Long-slit spectra covering the wavelength range 5000-9500 A have beenobtained for three Virgo cluster ellipticals. Measurements of featuresin the spectra are presented, and their implications are discussed withparticular reference to (1) anomalous r-i gradients; (2) ionized gas inthe nucleus of NGC 4472; (3) nuclear emission line spectrum of M87; and(4) radial absorption line gradients in NGC 4472 with emphasis on the NaI 8190 A feature.
| 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.
| Photographic astrometry of binary and proper-motion stars. IV
Parallax data are given for 62 binary and proper motion stars based onobservations obtained between May 1987 and March 1988. The datapresented in tabular form include reference positions, identifiers (BDand GC numbers, if any), visual magnitudes, and spectral types. Massratio results for eight binary stars are also presented. Notes areprovided which indicate the inclusion or replacement of previousmeasurements and which reductions have been applied.
| Space motions of low-mass stars.
Radial-velocity measures are presented for 225 stars, most of which aredwarf K and M stars. The data were obtained with the CfA digitalspeedometer, whose uncertainty is less than 1 km/s. Calibrations ofthree earlier radial-velocity studies and comparisons with three othercontemporary ones lead to the evaluation of the standard error for anindividual star as determined in each investigation. The data from twomasks, matching solar type and M type stars, form a ratio that measuresstellar surface temperature quite closely and appear to be useful indetecting the presence of unseen companions. A few previouslyunrecognized binaries have been detected; those with most certaintyinclude stars nos. 366B, 453, and 46A of the McCormick lists of dwarfstars.
| H-alpha photometry of dwarf K and M stars
Attention is given to the distribution of stars in the N-W, R-I planefor the case of 188 dM and dK stars for which H-alpha photometry hasbeen obtained. Most are found to lie along a single 'main sequence' ofabsorption which slopes up towards 0 EW with increasing R-I. Theabsorption EWs are noted to be large by comparison with photosphericmodel predictions, implying either that the models are in error or thatchromospheres are present in virtually all late-type dwarfs, and areresponsible for the H-alpha distribution feature in both absorption andemission.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Hydra |
| Ascensió Recta: | 09h06m45.35s |
| Declinació: | -08°48'24.6" |
| Magnitud Aparent: | 9.559 |
| Distancia: | 14.522 parsecs |
| Moviment propi RA: | -301.2 |
| Moviment propi Dec: | 208 |
| B-T magnitude: | 11.599 |
| V-T magnitude: | 9.728 |
Catàlegs i designacions:
|
