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מאמרים קשורים
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.
| Magnetic activity on AB Doradus: temporal evolution of star-spots and differential rotation from 1988 to 1994.
Surface brightness maps for the young K0 dwarf AB Doradus arereconstructed from archival data sets for epochs spanning 1988 to 1994.By using the signal-to-noise enhancement technique of Least-SquaresDeconvolution, our results show a greatly increased resolution of spotfeatures than obtained in previously published surface brightnessreconstructions. These images show that for the exception of epoch1988.96, the starspot distributions are dominated by a long-lived polarcap, and short-lived low to high latitude features. The fragmented polarcap at epoch 1988.96 could indicate a change in the nature of the dynamoin the star. For the first time we measure differential rotation forepochs with sufficient phase coverage (1992.05, 1993.89, 1994.87). Thesemeasurements show variations on a timescale of at least one year, withthe strongest surface differential rotation ever measured for AB Doroccurring in 1994.86. In conjunction with previous investigations, ourresults represent the first long-term analysis of the temporal evolutionof differential rotation on active stars.
| 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.
| 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.
| 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
| Comparisons of images derived from independent Zeeman Doppler imaging codes
We compare surface brightness and magnetic field surface maps for the K0dwarf AB Doradus, obtained using two independently developed ZeemanDoppler imaging codes. We find that even the fine structure in the twosets of images shows excellent agreement. Magnetic field maps appear tobe less sensitive to line-modelling effects than brightness maps. Weargue that these results point to the consistency and reliability ofDoppler imaging techniques even when using poorly sampled data sets,provided that the spectra used are of sufficiently high signal-to-noiseratio.
| Multisite observations of surface structures on AB Doradus in 1994 November
We present time-resolved optical spectroscopy and broad-band photometryof the rapidly rotating southern K0 dwarf star AB Doradus, obtainedduring 1994 November. The data were obtained as part of a collaborationdedicated to MUlti-SIte COntinuous Spectroscopy (MUSICOS), and entailedcoordinated observations on three continents to obtain the fullest phasecoverage possible subject to limitations of local weather conditions.The Doppler images from the three consecutive nights of the run showexcellent mutual agreement, with a dark polar cap and numerousintermediate- and low-latitude features. Simultaneous optical photometryshowed numerous short-duration U-band flares, and two longer durationoptical flares with durations of the order of hours. The latter producedbroad-band continuum enhancements throughout the optical spectrum. Wheresimultaneous spectroscopy was available, both types of flare were seento have counterparts in Hα and the Caii H line. Simultaneoustime-resolved ultraviolet spectroscopy from the Goddard High ResolutionSpectrograph (GHRS) aboard the Hubble Space Telescope, reportedelsewhere, shows that at least one of the short-duration U-band flareswas also observed in Civ with the GHRS. Time-series Hα spectrashowed significant evolution of the circumstellar prominence system overfive consecutive stellar rotations. One prominence underwent a dramaticincrease in distance from the stellar rotation axis. We speculate thatthis event may have been associated with one of the long-durationflares.
| Magnetic cycles of HR 1099 and LQ Hydrae
We present in this paper a 6-yr time series of magnetic (and brightness)surface images of the K1 subgiant of the RS CVn system HR 1099 (=V711Tauri) and of the young K0 dwarf LQ Hydrae, reconstructed (with the helpof a dedicated maximum entropy image reconstruction software) fromZeeman--Doppler imaging observations collected at the Anglo-AustralianTelescope. All the stellar magnetic images that we reconstruct host atleast one high-contrast feature in which the field is predominantlyazimuthal, thus confirming that such surface structures (alreadydetected in previous similar studies) are indeed real. We take this asstrong evidence that dynamo processes of late-type rapid rotatorsoperate throughout the whole stellar convective envelope, rather thanbeing confined to an interface layer between the convective andradiative zones as in the Sun. The latitudinal polarity pattern ofazimuthal and radial fields that we observe at the surface of both starssuggests that these magnetic regions respectively reveal the toroidaland poloidal components of the large-scale dynamo field. The spatialstructure of these two magnetic field components becomes increasinglymore complex (with higher axisymmetric spherical harmonic degrees) forlarger rotation rates and deeper convective zones. The strength of thetoroidal and poloidal components is typically a few hundred G, more thantwo orders of magnitude stronger than in the Sun. Long-term evolution ofthe toroidal and poloidal components of the large-scale field is clearlydetected in our time series. We also report the detection of smallfluctuations in the orbital period of HR 1099, with a peak-to-peakamplitude of about 36+/-1 s (i.e. 0.015 per cent) and a period of about18+/-2 yr (assuming sinusoidal variations around the nominal value). Themost plausible way of explaining such fluctuations is that thequadrupole moment of the K1 subgiant is varying with time, and that thismodulation is driven by the magnetic activity cycle of the primary staritself (through a periodic exchange between kinetic and magnetic energywithin the convective zone). It provides in particular an independentconfirmation that a dynamo operates within the whole convective zone,and suggests that the average azimuthal field in the convective envelopeis of the order of 6 kG.
| Magnetic topology and prominence patterns on AB Doradus
We report new Zeeman--Doppler imaging observations of the rapidlyrotating young K0 dwarf AB Doradus, obtained with the Anglo-AustralianTelescope in 1996 December. From such observations, simultaneousbrightness and magnetic images of the stellar photosphere of AB Dor werereconstructed at three different epochs. The magnetic topology of AB Doris found to be very complex, with at least 12 different radial fieldregions of opposite polarities located all around the star. Significantazimuthal field fluxes are also detected in the form of one negativepolarity region close to the equator, a series of positive polaritypatches at intermediate latitudes and an almost complete ring ofnegative polarity encircling the rotational pole at high latitudes. Inparticular, the azimuthal polarities we reconstruct are in very goodagreement with those obtained by Donati & Cameron, confirming thatthis field component is directly related to the dynamo-generatedlarge-scale toroidal magnetic structure. The triple polarity latitudinalpattern observed for this structure in the upper hemisphere of AB Dorindicates that the degree of the underlying large-scale poloidalstructure in an axisymmetric spherical harmonics expansion is equal toor greater than five. It also strengthens the idea that the dynamoprocesses operating in AB Dor feature a non-solar component distributedthroughout the convective zone. From the subtle distortion of successivebrightness images, we can also confirm the surface differential rotationfirst measured on this star by Donati & Cameron in both sense andmagnitude, with a pole rotating more slowly than the equator by aboutone part in 220. Finally, the rotation periods we measure for fourprominences (from the recurrence rate of their spectral signatures inBalmer lines) confirm the presumption that such clouds are anchored atintermediate to high latitudes. The intrinsic variability of theseprominences is not associated with any abrupt changes in thephotospheric brightness or magnetic distributions, implying that theyessentially result from the reorganization of coronal field lines.
| Stellar Tomography
I review recent progress in the field of stellar surface imaging, withparticular reference to advanced methods for mapping surface-brightnessinhomogeneities and the surface vector magnetic field on magneticallyactive late-type stars. New signal enhancement techniques, utilisingprofile information from hundreds or thousands of photospheric linessimultaneously, allow images to be derived for stars several magnitudesfainter than was previously possible. For brighter stars, the sametechniques make it possible to map features as small as two or threedegrees in extent on the stellar surface. This opens up whole new areasof research, such as the ability to use starspot tracking to studysurface differential rotation patterns on single and binary stars, andto follow the secular evolution of the magnetic field itself.
| Differential rotation and magnetic polarity patterns on AB Doradus
In this paper, we present the first magnetic images of the rapidlyrotating young K0 dwarf AB Doradus. Simultaneous brightness images arealso reconstructed. These images are obtained from two independent datasets recorded four to six nights (eight to twelve rotation cycles)apart, with the UCL Echelle Spectrograph of the Anglo-AustralianTelescope in 1995 December. All images are recovered from sets of`average profiles' obtained through a least-squares deconvolutionprocess of about 1500 lines throughout the whole visible spectrum. Wefind that about 20 per cent of the surface of AB Dor is covered with asignificant (>200G) field, whose flux within these magnetic regionsis typically 500 G, with peaks up to 1.5 kG. The associated magneticfield topology is essentially radial (in 1995 December) and features analternating east-west polarity structure at intermediate to highlatitudes, comprising up to 12 regions of opposite polarities. Wesuspect that this pattern represents the emergence of buoyant flux tubesfrom an underlying toroidal field structure. The toroidal field itselfis also detected at the photospheric level, and switches from positivepolarity at intermediate latitudes to negative polarity in circumpolarregions. Altogether, it suggests that the associated dynamo is probablynot purely solar-like (i.e. confined to an overshoot layer at the baseof the convective zone), but must also feature a significant componentdistributed throughout the whole convective envelope. From the evolutionof brightness maps throughout eight rotations, we infer that the pole ofAB Dor rotates more slowly than the equator, by about one part in 220.The corresponding `lap time' required for the equatorial region to lapthe pole is thus of the order of 110d, very close to the solar value of120d. Along with the information that the photometric period has been insteady decrease since 1988, our result implies that cool features havemoved equatorward on average on AB Dor. Repeated observations of theH?-absorbing circumstellar prominence system indicate rotationperiods for individual prominences that are significantly longer thanthose obtained for the mid-latitude magnetic features. We infer that ifthe prominences corotate with the footpoints of the magnetic structuresin which they form, they must be anchored at latitudes greater than 60deg.
| 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 Evolution of Surface Structures on Ab-Doradus
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995MNRAS.277.1145U&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.
| New limits on starspot lifetimes for AB Doradus
I present a set of maximum entropy reconstructions of the starspotdistribution on the surface of the rapidly rotating K0 dwarf AB Doradus,obtained on the night of 1992 December 14. The Doppler imaging code usedin the reconstructions has been modified to incorporate a newdata-weighting scheme that allows us to reconstruct stellar surfaceimages from the profiles of several photospheric lines observedsimultaneously. Comparison of the 1992 December image with thepreviously published images of the star in 1992 January shows verylittle change in the low- to intermediate-latitude spot configurationover the intervening eleven months. This is consistent with earlierreports of the long-term stability of the rotational phases oflight-curve minima and maxima on this star. The structure in thehigh-latitude `polar crown' is not so repeatable, and it appears that anew spot emerged between 1992 January and December. It is not yet clearwhether the short-term variations in the star's light-curve morphologymay be linked to either high-latitude rotational shear or rapidevolution of the high-latitude magnetic structures.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| Doppler Images of Ab-Doradus in 1992JAN
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..814C&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.
| Catalogue of Variable or Suspected Stars Nearby the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&AS...85..971P&db_key=AST
| UBV (RI)c photometry of faint nearby stars.
Not Available
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Relations between spectral types, absolute magnitudes, and colour indices of red dwarfs in the Cousins photometric system
Abstract image available at:http://adsabs.harvard.edu/abs/1984A&A...132..385T
| Predicted infrared brightness of stars within 25 parsecs of the sun
Procedures are given for transforming selected optical data intoinfrared flux densities or irradiances. The results provide R, T(eff)blackbody approximations for about 2000 of the stars in Woolley et al.'sCatalog of Stars (1970) within 25 pc of the sun, and additional whitedwarfs, with infrared flux densities predicted for them at ninewavelengths from 2.2 to 101 microns including the Infrared AstronomySatellite bands.
| Luminosity and motion of large proper-motion stars. I - Stars with annual proper motion larger than 1 arcsec
The luminosities and motions of stars brighter than visual magnitude 15and annual proper motion greater than one arcsec given in a catalogpublished by the author (1979) are discussed on the basis of the (RI)photometry available for these objects. Pending subsequent discussionsof data contained in two additional catalogs, it is concluded that thefirst catalog contains 100 subdwarfs extending to an infrared magnitudeof +11.5 mag. If these are halo objects, the number density-luminosityfunction has a steeper slope than the general luminosity function,indicating that the mass density may be greater than normallyrecognized. The luminosity law for the old disk stars in this catalogclosely conforms to the slope of the general luminosity function fromvisual magnitude +4.5 to +13; however, there is an excess of stars oflower luminosity.
| Nearest stars.
Not Available
| Variabilite D'etoiles Naines Rouges
Not Available
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| קבוצת-כוכבים: | מפרש |
| התרוממות ימנית: | 09h44m29.83s |
| סירוב: | -45°46'35.4" |
| גודל גלוי: | 10.223 |
| מרחק: | 9.816 פארסק |
| תנועה נכונה: | -464.2 |
| תנועה נכונה: | -582.1 |
| B-T magnitude: | 11.936 |
| V-T magnitude: | 10.365 |
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