Contents
Images
Upload your image
DSS Images Other Images
Related articles
Observation and modelling of main-sequence star chromospheres - XVIII. Observations of the Ca II resonance lines and H? line for dM4 stars and dK5 stars
We use 665 high-resolution spectra for 60 different dM4 stars and 1088high-resolution spectra for 97 different dK5 stars from the EuropeanSouthern Observatory (ESO) and Observatoire de Haute Provence (OHP) databases. We present 179 new measurements of the Ca II resonance lines and615 new measurements of the H? line for dM4 stars. We also present701 new measurements of the Ca II resonance lines and 1088 newmeasurements of the H? line for dK5 stars. We also compiled othermeasurements available in the literature.We cross-correlate the activity diagnostics, namely the Ca II resonanceline characteristics, the H? line characteristics andLX. We set new constraints on some empirical relationshipsbetween these parameters that are important for constraining thechromospheric modelling of these stars.We study the Ca II line mean equivalent width (EW) as a function ofabsolute magnitude (Mv) for three spectral types: dK5, dM1and dM4. We show that the magnetic activity level is rather constantwith Mv for both dM4 and dK5 stars in contrast to dM1 starsfor which the magnetic activity level increases with diminishingMv. In other words, only dM1 stars show this particulardependence of the level of magnetic activity with Mv.From the correlations of the magnetic activity indices with P/sin i, wefind that the Ca II EW and LX grow increasingly faster as thespectral type increases from dK5, dM1 to dM4. The exponents in the CaII-P/sin i correlations are -0.80, -1.53 and -3.72 for dK5 stars, dM1stars and dM4 stars, respectively.We also find that the X-ray luminosity grows faster than thechromospheric Ca II emission when the rotation rate increases. Moreover,we found that the exponent on P/sin i for both the Ca II andLX correlations is about twice smaller for dK5 stars than fordM1 stars. Therefore, the level of magnetic activity in dK5 and dM4stars is more dependent on rotation than on the stellar radius, theopposite result to that found for dM1 stars.
| Observation and modelling of main-sequence star chromospheres - XVI. Rotation of dK5 stars
Using two different spectrographs, High Accuracy Radial velocity PlanetSearch (HARPS) (European Southern Observatory) and SOPHIE (Observatoirede Haute Provence), we have measured v sin i for a sample of dK5 stars.These are the first measurements of v sin i for most of the starsstudied here.We measured v sin i to an accuracy of 0.3 km s-1 and adetection limit of about 0.5-1 km s-1. All our targets havesimilar (R - I)c colour. This is an advantage and facilitatesthe determination of the narrowest line profiles for v sin i ˜ 0.In our total sample, we detected rotation for 22 stars (three dK5e and19 dK5 stars), and we did not detect rotation in a further 22 stars.This result shows that there are many dK5 slow rotators, and many morethan for dM1 stars. We also report on a newly discovered dK5e star, McC522, which is also the fastest rotator in our sample.We determine radii and effective temperatures for all our target stars.The effective temperatures were derived using the (R - I)ccolour and empirical far-red colour-effective temperature correlations,and the radii were derived from the standard formulae relatingMbol, bolometric correction and Teff.We find that the distribution of P/sin i (the projected rotation period)is rather homogeneous, i.e. the distribution of the 22 detected stars asa function of P/sin i is approximately flat and does not show anymaximum, unlike for dM1 stars, a close spectral type. We find that thedistribution in v sin i is bimodal, as in dM1 stars, with fast dK5erotators and slower dK5 rotators. Based on observations available atObservatoire de Haute Provence and the European Southern Observatorydata bases and on Hipparcos parallax measurements.
| 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.
| 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.
| 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
| New neighbours. V. 35 DENIS late-M dwarfs between 10 and 30 parsecs
This paper reports updated results on our systematic mining of the DENISdatabase for nearby very cool M-dwarfs (M 6V-M 8V, 2.0 <= I-J <=3.0, photometric distance within 30 pc), initiated by Phan-Bao et al.(\cite{phan-bao}, hereafter Paper I). We use M dwarfs with well measuredparallaxes (HIP, GCTP, ...) to calibrate the DENIS (MI, I-J)colour-luminosity relationship. The resulting distance error for singledwarfs is about 25%. Proper motions, as well as B and R magnitudes, weremeasured on archive Schmidt plates for those stars in the DENIS databasethat meet the photometric selection criteria. We then eliminate thegiants by a Reduced Proper Motion cutoff, which is significantly moreselective than a simple proper motion cutoff. It greatly reduces theselection bias against low tangential velocity stars, and results in anearly complete sample. Here we present new data for 62 red dwarfcandidates selected over 5700 square degrees in the DENIS database. 26of those originate in the 2100 square degrees analysed in Paper I, withimproved parameters here, and 36 were found in 3600 additional squaredegrees. 25 of those are new nearby dwarfs. We determine from thatsample of 62 stars a stellar density for 12.0 <= MI <=14.0 of /lineΦ{Icor}=(2.2 +/- 0.4)x 10-3 starspc-3 mag-1. This value is consistent withphotometric luminosity functions measured from deeper and smaller-fieldobservations, but not with the nearby star luminosity function. Inaddition we cross-identified the NLTT and DENIS catalogues to find 15similar stars, in parts of the sky not yet covered by thecolour-selected search. We present distance and luminosity estimates forthese 15 stars, 10 of which are newly recognized nearby dwarfs. Asimilar search in Paper I produced 4 red dwarf candidates, and we havethus up to now identified a total of 35 new nearby late-M dwarfs.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| 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.
| Standard stars: CCD photometry, transformations and comparisons
We discuss variations of the atmospheric extinction coefficients andtransformation equations to the standard UBVRI system based onobservations of standard stars during 1996-97 at Siding SpringObservatory using a thinned SITe CCD and coloured glass filters. In thetransformation from the initial natural system to the Landolt version ofthe standard system, a large nonlinear term related to the Balmerdiscontinuity was required for the U transformation. We then modifiedthe U filter, and the subsequent transformation to the SAAO version ofthe standard UBVRI system had only small nonlinear correction terms forU, B, and I. The correction terms relating to U and B are evidently dueto the Balmer discontinuity, while that relating to I seems to be due tothe Paschen discontinuity at a wavelegth of approximately 8200 Å.We also compared the results with Landolt's observations, and confirmedthe difference between the two sets of standard stars (SAAO andLandolt).
| Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
| 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
| New proper motion determination of Luyten catalogue stars (LTT) south of declination -40deg and right ascension between 16h and 24h.
Data are given for 285 LTT stars found in 23 areas, covering 25 squaredegrees each, south of declination -40deg and right ascension between16h and 24h. Four stars present differences in proper motion >=0.10arcsec, eleven present differences in position angle >20deg and onepresents those differences in both values.
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| 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
| 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.
| New light on faint stars. I - The luminosity function in the solar neighbourhood
From photoelectric photometry of red dwarf stars identified in anobjective prism survey, a magnitude-limited complete sample has beendefined. Applying photometric parallaxes, calibrated for theKron-Cousins system by observations of trigonometric parallax stars,this sample is used to determine the space densities of stars withabsolute magnitudes between + 7 and + 12. The resultant luminosityfunction is consistent with the Luyten and Wielen functions for thesolar neighbourhood. An analysis of the stellar kinematics shows littlesignificant evidence of a substantial local population of low spacemotion M-dwarfs.
| Erratum - Errors or Omissions in Star-Identifications in the General Catalogue of Trigonometric Stellar Parallaxes
Not Available
| Photometry of Southern Hemisphere red dwarf stars
Results are presented for a photometric investigation of aspectroscopically selected sample of red dwarf stars in the SouthernHemisphere. Absolute magnitudes and distances for the stars areestimated from broadband red colors. Three stars which may besubluminous are identified, as are several stars which may be within 25pc. The tangential velocity and velocity dispersion of the sample aresimilar to values found in other studies of nearby late-type stars.
| The space density and kinematics of dwarf M stars
The results of an objective-prism survey for dwarf stars, K7 and later,are presented. One hundred twenty-one red sensitive plates covering 1720sq. degrees of the southern sky were obtained with the Curtis Schmidttelescope at C.T.I.O. The resulting luminosity function rises from log N+ 10 = 7.9 at MV = 8 to about 8.7 at MV = 11 and12. About 75% of the dwarfs in this survey are identified with BPMstars, but inserting the proper motions given into the equations of themethod of mean absolute magnitudes yields values of MB aboutthree magnitudes brighter than the spectral types would indicate. Thatthe method of mean absolute magnitudes appears to be calibrated on starsof higher than average proper motion lends credence to the luminosityfunction result. A galactic mass density is found for the dwarfsconsidered.
| UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Τηλεσκόπιον |
| Right ascension: | 19h12m25.26s |
| Declination: | -55°52'07.6" |
| Apparent magnitude: | 11.242 |
| Distance: | 19.984 parsecs |
| Proper motion RA: | -272.1 |
| Proper motion Dec: | -168.3 |
| B-T magnitude: | 13.644 |
| V-T magnitude: | 11.441 |
Catalogs and designations:
|
