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Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| Photometric Observations of R Coronae Borealis in the Optical and Infrared
The results of long-term photometric observations of R CrB in the UBVJHKLM bands are presented. The temporal and color characteristics of theemission of the star itself and of its extended dust envelope areanalyzed in detail. No stable harmonic has been found in the semiregularvariations of the optical brightness of R CrB. Two harmonics withperiods P≈3.3 and 11.3 yrs have been detected in the brightnessvariations of the dust envelope; the minima of these variationscoincided in 1999, resulting in a record decrease in the LM brightnessof the envelope. This by chance coincided in time with a deep minimum ofthe visual brightness of the star, resulting in a unique decrease in thetotal brightness of the star and dust envelope. This enabled estimationof the bolometric flux of the hot dust clouds, which made up only a fewper cent of the bolometric flux of the dust envelope. The brightnessvariations of the dust envelope are not accompanied by appreciable colorchanges and are associated with variations of its optical depth τ(V)in the range 0.2 0.4. The dust envelope forms at a large and fairlyconstant distance from the star , from material in its stellar wind,whose intensity obeys a Reimers law. No variations synchronous withthose of the optical depth of the dust envelope, in particular, with theperiod P≈3.3 yrs, have been found in the optical emission of R CrB,suggesting that the stellar wind is not spherically symmetric. The dustenvelope consists of small grains (a gr≤0.01 µm), while theclouds screening the star from the observer are made up of large grains(a gr≈0.1 µm). The activity of R CrB, whose nature is unclear,is reflected in variations of the stellar-wind intensity and theappearance of dust clouds in the line of sight: these variations arerepeated by corresponding changes in the optical depth of the dustenvelope with a delay of 4 years (the time for a particle moving atV env≈45 km/s to move from the star to the boundary of the dustenvelope).
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| Determination of the temperatures of selected ISO flux calibration stars using the Infrared Flux Method
Effective temperatures for 420 stars with spectral types between A0 andK3, and luminosity classes between II and V, selected for a fluxcalibration of the Infrared Space Observatory, ISO, have been determinedusing the Infrared Flux Method (IRFM). The determinations are based onnarrow and wide band photometric data obtained for this purpose, andtake into account previously published narrow-band measures oftemperature. Regression coefficients are given for relations between thedetermined temperatures and the photometric parameters (B2-V1), (b-y)and (B-V), corrected for interstellar extinction through use ofHipparcos parallaxes. A correction for the effect of metallicity on thedetermination of integrated flux is proposed. The importance of aknowledge of metallicity in the representation of derived temperaturesfor Class V, IV and III stars by empirical functions is discussed andformulae given. An estimate is given for the probable error of eachtemperature determination. Based on data from the ESA HipparcosAstrometry Satellite.
| The Pulsational Nature of R-Coronae - Light and Radial Velocity Variations during 1990 and 1991
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993MNRAS.265..899F&db_key=AST
| Photometric Observations of R CrB Following the 1983 Minimum
Not Available
| What is the pulsation period of R Coronae Borealis?
A Fourier analysis of recently published photometry of R CoronaeBorealis (R CrB) indicates that the star may be multiperiodic.Photometry obtained during 1986-89 is best represented by a coherent51.8-d periodicity. In addition, there is evidence that the strongamplitude modulation of the light curve during this time is due to theinteraction between this periodicity and a 56.2-d periodicity. However,during 1985 and 1990, the light curve indicates the presence of anapproximately 44-d periodicity. There is no evidence for a coherentapproximately 44-d periodicity being present during 1986-89. Randomphase changes of a 44-d periodicity could account for the appearance ofthe light curve during 1986-89, but such phase changes would have to befrequent and substantial. The interaction between the periodic nature ofthe star and the onset of declines is also examined. A claim that thetime of onset of declines of R CrB can be linked to any one of threepossible periodicities is not supported by this analysis.
| R Coronae Borealis and Delta Coronae Borealis in 1990
UBV photometry of R CrB and Delta CrB has been obtained through the APTService on 71 nights in 1990. R CrB proved to be near-maximum-lightduring this time and showed its usual single period of 44.6 +/-0.6 days.Delta CrB, a chromospherically active star that was essentially constantin 1989, showed renewed variability in 1990 with an amplitude of about0.04 mag in V and a period of 60.8 +/-1.7 days, similar to its behaviortwo years earlier.
| Delta Coronae Borealis in 1987
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989PASP..101..175F&db_key=AST
| Pulsational periodicities in R Coronae Borealis
Photoelectric photometry of R CrB during the years 1985, 1986, and 1987is reported. Analysis of the data near maximum light indicates only oneperiod of pulsation: 43.8 + or - 0.1 days. Five clearly defined epochsof maximum light during these years can all be fit by this period,implying that phase coherence is maintained through depp fadings andthrough times when the pulsation becomes undetectable. Severe amplitudemodulation but not frequency modulation appears to be present. Whilesingle-mode pulsation was also present in 1971, more than one period waspresent in 1972. Periods of 26.8, 44.4, and 73.7 days are found in thatyear. Evidence suggests the third of these is an alias of the first two.It is likely that the 44-day period is the fundamental and the 27-day isthe first harmonic of radial pulsation.
| UBV Photometry of R Coronae Borealis
Not Available
| On the Photometric Features of R CrB Dust Envelope
Not Available
| R Coronae Borealis in 1985
Photoelectric photometry of R CrB during 1985 is presented and discussedbriefly. The low-amplitude pulsation is well defined, and the beginningsof a deep minimum were recorded in detail. The (U-B)/(B-V) behavior ofthe star during this early decline was consistent with similar data forthe star during the emergence from an earlier deep minimum and is notmuch different from the law of interstellar reddening.
| Photoelectric Observations of R CrB during the Recent Light Minimum
Not Available
| R Coronae Borealis
IAUC 4199 available at Central Bureau for Astronomical Telegrams.IAUC 4199 available at Central Bureau for Astronomical Telegrams.
| Not Available
Not Available
| Photoelectric Observations of R CrB
Not Available
| Photoelectric Observations of R CrB
Not Available
| A Photometric Study of Selected R Coronae Borealis Variables.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...172..383F&db_key=AST
| MK classifications for F and G-type stars. I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..916H&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Corona Boreale |
| Ascensione retta: | 15h47m40.76s |
| Declinazione: | +28°28'10.0" |
| Magnitudine apparente: | 7.436 |
| Distanza: | 92.507 parsec |
| Moto proprio RA: | -53.9 |
| Moto proprio Dec: | 50.2 |
| B-T magnitude: | 7.974 |
| V-T magnitude: | 7.481 |
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