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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.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Optical images of MCLD123.5+24.9: a cloud illuminated by the North star?
We present B R I images of a 1degr {x}1degr field centered on themolecular cloud (MCLD123.5+24.9) located in the large infrared cirrusknown as the Polaris Flare. The optical images are compared with IRASimages and an extinction map derived from stellar reddenings. We analysethe possibility for the North star (HD8890), only 1degr North of thefield, to be the source of MCLD123.5+24.9 optical emission. For widelyaccepted values of the dust albedo (omega = 0.6) and the assymetryparameter of the Henyey Greenstein phase function (0.7
| Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
| The reddening of Polaris
The B-V color excess of Polaris is obtained by using uvby-betaphotometry of 11 field stars within 0.75 deg of arc of Polaris anddereddening the field stars with the various color calibrations of theStromgren system. An apparent distance of 109 pc is estimated forPolaris, and a color excess of E(B-V) equals 0.02 + or - 0.02 is found.This result is taken as supporting the claims that Polaris is unreddenedor at worst very slightly reddened and therefore lies on the red edge ofthe Cepheid instability strip, as is expected for a small-amplitudeCepheid.
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Osservazione e dati astrometrici
| Costellazione: | Cefeo |
| Ascensione retta: | 05h14m00.70s |
| Declinazione: | +88°13'19.4" |
| Magnitudine apparente: | 8.591 |
| Distanza: | 253.165 parsec |
| Moto proprio RA: | -13.7 |
| Moto proprio Dec: | 7.1 |
| B-T magnitude: | 9.036 |
| V-T magnitude: | 8.628 |
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