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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.
| BVRJK Photometry and a Spectroscopic Study of the Algol Short-Period Binary VV Ursae Majoris
We present the first light curves in the infrared J and K filters of VVUMa and analyze them, together with a new set of BVR light curvesobtained in different runs from 1997 to 2000. Based on the spectra of VVUMa and standard stars in the region 8440-8870 Å, we classify theprimary component of the binary as a type A1.5-2 V star. Evidence ofperiodic small-amplitude variations in the brightness of the system isfound and is more clear during the secondary eclipse orbital phases. Aperiodicity of about 0.51 hr is in good agreement with a previousfinding based on Strömgren photometry, pointing to a real origin inthe system, presumably on low-amplitude pulsations of the primary star.The analysis of the BVRJK light curves, using a code based on ATLASmodel atmospheres, yields new orbital and stellar parameters. We deriveeffective temperatures Teff=9250+/-150 K andTeff=5600+/-100 K for the primary and secondary star,respectively. We challenge the current view that VV UMa is a system withunusually low mass components for their spectral type, and analternative solution is proposed, allowing masses of the stars in theexpected range for their spectral types that are in reasonable agreementwith the available photometric and spectroscopic data. From thevisual-infrared photometry we find no evidence of a significant infraredexcess in the system, deriving an interstellar reddeningE(B-V)<=0.10.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| 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
| High-resolution spectroscopy and direct imaging of the dwarf galaxy I ZW 18
Observations of the velocity profile of H-alpha emission in I Zw 18suggest that the ionized gas may form an incomplete shell, ring, ordouble structure several arcsec across. Several faint continuum objectsare noted along a line extending 1.5 arcsec northwest of the brightcondensations in I Zw 18. Results are presented for the effect ofGalactic interstellar Na I 5890-A absorption on the redshifted He I5876-A emission from I Zw 18. A helium abundance of about 0.234 + or -0.016 is implied for this object.
| H-alpha Observations of W UMa (BD +56 1400)
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Observation and Astrometry data
| Constellation: | Άρκτος Μεγάλη |
| Right ascension: | 09h31m29.15s |
| Declination: | +55°16'24.6" |
| Apparent magnitude: | 8.166 |
| Distance: | 298.507 parsecs |
| Proper motion RA: | -12.7 |
| Proper motion Dec: | -9.6 |
| B-T magnitude: | 8.299 |
| V-T magnitude: | 8.177 |
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