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An accurate determination of the distance to the Pipe nebula
Aims.We seek an accurate distance to the Pipe nebula. Methods: TheB-band linear polarimetry collected for stars from the Hipparcoscatalogue is used to investigate the dependence of the measuredinterstellar polarization as a function of the star's trigonometricparallax. Results: The linear polarization obtained for 82 Hipparcosstars in the general direction of the Pipe nebula are presented andanalysed. The distribution of the obtained position angles suggests theexistence of two polarizing components. One of them has low averagecolumn density and seems to be closer than ~70 pc to the Sun, while theother component has a higher column density and seems to belong to avery extended interstellar structure. The obtained parallax-polarizationdiagram indicates a low degree of polarization for stars withπH > 8 mas, while a steep rise in polarization isobserved for stars with πH ≈ 7 mas, corresponding to adistance of approximately 140 pc. Conclusions: Our analysis suggests adistance of 145 ± 16 pc to de Pipe nebula, meaning that thiscloud is part of the Ophiuchus dark cloud complex. There is evidencethat the largest filament of the Pipe nebula has collapsed along themagnetic field lines, indicating that magnetic pressure plays animportant role in the evolution of this cloud.Based on observations collected at Observatório do Pico dos Dias,operated by Laboratório Nacional de Astrofísica (LNA/MCT,Brazil). Tables 1 and 2 are only available in electronic form athttp://www.aanda.org
| 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.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| A photometric catalogue of stars in the direction of the bright cloud B in Sagittarius
The present catalog includes photometric data on stars in a 5.5 deg x5.5 deg area in the direction of the bright cloud B in Sagittarius,centered at l equals 357.7 deg, b equals plus 5.6 deg. V magnitudes andB-V and U-B colors are reported for nearly all HD and HDE stars in thefield and also for a number of interesting stars (402 stars), 21 propermotion stars, and 45 stars in a 15 arcmin radius circular regioncentered on the galactic cluster Trumpler 26 (Tr 26). Furthermore,photographic B, V, R, and IR magnitudes are listed for 274 stars in thefield of Tr 26. These data will be used for further studies ofinterstellar absorption in the Galaxy's central direction in relation tospecific objects (red variable stars, star clusters, diffuse objects).
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