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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
| A Search for Lithium-Rich Giants among Stars with Infrared Excesses
The unusual nature of the single, rapidly rotating, lithium-rich K giantHDE 233517, which is currently undergoing significant mass loss,prompted a search for giants with similar properties. High-dispersionspectroscopic observations were obtained of HD 219025, a knownlithium-rich infrared-excess giant, plus 39 stars from a list of G and Kgiants with excess far-infrared emission. The projected rotationalvelocities of the vast majority of infrared-excess giants appear to besimilar to those of normal G and K giants. Six giants have lithiumabundances at or above theoretical upper envelope values. The percentageof such stars in the sample of 39 infrared-excess giants is similar tothat of normal giants. The three giants with the largest lithiumabundances have previously been discovered. None of the sample of 39giants have an Hα line similar to the broadened and veryasymmetric line of HDE 233517. The star with optical properties mostsimilar to HDE 233517 is HD 219025.
| On a Rapid Lithium Enrichment and Depletion of K Giant Stars
A model scenario has recently been introduced by de la Reza andcolleagues to explain the presence of very strong Li lines in thespectra of some low-mass K giant stars. In this scenario all ordinary,Li-poor, K giants become Li rich during a short time (~105 yr) whencompared to the red giant phase of 5 x 107 yr. In this "Li period," alarge number of the stars are associated with an expanding thincircumstellar shell supposedly triggered by an abrupt internal mixingmechanism resulting in a surface new 7Li enrichment. This Letterpresents nearly 40 Li-rich K giants known up to now. The distribution ofthese Li-rich giants, along with 41 other observed K giants that haveshells but are not Li rich, in a color-color IRAS diagram confirms thisscenario, which indicates, also as a new result, that a rapid Lidepletion takes place on a timescale of between ~103 and 105 yr. Thismodel explains the problem of the presence of K giants with far-infraredexcesses presented by Zuckerman and colleagues. Other present and futuretests of this scenario are briefly discussed.
| Luminosity Class III Stars with Excess Far-Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...446L..79Z&db_key=AST
| SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).
The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84.
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| Takýmyýldýz: | Yilanci |
| Sað Açýklýk: | 17h16m27.69s |
| Yükselim: | -25°18'19.6" |
| Görünürdeki Parlaklýk: | 7.162 |
| Uzaklýk: | 162.866 parsek |
| özdevim Sað Açýklýk: | 18.6 |
| özdevim Yükselim: | -9.8 |
| B-T magnitude: | 8.68 |
| V-T magnitude: | 7.288 |
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