/ftp/cats/aliases/U/UScoCTIO



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J/AJ/120/479        Low-mass stars in the Upper Sco association  (Ardila+, 2000)
The following files can be converted to FITS (extension .fit .fgz or .fiZ)
	table2.dat table3.dat
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Query from: http://vizier.cds.unistra.fr/viz-bin/VizieR?-source=J/AJ/120/479
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Beginning of ReadMe : J/AJ/120/479 Low-mass stars in the Upper Sco association (Ardila+, 2000) ================================================================================ A survey for low-mass stars and brown dwarfs in the Upper Scorpius OB association. Ardila D., Martin E., Basri G. <Astron. J., 120, 479-487 (2000)> =2000AJ....120..479A ================================================================================ ADC_Keywords: Stars, pre-main sequence Keywords: open clusters and associations: individual (Scorpius-Centarus); stars: low-mass, brown dwarfs Abstract: The Upper Scorpius association is the OB association nearest to the Sun (145pc). Its young age ( 5Myr) makes it an ideal place to search for low-mass stars and brown dwarfs, as these objects should be relatively bright. We have performed a photometric search for the low-mass members of the association, using the R, I, and Z filters. The completeness limit is I 18.5, and the saturation limit is I 13. We obtain 138 candidate members, covering nearly the entire M spectral type range. We find an excess of brown dwarf candidates over the number predicted by a Miller-Scalo initial mass function. In addition, we have performed infrared imaging and low-resolution optical spectroscopy of selected candidates. We find that the infrared observations confirm the spectral types obtained with the optical photometry. Furthermore, we find Halpha in emission in 20 of the 22 objects observed spectroscopically. As Halpha is an indicator of youth, we believe that these 20 objects may belong to the association. One of them, UScoCTIO 128, has a very strong and constant Halpha line (equivalent width -130AA), and its position in the color-magnitude diagram suggests that it is a brown dwarf with mass 0.02M_sun_. Confirmation of this and the other candidates will have to wait for higher resolution observations that can reveal spectroscopic mass indicators such as LiI and gravity indicators such as KI and the subordinate lines of NaI. Description: We obtained photometry for eight fields of 80x80arcmin in Upper Sco using the 60cm Michigan Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory (CTIO), on 1998 April 1-5.