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A&A Supplement series, Vol. 121, February 1997, 213 - 222

Received September 13, 1995; accepted May 22, 1996

Spectroscopy of the open cluster Blanco 1

II. Htex2html_wrap_inline1485 emission as an indicator of relative age

P.M. Panagitex2html_wrap1507 - M.A. O'Delltex2html_wrap1509

Send offprint request: P.M. Panagi

tex2html_wrap1511  Joint Center for Mesoscale Meteorology, Universty of Reading, Reading, UK
tex2html_wrap1513  Visiting Fellow, Astronomy Centre, Univ. Sussex, Falmer, Brighton, BN1 9QH, UK
tex2html_wrap1515  Dept. Physics & Astronomy, Univ. St. Andrews, North Haugh, Fife, KY16 9SS, Scotland


We present the results of Htex2html_wrap_inline1487(6562Å) and Li I(6708Å) observations of 114 low-mass stars of the young open cluster Blanco 1. We also present observations of 30 stars in Ca II(K). This work extends the first Blanco 1 spectroscopic study of Panagi et al. (1994).

From a sample of four well-studied clusters, including Blanco 1, we find that the fraction of Htex2html_wrap_inline1489 emission-line stars amongst K dwarfs is a good indicator of relative age, with a smaller fraction indicative of older age. Blanco 1 shows a relatively small fraction of emitters, inconsistent with previous age estimates for the cluster. We estimate the cluster age to to be 90 tex2html_wrap_inline1491 25 Myr, slightly older than the Pleiades. The method is shown to be more sensitive to age than lithium and a useful alternative to other age measurement techniques.

The variation of Htex2html_wrap_inline1493 with (B-V) is similar to that observed in the older solar neighbourhood dwarfs, suggesting that, at least for the absorption-line stars, the contribution of stellar rotation to the equivalent width is unclear.

We combine both spectroscopy and photometry to revise cluster membership and give accurate positions for all these stars.

keywords: Galaxy: open clusters and associations: blanco 1 -- stars: activity -- stars: chromospheres -- stars: late-type

Copyright by the European Southern Observatory (ESO)