Journal
ASTRONOMICAL JOURNAL
Volume 143, Issue 5, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/143/5/114
Keywords
open clusters and associations: individual (Beta Pictoris moving group); stars: atmospheres; stars: pre-main sequence
Categories
Funding
- NSF [AST 09-07745, AST 06-07757, AST 09-08406]
- NSF REU [PHY-0851594]
- National Aeronautics and Space Administration
- National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0907745] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [908406] Funding Source: National Science Foundation
- Division Of Physics
- Direct For Mathematical & Physical Scien [0851594] Funding Source: National Science Foundation
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We investigate the use of the gravity sensitive neutral sodium (Na I) doublet at 8183 angstrom and 8195 angstrom (Na 8200 angstrom doublet) as an age indicator for M dwarfs. We measured the Na doublet equivalent width (EW) in giants, old dwarfs, young dwarfs, and candidate members of the beta Pic moving group using medium-resolution spectra. Our Na 8200 angstrom doublet EW analysis shows that the feature is useful as an approximate age indicator in M-type dwarfs with (V-K-s) >= 5.0, reliably distinguishing stars older and younger than 100 Myr. A simple derivation of the dependence of the Na EW on temperature and gravity supports the observational results. An analysis of the effects of metallicity shows that this youth indicator is best used on samples with similar metallicity. The age estimation technique presented here becomes useful in a mass regime where traditional youth indicators are increasingly less reliable, is applicable to other alkali lines, and will help identify new low-mass members in other young clusters and associations.
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