Cool Subdwarf Investigations (CSI): Spectral Sequence

Details Cool Subdwarf Investigations (CSI): Spectral Sequence Cool Subdwarf Investigations (CSI): Spectral Sequence

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...211.5911j&link_type=abstract

American Astronomical Society, AAS Meeting #211, #59.11; Bulletin of the American Astronomical Society, Vol. 39, p.842

Astronomy and Astrophysics

Astronomy

Scientific paper

Using new spectra of 88 K and M type subdwarfs, we consider novel methods for assigning their spectral types, and make steps toward developing a comprehensive spectral sequence for types K3.0VI to M6.0VI. The types are assigned based on the morphology of the spectra, and supporting abundance, kinematic, and trigonometric parallax information is used to provide a more complete picture of the observed subdwarfs, where available. The types and sequence presented link the spectral types of cool subdwarfs to their main sequence counterparts. We find that the CaHn (n = 1--3) and TiO5 indices
often used for subdwarf spectral typing are affected in complicated ways by combinations of subdwarfs' temperatures, metallicities, and gravities, and we use model grids to evaluate the trends in all three parameters. Because of the complex interplay of these three characteristics, it is not possible to identify a star as an "extreme subdwarf'' simply based on very low metallicity, and we suggest that the modifiers "extreme'' or "ultra'' not be used to imply low
and very low metallicity stars. In addition, we propose that "VI'' be used to identify a star as a subdwarf, rather than the confusing ``sd'' prefix, which is also used for hot O and B subdwarfs that are unrelated to the cool subdwarfs discussed in this paper.
These observations are made through SMARTS Consortium. This work has been supported by the National Science Foundation (AST05-07711).

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