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The luminosity index for M stars and the distance to the LMC
Author(s) -
SchmidtKaler TH.,
Oestreicher M. O.
Publication year - 1998
Publication title -
astronomische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.394
H-Index - 63
eISSN - 1521-3994
pISSN - 0004-6337
DOI - 10.1002/asna.2123190606
Subject(s) - physics , supergiant , stars , astrophysics , distance modulus , galaxy , luminosity , astronomy , blue supergiant , spiral galaxy , red supergiant , globular cluster
On the bases of the new classification system introduced by Malyuto et al. (1997) a new technique to determine luminosities for M type stars has been established. Due to the lack of accurate distances and their inhomogeneity especially for supergiants the intrinsic scatter is rather high with 0.4 to 0.5 mag. The uncertainty of the zeropoint is 0.07 to 0.08 mag. Applying our new method to M supergiant members of the LMC a distance modulus of 18.34 ± 0.09 mag is derived which agrees well with recent work. The luminosities of the stars range from those of galactic Iab to those of Ia‐Ia‐0 supergiants, i.e. the upper luminosity limit does not exceed that of their galactic counterparts. Like the CaII H and K emission technique of Wilson & Bappu (1957), for which a revised calibration is given, the new method spans an extremely wide range of luminosities. It is less universal, as it can be applied to M stars only, but not to K stars. On the other hand the Wilson‐Bappu‐method requires high resolution spectroscopy so that it is restricted to bright stars in our Galaxy. Our new technique may be applied to faint stars in nearby galaxies since it requires low resolution spectroscopy only.