A spectroscopic study of blue supergiant stars in Local Group spiral galaxies: Andromeda and Triangulum

Kavli Affiliate: Huawei Zhang

| First 5 Authors: Cheng Liu, Rolf-Peter Kudritzki, Gang Zhao, Miguel A. Urbaneja, Yang Huang

| Summary:

Low-resolution LAMOST and Keck spectra of blue supergiant stars distributed
over the disks of the Local Group spiral galaxies M 31 and M 33 are analyzed to
determine stellar effective temperatures, gravities, metallicities, and
reddening. Logarithmic metallicities at the center of the galaxies (in solar
units) of $0.30pm0.09$ and $0.11pm0.04$ and metallicity gradients of
$-0.37pm0.13$ dex/$R_{25}$ and $-0.36pm0.16$ dex/$R_{25}$ are measured for M
31 and M 33, respectively. For M 33 the 2-dimensional distribution of
metallicity indicates a deviation from azimutal symmetry with an off-centre
peak. The flux-weighted gravity-luminosity relationship of blue supergiant
stars is used to determine a distance modulus of 24.51$pm$0.13 mag for M 31
and 24.93$pm$0.07 mag for M 33. For M 31 the flux-weighted gravity–luminosity
relationship (FGLR) distance agrees well with other methods. For M 33 the
FGLR-based distance is larger than the distances from Cepheids studies but it
is in good agreement with work on eclipsing binaries, planetary nebulae ,
long-period variables, and the tip of the red giant branch.

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