skip to main content

Title: Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109

We present a quantitative analysis of the low-resolution (∼4.5 Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. A modified method of analysis is presented which does not require use of the Balmer jump as an independent T {sub eff} indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B-type BSGs analyzed by Evans et al. to derive the distance to NGC 3109 using the flux-weighted gravity-luminosity relation (FGLR). Using primarily Fe-group elements, we find an average metallicity of [ Z-bar ] = –0.67 ± 0.13, and no evidence of a metallicity gradient in the galaxy. Our metallicities are higher than those found by Evans et al. based on the oxygen abundances of early-B supergiants ([ Z-bar ] = –0.93 ± 0.07), suggesting a low α/Fe ratio for the galaxy. We adjust the position of NGC 3109 on the BSG-determined galaxy mass-metallicity relation accordingly and compare it to metallicity studies of H II regions in star-forming galaxies. We derive an FGLR distance modulus of 25.55 ± 0.09 (1.27 Mpc) that compares well with Cepheid and tip of the redmore » giant branch distances. The FGLR itself is consistent with those found in other galaxies, demonstrating the reliability of this method as a measure of extragalactic distances.« less
Authors:
; ;  [1] ; ;  [2] ;  [3] ; ;  [4] ;  [5]
  1. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
  2. Institute for Astro and Particle Physics, A-6020 Innsbruck University (Austria)
  3. UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh (United Kingdom)
  4. Departamento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción (Chile)
  5. European Southern Observatory, La Silla Paranal Observatory (Chile)
Publication Date:
OSTI Identifier:
22357077
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 785; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; COMPARATIVE EVALUATIONS; DISTANCE; DWARF STARS; GALAXIES; GIANT STARS; GRAVITATION; LUMINOSITY; MASS; METALLICITY; METALS; OXYGEN; RED SHIFT; RELIABILITY; RESOLUTION; SPECTRA; SPECTROSCOPY; STARS