skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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

Citation Formats

Hosek, Matthew W. Jr., Kudritzki, Rolf-Peter, Bresolin, Fabio, Urbaneja, Miguel A., Przybilla, Norbert, Evans, Christopher J., Pietrzyński, Grzegorz, Gieren, Wolfgang, and Carraro, Giovanni, E-mail: mwhosek@ifa.hawaii.edu, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: Miguel.Urbaneja-Perez@uibk.ac.at, E-mail: Norbert.Przybilla@uibk.ac.at, E-mail: chris.evans@stfc.ac.uk, E-mail: pietrzyn@astrouw.edu.pl, E-mail: wgieren@astro-udec.cl, E-mail: gcarraro@eso.org. Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109. United States: N. p., 2014. Web. doi:10.1088/0004-637X/785/2/151.
Hosek, Matthew W. Jr., Kudritzki, Rolf-Peter, Bresolin, Fabio, Urbaneja, Miguel A., Przybilla, Norbert, Evans, Christopher J., Pietrzyński, Grzegorz, Gieren, Wolfgang, & Carraro, Giovanni, E-mail: mwhosek@ifa.hawaii.edu, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: Miguel.Urbaneja-Perez@uibk.ac.at, E-mail: Norbert.Przybilla@uibk.ac.at, E-mail: chris.evans@stfc.ac.uk, E-mail: pietrzyn@astrouw.edu.pl, E-mail: wgieren@astro-udec.cl, E-mail: gcarraro@eso.org. Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109. United States. doi:10.1088/0004-637X/785/2/151.
Hosek, Matthew W. Jr., Kudritzki, Rolf-Peter, Bresolin, Fabio, Urbaneja, Miguel A., Przybilla, Norbert, Evans, Christopher J., Pietrzyński, Grzegorz, Gieren, Wolfgang, and Carraro, Giovanni, E-mail: mwhosek@ifa.hawaii.edu, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: Miguel.Urbaneja-Perez@uibk.ac.at, E-mail: Norbert.Przybilla@uibk.ac.at, E-mail: chris.evans@stfc.ac.uk, E-mail: pietrzyn@astrouw.edu.pl, E-mail: wgieren@astro-udec.cl, E-mail: gcarraro@eso.org. 2014. "Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109". United States. doi:10.1088/0004-637X/785/2/151.
@article{osti_22357077,
title = {Quantitative spectroscopy of blue supergiants in metal-poor dwarf galaxy NGC 3109},
author = {Hosek, Matthew W. Jr. and Kudritzki, Rolf-Peter and Bresolin, Fabio and Urbaneja, Miguel A. and Przybilla, Norbert and Evans, Christopher J. and Pietrzyński, Grzegorz and Gieren, Wolfgang and Carraro, Giovanni, E-mail: mwhosek@ifa.hawaii.edu, E-mail: kud@ifa.hawaii.edu, E-mail: bresolin@ifa.hawaii.edu, E-mail: Miguel.Urbaneja-Perez@uibk.ac.at, E-mail: Norbert.Przybilla@uibk.ac.at, E-mail: chris.evans@stfc.ac.uk, E-mail: pietrzyn@astrouw.edu.pl, E-mail: wgieren@astro-udec.cl, E-mail: gcarraro@eso.org},
abstractNote = {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 red 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.},
doi = {10.1088/0004-637X/785/2/151},
journal = {Astrophysical Journal},
number = 2,
volume = 785,
place = {United States},
year = 2014,
month = 4
}
  • Metal-poor massive stars typically end their lives as blue supergiants (BSGs). Gamma-ray bursts (GRBs) from such progenitors could have an ultra-long duration of relativistic jets. For example, Population III (Pop III) GRBs at z {approx} 10-20 might be observable as X-ray-rich events with a typical duration of T{sub 90} {approx} 10{sup 4}(1 + z) s. The recent GRB111209A at z = 0.677 has an ultra-long duration of T{sub 90} {approx} 2.5 Multiplication-Sign 10{sup 4} s and it has been suggested that its progenitor might have been a metal-poor BSG in the local universe. Here, we suggest that luminous UV/optical/infrared emissionmore » is associated with this new class of GRBs from metal-poor BSGs. Before the jet head breaks out of the progenitor envelope, the energy injected by the jet is stored in a hot plasma cocoon, which finally emerges and expands as a baryon-loaded fireball. We show that the photospheric emissions from the cocoon fireball could be intrinsically very bright (L{sub peak} {approx} 10{sup 42}-10{sup 44} erg s{sup -1}) in UV/optical bands ({epsilon}{sub peak} {approx} 10 eV) with a typical duration of {approx}100 days in the rest frame. Such cocoon emissions from Pop III GRBs might be detectable in infrared bands at {approx}years after Pop III GRBs at up to z {approx} 15 by upcoming facilities such as the James Webb Space Telescope. We also suggest that GRB111209A might have been rebrightening in UV/optical bands up to an AB magnitude of {approx}< 26. The cocoon emission from local metal-poor BSGs might have been observed previously as luminous supernovae without GRBs since they can be seen from the off-axis direction of the jet.« less
  • We present chemical abundance measurements of three stars in the ultrafaint dwarf galaxy Horologium I, a Milky Way satellite discovered by the Dark Energy Survey. Using high-resolution spectroscopic observations, we measure the metallicity of the three stars, as well as abundance ratios of several α-elements, iron-peak elements, and neutron-capture elements. The abundance pattern is relatively consistent among all three stars, which have a low average metallicity of [Fe/H] ~ –2.6 and are not α-enhanced ([α/Fe] ~ 0.0). This result is unexpected when compared to other low-metallicity stars in the Galactic halo and other ultrafaint dwarfs and suggests the possibility ofmore » a different mechanism for the enrichment of Hor I compared to other satellites. Here, we discuss possible scenarios that could lead to this observed nucleosynthetic signature, including extended star formation, enrichment by a Population III supernova, and or an association with the Large Magellanic Cloud.« less
  • We have derived the star formation history (SFH) of the blue compact dwarf galaxy I Zw 18 through comparison of deep HST/ACS data with synthetic color-magnitude diagrams (CMDs). A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We confirm that I Zw 18 is not a truly young galaxy, having started forming stars earlier than ∼1 Gyr ago, and possibly at epochs as old as a Hubble time. In I Zw 18's main body we infer a lower limit of ≈2 × 10{sup 6} M {sub ☉} for the mass locked up in oldmore » stars. I Zw 18's main body has been forming stars very actively during the last ∼10 Myr, with an average star formation rate (SFR) as high as ≈1 M {sub ☉} yr{sup –1} (or ≈2 × 10{sup –5} M {sub ☉} yr{sup –1} pc{sup –2}). On the other hand, the secondary body was much less active at these epochs, in agreement with the absence of significant nebular emission. The high current SFR can explain the very blue colors and the high ionized gas content in I Zw 18, resembling primeval galaxies in the early universe. Detailed chemical evolution models are required to quantitatively check whether the SFH from the synthetic CMDs can explain the low measured element abundances, or if galactic winds with loss of metals are needed.« less
  • We have obtained {ital V}- and {ital I}-band photometry for about 17,500 stars in the field of the dwarf irregular galaxy NGC 3109, located in the outskirts of the Local Group. The photometry allows us to study the stellar populations present inside and outside the disk of this galaxy. From the {ital VI} color-magnitude diagram, we infer metallicities and ages for the stellar populations in the main body and in the halo of NGC 3109. The stars in the disk of this galaxy have a wide variety of ages, including very young stars of age {approximately}10{sup 7} yr. Our mainmore » result is to establish the presence of a halo consisting of Population II stars, extending out to about 4&arcmin;5 (or 1.8 kpc) above and below the plane of this galaxy. For these old stars we derive an age of over 10{sup 10} yr and a metallicity of [Fe/H]thinsp=thinsp{minus}1.8thinsp{plus_minus}thinsp0.2. We construct a deep luminosity function, obtaining an accurate distance modulus ({ital m}thinsp{minus}thinsp{ital M}){sub 0}thinsp=thinsp25.62thinsp{plus_minus}thinsp0.1 for this galaxy based on the {ital I}-magnitude of the red giant branch tip and adopting {ital E}({ital V}{minus}{ital I})thinsp=thinsp0.05. {copyright} {ital {copyright} 1999.} {ital The American Astronomical Society}« less
  • We present high-resolution (R {approx} 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the 'ultra-faint' dwarf spheroidal galaxy (dSph) Booetes I, absolute magnitude M{sub V} {approx} -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Booetes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halomore » shows that Boo-1137 is 'normal' with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] {approx}<-3.0. The alpha-elements Mg, Si, Ca, and Ti are all higher by DELTA[X/Fe] {approx} 0.2 than the average halo values. Monte Carlo analysis indicates that DELTA[alpha/Fe] values this large are expected with a probability {approx}0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo-1137 relative abundances with respect to halo values, and the fact that the alpha-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.« less