Miriam Garcia | UNIFE Universidad Femenina del Sagrado Corazón (original) (raw)

Papers by Miriam Garcia

The important role of metallicity on massive star evolution and the combination of multi-object s... more The important role of metallicity on massive star evolution and the combination of multi-object spectrographs and 10m class telescopes, have lead to numerous systematic studies of massive stars in Local Group galaxies. While color based quests of blue massive stars are relatively successful, they must be confirmed with spectroscopy and usually lead to lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies, presented in . One of the key points of the method is the photometric criterion to choose candidate OB stars from the reddening-free Q parameter, that could be easily extended to include from GALEX to near-IR photometry. While not a new idea, one of our code's strong advantages is the automatic determination of evolutionary masses for the members, enabling a quick and more insightful choice of candidates for spectroscopy, and the identification of potential advanced evolutionary stages. We present our work on the very metal-poor irregular IC 1613 (Garcia et al. 2010a). The association properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the galaxy's structure and recent star formation history.

Astrophysics and Space Science Proceedings, 2010

... Miriam Garcia and Artemio Herrero Instituto de Astrof??sica de Canarias, V??a L??ctea S/N, E-... more ... Miriam Garcia and Artemio Herrero Instituto de Astrof??sica de Canarias, V??a L??ctea S/N, E-38200 La Laguna (Tenerife), Spain, e-mail: mgg@iac.es,ahd ... & J. Puls, IAU Symposium 250, 89 7. Hillier, DJ, & Miller, DL 1998, ApJ, 496, 407 8. Howarth, ID, Siebert, KW, Hussain, GAJ, & ...

Astrophysical Journal, 2002

We derived photospheric parameters, mass-loss rates, and wind velocities of Galactic O6-O7 stars ... more We derived photospheric parameters, mass-loss rates, and wind velocities of Galactic O6-O7 stars by analyzing high-resolution spectra in the far-UV and UV ranges with line-blanketed, hydrodynamic, non-LTE spherical models. We combined spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) in the range 905-1187 Å and International Ultraviolet Explorer (IUE) archival spectra (1150-3250 Å) and used the WM-BASIC code of Pauldrach et al. to compute model spectra. Lines in the FUSE range include high ionization stages (e.g., O VI) and lower abundance non-CNO elements (e.g., P V). Analyzed in addition to the N IV, N V, Si IV, and C IV lines in the IUE range, these features play a crucial role in uniquely constraining the stellar parameters, assessing the presence of shocks in the wind, and quantifying the effects of the resulting soft X-rays on the wind ionization. The effective temperatures derived from the consistent analysis of the far-UV and UV spectra are significantly (~6000 K or 15% on average, or between 4000 and 8000 K) lower than most values previously derived for some of our targets and lower than typical values assigned to their spectral types from different compilations. This result has great implications for our understanding of the evolution of massive stars and the characterization of young stellar populations, as well as for energy balance calculations of H II regions. Based on observations with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated by The Johns Hopkins University under NASA contract NAS5-32985, and on IUE observations from the MAST and INES archives.

UV Astronomy 2011, 2011

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800... more The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the

UV Astronomy 2011, 2011

ABSTRACT The Local Group galaxies enable us to study the impact of metallicity on the structure a... more ABSTRACT The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association’s color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC1613 as illustration of the potential of the method. Because of its large field of view and high spatial resolution at ultraviolet (UV) wavelengths, ISSIS at the WSO is a powerful discovery machine of resolved blue massive stars in nearby galaxies. Our code can be easily modified to choose candidate OB stars based on ISSIS magnitudes on the UV, where hot young massive stars are intrinsically brighter and their color degeneracy is broken. The combination of our algorithm and ISSIS’s panchromatic photometry can readily produce a list of the most massive stars of the Local Group. KeywordsGalaxies: Local Group–Galaxies: OB associations–Stars: massive–Stars: photometry–Ultraviolet: stars–Ultraviolet: photometry

Astrophysics and Space Science, 2011

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800... more The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the λ WSO will enable quantitative spectroscopic analyses of blue massive stars in the Local Group beyond the Magellanic Clouds. The results will lead to the characterization of their winds as a function of metallicity, and shed new light on current urging questions regarding radiation driven winds.

The Astrophysical Journal, 2014

We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC 1613. Beca... more We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity ( 1/10 Z ⊙ , from H II regions), studies in this Local Group dwarf galaxy could become a significant step forward from the SMC towards the extremely metal-poor massive stars of the early Universe. We present HST-COS data covering the ∼1150-1800Å wavelength range with resolution R∼2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the SEI method. The v ∞ -Z relationship has been revisited. The terminal velocity of IC 1613 O-stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analogue stars. We -2find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the v ∞ /v esc ratio of the whole OB star sample in any of the studied galaxies. Finally, we present first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, in agreement with previous results on red supergiants. With the confirmed ∼1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's α/Fe ratio is sub-solar.

Tetrahedron, 1990

... 3, 123-132. (c) Cimino, G.; Alfano. G.; De Stefano, S. Experientia 1979, 35, 1136-1137. (d) C... more ... 3, 123-132. (c) Cimino, G.; Alfano. G.; De Stefano, S. Experientia 1979, 35, 1136-1137. (d) Capon, RJ; MacLeod, JK Aust. J. Chem. ... Rep., 3 (1986), pp. 123–132. G. Cimino, G. Alfano and S. DeStefano. Experientia, 35 (1979), pp. 1136–1137. RJ Capon and JK MacLeod. Aust. ...

Astrophysics and Space Science, 2011

Astrophysical Journal, 2004

We derived the stellar parameters of a sample of Galactic early-O type stars by analyzing their U... more We derived the stellar parameters of a sample of Galactic early-O type stars by analyzing their UV and far-UV spectra from the Far Ultraviolet Spectroscopic Explorer (905-1187 8), the International Ultraviolet Explorer, the Hubble Space Telescope STIS, and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (1200-2000 8). The data have been modeled with spherical, hydrodynamic, line-blanketed, non-LTE synthetic spectra computed with the WM-BASIC code. We obtain effective temperatures ranging from T eA ¼ 41,000 to 39,000 K for the O3-O4 dwarf stars and T eA ¼ 37,500 K for the only supergiant of the sample (O4 If + ). Our values are lower than those from previous empirical calibrations for early-O types by up to 20%. The derived luminosities of the dwarf stars are also lower by 6%-12%; however, the luminosity of the supergiant is in agreement with previous calibrations within the error bars. Our results extend the trend found for later O types in a previous work by Bianchi & Garcia.

Advances in Space Research, 2014

ABSTRACT We present an analysis of high resolution spectra in the far-UV -- UV range (~905-2000\A... more ABSTRACT We present an analysis of high resolution spectra in the far-UV -- UV range (~905-2000\AA) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) effective temperature scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.

The important role of metallicity on massive star evolution and the combination of multi-object s... more The important role of metallicity on massive star evolution and the combination of multi-object spectrographs and 10m class telescopes, have lead to numerous systematic studies of massive stars in Local Group galaxies. While color based quests of blue massive stars are relatively successful, they must be confirmed with spectroscopy and usually lead to lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies, presented in . One of the key points of the method is the photometric criterion to choose candidate OB stars from the reddening-free Q parameter, that could be easily extended to include from GALEX to near-IR photometry. While not a new idea, one of our code's strong advantages is the automatic determination of evolutionary masses for the members, enabling a quick and more insightful choice of candidates for spectroscopy, and the identification of potential advanced evolutionary stages. We present our work on the very metal-poor irregular IC 1613 (Garcia et al. 2010a). The association properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the galaxy's structure and recent star formation history.

Astrophysics and Space Science Proceedings, 2010

... Miriam Garcia and Artemio Herrero Instituto de Astrof??sica de Canarias, V??a L??ctea S/N, E-... more ... Miriam Garcia and Artemio Herrero Instituto de Astrof??sica de Canarias, V??a L??ctea S/N, E-38200 La Laguna (Tenerife), Spain, e-mail: mgg@iac.es,ahd ... & J. Puls, IAU Symposium 250, 89 7. Hillier, DJ, & Miller, DL 1998, ApJ, 496, 407 8. Howarth, ID, Siebert, KW, Hussain, GAJ, & ...

Astrophysical Journal, 2002

We derived photospheric parameters, mass-loss rates, and wind velocities of Galactic O6-O7 stars ... more We derived photospheric parameters, mass-loss rates, and wind velocities of Galactic O6-O7 stars by analyzing high-resolution spectra in the far-UV and UV ranges with line-blanketed, hydrodynamic, non-LTE spherical models. We combined spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) in the range 905-1187 Å and International Ultraviolet Explorer (IUE) archival spectra (1150-3250 Å) and used the WM-BASIC code of Pauldrach et al. to compute model spectra. Lines in the FUSE range include high ionization stages (e.g., O VI) and lower abundance non-CNO elements (e.g., P V). Analyzed in addition to the N IV, N V, Si IV, and C IV lines in the IUE range, these features play a crucial role in uniquely constraining the stellar parameters, assessing the presence of shocks in the wind, and quantifying the effects of the resulting soft X-rays on the wind ionization. The effective temperatures derived from the consistent analysis of the far-UV and UV spectra are significantly (~6000 K or 15% on average, or between 4000 and 8000 K) lower than most values previously derived for some of our targets and lower than typical values assigned to their spectral types from different compilations. This result has great implications for our understanding of the evolution of massive stars and the characterization of young stellar populations, as well as for energy balance calculations of H II regions. Based on observations with the NASA-CNES-CSA Far Ultraviolet Spectroscopic Explorer, which is operated by The Johns Hopkins University under NASA contract NAS5-32985, and on IUE observations from the MAST and INES archives.

UV Astronomy 2011, 2011

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800... more The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the

UV Astronomy 2011, 2011

ABSTRACT The Local Group galaxies enable us to study the impact of metallicity on the structure a... more ABSTRACT The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association’s color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC1613 as illustration of the potential of the method. Because of its large field of view and high spatial resolution at ultraviolet (UV) wavelengths, ISSIS at the WSO is a powerful discovery machine of resolved blue massive stars in nearby galaxies. Our code can be easily modified to choose candidate OB stars based on ISSIS magnitudes on the UV, where hot young massive stars are intrinsically brighter and their color degeneracy is broken. The combination of our algorithm and ISSIS’s panchromatic photometry can readily produce a list of the most massive stars of the Local Group. KeywordsGalaxies: Local Group–Galaxies: OB associations–Stars: massive–Stars: photometry–Ultraviolet: stars–Ultraviolet: photometry

Astrophysics and Space Science, 2011

The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800... more The spectrographs on-board the World Space Observatory (WSO) will provide access to the 1020–1800 Å wavelength range with unprecedented sensitivity. Previous observatories operating in the 1150–2000 Å range (such as IUE and HST-STIS) have proved extremely useful to study the winds of OB type stars, which leave their most prominent imprints in the far ultraviolet range. The addition of the λ WSO will enable quantitative spectroscopic analyses of blue massive stars in the Local Group beyond the Magellanic Clouds. The results will lead to the characterization of their winds as a function of metallicity, and shed new light on current urging questions regarding radiation driven winds.

The Astrophysical Journal, 2014

We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC 1613. Beca... more We present the first quantitative UV spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity ( 1/10 Z ⊙ , from H II regions), studies in this Local Group dwarf galaxy could become a significant step forward from the SMC towards the extremely metal-poor massive stars of the early Universe. We present HST-COS data covering the ∼1150-1800Å wavelength range with resolution R∼2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the SEI method. The v ∞ -Z relationship has been revisited. The terminal velocity of IC 1613 O-stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analogue stars. We -2find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the v ∞ /v esc ratio of the whole OB star sample in any of the studied galaxies. Finally, we present first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, in agreement with previous results on red supergiants. With the confirmed ∼1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's α/Fe ratio is sub-solar.

Tetrahedron, 1990

... 3, 123-132. (c) Cimino, G.; Alfano. G.; De Stefano, S. Experientia 1979, 35, 1136-1137. (d) C... more ... 3, 123-132. (c) Cimino, G.; Alfano. G.; De Stefano, S. Experientia 1979, 35, 1136-1137. (d) Capon, RJ; MacLeod, JK Aust. J. Chem. ... Rep., 3 (1986), pp. 123–132. G. Cimino, G. Alfano and S. DeStefano. Experientia, 35 (1979), pp. 1136–1137. RJ Capon and JK MacLeod. Aust. ...

Astrophysics and Space Science, 2011

Astrophysical Journal, 2004

We derived the stellar parameters of a sample of Galactic early-O type stars by analyzing their U... more We derived the stellar parameters of a sample of Galactic early-O type stars by analyzing their UV and far-UV spectra from the Far Ultraviolet Spectroscopic Explorer (905-1187 8), the International Ultraviolet Explorer, the Hubble Space Telescope STIS, and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (1200-2000 8). The data have been modeled with spherical, hydrodynamic, line-blanketed, non-LTE synthetic spectra computed with the WM-BASIC code. We obtain effective temperatures ranging from T eA ¼ 41,000 to 39,000 K for the O3-O4 dwarf stars and T eA ¼ 37,500 K for the only supergiant of the sample (O4 If + ). Our values are lower than those from previous empirical calibrations for early-O types by up to 20%. The derived luminosities of the dwarf stars are also lower by 6%-12%; however, the luminosity of the supergiant is in agreement with previous calibrations within the error bars. Our results extend the trend found for later O types in a previous work by Bianchi & Garcia.

Advances in Space Research, 2014

ABSTRACT We present an analysis of high resolution spectra in the far-UV -- UV range (~905-2000\A... more ABSTRACT We present an analysis of high resolution spectra in the far-UV -- UV range (~905-2000\AA) with non-LTE, spherical, hydrodynamical, line-blanketed models, of three O-type Galactic stars, and derive their photospheric and wind parameters. These data extend previously analyzed samples and fill a gap in spectral type coverage. The combined sample confirms a revised (downward) effective temperature scale with respect to canonical calibrations, as found in our previous works from UV and optical spectra, and in recent works by other authors.