Showing papers by "Katia Cunha published in 2002"
University of Texas at El Paso1, University of Montpellier2, University of Texas at Austin3, Indiana University4, University of São Paulo5, National University of San Marcos6, National University of Engineering7, University of Maryland, College Park8, Australian National University9, University of Concepción10, Herzberg Institute of Astrophysics11
TL;DR: In this paper, high-resolution infrared spectra were obtained for 12 red giant members of the Large Magellanic Cloud (LMC) with the Gemini South 8.3 m telescope and Phoenix spectrometer.
Abstract: High-resolution infrared spectra (� /D� = 50,000) have been obtained for 12 red giant members of the Large Magellanic Cloud (LMC) with the Gemini South 8.3 m telescope and Phoenix spectrometer. Two wavelength regions, at 15540 and 23400 A ˚ , were observed. Quantitative chemical abundances of carbon (both 12 C and 13 C), nitrogen, and oxygen were derived from molecular lines of CO, CN, and OH, while sodium, scandium, titanium, and iron abundances were obtained from neutral atomic lines. The 12 LMC red giants span a metallicity range from [Fe/H] = � 1.1 to [Fe/H] = � 0.3. It is found that values for both [Na/Fe] and [Ti/Fe] in the LMC giants fall below their corresponding Galactic values (at these same [Fe/H] abundances) by about � 0.1–0.5 dex; this effect is similar to abundance patterns found in the few dwarf spheroidal galaxies with published abundances. The program red giants all show evidence of first dredge-up mixing of material exposed to the CN cycle, that is, low 12 C/ 13 C ratios and lower 12 C with higher 14 N abundances. The carbon and nitrogen trends are similar to what is observed in samples of Galactic red giants, although the LMC red giants seem to show smaller 12 C/ 13 C ratios for a given stellar mass. This relatively small difference in the carbon isotope ratios between LMC and Galactic red giants could be due to increased extra mixing in stars of lower metallicity, as suggested previously in the literature. Comparisons of the oxygen-to-iron ratios in the LMC and the Galaxy indicate that the trend of [O/Fe] versus [Fe/H] in the LMC falls about 0.2 dex below the Galactic trend. Such an offset can be modeled as due to an overall lower rate of supernovae per unit mass in the LMC relative to the Galaxy, as well as a slightly lower ratio of supernovae of Type II to supernovae of Type Ia.
100 citations
TL;DR: Copper abundances for 40 red giant members of the massive Galactic globular cluster? Centauri, as well as 15 red giant member of the globular clusters NGC 288, NGC 362 and NGC 3201 were presented in this paper.
Abstract: Copper abundances are presented for 40 red giant members of the massive Galactic globular cluster ? Centauri, as well as 15 red giant members of the globular clusters NGC 288, NGC 362, NGC 3201, NGC 6752, and M4 (NGC 6121). The spectra are of relatively high spectral resolution and signal-to-noise ratio. Using these abundances, plus published literature values for field stars, the abundance trends of [Cu/Fe] are defined as a function of [Fe/H]. The lowest metallicity stars in ? Cen have [Fe/H] ~ -2.0, with the stars in this sample spanning a range from [Fe/H] ~ -2.0 to -0.8. In the field star sample, [Cu/Fe] rises from about -0.8 at [Fe/H] = -2.5 to about -0.4 at [Fe/H] ~ -1.4 and then rises rapidly to [Cu/Fe] ~ 0.0 at [Fe/H] = -1.1. The globular clusters (other than ? Cen) tend to also follow the trend as displayed by the field stars. Unlike the field stars, however, ? Cen displays a constant ratio of [Cu/Fe] ~ -0.5 all the way to [Fe/H] = -0.8. At the metallicity of [Fe/H] = -0.8, the values of [Cu/Fe] in ? Cen fall below the corresponding mean ratio in the field stars by roughly 0.5 dex. If copper is produced primarily in Type Ia supernovae (SNe Ia), as suggested in the literature, the lack of an increase in [Cu/Fe] in ? Cen would suggest very little contribution from SNe Ia to its chemical evolution within the metallicity range from [Fe/H] of -2.0 up to -0.8.
90 citations
TL;DR: In this article, the abundances of magnesium, aluminum and sulfur were derived for a sample of 23 low-v \sin i stars belonging to six northern OB associations of the Galactic disk within 1 kpc of the Sun.
Abstract: Non-LTE abundances of magnesium, aluminum and sulfur are derived for a sample of 23 low-v \sin i stars belonging to six northern OB associations of the Galactic disk within 1 kpc of the Sun. The abundances are obtained from the fitting of synthetic line profiles to high resolution spectra. A comparison of our results with HII region abundances indicates good agreement for sulfur while the cepheid abundances are higher. The derived abundances of Mg show good overlap with the cepheid results. The aluminum abundances for OB stars are significantly below the cepheid values. But, the OB star results show a dependence with effective temperature and need further investigation. The high Al abundances in the cepheids could be the result of mixing. A discussion of the oxygen abundance in objects near the solar circle suggests that the current mean galactic oxygen abundance in this region is 8.6-8.7 and in agreement with the recently revised oxygen abundance in the solar photosphere. Meaningful comparisons of the absolute S, Al and Mg abundances in OB stars with the Sun must await a reinvestigation of these elements, as well as the meteoritic reference element Si, with 3D hydrodynamical model atmospheres for the Sun. No abundance gradients are found within the limited range in galactocentric distances in the present study. Such variations would be expected only if there were large metallicity gradients in the disk.
23 citations
TL;DR: The abundances of He (LTE), C, N, and O (NLTE) were derived for 21 B stars in three young open clusters in this article, and the mean helium abundance for each cluster is close to the standard value, (He/H) 11:0.
Abstract: The abundances of He (LTE), C, N, and O (NLTE) were derived for 21 B stars in three young open clusters. Almost all the stars show subsolar CNO abundances. However, the mean oxygen abundance for each programme cluster appears to be in marginal agreement with the most recent revisions of the solar value. After consideration of the CN abundances in this sample, there is no clear evidence of internal mixing. Only three stars among the non-supergiants seem to show a nitrogen enhancement. Two of them have a fairly low projected equatorial velocity (admittedly, they may be rapid rotators seen pole-on); the third one is a denite fast rotator. In the lower gravity stars (three stars in this sample with log g< 3:0) some kind of mixing has apparently occurred. The supergiants do not dier signicantly from the other programme stars in their respective helium contents. The mean helium abundance for each cluster is close to the standard value, (He/H) 11:0.
17 citations