- ID:
- ivo://CDS.VizieR/J/ApJ/595/1154
- Title:
- Oxygen abundances in metal-poor stars
- Short Name:
- J/ApJ/595/1154
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present oxygen abundances derived from both the permitted and forbidden oxygen lines for 54 subgiants and giants with [Fe/H] values between -2.7 and solar with the goal of understanding the discrepancy in the derived abundances. A first attempt, using Teff values from photometric calibrations and surface gravities from luminosities obtained agreement between the indicators for turn-off stars, but the disagreement was large for evolved stars. We find that the difference in the oxygen abundances derived from the permitted and forbidden lines is most strongly affected by Teff, and we derive a new Teff scale based on forcing the two sets of lines to give the same oxygen abundances. These new parameters, however, do not agree with other observables, such as theoretical isochrones or Balmer-line profile based Teff determinations. Our analysis finds that one-dimensional, LTE analyses (with published non-LTE corrections for the permitted lines) cannot fully resolve the disagreement in the two indicators without adopting a temperature scale that is incompatible with other temperature indicators. We also find no evidence of circumstellar emission in the forbidden lines, removing such emission as a possible cause for the discrepancy.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/764/78
- Title:
- Oxygen abundances in nearby FGK stars
- Short Name:
- J/ApJ/764/78
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777nm OI triplet lines. We assign a kinematic probability for the stars to be thin-disk (P_1_), thick-disk (P_2_), and halo (P_3_) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P_2_>0.5) relative to thin-disk (P_1_>0.5) stars with [Fe/H]<~-0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H]>~-0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P_1_<0.7, P_2_<0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P_3_>0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V<-200km/s; halo stars with V>-200km/s follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.
- ID:
- ivo://CDS.VizieR/J/A+A/465/271
- Title:
- Oxygen abundances in nearby stars
- Short Name:
- J/A+A/465/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The abundances of iron and oxygen are homogeneously determined in a sample of 523 nearby (d<150pc) FGK disk and halo stars with metallicities in the range -1.5<[Fe/H]<0.5. Iron abundances were obtained from an LTE analysis of a large set of FeI and FeII lines with reliable atomic data. Oxygen abundances were inferred from a restricted non-LTE analysis of the 777nm OI triplet. We adopted the infrared flux method temperature scale and surface gravities based on Hipparcos trigonometric parallaxes.
- ID:
- ivo://CDS.VizieR/J/ApJ/735/71
- Title:
- Oxygen abundances in outlying HII regions
- Short Name:
- J/ApJ/735/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a search for outlying HII regions in the extended gaseous outskirts of nearby (D<40Mpc) galaxies and subsequent multi-slit spectroscopy used to obtain the HII region nebular oxygen abundances. The galaxies in our sample have extended HI disks and/or interaction-related HI features that extend well beyond their primary stellar components. We report oxygen abundance gradients out to 2.5 times the optical radius for these galaxies which span a range of morphologies and masses. We analyze the underlying stellar and neutral HI gas distributions in the vicinity of the HII regions to understand the physical processes that give rise to the observed metal distributions in galaxies. These measurements, for the first time, convincingly show flat abundance distributions out to large radii in a wide variety of systems and have broad implications for galaxy chemodynamical evolution.
- ID:
- ivo://CDS.VizieR/J/A+A/415/155
- Title:
- Oxygen abundances in the Galactic disk
- Short Name:
- J/A+A/415/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen abundances for the 72 program stars. Column one gives the Hipparcos number, columns 2-6 the derived oxygen abundances for the different indicators relative to the photospheric oxygen abundance {epsilon}(O)_{sun}_=8.83). Columns 7-11 give the abundances relative to our solar abundances, i.e. [O/H]_{sun}_=0 for all indicators. Columns 12-14 give the abundances for the triplet that have been corrected for NLTE effects according the the prescription in Gratton et al. (1999, Cat. <J/A+A/350/955>), and normalized to the new NLTE corrected abundance for the Sun. Column 15 gives the NLTE correction terms from Gratton et al. (1999, Cat. <J/A+A/350/955>) (GCEG) that were applied to the abundances in columns 12-14. Column 15 gives the empirical NLTE correction we determined (Eq. 1 in article}. Columns 16-19 give the measured equivalent widths for the forbidden [OI] line at 636.3nm and the permitted oxygen triplet lines at 777nm.
- ID:
- ivo://CDS.VizieR/J/ApJ/617/240
- Title:
- Oxygen abundances in the GOODS-North field
- Short Name:
- J/ApJ/617/240
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure nebular oxygen abundances for 204 emission-line galaxies with redshifts 0.3<z<1.0 in the Great Observatories Origins Deep Survey-North (GOODS-N) field using spectra from the Team Keck Redshift Survey, Cat. <J/AJ/127/3121>. We also provide an updated analytic prescription for estimating oxygen abundances using the traditional strong emission line ratio, R_23_, based on the photoionization models of Kewley & Dopita (2002ApJS..142...35K). We include an analytic formula for very crude metallicity estimates using the [NII]_{lambda}6584_/H{alpha} ratio.
- ID:
- ivo://CDS.VizieR/J/ApJ/757/164
- Title:
- Oxygen abundances of dwarf stars
- Short Name:
- J/ApJ/757/164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oxygen abundances of 67 dwarf stars in the metallicity range -1.6<[Fe/H]<-0.4 are derived from a non-LTE analysis of the 777nm OI triplet lines. These stars have precise atmospheric parameters measured by Nissen and Schuster (Cat. J/A+A/511/L10), who find that they separate into three groups based on their kinematics and {alpha}-element (Mg, Si, Ca, Ti) abundances: thick disk, high-{alpha} halo, and low-{alpha} halo. We find the oxygen abundance trends of thick-disk and high-{alpha} halo stars very similar. The low-{alpha} stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H] and have systematically lower oxygen abundances compared to the other two groups. Thus, we find the behavior of oxygen abundances in these groups of stars similar to that of the {alpha} elements. We use previously published oxygen abundance data of disk and very metal-poor halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygen abundance trends of stars in the solar neighborhood. Two field halo dwarf stars stand out in their O and Na abundances. Both G53-41 and G150-40 have very low oxygen and very high sodium abundances, which are key signatures of the abundance anomalies observed in globular cluster (GC) stars. Therefore, they are likely field halo stars born in GCs. If true, we estimate that at least 3%+/-2% of the local field metal-poor star population was born in GCs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/361/1063
- Title:
- Oxygen abundances of HII regions
- Short Name:
- J/MNRAS/361/1063
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new analysis of the main empirical calibrators of oxygen abundance for ionised gas nebulae. With that aim we have compiled an extensive sample of objects with emission line data including the near IR [SIII] lines and the weak auroral lines which allow for the determination of the gas electron temperature. For all the objects the oxygen abundances have been derived in a homogeneous way, using the most recent sets of atomic coefficients and taking into the account the effect of particle density on the temperature of O^+^. The residuals between directly and empirically-derived abundances as a function of abundance have been studied. A grid of photo-ionisation models, covering the range of physical properties of the gas, has been used to explain the origin of the uncertainties affecting each abundance calibrator. The range of validity for each abundance parameter has been identified and its average uncertainty has been quantified.
- ID:
- ivo://CDS.VizieR/J/ApJ/674/172
- Title:
- Oxygen abundances of LIRGs and ULIRGs
- Short Name:
- J/ApJ/674/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) dominate the star formation rate budget of the universe at z>~1, yet no local measurements of their heavy-element abundances exist. We measure nuclear or near-nuclear oxygen abundances in a sample of 100 star-forming LIRGs and ULIRGs using new, previously published, and archival spectroscopy of strong emission lines (including [OII] {lambda}{lambda}3726, 3729) in galaxies with redshifts <z>~0.1.
- ID:
- ivo://CDS.VizieR/J/ApJ/602/L117
- Title:
- Oxygen in Pleiades and M34 dwarfs
- Short Name:
- J/ApJ/602/L117
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the high-excitation O I {lambda}7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation {lambda}6053 feature mimic the O I abundance behavior. O abundances have also been derived from the [O I] {lambda}6300 feature in three Pleiades stars; the abundances exhibit a much lower mean value than do the cool dwarf triplet results. Inasmuch as the [O I] abundances are presumed to be free from NLTE effects, their mean values ([O/H]_6300_=+0.14) provide the current best estimate of the Pleiades O abundance. Spreads in [O/H]_Trip_ at a given temperature are also seen in both clusters; no correlation is found between the spreads and the chromospheric emission measures.
