- ID:
- ivo://CDS.VizieR/J/MNRAS/275/591
- Title:
- Outer regions of Galactic Bulge
- Short Name:
- J/MNRAS/275/591
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Digitized UK Schmidt plate photometry, calibrated with CCD photometry, is obtained in 18 regions over the Bulge. Stars are selected for spectroscopic follow-up from with a carefully chosen colour-magnitude window, optimized for efficient detection of bulge K giants. Some 1500 stellar spectra are obtained with the AAT AUTOFIB facility. We derive a radial velocity and metallicity for each star, and quantify the uncertainties in these measurements. Luminosity classification is derived both by visual classification and by using an automated routine based on Principal Component Analysis. There are two basic results from this survey: the discovery of the Sagittarius dwarf galaxy described by Ibata, Gilmore and Irwin (1994Natur.370..194I), and a study of the Galactic Bulge by Ibata and Gilmore (1995MNRAS.275..605I) The catalogue contains coordinates, photometry, radial velocities, luminosity classification and chemical abundances for approximately 1500 stars in lines of sight towards the Galactic Bulge. A detailed description of the selection of these stars, the methods used to derive the data, and the reliability of the data, is presented in the paper.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/809/91
- Title:
- Outflows in sodium excess objects
- Short Name:
- J/ApJ/809/91
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Van Dokkum and Conroy (2010Natur.468..940V) revisited the unexpectedly strong NaI lines at 8200{AA} found in some giant elliptical galaxies and interpreted them as evidence for an unusually bottom-heavy initial mass function. Jeong et al. (2013, J/ApJS/208/7) later found a large population of galaxies showing equally extraordinary Na D doublet absorption lines at 5900{AA} (Na D excess objects: NEOs) and showed that their origins can be different for different types of galaxies. While a Na D excess seems to be related to the interstellar medium (ISM) in late-type galaxies, smooth-looking early-type NEOs show little or no dust extinction and hence no compelling signs of ISM contributions. To further test this finding, we measured the Doppler components in the Na D lines. We hypothesized that the ISM would have a better (albeit not definite) chance of showing a blueshift Doppler departure from the bulk of the stellar population due to outflow caused by either star formation or AGN activities. Many of the late-type NEOs clearly show blueshift in their Na D lines, which is consistent with the former interpretation that the Na D excess found in them is related to gas outflow caused by star formation. On the contrary, smooth-looking early-type NEOs do not show any notable Doppler components, which is also consistent with the interpretation of Jeong et al. that the Na D excess in early-type NEOs is likely not related to ISM activities but is purely stellar in origin.
- ID:
- ivo://CDS.VizieR/J/MNRAS/455/2627
- Title:
- Oxygen abundance gradient in M81
- Short Name:
- J/MNRAS/455/2627
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the sensitivity of the methods available for abundance determinations in HII regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to five different sets of spectra of HII regions in the galaxy M81. Our sample contains 116 HII regions with galactocentric distances of 3 to 33kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of -0.010 to -0.002dex/kpc, and dispersions in the range 0.06-0.25dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ~0.06dex, and slopes in the range -0.008 to -0.006dex/kpc. The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A7
- Title:
- Oxygen abundance in disk galaxies
- Short Name:
- J/A+A/623/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the possible dependence of the radial oxygen abundance distribution on non-axisymmetrical structures (bar/spirals) and other macroscopic parameters such as the mass, the optical radius R25, the color g-r, and the surface brightness of the galaxy. A sample of disk galaxies from the third data release of the Calar Alto Legacy Integral Field Area Survey (CALIFA DR3) is considered. We adopted the Fourier amplitude A2 of the surface brightness as a quantitative characteristic of the strength of nonaxisymmetric structures in a galactic disk, in addition to the commonly used morphologic division for A, AB, and B types based on the Hubble classification. To distinguish changes in local oxygen abundance caused by the non-axisymmetrical structures, the multiparametric mass-metallicity relation was constructed as a function of parameters such as the bar/spiral pattern strength, the disk size, color index g-r in the Sloan Digital Sky Survey (SDSS) bands, and central surface brightness of the disk. The gas-phase oxygen abundance gradient is determined by using the R calibration We find that there is no significant impact of the non-axisymmetric structures such as a bar and/or spiral patterns on the local oxygen abundance and radial oxygen abundance gradient of disk galaxies. Galaxies with higher mass, however, exhibit flatter oxygen abundance gradients in units of dex/kpc, but this effect is significantly less prominent for the oxygen abundance gradients in units of dex/R25 and almost disappears when the inner parts are avoided (R>0.25R25). We show that the oxygen abundance in the central part of the galaxy depends neither on the optical radius R25 nor on the color g-r or the surface brightness of the galaxy. Instead, outside the central part of the galaxy, the oxygen abundance increases with g-r value and central surface brightness of the disk.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/3301
- Title:
- Oxygen abundance in Galactic disc Cepheids
- Short Name:
- J/MNRAS/444/3301
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We performed a non-local thermodynamic equilibrium (NLTE) analysis of the infrared oxygen triplet for a large number of Cepheid spectra obtained with the Hobby-Eberly Telescope. These data were combined with our previous NLTE results for stars observed with the Max Planck Gesellschaft Telescope with the aim of investigating the oxygen abundance distribution in the Galactic thin disc. We found the slope of the radial (O/H) distribution to be equal -0.058dex/kpc. However, we found some evidence that the distribution might become flatter in the outer parts of the disc. This is supported by the results of other authors who have studied open clusters, planetary nebulae and Hii regions. Some mechanisms of flattening are discussed.
1046. Oxygen abundance in M83
- ID:
- ivo://CDS.VizieR/J/ApJ/695/580
- Title:
- Oxygen abundance in M83
- Short Name:
- J/ApJ/695/580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained deep multiobject optical spectra of 49 HII regions in the outer disk of the spiral galaxy M83 (=NGC 5236) with the FORS2 spectrograph at the Very Large Telescope. The targets span the range in galactocentric distance between 0.64 and 2.64 times the R_25_ isophotal radius (5.4-22.3kpc), and 31 of them are located at R>R_25_, thus belonging to the extreme outer disk of the galaxy, populated by UV complexes revealed recently by the Galaxy Evolution Explorer satellite. In order to derive the nebular chemical abundances, we apply several diagnostics of the oxygen abundance, including R_23_, [NII]/[OII], and the [OIII]{lambda}4363 auroral line, which was detected in four HII regions.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/2715
- Title:
- Oxygen abundance maps of CALIFA galaxies
- Short Name:
- J/MNRAS/462/2715
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We construct maps of the oxygen abundance distribution across the discs of 88 galaxies using Calar Alto Legacy Integral Field Area survey (CALIFA) Data Release 2 (DR2) spectra. The position of the centre of a galaxy (coordinates on the plate) was also taken from the CALIFA DR2. The galaxy inclination, the position angle of the major axis, and the optical radius were determined from the analysis of the surface brightnesses in the Sloan Digital Sky Survey (SDSS) g and r bands of the photometric maps of SDSS Data Release 9. We explore the global azimuthal abundance asymmetry in the discs of the CALIFA galaxies and the presence of a break in the radial oxygen abundance distribution. We found that there is no significant global azimuthal asymmetry for our sample of galaxies, i.e. the asymmetry is small, usually lower than 0.05dex. The scatter in oxygen abundances around the abundance gradient has a comparable value, <~0.05dex. A significant (possibly dominant) fraction of the asymmetry can be attributed to the uncertainties in the geometrical parameters of these galaxies. There is evidence for a flattening of the radial abundance gradient in the central part of 18 galaxies. We also estimated the geometric parameters (coordinates of the centre, the galaxy inclination and the position angle of the major axis) of our galaxies from the analysis of the abundance map. The photometry-map-based and the abundance-map-based geometrical parameters are relatively close to each other for the majority of the galaxies but the discrepancy is large for a few galaxies with a flat radial abundance gradient.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A115
- Title:
- Oxygen abundances and properties of galaxies
- Short Name:
- J/A+A/550/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between stellar mass, metallicity and gas content for a magnitude- and volume-limited sample of 260 nearby late-type galaxies in different environments, from isolated galaxies to Virgo cluster members. We derive oxygen abundance estimates using new integrated, drift scan optical spectroscopy and the base metallicity calibrations of Kewley & Ellison (2008ApJ...681.1183K). Combining these measurements with ultraviolet to near- infrared photometry and HI 21cm line observations, we examine the relations between stellar mass, metallicity, gas mass fraction and star formation rate. We find that, at fixed stellar mass, galaxies with lower gas fractions typically also possess higher oxygen abundances. We also observe a relationship between gas fraction and metal content, whereby gas-poor galaxies are typically more metal-rich, and demonstrate that the removal of gas from the outskirts of spirals may increase the observed average metallicity by ~0.1dex. Although some cluster galaxies are gas-deficient objects, statistically the stellar-mass metallicity relation is nearly invariant to the environment, in agreement with recent studies. These results indicate that internal evolutionary processes, rather than environmental effects, play a key role in shaping the stellar mass - metallicity relation. In addition, we present metallicity estimates based on observations of 478 nearby galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/151
- Title:
- Oxygen abundances for giant HII regions in NGC 2403
- Short Name:
- J/ApJ/853/151
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents a spectroscopic investigation of 11 HII regions in the nearby galaxy NGC 2403. The HII regions are observed with a long-slit spectrograph mounted on the 2.16m telescope at XingLong station of National Astronomical Observatories of China. For each of the HII regions, spectra are extracted at different nebular radii along the slit-coverage. Oxygen abundances are empirically estimated from the strong-line indices R23, N2O2, O3N2, and N2 for each spectrophotometric unit, with both observation- and model-based calibrations adopted into the derivation. Radial profiles of these diversely estimated abundances are drawn for each nebula. In the results, the oxygen abundances separately estimated with the prescriptions on the basis of observations and models, albeit from the same spectral index, systematically deviate from each other; at the same time, the spectral indices R23 and N2O2 are distributed with flat profiles, whereas N2 and O3N2 exhibit apparent gradients with the nebular radius. Because our study naturally samples various ionization levels, which inherently decline at larger radii within individual HII regions, the radial distributions indicate not only the robustness of R23 and N2O2 against ionization variations but also the sensitivity of N2 and O3N2 to the ionization parameter. The results in this paper provide observational corroboration of the theoretical prediction about the deviation in the empirical abundance diagnostics. Our future work is planned to investigate metal-poor HII regions with measurable Te, in an attempt to recalibrate the strong-line indices and consequently disclose the cause of the discrepancies between the empirical oxygen abundances.
- ID:
- ivo://CDS.VizieR/J/A+A/423/677
- Title:
- Oxygen abundances in chromospherically active stars
- Short Name:
- J/A+A/423/677
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss oxygen abundances derived from [O I] 6300 and the O I triplet in stars spanning a wide range in chromospheric activity level, and show that these two indicators yield increasingly discrepant results with higher chromospheric/coronal activity measures. While the forbidden and permitted lines give fairly consistent results for solar-type disk dwarfs, spuriously high O I triplet abundances are observed in young Hyades and Pleiades stars, as well as in individual components of RS CVn binaries (up to 1.8dex). The distinct behaviour of the [O I]-based abundances which consistently remain near-solar suggests that this phenomenon mostly results from large departures from LTE affecting the O I triplet at high activity level that are currently unaccounted for, but also possibly from a failure to adequately model the atmospheres of K-type stars. These results suggest that some caution should be exercised when interpreting oxygen abundances in active binaries or young open cluster stars.
