- ID:
- ivo://CDS.VizieR/J/ApJ/770/138
- Title:
- Metallicities of Lyman limit systems and DLA
- Short Name:
- J/ApJ/770/138
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We assess the metal content of the cool (~10^4^K) circumgalactic medium (CGM) about galaxies at z<~1 using an H I-selected sample of 28 Lyman limit systems (LLS; defined here as absorbers with 16.2<~logN_HI_<~18.5) observed in absorption against background QSOs by the Cosmic Origins Spectrograph on board the Hubble Space Telescope. The N_HI_ selection avoids metallicity biases inherent in many previous studies of the low-redshift CGM. We compare the column densities of weakly ionized metal species (e.g., O II, Si II, Mg II) to N_HI_ in the strongest H I component of each absorber. We find that the metallicity distribution of the LLS (and hence the cool CGM) is bimodal with metal-poor and metal-rich branches peaking at [X/H]=~-1.6 and -0.3 (or about 2.5% and 50% solar metallicities). The cool CGM probed by these LLS is predominantly ionized. The metal-rich branch of the population likely traces winds, recycled outflows, and tidally stripped gas; the metal-poor branch has properties consistent with cold accretion streams thought to be a major source of fresh gas for star forming galaxies. Both branches have a nearly equal number of absorbers. Our results thus demonstrate there is a significant mass of previously undiscovered cold metal-poor gas and confirm the presence of metal enriched gas in the CGM of z<~1 galaxies.
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- ID:
- ivo://CDS.VizieR/J/A+A/557/A10
- Title:
- Metallicities of open clusters
- Short Name:
- J/A+A/557/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are a useful tool when investigating several topics connected with stellar evolution; for example the age or distance can be more accurately determined than for field stars. However, one important parameter, the metallicity, is only known for a marginal percentage of open clusters. We aim at a consistent set of parameters for the open clusters investigated in our photometric Delta-a survey of chemically peculiar stars. Special attention is paid to expanding our knowledge of cluster metallicities and verifying their scale. Making use of a previously developed method based on normalised evolutionary grids and photometric data, the distance, age, reddening, and metallicity of open clusters were derived. To transform photometric measurements into effective temperatures to use as input for our method, a set of temperature calibrations for the most commonly used colour indices and photometric systems was compiled. We analysed 58 open clusters in total. Our derived metallicity values were in excellent agreement with about 30 spectroscopically studied targets. The mean value of the absolute deviations was found to be 0.03dex, with no noticeable offset or gradient. The method was also applied using recent evolutionary models based on the currently accepted lower solar abundance value Z~0.014. No significant differences were found compared to grids using the former adopted solar value Z=0.02. Furthermore, some divergent photometric datasets were identified and discussed. The method provides an accurate way of obtaining properly scaled metallicity values for open clusters. In light of present and future homogeneous photometric sky surveys, the sample of stellar clusters can be extended to the outskirts of the Milky Way, where spectroscopic studies are almost impossible. This will help for determining galactic metallicity gradients in more detail.
- ID:
- ivo://CDS.VizieR/J/MNRAS/472/2963
- Title:
- Metallicities of Pristine stars
- Short Name:
- J/MNRAS/472/2963
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Pristine survey is a narrow-band, photometric survey focused around the wavelength region of the CaII H&K absorption lines, designed to efficiently search for extremely metal-poor stars. In this work, we use the first results of a medium-resolution spectroscopic follow-up to refine the selection criteria for finding extremely metal-poor stars ([Fe/H]<=-3.0) in the Pristine survey. We consider methods by which stars can be selected from available broad-band and infrared photometry plus the additional Pristine narrow-band photometry. The sample consists of 205 stars in the magnitude range 14<V<18. Applying the photometric selection criteria cuts the sample down to 149 stars, and from these we report a success rate of 70 per cent for finding stars with [Fe/H]<=-2.5 and 22 per cent for finding stars with [Fe/H]<=-3.0. These statistics compare favourably with other surveys that search for extremely metal-poor stars, namely an improvement by a factor of ~4-5 for recovering stars with [Fe/H]<=-3.0. In addition, Pristine covers a fainter magnitude range than its predecessors and can thus probe deeper into the Galactic halo.
- ID:
- ivo://CDS.VizieR/J/ApJ/779/102
- Title:
- Metallicities of RGB stars in dwarf galaxies
- Short Name:
- J/ApJ/779/102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectroscopic metallicities of individual stars in seven gas-rich dwarf irregular galaxies (dIrrs), and we show that dIrrs obey the same mass-metallicity relation as the dwarf spheroidal (dSph) satellites of both the Milky Way and M31: Z_{star}_{propto}M_{star}_^0.30+/-0.02^. The uniformity of the relation is in contradiction to previous estimates of metallicity based on photometry. This relationship is roughly continuous with the stellar mass-stellar metallicity relation for galaxies as massive as M_*_=10^12^M_{sun}_. Although the average metallicities of dwarf galaxies depend only on stellar mass, the shapes of their metallicity distributions depend on galaxy type. The metallicity distributions of dIrrs resemble simple, leaky box chemical evolution models, whereas dSphs require an additional parameter, such as gas accretion, to explain the shapes of their metallicity distributions. Furthermore, the metallicity distributions of the more luminous dSphs have sharp, metal-rich cut-offs that are consistent with the sudden truncation of star formation due to ram pressure stripping.
- ID:
- ivo://CDS.VizieR/J/ApJ/640/L43
- Title:
- Metallicities of RR Lyrae stars in Omega Cen
- Short Name:
- J/ApJ/640/L43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new spectroscopic metal abundances for 74 RR Lyrae (RRL) stars in {omega} Cen obtained with FLAMES. The well-known metallicity spread is visible among the RRL variables. The metal-intermediate (MI) RRL stars ([Fe/H]~-1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H]~-1.7), in good agreement with the corresponding zero-age horizontal-branch models with cosmological helium abundance Y=0.246.
- ID:
- ivo://CDS.VizieR/J/A+A/404/689
- Title:
- Metallicities of Slowly Pulsating B stars
- Short Name:
- J/A+A/404/689
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derived the stellar parameters (angular diameters, effective temperatures, metallicities) and interstellar reddenings for 20 Slowly Pulsating B (SPB) and 34 reference stars observed during the IUE satellite mission. The parameters were derived by means of an algorithmic procedure of fitting theoretical flux distributions to the low-resolution IUE spectra and optical spectrophotometric observations. Since the metallicity [m/H] has a special importance for pulsating B type stars, we focused our attention on that parameter. We found that the mean value of the metallicity of the considered SPB and reference stars amounts to [m/H]~-0.20. The results only slightly depend on the reduction procedure used for the IUE images (NEWSIPS and INES). The metal abundances obtained in this paper are in accordance with the average value of -0.2dex for stars in the solar neighborhood recently reported by other investigators.
- ID:
- ivo://CDS.VizieR/J/A+A/653/L8
- Title:
- Metallicities on multiple MSs of Omega Centauri
- Short Name:
- J/A+A/653/L8
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Omega Cen is a rare example of a globular cluster where the iron abundance of the stars spans more than one order of magnitude. Many spectroscopic investigations of its red-giant- and sub-giant- branches have revealed multiple peaks in the iron abundance distribution. The metallicity distribution of main-sequence (MS) stars is not well characterized yet, due to the faintness of the stars and lack of data. So far, almost all studies of MS stars are based on photometric measurements. Our goal is to investigate the metallicity distribution of a statistically significant sample of MS stars in Omega Cen. In particular, we aim at revisiting the metallicity difference between the red and blue MS of the cluster. We use MUSE spectra obtained for the central region of omega Cen to derive metallicities for ~4200 MS stars. We find that blue MS stars are on average ~0.1dex more metal-rich than their red counterparts. On the basis of this new estimate, we find that the two sequences can be fit on the Hubble Space Telescope color-magnitude diagram with two isochrones having the same global metallicity and age but a higher helium abundance for the blue MS, i.e. {DELTA}Y~<0.1. Furthermore, we determine the average metallicity of the five main populations along Omega Cen MS and these estimates are consistent with expectations from previous photometric studies.
- ID:
- ivo://CDS.VizieR/J/A+A/563/A15
- Title:
- Metallicity and kinematics in Galactic bar
- Short Name:
- J/A+A/563/A15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We observe red clump stars in four fields along the Galactic bar major axis (l=10{deg}, -6{deg}, 6{deg} and b=0{deg}, plus a field at l=0{deg}, b=1{deg}) with low-resolution spectroscopy from FLAMES/GIRAFFE (setup LR08) at the VLT, observing around the CaII triplet. We developed robust methods to extract radial velocity and metallicity estimates from these low signal-to-noise spectra. Results have been derived by fixing atmospheric parameters typical of a red clump star (Teff=4750K, logg=2.5). For some targets, the metallicity could not be derived.
- ID:
- ivo://CDS.VizieR/J/MNRAS/371/1793
- Title:
- Metallicity calibrations for UBV photometry
- Short Name:
- J/MNRAS/371/1793
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Calibrations are presented here for metallicity ([Fe/H]) in terms of the ultraviolet excess, [{Delta}(U-B) at B-V=0.6, hereafter D0.6], and also for the absolute visual magnitude (M_V_) and its difference with respect to the Hyades ({Delta}M^H^_V_) in terms of D0.6 and (B-V), making use of high-resolution spectroscopic abundances from the literature and Hipparcos parallaxes.
- ID:
- ivo://CDS.VizieR/J/MNRAS/464/194
- Title:
- Metallicity distribution in the GC
- Short Name:
- J/MNRAS/464/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4pc^2^ of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the Gottingen spectral library of synthetic PHOENIX spectra. The derived stellar metallicities range from metal-rich [M/H]>+0.3dex to metal-poor [M/H]<-1.0dex, with a fraction of 5.2^+6.0^_-3.1_ per cent metal-poor ([M/H]<=-0.5dex) stars. The metal-poor stars are distributed over the entire observed field. The origin of metal-poor stars remains unclear. They could originate from infalling globular clusters. For the metal-rich stellar population ([M/H]>0dex), a globular cluster origin can be ruled out. As there is only a very low fraction of metal-poor stars in the central 4pc^2^ of the Galactic Centre, we believe that our data can discard a scenario in which the Milky Way nuclear star cluster is purely formed from infalling globular clusters.
