- ID:
- ivo://CDS.VizieR/J/A+A/527/A18
- Title:
- EW of 6 subgiants of {omega} Cen
- Short Name:
- J/A+A/527/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analysed high-resolution UVES spectra of six stars belonging to the subgiant branch of {omega} Centauri, and derived abundance ratios of 19 chemical elements (namely Al, Ba, C, Ca, Co, Cr, Cu, Fe, La, Mg, Mn, N, Na, Ni, Sc, Si, Sr, Ti, and Y). A comparison with previous abundance determinations for red giants provided remarkable agreement and allowed us to identify the sub-populations to which our targets belong. We found that three targets belong to a low-metallicity population at [Fe/H]=-2.0dex, [alpha/Fe]=+0.4dex and [s/Fe]=0dex. Stars with similar characteristics were found in small amounts by past surveys of red giants. We discuss the possibility that they belong to a separate sub-population that we name VMP (very metal-poor, at most 5% of the total cluster population), which - in the self-enrichment hypothesis - is the best-candidate first stellar generation in {omega} Cen. Two of the remaining targets belong to the dominant metal-poor population (MP) at [Fe/H]=-1.7dex, and the last one to the metal-intermediate (MInt) one at [Fe/H]=-1.2dex. The existence of the newly defined VMP population could help to understand some puzzling results based on low-resolution spectroscopy (Sollima et al. 2005ApJ...634..332S , Villanova et al., 2007, Cat. J/ApJ/663/296) in their age differences determinations, because the metallicity resolution of these studies was probably not enough to detect the VMP population. The VMP could also correspond to some of the additional substructures of the subgiant-branch region found in the latest HST photometry (Bellini et al., 2010, Cat. J/AJ/140/631). After trying to correlate chemical abundances with substructures in the subgiant branch of {omega} Cen, we found that the age difference between the VMP and MP populations should be small (0+/-2Gyr), while the difference between the MP and MInt populations could be slightly larger (2+/-2Gyr).
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- ID:
- ivo://CDS.VizieR/J/ApJS/244/32
- Title:
- Extended Aperture Photometry of K2 RR Lyrae stars
- Short Name:
- J/ApJS/244/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Kepler Space Telescope observed thousands of RR Lyrae stars in the K2 mission. In this paper, we present our photometric solutions using extended apertures in order to conserve the flux of the stars to the highest possible extent. With this method, we are able to avoid most of the problems that RR Lyrae light curves produced by other pipelines suffer from. For post-processing, we apply the K2SC pipeline to our light curves. We provide the EAP (Extended Aperture Photometry) of 432 RR Lyrae stars observed in campaigns 3, 4, 5, and 6. We also provide subclass classifications based on Fourier parameters. We investigated in particular the presence of the Blazhko effect in the stars and found it to be 44.7% among the RRab stars, in agreement with results from independent samples. We found that the amplitude and phase modulation in the Blazhko stars may behave rather differently, at least over the length of a K2 Campaign. We also identified four anomalous Cepheid candidates in the sample, one of which is potentially the first Blazhko-modulated member of its class.
- ID:
- ivo://CDS.VizieR/J/AJ/128/2402
- Title:
- Extremely metal-poor star candidates abundances
- Short Name:
- J/AJ/128/2402
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present chemical abundances for 110 stars identified in objective-prism surveys as candidates for being very metal-poor. The abundances are derived from high-S/N, intermediate-resolution spectra obtained with the Keck Observatory Echellette Spectrograph and Imager (ESI). An additional 25 stars with well-determined abundances ranging from [Fe/H]=-1.5 to -3.2 were observed and the results used to help calibrate our analysis and determine the accuracy of our abundance determinations. Abundances for the program stars were measured for Fe, Mg, Ca, Ti, Cr, and Ba with an accuracy of approximately 0.3dex. Fifty-three of the stars in our sample have [Fe/H]<=-2, 22 have [Fe/H]<=-2.5, and 13 have [Fe/H]<=-2.9. Surprisingly, approximately one-third of the sample is relatively metal-rich, with [Fe/H]>-1.5. In addition to identifying a number of extremely metal-poor stars, this study also shows that moderate-resolution spectra obtained with the Keck ESI yield relatively accurate abundances for stars as faint as V=14 with modest exposure time (~20 minutes). This capability will prove useful if the so-far elusive stars at [Fe/H]<-4 turn out to be mostly fainter than V=15.
- ID:
- ivo://CDS.VizieR/J/A+A/501/519
- Title:
- Extremely metal-poor turnoff stars abundances
- Short Name:
- J/A+A/501/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18 EMP turnoff stars. VLT/UVES spectra at ~45000 and S/N ~130 per pixel (330-1000nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and Ba. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2dex larger than in giants of similar metallicity. Mg and Si abundances are ~0.2dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again ~0.4dex higher than in giants of similar [Fe/H] (6 stars only). For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D) effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/A+A/522/A26
- Title:
- Fe Abundances in metal-poor stars
- Short Name:
- J/A+A/522/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The determination of Lithium abundance A(Li) is extremely sensitive to the adopted temperature scale, so that a Teff bias might mimic a trend in A(Li). We present here VLT-UVES Li abundances for 28 halo dwarf stars between [Fe/H]=-2.5 and -3.5, 10 of which have [Fe/H]<-3. Four different Teff scales have been used: Direct Infrared Flux Method (IRFM) has been used on the basis of 2MASS infrared photometry; H{alpha} wings have been fitted against two synthetic grids computed by means of 1D LTE atmosphere models, and a grid of H{alpha} profiles computed by means of 3D hydrodynamical atmosphere models. As a result, we confirm previous claims that A(Li) does not exhibit a plateau below [Fe/H]=-3. A strong positive correlation with [Fe/H] appears, not influenced by the choice of the Teff estimator. From a linear fit, we obtain a strong slope of about 0.30 dex in A(Li) per dex in [Fe/H], significant to 2-3, and consistent within 1 among all the four Teff estimators. A significant slope is also detected in the A(Li)-Teff plane, driven mainly by the coolest stars in the sample (Teff<6250), which appear Li-poor. However, removing such stars does not alter significantly the behavior in the A(Li)-[Fe/H] plane. When the full sample is considered, the scatter in A(Li) increases by a factor of 2 towards lower metallicities, while the plateau appears very thin above [Fe/H]=-2.8. At this metallicity, the plateau lies at A(Li)3D,NLTE=2.199+/-0.086.
- ID:
- ivo://CDS.VizieR/J/AJ/149/183
- Title:
- gri photometry of variables in NGC 4258
- Short Name:
- J/AJ/149/183
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a ground-based survey for Cepheid variables in NGC4258. This galaxy plays a key role in the Extragalactic Distance Scale due to its very precise and accurate distance determination via very long baseline interferometry observations of water masers. We imaged two fields within this galaxy using the Gemini North telescope and the Gemini Multi-Object Spectrograph, obtaining 16 epochs of data in the Sloan Digital Sky Survey gri bands over 4yr. We carried out point-spread function photometry and detected 94 Cepheids with periods between 7 and 127 days, as well as an additional 215 variables which may be Cepheids or Population II pulsators. We used the Cepheid sample to test the absolute calibration of theoretical gri Period-Luminosity relations and found good agreement with the maser distance to this galaxy. The expected data products from the Large Synoptic Survey Telescope should enable Cepheid searches out to at least 10Mpc.
- ID:
- ivo://CDS.VizieR/J/ApJ/898/150
- Title:
- High-res. MIKE obs. of metal-poor stars
- Short Name:
- J/ApJ/898/150
- Date:
- 21 Mar 2022 08:50:22
- Publisher:
- CDS
- Description:
- Extensive progress has recently been made in our understanding of heavy-element production via the r-process in the universe, specifically with the first observed neutron star binary merger (NSBM) event associated with the gravitational-wave signal detected by LIGO, GW170817. The chemical abundance patterns of metal-poor r-process-enhanced stars provide key evidence for the dominant site(s) of the r-process and whether NSBMs are sufficiently frequent or prolific r-process sources to be responsible for the majority of r-process material in the universe. We present atmospheric stellar parameters (using a nonlocal thermodynamic equilibrium analysis) and abundances from a detailed analysis of 141 metal-poor stars carried out as part of the R-Process Alliance (RPA) effort. We obtained high-resolution "snapshot" spectroscopy of the stars using the MIKE spectrograph on the 6.5m Magellan Clay telescope at Las Campanas Observatory in Chile. We find 10 new highly enhanced r-II (with [Eu/Fe]>+1.0), 62 new moderately enhanced r-I (+0.3<[Eu/Fe]<~+1.0), and 17 new limited-r ([Eu/Fe]<+0.3) stars. Among those, we find 17 new carbon-enhanced metal-poor (CEMP) stars, of which five are CEMP-no. We also identify one new s-process-enhanced ([Ba/Eu]>+0.5) and five new r/s (0.0<[Ba/Eu]<+0.5) stars. In the process, we discover a new ultra-metal-poor (UMP) star at [Fe/H]=-4.02. One of the r-II stars shows a deficit in {alpha} and Fe-peak elements, typical of dwarf galaxy stars. Our search for r-process-enhanced stars by RPA efforts has already roughly doubled the known r-process sample.
- ID:
- ivo://CDS.VizieR/J/AJ/142/187
- Title:
- HST observations of 7 Pop.II variable stars
- Short Name:
- J/AJ/142/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new absolute trigonometric parallaxes and proper motions for seven Population II variable stars - five RR Lyr variables: RZ Cep, XZ Cyg, SU Dra, RR Lyr, and UV Oct; and two type 2 Cepheids: VY Pyx and {kappa} Pav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interferometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZ Cep, 2.12+/-0.16mas; XZ Cyg, 1.67+/-0.17mas; SU Dra, 1.42+/-0.16mas; RR Lyr, 3.77+/-0.13mas; UV Oct, 1.71+/-0.10mas; VY Pyx, 6.44+/-0.23mas; and {kappa} Pav, 5.57+/-0.28mas; an average {sigma}_{pi}_/{pi}=5.4%. With these parallaxes, we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RR Lyrae variable star absolute magnitudes, we then derive zero points for M_V_-[Fe/H] and M_K_-[Fe/H]-logP relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the distance of the Large Magellanic Cloud. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.
- ID:
- ivo://CDS.VizieR/J/A+A/419/139
- Title:
- JK photometry on 5 Galactic globular clusters
- Short Name:
- J/A+A/419/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The IR catalogs of the observed clusters are based on ground-based observations using the near-IR camera ARNICA@TNG equipped with a NICMOS-3 256x256 array detector. By using a magnification of 0.35"/px a total FoV of 1.5'x1.5' has been covered. The instrumental magnitudes have been calibrated into the Ferraro et al. (2000AJ....119.1282F) system. The catalogs for all the program clusters have been astrometrically corrected by using 2MASS catalogs, with an accuracy of <0.2arcsec.
- ID:
- ivo://CDS.VizieR/J/ApJS/61/667
- Title:
- Kinematics of Galactic old population
- Short Name:
- J/ApJS/61/667
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A catalog is presented of some 1200 Galactic objects which have radial velocities and abundances [Fe/H]<=-0.6. These data have been analyzed to yield information on the kinematic properties of the older populations of the Galaxy and on the interdependence between kinematics and abundance.
