2 results
Search Results
Now showing 1 - 2 of 2
- ItemA comparison between X-shooter spectra and PHOENIX models across the HR-diagram(Les Ulis : EDP Sciences, 2021) Lançon, A.; Gonneau, A.; Verro, K.; Prugniel, P.; Arentsen, A.; Trager, S.C.; Peletier, R.; Chen, Y.-P.; Coelho, P.; Falcón-Barroso, J.; Hauschildt, P.; Husser, T.-O.; Jain, R.; Lyubenova, M.; Martins, L.; Sánchez Blázquez, P.; Vazdekis, A.Aims. The path towards robust near-infrared extensions of stellar population models involves the confrontation between empirical and synthetic stellar spectral libraries across the wavelength ranges of photospheric emission. Indeed, the theory of stellar emission enters all population synthesis models, even when this is only implicit in the association of fundamental stellar parameters with empirical spectral library stars. With its near-ultraviolet to near-infrared coverage, the X-shooter Spectral Library (XSL) allows us to examine to what extent models succeed in reproducing stellar energy distributions (SEDs) and stellar absorption line spectra simultaneously. Methods. As a first example, this study compares the stellar spectra of XSL with those of the Göttingen Spectral Library, which are based on the PHOENIX synthesis code. The comparison was carried out both separately in the three arms of the X-shooter spectrograph known as UVB, VIS and NIR, and jointly across the whole spectrum. We did not discard the continuum in these comparisons; only reddening was allowed to modify the SEDs of the models. Results. When adopting the stellar parameters published with data release DR2 of XSL, we find that the SEDs of the models are consistent with those of the data at temperatures above 5000 K. Below 5000 K, there are significant discrepancies in the SEDs. When leaving the stellar parameters free to adjust, satisfactory representations of the SEDs are obtained down to about 4000 K. However, in particular below 5000 K and in the UVB spectral range, strong local residuals associated with intermediate resolution spectral features are then seen; the necessity of a compromise between reproducing the line spectra and reproducing the SEDs leads to dispersion between the parameters favored by various spectral ranges. We describe the main trends observed and we point out localized offsets between the parameters preferred in this global fit to the SEDs and the parameters in DR2. These depend in a complex way on the position in the Hertzsprung-Russell diagram (HRD). We estimate the effect of the offsets on bolometric corrections as a function of position in the HRD and use this for a brief discussion of their impact on the studies of stellar populations. A review of the literature shows that comparable discrepancies are mentioned in studies using other theoretical and empirical libraries. © A. Lançon et al. 2021.
- ItemMINCE: I. Presentation of the project and of the first year sample(Les Ulis : EDP Sciences, 2022) Cescutti, G.; Bonifacio, P.; Caffau, E.; Monaco, L.; Franchini, M.; Lombardo, L.; Matas Pinto, A. M.; Lucertini, F.; François, P.; Spitoni, E.; Lallement, R.; Sbordone, L.; Mucciarelli, A.; Spite, M.; Hansen, C.J.; Di Marcantonio, P.; Kučinskas, A.; Dobrovolskas, V.; Korn, A.J.; Valentini, M.; Magrini, L.; Cristallo, S.; Matteucci, F.Context. In recent years, Galactic archaeology has become a particularly vibrant field of astronomy, with its main focus set on the oldest stars of our Galaxy. In most cases, these stars have been identified as the most metal-poor. However, the struggle to find these ancient fossils has produced an important bias in the observations - in particular, the intermediate metal-poor stars (-2.5 < [Fe/H] <-1.5) have been frequently overlooked. The missing information has consequences for the precise study of the chemical enrichment of our Galaxy, in particular for what concerns neutron capture elements and it will be only partially covered by future multi object spectroscopic surveys such as WEAVE and 4MOST. Aims. Measuring at Intermediate Metallicity Neutron Capture Elements (MINCE) is gathering the first high-quality spectra (high signal-to-noise ratio, S/N, and high resolution) for several hundreds of bright and metal-poor stars, mainly located in our Galactic halo. Methods. We compiled our selection mainly on the basis of Gaia data and determined the stellar atmospheres of our sample and the chemical abundances of each star. Results. In this paper, we present the first sample of 59 spectra of 46 stars. We measured the radial velocities and computed the Galactic orbits for all stars. We found that 8 stars belong to the thin disc, 15 to disrupted satellites, and the remaining cannot be associated to the mentioned structures, and we call them halo stars. For 33 of these stars, we provide abundances for the elements up to zinc. We also show the chemical evolution results for eleven chemical elements, based on recent models. Conclusions. Our observational strategy of using multiple telescopes and spectrographs to acquire high S/N and high-resolution spectra for intermediate-metallicity stars has proven to be very efficient, since the present sample was acquired over only about one year of observations. Finally, our target selection strategy, after an initial adjustment, proved satisfactory for our purposes.