부산대학교 도서관

The Gaia DR3 GSP-Spec parameters, including metallicity, for VMP stars suffer from parameter degeneracy due to a lack of information in their spectra. Furthermore, the recommended quality cuts filter out the majority of the VMP stars because some of them are confused with hot stars or cool K and M-type giants. We aim to provide more precise metallicity estimates for VMP stars analysed by the GSP-Spec module by taking photometric information into account in the analysis. We reanalyzed FGK type stars in the GSP-Spec catalog by computing the Ca triplet equivalent widths from the published set of GSP-Spec stellar parameters. We compare these recovered equivalent widths with the values directly measured from public Gaia RVS spectra and investigate the precision of the recovered values and the parameter range in which the recovered values are reliable. We then convert the recovered equivalent widths to metallicities adopting photometric temperatures and surface gravities. The recovered equivalent widths agree with the directly measured values with a scatter of 0.05 dex for the stars that pass the GSP-Spec quality cuts. At the low metallicity end ([Fe/H]$<-1.5$), our metallicity estimates have a typical uncertainty of 0.18 dex, which is about half of the quoted GSP-Spec metallicity uncertainty at the same metallicity. Our metallicities also show better agreement with the high-resolution literature values than the original GSP-Spec metallicities at low metallicity. While the GSP-Spec metallicities show increasing scatter when misidentified ``hot'' stars and the subsets of the ``cool K and M-type giants'' are included, we can now identify them as FGK-type stars and provide metallicities that show a small scatter in the comparisons. Thanks to the recovery of these originally misclassified stars, we increase the number of VMP stars with reliable metallicity by a factor of $2-3$.
Comment: Revised after the first referee's report. The catalog will be publicly made available when accepted, or before upon reasonable request