分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a sample of 135,873 RR Lyrae stars (RRLs) with precise photometric-metallicity and distance estimates from our newly calibrated $P-\phi_{31}-R_{21}-$[Fe/H]/$P-R_{21}-$[Fe/H] and $G$ band absolute magnitude-metallicity relations. The $P-\phi_{31}-R_{21}-$[Fe/H] and $P-R_{21}-$[Fe/H] relations for type RRab and type RRc stars are obtained from nearly 2700 Gaia-identified RRLs with precise $\phi_{31}$ and $R_{21}$ measurements from the light curves and metallicity estimates from spectroscopy. Using 236 nearby RRLs with accurate distances estimated from parallax measurements with Gaia EDR3, new $G$ band absolute magnitude-metallicity relations and near-infrared period-absolute magnitude-metallicity relations are constructed. External checks, using other high-resolution spectroscopic sample of field RRLs and RRL members of globular clusters (GCs), show that the typical uncertainties in our photometric-metallicity estimates are about 0.24 and 0.16 dex for type RRab/c stars, respectively, without significant systematic bias with respect to high-resolution spectroscopic metallicity measurements. The accuracies of these metallicity estimates are much improved, especially for RRab stars, when compared to those provided by the Gaia DR3 release. Validations of our distance estimates, again by using members of GCs, show that the typical distance errors are only 3-4%. The distance modulus $\mu_0=18.503\pm0.001(stat)\pm0.040(syst)$ mag for the LMC and $\mu_0=19.030\pm0.003(stat)\pm0.043(syst)$ mag for the SMC are estimated from our RRab sample, respectively, and are in excellent agreement with previous measurements. The mean metallicities of the LMC and SMC derived in this work are also consistent with the previous determinations. Using our sample, a steep metallicity gradient of $-0.024\pm0.001$ dex/kpc is found for the LMC, while a negligible metallicity gradient is obtained for the SMC.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Dan Qiu
Hai-Jun Tian
Xi-Dong Wang
Jia-Lu Nie
Ted von Hippel
Gao-Chao Liu
Morgan Fouesneau
Hans-Walter Rix
摘要： We analyze 4\,050 wide binary star systems involving a white dwarf (WD) and usually a main sequence (MS) star, drawn from the large sample assembled by \citet[][hereafter, T20]{Tian_2020}. Using the modeling code BASE-9, we determine the system's ages, the WD progenitors' ZAMS masses, the extinction values ($A_V$), and the distance moduli. Discarding the cases with poor age convergences, we obtain ages for 3\,551 WDs, with a median age precision of $\sigma_{\tau}/\tau = 20$\%, and system ages typically in the range of 1-6 Gyr. We validated these ages against the very few known clusters and through cross-validation of 236 WD-WD binaries. Under the assumption that the components are co-eval in a binary system, this provides precise age constraints on the usually low-mass MS companions, mostly inaccessible by any other means.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present a sample of 135,873 RR Lyrae stars (RRLs) with precise photometric-metallicity and distance estimates from our newly calibrated $P-\phi_{31}-R_{21}-$[Fe/H]/$P-R_{21}-$[Fe/H] and $G$ band absolute magnitude-metallicity relations. The $P-\phi_{31}-R_{21}-$[Fe/H] and $P-R_{21}-$[Fe/H] relations for type RRab and type RRc stars are obtained from nearly 2700 Gaia-identified RRLs with precise $\phi_{31}$ and $R_{21}$ measurements from the light curves and metallicity estimates from spectroscopy. Using 236 nearby RRLs with accurate distances estimated from parallax measurements with Gaia EDR3, new $G$ band absolute magnitude-metallicity relations and near-infrared period-absolute magnitude-metallicity relations are constructed. External checks, using other high-resolution spectroscopic sample of field RRLs and RRL members of globular clusters (GCs), show that the typical uncertainties in our photometric-metallicity estimates are about 0.24 and 0.16 dex for type RRab/c stars, respectively, without significant systematic bias with respect to high-resolution spectroscopic metallicity measurements. The accuracies of these metallicity estimates are much improved, especially for RRab stars, when compared to those provided by the Gaia DR3 release. Validations of our distance estimates, again by using members of GCs, show that the typical distance errors are only 3-4%. The distance modulus $\mu_0=18.503\pm0.001(stat)\pm0.040(syst)$ mag for the LMC and $\mu_0=19.030\pm0.003(stat)\pm0.043(syst)$ mag for the SMC are estimated from our RRab sample, respectively, and are in excellent agreement with previous measurements. The mean metallicities of the LMC and SMC derived in this work are also consistent with the previous determinations. Using our sample, a steep metallicity gradient of $-0.024\pm0.001$ dex/kpc is found for the LMC, while a negligible metallicity gradient is obtained for the SMC.
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