| Autor: |
Nardiello, D, Bedin, L R, Burgasser, A, Salaris, M, Cassisi, S, Griggio, M, Scalco, M |
| Předmět: |
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| Zdroj: |
Monthly Notices of the Royal Astronomical Society; 11/30/2022, Vol. 517 Issue 1, p484-497, 14p |
| Abstrakt: |
As the James Webb Space Telescope (JWST) has become fully operational, early release data are now available to begin building the tools and calibrations for precision point-source photometry and astrometry in crowded cluster environments. Here, we present our independent reduction of NIRCam imaging of the metal-poor globular cluster M 92, which were collected under Director's Discretionary Early Release Science programme ERS-1334. We derived empirical models of the point spread function (PSF) for filters F 090 W, F 150 W, F 277 W , and F 444 W , and find that these PSFs: (i) are generally undersampled (FWHM ∼ 2 pixel) in F 150 W and F 444 W and severely undersampled (FWHM ∼ 1 pixel) in F 090 W and F 277 W ; (ii) have significant variation across the field of view, up to ∼15–20 per cent; and (iii) have temporal variations of ∼ 3–4 per cent across multi-epoch exposures. We deployed our PSFs to determine the photometric precision of NIRCam for stars in the crowded, central regions of M 92, measured to be at the ∼0.01 mag level. We use these data to construct the first JWST colour–magnitude diagrams of a globular cluster. Employing existing stellar models, we find that the data reach almost the bottom of the M 92 main sequence (∼0.1 M⊙), and reveal 24 white dwarf candidate members of M 92 in the brightest portion of the white dwarf cooling sequence. The latter are confirmed through a cross-match with archival HST UV and optical data. We also detect the presence of multiple stellar populations along the low-mass main sequence of M 92. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
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