Photometry and astrometry with JWST-I. NIRCam point spread functions and the first JWST colour-magnitude diagrams of a globular cluster

Nardiello, D ORCID: 0000-0003-1149-3659, Bedin, LR ORCID: 0000-0003-4080-6466, Burgasser, A, Salaris, M ORCID: 0000-0002-2744-1928, Cassisi, S, Griggio, M and Scalco, M (2022) Photometry and astrometry with JWST-I. NIRCam point spread functions and the first JWST colour-magnitude diagrams of a globular cluster. Monthly Notices of the Royal Astronomical Society, 517 (1). pp. 484-497. ISSN 0035-8711

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Abstract

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 F090W, F150W, F277W, and F444W, and find that these PSFs: (i) are generally undersampled (FWHM ∼2 pixel) in F150W and F444W and severely undersampled (FWHM ∼1 pixel) in F090W and F277W; (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.

Item Type:	Article
Additional Information:	This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2022 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords:	0201 Astronomical and Space Sciences; Astronomy & Astrophysics
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press (OUP)
Date of acceptance:	13 September 2022
Date of first compliant Open Access:	12 June 2023
Date Deposited:	12 Jun 2023 15:49
Last Modified:	04 Jul 2025 18:30
DOI or ID number:	10.1093/mnras/stac2659
URI:	https://researchonline.ljmu.ac.uk/id/eprint/19745

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