JWST-TST High Contrast: First Direct Spectroscopy of GJ 504 b Reveals Clouds and Possible Metal Enrichment

The Astronomical Journal 2026 Open access

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Authors: Aneesh Baburaj, Jean-Baptiste Ruffio, Marshall D. Perrin, Jerry W. Xuan, William O. Balmer, Yayaati Chachan, Quinn Konopacky, Travis Barman, Mathilde Mâlin, Kielan K. W. Hoch, Emily L. Rickman, Kimberly Ward-Duong
+18 more Laurent Pueyo, Julien H. Girard, Isabel Rebollido, Alexis Bidot, Christine Chen, Kadin Worthen, Cicero X. Lu, Jens Kammerer, Roeland P. van der Marel, Nikole K. Lewis, Jeff Valenti, Sara Seager, Chris Stark, Rémi Soummer, Jay Anderson, Charles-Philippe Lajoie, Mark Clampin, C. Matt Mountain
DOI: 10.3847/1538-3881/ae6919
Cited by: 1
References: 158

Abstract

Abstract Characterizing the coldest directly imaged companions through direct spectroscopy has only recently become possible with the James Webb Space Telescope. We present moderate-resolution ( R ∼ 2700) spectroscopic observations of the directly imaged planetary-mass companion (PMC), GJ 504 b, using the JWST/NIRSpec. The coldest imaged PMC of the pre-JWST era GJ 504 b is too faint for ground-based spectroscopy, with only photometric observations possible. Leveraging advanced postprocessing techniques with a forward-modeling framework, we detect the companion at high signal-to-noise (S/N > 300). We also present the first successful point-spread function (PSF) subtraction with angular differential imaging (ADI) in the NIRSpec point cloud, detecting GJ 504 b at S/N > 10 and reaching contrast limits

Fields of Study & Subjects

Astrophysics and Star Formation Studies Stellar planetary and galactic studies Astronomy and Astrophysical Research

Publication details

Journal / source
The Astronomical Journal
Publisher
American Astronomical Society
Volume
172
Issue
1
Pages
28–28
Publication date
18 June 2026
Language
EN