CaltechAUTHORS
Published May 1, 2025 | Version Published
Journal Article Open

The Diversity of Cold Worlds: A Blended-light Binary Straddling the T/Y Transition in Brown Dwarfs

Creators

  • 1. ROR icon Amherst College
  • 2. ROR icon American Museum of Natural History
  • 3. ROR icon The Graduate Center, CUNY
  • 4. ROR icon The University of Texas at Austin
  • 5. ROR icon University of California, Santa Cruz
  • 6. ROR icon University of Hertfordshire
  • 7. ROR icon California Institute of Technology
  • 8. ROR icon Trinity College Dublin
  • 9. Planétarium Rio Tinto Alcan, Montreal, Quebec, Canada
  • 10. ROR icon University of Montreal
  • 11. ROR icon NOIRLab
  • 12. ROR icon United States Naval Observatory
  • 13. ROR icon Goddard Space Flight Center
  • 14. ROR icon Jet Propulsion Lab
  • 15. ROR icon Ames Research Center
  • 16. ROR icon University of Tennessee at Knoxville

Abstract

We present the first brown dwarf spectral binary characterized with JWST: WISE J014656.66+423410.0, the coldest blended-light brown dwarf binary straddling the T/Y transition. We obtained a moderate resolution (R ∼ 2700) G395H spectrum of this unresolved binary with JWST/NIRSpec and we fit it to late T and Y dwarf spectra from JWST/NIRSpec, and model spectra of comparable temperatures, both as individual spectra and pairs mimicking an unresolved binary system. We find that this tightly separated binary is likely composed of two unequal-brightness sources with a magnitude difference of 0.50 ± 0.08 mag in IRAC [4.5] and a secondary 1.01 ± 0.13 mag redder than the primary in [3.6]–[4.5]. Despite the large color difference between the best-fit primary and secondary, their temperature difference is only 92 ± 23 K, a feature reminiscing of the L/T transition. Carbon disequilibrium chemistry strongly shapes the mid-infrared spectra of these sources, as a complex function of the metallicity and surface gravity. While a larger library of JWST/NIRSpec spectra is needed to conclusively examine the peculiarities of blended-light sources, this spectral binary is a crucial pathfinder to both understand the spectral features of planetary-mass atmospheres and detect binarity in unresolved, moderate-resolution spectra of the coldest brown dwarfs.

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

J.F. acknowledges support from NASA award JWST-GO-02124.001-A as well as support from the Heising-Simons Foundation, the National Science Foundation (Award Nos. 2009177 and 1909776), and NASA (Award No. 80NSSC22K0142). B.L. acknowledges support from the Heising-Simons Foundation via the 51 Pegasi b Fellowship. B.B. acknowledges support from the UK Research and Innovation Science and Technology Facilities Council (grant No. STX0010911). J.M.V. acknowledges support from a university research fellowship funded by the Royal Society and Science Foundation Ireland (URF1221932). This work was performed in part using high-performance computing equipment at Amherst College obtained under National Science Foundation grant No. 2117377. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed at doi:10.17909/jrmn-sr24. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support to MAST for these data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts.

Facilities: JWST - James Webb Space Telescope.

Software: SPLAT (A. J. Burgasser & Splat Development Team 2017)

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Bardalez_Gagliuffi_2025_ApJ_984_74.pdf

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Additional details

Related works

Is supplemented by
Dataset: 10.17909/jrmn-sr24 (DOI)

Funding

National Aeronautics and Space Administration
JWST-GO-02124.001-A
Heising-Simons Foundation
National Science Foundation
2009177
National Science Foundation
1909776
National Aeronautics and Space Administration
80NSSC22K0142
Science and Technology Facilities Council
STX0010911
Heising-Simons Foundation
51 Pegasi b Fellowship -

Dates

Available
2025-04-28
Published online

Caltech Custom Metadata

Caltech groups
Division of Physics, Mathematics and Astronomy (PMA), Infrared Processing and Analysis Center (IPAC)
Publication Status
Published