A Near-Infrared Spectral Library of Very Young Brown Dwarfs and Planetary-Mass Objects in the Orion Nebula Cluster

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Main Authors: Manjavacas, Elena, Gennaro, Mario, Betti, Sarah, Pueyo, Laurent, Balmer, William, Robberto, Massimo
Format: Preprint
Published: 2025
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author Manjavacas, Elena
Gennaro, Mario
Betti, Sarah
Pueyo, Laurent
Balmer, William
Robberto, Massimo
author_facet Manjavacas, Elena
Gennaro, Mario
Betti, Sarah
Pueyo, Laurent
Balmer, William
Robberto, Massimo
contents Age-benchmark brown dwarfs' and planetary-mass objects' spectroscopy is key to characterize substellar evolution. In this paper we present the JHK medium resolution (R~3000) spectra of 25 7-75 M_Jup (spectral types L3.0-M6.0) brown dwarfs and planetary-mass objects in the Orion Nebula Cluster obtained with MOSFIRE installed at the W. M. Keck I telescope. We obtained the spectral types of the targets in our sample using template brown dwarf and planetary-mass objects' spectra. We confirmed their extreme youth (<5 Myr) and membership to the cluster using spectral indices, and the diversity of their spectra even for targets with similar spectral types. Six of our targets presented Pa-beta and Bra-gamma emission lines, suggesting the existence of accreting protoplanetary disks to objects with masses as low as 7 M_Jup. After analyzing the emission lines of those objects, and measuring their accretion rates, we compared them to those of stars, brown dwarfs and planetary-mass objects, confirming that planetary-mass young objects deplete their disks quickly at young ages. Finally, we illustrate the spectral evolution of a 7-10 M_Jup planetary-mass object through its life from 1-3 Myr to 200 Myr old using one of our latest spectra type targets, and other targets from the literature with older age, but similar estimated masses. The spectra are publicly available for the community's use as data behind the figures.
format Preprint
id arxiv_https___arxiv_org_abs_2508_14035
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A Near-Infrared Spectral Library of Very Young Brown Dwarfs and Planetary-Mass Objects in the Orion Nebula Cluster
Manjavacas, Elena
Gennaro, Mario
Betti, Sarah
Pueyo, Laurent
Balmer, William
Robberto, Massimo
Solar and Stellar Astrophysics
Earth and Planetary Astrophysics
Age-benchmark brown dwarfs' and planetary-mass objects' spectroscopy is key to characterize substellar evolution. In this paper we present the JHK medium resolution (R~3000) spectra of 25 7-75 M_Jup (spectral types L3.0-M6.0) brown dwarfs and planetary-mass objects in the Orion Nebula Cluster obtained with MOSFIRE installed at the W. M. Keck I telescope. We obtained the spectral types of the targets in our sample using template brown dwarf and planetary-mass objects' spectra. We confirmed their extreme youth (<5 Myr) and membership to the cluster using spectral indices, and the diversity of their spectra even for targets with similar spectral types. Six of our targets presented Pa-beta and Bra-gamma emission lines, suggesting the existence of accreting protoplanetary disks to objects with masses as low as 7 M_Jup. After analyzing the emission lines of those objects, and measuring their accretion rates, we compared them to those of stars, brown dwarfs and planetary-mass objects, confirming that planetary-mass young objects deplete their disks quickly at young ages. Finally, we illustrate the spectral evolution of a 7-10 M_Jup planetary-mass object through its life from 1-3 Myr to 200 Myr old using one of our latest spectra type targets, and other targets from the literature with older age, but similar estimated masses. The spectra are publicly available for the community's use as data behind the figures.
title A Near-Infrared Spectral Library of Very Young Brown Dwarfs and Planetary-Mass Objects in the Orion Nebula Cluster
topic Solar and Stellar Astrophysics
Earth and Planetary Astrophysics
url https://arxiv.org/abs/2508.14035