Infrared spectroscopy of free-floating planet candidates in Upper Scorpius and Ophiuchus^⋆

¹ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
e-mail: herve.bouy@u-bordeaux.fr
² Department of Astronomy, Graduate School of Science, The University of Tokyo, Tokyo, Japan
³ National Astronomical Observatory of Japan, Tokyo, Japan
⁴ Centro de Astrobiología (CSIC-INTA), Depto. de Astrofísica, ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵ Grantecan S. A., Centro de Astrofísica de La Palma, Cuesta de San José, 38712 Breña Baja, La Palma, Spain
⁶ University of Vienna, Department of Astrophysics, Türkenschanzstraße 17, 1180 Wien, Austria
⁷ Institute of Astronomy, Faculty of Science, the University of Tokyo, Osawa 2-21-1, Miaka, Tokyo 181-0015, Japan
⁸ Kiso Observatory, Institute of Astronomy, Faculty of Science, the University of Tokyo, Mitake 10762-30, Kiso-machi, Kiso-gun, Nagano 397-0101, Japan
⁹ Canada – France – Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI 96743, USA
¹⁰ Depto. de Inteligencia Artificial, UNED, Juan del Rosal, 16, 28040 Madrid, Spain
¹¹ Depto. Estadística e Investigación Operativa. Universidad de Cádiz, Avda. República Saharaui s/n, 11510 Puerto Real, Cádiz, Spain
¹² AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
¹³ Núcleo de Astrofísica Teórica, Universidade Cidade de São Paulo, R. Galvão Bueno 868, Liberdade, 01506-000 São Paulo, SP, Brazil
¹⁴ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Rm. N204, Tucson, AZ 85721-0065, USA

Received: 22 April 2022
Accepted: 2 June 2022

Abstract

Context. A rich population of low-mass brown dwarfs and isolated planetary mass objects has been reported in the Upper Scorpius and Ophiuchus star-forming complex.

Aims. We investigate the membership, nature, and properties of 17 of these isolated planetary mass candidates using low-resolution near-infrared spectra.

Methods. We investigated the membership by looking for evidence of their youth using four diagnostics: the slope of the continuum between the J and Ks band, the H_cont, and the TLI-g gravity-sensitive indices. In addition, we compared the spectra to young and field (old) M and L-dwarf standards.

Results. All the targets but one are confirmed as young ultracool objects, with spectral types between L0 and L6 and masses in the range 0.004–0.013 M_⊙, according to evolutionary models. The status of the last target is unclear at this point.

Conclusions. Only one possible contaminant has been identified among the 17 targets, suggesting that the contamination level of the original sample must be low (≲6%).