Substellar and low-mass dwarf identification with near-infrared imaging space observatories^★

¹ Department of Physics and Astronomy, 102 Natural Science Building, University of Louisville, Louisville, KY 40292, USA
e-mail: benne.holwerda@louisville.edu
² Leiden Observatory, University of Leiden, Niels Bohrweg 2, 2333 CA, Leiden, The Netherlands
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁴ Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena, Chile
⁵ Department of Physics and Astronomy, University of Sussex, Brighton, BN1 9QH, Sussex, UK
⁶ Kavli Institute of Cosmology, c/o Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
⁷ School of Physics, The University of Melbourne, VIC 3010, Australia
⁸ ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), Australia
⁹ IPAC, California Institute of Technology, Pasadena, CA 91125, USA

Received: 15 February 2018
Accepted: 9 April 2018

Abstract

Aims. We aim to evaluate the near-infrared colors of brown dwarfs as observed with four major infrared imaging space observatories: the Hubble Space Telescope (HST), the James Webb Space Telescope (JWST), the Euclid mission, and the WFIRST telescope.

Methods. We used the SPLAT SPEX/ISPEX spectroscopic library to map out the colors of the M-, L-, and T-type dwarfs. We have identified which color–color combination is optimal for identifying broad type and which single color is optimal to then identify the subtype (e.g., T0-9). We evaluated each observatory separately as well as the narrow-field (HST and JWST) and wide-field (Euclid and WFIRST) combinations.

Results. The Euclid filters perform equally well as HST wide filters in discriminating between broad types of brown dwarfs. WFIRST performs similarly well, despite a wider selection of filters. However, subtyping with any combination of Euclid and WFIRST observations remains uncertain due to the lack of medium, or narrow-band filters. We argue that a medium band added to the WFIRST filter selection would greatly improve its ability to preselect brown dwarfs its imaging surveys.

Conclusions. The HST filters used in high-redshift searches are close to optimal to identify broad stellar type. However, the addition of F127M to the commonly used broad filter sets would allow for unambiguous subtyping. An improvement over HST is one of two broad and medium filter combinations on JWST: pairing F140M with either F150W or F162M discriminates very well between subtypes.