2006/10/19 by A. Brandeker, Alexis Brandeker, Ray Jayawardhana +4 · 1 citation
Physics and Astronomy · #Astro and Planetary Science #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Binary number #Brown dwarf #Low Mass #Ophiuchus #Physics #Spectral line #Spectroscopy #Star formation #Stars #Stellar, planetary, and galactic studies #Surface gravity #astro-ph
paper · pdf · doi:10.1086/510308
published as Astrophys.J.653:L61-L64,2006 · 4 pages, accepted to ApJL
arxiv created 2006/10/19 · openalex publication_date 2006/11/16 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Binary properties are an important diagnostic of the star and brown dwarf formation processes. While wide binaries appear to be rare in the substellar regime, recent observations have revealed Ophiuchus 162225-240515 (2MASS J16222521-2405139) as a likely young ultra-low-mass binary with an apparent separation of ≈240 AU. Here we present low-resolution near-infrared spectra of the pair from NTT/SOFI ( R ~ 600) and VLT/ISAAC ( R ~ 1400), covering the 1.0-2.5 μm spectral region. By comparing them to model atmospheres from Chabrier & Baraffe and Burrows et al., we confirm the surface temperatures to be T A = 2350 ± 150 K and T B = 2100 ± 100 K for the two components of the binary, consistent with earlier estimates from optical spectra. Using gravity-sensitive K I features, we find the surface gravity to be significantly lower than field dwarfs of the same spectral type, providing the best evidence so far that these objects are indeed young. However, we find that models are not sufficiently reliable to infer accurate ages/masses from surface gravity. Instead, we derive masses of M A = 13 M J and M B = 10 M J for the two objects using the well-constrained temperatures and assuming an age of 1-10 Myr, consistent with the full range of ages reported for the Oph region.