TY - JOUR
T1 - Near-infrared spectroscopy of young brown dwarfs in upper Scorpius
AU - Dawson, P.
AU - Scholz, A.
AU - Ray, T. P.
AU - Peterson, D. E.
AU - Rodgers-Lee, D.
AU - Geers, V.
N1 - This work was supported by Science Foundation Ireland within the Research Frontiers Programme under grant no. 10/RFP/AST2780.
PY - 2014/8/1
Y1 - 2014/8/1
N2 - Spectroscopic follow-up is a pre-requisite for studies of the formation and early evolution of brown dwarfs. Here, we present Infrared Telescope Facility/SpeX near-infrared spectroscopy of 30 candidate members of the young Upper Scorpius association, selected from our previous survey work. All 24 high-confidence members are confirmed as young very low mass objects with spectral types from M5 to L1, 15–20 of them are likely brown dwarfs. This high yield confirms that brown dwarfs in Upper Scorpius can be identified from photometry and proper motions alone, with negligible contamination from field objects (<4 per cent). Out of the six candidates with lower confidence, five might still be young very low mass members of Upper Scorpius, according to our spectroscopy. We demonstrate that some very low mass class II objects exhibit radically different near-infrared (0.6–2.5 μm) spectra from class III objects, with strong excess emission increasing towards longer wavelengths and partially filled in features at wavelengths shorter than 1.25 μm. These characteristics can obscure the contribution of the photosphere within such spectra. Therefore, we caution that near-infrared derived spectral types for objects with discs may be unreliable. Furthermore, we show that the same characteristics can be seen to some extent in all class II and even a significant fraction of class III objects (∼40 per cent), indicating that some of them are still surrounded by traces of dust and gas. Based on our spectra, we select a sample of objects with spectral types of M5–L1, whose near-infrared emission represents the photosphere only. We recommend the use of these objects as spectroscopic templates for young brown dwarfs in the future.
AB - Spectroscopic follow-up is a pre-requisite for studies of the formation and early evolution of brown dwarfs. Here, we present Infrared Telescope Facility/SpeX near-infrared spectroscopy of 30 candidate members of the young Upper Scorpius association, selected from our previous survey work. All 24 high-confidence members are confirmed as young very low mass objects with spectral types from M5 to L1, 15–20 of them are likely brown dwarfs. This high yield confirms that brown dwarfs in Upper Scorpius can be identified from photometry and proper motions alone, with negligible contamination from field objects (<4 per cent). Out of the six candidates with lower confidence, five might still be young very low mass members of Upper Scorpius, according to our spectroscopy. We demonstrate that some very low mass class II objects exhibit radically different near-infrared (0.6–2.5 μm) spectra from class III objects, with strong excess emission increasing towards longer wavelengths and partially filled in features at wavelengths shorter than 1.25 μm. These characteristics can obscure the contribution of the photosphere within such spectra. Therefore, we caution that near-infrared derived spectral types for objects with discs may be unreliable. Furthermore, we show that the same characteristics can be seen to some extent in all class II and even a significant fraction of class III objects (∼40 per cent), indicating that some of them are still surrounded by traces of dust and gas. Based on our spectra, we select a sample of objects with spectral types of M5–L1, whose near-infrared emission represents the photosphere only. We recommend the use of these objects as spectroscopic templates for young brown dwarfs in the future.
KW - Techniques: photometric
KW - Open clusters and associations: individual: Upper Scorpius
KW - Infrared: stars
UR - http://mnras.oxfordjournals.org/content/442/2/1586/suppl/DC1
U2 - 10.1093/mnras/stu973
DO - 10.1093/mnras/stu973
M3 - Article
SN - 0035-8711
VL - 442
SP - 1586
EP - 1596
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -