New members in the Upper Scorpius association from the UKIRT Infrared Deep Sky Survey Early Data Release†

Abstract

We present the results of a 9.3-deg² infrared (ZYJHK) survey in the Upper Scorpius association extracted from the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Cluster Survey Early Data Release. We have selected a total of 112 candidates from the (Z-J, Z) colour-magnitude diagram over the Z= 12.5-20.5 magnitude range, corresponding to M= 0.25-0.01 M_⊙ at an age of 5 Myr and a distance of 145 pc. Additional photometry in J and K filters revealed most of them as reddened stars, leaving 32 possible members. Among them, 15 have proper motion consistent with higher-mass members from Hipparcos and optical spectra with strong Hα in emission and weak gravity features. We have also extracted two lower-mass candidate members for which no optical spectra are in hand. Three members exhibit strong Hα equivalent widths (>20 Å), suggesting that they could still undergo accretion, whereas two other dwarfs show signs of chromospheric activity. The likelihood of the binarity of a couple of new stellar and substellar members is discussed as well.