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Register a new userNew members in the Upper Sco association from the UKIDSS Early Data Release
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We present the results of a 9.3 square degree 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 Msun 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 Halpha 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 Halpha equivalent widths (>20 Angstroms), 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.
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We present the results of a deep (J ~ 21 mag at 5 sigma) infrared photometric survey of a 0.95 square degree area in the central region of the Upper Sco association. The photometric observations consist of a deep (Y+J)-band images obtained with the WFCAM camera on the UKIRT InfraRed Telescope (UKIRT) with partly coverage in Z complemented by methane ON and OFF conducted with WIRCam on the Canada France Hawaii Telescope. We have selected five potential T-type objects belonging to the Upper Sco association on the basis of their blue methane colours and their J-CH4off colours. We have also identified a sample of 7-8 Upper Sco member candidates bridging the gap between known cluster M-types and our new T-type candidates. These candidates were selected based on their positions in various colour-magnitude diagrams and they follow the sequence of known Upper Sco members identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS). We present additional membership constraints using proper motion estimates from the multiple epochs available to us. We also present optical and near-infrared spectra obtained with the X--Shooter spectrograph on the Very Large Telescope for five L-type candidates covering the 0.6 to 2.5 micron wavelength range, none of them being confirmed as a young brown dwarf. We discuss the lack of detection of new candidate members as well as the possible turn down in the USco mass function as we are approaching the fragmentation limit.
We construct a sample of extremely red objects (EROs) within the UKIDSS Ultra Deep Survey by combining the Early Data Release with optical data from the Subaru/XMM-Newton Deep Field. We find a total of 3715 objects over 2013 sq. arcmin with R-K>5.3 and K<=20.3, which is a higher surface density than found by previous studies. This is partly due to our ability to use a small aperture in which to measure colours, but is also the result of a genuine overdensity of objects compared to other fields. We separate our sample into passively-evolving and dusty star-forming galaxies using their RJK colours and investigate their radio properties using a deep radio map. The dusty population has a higher fraction of individually-detected radio sources and a higher mean radio flux density among the undetected objects, but the passive population has a higher fraction of bright radio sources, suggesting that AGNs are more prevalent among the passive ERO population.
We conducted an exploratory search for quasars at z~ 6 - 8, using the Early Data Release from United Kingdom Infrared Deep Sky survey (UKIDSS) cross-matched to panoramic optical imagery. High redshift quasar candidates are chosen using multi-color selection in i,z,Y,J,H and K bands. After removal of apparent instrumental artifacts, our candidate list consisted of 34 objects. We further refined this list with deeper imaging in the optical for ten of our candidates. Twenty-five candidates were followed up spectroscopically in the near-infrared and in the optical. We confirmed twenty-five of our spectra as very low-mass main-sequence stars or brown dwarfs, which were indeed expected as the main contaminants of this exploratory search. The lack of quasar detection is not surprising: the estimated probability of finding a single z>6 quasar down to the limit of UKIDSS in the 27.3 square degrees of the EDR is <5%. We find that the most important limiting factor in this work is the depth of the available optical data. Experience gained in this pilot project can help refine high-redshift quasar selection criteria for subsequent UKIDSS data releases.
We present eight new T4.5-T7.5 dwarfs identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) Data Release 1 (DR1). In addition we have recovered the T4.5 dwarf SDSS J020742.91+000056.2 and the T8.5 dwarf ULAS J003402.77-005206.7. Photometric candidates were picked up in two-colour diagrams over 190 square degrees (DR1) and selected in at least two filters. All candidates exhibit near-infrared spectra with strong methane and water absorption bands characteristic of T dwarfs and the derived spectral types follow the unified scheme of Burgasser et al. (2006). We have found 6 new T4.5-T5.5 dwarfs, one T7 dwarf, one T7.5 dwarf, and recovered a T4.5 dwarf and a T8.5 dwarf. We provide distance estimates which lie in the 15-85 pc range; the T7.5 and T8.5 dwarfs are probably within 25 pc of the Sun. We conclude with a discussion of the number of T dwarfs expected after completion of the LAS, comparing these initial results to theoretical simulations.
We present near-infrared (1.15-2.50 microns) medium-resolution (R = 1700) spectroscopy of a sample of 23 brown dwarf candidates in the young Upper Sco association. We confirm membership of 21 brown dwarfs based on their spectral shape, comparison with field dwarfs, and presence of weak gravity-sensitive features. Their spectral types range from M8 to L2 with an uncertainty of a subclass, suggesting effective temperatures between 2700 and 1800 K with an uncertainty up to 300 K and masses in the 30-8 Mjup range. Among the non-members, we have uncovered a field L2 dwarf at a distance of 120-140 pc, assuming that it is single. The success rate of our photometric selection based on five photometric passbands and complemented partly by proper motion is over 90%, a very promising result for future studies of the low-mass star and brown dwarf populations in young open clusters by the UKIDSS Galactic Cluster Survey. We observe a large dispersion in the magnitude versus spectral-type relation which is likely the result of the combination of several effects including age dispersion, extent and depth of the association, a high degree of multiplicity and the occurrence of disks.
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