Identifying nearby field T dwarfs in the UKIDSS Galactic Clusters Survey

Abstract

We present the discovery of two new late-T dwarfs identified in the UKIRT Infrared Deep Sky Survey (UKIDSS) Galactic Clusters Survey (GCS) Data Release 2 (DR2). These T dwarfs are nearby old T dwarfs along the line of sight to star-forming regions and open clusters targeted by the UKIDSS GCS. They are found towards the Alpha Per cluster and Orion complex, respectively, from a search in 54 square degrees surveyed in five filters. Photometric candidates were picked up in two-colour diagrams, in a very similar manner to candidates extracted from the UKIDSS Large Area Survey (LAS) but taking advantage of the Z filter employed by the GCS. Both candidates exhibit near-infrared J-band spectra with strong methane and water absorption bands characteristic of late-T dwarfs. We derive spectral types of T6.5+/-0.5 and T7+/-1 and estimate photometric distances less than 50 pc for UGCS J030013.86+490142.5 and UGCS J053022.52-052447.4, respectively. The space density of T dwarfs found in the GCS seems consistent with discoveries in the larger areal coverage of the UKIDSS Large Area Survey, indicating one T dwarf in 6-11 square degrees. The final area surveyed by the GCS, 1000 square degrees in five passbands, will allow expansion of the LAS search area by 25%, increase the probability of finding ultracool brown dwarfs, and provide optimal estimates of contamination by old field brown dwarfs in deep surveys to identify such objects in open clusters and star-forming regions.

8 pages, 4 figures, 4 tables, accepted for publication to MNRAS

References in corpus (24)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
• The WFCAM Science Archive
• The UKIRT Infrared Deep Sky Survey Early Data Release
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• The UKIRT Infrared Deep Sky Survey First Data Release
• SDSS J1534+1615AB: A Novel T Dwarf Binary Found with Keck Laser Guide Star Adaptive Optics and the Potential Role of Binarity in the L/T Transition
• Near-infrared cross-dispersed spectroscopy of brown dwarf candidates in the Upper Sco association
• Exploring the substellar temperature regime down to ~550K
• New brown dwarfs in Upper Sco using UKIDSS Galactic Cluster Survey science verification data
• Eight new T4.5-T7.5 dwarfs discovered in the UKIDSS Large Area Survey Data Release 1
• A wide deep infrared look at the Pleiades with UKIDSS: new constraints on the substellar binary fraction and the low mass IMF
• Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey
• The substellar mass function in sigma Orionis. II. Optical, near-infrared and IRAC/Spitzer photometry of young cluster brown dwarfs and planetary-mass objects
• The Physical Properties of HD 3651B: An Extrasolar Nemesis?
• Contamination by field late-M, L and T dwarfs in deep surveys
• Proper motion L and T dwarf candidate members of the Pleiades
• Pleiades low-mass brown dwarfs: the cluster L dwarf sequence
• Proper motions of field L and T dwarfs
• New members in the Upper Sco association from the UKIDSS Early Data Release
• New constraints on the membership of the T dwarf S Ori 70 in the sigma Orionis cluster
• Two T dwarfs from the UKIDSS Early Data Release
• The ages of L dwarfs
• Southern Infrared Proper Motion Survey III: Constraining the mass function of low mass stars

Cited by in corpus (11)

• Further Defining Spectral Type "Y" and Exploring the Low-mass End of the Field Brown Dwarf Mass Function
• New isolated planetary mass objects and the stellar and substellar mass function of the sigma Orionis cluster
• A Comparison of Near-Infrared Photometry and Spectra for Y Dwarfs with a New Generation of Cool Cloudy Models
• Parallaxes and physical properties of 11 mid-to-late T dwarfs
• Self-consistent Models of Y Dwarf Atmospheres with Water Clouds and Disequilibrium Chemistry
• First T dwarfs in the VISTA Hemisphere Survey
• The distance to the cool T9 brown dwarf ULAS J003402.77-005206.7
• UKIDSS detections of cool brown dwarfs - proper motions of 14 known $>$T5 dwarfs and discovery of three new T5.5-T6 dwarfs
• Selection constraints on high redshift quasar searches in the VISTA kilo-degree infrared galaxy survey
• Cool White Dwarfs Found in the UKIRT Infrared Deep Sky Survey
• Near-Infrared Polarization from Unresolved Disks Around Brown Dwarfs and Young Stellar Objects