Article

Eight new T4.5–T7.5 dwarfs discovered in the UKIDSS Large Area Survey Data Release 1★

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 08/2007; 379(4):1423 - 1430. DOI: 10.1111/j.1365-2966.2007.12023.x
Source: arXiv

ABSTRACT We present eight new T4.5–T7.5 dwarfs identified in the UKIRT (United Kingdom Infrared Telescope) 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 deg2 (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.. We have found six 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.

0 Bookmarks
 · 
84 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report on new nearby L and late-M dwarfs (dphot≤ 30 pc) discovered in our search for nearby ultracool dwarfs (I–J≥ 3.0, later than M8.0) at low Galactic latitude (|b| < 15°) over 4800 deg2 in the Deep Near Infrared Survey of the Southern Sky (DENIS) data base. We used late-M (≥ M8.0), L and T dwarfs with accurate trigonometric parallaxes to calibrate the MJ versus I–J colour–luminosity relation. The resulting photometric distances have standard errors of ∼15 per cent, which we used to select candidates dphot≤ 30 pc. We measured proper motions from multi-epoch images found in the public archives ALADIN, DSS, 2MASS and DENIS, with at least three distinct epochs and time baselines of 10–21 yr. We then used a maximum reduced proper motion cut-off to select 28 candidates as ultracool dwarfs (M8.0–L8.0) and to reject one as a distant red star. No T dwarf candidates were found in this search, which required an object to be detected in all three DENIS bands. Our low-resolution optical spectra confirmed that 26 were indeed ultracool dwarfs, with spectral types from M8.0 to L5.5. Two contaminants and one rejected by the maximum reduced proper motion cut-off were all reddened F–K main sequence stars. 20 of these 26 ultracool dwarfs are new nearby ultracool dwarf members, three L dwarfs within 15 pc with one L3.5 at only ∼10 pc. We determine a stellar density of dwarfs pc−3 mag−1 over 11.1 ≤MJ≤ 13.1 based on this sample of M8–L3.5 ultracool dwarfs. Our ultracool dwarf density value is in good agreement with the measurement by Cruz et al. of the ultracool dwarf density at high Galactic latitude.
    Monthly Notices of the Royal Astronomical Society 01/2008; 383(3):831 - 844. · 5.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the discovery of 47 new T dwarfs in the Fourth Data Release (DR4) from the Large Area Survey (LAS) of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey with spectral types ranging from T0 to T8.5. These bring the total sample of LAS T dwarfs to 80 as of DR4. In assigning spectral types to our objects we have identified eight new spectrally peculiar objects, and divide seven of them into two classes. H2O-H-early have a H2O-H index that differs with the H2O-J index by at least two subtypes. CH4-J-early have a CH4-J index that disagrees with the H20-J index by at least two subtypes. We have ruled out binarity as a sole explanation for both types of peculiarity, and suggest that they may represent hitherto unrecognized tracers of composition and/or gravity. Clear trends in z'(AB) - J and Y - J are apparent for our sample, consistent with weakening absorption in the red wing of the KI line at 0.77mum with decreasing effective temperature. We have used our sample to estimate space densities for T6-T9 dwarfs. By comparing our sample to Monte Carlo simulations of field T dwarfs for various mass functions of the form psi(M) ~M-alphapc-3M-1solar, we have placed weak constraints on the form of the field mass function. Our analysis suggests that the substellar mass function is declining at lower masses, with negative values of alpha preferred. This is at odds with results for young clusters that have been generally found to have alpha > 0.
    Monthly Notices of the Royal Astronomical Society 01/2010; 406:1885-1906. · 5.52 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We describe the WFCAM Science Archive, which is the primary point of access for users of data from the wide-field infrared camera WFCAM on the United Kingdom Infrared Telescope (UKIRT), especially science catalogue products from the UKIRT Infrared Deep Sky Survey. We describe the database design with emphasis on those aspects of the system that enable users to fully exploit the survey data sets in a variety of different ways. We give details of the database-driven curation applications that take data from the standard nightly pipeline-processed and calibrated files for the production of science-ready survey data sets. We describe the fundamentals of querying relational databases with a set of astronomy usage examples, and illustrate the results.
    Monthly Notices of the Royal Astronomical Society 02/2008; 384(2):637 - 662. · 5.52 Impact Factor

Full-text (2 Sources)

Download
27 Downloads
Available from
May 22, 2014