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تسجيل مستخدم جديدDiscoveries from a Near-infrared Proper Motion Survey using Multi-epoch 2MASS Data
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We have conducted a 4030-square-deg near-infrared proper motion survey using multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778 proper motion candidates, 647 of which are not listed in SIMBAD. After comparison to DSS images, we find that 107 of our proper motion candidates lack counterparts at B-, R-, and I-bands and are thus 2MASS-only detections. We present results of spectroscopic follow-up of 188 targets that include the infrared-only sources along with selected optical-counterpart sources with faint reduced proper motions or interesting colors. We also establish a set of near-infrared spectroscopic standards with which to anchor near-infrared classifications for our objects. Among the discoveries are six young field brown dwarfs, five red L dwarfs, three L-type subdwarfs, twelve M-type subdwarfs, eight blue L dwarfs, and several T dwarfs. We further refine the definitions of these exotic classes to aid future identification of similar objects. We examine their kinematics and find that both the blue L and red L dwarfs appear to be drawn from a relatively old population. This survey provides a glimpse of the kinds of research that will be possible through time-domain infrared projects such as the UKIDSS Large Area Survey, various VISTA surveys, and WISE, and also through z- or y-band enabled, multi-epoch surveys such as Pan-STARRS and LSST.
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The UKIDSS Large Area Survey (LAS) began in 2005, with the start of the UKIDSS program as a 7 year effort to survey roughly 4000 deg$^2$ at high galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of 2-epoch J b
and observations, with an epoch baseline greater than 2 years to calculate proper motions. We present a near infrared proper motion catalogue for the 1500 deg$^2$ of the 2 epoch LAS data, which includes 135,625 stellar sources and a further 88,324 with ambiguous morphological classifications, all with motions detected above the 5$sigma$ level. We developed a custom proper motion pipeline which we describe here. Our catalogue agrees well with the proper motion data supplied for a 300 deg$^2$ subset in the current WFCAM Science Archive (WSA) tenth data release (DR10) catalogue, and in various optical catalogues, but it benefits from a larger matching radius and hence a larger upper proper motion detection limit. We provide absolute proper motions, using LAS galaxies for the relative to absolute correction. By using local 2nd order polynomial transformations, as opposed to linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by the UKIDSS pipeline. We present the results of proper motion searches for new brown dwarfs and white dwarfs. We discuss 41 sources in the WSA DR10 overlap with our catalogue with proper motions $>$300 $mas yr^{-1}$, several of which are new detections. We present 15 new candidate ultra-cool dwarf binary systems.
We report the first results of a multi-epoch search for wide (separations greater than a few tens of AU), low-mass tertiary companions of a volume-limited sample of 118 known spectroscopic binaries within 30 pc of the Sun, using the 2MASS Point Sourc
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warf. The L dwarfs have J-Ks colors near the extrema of known L dwarfs indicating that previous surveys for L dwarfs using color as a selection criterion may be biased. Followup near-infrared spectroscopy of 6 dwarfs confirm they are all late-type with spectral types ranging from M8 to T4. Spectroscopy also shows that some of the L dwarf spectra exhibit peculiar features similar to other peculiar blue L dwarfs which may indicate that these dwarfs have a relatively condensate free atmosphere or may be metal poor. Photometric distance estimates indicate that 22 of the new M, L and T dwarfs lie within 100 pc of the Sun with the newly discovered T dwarf, 2MASS J10595185+3042059, located at about 25 pc. Based on the colors and proper motions of the newly identified objects, several appear to be good subdwarf candidates. The proper motions of known ultracool dwarfs detected in our survey were also measured, including, for the first time, SDSS J085834.42+325627.6 (T1), SDSS J125011.65+392553.9 (T4) and 2MASS J15261405+2043414 (L7).
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