The possiblity of detection of ultracool dwarfs with the UKIRT Infrared Deep Sky Survey

Deacon, N. R.; Hambly, N. C.

doi:10.1111/j.1365-2966.2006.10795.x

Cited by 23 publications

(52 citation statements)

References 29 publications

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“…We compared the space densities obtained above with the results of numerical simulations computed assuming different IMFs and birth rates from Deacon & Hambly (2006). Details of the simulations are briefly summarized here.…”

Section: Comparison With Numerical Simulationsmentioning

confidence: 99%

A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density

Marocco¹,

Jones²,

Day-Jones³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from the United Kingdom Deep Infrared Sky Survey. Using the YJHK photometry from the Large Area Survey and the red-optical photometry from the Sloan Digital Sky Survey we selected a sample of 262 brown dwarf candidates and we have followed-up 196 of them using the echelle spectrograph X-shooter on the Very Large Telescope. The large wavelength coverage (0.30 − 2.48µm) and moderate resolution (R∼ 5000 − 9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low gravity M dwarfs. Using a spectral indices-based technique we identified 27 unresolved binary candidates, for which we have determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity for our targets, and we determined the distribution of the sample, which is centred at -1.7±1.2 km s −1 with a dispersion of 31.5 km s −1 . Using our results we estimated the space density of field brown dwarfs and compared it with the results of numerical simulations. Depending on the binary fraction, we found that there are (0.85±0.55)×10 −3 to (1.00±0.64)×10 −3 objects per cubic parsec in the L4-L6.5 range, (0.73 ± 0.47) × 10 −3 to (0.85 ± 0.55) × 10 −3 objects per cubic parsec in the L7-T0.5 range, and (0.74 ± 0.48) × 10 −3 to (0.88 ± 0.56) × 10 −3objects per cubic parsec in the T1-T4.5 range. We notice that there seem to be an excess of objects in the L to T transition with respect to the late T dwarfs, a discrepancy that could be explained assuming a higher binary fraction than expected for the L to T transition, or that objects in the high-mass end and low-mass end of this regime form in different environments, i.e. following different Initial Mass Functions.

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Section: Comparison With Numerical Simulationsmentioning

confidence: 99%

A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density

Marocco¹,

Jones²,

Day-Jones³

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…This filter is designed to allow such objects to be distinguished from main-sequence stars and high-z quasars (Leggett et al 2005). The UKIDSS ZYJHK system is described by Hewett et al (2006) and simulations of the projected results of the LAS concerning ultracool dwarfs described by Deacon & Hambly (2006).…”

Section: Introductionmentioning

confidence: 99%

Two T dwarfs from the UKIDSS early data release

Kendall¹,

Tamura

Tinney

et al. 2007

A&A

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Context. We report on the first ultracool dwarf discoveries from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release (LAS EDR), in particular the discovery of T dwarfs which are fainter and more distant than those found using the 2MASS and SDSS surveys. Aims. We aim to show that our methodologies for searching the ∼27 deg 2 of the LAS EDR are successful for finding both L and T dwarfs via cross-correlation with the Sloan Digital Sky Survey (SDSS) DR4 release. While the area searched so far is small, the numbers of objects found shows great promise for near-future releases of the LAS and great potential for finding large numbers of such dwarfs. Methods. Ultracool dwarfs are selected by combinations of their YJH(K) UKIDSS colours and SDSS DR4 z − J and i − z colours, or, lower limits on these red optical/infrared colours in the case of DR4 dropouts. After passing visual inspection tests, candidates have been followed up by methane imaging and spectroscopy at 4 m and 8 m-class facilities. Results. Our main result is the discovery following CH 4 imaging and spectroscopy of a T4.5 dwarf, ULAS J 1452+0655, lying ∼80 pc distant. A further T dwarf candidate, ULAS J 1301+0023, has very similar CH 4 colours but has not yet been confirmed spectroscopically. We also report on the identification of a brighter L0 dwarf, and on the selection of a list of LAS objects designed to probe for T-like dwarfs to the survey J-band limit. Conclusions. Our findings indicate that the combination of the UKIDSS LAS and SDSS surveys provide an excellent tool for identifying L and T dwarfs down to much fainter limits than previously possible. Our discovery of one confirmed and one probable T dwarf in the EDR is consistent with expectations from the previously measured T dwarf density on the sky.

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“…The method used here is based on the simulations used for Deacon & Hambly (2006). These are similar in principle to those of Burgasser (2004).…”

Section: Simulation Methodsmentioning

confidence: 99%

Southern infrared proper motion survey

Deacon¹,

Nelemans²,

Hambly

2008

A&A

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The stellar mass function is one of the fundamental distributions of stellar astrophysics. Its form at masses similar to the Sun was found by Salpeter (1955, ApJ, 121, 161) to be a power-law m −α with a slope of α = 1.35. Since then the mass function in the field, in stellar clusters and in other galaxies has been studied to identify variation due to environment and mass range. Here we use results from previous papers in the SIPS series to constrain the mass function of low mass stars (0.075 M < m < 0.2 M ). We use simulations of the local low mass stellar population to model the results of the SIPS-II survey. We then vary the input parameters of these simulations (the exponent of the mass function α and a stellar birthrate parameter β) and compare the simulated survey results with those from the actual survey. After a correction for binarity and taking into account potential errors in our model we find that α = −0.62 ± 0.26 for the quoted mass range.

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The possiblity of detection of ultracool dwarfs with the UKIRT Infrared Deep Sky Survey

Cited by 23 publications

References 29 publications

A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density

A large spectroscopic sample of L and T dwarfs from UKIDSS LAS: peculiar objects, binaries, and space density

Two T dwarfs from the UKIDSS early data release

Southern infrared proper motion survey

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