Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral
 typing from SDSS and 2MASS photometric colors

Zhang, ZH; Pokorny, R. S.; Jones, H. R. A.; Pinfield, D. J.; Chen, P. S.; Han, Zongsu; Chen, D.; Gálvez-Ortiz, M. C.; Burningham, B.

doi:10.1051/0004-6361/200810314

Cited by 47 publications

(28 citation statements)

References 39 publications

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“…There is also broad agreement between these results and observational work (e.g. Zhang et al 2009;Leggett et al 2010). Simulated i − z colours of the quasar sample over the SDSS passbands are also consistent with the corresponding SDSS photometry.…”

Section: Selection In Z Y Jsupporting

confidence: 83%

Selection constraints on high-redshift quasar searches in the VISTA Kilo-degree Infrared Galaxy survey

Findlay

Sutherland

Venemans

et al. 2011

Monthly Notices of the Royal Astronomical Society

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Copyright 2011 Elsevier B.V., All rights reserved.The European Southern Observatory's (ESO) Visible and Infrared Survey Telescope for Astronomy (VISTA) is a 4-m class survey telescope for wide-field near-infrared imaging. VISTA is currently running a suite of six public surveys, which will shortly deliver their first Europe wide public data releases to ESO. The VISTA Kilo-degree Infrared Galaxy survey (VIKING) forms a natural intermediate between current wide shallow and deeper more concentrated surveys, by targeting two patches totalling 1500 deg in the Northern and Southern hemispheres with measured 5?? limiting depths of Z??? 22.4, Y??? 21.4, J??? 20.9, H??? 19.9 and K??? 19.3 (Vega). This architecture forms an ideal working parameter space for the discovery of a significant sample of 6.5 ??? z ??? 7.5 quasars. In the first data release, priority has been placed on small areas encompassing a number of fields well sampled at many wavelengths, thereby optimizing science gains and synergy whilst ensuring a timely release of the first products. For rare object searches, e.g. high-z quasars, this policy is not ideal since photometric selection strategies generally evolve considerably with the acquisition of data. Without a reasonably representative data set sampling many directions on the sky, it is not clear how a rare object search can be conducted in a highly complete and efficient manner. In this paper, we alleviate this problem by supplementing initial data with a realistic model of the spatial, luminosity and colour distributions of sources known to heavily contaminate photometric quasar selection spaces, namely dwarf stars of spectral types M, L and T. We use this model along with a subset of available data to investigate contamination of quasar selection space by cool stars and galaxies and lay down a set of benchmark selection constraints that limit contamination to reasonable levels whilst maintaining high completeness as a function of both magnitude and redshift. We review recent follow-up imaging of the first VIKING high-z quasar candidates and find that the results lend considerable support for the choice of selection constraints. The methods outlined here are also applicable to rare object searches in a number of other ongoing and forthcoming projects. ?? 2011 The Authors. Monthly Notices of the Royal Astronomical Society ?? 2011 RAS

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Section: Selection In Z Y Jsupporting

confidence: 83%

Selection constraints on high-redshift quasar searches in the VISTA Kilo-degree Infrared Galaxy survey

Findlay

Sutherland

Venemans

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…References: 1 -this paper; 2 - Lodieu et al (2012);3 -Kirkpatrick et al (2010);4 -Lodieu et al (2012);5 -Bowler, Liu, & Dupuy (2010) and Schmidt et al (2010). ULAS and SDSS multi-epochs imaging (following Zhang et al 2009). Proper motions were calculated based on coordinate and epoch differences between SDSS and UKIDSS observations.…”

Section: Candidate Selectionmentioning

confidence: 99%

“…2 shows that the NIR spectra of UL1249 and UL1338 compare well with 2M1756 and 2M1158; thus, we classify them as sdL1 and sdL7, respectively. The 0.8 µm VO band is present in the spectra of latetype M and early-type L dwarfs (e.g., Bochanski et al 2007;Zhang et al 2009). The 0.8 µm VO absorption band coexists with the 2.3 µm CO absorption band in early-type sdL subdwarfs (e.g.…”

Section: Spectral Classification Of L Subdwarfsmentioning

confidence: 99%

Primeval very low-mass stars and brown dwarfs – I. Six new L subdwarfs, classification and atmospheric properties

Zhang

Pinfield

Galvez-Ortiz

et al. 2016

Mon. Not. R. Astron. Soc.

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We have conducted a search for L subdwarf candidates within the photometric catalogues of the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey. Six of our candidates are confirmed as L subdwarfs spectroscopically at optical and/or nearinfrared wavelengths. We also present new optical spectra of three previously known L subdwarfs (WISEA J001450.17-083823.4, 2MASS J00412179+3547133 and ULAS J124425.75+102439.3). We examined the spectral type and metallicity classification of subclasses of known L subdwarfs. We summarized the spectroscopic properties of L subdwarfs with different spectral types and subclasses. We classify these new L subdwarfs by comparing their spectra to known L subdwarfs and L dwarf standards. We estimate temperatures and metallicities of 22 late-type M and L subdwarfs by comparing their spectra to BT-Settl models. We find that L subdwarfs have temperatures between 1500 and 2700 K, which are higher than similar-typed L dwarfs by around 100-400 K depending on different subclasses and subtypes. We constrained the metallicity ranges of subclasses of M, L, and T subdwarfs. We also discussed the spectral-type and absolute magnitude relationships for L and T subdwarfs.

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“…Field dwarfs with spectral types T0-8 (effective temperature 1400-700 K) have typical colours of I − J > 4.5, J − H < 1.5, and J − K s < 2 mag (Tinney et al 2003;Zhang et al 2009); the early types have redder J − H and J − K s colours and higher effective temperatures than the later types. By extrapolating the σ Orionis cluster sequence using the field dwarf sequence, cluster members with a T spectral type appear to be at J ∼ 20 mag (see Sect.…”

Section: The Search For σ Orionis Lt-type Objectsmentioning

confidence: 99%

Candidate free-floating super-Jupiters in the young σ Orionis open cluster

Bihain

Rebolo

Osorio³

et al. 2009

A&A

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Context. Free-floating substellar candidates with estimated theoretical masses of as low as ∼5 Jupiter masses have been found in the ∼3 Myr old σ Orionis open cluster. As the overlap with the planetary mass domain increases, the question of how these objects form becomes important. The determination of their number density and whether a mass cut-off limit exists is crucial to understanding their formation. Aims. We propose to search for objects of yet lower masses in the cluster and determine the shape of the mass function at low mass. Methods. Using new-and (re-analysed) published IZJHK s [3.6]−[8.0]-band data of an area of 840 arcmin 2 , we performed a search for LT-type cluster member candidates in the magnitude range J = 19.5-21.5 mag, based on their expected magnitudes and colours. Results. Besides recovering the T type object S Ori 70 and two other known objects, we find three new cluster member candidates, S Ori 72-74, with J ≈ 21 mag and within 12 arcmin of the cluster centre. They have theoretical masses of 4 +3 −2 M Jup and are among the least massive free-floating objects detected by direct imaging outside the Solar System. The photometry in archival Spitzer [3.6]-[5.8]-band images infers that S Ori 72 is an L/T transition candidate and S Ori 73 a T-type candidate, following the expected cluster sequence in the mid-infrared. Finally, the L-type candidate S Ori 74 with lower quality photometry is located at 11.8 arcsec (∼4250 AU) of a stellar member of σ Orionis and could be a companion. After contaminant correction in the area complete to J = 21.1 mag, we estimate that there remain between zero and two cluster members in the mass interval 6-4 M Jup . Conclusions. We present S Ori 73, a new candidate T type and candidate σ Orionis member of a few Jupiter masses. Our result suggests a possible turnover in the substellar mass spectrum below ∼6 Jupiter masses, which could be investigated further by wider and deeper photometric surveys.

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Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

Cited by 47 publications

References 39 publications

Selection constraints on high-redshift quasar searches in the VISTA Kilo-degree Infrared Galaxy survey

Selection constraints on high-redshift quasar searches in the VISTA Kilo-degree Infrared Galaxy survey

Primeval very low-mass stars and brown dwarfs – I. Six new L subdwarfs, classification and atmospheric properties

Candidate free-floating super-Jupiters in the young σ Orionis open cluster

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