Photometric brown-dwarf classification. I. A method to identify and accurately classify large samples of brown dwarfs without spectroscopy

Abstract

Aims. We present a method, named photo-type, to identify and accurately classify L and T dwarfs onto the standard spectral classification system using photometry alone. This enables the creation of large and deep homogeneous samples of these objects efficiently, without the need for spectroscopy. Methods. We created a catalogue of point sources with photometry in 8 bands, ranging from 0.75 to 4.6 microns, selected from an area of 3344 deg^2, by combining SDSS, UKIDSS LAS, and WISE data. Sources with 13.0 < J < 17.5, and Y - J > 0.8, were then classified by comparison against template colours of quasars, stars, and brown dwarfs. The L and T templates, spectral types L0 to T8, were created by identifying previously known sources with spectroscopic classifications, and fitting polynomial relations between colour and spectral type. Results. Of the 192 known L and T dwarfs with reliable photometry in the surveyed area and magnitude range, 189 are recovered by our selection and classification method. We have quantified the accuracy of the classification method both externally, with spectroscopy, and internally, by creating synthetic catalogues and accounting for the uncertainties. We find that, brighter than J = 17.5, photo-type classifications are accurate to one spectral sub-type, and are therefore competitive with spectroscopic classifications. The resultant catalogue of 1157 L and T dwarfs will be presented in a companion paper.

15 pages, 12 figures, Accepted for publication in A & A

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Cited by in corpus (12)

• Physical properties of 15 quasars at $z\gtrsim 6.5$
• BOSS Ultracool Dwarfs I: Colors and Magnetic Activity of M and L dwarfs
• Three new VHS-DES Quasars at 6.7 < z < 6.9 and Emission Line Properties at z > 6.5
• A new bright z=6.82 quasar discovered with VISTA: VHS J0411-0907
• Physical properties and trigonometric distance of the peculiar dwarf WISE J181005.5$-$101002.3
• 49 new T dwarfs identified using methane imaging
• Ultracool dwarfs candidates based on six years of the Dark Energy Survey data
• A homogeneous sample of 34 000 M7-M9.5 dwarfs brighter than $J$=17.5 with accurate spectral types
• Catalog of Candidates for Quasars at 3 < z < 5.5 Selected among X-Ray Sources from the 3XMM-DR4 Survey of the XMM-Newton Observatory
• L dwarfs detection from SDSS images using improved Faster R-CNN
• Characterisation of the eclipsing post-common-envelope binary TIC 60040774
• Identifying and characterizing ultracool dwarfs ejected from post-encounter disintegrating systems