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A homogeneous sample of 34 000 M7-M9.5 dwarfs brighter than J=17.5 with accurate spectral types

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Title: A homogeneous sample of 34 000 M7-M9.5 dwarfs brighter than J=17.5 with accurate spectral types
Authors: Ahmed, S
Warren, SJ
Item Type: Journal Article
Abstract: The space density of late M dwarfs, subtypes M7–M9.5, is not well determined. We applied the photo-type method to iz photometry from the Sloan Digital Sky Survey and YJHK photometry from the UKIRT Infrared Deep Sky Survey, over an effective area of 3070 deg2, to produce a new, bright J(Vega) <  17.5, homogeneous sample of 33 665 M7–M9.5 dwarfs. The typical S/N of each source summed over the six bands is > 100. Classifications are provided to the nearest half spectral subtype. Through a comparison with the classifications in the BOSS Ultracool Dwarfs (BUD) spectroscopic sample, the typing is shown to be accurately calibrated to the BUD classifications and the precision is better than 0.5 subtypes rms; i.e. the photo-type classifications are as precise as good spectroscopic classifications. Sources with large χ2 >  20 include several catalogued late-type subdwarfs. The new sample of late M dwarfs is highly complete, but there is a bias in the classification of rare peculiar blue or red objects. For example, L subdwarfs are misclassified towards earlier types by approximately two spectral subtypes. We estimate that this bias affects only ∼1% of the sources. Therefore the sample is well suited to measure the luminosity function and investigate the softening towards the Galactic plane of the exponential variation of density with height.
Issue Date: 18-Mar-2019
Date of Acceptance: 24-Feb-2019
URI: http://hdl.handle.net/10044/1/68204
DOI: https://dx.doi.org/10.1051/0004-6361/201834591
ISSN: 0004-6361
Publisher: EDP Sciences
Journal / Book Title: Astronomy and Astrophysics
Volume: 623
Copyright Statement: © 2019 The European Southern Observatory (ESO).
Sponsor/Funder: Science and Technology Facilities Council
Science and Technology Facilities Council (STFC)
Funder's Grant Number: ST-N000838
ST/N000838/1
Keywords: Science & Technology
Physical Sciences
Astronomy & Astrophysics
stars: low-mass
catalogs
surveys
LOW-MASS STARS
DIGITAL SKY SURVEY
PHOTOMETRIC SYSTEM
T-DWARFS
CLASSIFICATION
LUMINOSITY
CALIBRATION
STELLAR
I.
Science & Technology
Physical Sciences
Astronomy & Astrophysics
stars: low-mass
catalogs
surveys
LOW-MASS STARS
DIGITAL SKY SURVEY
PHOTOMETRIC SYSTEM
T-DWARFS
CLASSIFICATION
LUMINOSITY
CALIBRATION
STELLAR
I.
0201 Astronomical and Space Sciences
Astronomy & Astrophysics
Publication Status: Published
Article Number: A127
Online Publication Date: 2019-03-18
Appears in Collections:Physics
Astrophysics
Faculty of Natural Sciences



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