A homogeneous sample of 34 000 M7−M9.5 dwarfs brighter than <i>J</i> = 17.5 with accurate spectral types

Ahmed, Saad; Warren, S. J.

doi:10.1051/0004-6361/201834591

Cited by 13 publications

(35 citation statements)

References 37 publications

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“…They applied the method to produce a sample of 1361 L and T dwarfs brighter than J = 17.5 (Skrzypek et al 2016). Ahmed & Warren (2019) extended this work to earlier spectral types and produced a sample of 33 665 M7 to M9.5 dwarfs, to the same magnitude limit. The accuracy of the spectral typing is better than one spectral sub-type, and is competitive with spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

“…In this paper we match the large phototype sample of M7 to M9.5 stars of Ahmed & Warren (2019) to Gaia DR2, to determine the relation between absolute magnitude and spectral type, as well as the MF, over this spectral range. Almost all multiple systems in the sample are observed as unresolved, and are identified by virtue of being overluminous.…”

Section: Introductionmentioning

confidence: 99%

“…To obtain an unbiased estimate of the MF requires selecting a volume-complete sample. For a given spectral type, the selection of appropriate upper and lower distance limits to define a sample that is unbiased with respect to multiplicity requires a careful consideration of: the flux limits of the sample of Ahmed & Warren (2019); the flux limits of the Gaia sample of sources with parallaxes; and the fact that unresolved multiple systems are brighter than single sources. Furthermore because luminosity is a strong function of spectral type, the optimal upper and lower distance limits that maximise sample size vary strongly with spectral type.…”

Section: Introductionmentioning

confidence: 99%

“…The layout of the remainder of the paper is as follows. In §2 we describe the sample of Ahmed & Warren (2019) and the matching to Gaia. In §3 we explain the principles of selecting a volume-complete sample as a function of G − J from the Gaia matched sample.…”

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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The absolute magnitudes MJ, the binary fraction, and the binary mass ratios of M7–M9.5 dwarfs

Laithwaite¹,

Warren²

2020

Monthly Notices of the Royal Astronomical Society

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We use the large homogeneous sample of late M dwarfs, M7 to M9.5, of Ahmed & Warren (2019) matched to Gaia DR2, to measure the relation between absolute magnitude and spectral type, and to infer the multiplicity fraction of the population, and the distribution of mass ratios in the binary systems. Binaries are identified photometrically as overluminous sources. In order to define a sample that is unbiased with respect to multiplicity we use distance limits that are a function of G − J colour to define a volume-complete sample of 2706 systems. The G − J colours are very precise, with random errors all less than 0.02. We measure absolute magnitudes MJ that are on average 0.5 mag. brighter than previous determinations. We find evidence that the discrepancies arise from differences in spectral types in different samples. The measured binary fraction is $16.5\pm 0.8\%$, of which $98\%$ are unresolved: both values are consistent with results of previous studies. The distribution of excess flux in the binaries, compared to the singles, is used to infer the mass ratio distribution f(q)∝qγ, where q = Ms/Mp. We infer a very steep distribution over this spectral range, with γ > 10 ($99\%$ probability). This says that unresolved ultracool M dwarf binaries reside almost exclusively in equal mass systems, and implies that the spectral types of the unresolved binaries match to with 0.5 spectral subtypes. The intrinsic scatter in absolute magnitude MJ for ultracool M dwarfs at fixed G − J colour is measured to be 0.21 mag.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…

…”

mentioning

confidence: 99%

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The absolute magnitudes MJ, the binary fraction, and the binary mass ratios of M7–M9.5 dwarfs

Laithwaite¹,

Warren²

2020

Monthly Notices of the Royal Astronomical Society

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Ultracool dwarfs identified using spectra in LAMOST DR7

Wang

Luo

Chen

et al. 2022

A&A

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In this work, we identify 734 ultracool dwarfs with a spectral type of M6 or later, including one L0. Of this sample, 625 were studied spectroscopically for the first time. All of these ultracool dwarfs are within 360 pc, with a Gaia G magnitude brighter than ∼ 19.2 mag. By studying the spectra and checking their stellar parameters (T eff , log g, and [M/H]) derived with the LAMOST pipeline, we found their cool red nature and their metallicity to be consistent with the nature of Galactic thin-disk objects. Furthermore, 77 of them show lithium absorption lines at 6708 Å, further indicating their young ages and substellar nature. Kinematics obtained through LAMOST radial velocities, along with the proper motion and parallax data from Gaia EDR3, also suggest that the majority of our targets are thin-disk objects. Kinematic ages were estimated through the relationship between the velocity dispersion and the average age for a certain population. Moreover, we identified 35 binaries, with 6 of them reported as binaries for the first time.

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J-PLUS: Discovery and characterisation of ultracool dwarfs using Virtual Observatory tools

Mas-Buitrago¹,

Solano²,

González‐Marcos³

et al. 2022

A&A

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Context. Ultracool dwarfs (UCDs) comprise the lowest mass members of the stellar population and brown dwarfs, from M7 V to cooler objects with L, T, and Y spectral types. Most of them have been discovered using wide-field imaging surveys, for which the Virtual Observatory (VO) has proven to be of great utility. Aims. We aim to perform a search for UCDs in the entire Javalambre Photometric Local Universe Survey (J-PLUS) second data release (2 176 deg 2 ) following a VO methodology. We also explore the ability to reproduce this search with a purely machine learning (ML)-based methodology that relies solely on J-PLUS photometry. Methods. We followed three different approaches based on parallaxes, proper motions, and colours, respectively, using the VOSA tool to estimate the effective temperatures and complement J-PLUS photometry with other catalogues in the optical and infrared. For the ML methodology, we built a two-step method based on principal component analysis and support vector machine algorithms. Results. We identified a total of 7 827 new candidate UCDs, which represents an increase of about 135 % in the number of UCDs reported in the sky coverage of the J-PLUS second data release. Among the candidate UCDs, we found 122 possible unresolved binary systems, 78 wide multiple systems, and 48 objects with a high Bayesian probability of belonging to a young association. We also identified four objects with strong excess in the filter corresponding to the Ca ii H and K emission lines and four other objects with excess emission in the Hα filter. Follow-up spectroscopic observations of two of them indicate they are normal late-M dwarfs. With the ML approach, we obtained a recall score of 92 % and 91 % in the 20×20 deg 2 regions used for testing and blind testing, respectively. Conclusions. We consolidated the proposed search methodology for UCDs, which will be used in deeper and larger upcoming surveys such as J-PAS and Euclid. We concluded that the ML methodology is more efficient in the sense that it allows for a larger number of true negatives to be discarded prior to analysis with VOSA, although it is more photometrically restrictive.

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

Cited by 13 publications

References 37 publications

The absolute magnitudes MJ, the binary fraction, and the binary mass ratios of M7–M9.5 dwarfs

The absolute magnitudes MJ, the binary fraction, and the binary mass ratios of M7–M9.5 dwarfs

Ultracool dwarfs identified using spectra in LAMOST DR7

J-PLUS: Discovery and characterisation of ultracool dwarfs using Virtual Observatory tools

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