Benchmark low-mass objects in Moving Groups

A kinematically hot population of young stars in the solar neighbourhood

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa909 ◽

2020 ◽

Vol 494 (2) ◽

pp. 2429-2439 ◽

Cited By ~ 1

Author(s):

A S Binks ◽

R D Jeffries ◽

N J Wright

Keyword(s):

Young Stars ◽

Solar Neighbourhood ◽

Mass Distributions ◽

Systematic Effort ◽

Low Mass ◽

Moving Groups

ABSTRACT In the last three decades several hundred nearby members of young stellar moving groups (MGs) have been identified, but there has been less systematic effort to quantify or characterize young stars that do not belong to previously identified MGs. Using a kinematically unbiased sample of 225 lithium-rich stars within 100 pc, we find that only 50 ± 10 per cent of young (≲125 Myr), low-mass (0.5 < M/M⊙ < 1.0) stars, are kinematically associated with known MGs. Whilst we find some evidence that five of the non-MG stars may be connected with the Lower Centaurus–Crux association, the rest form a kinematically ‘hotter’ population, much more broadly dispersed in velocity, and with no obvious concentrations in space. The mass distributions of the MG members and non-MG stars are similar, but the non-MG stars may be older on average. We briefly discuss several explanations for the origin of the non-MG population.

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PLANETS AROUND LOW-MASS STARS (PALMS). V. AGE-DATING LOW-MASS COMPANIONS TO MEMBERS AND INTERLOPERS OF YOUNG MOVING GROUPS

The Astrophysical Journal ◽

10.1088/0004-637x/806/1/62 ◽

2015 ◽

Vol 806 (1) ◽

pp. 62 ◽

Cited By ~ 18

Author(s):

Brendan P. Bowler ◽

Evgenya L. Shkolnik ◽

Michael C. Liu ◽

Joshua E. Schlieder ◽

Andrew W. Mann ◽

...

Keyword(s):

Age Dating ◽

Low Mass Stars ◽

Low Mass ◽

Moving Groups

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A Radial velocity survey of spatially resolved young, low-mass binaries

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732156 ◽

2018 ◽

Vol 618 ◽

pp. A5 ◽

Cited By ~ 2

Author(s):

Stephen Durkan ◽

Markus Janson ◽

Simona Ciceri ◽

Wolfgang Brandner ◽

Joshua Schlieder ◽

...

Keyword(s):

Radial Velocity ◽

Solar Neighborhood ◽

Activity Level ◽

Activity Levels ◽

Old Field ◽

Triple Systems ◽

Chromospheric Activity ◽

Low Mass ◽

Orbital Periods ◽

Moving Groups

The identification and characterisation of low-mass binaries is of importance for a range of astrophysical investigations. Low-mass binaries in young (∼10–100 Myr) moving groups (YMGs) in the solar neighborhood are of particular significance as they provide unique opportunities to calibrate stellar models and evaluate the ages and coevality of the groups themselves. Low-mass M-dwarfs have pre-main sequence life times on the order of ∼100 Myr and therefore are continually evolving along a mass-luminosity track throughout the YMG phase, providing ideal laboratories for precise isochronal dating, if a model-independent dynamical mass can be measured. AstraLux lucky imaging multiplicity surveys have recently identified hundreds of new YMG low-mass binaries, where a subsample of M-dwarf multiples have estimated orbital periods less than 50 yr. We have conducted a radial velocity survey of a sample of 29 such targets to complement the astrometric data. This will allow enhanced orbital determinations and precise dynamical masses to be derived in a shorter timeframe than possible with astrometric monitoring alone, and allow for a more reliable isochronal analysis. Here we present radial velocity measurements derived for our sample over several epochs. We report the detection of the three-component spectroscopic multiple 2MASS J05301858-5358483, for which the C component is a new discovery, and forms a tight pair with the B component. Originally identified as a YMG member, we find that this system is a likely old field interloper, whose high chromospheric activity level is caused by tidal spin-up of the tight BC pair. Two other triple systems with a tight pair exist in the sample, 2MASS J04244260-0647313 (previously known) and 2MASS J20163382-0711456, but for the rest of the targets we find that additional tidally synchronized companions are highly unlikely, providing further evidence that their high chromospheric activity levels are generally signatures of youth.

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A Pan-STARRS1 Search for Substellar Young Moving Group Members

Proceedings of the International Astronomical Union ◽

10.1017/s1743921315006481 ◽

2015 ◽

Vol 10 (S314) ◽

pp. 54-57

Author(s):

Kimberly M. Aller ◽

Michael C. Liu ◽

Eugene A. Magnier

Keyword(s):

Large Scale ◽

Spectral Characteristics ◽

Mass Function ◽

Initial Mass Function ◽

Valuable Insight ◽

Near Ir ◽

Group Members ◽

Low Mass ◽

Moving Groups ◽

Ir Photometry

AbstractYoung moving groups (YMGs) are coeval, comoving groups of stars which have migrated from their birthsites after formation. In the substellar regime, YMG members are key benchmarks to empirically define brown dwarf evolution with age and to study the lowest mass end of the initial mass function. We have combined Pan-STARRS1 (PS1) proper motions with optical+IR photometry from PS1, 2MASS and WISE to perform a large-scale (≈30,000 deg2) systematic search for substellar members down to ≈10 MJup. We have obtained near-IR spectroscopy of a large sample of ultracool candidate YMG members to assess their youth via gravity-sensitive absorption features. We have identified several new intermediate-gravity candidate members of the AB Dor Moving Group, potentially greatly expanding the substellar membership. These new candidate members bridge the gap between the known low-mass stellar and planetary-mass members and yield valuable insight into the spectral characteristics of young brown dwarfs.

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β PICTORIS AND AB DORADUS MOVING GROUPS: LIKELY NEW LOW-MASS MEMBERS

The Astronomical Journal ◽

10.1088/0004-6256/140/1/119 ◽

2010 ◽

Vol 140 (1) ◽

pp. 119-128 ◽

Cited By ~ 60

Author(s):

Joshua E. Schlieder ◽

Sébastien Lépine ◽

Michal Simon

Keyword(s):

Low Mass ◽

Moving Groups

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Spectroscopy and kinematics of low-mass members of young moving groups

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2010.17361.x ◽

2010 ◽

Vol 409 (2) ◽

pp. 552-566 ◽

Cited By ~ 24

Author(s):

M. C. Gálvez-Ortiz ◽

J. R. A. Clarke ◽

D. J. Pinfield ◽

J. S. Jenkins ◽

S. L. Folkes ◽

...

Keyword(s):

Low Mass ◽

Moving Groups

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Spectral characterization of newly detected young substellar binaries with SINFONI

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935319 ◽

2019 ◽

Vol 627 ◽

pp. A167 ◽

Cited By ~ 1

Author(s):

Per Calissendorff ◽

Markus Janson ◽

Rubén Asensio-Torres ◽

Rainer Köhler

Keyword(s):

Adaptive Optics ◽

Spectral Type ◽

Binary Systems ◽

Equal Mass ◽

Spectral Characterization ◽

Evolutionary Models ◽

Low Mass ◽

Moving Groups ◽

Integral Field Spectrograph ◽

Guide Star

We observe 14 young low-mass substellar objects using the VLT/SINFONI integral field spectrograph with laser guide star adaptive optics to detect and characterize three candidate binary systems. All three binary candidates show strong signs of youth, with two of them likely belonging to young moving groups. Together with the adopted young-moving-group ages we employ isochrones from the BT-Settle CIFIST substellar evolutionary models to estimate individual masses for the binary components. We find 2MASS J15104786–2818174 to be part of the ≈30−50 Myr Argus moving group and to be composed of a 34−48 MJup primary brown dwarf with spectral type M9γ and a fainter 15−22 MJup companion, separated by ≈100 mas. 2MASS J22025794–5605087 is identified as an almost equal-mass binary in the AB Dor moving group, with a projected separation of ≈60 mas. Both components share spectral type M9γ/β, which with the adopted age of 120−200 Myr yields masses in the range of 50−68 MJup for each component individually. The observations of 2MASS J15474719–2423493 are of lower quality and we obtain no spectral characterization for the target, but resolve two components separated by ≈170 mas which with the predicted young field age of 30−50 Myr yields individual masses below 20 MJup. Out of the three candidate binary systems, 2MASS J22025794–5605087 has unambiguous spectroscopic signs of being a bona-fide binary, while the other two will require second-epoch confirmation. The small projected separations between the binary components correspond to physical separations of ≈4−7 AU, meaning that astrometric monitoring of just a few years would be adequate to generate constrained orbital fits and dynamical masses for the systems. In combination with their young ages, these binaries will prove to be excellent benchmarks for calibrating substellar evolutionary models down to a very low-mass regime.

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A kinematically unbiased, all-sky search for nearby, young, low-mass stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3019 ◽

2019 ◽

Vol 491 (1) ◽

pp. 215-234 ◽

Cited By ~ 2

Author(s):

Alexander S Binks ◽

Matthieu Chalifour ◽

Joel H Kastner ◽

David Rodriguez ◽

Simon J Murphy ◽

...

Keyword(s):

Young Star ◽

Photometric Data ◽

Young Stars ◽

Stellar Clusters ◽

Late Type ◽

Low Mass Stars ◽

Near Ir ◽

Field Star ◽

Low Mass ◽

Moving Groups

ABSTRACT The past two decades have seen dramatic progress in our knowledge of the population of young stars of age $\lt \!200\,$ Myr that lie within $150\,$ pc of the Sun. These nearby, young stars, most of which are found in loose, comoving groups, provide the opportunity to explore (among many other things) the dissolution of stellar clusters and their diffusion into the field star population. Here, we exploit the combination of astrometric and photometric data from Gaia and photometric data from GALEX (UV) and 2MASS (near-IR) in an attempt to identify additional nearby, young, late-type stars. Specifically, we present a sample of 146 GALEX UV-selected late-type (predominantly K-type) field stars with Gaia-based distances $\lt \!125\,$ pc (based on Gaia Data Release 1) that have isochronal ages $\lt \!80\,$ Myr even if equal-components binaries. We investigate the spectroscopic and kinematic properties of this sample. Despite their young isochronal ages, only ∼10 per cent of stars among this sample can be confidently associated with established nearby, young moving groups (MGs). These candidate MG members include five stars newly identified in this study. The vast majority of our sample of 146 nearby young star candidates have anomalous kinematics relative to the known MGs. These stars may hence represent a previously unrecognized population of young stars that has recently mixed into the older field star population. We discuss the implications and caveats of such a hypothesis – including the intriguing fact that, in addition to their non-young-star-like kinematics, the majority of the UV-selected, isochronally young field stars within $50\,$ pc appear surprisingly X-ray faint.

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A Review on Substellar Objects below the Deuterium Burning Mass Limit: Planets, Brown Dwarfs or What?

Geosciences ◽

10.3390/geosciences8100362 ◽

2018 ◽

Vol 8 (10) ◽

pp. 362 ◽

Cited By ~ 7

Author(s):

José Caballero

Keyword(s):

Brown Dwarfs ◽

Open Clusters ◽

Formation Mechanisms ◽

Mass Limit ◽

Low Mass Stars ◽

Open Clusters And Associations ◽

Substellar Objects ◽

History Of ◽

Low Mass ◽

Moving Groups

“Free-floating, non-deuterium-burning, substellar objects” are isolated bodies of a few Jupiter masses found in very young open clusters and associations, nearby young moving groups, and in the immediate vicinity of the Sun. They are neither brown dwarfs nor planets. In this paper, their nomenclature, history of discovery, sites of detection, formation mechanisms, and future directions of research are reviewed. Most free-floating, non-deuterium-burning, substellar objects share the same formation mechanism as low-mass stars and brown dwarfs, but there are still a few caveats, such as the value of the opacity mass limit, the minimum mass at which an isolated body can form via turbulent fragmentation from a cloud. The least massive free-floating substellar objects found to date have masses of about 0.004 Msol, but current and future surveys should aim at breaking this record. For that, we may need LSST, Euclid and WFIRST.

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