scholarly journals A kinematically hot population of young stars in the solar neighbourhood

2020 ◽  
Vol 494 (2) ◽  
pp. 2429-2439 ◽  
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.

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

2019 ◽  
Vol 491 (1) ◽  
pp. 215-234 ◽  
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.

scholarly journals The Observational Evidence for Accretion

1997 ◽  
Vol 182 ◽  
pp. 391-405 ◽  
Author(s):  
Lee Hartmann
Keyword(s):  
Large Range ◽  
Observational Evidence ◽  
Young Stars ◽  
Young Stellar Objects ◽  
Stellar Objects ◽  
T Tauri ◽  
Accretion Rates ◽  
Low Mass ◽  
Stellar Magnetospheres ◽  
Mass Ejection

Outflows from low-mass young stellar objects are thought to draw upon the energy released by accretion onto T Tauri stars. I briefly summarize the evidence for this accretion and outline present estimates of mass accretion rates. Young stars show a very large range of accretion rates, and this has important implications for both mass ejection and for the structure of stellar magnetospheres which may truncate T Tauri disks.

scholarly journals Birth sites of young stellar associations and recent star formation in a flocculent corrugated disc

2020 ◽  
Vol 499 (4) ◽  
pp. 5623-5640
Author(s):  
Alice C Quillen ◽  
Alex R Pettitt ◽  
Sukanya Chakrabarti ◽  
Yifan Zhang ◽  
Jonathan Gagné ◽  
...  
Keyword(s):  
Space Distribution ◽  
Solar Neighbourhood ◽  
Low Velocity ◽  
Stellar Association ◽  
Stellar Orbits ◽  
Pattern Speeds ◽  
Moving Groups ◽  
Orbit Integration ◽  
Stellar Associations ◽  
Spiral Arm

ABSTRACT With backwards orbit integration, we estimate birth locations of young stellar associations and moving groups identified in the solar neighbourhood that are younger than 70 Myr. The birth locations of most of these stellar associations are at a smaller galactocentric radius than the Sun, implying that their stars moved radially outwards after birth. Exceptions to this rule are the Argus and Octans associations, which formed outside the Sun’s galactocentric radius. Variations in birth heights of the stellar associations suggest that they were born in a filamentary and corrugated disc of molecular clouds, similar to that inferred from the current filamentary molecular cloud distribution and dust extinction maps. Multiple spiral arm features with different but near corotation pattern speeds and at different heights could account for the stellar association birth sites. We find that the young stellar associations are located in between peaks in the radial/tangential (UV) stellar velocity distribution for stars in the solar neighbourhood. This would be expected if they were born in a spiral arm, which perturbs stellar orbits that cross it. In contrast, stellar associations seem to be located near peaks in the vertical phase-space distribution, suggesting that the gas in which stellar associations are born moves vertically together with the low-velocity dispersion disc stars.

scholarly journals Benchmark low-mass objects in Moving Groups

2013 ◽  
Vol 47 ◽  
pp. 05007
Author(s):  
M.C. Gálvez-Ortiz ◽  
M. Kuznetsov ◽  
J.R.A. Clarke ◽  
Ya.V. Pavlenko ◽  
D.J. Pinfield ◽  
...  
Keyword(s):  
Low Mass ◽  
Moving Groups

Speckle Interferometry of Two Low-mass Triple Systems in the Solar Neighbourhood

2007 ◽  
pp. 125-128
Author(s):  
E.V. Malogolovets ◽  
Y.Y. Balega ◽  
K.-H. Hofmann ◽  
D. A. Rastegaev ◽  
G. Weigelt
Keyword(s):  
Speckle Interferometry ◽  
Solar Neighbourhood ◽  
Triple Systems ◽  
Low Mass

scholarly journals Eccentricity distribution of wide low-mass binaries

2020 ◽  
Vol 496 (1) ◽  
pp. 987-993 ◽  
Author(s):  
Andrei Tokovinin
Keyword(s):  
Stellar Dynamics ◽  
Statistical Information ◽  
Solar Neighbourhood ◽  
Wide Binary ◽  
Eccentric Orbits ◽  
Wide Pairs ◽  
Low Mass ◽  
Orbital Periods ◽  
Relative Motions

ABSTRACT Distribution of eccentricities of very wide (up to 10 kau) low-mass binaries in the solar neighbourhood is studied using the catalogue of El-Badry and Rix (2018) based on Gaia. Direction and speed of relative motions in wide pairs contain statistical information on the eccentricity distribution, otherwise inaccessible owing to very long orbital periods. It is found that the eccentricity distribution is close to the linear (thermal) one f(e) = 2e. However, pairs with projected separations <200 au have less eccentric orbits, while f(e) for wide pairs with s > 1 kau appears to be slightly superthermal, with an excess of very eccentric orbits. Eccentricity of any wide binary can be constrained statistically using direction and speed of its motion. The thermal eccentricity distribution signals an important role of the stellar dynamics in the formation of wide binaries, although disc-assisted capture also can produce such pairs with eccentric orbits.

scholarly journals Testing Pre-Main Sequence Models with Young Binaries

2001 ◽  
Vol 200 ◽  
pp. 472-482
Author(s):  
Francesco Palla
Keyword(s):  
Binary System ◽  
Binary Systems ◽  
Main Sequence ◽  
Young Stars ◽  
System A ◽  
Spectroscopic Binary ◽  
Low Mass ◽  
Good Agreement

I will discuss several tests to gauge the accuracy of pre–main-sequence (PMS) models. Methods to determine the mass of young stars are overviewed, with emphasis on the information provided by double-lined, spectroscopic binary systems. A comparison of the dynamically determined masses with those estimated using the PMS models of Palla & Stahler (1999) is presented. Good agreement between empirical and theoretical masses is found. The analysis of the inferred ages from the isochrones shows a remarkable coevality within each binary system. A complete assessment of the accuracy of PMS tracks needs the identification of eclipsing systems of low-mass.

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

2015 ◽  
Vol 806 (1) ◽  
pp. 62 ◽  
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

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

2018 ◽  
Vol 618 ◽  
pp. A5 ◽  
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.

scholarly journals A Pan-STARRS1 Search for Substellar Young Moving Group Members

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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