Evolution of Low-Mass Stars and Substellar Objects. Contribution to the Galactic Mass Budget

VRI images within the belt of Orion and the Ori OB1a association reveal a pre-main sequence locus extending to below our completeness limit of about V=21. We report here on followup JHK imaging and optical and near–IR spectroscopy of the faintest and reddest of the PMS candidates. We find that they are unreddened mid-to-late M “stars” which fall on a few million year isochrone. Masses are largely substellar, reaching as low as about 0.02 M⊙ (20 Jovian masses). The space density of the substellar objects is high.

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Supergiants and their shells in young globular clusters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731500 ◽

2018 ◽

Vol 612 ◽

pp. A55 ◽

Cited By ~ 5

Author(s):

Dorottya Szécsi ◽

Jonathan Mackey ◽

Norbert Langer

Keyword(s):

Star Formation ◽

Globular Clusters ◽

Second Generation ◽

Massive Stars ◽

Low Mass Stars ◽

Hydrogen Burning ◽

Mass Budget ◽

Low Metallicity ◽

Low Mass ◽

Galactic Globular Clusters

Context. Anomalous surface abundances are observed in a fraction of the low-mass stars of Galactic globular clusters, that may originate from hot-hydrogen-burning products ejected by a previous generation of massive stars. Aims. We aim to present and investigate a scenario in which the second generation of polluted low-mass stars can form in shells around cool supergiant stars within a young globular cluster. Methods. Simulations of low-metallicity massive stars (Mi ~ 150−600 M⊙) show that both core-hydrogen-burning cool supergiants and hot ionizing stellar sources are expected to be present simulaneously in young globular clusters. Under these conditions, photoionization-confined shells form around the supergiants. We have simulated such a shell, investigated its stability and analysed its composition. Results. We find that the shell is gravitationally unstable on a timescale that is shorter than the lifetime of the supergiant, and the Bonnor-Ebert mass of the overdense regions is low enough to allow star formation. Since the low-mass stellar generation formed in this shell is made up of the material lost from the supergiant, its composition necessarily reflects the composition of the supergiant wind. We show that the wind contains hot-hydrogen-burning products, and that the shell-stars therefore have very similar abundance anomalies that are observed in the second generation stars of globular clusters. Considering the mass-budget required for the second generation star-formation, we offer two solutions. Either a top-heavy initial mass function is needed with an index of −1.71 to −2.07. Alternatively, we suggest the shell-stars to have a truncated mass distribution, and solve the mass budget problem by justifiably accounting for only a fraction of the first generation. Conclusions. Star-forming shells around cool supergiants could form the second generation of low-mass stars in Galactic globular clusters. Even without forming a photoionizaton-confined shell, the cool supergiant stars predicted at low-metallicity could contribute to the pollution of the interstellar medium of the cluster from which the second generation was born. Thus, the cool supergiant stars should be regarded as important contributors to the evolution of globular clusters.

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Evidence for a Turnover in the Initial Mass Function of Low-Mass Stars and Substellar Objects: Analysis from an Ensemble of Young Clusters

The Astrophysical Journal ◽

10.1086/591473 ◽

2008 ◽

Vol 683 (2) ◽

pp. L183-L186 ◽

Cited By ~ 68

Author(s):

M. Andersen ◽

M. R. Meyer ◽

J. Greissl ◽

A. Aversa

Keyword(s):

Mass Function ◽

Initial Mass Function ◽

Initial Mass ◽

Low Mass Stars ◽

Substellar Objects ◽

Low Mass ◽

Young Clusters

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A Search for Lithium in Brown Dwarf Candidates

International Astronomical Union Colloquium ◽

10.1017/s0252921100017693 ◽

1993 ◽

Vol 137 ◽

pp. 171-173

Author(s):

Rafael Rebolo ◽

Eduardo L. Martin ◽

Antonio Magazzu

Keyword(s):

High Resolution ◽

Resonance Line ◽

Brown Dwarfs ◽

Brown Dwarf ◽

Low Mass Stars ◽

Substellar Objects ◽

Low Mass

AbstractWe are conducting a search for lithium in very low mass objects with the aim of discriminating between stellar and substellar objects. Lithium is expected to be preserved in brown dwarfs with M/M⊙ ≤0.06, while it is known to be efficiently destroyed in low mass stars. In this paper we present high resolution observations in the region of the λ 6708 Li I resonance line of 5 very low mass dwarfs. In none of them lithium is detected, implying a Li destruction in their atmospheres of about four orders of magnitude. Our results suggest that these objects are probably very low mass stars rather than brown dwarfs.

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Very Low Mass Stars and Substellar Objects in the Pleiades

The Astrophysical Journal ◽

10.1086/177316 ◽

1996 ◽

Vol 464 ◽

pp. 238 ◽

Cited By ~ 7

Author(s):

D. M. Willliams ◽

R. P. Boyle ◽

W. T. Morgan ◽

G. H. Rieke ◽

J. R. Stauffer ◽

...

Keyword(s):

Low Mass Stars ◽

Substellar Objects ◽

Low Mass

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The First Proto-Brown Dwarf Binary Candidate Identified through Dynamics of Jets

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316007973 ◽

2015 ◽

Vol 11 (S315) ◽

Author(s):

Tien-Hao Hsieh ◽

Shih-Ping Lai ◽

Arnaud Belloche ◽

Friedrich Wyrowski

Keyword(s):

Binary System ◽

Orbital Motion ◽

Brown Dwarf ◽

Low Mass Stars ◽

Core Mass ◽

Substellar Objects ◽

Current Mass ◽

Low Mass ◽

Dynamical Features ◽

First Time

AbstractThe formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD at the embedded phase (proto-brown dwarf). IRAS16253 is classified as a Very Low Luminosity Object (VeLLO, Lint < 0.1L⊙), which is considered as a proto-brown dwarf candidate. We use the IRAM 30m, APEX telescopes and the SMA to probe the molecular jet/outflow driven by IRAS 16253 in CO (2–1), (6–5), and (7–6) and study its dynamical features and physical properties. We detect a wiggling pattern in the position-velocity diagrams of the jets. Assuming that this pattern is due to the orbital motion of a binary system, we obtain the current mass of the binary is ~0.026 M⊙. Together with the low parent core mass, IRAS16253 will likely form one or two proto-BD in the future. This is the first time that the current mass of a proto-BD binary system is identified through the dynamics of the jets. Since IRAS16253 is located in an isolated environment, we suggest that BDs can form through fragmentation and collapse like low mass stars.

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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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Magnetic Activity and Rotation in Brown Dwarfs and Low Mass Stars

Symposium - International Astronomical Union ◽

10.1017/s0074180900211078 ◽

2003 ◽

Vol 211 ◽

pp. 427-435 ◽

Cited By ~ 2

Author(s):

Gibor Basri ◽

Subanjoy Mohanty

Keyword(s):

Theoretical Work ◽

Magnetic Activity ◽

Stellar Rotation ◽

Low Mass Stars ◽

Strong Activity ◽

Substellar Objects ◽

Substantial Progress ◽

Solar Type ◽

Low Mass ◽

M Stars

One of the triumphs of the last 2 decades has been the establishment of the relation between stellar rotation and magnetic activity in solar-type stars. Rapid rotation produces strong activity, which in turn provides magnetic braking to reduce rotation. A solar-type dynamo cannot operate in fully convective stars, so it is of interest to study mid and late M stars. Hints that a dramatic change occurs in very low-mass stars and substellar objects appeared in 1995. The past 7 years have seen substantial progress on this question, with the conclusion that the rotation-activity connection indeed breaks down. As one goes to the bottom of the main sequence and below, the amount of magnetic activity takes a sudden fall, with a concomitant increase in the spindown times of the objects. We summarize these results, and some theoretical work which helps explain them. We also present some remaining mysteries, such as why very young objects seem excessively active, and flaring in objects with no other signs of magnetic activity.

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Atmosphere models for very low mass stars, brown dwarfs and exoplanets

Symposium - International Astronomical Union ◽

10.1017/s0074180900116729 ◽

1997 ◽

Vol 189 ◽

pp. 227-233

Author(s):

I. Baraffe ◽

F. Allard

Keyword(s):

Main Sequence ◽

Accurate Determination ◽

Brown Dwarfs ◽

Considerable Effort ◽

Low Mass Stars ◽

The Past ◽

Substellar Objects ◽

Cool Stars ◽

Low Mass

Over the past decade considerable effort, both observational and theoretical, has been directed towards a more accurate determination of the stellar lower main sequence and of the sub-stellar domain covered by Brown Dwarfs and Planets. Astronomers have been looking for brown dwarfs for more than a decade, either with standard astronomical technics or with microlensing experiments. A breakthrough in the search for brown dwarfs was very recently achieved with the discovery of the first cool brown dwarf GL 229B (Nakajima et al. 1995). At the same epoch, the search for planets blossomed with the discovery of a Jupiter - mass companion of the star 51 Pegasi (Mayor and Queloz 199,5). Now, the number of faint, cool stars and substellar objects is rising rapidly.

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