scholarly journals Binarity in the Orion Trapezium Cluster

2001 ◽  
Vol 200 ◽  
pp. 169-180 ◽  
Author(s):  
Mark J. McCaughrean
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Young Stars ◽  
Low Mass Stars ◽  
Dark Clouds ◽  
Low Mass ◽  
Observational Errors ◽  
Orion Trapezium

We summarise the results of recent optical and near-infrared imaging studies of the binary fraction among young low-mass stars in the dense Orion Trapezium Cluster. Over the separation range ∼ 30–500 AU and within the observational errors, there appears to be no excess of binary systems in the cluster relative to the main sequence field star population. Over the separation range ∼ 1000–5000 AU, the cluster is deficient in binaries relative to the field. Both results are in contrast to those found for the more distributed population of young stars in the Taurus-Auriga dark clouds, which is overabundant in binaries by roughly a factor of two. We briefly discuss possible origins for this difference and observational tests which may distinguish between them, and the implications these results have for our understanding of the typical environment where most young stars are born.

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 The rotational evolution of young low mass stars

2007 ◽  
Vol 3 (S243) ◽  
pp. 231-240 ◽  
Author(s):  
Jérôme Bouvier
Keyword(s):  
Angular Momentum ◽  
Accretion Disk ◽  
Main Sequence ◽  
Young Stars ◽  
Sequence Evolution ◽  
Main Sequence Stars ◽  
Low Mass Stars ◽  
Rotational Evolution ◽  
Low Mass

AbstractStar-disk interaction is thought to drive the angular momentum evolution of young stars. In this review, I present the latest results obtained on the rotational properties of low mass and very low mass pre-main sequence stars. I discuss the evidence for extremely efficient angular momentum removal over the first few Myr of pre-main sequence evolution and describe recent results that support an accretion-driven braking mechanism. Angular momentum evolution models are presented and their implication for accretion disk lifetimes discussed.

scholarly journals Mass-Luminosity Relations of Very Low Mass Stars

2003 ◽  
Vol 211 ◽  
pp. 413-416 ◽  
Author(s):  
D. Ségransan ◽  
X. Delfosse ◽  
T. Forveille ◽  
J.L. Beuzit ◽  
C. Perrier ◽  
...  
Keyword(s):  
Adaptive Optics ◽  
Main Sequence ◽  
Near Infrared ◽  
Radial Velocities ◽  
Low Mass Stars ◽  
Multiple Stars ◽  
Low Mass

We present new accurate masses at the bottom of the main sequence as well as an improved empirical mass-luminosity relation for very low mass stars in the visible and near infrared. Masses were obtained by combining very accurate radial velocities and adaptive optics images of multiple stars obtained at different orbital phases.

scholarly journals The Low-Mass Stellar Luminosity Function of the 30 Dor Starburst Cluster

1998 ◽  
Vol 11 (1) ◽  
pp. 136-136
Author(s):  
Hans Zinnecker
Keyword(s):  
Globular Clusters ◽  
Luminosity Function ◽  
Main Sequence ◽  
Near Infrared ◽  
Young Stellar Objects ◽  
Integration Time ◽  
Low Mass Stars ◽  
Hii Region ◽  
Low Mass ◽  
The Imf

Abstract Diffraction limited near-infrared H-band (1.6 μm) NICMOS HST images are scheduled to be obtained in mid-October 1997 of the young cluster NGC 2070 (age 3.5 Myr) in the 30 Dor giant HII region in the LMC. The aim is to search for the low-mass (M < 2 Mʘ) low-luminosity, red pre-Main Sequence stellar population and to establish the H-band infrared luminosity function. With the NICMOS we can now determine whether the IMF in this prototypical extragalactic starburst cluster is deficient in subsolar low-mass stars or not. The best ground-based data can sample only M > 2 Mʘ. In principle, NICMOS in the H-band (F160W) is sensitive enough to reach a magnitude of ~ 23.5 in a relatively short integration time, which indeed corresponds to the fantastic possibility to detect young stellar objects with masses near the hydrogen burning limit (M=0.1 Mʘ) according to pre-Main Sequence evolutionary models. Even if we could reach only H = 22.5 (i.e. M=0.4 Mʘ), our observations will still go a long way in directly answering, by star counts, whether the IMF in starburst galaxies is low-mass deficient or not, with all the corresponding far-reaching implications. The observations would also tell us whether the 30 Dor cluster can be regarded as a prototype young globular cluster. This possibility would be ruled out, if we found NGC 2070 to be low-mass deficient, because old globular clusters do have a rich population of low-mass stars.

scholarly journals A Near-Infrared Imaging Survey of the Lupus 3 Dark Cloud: A Modest Cluster of Low-Mass, Pre–Main-Sequence Stars

2000 ◽  
Vol 119 (2) ◽  
pp. 873-881 ◽  
Author(s):  
Yasushi Nakajima ◽  
Motohide Tamura ◽  
Yumiko Oasa ◽  
Tadashi Nakajima
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Infrared Imaging ◽  
Main Sequence Stars ◽  
Near Infrared Imaging ◽  
Dark Cloud ◽  
Low Mass

scholarly journals IRAS and Star Formation in Dark Clouds

1987 ◽  
Vol 115 ◽  
pp. 19-31 ◽  
Author(s):  
J. P. Emerson
Keyword(s):  
Star Formation ◽  
Point Source ◽  
Young Stars ◽  
Low Mass Stars ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Low Mass ◽  
Point Source Catalog

As a first step in systematically studying star formation in dark clouds we report a search for IRAS Point Source Catalog detections lieing within the boundaries of Southern Dark Clouds in the catalog of Hartley et al. (1986). To aid in further classifying the 1099 objects by their infrared colours the colours of the whole IRAS Point Source Catalog are discussed and plotted, and the regions occupied by various types of objects tabulated. The presence of Cirrus makes it difficult to confidently identify protostellar like objects from IRAS data alone. Nevertheless 247 sources have colours characteristic of objects deeply embedded in the dark clouds and are probably at least young stars of low mass. These sources appear to be located at random positions within the dark cloud volumes and there is no evidence to suggest that formation of low mass stars in this dark cloud sample is externally triggered.

scholarly journals X-ray Emission from Young Stars in Suburban Orion

2004 ◽  
Vol 219 ◽  
pp. 228-232
Author(s):  
K. Briggs ◽  
M. Güdel ◽  
M. Audard ◽  
K. Smith ◽  
R. Mewe ◽  
...  
Keyword(s):  
Main Sequence ◽  
Rotation Period ◽  
Magnetic Activity ◽  
Young Stars ◽  
Rossby Number ◽  
Low Mass Stars ◽  
X Ray ◽  
Star Forming ◽  
Low Mass ◽  
Pms Stars

X-ray emission from > 100 pre-main sequence (PMS) stars in the Orion star-forming complex is studied in a 20-ks observation by XMM-Newton. No relation between the ratio of X-ray and bolometric luminosities, LX/Lbol, and rotation period or Rossby number is exhibited, though the action of a solar-like dynamo is not excluded because all stars would appear to be in the “saturated regime” of such a dynamo. Low-mass stars showing a strong U — V excess have lower median X-ray luminosity, suggesting that accretion suppresses magnetic activity.

scholarly journals Astrometric orbits of spectral binary brown dwarfs – I. Massive T dwarf companions to 2M1059−21 and 2M0805+48

2020 ◽  
Vol 495 (1) ◽  
pp. 1136-1147 ◽  
Author(s):  
J Sahlmann ◽  
A J Burgasser ◽  
D C Bardalez Gagliuffi ◽  
P F Lazorenko ◽  
D Ségransan ◽  
...  
Keyword(s):  
Orbit Determination ◽  
Binary Systems ◽  
Near Infrared ◽  
Brown Dwarfs ◽  
Mass Measurements ◽  
Low Mass Stars ◽  
Short Period ◽  
First Results ◽  
Low Mass ◽  
Individual Mass

ABSTRACT Near-infrared spectroscopic surveys have uncovered a population of short-period, blended-light spectral binaries composed of low-mass stars and brown dwarfs. These systems are amenable to orbit determination and individual mass measurements via astrometric monitoring. Here, we present first results of a multiyear campaign to obtain high-precision absolute astrometry for spectral binaries using the Gemini-South and Gemini-North GMOS imagers. We measure the complete astrometric orbits for two systems: 2M0805+48 and 2M1059−21. Our astrometric orbit of 2M0805+48 is consistent with its 2-yr radial velocity orbit determined previously and we find a mass of $66^{+5}_{-14} M_\mathrm{Jup}$ for its T5.5 companion. For 2M1059−21, we find a 1.9-yr orbital period and a mass of $67^{+4}_{-5} M_\mathrm{Jup}$ for its T3.5 companion. We demonstrate that sub-milliarcsecond absolute astrometry can be obtained with both GMOS imagers and that this is an efficient avenue for confirming and characterizing ultracool binary systems.

GLOBULES, DARK CLOUDS, AND LOW MASS PRE-MAIN SEQUENCE STARS

1981 ◽  
Vol 96 ◽  
pp. 125-151 ◽  
Author(s):  
A. R. Hyland
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Near Infrared ◽  
Far Infrared ◽  
Evolutionary Status ◽  
Dark Clouds ◽  
Infrared Surveys ◽  
Clear Identification ◽  
Low Mass ◽  
Infrared Wavelengths

The current observational and theoretical literature on Bok globules and their relationship to star formation is reviewed. Recent observations of globules at optical, infrared, and far infrared wavelengths are shown to provide important constraints on their structure and evolutionary status, and the suggestion that many globules are gravitationally unstable is seriously questioned.Dark clouds associated with T associations are well-known sites of recent and continuing star formation. In recent years molecular observations and far infrared surveys have provided maps of such regions from which possible sites of star formation may be identified. Optical (Hα) and near infrared surveys have enabled a clear identification of pre-main sequence (PMS) objects within the clouds. Methods of distinguishing these from background objects and the nature of their infrared excesses are examined in the light of recent observations in the near and far infrared. The perennial question as to the existence of anomalous reddening within dark clouds is also investigated.

scholarly journals Rotational and Candidate-Eclipsing-Binary Light Curves for Pre-Main-Sequence Stars in the Chamaeleon I Star-Forming Cloud

2009 ◽  
Vol 26 (1) ◽  
pp. 31-36 ◽  
Author(s):  
Warrick A. Lawson ◽  
Lisa A. Crause
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Near Infrared ◽  
Eclipsing Binaries ◽  
Stellar Rotation ◽  
Low Mass Stars ◽  
X Ray ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

AbstractWe present the results of a photometric survey for variability in ten X-ray-emitting low-mass stars in the Chamaeleon region. Eight of the stars we observed are bona fide pre-main-sequence members of the ∼2 Myr-old Chamaeleon I star-forming cloud. The other two stars are young with high levels of relative X-ray emission, but with discordant proper motions they are probable non-members of the cloud. In six of the stars we monitored, periodic variations on timescales of 2.5–11.5 d were detected, that we ascribe to stellar rotation and the presence of cool starspots. Two other stars, CHXR 20 and CHXR 85, show large amplitude variations at visual and near-infrared wavelengths and are candidate eclipsing binaries. Compared to the rotational properties of low-mass stars in the ≈8 Myr-old η Chamaeleontis cluster, we find that the older η Chamaeleontis stars have several times higher surface specific angular momentum than the younger Chamaeleon I stars. The apparent increase in angular momentum between ∼2 and 8 Myr might be due to changes in stellar internal structure as the stars evolve, or evidence for a different rotational history between members of the two star-forming regions.

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