scholarly journals On the mass segregation of cores and stars

2019 ◽  
Vol 490 (1) ◽  
pp. 350-358
Author(s):  
Hayley L Alcock ◽  
Richard J Parker
Keyword(s):  
Main Sequence ◽  
Dynamical Evolution ◽  
Initial Mass Function ◽  
Fragmentation Model ◽  
Main Sequence Stars ◽  
Apparent Contradiction ◽  
Star Forming ◽  
Star Forming Regions ◽  
Mass Segregation ◽  
Massive Cores

ABSTRACT Observations of pre- and proto-stellar cores in young star-forming regions show them to be mass segregated, i.e. the most massive cores are centrally concentrated, whereas pre-main-sequence stars in the same star-forming regions (and older regions) are not. We test whether this apparent contradiction can be explained by the massive cores fragmenting into stars of much lower mass, thereby washing out any signature of mass segregation in pre-main-sequence stars. Whilst our fragmentation model can reproduce the stellar initial mass function, we find that the resultant distribution of pre-main sequence stars is mass segregated to an even higher degree than that of the cores, because massive cores still produce massive stars if the number of fragments is reasonably low (between one and five). We therefore suggest that the reason cores are observed to be mass segregated and stars are not is likely due to dynamical evolution of the stars, which can move significant distances in star-forming regions after their formation.

The Multiplicity of Pre–Main‐Sequence Stars in Southern Star‐forming Regions

1997 ◽  
Vol 481 (1) ◽  
pp. 378-385 ◽  
Author(s):  
A. M. Ghez ◽  
D. W. McCarthy ◽  
J. L. Patience ◽  
T. L. Beck
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Star Forming Regions

scholarly journals Determination of kinematic distances of pre-main-sequence stars in star-forming regions

2009 ◽  
Vol 5 (S266) ◽  
pp. 395-398
Author(s):  
Phillip A. B. Galli ◽  
Ramachrisna Teixeira ◽  
Christine Ducourant ◽  
Claude Bertout
Keyword(s):  
Main Sequence ◽  
Young Stars ◽  
Formation Mechanisms ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Know How ◽  
Star Forming Regions ◽  
Moving Groups ◽  
Kinematic Properties

AbstractMany studies of star-forming regions have been carried out since the discovery of compact Hii regions in the late 1960s. The kinematic properties of young stars in the nearest regions with ongoing and recent star formation provide essential tests of their formation mechanisms. The detection of coeval moving groups allows determination of individual distances through the convergent-point method. As a result, the main physical properties of these stars and their early evolutionary stages can be determined if we know how distant they are.

scholarly journals Binary Frequency Among Pre-Main Sequence Stars in Taurus and Ophiuchus

1989 ◽  
Vol 8 ◽  
pp. 117-118
Author(s):  
M. Simon
Keyword(s):  
Binary Systems ◽  
Main Sequence ◽  
Young Stars ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Lunar Occultation ◽  
Star Forming Regions ◽  
Powerful Means ◽  
Comparable Sample

AbstractThe lunar occultation technique applied in the IR offers a powerful means of identifying binaries among obscured young stars. Our program has revealed binaries with separations from 1 to 100 AU in the Taurus and Ophiuchus star forming regions to about K=9 mag. To date, 29 objects have been observed; 6 were discovered to be binaries. The observed binary frequency is about half that expected from the binary statistics of a comparable sample of field stars. The discrepancy is probably attributable to our insensitivity to binary systems with secondary mass much less than that of the primary.

scholarly journals The VMC survey – XXXIV. Morphology of stellar populations in the Magellanic Clouds

2019 ◽  
Vol 490 (1) ◽  
pp. 1076-1093 ◽  
Author(s):  
Dalal El Youssoufi ◽  
Maria-Rosa L Cioni ◽  
Cameron P M Bell ◽  
Stefano Rubele ◽  
Kenji Bekki ◽  
...  
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Stellar Populations ◽  
Magellanic Clouds ◽  
Main Sequence Stars ◽  
Spiral Arms ◽  
Star Forming ◽  
Star Forming Regions ◽  
Tidal Interactions ◽  
Using Data

ABSTRACT The Magellanic Clouds are nearby dwarf irregular galaxies whose morphologies show different properties when traced by different stellar populations, making them an important laboratory for studying galaxy morphologies. We study the morphology of the Magellanic Clouds using data from the Visible and Infrared Survey Telescope for Astronomy survey of the Magellanic Clouds system. We used about 10 and 2.5 million sources across an area of ∼105 and ∼42 deg2 towards the Large and Small Magellanic Cloud (LMC and SMC), respectively. We estimated median ages of stellar populations occupying different regions of the near-infrared (J − Ks, Ks) colour–magnitude diagram. Morphological maps were produced and detailed features in the central regions were characterized for the first time with bins corresponding to a spatial resolution of 0.13 kpc (LMC) and 0.16 kpc (SMC). In the LMC, we find that main-sequence stars show coherent structures that grow with age and trace the multiple spiral arms of the galaxy, star-forming regions become dimmer as we progress in age, while supergiant stars are centrally concentrated. Intermediate-age stars, despite tracing a regular and symmetrical morphology, show central clumps and hints of spiral arms. In the SMC, young main-sequence stars depict a broken bar. Intermediate-age populations show signatures of elongation towards the Magellanic Bridge that can be attributed to the LMC–SMC interaction ∼200 Myr ago. They also show irregular central features suggesting that the inner SMC has also been influenced by tidal interactions.

scholarly journals Star formation activity and the spatial distribution and mass segregation of dense cores in the early phases of star formation

2019 ◽  
Vol 629 ◽  
pp. A135 ◽  
Author(s):  
Sami Dib ◽  
Thomas Henning
Keyword(s):  
Spatial Distribution ◽  
Star Formation ◽  
Large Scale ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Star Formation Activity ◽  
Mass Segregation ◽  
Massive Cores

We examine the spatial distribution and mass segregation of dense molecular cloud cores in a number of nearby star forming regions (the region L1495 in Taurus, Aquila, Corona Australis, and W43) that span about four orders of magnitude in star formation activity. We used an approach based on the calculation of the minimum spanning tree, and for each region, we calculated the structure parameter 𝒬 and the mass segregation ratio ΛMSR measured for various numbers of the most massive cores. Our results indicate that the distribution of dense cores in young star forming regions is very substructured and that it is very likely that this substructure will be imprinted onto the nascent clusters that will emerge out of these clouds. With the exception of Taurus in which there is nearly no mass segregation, we observe mild-to-significant levels of mass segregation for the ensemble of the 6, 10, and 14 most massive cores in Aquila, Corona Australis, and W43, respectively. Our results suggest that the clouds’ star formation activity are linked to their structure, as traced by their population of dense cores. We also find that the fraction of massive cores that are the most mass segregated in each region correlates with the surface density of star formation in the clouds. The Taurus region with low star forming activity is associated with a highly hierarchical spatial distribution of the cores (low 𝒬 value) and the cores show no sign of being mass segregated. On the other extreme, the mini-starburst region W43-MM1 has a higher 𝒬 that is suggestive of a more centrally condensed structure. Additionally, it possesses a higher fraction of massive cores that are segregated by mass. While some limited evolutionary effects might be present, we largely attribute the correlation between the star formation activity of the clouds and their structure to a dependence on the physical conditions that have been imprinted on them by the large scale environment at the time they started to assemble.

Clustering of Pre–Main‐Sequence Stars in the Orion, Ophiuchus, Chamaeleon, Vela, and Lupus Star‐forming Regions

1998 ◽  
Vol 497 (2) ◽  
pp. 721-735 ◽  
Author(s):  
Yasushi Nakajima ◽  
Kengo Tachihara ◽  
Tomoyuki Hanawa ◽  
Makoto Nakano
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Star Forming ◽  
Star Forming Regions

Stellar Kinematics in Star-Forming Regions

1984 ◽  
Vol 88 ◽  
pp. 263-264
Author(s):  
Robert D. Mathieu ◽  
David W. Latham ◽  
Lee Hartmann
Keyword(s):  
Radial Velocity ◽  
Measurement Errors ◽  
Main Sequence ◽  
Stellar Kinematics ◽  
Late Type ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Central Wavelength ◽  
Star Forming ◽  
Star Forming Regions

High-precision radial-velocity studies of three young, star-forming regions - λ Orionis, NGC 2264 and Taurus-Auriga - are under way; study of the Orion cluster (with L. Marschall, in conjunction with the Yale proper-motion study) is beginning this winter. Single-order (~50 A, central wavelength 5200A) echelle spectra have been obtained for late-type pre-main sequence stars. Due to the spectral peculiarities and stellar rotation associated with pre-main sequence stars, our radial-velocity precisions are often somewhat poorer than those obtained for late-type dwarfs or giants. Measurement errors of 0.7-1.5 km/sec are typical, although some stars do not permit any radial velocity measurement at all. We summarize preliminary findings for each region:

scholarly journals Stellar Kinematics in Star-Forming Regions

1987 ◽  
Vol 115 ◽  
pp. 61-61
Author(s):  
Robert D. Mathieu
Keyword(s):  
Radial Velocity ◽  
Measurement Errors ◽  
Main Sequence ◽  
Stellar Kinematics ◽  
Stellar Rotation ◽  
Main Sequence Stars ◽  
Central Wavelength ◽  
Star Forming ◽  
Star Forming Regions ◽  
Radial Velocity Measurement

High-precision radial-velocity studies of four star-forming regions: λ Orionis, NGC 2264, the Trapezium cluster and Taurus-Auriga, are completed or in process (in collaboration with Latham, Marschall and Hartmann). Single-order (∼ 50 Å, central wavelength 5200 Å) echelle spectra have been obtained for late-type pre-main sequence stars. Measurement errors of 0.7 – 1.5 km/sec are typical, although some stars do not permit any radial-velocity measurement due to stellar rotation or spectral peculiarities.

scholarly journals Observations of prestellar cores: Probing the initial conditions for the IMF

2006 ◽  
Vol 2 (S237) ◽  
pp. 132-140
Author(s):  
Philippe André
Keyword(s):  
Main Sequence ◽  
Initial Conditions ◽  
Main Sequence Stars ◽  
Nearby Star ◽  
Star Forming ◽  
Physical Mechanisms ◽  
Star Forming Regions ◽  
Prestellar Cores ◽  
Stellar Masses ◽  
The Imf

AbstractSeveral (sub)millimeter-wave studies of nearby star-forming regions have revealed self-gravitating prestellar condensations that seem to be the direct progenitors of individual stars and whose mass distribution resembles the IMF. In a number of cases, small internal and relative motions have been measured for these condensations, indicating they are much less turbulent than their parent cloud and do not have time to interact before evolving into protostars and pre-main sequence stars. These findings suggest that the IMF is at least partly determined by pre-collapse cloud fragmentation and that one of the keys to understanding the origin of stellar masses lies in the physical mechanisms responsible for the formation and decoupling of prestellar cores within molecular clouds.

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