scholarly journals Mass segregation effects in very young open clusters

2007 ◽  
Vol 3 (S248) ◽  
pp. 481-483
Author(s):  
L. Chen ◽  
R. de Grijs ◽  
J. L. Zhao
Keyword(s):  
Star Formation ◽  
Strong Support ◽  
Open Clusters ◽  
Proper Motions ◽  
Star Forming ◽  
Star Forming Regions ◽  
Mass Segregation ◽  
The Way

AbstractWe derived proper motions and membership probabilities of stars in the regions of two very young (~ 2–4 Myr-old) open clusters NGC 2244 and NGC 6530. Both clusters show clear evidence of mass segregation, which provides strong support for the suggestion that the observed mass segregation is – at least partially – due to the way in which star formation has proceeded in these complex star-forming regions (“primordial” mass segregation).

scholarly journals OB stars towards NGC 6357 and NGC 6334

2017 ◽  
Vol 12 (S330) ◽  
pp. 341-342
Author(s):  
Delphine Russeil
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Stellar Population ◽  
Proper Motions ◽  
Massive Star Formation ◽  
Ob Stars ◽  
Stellar Cluster ◽  
Star Forming ◽  
Star Forming Regions ◽  
Ngc 6334

AbstractThe star forming regions NGC6334 and NGC6357 are amid the most active star-forming complexes of our Galaxy where massive star formation is occuring. Both complexes gather several HII regions but they exhibit different aspects: NGC6334 is characterised by a dense molecular ridge where recent massive star formation is obvious while NGC6357 is dominated by the action of the stellar cluster Pismis 24 which have shaped a large cavity. To understand and compare the formation of massive stars in these two regions requires to precise the distance and characterise the proper motions of the O to B3 stellar population in these regions.

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.

scholarly journals The Variation of the Initial Mass Function in Clusters

2004 ◽  
Vol 221 ◽  
pp. 237-246
Author(s):  
K. L. Luhman
Keyword(s):  
Star Formation ◽  
Brown Dwarfs ◽  
Mass Function ◽  
Open Clusters ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Star Forming ◽  
Star Forming Regions

I review recent measurements of the initial mass function of stars and brown dwarfs in star-forming regions and open clusters and summarize the implications of these data for theories of star formation.

scholarly journals X-Ray Coronae from Stars

1998 ◽  
Vol 188 ◽  
pp. 13-16
Author(s):  
R. Pallavicini
Keyword(s):  
Open Clusters ◽  
Temperature Structure ◽  
List Type ◽  
Star Forming ◽  
Spectroscopic Observations ◽  
Star Forming Regions ◽  
Complete Mapping ◽  
Sky Survey ◽  
Order Of Magnitude ◽  
Age Range

A number of major advances in stellar coronal physics have occurred since 1990 mainly as a consequence of imaging observations by ROSAT and spectroscopic observations by ASCA. These can be summarised as follows: 1.an all-sky survey has been performed by ROSAT at a sensitivity of ~ 2 × 10−13 erg cm−2 s−1, complemented by pointed observations an order of magnitude deeper;2.complete mapping and deeper pointings have been obtained for virtually all open clusters closer than ~ 500 pc, and covering the age range from ~ 30 Myr to ~ 700 Myr;3.complete mapping and deeper paintings have been obtained for several Star Forming Regions (SFRs) covering the age range ~ 1 to ~ 10 Myr;4.spectroscopic observations of bright coronal sources have been obtained with EUVE and ASCA allowing the derivation of the temperature structure and elemental abundances.

scholarly journals The Connection between Molecular Gas and Star Formation in XUV Disks

2016 ◽  
Vol 11 (S321) ◽  
pp. 214-216
Author(s):  
Linda C. Watson
Keyword(s):  
Star Formation ◽  
Molecular Hydrogen ◽  
Optical Disk ◽  
Molecular Gas ◽  
Star Forming ◽  
Star Forming Regions

AbstractWe found that star-forming regions in extended ultraviolet (XUV) disks are generally consistent with the molecular-hydrogen Kennicutt-Schmidt law that applies within the inner, optical disk. This is true for star formation rates based on Hα + 24 μm data or FUV + 24 μm data. We estimated that the star-forming regions have ages of 1 − 7 Myr and propose that the presence or absence of molecular gas provides an additional “clock” that may help distinguish between aging and stochasticity as the explanation for the low Hα-to-FUV flux ratios in XUV disks. This contribution is a summary of the work originally presented in Watson et al. (2016).

scholarly journals Survey of ortho-H2D+ in high-mass star-forming regions

2020 ◽  
Vol 644 ◽  
pp. A34
Author(s):  
G. Sabatini ◽  
S. Bovino ◽  
A. Giannetti ◽  
F. Wyrowski ◽  
M. A. Órdenes ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Strong Dependence ◽  
Cosmic Ray ◽  
High Mass ◽  
Clear Correlation ◽  
Mass Star ◽  
Large Sample ◽  
Star Forming ◽  
Star Forming Regions

Context. Deuteration has been suggested to be a reliable chemical clock of star-forming regions due to its strong dependence on density and temperature changes during cloud contraction. In particular, the H3+ isotopologues (e.g. ortho-H2D+) seem to act as good proxies of the evolutionary stages of the star formation process. While this has been widely explored in low-mass star-forming regions, in the high-mass counterparts only a few studies have been pursued, and the reliability of deuteration as a chemical clock remains inconclusive. Aims. We present a large sample of o-H2D+ observations in high-mass star-forming regions and discuss possible empirical correlations with relevant physical quantities to assess its role as a chronometer of star-forming regions through different evolutionary stages. Methods. APEX observations of the ground-state transition of o-H2D+ were analysed in a large sample of high-mass clumps selected from the ATLASGAL survey at different evolutionary stages. Column densities and beam-averaged abundances of o-H2D+ with respect to H2, X(o-H2D+), were obtained by modelling the spectra under the assumption of local thermodynamic equilibrium. Results. We detect 16 sources in o-H2D+ and find clear correlations between X(o-H2D+) and the clump bolometric luminosity and the dust temperature, while only a mild correlation is found with the CO-depletion factor. In addition, we see a clear correlation with the luminosity-to-mass ratio, which is known to trace the evolution of the star formation process. This would indicate that the deuterated forms of H3+ are more abundant in the very early stages of the star formation process and that deuteration is influenced by the time evolution of the clumps. In this respect, our findings would suggest that the X(o-H2D+) abundance is mainly affected by the thermal changes rather than density changes in the gas. We have employed these findings together with observations of H13CO+, DCO+, and C17O to provide an estimate of the cosmic-ray ionisation rate in a sub-sample of eight clumps based on recent analytical work. Conclusions. Our study presents the largest sample of o-H2D+ in star-forming regions to date. The results confirm that the deuteration process is strongly affected by temperature and suggests that o-H2D+ can be considered a reliable chemical clock during the star formation processes, as proved by its strong temporal dependence.

scholarly journals Submillimeter Array Observations of Magnetic Fields in Star Forming Regions

2010 ◽  
Vol 6 (S270) ◽  
pp. 103-106
Author(s):  
R. Rao ◽  
J.-M. Girart ◽  
D. P. Marrone
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Computational Models ◽  
Dominant Role ◽  
Theoretical Models ◽  
Mass Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Low Mass

AbstractThere have been a number of theoretical and computational models which state that magnetic fields play an important role in the process of star formation. Competing theories instead postulate that it is turbulence which is dominant and magnetic fields are weak. The recent installation of a polarimetry system at the Submillimeter Array (SMA) has enabled us to conduct observations that could potentially distinguish between the two theories. Some of the nearby low mass star forming regions show hour-glass shaped magnetic field structures that are consistent with theoretical models in which the magnetic field plays a dominant role. However, there are other similar regions where no significant polarization is detected. Future polarimetry observations made by the Submillimeter Array should be able to increase the sample of observed regions. These measurements will allow us to address observationally the important question of the role of magnetic fields and/or turbulence in the process of star formation.

scholarly journals An uncertainty principle for star formation – IV. On the nature and filtering of diffuse emission

2019 ◽  
Vol 488 (2) ◽  
pp. 2800-2824 ◽  
Author(s):  
Alexander P S Hygate ◽  
J M Diederik Kruijssen ◽  
Mélanie Chevance ◽  
Andreas Schruba ◽  
Daniel T Haydon ◽  
...  
Keyword(s):  
Star Formation ◽  
Compact Star ◽  
Critical Length ◽  
Electromagnetic Spectrum ◽  
H Ii Regions ◽  
Diffuse Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
Compact Component ◽  
Astronomical Images

Abstract Diffuse emission is observed in galaxies in many tracers across the electromagnetic spectrum, including tracers of star formation, such as H α and ultraviolet (UV), and tracers of gas mass, such as carbon monoxide (CO) transition lines and the 21-cm line of atomic hydrogen (H i). Its treatment is key to extracting meaningful information from observations such as cloud-scale star formation rates. Finally, studying diffuse emission can reveal information about the physical processes taking place in the interstellar medium, such as chemical transitions and the nature of stellar feedback (through the photon escape fraction). We present a physically motivated method for decomposing astronomical images containing both diffuse emission and compact regions of interest, such as H ii regions or molecular clouds, into diffuse and compact component images through filtering in Fourier space. We have previously presented a statistical method for constraining the evolutionary timeline of star formation and mean separation length between compact star-forming regions with galaxy-scale observations. We demonstrate how these measurements are biased by the presence of diffuse emission in tracer maps and that by using the mean separation length as a critical length-scale to separate diffuse emission from compact emission, we are able to remove its biasing effect. Furthermore, this method provides, without the need for interferometry or ancillary spectral data, a measurement of the diffuse emission fraction in input tracer maps and decomposed diffuse and compact emission maps for further analysis.

scholarly journals Masers as probes of proto-planetary discs

2004 ◽  
Vol 202 ◽  
pp. 362-364
Author(s):  
A.M.S. Richards ◽  
R. J. Cohen ◽  
M. Crocker ◽  
E. E. Lekht ◽  
V. Samodourov ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Radio Telescope ◽  
Keplerian Orbit ◽  
Proper Motions ◽  
Central Mass ◽  
Maser Emission ◽  
Star Forming ◽  
Star Forming Regions ◽  
Velocity Variations ◽  
Water Maser

Water maser emission from star forming regions has been monitored for several decades using the Puschino radio telescope, showing radial velocity variations consistent with material in Keplerian orbit around protostars. MERLIN and the EVN are now being used to image the 22 GHz emission on au scales and measure proper motions. This will distinguish discs from outflows, and provide an estimate of the central mass and possibly orbiting condensations.

scholarly journals A radio polarimetric study to disentangle AGN activity and star formation in Seyfert galaxies

2020 ◽  
Vol 499 (1) ◽  
pp. 334-354
Author(s):  
Biny Sebastian ◽  
P Kharb ◽  
C P O’Dea ◽  
J F Gallimore ◽  
S A Baum
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Seyfert Galaxies ◽  
Starburst Galaxies ◽  
Shock Acceleration ◽  
Very Large Array ◽  
Star Forming ◽  
Array Configuration ◽  
Star Forming Regions ◽  
Tentative Evidence

ABSTRACT To understand the origin of radio emission in radio-quiet active galactic nucleus (AGN) and differentiate between the contributions from star formation, AGN accretion, and jets, we have observed a nearby sample of Seyfert galaxies along with a comparison sample of starburst galaxies using the Expanded Very Large Array (EVLA) in full-polarization mode in the B-array configuration. The radio morphologies of the Seyfert galaxies show lobe/bubble-like features or prominent cores in radio emission, whereas the starburst galaxies show radio emission spatially coincident with the star-forming regions seen in optical images. There is tentative evidence that Seyferts tend to show more polarized structures than starburst galaxies at the resolution of our observations. We find that unlike a sample of Seyfert galaxies hosting kilo-parsec scale radio (KSR) emission, starburst galaxies with superwinds do not show radio-excess compared to the radio–FIR correlation. This suggests that shock acceleration is not adequate to explain the excess radio emission seen in Seyferts and hence most likely have a jet-related origin. We also find that the [O iii] luminosity of the Seyferts is correlated with the off-nuclear radio emission from the lobes, whereas it is not well correlated with the total emission which also includes the core. This suggests strong jet–medium interaction, which in turn limits the jet/lobe extents in Seyferts. We find that the power contribution of AGN jet, AGN accretion, and star formation is more or less comparable in our sample of Seyfert galaxies. We also find indications of episodic AGN activity in many of our Seyfert galaxies.

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