scholarly journals Detection of Synchrotron Emission from a Unique Herbig Haro Object in Orion

1990 ◽  
Vol 140 ◽  
pp. 329-330 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
T. Cornwell ◽  
B. Reipurth ◽  
M. Roth
Keyword(s):  
Magnetic Field ◽  
Thermal Emission ◽  
Radio Continuum ◽  
Mass Star ◽  
Synchrotron Emission ◽  
Synchrotron Source ◽  
The Core ◽  
The North ◽  
Low Mass ◽  
Hh Object

We have obtained radio continuum observations of an HH object, known as the “streamer” in Orion using the VLA in a number of configurations at λ2, 6 and 20cm. This object is located several arc-minutes to the north of HH34 in L1641 cloud and exhibits a remarkably long and narrow structure with dimensions of 5′ × 10′ in optical photographs unlike the morphology of any other HH object. Based on radio continuum observations, we have detected a significant linearly polarized emission at λ6cm from the core of the streamer indicating highly uniform magnetic field geometry. This unusual result suggests that the source responsible for producing the nebulosity is a nonthermal-emitting radio source. Because of the presence of a number of newly born low-mass stars in L1641 and because of the detection of a highly reddened 2μm source coincident with the synchrotron source, it is likely that the source at the core of the streamer is a low-mass star responsible for the non-thermal emission and the HH nebulosity. Presence of synchrotron emission associated with a newly born star supports further view that the magnetic field plays a strong role in the early phase of star formation.

Dust discs around low-mass main-sequence stars

1988 ◽  
Vol 325 (1587) ◽  
pp. 423-437 ◽  
Keyword(s):  
Thermal Emission ◽  
Orbital Evolution ◽  
Prima Facie ◽  
Mass Star ◽  
Orbital Inclination ◽  
Sources And Sinks ◽  
Central Regions ◽  
Low Mass ◽  
The Difference ◽  
Two Sides

Current understanding of the formation of circumstellar discs as a natural accompaniment to the process of low-mass star formation is briefly reviewed. Models of the thermal emission from the dust discs around the prototype stars a Lyr, a PsA, P Pic and 8 Eri are discussed, which indicate that the central regions of three of these discs are almost devoid of dust within radii ranging between 17 and 26 AU, with the temperature of the hottest dust lying between about 115 and 210 K. One possible explanation of the dust-free zones is the presence of a planet at the inner boundary of each cloud that sweeps up grains crossing its orbit. The discs have outer radii that range between about 250 and 800 AU and have dust masses that are unlikely to exceed about 300 Earth masses. Assuming a gas: dust ratio of 100:1 for the pre-mainsequence disc this corresponds to a mass of ca. 0.1 M Q comparable to that of the premain-sequence star HL Tau. The colour, diameter and thickness of the optical image of P Pic, obtained by coronagraphic techniques, have provided further information on the size, radial distribution of number density and orbital inclination of the grains. The difference in surface brightness on the two sides of the disc is puzzling, but might be explained if the grains are elongated and aligned by the combined effects of a stellar wind and a magnetic field of spiral configuration. Finally, we discuss the orbital evolution and lifetimes of particles in these discs, which are governed primarily by radiation pressure, Poynting-Robertson drag and grain-grain collisions. Although replenishment of these discs may be occurring, for example by grains ejected from comets, discs of initial radius ca. 1000 AU can survive Poynting-Robertson depletion over the stellar age and there is no prima facie evidence as yet in favour of a balance between sources and sinks of dust.

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 ALMA resolves the hourglass magnetic field in G31.41+0.31

2019 ◽  
Vol 630 ◽  
pp. A54 ◽  
Author(s):  
M. T. Beltrán ◽  
M. Padovani ◽  
J. M. Girart ◽  
D. Galli ◽  
R. Cesaroni ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Velocity Gradient ◽  
Flux Ratio ◽  
High Mass ◽  
Continuum Emission ◽  
Mass Star ◽  
Star Forming ◽  
The Core ◽  
Molecular Core ◽  
The Magnetic Field

Context. Submillimeter Array (SMA) 870 μm polarization observations of the hot molecular core G31.41+0.31 revealed one of the clearest examples up to date of an hourglass-shaped magnetic field morphology in a high-mass star-forming region. Aims. To better establish the role that the magnetic field plays in the collapse of G31.41+0.31, we carried out Atacama Large Millimeter/ submillimeter Array (ALMA) observations of the polarized dust continuum emission at 1.3 mm with an angular resolution four times higher than that of the previous (sub)millimeter observations to achieve an unprecedented image of the magnetic field morphology. Methods. We used ALMA to perform full polarization observations at 233 GHz (Band 6). The resulting synthesized beam is 0′′.28×0′′.20 which, at the distance of the source, corresponds to a spatial resolution of ~875 au. Results. The observations resolve the structure of the magnetic field in G31.41+0.31 and allow us to study the field in detail. The polarized emission in the Main core of G31.41+0.41is successfully fit with a semi-analytical magnetostatic model of a toroid supported by magnetic fields. The best fit model suggests that the magnetic field is well represented by a poloidal field with a possible contribution of a toroidal component of ~10% of the poloidal component, oriented southeast to northwest at approximately −44° and with an inclination of approximately −45°. The magnetic field is oriented perpendicular to the northeast to southwest velocity gradient detected in this core on scales from 103 to 104 au. This supports the hypothesis that the velocity gradient is due to rotation of the core and suggests that such a rotation has little effect on the magnetic field. The strength of the magnetic field estimated in the central region of the core with the Davis–Chandrasekhar-Fermi method is ~8–13 mG and implies that the mass-to-flux ratio in this region is slightly supercritical. Conclusions. The magnetic field in G31.41+0.31 maintains an hourglass-shaped morphology down to scales of <1000 au. Despite the magnetic field being important in G31.41+0.31, it is not enough to prevent fragmentation and collapse of the core, as demonstrated by the presence of at least four sources embedded in the center of the core.

scholarly journals The Hα Emission of the PMS Star Serpens/SVS 2

1990 ◽  
Vol 140 ◽  
pp. 318-318
Author(s):  
A.I. Gomez De Castro
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Major Axis ◽  
Mass Star ◽  
Polarization Pattern ◽  
Bipolar Structure ◽  
Dust Disk ◽  
Hα Emission ◽  
Low Mass ◽  
The Magnetic Field

Serpens is a region of low mass star formation where the magnetic field seems to play a fundamental role. The major axis of the Serpens outflows are aligned with the magnetic field. The most outstanding object in the region is the Serpens Reflection Nebula, SRN. This is characterized by a rather complex bipolar structure with several knots of gas and dust embedded in both nebular lobes. The western lobe is directed out of the cloud toward the observer. The SRN is illuminated by the PMS star Serpens/SVS 2. The star is surrounded by a dust disk; the polarization pattern of the disk can be interpreted as produced by dust grains aligned by the magnetic field frozen-in with the disk.

scholarly journals Search for radio jets from massive young stellar objects

2020 ◽  
Vol 645 ◽  
pp. A29
Author(s):  
Ü. Kavak ◽  
Á. Sánchez-Monge ◽  
A. López-Sepulcre ◽  
R. Cesaroni ◽  
F. F. S. van der Tak ◽  
...  
Keyword(s):  
Field Of View ◽  
Radio Continuum ◽  
High Mass ◽  
Mass Star ◽  
Low Mass Stars ◽  
Star Forming ◽  
Radio Jets ◽  
Star Forming Regions ◽  
Nonthermal Emission ◽  
Low Mass

Context. Recent theoretical and observational studies debate the similarities of the formation process of high- (>8 M⊙) and low-mass stars. The formation of low-mass stars is directly associated with the presence of disks and jets. Theoretical models predict that stars with masses up to 140 M⊙ can be formed through disk-mediated accretion in disk-jet systems. According to this scenario, radio jets are expected to be common in high-mass star-forming regions. Aims. We aim to increase the number of known radio jets in high-mass star-forming regions by searching for radio-jet candidates at radio continuum wavelengths. Methods. We used the Karl G. Jansky Very Large Array (VLA) to observe 18 high-mass star-forming regions in the C band (6 cm, ≈1′′.0 resolution) and K band (1.3 cm, ≈0′′.3 resolution). We searched for radio-jet candidates by studying the association of radio continuum sources with shock activity signs (e.g., molecular outflows, extended green objects, and maser emission). Our VLA observations also targeted the 22 GHz H2O and 6.7 GHz CH3OH maser lines. Results. We have identified 146 radio continuum sources, 40 of which are located within the field of view of both images (C and K band maps). We derived the spectral index, which is consistent with thermal emission (between − 0.1 and + 2.0) for 73% of these sources. Based on the association with shock-activity signs, we identified 28 radio-jet candidates. Out of these, we identified 7 as the most probable radio jets. The radio luminosity of the radio-jet candidates is correlated with the bolometric luminosity and the outflow momentum rate. About 7–36% of the radio-jet candidates are associated with nonthermal emission. The radio-jet candidates associated with 6.7 GHz CH3OH maser emission are preferentially thermal winds and jets, while a considerable fraction of radio-jet candidates associated with H2O masers show nonthermal emission that is likely due to strong shocks. Conclusions. About 60% of the radio continuum sources detected within the field of view of our VLA images are potential radio jets. The remaining sources could be compact H II regions in their early stages of development, or radio jets for which we currently lack further evidence of shock activity. Our sample of 18 regions is divided into 8 less evolved infrared-dark regions and 10 more evolved infrared-bright regions. We found that ≈71% of the identified radio-jet candidates are located in the more evolved regions. Similarly, 25% of the less evolved regions harbor one of the most probable radio jets, while up to 50% of the more evolved regions contain one of these radio-jet candidates. This suggests that the detection of radio jets in high-mass star-forming regions is more likely in slightly more evolved regions.

The innermost regions of massive protostars traced by masers, high-resolution radio continuum, and near-infrared imaging

2017 ◽  
Vol 13 (S336) ◽  
pp. 289-290
Author(s):  
Fabrizio Massi ◽  
Luca Moscadelli ◽  
Carmelo Arcidiacono ◽  
Francesca Bacciotti
Keyword(s):  
Near Infrared ◽  
Infrared Imaging ◽  
High Spatial Resolution ◽  
Radio Continuum ◽  
High Mass ◽  
Mass Star ◽  
Near Infrared Imaging ◽  
Stellar Objects ◽  
First Results ◽  
Low Mass

AbstractWhether high-mass stars (M > 7M⊙) emerge from a scaled-up version of the low-mass star formation scenario, i. e. through disk-mediated accretion, is still debated. We present the first results of an observational programme aimed to map the innermost regions of high-mass stellar objects by combining together high-spatial resolution maser and radio continuum observations, and near-infrared imaging.

scholarly journals A centrally concentrated sub-solar-mass starless core in the Taurus L1495 filamentary complex

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Kazuki Tokuda ◽  
Kengo Tachihara ◽  
Kazuya Saigo ◽  
Phillipe André ◽  
Yosuke Miyamoto ◽  
...  
Keyword(s):  
Star Formation ◽  
Initial Conditions ◽  
Volume Density ◽  
Mass Star ◽  
Brown Dwarf ◽  
Solar Mass ◽  
Star Forming ◽  
The Core ◽  
Order Of Magnitude ◽  
Low Mass

Abstract The formation scenario of brown dwarfs is still unclear because observational studies to investigate its initial condition are quite limited. Our systematic survey of nearby low-mass star-forming regions using the Atacama Compact Array (aka the Morita array) and the IRAM 30-m telescope in 1.2 mm continuum has identified a centrally concentrated starless condensation with a central H2 volume density of ∼106 cm−3, MC5-N, connected to a narrow (width ∼0.03 pc) filamentary cloud in the Taurus L1495 region. The mass of the core is $\sim {0.2\!-\!0.4}\, M_{\odot }$, which is an order of magnitude smaller than typical low-mass pre-stellar cores. Taking into account a typical core to star formation efficiency for pre-stellar cores (∼20%–40%) in nearby molecular clouds, brown dwarf(s) or very low-mass star(s) may be going to be formed in this core. We have found possible substructures at the high-density portion of the core, although much higher angular resolution observation is needed to clearly confirm them. The subsequent N2H+ and N2D+ observations using the Nobeyama 45-m telescope have confirmed the high-deuterium fractionation (∼30%). These dynamically and chemically evolved features indicate that this core is on the verge of proto-brown dwarf or very low-mass star formation and is an ideal source to investigate the initial conditions of such low-mass objects via gravitational collapse and/or fragmentation of the filamentary cloud complex.

scholarly journals 3D shape of Orion A with Gaia DR2 An informed view on Star Formation Rates and Efficiencies

2018 ◽  
Vol 14 (S345) ◽  
pp. 27-33
Author(s):  
Josefa E. Großschedl ◽  
João Alves ◽  
Stefan Meingast ◽  
Birgit Hasenberger
Keyword(s):  
Star Formation ◽  
Formation Rate ◽  
Young Stellar Objects ◽  
Mass Star ◽  
Orion Nebula ◽  
Stellar Objects ◽  
Star Forming ◽  
The North ◽  
Low Mass ◽  
The Rich

AbstractThe giant molecular cloud Orion A is the closest massive star-forming region to earth (d ∼ 400 pc). It contains the rich Orion Nebula Cluster (ONC) in the North, and low-mass star-forming regions (L1641, L1647) to the South. To get a better understanding of the differences in star formation activity, we perform an analysis of the gas mass distribution and star formation rate across the cloud. We find that the gas is roughly uniformly distributed, while, oddly, the ONC region produced about a factor of ten more stars compared to the rest of the cloud. For a better interpretation of this phenomenon, we use Gaia DR2 parallaxes, to analyse distances of young stellar objects, using them as proxy for cloud distances. We find that the ONC region indeed lies at about 400 pc while the low-mass star-forming parts are inclined about 70∘ from the plane of the sky reaching until ∼470 pc. With this we estimate that Orion A is an about 90 pc long filamentary cloud (about twice as long as previously assumed), with its “Head” (the ONC region) being “bent” and oriented towards the galactic mid-plane. This striking new view allows us to perform a more robust analysis of this important star-forming region in the future.

scholarly journals The resolved radio–FIR correlation in nearby galaxies with Herschel and Spitzer

2011 ◽  
Vol 7 (S284) ◽  
pp. 400-403
Author(s):  
Fatemeh S. Tabatabaei ◽  
Eva Schinnerer ◽  
Eric Murphy ◽  
Rainer Beck ◽  
Annie Hughes ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Diffusion Length ◽  
Spatial Scales ◽  
Cosmic Ray ◽  
Far Infrared ◽  
Scale Dependence ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Synchrotron Emission ◽  
Nearby Galaxies

AbstractWe investigate the correlation between the far-infrared (FIR) and radio continuum emission from NGC6946 on spatial scales between 0.9 and 17 kpc. We use the Herschel PACS (70, 100, 160μm) and SPIRE (250μm) data from the KINGFISH project. Separating the free-free and synchrotron components of the radio continuum emission, we find that FIR is better correlated with the free-free than the synchrotron emission. Compared to a similar study in M33 and M31, we find that the scale dependence of the synchrotron–FIR correlation in NGC6946 is more similar to M31 than M33. The scale dependence of the synchrotron–FIR correlation can be explained by the turbulent-to-ordered magnetic field ratio or, equivalently, the diffusion length of the cosmic ray electrons in these galaxies.

scholarly journals Revisiting the Distance to Radio Loops I and IV Using Gaia and Radio/Optical Polarization Data

2021 ◽  
Vol 922 (2) ◽  
pp. 210
Author(s):  
G. V. Panopoulou ◽  
C. Dickinson ◽  
A. C. S. Readhead ◽  
T. J. Pearson ◽  
M. W. Peel
Keyword(s):  
Magnetic Field ◽  
Galactic Center ◽  
Classical Method ◽  
Dust Emission ◽  
Galactic Latitude ◽  
Synchrotron Emission ◽  
Optical Polarization ◽  
The North ◽  
Significant Alignment ◽  
North Polar

Abstract Galactic synchrotron emission exhibits large angular scale features known as radio spurs and loops. Determining the physical size of these structures is important for understanding the local interstellar structure and for modeling the Galactic magnetic field. However, the distance to these structures is either under debate or entirely unknown. We revisit a classical method of finding the location of radio spurs by comparing optical polarization angles with those of synchrotron emission as a function of distance. We consider three tracers of the magnetic field: stellar polarization, polarized synchrotron radio emission, and polarized thermal dust emission. We employ archival measurements of optical starlight polarization and Gaia distances and construct a new map of polarized synchrotron emission from WMAP and Planck data. We confirm that synchrotron, dust emission, and stellar polarization angles all show a statistically significant alignment at high Galactic latitude. We obtain distance limits to three regions toward Loop I of 112 ± 17 pc, 135 ± 20 pc, and <105 pc. Our results strongly suggest that the polarized synchrotron emission toward the North Polar Spur at b > 30° is local. This is consistent with the conclusions of earlier work based on stellar polarization and extinction, but in stark contrast with the Galactic center origin recently revisited on the basis of X-ray data. We also obtain a distance measurement toward part of Loop IV (180 ± 15 pc) and find evidence that its synchrotron emission arises from chance overlap of structures located at different distances. Future optical polarization surveys will allow the expansion of this analysis to other radio spurs.

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