scholarly journals Distortion of magnetic fields in Barnard 68

2019 ◽  
Vol 72 (1) ◽  
Author(s):  
Ryo Kandori ◽  
Motohide Tamura ◽  
Masao Saito ◽  
Kohji Tomisaka ◽  
Tomoaki Matsumoto ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Critical Mass ◽  
Polarized Light ◽  
Evolutionary Status ◽  
Core Mass ◽  
The Core ◽  
Magnetic Field Modeling ◽  
Inclination Angles

Abstract The magnetic field structure, kinematical stability, and evolutionary status of the starless dense core Barnard 68 (B68) are revealed based on the near-infrared polarimetric observations of background stars, measuring the dichroically polarized light produced by aligned dust grains in the core. After subtracting unrelated ambient polarization components, the magnetic fields pervading B68 are mapped using 38 stars and axisymmetrically distorted hourglass-like magnetic fields are obtained, although the evidence for the hourglass field is not very strong. On the basis of simple 2D and 3D magnetic field modeling, the magnetic inclination angles on the plane-of-sky and in the line-of-sight direction are determined to be 47° ± 5° and 20° ± 10°, respectively. The total magnetic field strength of B68 is obtained to be $26.1 \pm 8.7\, \mu \mbox{G}$. The critical mass of B68, evaluated using both magnetic and thermal/turbulent support, is $M_{\rm cr} = 2.30 \pm 0.20\, {M}_{\odot }$, which is consistent with the observed core mass of $M_{\rm core}=2.1\, M_{\odot }$, suggesting a nearly critical state. We found a relatively linear relationship between polarization and extinction up to AV ∼ 30 mag toward the stars with deepest obscuration. Further theoretical and observational studies are required to explain the dust alignment in cold and dense regions in the core.

scholarly journals Distortion of magnetic fields in the pre-stellar core Barnard 68

2008 ◽  
Vol 4 (S259) ◽  
pp. 107-108 ◽  
Author(s):  
Ryo Kandori ◽  
Motohide Tamura ◽  
Ken-ichi Tatematsu ◽  
Nobuhiko Kusakabe ◽  
Yasushi Nakajima ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Flux Ratio ◽  
Field Structure ◽  
Wide Field ◽  
Stellar Core ◽  
The Core ◽  
Cloud Cores ◽  
The Stability

AbstractMagnetic fields are believed to play an important role in controlling the stability and contraction of molecular cloud cores. In the present study, magnetic fields of a cold pre-stellar core, Barnard 68, have been mapped based on wide-field near-infrared polarimetric observations of background stars. A distinct “hourglass-shaped” magnetic field is identified toward the core, as the observational evidence of magnetic field structure distorted by mass accumulation in a pre-stellar core. Our findings on the geometry of magnetic fields as well as the mass-to-magnetic flux ratio are presented.

scholarly journals Magnetic fields in massive star forming regions: wide-field NIR polarimetry of M42 and Mon R2

2008 ◽  
Vol 4 (S259) ◽  
pp. 97-98 ◽  
Author(s):  
Nobuhiko Kusakabe ◽  
Motohide Tamura ◽  
Ryo Kandori ◽  
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Massive Star ◽  
Near Infrared ◽  
Polarized Light ◽  
Field Structure ◽  
Wide Field ◽  
Magnetic Field Structure ◽  
Star Forming ◽  
Star Forming Regions

AbstractMagnetic fields are believed to play an important role in star formation. We observed M42 and Mon R2 massive star forming regions using the wide-field (8′ × 8′) near-infrared imaging polarimeter SIRPOL in South Africa. Magnetic fields are mapped on the basis of dichroic polarized light from hundreds of young stars embedded in the regions. We found “hourglass shaped” magnetic field structure toward OMC-1 region, which is very consistent with magnetic fields traced by using dust emission polarimetry at sub-mm to FIR wavelengths. In the Mon R2 region, we found “S-shaped” magnetic field structure across the massive protostar IRS 1 and IRS 2. We will present the results of comparison of magnetic fields at NIR with those at other wavelengths.

scholarly journals Near Infrared Polarimetry of Dark Clouds and Star Forming Regions - Two Micron Polarization Survey of T Tauri Stars

1990 ◽  
Vol 140 ◽  
pp. 327-328
Author(s):  
M. Tamura ◽  
S. Sato
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Near Infrared ◽  
Background Field ◽  
Star Forming ◽  
Dark Clouds ◽  
Star Forming Regions ◽  
Stellar Sources ◽  
Geometrical Relationship ◽  
The Magnetic Field

Infrared polarimetry is one of the most useful methods to delineate the magnetic field structure in dark clouds and star-forming regions, where the intracloud extinction is so large that optical polarimetry is inaccessible. We have been conducting a near-infrared polarization survey of background field stars and embedded sources toward nearby dark clouds and star-forming regions (Tamura 1988). Particularly, the magnetic field structure in the denser regions of the clouds are well revealed in Heiles Cloud 2 in Taurus, ρ Oph core, and NGC1333 region in Perseus (Tamura et al. 1987; Sato et al. 1988; Tamura et al. 1988). This survey also suggests an interesting geometrical relationship between magnetic field and star-formation: the IR polarization of young stellar sources associated with mass outflow phenomena is perpendicular to the magnetic fields. This relationship suggests a presence of circumstellar matter (probably dust disk) with its plane perpendicular to the ambient magnetic field. Combining with another geometrical relationship that the elongation of the denser regions of the cloud is perpendicular to the magnetic field, the geometry suggests that the cloud contraction and subsequent star-formation have been strongly affected by the magnetic fields. Thus, it is important to study the universality of such geometrical relationship between IR polarization of young stellar sources and magnetic fields. In this paper, we report the results on a 2 micron polarization survey of 39 T Tauri stars, 8 young stellar objects and 11 background field stars in Taurus dark cloud complex.

scholarly journals Characterising the surface magnetic fields of T Tauri stars with high-resolution near-infrared spectroscopy

2019 ◽  
Vol 630 ◽  
pp. A99 ◽  
Author(s):  
A. Lavail ◽  
O. Kochukhov ◽  
G. A. J. Hussain
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Large Scale ◽  
Near Infrared ◽  
Field Measurements ◽  
T Tauri Stars ◽  
Small Scale ◽  
Surface Magnetic Field ◽  
T Tauri

Aims. In this paper, we aim to characterise the surface magnetic fields of a sample of eight T Tauri stars from high-resolution near-infrared spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are firstly to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, secondly to expand the sample of stars with measured surface magnetic field strengths, thirdly to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and fourthly to compare the magnetic field modulus ⟨B⟩ tracing small-scale magnetic fields to those of large-scale magnetic fields derived by Stokes V Zeeman Doppler Imaging (ZDI) studies. Methods. We modelled the Zeeman broadening of magnetically sensitive spectral lines in the near-infrared K-band from high-resolution spectra by using magnetic spectrum synthesis based on realistic model atmospheres and by using different descriptions of the surface magnetic field. We developped a Bayesian framework that selects the complexity of the magnetic field prescription based on the information contained in the data. Results. We obtain individual magnetic field measurements for each star in our sample using four different models. We find that the Bayesian Model 4 performs best in the range of magnetic fields measured on the sample (from 1.5 kG to 4.4 kG). We do not detect a strong rotational variation of ⟨B⟩ with a mean peak-to-peak variation of 0.3 kG. Our confidence intervals are of the same order of magnitude, which suggests that the Zeeman broadening is produced by a small-scale magnetic field homogeneously distributed over stellar surfaces. A comparison of our results with mean large-scale magnetic field measurements from Stokes V ZDI show different fractions of mean field strength being recovered, from 25–42% for relatively simple poloidal axisymmetric field topologies to 2–11% for more complex fields.

scholarly journals Near-infrared Polarimetry and Interstellar Magnetic Fields in the Galactic Center

2012 ◽  
Vol 10 (H16) ◽  
pp. 387-387
Author(s):  
S. Nishiyama ◽  
H. Hatano ◽  
T. Nagata ◽  
M. Tamura
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Near Infrared ◽  
Galactic Center ◽  
Smooth Transition ◽  
The Magnetic Field

AbstractWe present a large-scale view of the magnetic field (MF) in the central 3° × 2° region of our Galaxy. There is a smooth transition of the large-scale MF configuration in this region.

scholarly journals Models of Type II Supernova Explosions

1986 ◽  
Vol 7 ◽  
pp. 629-633
Author(s):  
Wolfgang Hillebrandt
Keyword(s):  
Main Sequence ◽  
Critical Mass ◽  
Iron Core ◽  
Heavy Nuclei ◽  
Core Mass ◽  
The Core ◽  
Supernova Explosions ◽  
M Stars ◽  
Chandrasekhar Limit ◽  
Carbon Burning

Present stellar evolution codes predict that stars with He-core masses above approximately 2 M⊙, corresponding to main sequence masses of at least 8 M⊙ burn carbon non-violently. After hydrostatic core carbon burning all those stars contain O-Ne-Mg cores but their further evolution is strongly dependent on the stellar entropy and thus on the main sequence and the core mass. If the He-core mass is below 3 M⊙ the O-Ne-Mg core grows due to carbon-burning in a shell and the crucial question is, whether or not it grows beyond the critical mass for Neignition (≅1.37 M⊙). Stars with He-cores less massive than about 2.4 M⊙ will never ignite Ne, but due to electron-captures, mainly on Ne and Mg, their cores will contract until O-burning begins. Since the matter of the O-Ne-Mg core is weakly degenerate O-burning propagates as a (subsonic) deflagration front and incinerates a certain fraction of the core into a nuclear statistical equilibrium (NSE) composition of iron-group elements (Nomoto, 1984). If, on the other hand, the mass of the O-Ne-Mg core is slightly larger than 1.37 M⊙ Ne and O burn in a shell from about 0.6 M⊙ to 1.4 M⊙, but again the outcome is a NSE-composition (Wilson et al., 1985). In both cases the core-mass finally exceeds the Chandrasekhar limit because electron captures on free protons and heavy nuclei lower the electron concentration and consequently also the effective Chandrasekhar mass. The cores, therefore, continue to contract and finally collapse to neutron star densities with iron-core masses between 0.7 and 1.4 M⊙.

scholarly journals Magnetic field observations of low-mass stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 339-344
Author(s):  
Ansgar Reiners
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Measurements ◽  
Polarized Light ◽  
M Dwarfs ◽  
Magnetic Field Generation ◽  
Low Mass Stars ◽  
Strong Magnetic Fields ◽  
Direct Measurements ◽  
Low Mass

AbstractDirect measurements of magnetic fields in low-mass stars of spectral class M have become available during the last years. This contribution summarizes the data available on direct magnetic measurements in M dwarfs from Zeeman analysis in integrated and polarized light. Strong magnetic fields at kilo-Gauss strength are found throughout the whole M spectral range, and so far all field M dwarfs of spectral type M6 and later show strong magnetic fields. Zeeman Doppler images from polarized light find weaker fields, which may carry important information on magnetic field generation in partially and fully convective stars.

The Influence of Light Variations on the Stellar Magnetic Fields Measurements

1976 ◽  
Vol 32 ◽  
pp. 441-448
Author(s):  
F.A. Catalano ◽  
G. Strazzulla
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Radiation Field ◽  
Polarity Reversal ◽  
Effective Magnetic Field ◽  
Surface Field ◽  
Oblique Rotator ◽  
Inclination Angles ◽  
Stellar Magnetic Fields

SummaryIn the frame of the oblique rotator the radiation field is assumed to depend on the magnetic colatitude. Introducing this dependence in the effective magnetic field formula, a new expression for this has been derived.The calculations carried out in the case of a dipolar surface field having a polar intensity of 104gauss show that the amplitude of the variation and the polarity reversal both depend on the combination of the obliquity and inclination angles.

scholarly journals The FRIGG project: From intermediate galactic scales to self-gravitating cores

2018 ◽  
Vol 611 ◽  
pp. A24 ◽  
Author(s):  
Patrick Hennebelle
Keyword(s):  
Initial Conditions ◽  
Critical Mass ◽  
Adaptive Mesh ◽  
Direct Consequence ◽  
Small Scale ◽  
Core Mass ◽  
Numerical Resolution ◽  
The Core ◽  
Prestellar Cores ◽  
Hydrodynamical Simulations

Context. Understanding the detailed structure of the interstellar gas is essential for our knowledge of the star formation process.Aim. The small-scale structure of the interstellar medium (ISM) is a direct consequence of the galactic scales and making the link between the two is essential.Methods. We perform adaptive mesh simulations that aim to bridge the gap between the intermediate galactic scales and the self-gravitating prestellar cores. For this purpose we use stratified supernova regulated ISM magneto-hydrodynamical simulations at the kpc scale to set up the initial conditions. We then zoom, performing a series of concentric uniform refinement and then refining on the Jeans length for the last levels. This allows us to reach a spatial resolution of a few 10−3 pc. The cores are identified using a clump finder and various criteria based on virial analysis. Their most relevant properties are computed and, due to the large number of objects formed in the simulations, reliable statistics are obtained.Results. The cores’ properties show encouraging agreements with observations. The mass spectrum presents a clear powerlaw at high masses with an exponent close to ≃−1.3 and a peak at about 1–2 M⊙. The velocity dispersion and the angular momentum distributions are respectively a few times the local sound speed and a few 10−2 pc km s−1. We also find that the distribution of thermally supercritical cores present a range of magnetic mass-to-flux over critical mass-to-flux ratios, typically between ≃0.3 and 3 indicating that they are significantly magnetized. Investigating the time and spatial dependence of these statistical properties, we conclude that they are not significantly affected by the zooming procedure and that they do not present very large fluctuations. The most severe issue appears to be the dependence on the numerical resolution of the core mass function (CMF). While the core definition process may possibly introduce some biases, the peak tends to shift to smaller values when the resolution improves.Conclusions. Our simulations, which use self-consistently generated initial conditions at the kpc scale, produce a large number of prestellar cores from which reliable statistics can be inferred. Preliminary comparisons with observations show encouraging agreements. In particular the inferred CMFs resemble the ones inferred from recent observations. We stress, however, a possible issue with the peak position shifting with numerical resolution.

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