scholarly journals Polarization of background starlight and the structure of the interstellar magnetic field

1991 ◽  
Vol 147 ◽  
pp. 417-423
Author(s):  
Alyssa A. Goodman ◽  
Philip C. Myers ◽  
Pierre Bastien
Keyword(s):  
Magnetic Field ◽  
Position Angle ◽  
Three Dimensions ◽  
Local Magnetic Field ◽  
Line Of Sight ◽  
Dark Cloud ◽  
Interstellar Clouds ◽  
Dark Clouds ◽  
Entire Complex ◽  
Local Plane

We discuss the use of polarization maps of background starlight in studying the structure of the interstellar magnetic field. We make the assumption that the polarization observed is due to magnetically aligned dust grains associated with interstellar clouds along the line of sight, and that the position angle (ΘE) of polarization observed gives the direction (modulo 180°) of , the plane-of-the-sky projection of the (line-of-sight-averaged) magnetic field.There are two basic points in this paper. (1.) Out of context, the projected orientation of an elongated dark cloud may appear special (e.g. roughly "parallel" or “perpendicular”) in relation to the local (plane-of-the-sky) field direction given by polarization observations, but, when the view is expanded to include an entire complex of dark clouds, the shape and orientation of clouds within a complex often appears unrelated to the field structure. (2.) the dispersion in the postion angle of polarization observed in a region of the sky contains information about the ratio of the strength of the uniform (straight) component of the local magnetic field as compared to the dispersion (nonuniform component) in the field. Furthermore, in a region where Zeeman measurements covering the same region as polarization observations have been made, the uniform-to-nonuniform ratio deduced for the field from polarization data, can be combined with information about the line-of-sight field and an estimate of the correlation length of the field, to describe the magnetic field in three dimensions. We discuss the results of such an analysis for the dark cloud Lynds 204 (L204).

scholarly journals Polarization of background starlight and the structure of the interstellar magnetic field

1991 ◽  
Vol 147 ◽  
pp. 417-423
Author(s):  
Alyssa A. Goodman ◽  
Philip C. Myers ◽  
Pierre Bastien
Keyword(s):  
Magnetic Field ◽  
Position Angle ◽  
Three Dimensions ◽  
Local Magnetic Field ◽  
Line Of Sight ◽  
Dark Cloud ◽  
Interstellar Clouds ◽  
Dark Clouds ◽  
Entire Complex ◽  
Local Plane

We discuss the use of polarization maps of background starlight in studying the structure of the interstellar magnetic field. We make the assumption that the polarization observed is due to magnetically aligned dust grains associated with interstellar clouds along the line of sight, and that the position angle (ΘE) of polarization observed gives the direction (modulo 180°) of , the plane-of-the-sky projection of the (line-of-sight-averaged) magnetic field.There are two basic points in this paper. (1.) Out of context, the projected orientation of an elongated dark cloud may appear special (e.g. roughly "parallel" or “perpendicular”) in relation to the local (plane-of-the-sky) field direction given by polarization observations, but, when the view is expanded to include an entire complex of dark clouds, the shape and orientation of clouds within a complex often appears unrelated to the field structure. (2.) the dispersion in the postion angle of polarization observed in a region of the sky contains information about the ratio of the strength of the uniform (straight) component of the local magnetic field as compared to the dispersion (nonuniform component) in the field. Furthermore, in a region where Zeeman measurements covering the same region as polarization observations have been made, the uniform-to-nonuniform ratio deduced for the field from polarization data, can be combined with information about the line-of-sight field and an estimate of the correlation length of the field, to describe the magnetic field in three dimensions. We discuss the results of such an analysis for the dark cloud Lynds 204 (L204).

Polarimetric and photometric observations of CB54, with analysis of four other dark clouds

2021 ◽  
Vol 503 (4) ◽  
pp. 5274-5290
Author(s):  
A K Sen ◽  
V B Il’in ◽  
M S Prokopjeva ◽  
R Gupta
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Galactic Plane ◽  
Photometric Data ◽  
Dust Particles ◽  
Dark Cloud ◽  
Dark Clouds ◽  
High Polarization ◽  
Field Parallel ◽  
Photometric Observations

ABSTRACT We present the results of our BVR-band photometric and R-band polarimetric observations of ∼40 stars in the periphery of the dark cloud CB54. From different photometric data, we estimate E(B − V) and E(J − H). After involving data from other sources, we discuss the extinction variations towards CB54. We reveal two main dust layers: a foreground, E(B − V) ≈ 0.1 mag, at ∼200 pc and an extended layer, $E(B-V) \gtrsim 0.3$ mag, at ∼1.5 kpc. CB54 belongs to the latter. Based on these results, we consider the reason for the random polarization map that we have observed for CB54. We find that the foreground is characterized by low polarization ($P \lesssim 0.5$ per cent) and a magnetic field parallel to the Galactic plane. The extended layer shows high polarization (P up to 5–7 per cent). We suggest that the field in this layer is nearly perpendicular to the Galactic plane and both layers are essentially inhomogeneous. This allows us to explain the randomness of polarization vectors around CB54 generally. The data – primarily observed by us in this work for CB54, by A. K. Sen and colleagues in previous works for three dark clouds CB3, CB25 and CB39, and by other authors for a region including the B1 cloud – are analysed to explore any correlation between polarization, the near-infrared, E(J − H), and optical, E(B − V), excesses, and the distance to the background stars. If polarization and extinction are caused by the same set of dust particles, we should expect good correlations. However, we find that, for all the clouds, the correlations are not strong.

scholarly journals Infrared polarimetry of dark clouds - II. Magnetic field structure in the   Ophiuchi dark cloud

1988 ◽  
Vol 230 (2) ◽  
pp. 321-329 ◽  
Author(s):  
S. Sato ◽  
M. Tamura ◽  
T. Nagata ◽  
N. Kaifu ◽  
J. Hough ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Structure ◽  
Dark Cloud ◽  
Magnetic Field Structure ◽  
Dark Clouds

scholarly journals OH Maser sources in W49N: probing differential anisotropic scattering with Zeeman pairs

2012 ◽  
Vol 8 (S287) ◽  
pp. 470-474
Author(s):  
Avinash A. Deshpande ◽  
W. M. Goss ◽  
J. E. Mendoza-Torres
Keyword(s):  
Magnetic Field ◽  
Galactic Plane ◽  
Position Angle ◽  
Anisotropic Scattering ◽  
Local Magnetic Field ◽  
High Angular Resolution ◽  
Apparent Velocity ◽  
Image Position ◽  
Electron Density Irregularities ◽  
Maser Sources

AbstractOur analysis of a VLBA 12-hour synthesis observations of the OH masers in W49N has provided detailed high angular-resolution images of the maser sources, at 1612, 1665 and 1667 MHz. The images, of several dozens of spots, reveal anisotropic scatter broadening; with typical sizes of a few tens of milli-arc-seconds and axial ratios between 1.5 to 3. The image position angles oriented perpendicular to the galactic plane are interpreted in terms of elongation of electron-density irregularities parallel to the galactic plane, due to a similarly aligned local magnetic field. However, we find the apparent angular sizes on the average a factor of 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred earlier. The average position angle of the scattered broadened images is also seen to deviate significantly (by about 10 degrees) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, we find significant differences in the scatter broadened images for the two hands of polarization, even when apparent velocity separation is less than 0.1 km/s. Here we present the details of our observations and analysis, and discuss the interesting implications of our results for the intervening anisotropic magneto-ionic medium, as well as a comparison with the expectations based on earlier work.

scholarly journals Is the Magnetic Field Preserved During Core Formation?

2004 ◽  
Vol 221 ◽  
pp. 97-103
Author(s):  
Brenda C. Matthews ◽  
Shih-Ping Lai ◽  
Richard M. Crutcher ◽  
Christine D. Wilson
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Position Angle ◽  
Dark Cloud ◽  
Field Orientation ◽  
Nearby Star ◽  
Star Forming ◽  
Ordered Fields ◽  
Field Geometry ◽  
The Magnetic Field

We present recent JCMT and BIMA array polarimetry data of nearby star-forming regions in order to compare the core and cloud-scale magnetic field geometries in two regions of Orion. The similarity of the magnetic field geometry in these cores to that of their ambient clouds is contrasted with JCMT data toward the Barnard 1 dark cloud in Perseus, which reveal a different magnetic field orientation between the majority of the cores and the surrounding cloud; each of the cores exhibits a different mean polarization position angle. We conclude that the preservation of the magnetic field geometry is better in cores formed within clouds with ordered large scale structures. In Barnard 1, the cores may quickly exhibit a different polarization pattern if they have, for example, rotation which differs from the large scale cloud motions, or a weaker component of ordered fields. This could also explain why the cores exhibit such different geometries from each other in Barnard 1.

scholarly journals Rotating vector model for magnetars

2021 ◽  
Vol 502 (1) ◽  
pp. 1549-1556
Author(s):  
H Tong ◽  
P F Wang ◽  
H G Wang ◽  
Z Yan
Keyword(s):  
Magnetic Field ◽  
Magnitude Estimation ◽  
Position Angle ◽  
Vector Model ◽  
Line Of Sight ◽  
Estimation Formula ◽  
Emission Point ◽  
Order Of Magnitude ◽  
Field Geometry ◽  
The Magnetic Field

ABSTRACT The modification of the rotating vector model in the case of magnetars are calculated. Magnetars may have twisted magnetic field compared with normal pulsars. The polarization position angle of magnetars will change in the case of a twisted magnetic field. For a twisted dipole field, we found that the position angle will change both vertically and horizontally. During the untwisting process of the magnetar magnetosphere, the modifications of the position angle will evolve with time monotonously. This may explain the evolution of the position angle in magnetar PSR J1622-4950 and XTE J1810-197. The relation between the emission point and the line of sight will also change. We suggest every magnetospheric models of magnetars also calculate the corresponding changes of position angle in their models. Order of magnitude estimation formula for doing this is given. This opens the possibility to extract the magnetic field geometry of magnetars from their radio polarization observations.

Observations of magnetic aspect effects in auroral radar backscatter

1985 ◽  
Vol 63 (3) ◽  
pp. 402-408 ◽  
Author(s):  
J. A. Koehler ◽  
G. J. Sofko ◽  
V. Mehta ◽  
A. G. McNamara ◽  
D. R. McDiarmid
Keyword(s):  
Magnetic Field ◽  
Spectral Characteristics ◽  
Local Magnetic Field ◽  
Line Of Sight ◽  
Narrow Beam ◽  
Radar Backscatter ◽  
Aspect Angle ◽  
Series Of Experiments ◽  
Cw Radar

A series of experiments have been performed to investigate VHF auroral backscatter. The equipment is basically a bistatic CW radar using narrow beam antennas. One objective has been to investigate the dependence of backscatter power and spectral characteristics on aspect angle: the angle between the line of sight and the local magnetic field in the scattering region. The results indicate that the effects of aspect angle are much more complex than earlier measurements have indicated.

scholarly journals Role of Magnetic Fields in Star Formation

2009 ◽  
Vol 5 (H15) ◽  
pp. 438-439 ◽  
Author(s):  
Richard M. Crutcher
Keyword(s):  
Magnetic Field ◽  
Distribution Function ◽  
Star Formation ◽  
Probability Distribution Function ◽  
Volume Density ◽  
Line Of Sight ◽  
Formation Theory ◽  
Dark Clouds ◽  
The Core

AbstractI describe two recent projects to test star formation theory using Zeeman observations. First, using Bayesian analysis, the probability distribution function of the magnitude of the total magnetic field strength Bt and its dependence on volume density n(H) were inferred from Zeeman observations of the line-of-sight strengths Bz. The result was that from one molecular cloud to another Bt ranges uniformly between values close to zero and a maximum B0, and that B0 scales as n2/3. Second, observations of the ratio of the mass/flux (M/Φ) between the core and envelope regions of four dark clouds yielded values < 1. All of these results disagree with predictions of the strong magnetic field, ambipolar diffusion driven theory of star formation.

scholarly journals Magnetic Field Structure in Dark Clouds

1987 ◽  
Vol 115 ◽  
pp. 48-50
Author(s):  
M. Tamura ◽  
T. Nagata ◽  
S. Sato ◽  
M. Tanaka ◽  
N. Kaifu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Mode ◽  
Polarization Degree ◽  
List Type ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Central Regions ◽  
Field Geometry ◽  
Cloud Complex ◽  
The Magnetic Field

The magnetic field geometry in the central regions of two dark clouds has been mapped by measuring the polarization at 2.2 μm of background stars and of stars embedded in the clouds. The observations were done with the Kyoto polarimeter on the Agematsu 1m IR telescope in December 1984 for Heiles Cloud 2 in the Taurus dark cloud complex, and on the UKIRT 3.8m in May and July 1985 for the ρ Ophiuchus dark cloud core. The main results are: i)Most of the stars in both regions show polarization and their maxima are 2.7% in Heiles Cloud 2 and 7.6% in ρ Oph, respectively. There are similar positive relations between polarization degree and extinct ion Av's.ii)The distribution of position angles for Heiles Cloud 2 shows a single mode at about 50° and that for ρ Oph shows a bimode, at about 50° and 150°.iii)The magnetic fields, as delineated by the infrared polarization, appear perpendicular to the flattened elongations of the molecular clouds.

scholarly journals The Spectral and Spatial Decomposition of Extragalactic Radio Sources

1996 ◽  
Vol 175 ◽  
pp. 489-490
Author(s):  
L. Rudnick ◽  
D.M. Katz-Stone
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Local Magnetic Field ◽  
Line Of Sight ◽  
Radio Sources ◽  
Relativistic Electrons ◽  
Synchrotron Emission ◽  
Spatial Decomposition ◽  
Intensity Images ◽  
Spectral Tomography

We have developed a new set of techniques for extracting information from maps of synchrotron emission. Some of these methods are used to determine the shape of the spectrum and then to isolate the contributions of the number and energy of relativistic electrons and the local magnetic field strength to the total intensity images. These are discussed in Katz-Stone, Rudnick & Anderson (1993), Katz-Stone & Rudnick (1994), and Rudnick, Katz-Stone & Anderson, (1994). Here, we describe a method - called spectral tomography - to remove confusion from various features along the line of sight. We find that both structural and spectral confusion are commonplace, and therefore our dynamical and radiative models of extragalactic sources need significant revision.

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