Interstellar Polarization in the Taurus Dark Clouds: Wavelength‐dependent Position Angles and Cloud Structure near TMC‐1

Messinger, David W.; Whittet, D. C. B.; Roberge, W. G.

doi:10.1086/304610

Cited by 31 publications

(26 citation statements)

References 37 publications

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“…As discussed earlier, both stars show intrinsic polarization and rotation in their polarization angle. In both the cases, the polarization angle seems to decrease with increasing wavelength, which is similar to observations in Messinger et al (1997) toward the direction of Taurus dark cloud.…”

Section: Determination Of Distance To L1570supporting

confidence: 86%

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

Eswaraiah

Maheswar

Pandey

et al. 2013

A&A

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Aims. We aim to map the magnetic field geometry and to study the dust properties of the starless cloud, L1570, using multi-wavelength optical polarimetry and photometry of the stars projected on the cloud. Methods. The direction of the magnetic field component parallel to the plane of the sky of a cloud can be obtained using polarimetry of the stars projected on and located behind the cloud. It is believed that the unpolarized light from the stars background to the cloud undergoes selective extinction while passing through non-spherical dust grains that are aligned with their minor axes parallel to the cloud magnetic field. The emerging light becomes partially plane polarized. The observed polarization vectors trace the direction of the projected magnetic field of the cloud. We made R-band imaging polarimetry of the stars projected on a cloud, L1570, to trace the magnetic field orientation. We also made multi-wavelength polarimetric and photometric observations to constrain the properties of dust in L1570. Results. We estimated a distance of 394 ± 70 pc to the cloud using 2MASS JHK s colors. Using the values of the Serkowski parameters, σ 1 , , λ max , and the position of the stars on the near-infrared color-color diagram, we identified 13 stars that could possibly have intrinsic polarization and/or rotation in their polarization angles. One star, 2MASS J06075075+1934177, which is a B4Ve spectral type, shows diffuse interstellar bands in the spectrum in addition to the Hα line in emission. There is an indication for slightly bigger dust grains toward L1570 on the basis of the dust grain size-indicators such as λ max and R V values. The magnetic field lines are found to be parallel to the cloud structures seen in the 250 μm images (also in the 8 μm and 12 μm shadow images) of L1570. Based on the magnetic field geometry, the cloud structure, and the complex velocity structure, we conclude that L1570 is in the process of formation due to the converging flow material mediated by the magnetic field lines. A structure function analysis showed that in the L1570 cloud region the large-scale magnetic fields are stronger than the turbulent component of the magnetic fields. The estimated magnetic field strengths suggest that the L1570 cloud region is subcritical and hence could be strongly supported by the magnetic field lines.

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Section: Determination Of Distance To L1570supporting

confidence: 86%

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

Eswaraiah

Maheswar

Pandey

et al. 2013

A&A

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“…Such a wavelength dependence is similar to the Serkowski law (Serkowski et al 1975) and the Wilking law (Wilking et al 1982) and is often found in the aperture polarimetry of T Tauri stars (e.g. Hodapp 1984;McGreor et al 1994;Messinger et al 1997;Whittet et al 2001;Pereyra et al 2009). We would like to point out that Serkowski's and Wilking's laws are intended to fit the interstellar polarization, where the polarization is produced by dichroic extinction, and the above similarity is met by chance.…”

Section: Effects Of the Disk Height And The Grain Sizesupporting

confidence: 74%

Polarization disks in near-infrared high-resolution imaging

Murakawa

2010

A&A

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A polarization disk is a characteristic feature of optical and near-infrared (NIR) polarimetric images of young stellar objects (YSOs) and is regarded as convincing evidence that a dust disk is present. We analyze high-resolution linear polarization maps of a sample of low-mass YSO disk models by means of radiative transfer calculations to investigate the effects of the disk geometry and grain sizes on polarization properties. Our modeling assumes spherical grains with a power-law size distribution of n (a) ∝ a −3.5 ; 0.005 μm ≤ a ≤ a max and with a fixed a max of 0.25 μm for the outer envelope and a different a max for the disk. The parameters to examine are the disk height (i.e. the ratio of the disk height to the outer disk radius H of 0.1 to 1.0) and the dust sizes in the disk (i.e. a max of 0.25 to 1000.0 μm). In a near pole-on view, the polarization vectors are centro-symmetrically aligned even towards the disk, but the degree of polarization can be different from the envelope. We predict that the pole-on disk can be distinguished from the envelope. In contrast, the model images show a bipolar nebulosity and a polarization disk with a vector alignment in edge-on view. The polarization is low (<10%) for large grains or low H values and high (up to ∼80%) for small grains and high H values. In contrast, comparably constant polarizations (20-40%) are obtained in the optical. The wavelength dependence in low NIR polarization cases is often detected in many T Tauri stars, suggesting that grain growth or an advanced disk accretion is expected in these objects. The opposite trend in high NIR polarization cases, which is found in some low-mass protostars, is reproduced with spherical grain models. To understand our results, we developed a generalized scattering model, which is an extension of the vector alignment mechanism. In the lowmass star disk case, multiple-scattered light behaves as if it chooses paths of comparably low optical density region (e.g. the disk surface), avoiding a high density, equatorial region, which we call the roundabout effect. The single-scattered light does not reach the observer, and the double-scattered light contributes the most flux. However, the effect of the first scattering still appears in the final polarization status. The higher the disk height in our models, the closer to 90 • the scattering angle on the disk surface, resulting in a higher polarization. The variety of the wavelength dependence on the polarization is also an example of the roundabout effect. In the optical, only stray light passed through the envelope reaches the observer. Thus, the optical polarization is characterized by scattering by small grains in the envelope. On the other hand, since the NIR photons can pass through a somewhat inner part of the disk, the NIR polarization can still offer information on the dust and geometry of the disk. We expect that a polarization disk analysis in high-resolution data, such as the one we present, offers opportunities to investigate the grain growth and dust se...

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“…Linear interstellar polarization is observed to peak at wavelengths in the visible or near-infrared along different lines of sight, and a close correlation between these peak wavelengths and the maximum size of the aligned grains is predicted by interstellar extinction models. Longer peak wavelengths are found mostly in denser clouds (Messinger et al 1997), pointing toward larger grains there. However, for the wavelength of maximum polarization to be a unique indicator of maximum grain size, grains of all sizes must be aligned with equal efficiency in all environments, and grains of all sizes must be nonspherical to the same degree.…”

Section: X-ray Halos As Tracers Of Large Interstellar Grainsmentioning

confidence: 93%

“…These include the wavelength of peak linear interstellar polarization (e.g., Messinger, Whittet, & Roberge 1997), the dust albedo at near-infrared wavelengths (Kim, Martin, & Hendry 1994;Witt, Oliveri, & Schild 1990;Lehtinen & Mattila 1996;Witt et al 1994), and the shape and intensity of X-ray halos surrounding point sources of X-rays (Mauche & Gorenstein 1986;Mathis & Lee 1991;Predehl & Klose 1996). Linear interstellar polarization is observed to peak at wavelengths in the visible or near-infrared along different lines of sight, and a close correlation between these peak wavelengths and the maximum size of the aligned grains is predicted by interstellar extinction models.…”

Section: X-ray Halos As Tracers Of Large Interstellar Grainsmentioning

confidence: 99%

X-Ray Halos and Large Grains in the Diffuse Interstellar Medium

Witt

Smith

Dwek

2001

The Astrophysical Journal

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Recent observations with dust detectors on board the interplanetary spacecrafts Ulysses and Galileo have recorded a substantial flux of large interstellar grains with radii between 0.25 and 2.0 mm entering the solar system from the local interstellar cloud. The most commonly used interstellar grain size distribution is characterized by an Ϫ3.5 a power law in grain radii a and extends to a maximum grain radius of 0.25 mm. The extension of the interstellar grain size distribution to such large radii will have a major effect on the median grain size and on the amount of mass needed to be tied up in dust for a given visual optical depth. It is therefore important to investigate whether this population of larger dust particles prevails in the general interstellar medium or whether it is merely a local phenomenon. The presence of large interstellar grains can be inferred mainly from their effect on the intensity and radial profile of scattering halos around X-ray sources. In this Letter, we examine the grain size distribution that gives rise to the X-ray halo around Nova Cygni 1992. The results of our study confirm the need to extend the interstellar grain size distribution in the direction of this source to and possibly beyond 2 mm. The model that gives the best fit to the halo data is characterized by (1) a grain size distribution that follows an power law up to Ϫ3.5 a 0.50 mm, followed by an extension from 0.50 to 2.0 mm, and (2) silicate and graphite (carbon) dust-to-gas Ϫ4.0 a mass ratios of 0.0044 and 0.0022, respectively, consistent with solar abundance constraints. Additional observations of X-ray halos probing other spatial directions are badly needed to test the general validity of this result.

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Interstellar Polarization in the Taurus Dark Clouds: Wavelength‐dependent Position Angles and Cloud Structure near TMC‐1

Cited by 31 publications

References 37 publications

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

A study of the starless dark cloud LDN 1570: Distance, dust properties, and magnetic field geometry

Polarization disks in near-infrared high-resolution imaging

X-Ray Halos and Large Grains in the Diffuse Interstellar Medium

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