Interstellar extinction and polarization - a spheroidal dust grain approach perspective

Abstract

We extend and investigate the spheroidal model of interstellar dust grains used to simultaneously interpret the observed interstellar extinction and polarization curves. We compare our model with similar models recently suggested by other authors, study its properties and apply it to fit the normalized extinction A(λ)/AV and the polarizing efficiency P(λ)/A(λ) measured in the near‐infrared to far‐ultraviolet region for several stars seen through one large cloud. We conclude that the model parameter Ω being the angle between the line of sight and the magnetic field direction can be more or less reliably determined from comparison of the theory and observations. This opens a way to study the spatial structure of interstellar magnetic fields by using multiwavelength photometric and polarimetric observations.

Tracing the ISM magnetic field morphology: the potential of multi-wavelength polarization measurements

“…Resolving complex density and magnetic field structures, however, is currently ambiguous because of open questions about interstellar dust composition and the absence of a consistent theory of grain alignment mechanisms (Hoang et al 2007;Das et al 2010). A reliable theory about the dominating grain alignment mechanisms inside the ISM (e.g.…”

“…Therefore, ∆C λ must be weighted with cos(2Φ) where the factor can be expressed as a function of β, Θ and ω (for details see Hong & Greenberg 1980;Das et al 2010). …”

Polarizing efficiency as a guide of grain growth and interstellar magnetic field properties

“…In general, the dust grain characteristics and the magnetic field can vary along the line of sight. As a basic model we use that of imperfectly aligned spheroidal particles in a regular magnetic field that was earlier applied to simultaneously analyse the interstellar extinction and polarization curves in a wide spectral range (Voshchinnikov & Das 2008;Das et al 2010;Siebenmorgen et al 2014). We consider the time evolution of the grain size distribution due to accretion and coagulation processes ) and involved new optical constants of grain materials (Jones 2012;Jones et al 2013).…”

Radiative transfer with POLARIS

“…One way to improve our knowledge about the involvement of magnetic fields in the star formation process is to trace its morphology with the help of dust grains. In addition to magnetic fields, dust grains also play a central role in the ISM -from heating and cooling processes, astrochemistry, to the polarization effects of light (Das et al 2010). Non-spherical rotating dust particles have the tendency to align with their shorter axis along the local magnetic field direction (Martin 1974;Voshchinnikov 2012).…”