Engineering topics

Manso Sainz, R

Publications and source records attributed to Manso Sainz, R.

3 records

DOE OSTI2012

HANLE EFFECT FOR STELLAR DIPOLES AND QUADRUPOLES

We derive exact expressions for the degree of lineal polarization over a resolved or integrated stellar disc due to resonance scattering and the Hanle effect from a dipolar or quadrupolar distribution of magnetic fields. We apply the theory of scattering polarization within the formalism of the spherical tensors representation for the density matrix and radiation field. The distribution of linear polarization over the stellar disk for different configurations of the magnetic field is studied and its topology discussed. For an unresolved dipole, the resulting polarization can be expressed in terms of just three functions (of the inclination angle and effective dipole strength) that are calculated numerically and their behavior discussed. Dipolar and (aligned) quadrupoles are considered in some detail, but the techniques here-in particular, the extensive use of the spherical tensor formalism for polarization-can easily be applied to more general field configurations.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

SCATTERING POLARIZATION IN THE Ca II INFRARED TRIPLET WITH VELOCITY GRADIENTS

Magnetic field topology, thermal structure, and plasma motions are the three main factors affecting the polarization signals used to understand our star. In this theoretical investigation, we focus on the effect that gradients in the macroscopic vertical velocity field have on the non-magnetic scattering polarization signals, establishing the basis for general cases. We demonstrate that the solar plasma velocity gradients may have a significant effect on the linear polarization produced by scattering in chromospheric spectral lines. In particular, we show the impact of velocity gradients on the anisotropy of the radiation field and on the ensuing fractional alignment of the Ca II levels, and how they can lead to an enhancement of the zero-field linear polarization signals. This investigation remarks on the importance of knowing the dynamical state of the solar atmosphere in order to correctly interpret spectropolarimetric measurements, which is important, among other things, for establishing a suitable zero-field reference case to infer magnetic fields via the Hanle effect.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2012

MODEL SELECTION FOR SPECTROPOLARIMETRIC INVERSIONS

Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios (S/Ns) favor models without gradients along the line of sight. If the observations show clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large S/Ns favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future.

79 ASTRONOMY AND ASTROPHYSICS↗