[Astronomy seminar] Astronomy seminar via zoom, 2 October 10:30: Ernest Alsina

Mon Sep 28 12:28:25 CEST 2020

Dear all,

On Friday October 2 at 10:30 we will have the next Astronomy Seminar, remotely via zoom.

Our speaker is Ernest Alsina from Locarno, Switzerland.

Title:
Magnetic sensitivity of the H I Lyman-α scattering polarization wings in the solar disk radiation.

Abstract:
The linear polarization signals arising from scattering processes in the H I Lyman-α line in the solar disk radiation represent a valuable observable for probing the chromosphere-corona transition region (TR) and the underlying chromospheric plasma. Whereas the line-center signal encodes information on the magnetic activity and geometry of the TR, the broad large-amplitude scattering polarization signals in the wings, produced through the joint action of partial frequency redistribution and J-state interference, had generally thought to be insensitive to the influence of magnetic fields. However, our investigations show that such Q/I and U/I wing signals are in fact sensitive to the presence of chromospheric magnetic fields with a significant longitudinal component. This sensitivity arises from the magneto-optical (MO) effects that introduce a coupling between the transfer equations for Stokes Q and U and it becomes appreciable for field strengths similar to those for which the Hanle effect operates in the line core (approximately between 5 and 100 gauss), being well below those required for sizable signals to be produced through the familiar Zeeman effect.

In this talk, we begin by giving a primer on the main physical mechanisms that give rise to polarization phenomena in this line. We then show the results of a series of numerical radiative transfer calculations, highlighting the sensitivity to MO effects both in its wing and frequency-integrated linear polarization signals. The theoretical results presented here further enhance the diagnostic interest of the unprecedented spectropolarimetric and broadband observations obtained by the Chromospheric Lyman-Alpha Spectropolarimeter (CLASP) sounding rocket mission.

https://www.albanova.se/event/astronomy-seminar-via-zoom-ernest-alsina/

We will have the colloquium using zoom. You will find the invitation at the end of this email.

Some guidelines:

1) Join the session with your microphone muted.

2) When you have a question, press the “raise hand button” and wait till you are asked to ask your question.

3) The session will be online from 10:20, please join at least a few minutes early as we would like to start 10:30 sharp.

We hope to see all of you there!

Arjan & Janet

Upcoming events:
9/10: Enric Palle (IAC, Spain)
16/10: Charlotte Angus (DARK, Denmark)
23/10: Anders Jerkstrand (SU)
30/10: Höstlov

=========================================
Janet Ting-Wan Chen is inviting you to a scheduled Zoom meeting.

Topic: Astronomy seminar of Ernest Alsina
Time: Oct 2, 2020 10:20 AM Stockholm

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