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

[Astronomy seminar announcements]

A reminder of the seminar in 20 min:

> https://stockholmuniversity.zoom.us/j/67108321819 <https://stockholmuniversity.zoom.us/j/67108321819>
Arjan and Janet


> On 28 Sep 2020, at 12:28, Janet Ting-Wan Chen <janet.chen at astro.su.se> wrote:
> 
> 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/ <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
> 
> Join Zoom Meeting
> https://stockholmuniversity.zoom.us/j/67108321819 <https://stockholmuniversity.zoom.us/j/67108321819>
> 
> Meeting ID: 671 0832 1819
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> 

-------------------------------------------
Dr. Arjan Bik
Stockholm University
AlbaNova University Center
Department of Astronomy
SE-106 91 Stockholm - Sweden
Tel: +46 (0) 85537 8549
https://www.su.se/english/profiles/abik
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