SOTSP: HOP321 (umbral dots) w/GREGOR
2016-08-28T08:05:00 to 2016-08-28T09:05:00
Science Goal: Observational Exploration of the Height Variation of Magnetic Fields and Chromospheric Dynamics In and Above Umbral Dots
Program: Fast map, 164x164", 1-side, Q65, no repeat
Target: Active Region
xcen=-75 ycen=33
Instrument: SOTSP
HOP/JOP: 321
Description:
Main Objectives: We wish to explore the height dependence of the mangnetic field vector in the deep photosphere of umbral dots, and to search for any chromospheric response to the umbral dot phenomenon. Scientific Justification: In order to better understand their convective origin and the role that umbral dots play in the subsurface structure of the sunspot magnetic field and the overall energy balance of umbrae, it is important to have a firm observational description of the magnetic field strength and geometry within and surrounding them. Hinode has been used to explore the structure of umbral dots (Sobotka and Jurcak 2010), with the conclusion that little reduction in the field strength and no change in inclination is seen in measurements using the 630 nm lines of Fe I. This observational result in the 630 nm lines from Hinode was foreseen by Degenhardt and Lites (1993), who constructed a theoretical model of a field-free inclusion (and umbral "flux tube") within a surrounding strong vertical field. Degenhardt and Lites synthesized not only the 630 nm Fe I lines, but also the 1565 nm Fe I lines. Unlike the visible lines, the synthesized near-infrared 1565 nm lines showed considerable reduction in field strength because they form at somewhat lower layers than their visible counterparts. In view of these theoretical results, we propose to make simultaneous observations of umbral dots in the Fe I lines at 630 nm and 1565 nm, the latter being observed from the ground with the Grating Infrared Spectrograph (GRIS) at the new 1.5 m GREGOR telescope at Tenerife. The aim is to explore the observed variation of the umbral dot magnetic field vector when observed at the heights where these two diagnostic lines form. It should be noted that field diagnostics are very robust because of the large magnetic splitting present in umbrae, and the GREGOR/GRIS combination has proven observational capability for ~0.4 arcsecond resolution at 1.56 microns.
