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12-μM Observations at the 1991 Eclipse

Published online by Cambridge University Press:  03 August 2017

D. E. Jennings ,
D. Deming ,
G. Mccabe ,
R. Noyes ,
G. Wiedemann  and
F. Espenak
D. E. Jennings
Affiliation:
Code 693, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A.
D. Deming
Affiliation:
Code 693, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A.
G. Mccabe
Affiliation:
Hughes/STX Corporation, Lanham, MD, U.S.A.
R. Noyes
Affiliation:
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A.
G. Wiedemann
Affiliation:
European Southern Observatory, Karl-Schwarzschildstrasse 2, D-8046 Garching bei München, Germany
F. Espenak
Affiliation:
Code 693, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, U.S.A.

Abstract

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The 11 July 1991 total solar eclipse over Mauna Kea was a unique opportunity to study the limb profile of the 12.32 μm MgI emission line. Our observations used the NASA 3-meter Infrared Telescope Facility,1 and a new Goddard large cryogenic grating spectrometer. Spectra of the line were taken in the slitless mode at second contact. The results show that the emission peaks within ~ 300 km of the 12-μm continuum limb. This agrees with recent theoretical predictions for this line as a NLTE upper photospheric emission feature. However, the increase in optical depth for this extreme limb-viewing situation means that most of the observed emission arises from above Tmin, and we find that this emission is extended to altitudes well in excess of the model predictions. The line emission can be traced to altitudes as high as 2000 km above the 12-μm continuum limb, whereas theory predicts it to remain observable no higher than 500 km above the continuum limb. The substantial limb-extension observed in this line is qualitatively consistent with limb-extensions seen by other observers in the far-IR continuum, and may be indicative of departures from gravitational hydrostatic equilibrium in the upper solar atmosphere, and/or may result from temperature and density inhomogeneities. The extended altitude of formation of this line enhances its value as a Zeeman probe of magnetic fields.

Keywords

eclipsesinfrared: starsMg ISun: atmosphere
Type
Part 2: Infrared Observations of the 1991 Total Solar Eclipse
Information
Symposium - International Astronomical Union , Volume 154: Infrared Solar Physics , 1994 , pp. 151 - 160
Copyright
Copyright © Kluwer 1994 

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