Calibration of Mt. Wilson Observatory Magnetic Fields for 1967 to 2013
Abstract
Magnetograms using FeI λ5250Å between Jan. 3, 1967 and Jan. 22, 2013 have been reduced and posted at:
ftp://howard.astro.ucla.edu/pub/obs/fits/ Prior to Dec. 12, 1981 the optical system for each wing of the spectral line used sampling based on the edge of a prism for the inner boundary and an adjustable blind on the outer boundary. Both the blue and red prism positions were adjustable but established parameter values were targets. We have no way of determining the actual values during the observations. The Babcock(1953, Ap. J. 118,387) approach which depends on a circular polarizer, and a known displacement of the spectral line was used with a target displacement established. According to studies by Tanenbaum (1970, PhD thesis, UC Berkeley) the sensitivity of the system did not depend on position on the solar surface. We are not able to verify these parameters and conclusions. For the years 1967 to 1971 there are indications that the calibrations were not done consistently. After Dec. 12, 1981 a pair of fiber-optic image reformators were used to select the portions of the spectral line and redirect the photons to the photomultipliers. A new reduction system was implemented to convert the signals into magnetic fields. This new system includes the recording of the profile of the observed line along with the determination of calibration coefficients from the profile. These coefficients are observed to depend on the center-to-limb angle and this effect is included in the magnetic field determination. We provide magnetic field values for the older data both with and without the center-to-limb angle effect.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH41B..01U
- Keywords:
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- 7511 Coronal holes;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7524 Magnetic fields;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7529 Photosphere;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY;
- 7594 Instruments and techniques;
- SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY