Detection of a temperature deficit in magnetic faculae at the solar photosphere

Journal Article · Thu Oct 01 04:00:00 EDT 1981 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/159297· OSTI ID:5542618

Foukal, P; Duvall, T Jr; Gillespie, B

We have used the vacuum telescope and 512 channel diode array at Kitt Peak National Observatory to perform photometric scans of the photosphere in narrow bands (..delta..lambda = 0.25 A) of exceptionally clean continuum. Simultaneous two-color rasters were obtained at each of two pairs of green and red wavelengths; lambdalambda4980.96, 6641.85 and lambdalambda5256.31, 7008.80. Through subtraction of either raster pair, we are able to easily observe faculae in monochromatic continuum across the entire solar disc. Our observations at heliocentric angles theta< or =40/sup 0/ (..mu.. = cos theta> or =0.77) indicate that the faculae have brightness contrast in the range 0.92--1.0 and contain cooler material than the photosphere at equal continuum optical depth around tau = 1. We also observe that the faculae show limb brightening of about 1.08 relative to the photosphere at ..mu..<0.7, in this clean continuum. This result confirms the prediction of a hot interior wall of the facular Wilson depression. But small-diameter magnetic flux tubes must also contain hot, optically thin gas overlying the cool base of the Wilson depression, since the network contrast observed near disc center decreases rapidly when our passbands are allowed to include weak absorption lines. We discuss the usefulness of our photometric subtraction technique to the general study of small-amplitude temperature variations at the photosphere.

• Research Organization: Atmospheric and Environmental Research, Inc.
• OSTI ID: 5542618
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 249:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics &amp; Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
FACULAE
MAGNETIC FIELDS
MAGNETIC FLUX
PHOTOMETRY
PHOTOSPHERE
SOLAR ACTIVITY
SOLAR ATMOSPHERE