Solar Physics Division Meeting 2000, June 19-22
Session 11. Solar Chromosphere
Oral, Chair: R. J. Rutten, Wednesday, June 21, 2000, 8:30-10:00am, Forum

[Previous] | [Session 11] | [Next]

[11.04] Does the Sun have a Full Time COmosphere?

T.R. Ayres (U.\ Colorado [CASA])

Strong lines of the 5~\mum bands of carbon monoxide display surprisingly cool brightness temperatures at the extreme edge of the solar disk, and curious off-limb emissions protruding hundreds of kilometers into the supposedly hot chromosphere, an environment too hostile for molecules to exist. A straightforward---but controversial---proposal is that the low chromosphere is not pervasively hot at all, but instead is permeated by cool clouds, a ``COmosphere'' if you will (because the formation mechanism originally envisioned was a CO-inspired autocatalytic ``molecular cooling catastrophe'').

More recently, Carlsson & Stein have invoked a purely dynamical process to explain the existence of molecule-laden gas at high altitudes. In their view, the solar chromosphere is a spatially and temporally intermittent wave-driven phenomenon; the time average thermal structure in the classical chromospheric layers is cool, not hot. Nevertheless, Kalkofen, Ulmschneider, & Avrett have criticized several of the key assumptions of the dynamical simulation, calling into question the existence of a cool ``part time'' COmosphere. The cause of the supraphotospheric molecular gas thus remains controversial.

Here, I will describe measurements of the off-limb emissions of CO, obtained under exceptional observing conditions in May~1996 with the Infrared Imaging Spectrometer (IRIS) on the 1.5-m McMath-Pierce telescope at Kitt Peak. I will compare these data with theoretical off-limb CO simulations based on time slices from the Carlsson-Stein dynamical model. Finally, I will demonstrate through simple UV continuum formation models that there need not be any contradiction between the existence of substantial amounts of cool gas well above the classical temperature minimum, and the observation of ubiquitous ultraviolet line and continuum emission from the solar outer atmosphere.

This work was supported by NSF grant AST-9618505.

The author(s) of this abstract have provided an email address for comments about the abstract:

[Previous] | [Session 11] | [Next]