Infrared imaging of sunspots and faculae at the photospheric opacity minimum

Continuum observations at 1.63-microns using a PtSi IR CCD camera have yielded images of the deepest observable layers in an active region. When these are compared with spectroheliograms in visible continuum and in the Ca K wing, it becomes evident that faculae are seen near disk center as low-contrast, dark structures; also, the ratio of umbral intensity for small relative to large spots is substantially lower at 1.63 microns than in the red continuum. These findings suggest that, at the deepest observable layers, faculae as well as spots contain plasma which is cooler than the surrounding photosphere at equal optical depth; they can be explained straightforwardly if flux tubes of all diameters exhibit convective heat flow along their axes.