Properties of Small Dark Features Observed in the Pure Near-Infrared and Visible Continua

Abstract

High-resolution images in the visible and near-infrared (NIR) continua at around 1560 nm were obtained of solar active regions NOAA AR 10707 and AR 10486 with the Dunn Solar Telescope (DST) at the National Solar Observatory/Sacramento Peak (NSO/SP) on 2004 December 1 and 2 and 2003 October 29. The images were taken with the high-order adaptive optics (HOAO) system, and the spatial resolution was close to the diffraction limit of the 76 cm aperture DST in both wavelengths. For the 2004 December run, the NIR observations were made with a newly developed Lyot filter system, which was designed at the Center for Solar-Terrestrial Research (CSTR)/New Jersey Institute of Technology (NJIT). The filter has a bandpass of 2.5 A that allows us to observe the pure NIR continuum at the opacity minimum. Our data show that all dark features in the NIR are also dark in the visible light. There is no evidence showing the existence of so-called dark faculae, i.e., faculae that have negative contrasts in the NIR but positive contrasts in the visible. The negative peak contrasts of these small pores are about 50% in the visible and 25% in the NIR, and their dimensions are in the range of 1''-4''.