Comparison of facular contrast in the visible and near-infrared

In this paper, we compare the contrast of faculae, in visible light and in the near infrared (NIR), that were associated with active region NOAA 8518 as it crossed the solar disk, on April 19, 20, and 25, 1999. At the Big Bear Solar Observatory (BBSO), we obtained NIR continuum images at 1.6 mum with an Indium Gallium Arsenide (In Ga As) NIR digital camera. In addition, we obtained high-resolution longitudinal magnetograms and visible light filtergrams at 6103 A with the newly developed Digital Vector Magnetograph (DVMG). Our data show that the contrast of faculae has the same sign in both visible light and in the NIR. So called "dark faculae", i. e., faculae which are bright in the visible and simultaneously dark in the NIR, are not found in our study. We believe that dark faculae are simply pores which were unresolved in previous observations. We also determined a threshold for the magnetic field strength for faculae. If the strength of the magnetic field is below the threshold the magnetic elements appear as faculae. However, if the strength of the magnetic field is above the threshold the magnetic feature appears as a pore.