A STUDY OF MAGNETIC BRIGHT POINTS IN THE Na i D1 LINE

High-cadence, multiwavelength, optical observations of solar magnetic bright points (MBPs), captured at the disk center using the ROSA and IBIS imaging systems on the Dunn Solar Telescope, are presented. MBPs manifesting in the Na i D1 core are found to preferentially exist in regions containing strong downflows, in addition to cospatial underlying photospheric magnetic field concentrations. Downdrafts within Na i D1 bright points exhibit speeds of up to 7 km s−1, with preferred structural symmetry in intensity, magnetic field, and velocity profiles about the bright point center. Excess intensities associated with G-band and Ca ii K observations of MBPs reveal a power-law trend when plotted as a function of the magnetic flux density. However, Na i D1 observations of the same magnetic features indicate an intensity plateau at weak magnetic field strengths below ≈150 G, suggesting the presence of a two-component heating process: one which is primarily acoustic and the other predominantly magnetic. We suggest that this finding is related to the physical expansion of magnetic flux tubes, with weak field strengths (≈50 G) expanding by ∼76%, compared to a ∼44% expansion when higher field strengths (≈150 G) are present. These observations provide the first experimental evidence of rapid downdrafts in Na i D1 MBPs and reveal the nature of a previously unresolved intensity plateau associated with these structures.