The bar pattern speed of dwarf galaxy NGC 4431

We present surface photometry and stellar kinematics of NGC 4431, a barred dwarf galaxy in the Virgo Cluster undergoing a tidal interaction with one of its neighbors, NGC 4436. We measured its bar pattern speed using the Tremaine-Weinberg method and derived the ratio of the corotation radius, D_L, to the bar semimajor axis, a_B. We found D_L/a_B=0.6^{+1.2}_{-0.4} at 99% confidence level. Albeit with large uncertainty, the probability that the bar ends close to its corotation radius (i.e., 1.0<=D_L/a_B<=1.4) is about twice as likely as that the bar is much shorter than the corotation radius (i.e., D_L/a_B>1.4).