Spectro-photometry of 1A 0535+262

The H{alpha} line profiles show single-peaked profiles in most cases. This is consistent with the previously reported orbital inclination of i=37{deg}+/-2{deg}. Unlike the H{alpha} lines, the HeI {lambda}6678 lines show a maximal intensity in October 2020, which is one month before the giant X-ray outburst in 2020.

Based on the behavior of the equivalent widths of the H{alpha} and HeI {lambda}6678 lines, and the V-band magnitude, we find two mass ejection processes from the Be star to the Be disk on MJD 55820 and MJD 56600. The V/R quasi-period is about two years during 2011-2015, which is different from 1994 to 1995. Furthermore, the periods I -> II -> III -> IV in the (B-V) color index versus V-band magnitude diagram constitute a cycle.

From the behavior of the V/R ratio of H{alpha} lines, and the variability of the V band, we believe that the precession of the density perturbation inside the disk is retrograde.