This week we have a rare look at a southern hemisphere target. The star of interest is in the field around Gaia19eyy, a regularly erupting HerbigAeBe star – but this is a story for a different week.
The object we are looking at is BS Vel. It is classified as an eruptive variable and only mentioned in two previous publications (one from 1949, one from 1999) which investigate randomly varying and flaring stars. According to Gaia the star is relatively nearby, about 180pc. The light curves we have from the object, are in part showing that there is also other variability in the object, and that this also changes – an excellent way of showing why we are doing long term monitoring.
The three parts of the light curve are all scaled in the same way, i.e. they show the same range of magnitudes and time. We have, in all cases, shifted the magnitudes a bit (the same in all plots) to ensure all the details are visible. Each plot hence shows about 45days, i.e. a month and a half. The first plot shows the behaviour roughly 125 days prior to the second plot. The third plot shows the behaviour 230 days after the second plot. So all in all we look at one year in total.
The first two parts of the light curve, clearly indicate a variability with a period of about 9 days. But already there are differences in the shape of the features. While in plot one they are saw tooth like, they look more rounded or sine-shaped in the second plot. The amplitudes are roughly 0.2mag in all filters, slightly larger at shorter wavelength. In the third plot however, all periodic signal seems to have completely disappeared. On top of that, the star has increased its average brightness by about 0.1mag in all filters.
The periodic signal could be caused by spots on the surface. The change in shape can be attributed to changes in the position and properties of the spot (or group of spots). A lack of spots after a certain time is also not a surprise, but it is not clear why the star as a whole has increased in brightness. It will be interesting to see what the star does next year.