This week we have a detailed look at the light curve of V505Ori. This is one of the three targets in the Sigma Ori field observed by HOYS, which we plan on following up while there are UV spectra taken of it over the next few weeks with the HST. We have briefly discussed the light curves of all the targets in this field in the Lightcurve of the Week 93 post some weeks ago. In this post we asked everyone to start following up this field as often as possible in preparation for the HST spectra.

We now have some nice data over the past few weeks, which allow a closer look at this object. We show the B, V, R, and I data of the star in the above figure. For better visibility the magnitudes in some of the filters are shifted (see legend in the plot).

We can see that the star shows variability in all filters, with amplitudes typically higher at shorter wavelengths. The variations can be in excess of two magnitudes, probably up to 3mag in B, and occur of timescales of one to two days. This makes it very obvious why this monitoring is important in preparation for the HST observations as the flux of the star can vary by a factor of 15 from one day to the next. This will of course have a large influence on the signal to noise of the spectra.

The dimming events visible in the light curve appear to occur roughly every seven days. Indeed a more detailed analysis shows that the light curve is quasi periodic with a period of 7 days and 2 hours for the entirety of the available data and in all filters. Each of the dimming events has a different depth. Hence, this might indicate that this object is an AA-Tau type source, with an inner disk warp, periodically obscuring the central star. In some cases, as e.g. at JD=2459100 the dimming even does not happen, most likely caused by the absence of material in the inner disk warp at the time of transit.