You will be shocked to hear I found a bit of time (lunchbreak) this week, so we can follow up last weeks post and look at the period of the young star V1174Ori.
Last week we saw in the light curve of the object that there were short dimming events every 29 days in our data. However, the literature seems to suggest a period of 2.635d. In the above four plots we show the periodograms (top left), light curves (top right), and phase folded light curve (bottom) for the four filters (B, V, R, I) for which we have data – we only include the last 4yr.
It turns out that the ‘best’ period seems to be indeed 2.6346059d (or 2d 15h 13m 50s). If one uses this period the eclipses (primary and secondary) do line up very nicely. The duration of the primary eclipse is only 0.04 of the period, i.e. about 2.5hr. This is hence the reason we only see the eclipse every 29 days if we observe at the same time each day, as the eclipses will be out of synch with the observations for 11 cycles. It turns out the the period fits 11.007 times into 29d. Thus, if one observes at exactly the same time each day, and catches an eclipse, one keeps seeing the eclipse 0.04/0.007 = 6 times before they again all get out of alignment with the observing cadence.
Can we learn more from the light curve? Yes we can. The primary (deep) and secondary (shallow) eclipses happen exactly half a period apart. Thus, the orbit of the binary is circular. This is to be expected for such a close orbit due to tidal circularisation, but it is always good to check. Furthermore, we can see that the depth of the eclipses changes a lot with the filter. In the Blue the eclipses are one mag deep, in the Visual 0.9mag, in the Red 0.7mag and in the Infrared 0.6mag. Thus, the shorter the wavelengths, the deeper the primary eclipse. The opposite is the case for the secondary eclipse. It is about 0.2mag deep in the Infrared, about 0.15mag in the Red, about 0.05-0.10 in the Visual, and barely noticeable in the Blue. Thus, the two components of the binary do have very different temperatures. During the primary eclipse the colder object occults the hotter object, and during the secondary eclipse the hotter object blocks light from the colder object. With a bit of effort one can hence try to fit the two temperatures and radii of the system to model the light curve. This again needs a bit of time – more than a lunch break, so don’t expect this for next week’s post 😉