This week we look at another young star called TY Ori. It is situated in the Sigma-Ori target field of HOYS. This is a fun field as it contains a large number of of variable young stars, which are part of the large Orion star formation complex.
We show about 260 days of V and I HOYS data in the light curve above. The V data is shifted down by one magnitude for ease of viewing. The star shows the ‘usual’ behaviour behaviour expected for a young star. However, it turns out that with the exception of outbursts in brightness, even in this very short part of the light curve, shows multiple ways young stars do vary.
- There a various dimming events, usually called dips. They reach as much as two magnitudes in V, and can be as short as one day. These do indicate dense compact structures in the inner disk.
- There are longer term, more smooth and low amplitude variations. These are visible as changes of the upper envelope of data points over time. Such behaviour can be caused by changes in the mass accretion rate or structures in the outer disk, moving in front of the star.
- During the first half of the data shown, the star seems very erratic with what looks like random variations by one magnitude. In the second half the star has calmed down, with the exception of the occasional dip. However, a closer look shows that the fluctuations in the first part are actually periodic roughly every six days. This either means there are surface spots (hot or cold) or stable disk structures like in AA Tau.
A much more detailed analysis is needed, in particular of the colours, to characterise this source. The data shown here, however, nicely illustrates that placing young stars into a category such as periodic, AA Tau, dipper, burster or others is not as simple as it seems. Many stars belong to more than one category and they will move in and out of them over time, sometimes even within less than an observing season. Maybe next year there will be outbursts. We will find out.