This week we have another look at an object in the Orion Nebula (M42). We look at the star T-Ori, which is situated in the outskirts of M42 and known as an Herbig Ae/Be star. Thus, it is a slightly more massive young star.

As discussed in last weeks post, we do now have almost 3000 days worth of monitoring of this region with almost daily cadence – except of course for the time where the Sun gets in the way. However, we only show a small part of the V and I-band data in the figure above. It gives a good overview on how the brightness of this star changes over time.

As in many of the examples we have already seen, there are short duration (one to a few days) dipping events that occur at semi regular intervals or randomly. Overlaid on those are longer term trends of increasing and decreasing brightness. In this case the star can vary by up to two magnitudes within a week.

The shorter term dips are clearly caused by disk material close to the star. The longer term changes are either due to larger disk structures further out in the disk, or changes to the mass accretion rate of the star. We also note that the star is unusually blue, with a V-I colour during the bright state of about -0.5mag. During the dimming events the colour turns redder, as expected from occultations by dust.