This week we look at the light curve of the variable star V1787Ori. It is situated South of the Orion Nebula in the HOYS target field called L1641N. This is a dark cloud that contains many very young forming stars. The star is known as a Herbig AeBe star. This means it is a slightly more massive star of spectral type A or B that shows emission lines in its spectrum. These are usually caused by the accretion process of material onto those stars. The optical image of the star shows that it is surrounded by a faint, red emission nebula. Furthermore, there are two faint red stars within 10 arcsec of it. Based on the parallax, all three of them could form a multiple system. However, the star furthest away has a very different proper motion, so in all likelihood is just close to the object by chance.
In the light curve above we sow the V, R, and I-band data. Note the values are shifted slightly to make all details visible better. We can see that the star undergoes longer term, slow, changes, i.e. increase and decrease in brightness. These can be at times interrupted by very fast jumps. For example the 0.2mag drop roughly in the middle of the data shown, happened over just three days. It is most likely that these changes are caused by mass accretion rate variations. During the phases of slow and steady changes, what seems to be noise in the data is actually corelated in all filters. Hence, these are real variations of the order of less than a few percent. These again, can either be caused by rapid, small changes in the accretion rate or small line of sight extinction changes.
You might wonder why the V-data stops before the R and I-band data. The data is there and we have just not yet managed to process all the images into the database. Thus if you query the light curve yourself, more of the V-data should appear as we are working our way through the processing. Again: If you are interested in helping us with the image processing and data quality control, please get in touch and we will provide details and training. Thank you!