This week we look at the known emission line star 2MASS J07085128-1043023. It is situated at the edge of a small cloud with an embedded cluster containing Gaia19fct. We added this source field to our target list after it became apparent that Gaia19fct is an erupting young star, probably an EXOri type object (named after the prototype EX-Lup – but that is a different story).
We show the V, R, and I band data of the star in the above figure, zoomed into the last observing season. We do have data for the object now for the last three years. In the first year we also have data taken in the Halpha filter, which shows that indeed the object is an emission line star with the R-Halpha colour being roughly 0.5mag.
The light curve shows that the star is typically extremely constant. For weeks a a time it does not change its brightness within the measurement uncertainties, which are of the order of just a few percent or 0.04mag. But one can see a small increase in brightness of 0.1mag for about 20 days. This could well be caused by a small change in the mass accretion rate onto the star.
In the long term the star is also quite interesting. It keeps its general steady behaviour but the jumps in brightness. For example in the I-Band the star has a median brightness of 12.82 in year one, 12.94 in year two and 12.98 in year three. Thus, the peak in year three is as bright as the typical brightness in year one. Thus, it seems there are long term changes in the mass accretion rate. Further Halpha data would be very useful to investigate if R-Halpha changes as well.
However, the Gaia parallax places the star far in the background to the cloud and cluster with Gaia19fct, at almost 2.7kpc distance. Given this and the brightness changes being larger in the I-band than the V-band, it could also be a background Be type star. Only a spectrum will tell……