With the summer targets now all visible for all of the night, we have a look at a star in the IC5146 (Cocoon Nebula) field. This is also the field that the participants in our HOYS-LCO project have been observing for most of the last year. This project is ending on July 31st, and we have now stopped accepting new participants. We hope that everyone who participated had an enjoyable experience and continues to engage with our project.

The object we look at is a semi regular variable star. These are typically giant stars in the background to our fields of foreground star forming regions. Indeed, according to Gaia, the star has a distance of about 5360pc. We are now in the sixth observing season for this field and one can see the name giving semi regular variations in brightness. The amplitude changes with wavelength with about 1.5mag variations in the I-Band to 3mag variability in the Visual filter.

The ASAS-SN survey finds an approximate period of the object of about 260days. This is also evident in our light curve. The shape of the variations do however change slightly with each period. Also evident are the seasonal gaps (winter) where the object gets too low in the sky – too close to the Sun – to be observable. With a lot of dedication (just before sunrise observing in the spring) and telescopes very far North, these gaps can be minimised.