Variable brightness stars

http://legacysurvey.org/viewer?ra=179.5347&dec=-2.5541&zoom=15&layer=decals-dr5

This one poses a question or two! The bright blue star in the centre of this thumbnail image definitely varies in brightness relative to the pair to the left, which made me think it might be a supernova. But then the red star below and to the left also varies in brightness quite noticeably when you look at the individual cutouts.

Are the stars actually varying in brightness, are they being obscured by varying amounts of drifting dust in the space between us and them, is this an artefact of the variable efficiency of the detectors used or perhaps a change in the detectors mounted on the telescope?

The single image cutouts are each auto-scaled for brightness, so a constant-brightness star would not necessarily look equally bright in each image – depending on, eg, the seeing.

I really should make the single-image cutouts more visually useful!

We calibrate and correct for atmospheric extinction and detector efficiency (which changes very very slowly, like a few percent per year, as dust accumulates on the mirrors and as their reflective coatings degrade). And interstellar dust would be moving extremely slowly for the most part.

cheers,
–dustin

Hi Dustin

I realised that individual cutouts have different absolute brightness, which is why I have been taking clips into Photoshop and enhancing the tonal gradation to bring the star of interest into prominence. This is how I can see that the star of interest is varying in brightness by comparison with the neighbouring objects.

(I also noticed that the cutouts seem to be reversed compared with the image in the browser!)