Planet Hunters Talk

Binary with two variable star types or a single semiregular variable?

  • Ophiuchus13 by Ophiuchus13

    Hi there!

    A Dutch longtime astronomy afficionado here - invested a lot of time in the first Galaxy Zoo in the past and decided today to try my hand at the Planet Hunters project. Apart from just maybe finding a planet or two between all the gathered light curves (of course!) I decided to see if I'm able to recognize the different types of variable stars present between them (because hey, nothing wrong with getting my astronomy knowledge back up to speed, right?). With what I know about the more common, 'familiar' types of variables I think I'm not doing too bad for now - this one, however, was a tough one, and while I do have some possible ideas about what I'm seeing here I hope to get some insight from a more experienced variable star hunter 😃

    I came across the Q1-2 part of this light curve and it seems there are two periods of variablilty present - a large-amplitude, not very regular with a period of around 30 days and a very small-amplitude and rapid one. I have the idea it might mean that we're looking at a binary consisting of a semiregularly pulsating red giant and a flaring red dwarf (the peaks in brightness being very modest due to the dwarf being outshone by the giant, the flares therefore contributing a much smaller percentage to the system's total brightness). The other option I thought about was the presence of just a single red giant where the smaller component of variability is the result of instability at the stellar surface ('brighter' and 'fainter' features of the star rotating into view). Either way, I'm pretty sure a red giant is present due to the object being 3 magnitudes brighter in the K-band (or it has to be a very very nearby red dwarf with an apparent magnitude of 11).

    Feel free to break my theory apart - any alternative ideas and explanations are welcome 😉

    Posted

  • davidbundy77 by davidbundy77

    Hi, I am not an expert but I am keen to learn about variable stars too.

    I agree with your analysis that this is a red giant. The brightness difference in J-H Bands of 0.667 magnitudes also suggests a red star and the picture on Aladin Lite certainly looks red. Unfortunately the star doesn't have a SIMBAD reference to confirm its spectrum.

    I don't think the smaller dips are regular enough for a binary. The amplitudes of these dips are quite small (~0.1%), so I think these are just starspots.

    Posted