Monday, March 17, 2008

Flare Research - Well damn...

ResearchBlogging.orgIn my attempt to determine whether or not close in planets can induce super flares on stellar type stars, one of the approaches I was taking was to attempt to determine whether or not close in planets could even perturb the stellar atmospheres. The reasoning behind this was that if they can't even do that much, then there's no real chance that they could do enough to cause these mega flares.

In looking over the titles in the most recent Astrophysical Journal, one jumped out at me: The On/Off Nature Of Star-Planet Interactions.

I figured that was worth a read. So what did I learn as I read through it? That the question I was asking had already been answered... 5 years ago.

The approach that Shkolnik et al. took was similar to one of the approaches I wanted to take, but couldn't at the present time because I'm trying to draw conclusions from publicly available data before we start writing up proposals for telescope time. The approach they took also involves the S-values I mentioned in my last post. But instead of looking at the average value in relation to how close the planet was, they took many frequently spaced measurements of these quantities for several systems with close in planets to see how they changed (something I couldn't do at the present time). They then looked for periodic changes in the chromospheric activity. If they found them, they then compared them to the period of the known planet. If they matched, then it is a good bet that the planet is inducing the activity.

The systems they targeted have very close in planets (<0.06 AU where 1 AU is the distance between the Earth and the Sun). Overall, there's less than 20 systems with this criteria, and they observed five. One didn't show any sort of significant variation, three did, but with no correlation with the planetary orbit, and one (HD 179949), matched the period of the planet.

So it looks like one of the major questions I'd been asking (whether or not stars atmospheres can be messed with due to close in planets) has already been pretty definitively answered: YES!

That's great news, because it definitely lends credence to the original hypothesis. However, we still haven't placed any sort of upper limit on how much these planets can excite these stars. Enough to cause flares two orders of magnitude bigger than anything we've ever seen on the Sun? That's the big question, and now that we know these atmospheres can definitely be perturbed, it's likely that we might be having to apply for some observation time here soon.

We've already started moving that way with some respect. Dr. Melott and I have been working on talking to planet hunter Paul Butler, to see if he can add a few of our stars to his target list since eight of the nine planets that have been seen to have these super flares have never been observed for planets. But more on how that all turns out later.

Shkolnik, E., Walker, G.A., Bohlender, D.A. (2003). Evidence for Planet-induced Chromospheric Activity on HD 179949. The Astrophysical Journal, 597(2), 1092-1096. DOI: 10.1086/378583


Bart said...

Have you considered the magnetic fields of the star and planet to be a factor? I was just reading about IOs effect on Jupiter, and it rung a bell with what your looking into. The solar flares on our own sun are created by magnetic fields, so perhaps a close planet with a strong magnetic field could cause even larger flares.

Jon Voisey said...

Yes. In fact, that's the entire idea as I stated in my first post in this series.