MSRAL 2013 Presentation--Part 2: Direct Imaging of Explanets

There's no longer any question that planetary systems appear to be the norm and not the exception.  But what does it take to observe them?  Can only the pros do it?  Or does an amateur have a fighting chance?

How might an amateur be able to observe an exoplanet?

To answer that question, we'll first ask:  how might an exoplanet be observed?  Let's not worry about technology just yet...assuming that we have the equipment, what techniques might allow us to "see" a distant world?  And can amateurs do them?

The most obvious answer is to take a picture of one!  After all, we're used to seeing things every day.  Much of what we know exists is because we can lay our eyes on it.  So, is it possible to take a picture of another world?  Surely planets are too small and too distant and near stars that are too bright for us to take a picture of one.  Direct imaging of an exoplanet isn't possible with even the best equipment available.  Right?

Well...

Three images of Beta Pictoris taken over 7 years time.

In 2009 the ESO's VLT imaged Beta Pictoris.  It did so in such a way so as to remove much of the star's glare.  What was left revealed a bright spot.  In 2009, a second image was taken.  Then again in 2010.  The resulting images reveal a planet in a near Saturn sized orbit.  

OK, there's more data behind the pictures.  These three images aren't enough to convince many that the bright spot is a planet.  It could be another star with a high proper motion.  And these images do nothing to show the object has or can change directions as one would expect an orbiting planet to do.  But supplementary data exists to show that the bright spot is, indeed, a planet with roughly the mass of 7-11 Jupiters.

And it was caught on film!  Well...caught on camera anyway.

And it's not the only system where exoplanets been imaged.  Hubble has imaged Fomalhaut over several years to reveal a similar bright object projected to orbit its host star.

A bright dust ring and embedded exoplanet imaged around Fomalhaut. 

Yeah, OK.  Hubble the VLT, these are some serious telescopes!  Certainly there's nothing a typical amateur can do to directly image an exoplanet...

...or is there?

Photo taken by Rolf  Wahl Olsen showing the dust disk surrounding Beta Pictoris

In 2011 Rolf Olsen took an image of Beta Pictoris.  Well, many images actually...and some of Alpha Pictoris as well.  When processed together, an image emerged that shows the dust disk surrounding Beta Pictoris.

How did he do this?  

The basis technique is to image the target star...the one with the dust disk.  Then image a comparison star.  The trick is to image a comparison star under the exact same conditions as the target star.  Color, magnitude, altitude, exposure time, etc...anything that may be different and effect the amount of captured light should be as identical to the target star as possible.  Scientific papers on the Beta Pictoris system suggest using Alpha Pictoris for its proximity and similarity.

We now have two images...one of a star that we presume has "extra" light around it reflected from a planetary disk--or even a planet!  And a second with a "normal" star without any extra sources of light around it.  Subtract the two.  In theory, the resulting image will only have the "extra" sources of light in it.  i.e.: the reflection of the dust ring or...if extremely lucky...the reflection of light off an exoplanet!

In Rolf's image, the dashed line marks the known orientation of the dust disk.  The bright "wings" off the star in the image align pretty darn well with the expected orientation!  When you sit back and think about it, this is a phenomenal piece of work!  Even f you don't want to spend the time to think about it, this is a phenomenal piece of work!  Just trust me on that :)

Sure, not exactly an exoplanet image.  And it may yet be a long time...maybe never...before we have the technology to truly image an exoplanet from our backyards.  But this is impressively close!  

Beta Pictoris doesn't spend a whole lot of time in my observable sky.  But I wonder if this can be repeated with, say, Fomalhaut???

I'm itching to try!!!

MSRAL 2013 Presentation--Part 1: My First Observer Transit

This is the first of what should be a several part blog of my presentation on exoplanet observing given to the Mid-States Regional Astronomical League convention at Mahoney State Park in Nebraska on April 18th 2013 (yikes, that sentence kinda runs on and on...)  I'll try and get to the remaining parts over the next week or two with the plan of blogging what I should have said during the presentation ;)

I'll skip the bit about the broken Kepler satellite and the just announced Transiting Exoplanet Survey Satellite (TESS)...lots of better information on those missions elsewhere on the net!  Instead I'll jump straight ahead to the video challenge...

Can you spot the exoplanet in this data?

Believe it or not, there is at least one exoplanet in that video!  Good luck finding it!

Some things to note while watching the video:

1)  The frames were take on an Alt/Az mount!

2)  While in most frames the star images are reasonable (though maybe not pretty picture quality!) there are plenty of frames in there where the tracking was less than perfect.

3)  It's fun to look for the cosmic ray hits in the frames early in the video.  It is fun.  Try it.  It's easier early in the video when the background is dark.  OK, stop trying now...this video isn't high enough quality to see them, but they're there.

4)  The hot pixels are a little disconcerting the way they never move while the stars do.  Again, easier to note earlier in the video.  Again, the video isn't high enough quality to really see them...sigh.

5)  The background increases quite substantially over the course of the video.

6)  There is significant vignetting.

7)  There are dust donuts.  These are easier to see later in the video as the background raises.

8)  See what else you can notice.  Comment about it so others can notice it too!

Noticing these sorts of things is one reason why I'm so interested in exoplanet observing.  Other than general curiosity, I'm not particularly interested in exoplanets.  I mean I'd like to know more about them, but not so much that I feel I need to study them in depth.  So why observe them?  Partly the challenge, but mostly the noticing.  I enjoy tinkering with software/hardware and seeing what I can learn about them.  A long series of short exposures can tell you quite a bit about your equipment and technique!

But back to the exoplanet!  To help you out, here's a finder image with the parent star indicated.

XO-2b finder image

The movie frames are mostly upside down (though often sideways as well!) from the finder frame if that helps.  The specific exoplanet we're looking for is XO-2b.  This data happens to be the first full transit I was able to measure and I'm pretty proud of it :)

But you still can't see the exoplanet can you?  How about now?

XO-2b transit lightcurve

OK, what happened there?  That's not an image!  Well, no, it's not.  But it is an observation and it is an exoplanet.  Scientific observing tends to be much different than optical observing.  A friend of mine who knows I'm into astronomy once sent me a link to an article about the first direct observation of a black hole.  The article had a nice "artist's rendition" of a black piece of sky with a star being stretched and swirled tightly around it.  My friend thought this was a real image, that scientists had managed to take a picture of a real live black hole!  Reading the article, it was hard not to draw that conclusion!  The reality is way more abstract.  In this case the "direct observation" of a black hole amounted to plots not too different from the one of XO-2b above.  I believe the plots were light curves of x-rays emitted by some cloud of matter as it swirled faster and faster until it crossed the event horizon.  I was never able to chase down the raw data that "showed" the black hole.

But scientists are very comfortable with their plots and graphs.  There is much more to see in the charts and graphs than one can hope to observe with eyes alone.  In this case, we have a plot that allows us to "see" an exoplanet!

The plot itself is a plot of amplitude (y-axis) vs time (x-axis).  In a future part to this MSRAL blog, I'll detail exactly how the computations are performed.  For now, it's enough to know that the plot is of amplitude vs time.  Each point represents data from a single frame with the entire plot spanning several hours of data (and I was awake for all of them on this particular occasion--thankfully this would prove *not* to be the normal case!)

The line represents a best fit of the data to a model predicting the XO-2b transit.  The data looks a mess with barely a dip discernible, but the line has a nice dip exactly where it should were XO-2b transiting its host star during the observed time period!

At this point, you may be asking yourself: why are there two plots?  Again, more detail on that later, but basically the top plot is the "raw" data and the bottom plot has "systematic errors" removed.  In this case, the "systematic errors" were virtually nonexistent and had little impact on the raw data.  They didn't.  Really.  For now, trust me on that.  Really. :)

And that's it!  With data take with an 11" SCT on an alt/az mount repositioned several times during the evening with increasing light pollution (the increasing background was light pollution from several sources) I was able to observe the transit of XO-2b.  

Luck?

Not really.  Sure, we've only had convincing evidence of exoplanets for a few decades now--hardly any time at all.  But like so many things in science, once you know what you're looking for, it becomes easier to find it!  You can go to Exoplanet Transit Database to see all the transits I've reported thus far.  I still have about a dozen or so unreported transits sitting on my hard drive, but more on that latter!

Is this the easiest, best way to observe exoplanets?  Not by a long shot!  But it worked.  This was just the beginning of a journey.  Well, actually, the beginning was the 3-4 utter failures attempted before this one!  But we'll call this the beginning...for now...And I have improved over time as can be seen by comparing these two light curves of Hat-P-12b.

My 4th ever full transit: Hat-P-12b

My 29th ever full transit: Hat-P-12b

The dip in the plot indicating an exoplanet transiting in front of it's host star is significantly more pronounced in my later attempt at this target.  It's hard to tell from these plots but the main reason for this is increased data quality due to a more refined technique.

The journey continued...with a brief hiatus as we moved from Illinois to Missouri...and continues still.  The goal?  Well, there are several goals.  Selfishly, I'm after continued improvement.  I'd like to perfect the craft and learn whatever I can along the way.  Less selfishly, I'd like to pass this knowledge on.  It's nice to learn from one's own mistakes, but a truly clever person learns from the mistakes of others!  I've made more than my share of mistakes...how many clever people are there out there to learn from them?