Monthly Archives: September 2007

Tonight’s the Night

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Tonight, Sept. 30/Oct 1, is the night to follow-up to confirm whether HD 17156b can be observed in transit. Earlier this morning, I sent the following e-mail to the Transitsearch Observers list:

Hello Everyone,

I’d like to alert you to an important follow-up opportunity TONIGHT to observe HD 17156 for a possible transit by its companion planet. North American Observers are best situated for the event.

HD 17156 b has been the topic of several blog posts on oklo.org, see: [1], [2], [3], [4], [5].

Photometry taken by Jose Manuel Alemenara Villa on the Sept. 9/10 opportunity was suggestive of a possible transit with duration 169 minutes, a photometric depth of 0.007 magnitudes, and a mid-transit time of HJD ~ 2454353.614. These values are all quite close to what one would expect if HD 17156b is really transiting.

If the event observed by Alemenara Villa is due to a transit, then the next transit will be centered at HJD~2454374.83 (CE 2007 October 01 07:55 UT Monday) with the transit beginning at about 06:30 UT.

Observing should start as soon as possible this evening, and observers are encouraged to take photometry for as long as possible.

My fit to the published radial velocities predicts a transit midpoint centered at HJD 2454374.87 (CE 2007 Oct. 01 08:52 UT Monday), with a +/- 0.3d uncertainty in the time of central transit. The Alemenara Villa event sits nicely inside this window.

Thanks very much!
best regards,
Greg

It looks like much of the Southwest is clouded out, and although the skies outside here in Santa Cruz are currently cobalt blue, it’s predicted that clouds and even rain will materialize after midnight. SoCal, however, and many locations in the midwest and east look good to go. Here’s a selection of California predictions from the clear sky clock. This is a cool graphical tool for use in scheduling observations. Dark blue is good, white is bad.

Systemic in the Classroom

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In our development of the systemic console and the systemic backend, we’ve strived to build a professional-quality tool that can be used by the general public. There’s no better way to get a sense of them planetary discovery process than to participate yourself, and so we’d like to encourage astronomy instructors to fold the systemic console into their curricula.

This link points to a Word format document of a sample homework assignment that makes use of both the console and the systemic backend. We’ve had good success with this particular problem set at UCSC, and it’s currently being implemented at MIT as well. The level has been found to be appropriate to an astrobiology class for science majors. There’s no math prerequisite, so it can also be fully useful for a non-major survey course.

If you’re an astronomy instructor and you’d like to incorporate hands-on planet finding into your course, let me know, and we can set up a fit submission aggregator for your students on the systemic backend.

Seeing in the Dark

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This evening (Sept. 19th) the US Public Broadcasting Service is running a documentary on amateur astronomy which will include a section on extrasolar planets. The production is called Seeing in the Dark and it looks like it should be a very interesting and well done program.

Featured in the film are my friends and collaborators Ron Bissinger and Debra Fischer. Ron (whose day job is CEO of Alpha Innotech) has been a core member of Transitsearch.org from the beginning, and has consistently obtained great observations of transiting planets. Debra (an astronomy professor at SFSU) has, among her many accomplishments, discovered literally scores of extrasolar planets using the radial velocity technique. Both Ron and Debra’s work has been the focus of many past posts on this website.

So tonight, set your telescopes to acquire HD 185269, enable the robotic photometric observing mode, and sit down in front of the tube with a bowl of popcorn!

follow-up still in order…

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potomac river

In the last post, I pretty much wrote off HD 17156 b, which was the subject of last week’s transitsearch.org photometric follow-up campaign. Ron Bissinger observed the star during the latter part of the transit window, and saw no evidence of a transit. Tonny Vanmunster wrote with the news that Belgium was clouded out.

Soon after the post went up, however, Jose Manuel Almenara Villa of the Instituto de Astrofisica de Canarias posted a comment:

Hi Greg,

I observed HD17156 in the transit window. Unfortunately the night was windy, affecting the small telescope so the photometry is not so clear as we would wish. Anybody else observe?

It’s possible that I have a central transit. I can show you some plots if you want. I will try to observe again on December 3 (I think that is my next opportunity).

Regards,
Jose

On Saturday, Jose sent me his photometric plots, I should point out that he emphasized once again that the night was windy. In his plots (I’ve rewritten the labels in illustrator so that they show up better on the narrow blog-page format) the black dots are individual observations (R filter, 7 s exposures), the red dots bin 6 observations, and the blue dots bin 12 observations.

On the night before the night of the transit window, he got baseline photometry which shows considerably less scatter, and which does a nice job of showing his excellent photometric technique:

He fit a simple trapezoidal transit template to his data. The resulting fit has a duration of 169 minutes, a depth of 0.007 magnitudes, and a mid-transit time (HJD) ~ 2454353.614. These values are all quite close to what one would expect if HD 17156 b really is transiting. The possible event ends just prior to the start of Ron Bissinger’s time series.

So what to think? It’s most important to reiterate Jose’s point that the weather was not particularly good, and that a block of critical data is missing during the event itself. I myself have contracted transit fever several times in the past, and have built up sufficient immunity to refrain from getting too excited. I think a conservatively realistic assessment would say that there’s still an 11% chance that HD 17156 b transits are occurring, and that the uncertainty in the window has been narrowed down significantly. Over the long run, if transitsearch.org is going to succeed, then its important to stay cautiously optimistic. The good thing about a transit is that it repeats with clockwork regularity (barring the unlikely, but tough-luck situation where dynamically induced precession of the node induces transit seasons.) The next chance to observe HD 17156 during the transit window falls to North America on Oct. 1, where hopefully there’ll be multiple observers on the sky. We’re bad – We’re Nationwide…

To end on a heartfelt note, I think that the global collaborative efforts that go into these transitsearch campaigns have been both fun and inspiring, even when the result is the high-probability flat-line light curve. It would be exciting, though, if Jose ends up leading a discovery paper with the other participating observers as co-authors.

Results

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It’s not looking good for transits by HD 17156 b. Ron Bissinger of Pleasanton, California obtained a block of photometric data that covered a significant chunk of the transit window. His time series lasts from JD 2454353.68 through 2452353.88, and shows no hint of an event:

His observations were taken just after the peak of the transit midpoint histogram:

No word yet on whether anyone in Europe or the eastern US were able to observe during the first half of the window. If you got data, let me know.

Also, the Gliese 176 window has opened up. If you’ve got a telescope, a CCD, and a free evening, you know what to do!

Discover a planet

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My tight 30-minute layover in Denver turned into an eight-hour delay yesterday when a solenoid somewhere in our Boeing 777 malfunctioned just prior to pushback, giving me an unexpected opportunity to attempt to catch up on all the work that’s been piling up.

After 6 hours of tapping on the laptop, I’d exhausted my effectiveness, so I bought glossy magazines from the airport newstand. In the latest issue of Portfolio from Conde Nast, you can read an in-depth Vanity Fair style puff piece on ex-Tyco CFO Mark Swartz’s life in the Big House, and, in one of the advertisements, you’re encouraged to use a Visa “Signature” card to charge up some of the finer experiences in life. Quite to my surprise, #17 on a list that includes “See the Tony Awards live”, and “Test-drive a supercar”, is “Discover a planet”.

Now regular visitors to oklo.org all know that you can get your planet-discovery experience right here on the systemic backend without ever having to reach for your wallet. In fact, just yesterday, we learned from Gregory’s latest preprint on astro-ph that Eric Diaz (and a number of other systemic users) appear to have made the first characterizations of the most statistically probable planetary system fits to the HD 11964 radial velocity data set.

The HD 11964 data set was published by Butler et al. (2006). Two planets are already known to orbit this star. HD11964 b has roughly 1/3rd of a Saturn mass and a ~38-day orbit, whereas HD 11964 c is a sub-Jovian mass planet on a ~2110-day orbit. There’s a wide dynamically stable gap between the two planets, making this system a fertile hunting ground for additional companions.

Gregory does an extensive statistical analysis and argues that there’s strong evidence for a sub-Saturn mass planet on a year-long orbit. Eric Diaz’s version of this planet shows up in the fit that he submitted to systemic back in July 2007:

Eric also suggests the presence of a 12.4-day planet in the system. The Gregory analysis suggests that this planet is not statistically significant, but I’m going to add it to the transitsearch.org unpublished candidates list. There’s certainly no reason not to have a look-see if anyone has unused photometric capability.

HD 17156 at inferior conjunction (right now!)

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It’s 01:58 UT Sep. 10, and HD 17156 has moved into its transit window. Hopefully photometric transit observers across Europe have clear skies. If you’re collecting data, drop us a note on the comments page!


Sep 09, 2007 Europe Satellite Map Source.

Most of California looks pretty good for catching the latter part of the transit window once it gets dark tonight. I was up on Mt. Hamilton last night, and even though it was clear, there was a strong smell of smoke in the air. Bits of gray ash from the nearby forest fires were floating down like snow, and so they couldn’t open the dome of the 36-inch.


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The odds of a HD 17156 transit are 10.9%, so its best not to get hopes up too high. Its always good to have the next candidate ready to go, and as luck has it, there’s another good one in the hopper.

Endl et al. have published a preprint describing the discovery of a Neptune-mass planet orbiting the nearby red dwarf star Gliese 176 (aka HD 285968). This discovery is further evidence in favor of the core-accretion prediction that Neptune planets should be common around low-mass stars whereas Jovian-mass planets should be relatively rare. Endl et al.’s new planet has an orbital period of 10.24 days, an a-priori transit probability of 3%, and an expected transit depth of 0.4%. This is a low-amplitude signal, but it is nevertheless accessible to many experienced amateur astronomers. The discovery paper makes no mention of a photometric transit search, making this planet a very attractive Transitsearch.org candidate. The star is located at RA 04:43, Dec +18:57, and the next transit window is centered on Sep. 15, 2007.

fit to be timed

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One reason why extrasolar planets are so exciting is because they are accessible. You don’t need a Ph.D. or a large laboratory or a space-borne telescope to make an important discovery. There are very few areas in science where such a wide pool of workers can contribute in a fully meaningful way.

On the systemic backend, the focus is largely on planet characterization through the analysis of radial velocity data. At Transitsearch.org, the goal is to provide the information that will allow small telescope observers to discover transiting planets. Transitsearch, however, is mainly a repository for transit predictions. We maintain information about when and where to look, but we fall short when it comes to explaining how to obtain high-precision photometry. There has long been a need for a good end-to-end manual on the art and science of photometric transit detection.

Bruce Gary is an experienced observer of transiting extrasolar planets, and is a member of the XO network, which has had made several discoveries over the past year and a half (see e.g. here). Bruce has written a book, Exoplanet Observing for Amateurs which he’s made available for free in .pdf form.

Bruce has also launched the Amateur Exoplanet Archive (AXA), which is a repository for light curves obtained for known transiting planets. If you get a photometric transit time series of one of the planets, then make sure that you submit it to Bruce’s archive. With all the data in one place, everyone will have easy access for analysis projects.

Transit midpoint times can be measured from individual light curves, and a sequence of midpoint times can be used to improve the characterization of a particular planetary system. To this end, Stefano has extend the .sys file format used by the systemic console to include “transits” data files (which take a .tds suffix, and which are separate from the .vels files that the console has used all along). If you have transit data, it’s simple to implement one of these files for yourself.

To see how it works, consider the recently discovered transiting planet XO-2. The published radial velocity data for this planet is already bundled with the console. On the AXA site, a total of five transits have already been archived for XO-2. Each of these transits has a measured Heliocentric Julian Date (HJD) for the time of transit midpoint, along with an associated uncertainty. I copied these data into a newly created “X0-2.tds” file in my console’s datafiles folder:

I then added the following lines to the .sys file for the XO-2 system:

Having done that, I launched the latest (“unstable” Aug. 21, 2007 version) of the systemic console. Stefano has been steadily improving the console’s algorithms, user interface, and performance. If you’ve been working with the standard stable downloadable console, you’ll immediately notice that there’s a lot of new functionality. We’ll be getting a manual out as soon as the much-anticipated Systemic Jr write-up is completed, but in the meantime, there’s a wide variety of resources on the backend that can help you navigate the latest console features.

With the .tds file linked in, the observed transit midpoint times appear as vertical red lines in the radial velocity timeline window. If the “fit transits” option is unchecked, then the console considers only the radial velocity data. If the “fit transits” option is checked, however, then the observed transit times are included as data to be fit. The uncertainties in the transit midpoints can be very small, and so this provides a very strong constraint on the period of the orbit and the time at which the planet crosses the plane containing the line of sight to the Earth. Note that the transit fitting can be done in a fully self-consistent N-body fashion if integration is enabled.

Try it for yourself!

As more transit data is accumulated, it will become possible to do some increasingly sophisticated analyses. Transit timing is potentially a very powerful method for detecting additional, as-yet unseen perturbing bodies in a given system. Objects like Gl 436 b are especially good candidates for this type of approach, and quite a bit of photometric data is being accumulated during the Gl 436 transits.

HD 17156 b

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Last week, I wrote a post introducing HD 17156 b, a Jovian planet on a highly eccentric 21.2-day orbit around a V=8.17 solar-type star lying 250 light-years away in Cassiopeia (RA=2h 50m, Dec=72 deg).

A photometric check for transits by HD 17156 b was reported in the discovery paper, but due to the nearly three-week orbital period, it was only possible to rule out about 25% of the transit window. Given the highly favorable geometry of the planetary orbit, this means that there’s an impressive ~11% chance (8.25% if you take the discount) that the planet can be observed in transit. The expected transit depth is a very respectable 1%, and given the bright parent star, it’s a straightforward detection for small-telescope observers everywhere in the Northern Hemisphere.

What’s it worth to catch HD 17156 b in transit? From a crass cash-money standpoint, one can estimate a dollar value. Because the planet has a long period and an eccentric orbit, it would be the first transiting example of its kind, and would thus be expected to generate a fairly large number of citations. From a career standpoint, an ADS citation is worth at least $100 (see, e.g. here). Based on the citation count for the TrES-1 discovery paper (144 citations in three years) it’s reasonable to expect that at one decade out, a HD 17156 b transit would garner of order 200 citations, for a conservative total value of 20K. Given the 10% probability of the transit coming through, the resulting expectation value is equivalent to having twenty Benjamins floating down from the black velvet of the night sky.

I used the systemic console’s bootstrap utility to generate a set of orbital fits to the published radial velocities for HD 17156. Each orbital fit describes a unique sequence of central transit times. For a particular transit opportunity, the aggregate of predicted central transit times from the different fits can be plotted as a histogram. Here’s the resulting plot for the transit opportunity that’ll occur next Monday (HJD 2454353.68):

The uncertainty in the time of central transit is ~0.3 days. A window this narrow is rare for a planet that hasn’t yet been thoroughly checked. In fact, as far as Transitsearch.org opportunities are concerned, it doesn’t get much better than this. Extending our opportunity cost analysis, the expected monetary return for observations within the 1-sigma transit window is an impressive $114 per hour. (Only rarely does the expected return per hour exceed minimum wage for existing transit opportunities.)

Scientifically, a transit by HD 17156 b would certainly be very exciting. The planet should be heating up very rapidly during its periastron passage, which should spur the generation of hemispheric-scale vortices and an 8-micron light curve that’s detectable with the Spitzer telescope. Observation of the secondary eclipse (assuming it occurs) would allow for a measurement of the global planetary temperature near the orbital apastron.

The frame above is from a hydrodynamical study of HD 17156 b that Jonathan Langton has just finished computing. If all the talk of dollars, ephemerides, opportunity cost, and expectation value is leaving you stressed out, then just kick back with this fat 1.0 MB .mov of the simulation and get your groove on.