systemic

With HAT-P-13c rapidly coming ’round the mountain, there was a very timely update on astro-ph last night. Josh Winn and his collaborators have obtained an additional slew of radial velocities which (1) demonstrate using the Rossiter-McLaughlin effect that the inner planet b’s orbit is likely well aligned with the stellar equator, (2) modify the orbital parameters, including the period of the outer massive planet, and (3) hint at a third body further out in the system.

How do these updates affect the unfolding story?

The Rossiter-McLaughlin measurement gives an estimate of the angle λ = -0.9°±8.5°, which is the angular difference between the sky-projected orbital angular momentum vector and sky-projected stellar spin vector. A non-intuitive mouthful. If we’re viewing the star edge-on, then λ = -0.9° amounts to a determination that the planet’s orbital plane is well-aligned with the star’s equator. (See this post for a discussion of what can happen if the star’s rotation axis is tipped toward the Earth). The good news from the measurement is that it’s a-priori more likely that planets b and c are coplanar — that happy state of affairs which will permit direct measurements of planet b’s interior structure and tidal quality factor. If, on the other hand, the planets b and c have a large mutual inclination, then b’s node will precess, and measurement of a small value for λ will occur only at special, relatively infrequent, times during the secular cycle. A close to co-planar configuration also increases the likelihood that the outer planet can be observed in transit.

With their beefed-up data set of out-of-transit Doppler velocities, Winn and his collaborators are able to get a better characterization of the planetary orbits. The best-fit orbital period and eccentricity of the outer planet are slightly modified when the new data are included. The best-guess center of the transit window for c has “slipped” to April 28, 2010, with a current 1-σ uncertainty of 2 days.

The later date, however, is not an excuse for procrastination! Measuring the TTV for this system is a giant opportunity for the whole ground-based photometric community, and a definitive result will require lots of good measurements of lots of transits starting now (or better yet, last month.) I’ll weigh in in detail on this point, along with the challenge posed by Mr. D very shortly…

It’s 4pm Wednesday Jan 13th here in Santa Cruz, and the HD 80606b transit has been underway for a few hours. A whole slew of observers worldwide are watching the event, with Northern Europe getting the best view (if the weather is clear).

Last weekend, the Spitzer telescope carried out an 84-hour observation of the system during the window surrounding the secondary eclipse. Our goal was to watch the planet heat up and then cool down rapidly as the unheated night side rotates into view.

Good luck to everyone who’s out there on the sky!

As the decade draws to a close, it’s hard not to be amazed at the progress that’s been made on every research front related to extrasolar planets.

An area that I think is now ripe for progress comprises coordinated multi-observer checks for transits by super-Earth/sub-Neptune planets. There are now over thirty known extrasolar planets with Msin(i)’s less than that of Gliese 436b (which tips the scales at 23 Earth masses). Of these, only CoRoT-7b has so far been observed to transit, and it’s very probable that the current catalog of low-mass RV-detected planets contains one or more transiting members. Needless to say, it’d be very interesting to locate them.

To my knowledge, the lowest-amplitude transits that have been observed by amateur astronomers have been those by HD 149026b. This anomalously dense Saturn-mass planet induces a photometric transit depth of roughly 0.4%.  State-of-the-art amateur detections show the transit very clearly. Here’s an example (the observer was Luboš Brát of the Czech Republic) taken from the TRESCA database:

The identification of transits by small planets certainly won’t be a picnic. Super-Earths and  sub-Neptunes orbiting G and K stars present targets that are intrinsically much tougher than HD 149026. Unless the parent star is a red dwarf, the expected transit depths will generally be less than 0.1%, and it’ll be extremely difficult for a single small-telescope observer to obtain a definitive result.

On the other hand, if a platoon of experienced observers mount a coordinated campaign on a single star, then there’s a possibility that a startlingly good composite light curve might be obtained. In theory, if one were to combine the results from sixteen independent observers, one could obtain a light curve of the equal signal-to-noise as the HD 149026b curve shown above, but for a planet with a transit depth of only 0.1%.

I spent time this weekend making sure that the transitsearch.org transit predictions for the known RV-detected low-mass planets are as up-to-date and accurate as possible. I found that HD 7924 is a good candidate star with which to test a coordinated observing strategy. The star harbors a low-mass RV-detected planet was announced earlier this year (discovery paper here):

HD 7924b has Msin(i)~10 Earth Masses, a P=5.3978d orbital period, and a 6.7% a-priori chance of being observable in transit. The (folded) photometry in the discovery paper is of quite high quality, and shows that the star is not photometrically variable. The photometry also indicates that transits with depth greater than 0.05% are probably not occurring. The parent star, HD 7924 is a K-dwarf, with a radius of something like 78% that of the Sun, which means that if the planet is a sub-Neptune it’ll have a central transit depth of order 0.075%, whereas if it is a rocky object, the depth will likely be less than 0.05%. The 1-sigma uncertainty on the time of the transit midpoint is about 0.35 days. The parent star has V=7.2, and with Dec=+76 deg, it’s circumpolar for high-latitude observers (RA=01h 21m).

Here are the next predicted transit midpoints (dates and times are UT):

HJD        Y    M  D  H  M
2455182.04 2009 12 16 12 51
2455187.01 2009 12 21 12 14
2455192.41 2009 12 26 21 48
2455197.81 2010  1  1  7 21
2455203.20 2010  1  6 16 54
2455208.60 2010  1 12  2 28

Because HD 7924b’s period is known to an accuracy of 0.0013 days (2 minutes), participating Northern-hemisphere observers can obtain data during any of the upcoming opportunities. Their light curves, once standardized, can in theory be stacked to obtain increased precision. It would be very interesting to get a sense of the practical limits inherent in such an approach. I think the best way to test the limits is to give the observations a try!

A quick addendum to the previous post. After a rather lengthy and undeserved “vacation”, Transitsearch.org is back on the air. The old website is running as a placeholder, and updated content will follow on soon.

I’ve moved the front-end of the transitsearch site to the hosting service that runs oklo.org, so the real URL is www.oklo.org/transitsearch/ By Dec. 10th, the domain name transfer will be complete, and the old www.transitsearch.org address should properly redirect.

Further updates can be had by subscribing to Transitsearch.org’s twitter stream: http://twitter.com/Transitsearch. We’re planning events to surround the next ’606 day, and we’re also planning to organize a campaign for the HAT-P-13c transit opportunity that’s centered on April 12, 2010.

Grant-proposal season puts a crimp on one’s style. Despite many interesting developments in the field over the past few weeks, I haven’t had time to write. I’m glad that’ll change shortly.

We’re also very close to getting upgraded versions of the systemic backend and a new Transitsearch-related project on line. In the interim, here’s a link to the old transitsearch.org candidates page. I have it running on our server here at UCO/Lick, and it’s updated every 10 minutes. This information should also soon be available at JPL’s NStED site.

Full-resolution Poster-sized .pdf of the above.

The next HD 80606 transit is coming up this week. While the sky position of the star will be much more favorable during the coming January event, observers across the US have an opportunity to get photometric measurements of the ingress early Thursday morning.

The transit begins just after 11 AM UT on Sept. 24, and will unfold over the next 12 hours, meaning that observers in Japan and East Asia will be able to catch the egress.

Josh Winn of MIT is organizing a repeat of the successful June campaign (detailed in this post). If you’re a capable photometric observer, and if you’re interested in participating in the campaign, definitely get in touch with him.

An unsung advantage of long-period transiting planets is that the occultations occur on a civilized timescale. An interval of 111.4357 days is long enough not to feel pressured, rushed, or in constant danger of getting scooped. This is in stark contrast, to, say, managing your affairs with a fixed 2.2185733 day turn-around time.

Earlier this summer, there were two papers, one by Pont et al. and one by Gillon which presented complete, leisurely analyses that combine all of the available photometric and RV data for the HD 80606 system taken through the Valentine’s Day 2009 transit. These papers adopted a fully Bayesian approach to analyzing the heterogeneous data sets, and were able to improve the system’s vital stats: The planet has a radius very similar to Jupiter. The full duration of the transit is close to 12 hours (and uncertain to a bit more than an hour). With high confidence, the planet’s orbit is badly misaligned with the stellar equator — just as expected from the Kozai migration hypothesis.

Last night, Josh Winn sent me a new preprint that reports results from an extensive campaign that he spearheaded to observe the June 4th/5th 2009 transit. June, to put it mildly, is not exactly an ideal time to observe HD 80606 from Earth. The nights in the Northern Hemisphere are short, and the star sets early. At any given spot, you can get at best a few hours of uninterrupted data. Nevertheless, it was of great interest to bag the transit. The ingress was weathered out during the February event, and so the analyses of Pont et al. and Gillon had to lean rather heavily on the Good Reverend Bayes.

Josh’s strategy was to recruit an East-to-West swath of observers in Massachusetts, New Jersey, Florida, Indiana, Texas, Arizona, California, and Hawaii. The idea was that 168 electoral votes would be enough to tilt the contest in favor of the good guys.

The multi-state strategy paid off. By stringing together the individual photometric blocks, the first half of the transit was nicely resolved. At the finish line, on the summit of Mauna Kea, the Keck telescope stepped up to the podium to obtain a series of mid-transit spectroscopic measurements that further confirmed the severe spin-orbit misalignment.

.ppt-ready higher resolution version

This is just the sort of project that underscores the great value of ad-hoc collaborations. The Florida ingress observations, for example, were made using the University of Florida’s recently refurbished Rosemary Hill Observatory, 30 miles from Gainesville. The DeKalb observations, made by Indiana amateur Donn Starkey, produced reduced data that were among the best in the entire aggregate. Mount Laguna Observatory, run by San Diego State University, has generated many cutting-edge exoplanet observations, including critical photometry in the Fall 2007 HD 17156b campaign. The University of Hawaii 2.2m telescope turned out photometry with astonishing rms=0.00031 precision. And as the cherry on top, the simultaneous commandeering of not one but two major telescopes on Mauna Kea? It seems that perhaps someone has made a Faustian bargain.

Without regard to order of likelihood, I thought it’d be interesting to lay out a few very specific scenarios by which the first extrasolar world with a 1 million+ habitability valuation could be discovered.

A favorite space-art trope is the habitable moon orbiting the giant planet (which is generally well-endowed with an impressive ring system). Smoggy frigid Titan is the best our solar system can do along these lines, but there’s nothing preventing better opportunities for habitability lying further afield.

I’ve always been intrigued by the fact that the regular satellite systems of the solar system giants each contain of order 2 parts in 10,000 of the mass of the parent planet. At present, there’s no reason to expect that this scaling is any different for extrasolar planets, and given the example of Titan, there doesn’t seem to be anything to prevent the bulk of a given planet’s satellite mass from being tied up in a single large body. Furthermore, since it’s my weblog, I’ll take the liberty of assuming that the satellite mass fraction scales with stellar metallicity.

Image source.

It’s perfectly reasonable to imagine, then, that HD 28185b is accompanied by a 0.63 M_earth, 0.86 R_earth satellite with an orbital radius of a million kilometers. HD 28185b itself has Msin(i)=5.7 Mjup, and the metallicity of HD 28185 is [Fe/H]=+0.24.

Now, for a long shot: let’s assume that on July 11th, 2009, a cadre of small telescope observers in Australia, South Africa and South America discover that HD 28185b transits its parent star. The geometric a-priori odds of the transit are ~0.5%. The expected transit depth is an eminently detectable 1%. A transit of moderate impact parameter lasts about 12 hours.

If a detection is made on July 11th, 2009, it’s a sure thing that the following transit (July 29th, 2010) will be the subject of great scrutiny. The current ground-based state of the art using orthogonal transfer arrays is demonstrating 0.4 mmag photometry with 80 second cadence. At this level, with spot filters and several observatory-class telescopes participating, the piggyback detection of the satellite transit is a many-sigma detection.The cake would be iced on Aug 16th, 2011, when the ~25 second difference in midpoint-to-midpoint intervals would be detected. We’d then be in possession of a potentially habitable terrestrial world warmed by an admirably bright and nearby parent star. Accurate mass and radius determinations would be fully forthcoming. All from the ground, and all at a total cost measured in thousands of dollars of amortized telescope time on existing facilities.

Admittedly, the odds of this specific scenario are slim. I estimate one in two thousand. The payoff, however, is massive. HD 28185bb (with the properties given above) is worth a staggering 100 million dollars. In expectation, then, that’s 50,000 dollars for fully covering the transit window this July…

The visible universe contains of order 30,000,000,000,000,000,000,000 planets, and so this web log’s rather single-minded focus on HD 80606b (a staggering eight out of the nine most recent posts) is likely starting to wear a little thin, even for the Kid606 fan base. One more post, though, and then I’ll move along.

First, I was jazzed to get an e-mail from Mauro Barbieri (of 17156, etc. fame) reporting that two Italian amateur observers (Alessandro Marchini from Siena, Tuscany, and Giorgio Corfini, from Lucca, Tuscany) got discovery photometry of the HD 80606b transit on Feb. 13th/14th. Their light curves are of quite high quality, and, like all the European observations show the leisurely egress from transit:

Excellent work!

A few long-time readers may recall that in the transit fever post from several years ago, I tried on a “tough guy” persona with regards to partial transits:

The transit detection problem is tough in part because it’s extraordinarily easy for systematic effects to seemingly conspire to produce an apparent signal. I would not feel confident in announcing a transit until I’ve seen multiple full-transit light curves. On the other hand, though, the false alarms play an important role. They get observers out on the sky, and spur the collection of enough data to truly rule out an event.

This hard-line attitude resulted from catching numerous infections of ingressia in which a time-series seems to show a transit starting just as observations are ending:

and egressia in which a transit seems to be ending just as observations are starting:

With HD 80606b, however, it’s perfectly certain that we’re not dealing with a virulent case of egressia. The transit did occur and that it will occur in the future. This confidence stems both from the fact that there are at least seven independent photometric data sets showing the egress, and from the fact that the French-Swiss team (Moutou et al. 2009) observed the transit spectroscopically via the Rossiter-McLaughlin effect.

The Rossiter-McLaughlin effect arises when a transiting planet occults part of a rotating star. When a planet passes in front of the oncoming limb, it blocks out blue-shifted light, whereas it blocks out red-shifted light when covering the outgoing limb. The resulting distortions in the spectra are interpreted as a positive and then negative shift in the radial velocity of the star. The amplitude of this effect is thus due both to the spin velocity of the star as well as to the total flux blocked out during transit:

Moutou et al.’s detection of the Rossiter-McLaughlin effect for HD 80606b provided drop-dead confirmation of the transit, and also hinted that the planetary orbital plane is not aligned with the equator of the star (which is not surprising, given the probable history of the ’606 system). Here’s a re-working of the diagram from the Moutou et al. paper that takes the London and Arizona photometry into account (you may want to make your browser window wider):

Illustrator .ai file for above image

The Arizona and London photometry rule out transits longer than ~12 hours, which strengthens Moutou et al.’s conclusion that the system is far from having the stellar equator aligned with the orbital plane.

Earlier this week, I was having an e-mail conversation with Bruce Gary, who runs the Amateur Exoplanet Archive (a.k.a. AXA). The AXA is a repository for photometric transit data from small telescopes, and a first stop for anyone interested in the detection of planets via transit timing.

Bruce wrote:

By the way, does the Rossiter-McLaughlin effect refer to the Dean McLaughlin who speculated about Mars, and who worked at the Univ Michigan Observatory in the late 1950s & early 1960s?

A bit of ADS sleuthing reveals that the two McLaughlins are one and the same. In 1924, Richard Rossiter and Dean McLaughlin simultaneously published the first measurements of spin-orbit alignment in eclipsing binary systems. Both men were at the University of Michigan — Rossiter as an assistant professor and McLaughlin as a 23-year old graduate student. McLaughlin used the famous eclipsing binary Algol to measure the time-dependent radial velocity skew in the brighter star of the system during the partial eclipse. His paper, “Some Results from a Spectroscopic Study of the Algol System”, makes a nice read today, and has garnered 45 citations since 2000. Its single figure shows the now-familiar effect, albeit with a factor-of-a-thousand increase in the scale of the y-axis:

McLaughlin remained at the University of Michigan during a productive career that ended with his untimely death in 1965. He seemed to have had a sensibility that was quite in line with oklo.org. Consider, for instance, this abstract from 1944:

Bruce later wrote back with small-world anecdote:

As I was finishing high school my father counseled me to not choose astronomy for a profession because Dean McLaughlin’s two boys were in his Ann Arbor High School English class and their clothes gave the impression that the McLaughlins were a poor family! That influenced my decision to enter the University of Michigan’s School of Engineering, but after a year my childhood hobby won out and I switched to Literature, Science and Arts so I could major in astronomy.

Nice!

Image Source: Mearth Live.

Update 4 : Feb. 14 2009, 07:12:00 UT

The first reports are coming in. Gregor Srdoc in Croatia got a lightcurve through most of the night for HD 80606 combined with HD 80607. No sign of a transit, but the data is relatively noisy due to imperfect weather.

Veli-Pekka Hentunen reports that weather conditions in Finland were bad generally, and were specifically bad in Varkaus.

At least four sets of observations from various locations in Arizona are currently underway, including both the 40” and the 1.3m at USNO Flagstaff under the able command of Paul Shankland.

Jonathan Irwin reports that data from Mearth through 5 UT shows no sign of an egress.

Ohio State Grad Student Jason Eastman reports on his remote Demonex observations (from the comments page):

Halfway through the night…

We started observing at UT 02:30 in the V band. No sign of an egress at the ~0.005 mag level.

http://www.astronomy.ohio-state.edu/~jdeast/demonex/HD80606b.R.2009-02-14.jpg

That link will be updated with the entire night’s data in the morning.

So it’s not looking particularly good for a transit, but I’m really happy that data is coming in. We’ll have a definitive answer sometime tomorrow.

Thanks to everyone who observed. It’s really cool how a planet 190 light years away can bring observers all over the globe into a common mission.

Update 3 : Feb. 13 2009, 23:29:00 UT

We’re now closing in on the moment of inferior conjunction, which hopefully will wind up being the midpoint of a central transit. The current weather in Europe looks like it’s clear for observers in Finland and Northern Italy, so it’s now quite likely that we’ll get a definitive answer from the campaign.

No word yet on whether an ingress was observed, but Jonathan Irwin did send a nice light curve from last night’s baseline run with Mearth. He writes:

Here’s our entire night of data (about 11 hours) from one telescope, using 80607 as the comparison star. Raw and binned x12 (about 5 minutes per bin). We are getting rms scatter of about 1.6 times Poisson with this fairly quick reduction.

There is usually a slight offset when the target crosses the meridian (data point 777) due to flat-fielding error, that I have not removed in this – over the ~20 arcsec separation of the pair it’s pretty small. There is also a bit of a blip there as my guide loop recovers its lock after crossing – still needs a little tuning :)

Fingers crossed for tonight!

Update: Clear Skies in Arizona. Dave Charbonneau writes:

http://mearth.sao.arizona.edu/live/

Clear skies. You can even watch the images in real time, and see how many
MEarth scopes are on ’606…

Update 2 : Feb. 13 2009, 17:04:00 UT

It’s now the middle of the night in the Far East, and the transit window has opened. The weather in Japan looks a little spotty, but Southern China is in the clear.

Observers in Arizona reported good weather last night, but the forecast is a little iffy for tonight.

In addition, I just got an e-mail (UT 17:48) from Gregor Srdoc in Croatia, who is on the sky under quite good conditions just after nightfall…

Update 1 : Feb. 13 2009, 06:03:03 UT

There’s about a half-day left until the possible start of the ingress. On the map above, I’ve marked the locations of confirmed observers with small red dots. HD 80606b is 190 light years above the spot labeled with the orange circle.

Observers in the US are currently taking data of both HD 80606 and its binary companion, HD 80607. It’s always good to have an out-of-transit baseline photometric time series.

Dave Charbonneau checked in with a status report:

MEarth is ready. You can watch us in real time at
http://mearth.sao.arizona.edu/live/

If the roof is closed, it is cloudy.

The up-to-the-minute stop-action animations showing the disconcertingly reptilian movements of the telescopes are completely mesmerizing. Mearth (pronounced “mirth”) is located at the Fred Lawrence Whipple Observatory on Mt. Hopkins in Arizona, and spends most of its nights searching for potentially habitable terrestrial planets transiting nearby M dwarfs. The telescopes have a list of ~2000 nearby red dwarf stars. Each star is subjected to repeated visits of ~30-45 minute duration. The idea is to catch transiting planets in progress and to broadcast the information to larger telescopes that can obtain immediate real-time photometric confirmation of a discovery. (For a more detailed overview of Mearth, see Irwin, Charbonneau, Nutzmann & Falco 2008.)

Update 0 : Feb. 12 2009, 22:47:40 UT

I’ll be posting updates on the global HD 80606b transit campaign as I get them, with newer updates going to the top of this post.

A number of observers have indicated that they’ll be on the sky. Right now, it looks like telescopes are confirmed for Finland, Israel, Italy, Japan and the US. Given the vagaries of the weather, however, it would be great if we can get as much coverage as possible. As Vince Lombardi would have put it, “We’re looking at 15%, so if you can get 1%, get out there and give 110%!”

Everyone is encouraged to comment as the campaign progresses (click the number next to the post title to access the discussion page). I’ve lifted the restriction that only allows registered oklo users to comment, but all comments are now held for moderation, in order to keep the Viagra contingent off the air.