# Amateur Network Bags a Transit

The news from Transitsearch couldn’t be better. Long a champion of amateur involvement in the exoplanet hunt, I was delighted to see, via Greg Laughlin’s systemic site, that this globally dispersed team of amateur astronomers is behind the confirmed transit observation of the planet HD 17156 b. Amateurs in Italy, the Canary Islands and California made key observations in early September, with confirmatory data coming in from Massachusetts and California on the night of September 30/October 1 as observers heeded Laughlin’s online call to participate.

Greg has the details and more about the individual observers at his site. The Transitsearch mode is to look at known planet-bearing stars during those times transits might conceivably occur. And it makes stunningly good sense because of two facts: 1) The tools available to dedicated amateurs today are fully capable of this kind of high-quality work; and 2) Telescope time at the major observatories around the world is obviously limited. The Internet allows this network of amateurs to collaborate, making serious contributions to our exoplanetary knowledge.

HD 17156 b is quite an interesting place. Its radius seems to be a bit larger than Jupiter’s, while its orbital period is 21.2 days. Note that this is almost four times longer than any other known transiting exoplanet. Note too that HD 17156 b’s orbit is highly eccentric, so much so that the planet experiences a 26-fold variation in the amount of flux it receives from its star. Interesting weather patterns doubtless emerge, as Laughlin notes, with the night side glowing with its own radiation. I poached the image below from the systemic site, but have a look at the full animation, showing Jonathan Langton’s hydrodynamical study of this world.

So there’s the method: Use Doppler radial velocity data to find exoplanets and check for transits with an ad hoc network of amateurs coordinating their work over the Internet. Can the Spitzer space telescope catch HD 17156 b in secondary transit? If so, says the discovery paper, that will enable “…a much-improved constraint on the still-uncertain radius of the parent star. In the event that secondary transits can be observed, a direct measurement of the excess tidally generated luminosity from the planet is a distinct possibility…”

The paper is Barbieri, Alonso et al., “HD 17156b: A Transiting Planet with a 21.2 Day Period and an Eccentric Orbit,” available online. Nice work!

Comments on this entry are closed.

• ljk October 8, 2007, 17:21

Precise Photometry and Spectroscopy of Transits

Authors: Joshua N. Winn

(Submitted on 4 Oct 2007)

Abstract: A planetary transit produces both a photometric signal and a spectroscopic signal. Precise observations of the transit light curve reveal the planetary radius and allow a search for timing anomalies caused by satellites or additional planets. Precise measurements of the stellar Doppler shift throughout a transit (the Rossiter-McLaughlin effect) place a lower bound on the stellar obliquity, which may be indicative of the planet’s migration history.

I review recent results of the Transit Light Curve project, and of a parallel effort to measure the Rossiter effect for many of the known transiting planets.

Comments: 8 pages, to appear in “Extreme Solar Systems,” ASP Conference Series, ed. Debra Fischer, Fred Rasio, Steve Thorsett and Alex Wolszczan

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0710.1098v1 [astro-ph]

Submission history

From: Joshua N. Winn [view email]

[v1] Thu, 4 Oct 2007 20:51:11 GMT (139kb)

http://arxiv.org/abs/0710.1098

• ljk November 6, 2007, 0:48

A search for transiting extrasolar planet candidates in the OGLE-II microlens database of the galactic plane

Authors: I. Snellen, R. van der Burg, M. de Hoon, F. Vuijsje (Leiden Observatory)

(Submitted on 4 Nov 2007)

Abstract: In the late 1990s, the Optical Gravitational Lensing Experiment (OGLE) team conducted the second phase of their long-term monitoring programme, OGLE-II, which since has been superseded by OGLE-III. All the monitoring data of this second phase, which was primarily aimed at finding microlensing events, have recently been made public. Fields in the OGLE-II survey have typically been observed with a cadence of once per night, over a period of a few months per year. We investigated whether these radically differently sampled data can also be used to search for transiting extrasolar planets, in particular in the light of future projects such as PanSTARRS and SkyMapper, which will monitor large fields, but mostly not at a cadence typical for transit studies. We selected data for ~15700 stars with 13.0 less than I less than 16.0 in three OGLE-II fields towards the galactic disc in the constellation Carina, each with 500-600 epochs of I-band photometry. These light curves were first detrended using Sys-Rem, after which they were searched for low amplitude transits using the Box Least Squares algorithm. The detrending algorithm significantly decreased the scatter in the light curves, from an average of 0.5% down to 0.2-0.3% for stars with I less than 15. Several dozens of eclipsing binaries and low amplitude transits were found, of which 13 candidates exhibit transits with such depth and duration that they are possibly caused by an object with a radius less than twice that of Jupiter. Eleven out of these thirteen candidates show significant ellipsoidal light variations and are unlikely to host a transiting extrasolar planet. However, OGLE2-TR-L9 (CAR_SC2_75679), is an excellent planet candidate comparable to the known OGLE-III transiting planets, and deserves further follow-up observations.

Comments: 8 Pages LaTeX, accepted by A&A

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0711.0500v1 [astro-ph]

Submission history

From: Ignas Snellen [view email]

[v1] Sun, 4 Nov 2007 08:20:28 GMT (645kb)

http://arxiv.org/abs/0711.0500

• ljk December 14, 2007, 12:32

Improved parameters for the transiting planet HD 17156b: a high-density giant planet with a very eccentric orbit

Authors: M. Gillon (1, 2), A. H. M. J. Triaud (1), M. Mayor (1), D. Queloz (1), S. Udry (1), P. North (3) ((1) Observatoire de Geneve, Sauverny, Switzerland; (2) Institut d’Astrophysique et de Geophysique, Universite de Liege, Liege, Belgium; (3) Laboratoire d’Astrophysique, Ecole Polytechnique Federale de Lausanne (EPFL), Observatoire de Sauverny, Versoix, Switzerland)

(Submitted on 13 Dec 2007)

Abstract: We report here high-precision transit photometry for the recently detected planet HD 17156b. Using these new data with previously published transit photometry and radial velocity measurements, we perform a combined analysis based on a Markov Chain Monte Carlo approach. The resulting mass M_p = 3.111 (+0.035-0.013) M_Jup and radius R_p = 0.964 (+0.016-0.027) R_Jup for the planet places it at the outer edge of the density distribution of known transiting planets with a density = 3.47 (+0.35-0.18) Jupiter’s one. The obtained transit ephemeris is T_tr = 2454438.4835 (+0.0009-0.0025) + N 21.21725 (+0.00048-0.00043) BJD. The derived plausible tidal circularization time scales for HD 17156b are larger than the age of the host star. The measured high orbital eccentricity e = 0.6717 (+0.0028-0.0027) can thus not be interpreted as the clear sign of the presence of another body in the system.

Comments: 6 pages, 3 figures, 1 table

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.2073v1 [astro-ph]

Submission history

From: Michael Gillon [view email]

[v1] Thu, 13 Dec 2007 00:52:48 GMT (45kb)

http://arxiv.org/abs/0712.2073

• ljk December 18, 2007, 10:52

A Possible Spin-Orbit Misalignment in the Transiting Eccentric Planet HD 17156b

Authors: Norio Narita, Bun’ei Sato, Osamu Ohshima, Joshua N. Winn

(Submitted on 16 Dec 2007)

Abstract: We present simultaneous photometric and spectroscopic observations of HD 17156b spanning a transit on UT 2007 November 12. This system is of special interest because of its 21-day period (unusually long for a transiting planet) and its high orbital eccentricity of 0.67. By modeling the Rossiter-McLaughlin effect, we find the angle between the sky projections of the orbital axis and the stellar rotation axis to be $62^{\circ} \pm 25^{\circ}$. Such a large spin-orbit misalignment, as well as the large eccentricity, could be explained as the relic of a previous gravitational interaction with other planets or with a binary companion star.

Comments: 12 pages, 2 figures, 3 tables. Submitted to PASJ Letters

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0712.2569v1 [astro-ph]

Submission history

From: Norio Narita [view email]

[v1] Sun, 16 Dec 2007 12:28:23 GMT (83kb)

http://arxiv.org/abs/0712.2569

• ljk January 10, 2008, 15:33

Parameters and Predictions for the Long-Period Transiting Planet HD 17156b

Authors: Jonathan Irwin, David Charbonneau, Philip Nutzman, William F. Welsh, Abhijith Rajan, Marton Hidas, Timothy M. Brown, Timothy A. Lister, Donald Davies, Gregory Laughlin, Jonathan Langton

(Submitted on 9 Jan 2008)

Abstract: We report high-cadence time-series photometry of the recently-discovered transiting exoplanet system HD 17156, spanning the time of transit on UT 2007 October 1, from three separate observatories. We present a joint analysis of our photometry, previously published radial velocity measurements, and times of transit center for 3 additional events. Adopting the spectroscopically-determined values and uncertainties for the stellar mass and radius, we estimate a planet radius of Rp = 1.01 +/- 0.09 RJup and an inclination of i = 86.5 +1.1 -0.7 degrees. We find a time of transit center of Tc = 2454374.8338 +/- 0.0020 HJD and an orbital period of P = 21.21691 +/- 0.00071 days, and note that the 4 transits reported to date show no sign of timing variations that would indicate the presence of a third body in the system. Our results do not preclude the existence of a secondary eclipse, but imply there is only a 9.2% chance for this to be present, and an even lower probability (6.9%) that the secondary eclipse would be a non-grazing event.

Due to its eccentric orbit and long period, HD 17156b is a fascinating object for the study of the dynamics of exoplanet atmospheres. To aid such future studies, we present theoretical light curves for the variable infrared emission from the visible hemisphere of the planet throughout its orbit.

Comments: 20 pages, 4 figures, 1 table, AASTeX preprint format. Submitted to ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0801.1496v1 [astro-ph]

Submission history

From: Jonathan Irwin [view email]

[v1] Wed, 9 Jan 2008 20:32:51 GMT (186kb)

http://arxiv.org/abs/0801.1496

• ljk March 22, 2008, 22:43

Orbital Dynamics Of A Second Planet In HD17156

Authors: Donald Short, William F. Welsh, Jerome A. Orosz, Gur Windmiller

(Submitted on 20 Mar 2008)

Abstract: In this letter we report the possible existence of a second planet in the transiting extrasolar planet system HD17156 and its interactive dynamics with the previously known planet. The analysis is achieved through the \POFP\ optimization software which is based on a full integration of the system’s multiple-body Newtonian equations of motion. The two-planet solution yields a significantly improved fit to the previously published radial velocities. The two planets are strongly interacting and exchange angular momentum, yet remain stable as they mutually excite orbital eccentricities and periastron advances.

Comments: Submitted to ApJ Letters, 4 pages, 5 figures

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0803.2935v1 [astro-ph]

Submission history

From: Gur Windmiller [view email]

[v1] Thu, 20 Mar 2008 18:09:32 GMT (53kb)

http://arxiv.org/abs/0803.2935

• ljk December 24, 2012, 11:53

Exoplanet Detection and the Amateur Astronomer

by Joshua Rieger

Joshua Rieger is a native of Texas with an avid interest in astronomy and is on a personal quest to help Icarus Interstellar develop the knowledge infrastructure to galvanize the global amateur astronomy community into a focused effort that will see amateurs hunt for exoplanets. His ambition is to help Icarus develop a ‘wiki’ full of knowledge and information that will help educate and organize the community toward this objective.

When you think of an astronomer, what do you picture? A house-sized observatory, filled with scientists, giddy as color images come rolling in? Or do you picture a handful of scientists, sorting through endless mounds of data that have been collected over a couple hours of observation without any of the breathtaking images you see in books? If you imagined the latter, you would have a much more realistic idea of what it means to be a professional astronomer.

Professionals in the field of astronomy simply cannot use their observatories at their whim. The operation costs of these professional installations are staggering. When taken into account the amount of money and energy required to run an observatory, one begins to realize why we are unable to spend more time searching the night sky for extrasolar planets.

With billions and billions of stars in the Milky Way, it is nearly impossible for professional astronomers to continue collecting data on previously discovered exoplanets, let alone observe each star, looking for a new exoplanetary system.

The Gemini Observatory, located in both the Hawaiian Islands and the mountains of Chile, is comprised of two 26.9′ telescopes. The government budget for the construction of this observatory was $193 million dollars, while consuming another$10 million dollars per year in operating costs.

Since this project was a venture between seven countries, the Gemini Observatory maintains an “open sky” policy, meaning any country is free to use the facility within reason. Requests for reserved time are sorted through, and only the most relevant are accepted. Once this happens, the allotted time per request may be as long as a few nights, or as little as an hour. With numbers like that, the importance of the amateur community begins to come into perspective.