Transit Probability

Many of you had some trouble with the worksheet problem about the transit probability of a planet. Consider the sketch below:

The star is the big orange circle in the middle, and the filled blue circles show two extreme planet-orbit inclinations, above and below which the planet does not transit. Note that the orbit planes for the two configurations are parallel to the blue solid lines, not the black lines. The two orbit configurations are separated by and angle of approximately 2 Rstar/a (purple trace), obtained using the "skinny angle" property that the sine of a small angle is the small side over the long side.

With those definitions in mind, the transit probability is related to the solid angle traced out by the two extreme transit configurations, which is

as well as the total solid angle at a semimajor axis a, or:

The probability is the ratio of these two solid angles:

For more on all things transit, including eccentric orbits and other properties of the transit geometry, see Prof. Josh Winn's (MIT) excellent book chapter here:

http://arxiv.org/pdf/1001.2010v4

RV Plots for Thursday's Worksheet

Here are the radial velocity time series for two exoplanets. The mass of the star is listed under each plot. Problem 1 on the worksheet asks you to measure the masses of the planets in each system (assume e = 0, and i = 90 degrees).

 Mstar = 1.8 Msun

 Mstar = 1.7 Msun

Josh Carter's Exoplanet Talk

Tuesday 3pm in 370 Cahill:

Josh Carter, Harvard-Smithsonian Center for Astrophysics

Kepler's Multi-Eclipsing Hierarchical Triples: Accurate Masses and Radii, Transiting Circumbinary Planets
The Kepler mission has opened a new era of high-precision time-series photometry. It has allowed for the wholesale detection of planetary systems and the detailed characterization of both stars and planets. The Kepler data quality and restricted mission scope has also led to the unveiling of novel events.  Amongst these are the discovery of hierarchical multi-eclipsing systems including those with transiting circumbinary planets (e.g., KOI-126, Kepler-16). These systems are observationally biased to have small periods and period ratios and, consequently, have short (Kepler mission lifetime) secular variation timescales. This dynamical information is encoded in variable eclipse morphologies.  I describe photometric-dynamical fits to the these light curves.  I present results from these fits; namely, I report accurate absolute bulk parameters (stellar and planetary masses and radii) that are determined free of typical model-dependencies.  I compare these parameters with theoretical expectations and comment on the efficacy of stellar models. I briefly address the search for additional transiting circumbinary planets in the Kepler data and discuss future applications of this work.

Schedule your final exam!

The final exam will be a half-hour oral exam with Professor Johnson and me (and maybe a guest scientist!), sometime during the exam period from Dec 7-9. Please follow this link to fill out a form indicating your preferred exam times.

All the stars

LaTeX Math Symbols

It's great seeing so many people use online LaTeX editors! Here's a handy guide to LaTeX math symbols:

http://web.ift.uib.no/Teori/KURS/WRK/TeX/symALL.html

Also, FYI, LaTeX is pronounced "Lay-Tek." My fellow grad students and I at Berkeley once spent the better part of a Stellar Structure study session debating this point. Somehow we all did well on the final...

Prof. is back

Hey everyone, I'm finished with my battle against bronchitis. Short story: I won. Yay! I'm looking forward to being back in the classroom.

Juliette stumbled upon my most recent Astrobites contribution about preparing for grad school. I wrote that post this past summer, and I didn't think to connect it to our course. But it makes perfect sense to do so, so check out Juliette's blog and follow the link from there.

I wrote another Astrobites post last year that went viral, at least throughout the astronomy community. I think all Caltech students should check it out, and talk to me if it strikes a nerve.

Finally, we had our first two blog posts come in as part of the Professional Astronomers series. Write your first post soon, with your initial thoughts and impressions about what the process of going pro is all about. Then get going on your interviews! Talk to me if you need recommendations for interview subjects. But don't wait.