Astronomy 94: Exoplanet Research
at the Peter van de Kamp Observatory
Archive of Assignments
Week 14
Mon., Apr. 29: For class tomorrow, please read this short article from American Scientist, "Why Does Nature Form Exoplanets Easily?."
Week 13
Sat., Apr. 20: Read the New York Times article about the Kepler discovery of two Earth-like planets that appear to be in their stars' habitable zones. (Of course, you can find many other sources for this news.) Here are the abstracts of the two (peer-reviewed) scientific articles that actually describe these discoveries: "A super-Earth-sized planet orbiting in or near the habitable zone around a Sun-like star," Barclay et al. and "Water Planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the case of Kepler-62e and -62f," Kaltenegger, Sasselov, and Rugheimer. Please read the abstracts, although you don't have to read the papers (though feel free!).
Week 12
Mon., Apr. 15: There is no particular assignment for this week. But if you'd like to do a little preparation for Philip and Kelley's presentations, here's a short paper on tidal circularization that Philip recommends and one on habitable zones that Kelley recommends. That second one is longer... but even just skimming these papers, and spending a few minutes looking at the figures could be worthwhile.
Week 11
Mon., Apr. 8: Schedule your presentation date. Access my Astro 94 class calendar, and sign up for one of the free slots. Note that they are our last three class meetings: April 16, 23, and 30, as well as Thursday night, May 2. Please let me know if you have trouble accessing (or making an appointment on) the calendar.
Week 10
Mon., Apr. 1: Catherine and Jamie will be giving their presentations on Tuesday. Catherine's is on the correlation between heavy element content of stars and presence of high-mass planets. Here are a few pages of background reading from the Exoplanet Handbook that you can take a look at (optionally) in preparation for the presentation. Jamie will be talking about pulsar planets. Optional recommended background reading is the first several pages of sec. 4.1 of the Exoplanet Handbook (I don't have a pdf available right now; the whole book is available electronically via Tripod).
Week 9
Tue., Mar. 26: Download the AstroImageJ software and install it on your computer. I have put together a (huge, 10GB) file containing the data we took of KELT-4 on February 21. You can download that, too, and unpack it. I'll post directions here shortly for looking at the data and for reducing it.
Sun., Mar. 24: For Tuesday's class take a look at Winn, "The Rossiter-McLaughlin Effect for Exoplanets," IAU 276, 230. If you don't have time, you don't have to read it thoroughly, but it will help you prepare for class, and the article is not long.
If you haven't let me know how your presentation research/preparation is going in the last few days you should get in touch. Don't forget I have extra office hours this week.
Week 8
Sun., Mar. 17: Researching your presentation topic is your assignment for this week. update: This is still true!
Week 7
Mon., Mar. 4: Please post a question about this week's reading (or the talk, or any of the links on the class website, or anything from previous weeks) on the Moodle discussion board.
Thu., Feb. 28: For class on Tuesday, March 5, please read this short conference review paper by Bill Borucki on initial results from Kepler. Also, go onto iTunes and watch Borucki's talk on Kepler results, given at Villanova last year. It's in the NASA science video series and you can find it simply by searching the iTunes store for his name; the title is "NASA Kepler Space Mission." Note that the talk starts at the 4 minute mark, but you might want to start watching from 2:00 to hear the biographical introduction of the speaker (he worked on the Apollo Moon missions). The talk ends at 52:00, but the questions following the talk are (some of them) interesting. Note that Borucki's talk is aimed at a relatively general audience, though it's a Physics and Astronomy Department colloquium, but one nice thing about the talk is he periodically delves deeply - but quickly - into interesting, detailed astrophysics. For example, near the beginning of the talk he describes planetary formation theory, including a description of the dynamical drag of the gaseous disk on the rocky planetessimals. He relates some important quantitative results from the first few years of the Kepler mission, including the prevalence of "super earths." His discussion of habitable zones in the middle of the talk is interesting. He describes some of the technical details of the Kepler mission, and at the end he speculates about the future, including such things as photometric characterization of biomarkers on exoplanet surfaces. Overall, his theme is that Kepler seeks an answer to the basic question, "Are Earths common or rare?" and he asserts that if they're common, then life is probably common in the Galaxy.
Week 6
By 9:30 am on Tuesday, post a question on Moodle about the observational reading, solar system structure and formation, or a plot of exoplanet properties/trends.
Fri., Feb. 22: For now, the only preparation for Tuesday's class is to (re-)read the two short chapters from a introductory textbook on observational astronomy ("Observing the Universe" by Norton) - on detectors and on data reduction. And to review the solar system structure and formation material: a chapter from Bennett's "Cosmic Perspective" and a chapter from the more advanced "Foundations of Astrophysics" by Ryden and Peterson, and the questions on the Moodle discussion forum.
From last Tuesday's class, here are some images and movies we looked at: Simulation of planet formation; Matthew Bate, from the University of Exeter, has many nice simulations of star and protoplanetary disk formation. Rory Barnes at U. Washington has some simulations of planetary migration, among other things. You can also check out: Scott Kenyon at Harvard describes the results of simulations of the formation of earth-like planets. A short summary of planet formation results from the Carnegie's Department of Terrestrial Magnetism. Pages from a Caltech class on the formation and evolution of planetary systems with a lot of great links, including the paper by Robin Canup on the formation of the Moon (simulation images we looked at in class are near the end). And here are real-time images of the Sun and a model of Kepler-7b.
Week 5
Mon., Feb. 18: After reading the two chapters on solar system properties and formation (Bennett Ch. 4 and Ryden & Peterson Ch. 8, described below), please post at least one question on the Moodle discussion forum prior to midnight on Monday. We'll use these questions as a basis for our class work and discussion on Tuesday. If you don't have any questions about the reading (come on, I bet you do! - you should definitely take a look at the end-of-chapter questions in both books and see if you can answer them) then you can ask about any other aspect of the material we've covered in class so far, or really, anything related to exoplanets. By the way, how about that real-time demonstration last Friday of the importance of planetary impacts?
We'll go to the telescope again this week, and start taking a look at real data next week in class. In preparation for that, read these two short chapters from a introductory textbook on observational astronomy ("Observing the Universe" by Norton) - on detectors and on data reduction. If you've got time today, go for it, but this is really material for next week. Note that each chapter is only about five pages long.
Fri., Feb. 15: I have two readings on the properties and formation of the Solar System: A chapter from Bennett's "Cosmic Perspective" and a chapter from the more advanced "Foundations of Astrophysics" by Ryden and Peterson. The latter textbook is on the reserve shelf at Cornell (and some of the chapters following the one I've assigned provide further details about the solar system, and you might enjoy having a look at them, too). Please read both the Bennett and the Ryden & Peterson for Tuesday, but skim parts of the Bennett that seem too simple to you and parts of the Ryden & Peterson that seem too complicated.
On Sunday, I will provide some more reading, on observational techniques. We will not discuss every aspect of all the reading on Tuesday; some of the discussion will be deferred to the following week. But do as much of the reading as you can before class on Tuesday. And I will also - probably - send out a short question or two for you to answer and hand in before class. Look for that on Sunday night.
Week 4
Sun., Feb. 10: For Tuesday's class, please read and be ready to discuss "Kepler-7b: A Transiting Planet with Unusually Low Density," Latham et al., 2010, Astrophysical Journal, 713, L140.
Take a look at the slides from last week's class (spectra of stars and radial velocities, mostly).
Here is a one page review sheet. Look it over and make sure you can answer the questions preceded by arrows. You don't have to hand anything in, but do get in touch if you have any questions. I'll be in my office from 3:30 to 5:00 pm on Monday.
Please check your email after 9PM on Monday night. I'll have one additional question at that point that I'd like you to think about for class on Tuesday, and I'll solicit questions about the Latham et al. paper on Kepler-7b (or on any other topic).
Week 3
Mon., Feb. 4: I've now annotated the second and third pages of the Beatty et al. article. Looking over my annotations (and those for the first page, linked below) might help you with some of the jargon and some of the small-scale concepts in the paper. I will likely not post annotations for the last few pages in the paper, because that's where the material from the first few pages is synthesized and so you can refer to the first three pages for jargon definitions. And relatedly, questions that you have about the second half of the paper are probably things we should be talking about as a group, in class.
Sun., Feb. 3: There is a small assignment due by 8:30 pm on Monday night. The linked document is identical to the email sent out on Sunday afternoon. You should post your question about the Beatty et al. paper to the discussion I've set up on Moodle.
You should read the last two pages of Ryden & Peterson, Ch. 12, on the properties of exoplanets (as of a few years ago). The book is also available on the reserve shelf at Cornell, behind the front desk.
The main reading for next week (class on Tuesday, Feb 5), is the recent paper on the newly discovered (using data from our Peter van de Kamp Observatory, among others) transiting exoplanet, KELT2Ab. I gave out hardcopy of the paper at the end of class this week. If you need a new copy or prefer an electronic copy, you can get one via ADS (which links directly to the Astrophysical Journal's website).
A few days before class, I will ask you to post questions about the paper. The paper is relatively short but, as with all scientific papers, it is dense. You will need to read it more than once. And without knowing all the jargon and the context, it will be impossible to understand every aspect of it. To help you get started, I've annotated just the first page (so far). Have a look, and let me know if you have any questions. By all means, if you see a term you don't understand, look it up. And to get some context (and see some images Eric Jensen made that demonstrate the relative size and resolution of the KELT discovery images and our follow-up images), have a look at this article on the College's website.
Week 2
The reading for class the second week, is some basic review of Kepler's laws and Newton's laws of motion, gravity, and orbits. This very well may be new to you or some or even all of it may be familiar (but perhaps you still could benefit from some review). I've put an Astro 1 textbook "The Essential Cosmic Perspective" on reserve at Cornell. Take a look at Kepler's Laws on p. 67 in Ch. 3 and read the next few pages (or all of the rest of the chapter, if you'd like). And also read or skim Ch. 4, paying special attention to Newton's laws of motion, gravity, angular momentum, and orbits. The bit about tides at the end of the chapter is also interesting, and relevant to exoplanet studies. But the most important thing in Ch. 4 is Newton's version of Kepler's third law, on p. 100.
A pdf of the above, optional reading is available. Note that the book is also available on the reserve shelf -- behind the front desk; you have to ask for it -- in Cornell. It is being shared by Astro 1, so you might have to ask the librarian to look for it there.
There is no written assignment for Tuesday's class. But I would like you to read five pages from a sophomore level astrophysics textbook, Ryden & Peterson's Foundations of Astrophysics. The book is on reserve at Cornell. I'm also posting here the five pages in question (pp. 298-302). If you read the book in person, you may be tempted to read the next few pages, which are also good. In any case, read the paragraph below before you start reading Ryden & Peterson.
The first couple of pages in the short reading above are about extracting exoplanet masses from radial velocity curves of their host stars, based on Kepler's third law. In the Cosmic Perspective background reading I recommended, Newton's version of Kepler's third law was stated on p. 100. It is the starting point for weighing planets (and stars). It is eqn. 12.15 at the beginning of the Ryden & Peterson reading. Note that a_A and a_B in this equation are the distances from the star and planet, respectively, to their common center of mass. This version of Kepler's third law is exact. When one object is much more massive than the other then, to good approximation, the mass of the lighter object, M_B, can be ignored, and the sum (a_A + a_B) is just a, the separation between the planet and the star, and we have a^3 = GMP^2/4pi^2. To prepare for class, derive this simplified version of Kepler's third law by equating the centripetal acceleration of an exoplanet in a circular orbit to the acceleration due to gravity between it and its host star. You can look up centripetal force or acceleration in wikipedia if you feel a need to review its derivation or just be reminded of the formula (which is most usefully expressed in terms of the circular speed, v, and the distance from the center of motion, which we can equate to, a, the star-exoplanet distance). To get the expression to look like Kepler's third law, you'll want to note that for circular motion the velocity, v = 2pi*r/P where r is the radius of the circle and P is the period of the circular motion. This is all well and good if you want to do something like weigh the Sun given the Earth's orbital period and semi-major axis. But to weigh the lighter object (e.g. the Earth or the exoplanet) the orbital velocity of the heavier object (e.g. the Sun or exoplanet's host star) must be measured. Pages 298-300 show how the exoplanet mass is derived from observable quantities.
Week 1
Each week there will be a modest amount of reading, and usually one or two problems to solve or questions to answer about the week's topic. Students will be expected to do work ahead of class, much like a seminar, and come to class ready to share their solutions. We will discuss these readings and questions in our weekly class meetings. We will also look over and discuss data we obtain at the telescope. Some weeks we will observe for a few hours one night. Other weeks, we will work either together or individually to reduce and analyze data.
Our first assignment is posted. There is no reading other than the assignment itself. Please bring your answers to class on Tuesday. And: here are David's solutions.
Week 0: before the semester
See our zeroth assignment, for you to do before classes start. And: Spend some time reading/exploring the first three sites in the Links section on the right side of the front page.
Some optional background reading for winter break:
I've been noticing some articles in the press about the gravitational stability of the solar system. Here's one suggesting the solar system may have once had an additional large planet, since lost. And one about orbital migration in the solar system. Here's a video showing two realizations of the so-called Nice model (Nice, like the city in France) of solar system orbital evolution. Many known exoplanet systems have hot Jupiters -- giant planets very close to the parent star -- and other properties that are hard to understand if planets' present-day positions indicate the locations where they were formed. Planetary migration is apparently quite common, and study of exoplanet systems seems to inform, and be informed by, study of our own solar system.
Return to the main class page.
This page is maintained by David Cohen
cohen -at- astro.swarthmore.edu
Last modified: May 6, 2013