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

Major Blogging Assignment

One of the main goals of Ay20 as stated on the course website is that, "Students will understand what it means to be a professional astronomer." Jackie and I put a lot of thought into these goals and we fully intend to meet them by the end of term.


Pursuant to this goal, your assignment is to team up with 2-3 of your classmates and put together a series of 3-4 blog entries on the overarching topic of: "What does it take to be a professional astronomer." This topic, as stated, is broad and a bit ill defined by design. Tackle it as you see fit. However, here are some concrete suggestions:

1. Write down your impressions as of right now. What does it take to be a professional astronomer. What is the ultimate goal? What is your goal? This can form the basis of your first post.
2. Interview a grad student and a postdoc, perhaps several. Or interview a junior faculty member, or well-established prof. Write a friendly yet professional email to your prospective interviewee, invite them to lunch or out for an afternoon coffee/tea at the Red Door. The Q&A (questions in bold, responses in normal text) can form the basis of a second blog post. What is the typical career arc of a pro? What is a postdoc? Where did they apply to grad school? Where did they start out as an undergrad? What do they know now that they wish they knew at your age? What are their career aspirations?
3. What are alternative career arcs? What are the prospects in engineering, working at observatories, national labs, or in industry?
4. Find articles on this topic online. Check out the discussions on astrobetter and read the career development posts on astrobites. What have you learned and how has your impression from step 1 changed now that you've researched the topic? This can be your third (or fourth) post.

Share the various tasks (interviewing, reading, writing) among your team members. Meet regularly to compare notes. Use Google Docs to write collaboratively. Talk to Jackie and myself. 

This assignment is due before the end of term, the sooner the better. What ever you do, please do not wait to do this all in one or two nights. Start now! And have fun with it.