Exoplanet Transit Lab

Experiment description

https://github.com/anjavdl/PHY517_AST443/blob/master/exoplanet/transit_planet_lab.pdf

Selecting your targets

Note: the following needs to be done as part of Homework 2. For Homework 2 you should only submit the plot specified below (3.), as well as your requested observation dates (11.). However, your lab report should include a section of how you selected your target.

1. You can find the current catalog of known exoplanets at http://exoplanet.eu/catalog/all_fields/. Filter the catalog to include only exoplanets detected as "primary transits" and download it.
   Note: topcat (see Astro Software page) is a great tool for viewing the table, especially in VOTable format.
   Also note: if you are interested in observing exoplanet candidates, you could also include the catalog of TESS Objects of Interest.

2. The catalog does not tell you the transit depth, but you can calculate it from the data given in the table. Figure out how, and make a new column with transit depths.

3. Use topcat to plot the transit depth vs. the brightness of the host star. Select stars that are bright (V~<12, but the brighter, the better!) with a relatively large transit signature (more than 0.008). Which are your best targets?

4. Use the R.A. and Dec. coordinates to select stars that are observable from Stony Brook in the next month.

5. Figure out how to calculate the expected mid-points of transits, given the data in the table (note: the time specified for the primary transit in the table is its mid-point). For the stars that you have selected, calculate the transit times in the next 1-2 months. You will have to write a small program (in the language of your choice) for this step.

6. The catalog also does not tell you the duration of the transit, but again, you can calculate it. To do so, derive an estimate of the transit duration under the assumption that the planet crosses directly across the center of the star. This is an upper limit to the real duration (why?), but should not be too far off. To keep the duration of the data taking to a reasonable time, try to select stars with transit durations shorter than about 3 hours.

7. To detect a transit, we need to compare the flux of the host star before, during, and after the transit. That means that you need to take (enough) data for each of these, i.e. your observations should start ~1 hour before the beginning of the transit, and last until ~1h after the end of the transit.

8. You can use twilight time to set up, but because some of the set-up steps require reasonably dark sky, you should not expect to finish setting up before the end of twilight (dashed line on StarAlt). Expect the total set-up time to take about 2 hours.

9. Select transits that occur at night-time, and when the star is well observable (ideally >40°) for the entire duration of your observations. You can use the script rdj2aau.py to convert (R.A., Dec., MJD) to (azimuth, altitude, UTC). To use the script, prepare a text file with all your candidate events (each row should be one event, i.e. one set of RA, Dec, JD, separated by a whitespace). Run it as python rdj2aau.py in.txt out.txt.

10. Choose 3 transits, staggering them out within the next month. The later two dates are your back-up dates in case the observations on the first night fail due to weather or technical problems. Note that the transits can be for different stars / planets. Also note that you need to avoid days ±3 days around Full Moon. If the Moon is bright, make sure your target is 40° away from it (StarAlt will tell you the distance in degrees). Refer to the Mt. Stony Brook observing calendar for scheduling constraints and available dates.

11. Send me (by e-mail) your choice of dates - first come, first serve. Include the results of your calculation for the mid-transit time, the transit duration, and the magnitude dip. Include a StarAlt plot for each transit, where you mark the beginning, mid-point, and end of the transit, as well as the planned beginning and end of the observations. When should you arrive at the telescope?

Preparing your observations

Agree with the instructor and the TA on when to meet. Remember that you need to start observing approximately an hour before the beginning of the transit, and will need about 2 hours to get set up and take calibration data.

Make sure that you have read the lab manual, and understand the steps for taking and analyzing your data. Make sure that you are familiar with operating the CCD camera and the telescope. Bring copies of these manuals.

Look up the spectral type of your star, e.g. on simbad. Also consider how much moonlight and/or twilight there will be. What filter should you choose for your observations?

You need to bring:

• The StarAlt plot of your target, with the ingress, mid-point, and egress marked. Also mark when you should start observing, and until you need to be observing.
• A finder chart (N up, E left) of your target field, matched to the FOV of the camera (you can calculate the latter from the focal length of the telescope and the physical size of the pixels).
• A finder chart (N up, W left) of your target field, matched to the FOV of the finderscope (~5°).