UT Sep 16, 2023: Photometry of exoplanet transit by KELT-16b

Michael Richmond
Sep 16, 2023

On the night of Sep 15/16, 2023, under very good conditions, RIT Physics major Myrra Small, AST graduate student DJ Klyde, and I acquired images of the star KELT-16 as part of Myrra's independent study project. On this evening, the planet known as "KELT-16b" was predicted to pass in front of its host star. We hoped to measure the tiny drop -- only about 1 percent -- in the star's brightness due to the planet's passage.

RIT physics major Joey Root also came to the observatory, but he worked outside on the lawn, taking pictures of constellations and the Milky Way with his cell phone's camera.

KELT-16b

One can find a summary of information on this system in on the NASA Exoplanet Archive. This planet is a pretty challenging target, as the depth of its transits is only 1.1 percent.

These observations involved:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ASI 6200MM CMOS camera
• V filter, 60-second exposures
• images binned 4x4
• no guiding
• focus position
  • in clear: 1.036 yields FWHM 2.0 at T = 65??

Notes from the night:

• Cool and a bit breezy. No clouds at all.
• no moon
• we collimated the telescope at the start of the run and greatly improved the PSF. The out-of-focus PSF now looks centered:

  

  Focusing the telescope now yields a FWHM less than 2 pixels, just as it did a month or more ago. Good.

The position of the target is

   RA =  20:57:04.45   Dec = +31:39:39.7 

The star's magnitude is V = 11.7.

Here's a chart made from a median of a number of the V-band images we took tonight.

We acquired data over the period 9:00 PM to 01:00 AM, which should include the entire transit as well as time before and after the event.

The quality of the measurements was high. Ensemble photometry of 60-second exposures of the V = 11.7 target yields a scatter of about 0.005 mag, as the sigma-vs-mag diagram below indicates.