UT Sep 06, 2023: Photometry of exoplanet transit by WASP-177b (and telescope lesson)

Michael Richmond
Sep 07, 2023
Sep 23, 2024

On the night of Sep 05/06, 2023, under good conditions, RIT Physics major Myrra Small and I acquired images of the star WASP-177 as part of her independent study project. On this evening, the planet known as "WASP-177b" was predicted to pass in front of its host star. We hoped to measure the tiny drop in the star's brightness due to the planet's passage.

I also helped a pair of local amateur astronomers with a new telescope they had acquired ...

WASP 177

The planet in this system was first noticed by the WASP project in the year 2019; one can find a summary of information on the system on the NASA Exoplanet Archive. Because the planet is relatively large, it blocks enough of its star's light to create a dip of up to 1.8 percent or 0.018 magnitudes.

These observations involved:

• Meade 12-inch telescope
• no focal reducer, so working at f/10
• ASI 6200MM CMOS camera
• clear filter, 60-second and mostly 30-second exposures
• images binned 4x4
• no guiding
• focus position
  • in clear: 1.217 yields FWHM 5.5 at T = 75/24

Notes from the night:

• Very warm and humid, temperatures in the seventies all night
• better to put dome slit panel into raised position, as the target never rises very high in the sky
• waning gibbous Moon was bright again
• heard a deer snort in the woods to the south of the observatory, and encountered many mosquitoes
• the telescope is definitely mis-collimated to some degree. The issue probably dates back to Sep 02, when I had to use the silver focus knob to accommodate the high-speed occultation camera. We'll have to go through a collimation procedure soon -- I tried doing a bit this evening, but didn't have time to make much of an improvement

The position of the target is

   RA =  22:19:11.28   Dec = -01:50:03.95

The star's magnitude is V = 12.3.

• chart of V347 Aur field from AAVSO

Here's a chart from the DSS2 Red plates, 0.6 degrees on a side.

The picture below is based on one of the images taken tonight, UT 2023 Sep 06.

I've marked the location of several comparison stars.

  star       AAVSO ID            B          V         r   
--------------------------------------------------------------
   A        HD 211788             9.34      8.79

   B      TYC 5225-1081-1        10.873    10.447             APASS9 magitudes

   D      TYC 5225-1551-1        12.634    12.154    11.930   APASS9 magnitudes
--------------------------------------------------------------------------

 

We acquired data over the period 11:05 PM to 02:31 AM, which should include the entire transit as well as time before and after the event.

Early in the evening, I helped a pair of local amateur astronomers, Liz and Ann, figure out how to use a telescope they had just acquired. The mount was a little bit tricky, but we figured out a reasonable way to point it.

I hope that they will enjoy using their telescope -- it gave us a good view of the Moon!