Messung der Transitlichtkurve des Exoplaneten KELT-23Ab am 21./22. März 2025

Measurement of the transit light curve of the exoplanet KELT-23Ab on March 21/22, 2025

Contribution by Dr. Gerold Holtkamp, June 2025

The measurements were taken from 10:21 PM UTC on March 21, 2025, to 2:37 AM UTC on March 22, 2025, in Osnabrück, Sonnenhügel. The moon was 55% illuminated and 98° distant. It rose at 3:30 AM UTC on March 22, 2025. It was therefore not relevant for the measurement.

The measurement technique used:
Telescope: Skywatcher Newton 250/1200 mm
Mount: Skywatcher AZ-EQ6
Filter: Luminanz (Antlia)
Camera: QHY268M with gain 60, offset 20, chip temperature -10° C
Guiding: Skywatcher Guidescope Evoguide 50 ED with camera ZWO ASI120mm

NINA was used for camera and mount control.

*The measured transit light curve in the exoclock representation*

The present measurement and the subsequent evaluation with the hops software of the Exoclock-Project resulted in:

Rp/Rs = 0.1337 +/- 0.0051 (expected 0.132 +/- 0.0006) *
--> Rp = 0.1337 x 696,340 = 93,101 +/- 3,551 km. [1]

The exoplanet KELT-23Ab is significantly larger than Jupiter (radius = 69,911 km). The system is 411 light-years from Earth.

*The own measurement of the transit center together with the other values available at Exoclock*

The value of the transit's temporal center, which is important for the Exoclock project and is expressed as the difference between the observed and the expected value, is O-C = 2.97 +/- 1.43 minutes**, which is above the expected value, even when the error limits are taken into account.

The measurement of the transit light curve of the exoplanet TOI-1516b was published on the Exoclock project website. [2]

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* [Rp = Rplanet, Rs = Rstar]
If the star's radius is known, the planet's radius is determined directly from the dip in the light curve. (see also https://kosmos-os.de/messung-der-transitlichtkurven-der-exoplaneten-wasp-84b-und-kps-1b-am-7-und-8-maerz-2024)

** [O = Observed, C = Calculated]

[1]
Data on the star system and the exoplanet at
https://exoplanetarchive.ipac.caltech.edu/overview/KELT-23A
The radius of the parent star was taken as 1.00 +0.036/-0.039 (Gaia DR2) x the radius of the Sun. The radius of the Sun was assumed to be 696,340 km. The parent star therefore has a radius of 696,340 km.

[2]
https://www.exoclock.space/database/observations/KELT-23Ab_4084_2025-03-22_Gerold_1561_Lum/