Messung der Transitlichtkurve des Exoplaneten Qatar-8b am 31. März/1. April 2025

Measurement of the transit light curve of the exoplanet Qatar-8b on March 31/April 1, 2025

Contribution by Dr. Gerold Holtkamp, June 2025

The measurements were taken from 9:26 p.m. UTC on March 31, 2025, to 3:06 a.m. UTC on April 1, 2025, in Osnabrück, Sonnenhügel. The moon was 10% illuminated and 78° distant. It set on March 22, 2025, at 10:30 p.m. UTC. 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 = 0.0909 +/- 0.0067 (expected 0.1014 +/- 0.0031) *
--> Rp = 0.0909 x 930,310 = 84,565 +/- 6,233 km. [1]

The exoplanet Qatar-8b is significantly larger than Jupiter (radius = 69,911 km). The system is 916 light-years from Earth.

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

The value of the temporal center of the transit, which is important for the Exoclock project and is expressed as the difference between the observed and the expected value, is O-C = 6.97 +/- 3.17 minutes**, which is significantly higher than the expected value, even when the error limits are taken into account.

The measurement of the transit light curve of the exoplanet Qatar-8b 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/qatar-8
The radius of the parent star was taken as 1.336 +0.058/-0.045 (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 930,310 km.

[2]
https://www.exoclock.space/database/observations/Qatar-8b_2482_2025-04-01_Gerold_1561_Lum/