Transitlichtkurve des Exoplaneten Qatar-1b am 6./7. April 2025

Transit light curve of the exoplanet Qatar-1b on June 6th/7th April 2025

Contribution by Dr. Gerold Holtkamp, June 2025

The measurements were taken from 10:07 p.m. UTC on April 6, 2025, to 2:24 a.m. UTC on April 7, 2025, in Osnabrück, Sonnenhügel. The moon was 70% illuminated and 93° distant. It set at 3:03 a.m. UTC on April 7, 2025, and was therefore in the sky for the entire measurement period. However, because it was 93° distant, it could not shine into the telescope.

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 = 0.1524 +/- 0.004 (expected 0.1463 +/- 0.0006) *
–> Rp = 0,1524 x 576.569 = 87.869 +/- 2.306 km. [1]

The exoplanet Qatar-1b is thus slightly larger than Jupiter (radius = 69,911 km). The large dip in the transit light curve is due to its relatively small parent star. The system is 607 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 = -0.02 +/- 0.89 minutes**, which is almost exactly the expected value.

The measurement of the transit light curve of the exoplanet Qatar-1b 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-1
The radius of the parent star was taken as 0.828 +0.067/-0.050 (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 576,569 km.

[2]
https://www.exoclock.space/database/observations/Qatar-1b_6498_2025-04-07_Gerold_1561_Lum/