Messung der Transitlichtkurve des Exoplaneten HAT-P-12b am 7./8. März 2025

Measurement of the transit light curve of the exoplanet HAT-P-12b on March 7/8, 2025

Contribution by Dr. Gerold Holtkamp, June 2025

The measurements were taken from 9:42 PM UTC on March 7, 2025, to 2:00 AM UTC on March 8, 2025, in Osnabrück, Sonnenhügel. The moon was 64% illuminated and 87° distant. It set around 4:25 AM UTC.

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 = 0.1432 +/- 0.0042 (expected 0.1406 +/- 0.0013) *
–> Rp = 0,1432 x 424.071 = 60.727 +/- 1.781 km. [1]

The exoplanet HAT-P-12b is therefore slightly smaller than Jupiter (radius = 69,911 km). Nevertheless, the transit light curve shows a dip of more than 27 mmag, which is due to the small size of the parent star (radius (HAT-12) = 0.609 x radius (Sun)). The system is 466 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 expected values, agrees well with the expected value at O-C = -0.85 +/- 0.98 minutes.** Therefore, our own measurement lies almost at the zero line in the diagram above.

The measurement of the transit light curve of the exoplanet HAT-P-12b 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/HAT-p-12b
The radius of the parent star was taken as 0.609 +0.040/-0.032 (Gaia DR2) x the radius of the Sun. The radius of the Sun was assumed to be 696,340 km.

[2]
https://www.exoclock.space/database/observations/HAT-P-12b_2862_2025-03-07_Gerold_1561_Lum