Europlanet Science Congress 2021
Virtual meeting
13 – 24 September 2021
Europlanet Science Congress 2021
Virtual meeting
13 September – 24 September 2021
EPSC Abstracts
Vol. 15, EPSC2021-107, 2021, updated on 21 Jul 2021
European Planetary Science Congress 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Taurus Hill Observatory season 2020/2021 exoplanet review. HAT-P-38b (Hiisi) and secondary eclipse of the HAT-P-32b exoplanet.

Harri Haukka1,2, Veli-Pekka Hentunen2, Markku Nissinen2, Tuomo Salmi2, Hannu Aartolahti2, Jari Juutilainen2, Esa Heikkinen2, and Harri Vilokki2
Harri Haukka et al.
  • 1Finnish Meteorological Institute, Space Research and Observation Technologies, Helsinki, Finland (
  • 2Taurus Hill Observatory, Varkaus, Finland (

Taurus Hill Observatory (THO) [1], observatory code A95, is an amateur observatory located in Varkaus, Finland. The observatory is maintained by the local astronomical association Warkauden Kassiopeia. THO research team has observed and measured various stellar objects and phenomena. Observatory has mainly focused on exoplanet light curve measurements (over 170 measurements so far) [4], observing the gamma rays burst, supernova discoveries and monitoring [2]. We also do long term monitoring projects [3].

The results and publications that pro-am based observatories, like THO, have contributed, clearly demonstrates that pro-amateurs are a significant resource for the professional astronomers now and even more in the future.

HAT-P-38 and HAT-P-38b (Horna and Hiisi)

The object is located in RA 2h 21min 32s and DE + 32 ° 14 ’46”. From Finland, the object is high in the southern sky only in autumn. In addition, the transit time of the object is such that transit occur quite rarely at night. Considering the uncertain autumn weather in Finland, the probability of detecting a complete transit is quite uncertain in Finland.

Taurus Hill Observatory detected the HAT-P-38b  first time on 18 September 2020 and for the second time on 8 November 2020. Based on our observations, the timing of the transit deviated from the forecast by almost an hour. The transit took place clearly ahead of schedule. It is an indication that the rotation time of the exoplanet is possibly slightly shorter than recorded in the original catalog values. In this case, the transit catalog times are no longer valid. Observations made by other observers also confirm this. It is therefore worth monitoring the object to see if such an observed change is indeed regular.

In the first observation the dimming was 13.6 mmag and in the second it was clearly less, only 6.8 mmag. The length of the transit also varied slightly, from 178 minutes on the first occasion to 185 minutes on the second occasion.

Figure 1: HAT-P-38b transit observed at THO.

Secondary eclipse caused by the HAT-P-32b exoplanet

Last winter, for the first time in Taurus Hill Observatory, a rather challenging exoplanet was observed to transit behind its own parent star. Such an observation was made in Taurus Hill Observatory on February 17, 2021 from the exoplanet HAT-P-32b. Normal transit of a similar object had been observed in Taurus Hill Observatory a few times before. After an observation tip from the Pulkova Observatory, an attempt was made to observe this secondary eclipse in Taurus Hill Observatory. According to forecasts, the subject would have to dim about 3-4 mmag and the duration of the eclipse would be about 120 minutes. The fading according to the forecasts was barely visible in the measurements of the Taurus Hill Observatory Observatory. Although the detection of a “behind transit” of a star would require better accuracy, at least the measurement results obtained from the light curve, the timing, and the intensity of the dimming were fully consistent with the predictions. Thus, there is strong evidence that the first observation of secondary eclipse in Taurus Hill Observatory was real.

Figure 2: Secondary eclipse caused by the HAT-P-32b observed at THO.

TESS candidates have joined as new targets

The Taurus Hill Observatory began observing TESS candidates, or TOI objects, in the autumn of 2020. In total, these objects have now been observed 21 times in Taurus Hill Observatory. There have been seven different TESS candidates on the list. These selected targets have been fairly easy to detect, with a change in brightness caused by transits in between 7 and 20 mmag. The findings have been uploaded to the TRESCA ETD database. Although transits have been clearly observable in all observations, the timing of transits or the magnitude of dimming in most of them have been somewhat different from the catalog values, according to measurements by the Taurus Hill Observatory. This is probably mainly due to the huge number of observations of new uncertain objects and the rather modest resolution equipment of the TESS satellite itself. It is very possible that not nearly all of the observed TESS candidates will be confirmed as new exoplanets.

Figure 3: TOI1516.01b transit observed at THO.


The Taurus Hill Observatory will acknowledge the cooperation partners, Pulkova Observatory, Finnish Meteorological Institute and all financial supporters of the observatory.


[1] Taurus Hill Observatory website (

[2] A low-energy core-collapse supernova without a hydrogen envelope; S. Valenti, A. Pastorello, E. Cappellaro, S. Benetti, P. A. Mazzali, J. Manteca, S. Taubenberger, N. Elias-Rosa, R. Ferrando, A. Harutyunyan, V.-P. Hentunen, M. Nissinen, E. Pian, M. Turatto, L. Zampieri and S. J. Smartt; Nature 459, 674-677 (4 June 2009); Nature Publishing Group; 2009.

[3] A massive binary black-hole system in OJ 287 and a test of general relativity; M. J. Valtonen, H. J. Lehto, K. Nilsson, J. Heidt, L. O. Takalo, A. Sillanpää, C. Villforth, M. Kidger, G. Poyner, T. Pursimo, S. Zola, J.-H. Wu, X. Zhou, K. Sadakane, M. Drozdz, D. Koziel, D. Marchev, W. Ogloza, C. Porowski, M. Siwak, G. Stachowski, M. Winiarski, V.-P. Hentunen, M. Nissinen, A. Liakos & S. Dogru; Nature - Volume 452 Number 7189 pp781-912; Nature Publishing Group; 2008

[4] Transit timing analysis of the exoplanet TrES-5 b. Possible existence of the exoplanet TrES-5 c; Eugene N Sokov,  Iraida A Sokova, Vladimir V Dyachenko, Denis A Rastegaev, Artem Burdanov, Sergey A Rusov, Paul Benni, Stan Shadick, Veli-Pekka Hentunen, Mark Salisbury, Nicolas Esseiva, Joe Garlitz, Marc Bretton, Yenal Ogmen, Yuri Karavaev,Anthony Ayiomamitis, Oleg Mazurenko, David Alonso, Sergey F Velichko; Monthly Notices of the Royal Astronomical Society, Volume 480, Issue 1, October 2018, Pages 291–301, sty1615

How to cite: Haukka, H., Hentunen, V.-P., Nissinen, M., Salmi, T., Aartolahti, H., Juutilainen, J., Heikkinen, E., and Vilokki, H.: Taurus Hill Observatory season 2020/2021 exoplanet review. HAT-P-38b (Hiisi) and secondary eclipse of the HAT-P-32b exoplanet., European Planetary Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-107,, 2021.