Four New Ground-based Observations of the Hot Neptune-like Exoplanet TOI-1728b

Abstract

This paper presents results from four recent photometric observations of the hot Neptune-like exoplanet TOI-1728b conducted at the Meshtitsa Observatory, a private citizen science facility near Pernik, Bulgaria, on December 15 and 29, 2025, and January 12 and 19, 2026. Using a 0.25-m telescope, we captured R-band light curves and performed data reduction, airmass detrending, initial modelling, and outliers inspection via AstroImageJ. The ground-based observations were combined with historical TESS photometric data and radial velocity measurements. Fitting and analysis were executed using the Exo-Striker software applying nested sampling. Our results are consistent with the already known parameters of the planet within the uncertainties. We provide fitted values for the orbital period ($$P=3.491402^{+0.000001}_{-0.000001}$$ d), transit mid-time ($$T_0=2458839.7833^{+0.0005}_{-0.0005}$$ BJD_TDB), inclination ($$i=87.13^{+1.83}_{-1.28}{}^\circ$$), scaled semi-major axis ($$a/R_{\star}=11.59^{+2.09}_{-1.53}$$), and planetary radius ratio ($$R_p/R_{\star}=0.0685^{+0.0044}_{-0.0042}$$). The data consistency confirms the stability of the planet's orbit over the extended baseline and agrees with published values. Our results demonstrate the capability of citizen science observatories to contribute scientifically valuable measurements to exoplanetary research when combined with space-based photometry.