The sub-Saturn Mass Transiting Planet HAT-P-12b

TL;DR

This study provides refined measurements of the transiting exoplanet HAT-P-12b, including its orbital parameters and physical properties, using new photometric data and comprehensive modeling, confirming its consistency with standard irradiated gas giant models.

Contribution

The paper offers improved ephemeris and physical parameters for HAT-P-12b through new observations and detailed modeling, enhancing understanding of this sub-Saturn mass planet.

Findings

Refined orbital period of 3.21305961 days.

Host star mass and radius precisely measured.

Planet's properties align with standard irradiated gas giant models.

Abstract

We present new photometric data of the transiting planet HAT-P-12b observed in 2011. Our three transit curves are modelled using the JKTEBOP code and adopting the quadratic limb-darkening law. Including our measurements, 18 transit times spanning about 4.2 yr were used to determine the improved ephemeris with a transit epoch of 2,454,187.85560$\pm$0.00011 BJD and an orbital period of 3.21305961$\pm$0.00000035 d. The physical properties of the star-planet system are computed using empirical calibrations from eclipsing binary stars and stellar evolutionary models, combined with both our transit parameters and previously-known spectroscopic results. We found that the absolute dimensions of the host star are $M_{\rm A}$=0.73$\pm$0.02 M$_\odot$, $R_{\rm A}$=0.70$\pm$0.01 R$_\odot$, log $g_{\rm A}$=4.61$\pm$0.02, $\rho_{\rm A}$=2.10$\pm$0.09 $\rho_{\odot}$, and $L_{\rm A}$=0.21$\pm$0.01 L$_\odot$. The planetary companion has $M_{\rm b}$=0.21$\pm$0.01 M$_{\rm Jup}$, $R_{\rm b}$=0.94$\pm$0.01 R$_{\rm Jup}$, log $g_{\rm b}$=2.77$\pm$0.02, $\rho_{\rm b}$=0.24$\pm$0.01 $\rho_{\rm Jup}$, and $T_{\rm eq}$=960$\pm$14 K. Our results agree well with standard models of irradiated gas giants with a core mass of 11.3 M$_{\oplus}$.