[Paper Review] Observing transiting exoplanets with the MicroObservatory: 43 new transit light curves of the hot Jupiter HAT-P-32b

Martin Fowler, Frank Sienkiewicz+2 more|arXiv (Cornell University)|Jul 27, 2020

Stellar, planetary, and galactic studies4 citations

TL;DR

This study presents 43 new transit light curves of the hot Jupiter HAT-P-32b observed over 7 years using the MicroObservatory robotic telescope network. It improves the system's ephemeris with a root-mean-square residual of 3.0 minutes, enhancing mid-transit time predictions for future space missions like JWST and ARIEL by up to 1.7 minutes, demonstrating the utility of small telescopes for exoplanet ephemeris maintenance and stellar variability studies.

ABSTRACT

Observations of 43 complete transits of the hot Jupiter exoplanet HAT-P-32b using the MicroObservatory 0.15-m robotic telescope network covering a period of 7 years are presented. Compared with the most recent ephemeris for the system, the precision of the mid-transit times yielded a root-mean-square value from the predicted model of 3.0 min. The estimated system parameters based on EXOFAST modelling are broadly consistent with those of the default parameter values listed in the NASA Exoplanet Archive. An updated orbital period of 2.15000815 +/- 0.00000013 d and ephemeris of 2458881.71392 +/- 0.00027 BJDTDB is consistent with recent studies of the system using larger telescopes. Using this updated ephemeris, the predicted mid-transit time for a notional observation of HAT-P-32b by the NASA JWST mission in mid-2021 is improved by 1.4 min compared with the discovery ephemeris and is ~8 times more precise. Likewise, the mid-transit time for an observation by the ESA ARIEL mission in 2020 is improved by 1.7 min. Thus, observations of transiting exoplanets by MicroObservatory and other users of small telescopes can contribute to the maintenance of the ephemerides of targets for future space-based telescope missions. We also note that one of the HAT-P-32 field stars is a {\\delta} Scuti pulsating variable and that characterization using the same observations as this study further demonstrates the utility of MicroObservatory for the observation of stellar variability, whilst simultaneously observing transiting exoplanets for ephemeris maintenance.

Motivation & Objective

• To maintain accurate mid-transit time predictions for HAT-P-32b using ground-based observations from small telescopes.
• To assess the precision and reliability of transit timing measurements from the MicroObservatory network for exoplanet systems.
• To evaluate the utility of small telescopes in supporting future space-based exoplanet missions through improved ephemerides.
• To investigate stellar variability in the HAT-P-32b field, identifying a δ Scuti pulsating variable star.

Proposed method

• Observing 43 complete transits of HAT-P-32b using the MicroObservatory 0.15-m robotic telescope network over a 7-year baseline.
• Reducing and analyzing photometric light curves from the telescope network to extract mid-transit times.
• Fitting the observed transit times to a linear ephemeris model to refine orbital period and mid-transit time.
• Applying the EXOFAST modeling package to estimate system parameters and validate consistency with archival data.
• Comparing the updated ephemeris with predictions from the discovery ephemeris and recent studies using larger telescopes.
• Characterizing a field star as a δ Scuti pulsating variable using the same photometric data set.

Experimental results

Research questions

• RQ1 Can small robotic telescopes like MicroObservatory provide sufficiently precise transit timing measurements to support future space-based exoplanet missions?
• RQ2 How does the updated ephemeris for HAT-P-32b compare with the discovery ephemeris and recent high-precision studies using larger telescopes?
• RQ3 To what extent do the mid-transit time predictions for HAT-P-32b improve for JWST and ARIEL when using the new ephemeris?
• RQ4 What is the impact of stellar variability in the field of view on transit timing and photometric analysis?
• RQ5 Can the same photometric data used for exoplanet transit monitoring also enable the detection and characterization of stellar pulsations?

Key findings

• The root-mean-square residual between observed and predicted mid-transit times is 3.0 minutes, indicating high precision in the updated ephemeris.
• The updated orbital period is 2.15000815 ± 0.00000013 days, consistent with values from larger telescopes and the NASA Exoplanet Archive.
• The mid-transit time ephemeris is 2458881.71392 ± 0.00027 BJDTDB, improving prediction accuracy for future missions.
• For a notional JWST observation in mid-2021, the predicted mid-transit time is improved by 1.4 minutes compared to the discovery ephemeris.
• For an ARIEL observation in 2020, the improvement is 1.7 minutes, demonstrating enhanced mission planning precision.
• One field star is identified as a δ Scuti pulsating variable, confirming the dual utility of the data for exoplanet and stellar variability science.