EXOA14 | Transit timing trends and light curve archiving: challenges for the next fifty years

EXOA14

Transit timing trends and light curve archiving: challenges for the next fifty years

Convener: Elisabeth Adams | Co-conveners: Filip Walter, Günther Wuchterl, Lauren Sgro, Brian Jackson

Orals MON-OB2

| Mon, 08 Sep, 09:30–10:30 (EEST)

Room Neptune (rooms 22+23)

Posters TUE-POS

| Attendance Tue, 09 Sep, 18:00–19:30 (EEST) | Display Tue, 09 Sep, 08:30–19:30

Finlandia Hall foyer, F236

Vimeo: EXOA14 – Transit timing trends and light curve archiving: challenges for the next fifty years

A quarter century after the first exoplanet transit was observed, there are now over 4000 known transiting exoplanets. Many planets now have 100-1000+ transit light curves stretching spanning 3+ decades thanks to prediscoveries. This historical record provides a valuable resource to search for temporal changes over both short and long timescales, leading to many subfields of exoplanetary research including: finding small companion planets using transit timing variations; identifying changing orbital periods due to orbital decay, precession, or other effects; searching for seasonal atmospheric changes; tracking starspot crossings; or searching for exomoons.

All of these endeavors, however, require precise transit record-keeping for reliable results, since they must combine results from many instruments and research groups. However, the steady stream of new data combined with the lack of any authoritative archive makes it difficult even to compile a complete and accurate list of past observations. Worse, errors that have crept into the scientific literature are hard to eliminate, since they may pass through multiple published works before being identified. It is also often not possible to return to the original data since many papers continue to be published without making public transit light curve data, sometimes without even providing individual transit midtimes.

This session aims to bring the community together to discuss problems relating to long-term transit studies. Relevant session topics include: (1) the challenges of precise and accurate timing, including best practices for small and citizen science telescopic observations; (2) recommendations for best publication and citation practices, including transit light curve archiving and proper identification and tracking of prior observations; and (3) any research topics in long-term transit studies that would benefit from improved archival practices. We also welcome presentations on long-term studies of planetary occultations (or secondary eclipses), which are subject to the same archival issues and are even less likely to have publicly available source data.

This session is co-organized by both the Exoplanet Transit Database and the Short Period Period Group, or SuPerPiG, which is leading a NASA-funded pilot effort to investigate, compile, and archive lightcurves from the transit literature.

Session assets

Orals: Mon, 8 Sep, 09:30–10:30 | Room Neptune (rooms 22+23)

Chairpersons: Brian Jackson, Elisabeth Adams

09:30–09:42

EPSC-DPS2025-1050

On-site presentation

Reassessing possibly doomed worlds

Elisabeth Adams, Brian Jackson, Amanda Sickafoose, Jeffrey Morgenthaler, Rachel Huchmala, Malia Barker, Hannah Worters, and Marvin Rothmeier

The first exoplanet with a decaying orbit, WASP-12 b, was observed to not follow a linear transit ephemeris after eight years of observational data (Maciejewski et al. 2016). In the decade since that discovery, at least 18 other planets have been presented with evidence of varying quality for decreasing orbital periods, and thus possible orbital decay, although none has yet proven as compelling as WASP-12 b. The challenge for detection of orbital decay is that it is a small signal that takes years to build up over repeated observations, and by necessity data from many instruments and research groups must be combined. Deep dives into several initially promising systems have led instead to the identification of errors in the published literature (Adams et al. 2024) and the elimination of some candidates.

We report on the ongoing efforts of the Short Period Planet Group (SuPerPiG) to monitor over 70 ultra-hot Jupiters for signs of orbital decay. New data include hundreds of new midtimes derived from ground-based transit observations and from TESS observations where available. These are combined with data from the literature and from citizen scientists, such as the Exoplanet Transit Database (ETD). A careful literature review has been conducted for some promising systems, with the goal of creating a cleaned archival data set so that exoplanets that are likely to exhibit orbital decay may continue to be monitored for decades to come. We find that most ultra-hot Jupiters do not exhibit orbital decay, including a sizeable population that would have detected WASP-12 b like decay if it were happening. We also present the most promising systems for long-term timing deviations using the current data.

How to cite: Adams, E., Jackson, B., Sickafoose, A., Morgenthaler, J., Huchmala, R., Barker, M., Worters, H., and Rothmeier, M.: Reassessing possibly doomed worlds, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1050, https://doi.org/10.5194/epsc-dps2025-1050, 2025.

09:42–09:54

EPSC-DPS2025-215

ECP

On-site presentation

Doomed Worlds II: Reassessing Suggestions of Orbital Decay for TrES-5 b

Marvin Rothmeier, Elisabeth R. Adams, Brian Jackson, Karsten Schindler, André Beck, Malia Barker, Jeffrey P. Morgenthaler, Amanda A. Sickafoose, Luigi Mancini, John Southworth, and Daniel Evans

TrES-5 b is one of only three ultra-hot Jupiters with suggestions of a possibly decreasing orbital period that have persisted through multiple independent analyses (Maciejewski et al. 2021; Hagey et al. 2022; Ivshina & Winn 2022; Wang et al. 2024; Yeh et al. 2024). While WASP-12 b’s decreasing period is well-explained by tidally induced orbital decay (Patra et al. 2017), and stellar acceleration has been proposed for WASP-4 b (Bouma et al. 2020), the cause of the apparent trend for TrES-5 b has not been satisfactorily explained. This work extends the previous observations by four years with 14 new ground-based transits from 2016-2024 and two newly-published midtimes for data from 2007 and 2009. Four TESS Sectors (75, 77, 82, and 84) have also been included for the first time. With the new data, the case for a decreasing orbital period is much weaker than before. The revised rate of period change, P_dot = 4.2 +- 2.2 ms/yr^-1, is less than half that found in previous work and the preference for a quadratic model over a linear model, as measured through ∆BIC, has been falling since 2020, with a current value of 6. Furthermore, these results are not robust to outliers; removing a single early transit midtime causes the effect to vanish (∆BIC= −1). No other significant periodic signals in the transit timing data are identified. The current data are well explained by a linear ephemeris, implying that there is no orbital decay for TrES-5 b.

How to cite: Rothmeier, M., Adams, E. R., Jackson, B., Schindler, K., Beck, A., Barker, M., Morgenthaler, J. P., Sickafoose, A. A., Mancini, L., Southworth, J., and Evans, D.: Doomed Worlds II: Reassessing Suggestions of Orbital Decay for TrES-5 b, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-215, https://doi.org/10.5194/epsc-dps2025-215, 2025.

09:54–10:06

EPSC-DPS2025-1287

Virtual presentation

Probing Transit Timing Variations Amid Heteroscedasticity: Lessons from HAT-P-7b and TrES-2b

Ozgur Basturk, Adrian Barker, Selim O. Selam, Craig D. Duguid, Ahmet C. Kutluay, Ufuk Senguler, Sina A. Turgay, Selcuk Yalcinkaya, Mohammad Niaei, Burak Duru, and Anisha Zamir

It has been more than 25 years since the first light curve of a planetary transit has been published (Charbonneau et al. 2000). Since then, thousands of light curves have been published for many of the discovered planets. Although photometric observation of a planetary transit is conceptually straightforward, variations in data reduction, modeling approaches, and analysis tools have introduced significant heteroscedasticity into the resulting light curves — and consequently into the derived parameters. Among these, the timing of mid-transit is particularly sensitive, as its measurement and associated uncertainty are highly model-dependent. Yet mid-transit times form the backbone of Transit Timing Variation (TTV) analyses, through which one can probe the presence of additional planetary companions, tidal interactions with the host star, apsidal precession, and magnetic activity.

Properly addressing the sources of heteroscedasticity in TTV datasets is essential for disentangling genuine physical signals from observational systematics. In practice, this manifests in TTV diagrams as short-term scatter exceeding the quoted timing uncertainties — particularly between datasets acquired with different instruments, reduction pipelines, or modeling techniques.

We have been monitoring a sample of hot Jupiter systems (Basturk et al. 2020, 2022, 2023; Yalcinkaya et al. 2024), some of which are candidates for orbital decay due to strong tidal interactions. To date, definitive evidence for orbital decay has been reported in only two systems: WASP-12b (Yee et al. 2020) and WASP-4b (Basturk et al. 2025, and references therein). To systematically investigate the heteroscedasticity issue in TTV data, we focused on two well-observed systems, HAT-P-7 and TrES-2. Both were continuously monitored by the Kepler spacecraft during its primary mission, supplemented by numerous ground-based observations and, more recently, multiple sectors of TESS photometry.

We compiled all available transit light curves for these systems, modeled them uniformly using the EXOFAST suite (Eastman et al. 2013), and derived mid-transit times to construct homogeneous TTV datasets for each planet. Our analysis revealed significant variance discrepancies between different data subsets — often exceeding the reported timing uncertainties. In this study, we present our methodology for addressing this issue and discuss the implications for interpreting the observed TTV signals in the context of tidal interaction theory.

How to cite: Basturk, O., Barker, A., Selam, S. O., Duguid, C. D., Kutluay, A. C., Senguler, U., Turgay, S. A., Yalcinkaya, S., Niaei, M., Duru, B., and Zamir, A.: Probing Transit Timing Variations Amid Heteroscedasticity: Lessons from HAT-P-7b and TrES-2b, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-1287, https://doi.org/10.5194/epsc-dps2025-1287, 2025.

10:06–10:18

EPSC-DPS2025-2059

ECP

On-site presentation

Characterizing transit timing and duration variations caused by systemic proper motion

Simone Hagey, Uyen Pham, and Aaron Boley

Gravitational interactions between stars and planets, including mutual planet-planet interactions, cause planetary orbits to change with time. Such changes include apsidal or nodal precession, i.e., variations in the alignment of the orbit, as well as deviations in a planet's semi-major axis, eccentricity, or inclination. Over decade-long time periods, those orbital changes give rise to small but detectable observational signatures, especially among short-period planets, such as drifts in the timing and duration of exoplanet transits. If characterized, these secular orbital changes can reveal a wealth of information about exoplanetary systems, including insights into planetary interiors.

However, exoplanet host stars are in constant motion relative to the Sun, gradually altering both their distance from Earth and the apparent orientation of their planetary orbits in the sky. This systemic proper motion introduces additional transit timing and duration variations that could mimic true signatures of orbital evolution, risking misinterpretation of the underlying physical mechanisms. As the number of transiting exoplanets with observations spanning decades continues to grow, it will become increasingly important to determine whether the proper motion of transiting exoplanet host stars plays a significant role in observing secular variations.

Here, we present the first large-scale statistical analysis of proper motion-induced transit timing and duration variations, combining precise astrometric measurements from the Gaia space telescope with stellar and planetary parameters from the NASA Exoplanet Archive for a population of over 4000 transiting exoplanets. We find that in many cases, these secular trends are measurable on decade timescales and can dominate signatures of true dynamical evolution, particularly in the case of transit durations.

The goal of this work is not only to highlight the significance of these effects across the exoplanet population, but also to provide a database to serve as a practical tool for aiding long-term orbit monitoring. In this talk, we provide an update on the project, highlight systems of particular interest, and discuss the broader implications for studies of orbital evolution and ephemeris refinement.

How to cite: Hagey, S., Pham, U., and Boley, A.: Characterizing transit timing and duration variations caused by systemic proper motion, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-2059, https://doi.org/10.5194/epsc-dps2025-2059, 2025.

10:18–10:30

EPSC-DPS2025-857

ECP

On-site presentation

Constraining The Parameters of an Earth-Sized Exoplanet Orbiting an M3 Star

Francis Zong Lang and Brice-Olivier Demory and the TOI4616

Context. The population of rocky exoplanets is abundant, and cool stars such as M dwarfs provide a unique
opportunity to detect these objects, which could have implications for the study of astrobiology. Both theoretical models
and observations have shown that these tend to lie in the host stars’ habitable zone. The proximity of such planets
to their host star also provides an opportunity for atmospheric studies.
SAINT-EX (Searching And characterisINg Transiting EXoplanets) consists of a one-meter telescope optimized to
obtain high-precision light curves of transiting planets orbiting ultracool stars. The two main objectives of SAINT-
EX are: -The search for terrestrial exoplanets orbiting ultra-cool stars, and -To give ground-based support to the
ESA CHEOPS mission. Another outcome of this mission is the characterization of orbital periods and stellar
variability in brown dwarfs and ultra-cool stars.
Aims. TOI4616, a system with a planet of size 1.22R and an orbital period of 1.554 days, was detected by the
NASA TESS mission and later characterized with the SAINT-EX telescope. We study this system to characterize
the properties of the planet and its host star and use transit photometry to constrain critical parameters of the planet,
such as its mass and orbital dynamics. Employing a series of aperture and PSF photometry methods to determine
the crowding metric and the flux fraction to compute an accurate transit depth obtained from the SAINT-EX light
curves and constrain the necessary planetary parameters.
Methods. We make use of the Monte-Carlo technique to compare the transit depth with the data from SAINT-EX
and those from the TESS
Results. The validation of an orbital period of 1.554 days reinforces our understanding of rocky exoplanets around
low-mass stars. We expect TOI4616 to be a rocky exoplanet with the possibility of hosting an atmosphere. Transmission spectroscopy analysis might offer insights into the exoplanet’s atmosphere, revealing potential
molecular constituents. Investigating the planet’s stability in this system would reveal potential interactions with
other bodies and the system’s long-term stability.

How to cite: Zong Lang, F. and Demory, B.-O. and the TOI4616: Constraining The Parameters of an Earth-Sized Exoplanet Orbiting an M3 Star, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-857, https://doi.org/10.5194/epsc-dps2025-857, 2025.

Posters: Tue, 9 Sep, 18:00–19:30 | Finlandia Hall foyer

Display time: Tue, 9 Sep, 08:30–19:30

Chairperson: Elisabeth Adams

F236

EPSC-DPS2025-723

On-site presentation

Metrics for Optimizing Searches for Orbital Precession and Tidal Decay via Transit- and Occultation-Timing

Brian Jackson, Elisabeth Adams, Rachel Huchmala, Malia Barker, Marvin Rothmeier, Jeffrey Morgenthaler, and Amanda Sickafoose

Short-period exoplanets may exhibit orbital precession driven by several different processes, including tidal interactions with their host stars and secular interactions with additional planets. This motion manifests as periodic shifts in the timing between transits which may be detectable via high-precision and long-baseline transit- and occultation-timing measurements. Detecting precession and attributing it to a particular process may constrain the tidal responses of planets and point to the presence of otherwise undetected perturbers. However, over relatively short timescales, orbital decay driven by the same tidal interactions can induce transit-timing signals similar to the precession signal, and distinguishing between the two processes requires robust assessment of the model statistics. In this context, occultation observations can help distinguish the two signals, but determining the precision and scheduling of observations sufficient to meaningfully contribute can be complicated. In this presentation, we will draw on earlier work focused on searches for tidal decay to map out simple metrics that facilitate detection of precession and how to distinguish it from tidal decay. We will also discuss properties for a short-period exoplanet system that can maximize the likelihood for detecting such signals and prospects for contributions from citizen science observations.

How to cite: Jackson, B., Adams, E., Huchmala, R., Barker, M., Rothmeier, M., Morgenthaler, J., and Sickafoose, A.: Metrics for Optimizing Searches for Orbital Precession and Tidal Decay via Transit- and Occultation-Timing, EPSC-DPS Joint Meeting 2025, Helsinki, Finland, 7–13 Sep 2025, EPSC-DPS2025-723, https://doi.org/10.5194/epsc-dps2025-723, 2025.