Transiting exocomets detected in broadband light by TESS in the $β$ Pictoris system

Abstract: We search for signs of falling evaporating bodies (FEBs, also known as exocomets) in photometric time series obtained for $\beta$ Pictoris after fitting and removing its $\delta$ Scuti type pulsation frequencies. Using photometric data obtained by the TESS satellite we determine the pulsational properties of the exoplanet host star $\beta$ Pictoris through frequency analysis. We then prewhiten the 54 identified $\delta$ Scuti p-modes and investigate the residual photometric time series for the presence of FEBs. We identify three distinct dipping events in the light curve of $\beta$ Pictoris over a 105-day period. These dips have depths from 0.5 to 2 millimagnitudes and durations of up to 2 days for the largest dip. These dips are asymmetric in nature and are consistent with a model of an evaporating comet with an extended tail crossing the disk of the star. We present the first broadband detections of exocomets crossing the disk of $\beta$ Pictoris, consistent with the predictions made 20 years earlier by Lecavelier Des Etangs et al. (1999). No periodic transits are seen in this time series. These observations confirm the spectroscopic detection of exocomets in Calcium H and K lines that have been seen in high resolution spectroscopy.

• The paper detects three significant transit events in β Pictoris, confirming exocomet activity through broadband photometric evidence.
• It employs MCMC statistical fitting and frequency analysis to isolate and model transit events after removing δ Scuti pulsations.
• The results support theoretical models of cometary tails, with asymmetric transit profiles and non-periodic occurrences reflecting dynamic orbits.

Detection of Transiting Exocomets in the $\beta$ Pictoris System Using TESS

The paper presented investigates the detection of transiting exocomets in the $\beta$ Pictoris system through observations made by the Transiting Exoplanet Survey Satellite (TESS). The research confirms and complements prior spectroscopic findings with broadband photometric evidence, providing a more comprehensive understanding of the system's dynamical processes and reinforcing the model predictions of cometary bodies transiting stellar disks.

The $\beta$ Pictoris system, known for its prominent debris disk and young age, continues to be an exemplary model for studying the formation and evolution of planetary systems. Prior studies have identified transient absorption features in the system, indicative of exocomets, via spectroscopic data. This paper capitalizes on photometric data from TESS, employing a methodological approach to isolate and analyze dips in the observed light curve of $\beta$ Pictoris, which are consequent to cometary transits.

A detailed frequency analysis was employed to model and subtract the impacts of $\delta$ Scuti pulsations of $\beta$ Pictoris, revealing residuals in the form of distinct dipping events. Over a span of 105 days, three prominent transit events were identified, characterized by depths ranging from 0.5 to 2 millimagnitudes and durations extending up to 2 days. These events exhibit asymmetric profiles, aligning with the theoretical models of exocomets possessing extensive tails passing in front of the star.

The researchers meticulously rule out instrumental artifacts and astrophysical false positives, reinforcing the assertion that these dips are indeed caused by exocomets. Utilizing an MCMC statistical fitting, the team models the largest transit event (identified at BTJD 1486.4) with parameters consistent with model simulations of cometary tails described by Lecavelier des Etangs et al., affirming the presence of a comet with an exponentially decaying tail in terms of optical depth.

This study does not find periodicity in the identified transits, which is reconcilable with the expectation of highly eccentric cometary orbits. The transverse velocity deduced from the model, although unexpectedly low relative to spectroscopically determined radial velocities, points to the complexity and variability in the dynamical evolution of these bodies within the system.

The implications of this work extend both practically, as exemplifying TESS's capability in exocomet detection, and theoretically, by contributing to the understanding of comet-star interactions in young stellar environments. This study opens avenues for further observational campaigns and inspires enhanced modelling efforts that integrate photometric and spectroscopic data for a holistic understanding of the dynamics governing debris-laden environments like that of $\beta$ Pictoris.

In anticipation of future developments, dedicated observational platforms may focus exclusively on such systems, benefitting from multi-wavelength approaches to discern the size distributions of cometary tails and refine orbital parameters. The gathering and subsequent analysis of a broader dataset will undoubtedly enrich the current paradigm, unraveling the intricate details of minor bodies' interactions within nascent planetary systems.