Abstract
Abstract Magnetospheric clouds have been proposed as explanations for depth-varying dips in the phased light curves of young, magnetically active stars such as σ Ori E and RIK-210. However, the stellar theory that first predicted magnetospheric clouds also anticipated an associated mass-balancing mechanism known as centrifugal breakout for which there has been limited empirical evidence. In this paper, we present data from the Transiting Exoplanet Survey Satellite, Las Cumbres Observatory, All-Sky Automated Survey for Supernovae, and Veloce on the 45 Myr M3.5 star TIC 234284556, and propose that it is a candidate for the direct detection of centrifugal breakout. In assessing this hypothesis, we examine the sudden (∼1 day timescale) disappearance of a previously stable (∼1 month timescale) transit-like event. We also interpret the presence of an anomalous brightening event that precedes the disappearance of the signal, analyze rotational amplitudes and optical flaring as a proxy for magnetic activity, and estimate the mass of gas and dust present immediately prior to the potential breakout event. After demonstrating that our spectral and photometric data support a magnetospheric cloud and centrifugal breakout model and disfavor alternate scenarios, we discuss the possibility of a coronal mass ejection or stellar wind origin of the corotating material and we introduce a reionization mechanism as a potential explanation for more gradual variations in eclipse parameters. Finally, after comparing TIC 234284556 with previously identified “flux-dip” stars, we argue that TIC 234284556 may be an archetypal representative of a whole class of young, magnetically active stars.
Highlights
Young ( 100 Myr) stars have important implications for planet formation, evolution, and habitability because they tend to be magnetically active (e.g. Feigelson et al 1991; Vidotto et al 2014b) with strong magnetic fields, their planets tend to be rapidly evolving (Mann et al 2020), and their protoplanetary disks may not yet have dissipated (e.g. Williams & Cieza 2011)
We have presented our analysis of TESS Input Catalog (TIC) 234284556, a 45 Myr M dwarf, that has transit-like dips that change in depth and duration over two sectors of Transiting Exoplanet Survey Satellite (TESS) data
Besides more gradual depth and duration variations that occur over ∼10 day timescales, we take note of a sudden disappearance of the dip over a ∼1 day period—and see the dip reappear in Las Cumbres Observatory (LCO) data about 100 days later
Summary
Young stars exhibit many different classes of photometric variability. One type is the quasi-periodic dimming events of the “dipper” stars, likely caused by nonuniformly distributed gas and dust in the protoplanetary disk (Bodman et al 2017; Cody & Hillenbrand 2010; Ansdell et al 2016). Townsend et al (2013) did not detect any photometric evidence of a breakout event around σ Ori E — nor did the more recent work of Shultz et al (2020) in spectroscopic data spanning 20 years around one of σ Ori E’s B-type analogs — leading to to a consideration of alternate mechanisms, such as the diffusion-plusdrift model of Owocki & Cranmer (2018). We observe a 1.2%-deep dip that had been present in data from the previous 24 days disappear within a ∼1-day interval We interpret this as evidence for a potential centrifugal breakout event, with more gradual changes in eclipse parameters hinting at a separate role for an additional mass-balancing mechanism.
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