Identifying low-amplitude pulsating stars through microlensing observations

Abstract

One possibility for detecting low-amplitude pulsational variations is through gravitational microlensing. During a microlensing event, the temporary brightness increase leads to improvement in the signal-to-noise ratio, and thereby better detectability of pulsational signatures in light curves. We explore this possibility under two primary considerations. The first is when the standard point-source and point-lens approximation applies. In this scenario, dividing the observed light curve by the best-fitted microlensing model leads to residuals that result in pulsational features with improved uncertainties. The second is for transit events (single lens) or caustic crossing (binary lens). The point-source approximation breaks down, and residuals relative to a simple best-fitted microlensing model display more complex behavior. We employ a Monte-Carlo simulation of microlensing of pulsating variables toward the Galactic bulge for the surveys of OGLE and of KMTNet. We demonstrate that the efficiency for detecting pulsational signatures with intrinsic amplitudes of <0.25 mag during single and binary microlensing events, at differences in χ2 of Δχ2 > 350, is $\sim 50-60\%$. The maximum efficiency occurs for pulsational periods P ≃ 0.1 − 0.3 days. We also study the possibility that high-magnification microlensing events of non-radially pulsating stars (NRPs) could be misinterpreted as planetary or binary microlensing events. We conclude that small asymmetric features around lightcurve peaks due to stellar pulsations could be misdiagnosed with crossing (or passing close to) small caustic curves.

Wavelet Transforms of Microlensing Data: Denoising, Extracting Intrinsic Pulsations, and Planetary Signals

“…and ξ ä [0, 360°]. We set t 0 = 0 for all simulated events and determine the photometric errors according to the OGLE observations (see Figure 1 of Sajadian et al 2021). We generate data points by considering different cadences and assuming continuous observations during [−3.5t E , 3.5t E ].…”

“…We note that discerning stellar pulsations could be done well for continuous data without large gaps (see the right-hand panel in Figure 6). Intrinsic pulsations change the shape of light curves, and as a result, the modeling of microlensing events with noisy stellar pulsations will offer incorrect best-fit parameters (see, e.g., Sajadian & Ignace 2020a, 2020bSajadian et al 2021).…”

Variation of the stellar color in high-magnification and caustic-crossing microlensing events

“…Such measurements are done by multiband follow-up microlensing observations with the ROME/REA project. More recently, the chromatic deviations in HM or CC microlensing events due to radially and non-radially pulsating source stars were studied extensively (Sajadian & Ignace 2020a,b;Sajadian et al 2021). All of these studies emphasize the importance of detection and characterization of chromatic deviations during microlensing events.…”