AAVSO: American Association of Variable Star Observers

Photometry, Period Study, and Light Curve Modeling of the HADS Variables BN Trianguli and V488 Geminorum

Volume 50 number 2 (2022)

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Kevin B. Alton
UnderOak Observatory, 70 Summit Avenue, Cedar Knolls, NJ 07927; kbalton@optonline.net


Multi-bandpass (BVIc) CCD-derived photometric data were acquired from BN Tri and V488 Gem (ATO J106.2184+10.4567) at Desert Blooms Observatory (DBO). Both of these pulsating variables are classified as high amplitude δ Scuti-type systems. Analysis of precise time-series light curve data from each target was accomplished using discrete Fourier transformation (DFT) which in both cases revealed a dominant fundamental mode (f0) of oscillation along with associated harmonics. Furthermore, BN Tri exhibited two other statistically meaningful but low amplitude independent pulsation modes, while V488 Gem may possess up to four other independent oscillations. New times of maximum (ToMax) produced from both targets were combined with other ToMax timings mined from other sources (SuperWASP, TESS, and AAVSO-VSX) in order to update their corresponding linear ephemerides. Preliminary evidence suggests a secular increase in the fundamental oscillation period of BN Tri between 1999 and 2021. In contrast, secular analysis of the fundamental pulsation period for V488 Gem (ATO J106.2184+10.4567) revealed a sinusoidal-like variation in the pulse timing differences. These residuals, believed to result from a light-travel time effect (LiTE), were fit using simplex optimization. The resulting LiTE simulation suggested that V488 Gem is a binary system with a stellar-sized object in an eccentric orbit (7.91 ± 0.09 y). The evolutionary status, age, and physical nature of both HADS variables were investigated using the PAdova and TRieste Stellar Evolution Code for generating stellar tracks and isochrones. The totality of results including residence in the Galactic thin disk, near solar metallicity, mass predictions, and effective temperature estimates firmly support classification for both stars as high amplitude \delta Scuti-type variables.