From multicolor-photometric observations to a guaranteed mass of AL Cas

Abstract

We utilize the PAdova and TRieste Stellar Evolution Code (PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters. Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the Wilson-Devinney (W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary (f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference ΔT = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe (DCRL method) and depending on calculation of the W-D code (DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M 1 = 1.19±0.23 M ⊙ with M 2 = 0.76±0.18 M ⊙ by the DCRL method and M 1 = 1.22±0.26 M ⊙ with M 2 = 0.78±0.20 M ⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period (P orb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the (O – C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body (M 3 sin i′ = 0.279 M ⊙) is derived from our two methods.

A study of the physical properties of an active asteroid (6478 Gault)

“…The Yunnan Faint Object Spectrograph and Camera (YFOSC) mounted on the Cassegrain telescope of 2.4 m aperture can quickly switch from photometry to spectroscopy. The detailed parameters of the telescope and YFOSC can be found in Wang et al (2019). We used Grism 3, which provides a relatively low dispersion (R ∼ 2000 at 600 nm pixel −1 ) and wide wavelength coverage (3400 ∼ 9100Å).…”

R-mode instability in compact stars

“…The instability window of neutron star(NS) is plotted with n = 1 polytrope. For the strange star(SS) and color-flavor-locked phase strange star(CSS), the corresponding EOSs are described in [55] . Above the critical frequency, the growth of the r-modes due to gravitational wave(GW) emission is the most dominant effect and the star emit GW and lose angular momentum until the effect of viscosities is the dominant one.…”

“…Most of the uncertainty related to the r-mode instability has to do with its damping mechanisms. Previous studies have tried to constrain the physics behind the r-mode instability of compact stars, especially the EOS of cold dense matter or the additional damping mechanisms(exotic matter [55], the viscous Ekman layer [24,25], Mutual friction [56,57] ), by comparing the r-mode instability windows with the observational data of the spin frequency and surface temperature of the compact stars [16,44,57,58,59].…”

“…With the constraints from GW170817 [60,61,62], investigations on the r-mode instability window of SSs with unpaired and CFL phase strange quark matter (SQM) are discussed in [55], especially the effect of shear viscosity due to the existence of a crust. The r-mode instability windows for CSS with different energy gaps and effective bag constants are given out in Figure 2.…”

“…For the CSSs, the damping mechanisms due to the existence of the crust are important for us to consider when drawing any conclusions. As we can see from these works [44,55,56,57], the "minimal" model has been described, and that is often considered in compact star physics, needs to be re-evaluated and additional physics must be included. And the urgent need for an improved understanding of the various elements in the model of r-mode instability.…”