V1224 Cas - an EL CVn-type Eclipsing Binary Consisting of a Helium White Dwarf Precursor and a Delta Scuti Pulsator

TL;DR

This paper reports the discovery and analysis of V1224 Cas, an EL CVn-type eclipsing binary with a pulsating Delta Scuti star and a low-mass pre-He white dwarf, including spectroscopic and photometric characterization.

Contribution

It introduces V1224 Cas as a new EL CVn-type binary candidate with detailed component parameters and evidence of Delta Scuti pulsations, expanding the known types of such systems.

Findings

V1224 Cas is a short-period detached binary with a low-mass pre-He white dwarf.

The primary star is an A3-type with significant pulsations.

The system exhibits multi-periodic light variations consistent with Delta Scuti pulsations.

Abstract

We report the discovery of a new eclipsing EL CVn-type binary, consisting of a $\delta$ Sct-type pulsator and a thermally bloated low-mass pre-He white dwarf (WD). Spectroscopy and time-series $BV$ photometry of V1224 Cas were carried out. The spectroscopy reveals a spectral type of A3 for the star. Light-curve modelling indicate that V1224 Cas is a short-period detached system containing a possible low-mass WD with an effective temperature of about 9516 K. Based on the effective temperature and the surface gravity of the A-type primary star from the spectroscopic results, the absolute parameters of the components were estimated as: $M_{P}$=2.16$\pm$0.22$M_{\sun}$, $R_{P}$=3.54$\pm$0.12$R_{\sun}$, $L_{P}$=55.9$\pm$6.9$L_{\sun}$, $M_{S}$=0.19$\pm$0.02$M_{\sun}$, $R_{S}$=0.97$\pm$0.04$R_{\sun}$, and $L_{S}$=6.9$\pm$0.6$L_{\sun}$. We therefore introduce V1224 Cas as a new EL CVn-type binary candidate. The light curves in both filters all show multi-periodic pulsations, superimposed on binary effects. We performed a preliminary frequency analysis of the light residuals after removing the synthetic eclipsing curve from the original observational data. The results suggest that the rapid light variations among the light curves could be attributed to the $\delta$ Sct-type primary component. We therefore conclude that V1224 Cas is very likely a WD+$\delta$ Sct binary.