# Photometric investigation and orbital period analyses of the W UMa binaries FP Lyn, FV CVn and V354 UMa

## TL;DR

This study presents new photometric data and orbital period analyses of three W UMa binaries, revealing their contact nature, asymmetric light curves, and period variations likely caused by mass transfer and angular momentum loss.

## Contribution

It provides detailed photometric solutions, spot modeling, and orbital period analysis for FP Lyn, FV CVn, and V354 UMa, including the first investigation of their period variations.

## Key findings

- FP Lyn and V354 UMa show secular period increases due to mass transfer.
- FV CVn exhibits a cyclic period variation likely caused by a third body.
- All three systems are shallow contact binaries with specific mass ratios and fill-out factors.

## Abstract

New light curves and photometric solutions of FP Lyn, FV CVn and V354 UMa are presented. It is found that these three systems are W-subtype shallow contact binaries. In addition, it is obvious that the light curves of FP Lyn and V354 UMa are asymmetric. Therefore, a hot spot was added on the primary star of FP Lyn and a dark spot was added on the secondary star of V354 UMa. At the same time, we added a third light to the photometric solution of FP Lyn for the final result. The obtained mass ratios and fill-out factors are $q=1.153$ and $f=13.4\%$ for FP Lyn, $q=1.075$ and $f=4.6\%$ for FV CVn, $q=3.623$ and $f=10.7\%$ for V354 UMa. The investigations of orbital period of these three systems indicate that the periods are variable. FP Lyn and V354 UMa were discovered existing the secular increase component with a rate of $dp/dt=4.19\times10^{-7}$ d yr$^{-1}$ and $dp/dt=7.70\times10^{-7}$ d yr$^{-1}$ respectively, which are feasibly caused by the conservative mass transfer from the less massive component to the more massive component. In addition, some variable components were discovered for FV CVn, which is a rate of $dp/dt=-1.13\times10^{-6}$ d yr$^{-1}$ accompanied by a cyclic oscillation with amplitude and period of 0.0069 days and 10.65 yr. The most likely explanation for the long-term decrease is angular momentum loss. And the existence of an additional component is the most plausible explanation for the periodic variation.