# Finite size effects on the light curves of slowly-rotating neutron stars

## TL;DR

This study investigates how the size and shape of hot spots on slowly-rotating neutron stars influence their light curves, revealing when simplified models are adequate and how spot geometry impacts observational signals.

## Contribution

It introduces a detailed analysis of the effects of hot spot size and shape on neutron star light curves, extending beyond point-like approximations.

## Key findings

- Point-like approximation valid for spots with opening angles less than 5°
- Annular spots produce similar light curves to circular spots for angles less than 35°
- Light curve shape depends significantly on hot spot geometry and size

## Abstract

An important question when studying the light curves produced by hot spots on the surface of rotating neutron stars is, how might the shape of the light curve be affected by relaxing some of the simplifying assumptions that one would adopt on a first treatment of the problem, such as that of a point-like spot. In this work we explore the dependence of light curves on the size and shape of a single hot spot on the surface of slowly-rotating neutron stars. More specifically, we consider two different shapes for the hot spots (circular and annular) and examine the resulting light curves as functions of the opening angle of the hot spot (for both) and width (for the latter). We find that the point-like approximation can describe light curves reasonably well, if the opening angle of the hot spot is less than $\sim 5^\circ$. Furthermore, we find that light curves from annular spots are almost the same as those of the full circular spot if the opening angle is less than $\sim 35^\circ$ independently of the hot spot's width.