# Time-Series Surveys and Pulsating Stars: The Near-Infrared Perspective

## TL;DR

This review discusses the benefits and challenges of near-infrared surveys for observing pulsating stars in the Milky Way, emphasizing the importance of understanding interstellar extinction for accurate mapping.

## Contribution

It provides a comprehensive overview of near-infrared surveys, analyzes the impact of extinction law uncertainties, and highlights the need for improved extinction characterization.

## Key findings

- Near-infrared surveys reach larger Galactic volumes than optical surveys.
- Interstellar extinction significantly affects observations even in near-infrared bands.
- Uncertainty in the extinction law hampers accurate correction and mapping.

## Abstract

The purpose of this review is to discuss the advantages and problems of near-infrared surveys in observing pulsating stars in the Milky Way. One of the advantages of near-infrared surveys, when compared to optical counterparts, is that the interstellar extinction is significantly smaller. As we see in this review, a significant volume of the Galactic disk can be reached by infrared surveys but not by optical ones. Towards highly obscured regions in the Galactic mid-plane, however, the interstellar extinction causes serious problems even with near-infrared data in understanding the observational results. After a review on previous and current near-infrared surveys, we discuss the effects of the interstellar extinction in optical (including {\it Gaia}) to near-infrared broad bands based on a simple calculation using synthetic spectral energy distribution. We then review the recent results on classical Cepheids towards the Galactic center and the bulge, as a case study, to see the impact of the uncertainty in the extinction law. The extinction law, i.e. the wavelength dependency of the extinction, is not fully characterized, and its uncertainty makes it hard to make the correction. Its characterization is an urgent task in order to exploit the outcomes of ongoing large-scale surveys of pulsating stars, e.g. for drawing a map of pulsating stars across the Galactic disk.