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.
Highlights
What we call “near-infrared” here is the wavelength range covered by the photometric bands of JHK
APOGEE and its successor APOGEE-2 ([43]) together with other modern near-IR high-resolution spectrographs like GIANO ([74]) and WINERED ([34, 75]) will play important roles in collecting detailed information such as radial velocities and chemical abundances of pulsating stars, but this is beyond the scope of this review
The SED affected by a large extinction, keeps more photons in the longer wavelength part of the G band, as illustrated in Figure 1, so that the sensitivity to the extinction gets closer to that of a photometric band at for a longer-λ range
Summary
What we call “near-infrared” (hereafter near-IR) here is the wavelength range covered by the photometric bands of JHK. The Spitzer Legacy Program “Surveying the Agents of a Galaxy’s Evolution” (SAGE, [55]) and its related programs (SAGE-Var, in particular; [79]) collected a comprehensive dataset in the mid IR for pulsating stars and other objects in the Magellanic Clouds ([77,78,79]) In this proceedings book, Whitelock et al ([102]) discuss mid-IR characteristics of large amplitude variables in the LMC and IC 1613 by combining the SAGE-Var data and other datasets. APOGEE and its successor APOGEE-2 ([43]) together with other modern near-IR high-resolution spectrographs like GIANO ([74]) and WINERED ([34, 75]) will play important roles in collecting detailed information such as radial velocities and chemical abundances of pulsating stars, but this is beyond the scope of this review
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