An extremely low mid-infrared extinction law toward the Galactic Center and 4% distance precision to 55 classical Cepheids

TL;DR

This study derives an extremely low mid-infrared extinction law toward the Galactic Center using 55 Cepheids, achieving 4% distance precision and estimating the solar Galactocentric distance with high accuracy.

Contribution

It provides the first detailed measurement of a very low mid-infrared extinction law toward the Galactic Center and refines the distance to the Galactic Center with unprecedented precision.

Findings

Extremely low and steep mid-infrared extinction law determined.

Achieved 4% distance precision for 55 Cepheids.

Estimated the solar Galactocentric distance as 8.10±0.19±0.22 kpc.

Abstract

Distances and extinction values are usually degenerate. To refine the distance to the general Galactic Center region, a carefully determined extinction law (taking into account the prevailing systematic errors) is urgently needed. We collected data for 55 classical Cepheids projected toward the Galactic Center region to derive the near- to mid-infrared extinction law using three different approaches. The relative extinction values obtained are AJ/AKs = 3.005, AH/AKs = 1.717, A[3.6]/AKs = 0.478, A[4.5]/AKs = 0.341, A[5.8]/AKs = 0.234, A[8.0]/AKs = 0.321, AW1/AKs = 0.506, and AW2/AKs = 0.340. We also calculated the corresponding systematic errors. Compared with previous work, we report an extremely low and steep mid-infrared extinction law. Using a seven-passband 'optimal distance' method, we improve the mean distance precision to our sample of 55 Cepheids to 4%. Based on four confirmed Galactic Center Cepheids, a solar Galactocentric distance of R_0 = 8.10\pm0.19\pm0.22 kpc is determined, featuring an uncertainty that is close to the limiting distance accuracy (2.8%) for Galactic Center Cepheids.