Comparison of two different extinction laws with Hipparcos observations

TL;DR

This study compares two interstellar extinction laws using Hipparcos data, constructing an extinction map of the galactic plane and evaluating model accuracy in predicting observed stellar properties.

Contribution

It introduces a new extinction map based on an inverse method and compares two extinction laws, showing improved fit with Hipparcos observations.

Findings

The extinction model better fits Hipparcos data than previous models.

An analytic expression for extinction as a function of galactic longitude and distance is provided.

Current models still lack the detail of a comprehensive extinction map.

Abstract

Interstellar absorption in the galactic plane is highly variable from one direction to another. In this paper colour excesses and distances from a new open cluster sample are used to investigate the spatial distribution of the interstellar extinction. An inverse method (Tarantola & Valette, 1982) is used to construct the extinction map in the galactic plane below $|b| < 10^{o}$. The $A_{v} (r,l) $ diagrams are compared with those derived from individual stars (Arenou et al. 1992, Neckel & Klare 1980). An analytic expression for the interstellar extinction as a function of galactic longitude and distance in the solar neighborhood is given. The comparison of the model predictions with Hipparcos observations in the 4-dimensional space of ($V$, $B-V$, $H_v$, $r$) shows that our extinction model provides a better fit to the data. However, a new and more detailed extinction model is still lacking.