Phosphorus (P) is of particular interest in astrobiology and galactic chemical evolution, and this element plays crucial roles in various biological materials such as genes (DNA and RNA) that are required in all kinds of life, at least, on Earth. However, measurements of the P abundance have been scarcely done. This is because P shows no absorption lines in the optical range, while there are a few lines available in the UV and near-IR ranges. Recent studies making use of a couple of near-IR lines are increasing the measurements of P in nearby stars, mostly within 200 pc. This program aims to extend the mapping of the P abundance to over several kpc by observing Cepheid variables. They show tight radial abundance gradients in various elements as functions of the Galactocentric distance. With this program, we would be able to present the gradient of the Cepheids’ P abundance and compare its slope with those in other elements for the first time. The difference in the slopes in various elements would reveal the difference in chemical evolution, giving crucial information on cosmic nucleosynthesis. Cepheids are young, 10–200 Myr old, and their abundances would trace the present-day distribution of phosphorus in the Milky Way, which serves as the basic input to astrobiology and astrochemistry.
This document was translated from LATEX by HEVEA.