A catalog of early-type stars toward the Galactic center

TL;DR

This study conducted a large-scale survey of early-type stars toward the Galactic center to analyze their kinematics and determine the nature of the Sagittarius spiral arm, providing insights into its structure and star formation activity.

Contribution

It presents a comprehensive catalog of early-type stars with estimated distances and extinctions, enabling the study of the Galactic structure and spiral arm characteristics.

Findings

Identified 9571 early-type star candidates beyond the Sagittarius arm

Detected increased absorption indicating the presence of the Sagittarius arm at certain distances

Provided a large dataset for future kinematic and structural analysis of the Galactic center region

Abstract

It is still unclear whether the Sagittarius spiral arm is a major spiral arm in the Galaxy or whether it just outlines a region of enhanced star formation because of the local compression of gas. The best way to separate these scenarios out is to study the kinematics across the arm to determine the velocity perturbation it induces. A survey of early-type stars in the direction of the Galactic center is performed covering an area of 100 square degrees with the aim of identifying candidates for a radial velocity study. Objective prism plates were obtained with the 4deg prism on the ESO Schmidt telescope using IIaO, 4415, and IIIaJ emulsions. The plates were digitized and more than 100k spectra were extracted down to a limiting magnitude of B = 15m. The spectra were cross-correlated with a template with Balmer lines, which yielded a candidate list of 12675 early-type stars. Magnitudes and equivalent widths of strong lines were calculated from the spectra, which allowed us to estimate the individual extinctions and distances for 11075 stars. The survey identified 9571 candidate stars with a spectral type earlier than A1 and B < 14.5m out to distances of more than 2kpc, which is beyond the Sagittarius arm. This is indicated by the increase of absorption in the plane at distances larger than 0.5kpc.