NEBULAR: A simple synthesis code for the hydrogen and helium nebular spectrum

TL;DR

NEBULAR is a lightweight, versatile code designed to synthesize hydrogen and helium nebular spectra, including various continua and line series, useful for analysis and educational purposes.

Contribution

It introduces a simple, interpolative tool that efficiently generates nebular spectra from publicly available data without requiring prior data structure knowledge.

Findings

Supports a range of densities, temperatures, and wavelengths

Includes free-free, free-bound, and two-photon continua

Enables spectrum resampling for comparison with observations

Abstract

NEBULAR is a lightweight code to synthesize the spectrum of an ideal, mixed hydrogen and helium gas in ionization equilibrium, over a useful range of densities, temperatures and wavelengths. Free-free, free-bound and two-photon continua are included as well as parts of the HI, HeI and HeII line series. NEBULAR interpolates over publicly available data tables; it can be used to easily extract information from these tables without prior knowledge about their data structure. The resulting spectra can be used to e.g. determine equivalent line widths, constrain the contribution of the nebular continuum to a bandpass, and for educational purposes. NEBULAR can resample the spectrum on a user-defined wavelength grid for direct comparison with an observed spectrum; however, it can not be used to fit an observed spectrum.