The Imaging Vector Magnetograph at Haleakalā IV: Stokes Polarization Spectra in the Sodium D1 589.6 nm Spectral Line

The Imaging Vector Magnetograph (IVM) at the Mees Solar Observatory, Haleakalā, Maui, Hawai’i, obtained many years of vector magnetic-field data in the photospheric Fe i 630.25 nm line. In the latter period of its operation, the IVM was modified to allow routine observations in the chromospheric Na i D 1 line, as well as the Fe i line. We describe the sodium observational data in detail, including the data-reduction steps that differ from those employed for the Fe i 630.25 nm line, to obtain calibrated Stokes polarization spectra. We have performed a systematic comparison between the observational data and synthetic NLTE Na i D 1 Stokes spectra derived for a variety of solar-appropriate atmospheric and magnetic configurations. While the Na i D 1 Stokes polarization signals from the solar atmosphere are expected to be weak, they should generally be within the IVM capability. A comparison between synthetic spectra and observational data indicates that this is indeed the case.