The Unusual Object IC 2144/MWC 778

TL;DR

This study investigates the reflection nebula IC 2144 and its peculiar emission-line star MWC 778 using high-resolution optical and near-infrared spectroscopy, revealing its properties, distance, and potential pre-main-sequence nature.

Contribution

The paper provides detailed spectroscopic analysis of IC 2144 and MWC 778, suggesting the star's pre-main-sequence status and characterizing the nebula's properties for the first time.

Findings

MWC 778 shows F- or G-type absorption features.

Distance to IC 2144 is about 1.0 kpc.

MWC 778 has an IR luminosity of approximately 510 L_solar.

Abstract

IC 2144 is a small reflection nebula located in the zone of avoidance near the Galactic anticenter. It has been investigated here largely on the basis of Keck/HIRES optical spectroscopy (R ~ 48,000) and a SpeX spectrogram in the near-IR (R = 2000) obtained at the NASA IRTF. The only star in the nebula that is obvious in the optical or near-IR is the peculiar emission-line object MWC 778 (V = 12.8), which resembles a T Tauri star in some respects. What appear to be F- or G-type absorption features are detectable in its optical region under the very complex emission line spectrum; their radial velocity agrees with the CO velocity of the larger cloud in which IC 2144 is embedded. There are significant differences between the spectrum of the brightest area of the nebula and of MWC 778, the presumed illuminator, an issue discussed in some detail. The distance of IC 2144 is inferred to be about 1.0 kpc by reference to other star-forming regions in the vicinity. The extinction is large, as demonstrated by [Fe II] emission line ratios in the near-IR and by the strength of the diffuse interstellar band spectrum; a provisional value of A_V of 3.0 mag was assumed. The SED of MWC 778 rises steeply beyond about 1 $\mu$m, with a slope characteristic of a Class I source. Integration of the flux distribution leads to an IR luminosity of about 510 L_solar. If MWC 778 is indeed a F- or G-type pre--main-sequence star several magnitudes above the ZAMS, a population of faint emission Halpha stars would be expected in the vicinity. Such a search, like other investigations that are recommended in this paper, has yet to be carried out.