IfA-08-142

The Unusual Object IC 2144/MWC 778

G. H. Herbig
Institute for Astronomy University of Hawaii

William D. Vacca
SOFIA-USRA, NASA Ames Research Center,

To appear in The Astronomical Journal

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 of 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 AV of 3.0 mag was assumed. The SED of MWC 778 rises steeply beyond about 1 μm, 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 Hα 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.

Subject headings: (ISM:) reflection nebulae — stars: emission-line — stars: pre–main sequence — stars: individual (MWC 778)