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There is considerable controversy surrounding the nature of M1-78, a compact nebula located beyond the Perseus arm. It was first classified as a planetary nebula and is nowadays generally considered to be a compact HII region. To investigate the nature M1-78 further, we present a detailed spectroscopic study of M1-78 in the optical and near-infrared. M1-78 is a high-density nebula with substantial physical differences between its two main morphological zones: a bright arc to the SW and a blob of emission in the NE. Specifically, the blob in the NE has a higher electron temperature and visual extinction than the SW arc. The most important result, however, is the confirmation of a nitrogen enrichment in M1-78. This enrichment is stronger at the location of the NE blob and is correlated with a defficiency in the O abundance and a (dubious) He enrichment. Such an abundance pattern is typical of ejecta nebulae around evolved massive stars such as Wolf-Rayet and Luminous Blue Variable stars. The spatial variations in the physical conditions and chemical abundances and the presence of more than one possible ionizing source indicates, however, that M1-78 is better described as a combination of a compact HII region + ejecta. Finally, we detect H2 emission that extends over a large (~30 arcsec) area around the ionized nebula. Analysis of the near-infrared H2 lines indicates that the excitation mechanism is UV fluorescence.
The Fan Region is one of the dominant features in the polarized radio sky, long thought to be a local (distance < 500 pc) synchrotron feature. We present 1.3-1.8 GHz polarized radio continuum observations of the region from the Global Magneto-Ionic M
We have observed the compact HII region complex nearest to the dynamical center of the Galaxy, G-0.02-0.07, using ALMA in the H42a recombination line, CS J=2-1, H13CO+ J=1-0, and SiO v=0, J=2-1 emission lines, and 86 GHz continuum emission. The HII r
We report on the discovery of an isolated, compact HII region in the Virgo cluster. The object is located in the diffuse outer halo of NGC 4388, or could possibly be in intracluster space. Star formation can thus take place far outside the main star
The expansion of HII regions can trigger the formation of stars. An overdensity of young stellar objects (YSOs) is observed at the edges of HII regions but the mechanisms that give rise to this phenomenon are not clearly identified. Moreover, it is d
We present a study of the LMC compact HII region N11A using Hubble Space Telescope imaging observations which resolve N11A and reveal its unknown nebular and stellar features. The presence of a sharp ionization front extending over more than 4 (1 pc)