M1-78: a nitrogen-rich Galactic compact HII region beyond the Perseus arm
| Autor: | Arjan Bik, Adal Mesa-Delgado, César Esteban, E. Puga, N. L. Martin-Hernandez |
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| Jazyk: | angličtina |
| Rok vydání: | 2008 |
| Předmět: |
Physics
Nebula Astrophysics::High Energy Astrophysical Phenomena Astrophysics (astro-ph) Perseus Arm FOS: Physical sciences Astronomy and Astrophysics Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Planetary nebula Stars Luminous blue variable Space and Planetary Science Ionization Electron temperature Astrophysics::Solar and Stellar Astrophysics Astrophysics::Earth and Planetary Astrophysics Ejecta Astrophysics::Galaxy Astrophysics |
| Popis: | 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. 14 pages, 8 figures. Accepted for publication in A&A |
| Databáze: | OpenAIRE |
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