Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984mnras.207..611d&link_type=abstract
Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 207, April 1, 1984, p. 611-619.
Astronomy and Astrophysics
Astronomy
32
Astronomical Spectroscopy, Hydroxyl Emission, Interstellar Masers, Stellar Envelopes, Astronomical Coordinates, Astronomical Maps, Asymmetry, M Stars, Supergiant Stars
Scientific paper
The 1612 MHz OH maser emission from the supergiant star NML Cyg has been mapped with MERLIN in its spectral-line mode. The resultant maps reveal the presence of significant departures from the uniformly expanding shell model. There is an outward displacement of the emission in the west and northwest of the envelope to a radius of 2.5 arcsec, in contrast to the 1.5 arcsec radius of the emission to the southeast. It is suggested that photodissociation of H2O by UV photons from Cyg OB2 could cause this asymmetry. The data also suggest that the inner regions of the envelope are expanding at 34 km/s while the outer ones expand at 20 km/s. This may be due to a threefold increase in the luminosity of the central star. The data imply that the radial velocity of the central star is +2 + or - 2 km/s, in approximate agreement with the value determined from thermal SiO data.
Booth Roy S.
Diamond Phil J.
Norris Ray P.
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