Wehres, N., Ochsendorf, B. B., Tielens, A. G. G. M., Cox, N. L. J., Kaper, L., Bally, J. and Snow, T. P. (2017). Medium-resolution echelle spectroscopy of the Red Square Nebula, MWC 922. Astron. Astrophys., 601. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Medium-resolution echelle spectra of the Red Square Nebula surrounding the star MWC 922 are presented. The spectra have been obtained in 2010 and 2012 using the X-shooter spectrograph mounted on the Very Large Telescope (VLT) in Paranal, Chile. The spectrum covers a wavelength range between 300 nm-2.5 mu m and shows that the nebula is rich in emission lines. Aims. We aim to identify the emission lines and use them as a tool to determine the physical and chemical characteristics of the nebula. The emission lines are also used to put constraints on the structure of the nebula and on the nature of the central stars. Methods. We analyzed and identified emission lines that indicated that the Red Square Nebula consists of a low density bipolar outflow, eminent in the broad emission component seen in [Fe II], as well as in P Cygni line profiles indicative of fast outflowing material. The narrow component in the [Fe II] lines is most likely formed in the photosphere of a surrounding disk. Some of the emission lines show a pronounced double peaked profile, such as Ca II, indicating an accretion disk in Keplerian rotation around the central star. [O I] emission lines are formed in the neutral atomic zone separating the ionized disk photosphere from the molecular gas in the interior of the disk, which is prominent in molecular CO emission in the near-IR. [NII] and [S II] emission clearly originates in a low density but fairly hot (7 000-10 000 K) nebular environment. Hi recombination lines trace the extended nebula as well as the photosphere of the disk. Results. These findings put constraints on the evolution of the central objects in MWC 922. The Red Square shows strong similarities to the Red Rectangle Nebula, both in morphology and in its mid-IR spectroscopic characteristics. As for the Red Rectangle, the observed morphology of the nebula reflects mass-loss in a binary system. Specifically, we attribute the biconical morphology and the associated rung-like structure to the action of intermittent jets blown by the accreting companion in a dense shell, which has been created by the primary. We stress, though, that despite the morphological similarities, these two objects represent very different classes of stellar objects.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Wehres, N.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ochsendorf, B. B.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Tielens, A. G. G. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Cox, N. L. J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Kaper, L.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Bally, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Snow, T. P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-232012
DOI: 10.1051/0004-6361/201628723
Journal or Publication Title: Astron. Astrophys.
Volume: 601
Date: 2017
Publisher: EDP SCIENCES S A
Place of Publication: LES ULIS CEDEX A
ISSN: 1432-0746
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
DIFFUSE INTERSTELLAR BANDS; CRYSTALLINE SILICATE DUST; GALACTIC FSCMA STARS; FE-II; EVOLVED STARS; MODELING PHOTOLUMINESCENCE; TRANSITION-PROBABILITIES; ABSORPTION-SPECTRA; MOLECULAR CLOUDS; INFRARED-SPECTRAMultiple languages
Astronomy & AstrophysicsMultiple languages
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/23201

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