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Title: Post-outburst phase of McNeil's nebula (V1647 Orionis)
Authors: Ojha, D. K
Ghosh, S. K
Tej, A
Verma, R. P
Vig, S
Anupama, G. C
Sahu, D. K
Parihar, P. S
Bhatt, B. C
Prabhu, T. P
Maheswar, G
Bhatt, H. C
Anandarao, B. G
Venkataraman, V
Keywords: Stars: formation;Stars: pre-main-sequence;Stars: variables;ISM: individual: (McNeil's nebula);Reflection nebulae
Issue Date: Mar-2006
Publisher: Blackwell Publishing
Citation: MNRAS, Vol. 368, No. 2, pp. 825 – 836
Abstract: We present a detailed study of the post-outburst phase of McNeil's nebula (V1647 Orionis) using optical B, V, R, I and near-infrared (NIR) J, H, K photometric and low-resolution optical spectroscopic observations. The observations were carried out with the Himalaya Faint Object Spectrograph Camera (HFOSC), NIR camera (NIRCAM), the Tata Institute of Fundamental Research (TIFR) Near-Infrared Camera (TIRCAM) and NICMOS cameras on the 2-m Himalayan Chandra Telescope (HCT) and 1.2-m Physical Research Laboratory (PRL) telescopes during the period 2004 February–2005 December. The optical and NIR observations show a general decline in the brightness of the exciting source of McNeil's nebula (V1647 Ori). Our recent optical images show that V1647 Ori has faded by more than 3 mag since February 2004. McNeil's nebula has also faded considerably. The optical/NIR photometric data also show a significant variation in the magnitudes (ΔV= 0.78, ΔR= 0.44, ΔI= 0.21, ΔJ= 0.24 and ΔH= 0.20 mag) of V1647 Ori within a period of one month, which is possibly undergoing a phase similar to eruptive variables, like EXors or FUors. The optical spectra show a few features such as strong Hα emission with blue-shifted absorption and the Ca ii IR triplet (8498, 8542 and 8662 Å) in emission. As compared to the period just after outburst, there is a decrease in the depth and extent of the blue-shifted absorption component, indicating a weakening in the powerful stellar wind. The presence of the Ca ii IR triplet in emission confirms that V1647 Ori is a pre-main-sequence star. The long-term, post-outburst photometric observations of V1647 Ori suggest an EXor rather than an FUor event. An optical/IR comparison of the region surrounding McNeil's nebula shows that the optical nebula is more widely and predominantly extended to the north, whereas the IR nebula is relatively confined (diameter ~60 arcsec), but definitely extended, to the south, too. The large colour gradient from north to south and the sudden absence of an optical nebula to the south are suggestive of a large-scale disc-like structure (or envelope) surrounding the central source that hides the southern nebula.
Appears in Collections:Publications based on data from IAO, Hanle
IIAP Publications

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