EDP Sciences
Free access
Volume 446, Number 3, February II 2006
Page(s) 1021 - 1026
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20053403
A&A 446, 1021-1026 (2006)
DOI: 10.1051/0004-6361:20053403

Post-outburst radio observation of the region around McNeil's nebula (V1647 Orionis)

S. Vig1, S. K. Ghosh1, V. K. Kulkarni2 and D. K. Ojha1

1  Tata Institute of Fundamental Research, Mumbai 400 005, India
    e-mail: sarita@tifr.res.in
2  National Centre for Radio Astrophysics, Pune 411 007, India

(Received 11 May 2005 / Accepted 10 October 2005 )

We present post-outburst (~100 days after outburst) radio continuum observation of the region ($\sim $ $30'\times
30'$) around McNeil's nebula (V1647 Orionis). The observations were carried out using the Giant Metrewave Radio Telescope (GMRT), India, at 1272 MHz on 2004 Feb. 14.5 UT. Although 8 sources have been detected within a circular diameter of 25' centred on V1647 Ori, we did not detect any radio continuum emission from McNeil's nebula. We assign a $5\sigma$ upper limit of 0.15 mJy/beam for V1647 Ori where the beam size is $5.6''\times2.7''$. Even at higher frequencies of 4.9 and 8.5 GHz (VLA archival data), no radio emission has been detected from this region. Three scenarios, namely emission from a homogeneous HII region, ionised stellar wind and shock-ionised gas, are explored in the light of our GMRT upper-limit. For the case of a homogeneous HII region, the radius of the emitting region is constrained to be $\la $26 AU corresponding to a temperature $\ga $2500 K, which is consistent with the reported radio and H$\alpha$ emission. In the ionised stellar wind picture, our upper limit of radio emission translates to $\dot{M}/v_{\infty}< 1.2{-}1.8\times10^{-10}~ M_{\odot}\rm\, yr^{-1} \,km^{-1} \,s$. On the other hand, if the stellar wind shocks the dense neutral (molecular) cloud, the radio upper limit implies that the fraction of the wind encountering the dense obstacle is <50%. Based on a recent measurement of X-ray outburst and later monitoring, the expected radio emission has been estimated. Using our radio limit, the radius ($\la $36 AU) and electron density ($\ga $ $ 7.2\times10^7$ cm-3) of the radio emitting plasma have been constrained using a two phase medium in pressure equilibrium for a volume filling factor of 0.9.

Key words: stars: formation -- stars: individual: V1647 Orionis -- radio continuum: stars -- stars: circumstellar matter

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