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تسجيل مستخدم جديدV1647 Orionis (IRAS 05436-0007) : A New Look at McNeils Nebula
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We present a study of the newly discovered McNeils nebula in Orion using the JHKs-band simultaneous observations with the near-infrared (NIR) camera SIRIUS on the IRSF 1.4m telescope. The cometary infrared nebula is clearly seen extending toward north and south from the NIR source (V1647 Orionis) that illuminates McNeils nebula. The compact nebula has an apparent diameter of about 70 arcsec. The nebula is blue (bright in J) and has a cavity structure with two rims extending toward north-east and north-west. The north-east rim is brighter and sharp, while the north-west rim is diffuse. The north-east rim can be traced out to ~ 40 arcsec from the location of the NIR source. In contrast, no cavity structure is seen toward the south, although diffuse nebula is extended out to ~ 20 arcsec. New NIR photometric data show a significant variation in the magnitudes (> 0.15 mag) of the source of McNeils nebula within a period of one week, that is possibly under the phase of eruptive variables like FUors or EXors.
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We present Sloan Digital Sky Survey and United States Naval Observatory observations of the V1647 Ori protostar and surrounding field near NGC 2068. V1647 Ori, the likely driving source for HH 23, brightened significantly in November 2003. Analysis o
f SDSS imaging acquired in November 1998 and February 2002 during the quiescent state, recent USNO photometry, and published 2MASS and Gemini data shows that the color changes associated with brightening suggest an EXor outburst rather than a simple dust clearing event.
We present a detailed study of the post-outburst phase of McNeils nebula (V1647 Ori) using optical B,V,R,I and NIR J,H,K photometric and low resolution optical spectroscopic observations. The observations were carried out with the HFOSC, NIRCAM, TIRC
AM and NICMOS cameras on the 2m HCT and 1.2m PRL telescopes during the period 2004 Feb-2005 Dec. The optical/NIR observations show a general decline in brightness of the exciting source of McNeils nebula (V1647 Ori). Our recent optical images show that V1647 Ori has faded by more than 3 mags since Feb 2004. The optical/NIR photometric data also show a significant variation in the mags (Delta V = 0.78 mag, Delta R = 0.44 mag, Delta I = 0.21 mag, Delta J = 0.24 mag and Delta H = 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 Halpha emission with blue-shifted absorption and the CaII IR triplet (8498A, 8542A and 8662A) 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 CaII IR triplet in emission confirms that V1647 Ori is a PMS 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 McNeils nebula shows that the optical nebula is more widely and predominantly extended to the north, whereas the IR nebula is relatively confined (dia ~ 60 arcsec), but definitely extended, to the south, too.
We present a detailed study of McNeils nebula (V1647 Ori) in its ongoing outburst phase starting from September 2008 to March 2013. Our 124 nights of photometric observations were carried out in optical V, R, I and near-infrared J, H, K bands, and 59
nights of medium resolution spectroscopic observations were done in 5200 - 9000 Ang wavelength range. All observations were carried out with 2-m Himalayan Chandra Telescope and 2-m IUCAA Girawali Telescope. Our observations show that over last four and a half years, V1647 Ori and the region C near Herbig-Haro object, HH 22A, have been undergoing a slow dimming at a rate of ~0.04 mag/yr and ~0.05 mag/yr respectively in R-band, which is 6 times slower than the rate during similar stage of V1647 Ori in 2003 outburst. We detected change in flux distribution over the reflection nebula implying changes in circumstellar matter distribution between 2003 and 2008 outbursts. Apart from steady wind of velocity ~350 km/s we detected two episodic magnetic reconnection driven winds. Forbidden [O I] 6300 Ang and [Fe II] 7155 Ang lines were also detected implying shock regions probably from jets. We tried to explain the outburst timescales of V1647 Ori using the standard models of FUors kind of outburst and found that pure thermal instability models like Bell & Lin (1994) cannot explain the variations in timescales. In the framework of various instability models we conclude that one possible reason for sudden ending of 2003 outburst in 2005 November was due to a low density region or gap in the inner region (~ 1 AU) of the disc.
We present post-outburst (~ 100 days after outburst) radio continuum observation of the region (~ 30 x 30) around McNeils nebula (V1647 Orionis). The observations were carried out using the Giant Metrewave Radio Telescope (GMRT), India, at 1272 MHz o
n 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 McNeils nebula. We assign a 5-sigma upper limit of 0.15 mJy/beam for V1647 Ori where the beam size is 5.6 x 2.7. 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 homogeneous HII region, ionised stellar wind and shock ionised gas, are explored in the light of our GMRT upper-limit. For the case of homogeneous HII region, the radius of the emitting region is constrained to be <~ 26 AU corresponding to a temperature >~ 2,500 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 the ratio of mass loss rate and terminal velocity, (M_dot/v_infinity) < 1.2-1.8 x 10^(-10) (M_sun/yr)/(km/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 (<~ 36 AU) and electron density (>~ 7.2 x 10^7 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.
We report a ~38 ks X-ray observation of McNeils Nebula obtained with XMM on 2004 April 4. V1647 Ori, the young star in outburst illuminating McNeils Nebula, is detected with XMM and appears variable in X-rays. We investigate the hardness ratio variab
ility and time variations of the event energy distribution with quantile analysis, and show that the large increase of the count rate from V1647 Ori observed during the second half of the observation is not associated with any large plasma temperature variations as for typical X-ray flares from young low-mass stars. X-ray spectral fitting shows that the bulk (~75%) of the intrinsic X-ray emission in the 0.5-8 keV energy band comes from a soft plasma component (0.9 keV) reminiscent of the X-ray spectrum of the classical T Tauri star TW Hya, for which X-ray emission is believed to be generated by an accretion shock onto the photosphere of a low-mass star. The hard plasma component (4.2 keV) contributes ~25% of the total X-ray emission, and can be understood only in the framework of plasma heating sustained by magnetic reconnection events. We find a hydrogen column density of NH=4.1E22 cm-2, which points out a significant excess of hydrogen column density compared to the value derived from optical/IR observations, consistent with the picture of the rise of a wind/jet unveiled from ground optical spectroscopy. The X-ray flux observed with XMM ranges from roughly the flux observed by Chandra on 2004 March 22 (~10 times greater than the pre-outburst X-ray flux) to a value two times greater than that caught by Chandra on 2004 March 7 (~200 times greater than the pre-outburst X-ray flux). We have investigated the possibility that V1647 Ori displays a periodic variation in X-ray brightness as suggested by the combined Chandra+XMM data set (abridged).
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