اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدThe Hubble-type outflows from the high excitation, poly-polar planetary nebula NGC 6302
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Spatially resolved profiles of the Halpha and [NII] lines have been obtained at unprecendented signal--to--noise ratios over the outflowing lobes of the high--excitation, poly--polar planetary nebula NGC~6302. A deep image in the light of [NII]6584 A was also obtained of the extremities of the prominent north--western lobe. The Manchester Echelle spectrometer combined with the 2.1--m San Pedro Martir telescope (Mexico) was used for these observations. Firstly, an accurate value of the systemic heliocentric radial velocity of Vsys = -29.8 +/- 1 km/s has been established. Also, from `velocity ellipses across its diameter from previous observations the parallel--sided north--western lobe is shown to have a circular section with a tilt of its axis to the plane of the sky of 12.8 deg. With this starting point the pv arrays of profiles have been very closely simulated, using the SHAPE code, with Hubble-type outflows. The faint extremities of the north--western outflow are shown to be expanding at 600 km/s. The prominent lobes of NGC~6302 have then been generated in an eruptive event with a dynamical age of 1900 y for the expansion proper-motion distance of 1.04 +/- 0.16 kpc as measured here by comparing a 1956 image with that taken in 2002. Kinematical evidence of a high--speed `skirt around the nebular core, expanding nearly orthogonally to the lobes, is also presented as are the unusual motions at the western extremities of the NW lobe.
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Planetary nebulae expand on time scales of 10^3-10^4 yr. For nearby objects, their expansion can be detected within years to decades. The pattern of expansion probes the internal velocity field and provides clues to the nebula ejection mechanism. In
the case of non-symmetric nebulae, and bipolar nebulae in particular, it can also provide information on the development of the morphology. We have measured the expansion proper motions in NGC 6302 from two epochs of HST imaging, separated by 9.43 years. This is used to determine the expansion age and the structure of the velocity field. We use HST images in the [N II] 6583{AA} filter from HST WF/PC2 and WFC3. The proper motions were obtained for a set of 200 individual tiles within 90 of the central star. The velocity field shows a characteristic linear increase of velocity with radial distance (a so-called Hubble flow). It agrees well with a previous determination by Meaburn et al. (2008), made in a lobe further from the star, which was based on a much longer time span. The pattern of proper motion vectors is mostly radial and the origin is close to the position of the central star directly detected by Szyszka et al. (2009). The results show that the lobes of NGC 6302 were ejected during a brief event 2250 pm 35yr ago. In the inner regions there is evidence for a subsequent acceleration of the gas by an additional 9.2 km/s, possibly related to the onset of ionization. The dense and massive molecular torus was ejected over 5000yr, ending about 2900yr ago. The lobes were ejected after a short interlude (the jet lag) of sim 600 yr during a brief event. The torus and lobes orig- inate from separate mass-loss events with different physical processes. The delay between the cessation of equatorial mass loss and the ejection of the lobes provides an important constraint for explaining the final mass-loss stages of the progenitor stellar system.
NGC 6302 is one of the highest ionization planetary nebulae known and shows emission from species with ionization potential >300eV. The temperature of the central star must be >200,000K to photoionize the nebula, and has been suggested to be up to ~
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The high excitation planetary nebula, NGC 6302, has been imaged in two far-ultraviolet (FUV) filters, F169M (Sapphire; {lambda}$_{rm eff}$: 1608 {AA}) and F172M (Silica; {lambda}$_{rm eff}$: 1717 {AA}) and two NUV filters, N219M (B15; {lambda}$_{rm e
ff}$: 2196 {AA}) and N279N (N2; {lambda}$_{rm eff}$: 2792 {AA}) with the Ultra Violet Imaging Telescope (UVIT). The FUV F169M image shows faint emission lobes that extend to about 5 arcmin on either side of the central source. Faint orthogonal collimated jet-like structures are present on either side of the FUV lobes through the central source. These structures are not present in the two NUV filters nor in the FUV F172M filter. Optical and IR images of NGC 6302 show bright emission bipolar lobes in the east-west direction with a massive torus of molecular gas and dust seen as a dark lane in the north-south direction. The FUV lobes are much more extended and oriented at a position angle of 113{deg}. They and the jet-like structures might be remnants of an earlier evolutionary phase, prior to the dramatic explosive event that triggered the Hubble type bipolar flows approximately 2200 years ago. The source of the FUV lobe and jet emission is not known, but is likely due to fluorescent emission from H$_2$ molecules. The cause of the difference in orientation of optical and FUV lobes is not clear and, we speculate, could be related to two binary interactions.
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