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 Hubble Images Searchlight Beams from a Preplanetary Nebula

The NASA/ESA Hubble Space Telescope has been at the cutting edge of research into what happens to stars like our sun at the ends of their lives. One stage that stars pass through as they run out of nuclear fuel is called the preplanetary or protoplanetary nebula stage. This Hubble image of the Egg Nebula shows one of the best views to date of this brief but dramatic phase in a star's life.
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The egg-shaped remains of a dying star has a hollow shell that is "unusually" rich in the complex organic molecules, say Australian and Vietnamese researchers.
The study, from the current issue of The Astrophysical Journal, used the Very Large Array (VLA) in New Mexico to probe the interior of the Egg Nebula, also known as CRL2688.

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Title: Resolving the Multiple Outflows in the Egg Nebula with Keck II Laser Guide Star Adaptive Optics
Authors: D. Le Mignant, R. Sahai, A. Bouchez, R. Campbell, M. van Dam, J. Chin, E. Johansson, S. Hartman, R. Lafon, J. Lyke, P. Stomski, D. Summers, P. Wizinowich

The Egg Nebula has been regarded as the archetype of bipolar proto-planetary nebulae, yet we lack a coherent model that can explain the morphology and kinematics of the nebular and dusty components observed at high-spatial and spectral resolution. Here, we report on two sets of observations obtained with the Keck Adaptive Optics Laser Guide Star: H to M-band NIRC2 imaging, and narrow bandpath K-band OSIRIS 3-D imaging-spectroscopy (through the H2 2.121micron emission line). While the central star or engine remains un-detected at all bands, we clearly resolve the dusty components in the central region and confirm that peak A is not a companion star. The spatially-resolved spectral analysis provide kinematic information of the H_2 emission regions in the eastern and central parts of the nebula and show projected velocities for the H_2 emission higher than 100 km/s. We discuss these observations against a possible formation scenario for the nebular components.

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Blobrana


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CRL2688
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This Hubble telescope picture of the Egg Nebula, also known as CRL2688, shows a pair of mysterious "searchlight" beams emerging from a hidden star and criss-crossed by numerous bright arcs.
The nebula is a large cloud of dust and gas ejected by the star, expanding at a speed of 20 km/s.



A dense cocoon of dust (the dark band in the centre) enshrouds the star and hides it from our view. Starlight escapes more easily in directions where the cocoon is thinner and is reflected towards us by dust particles in the cloud, giving it its overall appearance.
Objects like CRL2688 are rare because they are in a very short evolutionary phase. However, they may hold the key to our understanding of how red giant stars transform themselves into planetary nebulae.

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Egg Nebula
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Title: Proper-Motion Measurements of the Cygnus Egg Nebula
Authors: Toshiya Ueta (USRA SOFIA/NASA Ames Research Center), Koji Murakawa (Max-Planck Institute for Radio Astronomy), Margaret Meixner (STScI)

Reserchers present the results of proper-motion measurements of the dust shell structure in the Egg Nebula (AFGL 2688, CRL 2688, V1610 Cyg), based on the archived two-epoch imaging-polarimetry data in the 2 micron band taken with NICMOS on-board the Hubble Space Telescope.
They measured the amount of motions of local structures in the nebula by determining their relative shifts over an interval of 5.5 years. The dynamical age of the nebula is found to be roughly 350 years based on the overall motion of the nebula that exhibits a Hubble-law-esque linear relation between the measured proper motion and the projected radial distance from the origin of the expansion.
By adopting the de-projected velocity of 45 ±9 km/s at the tips of the bipolar lobes, their proper-motion measurements indicate that the distance to the Egg Nebula is about 420 ±60 pc, and that the lobes are inclined at 7.7± 1.9 degrees with respect to the plane of the sky. The refined distance estimate yields the luminosity of the central star of 3.3 x 10^3 soar luminosity, the total shell mass of 1.2 solar masses, and the mass loss rate (the upper limit) of 3.6 x 10^(-3) solar masses per year.



Assuming 0.6 solar mass central post-AGB stellar mass, the initial mass of the Egg is 1.8 solar masses. Upon analysis, they also discovered that the central star of the Egg Nebula has proper motion of its own at the rate of (14, -10) mas/year and that the apparent bipolar lobes consist of multiple outflows at distinct inclination angles projected onto each other.


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The star in the centre of the Egg Nebula in Cygnus is casting away shells of gas and dust as it slowly transforms itself into a white dwarf star.


Position(2000): R.A. 21 02 18.7, Dec. +36° 41' 37
Size 14'1 x 14'1

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