2009/06/16 by M. Matsuura, A. K. Speck, Basil Menzi Mchunu +8 · 81 citations
Physics and Astronomy · #Astro and Planetary Science #Astrobiology #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Emission nebula #Geology #Helix (gastropod) #Nebula #Paleontology #Physics #Planetary nebula #Protoplanetary nebula #Stars #Stellar, planetary, and galactic studies #astro-ph.SR
paper · pdf · doi:10.1088/0004-637x/700/2/1067
published in The Astrophysical Journal 700(2), 1067-1077 (IOP Publishing) · ApJ, in press. High resolution image of figure 2 is available from http://zuserver2.star.ucl.ac.uk/~mikako/helix_figure.eps Draft with high resolution images is available from http://zuserver2.star.ucl.ac.uk/~mikako/helix_maintext.pdf
arxiv created 2009/06/16 · openalex publication_date 2009/07/08 · arxiv updated 2015/05/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present a deep and wide field-of-view (4' × 7') image of the planetary nebula (PN) NGC 7293 (the Helix Nebula) in the 2.12 μm H 2 v = 1 → 0 S(1) line. The excellent seeing (0 4) at the Subaru Telescope, allows the details of cometary knots to be examined. The knots are found at distances of 2 2–6 4 from the central star (CS). At the inner edge and in the inner ring (up to 4 5 from the CS), the knot often show a "tadpole" shape, an elliptical head with a bright crescent inside and a long tail opposite to the CS. In detail, there are variations in the tadpole shapes, such as narrowing tails, widening tails, meandering tails, or multipeaks within a tail. In the outer ring (4 5–6 4 from the CS), the shapes are more fractured, and the tails do not collimate into a single direction. The transition in knot morphology from the inner edge to the outer ring is clearly seen. The number density of knots governs the H 2 surface brightness in the inner ring: H 2 exists only within the knots. Possible mechanisms which contribute to the shaping of the knots are discussed, including photoionization and streaming motions. A plausible interpretation of our images is that inner knots are being overrun by a faster wind, but that this has not (yet) reached the outer knots. Based on H 2 formation and destruction rates, H 2 gas can survive in knots from formation during the late asymptotic giant branch phase throughout the PN phase. These observations provide new constraints on the formation and evolution of knots, and on the physics of molecular gas embedded within ionized gas.