HUBBLE SPACE TELESCOPE IMAGING OF THE BINARY NUCLEUS OF THE PLANETARY NEBULA EGB 6
- Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
- Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
- Departement de Physique, Universite de Montreal, C.P. 6128 Succ. Centre-Ville, Montreal, Quebec H3C 3J7 (Canada)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy)
EGB 6 is an ancient, low-surface-brightness planetary nebula. The central star, also cataloged as PG 0950+139, is a very hot DAOZ white dwarf (WD) with an apparent M dwarf companion, unresolved from the ground but detected initially through excesses in the JHK bands. Its kinematics indicates membership in the Galactic disk population. Inside of EGB 6 is an extremely dense emission knot-completely unexpected since significant mass loss from the WD should have ceased {approx}10{sup 5} yr ago. The electron density of the compact nebula is very high (2.2 Multiplication-Sign 10{sup 6} cm{sup -3}), as indicated by collisional de-excitation of forbidden emission lines. Hubble Space Telescope imaging and grism spectroscopy are reported here. These resolve the WD and apparent dM companion-at a separation of 0.''166, or a projected 96{sub -45}{sup +204} AU at the estimated distance of 576{sub -271}{sup +1224} pc (using the V magnitude). Much to our surprise, we found that the compact emission nebula is superposed on the dM companion, far from the photoionizing radiation of the WD. Moreover, a striking mid-infrared excess has recently been reported in the Spitzer/IRAC and MIPS bands, best fit with two dust shells. The derived ratio L{sub IR}/L{sub WD} = 2.7 Multiplication-Sign 10{sup -4} is the largest yet found for any WD or planetary nucleus. The compact nebula has maintained its high density for over three decades. We discuss two possible explanations for the origin and confinement of the compact nebula, neither of which is completely satisfactory. This leaves the genesis and confinement of the compact nebula an astrophysical puzzle, yet similar examples appear in the literature.
- OSTI ID:
- 22126645
- Journal Information:
- Astrophysical Journal, Vol. 769, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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