Mathematics – Probability
Scientific paper
Sep 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.3908k&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #39.08; Bulletin of the American Astronomical Society, Vol. 24, p.1181
Mathematics
Probability
1
Scientific paper
We have obtained ROSAT PSPC observations of the Dumbbell Nebula (NGC6853) in an attempt to detect extended emission that would be expected according to the two-wind model (Kwok, Purton and FitzGerald, Ap.J. Lett., 219, L25, 1978; Balick, AJ 94, 671, 1987). EINSTEIN and EXOSAT observations of several other PN have yielded detections interpreted as purely stellar in origin (Tarafdar and Apparao ApJ, 327, 342, 1988; Apparao and Tarafdar ApJ, 344, 826, 1990). We chose the Dumbbell for its extended size ( 7 arcmin), its nearness (d 250pc [Kaler ApJ 271, 188, 1983]), its low reddening (Av=0.44 [Cahn, Kaler and Stanghellini, A&A Suppl. 94, 399, 1992]), and for a hint of extended x-ray emission in the EINSTEIN IPC data (Kwitter, Chu and Downes, Bull. AAS, 23, 914, 1991). We successfully detected x-ray emission from the Dumbbell in 5.32 ksec pointed observations with the ROSAT PSPC, accumulating a total of 2057 source counts. The integrated spectrum shows all emission to be below 0.4 keV. The raw emission contours appear to indicate an extended source; however, this interpretation is complicated by the uncertainty in the PSF of the PSPC in the lowest energy bins where the Dumbbell's emission is concentrated. Comparison of the Dumbbell's image with that from a known point source with a similarly soft x-ray spectrum (the white dwarf HZ 43) indicates a high probability that the emission from the Dumbbell is not, in fact, extended. This result would be in contradiction to the claim by Kreysing et al. (A&A, in press) of extended x-ray emission from the Dumbbell, which was based on 174 source counts detected in ROSAT's All Sky Survey. More careful analysis is needed to clearly define whether the emission is extended or not; our upcoming ROSAT HRI observations will be instrumental in resolving this question. K.B.K. acknowledges support from NASA grant NAG5-1888, Y.-H.C. from NASA grant NAG5-1900, and J.B.K. from NSF grant AST91-15030.
Chu Y.-H. Y.-H.
Kaler James B.
Kwitter Karen B.
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