An Optical Study of the Circumstellar Environment Around the Crab Nebula

Details An Optical Study of the Circumstellar Environment Around the Crab Nebula An Optical Study of the Circumstellar Environment Around the Crab Nebula

Jan 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aj....113..354f&link_type=abstract

Astronomical Journal v.113, p. 354-363 (1997)

Astronomy and Astrophysics

Astronomy

32

Scientific paper

Long-slit spectra of two peripheral regions around the Crab Nebula show no Hα emission down to a flux level of 1.5 x 10(-7) erg cm(-2) s(-1) sr(-1) (0.63 Rayleigh), corresponding to an emission measure limit of 4.2 cm(-6) pc (3sigma ) assuming A_V = 1.6(m) and T_e = 7000 K. This is below the flux levels reported by Murdin & Clark [Nature, 294, 543 (1981)] for a Hα halo around the Crab. Narrow Hβ emission as described by Murdin [MNRAS, 269, 89 (1994)] is detected but appears to be galactic emission unassociated with the remnant. A review of prior searches indicates no convincing observational evidence to support either a high- or low-velocity envelope around the remnant. Spectral scans confirm a well-organized, N-S expansion asymmetry of the filaments with a ~ 500 km s(-1) central velocity constriction as described by MacAlpine et al. [ApJ, 342, 364 (1989)] and Lawrence et al. [AJ, 109, 2635 (1995)] but questioned by Hester et al. [ApJ, 448, 240 (1995)]. The velocity pinching appears to coincide with an east-west chain of bright [O III] and helium-rich filaments. This expansion asymmetry might be the result of ejecta interaction with a disk of circumstellar matter, but such a model may be inconsistent with H and He filament abundances in the velocity constriction zone. A re-analysis of the remnant's total mass suggests that the filaments contain 4.6 +/- 1.8 Msun in ionized and neutral gas, about twice that of earlier estimates. For a 10 Msun progenitor, this suggests that =~ 4 Msun remains to be detected in an extended halo or wind.

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