Robert M. Hjellming

The shapes and shaping of the planetary nebulae IC 3568, NGC 40, and NGC 6543

Radio and optical images of three compact planetary nebulae, NGC 6543, IC 3568, and NGC 40, are found to reveal a variety of morphological and ionization signatures of wind shaping and heating. Both NGC 6543 (one of the most morphologically complex planetaries in the sky) and IC 3568 (one of the simplest) exhibit large density changes on size scales corresponding to sound-crossing times of about a century, arguing that the density gradients are sustained by shocks driven by stellar winds. All of the available data show the structure and ionization of IC 3568 to conform to simple hydrodynamic models of nebulae that are shaped by interior stellar winds. NGC 6543 also shows very local changes in optical line ratios that are best understood in the same manner. 34 references.

Simultaneous radio and X-ray observations of MXB1837+05 /Ser X-1/

DURING a continuing program of radio observations of X-ray sources carried out with the NRAO very large array (VLA), we have made high sensitivity searches for radio emission from MXB1837 + 05 = Ser X − 1 (ref. 1), particularly during the SAS 3 MIT world-wide X-ray burster watch in June 19772. Observations of MXB1837 + 05 were carried out on 26 April, 12 and 13 June 1977, with six 25-m antennas of the VLA operated at 4,884 MHz with system temperatures of ∼60 K and bandwidths of 50 MHz. Upper limits of 1 mJy were obtained for the time-averaged radio emission from Ser X − 1 during the three periods of observation, and no short time scale radio emission was detected during or after the times X-ray bursts were observed on 12 and 13 June 1977.