The Optical Proper Motions of HH 7–11 and Cepheus E

Abstract

A key ingredient in understanding the dynamics of stellar outflows is their proper motion. We have used optical images in the [S II] emission at 6717/6731 A and the red Digitized Palomar Observatory Sky Survey (DSS) plates to determine the proper motion of the HH 7–11 system and the optical knot of Cep E (HH 377). The DSS plate measurements span nearly 37 years for both HH 7–11 and HH 377 and have a wide field of view, which allows an accurate determination of the proper motions despite their relatively low angular resolution. The optical images, with higher angular resolution, cover a shorter period, 7 and 4 years, respectively, for HH 7–11 and HH 377 and have been used to complement the DSS measurements. From the DSS plates we have found that HH 377 has a proper motion of 0031 ± 0003 yr-1 with P.A. = 206°; i.e., it is moving away from IRAS 230111+63, which at a distance of 730 pc corresponds to a tangential velocity of 107 ± 14 km s-1. The values obtained from the optical images are consistent with these measurements. Similarly, the proper motions of HH 7–11 range from 0015 ± 0009 yr-1 (HH 9) to 0044 ± 0007 yr-1 (HH 11), and the flow is moving away from SVS 13 with mean P.A. ~ 136°. At a distance of 330 pc, these motions correspond to tangential velocities of ~25–70 km s-1, i.e., comparable to the original values obtained by Herbig & Jones (1983). The measurements from the optical CCD [S II] images are again consistent with these motions, although in detail there are some differences, particularly for HH 7 and HH 10.