Open AccessThe Orion nebula (M42) Herbig–Haro object, HH 201, within the tip of a molecular finger
Author(s) -
Graham M. F.,
Meaburn J.,
Redman M. P.
Publication year - 2003
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2003.06692.x
Subject(s) - physics , astrophysics , orion nebula , herbig–haro object , emission spectrum , astronomy , line (geometry) , spectrograph , photoevaporation , context (archaeology) , planetary nebula , proper motion , spectral line , stars , star formation , paleontology , geometry , mathematics , biology
The most prominent Herbig–Haro (HH) object, HH 201, in the Orion nebula is investigated using optical spectroscopy along with optical and infrared images. An infrared Subaru H 2 v = 1–0 S(1) image of the region surrounding the optical line emission of HH 201 has yielded the discovery of a faint H 2 finger associated with HH 201. The H 2 finger is seen to share a common width and orientation with the optical line emission. Therefore, it is unlikely that the association is caused by a chance superposition along the line of sight. The finger is found to precede the optical line emission, which is inconsistent with this H 2 emission being produced within a bowshock. The origin of this finger is discussed in the context of the current understanding of HH objects and the Orion molecular fingers. Multi‐epoch HST [S ii ] 6716‐ and 6731‐ Å images are used to measure the proper motions of the various knots present in the filamentary structure of HH 201. Tangential velocities of between 40 and 178 km s −1 are found. Two new knots with associated proper motions are found in the wake of HH 201 and the general structure of the tangential flow is shown by means of a multi‐epoch difference image. [S ii ] 6716‐ and 6731‐ Å spectra taken with the RGO spectrograph are used to spectroscopically resolve the velocity profile of HH 201 into distinct components with radial velocities of between −267 and −9 km s −1 . Using the [S ii ] 6716‐ and 6731‐ Å line ratios, the local electron density of gas at the various velocities is found to be between 830 and 12 200 cm −3 . Combining radial and tangential velocities, the angle between the direction of motion and the line of sight is found to be approximately 30°. Assuming that the emission knots and velocity components correspond to condensations in a bowshock, a shock velocity at the head of HH 201 of 295 km s −1 is established. Using this combination of optical and infrared data, the morphology and kinematics of HH 201 and its immediate environs are elucidated.