A variable jet model for the Hα emission of HH 444

¹ Instituto de Ciencias Nucleares, UNAM, Ap. 70-543, 04510 D. F. México, México e-mail: raga@nucleares.unam.mx
² Departament de Física i Enginyeria Nuclear, EUETIB, Universitat Politecnica de Catalunya, Compte d'Urgell 187, 08036 Barcelona, Spain
³ Instituto de Geofísica, UNAM, 04510 D. F. México, México

Received: 18 December 2009
Accepted: 7 March 2010

Abstract

Context. HH 444 is one of the first Herbig-Haro (HH) jets discovered within a photoionized region.

Aims. We re-analyze the Hα and red [S II] HST images of HH 444, and calculate the width of the jet as a function of distance from the source. We compare the Hα image with predictions from variable ejection velocity jet models.

Methods. The determination of the jet's width is done with a non-parametric, wavelet analysis technique. The axisymmetric, photoionized jet simulations are used to predict Hα maps that can be directly compared with the observations.

Results. Starting with a thin jet (unresolved at the resolution of the observations), we are able to produce knots with widths and morphologies that generally agree with the Hα knots of HH 444. This agreement is only obtained if the jet axis is at a relatively large, ~45° angle with respect to the sky. This agrees with previous spectroscopic observations of the HH 444 bow shock, which imply a relatively large jet axis/plane of the sky angle.

Conclusions. We conclude that the general morphology of the chain of knots close to V510 Ori (the HH 444 source) can be explained with a variable ejection velocity jet model. For explaining the present positions of the HH 444 knots, however, it is necessary to invoke a more complex ejection velocity history than a single-mode, periodic variability.