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Context. HH 444 is one of the first Herbig-Haro (HH) jets discovered wit hin a photoionized region. Aims. We reanalize the Hand 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 Himage with predictions from variable ejection velocity jet models. Methods. The determination of the width of the jet is done with a non-parametric, wavelet analysis technique. The axisymmetric, photoionized jet simulations are used to predict Hmaps which 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 which have widths and morphologies which are in general agreement with the Hknots 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 is in agreement 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 p resent positions of the HH 444 knots, however, it is necessary to invoke a more complex ejection velocity history than a single-mode, periodic variability.

A variable jet model for the Hαemission of HH 444