The Time Evolution of HH 1 from Four Epochs of HST Images

Abstract

We present an analysis of four epochs of Hα and [S II] λλ 6716/6731 Hubble Space Telescope (HST) images of HH 1. For determining proper motions, we explore a new method based on the analysis of spatially degraded images obtained convolving the images with wavelet functions of chosen widths. With this procedure, we are able to generate maps of proper motion velocities along and across the outflow axis, as well as (angularly integrated) proper motion velocity distributions. From the four available epochs, we find the time evolution of the velocities, intensities, and spatial distribution of the line emission. We find that over the last two decades HH 1 shows a clear acceleration. Also, the Hα and [S II] intensities first dropped and then recovered in the more recent (2014) images. Finally, we show a comparison between the two available HST epochs of [O III] λ 5007 (1994 and 2014), in which we see a clear drop in the value of the [O III]/Hα ratio.