The time evolution of HH 1 from four epochs of HST images

TL;DR

This study analyzes four epochs of HST images of HH 1 to investigate its proper motions, velocity evolution, and emission line intensity changes over two decades, revealing acceleration and emission variations.

Contribution

Introduces a new wavelet-based method for analyzing proper motions in astronomical images, enabling detailed velocity and emission evolution studies of HH 1.

Findings

HH 1 shows clear acceleration over two decades.

Hα and [S II] intensities first dropped then recovered.

[O III]/Hα ratio decreased between 1994 and 2014.

Abstract

We present an analysis of four epochs of H$\alpha$ and [S II] $\lambda\lambda$ 6716/6731 HST images of HH 1. For determining proper motions we explore a new method based on 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 H$\alpha$ and [S II] intensities have 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] $\lambda$ 5007 (1994 and 2014), in which we see a clear drop in the value of the [O III]/H$\alpha$ ratio.