{
  "id": "1610.01951",
  "version": "v1",
  "published": "2016-10-06T17:08:12.000Z",
  "updated": "2016-10-06T17:08:12.000Z",
  "title": "The time evolution of HH~2 from four epochs of HST images",
  "authors": [
    "A. C. Raga",
    "B. Reipurth",
    "P. F. Velázquez",
    "A. Esquivel",
    "J. Bally"
  ],
  "comment": "17 pages, 10 figures. Accepted for publication in The Astronomical Journal",
  "categories": [
    "astro-ph.GA"
  ],
  "abstract": "We have analyzed four epochs of H$\\alpha$ and [S~II] HST images of the HH~1/2 outflow (covering a time interval from 1994 to 2014) to determine proper motions and emission line fluxes of the knots of HH~2. We find that our new proper motions agree surprisingly well with the motions measured by Herbig \\& Jones (1981), although there is partial evidence for a slight deceleration of the motion of the HH~2 knots from 1945 to 2014. We also measure the time-variability of the H$\\alpha$ intensities and the [S~II]/H$\\alpha$ line ratios, and find that knots H and A have the largest intensity variabilities (in $1994\\to 2014$). Knot H (which now dominates the HH~2 emission) has strengthened substantially, while keeping an approximately constant [S~II]/H$\\alpha$ ratio. Knot A has dramatically faded, and at the same time has had a substantial increase in its [S~II]/H$\\alpha$ ratio. Possible interpretations of these results are discussed.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-10-06T17:08:12.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "hst images",
      "time evolution",
      "determine proper motions",
      "largest intensity variabilities",
      "proper motions agree"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 17,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}