Rotation Curve of our Milky Way Galaxy

Joachim Köppen, Strasbourg, 2011/12

To startup the ESA-Haystack telescope, follow the procedures

• Click Record to start recording the data
• The positions in the Galactic Plane to observe are: G10, G20, … , and G90. The position of the galactic centre (SgrA) does not give information for the rotation curve.
• Use a frequency span of 1.5 or 2 MHz, and set the centre frequency so that you get the entire Galactic feature
• Observe each position for 5 min

Interpretation (more details):

• Import the text file with the data into Excel
• For each position (Galactic longitude l) do the following
  • get the average from all the spectra taken here, and plot it in a Scatter Plot
  • Determine the lowest frequency which shows Galactic emission
  • Convert this frequency to radial speed, by
    vrad_max = -(fmin/1420.406 – 1)*299792.458 – VLSR
    where VLSR is the value of the 6th column, the correction to the Local Standard of Rest for the direction we had observed
  • Oort’s formula then gives the rotational velocity
    vrot(R) = vrad_max + vsun*sin l for radius R = Rsun * sin l
    with vsun = 210 km/s and Rsun = 8.5 kpc

| back to Main page | ESA-Haystack Radio Telescope (1.4 GHz) | ESA-Dresden Ratio Telescope (10GHz) | to my HomePage |

last update: Sept. 2011 J.Köppen