Radio Observations &
Galactic Rotation
The WVU Small Radio Telescope Project
| Brian Kent | |
| Honors Symposium | |
| April 25, 2003 |
| Obtained in January 2001 from the National Radio Astronomy Observatory at Green Bank | |
| 2.1 meter dish, observations at L-band | |
| Designed to observe the only radio transition of neutral hydrogen |
Telescope Operations
&
Specifications
| 2.1 meter primary reflector | ||
| F/D = 0.375 | ||
| (Cassegrain Focus) | ||
| Pre-Amp frequency: | ||
| 1400-1440 MHz | ||
| L.O. frequency: | ||
| 1370-1800 MHz | ||
| FWHM Beamwidth: | ||
| ~ 7 degrees | ||
| Stepping motors control altitude and azimuth motion | ||
| Analog | ||
| 40 kHz Channel Spacing | ||
| Manual Configuration of spectral bandwidth | ||
| Digital | ||
| 7.81 kHz Channel Spacing | ||
| 4 Observing modes: 125, 250 500 and 1200 kHz | ||
Antenna Temperature to
Flux Density
Neutral Hydrogen in the Galaxy
| Hyperfine transition | ||
| 1420.4058 MHz / 21 centimeters | ||
| Occurs from change in orientation of the magnetic dipole | ||
| HI is observed throughout the Milky Way galaxy and is an important tool in studying other galaxies | ||
| Predicted in the 1940’s by Hendrick van de Hulst | ||
| (Van De Hulst, H. C., 1945, Ned. Tijdschr. Natuurk,, 11, 201) | ||
| and subsequently discovered by observation in 1951 | ||
| (Ewen, H. I. & Purcell, E. M., 1951, Nature, 168, 350; Muller, C. A. & Oort, | ||
| J. H., 1951, Nature, 168, 357) | ||
HI Spectra along
the Galactic Plane
Determination of
Tangential Velocity
Tangential Velocity measured from spectra
How fast does a galaxy rotate?
| Angular velocity w is given by |
Determination
of
Column Density NH
| The amount of hydrogen per square centimeter (column density), NH is given by |
| Instrumentation upgrades have been completed – new receiver and calibration systems | |
| Study of neutral hydrogen and galactic rotation comparable to results from larger telescopes | |
| System available for physics students interested in radio astronomy |