Radio Astronomy, Positional Astronomy And The Galactic Centre

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Radio Astronomy, Positional Astronomy And The
Galactic Centre
Jess Broderick Supervisor Dr George Warr
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Outline

• What do we find at the Galactic Centre by
  studying it at radio wavelengths?
• How do we know where to point our radio
  telescopes to observe the Galactic Centre?
• Discussion of the results obtained.

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Sgr A - 21 cm wavelength radio continuum image
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Sgr A

• Diameter upper limit 3 billion km.
• Mass 2.6 million solar masses.
• Strong evidence that Sgr A is a gigantic black
  hole!
• Source of radio emissions is non-thermal
  synchrotron radiation.

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Celestial Coordinate Systems

• Equatorial coordinate system
• Horizon coordinate system
• Can convert between these respective coordinate
  systems.

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Equatorial Coordinate System
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Equatorial Coordinate System
North Celestial Pole
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Horizon Coordinate System
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Horizon Coordinate System
North Celestial Pole
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Converting Between Coordinate Systems

• Aim is to obtain the azimuth and altitude of the
  Galactic Centre at a particular time and
  location, from the known right ascension and
  declination values.
• RA 17h45m40s DEC -29028 (J2000)
• Need a variety of parameters to allow for an
  accurate transformation.

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Precession

• RA RA(2000)
• (3.075 1.336ysin(RA)tan(Dec))
• Dec Dec(2000) 20.04ycos(RA)
• y years from 1 January 2000

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Nutation

• delta RA (0.91750.3978sin(RA)tan(Dec))dL -
  dEcos(RA)tan(Dec)
• delta Dec 0.3978cos(RA)dL dEsin(RA)
• delta RA and delta Dec are added to the mean
  coordinates to obtain a more accurate set of
  coordinates.

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Parameters Required

• Corrected Right Ascension and Declination values
• Latitude and Longitude of observer
• Date, Universal Time
• Julian Day
• Local Sidereal Time
• Local Hour Angle

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Transformation Equations

• tan(Az)
• sin(H) / sin(H)sin(f) - tan(d)cos(f)
• sin(Al)
• sin(f)sin(d) cos(f)cos(d)cos(H)
• f Latitude of observer
• d Declination
• H Local Hour Angle

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Summary

• Main radio source at the Galactic Centre is Sgr
  A. Within Sgr A, Sgr A is the most intense radio
  emitter.
• Needed to convert the right ascension and
  declination of the Galactic Centre to its
  altitude and azimuth at a given location and
  time.
• Radio source was detected.