Asteroids Rotation Period

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Asteroids Rotation Period
Surface composition
spectroscopy
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Observations reveal
Time-dependent brightness variations
Rotation period of the asteroid around its axis
Due to
Different reflectivity across the asteroid
Non spherical shape of the asteroid
Average rotation period 10 h
Typical brightness variation 0.2 mag
Fast rotators period 2 h
Slow rotators period few weeks
Most rotators period 7 h 30 h
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Asteroid Rotation Period Determination
Non spherical shape- rugby ball
Time-dependent brightness variations
for most asteroids are due to
Cross section changes (as seen by the Earth)
Light reflected towards us varies- Brightness
appears to vary
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Asteroid Rotation Period Determination
Shape is 180 degrees symmetrical around an axis
perpendicular to its greatest dimension
Rugby-ball shaped asteroid
Other side of the asteroid
max
max
min
max
min
same side of the asteroid-full revolution
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Asteroid Photometry
Magnitude system
The scale that traditionally has being used to
denote the brightness of an object
brightness
Based on the eye
Brighter stars 1st mag Dimmest stars 6st
mag
The intensity becomes 10 times larger every -2.5
magnitudes eg. 6st mag star is 100 times fainter
than 1st mag star
Real intensity
Or in mathematics
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Asteroid photometry process

• Every certain interval of time take a picture
• in each picture measure the signal from the
  asteroid
• Measure the signal from at least one comparison
  star of similar color in the vicinity of the
  asteroid

Is the comparison star variable?
Pick 2 or more comparison stars and use the
average intensity
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Asteroid photometry process-continued

• Calculate ?m from each measurement (we need to
  know the brightness variation and not the actual
  brightness of the asteroid )
• Plot ?m vs time (eg. pictures are 3min apart)
• Calculate the period by measuring the time
  between consequitive maxima or minima of the same
  amplitude

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Exercise procedure
Short period lt 4h Bright enough Be observable
most of the night

• Pick an asteroid
• Plan an observation
• Submit a request to the telescope
• Analyse the data

List of asteroids 1727 Mette
Cartes du Ciel
Avis