Rotation period. Study the photometric curve. Shape. Is it binary?. Asteroids Rotation Period. spectroscopy. Surface composition. Observations reveal:. Time-dependent brightness variations. Rotation period of the asteroid around its axis. Due to:.
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Rotation period Study the photometric curve Shape Is it binary? Asteroids Rotation Period spectroscopy Surface composition
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
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
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 min max same side of the asteroid-full revolution
Asteroid Photometry Magnitude Intensity 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 staris 100 times fainter than1st mag star Real intensity: Or in mathematics :
Known brightness Magnitude Intensity 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 onecomparison 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
Asteroid photometry process-continued : • Calculate Δm from each measurement (we need to know the brightness variation and not the actual brightness of the asteroid ) • Plot Δm vs time (eg. pictures are 3min apart) • Calculate the period by measuring the time between consequitive maxima or minima of the same amplitude
Exercise procedure Short period : < 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