Asteroids Rotation Period Study the photometric curve Rotation period Shape Is it binary? Surface composition spectroscopy

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 Typical brightness variation : 0.2 mag Average rotation period: 10 h Fast rotators period: 2 h Slow rotators period: few weeks Most rotators period: 7 h –30 h

Asteroid Rotation Period Determination Time-dependent brightness variations for most asteroids are due to: Non spherical shape- rugby ball 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 max min max min Other side of the asteroid same side of the asteroid- full revolution

Asteroid Photometry Magnitude system Brighter stars : 1 st mag Dimmest stars : 6 st mag brightness Based on the eye Real intensity: The intensity becomes 10 times larger every -2.5 magnitudes eg. 6 st mag star is 100 times fainter than 1 st mag star Or in mathematics : Magnitude Intensity The scale that traditionally has being used to denote the brightness of an object

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 one comparison star of similar color in the vicinity of the asteroid Known brightness Pick 2 or more comparison stars and use the average intensity Is the comparison star variable?

 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 Asteroid photometry process-continued :

Exercise procedure  Pick an asteroid  Plan an observation  Submit a request to the telescope  Analyse the data Short period : < 4h Bright enough Be observable most of the night List of asteroids 1727 Mette Cartes du Ciel Avis