PHYSICAL CHARACTERIZATION OF ASTEROIDS
NEON Group 5:Koraljka MužićNikola VitasGrzegorz Nowak Mario MarsSimone Marchi (tutor)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
OUTLINE
# Introduction
# Photometry of 1980 Tezcatlipoca
# Spectroscopy of 2 Pallas and 25 Phocaea
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Asteroid observations
# Photometry: information about the shape of the body and scattering properties of the surface
# Spectroscopy: information about the chemical composition and homogeneity of the surface
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
Asteroid classification
Asteroid classification
Three spectral complexes:
S – type: consisted mostly of silicates, with addition of different elements Moderately steep slope for λ<0.7μm, silicon absorption feature at 1 μm
C - type: carbon rich silicate compositionFlat spectra, shallow absorption features, if present at allVery low albedos
X – type: carbon rich and metal rich;a generally featureless spectra, with slight to moderately red slope;A subtle UV absorption feature, at λ<0.55μm; occasionally shallowabsorption feature at λ>0.85μm
PHYSICAL CHARACTERIZATION OF ASTEROIDS: INTRODUCTION
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# 1980 Tezcatlipoca (NEO): DATA
# Absolute magnitude, 13.92
# Diameter, D = 4.3 km (Gehrels, 1994)
# Rotation period, P = 7.2523 h (Wisniewski et al, 1997)
# Geometric albedo, g = 0.25
# Spectral type, S
# Discovered 19/06/1950 by Wilson, A. G. at Palomar
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Orbit of Tezcatlipoca [25/07/2006]Sun – Target – Earth angle = 59º
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Observations of 1980 Tezcatlipoca at OHP
# Two nights: 25/07/2006 (63 frames), 30/07/2006 (55 frames)
# Telescope: 1.20 cm
# Detector: CCD TK1024
# Filter: R
# Exposure time: 120 s
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# 1980 Tezcatlipoca in 12’x12’ star field
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# 1980 Tezcatlipoca in 12’x12’ star field
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Selected reference stars and 1980 Tezcatlipoca# Photometry: information about the shape of the body and homogeneity of the surface
# Spectroscopy: information about the chemical composition
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# The instrumental magnitude variation of 20 selected reference stars [25/07/2006]
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Tezcatlipoca / photometric observations: line = original data, squares = corrected values
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Previous observations (Kaasalainen et al, 2004)
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Composite light curve plot of the two observations of Tezcatlipoca
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Model of Tezcatlipoca or What did we conclude?
# Rough dimensions a/b = 1.4, b/c = 1.4 (Kaasalainen et al, 2004)# Considerable irregularities
# The high solar phase angles and shadowing effects can explain high amplitudes of the light curve even if the model is not highly elongated.# The “barrel-like” model may also represent a “bone” shape of the asteroid…
# …though we cannot expect narrow “waist” if the object is not highly elongated.
# New observations are necessary to confirm the model and to explain the systematic effects indicated by the difference between data obtained with R and V filter.
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
5th NEON SCHOOL, OHP, 2006
Spectroscopy of Pallas (2)
# General informations about Pallas.
# Observations and data reduction.
# Spectra and their slopes.
# Variations of the spectrum.
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
5th NEON SCHOOL, OHP, 2006
Discovery
Discoverer Heinrich Wilhelm Olbers
Discovery date March 28, 1802
Orbital elements
Eccentricity (e) 0.231
Semi-major axis (a) 2.773 AU
Orbital period (P) 4.62 years
Inclination (i) 34.840
Longitude of the ascending node (Ω) 173.150
Argument of perihelion 310.450
Physical characteristics
Dimensions 570x525x500 km
Mass 2.2x1020 kg
Density 2.8 g/cm3
Surface gravity 0.18 m/s2
Escape velocity 0.32 km/s
Rotational period 7.81 h
Absolute magnitude 4.18
Spectral class B-type asteroid
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Size comparison: the first 10 asteroids profiled against Earth’s Moon. Pallas is the second on the left.
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# B-type
# Relatively uncommon type of carbonaceous asteroid, falling into the wider C-group,
# generally similar to the C-type objects,
# ultraviolet absorption below 0.5 um is small or absent,
# spectra is rather slightly bluish than reddish, #the albedo also tends to be greater than the generally very dark C-type.
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Reflectance spectra of C class asteroids (Gaffey et al, 1993)
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
1. The spectra were obtained with the 1.93 m telescope in conjunction with the CARELEC spectrograph 26/07/2006.
2. We used solar-like spectrum combined from three reference G2-type stars to divide the asteroid spectra and obtain the reflectivity of the asteroid.
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Reflectance spectra of C class asteroids (Gaffey et al, 1993)
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Reflectance spectra of C class asteroids (Gaffey et al, 1993)
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
Spectroscopy of Phocaea (25)
# Discovered by J. Chacornac on April 6, 1853
# Member of the main asteroid belt
# Distance ~3 AU
# Diameter 75.1 km
# Rotation period 9.954 h
# Inclination 21.58°
# Silicaceous-type [spectral class S]
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# S-type asteroids
# 13-17% of known asteroids
# Composition silicate & Fe-Ni core
# Dominate the inner asteroid belt
# Reflect ~15%
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Phocaea group in main belt
# Mean orbital radius between 2.25 and 2.5 AU
# Inclination between 18° and 32°
# Eccentricity >0.1
# Distribution is determined byGravitational influence ofJupiter
Phocaea group
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Olivine & pyroxene
# Fe2SiO4 [fayalite] and Mg2SiO4 [forsterite]
# XY(Si; Al)2O6 [XY = calcium, sodium, magnesium, iron, chronium mixed mineral]
Pyroxene
Olivine
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Reflectance spectra of C class asteroids (Gaffey et al, 1993)
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
PHYSICAL CHARACTERIZATION OF ASTEROIDS
5th NEON SCHOOL, OHP, 2006
# Reflectance spectra of C class asteroids (Gaffey et al, 1993)
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
THANK YOU FOR YOUR ATTENTION!
5th NEON SCHOOL, OHP, 2006