PHYSICAL CHARACTERIZATION OF ASTEROIDS
NEON Group 5:
Koraljka Mužić
Nikola Vitas
Grzegorz Nowak
Mario Mars
Simone Marchi (tutor)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS
OUTLINE
# Introduction
# Photometry of 1980 Tezcatlipoca
# Spectroscopy of 2 Pallas and 25 Phocaea
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS
# 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
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS INTRODUCTION
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 composition
Flat spectra, shallow absorption features, if present at all
Very 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 shallow
absorption feature at λ>0.85μm
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# 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
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# Orbit of Tezcatlipoca [25/07/2006]
Sun – Target – Earth angle = 59º
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# 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
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# 1980 Tezcatlipoca in 12’x12’ star field
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# 1980 Tezcatlipoca in 12’x12’ star field
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# 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
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# The instrumental magnitude variation of 20
selected reference stars [25/07/2006]
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# Tezcatlipoca / photometric observations:
line = original data, squares = corrected values
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# Previous observations (Kaasalainen et al, 2004)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# Composite light curve plot of the two observations
of Tezcatlipoca
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS PHOTOMETRY
# 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.
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
Spectroscopy of Pallas (2)
# General informations about Pallas.
# Observations and data reduction.
# Spectra and their slopes.
# Variations of the spectrum.
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS: SPECTROSCOPY
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
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Size comparison: the first 10 asteroids profiled
against Earth’s Moon. Pallas is the second on the left.
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# 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 Ctype.
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Reflectance spectra of C class asteroids
(Gaffey et al, 1993)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
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.
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Reflectance spectra of C class asteroids
(Gaffey et al, 1993)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Reflectance spectra of C class asteroids
(Gaffey et al, 1993)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
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]
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# S-type asteroids
# 13-17% of known asteroids
# Composition silicate & Fe-Ni core
# Dominate the inner asteroid belt
# Reflect ~15%
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# 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 by
Gravitational influence of
Jupiter
Phocaea group
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Olivine & pyroxene
# Fe2SiO4 [fayalite] and Mg2SiO4 [forsterite]
# XY(Si; Al)2O6 [XY = calcium, sodium, magnesium, iron, chronium
mixed mineral]
Pyroxene
Olivine
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Reflectance spectra of C class asteroids
(Gaffey et al, 1993)
5th NEON SCHOOL, OHP, 2006
PHYSICAL CHARACTERIZATION OF ASTEROIDS:
ASTEROIDS SPECTROSCOPY
# Reflectance spectra of C class asteroids
(Gaffey et al, 1993)
5th NEON SCHOOL, OHP, 2006
THANK YOU FOR YOUR ATTENTION!
5th NEON SCHOOL, OHP, 2006