PHYSICAL CHARACTERIZATION OF ASTEROIDS NEON Group 5: Koraljka Mužić Nikola Vitas Grzegorz Nowak

PHYSICAL CHARACTERIZATION OF ASTEROIDS

NEON Group 5:Koraljka MužićNikola VitasGrzegorz Nowak Mario MarsSimone Marchi (tutor)

5th NEON SCHOOL, OHP, 2006



OUTLINE

# Introduction

# Photometry of 1980 Tezcatlipoca

# Spectroscopy of 2 Pallas and 25 Phocaea



# 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



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



# 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



# Orbit of Tezcatlipoca [25/07/2006]Sun – Target – Earth angle = 59º




# 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




# 1980 Tezcatlipoca in 12’x12’ star field




# 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




# The instrumental magnitude variation of 20 selected reference stars [25/07/2006]




# Tezcatlipoca / photometric observations: line = original data, squares = corrected values




# Previous observations (Kaasalainen et al, 2004)




# Composite light curve plot of the two observations of Tezcatlipoca




# 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: SPECTROSCOPY


Spectroscopy of Pallas (2)

# General informations about Pallas.

# Observations and data reduction.

# Spectra and their slopes.

# Variations of the spectrum.



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



# Size comparison: the first 10 asteroids profiled against Earth’s Moon. Pallas is the second on the left.




# 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.




# Reflectance spectra of C class asteroids (Gaffey et al, 1993)




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.




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]




# S-type asteroids

# 13-17% of known asteroids

# Composition silicate & Fe-Ni core

# Dominate the inner asteroid belt

# Reflect ~15%




# 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




# Olivine & pyroxene

# Fe2SiO4 [fayalite] and Mg2SiO4 [forsterite]

# XY(Si; Al)2O6 [XY = calcium, sodium, magnesium, iron, chronium mixed mineral]

Pyroxene

Olivine


THANK YOU FOR YOUR ATTENTION!


PHYSICAL CHARACTERIZATION OF ASTEROIDS NEON Group 5: Koraljka Mužić Nikola Vitas Grzegorz Nowak

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