Observing Asteroids CCD

Observing Asteroids with CCD:Measuring some characteristics

with “backyard” instruments

Presented to:

Chagrin Valley Astronomical Society

September 3, 2011

By Ron Baker, CVAS member

Introduction:

CCD observations of asteroids by “backyard” astronomers can yield many characteristics including:

• Orbital elements• Rotational period• Absolute magnitude• Light scattering properties of the surface• Orientation of spin axis• Size & shape

All with telescopes in the 8 to 14 inch range and commonly available CCD cameras.

Main-belt asteroid 581 Tauntonia

FOV 12 X 8 arcmin, 120-sec exposure, mag 14.8V, 12-inch SCT, February 2010, IHO

Astrometry & PhotometryMeasuring the position and brightness of 581 Tauntonia

Reference stars from the CMC-14 catalog selected by Astrometrica.

Characteristics of Asteroids

• Orbital elements

• Family

• Rotational period

• Amplitude

• Absolute magnitude (H)

• Phase slope parameter (G)

• Taxonomic class

• Albedo

• Diameter

• Equitorial elongation

• Spin axis

• Shape



• Family


• Amplitude



• Taxonomic class

• Albedo

• Diameter


• Spin axis

• Shape

Astrometry (from backyard observations)



• Family


• Amplitude



• Taxonomic class

• Albedo

• Diameter


• Spin axis

• Shape

Astrometry (from backyard observations)Photometry (from backyard observations)



• Family


• Amplitude



• Taxonomic class

• Albedo

• Diameter


• Spin axis

• Shape


Spectroscopy, Satellite Imaging, Radar (from professional observations)



• Family


• Amplitude



• Taxonomic class

• Albedo

• Diameter


• Spin axis

• Shape


Spectroscopy, Satellite Imaging, Radar (from professional observations)Modeling (backyard and professional collaborations)


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Minor Planet Center (MPC)

• Operates with authority of IAU.

• MPC accepts observations from specially designated observatories. Official observatory code for IHO: [H75]

• Large scale surveys do most of the discovering now. Examples include Catalina Sky Survey, Linear & Wise.

• Follow up observations on newlydiscovered objects are critical.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Minor Planet Center (MPC)

• A set of 3 or more observations separated in time are needed to determine an initial set of orbital elements.

• Follow-up observations of new objects are needed several weeks after discovery to confirm the object’s existence and to improve the set of orbital elements.

• The MPC publishes lists of new objects needing confirmation. Some turn out to be Near Earth Objects (NEO) which cross the Earth’s orbit and are potentially hazardous, others are much more distant and pose no threat.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape1998 KN3, Stack of 48 images, 60-sec each, 12-inch SCT, March 2010, IHO


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape1998 KN3, Stack of 48 images, 60-sec each, 12-inch SCT, March 2010, IHO


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Apollo NEO 88254 (2001 FM129)Potentially Hazardous Asteroid (PHA)

Discovered March 2001 by the Linear Survey

64 exp, unfiltered, 8-sec each, 12-inch SCT, mag 14, March 2010, IHO


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Apollo NEO 88254 (2001 FM129)Potentially Hazardous Asteroid (PHA)

Discovered March 2001 by the Linear Survey

Graphic from JPL’s Small-Body Database Browser


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Long Period Comet C2010 F1 (Boattini)Discovered February 2010 by the Catalina Sky Survey

24 exp, unfiltered, 120-sec each, 12-inch SCT, mag 19, March 2010, IHO


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Long Period Comet C2010 F1 (Boattini)Discovered February 2010 by the Catalina Sky Survey

Graphic from JPL’s Small-Body Database Browser


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Major asteroid families

• Main Belt asteroidsSemi-major axis 2-3 AU (between Mars & Jupiter).More than 500,000 known to exist.

• Near-Earth objectsCross Earth orbitApollo, Aten, AmorNearly 7,500 are known at present time.

• TrojansOccupies an orbit similar to a planet.Gravitationally locked before/after a planet.Most are associated with Jupiter, but also Neptune and Mars. The first Earth Trojan was recently discovered.

• Trans-Neptunian and Kuiper Belt objectsMany sub-classes, semi-major axis 30 AU to 500+ AU


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Atiras 1Atens 672Apollos 3,770Amors 3,022Hungarias 10,102Phocaeas 11,632Mars-Crossers 7,184Main-Belt 527,886Hildas 3,308Jupiter Trojans 5,073Centaurs 227Plutinos 241Classical TNOs 882Other TNOs 35Scattered-Disk Objects 169

Family Census DataFrom the Minor Planet Center (September 2011)

http://en.wikipedia.org/wiki/163693_Atira

http://en.wikipedia.org/wiki/Aten_asteroid

http://en.wikipedia.org/wiki/Apollo_asteroid

http://en.wikipedia.org/wiki/Amor_asteroid

http://en.wikipedia.org/wiki/Hungaria_asteroid

http://en.wikipedia.org/wiki/Phocaea_family

http://en.wikipedia.org/wiki/Mars-crossing_Asteroid



http://en.wikipedia.org/wiki/Main-belt_Asteroid



http://en.wikipedia.org/wiki/Hilda_asteroid

http://en.wikipedia.org/wiki/Trojan_asteroid

http://en.wikipedia.org/wiki/Centaur_(minor_planet)

http://en.wikipedia.org/wiki/Plutoid

http://en.wikipedia.org/wiki/Trans-Neptunian_object

http://en.wikipedia.org/wiki/Trans-Neptunian_object

http://en.wikipedia.org/wiki/Scattered-disc_object




Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Rotational period is the time required for the

asteroid to make one complete rotation about its

own axis in relation to the Earth.

• Asteroids have irregular shapes. During rotation,

the asteroid presents a varying surface area to our

line of sight.

• The period and amplitude is determined from a

lightcurve, which is built by plotting observations

obtained in a time series of images. There is

usually no need to place the instrumental

magnitudes on a standard magnitude system.

• When observations are made on succeeding

nights, the lightcurve plot must be phased.

Phased plots are usually bi-modal.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

A collaborative observing campaign was formed in the fall of 2010 to study asteroid 1082 Pirola. The results of the project are used here to describe how photometry can determine the rotational period and absolute magnitude of an asteroid. Details about this study can be found in the Minor Planet Bulletin article listed in the references.

• The rotational period and some other characteristics were unknown before the study.

• Lightcurves and data points for use in constructing a phase curve were obtained during the several months before and after opposition. The lightcurve data were archived for future spin axis and shape modeling.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape First time series: duration 6 hours.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape 2 time series separated by 24 days.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape With trial and error, the data is phased to 1 rotational period using the Fourier routine built into MPO Canopus.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape Complete coverage from 3 sessions, increasing precision.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape A session late in the apparition shows the amplitude has increased. But the rotational period remains consistent.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape Differential photometry & period analysis: MPO Canopus.(Credits R. Baker, F. Pilcher, V. Benishek, 2010)


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

H-G parameters were originally defined by the International Astronomical Union in 1985.

• Absolute magnitude (H) is a calculated value based on observed magnitudes. It represents the magnitude of an asteroid when 1 AU from both the Earth and the Sun, and at 0 degree phase angle (actually impossible orientationgeometrically).

• Phase slope parameter (G) describes how an asteroid brightens due strictly to change in phase angle, especially near opposition.

• Estimated magnitude of an asteroid can be predicted using these parameters.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Phase Angle

• Asteroids move throughphases (similar to the Moon or Venus).

• Asteroid phases are defined by an angle formed by 2 lines. The first line runs from the asteroid through the Earth, the second from the asteroid through the Sun.

• The phase angle approaches 0 degrees when the asteroid is at opposition.

• Most asteroids do not cross the ecliptic right at opposition. So the minimum phase angle is usually at least a few degrees (and often much more) above or below the ecliptic.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Changing Brightness

• Due to rotation: The amplitude of a typical lightcurve is between 0.1 and 0.5 magnitude. Most asteroids have a rotational period greater than 4 hours but less than 1 day.

• Due to changing distance: The distance from the Earth and also the Sun influence the asteroid’s apparent brightness. These changes occur slowly over several weeks and months.

• Due to changing phase: Changes slowly over several months. The change is linear at phase angles greater than roughly 7 degrees. But a surge in brightness is often observed at smaller phase angles. (Opposition effect.)


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Phase Curve

• The effects on brightness due to rotation and change in distance must be removed from the observations. Result is reduced magnitude.

• The phase curve plot yields an estimated measurement of absolute magnitude (H) and the phase slope parameter (G).

• H & G studies require standard magnitudes from observations in the V-band covering a wide range of phase angles. For best results the minimum phase angle should be < 1 degree.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Differential standard V-band photometry: AstrometricaH-G utility: MPO Canopus(Credits R. Baker, F. Pilcher, V. Benishek, 2010)


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Spectroscopy:

Asteroids are placed in taxonomic classes on the

basis of their spectral classification.

• Reflectance spectrum is a plot showing

varying levels of reflectivity dependent on

wave length.

• Horizontal axis is the wavelength in microns.

Vertical axis is the reflectance or albedo. This

is the ratio of incident sunlight reflected back

from the surface.

• Spectral features such as absorption bands

reveal the presence of specific minerals.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

The ECAS and SMASSII spectroscopic surveys

provide the data used by astronomers to assign

classes.

• Eight-Color Asteroid Survey (ECAS) was

conducted in 1984. Most asteroids were

found to fit into 3 broad categories:

carbon, stone and metallic. 14 classes were

established.

• The Small Main-Belt Asteroid Spectroscopic

Survey (SMASSII) made high resolution

observations in 2002. Total of 22 classes.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Satellite Observations

The diameter of some asteroids have been

measured directly by orbiting satellites. The

observations are made in the Infrared band of the

spectrum.

• Infrared Astronomical Satellite (IRAS)

The Supplemental IRAS Minor Planet Survey

(SIMPS) is based on IRAS, and contains data

relative to asteroids.

• Wide-Field Infrared Survey Explorer (WISE)

Research is currently underway on the vast

amount of data produce by this survey.

http://en.wikipedia.org/wiki/IRAS

http://wise.ssl.berkeley.edu/




Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

Radar

The Arecibo Observatory and Goldstone Solar

System Radar are used to measure many asteroid

characteristics, including the diameter of larger

objects.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

A mathematical relation exists between diameter,

albedo and absolute magnitude (H). It is possible

for a large asteroid with a small albedo can have

the same absolute magnitude (H) as a smaller

asteroid with a larger albedo.

• When an asteroid’s diameter has been

measured directly, albedo can be calculated

using the observed absolute magnitude (H).

• Diameter can also be estimated by using the

observed absolute magnitude (H) and an

assumed value for albedo.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

The equitorial elongation of an asteroid can be

estimated from the amplitude of the lightcurve.

• The amplitude normally decreases as the

phase angle decreases, then increases again

after opposition.

• Observations recorded near 0 degrees phase

angle should be used for the calculation.


Orbital elements

Family

Rotation period

Amplitude

Abs mag (H)

Phase slope (G)

Taxonomy

Albedo

Diameter

Elongation

Spin axis

Shape

The spin axis is referenced to the ecliptic, and

defined by the ecliptic longitude & latitude. An

asteroid’s shape can be estimated with special

modeling software.

• Mathematically intensive.

• Requires significant amounts of lightcurve data

preferably at many phase angles.

• Data from several apparitions are needed.

Duration of these studies is long-term.

• Suitable for collaborations between

professional and amateur astronomers.

Characteristics of Asteroids(Summary)


• Family


• Amplitude



• Taxonomic class

• Albedo

• Diameter


• Spin axis

• Shape


Spectroscopy, Satellite Imaging, Radar (from professional observations)Modeling (backyard & professional collaborations)

Organizations

Association of Lunar and Planetary Observers. http://alpo-astronomy.org/

British Astronomical Association, Asteroid and Remote Planets Section.http://britastro.org/asteroids/table%20of%20contents.htm

JPL Small-Body Database Browser. http://ssd.jpl.nasa.gov/sbdb.cgi

Minor Planet Center. http://www.minorplanetcenter.net/

Books

Asteroids and How to Observe Them. Roger Dymock. Springer-Verlag.http://www.springerlink.com/

Lightcurve Photometry and Analysis. Brian D. Warner. Springer-Verlag.http://www.springerlink.com/

Software

Astrometrica. http://www.astrometrica.at/

MPO Canopus. Bdw Publishing. http://www.minorplanetobserver.com/

http://alpo-astronomy.org/



http://britastro.org/asteroids/table of contents.htm

http://ssd.jpl.nasa.gov/sbdb.cgi

http://www.minorplanetcenter.net/

http://www.springerlink.com/

http://www.springerlink.com/

http://www.astrometrica.at/

http://www.minorplanetobserver.com/

References:

Baker, R., Pilcher, F., Benishek, V. (2011). “Photometric Observations and Analysisof 1082 Pirola.” Minor Planet Bulletin 38-2, 111-114. http://www.minorplanet.info/mpbdownloads.html

Bus, S. J., Binzel, R. P. (2002). “Phase II of the small main-belt asteroid spectroscopic survey: A feature-based taxonomy.” Icarus 158, 146-177.http://fkometes.pagesperso-orange.fr/documents%20pdf/bus_spectrum0_sdarticle.pdf

Dymock, R., Miles, R. (2009). “A method for determining the V magnitude of asteroids from CCD images.” Journal of the British Astronomical Association 119, 149-156.http://britastro.org/asteroids/JBAA%20119%20149-156%20Dymock1.pdf

Harris, A.W. (1989). “The H-G Asteroid Magnitude System: Mean Slope parameters.” Lunar Planetary Science XX, 375-376.http://www.lpi.usra.edu/meetings/lpsc1989/pdf/1192.pdf

Tedesco, E.F., Noah, P.V., Noah, M., and Price, S.D. (2002). “The Supplemental IRASMinor Planet Survey.” The Astronomical Journal 123, 1056-1085. http://iopscience.iop.org/1538-3881/123/2/1056/pdf/1538-3881_123_2_1056.pdf

Warner, B.D. (2007). “Initial Results from a Dedicated H-G Project.” The Minor Planet Bulletin 34-4, 113-119.http://www.minorplanet.info/mpbdownloads.html

http://www.minorplanet.info/mpbdownloads.html

http://fkometes.pagesperso-orange.fr/documents pdf/bus_spectrum0_sdarticle.pdf



http://britastro.org/asteroids/JBAA 119 149-156 Dymock1.pdf



http://www.lpi.usra.edu/meetings/lpsc1989/pdf/1192.pdf

http://iopscience.iop.org/1538-3881/123/2/1056/pdf/1538-3881_123_2_1056.pdf







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Observing Asteroids CCD