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Photometric Photometric Observation of Observation of
((11Japan Spaceguard Association, Japan Spaceguard Association, 22Seoul University, Seoul University, 33Aizu University, Aizu University, 44National Astronomical Observatory of Japan, National Astronomical Observatory of Japan, 55ISAS(Institute of Space ISAS(Institute of Space and Astronautical Science)/JAXA(Japan Aerospace Exploration Agency)and Astronautical Science)/JAXA(Japan Aerospace Exploration Agency)
우라카와 세이다로Сейтаро Уракаба
Outline Outline
Introduction Introduction Asteroid Explorer HayabusaAsteroid Explorer Hayabusa Primitive Body Missions of JapanPrimitive Body Missions of Japan 107P/4015 Wilson-Harrington107P/4015 Wilson-Harrington Observations Observations Data Reduction Data Reduction Results (Rotational Period; Rotational Direction; Results (Rotational Period; Rotational Direction;
Pole Direction; Shape Model ) Pole Direction; Shape Model ) SummarySummary
Welcome Home Welcome Home Asteroid ExplorerAsteroid Explorer Hayabusa Hayabusa
June 13, 2010 Asteroid explore Hayabusa return to the earth.
Welcome Home Welcome Home Asteroid ExplorerAsteroid Explorer Hayabusa Hayabusa
May 9, 2003: Lift off
Sep 12, 2005: Arrive asteroid Itokawa
Nov, 2005: Two times touch down and Nov, 2005: Two times touch down and collect the sample.collect the sample.
Welcome Home Welcome Home Asteroid ExplorerAsteroid Explorer Hayabusa Hayabusa
June 13 , 2010, at 10:54 (UT) Capsule release
June 13 , 2010, at 14:08 (UT) Touch down in Australia
Scientific Purpose of Hayabusa MissionScientific Purpose of Hayabusa Mission
Asteroids and comets preserve the condition at the Asteroids and comets preserve the condition at the birth of solar system.birth of solar system.
We can obtain a clue on the birth of solar system We can obtain a clue on the birth of solar system by analyzing the sampleby analyzing the sample in detail.in detail.
Primitive bodies (asteroids and comets) have not Primitive bodies (asteroids and comets) have not accepted much thermal influences since the early stage accepted much thermal influences since the early stage of solar system. In addition to it, the objects have not of solar system. In addition to it, the objects have not been weathered.been weathered.
Taxonomy of AsteroidsTaxonomy of AsteroidsInner asteroid belt:Inner asteroid belt:S-type asteroids are dominated.S-type asteroids are dominated.
New Explorer (Development of new ion engine)New Explorer (Development of new ion engine)
Candidate of target: D-type or Dormant comet Candidate of target: D-type or Dormant comet (for example 107P/4015 Wilson-Harrignton)(for example 107P/4015 Wilson-Harrignton)
In order to design the mission, the physical properties of WH In order to design the mission, the physical properties of WH (rotational period, rotational direction, pole direction, shape) (rotational period, rotational direction, pole direction, shape)
are needed.are needed.
Such physical properties are obtainedSuch physical properties are obtained by the photometric observation (the light-curve of WH).by the photometric observation (the light-curve of WH).
The mission can provide insights on the unknown link The mission can provide insights on the unknown link between asteroids and comets.between asteroids and comets.
Semi-major axis Semi-major axis 22.638AU.638AUEccentricityEccentricity 0.6240.624InclinationInclination 22.78°.78°Argument of perihelionArgument of perihelion 9191.25°.25°Longitude of ascending nodeLongitude of ascending node 270270.57°.57°Period Period 44.28 year.28 year
Fernandez et al. 1997
A comet was discovered in 1949 A comet was discovered in 1949 at the Palomar observatory. The at the Palomar observatory. The faint tail can see. The comet faint tail can see. The comet named as 107P/Wilson-named as 107P/Wilson-Harrington. However, the comet Harrington. However, the comet was lost by the insufficient was lost by the insufficient observation.observation.
A near earth asteroid (4015) A near earth asteroid (4015) was discovered in 1979.was discovered in 1979.
The continuous observations The continuous observations identified that 107P/Wilson-identified that 107P/Wilson-Harrington and asteroid Harrington and asteroid (4015) were the same object.(4015) were the same object.
Past Study of Wilson-Harrington Past Study of Wilson-Harrington
Rotational period: two solutions Rotational period: two solutions for 0.148 day (3.556 hour) or for 0.148 day (3.556 hour) or 0.254 ±0.002day (6.1 ±0.05 hour)0.254 ±0.002day (6.1 ±0.05 hour)
University of Hawaii 2.2m (PI: Dr.Ishiguro)Dec 18, 2009
Kiso Observatory 1.05m (PI: Dr.Kitazato)Aug 17, 19, 20, Dec 12, 2009 / 4 days
Lulin Observatory 1.0m (PI: Dr.Kitazato)Dec 7-10, 2009 / 4 days
Okayama Astrophysical Observatory 0.5m (PI: Dr.Kuroda)Nov 7, 2009 – Dec 21, 2009 / 19 days
Bise Spaceguard Center 1.0mSep 6, 2009 – Mar 11, 2010 / 43 days
Bias and flat field calibrationBias and flat field calibration Aperture photometry (IRAF)Aperture photometry (IRAF) Relative photometry by using reference starsRelative photometry by using reference stars
Data ReductionData Reduction
Rotational PeriodRotational PeriodMethod of period analysis: Lomb-Scargel Periodgram (Lomb 1976 & Scargel 1982).We use the photometric precise data (Data of December).
Candidate 1:0.2592 day
Candidate 2:0.2979 day
Candidate 3:0.0993 day
Rotational Period Rotational Period Results: 0.2979day (7.15 h)
*Unusual six-peak light-curve(The light-curve represented the cross section area of asteroid. When the shape of asteroid is an ellipsoidal body, the shape of typical light-curve is double-peak.)
*The past data consist with the period of candidate 2 (0.2979 day). When we made the folded light-curve with other candidates, the shape of light-curve was not good.
The light-curve shape is not good. The light-curve shape is good.
Determination of Pole Direction by Determination of Pole Direction by Epoch MethodEpoch Method
Epoch method (Magnusson 1986) : Phase shift in the light-curve→ Pole direction
We search θ value which minimizes the residuals between the left-hand and the right-hand.
Phase shift (Observational values)
Phase shift (Theoretical values)
(T : The time when a specific feature (for example, the flux minimum) appears, P: Rotational Period, n: Number of rotation during the observation term, θ: A vector that is related with the pole direction.
Determination of Pole Direction by Determination of Pole Direction by Epoch MethodEpoch Method
Candidate 1λ: 320°±15β: -20 °±15
Candidate 2λ= 140±15°β= -20±15
Shape ModelShape Model
Light-curve Light-curve →→ Shape Model Shape Model (The software is developed and distributed by Kassalainen et (The software is developed and distributed by Kassalainen et al. 1992.)al. 1992.)
edge on pole onLike hexagonal shape
Summary Summary
We introduced the primitive body mission of Japan. We introduced the primitive body mission of Japan. →→The target candidate of Hayabusa Mk2 is 107P/4015 Wilson-The target candidate of Hayabusa Mk2 is 107P/4015 Wilson-
Harrignton.Harrignton. We found the following properties from the light-curve of WH,We found the following properties from the light-curve of WH, Rotational period: 0.2979 day (7.15 hour)Rotational period: 0.2979 day (7.15 hour)→→Hayabusa Mk2 can Hayabusa Mk2 can
touch down. touch down. Rotational direction: Retrograde rotationRotational direction: Retrograde rotation Pole direction: (λ,βPole direction: (λ,β )) =(320°,-20 °) or (140°,-20 °)=(320°,-20 °) or (140°,-20 °) Shape: Like hexagonal shapeShape: Like hexagonal shape In order to calculate the precise rotational period, it is important In order to calculate the precise rotational period, it is important
to observe the target from multi-longitude location. WH is not to observe the target from multi-longitude location. WH is not the only target. There is the possibility of the target change. We the only target. There is the possibility of the target change. We would like to collaborate with Maidanak observatory and other would like to collaborate with Maidanak observatory and other observatories for the next ground-base observation campaign. observatories for the next ground-base observation campaign.