Photometric Observation of 107P/4015 Wilson-HarringtonSeitaro Urakawa1, Shin-ichiro Okumura1, Kota Nishiyama1, Tsuyoshi Sakamoto1, Masateru Ishiguro2, Kouhei Kitazato3, Daisuke Kuroda4, Sunao Hasegawa5, Makoto Yoshikawa1,5 (1Japan Spaceguard Association, 2Seoul University, 3Aizu University, 4National Astronomical Observatory of Japan, 5ISAS(Institute of Space and Astronautical Science)/JAXA(Japan Aerospace Exploration Agency)

Outline Introduction Asteroid Explorer Hayabusa Primitive Body Missions of Japan107P/4015 Wilson-HarringtonObservations Data Reduction Results (Rotational Period; Rotational Direction; Pole Direction; Shape Model ) Summary

Welcome Home Asteroid Explorer Hayabusa June 13, 2010 Asteroid explore Hayabusa return to the earth.

Welcome Home Asteroid Explorer Hayabusa May 9, 2003: Lift offSep 12, 2005: Arrive asteroid ItokawaNov, 2005: Two times touch down and collect the sample.

Welcome Home Asteroid Explorer Hayabusa June 13 , 2010, at 10:54 (UT) Capsule releaseJune 13 , 2010, at 14:08 (UT) Touch down in Australia

Scientific Purpose of Hayabusa MissionAsteroids and comets preserve the condition at the birth of solar system.We can obtain a clue on the birth of solar system by analyzing the sample in detail. Primitive bodies (asteroids and comets) have not accepted much thermal influences since the early stage of solar system. In addition to it, the objects have not been weathered.

Taxonomy of AsteroidsInner asteroid belt:S-type asteroids are dominated.S-type asteroid:Silicate componentCenter asteroid belt:C-type asteroids are dominated.C-type asteroid:Carbonaceous componentOuter asteroid belt (Trojan):D-type asteroids increases.D-type asteroid:More primitive component, Organic matter, Comet survivors!?

Primitive Body Missions of JapanC-type S-type D-type orDormant Comets More Primitive BodyMore Difficult MissionHayabusa Itokawa Hayabusa 2 1999 JU3 Hayabusa Mk2Wilson-Harrington(Candidate)

Hayabusa Mk2 missionNew Explorer (Development of new ion engine)Candidate of target: D-type or Dormant comet (for example 107P/4015 Wilson-Harrignton) In order to design the mission, the physical properties of WH (rotational period, rotational direction, pole direction, shape) are needed.Such physical properties are obtained by the photometric observation (the light-curve of WH).The mission can provide insights on the unknown link between asteroids and comets.

107P/4015 Wilson-Harrington Semi-major axis 2.638AUEccentricity 0.624Inclination 2.78Argument of perihelion91.25Longitude of ascending node270.57Period 4.28 yearA comet was discovered in 1949 at the Palomar observatory. The faint tail can see. The comet named as 107P/Wilson-Harrington. However, the comet was lost by the insufficient observation.A near earth asteroid (4015) was discovered in 1979.The continuous observations identified that 107P/Wilson-Harrington and asteroid (4015) were the same object.

Past Study of Wilson-Harrington Spectral type: C-type (NASA/JPL database)Rotational period: two solutions for 0.148 day (3.556 hour) or 0.254 0.002day (6.1 0.05 hour)Rotational direction: unknownPole direction: unknownShape: unknown

ObservationsUniversity of Hawaii 2.2m (PI: Dr.Ishiguro)Dec 18, 2009Kiso 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 daysOkayama Astrophysical Observatory 0.5m (PI: Dr.Kuroda)Nov 7, 2009 Dec 21, 2009 / 19 daysBise Spaceguard Center 1.0mSep 6, 2009 Mar 11, 2010 / 43 days

Data ReductionBias and flat field calibrationAperture photometry (IRAF)Relative photometry by using reference stars

Rotational 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 dayCandidate 3:0.0993 day

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.

Rotational DirectionAppearance Rotation(Red circled asteroid) True Rotation(Green circled asteroid) Observer Prograde rotationRetrograde rotationAppearance Rotation :The rotation is determined by the light-curve.True Rotation :The rotation is slightlyshorter or longer than theappearance rotation.Retrograde rotation:The true period is longer than the appearance period.Prograde rotation:The true period is shorter than the appearance period.Asteroid

Rotational DirectionWe calibrated the difference between the appearance rotation and the true rotation. Assume prograde rotationAssume retrograde rotationThe light-curve shape is not good.The light-curve shape is good.

Determination of Pole Direction by Epoch MethodEpoch method (Magnusson 1986) : Phase shift in the light-curvePole directionWe search 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, : A vector that is related with the pole direction.

Determination of Pole Direction by Epoch MethodCandidate 1: 32015: -20 15Candidate 2=14015= -2015

Shape ModelLight-curve Shape Model (The software is developed and distributed by Kassalainen et al. 1992.) edge onpole onLike hexagonal shape

Summary We introduced the primitive body mission of Japan. The target candidate of Hayabusa Mk2 is 107P/4015 Wilson-Harrignton.We found the following properties from the light-curve of WH, Rotational period: 0.2979 day (7.15 hour)Hayabusa Mk2 can touch down. Rotational direction: Retrograde rotation Pole direction: (,=(320,-20 ) or (140,-20 ) Shape: Like hexagonal shape In order to calculate the precise rotational period, it is important to observe the target from multi-longitude location. WH is not the only target. There is the possibility of the target change. We would like to collaborate with Maidanak observatory and other observatories for the next ground-base observation campaign.