1. Photometric Observation of 107P/4015 Wilson-Harrington Seitaro Urakawa 1, Shin-ichiro Okumura 1, Kota Nishiyama 1, Tsuyoshi Sakamoto 1, Masateru Ishiguro 2, Kouhei Kitazato 3, Daisuke Kuroda 4, Sunao Hasegawa 5, Makoto Yoshikawa 1,5 ( 1 Japan Spaceguard Association, 2 Seoul University, 3 Aizu University, 4 National Astronomical Observatory of Japan, 5 ISAS(Institute of Space and Astronautical Science)/JAXA(Japan Aerospace Exploration Agency) ( 1 Japan Spaceguard Association, 2 Seoul University, 3 Aizu University, 4 National Astronomical Observatory of Japan, 5 ISAS(Institute of Space and Astronautical Science)/JAXA(Japan Aerospace Exploration Agency) 우라카와 세이다로 Сейтаро Уракаба

2. Outline  Introduction Asteroid Explorer Hayabusa Asteroid Explorer Hayabusa Primitive Body Missions of Japan Primitive Body Missions of Japan  107P/4015 Wilson-Harrington  107P/4015 Wilson-Harrington  Observations  Data Reduction  Results (Rotational Period; Rotational Direction; Pole Direction; Shape Model )  Summary

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

4. Welcome Home Asteroid Explorer Hayabusa May 9, 2003: Lift off Sep 12, 2005: Arrive asteroid Itokawa Nov, 2005: Two times touch down and collect the sample.

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

6. Scientific Purpose of Hayabusa Mission Scientific Purpose of Hayabusa Mission Asteroids 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.

7. Taxonomy of Asteroids Taxonomy of Asteroids Inner asteroid belt: S-type asteroids are dominated. S-type asteroid: Silicate component Center asteroid belt: C-type asteroids are dominated. C-type asteroid: Carbonaceous component Outer asteroid belt (Trojan): D-type asteroids increases. D-type asteroid: More primitive component, Organic matter, Comet survivors!?

8. Primitive Body Missions of Japan Primitive Body Missions of Japan C-type S-type D-type or Dormant Comets More Primitive Body More Difficult Mission Hayabusa Itokawa Itokawa Hayabusa 2 1999 JU3 1999 JU3 Hayabusa Mk2 Wilson-Harrington(Candidate)

9. Hayabusa Mk2 mission New Explorer (Development of new ion engine) 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 (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.

10. 107P/4015 Wilson-Harrington Semi-major axis 2.638AU Eccentricity 0.624 Inclination 2.78° Argument of perihelion 91.25° Longitude of ascending node 270.57° Period 4.28 year Fernandez et al. 1997 A 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.

11. Past Study of Wilson-Harrington P=6.1h Osip and Campine1995 P=3.556h Harris and Young 1983 Spectral type: C-type (NASA/JPL database) (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: unknown Pole direction: unknown Shape: unknown

12. Observations Observations 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 1.0m Sep 6, 2009 – Mar 11, 2010 / 43 days

13.  Bias and flat field calibration  Aperture photometry (IRAF)  Relative photometry by using reference stars Data Reduction

14. Rotational Period Method 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

15. 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.

16. Rotational Direction Appearance Rotation (Red circled asteroid) True Rotation (Green circled asteroid) Observer Prograde rotation Retrograde rotation Appearance Rotation : The rotation is determined by the light-curve. True Rotation : The rotation is slightly shorter or longer than the appearance rotation. Retrograde rotation: The true period is longer than the appearance period. Prograde rotation: The true period is shorter than the appearance period. Asteroid ≠

17. Rotational Direction Prograde Retrograde We calibrated the difference between the appearance rotation and the true rotation. Assume prograde rotation Assume retrograde rotation The light-curve shape is not good. The light-curve shape is good.

18. Determination of Pole Direction by Epoch 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.

19. Determination of Pole Direction by Epoch Method Candidate 1 λ: 320°±15 β: -20 °±15 Candidate 2 λ= 140±15° β= -20±15

20. Shape Model Light-curve → Shape Model (The software is developed and distributed by Kassalainen et al. 1992.) edge on pole on Like hexagonal shape

21. 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 period: 0.2979 day (7.15 hour)→Hayabusa Mk2 can touch down. Rotational direction: Retrograde rotation Rotational direction: Retrograde rotation Pole direction: (λ,β ） =(320°,-20 °) or (140°,-20 °) Pole direction: (λ,β ） =(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.