Abstract
A 3-D shape model of the sixth largest of the main belt asteroids, (704) Interamnia, is presented. The model is reproduced from its two stellar occultation observations and six lightcurves between 1969 and 2011. The first stellar occultation was the occultation of TYC 234500183 on 1996 December 17 observed from 13 sites in the USA. An elliptical cross section of (344.6 ± 9.6 km) × (306.2 ± 9.1 km), for position angle P = 73.4 ± 12.5° was fitted. The lightcurve around the occultation shows that the peak-to-peak amplitude was 0.04 mag. and the occultation phase was just before the minimum. The second stellar occultation was the occultation of HIP 036189 on 2003 March 23 observed from 39 sites in Japan and Hawaii. An elliptical cross section of (349.8 ± 0.9 km) × (303.7 ± 1.7 km), for position angle P = 86.0 ± 1.1° was fitted. A companion of 8.5 mag. of the occulted star was discovered whose separation is 12 ± 2 mas (milli-arcseconds), P = 148 ± 11°. A combined analysis of rotational lightcurves and occultation chords can return more information than can be obtained with either technique alone. From follow-up photometric observations of the asteroid between 2003 and 2011, its rotation period is determined to be 8.728967167 ± 0.00000007 hours, which is accurate enough to fix the rotation phases at other occultation events. The derived north pole is λ2000 = 259 ± 8°, β2000 = -50 ± 5° (retrograde rotation); the lengths of the three principal axes are 2a = 361.8 ± 2.8 km, 2b = 324.4 ± 5.0 km, 2c = 297.3 ± 3.5 km, and the mean diameter is D = 326.8 ± 3.0 km. Supposing the mass of Interamnia as (3.5 ± 0.9) × 10-11 solar masses, the density is then ρ = 3.8 ± 1.0 g·cm-3.
Highlights
A stellar occultation by an asteroid offers a unique opportunity to obtain information on the accurate size and shape of the occulting asteroid as well as about possible duplicity of the occulted star
The first successful photoelectric observation was obtained at Uttar Pradesh State Observatory, India during the occultation of BD −5 5863 by (2) Pallas on October 2, 1961 [2] [3]
This paper shows an instance of unique determination of a pole and an ellipsoidal model of an asteroid by combination of its occultations and photometric observations
Summary
A stellar occultation by an asteroid offers a unique opportunity to obtain information on the accurate size and shape of the occulting asteroid as well as about possible duplicity of the occulted star. Follow-up photometric observation around the occultation observation gives a rotation phase at the time of occultation and an amplitude of its lightcurve This information is significant in order to determine a pole and 3-D shape of the asteroid. We have two occultation cross sections with enough chords for the 1996 December 17 and 2003 March 23 events and lightcurves of (704) Interamnia. Occultation Observations (704) Interamnia was discovered by Vincenzo Cerulli in 1910 It has an assumed diameter of 317 km [6], and is the sixth largest among the main belt asteroids. We can obtain valid cross sections of Interamnia with enough chords from only the 1996 and the 2003 events as is discussed in the following subsections.
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