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Susan D. Benecchi

2010 Research Report

        The catch word for Benecchi's work this year is “archive dataset analysis.” She has been using Transneptunian objects (TNOs), and binaries in particular, as test particles for understanding the physical and photometric properties of the current Kuiper Belt and to trace the dynamical conditions of the protoplanetary disk.

Re-analysis of data from seven HST/ACS HRC visits and 2 HST/STIS visits to (47171) 1999 TC36, a known binary, revealed a 2 component primary (i.e. a triple system) with the inner pair orbiting in 1.906 days. The data reveal precession in the system (all three components), visible on a 3 year timescale and when compared to other multiple systems in the Kuiper Belt (47171) 1999 TC36 is more similar to other TNBs than to systems such as Pluto and Haumea (Figure 1).

In an effort to pull every detail out of a number of TNO datasets obtained with HST, Benecchi published a techniques paper on HST astrometry of moving targets (Benecchi et al. 2010), which was never previously well documented. 1428 individual astrometric measurements of 256 Transneptunian objects were reported and submission of these measurements to the Minor Planet Center increased the arc-length of 62 (24.2 percent) of the 256 total objects by 3-8 years, and increased the fractional arc length of 131 (51.1percent) objects by 30 percent.

She also performed a re-analysis of 2 large TNO datasets (one optical and one infrared) that had previously published pieces (techniques, individual object focus), but never as a complete package (Benecchi et al. 2011, submitted 2010). The results from this work include a significant increase in the number of TNO colors analyzed in an especially uniform and consistent manner, in particular in the infared (Figure 2). The sample measures objects ~50km smaller than previous surveys. No new correlations between color and dynamical properties (semi-major axis, eccentricity, inclination and perihelion) were found. However, the data support the hypothesis that Classical objects with i<6° come from a different distribution than either the Resonant or excited populations in the visible (at the >99.99 percent level with a K-S test) and in the infrared (at a lower significance level). The dataset also point out the ease of identifying Haumea family objects with the HST infrared filters F110W and F160W (Figure 3) and find 5 potentially interesting lightcurve targets for future study. 

            Work also continued with the Deep Ecliptic Survey (DES; Gulbis et al. 2010) where we continued our analysis of the dataset and found statistically different inclination distributions among the various TNO dynamical classes in our debiased dataset.

            A side project was the archiving of the P445.3 (Pluto) occultation dataset which was collected in 2008 to the PDS. It is expected that additional occultation datasets, perhaps of TNO occultations in the coming years, will be routinely added to the PDS archive now that the process has been understood by our research group (MIT, led by Elliot & Person).






From Benecchi et al. 2010 

Figure 1. Comparison of angular momenta for Solar System multiples. Normalized angular momentum plotted vs. semi-major axis scaled by the Hill radius, RHill, of the system for all binaries and triples in the Kuiper Belt with determined orbits (Noll et al. 2008; Grundy et al. 2009) and all other solar system triple systems. Where rotational periods are known, we use them, where they are unknown we assume a period of 8 hours. Dobrovolskis et al. 1997 find that objects with J/J’ > 0.39 cannot have formed through rotational fission. Canup (2005) suggest that such systems are likely to be formed by a single catastrophic collision, however, if J/J’ > 0.8 additional considerations exist and formation by collision is limited. Systems with J/J’>0.8, including (47171) 1999 TC36, were most likely to formed through three-body gravitational interactions/capture as suggested by Goldreich et al (2002) (Chiang et al. 2007) or via the Nesvorny (2008) formalism.

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From Benecchi et al. 2011 (submitted Dec. 2010) 

Figure 2. HST Color-color plots. The Sun is denoted as “S” in each plot. Objects are identified with respect to their general dynamical classifications with orange squares notating Cold Classical objects, blue diamonds notating Hot objects and black triangles notating Resonant objects. Our optical colors span the full range of possible colors from 2000 JG81 which is slightly bluer than the Sun to 1998 XY95, 1993 SC and 1996 TQ66, which are comparably very red. These data show no statistically significant differences between the colors of the three dynamical populations described in the text. The objects with overlapping optical and infrared colors are clustered around F110W-F160W of 0.58 with the exception of 2000 CE105 which is significantly bluer.

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From Benecchi et al. 2011 (submitted Dec. 2010) 

Figure 3. Color vs. HV magnitude. Objects are identified with respect to their general dynamical classifications with orange squares notating Cold Classical objects, blue diamonds notating Hot objects and black triangles notating Resonant objects. These data show no statistically significant differences in the color distribution between dynamical class and HV. The two outliers in the right panel, (86047) 1999 OY3 and (24835) 1995 SM55, have been identified as Haumea collision family members (Ragozzine & Brown, 2007). The colors of these objects are notably different than the colors of any other TNOs in these filters.








Benecchi, S. D. and Noll, K. S. 2010. HST Astrometry of Transneptunian Objects. ApJ Supplements 189, 336-340.

Gulbis, A. A. S., Elliot, J. L., Adams, E. R., Benecchi, S. D., Buie, M. W., Trilling, D. E., and  Wasserman, L. H. Unbiased Inclination Distributions for Objects in the Kuiper Belt. Astron. J. 140, 350-369.

Benecchi, S. D., Noll, K. S., Grundy, W. M., and Levison, H. F. 2010. (47171) 1999 TC36, A Transneptunian Triple. Icarus, 207, 978-991.


Archived (PDS) Dataset:

Benecchi, S. D., McCarthy, D. W., Kulesa, C. A., Hubbard, W. B., Person, M. J., Elliot, J. L., Gulbis, A. A. S. 2010. P445.3 (Pluto) Occultation V1.0, NASA Planetary Data System, EAR-P-I0962/I0964-5-BENECCHIOCC-V1.0.


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