Short-term variability of Binary and Multiple Trans-Neptunian Objects
Binarity study supplies a vast set of information, such as mass, density, albedo, size of each component of the system, as well as important clues about formation and evolution of the Trans-Neptunian belt (Noll et al. (2008)). Some approaches can be used to complement the binarity study, such as spectroscopy (Carry et al. (2011)), and photometric studies. The short-term variability allows us to retrieve rotation periods from the photometric periodicities and also provides constraints on the shape (or surface heterogeneity) using the lightcurve amplitude.
In collaboration with Keith S. Noll, we worked on the short-term variability of Binary Trans-Neptunian Objects and have already derived some rotational and physical properties characteristic of the binary population. We have shown that rotational and physical properties of the binary and of the non-binary populations are different thanks to statistical studies and search for correlations and anti-correlations between physical and orbital parameters. The binary population has a higher mean rotational period probably due to tidal effects between the system components and higher shape deformation that may give us information about the system genesis.
A detailed study has been accepted for publication in Astronomy and Astrophysics and is available here.
Mutual event in the Sila-Nunam system
A mutual event is produced when the two components alternate in passing in front of one another, eclipse and occultation between the primary and its satellite. Observations of mutual events between components of a binary/multiple system have been used to constrain binary/multiple asteroid mutual orbits, shapes, and densities (Descamps et al., (2007)). Observations of mutual events in the Trans-Neptunian belt is very challenging. Before 2012, mutual events have been observed only for three systems in the Trans-Neptunian belt: 2001 QG298 (special case of contact binary) (Lacerda, (2011), Sheppard and Jewitt (2004)), Haumea (Ragozzine and Brown, (2010), webpage), and Pluto-Charon (Binzel and Hubbard, (1997)). Detection and analysis of mutual events are not trivial and require a considerable observational and coordinated effort. Several observational campaigns have been planned to observe mutual events in the Sila-Nunam (formerly (79360) 1997 CS29) system and are partially reported in Grundy et al. (2012). In fact, thanks to exhaustive observational runs with the Hubble Space Telescope during the last ten years, the orbit of this system is well known. During the next few years (usually called a season), the two components of this system will alternate in passing in front of one another, and so, mutual events (eclipse and occultation) between the primary and its satellite will be observable (figure 1).
Figure 1: Schematic views of mutual events as seen from Earth on the instantaneous sky plane between 2009 and 2017. Credits: Grundy et al. (2012).
On UT 8 February 2013, thanks to a coordinated effort evolving four telescopes around the world to have a 24h coverage, we observed the first full event in the Sila-Nunam system. We used the Telescopio Nationale Galileo (TNG) at the Roque de los Muchachos Observatory in the Canary Islands, the du Pont telescope at Las Campanas Observatory, ARC at Apache Point Observatory (APO) and the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. The obtained lightcurve is consistent with two objects of similar, but perhaps not identical, size and albedo (see figure 2).
Figure 2: Combined lightcurve for the UT 7/8 February 2013 mutual event in the Sloan r’ and Bessel V filters. Triangles are observations collected with the TNG, diamonds are observations collected using the du Pont, asterisks are observations collected using the ARC at APO, and squares are observations collected using the IRTF. The red dashed line is the event prediction (Grundy et al. (2012)), while the green curve is a Gaussian fit to the data points. The vertical dashed lines indicate the locations of the first contact, minimum light, and last contact. Credits: Benecchi et al. (2013).
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