Datura family: the 2009 update

Abstract

Context. Research of asteroid families has been recently refreshed by the discovery of very young ones. These families are of great interest because they represent the product of their parent body fragmentation before orbital and physical evolutionary processes can change them. A cluster of seven objects around the largest body (1270) Datura is of particular interest because it has enough known members and resides in the inner part of the main asteroid belt, facilitating observations. Aims. We carried out photometric observations of the two largest members of the Datura family -asteroids (1270) Datura and (90265) 2003 CL5 -with the goal of inferring their physical parameters. We also used numerous astrometric observations of Datura-family members in the past few years to revisit the age of this cluster. Methods. We performed numerous photometric observations of (1270) Datura over several oppositions. We then used the lightcurve inversion method to determine the spin state and shape of this asteroid. In the case of (90265) 2003 CL5, for which only limited lightcurve data have been acquired so far, we used Fourier analysis to determine the synodic rotation period during the 2008 apparition. We also used backward numerical integration of the improved orbits of Datura family members to reduce uncertainty in its age. Results. We determined the rotation state of (1270) Datura, the largest member of its own family. Its major properties are a short rotation period of ∼3.36 h and small obliquity, which, however, exhibits ∼±15 • excursions because of a forced Cassini state of the proper nodal frequency. Any possible initial non-principal rotation state has probably been damped and the asteroid rotates about the shortest axis of the inertia tensor. Its global shape, although convex in our representation, may reflect regions related to the excavation of the family members from the parent body surface. Interestingly, the second largest member of the Datura family -(90265) 2003 CL5 -appears to be very slow rotator with the rotation period ∼24 h. The large amplitude of its rotation curve suggests that its shape is extremely elongated, possibly bi-lobed. Improved orbits of the family members allow us to re-determine the possible age of this family. We find an age that is slightly older than previously reported. Using a conservative approach, we obtain an age in the 450 to 600 kyr range. With strengthened, but plausible, conditions, we find that the current data may support an age of 530±20 kyr. Further astrometric and photometric observations of the Datura cluster members are needed to determine its age more accurately.

The young Datura asteroid family

“…In Vokrouhlický et al (2009) we also reported observations of the second largest member in this family, (90265) 2003 CL5, for which we were able to determine a rough value of synodic rotation period of 23.42 h. Unfortunately, our data were too few to say more about rotation state of this asteroid. We also took advantage of improved orbital elements of Datura members and constrained its age to be between 450 and 600 kyr.…”

“…V − R is the measured color index, apparent brightness in V and R filters, given in standard Johnson-Cousins photometric system. V09 stands for Vokrouhlický et al (2009). per rotation, is less likely but cannot be ruled out at this moment. Composite lightcurve with the data folded with the derived period is presented in Fig.…”

“…In the next five columns, its helio-and geocentric distances, solar phase angle and geocentric ecliptic longitude and latitude (equinox J2000) are given. The telescope used is specified in the last column, except for the 2008 observations of (90265) where the reference to Vokrouhlický et al (2009) is given. A line with "L" is added in the cases where also sparse data from the Lowell photometric database were used for creating a convex shape model of the particular asteroid.…”

“…We also took advantage of improved orbital elements of Datura members and constrained its age to be between 450 and 600 kyr. More recently, Rosaev & Plavalova (2015) briefly analyzed updated orbital catalogs of asteroids and reported discovery of three new members in this family (compared to seven known previously, Vokrouhlický et al 2009).…”

“…First, in Sects. 2 to 4, we collect photometric observations of the largest members in this family (except for (1270) Datura that was analyzed in our previous study Vokrouhlický et al 2009). For three cases, asteroids (90265) 2003 CL5, (60151) 1999 UZ6 and(89309) 2001 VN36, which are the second to fourth largest fragments in the family, we obtained enough data to resolve pole position and rough (convex) shape.…”