Photometry of the most ancient asteroids

all targets for the project. Before observing one, please see asteroids that need attention and those alrady observed, and/or contact us.
Mountain View


We would like to determine shapes and spin poles (rotaion period and direction in the sky of the rotation axis) of the asteroids members of our recently discovered primordial asteroid family. These are the low-albedo asteroids (i.e. wil geometric visible albedo < 0.12) in between the "Primordial" and the "Polana" lines in the Figure above (the Figure is adapted from the piublication by Delbo, M., Walsh, K., Bolin, B., Avdellidou, C. & Morbidelli, A. 2017. Identification of a primordial asteroid family constrains the original planetesimal population. Science 357, 1026--1029.). This is a very special asteroid family, which could be as old as the Solar System, i.e. 4.5 Gyr. -- this is the reason why it is called "primordial".

The working hypotheis that we want to test is: according to theories of asteroid orbital evolution, under the influence of the Yarkovsky effect, members of the inward side of the primordial family should have a statistical predominance of retrograde objects.
The inward side of the primordial family is readly visible in the figure above. This is formed by the asteroids between the Primordial and the Polana border (the dashed dotted and the solid line). On the other hand, in the region where members of the primordial family overlap those of other known families, i.e. the outward side, membership is more diffcilt to be etablished. So, here we focus on the inward side only. All asteroids that are marked with "Low albedo", i.e. solid black circles in the figure above are potential targets for this study. The list of these asteroids can be found by clicking here.
Jump to immediate objectives, or keep reading should you want more background on asteroid families.


A collisional family of asteroids is a group of these objects that originated from the fragmentation of a parent asteroid. So, each memeber of the family is a fragment of the parent. Members are initially on very nearby orbits, but the Yarkovsky thermal forces cause a secular change of their orbital semimajor axes (a). Prograde rotators have their semimajor axes values increased, while retrograde rotators have them deacreased. The semimajor axis drift rate is proportional to 1/D (where D is the asteroid diameter).
This way, in general, the family builds an inward and an outward side (also called hears) and the distribution of the memeber asteroids in 1/D vs a look like the letter "V". This is why the 1/D vs a plot of families are called V-shapes. See figure below that show the case of the Erigone's family. As demonstrated by Hanus, J. et al. (2013), retrograde and prograde rotators are preferentially found in the inward and outward side of families, respectively.
Mountain View


Photometric obsevations are used to determine light curves of the members of the primordial family. Small telescopes are particularly well suited to do this project. Some of the asteroids are birght enough that can be observed with a 30 - 40 cm equipped with a good CCD.


Observations can be done in R filter.
If the rotation period of an asteroid is very large, the observer could consider to perform recursive observation of 2 or 3 targets, during the same night.
Asteroid LC if possible should be repeated at different epochs, when the target is at a different place on its orbit.
If the observres cannot reduce the data themshelves they can share their data with us. Please do not forget to obtain flat, dark and bias!


The list can be found by clicking here It contains all the primordial family members of the inward side. The second list "Asteroids that need ATTENTION" below contains only the brigter asteroids that can be observed during these months. i.e. January - February 2019 and notes on other targets not necessarly visible.
You can see notes and the progress of the obserations.

Asteroids that need ATTENTION:

JAN - FEB 2019 asteroids

284 Amalia -- rotation period is 8.55 h
2171 Kiev -- rotation period is 18.79 h
2259 Sofievka -- rotation period is 31.60 h
2575 Bulgaria -- rotation period is 8.62 h


933 we have a preliminary and likely wrong solution of the spin pole. To be followed up.
2776 We have one lightcurve but of low amplitude. It could be cool to get more.
2536 32 lightcurve available already, but not pole and shape solution yet.
2322 Please Observe it and report. No information so far.
4231 no information so far.
13066 no information so far.
2778 does NOT need more observations. It has been finished being followed up very nicely already. It also has fast period. Observations have been obtained Matthieu Conjat with the 0.4m Schaumasse reflector of the observatory of Nice. Matthieu has a good lightcurve. (See image below). Convex inversion by Josef Hanus will be started as soon as he finds time

Asteroids already observed by this program

LightCurve Position in the V-Shape Notes

It has been finished being followed up very nicely already. It also has fast period. Observations have been obtained Matthieu Conjat with the 0.4m Schaumasse reflector of the observatory of Nice. Matthieu has a good lightcurve. Convex inversion by J. Hanus will be started as soon as he finds time. M. Delbo sees a nice minimum in the solution (Dafeed).

917 Lyka by Matthieu Conjat @ OCA

2773 Brooks by Matthieu Conjat @ OCA


University Cote D'azur, Observatoire de la Cote d'Azur.
Astronomical Institute, Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
European Space Acency, Noordwjik, The Netherlands.


Marco Delbo +33 6 85240371
Matthieu Conjat
Chrysa Avdellidou