Lightcurves of Hildas and Trojans

A lightcurve of a minor solar system body can give its rotational period. Lightcurves obtained over a sufficient period of time when as an object orbits the Sun can yield information on the shape and rotational axis orientation of the object.

I made these lists is to have an unbiased list of objects for rotational period study. To do, say, a proper statistical comparison of rotational periods of different classes of objects, or a comparison of rotational periods with some theoretical model, one must have a list of objects defined by some property other than period. If you took just the objects that had measured periods you might lead astray. The lists of objects with measured lightcurves may be systematically lacking in some types of lightcurves. Perhaps very long rotational period objects have been under-observed, simply because of the amount of time needed to get lightcurves of very long period objects. Perhaps nearly spherical objects have been under-observed as they have very uninteresting lightcurves. By defining a list of objects by some property other than rotation, then measuring the rotational periods of all the objects in the list, you would have a much better idea of the true distribution of rotational periods than if you just went to a list of measured objects and took the observed periods.

Hilda100 and Trojan100 Lists

The following 2 lists are the 100 Hildas and 100 Trojans with the lowest H magnitude values. If all objects have the same albedo, then the lower H mag objects are larger, so the lists are arranged from larger to smaller bodies. The H mag values are taken from the JPL HORIZONS system database. These only include objects observed astrometrically at 2 or more oppositions.

I searched for lightcurve information for the objects in these lists using the latest Asteroid Lightcurve Database (LCDB) (Warner, Harris, and Pravec). I plan to update the lightcurve information as updates of the LCDB become available.

The objects are listed in increasing H magnitude. These tables were made utilizing the JPL Small Body Search Engine. The first column is simply a sequence number, 1 to 100. The second and third columns give the asteroid number and name (if available). The fourth column gives the rotational period in hours from the LCDB, if available. The last column gives the quality code of the lightcurve, as taken from the LCDB. If the SAM flag is set to "Y", an "M" (for Model) is given.

The Hilda100 list

The Trojan100 list

Upcoming Oppositions of Hildas

To most efficiently observe lightcurves, one targets objects that can be observed for a long portion of each night. That means targeting objects that are near opposition, so that they can be observed for many hours on either side of the middle of the night, and objects that have a declination that allows a long period of time with low airmass as seen from your observatory.

To help observers make initial plans to observe lightcurves of Hildas, I have made tables listing some basic information about the upcoming oppositions of objects in the Hilda100 list. For each Hilda, I computed a table showing the dates of opposition from start of 2020 until the end of 2027.

For example, here is the table for 1911 Schubart:

1911 Schubart (1973 UD)         
  2020-Sep-26  Dec= +03  ap= 15.6  el= 177.8  r= 4.0 rp= 11.915   1911
  2021-Nov-26  Dec= +22  ap= 14.8  el= 178.4  r= 3.4 rp= 11.915   1911
  2023-Feb-10  Dec= +13  ap= 14.7  el= 178.6  r= 3.4 rp= 11.915   1911
  2024-Apr-13  Dec= -11  ap= 15.5  el= 177.8  r= 3.9 rp= 11.915   1911
  2025-May-30  Dec= -23  ap= 16.1  el= 178.7  r= 4.5 rp= 11.915   1911
  2026-Jul-08  Dec= -22  ap= 16.3  el= 179.7  r= 4.7 rp= 11.915   1911
  2027-Aug-15  Dec= -12  ap= 16.2  el= 178.6  r= 4.5 rp= 11.915   1911

The first column is the date when the object has a maximum in its solar elongation angle. This is very close to the time of opposition. The remainder of each line refers to values on that date.

The second column gives the declination.

The third column gives an estimate of the object's visual magnitude.

The fourth column gives the maximum solar elongation angle.

The fifth column gives the heliocentric distance.

The sixth column is the rotational period (hours) and the last is the object number.

These tables were made utilizing the JPL HORIZONS Ephemeris Generator. Values for position, magnitude, solar elongation and heliocentric distance were requested for each day from 2020 to 2027. A FORTRAN program was written to go through these files, find the times of local maxima of the solar elongation, then output the information in the table format.

Here the oppositions for all objects are arranged in a chronological order:

Hilda oppositions in 2020-2027

This link gives a single file that has information for all 100 Hildas, but separately for each object:

All 100 Hildas, ordered as in Hilda100 list