Minor planet Haumea was at opposition and well placed in the sky in the second half of April 2023. At magnitude 17.3, it is faint, but well within the reach of Moana using the luminance filter and 5mn exposure.

Haumea has a few particularities, all related: a rapid rotation rate (3.9 hours) and an unusual shape. Rather than being an oblate ellipsoid like most planets, it is a Jacobi ellipsoid, resembling more a rugby ball (or an American foot ball). The fact than such a shape allows hydrostatic equilibrium in theory is already amazing (after all even Lagrange missed this solution), but the fact that shape is actually found in nature is even more incredible.

The dwarf planet Haumea is believed to rotate in just under 4 hours. This rapid rotation causes the dwarf planet to be elongated in appearance. Credit Stephanie Hoover, Wiki commons.

From here it became very tempting to not only image Haumea, but also derive a light curve exceeding one period. The acquisition was uneventful (I was asleep while the scope was hard at work, following the sequence preprogrammed in NINA) and it was the opportunity to test the new Orbital Object Sequence module. OOS worked well, although it throws an exception each time the sequence is loaded. I processed the images and extracted the light curve in Tycho Tracker as usual. The observation matches almost exactly the 3.9 hours of period published.

Stacked image of Haumea
Point Spread function of Haumea
Haumea light curve, period 3.9 hours.

Here are the imaging raw datasets for the 2 days of observation (more 12 hours in 2 nights) and the calibration data:

During the second night of observation, conditions deteriorated at the end of the run (hence the data splitting below). The curves, however show reasonable correlation between the 2 days, once phase shifted to align.

Light cuve from the second day of observation

Last I looked for other objects in the field. To my disappointment there was no other asteroid nor minor planet (Makemake was in the same area, also at opposition, but out of my field, which is after all rather narrow). I found however an obscure magnitude 16 variable star with a 7 hours period at the periphery of the field. It was matching the length of the observation run pretty well. So I ran a light curve on that, as below. The curve is much cleaner than Haumea’s, probably because this object is 1 magnitude brighter.

Although the light curve is lacking a bit at the end to cover a full period, the 7.2 hours period of that star is fitting well.

Here is this G0 variable star’s (poetically named CSS_J143034.8+150740) detail:

Mag(selected band): 16.088
Classification: G0
Temperature: 6256 K
Period: 0.299 days
Period: 7.175 hours
Mag Min: 16.350
Mag Max: 16.120
Amplitude: 0.230
Name: [CSS_J143034.8+150740]

Light curve of 7 hours variable star [CSS_J143034.8+150740] which happened to also be in the field.