Observing Trans Neptunian Objects, etc

[Dr Paul Leyland]

I am very pleased to see a page in the Handbook which gives information on TNOs and similar objects in the outer solar system. With the exception of Pluto they have been sadly neglected in my opinion.

Does anyone other than myself observe these things? If not, I would urge imagers with 30cm or larger apertures to give them a try. In addition to the challenge of finding such small and remote bodies, there is useful scientific work to be done. A good number are marked by the Minor Planet Center as needing further astrometric observations in order to refine their orbits and, in a number of cases, to decide between one of several candidate orbits.

The subject includes “, etc”. By this I mean thing such as Centaurs, Uranian Trojans which are not strictly TNOs.

Paul

[Grant Privett]

Silly question, are there many TNOs etc below 20th mag that are uncertain in their orbits or are we thinking 20-21 mainly here?

[Dr Paul Leyland]

To be quite honest, I don’t know. I’ve not tried to find out. It would not surprise me to find a few in the 19-20 range but fainter than 20 are likely to be more common.

That said, I can take measurable images at  magnitude 20.5 unfiltered in 51.5 minutes (see https://britastro.org/observations/observation.php?id=20181108_230500_5f60877f698839f2 for an example) and 22.2 in 178 minutes (see https://britastro.org/observations/observation.php?id=20200113_230000_a5cc9ad9ed617011) with a 0.4m on a decent night.

Owners of smaller scopes need to multiply by the square of the aperture ratio. A 30cm, say, takes (0.4/0.3)^2 as long — 92 minutes and 316 minutes (5h16m)  respectively. The figures for a C14 (0.356m) are 65 minutes and 225 minutes, or 3h45m.

I accept that over five hours is almost certainly too long for most people. Nonetheless observers equipped with telescopes in the 30-40cm class should be able to do useful research by measuring objects which are significantly below mag 21.

[Richard Miles]

Eamonn Ansboro has been a keen observer of TNOs and John Saxton has measured a rotational lightcurve too.

The orbits of the brighter ones are well tied down and very few bright ones are discovered.

I’ve done the latest list for the 2022 Handbook and since 2014 only one bright TNO in the Top 25 has been found, namely 2018 VG18.

Of course the most effective thing that amateurs can do is to observe stellar occultations by TNOs.

Richard

[Dr Paul Leyland]

Thanks Richard.

To be honest, the possibility of occultations had completely skipped my mind. This is probably because I have never tried observing one because I am not geared up for accurate timing on a cadence of several Hertz. Unfortunately there are no TNO occultations predicted for here until after I return to the UK.

(174567) Varda, (225088) Gonggong, (145452) 2005 RN43 and (50000) Quaoar are all reported by the MPC as having 3 variant orbits available with discrepancies between them of up to 3 arcsec though are also status 1. They are mag 20.2, 21.4, 19.9 and 18.9 respectively. (523692) 2014 EZ51 is status 4 and mag 21.5 right now.

Incidentally, why are TNOs et al. ordered by H in the Handbook? It would seem to me to be more useful for observers if they were ordered by opposition date or magnitude.

[Dr Paul Leyland]

Although I stated I can reach 20.5 in 51.5 minutes on a decent night, tonight was not decent with poor seeing and ok-ish transparency some of the time. The killer, though, was intermittent thin cloud going by. Not yet had chance to go through the subs and through out the particularly bad ones. I had difficulty imaging (50000) Quaoar at V=18.9 in 102 minutes. Most certainly not helped by it being 3 arcseconds away from a star which is 0.7 magnitudes brighter.

An image may appear on my personal page eventually but it will not be pretty.

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