CFHT Information Bulletin, number 39, Second Semester 1998



Observing Near Earth Asteroids and Trans Neptunian Objects from Waimea

Christian Veillet (CFHT, veillet@cfht.hawaii.edu), Dave Balam (UVic, balam@beluga.phys.Uvic.ca) , Chris Aikman (DAO, Chris.Aikman@hia.nrc.ca)

1) Any need to observe asteroids at CFHT?

Near Earth Asteroids (NEAs) are asteroids with an orbit which can bring them close to the Earth's orbit, and then potentially to the Earth itself. Some of them are listed as Potentially Hazardous Asteroids (PHAs). This denomination, clearly subjective, will depend on how close they could be to the Earth.... The present limit for that list is 0.05 astronomical unit (AU), and the closest approach to the Earth of a known object for the next 100 years is 0.0059 AU ((2340) Hathor), i.e. more than twice the distance of the Moon.

NEAs are discovered generally when close to the Earth, where they are bright and have an apparent fast motion. Then they are easy to detect among the other more classical asteroids. Dedicated observing programs on a few telescopes around the world make most of the discoveries of the NEAs. As soon as they are detected, predictions for the following nights are made available to all the observers who will try to follow them for getting enough positions to build a preliminary orbit which will confirm whether or not that they are real NEAs. Very quickly they become difficult to observe, as their distance from the Earth is rapidly increasing, making them too faint for most of the instruments used in the asteroid observation community. If their orbit based on a 10 day arc (a very short one for long term predictions) is suggesting that they could come close to the Earth, we need to have more observations for improving the orbital elements and the quality of the predictions. This is where a larger telescope, with the possibility of tracking a moving object, is needed. What you need is to be able to give a good astrometric position of a 21 to 23 mag object moving at 3' hr-1, or around 8 pixels/mn with STIS2 on MOS. CFHT is an excellent telescope for the job, being able to guide on a star and move the guide probe according to the motion of the asteroid with high accuracy.

Trans Neptunian Objects (TNOs) are small Solar System bodies orbiting beyond Neptune, between 30 and 50 AU far from the Sun. They form the Kuiper Belt. The Kuiper Belt plays an important role in our understanding of the formation and evolution of the Solar System. The two following statements are generally accepted:

2) NEA observations (May 1998)

We observed for three nights allocated by CTAC (2) and CFGT (1) in a joint program dedicated to NEAs and TNOs. No object list was provided at the time of the request, as the objects to be observed are mainly those which have been discovered one to two months before the run. We selected a short list of 5 asteroids recently discovered and probably to be classified as PHAs. We added an unusual asteroid not observed for a long time. Here is a summary of our observations:

designation

arc before run

(days)

arc after run

(days)

1st approach < 0.05AU before 2100

1998 HH49

5

32

1998 FH12

26

66

0.0397 (2047)

1998 FW04

11

72

0.0075 (2013)

1998 FL03

7

69

0.045 (2090)

1998 FG02

10

70

0.0220 (2032)

1995 WQ05

93

2.5 yr

(not a concern)

Close approach computations are taken from the MPC information at http://cfa-www.harvard.edu/iau/lists/PHACloseApp.html.

3) TNO observations (1997-1998)

The recovery of TNOs has been initiated by CV in discretionary-time with MOS in imaging mode, mainly to prove that CFHT and MOS-STIS2 in imaging mode were an excellent combination for this kind of work. The following table summarizes what has been done for TNO recovery since 1996 (objects from the 1998 May run in boldface).

designation

observation date

arc before run

arc after run

comments

1994 JR01

1997 05 28

~3 yr

~3 yr

Observed at nearly the same time at other places, the first TNO recovered with MOS

1996 RR20

1997 06 28-29

62 days

~290 days

2nd opposition recovery

1997 CQ29

1998 02 16-18

57 days

~380 days

2nd opposition recovery

1997 CR29

1998 02 16-18

63 days

~380 days

2nd opposition recovery

1997 CV29

1998 02 16-18

62 days

~375 days

2nd opposition recovery

1993 FW

1998 05 31

5 oppositions

6 oppositions

One night only - already extensively observed

1994 ES2

1998 05 29-31

1.0 yr

4.2 yr

Not observed since 1995

1996 KV1

1998 05 29-31

87 days

2.0 yr

2nd opposition recovery (not found in 1997)

1997 RT5

1998 29-31

51 days

~355 days

2nd opposition recovery

1997 QJ4

1998 05 31

38 days

270 days?

One night only, two nights needed for a 2nd opposition recovery. Identification could be wrong.

We mention here that the increasing number of discoveries with the various programs, including those with the coming CFH12k, will increase the need for a follow-up of these TNOs, the only way to get a sufficiently good orbit for dynamical studies of the Kuiper Belt. This program will hopefully continue for some years.

4) Remote observing from Waimea.

Remote observing from Waimea had been tried prior to the run by one of us (CV) while using D-time, on both MOS and UH8k. It had been found very efficient: with the new link between Waimea and the summit, you see no difference in the display time of the images, and you are much more productive if you have to reduce your data in real time at 800m than at 4200m!

For our three nights run in May, CV decided to observe from Waimea, as DB and CA were staying in Victoria. An HP terminal has been added on the desk of CV's office (the Waimea observing room is not ready yet!). A live phone link was maintained all throughout each night, allowing efficient communication with the OA. Most of the images were examined and reduced as soon as available on the Waimea computers. Others were examined in Victoria, with many e-mail exchanges taking place during the observations between the three of us. We have been able to send to the Minor Planet Center the positions of all the objects observed within two days after the run, with the orbits of the NEAs recomputed including the new observations for a final check of the identifications.

In order to follow the safety regulations at the summit (no-one may remain there alone), M.-C. Hainaut on one night and D. Shaytor on the other two agreed to accompany the OA. We thank them for their contribution! Remote observing from Waimea is not a supported operation mode for the moment, but it is clearly a mode which we will offer to observers as soon as the various obstacles (observing room in Waimea, safety issues at the summit, lodging in Waimea, ...) have been solved. Any instrument which does not require the observer(s) at the summit (imaging runs with CFH12k, MOS or OSIS, AOB, ...) are good candidates for remote observing. And don't forget that 90% of Keck observations are made from Waimea.

5) Need to know more?

Details on the observations, positions sent to MPC and, for 2nd opposition recovery, links to the Minor Planet Electronic Circulars, and pictures of some of the recovery images, can be found on the CFHT web site at http://www.cfht.hawaii.edu/~veillet/astero.html.





Editor: Dr. Timothy M. C. Abbott, tmca@cfht.hawaii.edu
Copyright © 1998, CFHT Corporation. All rights reserved.