Back to TASS meetings page There was a small, informal conference on Near Earth Objects held at the Center for Astrophysics (Cambridge, MA) on July 27, 1997. Brian Marsden was kind enough to invite me, as a representative of TASS, despite the fact that we really aren't in the same league as most of the players in the business. Herb Johnson and I drove up to Cambridge on Saturday, attended the meeting from 10:00 AM to 4:00 PM on Sunday, then drove back to New Jersey that night. Here's a brief report on the current NEO searches.
There are three major programs currently in operation, and a fourth which hopes to begin this fall. I'll list their official names, and the names of some (certainly not all) of the people who work on them:
Spacewatch has been running since, um, around 1990, using a 36-inch telescope at Kitt Peak. No one from Spacewatch was present at this meeting, unfortunately. NEAT has been observing regularly since December 1995, using a 1-m Air Force GEODSS telescope on Maui. LINEAR also uses Air Force facilities, another GEODSS telescope; they started looking for asteroids (in addition to their regular task of looking for satellites) around December, 1996. LONEOS hasn't started yet -- they are still working on their camera and telescope.
Let me now run through the notes I took during the presentations: these are terse, but will convey a lot of information (I hope). I'll let Herb Johnson provide a different view of the meeting, which I suspect will focus more on the importance of amateur astronomers to the current asteroid research programs.
NEAT: Helin, Rabinowitz
- uses Air Force 1-m telescope on Maui, NASA/JPL 2Kx2K CCD camera
- started in Dec 1995
- get 6 nights per dark run
- March 1996: discovered first "interesting" object, many since then
including 3-km object with high i
- new, faster electronics yields more data, even with fewer hours
- to date, 13 NEAs: 5 Apollos, 8 Amors, 2 Atens
* a group of 15-20 enthusiastic amateurs regularly help with followup
- take 3 images at 12-minute intervals. each is 20 sec long
reach V=19.5
field of view 1.5x1.5 degrees (about 2.5 arcsec/pix)
only pay attention to things which move in all 3 images
thus motion must be >= 10 arcsec/hour
- would like to donate 2 more CCD cameras to Air Force for 2 more
GEODSS sites, then use those sites part-time as well
each camera costs about $100K
- look within +/- 10 degrees of ecliptic, +/- 40 degrees of opposition
- total so far: over 10,000 detections
- their detections of objects with high inclination fall off about 0.5 mag
brighter than objects with low inclination
- just started using new camera: Loral 4Kx4K CCD
SDSU electronics
TEC cooler, reaches about 0 degrees C with air cooling (?)
chip cost $22K, electronics $15K, computer $30K
can image up to 250 sq.deg. per night
- processing now takes longer than acquisition
- new electronics faster, but shorter exposures not reaching as faint
as old, longer exposures
LINEAR: Stokes
- Lincoln Labs works with GEODSS in space surveillance for Air Force
- have tested a camera based on special 1960x2560 CCD which is designed
to track satellites: has 8 frame-storage areas on chip, plus
very fast readout and low readout noise
- but currently using 1Kx1K CCD chip for asteroid searches
- using 1-m GEODSS telescope, reaches mag=22 at 70-second exposure
- procedure is to take 5 images of same field, at intervals 5-30 minutes,
and use all 5 images to find moving objects
(other groups use either 2 or 3 frames per field)
count objects as valid if appear on >= 4 of 5 frames
don't need to remove CRs, because 5 frames is enough to kill
coincidences
- they do NOT keep catalogs of the stationary objects
- process data in real time
- have looked and discovered objects at low galactic latitude!
- still trying different observing strategies
- first run (Dec 96): 75 observing hours yielded 49 new objects, 1 new NEO
- second run (Jan 97): bad weather, one night stands
- Mar 97 run: 324 new objects, mag 16-20 in V
- Apr 97 run: 659 new objects, 2 NEOs
- May 97 run: bad weather, 278 new objects, 1 NEO
- total: 1310 new MPC designations, 4 new NEOs
- future: more search time per night
move to new, bigger CCD chip with fast readout
test different strategies
LONEOS: Koehn, Bowell
- camera coming from U of Washington today
is 2-chip mosaic, each 2Kx4K
but one of the two chips is dead
so have 2Kx4K camera
readnoise lower than expected, can readout in 15-20 sec
- telescope close to completion
- plan: use 3 imags to build 3 lists, detect objects on lists
software is mostly complete
using 3 big PCs with Linux for processing
will take 3 hours to backup a night onto tape
- add each night's images into giant "all-sky" image, which grows
in size and depth as more and more data is placed into it
- plan to use "all-sky" image to remove stationary objects
- plan to bin data to look for faint, extended source (comets)
most comets are found when very extended, V < 14
- plan to do lots of science beyond solar system with all-sky map
- initially will operate in stare-mode; after fall 97, try scanning
- each image about 5 sq.deg., can scan at > 100 sq.deg. per hour
- observing tool: Hierarchical Observing Protocal (HOP)
how best to carry out observations? most efficiently?
if goal is to make the final few observations which will nail
down orbit of almost-numbered asteroid, want to make observations
at exactly the right time
only a few, well-placed observations will do the job
tool allows user to select limits on Declination, apparent mag limit,
galactic latitude limit, etc.
for some given asteroid, it then shows the critical times at which
the asteroid should next be observed
looking on just 2 occasions in 5 years can be better than looking
10 times -- if those 2 are at the right time
plan is to have HOP tool on WWW to generate "best asteroid for tonight"
can't handle fast-moving objects which need observations _now_
could use this for quick list generation when some night turns
out so bad that regular observing program is ruined
- Marsden: there are > 100 amateur astronomers who contribute followup
observations of asteroids regularly --- this tool could help them
- Stokes: if search programs grow large enough, so that they cover
almost all the (observable) sky every month, then followup
may not be so important: searches will do followup by accident
(some discussion follows ... it appears that it will be a number
of years before the search programs become so large)
MPC: Williams
- explains process by which MPC identifies NEOs from incoming reports
- note that the MPC has "NEO Confirmation Page"
http://cfa-www.harvard.edu/~graff/NEO/ToConfirm.html
- MPC compares one-night-stands only within each program in real time;
one month later, compares one-night-stands between programs
- 151 MPECs so far this year
9 announced recoveries of NEOs so far
Czech Republic has _two_ very active followup groups
Dave Balam at DAO also very active
- MPC has tool of its own: OBSPLANNER provides list of "nearly-numbered"
asteroids to users
but MPC lacks computing power to support open WWW server
Funding discussion: Huebner et al.
- Huebner is from NASA Headquarters, interacts with funding agencies
- Congress wants to know "How long will NEO Search Program take?"
real answer: open-ended, can't give fixed period
was a mistake to claim (several years ago) that 10 years would suffice
- must emphasize that _discovery_ and _followup_ are not the
same, but that both are necessary
- none of the current NEO search programs are "mature"
- Bowell: one _cannot_ do the Spaceguard Survey with the money currently
being spent on NEAT + Spacewatch + LONEOS; these programs are only
precursors to true Spaceguard
- also need money for MPC to catalog and organize observations
- also need money for followup; cannot just search for objects
- Congress has asked for information on NEOs with diameter > 1 km
Software for finding asteroids interactively: Buie
- uses IDL
- code is available for free on WWW
see http://www.lowell.edu/users/buie/
- first, one must take several images of the same field
- one routine to use 24-bit color to find moving objects
they appear as colored red/blue, stationary objects are white
works well even in crowded fields
- another routine for measuring positions of objects in a frame
uses USNO A1.0 catalog
starfield registration by human eye and hand
makes plate solution, then can derive position of any object
- currently searching with Lowell 42-inch, using 3-minute exposures
willl eventually be able to keep up with observations in real time
Bigelow Survey: Larsen
- uses 43-cm Catalina Schmidt camera
- Loral "485" 4Kx4K CCD chip
field size 2.9x2.9 degrees, 2.5 arcsec/pixel
TEC cooler, 50 degrees C below ambient
camera still under construction -- ready Aug/Sept 97
- hope for V=19.5 in 2-3 minute exposures
- data reduction won't keep up with acquisition
- trying to arrange to use Mt. Lemmon 1.5-m telescope
will need some work
- hope to get 3-4 nights per dark run
- project is limited by man power
group has more telescope time than they can use
Aten Survey: Tholen
- Atens are objects with aphelion almost _exactly_ 1 AU
thus, they spend a lot of time near the Earth's position
can be more dangerous than objects which cross Earth's orbit obliquely
- must look for these Aten asteroids far from opposition
because they never appear at oppostion
all other NEO surveys look near opposition, so they can't find them
but objects far from opposition are faint, due to large phase angle
- uses UHawaii 2-m telescope plus 8Kx8K CCD mosaic camera
field of view 18x18 arcmin
uses "VR" filter, since has to share telescope with Jewitt group
only gets 1/4 of each night for this project
- limited by trailing losses, but can reach to mag 22-23
- so far, 1 year of observations Feb 96-Feb 97
15 nights, many lost to weather
total of 92 fields, about 8.9 sq.deg.
no Atens found so far
- needs more telescope time!
- low budget project: no salary, uses facility instrument
TASS: Richmond
- explores different range of parameter space than other surveys
bright objects, V=7-14
note that most comets are discovered in this mag range
- all work done on volunteer basis, no budget
- current "Mark III" cameras based on KAF-0400 512x768 CCDs
with 135mm camera lens, yields field of view 3 degrees
scale is 13.9 arcsec/pixel
- currently 7 such triplets are in operation
- drift scan on celestial equator
- triplets give 3 observations of same field, sep by one hour
- make catalog of objects detected in each frame
- need to compare catalogs from scans within a night,
also can compare scans from different nights, different sites
but haven't yet written the moving-object software
- future plans: "Mark IV" camera
based on Ford Aerospace 2Kx2K chips
yields field of view about 8x8 deg.
plan to take stare-mode frames
will reach a bit deeper, down to mag 15 or so
AMOS: Africano
- uses Air Force telescopes on Haleakela
AF has new 4-m telescope, will acquire first light December 1997
will have IR imager initially, then visible-light imager next year
- observational programs are collaborations with outside astronomers
- space-surveillance people impressed by high precision of astrometry
when one uses stars as fiducials
- several telescopes involved in search program
Baker-Nunn camera can be used for search (needs CCD camera)
GEODSS can be used for followup (has NASA/JPL CCD)
1.2-m telescope can acquire multicolor data with many filters
- example of multicolor and light curve work
1991vh shows evidence for binarity in light curves
light curve looks different at different phase angles
could be companion ... or could be unusual shape/rotation
- 1.2-m telescope gets only 15 hours per week
hard to do multicolor work with so little time
easier to do followup astrometry
so far, 270 new discoveries, down to mag 21.5
- Air Force needs more telescope time
so have purchased small, off-the-shelf "Raven" telescope system
16-inch telescope, SBIG 1534x1000 CCD, all commercial
setup in just a few days, cost only about $30K (?)
can use this telescope to look at bright objects,
free up big telescopes for other projects
- future: continue asteroid observations
demonstrate that Raven system can be made completely autonomous
McDonald Observatory asteroid search: Shelus
- 76-cm telescope w/ prime focus corrector
yields unvignetted field 1.1x1.1 degree
telescope must be operated manually
- 2Kx2K CCD camera yields 46x46-arcmin field, 1.35 arcsec/pix
- reaches R=21.5 in 3-min exposure
- have 10-12 runs per year, each run has 3-4 nights
- get 30-60 pairs of frames per night, blink at the telescope
- measured positions are good to 0.4 arcsec, consistent with catalog errors