Using Skymorph to obtain pre-discovery positions on NEAT images

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Juan Lacruz, La Cañada Obs. J87

First draft Oct 2003, last revision Nov 2005

1 - Introduction

SkyMorph is a system based in the database of images from NEAT (three telescope net) and other surveys which in combination with the JPL perturbed ephemerides calculator Horizons allows the user to retrieve images of specific areas of the sky where a given object could have been imaged.

To help the SkyMorph team understand SkyMorph usage, and to justify continued SkyMorph funding, they need to collect information on the science impact of SkyMorph. They would appreciate users sending in information on the discoveries, papers, notices and scientific investigations that the SkyMoprh site has facilitated. Please send information in any format you find convenient to Steve Pravdo

2 - Connecting to Skymorph

Skymorph, a project supported by NASA's AISR program is publicly available at :
http://skys.gsfc.nasa.gov/skymorph/skymorph.html
To find images containing pre discovery positions of a moving object, select :
Look for an asteroid or other moving object

3 - Orbital elements

When the Skymorph interface opens, the user may select to enter a designation of a catalogued moving object or the orbital elements.

3.1 Catalogued object

Skymorph checks Horizons JPL database to retrieve the orbital data, be aware that for the most recent discoveries the orbit is usually of a low quality (just a Väisälä aproximation) and the predicted position may be far off the actual.

As more observations are gathered the orbit quality improves, the minor plabet center publishes in the daily orbit update (DOU) the new orbits from recent observations.

The quality of the orbit and a rough idea of the temporal validity for the predicted ephemeris follows :

  • Väisälä, one month
  • One opposition, one year
  • Perturbed one opposition, some years
  • Multiple opposition, many years

Subsequent orbit improvements, as published in DOUs, may take a few days to get updated in Horizons. You may want to manually enter the latest mpc elements published in the DOU to avoid waiting for the update.

3.2 Non Catalogued object

Provide the following data:

  • Epoch
  • Eccentricity
  • Perihelion distance
  • Perihelion date
  • Longitude of the ascending node
  • Argument of the perihelion
  • Inclination
  • H magnitude

The latest mpc orbital elements may be obtained using the Minor Planet Ephemeris Service (MPES), once all the orbital elements have been entered, click on submit query. Skymorph will show a list of the images potentially containing the object.

Select the files to download and click on display images, after a while the images are displayed on the screen, just double click on them to save the fits files to the PC.

Note the date and time of middle exposure in the list of files to later use it in astrometry.

4 - The Telescopes

The NEAT images are from CCDs mounted on the following telescopes :

  1. 566, Haleakala NEAT/GEODSS, active since 1995 Dec to 1999 Feb
  2. 608, Haleakala AMOS, active since 2000 Feb
  3. 644, Palomar Mountain NEAT, active since 2001 June

To find out which telescope took an image :

The 644 images can be easily recognized by the suffix letter standing for the CCD chip of the three shooter (a, b or c).

566 can be distinguished from 608 by the date, they never worked at the same time

5 - Setup data

For the astrometric reduction some values like the pixel scale etc are needed :

566-Haleakala-NEAT/GEODSS (since 1995) (1 m F2.2)

Pixels 4080x4080 PixelWide=15 microns
PixelHigh=15 microns
FocalLength=2186.0
Resolution=1.4 "/pixel
Longitude=156.2580 W
Latitude=20.7080
Height=3000.0

608-Haleakala-AMOS (since 01/aprl 2000) (1.2 m F1.9)

Pixels 4080x4080
PixelWide=15 microns
PixelHigh=15 microns
FocalLength=2316.5
Resolution=1.4 "/pixel
Longitude=156.2580 W
Latitude=20.7080
Height=3000.0

644-Palomar Mountain/NEAT (1.2 m F 2.5 Oschin)

Pixels 4080x4080x3
PixelWide=15 microns
PixelHigh=15 microns
FocalLength=3075.7
Resolution=1 "/pixel
Longitude=116.8590 W
Latitude=33.3570
Height=1000.0

Important Note on BZERO and BSCALE:

NEAT images store signed 16bit integers (i.e, values between -32768 to +32767), but NEAT/SkyMorph software does not include, in the FITS header, the keywords :

BZERO = 32768
BSCALE = 1

The astrometry or visualization package may thus fail to represent the values. You can manually add these keywords to the FITS header, the program will then convert the pixel values from the range -32768 to +32767 to values between 0 and 65535 by adding 32768 (BZERO)and multiplying with 1 (BSCALE).
For Astrometrica users there's a workaround, you may want to add the following lines to the [Settings] section of the .cfg file you're using with Astrometrica, this would have the same effect as if the parameters were found in the FITS header.

6 - Skymorph uses JPLs Horizons perturbed ephemeris

Care should be taken when identifying the objects, in particular whilst Horizons invoked by Skymorph uses perturbed ephemeris, other systems like MPChecker and some astrometry reduction packages do not. Thus, the position of the object should be close to that predicted by Skymorph and probably quite off from that predicted by the astrometry package.

7 - Astrometrica ready to use .cfg files

Downloads available for ready to use astrometrica cfg files,

  1. 566.cfg
  2. 608.cfg
  3. 644.cfg

8 - References

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