Survey Strategy

Merged list of ChaMP Survey Fields

Aitoff Projection showing ChaMP Fields


  1. Main survey: >20° from galactic plane.A
    Galactic Plane Survey: < 10 deg. from galactic plane
  2. No subarray fields: reduced area and more complicated processing
  3. No grating observations
  4. No TOO's. Probably excellent for next year. (Coordinates unknown now.)
  5. No planetary observations.B
  6. Short exposures included except NGC galaxies
    Galactic Plane Survey: > 30 ksecs
  7. No SNR
  8. Galaxies and galaxy clusters:C
  9. Galactic Plane Survey: >10% contamination by a diffuse/distributed X-ray or optical source.
Detailed rejections:


A Galactic Latitude (Paul Green)

To remind ourselves about extinction...

It's characterized by optical astronomers via a color excess

E(B-V)= (B-V) - (B-V)0
which translates to visual extinction AV via

AV= R* E(B-V)
where R is 3.1±0.1 Fortunately, this constant holds for almost any optical wavelength of interest, not just V band (except where large dust particles dominate, like in young star forming regions).

Derive the absolute extinction at any wavelength (Al) via

Al = E(B-V) * [a*Rv + b]
Values of a and b are functions of wavelength x in units of inverse microns. I put the formulae from Cardelli, J. A., Clayton, G. C., & Mathis, J. S. 1989, ApJ, 345, 245

For efficient selection and classification of objects from color-color plots, we should not tolerate any more reddening than E(B-V)= 0.1

Crudely, E(B-V) can be related to Galactic latitude via

E(B-V)= A + B*cosec(|b|)
where nobody agrees on A and B. (There's no REAL correlation because the data are not very conclusive - see Sparks et al. 1987, MNRAS, 225, 769). However, A=0 and B=0.03 is the best guess for a smooth function, so that on average, we want to include only

sin|b| > 0.3

|b| > 17.5°, call it 20°
The equation

E(B-V)= -0.055 + 1.987e-22*NhGal
is eq.7 of Burstein & Heiles 1978, ApJ, 225, 40 and assumes a constant dust-to-gas ratio.

This means reddening is discounted for Galactic columns Nh>2.77e20. This is certainly not correct, esp. in application to the far UV or soft X-rays, but the errors in the determination of the reddening law are about 0.04mag in E(B-V) due to scatter in the data. To exclude negative reddenings then, it is reasonable to use

E(B-V)=max[0,-0.055 + 1.987e-22*NhGal)]
Requiring E(B-V)< 0.1 thus means Nh>8e20, which is justifiable from the point of view of facilitating comparison with previous soft X-ray (esp. ROSAT) observations.

B Planetary Observations:

The observing will be complicated and may involve nudge mode. They are extremely bright in the visual. Coordinates are not yet known. For Jupiter, auoral emission extends out to Io.

C Galaxies and Galaxy clusters (Alexey Vikhlinin):

Criteria still being formalized and quantified. Several tests are made:

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Date Last Modified: 22 April 2002
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