The Chandra Multiwavelength Project (ChaMP)

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Дата индексирования: Tue Oct 2 06:13:53 2012
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Поисковые слова: stellar nursery

Merged list of ChaMP Survey Fields

Aitoff Projection showing ChaMP Fields

Summary

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

Detailed rejections:

No pointings closer than 10° to the LMC and SMC and 7° of M31
PI surveys (some): overlap with science (eg. ELAIS:N1.1 and ELAIS:N1.2, HDF, HDFS, Lockman Hole )
MBM 12 molecular cloud behind superbubble

Rationale

^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 A_V via

A_V= 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:

visual inspection on POSS. This also identifies other optically bright extended objects such as 47 Tuc.
visual inspection of galaxy clusters on ROSAT images. This identifies fields where bright X-ray background prevents identification of faint X-ray sources.
Extend of source:
To make sure that our field would not be contaminated by point sources related to the target, I required that
1 Mpc around a cluster should fit into 3´ => z>0.3
20 kpc around a galaxy should fit into 3´ => z>0.004
Target which might be extended in X-rays (not quasars) were checked and those with the surface brightness outside 3´ exceeding two times the X-ray background were removed.

Date Last Modified: 22 April 2002
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