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completeness and limiting magnitude
03-26-2008, 15:36
Post: #1
completeness and limiting magnitude
Hi all,

I am working on WIRCam images and thinking a way to estimate the completeness and limiting magnitude of my image. One method is to add artificial stars on the image and try to detecting these artificial stars with photometric tool, eg. SExtractor or DAOPHOT. So, I looked the Terapix webpage and found stuff and SkyMaker. These software seems to be the tool I am looking for. But I still have few questions.

Can SkyMaker simulate the sky with the IR background? It will be more realistic if SkyMaker can use real background, say extracted from SExtractor. Or that is the building function of SkyMaker?

Cheers,

Chi-hung
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03-26-2008, 18:19
Post: #2
RE: completeness and limiting magnitude
Chi-hung,

This a good question, and one already posed on the forum a few weeks back. I am still doing things the 'old-fashioned' way myself (adding fake stars) but yes, in theory, skymaker and stuff should be able to make much more realistic simulations. I haven't done it myself however. There is no reason why you couldn't use skymaker to make a noiseless image with galaxies, and then add that to your real IR sky (with the galaxies removed using sextractor). Then run sextractor again to see what you get!

cheers
henry
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03-27-2008, 13:17
Post: #3
RE: completeness and limiting magnitude
Hi Henry,

Thanks for you message. Yes, I checked the post on the forum. I also tried to use SkyMaker today. I think it works for me. What I did is lower the background level by setting high value for BACK_MAG and AUREOLE_RADIUS to be 0. So, I would like to ask few questions>

1. Is there any to set background to be exact 0 ? So that I can add this simulated image to any image?

2. If I am going to add simulated image to WIRCam image produce by SWARP, do I have to set gain to be same value as the one I found in FITS header? What will be happened if the values are not consistent to each other ?

3. I can not compile SkyMaker on my MAC. The problem seems to be the math library of MAC system. There is no static math library (libm or -lm) on MAC. So, I have to remove -static option when compiling. However, it gives me another error message. I attached the message as the followed.

ld_classic: alterimage.o incompatible, file contains unsupported type of section 17 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: fft.o incompatible, file contains unsupported type of section 14 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: galaxies.o incompatible, file contains unsupported type of section 16 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: image.o incompatible, file contains unsupported type of section 16 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: imaout.o incompatible, file contains unsupported type of section 14 (__IMPORT,__pointers) in load command 0 (must specify "-dynamic" to be used)
ld_classic: list.o incompatible, file contains unsupported type of section 15 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: main.o incompatible, file contains unsupported type of section 13 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: makeit.o incompatible, file contains unsupported type of section 13 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: prefs.o incompatible, file contains unsupported type of section 15 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: psf.o incompatible, file contains unsupported type of section 16 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: random.o incompatible, file contains unsupported type of section 15 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: simul.o incompatible, file contains unsupported type of section 14 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: stars.o incompatible, file contains unsupported type of section 15 (__IMPORT,__jump_table) in load command 0 (must specify "-dynamic" to be used)
ld_classic: warning /usr/local/lib/libm.a archive's cputype (18, architecture ppc) does not match cputype (7) for specified -arch flag: i386 (can't load from it)

Well, I am happy with SkyMaker on Linux now. I would happier if I can have your answer. Thanks for helping in advance.

Cheers,

Chi-hung
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04-13-2008, 16:49
Post: #4
RE: completeness and limiting magnitude
Quote:Hi Chi-hung,
sorry for the delay, I have been traveling during the two past weeks.
Answers to your questions:
[quote]1. Is there any to set background to be exact 0 ? So that I can add this simulated image to any image?

Well, "almost", since in SkyMaker the background level is expressed in magnitudes, with a maximum of 99 mag.arcsec-2, which should be close to 0 to a good approximation Big Grin.

Quote:If I am going to add simulated image to WIRCam image produce by SWARP, do I have to set gain to be same value as the one I found in FITS header? What will be happened if the values are not consistent to each other ?

You have to use the same effective gain as in the image you plan to add the simulation to. By effective gain I mean a gain that takes into account any averaging / flux scaling the data has been through.

Quote:I can not compile SkyMaker on my MAC. The problem seems to be the math library of MAC system. There is no static math library (libm or -lm) on MAC. So, I have to remove -static option when compiling. However, it gives me another error message. I attached the message as the followed.

Yes I have to make the software compile dynamically by default. I will try to release a Mac binary for the next release.
- Emmanuel.
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