Re: [APML] OT: M17 in near-IR

[Wei-Hao Wang <whwang@gmail.com>]

Hi Joe,

Thank you very much.

All near-IR cameras have to be cooled to liquid nitrogen temperature.  The 
near-IR camera on HST even uses liquid helium.  In addition, at room 
temperature, 300K, the peak of  balckbody radiation is located at around 
10 um.  At 2 um, there is significant emission from everything on earth.  
To be able to observe at 2 um, the pupil stop in front of the camera has to 
be carefully designed so that the camera can only see its own cooled body 
and the sky (which is also cold), but not the warm telescope and mirror edges.

ULBCAM is cooled.  Otherwise it just cannot operate.  But because this is
just a low-budget prototype, we didn't make a pupil stop otherwise the optics
will get much more complicated.  (It even doesn't have a shutter.)  It
sees lot of
thermal emission from the telescope if we observe wavelengths longer than 1.8 
um.  At shorter wavelengths, filters will block the thermal emission from the
telescope so it is fine.

For astronomers, the near-IR era has just started in a slow way.  The
technology
at near-IR is still not as mature as CCDs.

Cheers,

Wei-Hao


On Sun, 5 Sep 2004 06:47:25 -0400, joe <jmize@svic.net> wrote:
> Wei-Hao;
> 
>      Thkx for posting this interesting image.  Waaay back in 1994 the old
> defunct magazine "CCD Astronomy" got me interested in NIR CCD's with their
> article in their Summer issue, 'The Many Hues of Astronomical Color
> Imaging'.  They compared Hubble filters to amateur color RGB filters.  I
> noticed how much more detail and stars, although highly shifted into the
> green, were captured with the Hubble filters than common amateur RGB
> filters.
> 
>      Recently either "S&T" or "Astronomy" published in their 'New Notes' a
> much better balanced NIR image of the Flame nebula taken by the Hale
> telescope.  The article states;  "The infrared colors, Ks, H and J are shown
> here as red, green and blue."
> 
>      Using the Flame article's statement I went searching for information
> and found the Ks filter at BARR Associates and the H and J filters at OCLI.
> Although I did find the filters I haven't found much more information on
> them.
> 
> Ks (red)  = 2.150um, (1900-2400nm, Band Pass)
> H (green) =  1.635um, (1400-1800nm, Iron)
> J (blue) =  1.250um, (1100-1400)
> 
>      Your M17 is almost unrecognizable, that's what I like about NIR.  The
> information you provide about the 1.8um range picking up telescope thermal
> emission is interesting.  Palomar was able to image with their WF IR camera,
> (red = 2.12um, green = 2.270nm, blue = 2.166um), probably because they chill
> their camera.
> 
>      Although I still haven't transitioned across to CCD from film I'm still
> interested in NIR CCD.  One day soon, hopefully, I intend to take the
> plunge.  Meanwhile I collect images and information about NIR CCD imagery.
> I may, probably am, off base with my scraps and pieces of information I've
> collected but one day I hope to experiment in NIR CCD imagery here on Earth
> with my modest equipment.
> 
>      Thank you for your informative posts, keep them coming.  Thkx...joe  :)
> 
> "May You Go Among The Imperishable Stars"
> 
> Joe Mize:     jmize@svic.net
> StarFields Observatory   http://www.cav-sfo.com
> Chiefland, FL    29:24'33.4"N    82:51'37.7"W
> Moon Phase:     http://tycho.usno.navy.mil/cgi-bin/phase.gif
> 

-- 
________________________________________________________________
Wei-Hao Wang  :)

Institute for Astronomy at University of Hawaii

Address:                       
2680 Woodlawn Drive         Personal Website:
Honolulu, HI 96822             http://www.ifa.hawaii.edu/~wang
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