Hubble question

I was recently reading an article on the future Hubble updates in
Science News and I was a little confused. The article covers a number
of subjects including the new Cosmic Origins Spectrograph and the
older STIS (Space Telescope Imaging Spectrograph).

"Another new device the crew will install is the Cosmic Origins
Spectrograph, or COS, which will separate ultraviolet light into its
components. The spectra will provide new information on..."

But then later we read

"Installed in 1997, STIS separates ultraviolet light into its
component wavlengths to reveal the..."

Anyways, it is clear from the stuff after the elipses that these two
devices ultimately perform different functions. But how are they
really different? I mean how much difference can there be between two
devices that separate ultraviolet light into its component
wavelengths. Is the new one simply more sophisticated?

Matt

On Sep 26, 7:04*pm, Matt Menge wrote:

Anyways, it is clear from the stuff after the elipses that these two
devices ultimately perform different functions. *But how are they
really different? *I mean how much difference can there be between two
devices that separate ultraviolet light into its component
wavelengths. *Is the new one simply more sophisticated?

ellipses.

Anyways, I guess I am questioning the value of replacing one
ultraviolet spectrograph with another one. It doesn't seem like a
good use of our tax money.

Regards,

Matt

Matt Menge writes:

Anyways, it is clear from the stuff after the elipses that these two
devices ultimately perform different functions. But how are they
really different? I mean how much difference can there be between two
devices that separate ultraviolet light into its component
wavelengths. Is the new one simply more sophisticated?


From the STIS instrument handbook, [1]

: The primary design goal of COS is to improve the sensitivity to point
: sources in the far-UV (from about 1100 to 1800 AA). In this wavelength
: range the throughput of the COS FUV channel exceeds that of the STIS
: FUV-MAMA by factors of 10 to 30, and the combination of the
: spectroscopic resolving power (~ 20,000) and wavelength coverage (300
: to 370 AA per setting) of the medium resolution COS FUV modes results
: in a discovery space (throughput times wavelength coverage) for
: observations of faint FUV point sources that is at least 10 times
: larger for most targets than that of STIS modes with comparable
: resolution, and is as much as 70 times greater for faint
: background-limited point sources.

Another obvious difference is that STIS was designed for spatially
resolved spectroscopy, whereas COS is designed for point sources.

Currently, HST has zero UV spectrographs, so one might also consider
STIS and COS backups for each other.

Craig


References
[1] http://www.stsci.edu/hst/stis/docume...entcycle5.html


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Craig B. Markwardt, Ph.D. EMAIL:
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"Matt Menge" wrote in message
...
I was recently reading an article on the future Hubble updates in
Science News and I was a little confused. The article covers a number
of subjects including the new Cosmic Origins Spectrograph and the
older STIS (Space Telescope Imaging Spectrograph).

"Another new device the crew will install is the Cosmic Origins
Spectrograph, or COS, which will separate ultraviolet light into its
components. The spectra will provide new information on..."

But then later we read

"Installed in 1997, STIS separates ultraviolet light into its
component wavlengths to reveal the..."

Anyways, it is clear from the stuff after the elipses that these two
devices ultimately perform different functions. But how are they
really different? I mean how much difference can there be between two
devices that separate ultraviolet light into its component
wavelengths. Is the new one simply more sophisticated?

STIS broke down 4 years ago and needs a replacement circuit board. As I
understand from a recent article in New Scientist, COS needs STIS anyway;
but as Craig has said, STIS was designed for spectroscopy of extended
sources, whereas COS is for point sources.

On Sep 26, 10:02*pm, Craig Markwardt

COS FUV modes results
: in a discovery space (throughput times wavelength coverage) for
: observations of faint FUV point sources that is at least 10 times
: larger for most targets than that of STIS modes with comparable
: resolution, and is as much as 70 times greater for faint
: background-limited point sources.

Ok, this does seem a lot more powerful. Thank you.

Matt

Do you guys really have to put up with all this spam all the time?

"Matt Menge" wrote in message
...
Do you guys really have to put up with all this spam all the time?

You've just added to it. What else is there?

Matt Menge wrote:
Do you guys really have to put up with all this spam all the time?

Filters, learn to use your filters!