From: slane@head-cfa.harvard.edu (Patrick Slane)
Newsgroups: sci.astro,sci.space
Subject: Re: Japanese X-ray satellite: Astro_D
Date: 16 Nov 92 13:25:56 GMT
Organization: Smithsonian Astrophysical Observatory, Cambridge, MA,  USA

From article <BxL4vr.EIw@constellation.ecn.uoknor.edu>, by rwmurphr@wildcat.ecn.uoknor.edu (Robert W Murphree):
> nousek@astro.psu.edu (John A. Nousek) writes:
> 
>>The instruments consist of four conical foil X-ray telescopes
>>built by Pete Serlimitsos of Goddard Space Flight Center, two
>>X-ray CCD cameras built by George Ricker of MIT (with Penn State
>>Co-I's) and two gas scintillation proportional counters built
>>by Prof. Makashima of Tokyo University.  The four telescopes

[remaining summary deleted]

>      
> I gather that Astro-D is a superlative x-ray spectrometer.
> Is it "the first x-ray spectrometer" or only the first wiht
> with this wide and bandwidth, resolution, and apeture?

The imaging capabilities are not to be ignored. However, the
spectroscopy WILL be the cause of much excitement. The fact
that it will be spatially resolved (at low angular resolution)
is, for course, very important for sources with significant extent
(e.g. clusters, SNRs...)

> Is the 1 arc minute resolution a significant handicap for
> many objects?  

Yes, it is. The Einstein and ROSAT catalogs are filled with sources
observed with the High Resolution Imager (HRI) which reveal very
significant structure on small angular scales; better spectroscopy
with HRI-like spatial resolution (the HRI provides very little
spectral information) would be great. We'll have to wait for AXAF-I
to get this, but there are still LOTS of other exciting science that 
Astro-D will address. There are many, many objects for which the lower
resolution will not be a serious handicap.

> Is this a "major" observatory like ROSAT
> and/or AXAF.  

The term "major" may be a bit subjective here. The fact that, like Einstein,
ROSAT and AXAF (when launched), Astro-D is characterized by high
sensitivity with a range of capabilities, and an active Guest Investigator 
program, I would certainly consider it a "major" observatory.

> science, and the fact that the japansese have launched 3-4
> small missions in the x-ray band in 10 years may actually
> be much more significant in terms of science than a behemoth
> like AXAF that gets launched every 10-15 years or not at all.
> The US hasn't launched any free-flyers in the X-ray since 
> HEAO or Eistein 10 years ago, have they? A few detectors on
> other people's satellites of course, but nothing big since
> Einstein.

Yes, the US space program has had it's difficulties with the concept
behind these "Great Observatories" and this is changing. AXAF, while
still undeniably a "big science" project, has been streamlined and
divided into two missions. AXAF-I will provide the very high angular
resolution mirrors necessary to do arc-second imaging - and will have
spectral resolution like that of Astro-D (using a CCD developed by the
same folks who are providing the Astro-D versions) plus gratings for
higher resolution studies. AXAF-S will provide higher spectral resolution
capabilities, with lower angular resolution mirrors. And though these
missions are long overdue, the US x-ray community has hardly been
sitting on its collective hands. Let's not forget that ROSAT was launched
by the US and carries the HRI which is a US instrument, and that MAJOR
portions of Astro-D (as John noted) were developed by US investigators.
I know this is the "few detectors on other people's satellites" you
were talking about, but between the two missions you've got US mirrors,
CCDs, an HRI and a launch...

..........................................................................
						"Images of broken light
Pat Slane					 Which dance before me
Harvard-Smithsonian Center for Astrophysics	  like a million eyes
slane@cfa.harvard.edu				 They call me on and on
						 Across the Universe"
..........................................................................
Newsgroups: sci.astro