The email address for requesting paper copies, given in part 1.C of the
recently issued news bulletin on NRA #94-OSS-13, has a mistake.
the correct address is:

e…@stars.gsfc.nasa.gov

We apologize for any inconvenience this may have caused.

The EGO Center

The latest edition of the EUVE sky survey catalog, Appendix F of NRA 94-OSS-13,
is now available on the CEA/EUVE ftp site, and via the World Wide Web. The new
catalog supercedes an earlier version which was made available in August.  

The documented listings include positions, count rates for every bandbass with a
detection, a detection quality rating, and possible ID names for each source
in the all-sky survey and deep survey. A list of other possible detections by
EUVE is also supplied.  

To get this catalog, obtain either the PostScript file /pub/nra/Appendix_F.ps
or the ASCII file /pub/nra/text/Appendix_F.txt from the ftp site at:

         cea-ftp.cea.berkeley.edu

The EUVE Guest Observer Center

Sulkanen wrote:

I think that this dimensional analysis for the x-ray luminous mass
and gravitational mass may overestimate M(p)/M(g) compared to the
actual method of doing some of this (Fabricant et al.); e.g.,
since cluster plasma is centrally condensed the effective
luminosity radius is smaller than 3 Mpc (it’s more like a few core
radii at most – see Sarazan Rev Mod Phys ’86 p.78).  A good
estimate of M(g) for radii much larger than the core radius of the
cluster gives M_g(r) = 1.08 x 10^14 B T (keV) R (Mpc) Msol
(Mushotzky, preprint X-Ray 94-8), where B is a parameter related
to the exponent of the King-like profile of the cluster x-ray
surface brightness, and is in the range of 0.6 – 0.8. When the
smoke clears the error could easily be an order of magnitude for
M(p)/M(g). You also need to demonstrate the egregious error that
x-ray observers are now making in their data analysis that leads
to many clusters with a gravitational mass in large excess
compared to the x-ray luminous mass. I doubt that all of them are
making systematic errors like the one that plagued the analysis of
the ROSAT observation of N2300.

My reply:

My simple formula for the plasma mass, which assumes an even
distribution, does overstate plasma mass, but not by that much.  I
compared the sum of the plasma masses for 20 clusters cited by
Sanders, with masses determined by Jones and Forman on the basis
of detailed data, with the sum of the masses derived from my
formula M(p) = .37 T^-.25 R^1.5 L^.5, where L is x-ray luminosity
in units of 10^44 ergs/s T is kev and R is Mpc(assumed to be
3Mpc).  The Jones and Forman mass was smaller than mine by a
factor of 1.7, although in individual cases the ratio was as great
as 5 or as little as 0.7.   In the case of Coma, where there were
several estimates available in the literature, they ranged from
3.1-4.8 x10^14 solar masses as compared with the formula value of
4.0.

The Mushotzky formula for gravitational mass quoted above is just
about twice the formula I gave.  But this is a bit strange, since
my formula M(g)=.34 TR should also overestimate gravitational mass
since it assumes a constant T out to R, while in reality T will
fall with R.  When I compared the masses of Coma, Centaurus and
A2256 from my formula with those of detailed models, I get a sum
of 24(in units of 10^14 s.m.) for my formula and a range of 25-78
in the detailed estimates.  So in these few cases, mine are within
the limits set by more detailed models.

I had previously, using known empirical correlations of T and L,
estimated that the ratio of visible mass (plasma plus stars)
gravitational energy to plasma kinetic energy(or visible mass to
gravitational mass) was .75-.95 for an average cluster going from
L=1 to 100.  The ratio of magnetic energy to kinetic energy varied
over the same range from .57-.02.  With a 1.7 smaller plasma mass
and twice as big gravitational mass we get .22-.28 for M(v)/M(g)
and .97–.03 for E(m)/E(k).  So, even with these corrections, the
typical fraction of gravitational mass that is "missing" is about
1/3 and for the brightest clusters, 2/3, not .9 or .95.  And I
doubt that in the general case the factor of two increase in
gravitational mass is real.

There’s no real disagreement between my results and the more
detailed ones.  I was talking about averages.  In individual
clusters, the ratio of gravitational mass to visible mass is going
to be greater or less.  But there were other simplifying
assumptions that I used, such as the magnetic field being always 2
microgauss and the radius begin 3 Mpc.  To get a better idea of
the fraction of confining field that can be explained by visible
matter or magnetic fields would involve measuring magnetic fields
in many more clusters.

 But the key point remains.  For the average of all clusters, at
 least half and probably a lot more of the confining field is
 observable as due to visible matter and magnetic fields.  I don’t
 see how the "best" case individual clusters can be used as
 evidence for non-baryonic matter, since it is really difficult to
 imagine  a process that would separate this stuff into some
 clusters and not others. And if we use an average value, it’s
 nowhere near the 95% required by the need to fill up an omega
 equal one universe. Moreover, I don’t see how, given the
 uncertainties of all these estimates, and given the certainty
 that some baryonic matter is dark, how a factor of two (at most)
 discrepancy can be used to justify the need for non-baryonic
 matter.

PHYSICS NEWS UPDATE
A digest of physics news items by Phillip F. Schewe, American
Institute of Physics
Number 195  September 20, 1994                   physn…@aip.org

NEUTRON STAR MASSES, at least for binary systems consisting
of two neutron stars, seem to lie in a relatively narrow range.  Lee
Samuel Finn of Northwestern (708-491-4568) has studied the
observations made of four such systems and found that with high
statistical certainty the eight neutron star masses all fall within a range
of 1.3 and 1.6 solar masses.  Finn works only with this small sample
of double neutron star binaries (only a few more are known in
addition to the four he considered) because their tight mutual orbit
affords a more precise mass determination than for other systems—
isolated neutron stars or those in orbit around white dwarfs or other
stars.  Finn expects that the apparent restriction in the neutron star
mass range (for which there is no theoretical explanation) will help
in the eventual interpretation of catastrophic events in which binary
partners spiral in toward each other. Events of this type will be
sought by the Laser Interferometer Gravitational Wave Observatory.
(Lee Samuel Finn, Physical Review Letters, 26 September 1994.)

A MAGNETIC FORCE MICROSCOPE (MFM) produces images of
a superconductor’s surface through the detection of the force between
a magnetic cantilever-mounted probe tip and the sample, which tries
to repel magnetic fields.  The MFM technique can attain a spatial
resolution of 20 nm, which is not as good as is possible with a
scanning tunneling microscope (STM).  However, since it senses a
much larger volume of the sample at any one moment, MFM is not
nearly as sensitive as STM to surface cleanliness or order.  This
might make MFM a better tool than STM for characterizing
superconductor surfaces.  The MFM can also image non-
superconductor materials.  As a demonstration, a team of scientists
at the University of Texas and Park Scientific Instruments (Sunnyvale,
CA) has used their MFM device to image magnetic structures in VHS
tape at room temperature, at 77 K, and at 6 K.  (C.W. Yuan et al.,
Applied Physics Letters, 5 Sept. 1994.)

TOYS WASHED OVERBOARD in a Central Pacific storm are
helping oceanographers study the pathways of ocean currents.  In
January 1992, 29,000 small plastic bath toys fell from a foundering
ship into the sea.  Curtis C. Ebbesmeyer of Evans Hamilton, Inc.
(Seattle) and W. James Ingraham of the National Oceanic and
Atmospheric Administration have coordinated computer simulations
with the actual recovery of some of the toys all along the Alaskan
coast in the two years since the event.  The same scientists performed
a similar operation a few years before when 61,000 Nike shoes
spilled from a boat into the Gulf of Alaska.  (Eos, 13 Sept. 1994.)

PROTONS MAY NOT BE SPHERICAL.  This is the conclusion of
Berthold Schoch at the ELSA accelerator in Bonn, Germany.  ELSA
shoots electrons at energies up to 1.2 GeV at protons in order to
study the proton shape and its excited states without actually
shattering it.  This type of research explores the middle ground
between particle physics, which regards a nucleus as a bunch of
quarks held together with gluons, and nuclear physics, which
normally views the nucleus as a collection of neutrons and protons
held together by mesons. This work will soon be aided by the advent
of the Continuous Electron Beam Accelerator Facility (CEBAF) in
Virginia, where construction is almost complete.  (Science News, 27
Aug.)

Dear Colleague:

We would be grateful if you would answer a few brief
questions about statistics.  This can be done by merely including this
message in yours, and checking your answers.

In return, we would be happy to provide you a free copy of
EASY RESAMPLING ANSWERS TO "FIFTY CHALLENGING PROBLEMS IN PROBABILITY"
(original non-resampling book published by F. Mosteller, this resampling
"work in progress" with many more than 50 problems is by Julian L. Simon)

1.  In your scientific work do you ever use inferential
statistics – hypothesis tests, confidence limits, etc?
__Yes  __ No

2.  Are you aware of the resampling approach to statistics
that has come into prominence since the 1970s?
__Yes  __ No

3.  Have you used any resampling methods – bootstrap,
permutation tests, or others – in your work?
__Yes  __ No

4.  Do you ever teach statistics?  __Yes  __ No

Thank you for your time.

                       Peter Bruce, Director
                       The Resampling Project
                       College of Business and Management
                       University of Maryland, College Park
                       syo…@netaxs.com

The Science and Engineering Television Network is a consortium of scientific
societies, labs and universities formed for the purposed of creating an
international satellite television network for scientists and engineers.
Participating organizations include the American Physical Society and the
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SETN asks all scientists, engineers and science students to respond to the
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For more information about SETN and its plans you should look at:
http://www.service.com/stv/setncall.html

Gary Welz

I’ve been hearing lately that the IAU either has, or is about to, "outlaw" the
use of Modified Julian Day numbers.  Can anyone shed some light on this?

The SoHO/CDS software library contains IDL software to convert between various
time formats (URL ftp://idlastro.gsfc.nasa.gov/contrib/thompson/time).  The
so-called "internal" uses MJD numbers to store the date information.  This is
convenient, because one can easily convert this into various civilian date
formats, using equations from the Astronomical Almanac Supplement.

Is there such a ban in place now, or is it simply being considered?  Would it
apply to internal formats within software, or only to external use such as
publications and (e.g. FITS) data files?

Thank you,

William Thompson

Hello!

I am looking for a centeroiding algorithm that precisely calculates the position
of a star image on a CCD chip for my astrometry software.
Until now, I simply calculate the "center of gravity" of the image, but a two
dimensional gauss-fit should give better results. Can anyone give me a hint where
to find such an algorithm? (Please e-mail directly to my adress)

Many thanks for any help!

  Clear Skies!
    Herbert  <Herbert.R…@jk.uni-linz.ac.at>

I am looking for current elements for the variable star Delta Scuti.  I
have the elements that appear in the General Catalog of Variable Stars – 4th Ed.
Any help would be appreciated.  Thanks.
Larry Gorski

Birkinshaw and Hughes claim a H_o of 65+/-25 km/s/Mpc. This observation
was done on Abell 2218 which had previously been investigated by McHardy
who determined an H_o of 24 +23/-10 km/s/Mpc. Birkinshaw claims to have
better x-ray data as well as SZ information as well. Regardless, if the
error bars can be trusted I agree that the SZ research is leaning towards
lower values of H_o. Nonetheless I am highly skeptical of a handful of
observations with shaky x-ray data.