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 Post subject: ENB No. 222 May 27 2007
PostPosted: Sat May 26, 2007 5:04 pm 
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The SOCIETY for POPULAR ASTRONOMY
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Electronic News Bulletin No. 222 2007 May 27
====================================================


Here is the latest round-up of news from the Society for Popular
Astronomy. The SPA is Britain's liveliest astronomical society, with
members all over the world. We accept subscription payments online
using our secure site and can take credit and debit cards. You can
join or renew via a secure server or just see how much we have to
offer by visiting http://popastro.c.topica.com/maagzieabyNXpcixLLVb/


ETA AQUARIDS
By Alastair McBeath, SPA Meteor Section Director

Following suggestions that the Eta Aquarids might produce stronger
activity than normal this year (see ENB 220), only a fairly ordinary, or
even slightly weak, return seems to have actually happened. A set of
visual results from Tim Cooper in South Africa, troubled by the
bright Moon as expected, showed quite typical Zenithal Hourly
Rates (ZHRs) of ~25-35 on most nights from April 29-30 to May
5-6, albeit not rising as much as we might have anticipated by the
latter date. May 6-7 produced the better rates in what Tim observed,
when ZHRs were ~50 +/- 15, which is below what was expected,
and also a little below the shower's general average.

Preliminary radio meteor activity analysed by Assistant Meteor
Director David Entwistle from Enric Fraile Algeciras (Spain), the
Observatoire de Lille (France), Dave Swan (England), Felix
Verbelen (Belgium) and himself, showed generally healthy meteor
echo counts throughout early May, much as usual, reaching a peak
from the Eta Aquarids on May 6-7, centred at a mean time of May
6, 20h50m UT, perhaps a few hours later than expected. Problems
in interpreting radio meteor data mean it is not possible to suggest a
likely equivalent ZHR, but my own assessment of the overall activity
graphs is that the Eta Aquarid peak in these five datasets did not seem
as clear as it sometimes can be. This may be due to interference
problems rather than genuinely lower meteor counts however. We
may have a better idea when more results are available. The radio
graphs and other details so far can be found at:
http://popastro.c.topica.com/maagzieabyNXqcixLLVb/ .


VERY EARLY STAR
McDonald Observatory, University of Texas

Astronomers in Texas recently used radioactive-decay techniques to
determine the age of a star called HE 1523-0901. They found it to be
extraordinarily old, 13.2 billion years, not far short of the supposed
age of the Universe of 13.7 billion years. Astronomers can measure
accurate ages only for the very rare old stars that contain large
amounts of radioactive elements such as uranium. In this case they
determined the uranium abundance from measurements made with a
spectrograph on one of the four 8.2-m telescopes that comprise the VLT
at ESO in Chile. HE 1523-0901 also contains thorium, another
radioactive element that is useful in age-dating of stars, but
uranium, with a half-life of 4.5 billion years, makes a better clock
than thorium, since thorium's half-life is about the same as the age
of the Universe. To measure the age of a star, it is necessary to
know the abundance not only of a radioactive element but also of one
or more of the elements produced as products of its radioactive decay.
In HE 1523-0901, the relevant elements that could be measured were
europium, osmium and iridium. The combination of two radioactive
elements with three decay products observed in this one star provided
six so-called 'cosmic clocks' and ought to have produced a reliable
age.


HOTTEST EXTRASOLAR PLANET YET DISCOVERED
University of Central Florida

Astronomers have used the Spitzer space telescope to measure the
hottest planet so far discovered, at 2000 C. The planet, HD 149026b,
was eclipsed behind its star, and although the planet cannot be seen
separately from the star the dimming during the eclipse showed how
much light the hot planet emits; the temperature follows from that.
To be so hot, it must absorb almost all the starlight that falls on
it. That means that its surface must be blacker than charcoal, which
is not unusual - the same is true of our Moon. The planet has to
re-radiate all that energy in the infrared. It is so hot that if one
could see it close up it would look like an ember in space, absorbing
all incoming light but glowing red-hot.

Discovered in 2005, HD 149026b is a bit smaller than Saturn, making it
the smallest extrasolar planet with a measured size. However, it is
more massive than Saturn, and is suspected of having a core 70-90
times the mass of the Earth. It has more 'heavy elements' (elements
other than hydrogen and helium) than exist in our whole Solar System,
outside the Sun.


MISSING MASS IN DWARF GALAXIES
NRAO

Astronomers studying dwarf galaxies formed from the debris of a
collision of larger galaxies found the dwarfs to be much more massive
than expected, and think that the additional material is 'missing
mass' that theorists said should not be present in that kind of dwarf
galaxy. The scientists used the Very Large Array radio telescope to
study a galaxy called NGC 5291, 200 million light-years from the
Earth. That galaxy collided with another one 360 million years ago,
and the collision shot streams of gas and stars outwards. Later, the
dwarf galaxies formed from the ejected debris. The visible portion of
a spiral galaxy, like our own Milky Way, lies mostly in a flattened
disc, usually with a bulge in the centre. The visible portion,
however, is surrounded by a much larger halo of mostly dark matter.
When spiral galaxies collide, the material expelled by the interaction
comes from the galaxies' discs, so astronomers did not expect that
dwarf galaxies formed from the collision debris would contain much, if
any, dark matter.

The dwarfs' masses were determined from the Doppler shift of radio
waves emitted by atomic hydrogen at a frequency of 1420 MHz.
The frequency shift indicated the rotational speed in the galaxy.
That, in turn, allowed the scientists to calculate the dwarf's mass.
They do not believe that it is anything mysterious, but merely cold
hydrogen molecules that are extremely difficult to detect.


THREE NEW SATELLITES OF SATURN DISCOVERED
IAU

Astronomers using the Japanese Subaru 8.2-m reflector at Mauna Kea
have discovered three new satellites orbiting Saturn, S/2007 S 1, S 2,
and S 3. They have orbital periods of 895, 793, and 992 days
respectively; S 2 and S 3 have retrograde orbits.


HUBBLE DETECTS RING OF DARK MATTER
ESA

Astronomers using the Hubble telescope report the existence of a ring
of dark matter 2.6 million light-years across in the cluster
ZwCl0024+1652 located 5 billion light-years away. The team found the
ring while they were trying to map the distribution of dark matter
within the cluster. Although astronomers cannot see dark matter, they
can infer its existence in clusters of galaxies by observing how its
gravity bends the light from background galaxies. Although invisible
matter has been found before in other galaxy clusters, it has not been
so largely separated from the galaxies and the hot gas that make up
the clusters. By seeing a dark-matter structure that is not traced by
galaxies and hot gas, astronomers can study how it behaves differently
from normal matter.

The astronomers noted that previous research involving spectroscopic
observations of the object had found two distinct groupings of
galaxies, indicating that there were really two clusters, that had
collided between 1 and 2 billion years ago. We have a head-on view of
the collision because it occurred fortuitously along the line of sight
from the Earth. From our perspective, the dark-matter structure looks
like a ring. The team created computer simulations showing what
happens when clusters of galaxies collide: the dark matter falls to
the centre of the combined cluster and sloshes back out. As the dark
matter moves outward, it begins to slow down under the pull of gravity
and pile up. The collision thereby created a ring of dark matter
which leaves distinct footprints in the apparent shapes of the
background galaxies.


EVIDENCE OF NEW TYPE OF BLACK HOLE
Science Daily

The XMM-Newton spacecraft has found evidence for the existence of an
'intermediate-mass black hole'. The existence of such things is
controversial because there is no accepted mechanism for how they
could form. (Of course, if one denied the existence of everything
that couldn't be explained, one would be left with precious little to
work with.) Astronomers experimenting with a new technique on XMM
data estimate that an X-ray source in the 'nearby' galaxy NGC 5408 is
related to a black hole with a mass of about 2,000 suns.


MUTUAL-OCCULTATION SEASON FOR URANIAN SATELLITES
New Scientist

For the first time, astronomers have observed one of Uranus's moons
passing in front of another --- a fleeting alignment that can offer
information that cannot be obtained in any other way. Researchers
hope that it will be the first in a bonanza of data returned from
Uranus this year. That is because the equatorial plane of Uranus,
which is also the plane in which its main satellites revolve, passes
through the Earth this year, an event that happens only twice in each
84-year circuit of Uranus around the Sun. Using the Faulkes telescope
in Australia, astronomers saw a dimming by abut 30% as the 1500-km
moon Oberon passed in front of the 1200-km Umbriel. Such observations
were not made during the last opportunity, in the late 1960s, because
it was more difficult then to record such events with adequate
time-resolution and anyway there was not so much interest in the
matter. Data from occultations could lead to better maps of the major
satellites and improve the determination of their orbits. Altogether
there are predicted to be 321 mutual occultations and eclipses of the
Uranian satellites during this eclipse season, which lasts until early
next year; about 150 of the events may be observable. Uranus has 27
moons, but scientists will mainly be concerned with the five largest
-- Miranda, Ariel, Umbriel, Titania and Oberon. This may also be a
good time to observe the Uranian ring system, while the rings are
seen 'edge on'.


MERGING STARS MAY EXPLAIN OUTBURST
New Scientist

Astronomers think that they have identified a new class of variable
stars, which become brighter than novae but not as bright as
supernovae, and may be caused by the merger of two stars. Using the
Palomar Observatory in California, the Keck I telescope in Hawaii and
the Spitzer space telescope, the observers found in the galaxy M85,
which lies about 60 million light-years away, an object that was not
bright enough to qualify as a supernova. The object stayed at about
the same brightness for more than two months and then gradually faded
away. Researchers believe that the observations point to a stellar
merger, of stars roughly as massive as the Sun. The object has been
dubbed a 'luminous red nova' because of its brightness and colour.
It adds to a growing category of temporarily bright objects that are
neither novae nor supernovae. They seem to range in brightness and
age, and include objects called M31 RV and V4332 Sagittarii, which
also both turned red when they brightened, and V838 Monocerotis. The
light outburst from the last-named object progressively illuminated a
pre-existing shell of dust around it, creating a dramatic spectacle
that has been repeatedly pictured by the Hubble telescope.



Bulletin compiled by Clive Down

Owing to holidays, the next scheduled bulletin will appear on June 24.


(c) 2007 the Society for Popular Astronomy


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