ENB No. 180 August 21 2005

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ENB No. 180 August 21 2005

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Electronic News Bulletin No. 180 2005 August 21

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/maadTatabjDzHciD1pRb/

Philip's, a publisher of astronomy books and planispheres for the
amateur astronomer, is sponsoring this bulletin. For information on
a Philip's title see the end of this bulletin.

By Alastair McBeath, SPA Meteor Section Director

Observations are continuing to come through to the Section, following last
weekend's Perseid maximum, so this is only a first review of what the
data so far shows. Meteor watch details have now arrived from Dave
Gavine (Edinburgh), Assistant Director Shelagh Godwin (SW France),
Alan Heath (Nottingham; visual and radio), Zoltan Hevesi (Hungary),
Robin Leadbeater (Cumbria; video), Tony Markham (Staffordshire),
Robin Scagell (Oxfordshire), Enrico Stomeo (Italy; video), Mark Vints
(Belgium), Chris Woodcock, and the Director (Northumberland), along
with notes from a dozen more observers via the SPA Observing Forum
(at http://popastro.c.topica.com/maadTatabjDzIciD1pRb/ see the "Perseids 2005"
topic for these), and preliminary information from Tom McEwan
(Ayrshire) and SPA Comet Director Jonathan Shanklin (Cambridgeshire).

>From these, it seems UK observations were possible somewhere on
every night from August 7-8 to 14-15 inclusive, though as so often,
conditions could be variable even at an individual site, let alone in different
parts of the country. August 11-12 and 12-13, the nights either side of
the maximum anticipated around 17:00-19:30 UT on August 12, as noted
last time, saw most watchers in action, where conditions allowed. Positive
reports have arrived from central to southern England and in south-west
Scotland for August 11-12, while August 12-13 was apparently better
across much of England, though as yet there are no details in from Wales
or Scotland for that night.

Zenithal Hourly Rates (ZHRs) were between 15-30 from August 7-8 to
10-11, rising to 40-60 by August 11-12, much as usual. August 12-13
saw ZHRs in excess of 100 for the first half of the night particularly,
though the earliest data was collected only from 19:30 UT over eastern
Europe, so it is possible the maximum kept to time, but was not seen by
our watchers. However, there are indications in the data so far that
Perseid rates may have pushed up to ~110-140 or so for roughly an hour
and a quarter centred on 23:15 UT. Whether this was a late normal
maximum, due to an unexpected additional peak, or simply an artefact of
the computed results, is not clear. Conditions for many observers were
not ideal during this potential maximum time, with limiting magnitudes
sometimes poorer than +5.0, plus often annoying amounts of mobile
cloud. Even so, it is interesting that observers with too poor skies to allow
formal meteor watching still saw better uncomputed Perseid rates near
this interval than earlier or later in the night under similar skies, which may
suggest this possible peak was a real feature. More data will tell, so if you
have results still to submit, please do not delay further! Information on
what to report and where to can be found off the SPA Meteor homepage
at: http://popastro.c.topica.com/maadTatabjDzJciD1pRb/ or see the "Observing
Meteors" booklet, free to all Section members by ordinary mail from our
Assistant Director.

Although the numbers are still too small for accuracy, the Perseids may
have been a little brighter than normal this year over the near-peak nights,
as their condition-corrected mean magnitude is presently +1.8, compared
to the August sporadics' value of +3.1 (very typical for the sporadics
generally). The brightest Perseid fireball spotted by our European
watchers was about magnitude -5. Around 30% of the Perseids left
persistent trains, compared to nearer 10% of sporadics.

Robin Leadbeater recorded the spectrum of a video-magnitude -4
Perseid at 22:59 UT on August 12, his first such capture. Though only
done as an early experiment, and so of relatively low resolution, this was
an excellent effort, probably recording spectral lines due to ionized
calcium at 393.4 and 396.8 nanometres, and ionized silicon at 634.7 and
637.1 nm, amongst others. Both ions are common in high-velocity
meteors like the Perseids. Details on Robin's spectroscopic meteor can
be found at: http://popastro.c.topica.com/maadTatabjDzKciD1pRb/ .

Perseid ZHRs had dropped back to 50-70 by August 13-14, and were
~20-30 by August 14-15. This followed the kind of pattern the shower
has shown previously, of a relatively swift decline in activity after the

Many thanks go to all our contributors who have made such a quick
preliminary overview possible. To make sure more can be established,
especially to confirm or deny the likelihood of the possible late peak on
August 12-13, please report your results soon!


Astronomers using the Spitzer infrared telescope have uncovered a
large population of quasars hidden inside dusty galaxies or positioned
in such a way that their dusty rings hide their light. In one small
patch of sky researchers found 21 examples of such quasars, of which 10
are believed to be inside fairly mature, giant elliptical galaxies,
and the rest are thought to be encased in thick, dusty galaxies that
are still forming stars. The implication, already suspected, of the
observation is that most super-massive black-hole growth is hidden by
dust. That result may allow astronomers to put together a more
complete picture of how and where quasars form.


A team of astronomers from the Netherlands and the UK has discovered
a 'jet-powered bubble' formed in the gas around a black hole in the
Milky Way. The discovery suggests that scientists may have been
under-estimating how much power black holes return into space instead
of merely swallowing material across their event horizons.

Jets of energy and particles flowing outwards at close to the speed of
light are a common feature of accreting black holes, ranging from
super-massive ones at the centres of active galactic nuclei to the
stellar-mass black holes that are thought to exist in certain X-ray
binary systems within our own Galaxy. However, what has now been
discovered is a large bubble surrounding the X-ray binary system
Cygnus X-1. The bubble is approximately 10 light-years across, and is
thought to be expanding with a speed of around 100 km per second. It
appears to have been formed by the action of a powerful outflow or jet
of energy and matter from the putative black hole over a time-scale of
about a million years. The new radio observations show a ring of
radio emission around a bubble in the nearby interstellar gas -- the
result of a strong shock that develops where the jet strikes the
rarefied gas of the interstellar medium. The jet that created the
bubble seems to be carrying more than 100,000 times the total
luminosity of our Sun, and yet the only evidence for that incredible
flow of energy is its impact on the tenuous gas between the stars,
resulting in the expanding bubble.

Astronomers already knew that super-massive black holes at the centres
of other galaxies produce enormous amounts of energy, but the new
finding indicates that something similar can happen in our Galaxy.
It also means that, after a massive star dies and turns into a black
hole, it is still capable of energising its surroundings, by
completely different mechanisms. The importance of that result is
that it demonstrates that Cygnus X-1 does not swallow all of the
infalling matter and energy, but rather redirects a considerable
fraction of it back into space. The team has ruled out the
possibility that the ring might be the low-luminosity remnant of the
supernova that spawned the black hole: since Cygnus X-1 moves in the
sky along a trajectory that is roughly perpendicular to the jet, it
cannot have been located in the centre of the ring.

New Scientist

GRBs are volleys of photons of very high energies. They come in two
classes. 'Long' bursts last from seconds to minutes and have been
found to coincide with supernovae, suggesting that they form when
massive stars explode and their cores collapse into black holes. But
until recently 'short' bursts -- lasting just a split-second -- have
proved elusive, because they have disappeared without a trace before
researchers could pinpoint or study them. That began to change on
2005 May 9, when the Swift space telescope detected a short burst and
pointed itself towards it in less than a minute, and caught a brief
X-ray afterglow. That allowed astronomers to identify a general
location for the burst, near a galaxy full of ancient stars. Now,
researchers have observed afterglows at longer wavelengths from two
bursts seen in July, homing in on their locations with 10 times the
accuracy of the May burst.

The gamma-ray satellite HETE-2 detected the first burst on July 9. It
lasted just one-tenth of a second but, two and a half days later, the
Chandra space telescope captured its X-ray afterglow, caused by matter
from the burst ramming into surrounding gas. Ground-based telescopes
in Chile and Hawaii then scanned the same region and found an
afterglow radiating at optical wavelengths. That afterglow lay about
10,000 light-years away from a galaxy that itself lies 1.8 billion
light-years from Earth. Then, Swift detected a 0.25-second burst on
July 24. The next day, the Very Large Array -- a collection of 27
radio dishes in New Mexico -- found an afterglow at radio wavelengths.
The afterglow came from within a galaxy full of old stars that lies
about 2.8 billion light-years from Earth. That burst too was found to
have an optical afterglow, making it the first short GRB identified at
X-ray, optical, and radio wavelengths.

The location of the bursts hints at their source. There had been
suggestions that flare-ups in highly magnetised neutron stars, called
magnetars, might produce short bursts. But such flare-ups can get
only so strong before they destroy the stars, putting an upper limit
on how far away a magnetar-based GRB can be observed. The recent
bursts occurred about 10 times farther away than that limit, ruling
out a magnetar source and thereby favouring the alternative
coalescence model, which attributes short bursts to mergers between
two neutron stars, or between a neutron star and a black hole.

University of California-Berkeley

Astronomers have discovered the first triple asteroid system -- two
small asteroids orbiting a larger one known since 1866 as 87 Sylvia.
Sylvia is one of the largest asteroids in the main belt between Mars
and Jupiter. Shaped like a lumpy potato, it is about 280 kilometres
in diameter and is located in the outer part of the belt. Four years
ago, Sylvia was discovered to have a moon, making it one of some 60
known binary asteroids. Seventeen of them are in the main asteroid
belt and have been imaged directly either by adaptive-optics systems
on large ground-based telescopes or by the Space Telescope. Now, a
second moon has been seen around Sylvia. Both moons orbit in nearly
circular orbits in the same plane and direction (prograde) as our Moon
orbits the Earth.

Because Sylvia was named after Rhea Sylvia, the mythical mother of the
founders of Rome, the twin moons have been named Romulus and Remus
after those founders. The closer one, orbiting about 710 km from
Sylvia, is Remus, a body about 7 km across and circling Sylvia every
33 hours. The other, Romulus, orbits at about 1360 km, measures
about 18 km across, and orbits in 87.6 hours. Sylvia has a rotation
period of 5 hours and 11 minutes, a characteristic value for


A Chandra X-ray Observatory survey of nearby Sun-like stars suggests
that they have nearly three times as much neon as there has been
thought to be in the Sun. The solar neon abundance has not been very
secure anyway, because neon has no spectral lines in the visible part
of the spectrum. However, in a gas heated to millions of degrees,
neon shines brightly in X-rays. Stars like the Sun are surrounded by
such super-heated gas; its presence round the Sun is betrayed by the
corona during solar eclipses, but observations of the corona are very
difficult to analyze. Now, Chandra has observed 21 Sun-like stars
within a distance of 400 light-years and found them to contain on
average almost three times as much neon as has been believed to exist
in the Sun. Unless the Sun is unusual, it must contain a lot more
neon than it has been given credit for. If true, that is something of
a relief to theoreticians, who have worried about a discrepancy
in the depth of the convection zone that occupies something like
the outermost third of the Sun's radius, between calculations based on
energy transport and observations of solar oscillations, which probe
the internal structure of the Sun. Neon atoms play a significant role
in energy transport, and an increase in the neon abundance by a factor
of three is just what is needed to remove the discrepancy.


Astronomers have compared Space-Telescope images of the supernova
2005cs in M51 with ones of the same region before the explosion, and
have identified the progenitor as a red supergiant whose mass was
about seven to 10 times that of the Sun. SN 2005cs belongs to a class
of exploding stars called 'Type II-plateau', which result from the
collapse and subsequent explosion of a massive star whose light
remains at a constant brightness (a plateau) for a period of time.


£4.99, ISBN 0540087017). SIR PATRICK MOORE takes the novice
astronomer on a guided tour of the stars and constellations of the
northern hemisphere. An accessible work, clearly and concisely

Bulletin compiled by Clive Down

(c) 2005 the Society for Popular Astronomy

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