COMET SECTION NEWS
By Jonathan Shanklin, Comet Section Director
The remains of comet 2010 X1 (Elenin) have been recovered after
perihelion by a Spanish observer, working at a remote mountain
location in the Cantabrian Mountains. The comet was probably a small
object as it had a faint absolute magnitude, and as it approached
perihelion it was seen to become more diffuse and fade. In October,
over a month after perihelion, Juan Gonzalez detected a cloud of
material in the expected location, though his observations were
doubted by many Internet 'experts'. They believed that it had
completely disintegrated, and when no object could be detected by deep
imaging, they poured scorn on the visual observation. They should
have remembered history. Similar scorn was heaped on George Alcock
when he drew intricate tail detail, but newer technology showed that
his visual observations were correct. The long-exposure photographs
of the mid-twentieth century had simply blurred out the structure. In
the case of the recent disputed observation, amateur wide-field CCD
imaging was able (after a few days) to provide the proof that the
visual observation was correct. A superb image taken remotely by
Rolando Ligustri showed a diffuse cloud of material representing the
disintegrated comet. The lesson is that visual observation still has
a part to play in scientific discovery.
There is a comet that is well placed for observation if you want to
see what one looks like. From light-polluted city skies comet 2009 P1
(Garradd) is not easy in binoculars, but in darker rural skies you get
a more impressive view. Observations so far show it to have a small,
moderately condensed coma about 4 or 5 minutes of arc in diameter, but
from my urban location I have not been able to see anything of a tail.
Its brightness has not changed much over the last month, as its
decreasing distance from the Sun is balanced by its increasing
distance from us. The comet will reach perihelion at 1.6 AU just
before Christmas, but it is then 2 AU from the Earth. It should be
around 7th magnitude, much as it is at the moment. In the new year it
will be receding from the Sun, but our distance from it is decreasing,
and the comet could become a little brighter. The comet is nearly
stationary in southern Hercules in November, but then accelerates
northwards, though it is still in Hercules at the end of the year.
http://www.ast.cam.ac.uk/~jds/PLANETS
By Andrew Robertson, SPA Planetary Section Director
MERCURY reaches eastern elongation on the 14th (23°) but being at only
4° altitude at sunset is effectively unobservable from the UK.
VENUS is only slightly better placed, being at 6° altitude at sunset
on the 14th, but as it is magnitude -3.9 (compared to Mercury's -0.2)
there is a good chance of locating it towards the end of the month
just after sunset in the SSW when it will be 8° altitude, provided
you have a clear sky and horizon.
MARS is an early-morning object. By mid-month at the end of
astronomical dark (0515 UT) it is at 47° altitude in the SSE shining
at magnitude 1.0 in Leo, near to Regulus which being a blue-white star
of magnitude 1.4 will make a pleasant pairing.
JUPITER is still king of the planets, having just passed opposition on
October 29 and shining at magnitude -2.8. It is observable most of
the night. Displaying a diameter of 49" it shows a wealth of detail
even in a small telescope, and I have been receiving lots of images
and sketches from SPA members.
Any reports of observations would be most welcome via:
http://popastro.com/planet/contact/ASTEROID 2005 YU55 TO APPROACH THE EARTH ON 2011 NOVEMBER 8
NASA
Near-Earth asteroid 2005 YU55 will pass within 0.85 lunar distances
of the Earth on November 8. The close approach of this 400-metre
C-type asteroid presents an excellent opportunity for optical, near-
infrared and radar observations. On November 8 and 9 the object will
reach visual magnitude 11 and should be easily visible in modest
telescopes. The closest approach to the Earth and the Moon will be
respectively 0.00217 AU and 0.00160 AU on November 8 at 23:28 and
November 9 at 07:13 UT. Discovered on 2005 December 28 by the
Spacewatch Program, the object has been previously observed with the
Arecibo radar in 2010 and shown to be a very dark, nearly spherical
object 400 metres in diameter. As well as aiding the interpretation
of the radar observations, visual and near-infrared observations could
define the object's rotational characteristics and provide constraints
on the nature of the object's surface roughness and mineral
composition. Since the asteroid will approach the Earth from the
Sunward direction, it will be a daylight object until the time of
closest approach. Although classified as a potentially hazardous
object, 2005 YU55 poses no threat of an Earth collision over at least
the next 100 years. However, this will be the closest approach to
date by an object of such a large size that we know about in advance,
and (as far as is known) such an event will not happen again until
2028 when asteroid (153814) 2001 WN5 will pass to within 0.6 lunar
distances.
ERIS IS PLUTO'S TWIN
ESO
Eris is one of the largest trans-Neptunian 'Kuiper-Belt' objects in
the outer Solar System; it was discovered in 2005, and its discovery
was one of the factors that led to the adoption by the IAU of a new
class of objects called dwarf planets and the re-classification of
Pluto from planet to dwarf planet in 2006. Eris is currently three
times further from the Sun than Pluto. In 2010 November, it occulted
a faint background star; such occurrences are rare and difficult to
observe, as Eris is so distant and its angular diameter is so small.
Occultations provide the most accurate, and often the only, way to
measure the shape and size of a distant Solar-System body.
Observations were attempted from 26 locations around the globe,
including several telescopes at amateur observatories, on the
predicted path of the shadow, but only at two sites, both in Chile, at
one of which there were two telescopes, was an actual occultation
observed. The combined observations from the two Chilean sites are
consonant with a model of Eris that is close to spherical.
While earlier observations by other methods suggested that Eris was
probably about 25% larger than Pluto, with an estimated diameter of
3000 km, the new study indicates that the two objects are pretty well
the same size. Eris's newly determined diameter stands at 2326 km,
with an accuracy assessed at 12 km -- but that is valid only on the
assumption that the object is a sphere. Pluto has a diameter
estimated to be between 2300 and 2400 km. Pluto's diameter is harder
to measure because of the presence of an atmosphere, albeit very
tenuous, which creates ambiguities in the understanding of occultation
light-curves.
The motion of Eris's satellite Dysnomia enables the mass of Eris to be
determined; it is 27% greater than that of Pluto. Together, its mass
and diameter give its density as 2.52 times that of water, implying
that Eris is probably a rocky body covered in a rather thin mantle of
ice. The surface of Eris appears to be extremely reflective,
reflecting 96% of the light that falls on it (a visible albedo of
0.96 -- brighter even than fresh snow), making Eris one of the most
reflective objects in the Solar System, along with Saturn's icy moon
Enceladus. The bright surface of Eris is most likely composed of a
nitrogen-rich ice mixed with frozen methane, whose presence is
suggested by the spectrum, coating the surface in a thin and very
reflective icy layer less than 1 mm thick. The layer of ice could
result from a nitrogen/methane atmosphere having condensed as frost
onto the surface as Eris moved away from the Sun in its elongated
orbit into an increasingly cold environment. The temperature of the
surface of Eris facing the Sun is estimated to be -238 C at most, and
even lower on the night side. The ice could turn back to gas as Eris
approaches its closest point to the Sun.
COMET STORM IN A NEARBY STAR SYSTEM
NASA
Astronomers using the Spitzer space telescope believe that they see
evidence of an ongoing 'Late Heavy Bombardment' in the 'nearby'
southern-hemisphere star system Eta Corvi, occurring at about the same
stage of formation of a planetary system as in our Solar System.
The Eta Corvi system is approximately one billion years old, which
researchers think is about the right age for such a storm. Some
scientists think that, about 4 billion years ago, about 600 million
years after the Solar System formed, the Kuiper Belt was disturbed by
a migration of Jupiter and Saturn, and that the shift in the Solar
System's gravitational balance scattered the icy bodies in the Kuiper
Belt, ejecting the vast majority into interstellar space and producing
a lot of dust in the belt. Some Kuiper-Belt objects, however, were
set on inward paths that crossed the orbits of the Earth and other
rocky planets. The resulting bombardment of comets lasted until 3.8
billion years ago. The barrage scarred our Moon and produced large
amounts of dust. Spitzer has observed around Eta Corvi a band of dust
whose spectrum resembles that of the Almahata Sitta meteorite, which
fell to Earth in fragments across Sudan in 2008. It is tempting to
imagine that the Eta Corvi dust band represents the remnants of an
obliterated giant comet, which might have been destroyed by a
collision with a planet or some other large body. The dust is located
close enough to Eta Corvi that Earth-like planets could exist in the
collision zone. A second, more massive ring of colder dust located
further out in the Eta Corvi system could be interpreted as a
reservoir of cometary bodies. That ring, discovered in 2005, matches
the size of the region in the Solar System known as the Kuiper Belt,
where icy and rocky left-overs from planet-formation linger. The
comets of Eta Corvi, and the Almahata Sitta meteorite, may have each
originated in the Kuiper Belts of their respective star systems.
BLUE STRAGGLERS IN NGC 188
Northwestern University
A consortium of astronomers led from Wyoming has published a study of
the old open star cluster NGC 188, which is to be found in Cepheus
only 5° from the celestial North Pole. The cluster has around 3,000
stars, all about the same age. In the ordinary course of their
evolution, stars burn out, starting from the brightest and most
massive ones which burn up their hydrogen much more quickly than those
of modest mass. In most cases they finish up by ejecting much of
their mass, leaving behind the compact stellar core as a white dwarf.
In NGC 188, as in many other clusters, we see a few stars that seem
anomalously young, blue and bright, ones that according to the age of
the cluster ought to have burnt up and become white dwarfs by now.
They are known as 'blue stragglers', and are unusually abundant in
NGC 188, which includes 21 of them. It was recognised in the 1960s by
W. H. (later Sir William) McCrea that blue stragglers arise from
binary-star systems in which the less-massive star collects the
expelled envelope of its companion in the final stages of the latter's
evolution, and thereby becomes an object that is more massive -- and
accordingly burns brighter and bluer -- than any of the stars that are
evolving normally as single objects in the cluster. The stripped core
of the formerly more-massive star remains as a white dwarf, still in
orbit with the rejuvenated blue straggler. The orbital periods are
typically of the order of 1000 days. The white-dwarf components of
the binaries are not actually detectable directly, being very faint,
but their existence is manifested by the orbital motion of their blue-
straggler companions.
Much of the NGC 188 data set was collected during the last decade by
the 3.5-m WIYN Telescope on Kitt Peak in Arizona, but a considerable
part was supplied from the Dominion Astrophysical Observatory in
Victoria, B.C., and a contribution was subscribed by the moderator of
these Bulletins from observations that he made in collaboration with
J. E. Gunn with their own radial-velocity spectrometer on the Palomar
200-inch reflector in the 1970s.
ANCIENT SUPERNOVA MYSTERY SOLVED
NASA
In 185 AD Chinese astronomers noted a "guest star" that appeared
in the sky and stayed for about 8 months. By the 1960s, scientists had
recognized that the object was the first documented supernova. Later,
they pinpointed its remnant, called RCW 86, located about 8,000
light-years away. The spherical remains, which cover an area of sky
larger than the Full Moon (and can be viewed online at
http://go.nasa.gov/pnv6Oy ) are larger than expected. New infrared
observations made with Spitzer space telescope and other instruments
indicate that the event was a 'Type Ia' supernova, created by the
relatively peaceful death of a star like our Sun, which then shrank to
become a white dwarf. The white dwarf is thought to have blown up
later as a supernova after siphoning matter from a nearby star. The
observations also show for the first time that a white dwarf can
create a cavity around it before blowing up in a Type Ia event.
A cavity would explain why the remains of RCW 86 are so big. When
the explosion occurred, the ejected material would have travelled
unimpeded by gas and dust and spread out quickly.
VISTA FINDS NEW GLOBULAR CLUSTERS
ESO
Two previously unknown globular clusters were found in new images from
ESO's VISTA survey telescope, adding to the total of 158 known
globular clusters in our Milky Way. The two faint clusters are known
as VVV CL001 and VVV CL002. This small and faint grouping may also be
the globular clusters that are the closest known to the centre of the
Milky Way. As well as globular clusters, VISTA is finding many open,
or 'galactic'. clusters, which generally contain fewer, younger, stars
than globular clusters and are far more common. Another newly
announced cluster, VVV CL003, seems to be an open cluster that lies in
the direction of the Galactic centre, but much further away, about
15000 light-years beyond the centre. It is the first such cluster to
be discovered on the far side of the Milky Way. The newly found
clusters are so faint that it is no wonder that they have remained
un-discovered until now. Because of the absorption of visible
starlight by interstellar dust, such objects can be seen only in
infrared light.
HOW MILKY WAY KILLED OFF SATELLITE GALAXIES
RAS
Researchers have noticed for the first time the existence of a new
signature of the birth of the first stars in our Galaxy. More than 12
billion years ago, the intense ultraviolet light from those stars
dispersed the gas of our Galaxy's nearest companions, virtually
putting a halt to their ability to form stars and consigning them to a
dim future. That explains why some galaxies were killed off, while
stars continued to form in more distant objects. The first stars of
the Universe appeared about 150 million years after the Big Bang.
Back then, the hydrogen and helium gas filling the Universe was cold
enough for its atoms to be electrically neutral. As the ultraviolet
light of the first stars propagated through the gas, it broke apart
the proton--electron pairs that make up hydrogen atoms, returning them
to the so-called plasma state in which they existed in the first
moments of the Universe. That process, known as re-ionization, also
resulted in significant heating, which had dramatic consequences --
the gas became so hot that it escaped the weak gravity of the galaxies
of lowest mass, thereby depriving them of the material needed to form
stars.
The process appears to explain the small number and large ages of the
stars seen in the faintest dwarf-galaxy satellites of the Milky Way,
and why galaxies like the Milky Way have so few satellites around
them. The model appears to match observations of our Galaxy and its
neighbourhood and suggests that the first stars of our Galaxy played a
major role in the photo-evaporation of the satellite galaxies' gas.
It is not large nearby galaxies but our own that caused the demise of
its tiny neighbours, evaporating them through its intense radiation.
COMPLEX CARBON COMPOUNDS EXIST THROUGHOUT THE UNIVERSE
University of Hong Kong
Astronomers at the University of Hong Kong have shown that a substance
commonly found throughout the Universe contains a mixture of component
molecules having many carbon atoms in both 'aromatic' (benzene-ring)
and 'aliphatic' (chain-like) arrangements. The compounds are so
complex that their chemical structures resemble those in coal and
petroleum. Since coal and oil are remnants of ancient life, such
matter was thought to arise only from living organisms, but the team's
discovery suggests that complex carbon compounds can be synthesized in
space even in the absence of life forms.
The researchers investigated a set of infrared emissions detected in
stars, interstellar space, and galaxies -- spectral signatures known
as 'unidentified infrared emission features'. The features have been
supposed to come from simple molecules made of carbon and hydrogen
atoms, called polycyclic aromatic hydrocarbon (PAH) molecules. From
observations taken by the Infrared Space Observatory and Spitzer, the
observers show that the spectra cannot be explained by PAH molecules
but must arise from chemical structures that are much more complex.
From spectra of novae, they show that stars can make such complex
compounds on extremely short time scales (weeks). Not only are stars
producing such matter, but they are also ejecting it into interstellar
space in the form of what astronomers call dust. The work supports
an earlier idea that old stars can act as molecular factories.
Interestingly, the compounds in star dust are somewhat similar to some
found in meteorites, so they must have been present in the early Solar
System, of which many meteorites are thought to be relics.
Topic: Early November Astronomy Bulletin (Read 965 times)