Two drawings of Sunspot activity
By Vaughan Cooper
2001 March 30th, 14.10 UT 2001 September 8th, 14.00 UT
Rotation No. 1974 Rotation No. 1980
P -26.08 Bo -6.62 Lo 130.36 P +22.7 Bo +7.2 Lo 148.5
Active Areas Spots Active Areas Spots
N. 4 33 N. 2 7
S. 2 18 S. 3 38
Total 6 51 R=111 Total 5 45 R=95
Both with a 147mm Reflector. Ant III
by Ivor Clarke, Editor
From all over the universe, bubbles of energy are expanding away from
their source and are heading our way. Some will have passed us by
years ago, but there are a lot still coming. These bubbles are invisible
until you stand at their expanding boundary and look back to the way they
came. Then you can see them if there are enough photons left.
There are most properly millions upon millions of bubbles in the universe
heading our way, rushing away from the star that formed them at the speed
Now and then a few photons will hit a mirror and be focused onto a
detector. Then they will give up some of their secrets to the scientists
examining the way the colours of light and the dark bands hidden within
it reveal the formation of different elements millions of light years away
and millions of years ago. Without this information we would not
understand the universe as well as we do today.
Many amateurs help in the task of spotting the žrst sign of another
bubble of light reaching us from a distance galaxy. It always amazes
me how much can be read from a few photons which can be up to 90% of the
age of the universe. They have travelled on edge of their bubble
across the universe. How many times has the information they preserve
in their wave bands been detected and read by alien senses before the bubble
as swept on out of reach?
The Europan Single Current Sea
by Mike Frost
(Newcomers to these stories should be aware that I try to stick to known
Veterans will know that I don‘t always succeed.)
I was sat in the pub, of course, with my old friend Clive, stalwart
of the Interplanetary Dangerous Sports Club. I always look forward
to hearing of Clive‘s latest exploits, but sometimes he can be very frustrating.
Like when you‘re trying to tell him your own stories.
"So there we were at Victoria Falls," I was trying to tell him, "watching
the bungee jumpers"
Clive stifled a yawn. "Fascinating. . . Is it your round yet,
I was annoyed. At times, I could spend hours helping Clive hone
his tall stories — he should at least indulge me when I wanted to tell
him about my own adventures. Sulkily, I gave up and asked him where
he‘d got to lately.
Clive brightened up. "Europa!"
I was really annoyed. Clive didn‘t want to know about my trips
to the back of beyond, but was quite happy to bore me with journeys into
his own back yard. "Which bit of Europe? Majorca? Moldova?
Clive tutted. "Not Europe, Frosty. Europa; moon of Jupiter."
"Ooohhhhh. . . Hang on a second! Isn‘t that moon in quarantine?"
"Exactly!" said Clive, "So there are people around who are quite prepared
to pay very good money for a guided tour."
Well, I wouldn‘t have called it tourism. More like people trafficking,
if you asked me. But there was no doubt that Clive had stumbled on
a lucrative venture. There were any number of bored millionaires
with more money than sense and a burning desire to visit the more obscure
bits of the solar system.
But, Europa! It was one of the few places in the Solar
System that was thought to have any possibility of harbouring life.
Mars, another likely candidate, was only expected to yield fossils; but
Europa was known to have an ocean of liquid water, which, for all we knew,
was teeming with life.
For that reason, whilst scientists figured out the best way to construct
a completely sterile probe, Europa was strictly off-limits to exploration.
I suspected that this would make visiting the moon appealing to a certain
category of irresponsible fool. Two categories, in-fact. Multi-millionaires
seeking to go somewhere nobody else had ever been.
"So who was your client?" I enquired. Clive shook his head.
"Confidential, I‘m afraid. Details on a need-to-know basis, and
you don't need to know. Let‘s call him Dennis. He was something
big in the city, venture capitalist I think. Made his money on the
Internet start-ups and knew when to cash his share options."
Clive was sounding suspiciously well-informed financially. It
soon became clear why.
* * * * *
"Dennis and I (explained Clive) set off from Earth as inconspicuously
as possible. I‘d filed flight plans to the Moon, but as soon as we
were clear of low Earth orbit, I turned on the ion drive and reset course
Because of the clandestine nature of our journey, I'd have preferred
to stay radio silent. But for Dennis, this was completely out of
He spent the first week continuously on his mobile phone.
'Nigel!! Hi! Yeah, I‘m on the spaceship! How‘s the Citibank
deal going?? Great! Great! Take them for another five million!
OK, gotta ring off — we‘re just coming to the asteroid belt.'
It was quite exciting at first, Frosty, to be in the presence of so
much cashflow, but he never stopped! And when we did get out of radio
range, he turned on to me.
I guess it was just to have someone to talk to, but he only had one
topic of conversation — finance! I‘ll tell you, there wasn‘t much
I didn‘t know about OEIC‘s, ISA‘s and TESSA‘s by the time we got to Jupiter.
We had so little in common, you see. Even the things you‘d think
we‘d agree on — like booze. I was a beer man and he was into imported
lagers. And I could barely eat the things he‘d stocked in the galley
— in fact, I could hardly pronounce most of them!
But worst of all was his exercise regime. Frosty, I know you have to
keep yourself fit when you‘re in space, otherwise your muscles waste away.
But Dennis was a fanatic — when he wasn‘t on the phone, he‘d spend days
on end in our gym.
And you know the very worst thing of all. HE ONLY HAD ONE PAIR
OF SOCKS!! The whiff, Frosty, it was horrible — I can still smell
[I was beginning to understand Clive‘s situation. Two people
locked together in a spaceship can really get on each other‘s nerves. Especially
when one of them is Clive.]
Well eventually, Frosty, we reached the Jupiter system — and not a
moment too soon. We started from a wide Jupiter orbit, then swung
rapidly in to the inner Jovian system, the better to avoid spending time
in Jupiter‘s radiation field. So I parked us quickly into orbit round
Europa, and guided the spaceship gently down on to the surface of Europa,
on the side opposite from Jupiter.
Imagine, that, Frosty. We were the first people ever to land
on Europa! Mind you, the view wasn‘t exactly stunning — just
ridge after ridge of ice, without even Jupiter to look at.
The surface of Europa is made completely of ice sheets, between ten
and fifty kilometers thick. From long range observation, I had identified
a landing point where the ice crust was particularly thin. As soon
as we landed, we set up drilling equipment and began to bore our way through
the ice crust.
I say ”we" — in fact, I did most of the boring with the drill.
Dennis bored me with statistics.
'You know, Clive, you should really consider the emerging markets for
your ISA allowance. Mexico is up thirty percent this fiscal.' And
all whilst pedaling that darned exercise bike!! In those darned socks!!
[I was going to ask why, if Dennis was so wealthy, he needed to darn
his socks, but I decided not to interrupt Clive mid-rant]
After two days of drilling, the drill bit broke through into the sea
beneath the ice-crust. This, if anywhere, was where we would find
life on Europa. It took another two days to widen out the borehole
wide enough to fit our mini-submarine — two days in which I found more
about investment trusts than I ever wanted to know.
Finally, we were ready to make the historic first voyage into the oceans
of Europa. Of course, we had taken all the precautions to avoid contamination
— I‘d scrubbed the sub all over with Dettol, and even poured a bottle and
a half of Domestos over it.
As we descended towards the sea of Europa, Dennis finally seemed to
pick up some interest in the mission he‘d paid so much for.
'This will be just so cool to mention to the boys back at the racket
club. They won‘t sneer at me again, I‘ll tell you!'
At last — the moment when we emerged into the ocean. I switched
on the flash lights, expecting us to see . . . what?? Squid, sharks,
jellyfish . . . who could guess? What we actually saw was . . . nothing
at all. No fish, no plankton, no seaweed. Nothing at all.
Dennis was not very pleased.
'I‘ve paid a lot of money for this trip, Clive. I‘m expecting a better
return on my investment.'
As though it was my fault!
We spent a week sailing the pitch black deeps of Europa, Frosty, and
it was profoundly depressing. No life at all. Just a completely inert,
endless, motionless ocean of water.
We were about to give up, on the point of returning to the borehole,
when I spotted something. Not very exciting, I‘ll grant you,
but we were desparate for anything different. Our sensors detected
a very weak current in the ocean — the only movement in the entire sea
not generated by our submarine.
We sailed towards the current, which welled up from the lowest reaches
of the ocean, and descended into it. As we headed downwards, the
current grew stronger, and the water temperature began to rise.
For twelve hours, with mounting excitement, we followed the trail back
to its source. Eventually our sonar started to pick up echoes from
beneath us — the ocean floor, five hundred kilometers below the ice crust.
And finally, with my heart beating fast, we reached the source of the only
current in the Europan ocean.
There in front of us was a hydrothermal vent — a crack in the ocean
floor, spewing out boiling water. The vent had to stretch down
to the molten core of Europa, kept hot by the pummeling of Jupiter‘s tides.
You see, Frosty, this was our luckiest break. Conditions here
were perfect for the formation of life — the warmth rising from the molten
interior, the water of the ocean, and a huge variety of chemicals spewed
out onto the ocean floor.
If we were going to find life anywhere on Europa, it would surely be
here. I could hardly control my excitement as I jettisoned
our sensors to detect living organisms.
We watched the telemetry for minutes, then hours, with growing frustration.
Not a sign of life. Not a twitch. Dennis was not well pleased.
'Pretty poor show, Clive, pretty poor show. I shouldn‘t have
picked you to run this expedition, should I? I shouldn't have listened
to her advice.'
I froze. 'Whose advice shouldn't you have listened to??'
'Oh, thought you knew. Your old girlfriend Clarissa recommended
you. Well, not exactly recommended. She said there'd
never be a dull moment with you around. Didn't I mention her before?
Clarissa and I are an item now, you know.'"
* * * * *
I could now understand exactly why Clive had taken against Dennis.
For all his protestations, Clive still had a thing for his old girlfriend.
I thought I‘d do well to change the subject.
"This is fascinating, Clive! It bears out Fred Hoyle‘s theories."
"Fred who? What theories?"
"Sir Fred Hoyle — famous astronomer. Very controversial.
He claimed that life didn‘t arise on Earth at all. It was his opinion
that life arrived in comets."
"Exactly. He thought that comets, along much of the rest of the
interstellar medium, were made up of organic material — microbes, amino
acids and so on — just sitting there in a state of suspended animation. In the early days of the Earth‘s formation, we were bombarded by millions
of comets, which provided the water for our oceans. Eventually, some
of the organic material would find its way down to the Earth‘s hydrothermal
vents - where it would thrive."
"Well maybe", said Clive, "but what has it got to do with Europa?
Comets might hit the surface of Europa, but they would never make it through
the ice crust."
”Exactly!! Europa probably formed without any hydrothermal vents.
An ocean of cometary water formed and froze over, without ever having the
chance to nurture any microbes. All the bugs in the ocean died off
billions of years ago. But much, much, later the tides of Jupiter
started to open up hot vents to the molten core. Too late to be seeded
by any organisms from outer space."
Clive nodded sagely. ”I‘d never heard about Sir Fred‘s theories,
but I had come to my own conclusion that the vents were perfect for nurturing
life — if only they had some living organisms to start with. And
a thought occurred to me."
I felt a chill go down my spine. "Oh, Clive. . ."
"I figured that here was a chance for immortality. Any bugs,
any microbes, in fact, any organic material at all — would thrive in the
hydrothermal vents on Europa. I could personally kick-start the whole
story of life on the moon. . ."
"But Clive," I said, horrified, "Yes, you could do it — but you‘d be
found out. By the time we come to explore Europa properly,
any DNA you leave behind will still be there, and still recognizable
as Earth-based. And from the DNA, scientists will be able to trace
precisely who vandalized the vents. You will be found out — shamed
"Exactly." said Clive. "So I dropped Dennis's socks down the vent."
Near Earth Objects
An edited report from off the Web by
The government a short time ago, asked a panel of experts for their
thoughts on the possibility of a collision between Earth and other Earth
orbit crossing bodies. This is an edited version of the text of the
report recommending that the UK help to fund a program of research into
the subject to access the problem and to žnd a solution.
Since its formation four and a half billion years ago, the Earth has
been under a constant barrage of objects from space. These objects
come in a very wide range, from dust to moons, with greatly different rates
of arrival. On average, hundreds of tonnes of dust enter the upper
atmosphere every day; every year objects of a few meters diameter enter,
some having effects on the ground. Every century or so there are
bigger impacts. For a long time there was an unwillingness to recognise
that the Earth was bombarded, but increasing knowledge of the meteoritic
flux over the last half century has shown otherwise.
Our understanding of the threat from NEO‘s, asteroids, long and short
period comets, is relatively new. Recently a government task force
examined the nature of the asteroids and comets that circulate within the
Solar System and looked at the facilities required to identify the orbits
and compositions of those objects coming close and how a world-wide effort
might be best organised and co-ordinated.
Asteroids and comets are remnants of the formation of the Solar System
about 4.5 billion years ago and range in size from pebbles or lumps of
ice, to rocky or icy worlds nearly 1,000 kilometres across. An asteroid
or comet will become a NEO if its trajectory intersects the orbit of the
Earth or is within 0.3 Astronomical Units. An object is said to be
potentially hazardous when it‘s 150 metres in diameter and its orbit comes
even closer, to within 0.05 AU (7.5 million kilometres, or about 20 times
the Earth to Moon distance). So far, 258 potentially hazardous objects
have been discovered.
Asteroids are made up of carbonaceous (carbon containing) materials,
rocks (silicates) or metal. They may comprise of piles of boulders
held together only by their own very weak gravitational forces, or be solid
lumps of stone or slabs of iron. They are not spherical bodies until
they are more than 100 miles in diameter owing to their weak gravity being
unable to pull the rocks, ice, dust and other materials into a ball and
may spin or tumble as they orbit the sun. There are many subcategories
of asteroids: each behaves differently when entering the Earth‘s atmosphere
and in its reaction to countermeasures.
Comets are essentially dirty snow-balls and include many particles
of dust. It is only when a comet comes near the Sun that these gases
evaporate, freeing the dust that forms the tail sometimes seen by the naked
Rough estimates of the numbers of Near Earth Objects of different sizes
can be made either by direct measurement using ground-based telescopes
or inferred from the numbers and sizes of craters on the Moon or the planet
Mercury. The atmosphere protects the surface of the Earth from most
small NEO‘s, which burn up or explode at high altitudes. Whether
they survive to impact the surface depends on a number of factors: their
size, composition, velocity and angle of approach.
The main effects of impacts are blast waves equivalent in some cases
to many megatons of energy, tsunamis (or ocean waves), along with the injection
of large amounts of material into the atmosphere, and electromagnetic changes
near the surface. As some two thirds of the Earth‘s surface is covered
by the sea, the chances of an ocean impact are greater than on land.
From measurements taken over recent years the orbits of over 400 NEO‘s
with a diameter above 1 kilometre (about half the estimated number) are
known. This allows us to hope with some confidence that no object
has been identified that is likely to hit the Earth over the next 50 years.
Smaller objects, which can also cause great destruction locally or regionally,
are known about even less.
Impacts from NEO‘s with diameters over 10 kilometres would have global
consequences, possibly resulting in the extinction of most living organisms,
ie, us. Such events are fortunately very rare. Impacts of objects
with diameters from a few kilometres in diameter to 10 kilometres are also
rare , possible only one per million years.
Objects with diameters around 1 kilometre are the most dangerous because
they are much more frequent and can give many more casualties per impact
than smaller ones. Impacts of smaller objects, with diameters of
a few hundred metres, would have dramatic local consequences, but are unlikely
to affect the Earth as a whole. For objects below about 50 metres
in size, the Earth‘s atmosphere usually provides adequate protection with
objects exploding at high altitude doing little harm.
By discovering and tracking the most dangerous of these objects, and
by studying further the consequences of impacts and the possibilities for
mitigation, it may soon be possible to exert some control over further
Most measurements can be made with ground-based telescopes and radars,
rather than with expensive space-based missions. While some dedicated
facilities are essential, much valuable work can be done by occasional
or serendipitous use of telescopes or spacecraft with different prime scientific
Because it is impossible to predict where new objects may come from,
the whole sky must be observe frequently and systematically. This
calls for specially designed wide-angled telescopes with advanced detector
arrays coupled to very fast computers. They need to operate automatically
and remotely, and be dedicated to the observations of NEO.
To determine the orbit of an object after its initial discovery, conventional
narrow-angle ground-based telescopes are needed in each hemisphere.
Because a newly discovered object rapidly becomes fainter as it moves away
from the Earth, follow-up observations must be made within days of discovery.
Uncertainties make it difficult to predict whether a particular asteroid
might cause a global or regional catastrophe. The use of ground-based
radar to determine the objects position, velocity, size, shape, gross structure
and spin when it is sufficiently near the Earth is possible, but not its
mass. For this, space rendezvous missions are needed. Relatively
inexpensive microsatellites could fulfil this purpose.
The United States is doing far more about NEO than the rest of the
world put together. The Minor Planet Centre is at the hub of observations
world-wide. In addition, military surveillance facilitates in space
and on the ground look continuously for objects and explosions in the upper
atmosphere. The only current activity in the Southern Hemisphere
is in Australia.
For the first time in the history of the Earth there are possibilities
for mitigating the effects of impacts by NEO and even, in the longer term,
for deflecting them entirely from collision with the Earth. But all
this depends on first improving our ability to detect such objects well
in advance and seeking to measure accurately their orbits and physical
Once an asteroid or comet on a collision course is identified and its
orbit tracked, its likely point and time of impact can generally be predicted.
Such accurate prediction is rarely possible for other natural hazards.
Wherever the impact, people could be moved to safety, given sufficient
warning and appropriate logistical support. However, extensive material
damage would nevertheless result.
An international effort to look into the practical possibilities of
deflection and a number of possible mechanisms have been considered for
deflecting or breaking up potentially hazardous NEO.
If ever there was an issue affecting the whole world, it is the threat
from Near Earth Objects. To understand and try to cope with the threat
requires an international response. This response should cover not
only understanding the science, so that dangerous Near Earth Objects may
be predicted and methods of mitigation assessed; but, equally important,
how all aspects of this response should be organised.
The new organisation must cover the identification and coordination
of the science, communication with the public and work on measures to react
to a possible impact, or to deflect or destroy an incoming object.
At the present time no international institution exists for this purpose.
Spaceguard is a collective term for a variety of activities which have
grown up in a number of countries over recent years and which have done
much to alert public opinion. But none has official recognition except
for the US Spaceguard Survey (the name given to the NASA survey), and so
far there are no specific coordinating mechanisms in any state or government,
not even in the United States.
The need for an international approach is essential and at the heart
of proposals for action to confirm the nature of the hazard and potential
levels of risk. The more we studied the subject the more we can see
how very little is currently known about Near Earth Objects, despite the
efforts of many scientists. We do not know accurately how many objects
of about 1 kilometre diameter there are; and their energies and compositions
are very uncertain.
We know very little indeed about smaller objects. Without this
knowledge we have only the roughest idea of the magnitude of the risk.
The science involved is wide-ranging, involving astronomy but also geophysics,
oceanography, climatology, biology and the social sciences.
The government Task Force has concluded that the overall needs, worldwide,
are as follows:
* For survey and discovery:
At least one dedicated 3 metre-class telescope in the southern hemisphere
and one in the northern; the survey of smaller Near Earth Objects;
the use of data from surveys being made for other purposes; the use
of sky survey archives; the use of space telescope missions where
* For accurate orbit determination:
One large telescope in each hemisphere, preferably dedicated; some
time by right on various existing instruments;
* For composition and gross properties:
Access to large telescopes and space rendezvous missions;
* For academic studies:
In particular of Near Earth Objects interactions with the atmosphere,
oceans, solid earth, climate and living things, including historical evidence;
the effects on people and society.
What fair contribution should Britain make to fulfilling these needs?
Taking into account existing telescopes or those under construction
in which the United Kingdom is a partner; the skills of British scientists
and engineers, industry; and that partnership with Europe in this
task is desirable.
To make a substantial contribution to the need both for surveys in
the southern hemisphere and for systematically discovering smaller Near
Earth Objects, a proposal to construct an advanced new 3 metre-class telescope
on an excellent site seems sensible. It may possible to refurbish
older existing telescopes for the systematic survey and discovery of these
objects, but it may generally be rejected because adapting such equipment
would be expensive and the resulting telescopes may not be competitive
for very long. Only a new dedicated telescope would make a satisfactory
contribution to the world effort. Because such a facility would be
expensive, this project should be shared with other countries, preferably
within Europe. The recommendations include that arrangements be made
for observational data obtained for other purposes by wide-field facilities,
such as the new British VISTA telescope, to be searched for Near Earth
Objects on a nightly basis.
No current space telescope is dedicated to the discovery of Near Earth
Objects. However, a number of existing and planned missions are,
and will be, able to detect objects incidentally when making observations
for quite different purposes. So it is strongly suggested that consideration
be given by space agencies to consider the use of space missions for incidental
observations of Near Earth Objects.
Apart from existing telescopes, the European Space Agency‘s proposed
GAIA mission and NASA‘s SIRTF mission could play a part in surveying the
sky for NEO‘s is one of the recommended projects. The potential in
GAIA and SIRTF for Near Earth Object research should and must be considered
as a factor in defining the missions and in scheduling their completion.
A particularly urgent requirement is for observations to determine
the orbits of NEO‘s discovered by United States telescopes but subsequently
lost. This needs one or more professionally run telescopes about
one metre that could immediately fulfil this need.
Space rendezvous missions to asteroids or comets give a unique insight
into the characteristics of the asteroid or comet being visited.
A systematic assessment of different types needs many missions, perhaps
as many as 20 to enable each type subsequently to be recognised by ground-based
techniques, of great importance should countermeasures be needed.
For this limited purpose it might be possible to use a series of essentially
identical micro satellites, each launched economically piggy-back with
other spacecraft; in this way the unit cost should be much below that of
current rendezvous missions. The United Kingdom is a leader in micro
satellite technology and a beginning could be made with a single demonstration
The Very Large Telescope - What We Hope to See
by Paritosh Maulik
In the last article we have seen the construction of the European Southern
Observatory Very Large Telescope Interfometer (VL TI), at Paranal,
Chile. In this article we shall discuss the objects astronomers are
interested in studying, and next time the various instruments employed
at the facility and briefly discuss the next generation of large telescope.
The Very Large Telescope Interferometric (VLTI) array, consisting of
8m Unit Telescopes (UTS) only, is referred as VL TI Main Array (VIMA).
The interferometer consisting of 1.8 m Auxiliary Telescopes (ATs) is called
VL TI Sub-Array (VISA).
UTI and UT2 have been in operation from early 2000. AT1 and AT2
are expected to be on line by early 2002. Then subjected to the availability
of funds all 4 UTs and 3 ATS may begin work in 2003.
WHAT WE HOPE TO SEE
The presence several extra-solar planets have now been confirmed and
this has led to an impetus toward detecting more. There are two basic
1) Precise Radial Velocity: the motion of the star around barycentre
of the star — planet system is measured. This method can not determine
the planetary mass and the inclination of the orbit.
2) Astrometric survey: the planets are viewed pole-on, and from
this method it is possible to calculate the planetary mass directly.
To get an idea about the time scale involved in such a project, about
200 target stars will be examined in near infrared with VISA; integration
time about 30 minute per star and 30 observations per night for 10 years.
This corresponds to 300 nights over a period of 10 years. Proper
and parallax motion will be studied and this will account for the presence
of planets, if any.
Low Mass Star and Brown Dwarfs
Although about 90% of the stars in our galaxy are of mass lower than
the sun, our knowledge on these objects is somewhat lacking, One
of the aims of the VLT will be to establish the observational mass — luminosity
relationship, especially at the lower mass end.
Until now these have been studied by the broad band photometry method.
This gives an idea about atmosphere of the stars, but the process going
on inside the star are primarily determined by its age and mass.
High precision parallax data from Hipparcos and spectroscopy from VISA
will yield information on small 0.03% solar mass brown dwarfs.
Young Stellar Objects
These objects often show phenomenon like infrared excess, variation
in luminosity and highly collimated jets with velocities of the order of
several hundred km/sec. These phenomena indicate the presence of
an accretion process and strong magnetic fields. Although the VLT
would not be able to resolve the innermost part of an accretion disc, the
high angular resolution, sensitivity and the infrared response will permit
the study the morphology of the disc. Also disc temperature distribution,
relative contribution from the scattered stellar light and thermal disc
emission, composition and the properties of the dust grains.
Stellar Surface Structures
On the outer surface of stars localised convection cells, convection
zones and magnetic fields are present. These are due to hydro-dynamic
and electro-hydrodynamic effects. These convection zones can be studied
by observing surface temperature and line of sight velocity measurements.
These time dependent variations of active areas will give an indication
about the processes of the generation of the magnetic fields. In
the disc of the star Betelgeuse some unresolved features have been detected.
These are likely to be the hot spots of emission caused by material rising
to the surface from the hotter interior. VL TI will be able to provide
us with a clearer picture. The selected sources will be surveyed
in detailed, say every month and also to include their local neighbourhood.
Theses stars show H-emission lines, but the emission pattern is variable
and complex. These are rapidly rotating (around 250 - 400 km/sec)
stars with a equatorial disc or ring and it is believed that the emission
is from the disc. The current model assumes that radiation pressure
carries the material from the rapidly rotating star to form the disc.
However there appears to be some discrepancies between the observations
and the model. The excellent resolving power of the VLTI will be
able to give a clearer image of the point like source and the emitting
Asymptotic Giant Branch (AGB)
These stars are in there giant phase, the helium is exhausted and it
is burning in the shell. These stars show a large convective atmosphere
from which material escapes at a rate of 108 to 104 solar mass per year
and this atmospheres appears to expand at a rate of 5 - 30km/sec. It
is accepted that there is a slowing down of the pulsation and formation
of the dust; and radiation pressure ejects the dust. The mass loss
controls the future of the AGB, this dust in the form of chemicals is added
to the interstellar dust and finally to the galaxy.
The process of dust formation and the chemical composition of the dust
and that of the star is not very well understood. High resolving
power and the mid-infrared range capability of the VLTI will be utilised
for this study.
The Galactic Centre
The central region of the Milky Way galaxy, 0.1 pc, will be examined
in the infrared range of 2 to 10 micron wavelength. The presence
of the central massive black hole will be carried out by measuring the
three-dimensional velocity field of the star cluster centred on IRS16.
It was originally detected as a strong infrared source. But later
lunar occultation studies showed that there are over 24 starts emitting
in the 2 micron region. Detailed analysis suggests perhaps these
are blue supergiant stars and emitting in short wavelengths, ultraviolet
and visible ranges. The surrounding dust cloud absorbs the radiation
and re-emits it in the infra-red region. If this is the case, then
these stars are young and have formed only 10 million years ago.
All these point to the fact that star formation is going on at the centre
of the our galaxy.
Sagittarius A* (Sgr A*), the first radio source to be identified by
Carl Jansky, is believed to be at the centre of the Milky Way galaxy.
Radio studies suggest that Srg A*, is in a Keplarian orbit, at a velocity
in excess of 1,000 k/sec, about a central massive object of 2.7x106 solar
mass. It has also been suggested that black holes of 10 solar masses
collapsed to form an enormous black hole at the galactic centre.
As the gasses spiral into the black hole it forms accretion discs and some
lost energy is sent out as radio beams. Molecular clouds also surrounds
the Srg A*. The VLT is expected to give a clearer picture of this
Active Galactic Nuclei (AGNs)
At the centre of the galaxy there appears to be a black hole of about
108 solar mass, accreting gasses. This object shows both continius
and emission lines and also in addition, infrared, radio, or x-ray sources
may be present. These features are more common in the redshift of
z - 2 i.e. about 0.8 - 0.9 times of the age of the universe. Although
we are certain that the accretion process is powering the system, the details
are not clear. For example, ultraluminus star bursts, radio sources
that are prominent in the elliptical galaxies but not in the spiral galaxies.
Seyfart galaxies behave similar to quasars, but on a much reduced scale.
Next time we will look at the telescopes various instruments employed
at the facility and briefly discuss the next generation of large telesccopes.