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Astronomical Society of Edinburgh

Journal

No. 50 - July 2006


Fettes College sundial
Multi-faced sundial at Fettes College.

Presidential news

In the last edition of the Journal which was published I referred to the 'Future of the City Observatory'. The Society did review its options at our Annual General Meeting in March 2006. The consensus was that we wished to continue to be associated with the historic Calton Hill Observatory if at all possible. Our main concern was that the Playfair building was in need of repair.

At a meeting with City Council officials in May we were informed that work will start this year on the Astronomer's House. The Council have identified £ 70k for roof repairs in this financial year. This is a start in the long overdue refurbishment. Much remains to be done.

I hope we can implement our plan to have Astronomy evening classes at the Calton Hill Observatory starting in October. Such classes have been successful over many years in Stirling and Dundee. There is no reason why they should not be equally successful in a population centre the size of Edinburgh. There are lectures run by the Royal Observatory on Blackford Hill. These should not be seen as competition. Our courses will be more central and accessible. In any case there is room for two courses in Edinburgh.

It is envisaged that there will be a course in the autumn and in the spring. Each course will consist of six to eight sessions on a suitable weekday evening. Following the Dundee model a course will be an introduction to the night sky and the solar system. Each session will last a maximum of two hours and will, if the weather is not suitable, consist of an illustrated talk and a question and answer debate. If the sky is clear the indoor session will be shortened to allow for observing.

It is hoped that each session will have a Society member as a lead presenter supported by another member who may specialist knowledge of that night's subject (and/or observing experience).

The details of the course have yet to be worked out. However, the title of the first one may be 'The Solar System'. The talks could be:

1. The Sun2. The Moon
3. The inner planets4. Mars
5. The outer planets6. Meteors
7. Comets8. The Kuiper Belt

There would have to be a charge for the course. That has to be worked out.

I hope that the courses can be organised and are successful. We will be carrying out essential educational work bring astronomy to the public and young people. In time it should boost the Society and recruit new members.

I would welcome the participation of members in the course development and in the delivery of the sessions.

Des Loughney, June 2006

Other news:

Congratulations to our Secretary, Graham Rule, who has received his BSc from the Open University.

Dave Gavine has been appointed Director of the BAA Aurora Section, succeeding Ron Livesey who held the post for 23 years. Ron remains as Assistant Director.

The Scottish Astronomy Weekend will be held in the Cowane Centre, Stirling, on October 13-15 2006. Like last year's Weekend it will be non-residential, i.e. delegates will require to make their own arrangements for accommodation and meals, for which lists will be provided. The main speaker will be Bob Marriott. For bookings and information please contact:
Dr Alex Houston, 41 Keirfold Ave, Tullibody, Clackmannanshire, FK10 3BE < alex.houston @ tinyonline.co.uk >


The March 29 eclipse from Libya

The solar eclipse of 2006 March 29 was total along a band that stretched from the NE coast of Brazil, across N Africa to Turkey and onwards through Asia to end in N Mongolia. Anyone viewing the event from Britain experienced only a shallow partial eclipse, with only the southern 20 % of the Sun's diameter hidden by the Moon at mid eclipse as seen from Edinburgh.

Like many in the UK, my first experience of a total solar eclipse came with the one on 1999 August 11. Unlike many in the UK, though, I chose not to risk the uncertain, and ultimately largely leaden, skies of Cornwall. Instead, I noticed that Edinburgh had a direct air link to Varna in Bulgaria, close to the centre line of the eclipse where it crossed the Black Sea and where the weather prospects were rather better. A holiday was duly arranged at the resort of Albena, and my wife Gillian and I, with our two (then) teenage offspring, enjoyed a superb view of totality with the Sun high in a cloudless sky.

I had never thought of myself as being afflicted by an eclipse-chasing bug, but something of the sort must have struck about then. The same seems to have happened to my good friend, Russell Eberst, a colleague at the Royal Observatory and a fellow satellite-enthusiast. Russell, together with his wife Margaret, had been frustrated by the Cornish experience, so we resolved to take a more active interest in forthcoming eclipses. That is how we found ourselves, with Gillian and Margaret, in an Orkney field in the early hours of 2003 May 11 in the hope of catching the annular solar eclipse at dawn. Sadly, all we saw was cloud, though the piper, the band and the bar helped the event go with a swing.

The Pickups and Ebersts share rather more than this interest in eclipses. Coincidentally, we have the same wedding anniversary and, remarkably, both Gillian and Margaret have the same birthday. The fact that this is March 29, the date of this year's eclipse, reinforced our determination to make the most of it, but this didn't stop Russell and Margaret tripping off to Madrid to catch the annular eclipse last October 3.

The March 29 eclipse was attractive for other reasons. For one thing, it had the longest duration of totality of any total eclipse between 2001 June 21 and 2009 July 22. In addition, land based observing sites with good prospects of clear weather were quite easily accessible from Europe. Our Google map of its track plots the point of longest eclipse, 4 minutes 7 seconds, just as the Moon's shadow enters Libya from Chad. By the time the umbra reaches the coast of Turkey observers could still expect a respectable 3 minutes and 45 seconds of totality.

Turkey, in fact, was probably the most popular destination for eclipse-chasers. Although the weather prospects were more uncertain than locations south of the N African coast, Turkey already had a thriving tourist industry, with many "eclipse packages" available and I expect that a number of ASE members took advantage. In the end, Turkey provided clear skies and a superb view of the spectacle. Horst Meyerdierks, for example, returned with several excellent photos of the event from his observing site on the southern Turkish coast and the BBC's Sky at Night cameras could not have been far away.

eclipse track
The track of the March 29 eclipse.

The Pickup-Eberst quartet, though, pushed the boat out, almost literally. We booked a cruise through Explorers (http://www.explorers.co.uk) that included a stopover in Benghazi with a journey inland to a chosen observation site in the Libyan Desert south of the Jalu Oasis. The cruise aboard the MV Perla also took in the ancient Minoan site of Knossos in Crete, linked to the myths of the Labyrinth and the Minotaur, as well as the Greek ruins of Cyrene E of Benghazi and the World Heritage site of Leptis Magna, the well-preserved Roman city near Tripoli. We also called at Santorini and, finally, Athens.

It became clear after we docked at Benghazi that the Libyan authorities were a little unaccustomed to, and uncomfortable with, the prospect of 700-plus foreigners trooping off the view Cyrene on March 28, the day before the eclipse. A trip that might have taken only a couple of hours each way, took twice as long, largely because our buses were required to travel in convoy, and to be escorted within the city limits of Benghazi. Also, if any bus needed a refuelling stop, then the whole convoy ground to a halt. The lessons learned on that day caused a rethink of our schedule for Eclipse Day, with our departure for the observing location brought forward by several hours.

As it was, the journey of some 500 km S from Benghazi took nine hours, which felt even longer for most of us since few of our 20 (or so) buses had working toilets. In various states of discomfort, then, we made it to our eclipse vantage point with only minutes to spare before first contact, the moment when the Moon's disk began to nibble away at the Sun's edge. Fortunately, we had been within the total eclipse track for the final few hours of our journey as we encountered more and more traffic along the well-made, and normally very quiet, roads into that part of the Sahara. The scenery was of flat sandy desert, with occasional distant views of the smoke and flaring stacks of the Libyan oil industry for which, probably, the roads were constructed in the first place. Increasingly, though, the desert was peppered with the vehicles, tents, vans and telescopes of eclipse watchers from all parts of the world. The only camels we saw were sitting smugly in the back of a passing truck.

In fact the place where we piled out of our buses fell a couple of kilometres short of our target destination, an encampment that the Libyans had built for the day and dubbed Eclipse City. Here were food, drink and toilets, but also more activity and wind-blown dust to the extent that we were probably better off where we were. We did call there after the eclipse, collecting, among other things, our free eclipse T-shirts.

For the anoraks among you, our actual observing site (plotted on our Google map) was at latitude 28 degrees 14.6 minutes N, longitude 21 degrees 31.0 minutes E, which placed us just 1.93 km S of the central line of the eclipse. There we enjoyed (to put it mildly!) 4 minutes 3 seconds of totality between 10:26:38 and 10:30:41 UTC, with the Sun 65 degrees high against a cloudless sky.

Our chosen observing equipment was limited to binoculars and our naked eyes. We are not astrophotographers, and suspected that anything we could produce would be outshone many times over by others around us. Also, my experience in Bulgaria suggested that there was more than enough to see and absorb without worrying about forgetting to remove the camera lens cap or, as in one sad report we heard after we returned to the ship, experiencing a camera memory card declaring "I'm full" just as totality got underway.

awaiting totality
The author awaiting totality.

I did ensure, though, that I had a pair of tripod-mounted binoculars, with a shade and screen to allow a reasonably sized projection of the Sun's disk. This proved a popular choice for it allowed many more people to follow and view the progress of the eclipse than was possible using properly filtered (of course) cameras or spotting scopes. It was also quick to set up and the image scale was such that we were able to confirm first contact within seconds of the expected time.

We drew a steady stream of visitors to our little outpost, many of them enthusiastic and friendly Libyan nationals eager to record the progress of the eclipse using their mobile phone cameras and, no doubt, transmit the pictures to their less fortunate friends. Something we did notice was that, Libya being a Muslim country, from time to time during the partial phase there were several long rows of men in different parts of the desert all paying homage in the direction of Mecca, though it was also obvious that there was no universal agreement about what direction that should be.

For most of the 78 minutes between first contact and the beginning of totality at second contact, the gradual fading of the light could almost pass unnoticed, presumably because the eye is so good at adjusting to the changing level. It was interesting, though, to judge the visibility of the planet Venus which was shining at magnitude -4.3 in the SW and rather lower than the Sun at the time. Soon after first contact, Venus was just visible to the unaided eye, but took some finding. Fifteen minutes before totality, it was obvious to anyone who glanced in that direction. By then, too, the shadows had become much sharper than normal because the E-W extent of the visible Sun was down to only 6 arc minutes from its usual 30 arc minutes. It was also about this time that changes in the micro climate ahead of the Moon's shadow generated a few stronger gusts of wind along with a few passing clouds, the latter probably of dust. Otherwise, there was only a light wind flowing across the site from the SW.

As excitement built towards second contact, my attention was on the diminishing arc of projected sunlight on my screen. Suddenly, the cry of "shadow bands" echoed around the desert which became alive with dancing bands of light and shade. To my eyes, they appeared as a multitude of fleeting torpedo-shaped ovals, a metre or two long in a N-S direction and tending to drift slowly to the NW, in the same direction and at about the same speed as the wind. The explanation appears to be that cells of different density in the atmosphere acted like lenses to refract the final slender rays of sunlight so that they sometimes augment, and sometimes detract from, the flux of light reaching any point on the ground. As the cells drift in the wind, so do the shadow bands. The mechanism is probably very similar to that which causes stars to twinkle at night.

I suspect that the shadow band phenomenon lasted for 30 seconds or more, though I missed its beginning and soon turned my attention back to my projection as mountains on the Moon's limb broke up the final sliver of the Sun's photosphere into a chain of points, the phenomenon of Bailey's Beads. As these disappeared, totality began, cheers rang out from all around, and it was time to turn a second pair of binoculars sunwards. The corona was immediately obvious, reaching out in streamers to E and W of the disk. With the Sun now approaching the minimum in its 11-years solar cycle, this was much as expected, signalling that the Sun's overall magnetic field is now less disturbed than that near solar maximum. Also obvious at first glance was a crimson prominence near the 10 o'clock position which (probably no coincidence) seemed to sit at the base of the longest coronal streamer. Spikes radiated outwards from the Sun's polar regions, reminding me of iron filings near a magnet in those long-ago physics experiments at school.

To the naked eye, the spectacle was awe-inspiring. The corona seemed to extend for several times the Sun/Moon's diameter, further than in most photographs I have seen, with the Moon's disk appearing as a stunning jet-black gem at its heart. The sky all around was dark like a deep twilight, but the lower few degrees in all directions was a much brighter red-to-yellow hue as we looked beyond the umbral shadow. After my experience in Bulgaria, I was not surprised that no stars were obvious in the eclipse sky. Venus was unmistakable, though, and I could make out Mercury (magnitude 0.9) with my naked eyes about halfway between Venus and the Sun. Forming an equilateral triangle with Mercury and Venus was Fomalhaut at magnitude 1.2, but this I failed to see. Russell saw both Mercury and Fomalhaut, but only through binoculars.

diamond ring and corona
Left: Third contact and the terminal diamond ring imaged by Dr Peter Morgan, a fellow eclipse chaser from Bradford.
Right: The corona. A montage of images with exposure times ranging from 1/1000 to 1/4 second, each unsharp masked. By ASE's own Horst Meyerdierks.

As the eclipse progressed and the Moon's disk drifted E in front of the Sun, the 10 o'clock prominence was obscured and several lesser prominences became visible above the Sun's W limb, each at the base of another coronal streamer. All too soon third contact was upon us as direct sunlight flashed into view through a couple of valleys, the double diamond ring effect soon giving way to a single dazzling diamond that drew gasps and more cheers. Over the following seconds, the corona faded and I tried (but failed miserably) to grab a decent photograph of the Moon's shadow as it raced away to the NE. Euphoria got the better of common sense in another way, and I neglected to check again for those shadow bands for which I, for one, will always remember this eclipse.

I have to admit, that we did not linger on the sand until fourth contact, but rather packed up and embarked on a (successful) hunt for a bus for our return trip, one with a functioning toilet! The talk on our long journey back to our ship in Benghazi, and for days afterwards, was of the experience we'd shared and the prospects of doing it all again at the next favourable eclipse, perhaps in the Gobi Desert in China in 2008. Oh, and Gillian and Margaret had a really happy birthday.

Incidentally, there were several enthusiasts from the BAA, the British Astronomical Association, among our shipmates, and the BAA is planning to produce a DVD with images and movies taken during the eclipse. Details at http://britastro.org/baa/content/view/82/2/.

Alan Pickup


Let there be rock - The story of the Hambleton meteorite

a rock in the hand ...
A rock in the hand is worth 10 in the field. Photo Rob Elliott.

The discovery of a new meteorite in the U.K. is big news. But when the new find is a Pallasite, then you need to re-calibrate your Big News Detector! To find a meteorite, even an ordinary chondrite is very rare, but to find one of the rarest types of meteorites (only 1 % of all falls are pallasites) then this is cause for excitement. The meteorite in question is the first of its kind to be discovered in the British Isles.

Rob Elliott of Fernlea Meteorites lives in Fife, Scotland. He has found several small meteorites, notably the small several gram stone Glenrothes while out fishing. However, he has always kept his eyes to the ground when rambling the countryside. This was to prove extremely fortunate last year when out with his wife Irene on the Yorkshire moors on a meteorite hunt. This area of moorland is an undeveloped piece of countryside and ideal for meteorite hunting as the land has remained unturned for a long period of time. A large rock weighing 17.6 kg was found and the magnet Rob always carries was attracted to this curious rock. It was thought to be a possible suspect in the search for extra terrestrial interlopers. It was duly hauled out of the muddy undergrowth and taken home where it ... sat outside for three months in the glorious Scottish wind, rain and sleet! Now, you and I as meteorite enthusiasts would probably balk at this location, but hear me out. It was thought to possibly be a meteorite due to the magnetism, but in reality it was more likely to be some iron slag. After all it had a thick and extremely friable rust covering and a strange sulphurous smell. So it wasn't going to be house guest just yet.

The nearest town to where this rock was found is the small village of Kilburn in North Yorkshire near the Hambleton Hills. The outline of the White Horse of Kilburn is a well-known landmark on the hillside. Narrow country lanes criss-cross the pasture land, many of which are shown as farm tracks. Strangely enough, they are shown up on satellite navigation systems as passable to all traffic and yet only safely negotiable by four-wheel drive vehicles. It was along such a track that the Elliotts drove, parked the Land Rover and went hunting for meteorites. This was in summertime with a lot of greenery. This can be an obstacle, as meteorites can be obscured by undergrowth for a large part of the year. Yet luck was on their side as the rock was found by a wall and relatively easy to retrieve.

After a couple of months Rob hacked off a sample which was sent to Dr. Monica Grady, now at The Open University. She is at the time of writing involved in the analysis of the Stardust samples supplied by NASA from the sample return mission to Comet Wild 2. Dr. Diane Johnson of the Planetary and Space Sciences Research Institute was asked by Monica to communicate directly with Rob as she was doing the SEM mineral analysis. It turns out that the meteorite is a main group pallasite with a really beautiful small scale Widmanstatten structure that is clearly visible in the SEM scan emailed to Rob.

The first I heard of this meteorite was from Rob in August or September 2005 when he mentioned by email that he might have found something of interest. The next I heard was when my wife Pamela was given a newspaper cutting from The Daily Record from January 14th 2006. I emailed Rob straight away and I was invited over to see him, Irene and the new find in January 2006. After the short drive from my home town of Edinburgh to the Elliott's I was ushered into their living room. We had a cup of tea and then the baby was brought out for me to coo and gurgle over.

I was instantly mesmerised. If Rob had brought in John Lennon's Rickenbacker and an autographed copy of Revolver I couldn't have been more in awe! I have seen many a polished slice of a pallasite but this was how it had lain untouched for decades even centuries. I was quite surprised at the weight of this rock, which was the only hint other than the small off cut, that this could be a rock of great value. It was found near the village of Kilburn in Yorkshire and was probably lifted from its original fall site by a farmer then ditched over a wall. This is pure speculation, and it is a wild guess that the grooved furrow on one side could have been caused by a plough.

The picture below shows Hambleton almost as it was found (bar the small piece cut off for analysis). Note the furrow along the top.

Hambleton, groove on top
Hambleton showing groove on top and cut end. Photo Angus Self.

Diane Johnson emailed Rob with some interesting details about the meteorite. Apparently it is from the main group of pallasites as found by the oxygen isotope data in the olivine. Two small blocks had been cut from the sample and were polished. They both show Fe-Ni metal and olivine. One other issue of interest is the discovery of iron sulphide and phosphorous. Although Diane suspects the phosphorous may be due to the weathering of the metal. Perhaps this was the cause of the unpleasant smell! As I write, the Meteoritical Society is still to publish this find in its bulletin but there is hope that by March 2006 it will be posted.

scanning electron microscope image
Scanning electron microscope image. Note scale on right. Image Open University.

Whilst chatting with Rob I found out there were one or two strange rumours about this meteorite. Somebody has been reporting that Rob witnessed it as it fell from the sky. Strange, as the weathering leads to believe it has lain unfound for 200 years or so. Exact terrestrial age is uncertain, but this is an approximation due to the thick rust coating.

There is also the possibility that it could be the result of a fireball seen in 1783 travelling from Scotland to London centred over the Yorkshire area of the Hambleton hills. I was given the following information by Eric Hutton who has an astronomy web site with a list of historic meteor sightings.

1783, France, England, Scotland Aug 18th
R. P. Greg in his catalogue 1860, gives the following entry...

A very celebrated and remarkable meteor. First seen in the Shetland Isles; like the planet Mars; 1/3 moon, from Mullingar to York; equal 2 full moons over Kent; appeared to burst into two straight over Lincolnshire, with a report 8' or 9' heard at Windsor afterwards; visible 20"; at once for an arc of 75 degrees; 60 miles high; 20 miles in a second; tail 10 > than body; turned a little to E. after partially bursting; left a streak and sparks; tail not much seen at first, perhaps foreshortened. In Ireland, seen moving parallel to horizon 10 degrees or 12 degrees high. Seen over Burgundy in France; altogether for a distance of 1200 miles. At Greenwich as a double bolide, very brilliant. Heard to explode also over York some minutes after.

Rob has been on local television in the Yorkshire area showing his find and several other meteorite hunters have been interested enough to try their luck at finding more. However, after five more days of searching the area Rob has found no further pieces of this meteorite.

As a wise man once said "seek and ye shall find". Keep looking, this stuff is out there! Let there be rock!

Thanks to:

Angus Self, FBIMS,
February-March 2006,
< gus @ angusself.co.uk >

BIMS logo


Let there be rock - addendum

Since writing the main part of this article I have had several more emails from Rob Elliott concerning Hambleton.

A further visit to The Open University was arranged where Rob met Profs. Monica Grady and Robert Hutchison with a view to more use of the SEM. Having Hambleton analysed by two generations of "Catalogue of Meteorites" authors was an event in itself! Hambleton continued to give very strange results, in particular some bizarre nickel rich areas, namely Ni 50 %, Fe 25 %, and S 25 %. Neither the OU nor the NMH can think of any mineral with this composition. Old data references are being studied but so far no similar mineral has been found. The 2:1:1 ratio is repeatable in regions right across the sample so they are leaning strongly towards the discovery of a new mineral.

Another slice has been cut from one of the highly weathered olivine rich areas. The professors seem to think this is another oddity worth sampling.

SEM at the Open University
From the left - Prof. Robert Hutchison, Dr. Diane Johnson, Prof. Monica Grady and Rob Elliott in front of the SEM at the Open University.

As of 18th May 2006 Rob had just received word that the Hambleton name and description/analysis has been accepted by the Met Society. Nickel in the plessitic octahedrite regions is anywhere up to 60 %, and they have high hopes that the nickel-rich FeS is a new mineral, although it still needs more study. In the abstracts, Hambleton is described as "a rare FeS-rich pallasite", with only one known other that shares this feature - the Phillips County (pallasite) from Colorado.

Angus Self,
May 2006,
< gus @ angusself.co.uk >

BIMS logo


Brown Dwarfs

Introduction

This article is based on research that was carried out in preparation for a talk to the Society in March 2006. The talk was inspired by the increased rate of detection of these objects. They are no longer theoretical and no longer rare or exotic.

The first brown dwarf was detected in 1995 although astrophysicists had predicted their existence for decades. Apparently there was no reason to rule out the existence of objects which have masses in between Jupiter sized bodies and the lowest mass objects which are capable of long term nuclear fusion within their cores.

Some people have argued that brown dwarves are misnamed. Firstly, they are not brown. They are envisaged as dim (in visible light) red objects with darker bands similar to the bands of Jupiter. Secondly, is a dwarf a meaningful term for an object that can be sixty times the mass of Jupiter? So far no one has thought of a better alternative name than 'sub-stellar object'.

Originally brown dwarves were called black dwarves. Now this term is reserved for the ultimate fate of white dwarves and neutron stars. As it will take a trillion years for these objects to cool to the state of blackness (no emission of visible light) none exist in the universe at the present time.

By all accounts Jill Tarter, who is the chief scientist of the SETI Institute, came up with the name 'Brown Dwarf'. She called, in a doctoral thesis in the 1970s, 'Sub Stellar Objects' 'Brown Dwarfs'.

The parameters of a brown dwarf

Brown dwarfs are defined relative to stars of solar mass, red dwarfs and Jupiter sized planets.

Solar Mass Stars

Stars of between 1.2 and 0.7 solar masses have similar spectra. They remain on the main sequence fusing hydrogen in a stable manner for ten billion years. These stars, such as our sun, when they run out of hydrogen, are massive enough to fuse carbon. They will become red giants and cast off planetary nebula. The remnant hot core will slowly cool as a white dwarf.

Red Dwarfs

Stars of between 0.7 and 0.08 solar masses evolve differently. They take a much longer time to reach the fusion stage (the main sequence) to condense from a mass of dust and gas. They spend millions of years condensing (the smaller the mass the longer it takes). The energy that is acquired from gravitational contraction is emitted in the infra red. During this phase red dwarves are indistinguishable from brown dwarves.

Once their cores are hot and dense enough fusion starts and proceeds at a leisurely pace. Fusion may continue for the lifetime of the universe. Their indefinite lives mean that red dwarves are now relatively plentiful in old globular clusters and in our galaxy. Even if the universe lasted long enough red dwarves could not become red giants. They do not have the mass to create the conditions in heir core that would allow the fusion of carbon.

Red dwarfs have surface temperatures of around 3500 K and K and M class spectra. The lower mass limit for a red dwarf is, by definition, 0.08 solar mass as that was thought to be the minimum mass that is required to produce the core temperature and pressure that will support nuclear fusion.

Brown Dwarves

It is now realised that high mass brown dwarves, approaching the 0.08 limit, can support fusion for about ten million years. It is not hydrogen that is burnt but heavy hydrogen (deuterium) and lithium.

The lower mass limit of a brown dwarf (and the notional boundary between these objects and a planet) is defined as 20 Jupiter masses (20 Jm). However, some authorities state that the boundary should be a spectrograph that indicates an object has a surface temperature of 1000 K.

Two new spectrographic classes have been created for brown dwarves. The first is called L and refers to the presence of lithium lines. Lithium is quickly and completely destroyed in a star. It will be present in the spectrum of a brown dwarf that has never undergone any fusion. To illustrate that nothing is clear cut lithium can be present in pre main sequence stars.

Brown dwarves can have a surface temperature of between 1500 K and 1000 K. Methane and water molecules can exist within this range. Their spectral lines characterise spectral class T.

The evolution of a high mass brown dwarf can be summarised as follows:

Although this will be the standard evolutionary history of a brown dwarf those in binary or other complex systems may gain mass and become stars. A brown dwarf may also gain mass by collision or impact.

Orion Nebula, visible light
Figure 1 - the Trapezium cluster in visible light (WFPC2).
STScI PRC00-19. NASA, C.R. O'Dell and S.K. Wong (Rice University).

Detection of Brown Dwarves

Infra red telescopes have detected brown dwarves within the neighbourhood of the solar system. More probably remain to be detected. At the moment, out to 17 light years, there are 60 stellar and sub stellar objects. These comprise 3 high mass stars, 7 solar mass stars, 45 red dwarfs, 5 white dwarfs and 7 brown dwarfs. These proportions may be galactic proportions.

The first brown dwarf to be detected is called Gliese 229B. It is 18 light years away. It rotates around Gliese 229A (a sun like star). Gliese 229B is 1/400,000 as bright as 229A in visible light. It is a T class brown dwarf and is thought to have a mass between 20 and 55 Jm.

A brown dwarf has been found with a 5 Jm planet.

A brown dwarf called LP 944-20 is 16.3 light years away in the constellation Fornax. It is thought to be about 60 Jm. On 15 December 1999 it emitted a small solar sized X ray flare which lasted for 2 hours. This shows that a brown dwarf may have stellar characteristics. Although fusion may have stopped or never started the interiors of a brown dwarf may be hot enough to generate turbulent and highly magnetised gases.

The Hubble telescope has photographed a star forming area of the Orion Nebula in visible light (figure 1). The same region in infra red light (figure 2) reveals a swarm of brown dwarfs. Perhaps the image suggests that brown dwarfs are very common objects in the galaxy.

Orion Nebula, infrared light
Figure 2 - the Trapezium cluster in infra red (NICMOS).
STScI PRC00-19. NASA, K.L. Luhman (Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.); and G. Schneider, E. Young, G. Rieke, A. Cotera, H. Chen, M. Rieke, R. Thompson (Steward Observatory, University of Arizona, Tuscon, Ariz.)

Brown Dwarfs and Life

The discovery that brown dwarfs are common must change the chances of life existing elsewhere in the galaxy. The chances must dramatically increase as they are more common than solar mass stars. Although small compared with our sun they can have planetary sized satellites and satellite systems. There is nothing to rule out an Earth type planet orbiting a brown dwarf which could b an abode for life - provided it was close enough. A brown dwarf can emit sufficient energy (albeit mostly within the infrared) to support life. As brown dwarves are more common than solar mass stars the life that evolves in their systems may be characteristic of our galaxy and the Universe as a whole. The most common form of eyes may only detect light in the infra red!

Further information:

Most of the information for this article was taken from websites on the Internet. Try 'Googling' Brown Dwarf / Brown Dwarfs / Brown Dwarves. Some sites that are recommended are:

Des Loughney, June 2006


About the ASE Journal

Editor: Dr D. Gavine, 29 Coillesdene Crescent, Edinburgh EH15 2JJ

Contents

Cover page

Presidential news

The March 29 eclipse from Libya

Let there be rock - The story of the Hambleton meteorite

Let there be rock - addendum

Brown dwarfs

About the ASE Journal


This journal as multiple web pages


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