*********************************** The SOCIETY for POPULAR ASTRONOMY *********************************** ==================================================== Electronic News Bulletin No. 266 2009 May 1 ==================================================== 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 at 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://www.popastro.com/ The Electronic News Bulletins are now sponsored by Astronomica. LYRIDS - FIRST NEWS By Alastair McBeath, SPA Meteor Section Director Weather conditions seem to have dashed most British observers' hopes for covering the moonless Lyrid shower this spring (prospects for it were given last time), with so far just two positive visual reports in to the Section, from "SNOW_JOKE" in Derbyshire, and myself in Northumberland, who were both able to see something of the activity on April 21-22. Elsewhere, those few people to report-in as yet have commented on either too much cloud, haze, mist or fog, to allow viable meteor watching. Activity seemed to be fairly normal from the Lyrids that night, with Zenithal Hourly Rates, ZHRs, around 13 after UT midnight, as confirmed by the International Meteor Organization's (IMO's) "live" Lyrids webpage, at http://www.imo.net/live/lyrids2009/ . Activity stayed at about 14 or 15 from roughly 02h to after 09h UT on April 22 in the IMO initial data, but few reports filled this lengthy interval, so its apparent consistency may be illusory. A fairly normal, if low-activity, return can be inferred from this so far. One curious effect this year was an apparent "cluster" of six, mostly single-station, fireballs seen from British locations between April 19 to 22. Although the Lyrids have a reputation for producing bright meteors near their maximum, these fireballs seem to have had relatively little to do with that shower for once. Too little information was available on some to determine a possible origin, but three at least were not Lyrids. Fireball "groups" like this are more often due to a human desire to see patterns even in randomness, but occasionally there may be more to such a supposed "cluster", and investigations remain on-going, just in case. Anyone else who saw a fireball (any meteor of magnitude -3 or brighter) around these dates, or at any other time, from the UK or nearby, is invited to send in full details to the SPA Meteor Section as soon as possible. Please see the "Making and Reporting Fireball Observations" webpage, at: http://snipurl.com/h127h , for information and a report form. Plus of course, anyone with still unsubmitted Lyrid meteor watch data is very welcome to send those in quickly too! APRIL 4-5 FIREBALL UPDATE By Alastair McBeath, SPA Meteor Section Director Three definite sightings from England, and one each from Ireland and Northern Ireland have reached the Section now on the ~23:32 UT, April 4-5 fireball, first mentioned last time. Sightings were made from Merseyside, Worcestershire, Cornwall, Counties Wicklow and Antrim. A further sighting from Buckinghamshire was reported perhaps around 23:00 UT that night, but this may have been of a separate event. The five main ~23:32 UT observations have not allowed an especially precise atmospheric trajectory to be estimated for this meteor. However, it is plausible the visible track was oriented between roughly south-north to SW-NE, starting over the Bristol Channel/St George's Channel area, or Pembrokeshire/Carmarthenshire of nearby southern Wales, and ending above SW to central-western Wales or Cardigan Bay. The end could conceivably have been further north, perhaps over the Lleyn Peninsula/Anglesey area, or even above the Irish Sea between Caernarfon Bay to Wicklow/Dublin, though it was likely closer to the Welsh than the Irish coast if so. Three observers reported quite severe fragmentation later in the flight, which may have happened over SW Wales or the southern Irish Sea between the St David's Head/southern Cardigan Bay to Carnsore Point/Cahore Point region. It has remained unclear whether the fireball reported by media sources was the same as this event or not. An early quote attributed to an Astronomy Ireland officer suggested that meteor was moving from the west across central Ireland. As such a path would have been wholly inconsistent with the data reported to the SPA so far, there may indeed have been a second brilliant meteor involved, possibly at almost exactly the same time. Regrettably, confusion has persisted over whether this "media fireball" happened on April 4-5 or 5-6, which has not helped resolve matters. FEBRUARY METEORITE & SPACE DEBRIS NOTES By Alastair McBeath, SPA Meteor Section Director Assistant Meteor Director David Entwistle recently noted a fresh L6 chondrite meteorite had been reported as recovered following the Texas fireball on February 13-14 this year (see ENB 262, http://snipurl.com/h0pzp ). This object was probably the largest single specimen found so far, at 1.7 kg. Other notes on the fireball, and follow-up links to the meteorites recovered, can be found on the General Chat Forum, at http://snipurl.com/h17dk . A couple of days earlier, on February 11, some ENB readers may recall hearing of the unexpected accidental collision between two Earth-orbiting satellites, Iridium 33 and Cosmos 2251. Although this created a large field of debris, the high orbital distance it happened at meant initially, it was thought likely to be at least years to decades before any objects would begin re-entering the atmosphere from the event. This has proven inaccurate, as the first seven small fragments (each around a centimetre in size or less), all from the Cosmos satellite, came down between March 12 and 30, as tracked by the US Air Force's Space Command radar. There are no reports so far that any produced visible meteors detectable from the surface, nor has an expectation that this may be so for those fragments still in orbit yet been raised. More similarly small fragments have come down during April, and it seems likely this will now be a continuing process. On April 11, the available fragment "reservoirs", that is the number of radar-detectable particles remaining in orbit, stood at 558 for the Cosmos satellite and 263 for the Iridium one. There is apparently no danger from these re-entries, with no radioactive materials on board either craft according to official sources, while the fragments seem to be too small to cause physical damage, even if one were to survive intact to the surface (which is highly unlikely anyway). My grateful thanks go to regular Section contributor Jeff Brower in Canada for providing details of the re-entered fragments and the state of the debris cloud, plus additional comments from David Entwistle. PRIMITIVE DUST SAMPLES ANALYSED RAS Whereas the planets in the inner Solar System, such as the Earth and Mars, once experienced harsh conditions and have changed substantially over the past 4.5 billion years, comets are believed to store the original material of the early Solar System. Cometary dust is therefore of interest as possibly being, or including, samples of primitive interstellar material. Dust particles collected from the upper atmosphere by NASA aircraft in 2003 April during the Earth's passage through the dust stream left behind by Comet 26P/Grigg- Skjellerup appear to include interplanetary material. The particles, which are only a few microns in diameter, were analysed by scientists from the UK, the US and Germany. Two grains have compositions thought to match the nebula from which the Solar System formed. One dust particle contained four pre-solar silicate grains with an unusual chemical composition that matches predictions for silicates formed from gas cooling after a supernova explosion. One of the grains, a fragment of olivine, was found next to a hollow globule of carbon, most likely of interstellar origin. Carbon-containing coatings are suspected to have enabled some of the fragile silicate grains to survive the space environment. Comparison with 'Deep Impact' observations of Comet 9P/Tempel 1 and analyses of samples collected by 'Stardust' from Comet 81P/Wild 2 demonstrated differences between the comets, which are all short-period comets with orbits constrained by Jupiter's gravitational field. Comet 81P/Wild 2 appears to have much higher levels of material formed in the inner Solar System; all the comets, however, contained materials such as carbonates that commonly indicate the presence of water. LEAST-MASSIVE EXOPLANET SO FAR DISCOVERED ESO An international team using the 3.6-m telescope at La Silla in Chile has discovered what may be the least massive planet so far detected outside our Solar System. Orbiting Gliese 581, an M-type star in the constellation Libra, the planet has a minimum mass only about twice as great as the Earth's, whereas most other exoplanets identified have been far more massive. (The actual mass of the planet cannot be determined, as it depends upon the unknown orbital inclination.) The planet joins three others previously detected around the same star, and takes the designation Gliese 581 e. As with the previous discoveries, its presence was detected by the radial-velocity technique. The observations are right at the limits of current technology. The recent announcement of the existence of Gliese 581 e also includes a correction to the orbital period of one of the other planets, Gliese 581 d, from 82 to 67 days. DEBRIS AROUND DEAD STARS RAS White-dwarf stars are the compact, hot remnants, comparable in size with the Earth, that are left behind when stars like our Sun reach the end of their lives. In theory their atmospheres should consist entirely of hydrogen and helium but are sometimes found to be contaminated with heavier elements like calcium and magnesium. Observations made with the Spitzer space telescope suggest that at least 1%--3% of white-dwarf stars are contaminated in that way through a rain of closely orbiting dust that may have originated from rocky bodies like asteroids and emits the infrared radiation observed by Spitzer. The dust is completely contained within the Roche limit of the star -- close enough that any object larger than a few metres would be torn apart by gravitational tides (the same phenomenon which led to the creation of Saturn's rings). That is the basis of the hypothesis that the dust discs around white dwarfs are produced by tidally disrupted asteroids. In order to pass so close to the white dwarf, an asteroid must be perturbed from its regular orbit further out, perhaps by a close encounter with as-yet-unseen planets. LOCAL STAR'S COOL COMPANION RAS 'Brown dwarfs' are star-like objects whose masses are too small to have created, in their cores,temperatures and pressures high enough to ignite the nuclear reactions upon which stellar energy depends. They have masses lower than those of stars but larger than those of gas-giant planets like Jupiter. Owing to their low temperatures they are very faint in visible light, and are best detected at infrared wavelengths. Astronomers have now discovered a particularly cool brown dwarf, orbiting the red dwarf star Wolf 940, some 40 light-years from the Earth. It appears to be about 440 times as far from its star as the Earth is from the Sun. It is roughly the same size as Jupiter, despite being between 20 and 30 times as massive, and the resemblance between the infrared spectra of the two objects is striking. Models of brown-dwarf spectra, which are dominated by absorptions due to water and methane, are sensitive to assumptions about their age and chemical make-up. In most cases the ages and compositions of brown dwarfs are unknown, and that can make it hard to tell where the models are right and where they are going wrong. In the case of Wolf 940, however, we can use what we know about the primary star to infer the properties of the brown dwarf, and that makes the pair a useful find; it can be thought of as a Rosetta Stone for decrypting what the light from such cool objects is telling us. YOUNGEST (AND PRESUMED LOWEST-MASS) BROWN DWARFS RAS Astronomers have found three brown dwarfs with estimated masses less than 10 times that of Jupiter, making them among the youngest and lowest-mass such objects so far detected. They were found in the star-forming region IC 348, almost 1000 light-years away, in the constellation Perseus. IC 348 is approximately 3 million years old -- extremely young astronomically -- which makes it a good place to search for the lowest-mass brown dwarfs. The ones now identified are isolated in space -- they are not orbiting any star, although they are gravitationally bound to IC 348. Their atmospheres all show evidence of methane absorption, which was used to select and identify the young objects. The team is said to have set out to find a population of brown dwarfs in order to help theoreticians to develop more accurate models, needed to test current star-formation theories, for the distribution of masses in a newly formed population. (But a special effort to find a particular constituent of the population, so far from helping to achieve a more accurate model, seems like a deliberate effort to bias the statistics!) The discovery of the dwarfs in IC 348 has allowed new limits to be set on the lowest-mass objects. Brown dwarfs cool with age, and current models estimate that their surfaces are at approximately 600-700 degrees Celsius. That is extremely cool for objects that have just formed, and implies that they have the lowest masses of any such object that has been seen to date, although no actual measurement of their masses has been possible. COMPLEX MOLECULES DETECTED RAS Scientists from the Max-Planck Institute have been using the IRAM 30-m telescope in Spain to observe the millimetre-wavelength emission from molecules in the star-forming region Sagittarius B2, close to the centre of our Galaxy. Large molecules of many different sorts have been detected in that region in the past, including alcohols, aldehydes, and acids. Two new molecules have now been discovered -- ethyl formate (C2H5OCHO) and n-propyl cyanide (C3H7CN); they are the most complex of their kind yet detected in interstellar space. DISTANT WATER RAS Astronomers have found the most distant signs of water to date. The water vapour is thought to be contained in a jet ejected from a super- massive black hole at the centre of a galaxy named MG J0414+0534. The water emission is seen as a maser, where molecules in the gas amplify and emit beams of microwave radiation in much the same way as a laser emits beams of light. The faint signal is only detectable as a result of serendipitous gravitational lensing, where the gravity of a massive galaxy in the foreground acts as a cosmic telescope, bending and concentrating light from the distant galaxy and making in this case a clover-leaf pattern of four images of MG J0414+0534. The water maser was detectable only in the two brightest images. The radiation from the water maser was emitted when the Universe was only about 2.5 billion years old, a fifth of its current age. SURVEY THROWS LIGHT ON FORMATION OF MASSIVE GALAXIES RAS First results from the 'GOODS' survey being made with the Hubble telescope indicate how the most massive galaxies in the early Universe assembled to form the most massive objects seen today. The observations are part of the 'Great Observatories Origins Deep Survey' (GOODS), a campaign that is using the Spitzer, Hubble and Chandra space telescopes together with the XMM Newton X-ray observatory to study distant parts of the Universe. Early results show that the most massive galaxies, which have masses roughly 10 times larger than the Milky Way's, were involved in significant levels of mergers and interactions when the Universe was just 2-3 billion years old. The GOODS results show that the galaxies did not form in a simple collapse in the early Universe, but that their formation was gradual, taking about 5 billion years. SPECTACULAR FLARING FROM EXTRAGALACTIC JET STScI Images taken in ultraviolet light have shown the brightening of a jet of gas blasting from the core of the giant elliptical galaxy M87, which is located 54 million light-years away in the Virgo Cluster. The outburst is coming from a blob of gas called HST-1, embedded in the jet, a powerful narrow beam of hot gas thought to be produced by a super-massive black hole in the core of the galaxy. HST-1, which is some 200 light-years from the galaxy's centre, was discovered and named in 1999 by Hubble astronomers, who have been following the activity for 7 years, obtaining a ultraviolet light-curve of the event. Other telescopes have been monitoring HST-1 in different wavelengths, including radio and X rays. The Chandra X-ray telescope was the first to report the brightening in 2000. In 2003, HST-1 had become brighter than M87's luminous core, and in 2005 it became 90 times brighter than it was in 1999. Then the flare began to fade, but it intensified again in late 2006, though the second outburst was fainter than the first one. Owing to holidays, the next edition of the Bulletin will be issued on May 31. Bulletin compiled by Clive Down (c) 2009 the Society for Popular Astronomy The Society for Popular Astronomy has been helping beginners to amateur astronomy -- and more experienced observers -- for more than 50 years. If you are not a member then you may be missing something. Membership rates are extremely reasonable, starting at just £16 a year in the UK. You will receive our bright quarterly magazine Popular Astronomy, regular printed News Circulars, help and advice in pursuing your hobby, the chance to hear top astronomers at our regular meetings, and other benefits. The best news is that you can join online right now with a credit card or debit card at our lively website: http://www.popastro.com/ Astronomica is the new sponsor of the SPA Electronic News Bulletin. 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