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SAAO’s New 1 Metre Telescope Needs A Name

The South African Astronomical Observatory (SAAO) is running a telescope naming competition for its new 1 metre telescope which is a recent addition to the collection of many national and international telescopes on our observing plateau near Sutherland in the Northern Cape.

The competition is open now till March 31 (extended from March 18) to learners in grade 6 to 12 countrywide; participants are encouraged to send their suggested names in any of the South African eleven official languages accompanied by a 60 word motivation stating why their name should be considered. “We are looking forward to the many exciting names that the learners will come up with, as well as meeting the winner of the competition at the telescope naming ceremony at Sutherland”, said Dr. Hannah Worters, an astronomer responsible for commissioning the new telescope.

The new telescope is the first South African optical telescope that will be remotely operable and potentially robotic, since the establishment of the SAAO observing location near Sutherland. It will be capable of taking images of areas of the sky seventy times larger than our existing 1m telescope. It uses the SHOC (Sutherland High Speed Optical Camera), a very high-speed camera which can take 70 images in one second to study rapid changes in star systems.

Our telescope operations manager, Dr. Ramotholo Sefako, says, “It is important to share our excitement about the arrival of this new telescope in some way with the rest of the South African community by having its name given by one of South Africa’s young learners.” He continued to say, “We also hope everyone will be as delighted about it as we are. Hopefully, a few school learners may end up being motivated enough to pursue careers in science in the future.”

The 1 metre will also be a teaching telescope mostly used by postgraduate astronomy students from South African universities to develop skills in observing, processing images taken with the telescope, where possible writing up results and publishing them in scientific journals, as well as acquiring technical expertise on aspects of operating a telescope.

Important information:

Competition is open to learners in grades 6 to 12 countrywide (South Africa).

Learner’s entry should be accompanied by a motivation (maximum 60 words); entries without motivation will not be considered.

Learners should include their full names, grade, name of their school and contact number in their entry.

For online click on this website: http://www.saao.ac.za/competition/ or post their entry by no later than 31 March to:

South African Astronomical Observatory
P.O. Box 9
Observatory
7935 

Prize: The winner and one parent or guardian will travel to Sutherland to attend the naming ceremony. The learner’s name will be inscribed on a plaque attached to the building that houses telescope. After the ceremony, the winner will be shown around the facility; if the weather permits she/he will get a chance to observe the spectacular Sutherland night sky using our visitor’s telescopes.

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Dwarf-Star Wars: the revenge of the degenerates

Nature Astronomy, Volume 1, Article Number 0029
http://dx.doi.org/10.1038/s41550-016-0029

A bizarre binary star system has been discovered where a degenerate white dwarf pulsar is “lashing” its red dwarf companion with its strong magnetic field and beamed radiation every minute as it spins on its axis. This is the conclusion reached by a small team of three South African and two UK astronomers who have just published a paper in the new journal Nature Astronomy, announcing their discovery of strongly polarized pulsed optical emission from a white dwarf, a so-called degenerate star, in the binary system known as AR Scorpii, establishing it to be a white dwarf pulsar.

Last July, the UK co-authors of the current paper, Professors Tom Marsh and Boris Gänsicke from the University of Warwick, together with their collaborators, announced in Nature the discovery of strongly pulsed emission, across wavelengths from the radio to ultraviolet, from the fast spinning white dwarf, which rotates once every 2 minutes. Their conclusions were that the system was dominated by non-thermal emission, characteristic of pulsars. The current paper firmly establishes the pulsar link with the discovery of pulsed polarization at extremely high levels, reaching 40%, which is amongst the highest polarization levels detected in astronomical objects.

The discovery was made in March 2016 with the venerable and modest sized 1.9-m diameter telescope at the South African Astronomical Observatory (SAAO) in Sutherland, formerly known as the Radcliffe reflector when it began operating about 70 years ago in Pretoria. The observations used the HIPPO photopolarimeter, an instrument which is only one of a few in the world capable of making such observations of fast varying polarization. “This is a demonstration that forefront science can still be done with modest sized telescopes and niche instruments”, said Dr David Buckley, lead author of the paper and an astronomer at the SAAO. “HIPPO was really the ideal instrument for this study”, confirmed Dr Stephen Potter, also at the SAAO, who, together with Dr Buckley, had conceived of this instrument over 15 years ago and managed its design, construction and commissioning, which was completed in 2007. He went on to say, “Polarimetry is an often overlooked discipline in astronomy, with perceptions of it being difficult to do, but the results can sometimes be revolutionary”, as in the case of the results presented in their Nature Astronomy paper.

One of Dr Buckley’s UK collaborators, Professor Tom Marsh of the University of Warwick, had alerted him to their discovery of the fast pulsations discovered in AR Scorpii during their 2015 observations, and plans were put in place for a more detailed follow-up campaign in 2016, utilizing telescopes across the globe, including in South Africa. “It occurred to me from the outset that this object was ripe for polarization observations”, said Dr Buckley, “so we successfully applied for observing time to do this in May”. However, after having a spell of good weather during an earlier observing week in March and having observed all of his main targets for the week, Dr Buckley decided to observe AR Scorpii for an hour or so on his penultimate night, “Just to take a quick peek since it was too tempting to wait”, he said. He was astounded to see, in only a matter of a few minutes of observing, huge values of linear polarization, changing over the 2 minute rotation period of the white dwarf. “It was extremely exciting to see this in real time and was more than my wildest expectations”, he said. Further observations were done on the following night and it is these two nights of observations which feature in their Nature Astronomy paper.

The detection of the strongly pulsed optical polarization, which varies periodically at the spin period of the white dwarf and its beat period with the 3.6 orbital period, has been explained in terms two mechanisms. One of them is beamed radiation and the other due to magnetic interactions between the two stars. Professor Pieter Meintjes, from the Physics Department of the University of the Free State, who took the lead on the theoretical modelling and interpretation, commented: “AR Sco shows all of the hallmarks of a pulsar (dense stellar objects about 20 km in size consisting of a spinning neutron star), including being dominated by synchrotron emission from relativistic particles, both from the white dwarf and in the stellar wind produced by its interactions with its red dwarf companion”.

But the big difference in the case of the AR Scorpii white dwarf pulsar is that at a diameter of ~6000 km, it is about 300 times larger than any neutron star pulsar. “This is why it is able to provide the huge energy generation seen over all wavelengths”, says Dr Buckley, “because its moment of inertia is 100,000 times higher than for a neutron star”. The conclusions in the paper, based on the slowing down of the white dwarf’s spin period, have led to the suggestion that the magnetic field of the white dwarf is very high, up to 500 million Gauss (the Earth’s and Sun’s field strengths are 0.5 and 1 Gauss, respectively, and a fridge magnetic is about 50 Gauss). “This will produce radiation due to the white dwarf’s strong magnetic field”, says Professor Meintjes, “and is also strong enough to pump the weaker field of the red dwarf companion, producing periodic emission from the coronal loops, producing radio emission”. It was the radio pulsations, first discovered from observations with the Australia Telescope and presented in the original Nature discovery paper, that were particularly intriguing. “The radio data was what really started to make us believe that this object had some unique properties, not unlike pulsars”, said Professor Marsh.  Although there is one other similar binary star, also with a fast spinning white dwarf, called AE Aquarii, “That object is quite different and, importantly, not polarized, so with weaker pulsar credentials”, says Professor Gänsicke.

Professor Meintjes calculations imply that so-called magnetohydrodynamic (MHD) instabilities occur in the surface layers of the red dwarf, due to the magnetic field of the white dwarf sweeping by every minute. This results in energy loss which can account for some of the observed optical properties and explain why the white dwarf is slowing down so fast, on the relatively short timescale of 10 million years. “In a very real sense, this is a tug of war between two dwarf stars”, says Dr Buckley, “where right now the red dwarf is being “slapped in the face” once a minute by its rapidly rotating degenerate white dwarf companion.” Eventually these strong interactions will slow down the white dwarf until it is synchronously locked to the 3.6 hour orbital period of the pair. Perhaps the biggest puzzle, however, is why the white dwarf is spinning so fast in the first place. This is most likely a result of mass transfer from the red dwarf during a previous evolutionary phase, but as Professor Marsh says, “The evolutionary path that AR Scorpii took to its current configuration is still an open question.”

Picture credit: University of Warwick and Mark A. Garlick : An artist’s impression of the binary star AR Scorpii, with the spinning white dwarf pulsar in the upper right emitting a beam of energetic particles and radiation from its two magnetic poles. This beam and the strong magnetic field of the white dwarf lashes the larger red dwarf companion star as the white dwarf rotates, once every 2 minutes. The magnetic interactions between the two stars produces strongly polarized and pulsed radiation and also causes strong electrical field generation, powering the ejection of charged particles at close to the speed of light. The drag by the red dwarf on the magnetic field of the spinning white dwarf is slowing its rotation, which will eventually synchronize with the 3.6 h orbital period in about 10 million years.
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SALT’s excellence and achievements recognised by DST

The Southern African Large Telescope (SALT) welcomes the 2016 Science Diplomacy Award given by the Department of Science and Technology as a result of the telescope consistently contributing to globally significant discoveries in astronomy. Science diplomacy is the use of scientific collaborations among nations to address common problems and build constructive international partnerships. The Science Diplomacy Awards recognise excellence and achievements in international scientific cooperation.

“This award recognises the scientific success of SALT, which is obtaining high-quality observations of the cosmos every night and distributing this information to partners around the world, expanding our understanding of the universe in which we live. This success is due to the ingenuity and dedication of a world-class team of South African and international scientists, engineers, and technicians who designed, built, and operate SALT. The telescope inspires a generation of young South Africans to dare to dream big, and to have the confidence and skill to bring those dreams into reality”, says Professor Ted Williams, the director of the South African Astronomical Observatory.

The Southern African Large Telescope has recently celebrated 11 years since its construction and inauguration in 2005. SALT is a 10 metre class telescope located in Sutherland in the Northern Cape. It has been in full science operations for 5 years, with its consortium of partners from South Africa, Poland, the United States, Germany, New Zealand, the United Kingdom and India who have made the building and operation of the telescope possible.

There are more than 150 international peer-reviewed scientific papers published thus far based on SALT data. Recent contributions of SALT to science include the discovery of the brightest supernova ever found and the unveiling of a massive supercluster of galaxies. The trend of SALT’s science output parallels that of other large international telescopes. However comparing operation costs, SALT produces science more cost-effectively than any other 10 metre class telescope. Numerous students are getting trained locally and internationally.

Since the building of SALT, the South African Astronomical Observatory has been actively involved in astronomy outreach by sharing scientific discoveries with the communities across South Africa with particular focus in Sutherland and Cape Town which is where our operations are located. As such, both locations have a thriving community engagement programme involving schools, teachers and society. Additionally, many visitors to Sutherland get an opportunity to see the telescope during the day.

Mr. Sivuyile Manxoyi, who is the head of SALT Collateral Benefits Programme says, “The building of SALT has not only contributed to science research advancement, but to socio-economic development in Sutherland and nearby towns through tourism. The other major benefit is education and outreach in science, which we continue to implement nationally. SALT continues to serve as an inspiration and to instill confidence that our country and its people have the potential to excel in science and technology.”

Links

http://www.dst.gov.za/index.php/media-room/communiques/2032-science-forum-south-africa-science-diplomacy-awards-2016
Information about the Southern African Large Telescope : http://www.salt.ac.za/

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Eta Carinae: Violent stellar wind collision in the binary star monster

Eta Carinae is a massive, bright stellar binary system. The more massive component is one of the largest and most luminous stars known. In the central region of the binary, the powerful stellar winds from both stars collide at speeds up to 10 million km per hour. An international research team led by Gerd Weigelt from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn including SA Astronomical Observatory postdoctoral fellow, Dr. Nicola Clementel has for the first time studied Eta Carinae using near-infrared interferometric imaging techniques. The team obtained unique images of the wind collision regions between the two stars. These discoveries improve our understanding of this enigmatic stellar monster. The observations were carried out with the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO).

“There is a long history of South African interest in this truly remarkable star, which continues to astonish us”, says Prof Patricia Whitelock (SAAO & UCT). During the ‘Great Eruption’ it would have been the second brightest star in our skies and its changes were followed and recorded by several well known people, including Burchell, Herschel and Maclear. Very much more recently, observations that led to our understanding that eta Carinae was actually a binary star were made from SAAO at Sutherland in the Northern Cape.

The more massive of the two stars in the Eta Carinae system, called the primary star, is a monster because it is about 100 times more massive and five million times more luminous than our sun. In late phases of the evolution, such massive stars lose huge amounts of gas before they explode as a supernova. Studies of this dramatic mass-loss process are important to improve our understanding of stellar evolution.

Both stars of the Eta Carinae binary system are so bright that the powerful radiation they produce drives matter from their surfaces in the form of massive, fast stellar winds. These high-velocity stellar winds violently collide in the space between the two stars. Extreme physical processes occur in this innermost region, where the very fast stellar wind from the less massive but hotter companion star crashes into the dense primary star wind with a velocity of about 3000 km per second (more than 10 million km per hour). In this collision region, temperatures reach many tens of millions of degrees, hot enough to emit X-rays. In the past, it was not possible to resolve this violent collision zone, because its extension is too small even for the largest telescopes.

For the first time, an international team of astronomers led by Gerd Weigelt from the Bonner Max Planck Institute for  Radio Astronomy has obtained extremely sharp images of Eta Carinae (see Fig. 1) by using a new imaging technique based on long-baseline interferometry. This technique combines the light from three or more telescopes to obtain multi-telescope images called interferograms. From a large number of interferograms, extremely sharp images can be reconstructed using sophisticated image reconstruction techniques. This interferometric imaging method can achieve a resolution that is proportional to the distance between the individual telescopes.

The new Eta Carinae observations were carried out with the AMBER interferometry instrument of ESO’s Very Large Telescope Interferometer(VLTI; Fig. 2). . The team combined the infrared light from three of the movable VLTI telescopes with 1.8-metre mirror diameter. Because the largest distance between the telescopes was about 130 metres, an angular resolution was obtained that is about 10 times higher than the resolution of the largest single telescope.
“Our dreams came true, because we can now get extremely sharp images in the infrared regime. The  ESO VLTI provides us with a unique opportunity to improve our physical understanding of Eta Carinae and many other key objects”, says Gerd Weigelt.

The applied high-resolution imaging technique allowed the team to obtain, for the first time, both direct images of the stellar wind zone surrounding the primary star and the collision zone in the central region between the two stars (Fig. 1). Because this technique provides both high spatial and spectral resolution, it was possible to reconstruct images at more than 100 different wavelengths distributed across the Brackett Gamma emission line of hydrogen. This is of great importance for astrophysical studies of Eta Carinae, because these multi-wavelength images show both the intensity and the velocity distribution of the collision region. Velocities can be  derived from the multi-wavelength images because of the Doppler effect. These results are important to improve physical models of the wind collision zone and to better understand how these extremely massive stars lose mass as they evolve.

“The unprecedented level of details of this VLTI multi-wavelength observations is at the same time fascinating and challenging. The high-quality data allow for better understanding of the physical properties, but also place stronger constrains which require an increased effort in modelling this fascinating object. These techniques and new instruments also provide new possibilities for studying stellar outflows.” explained Dr. Clementel.

Original paper: Weigelt et al.: VLTI-AMBER velocity-resolved aperture-synthesis imaging of Eta Carinae with a spectral resolution of 12 000, 2016, Astronomy & Astrophysics, Online Publication October 19 (DOI: 10.1051/0004-6361/201628832) : www.aanda.org/10.1051/0004-6361/201628832

Paper on the South African  perspective: South African Journal of Science 101, p. 525 -530  Eta Carinae : a South African perspective.

Further Information:

Max-Planck-Institut für Radioastronomie (MPIfR)

http://www.mpifr-bonn.mpg.de/2169/en

Research group Infrared Astronomy at MPIfR

http://www.mpifr-bonn.mpg.de/research/infrared

European Southern Observatory (ESO)

http://www.eso.org/public/

Very Large Telescope (VLT)

http://www.eso.org/public/teles-instr/paranal/

Astronomical MultiBEam combineR (AMBER)

http://www.eso.org/public/teles-instr/vlt/vlt-instr/amber/

NASA Video: Eta Car’s theoretical wind collision models

https://svs.gsfc.nasa.gov/11725

 

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SAAO ranked among the top ten research institutions in Africa

The South African Astronomical Observatory (SAAO) is among the top ten research institutions in Africa for Physical Sciences according to the Nature Index for the year covering 1 July 2015 to 30 June 2016. Each year, Nature, one of the best science journals in the world, ranks institutions from across the world according to the number of peer-reviewed science papers they produce. Several other South African research institutions also feature in the top ten list.

This achievement is even more remarkable when we consider that SAAO only produces astronomy and astrophysics related research output (peer-reviewed papers). At other institutions, such as universities, other branches of Physics also contribute towards the total number of Physical Sciences papers.

Dr. Stephen Potter, head of the astronomy division had this to say about the Nature Index results: “A pleasing statistic that reflects the high international standard of SAAO’s researchers. Equally impressive is the 42% of publications that are excluded from the “Nature index” measure of SAAO’s scientific output. The 42% represents the research made by other national and international researchers as well as students who have made use of the astronomical facilities operated, maintained and developed by the SAAO. A clear demonstration of SA Astronomy Observatory’s commitment to student development and international collaboration through astronomy.”

Globally, SAAO also ranks favourably when compared to other national observatories. The institution has a similar ranking to the National Optical Astronomy Observatory in the US, the Australian Astronomical Observatory as well as the Japanese Aerospace Exploration Agency.

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First Light for SAAO’s new telescope

SAAO has a brand new 1-metre telescope in Sutherland! We began the installation with the manufacturing team from APM Telescopes on Tuesday 2 August and by Friday the telescope had seen First Light. We are busy commissioning and characterising the telescope, whose first generation instrument will be SHOC. The project is led by Dr. Hannah […]

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A Giant Stellar Void in the Milky Way

A major revision is required in our understanding of our Milky Way Galaxy according to an international team led by Prof Noriyuki Matsunaga of the University of Tokyo. The Japanese, South African and Italian astronomers find that there is a huge region around the centre of our own Galaxy, which is devoid of young stars. The team publish their work in a paper in Monthly Notices of the Royal Astronomical Society.

The Milky Way is a spiral galaxy containing many billions of stars with our Sun about 26,000 light years from its centre. Measuring the distribution of these stars is crucial to our understanding of how our Galaxy formed and evolved. Pulsating stars called Cepheids are ideal for this. They are much younger (between 10 and 300 million years old) than our Sun (4.6 billion years old) and they pulsate in brightness in a regular cycle. The length of this cycle is related to the luminosity of the Cepheid, so if astronomers monitor them they can establish how bright the star really is, compare it with what we see from Earth, and work out its distance.

Despite this, finding Cepheids in the inner Milky Way is difficult, as the Galaxy is full of interstellar dust which blocks out light and hides many stars from view. Matsunaga’s team compensated for this, with an analysis of near-infrared observations made with a Japanese-South African telescope located at Sutherland, South Africa. To their surprise, they found hardly any Cepheids in a huge region stretching for thousands of light years from the core of the Galaxy.

Noriyuki Matsunaga explains: “We already found some while ago that there are Cepheids in the central heart of our Milky Way (in a region about 150 light years in radius). Now we find that outside this there is a huge Cepheid desert extending out to 8000 light years from the centre.”

This suggests that a large part of our Galaxy, called the Extreme Inner Disk, has no young stars. Co-author Michael Feast notes: “Our conclusions are contrary to other recent work, but in line with the work of radio astronomers who see no new stars being born in this desert.”

Another author, Giuseppe Bono, points out: “The current results indicate that there has been no significant star formation in this large region over hundreds of millions years. The movement and the chemical composition of the new Cepheids are helping us to better understand the formation and evolution of the Milky Way.”

Cepheids have more typically been used to measure the distances of objects in the distant Universe, and the new work is an example instead of the same technique revealing the structure of our own Milky Way.

Further information

The new work appears in “A lack of classical Cepheids in the inner part of the Galactic disc“, N. Matsunaga, M. Feast, G. Bono, N. Kobayashi, L. Inno, T. Nagayama, S. Nishiyama, Y. Matsuoka and T. Nagata, Monthly Notices of the Royal Astronomical Society, Oxford University Press, in press.

The copy of the paper is available for free download from http://mnras.oxfordjournals.org/lookup/doi/10.1093/mnras/stw1548

A preprint of the paper is available from http://arxiv.org/abs/1606.07943

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SALT tests a high accuracy and high precision calibration ruler for its High Resolution Spectrograph

Since last week, the Southern African Large Telescope (SALT) in Sutherland has been testing a Laser Frequency Comb, which is a calibration device that uses powerful lasers and photonic crystal fibres to produce the equivalent of a ruler that is both extremely long and has very finely spaced graduations. The pioneers of this decade old technology were awarded the Nobel Prize in Physics in 2005.

A team of laser physicists from the Heriot-Watt University, Derryck Reid and Richard McCracken, along with astronomers from SALT and South African Astronomical Observatory (SAAO), Éric Depagne, Rudi Kuhn, Nicolas Erasmus and Lisa Crause, installed the Laser Frequency Comb device on the SALT’s High Resolution Spectrograph (HRS) to perform the first routine comb-enabled scientific observations on a 10m-class telescope.

“The Laser Frequency Comb is a significant improvement in the way astronomers will calibrate their spectra in the future”, says Éric Depagne, project leader and HRS Instrument scientist. “It allows reaching much higher accuracies when measuring radial velocities, while adding something that is completely missing when using standard calibration sources – traceability. Since the electronic components and the optical devices are all linked to calibrated atomic clocks, we are sure that if we repeat the measurements in 20 years, they will be comparable to those we do today. And that is something fundamentally new”.

Professor Derryck Reid from Heriot-Watt University said: “We’ve been developing the Laser Frequency Comb at Heriot-Watt University for 10 years and to finally demonstrate it on the SALT telescope is really exciting. Its accuracy and precision allows astronomers to derive precise fundamental parameters for a wide range of astronomical objects, from the existence of planets around distant stars, to the determination of the variability of the first generation of stars and the measurements of isotopic ratios that provide detailed information on the nature of supernovae”.

Astronomers determine the composition of stars by using spectrographs to split the light into various colours, exactly like water droplets produce rainbows when it rains. Each element we know in the Universe has a unique signature. Sodium, for instance produces bright yellow light, Neon glows red, and Magnesium has a blueish hue. By identifying the individual signatures of elements in the spectra of celestial objects, astronomers can infer the chemical composition, and many more parameters, such as the speed at which objects move relative to the earth, their temperature, and their mass.

In certain studies, astronomers must look for small changes in the colour of light emitted by stars. For example, the gravitational pull of a planet orbiting a star imprints a tiny wobble on the star, causing the colour of the star’s light to fluctuate by a small amount. As astronomers search for smaller, more “Earth-like” planets they need better tools with which to measure these tiny fluctuations. The Laser Frequency Comb could provide the precision measurement capability which is needed for this exciting new science.

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A Sutherland robotic telescope spots an extrasolar planet

A Sutherland based robotic telescope KELT-South spotted an extrasolar planet KELT-10b during its routine observations. KELT-South (Kilodegree Extremely Little Telescope – South) is dedicated to the search of transiting planets orbiting especially bright stars.

Astronomers refer to these planets as “hot Jupiters” because of their composition and mass. They are gas giants similar to the planet Jupiter, except that they orbit extremely close to their host stars. The planet, KELT-10b, has a mass 30% less than Jupiter but is 40% larger in radius, which makes it very inflated. It orbits its host star about once every 4.2 days. According to calculations, KELT-10b has a surface temperature of about 1100 degrees Celsius – Jupiter has a surface temperature of about -145 degrees Celsius. KELT-10b’s host star is slightly hotter and larger than the sun. Although it is too dim to see with the naked eye, it is visible with a small telescope.

KELT-10b is especially interesting because of its very strong transit signal and a fairly bright host star. Those two properties make it such a valuable target for further investigation, to learn about the composition of its atmosphere, how heat is transferred from its star to the lower gas layers, and around to the back side of the planet through the winds.

According to the South African Astronomical Observatory (SAAO) based astronomer, Dr. Rudi Kuhn the process of finding these planets is quite involved, “There are numerous objects that appear to have the same characteristics as transiting planets but turn out to be something else. Careful, meticulous investigation is therefore required to identify real transiting planets. Thus, astronomers have to use separate methods for identifying and confirming possible transiting planets. Initial discoveries are made using the transiting technique, which determines the amount of light blocked by the planet when it moves in front of the star. The method used to confirm whether it is a transiting planet is the radial velocity or ‘wobble’ method, which measures the wavelength of light received from a star as it is tugged by the gravity of its planet.”

American based collaborator, Dr. Joshua Pepper says the discovery of KELT-10b is important because, “The goal of this search is to find transiting planets orbiting especially bright stars, as they are excellent targets for follow-up observations with big telescopes like the Southern African Large Telescope (SALT) to measure their atmospheres.” Since the discovery of 51 Pegasi in 1992 many more extrasolar planets have been detected. Before the discovery of 51 Pegasi, astronomers had believed that other planetary systems would have to be like ours, with small rocky planets close to the parent star and massive gaseous planets further out.

Ground-based surveys for extrasolar planets have become more successful, with their number reaching 130 so far. These surveys use small aperture wide-field robotic telescopes to obtain high-precision photometric light curves of relatively bright stars.

The Kilodegree Extremely Little Telescope (KELT) project deployed KELT-South to Sutherland in 2008 while Dr. Rudi Kuhn was busy with his Masters degree at the University of Cape Town. He developed the computer software that controls the telescope, which means the telescope can observe on its own, without an astronomer physically operating it. “Being involved in the construction of the telescope was the fulfilment of a childhood dream, enabling me to bring together my interest in both astronomy and computer programming” says Dr. Kuhn.

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Astronomers pinpoint echoes of ancient exploding star on our stellar doorstep

SALT_SAAO_UCT

Breakthrough for astronomers from UCT and the Southern African Large Telescope (SALT)

A team of astronomers has identified a rare star that exploded around 1,500 years ago. At the time, the star would have outshone all the stars of the Orion constellation, reaching a similar brightness to Jupiter in the night sky.

Dr Brent Miszalski, SALT astronomer at the South African Astronomical Observatory (SAAO), said: “Putting together the pieces of this cosmic puzzle has been a detective story bringing together the very latest astronomical equipment and millennia-old Chinese records of the variable night sky.”

The find was reported in a recently published paper by a team of astronomers based in South Africa, England, Chile, Spain and Mexico.

Amateur astronomers found the peculiar looking nebula, called Te 11, in the Orion constellation in 2010. Astronomers weren’t sure what to make of it, but have now resolved the conundrum. First observations of this star at the centre of the nebula (a cloud of gas and dust in outer space) showed it to be a double star system in a close orbit of almost 3 hours.

The team responsible for this discovery, a group of astronomers with expertise in the envelopes of old stars led by Dr Brent Miszalski at the SALT/SAAO, were soon joined by UCT astronomers Professor Patrick Woudt (Head of Astronomy at UCT), Professor Brian Warner and PhD student Ms Mokhine Motsoaledi, who had also directed their attention to this unusual star.

By noticing variations in the brightness of this star over several years, Professor Woudt and colleagues amassed high-speed observations recording the changes in the binary’s light. The jumps in the light curve imply that the star is a dwarf nova (a star hiccuping material nibbled off the companion). “Such a combination of a dwarf nova with a nebula is extremely rare,” said Prof Woudt.

Key to working out the nature of the Te 11 nebula was calculating its distance. Here the huge light collecting power of the 11-metre Southern African Large Telescope (SALT) in Sutherland was used to peer into the heart of the nebula, pinning down the temperature of one of the stars present. This was worked into the modelling of the light curve to yield a distance of around 1000 light years – putting Te 11 on the edge of the Orion-Eridanus superbubble. This distance confirmed the nebula could not be the ejected envelope of an old star like the Sun.

Looking back in time at Chinese historical records, Professor Warner found that there was a bright guest star in Orion during 483 CE near the position of Te 11. “This remarkable connection suggests that Te 11 is the leftovers of this explosion of more than 1500 years ago,” said Professor Warner.

“Pairings in astronomy as found in Te 11 are exceedingly rare, but it is anticipated that planned studies of the night sky will find a whole lot more,” said Professor Woudt.

South African astronomers are looking forward to using the upcoming MeerLICHT facility in Sutherland that may help find similar objects to Te 11.

MeerLICHT will be a dedicated wide-field optical telescope that will robotically follow the gaze of the Meerkat radio telescope array, a precursor array that will form part of the Square Kilometre Array, which will start early science this year.

Professor Woudt said: “Planned surveys with MeerKAT and MeerLICHT will scan the southern skies for more of these unusual objects, which can tell us more about the formation and the evolution of these compact binaries in the Milky Way”.

With a binary period of only 2.9 hours, the two stars in Te11 are separated only by about twice the Earth-Moon distance.

There is a long history of scientific collaboration between the University of Cape Town and the SAAO, which operates SALT on behalf of an international group of partners. UCT and SAAO have a number of joint staff positions and are partners in the MeerLICHT project.

MeerLICHT is a robotic telescope that will soon be installed in Sutherland and which will be permanently tied to the observing schedule of MeerKAT. As demonstrated in the case of Te 11, the Southern African Large Telescope proved fundamental in understanding the faint source of the transient signal.

“The unique combination of SALT, MeerKAT and MeerLICHT bodes very well for peering deeper into the transient southern skies in the coming years,” said Professor Woudt.

Read more at: http://adsabs.harvard.edu/abs/2016MNRAS.456..633M
A PDF of the paper can be found here: http://www.saao.ac.za/~brent/Te11.pdf

This is a joint-release with the UCT Astronomy department: http://www.ast.uct.ac.za/node/164

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