Archive | News RSS feed for this section

SALT sees double in The Hourglass Nebula

The Southern African Large Telescope (SALT) at the South African Astronomical Observatory (SAAO) in Sutherland has discovered a binary star system in The Hourglass Nebula, one of the most famous nebulae captured by the Hubble Space Telescope.

The Hourglass Nebula consists of two hourglass-shaped lobes of gas and what appears to be an eye staring right back at us. Shells of gas form the eye surrounding the hot central star that illuminates the nebula like a neon sign. Astronomers have long suspected the peculiar nebula to be formed by two interacting stars in a binary system, but until now no one could prove it. The SALT discovery of two stars orbiting each other every 18.15 days in The Hourglass Nebula firmly settles the matter and gives new insights into how a wide variety of close binary stars and hourglass-shaped nebulae may form.

An international team of astronomers, led by SALT Astronomer Dr Brent Miszalski at the SAAO, used SALT to peer into the “sparkle” of the eye of the Hourglass Nebula – its central star.

Dr Miszalski says, “A total of 26 SALT measurements were taken that detected the small movements of the central star towards or away from us caused by the gravity of a second companion star. This Doppler or “wobble” method, that can also be used to find planets around other stars, revealed a hidden companion orbiting the central star every 18.15 days.”

Co-author of the study, Mr Rajeev Manick, formerly a Masters student at SAAO and The University of Cape Town, and now completing his PhD at The Katholieke Universiteit Leuven in Belgium, analysed the SALT measurements and found that the companion must be a small, cool star about 5 times lighter than the Sun.

Another surprise came with the binary – the relatively wide separation between the two stars is remarkable. Co-author Professor Joanna Mikołajewska of the Nicolaus Copernicus Astronomical Center in Warsaw, Poland, a major partner in SALT, Prof. Mikołajewska says, “Previous authors have suggested that a nova explosion could explain many aspects of The Hourglass Nebula, but curiously we found the stars were too far apart for this to have ever been possible.”

Instead of a nova explosion, the orbital period indicates the Hourglass Nebula formed through an interaction that many close binary stars experience – a so-called common-envelope stage. In this scenario, the cooler companion spirals into the atmosphere of its larger companion and helps ejects the shared atmosphere which we now see as the nebula. The Hourglass Nebula is one of very few such examples to show an orbital period above 10 days, making it helpful to improve our understanding of this brief phase that many types of binary stars experience during their lifetime.

While astronomers still do not quite understand how hourglass-shaped nebulae form, the discovery of a binary in The Hourglass Nebula considerably strengthens the long suspected, but difficult to prove, connection between binary stars and hourglass-shaped nebulae. A famous example is the nebular remnant of Supernova 1987A that is often compared against The Hourglass Nebula because of its very similar shape. It is thought to have resulted from the merger of two massive stars before the supernova event. This process shares similarities with that which formed The Hourglass Nebula, hinting at some shared physics resulting in two of the most unusual nebulae in the sky.

Dr Miszalski says, “The combination of SALT’s enormous 11-metre mirror, highly sensitive instrumentation and flexible queue-scheduled operations was fundamental to making this difficult, cutting-edge discovery. We will continue searching other nebulae for new binary systems to gain more insights into their complex origins.”

The study entitled “SALT HRS discovery of the binary nucleus of the Etched Hourglass Nebula MyCn 18” was recently accepted for publication in the Publications of the Astronomical Society of Australia (PASA) journal and is available from https://arxiv.org/abs/1805.07602. The work is the result of a collaboration between astronomers at SAAO and SALT in South Africa, the Nicolaus Copernicus Astronomical Center in Poland, and The Katholieke Universiteit Leuven in Belgium.

Historical background:

The Hourglass Nebula was discovered by Margaret Walton Mayall and Annie Jump Cannon from photographs taken during 1938-1939 with telescopes located in Bloemfontein, South Africa. Its enigmatic beauty was only revealed much later by the Hubble Space Telescope in 1995 and soon drew widespread attention amongst the wider public, gracing the covers of the April 1997 issue of National Geographic and Pearl Jam’s 2000 album Binaural (Fig. 1). Now in 2018, the Southern African Large Telescope has finally proved the long suspected binary nature of its central star.

Continue Reading

Inauguration of the MeerLICHT telescope

On Friday May 25 – Africa Day 2018 – a new telescope has been inaugurated at the South African Astronomical Observatory (SAAO), near Sutherland, that will be an “eye of the MeerKAT radio array”, the country’s precursor to the Square Kilometre Array (SKA)

MeerLICHT, which means “more light” in Dutch, is an optical telescope that will simultaneously scan the Southern Skies together with MeerKAT. This creates a truly unique combination where astronomers will always be studying stars and galaxies in two parts of the spectrum at the same time.

The project is a Dutch – South African – United Kingdom collaboration involving researchers from six different institutes from the respective partner countries. It was decided to launch it on Africa Day to recognise and celebrate both our incredible African skies and the important partnerships between Europe and Africa that have led to this innovation.

MeerLICHT is a good example of projects aligned to the objective of the Multi-wavelength Astronomy (MWA) strategy, which was approved by the Department of Science and Technology (DST) in 2015.

The aim of the MWA strategy is to forge closer ties between radio, optical and gamma-ray astronomy communities and facilities to work together to achieve common scientific objectives and develop human capital.

Speaking at the inauguration of the telescope on Friday, the DST Director-General, Dr Phil Mjwara, said South Africa had chosen astronomy as the field of science to show its abilities in research on a global scale, to bolster technological development in the fields of telecommunication, Big Data and large-scale computing, and as the field best able to bring science to the people.

“MeerLICHT is also foreseen to play an important role in the astronomical education of people in southern Africa. The project team also hopes that the MeerLICHT project can grow into a stepping stone to allow other southern African countries to share in humanity’s fascination of the night sky,’ said Dr Mjwara.

Among the chief scientific goals of MeerLICHT is the study of stellar explosions, which need to be investigated intensely before they fade away again. “The study of exploding stars across the Universe will gain a whole new dimension”, states University of Cape Town Prof. Patrick Woudt, co-principal investigator of the MeerLICHT telescope.

The MeerLICHT telescope was purpose-built to combine excellent resolution with a wide field of view. It sees more than 13x the Full Moon while being able to see objects one million times fainter than is possible with the naked eye.

The telescope achieves this amazing combination by coupling a 65cm diameter main mirror with a single 100 megapixel detector, which is a full 10cm x 10cm in size. This camera uses the largest single detector used in optical astronomy anywhere in the world. The telescope was designed and built in the Netherlands, and then shipped to South Africa.

“We started work on the technical definition of this telescope back in 2012, and it is fantastic to see what amazing views it produces”, adds Radboud University Prof. Paul Groot, co-principal investigator.

The link with the MeerKAT radio array has astronomers across the world excited about the new combination. “For us, it was the reason to join this consortium. Flashes of radio emission known as Fast Radio Bursts may now be ‘caught in the act’ by both MeerKAT and MeerLICHT”, explains University of Manchester’s Prof. Ben Stappers, MeerLICHT collaborator, and leader of the MeerTRAP project.  “ Hopefully we can finally determine the origin of these enigmatic flashes”.

Prof. Rob Fender, of the Universities of Oxford and Cape Town, co-principal investigator of the telescope, was excited about the inauguration and beginning of operations of the telescope. “This is the beginning of a new phase of coordinated multi-wavelength research into the most extreme astrophysical events” , he said.

“Besides extreme astrophysics, typically associated with black holes and neutron stars, we will also study normal stars, in particular those that produce strong flares” adds Prof. Rudy Wijnands of the University of Amsterdam, “The simultaneous optical-radio monitoring of these stars will allow us to investigate the impact of such flares on the habitability of the planets around them.”

The MeerLICHT telescope will be housed at the Sutherland Observatory, run by the South African Astronomical Observatory. “MeerLICHT directly links the whole optical observatory, and especially our 10 meter SALT telescope, to the MeerKAT array. It fits perfectly in our strategy to turn the Sutherland Observatory into an efficient transient machine to study the dynamic Universe”, adds Dr. David Buckley of the South African Astronomical Observatory.

MeerLICHT is a South African – Netherlands – United Kingdom collaboration involving researchers from six different institutes from the respective (SKA) partner countries. The MeerLICHT consortium is a partnership between Radboud University Nijmegen, the University of Cape Town, the Netherlands Organisation for Scientific Research (NWO), the South African Astronomical Observatory (SAAO), the University of Oxford, the University of Manchester and the University of Amsterdam, in association with the South African Radio Astronomy Observatory (SARAO), the European Research Council and the Netherlands Research School for Astronomy (NOVA). The SAAO and SARAO are National Facilities of the National Research Foundation (NRF). The detector’s cryostat was built at the KU Leuven, Belgium.

 

Continue Reading

Dodging Asteroids

On a regular basis, various space debris, including sometimes threatening asteroids, comes close to or impacts the Earth. For example, in October 2017 asteroid 2012 TC4 passed by the Earth approximately 1/8th the distance between us and the moon. While this event did not present a threat, because there was no impact and because 2012 TC4 was only about 10 meters in diameter so would have burnt up in the atmosphere if it did enter, questions arise as to how to deal with asteroids that are more menacing and pose a risk of great harm. Dr. Nicolas Erasmus, an astronomer here at the South African Astronomical Observatory (SAAO), is co-author of a recently published paper that tries to address this problem.

In July 2016 Dr. Erasmus attended the Frontier Development Lab hosted by NASA’s Ames Research Center and SETI in Mountain View, California. The six-week workshop brought together planetary scientists and machine-learning experts to tackle various challenges that involve asteroids. As part of a team of four, Dr. Erasmus and his fellow team members were posed the following dilemma: “Could mankind deflect a hazardous asteroid on a crash course with Earth and if so which method would give us the best chance?”. To answer this, the team worked together to create a machine-learning algorithm called the “Deflector Selector”, which can be used to study a given population of potentially hazardous objects and then determine which technology has the best chance of deflecting them from Earth’s path.

To train the algorithm, a simulation of millions of hypothetical asteroids with the potential to hit the Earth was created. For each hypothetical impact, they simulated how far in advance of the collision it could be detected and the velocity change to the asteroid which would be required to avoid the collision with Earth. With the aid of this information, the team reviewed the capability of three technologies to induce this velocity change: a nuclear detonation, a kinetic impactor, and a gravity tractor. The technologies each work differently and present different challenges. Nuclear detonations release an explosive force that can impart momentum, which while effective, carries with it the dangers associated with launching nuclear warheads into space. The somewhat less effective kinetic impactor causes a change in momentum by crashing a spacecraft into the asteroid and is technologically the easiest method. Gravity tractors are more subtle and involve hovering a spacecraft near an asteroid, allowing its gravitational pull to nudge the asteroid in a different direction. The latter two technologies currently offer less potent results but have more predictable outcomes. Their effectiveness can also be enhanced with earlier detection and therefore longer lead times.

The benefit of using a machine learning algorithm to solve this dilemma is that while it takes a long time to generate the training data and train the algorithm with this data, it can provide clear answers extremely quickly when given a new unknown impact scenario which mankind might one day face.

A publication describing this work has been accepted by Acta Astronautica journal, and an open-access version of the paper can be downloaded from arXiv.org.

Continue Reading

Observing the fast and the furious: SAAO observes the first optical counterpart of a Gravitational Wave source

Following on from the major global announcement in October 2017 on the discovery of the first electromagnetic counterpart of a gravitational wave source, named GW170817, this new paper has just been published on observations undertaken at the South African Astronomical Observatory (SAAO), which are compared to the latest model predictions.  On 16 October 2017,the  SAAO, together with many other observatories world-wide, announced the important discovery of the first gravitational wave source counterpart (see: http://www.saao.ac.za/press-release/salt-and-saao-telescopes-investigate-the-origin-of-the-first-detection-of-gravitational-waves-produced-by-two-colliding-neutron-stars/). The preliminary results from the Southern African Large Telescope (SALT) and other telescopes at the SAAO were featured in a number of multi-institutional investigations utilizing a range of global facilities.

This recent paper brings together various observations made at the South African Astronomical Observatory (SAAO) to improve upon the original estimates of the luminosity of the remnant kilonova and compares the observations with recent models developed by a Japanese team. Lead author, Dr David Buckley, explains: “Our SALT spectroscopic results were improved upon by using simultaneous observations of the kilonova’s brightness at three different wavelengths using the MASTER-SAAO facility.”

The MASTER-SAAO is a southern hemisphere node of a global network of small robotic telescopes, operated from Russia, used to discover and observe “transient” events in the Universe. These include counterparts to gravitational wave sources and gamma ray bursts. The MASTER-SAAO observations were used to more accurately estimate the flux measurements made by SALT. These were then compared to recently published models. “It was fortuitous that only a matter of a few months before the observations, a preprint of a new paper on kilonova models was posted. I contacted the lead author, Professor Masaomi Tanaka of the National Astronomical Observatory of Japan (NAOJ), who kindly shared the detailed results in order for us to compare our results with these models”, says Buckley.

This allowed a direct comparison with the observations made in the optical with SALT and MASTER-SAAO and in the infrared with the Japanese Infrared Survey Facility (IRSF), also situated at the SAAO observatory site, near Sutherland. The results were very interesting, showing that the kilonova evolved rapidly, over a matter of days, from a very blue to a red object, pretty much as the models predicted. “I was quite struck by the matching of the observations to the predictions in the blue part of the spectrum”, explained Buckley, “using the just the known distance of the host galaxy. No other parameters needed tweaking.”

This initial blue component, which disappeared after about two days, was consistent with ultraviolet observations made at an earlier time by the Swift satellite. The South African Astronomical Observatory (SAAO) observations, taken over a period of about nine days, showed broad agreement with the predictions of the new kilonova models. These show a rapid reddening of the spectra over timescales of days. The results confirmed the conclusions of other investigators that the kilonova explosion, resulting from the rapid (less than a minute) merger of two neutron stars in orbit about each other, resulted in the ejection of a fast (5% to 10% the speed of light) outflow of material, which was observed at a high angle to the orbital plane of the neutron stars.

It was only through good fortune that the SALT observations were able to be undertaken. The information on the position of the optical counterpart to GW170817, crucial for any SALT follow-up, was only received several hours before the telescope could observe, from the US and Australian co-authors. As Dr Petri Väisänen, also one of the papers co-authors and the SALT astronomer observing that night commented, “After a flurry of messages and emails that afternoon in Sutherland, I finally got the coordinates in time to make the observation, which was only just reachable by SALT during the twilight. The Southern African Large Telescope was only the third observatory worldwide to provide a spectrum of the target, showing the anomalous behaviour and proving that this was no run-of-the-mill transient event.”

Once the target position had been determined a SALT target-of-opportunity observation was then undertaken using Director’s Discretionary Time. The first SALT observation was taken one and half days after the initial gravitational wave trigger. This delay was due to the time it took other imaging telescopes to survey the large area where the event occurred in order to locate its optical counterpart.  SALT was able to take one more observation, on 19 August, before it was well and truly lost as the kilonova faded rapidly and was overwhelmed by the bright twilight sky.

“We were really fortunate that the event did not happen two days later, otherwise we would never have had the opportunity to observe it with SALT”, says Väisänen. The SAAO and SALT had been poised for some time to make such an observation, since the original discovery of the first gravitational wave event in September 2015. Dr Stephen Potter, the SAAO astronomer with responsibility for attempting follow-up observations of gravitational wave sources expressed his delight at the results, “I had heard from one of our Chinese collaborators about the event and was in contact with David Buckley, who is principal investigator of the SALT transient programme, about triggering a SALT observation, once an accurate position was determined. We were getting rather desperate at the prospects of getting a precise enough position in time for a SALT observation. But in the end it came in the nick of time and we did it”

As it happened, Buckley was attending a conference on transients in Russia, when the news arrived of the detection of GW170817. However, it was only the following day, when he was travelling home, that the final all-important positional information became available. Other co-authors were able to ensure that the observations were undertaken and the data reduced quickly. Owing to the quick response of SALT and other SAAO telescopes, crucial information on the nature of the gravitational wave source was obtained. These have resulted in the publication of 8 refereed papers containing observations conducted at the South African Astronomical Observatory with the three different telescopes (SALT, MASTER-SAAO and IRSF), including the paper which is the subject of this press release.

The detection of an electromagnetic counterpart to a gravitational wave source, coming only two years after the first gravitational wave detection, bodes well for the study of future gravitational wave neutron star merger events. The ability of SALT to respond promptly and appropriately to transient alerts, in this case the GW170817 event, is one reason for the success of the observations reported here and will hopefully result in similar successes in the future.

[This Saturday, 27 January at 20h00, Dr David Buckley will be delivering a public lecture titled “Gravitational Waves: the new frontier in Astronomy”.]

LINK to the paper:

Monthly Notice of the Royal Astronomical Society, Volume 474, L71-75 (2018)- https://doi.org/10.1093/mnrasl/slx196
Continue Reading

SAAO helps to reveal the origins of fundamental structures in the wind of the supergiant star Zeta Puppis

A Canadian-led international team of astronomers recently discovered for the first time observational evidence in how some features at the surface of the hot massive supergiant star Zeta Puppis induce the formation of fundamental structures in its wind. The research team used the network of nano satellites of the BRIght Target Explorer (BRITE) mission to […]

Continue Reading

SALT and SAAO telescopes investigate the origin of the first detection of gravitational waves produced by two colliding neutron stars.

      

SALT and SAAO telescopes partake in an unprecedented international collaboration to investigate the origin of the first detection of gravitational waves produced by two colliding neutron stars.

The discovery marks the birth of a new era in astrophysics, the first cosmic event observed in both gravitational waves and light.  SALT and other SAAO telescopes have provided some of the very first data in what is turning out to be one of the most-studied astrophysical events ever.

The South African Astronomical Observatory (SAAO) and the Southern African Large Telescope (SALT) are among the 70 ground- and space-based observatories that observed the cataclysmic explosion of two colliding neutron stars, immediately after their gravitational shock waves were detected by the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European-based Virgo detector.

Neutron stars are the smallest, densest stars known. They are the remains of massive stars which exploded as supernovae. In this particular event, dubbed GW170817, two such neutron stars spiralled inwards and then collided, emitting gravitational waves that were detectable for about 100 seconds. The collision also resulted in a kilonova explosion of light, initially in the form of gamma rays which were detected by space-based telescopes.  The gamma rays were then followed by X-rays, ultraviolet, optical, infrared, and radio waves.

This allowed astronomers to localise the event within hours and launch follow-up observations by SALT and numerous other telescopes in South Africa and around the world.  South African activities also included the first observations contributing to published scientific results by the MeerKAT radio telescope under construction in the Karoo.

Gravitational waves from colliding black holes were first detected only two years ago, and have been detected three more times since then, leading to the 2017 Nobel Prize in Physics being awarded to three US scientists. Black hole collisions, however, are not expected to emit light.  GW170817 is the first time light and gravitational waves from the same event have been observed.

The significance of the present event lies in the combination of the gravitational waves and light.   “Imagine you have only one sense”, explains Petri Vaisanen, Head of SALT Astronomy Operations, who was the observer at SALT during the frantic search for the counterpart for the gravitational wave event.  “All your life you have merely looked at the world.  Two years ago you heard something, voices coming from somewhere around you.   But then, suddenly, you actually see someone talking. How much more will you understand about how the world works when you put those together?  Immensely more.  That to me sums up the momentous discovery, and hints at the possibilities going forward.”

August 18, 2017, the day and night following the LIGO detection and the initial successful searches in Chile for the counterpart, was a busy day for observational astronomers.  “After a flurry of messages and emails that afternoon in Sutherland, I finally got the coordinates”, continues Vaisanen.  “There was a new object, which had caused the whole of space-time to ripple, sitting at the outskirts of the galaxy NGC 4993 some 130 million light-years away.  I knew that everyone with a working telescope in the Southern Hemisphere was scrambling to get data on it.  We decided to drop all other plans for that evening, and went for a spectral observation with SALT, since you need a large telescope for such observations breaking up the light into all its colours.  It was a difficult observation since we had to do it in twilight, before it got properly dark.  I’m very proud of the whole team, SALT was only the third observatory to provide a spectrum of the target, and the first spectrum that clearly started showing anomalous behaviour proving that this was no run-of-the-mill transient event”.  

The significance of getting early observations stems from the afterglow of the collision changing very rapidly.  Piecing together the new science from the event requires combining observations spanning the first hours, days and weeks after the merger.  The first SALT spectrum has a very prestigious spot in the combined scientific paper, with thousands of authors and hundreds of institutions. In addition, several, more detailed scientific papers have also been written based on SALT, SAAO and other Sutherland observations.

“Finally, the irony of the moment for me, anxiously sitting at the telescope that evening looking at the new object, was that just three weeks before I had attended a meeting discussing the future of optical searches of gravitational waves and the SAAO part in it.  There were arguments that it could be decades before we are able to localise such events well enough for observations, and it would probably not be worth expending the effort.  It’s amazing how quickly things change.”

Sutherland telescopes reveal the details of the neutron star merger

Theorists have predicted that what follows the initial collision is a “kilonova” explosion— a phenomenon by which the material that is left over from the neutron star collision, which glows with light, is blown out of the immediate region, far out into space. The light-based observations from other large international telescopes show that heavy elements, such as lead and gold, are created in these collisions and subsequently distributed throughout the universe – confirming the theory that a major source for the creation of elements heavier than iron does, indeed, results from these neutron star mergers.

MASTER-Net full frame composite of GW170817 (Credit: MASTER-Net/NRF/SAAO)

The early SALT observations showed that the explosion was relatively bright and blue. Only two or three days later, further observations by SALT, SAAO and other major international telescopes showed that the light was rapidly fading and turning red, due to the dusty debris blocking the bluer light, as predicted by the theory of the evolution of a kilonova explosion. Simultaneously, MASTER (a joint Russian-South African optical telescope located in Sutherland) and  IRSF (Infra-Red Survey Facility; a joint Japanese-South African infrared telescope also in Sutherland) continued to monitor GW170817 for two weeks, showing that it gradually faded in the visible light but brightened in the infrared, consistent with the final stages of the afterglow from the surrounding debris.

The results of this unprecedented event have demonstrated the importance of collaborative multi-messenger observations and mark a new era in astronomy. “The ability of SALT and SAAO telescopes to respond rapidly to unexpected discoveries is a major reason for the success of these observations and will ensure similar successes in the future”, says Dr Stephen Potter, Head of Astronomy at the SAAO. “We are very proud to have played a major role in such a historical event thanks to the sterling efforts and expertise of SAAO and SALT staff who ensure that our observatory is at the forefront of world-class scientific endeavours.”

LIGO Press Release:   https://www.ligo.caltech.edu/page/press-release-gw170817

Multi-Messenger paper:  http://iopscience.iop.org/article/10.3847/2041-8213/aa91c9/meta

MeerKAT Press Release:  http://www.ska.ac.za/media-releases/meerkat-makes-its-debut-scientific-contribution-on-an-international-collaboration-and-major-discovery/

 

The South African Astronomical Observatory is funded by the National Research Foundation. For more information about SAAO : www.saao.ac.za

About the NRF: The National Research Foundation (NRF) was established on 1 April 1999 as an independent statutory body in accordance with the National Research Foundation Act. The NRF is a key public entity responsible for supporting the development of human resources for research and innovation in all fields of science and technology. The organisation is one of the major players in educating and training a new generation of scientists able to deal with South African and African needs. The organisation encourages public awareness and appreciation of science, engineering and technology, and facilitates dialogue between science and society. Its vision is to contribute to a prosperous South Africa based on a knowledge economy. For more information on the operations and programs within the NRF please visit www.nrf.ac.za

About SALT: The Southern African Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere and among the largest in the world. It has a hexagonal primary mirror array 11 metres across, comprising 91 individual 1m hexagonal mirrors. For more information about SALT please visit www.salt.ac.za

 

Continue Reading

CCD work begins on the WiNCam instrument

In the past week, a milestone was reached on the WiNCam (Wide-field Nasmyth Camera) instrument. This is an imaging camera system to be mounted on the new 1-m Lesedi telescope in Sutherland. It allows a wide field of imaging, 43-arcmin diameter, with a standard suite of astronomical filters. Notably, this is the largest charge-coupled device […]

Continue Reading

Discovery of one of the most luminous eruptions from a dying star: SALT contributes to a major international multi-wavelength effort led by South Africa.

A multinational group of astronomers have discovered what it might be the brightest nova (a luminous stellar eruption) ever observed. This mighty eruption was first detected on the 14th of October 2016 by the MASTER-instrument in Argentina. Since then it has attracted the interests of astronomers around the world, who have pointed their ground-based and space telescopes, in an attempt to understand the different aspects of the eruption.

Novae are actually binary stars, involving a white dwarf (dead star) pulling material from a close companion star that is very similar to the Sun. The material transferred to the white dwarf builds up on its surface leading to an increase in the pressure and density. When the pressure and density reach a critical stage, a thermonuclear eruption is triggered on the surface of the white dwarf equivalent to a million hydrogen bombs. During the eruption, the brightness of the star increases dramatically sometimes appearing as a new naked-eye star in the night sky hence the name nova or “new star”. The system survives the eruption and after a year or so from the nova event, the white dwarf resumes pulling material from its donor.

The new study led by Elias Aydi, a PhD student jointly affiliated with the South African Astronomical Observatory (SAAO) and the University of Cape Town (UCT), has been accepted for publication in the Monthly Notices of Royal Astronomical Society journal today. The study is based on optical observations from the Southern African Large Telescope (SALT) in Sutherland (South Africa), MASTER-instruments in Sutherland and Argentina, the Las Cumbres Observatory (LCO) telescope in Australia, the SMARTS, OGLE, and SOAR telescopes in Chile, and X-ray and ultraviolet observations from the Swift satellite.

The newly discovered very bright nova, named SMCN 2016-10a, is located toward the Small Magellanic Cloud (SMC), a small galaxy near the Milky Way, at a distance of around 200,000 light years away from us. When a Nova eruption takes place, the brightness of the star increases in a matter of a few days to reach a maximum and then decreases gradually. Nova SMCN 2016-10a reached a maximum brightness no previous nova in the SMC has ever attained. It is also at least as bright as Nova CP Pup and nova V1500 Cyg, the two brightest novae ever observed. “We are very excited to discover such extreme events which occur only rarely, especially in the SMC,” said the study’s leading author Elias Aydi. He then adds, “a combination of several factors such as the mass of the white dwarf, its temperature and chemical composition might be responsible for such a luminous eruption”. Despite the extreme brightness of the eruption, at a distance of 200,000 light years in a neighbouring galaxy, it is not possible for our naked eyes to see the nova. Such a distance also means that the eruption took place around 200,000 years ago and the light has just reached us now.
According to Aydi, “we used observations from the MASTER-instruments at Sutherland and Argentina along with the SMARTS telescope to estimate the maximum brightness reached during the eruption leading us to the main conclusion.” After its unprecedented peak brightness, the brightness of Nova SMCN 2016-10a decreased quickly in a matter of few days which tells us that the white dwarf is quite massive, probably about 1.3 times the mass of the Sun. The study co-author Patricia Whitelock, from the SAAO and UCT, stated that “In such systems, if the white dwarf keeps soaking up matter and grows beyond 1.4 times the mass of the Sun, there is a good chance that it will detonate in a really big explosion, what we call a supernova, blowing up both of the stars and anything else that gets in the way.”
SAAO astronomer, and co-author, Dr. David Buckley, explained how “The SALT high-resolution spectroscopy along with other data from the Las Cumbres Observatory have helped us understand the material involved in the eruption and even to measure their speeds, which reached just under a million kilometre per hour.” Buckley also elaborated on the ability of SALT, the biggest single optical telescope in the south, to follow up rapidly on such events providing us with particularly high-quality data.

According to study co-author Kim Page, an astronomer from the Swift satellite team and the University of Leicester in the UK, “Swift’s ability to respond rapidly, together with its daily planned schedule, makes it ideal for the follow-up of transients, including novae. We were able to follow Nova SMCN 2016-10a throughout its eruption, starting to collect very useful X-ray and UV data within a day of the eruption being reported.” The X-ray observations were essential to constrain the mass of the white dwarf in the system.

Nova events are frequently observed in the Milky Way with a rate of around 35 eruptions per year, but they are much rarer in the SMC. Nova SMCN 2016-10a is the first nova to erupt in the SMC since 2012, which adds importance to the event. From the Mullard Space Science Laboratory of the University College London, study co-author Paul Kuin says that “the present observations provide the kind of coverage in time and in spectral colour coverage what is needed to make progress in gaining an understanding of a nova in the neighbouring galaxy.” Kuin emphasizes that “Observing the nova in different wavelengths using world-class telescopes such as Swift and the SALT help us reveal the condition of matter in nova ejecta as if it were nearby.”
For more information contact:
Elias Aydi
email: eaydi@saao.ac.za
phone: +27 (0)21 460 9302
South African Astronomical Observatory and the University of Cape Town.

Dr. David Buckley
email: dibnob@saao.ac.za
phone: +27 (0)21 460 6286

The article can also be found on https://arxiv.org/abs/1710.03716

Other authors on this study include:
M. J. Darnley from Liverpool John Moores University, F. M. Walter from Stony Brook University, P. Mróz & A. Udalski from Warsaw University Observatory, S. Mohamed from the South African Astronomical Observatory and the University of Cape Town, P. Woudt from the University of Cape Town, S. C. Williams from Lancaster University and Liverpool John Moores University, M. Orio from the INAF–Osservatorio di Padova and the University of Wisconsin, R. E. Williams from the Space Telescope Science Institute (Baltimore), A. P. Beardmore and J. P. Osborne from the X-ray and Observational Astronomy Group – University of Leicester, A. Kniazev from the SALT, the South African Astronomical Observatory and the Special Astrophysical Observatory of RAS, V. A. R. M. Ribeiro from Universidade de Aveiro, University of Santiago and Botswana International University of Science & Technology, J. Strader and L. Chomiuk from Michigan State University.

Continue Reading

Recovery of nova spotted by ancient Koreans illuminates many stages of star system’s life cycle

On a cold March night in Seoul almost 600 years ago, Korean astronomers spotted a bright new star in the tail of the constellation Scorpius. It was seen for just 14 days before fading from visibility. From these ancient records, modern astronomers determined that what the Royal Imperial Astronomers saw was a nova explosion, but they have been unable to find the binary star system that caused it—until now.

The new study, published in the journal Nature today, is based on observations from the Southern African Large Telescope (SALT)  and the SAAO 1-meter telescope in Sutherland, Northern Cape, as well as the Las Campanas Observatories’ Swope and Dupont telescopes in Chile. The study pinpoints the location of the old nova, which now undergoes smaller-scale “dwarf nova” eruptions. The work supports the idea that novae go through a very long-term life cycle after erupting, fading to obscurity for thousands of years and then building back up to become full-fledged novae once more.

“This is the first nova that’s ever been recovered with certainty based on the Chinese, Korean, and Japanese records of almost 2,500 years,” said the study’s lead author Michael Shara, Chair of the SALT Board and a curator in the American Museum of Natural History’s Department of Astrophysics.

A nova is a colossal hydrogen bomb produced in a binary system where a star like the Sun is being cannibalized by a white dwarf—a dead star. It takes about 100,000 years for the white dwarf to build up a critical layer of hydrogen that it steals from the sun-like star, and when it does, it blows the envelope off, producing a burst of light that makes the star up to 300,000 times brighter than the sun for anywhere from a few days to a few months.

For years, Shara has tried to pinpoint the location of the binary star that produced the nova eruption in 1437, along with Durham University’s Richard Stephenson, a historian of ancient Asian astronomical records, and Liverpool John Moores University astrophysicist Mike Bode. Recently, they expanded the search field and found the ejected shell of the classical nova. They confirmed the finding with another kind of historical record: a photographic plate from 1923 taken at the Harvard Observatory station in Peru and now available online as part of the Digitizing a Sky Century at Harvard (DASCH) project.

“With this plate, we could figure out how much the star has moved in the century since the photo was taken,” Shara said. “Then we traced it back five centuries, and bingo, there it was, right at the center of our shell. That’s the clock, that’s what convinced us that it had to be right.”

Other DASCH plates from the 1940s helped reveal that the system is now a dwarf nova, indicating that so-called “cataclysmic binaries”—novae, novae-like variables, and dwarf novae—are one and the same, not separate entities as has been previously suggested. After an eruption, a Nova becomes “nova-like,” then a dwarf nova, and then, after a possible hibernation, comes back to being nova-like, and then a nova, and does it over and over again, up to 100,000 times over billions of years.

To get a better look at the present state of the binary system, Joanna Mikołajewska and Krystian Iłkiewicz, from the Copernicus Astronomical Center of the Polish Academy of Sciences, obtained several SALT spectra of the binary and the shell.  These data allowed them to identify the white dwarf companion and to determine its temperature and distance, to constrain the binary components’ masses, as well as to estimate the temperature, density and mass of the shell.

In August 2016, photometric monitoring of the system was carried out with three telescopes, and in particular, by Lisa Crause with the SAAO 1-meter telescope.  These observations revealed deep eclipses which allowed the team to very accurately derive the system’s orbital period.  In addition, the SAAO photometry (obtained over 11 days) demonstrated that the white dwarf rotates with a period of 1859 sec, the same periodicity that is present in X-ray observations.

According to Crause, “We knew from the data obtained in Chile that we were dealing with an eclipsing system, but since we didn’t know the orbital period, each night’s data from the 1-metre amounted to an additional piece of the puzzle.  After collecting light curves on several nights and putting all the data together we could work out the period – a key parameter for understanding the binary system.”

“In the same way that an egg, a caterpillar, a pupa and a butterfly are all life stages of the same organism, we now have strong support for the idea that these binaries are all the same thing seen in different phases of their lives,” Shara said. “The real challenge in understanding the evolution of these systems is that unlike watching the egg transform into the eventual butterfly, which can happen in just a month, the lifecycle of a nova is hundreds of thousands of years. We simply haven’t been around long enough to see a single complete cycle. The breakthrough was being able to reconcile the 580-year-old Korean recording of this nova event to the dwarf nova and Nova shell that we see in the sky today.”

http://www.nature.com/nature/journal/v548/n7669/full/nature23644.html?foxtrotcallback=true

Other authors on this study include K. Ilkiewicz, J. Mikolajewska, and K. Drozd from the Polish Academy of Sciences; Ashley Pagnotta, Jackie Faherty, and D. Zurek from the American Museum of Natural History; L.A. Crause from the South African Astronomical Observatory; I. Fuentes-Morales and C. Tappert from the Instituto de Fisica y Astronomia; J.E. Grindlay from the Harvard-Smithsonian Center for Astrophysics; A.F.J. Moffat from the Universite de Montreal; M.L. Pretorius from the South African Astronomical Observatory and the University of Cape Town; and L. Schmidtobreick from the European Southern Observatory.

Funding for this study was provided in part by the Polish NCN grant #DEC-2013/10/M/ST9/00086, the National Sciences and Engineering Research Council of Canada, FQRNT (Quebec), and the American Museum of Natural History’s Kathryn W. Davis Postdoctoral Scholar program, which is supported in part by the New York State Education Department and by the National Science Foundation under grant #s DRL-1119444 and DUE-1340006. 

Continue Reading

Catching a Glimpse of New Horizons

In the early hours of the morning on 03 June 2017, while most locals are sleeping, dozens of astronomers across South Africa will be looking up at the night sky in hopes of viewing a shadow from a mysterious, distant object.  They are part of a large, international effort to study the target of NASA’s New Horizons spacecraft extended mission.  New Horizons stunned the world in 2015 when it passed through the Pluto system and returned unprecedented images and information about Pluto and its five moons.  The extended mission will allow the spacecraft to collect data on an even more remote object, called 2014MU69 (Figure 1).

2014MU69 was discovered by the Hubble Space Telescope. It is dynamically classified as a classical Kuiper Belt object.  Because it is very faint, with a  26.3 visual magnitude, little is known about its physical properties.  A stellar occultation, during which the light of a distant star is blocked by 2014MU69, has been predicted to be observable from specific regions of the Southern Hemisphere on 03 June (Figure 2).  If successfully observed, this fleeting event could allow measurement of 2014MU69‘s size and shape, could detect rings, dust or debris, and could improve the positional accuracy, all of which would be vital information for planning the spacecraft encounter.  2014MU69 is located nearly 6.5 billion kilometers away with an estimated diameter of approximately 40 km, and the entire occultation will only last roughly 2 seconds. Thus, the observers need to be in exactly the right place, at the right time, with the right equipment to detect the brief dip in the starlight.

To optimize the likelihood of successful observing opportunities (and to avoid bad weather!), observers will be stationed in South Africa, Namibia, Chile, Brazil, Uruguay, and Argentina. Locally, SAAO observers will be using both the 74-inch telescope and the three Las Cumbres Observatory telescopes in Sutherland.  Multiple members of the ASSA (Astronomical Society of South Africa) are also contributing to the effort.  In Southern African alone, there are roughly three dozen overseas visitors who pre-shipped more than a dozen portable telescopes and specialized cameras (Figure 3).

“It is impressive to have so many people visiting South Africa and to see the amount of effort put in to taking the data. It’s a particularly challenging observation that can’t be done without international collaborators. If we are successful, this will be an occultation observation by the faintest object ever and will allow new, accurate measurements to help support New Horizons,” says Anja Genade, an SAAO/UCT student in the NASSP program whose research involves stellar occultations.

Currently, the spacecraft is approximately halfway between Pluto and 2014MU69, and it is scheduled to fly by the target on 01 January 2019. This will be the most distant Solar System object ever encountered by a spacecraft.  Pluto was revealed to be a dynamic, exciting object by New Horizons, and we are sure to expect further surprises and enlightenments from the extended mission as it explores the edge of our Solar System.

Continue Reading