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SALT plays key role in the global hunt for Dark Energy

The Southern African Large Telescope (SALT), the largest optical telescopes in the Southern Hemisphere, has played an important role as part of the international Dark Energy Survey’s (DES, https://www.darkenergysurvey.org/) quest to pin down dark energy, the mysterious force accelerating the expansion of the universe.

As part of the hunt, SALT conducted follow-up spectroscopy of supernovae – stars that explode at the end of their lives – discovered by DES. Supernovae are so bright that they can be seen on the other side of the Universe and astronomers can accurately calculate the distances to a small subclass of them – the so-called Type Ia supernovae. Once their distances are known, Type Ia supernovae can be used to measure the acceleration of the expansion of the universe. Sorting through the chaff of variable objects to find and classify the Type Ia jewels was the important role undertaken by SALT and several other of the world’s biggest telescopes.

Zoomed-in image of the supernova, highlighting it in one of the host galaxy’s spiral arms. For a brief time, the supernova can be as bright as the 100 billion stars of the host galaxy.
Image Credit: SALT/SAAO

“To measure the acceleration of the universe’s expansion by studying stars that died hundreds of millions of years ago takes the most powerful telescopes in the world, combined with meticulous analysis. SALT has provided a key contribution to the international Dark Energy Survey, the most sophisticated study of dark energy with supernovae yet” said Dr. Eli Kasai, former PhD student at SAAO, now lecturer at the University of Namibia, and Principal Investigator for the South African Astronomical Observatory DES program from 2014 to the end of the survey in 2018.

“We need to control systematic uncertainties to very high precision so that we have confidence in our conclusions. SALT, with its massive mirror and ability to rapidly target exciting new candidates, allows us to take a confirming spectrum when the supernova candidate is at its brightest. This translates into clean answers to exactly what kind of exploding star we are looking at.”, said Dr. Mathew Smith, who is based at Southampton University and was the PI of the SALT spectroscopic follow-up program of DES supernova candidates from 2013 to 2014.

DES began science observations in 2013, in Chile, South America, with an overall goal of measuring the expansion history of the Universe in order to place tight constraints on the quantity and properties of dark energy at an accuracy of about 1%. DES employs several methods of constraining dark energy, of which supernova observations, are a primary tool.

“20 years ago we discovered Dark Energy and the acceleration of the universe by carefully observing supernovae. Today, two decades later, dark energy is still one of the great mysteries of our time. These results, with the purest sample of supernovae to date, confirm yet again that dark energy is real, and will be a key target of investigation for the Square Kilometre Array (SKA), that will be built primarily in South Africa.” said Professor Bruce Bassett, a member of the SALT DES supernova follow-up program, astronomer at SAAO and head of the Data Science group at the South African Radio Astronomical Observatory (SARAO). SARAO has recently completed construction of the MeerKAT radio telescope that will form an important part of the Square Kilometre Array.

“Dark Energy is perceived to exist in the vast empty spaces between galaxies in the Universe known as voids and we believe that it is responsible for making galaxies move away from each other at ever-increasing speeds. In other words, it is responsible for the accelerated expansion of the Universe that we observe” said Prof. Roy Maartens, an SKA Chair in Astrophysics and Cosmology at the University of the Western Cape and a member of the SALT DES supernova follow-up program. He went on saying “observing more and more supernovae in many galaxies gives us a handle to quantify the properties of dark energy and also provides us insight into the true nature of supernovae”.

SALT consistently played a pivotal role of classifying into various types the discovered supernova candidates and successfully determining how far they were from Earth, two important parameters that were key to the success of the DES experiment, which came to an end at the end of February 2018. Spectral observations of the discovered SN candidates by SALT and other spectroscopic capable telescopes in DES played a crucial role in helping algorithms that could classify the discovered supernova candidates and determine their redshift using only the images in which such candidates were discovered. This type of classification and redshift determination is less accurate in comparison to that performed with spectroscopic data from SALT and other spectroscopic capable telescopes.

“The DES team has independently confirmed the existence of dark energy by combining four different cosmic probes: (1) supernova observations, (2) baryonic acoustic oscillations, (3) weak gravitational lensing and (4) galaxy clustering”, said Dr Eli Kasai. He continued by saying “The conclusions from DES from combining these four probes mean that for the first time we have been able to find strong evidence for cosmic acceleration and dark energy from a single experiment, instead of combining results from many different telescopes and different analyses.”

The past three weeks have seen the release of 8 DES papers to Arxiv.org, reporting the findings of the analyses of DES supernova data observed over the first three years of the survey. The papers made use of the survey’s spectroscopic data including that taken with SALT.

https://arxiv.org/search/astro-ph?query=Bassett+kasai&searchtype=author&abstracts=show&order=-announced_date_first&size=50

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SALT contributes to the discovery of a bingeing white dwarf

A new binary star system has been discovered in which a small white dwarf star is cannibalising its larger Sun-like companion. Such objects are actually quite common, but for this new object, the white dwarf binged on its neighbour at a prodigious rate, heating part of it to nearly a million degrees. The object, named ASASSN-16oh, was found on 2 December 2016 by the All-Sky Automated Survey for Supernovae (ASASSN), a network of about 20 optical cameras distributed around the globe which automatically surveys the entire sky every night in search of transient events, objects which suddenly appear. ASASSN-16oh was found to be in the Milky Way’s satellite galaxy, the Small Magellanic Cloud, at a distance of ~200,000 light years.

An artist’s impression of the supersoft X-ray binary system, ASASSN-16oh, with a small white dwarf star (left) accreting hot gas from its Sun-like companion (right), through an accretion disk. The stream of gas from the companion forms a flattened accretion disk and the gas gradually spirals down to the white dwarf, getting hotter as it does so. Eventually, the accreted gas impacts the equator of the white dwarf, heating it up to nearly a million degrees, emitting in soft X-rays.
Image credit: NASA/CXC/M.Weiss

Optical follow-up observations were conducted by the Southern African Large Telescope (SALT), the Polish OGLE telescope in Chile and the Las Cumbres Observatory (LCO) telescope network. It was also discovered to be a so-called “supersoft” X-ray source by the NASA Neil Gehrels Swift Observatory and the Chandra X-ray Observatory, produced by gas at temperatures of ~900,000 degrees. Such supersoft systems have previously always been associated with a thermonuclear runaway explosion on the surface of a white dwarf, as occurs in a hydrogen bomb, brought on by the accumulation of hot and dense accreted gas which eventually reaches a critical explosive limit.

“Supersoft sources are a really interesting class of transient events, and ASASSN-16oh is no exception”, says David Buckley, the Principal Investigator of the SALT Large Science Programme on transients, who is based at the South African Astronomical Observatory. “We were fortunate to be able to react quickly to its discovery and undertake crucial observations during the outburst phase”, he said. “Our SALT spectra showed all the hallmarks of a highly energetic system, with an intensely strong emission line from ionized helium which changed in velocity from night-to-night”, says Buckley. In addition, robotic observations were triggered with the LCO telescopes in South Africa, Chile and Australia, allowing for monitoring over a 34 hour period, beginning on Christmas Day 2016. “A nice Christmas present courtesy of the LCO Director who granted the time”, quipped Buckley. The SALT and LCO data were then quickly analysed by another member of the SALT transients collaboration, Andry Rajoelimanana, at the University of the Free State, in Bloemfontein, South Africa.

It became clear after the optical and X-ray observations were analyzed that ASASSN-16oh was no normal thermonuclear powered supersoft source. “In the past, the supersoft sources have all been associated with nuclear burning on the surface of white dwarfs,” said lead author Tom Maccarone, a professor in the Texas Tech Department of Physics & Astronomy, lead author of the ASASSN-16oh discovery paper that has just appeared in the December 3rd issue of Nature Astronomy.

If nuclear fusion is the cause of the supersoft X-rays from ASASSN-16oh then it should begin with an explosion and the emission should come from the entire surface of the white dwarf. However, the optical light does not increase quickly enough to be caused by an explosion and the Chandra X-ray data show that the emission is coming from a region smaller than the surface area of the white dwarf. The source is also a hundred times fainter in optical light than white dwarfs known to be undergoing fusion on their surface. These observations, plus the lack of evidence for gas expelled away from the white dwarf, provide strong arguments against fusion having taken place on the white dwarf.

Because no signs of nuclear fusion are present, the authors present a different scenario. As with the fusion explanation, the white dwarf pulls gas from its companion star, a red giant, in a process called disk accretion. The gas forms a large flattened rotating disk surrounding the white dwarf, becoming hotter as it spirals inwards, as shown in our illustration. The gas then falls onto the white dwarf, producing X-rays along an equatorial belt where the disk meets the star. The rate of inflow of matter through the disk varies by a large amount and when the rate of mass loss from the companion increases, the X-ray and optical brightness of the system becomes much higher.

“The transfer of mass is happening at a higher rate than in any system we’ve caught in the past,” added Maccarone. If the white dwarf keeps gaining mass it may reach a mass limit and destroy itself in a Type Ia supernova explosion, a type of event which was used to discover that the expansion of the universe is accelerating. The team’s analysis suggests that the white dwarf is already unusually massive, so ASASSN-16oh may be relatively close – in astronomical terms – to exploding as a supernova.

“Our result contradicts a decades-long consensus about how supersoft X-ray emission from white dwarfs is produced,” said co-author Thomas Nelson from the University of Pittsburgh. “We now know that the X-ray emission can be made in two different ways: by nuclear fusion or by the accretion of matter from a companion.”

Also involved in the study were scientists from Texas A&M University, NASA Goddard Space Flight Center, University of Southampton, University of the Free State in the Republic of South Africa, the South African Astronomical Observatory, Michigan State University, Rutgers State University of New Jersey, Warsaw University Observatory, Ohio State University and the University of Warwick.

NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra’s science and flight operations.

Publication Details:

“Unconventional origin of supersoft X-ray emission from a white dwarf binary”

Thomas J. Maccarone, Thomas J. Nelson, Peter J. Brown, Koji Mukai, Philip A. Charles, Andry Rajoelimanana, David Buckley, Jay Strader, Laura Chomiuk, Christopher T. Britt, Saurabh W. Jha, Przemek Mróz, Andrzej Udalski, Michal K. Szymański, Igor Soszyński, Radosław Poleski, Szymon Kozłowski10, Paweł Pietrukowicz, Jan Skowron, Krzysztof Ulaczyk

Nature Astronomy, Volume 2, No. 11, Article Number 2397-3366

https://doi.org/10.1038/s41550-018-0639-1

Full Article Available:

https://rdcu.be/bcmCu

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SALT chases hypervelocity stars

The Southern African Large Telescope(SALT) was recently involved in the identification of a hypervelocity star, flung across the galaxy by a supernova explosion that occurred 90 000 years ago. The discovery of this star and two others may help to solve a decades-old debate on how supernovae occur.

Video animation produced using Gaia Sky showing the path of the hypervelocity star candidate by Shen et al (2018), with its movement exaggerated by a factor of 300 billion times. The path of the candidate is first shown moving forward in time and subsequently going into the past, back to the supernova remnant. The circle indicates the location of the remnant of the supernova G70.0-21.5. Credits: S. Jordan, T. Sagrista

Credits: ESA/Gaia/DPAC, K. Shen, S. Jordan, T. Sagrista

Type Ia supernovae are the thermonuclear explosions of white dwarfs in binary star systems. They are one of the most common types of supernovae and have a fundamental importance as cosmological distance indicators. Despite this, the nature of the binary system and the details of the explosion has remained a mystery. Many theoretical models have arisen over the past few decades to explain how these stars explode, but there have been few pieces of direct evidence that any of these scenarios actually succeeds in nature.

One model, dubbed the “dynamically driven double-degenerate double-detonation” (D6) scenario, predicts the possibility that the other star in the binary system is another white dwarf that can survive the explosion of its companion. Such a surviving star would be flung away from the system when the gravitational pull of its companion disappeared and would continue zipping away at speeds between 1000 – 2500 km/s.

Shen et al. (2018) searched for such hypervelocity survivors in Gaia’s second data release in April 2018 and discovered three likely candidates. These stars were followed up with ground-based telescopes, including the Southern African Large Telescope (SALT), and found to possess many of the predicted features for survivors of D6 Type Ia supernovae: a lack of hydrogen and strong signatures of carbon, oxygen, and magnesium, as well as luminosities and temperatures unlike almost all other stars.  Furthermore, the past location of one of the stars is spatially coincident with a known supernova remnant, making it highly probable that it was ejected from a system that underwent a supernova.

The combination of Gaia, which precisely measured the high-speed motion of these hypervelocity stars in the plane of the sky, and the ground-based spectroscopic observations, which provided a measurement of the radial component of the stars’ motion, has shown that these are among the fastest freely moving stars in our Milky Way Galaxy.

Much follow-up work remains to be done to ascertain precise characteristics of these stars and the explosions that gave birth to their hypervelocity natures. However, it is very likely that these stars represent the first discoveries of surviving companions to Type Ia supernovae, and that they confirm the success of the D6 “dynamically driven double-degenerate double-detonation” model.

The team undertaking the observations and data analysis was led by Ken Shen, a researcher at the University of California at Berkeley (USA). The SALT observations were taken by Marissa Kotze at the Southern African Astronomical Observatory as part of a program led by Saurabh Jha from Rutgers, the State University of New Jersey (USA).

 

Figure 1: Orbital solution of the second white dwarf candidate for the D6-scenario, overlaid with H-alpha images from the Virginia Tech Spectral Line Survey (VTSS, Dennison et al. 1998). The blue trajectory extends 90,000 years into the past, the red trajectory extends the same amount of 90,000 years into the future. The green circle indicates the remnant of the supernova G70.0-21.5. Image credit: Shen et al. (2018)

Figure 2: The three hypervelocity candidates are shown here in the colour-magnitude diagram with the green, blue and orange circles. Some other white dwarfs are indicated in this diagram as well. The black circles and colored regions show the reliably measured stars from Gaia. Image credit: Shen et al. (2018)

The article by Shen et al. was published in the Astrophysical Journal on 20 September 2018.

Additional Links: https://www.cosmos.esa.int/web/gaia/iow_20181119

 

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The General Assembly of the International Astronomical Union to be hosted on African soil for the first time in 2024

Thursday 30 August 2018. Vienna, Austria

The International Astronomical Union (IAU) today announced the 32nd General Assembly of the IAU in 2024 will be hosted by Cape Town, South Africa. This will be the first time in the 105 year history of the IAU that the General Assembly will be held on the African continent. The award recognises the incredible strides that African astronomy has taken in recent years.

The South African astronomical community in collaboration with the Academy of Science of South Africa (ASSAf), and with strong support from the South African Government and astronomy stakeholders across the African continent, last week formally invited the IAU to Africa at the 30th IAU GA currently being held in Vienna, Austria.

Africa has a long and rich relationship with astronomy, dating back millennia. The world recognized the unique geographical importance of Africa in global astronomy almost two centuries ago with the establishment of the Royal Observatory, Cape of Good Hope in 1820. Since then Africa’s contributions to global human knowledge have both independently and collaboratively grown from strength to strength.

The beginning of the 21st century has seen a renewal of Africa’s strong heritage of astronomical excellence. The IAU has held Middle East and Africa Regional Meetings since 2008. The Entoto Observatory in Ethiopia, has been operating as an independent research centre since 2013.

Since the establishment of the IAU’s global Office of Astronomy for Development (OAD) in 2011, Africa has become the home of three such regional offices coordinating activities across East Africa from Ethiopia, West Africa from Nigeria, and Southern Africa from Zambia. The mandate of the regional offices is to ensure that the region benefits maximally from the practice of astronomy. In 2017, the 1-metre Marly telescope was installed in Burkina Faso as a research telescope as part of the University of Ouagadougou.

Africa is also host to the world-renowned HESS telescope in Namibia. The continent is developing the very exciting African Very Long Baseline Interferometry Network (AVN), and a number of countries are rapidly developing their own astronomy programmes and instruments. At the General Assembly currently underway in Vienna, Algeria, Ghana, Madagascar, Morocco and Mozambique all became new national members of the IAU.

Today, Africa is home to the largest optical telescope in the southern hemisphere (SALT), the largest and most powerful radio telescope in the southern hemisphere (MeerKAT) and will play host to a large part of the international Square Kilometre Array (SKA) Project, whose African partnership includes Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia, South Africa and Zambia.

The winning bid is particularly timeous as the SKA telescope is expected to start conducting science observations in the mid-2020s.

“The support for the bid from not only astronomers but also industry, academic institutions and government have been phenomenal, and its success is a testament to what we can accomplish through our united efforts. For astronomers, this is like winning the bid to host a Football World Cup or the Olympics. It’s time for Africa! We are excited and look forward to welcoming our colleagues from around the world to the first of hopefully many IAU General Assemblies on African soil.” says Dr Shazrene Mohamed, member of the bid committee, an astronomer at the South African Astronomical Observatory and the University of Cape Town.

The General Assembly in Cape Town in 2024 is an occasion to give voice to Africa in the global astronomical endeavour and will bring attention to the excellent science and education conducted on the continent. It is expected that the opportunity for many African astronomers to take part in one of the world’s biggest astronomy meetings will contribute to an enduring legacy of astronomy on the continent.

 

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Pluto: small, distant, and fascinating

Pluto is an interesting object located in the outer region of our Solar System.  Although only 2376 km in diameter, it hosts five moons and a thin atmosphere.  As shown in Figure 1, Pluto has a high orbital inclination (17 deg) and eccentricity (0.25), and it requires 248 years to travel once around the Sun.  At 120 deg., Pluto has unusually high obliquity, which is the angle between the rotational pole and the orbital plane.  Thus Pluto’s north pole (as defined by the right-hand rule) lies 40 deg. below the orbital plane. This combination of high orbital eccentricity and obliquity results in extreme seasons: Pluto’s most distant location from the Sun is nearly twice as far away as the closest, and each pole is exposed to the Sun for more than a century at a time.  This geometry is expected to strongly affect the atmosphere.

Figure 1: Schematic plot of Pluto’s orbit in our Solar System. In 2018, Pluto crossed the ecliptic plane and is moving away from the Sun. Pluto was at perihelion in 1990 and won’t be there again for more than two hundred years. Credit: A. Verbiscer; earthsky.org

Pluto’s micro-bar atmosphere was first definitively detected in 1988.  In 2002, measurements showed that the atmosphere had expanded, even though Pluto was moving away from the Sun.  By 2015, when NASA’s New Horizons spacecraft [https://www.nasa.gov/mission_pages/newhorizons/main/index.html] flew through the Pluto system, the atmosphere was roughly the same size it had been in recent years.  However, the story gets more intriguing: models of the mass and distribution of surface ice, which include thermal inertia, predict that Pluto’s atmosphere could collapse out completely.  For these reasons, continued observations of Pluto are important.

Figure 2: Image from NASA’s New Horizons spacecraft of Pluto and Charon. This image was taken in July 2015, while the spacecraft was 5.4 million km from the bodies. The colours are approximately those that would be seen by the human eye: it is obvious that Pluto and Charon have very differently-coloured surfaces. Credit: NASA/JHU APL/SwRI.

In August of 2017, researchers from the South African Astronomical Observatory (SAAO) and the Massachusetts Institute of Technology (MIT) observed a relatively rare event, a stellar occultation by the dwarf planet Pluto.   The stellar occultation technique requires accurate measurements of the positions of a distant star and a foreground body, in order to predict exactly when and where on Earth a shadow will fall.  In this case, Pluto was predicted to occult a star of approximately 15th visible magnitude, with the moderately-sized shadow path (less than 1/3 the diameter of Earth) falling over the northern Pacific Ocean.  The event was observed remotely from Cape Town, using NASA’s 3-m IRTF (Infrared Telescope Facility [http://irtfweb.ifa.hawaii.edu/]) with the high-speed, accurately-timed, visible-wavelength instrument MORIS (MIT Optical Rapid Imaging System). Figure 3 contains Images taken before and after the occultation, which show Pluto and it’s largest satellite, Charon, as they approach the star and then after they pass by.

Figure 3: Animated images of the Pluto system moving up to, and then past, the occultation star on 07 August 2017. Charon is clearly discernible from Pluto, with a separation of approximately 0.8 arcsec. These 60-sec images are subframes of an unfiltered dataset taken on NASA’s 3-m IRTF with MORIS. Discrete jumps occur between separate data cubes as well as during the occultation, when separate data were taken at significantly faster cadence. Credit: A. Sickafoose; N. Erasmus; SAAO

These data show that Pluto’s atmosphere still existed in late 2017.  They are currently being analyzed, along with additional occultation measurements from 2018, to determine the most recent measurements of Pluto’s atmospheric characteristics. Results will be presented at the 2018 American Astronomical Society’s Division of Planetary Sciences meeting [https://aas.org/meetings/dps50] in October
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SAAO to contribute to the global effort to detect Near Earth Objects

The South African Astronomical Observatory(SAAO) will play host to the next generation of asteroid-hunting telescopes as part of the NASA funded Asteroid Terrestrial-Impact Last Alert System (ATLAS). On 13 August NASA confirmed that it will fund two asteroid-hunting observatories in the Southern Hemisphere at a cost of US$3.8 million, SAAO will host the first with the location of the second still to be decided.

In 2013, NASA announced the Asteroid Grand Challenge (AGC) “to find all asteroid threats to human populations and know what to do about them.”  The 2013 meteor strike in Chelyabinsk, Russia in which a 20m rock exploded mid-air injuring numerous people was a clear reminder of the busy neighbourhood in which we live and of the destructive potential of asteroids.

The ATLAS project was designed to address these concerns and two telescopes are currently operational on the islands of Maui and Hawaii, run by the University of Hawaii. Since it began operations in 2015 ATLAS has discovered over 300 asteroids which pass near the Earth’s orbit. However, since these telescopes are located in the Northern Hemisphere they are blind to roughly 30% of the southern sky and therefore to any asteroids in that region.

The new telescope in Sutherland will aid in the detection, tracking and characterization of near-Earth objects (NEOs)  and address the current gaps in sky coverage by imaging the entire sky twice per night. This will be performed using a fully robotic 50-cm diameter telescope with a 110 MP CCD Camera.

The ATLAS system also has software which is optimized to detect fast-moving objects. In early June, the system assisted in providing data on the trajectory of a 1.8-metre asteroid called 2018 LA that entered the atmosphere over Southern Africa. Fragments of this asteroid were found in Botswana using this information.

The telescope will be able to detect a 100-meter diameter asteroid at a distance of 40 million kilometres (~ 3 weeks warning) and a 10-meter diameter asteroid at a distance of 4 million kilometres (~2 days warning). Newly discovered NEOs can then be followed up using SALT and other SAAO telescopes to determine the type, rotation rate, and other important information.

SAAO’s involvement in the ATLAS project offers an excellent opportunity for South African staff, scientists and students to collaborate with NASA and share valuable technology and expertise.

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SAAO/ASSA to host lunar eclipse viewing

During the evening of Friday, 27 July, one of nature’s grandest spectacles will be on display across southern Africa as the full Moon slips into the Earth’s shadow, a total lunar eclipse.

Professional astronomers from the South African Astronomical Observatory (SAAO) alongside members of the Astronomical Society of Southern Africa (ASSA), an association of amateur astronomers, will be offering the public a free viewing with an array of telescopes along the V&A Waterfront.

In addition, the SAAO will be hosting a free public viewing in Sutherland at the Roggeveld Primary School.

Image Credit: PublicDomainPictures.net

A composite image of the full progression of a Lunar Eclipse

“This spectacle will capture the attention of millions, and we are especially fortunate here to have what are front-row seats to it,” said Eddy Nijeboer, President of the ASSA. “This extraordinary event will not come again to the region until 2029. Families with children are especially encouraged to attend what will be both an enjoyable and educational experience.”

The evening’s observing programme will begin at sunset (18:00) with a tour of the Solar System with numerous instruments as large as 250mm in diameter. The planets Venus, Jupiter, Saturn and Mars will be visible for telescopic viewing, weather allowing. The full Moon first begins to darken as it enters the earth’s shadow at 19:15, with totality beginning at 21:30. The duration of total eclipse will be nearly two hours. The sight of the Moon in total eclipse will be striking with or without a visual aide.

The event will be the longest total lunar eclipse of the 21st century and in addition, Mars will be at its brightest for many years. Mars, the Earth, and the Sun will be roughly lined up on 27 July. Mars is on the opposite side of the Earth to the Sun, and hence the alignment is known as opposition. This coincides with the time when the planet is near its closest point to the Earth, and that night it will be about 57.7 million kilometres away. This means that Mars also appears near its largest apparent size in a telescope and is close to its maximum apparent brightness.

“For those new to astronomy, the evening may prove to be a mesmerizing introduction to core scientific principles,” said Dr Daniel Cunnama, Science Engagement Astronomer at the SAAO. “For experienced observers, the sight of the eclipse continues to be mesmerizing even when witnessed repeatedly. Young visitors will be entertained and perhaps be inspired to an interest in the wonders of nature and science.”

The event is hosted by the V & A Waterfront, part of its ongoing astronomy observing programme with the ASSA and SAAO.

Event Details(Cape Town):

Time: 18:00 – 24:00

Location: V&A Waterfront, Flagpole Terrace(alongside the amphitheatre)

Cost: Free

Event Details(Sutherland):

Time: 19:00 – 23:00

Location: Roggeveld Primary School in Sutherland

Cost: Free

For more details on the Eclipse see the following:

http://assa.saao.ac.za/lunareclipse2018/

 

 

 

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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.

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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.

 

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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.

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