At their November 2019 meeting in India, the SALT Board commissioned a study to explore the feasibility of pursuing the development of the SALT mini-tracker concept. The study report, along with the science case produced by Retha Pretorius and the initial 2018 SPIE paper are all included in the document: Mini-tracker Feasibility Study Report 2020.

Above: An artist’s impression of a kilonova, the result of two colliding and merging neutron stars, which was the source of the first gravitational wave event (GW170817) for which an electromagmetic counterpart was detected at different wavelengths (picture credit: Robin Dienel; Carnegie Institution for Science).

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, a new paper has just been published on observations undertaken at the SAAO, which are compared to the latest model predictions.

On 16 October 2017, SAAO and SALT, together with many other observatories world-wide, announced the important discovery of the first gravitational wave source counterpart (see http://www.salt.ac.za:8095/news/breaking-news-salt-gravitational-waves/). The preliminary results from SALT and other telescopes at 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 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.”

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.

The MASTER-SAAO telescope at Sutherland.

“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 IRSF facility, 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”, said Buckley, “using just the known distance of the host galaxy. No other parameters needed tweaking.”

This initial blue component, which disappeared after about 2 days, was consistent with ultraviolet observations made at an earlier time by the Swift satellite.

The SAAO observations, taken over a period of about 9 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 a few 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. SALT 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 1.2 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 didn’t happen two days later, otherwise we’d never have had the opportunity to observe it with SALT”, says Väisänen.

SALT and SAAO 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 and was overseas at the time, 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 is happened Buckley was attending a conference on transients in Russia, on board the conference dinner boat on the Moscow river, 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.

Because of the quick response of SALT and other SAAO telescopes, crucial information on the nature of the gravitational wave source was obtained. These have resulted now in the publication of 8 refereed papers containing observations conducted at the SAAO with the three different telescopes (SALT, MASTER-SAAO and IRSF), including the paper which is the subject of this press release.

As the final comment in the paper says: “The detection of an electromagnetic counterpart to a gravitational wave source, coming only 2 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.”

[David Buckley will be delivering a public lecture at SAAO on Saturday 27 Jan entitled “Gravitational Waves: the new frontier in Astronomy”.]

Primary contact:

Dr David Buckley

South African Astronomical Observatory

Tel: +27 (0)21 4606286  Cell: +27 (0)836499490

Publication:

“A comparison between SALT/SAAO observations and kilonova models for AT 2017gfo: the first electromagnetic counterpart of a gravitational wave transient – GW170817”

David A. H. Buckley, Igor Andreoni, Sudhanshu Barway, Jeff Cooke, Steven M. Crawford, Evgeny Gorbovskoy, Mariusz Gromadzki, Vladimir Lipunov, Jirong Mao, Stephen B. Potter, Magaretha L. Pretorius, Tyler A. Pritchard, Encarni Romero-Colmenero, Michael M. Shara, Petri Väisänen and Ted B. Williams.

Monthly Notice of the Royal Astronomical Society, Volume 474, L71-75 (2018)

https://doi.org/10.1093/mnrasl/slx196

Published: 18 Jan 2018; online version: 4 Dec 2017

What does multi-wavelength observations mean?

The illustration above shows our own galaxy in a variety of wavelengths. See the descriptions in the top right of each individual image to know in which wavelength range each was observed. It starts with a low energy (long wavelength) range and increase in energy as you move downwards through the images.

The optical picture should look more familiar, since that is how our eyes could see it in good conditions (if we were able to expose for a few seconds like cameras can). Our Milky Way has a very distinctive bulge in the near infrared because light travelling at those wavelengths can easily pass through the dense dust clouds that obscure it in other wavelengths. The spiral arms of our galaxy (where young stars are born) are beautifully visible in all the pictures, although they also suffer obscuration by their own dust in the optical wavelengths. And then there are bright features in some images that are not so prominent in others. See the bright spot that shows up in the x-ray and gamma ray wavelengths? That is a high-energy source. Accreting black holes are such sources.

Black holes were discovered when astronomers started studying the night sky using x-ray detectors. The first such detectors were launched high into the atmosphere in rockets or balloons, but later satellites were launched to study the universe in that particular wavelength range. Our atmosphere blocks x-rays (a good thing since prolonged exposure is harmful to humans) so to study them you have to get your detector above the atmosphere. There are several x-ray satellites orbiting the earth.

Accreting Black Holes

There are stellar mass black holes that are in binary pairs with companion stars. See the illustration for an artist’s impression of such a system where the yellow/orange star is the companion. Material flows from it’s surface toward the black hole (which is infinitely small and therefore invisible) and because they are orbiting around each other, the material swirls like water draining from a bathtub as it plunges down the gravitational well that the black hole creates in space. The in-spiralling material releases photons with increasing energy (coloured red, then blue and eventually white) as it moves ever closer to the black hole. We call this an accretion disc because material is being accreted into the black hole, thereby growing it in mass while the companion loses mass. When a large amount of mass is transferred in this way the system can become a microquasar, launching extremely energetic jets perpendicular to the accretion disc and increasing it’s brightness dramatically. These systems are also known as Black Hole binary systems.

One such system (BW Cir) was observed in optical and x-ray wavelengths. The x-ray data were obtained from the SWIFT, INTEGRAL and NuSTAR satellites. Simultaneous optical observations were done with SALT using the Berkely Visible Imaging Tube (BVIT), a visiting instrument currently occupying the auxiliary port on the telescope. The detector is capable of tagging every photon received to nanosecond accuracy, but requires a large collection area (i.e. a 10 meter class telescope like SALT) due to the low quantum efficiency of micro-channel plates (MCPs) in comparison to the more regularly used Charge Coupled Devices (CCDs). This allows us to bin photons together in 1 millisecond intervals, which is among the highest time-resolution achievable in the world.

After combining all the data and analysing it for correlations between the variations in brightness in the different wavelengths, PhD student Mayukh Pahari from the Inter-University Centre for Astronomy & Astrophysics and the University of Southampton (supervised by Poshak Gandhi) and various co-authors (including myself), published the results in:
http://adsabs.harvard.edu/abs/2017MNRAS.469..193P

The SALT Annual Report 2016 includes: Instrumentation News, Research highlights, and feedback on Education & Public Outreach initiatives.

A velocity map of the galaxy NGC 1325.

Spectroscopy is the most important tool for an astronomer.  It unlocks the hidden characteristics of objects too remote to be studied directly – things like the chemical composition of stars, the temperature, pressure and motion of interstellar gas clouds, the structure and mass of galaxies, and much more.  A spectrum is the measurement of the brightness of the light coming to us from an astronomical source, at each individual colour, or wavelength.  Think of a totally unromantic analysis of a rainbow, and you get the picture.  Astronomers use the term “resolution” to describe how finely the light is divided into its colours; a high-resolution spectrum can measure hundreds of thousands of colours!

A spectrograph is the instrument that is attached to a telescope to measure spectra.  The most common form of spectrograph accepts light from only a single point or along a single line from the image that a telescope produces.  This is fine if you are interested in an object like a star, which is just a single point of light as seen by even the most powerful telescope.  But what if an astronomer wants to measure the spectrum everywhere in an extended object, like a glowing cloud of gas or an entire galaxy?  This is the realm of “imaging spectroscopy”, and it requires a specialized type of spectrograph.  SALT, the largest optical telescope in the Southern Hemisphere, is rare among the giant telescopes of the world in that its Robert Stobie Spectrograph has an imaging spectroscopy mode.  This is accomplished with a device called a Fabry-Pérot interferometer.  It can efficiently produce spectra covering SALT’s entire field of view.

The galaxy NGC 908. SALT’s Fabry-Pérot system has simultaneously measured the spectrum of all the stars and gas in this galaxy.

A Fabry-Pérot interferometer is essentially a tunable filter that produces a narrow-band image at one or a series of wavelengths that you specify.  SALT has three etalons (the optical part of the Fabry-Pérot) that can give spectral resolutions of 300, 600, 1500, or 9000 over the wavelength range of 430 to 900 nm covering the entire 8 arc-minute diameter field of view of the RSS.  A typical observing program takes a series of images covering a 2 to 4 nm spectral range of interest for the particular target.  Figure 1 below shows an example of FP data of the Ha emission of the galaxy NGC 1325, taken on 02 November 2011 in the medium resolution (R 1500) mode.  The upper left panel is taken at central wavelength 659.7 nm, the upper right at 660.1nm, and the lower left in nearby continuum at 663.1 nm; exposures are 90 seconds each.  You can see the effect of the galaxy’s rotation, Doppler shifting the emission of the HII regions.  The velocity map of the galaxy, generated by fitting all 23 images in the series, is shown in the lower right panel.  A sample spectrum of one of the HII regions is shown in Figure 2, with fits to the Ha and [NII] lines.  There are over 10,000 such spectra measured in the data cube, extending to a radial distance of more than 12 kpc (40,000 light-years) from the center of the galaxy.

Figure 1. Fabry-Pérot observations of the galaxy NGC 1325.

In addition to the emission from the galaxy, you can see fuzzy ring-shaped emission in the images in Figure 1.  These are night sky spectral features, arising from OH radicals in the Earth’s atmosphere.  Since their wavelengths are accurately known, they can be used to provide a precise wavelength calibration for the data.

The steps in reducing FP data are typically: a) clean the cosmic rays, b) correct for an internal ghost reflection, c) flatten the data using twilight sky flats, d) measure the brightness of the foreground stars and use this to correct for the varying collecting area of the telescope, e) measure the night sky rings, then subtract them from the data, and finally f) fit the spectra point by point, to extract maps of line strength, velocity, and line width.  Then of course, use these maps to pursue your scientific goals.  There are software programs available in a not-quite-ready-for-prime-time state to accomplish all these reduction tasks.

Figure 2. Spectrum of one HII region of NGC 1325

As of September 2017, the RSS FP system is working in its TF, LR, and HR modes (tunable filter, low resolution, and high resolution).  The MR (medium resolution) etalon has suffered environmental damage over the years and is currently being refurbished by the manufacturer in the UK – we hope to have it back on-line in 2018.  The two higher resolution modes, MR and HR, use two etalons in series to isolate individual spectral features properly.  Because of mechanical instabilities that produce a particularly nasty reflection between the two etalons, we have had to resort to using a circular polarizer to eliminate the problem.  This unfortunately reduces the throughput of the HR system by a factor of three, requiring longer exposures.  We have a fix planned that should restore full sensitivity that should be in place in 2018.  Fortunately, the TF and LR modes are unaffected by this problem and have their full throughput.

There is full documentation of the RSS FP system on the SALT web pages, and the PIPT supports the preparation of FP observing proposals.  Like most tools, the FP is really good for some tasks, but the wrong solution for others (cf. hammers and screwdrivers).  The FP aficionados on the SALT staff are happy to consult and offer advice about the use of the system – contact Ted Williams, Encarni Romero Colmenero, or Blaise Tapsoba.

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.

An artists impression of the collision of two neutron stars. Image credit: Dana Berry, SkyWorks Digital, Inc.

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 from massive stars which exploded as supernovae. In this particular event, dubbed GW170817, two such neutron stars spiraled 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 milky way and SALT. Image credit: Chantal Fourie, SAAO.

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”.

Four early spectra taken with the SALT (at tc+1.2 d McCully et al. 2017; Buckley et al. 2017), ESO-NTT (at tc+1.4 d, Smartt et al. 2017), the SOAR 4-m telescope (at tc+1.4 d, Nicholl et al. 2017), and ESO-VLT-XShooter (at tc+2.4 d, Smartt et al. 2017)

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 science 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. Image 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/

MEDIA CONTACTS:

SAAO/Steve Crawford, +27 21 460 9359; crawford@saao.ac.za

SAAO/Stephen Potter, +27 21 460 9337; sbp@saao.ac.za

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

After studying at the University of Göttingen in Germany, Christian came to Cape Town in 2006 for three months in order to help with the PIPT. Three months turned into six, a year, and he somehow still hasn’t left, (editor: which is excellent news for SALT!) That gives him the opportunity to work on the PIPT, dabble with the Web Manager, help with Open Nights, and reply to emails sent to salthelp.

When he’s not busy with his work, he enjoys reading books and going for a run. He thinks that his age of 42 would be a good reason to try a marathon, but still needs some persuasion in this regard. One of his flaws is that after so many years he hasn’t managed to master the click sounds in the South African language isiXhosa.

Image credit: NASA/CXC/M.Weiss

Outer space looks black, at least relative to our eyes, but it wasn’t always the case!

Straight after the big bang, the Universe was a VERY hot dense place, too hot for atoms to form. It was a hot soup of subatomic particles, such as electrons and ions, called plasma. During this phase, light particles aka photons were continuously absorbed (more precisely scattered) by the subatomic particles in the Universe, in other words light was trapped by these subatomic particles, meaning the Universe was a dark “opaque” place. As space expanded, the Universe cooled down. After around 380,000 years from the big bang the Universe cooled enough for atoms to form. At this stage, known as the recombination era, electrons and nuclei combined to form atoms. These were mainly helium and hydrogen, which are still by far the most abundant elements in the Universe.

During the recombination era, the photons trapped by the subatomic particles were freed and the Universe for the very first time became “transparent”. We can resemble what happened to a flash of infinite number of light bulbs, more precisely orange light bulbs. Indeed, the electromagnetic radiations emitted during the recombination era were orange, and hence space was orange. While the Universe continuously expanded with time, these orange electromagnetic radiations were stretching into longer and longer wavelengths (redshifted). In a few million years, the orange radiation shifted toward the red and eventually infra-red to become microwave after around 13 billion years. This radiation is everywhere in the Universe but since our eyes are not sensitive to microwave, relative to us, space is black and of course not orange anymore. It was in 1964 when these microwave radiations were accidentally discovered by Arno Penzias and Robert Wilson. The two American astronomers were experimenting with their 6 meter radio telescope by pointing it towards different locations in the sky. In whatever direction they pointed their telescope, they detected a low, steady, mysterious noise in the microwave that persisted in their receiver. This microwave noise was indeed the afterglow of the big bang which we now call the Cosmic Microwave Background. It is the fingerprint of the big bang and one of the basis of the big bang theory.

Large telescopes like SALT allow us to look further back in time, unveiling the mysteries of space.

Moral of the story: Black is the new orange!!

** Elias Aydi is a PhD astronomy student.

Dr Rosalind Skelton

Dr Rosalind Skelton, known to all as Ros, has been part of the SALT Astronomy team for just over a year.

How did you become an astronomer?

I grew up in Rustenburg in the North West province of South Africa and spent many happy camping trips in the bushveld with my family, where the beautiful dark skies were endlessly fascinating. My curiosity about the Universe and love of maths and science led me to study Physics at the University of Cape Town. My elective courses in Astronomy were always my favourite (who wouldn’t love afternoon tutorials in the Planetarium, with the inspiring Tony Fairall as our guide to the night sky?). I joined the National Astrophysics and Space Science Programme (NASSP) for my Masters, where I started my first research in extragalactic astronomy. I then took a somewhat circuitous route around the world, spending almost 7 years abroad before returning to Cape Town. I did my PhD at the Max Planck Institute for Astronomy in Heidelberg, Germany, and a postdoc at Yale University in the USA before taking up a postdoctoral fellowship at the Observatory and then joining the SALT team last year.

What is your research on?

My research is on galaxy formation and evolution. I am particularly interested in the effects of environment on the quenching of star formation and the growth of galaxies. I am looking at how mergers and close companion galaxies impact galaxy properties in different environments, from the field to rich clusters, and at different times in the Universe’s history. I am part of the 3D-HST team, which has used exquisite Hubble Space Telescope data to study changes in galaxy populations from the “cosmic noon” (redshifts of approximately 1 to 2.5), when galaxies formed the bulk of their stars, to today.

What is your role on the SALT team?

As an extragalactic astronomer, I mainly make use of the long-slit and multi-object spectroscopy (MOS) capabilities of the RSS for my own research. I would like to improve the usability of SALT’s MOS tools, from the mask design software to the data reduction pipelines. I am the liaison astronomer for many of the MOS programmes and I manage the mask cutting process, as well as regularly observing on SALT.

What have been some of the challenges you’ve faced?

Apart from getting through a PhD in Astronomy, dealing with ups and downs in confidence at different stages and the cultural challenges of moving to new countries, I think the hardest thing has probably been the uncertainty along the way, not knowing whether I would get a job in this field that I love, while being able to stay in a place that I love near people I love. I feel very privileged to be part of the SALT team, to regularly spend time in the peaceful Karoo and continue working on the challenges of galaxy evolution in the Mother City.

What do you enjoy doing outside of astronomy?

I love dancing lindy hop, the vintage swing dancing style that developed with the big band jazz of the 1930s and 40s. Since its revival in the 1980s, lindy hop has become a global phenomenon, and our vibrant scene here in Cape Town is growing in leaps and bounds.

Image credit: Dr Tim-Oliver Husser. The closed ox-wagon encases the massdimm telescope, which has the sole task of measuring the twinkling of the stars.

The more scientific term for twinkling, and the one you’ll hear people at the Observatory referring to, is “the seeing”. The latter is caused by disturbances in the atmosphere, and the more turbulent it is, the more stars will appear to twinkle, the worse “the seeing” will be. For the purposes of astronomy, the more stable the atmosphere is, the better the science will be.

When the object you’re looking at, like a star, is being subjected to bad seeing, it will look much bigger and fluffier than it actually is. Think of a hosepipe where you can adjust the water setting: if you have it set to a fine misty spray, the water is scattered in a wide arc. When you have it set to a single jet of water, it sprays in a direct stream to the point you’re aiming. Similarly, when the seeing is good the starlight is arriving in a direct stream and more can be collected, therefore better quality science can be achieved.

Don’t twinkle, please don’t twinkle, little star…