The revolution in time-domain astronomy has arrived. Large-scale surveys are detecting events at an unparallelled rate, and discoveries of new and exotic objects abound. In just a few short years, the Large Synoptic Survey Telescope will begin operations in Chile. At that point, the rate of production of time-domain events will jump by a factor of at least a hundred. The traditional techniques of handling each detection individually will not scale to those current and future productions. The ANTARES project is a joint venture between NOAO and the University of Arizona Computer Science Department to develop a software infrastructure system to process time-domain events automatically at the scale and rate that LSST will generate them.

In March 2017, the Intermediate Palomar Transient Factory (iPTF) ceased operations. This Symposium was an appropriate opportunity to review the scientific returns from iPTF and its predecessor survey, the Palomar Transient Factory (PTF), and to summarise the lessons learned. Succeeding iPTF on the Palomar Observatory 48-inch Schmidt telescope is the Zwicky Transient Facility (ZTF), a new survey with an order of magnitude faster survey speed that is now being commissioned. I described the design and scientific rationale for ZTF. ZTF is prototyping new alert stream technologies being explored by the Large Synoptic Survey Telescope (LSST) to distribute millions of transient alerts per night to downstream science users. I described the design of the alert system and discussed it in the context of the wider LSST and community broker ecosystem.

“Deep learning” is finding more and more applications everywhere, and astronomy is not an exception. This talk described the application of convolutional neural networks to time-domain astronomy, specifically to light-curves of sources. The work that is discussed is based on a published paper to which reference can be made for more detail. The talk finished with a note cautioning new practitioners about the pitfalls lurking in out-of-the-box use of deep-learning techniques.

Over the years the European Southern Observatory (ESO) has offered a number of time-domain instruments that enable the user to achieve time resolution as small as milliseconds. They have been used for a wide range of applications, from binary studies with Lunar occultations, characterisation of X-ray binaries and exoplanet transits, to quasar variability. Furthermore, ESO provides a target-of-opportunity (ToO) rapid-response-mode (RRM) channel to trigger quick follow-up observations within as little delay as minutes after a transient has been detected. This talk reviewed the available time-domain observing modes and instruments at ESO, giving priority to FORS2, HAWKI and UltraCam. It described the ToO and RRM, and gave examples of the most common science cases that take advantage of those channels and capabilities.

The SALT transient follow-up programme began in 2016 and will continue for 5 semesters (until 31 Oct 2018), with an expectation of renewal thereafter. It is currently the only SALT Large Science Programme, and was awarded ~250 ksec. per semester, with a significant fraction (60%) given for the highest priority target-of-opportunity time. The aim is to characterise and study transients across a wide range of classes, currently including (from closest to most distant) cataclysmic variables, novæ and other associated eruptive variables, low- and high-mass X-ray binaries, OGLE and Gaia transients (including tidal disruption events), super-luminous and unusual core-collapse supernovæ, kilonovæ and other candidate optical counterparts to gravitational-wave events, flaring blazars and AGN, and gamma-ray bursts. This programme currently involves four SALT partners, of which South Africa is the major contributor of time (74%) and resources and includes five institutions with over 30 co-investigators. This talk reviewed the nature of the programme and highlighted some of the results to date.

Octocam is an 8-channel VIS and NIR imager and spectrograph to be installed at Gemini South in 2022. It provides simultaneous imaging in g’,r’,i’,z,Y,J,H,KS bands or simultaneous spectroscopy at a resolution of ∼4000, together with high time-resolution options. Additional capabilities such as spectropolarimetry or an Integral Field Unit could be added as an upgrade later. These properties makes it very well suited as a follow-up instrument for transient searches. It is planned as a dedicated follow-up instrument for LSST, and will start operations at the same time as the LSST main survey. Octocam was conceived as a consortium consisting of South-West Research Institute in San Antonio, Texas, IAA-CSIC in Granada, FRACTAL SLNE in Madrid, and George Washington University.

The Thai National Observatory (TNO) is equipped with a 2.4-m Ritchey-Chretien telescope and the high-speed versatile Ultraspec camera. The instrument employs a low-noise frame-transfer EMCCD, suitable for the observation of faint objects and for high-time-resolution astrophysics. We present some of the results obtained in the first four years of operation, focusing particularly on fast photometry of lunar and stellar occultations, and follow-up efforts on a few white-dwarf binaries. Among the latter is the polar cataclysmic variable UZ For. This system displays period changes and is suspected of hosting circumbinary planets. Our high-speed photometry data show a decreasing trend in the O–C diagram of UZ For. Using our new data set, we will investigate whether the period change in this binary is due to a possible third body, or to other mechanism(s).

This talk provided an overview and update of the LSST Project and a review of the Data Management system, with a focus on the products most relevant to the researchers of transients and variables. The open opportunities for user-defined Special Programmes such as Deep Drilling Fields were also presented.

TAOS II is a next-generation occultation survey with the goal of measuring the size distribution of the small end of the Kuiper Belt (objects with diameters 0.5–30 km). Such objects have magnitudes r > 30, and are thus undetectable by direct imaging. The project will operate three telescopes at San Pedro Mártir Observatory in Baja California, México. Each telescope will be equipped with a custom-built camera comprised of a focal-plane array of CMOS imagers. The cameras will be capable of reading out image data from 10,000 stars at a cadence of 20 Hz. The telescopes will monitor the same set of stars simultaneously to search for coincident occultation detections, thus minimising the false-positive rate. This talk described the project, and reported on the progress of the development of the survey infrastructure.

The Transiting Exoplanet Survey Satellite (TESS) is an MIT-led NASA mission that will spend two years searching for transiting exoplanets via an all-sky survey that starts in the Southern Hemisphere. Launched in 2018 April, TESS is expected to discover thousands of Earth- to Neptune-sized planets, and over ten thousand giant planets, around the closest, brightest, stars. These planets will become our best targets for learning more about planet formation and evolution, planet composition, and atmospheric make-up. More detailed information about TESS, and instructions on how to access and work with the data once they are available, was given in Workshop 3, Getting ready for TESS, held earlier during the Symposium (p. 224).

In the last decade Astronomy has been transformed by a deluge of data that will grow exponentially when near-future telescopes such as LSST and the SKA begin routine observing. Astroinformatics, a broad field encompassing many techniques in statistics, machine learning and data mining, is the key to extracting meaningful information from large amounts of data. This talk outlined Astroinformatics as a field, and gave a few examples of the use of machine learning and Bayesian statistics from my own work in survey Astronomy. The era of massive surveys in which we now find ourselves has the potential to revolutionise completely many fields, including time-domain Astronomy, but only if coupled with the powerful tools of Astroinformatics.

The recent spectacular progress in machine learning and artificial intelligence opens up exciting opportunities for time-domain and transient astronomy. This talk outlined the fundamental challenges that we will need to overcome in order to realise that potential, from discovering completely new classes to fully-automated follow-up campaigns.

MeerLICHT is a 65-cm optical telescope situated in Sutherland. The MeerLICHT project, as a part of the ThunderKAT project, will be linked to MeerKAT in real time, providing simultaneous optical and radio observations of the transient sky. Since transient events often require multi-wavelength observations within a short time-lapse, the combination of MeerLICHT and MeerKAT will provide invaluable information on emission at both wavelengths, including the relation between, and evolution of, emission from both wavelength windows. With the installation and commissioning of MeerLICHT now completed, early science with MeerLICHT has begun. The talk offered an overview of the MeerLICHT and ThunderKAT projects as a whole, presented early science results obtained with MeerLICHT, looked at future work with these projects, and discussed other related planned projects.

14 Workshops were held during the Symposium, and all but one submitted a report of the discussions that took place. The reports are arranged in the following order:

1. Radio Transients in the Era of Multi-Messenger Astrophysics………. 207

2. Stellar Variability: From Citizen Science to Citizen Astronomy………. 215

3. Getting Ready for TESS: an On-Hand Software Tutorial………. 220

4. 25 Years of the Southern Skies Monitoring by OGLE………. 226

5. A-Type Stars as a Unique Challenge in Time-Domain Studies………. 230

6. X-ray Binary Transients in the Magellanic Clouds and the Milky Way………. 236

7. Towards Science with LSST: Data Products and Communications………. 241

8. Supernovæ………. 245

9. Exploring Data Sonification to Enable, Enhance, and Accelerate the Analysis of Big, Noisy, and Multi-Dimensional Data ………. 251

10. New Instrumentation for Transient Follow-Up ………. 257

11. Nuclear Transients ………. 263

12. Accessing Data for Long-Term Variability ………. 269

13. Machine Learning for Transient Classification ………. 274

14. Calibration and Standardisation ………. 275

Radio emission from astrophysical transients allows us to derive calorimetry of kinetic feedback and detailed imaging in ways that are not possible at other wavelengths, and as such it forms an important part of the multi-messenger follow-ups of these events. The field is burgeoning, with a renaissance of interest in accretion, stellar explosions and jetted supernovæ, alongside newer classes of phenomena such as fast radio bursts and tidal disruption events. The purpose of this workshop was to discuss the infrastructure and techniques for detecting, identifying and probing radio transients, with a particular focus on how best to exploit transient alerts from multi-messenger facilities. We examined the type of transient alerts those facilities will broadcast, and methods for following them up, such as rapid-response triggering and shadowing. In break-out groups, participants chose a science question related to a particular radio transient type or class and discussed whether the planned transient strategies and observing techniques on the Square Kilometre Array will be adequate to address the particular question. The classes they chose included fast radio bursts, supernovæ, cataclysmic variable and unknown transients. Any proposed adaptation or suggestion was relayed to a panel of experts for further discussion. The second part of the workshop concentrated on the application of long baseline interferometry for detecting and measuring radio transients.

The contribution of citizens to research is irrefutable. Especially this century with the outburst of all-sky surveys, professional astronomers use citizen-science projects to engage the public in analysing and sorting large quantities of data, often leading to noteworthy discoveries. From crowdsourcing to acquiring data, citizens are leaving a significant mark in the science landscape, assisting professional astronomers with their work. In turn, citizen science is a means of increasing science literacy and public understanding of science. At the same time, the time domain enables a more active engagement of backyard observers in research. Citizen astronomers not only take data, but also reduce and analyse them, and participate in preparing scientific manuscripts.

The launch of NASA’s next exoplanet mission, the Transiting Exoplanet Survey Satellite (TESS), took place successfully on 2018 April 18, and has now commenced science operations. TESS is specifically designed to search for exoplanets transiting the closest and brightest stars using high-cadence photometric measurements. The images employed for detecting those planets can also be used for a wide variety of time-domain astronomy, especially when considering the full-frame images that TESS takes every 30 minutes. This (pre-launch) workshop familiarised participants with the details of how TESS will operate, described the expected data products and how to access them, introduced the software suite PyKE, which can be used to analyse TESS data, and highlighted ways for participants to request additional TESS targets.

The Optical Gravitational Lensing Experiment (OGLE) started at Las Campanas Observatory in 1992 with a pilot monitoring programme of two million stars in the Galactic Bulge. It is still operating today, collecting time-domain photometric data of a billion stars from the densest regions in the southern sky. Among its main achievements are discoveries of thousands of microlensing events, a few dozen extrasolar planets and candidates for black holes, a million variable stars, and thousands of quasars and supernovæ. It has made a major contribution to the studies of the dark-matter content of the Milky Way halo, the structure of the Galactic Bulge, the Magellanic Clouds, and new classes of variable stars. In this its 25th anniversary year, we presented a selection of the major scientific highlights of OGLE.

As photometric standards, A-Type stars have proved to be extremely useful; this is particularly true of Vega, the fundamental photometric standard. However, the identification of at least some main-sequence A-type stars as small-amplitude variables, while of interest as an issue of fundamental astrophysics, needs to be understood if they are to continue to be used as photometric standards. Flaring and Rossby waves are proposed in the literature as possible explanations, as was discussed during a well-attended Workshop debate. This report summarises the discussion, and suggests future investigations.

The X-ray sky is dominated by luminous galactic sources, variable on time-scales from milliseconds to years. Their eruptive behaviour is now under continuous monitoring by MAXI, Swift, INTEGRAL and other high-energy missions, and representing a superb exemplar of time-domain astronomy. Understanding the astrophysics of such variability requires multi-wavelength follow-up studies from a suite of ground- and space-based facilities. As SALT is a 100% Q-scheduled telescope, one of its key scientific capabilities is related to Target-of-Opportunity (ToO) programmes, and there has been a dedicated SALT Large Programme on Transients in place since 2016, a significant fraction of which has been devoted to the follow-up of X-ray binary transients. This Workshop addressed questions of how such programmes should evolve once the era of MeerKAT and MeerLICHT begins in ∼2018-9 (as well as other huge surveys at optical wavelengths), identifying the range of facilities that would be needed, and the key science topics. There is a clear and growing need for responses to transients to be faster (within minutes if possible), and to be multi-wavelength (particularly in radio and X-ray). Furthermore, extended ongoing coverage of such events (days to weeks for the next ‘V404 Cyg’-type outburst) will be needed for maximum astrophysical return. That would require careful management and coordination of a wide range of ground- and space-based facilities, and optimising coverage against logistical constraints that are often conflicting.