- RECENT HEADLINES
- Robotic telescopes and instrumentation for time domain astronomy
- Black hole caught having a snack
- Rapid SPRAT confirmation of a Gaia transient: its a dwarf nova!
- LT discovers the sixth eruption of a remarkable Recurrent Nova in M31
- LJMU scientists announce the arrival of SPRAT, an exciting new instrument on the Liverpool Telescope
The upcoming European Week of Astronomy and Space Science (EWASS) will include a Special Session (Sp6) entitled 'Robotic telescopes and instrumentation for time domain astronomy'. EWASS2015 is organised by the European Astronomical Society (EAS), and will be held in Tenerife, Spain, from June 22 to 26, 2015 (see the EWASS 2015 web-site).
In this special session we aim to address how current and future robotic facilities meet the scientific needs of the European time domain community. The session will feature both talks on scientific results as well as new and existing robotic facilities covering all areas of time domain astronomy. We also welcome abstracts introducing new instrumentation, as well as discussions on the technical and software challenges of robotic response.
The deadline for abstract submission is March 10, 2015. Those interested may register here, while abstracts can be submitted via the speaker portal: speaker portal. Contributed talks for session Sp6 will be between 15 and 20 minutes in duration (incl. questions), depending on the number of requests.
Aims and scope of the meeting
The past decade has seen robotic telescopes increasingly employed for the study of the time variable sky. Arrays of small telescopes covering large fields-of-view have proved to be powerful tools for the discovery of explosive transients (for example the MASTER robotic network) and transiting exoplanets (SuperWASP). The rapid reaction and flexible, remote scheduling capabilities of larger aperture robotic facilities such as the 2-metre Liverpool Telescope, based on La Palma, makes them powerful tools for the exploitation of time variable objects such as supernovae, gamma ray bursts, exoplanets and binary stars.
The next decade will see time domain science becoming an even more prominent part of the astronomical agenda. On the discovery side of things, new European facilities such as the Next Generation Transit Survey (NGTS) will build on the success of the SuperWASP project. New goals for the time domain community include the discovery of electromagnetic counterparts to astrophysical gravitational wave sources, and proposed facilities such as GOTO and BlackGEM aim to use dedicated arrays of small, independently pointed telescopes to address the large positional uncertainty of any gravitational wave detection.
The diversity of new survey missions on the horizon provides unprecedented opportunities for robotic follow-up and scientific exploitation. In the field of exoplanet science, NGTS and the next generation of space missions such as PLATO will build on the work of Kepler by discovering more planets with bright host stars in order to maximise the potential of ground based follow-up. The STELLA Robotic Observatory on Tenerife is a precursor to a potential PLATO follow-up facility dedicated to stabilised hi-resolution echelle spectroscopy for radial velocity studies and the characterisation of exoplanet host stars. The GREGOR solar telescope is also in the process of being equipped with a high resolution spectrograph for night-time robotic operations. The first telescope of the Stellar Observations Network Group (SONG) was also recently inaugurated on Tenerife. This 1-metre telescope is the prototype of a modern, global network of robotic telescopes, and will address a wide range of time domain topics, with a particular focus on exoplanet follow-up and the study of the internal structure and evolution of stars via asteroseismology.
For transient science, the next generation of synoptic surveys such as LSST will discover huge numbers of targets and facilities such as LOFAR, SKA and CTA will probe transient phenomena at previously unexplored wavelengths. An increasingly important part of time domain science will be the software challenges of rapid classification in order to make best use of available follow-up facilities. This new era of transient astronomy will demand deeper and an even more rapid reaction capability, and to that end plans are underway for a 4-metre robotic successor to the Liverpool Telescope, to come into operation on La Palma in approximately 2020.
In this session we aim to address how current and future robotic facilities meet the scientific needs of the European time domain community. Examples of the topics we would aim to cover include (but are not limited to):
- New robotic facilities for time domain science
- Upgrades for existing facilities
- Automated transient classification
- Linking transient discovery with rapid follow-up
- Robotic telescopes in the era of multi-messenger astronomy
- Novel detector technologies for rapid reaction
The scientific organising committee:
M.F. Bode (Liverpool John Moores University, UK)
C.M. Copperwheat (Liverpool John Moores University, UK)
C.J. Davis (Liverpool John Moores University, UK)
L.J. Goicoechea (Universidad de Cantabria, Spain)
I.A. Steele (Liverpool John Moores University, UK)
K. Strassmeier (Leibniz-Institut fuer Astrophysik Potsdam, Germany)
We don't as yet know very much about black holes, but one of the things we do know is that it's not a good idea to get too close to one of them! Their powerful gravitational pull can rip apart anything that passes nearby. Yet a star may have survived such a close encounter, an encounter that was recently observed by LJMU's David Bersier and colleagues using the Liverpool Telescope.
Only a few such stellar disruptions have been seen before. Close encounters are thought to be rare, and to date their discovery has largely been by accident. In order to catch such an uncommon event, astronomers need to look at a large fraction of the sky, and look often. This is what the All-Sky Automated Survey for Supernovae (ASAS-SN, pronounced "assassin") is designed to do. Its six small telescopes - four in Hawaii and two in Chile - scan the sky every night, looking for variable sources, transient objects, and sudden outbursts. ASAS-SN discoveries often trigger rapid follow-up observations on larger telescopes, particularly robotic facilities like the LT.
On January 25, 2014, an otherwise anonymous galaxy located a mere 650 million light years away in the constellation that contains the "Big Dipper", looked significantly brighter than usual. This object, nicknamed ASASSN-14ae, was initially thought to be a supernova, the explosion of a massive star, albeit an unusual one.
Several telescopes, including NASA's Swift observatory and the Liverpool Telescope, were immediately used to obtain more data. PhD student Thomas Holoien of Ohio State University led the effort and coordinated the observing campaign.
As the story unfolded it became clear that ASASSN-14ae was not a supernova, but was instead something entirely different: a Tidal Disruption Event, or TDE. Such an event is believed to occur when a star gets a little too close to a black hole, an object with a mass several million times that of our Sun. Luckily, the star in this case seems to have survived the encounter, with only a small chunk of matter being ripped off!
The amount of energy released during the event allowed researchers to calculate that only one thousandth of the mass of our sun - about the mass of the planet Jupiter - had been sucked into the black hole.
Light curves, showing how the brightness of the debris ripped from the star varied during the encounter, are shown to the right. As the debris falls towards the black hole it settles into an "accretion disk", where it gets hot and thus shines. The steady decline in brightness of this material, seen over a period of many weeks with Swift and the LT, matches what is expected of a TDE.
The Liverpool Telescope is the perfect machine to follow an event such as this. Although Holoien and his team needed access to a telescope for only ten minutes or so each night, observations were needed over a long period of time. The fact that the LT is entirely computer-controlled means that the observations could be scheduled remotely and all in one go: a very lengthy stay at an overseas observatory was thus not required. This is perhaps a less romantic way of observing, but is none-the-less a lot more efficient.
Monitoring the whole night sky every other night, the ASAS-SN survey has a good chance of detecting more of these events, and perhaps even more exotic cosmic catastrophes that we haven't thought of yet! In the meantime, the LT will be ready and waiting to react to ASAS-SN triggers and secure the observations needed to better understand these remarkable cosmic phenomenon.
The observations described here have recently been published in volume 445 of the Monthly Notices of the Royal Astronomical Society by Holoien, Bersier and their collaborators. A copy of the article is available here.
One of the secondary goals of the Gaia Space Telescope is to survey the whole sky for variables and transients, objects that suddenly increase in brightness. The Gaia Photometric Science Alerts programme hosted by Cambridge University in the U.K. has recently gone public, and one of the first alerts released has been robotically observed by the Liverpool Telescope. As part of a campaign of rapid follow-up observations with the newly-commissioned SPRAT spectrograph, a group of LJMU astronomers have just released the first Astronomer's Telegram based on a Gaia transient alert.
The transient Gaia14aat was detected by the Gaia Photometric Science Alerts programme with a magnitude of 15.7 on 10th October. The team, all part of the Liverpool Telescope group at LJMU, measured the object's position precisely. They then identified the progenitor of the outburst in archival Sloan Digital Sky Survey (SDSS) images as an object with an r-band (red) magnitude of 18.9. The target had thus suddenly brightened by over three magnitudes; that's an increase in luminosity of more than 15 times.
The question then was: what is Gaia14aat?
Using the SPRAT spectrograph installed on the Liverpool Telescope, the group obtained a 10 minute spectrum of the object on October 15th. The spectrum covers the wavelength range of 400 to 790 nanometres and exhibits emission lines from hot atomic hydrogen: a bright H-alpha line at 656 nm and fainter H-beta and H-gamma lines at 486 and 434 nm.
Observing with SPRAT involves first taking an image (so that the target can be identified and moved onto the spectrograph slit). This "white light" acquisition image can also be used for science, however, and was in this case used to estimate the r-band magnitude of the target, which by the date of the LT observations had faded to about 18.5, close to the SDSS value. The object had already returned to its quiescence state in the 5 days since the Gaia detection. Clearly, time is of the essence when observing Gaia transients!
Based on the duration and brightness of the transient and the emission features in the SPRAT spectrum, the team believe that Gaia14aat is a dwarf nova outburst in a hydrogen-rich cataclysmic variable. Dwarf novae are binary systems in which a white dwarf star accretes matter from a companion; cataclysmic variables are stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state.
Gaia14aat will undoubtedly be the first of many transients discovered by the Gaia Space Telescope and subsequently observed by the LT. These early observations illustrate the power of SPRAT for categorising faint transients, and the importance of rapid response and robotic operations. Exciting times lie ahead.
The LT has in recent weeks been doing what it does best: making exciting discoveries in time domain astronomy! A team led by Dr Matt Darnley of the Astrophysics Research Institute at LJMU has detected the latest eruption of a remarkable Recurrent Nova (RN) in the nearby galaxy M31. This object is particularly noteworthy because of the frequency of its eruptions. Most RNe undergo an outburst once every 10-100 years; the RN in M31 seems to erupt annually.
Darnley and his team were the first to spot the latest eruption of the nova and, thanks to the LT's robotic capabilities, have been able to monitor the event with images and spectra obtained every few hours/days over a period of a few weeks. They have certainly not let the grass grow under their feet, having made full use of the recently-commissioned optical spectrograph, SPRAT.
Novae are associated with nuclear explosions on the surface of a white dwarf, which results in a sudden brightening of the star. Recurrent nova outbursts are caused by the accretion of material from a companion star, usually a red giant, onto the white dwarf through an accretion disc.
As reported in an LT news item earlier this year, the true recurrent nature of the nova system in M31, designated M31N 2008-12a, was characterised following its fifth detected optical eruption in 2013. An international study co-led by Darnley and Dr Martin Henze of the European Space Astronomy Centre in Spain, along with independent work by the Intermediate Palomar Transient Factory (iPTF), uncovered the progenitor system of M31N 2008-12a and inferred the presence of an extremely high mass white dwarf as well as a high mass accretion rate. These are the tell-tale signs that M31N 2008-12a may one day evolve into a Type Ia Supernova explosion.
Such a high mass white dwarf leads to a very rapid evolution of the 'optical lightcurve' of each eruption. The nova fades very rapidly post-eruption. Consequently, despite five optical eruptions and three separate X-ray detections of the event in recent years, very little was known about the behaviour of the system during its eruptions - until now.
In anticipation of a sixth eruption towards the end of 2014, Darnley has been leading a campaign on the Liverpool Telescope (LT) to monitor M31N 2008-12a to detect any changes in its behaviour. This LT campaign was also designed to react rapidly following a newly detected eruption, to obtain as much data on the system as possible.
Nightly monitoring of M31N 2008-12a by the LT began towards the end of July 2014, and just before 10pm (GMT) on 2nd October a sixth eruption was detected. As planned, intensive photometric monitoring of the eruption using the IO:O optical imaging CCD camera on the LT was immediately implemented. In addition, and for the first time, the team deployed the newly commissioned SPRAT (SPectrograph for the Rapid Acquisition of Transients) instrument on the LT, a low-resolution though high throughput spectrograph designed specifically for the classification of transients like novae.
Remarkably, SPRAT has been mounted on the LT for less than a month before Darnley et al. used it to obtain the first spectra of an extragalactic nova ever taken with the LT. These data have led to spectroscopic confirmation of the nature of the eruption and have allowed the team to determine the expansion velocity of its ejecta.
As well as Matt Darnley and Martin Henze, the international collaboration also includes; Mike Bode (LJMU), Steve Williams (LJMU), Allen Shafter (San Diego State University, USA), Jan-Uwe Ness (ESAC), and former LJMU PhD student Rebekah Hounsell (Space Telescope Science Institute, USA). Iain Steele, Rob Smith, and Andrzej Piascik, all from the LT Group at LJMU, were instrumental in obtaining and analysing the SPRAT spectroscopic observations.
Astronomers from the Astrophysics Research Institute (ARI) of Liverpool John Moores University recently announced the successful commissioning of an exciting new instrument on the Liverpool Telescope to colleagues and collaborators at an international conference in Poland. The conference, which was held in Warsaw in early September, brought together researchers from across Europe who are interested in observing variables and "transients" - objects that vary in brightness suddenly and dramatically. The meeting focused on objects that will be discovered with the GAIA space telescope, an ESA mission that was launched late last year. The LT will undoubtedly be a key player in this area of astronomical research.
Affectionately known as SPRAT, the SPectrometer for the Rapid Acquisition of Transients will provide astronomers from LJMU, the rest of the UK, and overseas with the opportunity to rapidly observe and analyse the light from all manner of variable objects. SPRAT will be particularly useful for studying novae and type Ia supernovae - stars in binary systems that undergo sudden outbursts - and core-collapse supernovae, massive stars that at the end of their lives collapse under their own weight causing a massive explosion of light and energy. Both areas of research are of particular interest to astronomers at the ARI.
SPRAT was designed and built entirely by LJMU scientists and engineers subsidised mainly by internal LJMU funding. The instrument, the brainchild of Prof. Iain Steele, the Director of the Liverpool Telescope, was taken to La Palma in the Canary Islands on 30th August by a team from LJMU comprising Stuart Bates, Robert Smith and Andrzej Piascik. Joined by fourth team member Dirk Raback they spent the first week in September mounting the instrument on the telescope and carefully characterising it, in preparation for robotic use later in the month.
Andrzej, a PhD student at LJMU, has spent the last twelve months fine-tuning the performance of SPRAT in an optical lab in Liverpool Science Park (where the LT group is based). He joined the team on site and will present the instrument to the community at the Warsaw Conference. Meanwhile, testing will continue from Liverpool: software engineers Neil Clay, Chris Mottram and Steve Fraser will ensure that the instrument can be controlled remotely and robotically, that is, by the complex control system used to operate the telescope. Mike Tomlinson will provide IT support, while astronomers Jon Marchant, Rob Barnsley and Chris Davis will ensure that the data obtained are suitable for scientific use.
The commissioning of SPRAT brings the instrument suite on the LT to a grand total of six; a seventh instrument, the IO:I near-infrared imager, is currently being developed and will hopefully be commissioned later this year. In the meantime, SPRAT will undoubtedly prove to be an invaluable tool to a wide range of researchers in transient and time-domain astronomy.