The passage of interstellar comet 2I/Borisov in December 2019 offered a unique opportunity to acquire comprehensive data on an object originating from another planetary system, that left behind material in interplanetary space as it approached the Sun. Astronomers using a number of telescopes around the world, including the telescopes of the Isaac Newton Group (ING), monitored its behaviour spectroscopically and photometrically.

A first-of-its-kind exploding star - thought to have existed only in theory - originating from a Wolf-Rayet star was recently discovered by an international team of collaborators led by Avishay Gal-Yam from the Weizmann Institute of Science in Israel. Observations were made with several telescopes around the world, including the William Herschel Telescope (WHT) and through the Isaac Newton Group (ING) Override Programme of targets of opportunity, using the Auxiliary-port CAMera (ACAM) imager and spectrograph.

Black hole X-ray binaries (BHXBs) are essential to our understanding of extreme physics across the universe, such as accretion/ejection processes, supernova explosions, long gamma-ray bursts and gravitational-wave sources. About 60 BHXBs have been discovered to date in the Galaxy through transient outbursts but, unfortunately, only 17 are confirmed dynamically (i.e. have a mass function greater than ~3 solar masses), owing to difficulties in measuring the spectrum of the companion star at very faint quiescent luminosities.

Astronomers analysing simultaneous data obtained using the William Herschel Telescope and the Gran Telescopio Canarias, have been able to model the observed light curves of a transitional millisecond pulsar and conclude that the accretion of clumpy material through the magnetic barrier of the neutron star can produce the observed near-IR/optical variability and correlations.

Astronomers using ACAM on the William Herschel Telescope report the spectroscopic characterisation of

A/2017 U1 is the first known small body from interstellar space. It is visible in the centre of this 5-minute exposure using the ACAM imager on the William Herschel Telescope (WHT) on October 28, 2017. At the time of the observations, the WHT was able to lock on A/2017 U1 while it was travelling at a speed of 26 kilometres per second (the background, much more distant stars appear streaked because the telescope was tracking the motion of A/2017 U1).

A team of researchers led from the University of Warwick, UK is undertaking a transmission spectroscopy survey of hot Jupiters using the ACAM imager and spectrograph on the William Herschel Telescope. By observing spectroscopically an exoplanets transit across the face of its host star the team is able to detect changes in opacity in the exoplanets atmosphere as a function of wavelength. These early results have demonstrated the capabilities of ACAM to detect atmospheric opacity sources such as Rayleigh scattering, and to distinguish between clear and cloudy atmospheres with errors in the transmission spectrum of around 1 atmospheric scale height, comparable to Hubble Space Telescope.

An international team of astronomers has found a system of seven potentially habitable planets orbiting a star 39 light years away, three of which could have water on their surfaces increasing the possibility they could host life. Using ground and space instruments and telescopes, including the ACAM imager on the William Herschel Telescope, the team identified the planets as they passed in front of the ultracool dwarf star known as TRAPPIST-1. The star has around eight per cent of the mass of the Sun and is no bigger than Jupiter.

An international team led by researchers from the Instituto de Astrof

The William Herschel Telescope (WHT) has participated in 2014 and 2015 in a worldwide campaign to spectroscopically follow up Pluto from the ground in support of the encounter of NASAs New Horizons spacecraft with Pluto.

A large international team led by Klaas Wiersema from the University of Leicester has discovered circularly polarised optical emission in the afterglow of GRB 121024A. The study, published in Nature, used data mainly from FORS2 on the VLT, but also ACAM on the WHT. The ACAM data allowed the team to correctly identify a break in the light curve that confirmed the long standing prediction that an abrupt change of 90 degrees in the GRB linear polarisation happens when the Lorentz factor of the outwards jet decreases below a critical value.

On the 21st January 2014 astronomers reported the discovery of supernova SN2014J which reached its peak brightness on the 31st January. Some days later, this type Ia supernova started to fade. The image above demonstrates that SN2014J (marked with black lines) continued to be the brightest optical object in the galaxy even one month after the discovery.

Astronomers have used the ACAM instrument on the William Herschel Telescope in the discovery of a unique, isolated, compact elliptical galaxy.

Astronomers of the Herschel Multi-tiered Extragalactic Survey (HerMES) project announce today in the journal Nature the discovery of an unsually massive, maximum-starburst galaxy at a redshift of 6.34, or when the Universe was only 880 million years old. Because current theories of galaxy fomation and evolution predict smaller galaxies with slower rates of star production in the early Universe, the detection of such a galaxy is challenging.

The formation of asymmetric structures such as rings and jets in planetary nebulae (PNe) has been a matter of debate for a long time. The most popular hypothesis is that these features are produced in interacting binaries. Using data obtained with ACAM imager and spectrograph on the William Herschel Telescope, for the first time astronomers have been able to reliably relate jet ejections to mass transfer and accretion in a close binary in a planetary nebula.

The Herbig-Haro object 30 (HH30) is located in the L1551 dark cloud, at a distance of about 140 parsec, in the Taurus star-forming region. HH30 is considered a prototypical jet-disk system driven by a young stellar object (YSO). The impressive jet/counterjet structure extends several arcminutes in both directions from the exciting source, and shows an undulating morphology in the narrow-band [SII] images. Astronomers using ACAM at the William Herschel Telescope have been able to obtain a deep image of the HH30 field and have found an interesting explanation for the jet/counterjet system

XTE J1859+226 is a transient X-ray binary discovered in 1999 by the X-ray satellite RXTE. This type of binary system stays in quiescence for most of its life; however, from time-to-time the system can show an outburst at all wavelengths which can subsequently be detected by X-ray satellites. By combining the data taken using the INT and the WHT in 2000 with the photometry taken in 2008 with NOT, WHT and spectra from GTC, a lower limit to the mass of the black hole was set to 5.42 solar masses

Image of the Cigar Galaxy or M82 obtained using ACAM on the William Herschel Telescope. Credit: Pablo Rodr

Comet-like object P/2010 A2 was discovered by the LINEAR survey on January 6, 2010. Service observations carried out using ACAM on the William Herschel Telescope on January 21, 2010, show an asteroidal nucleus detached from the dust tail. Owing to its orbital parameters and its cometary appearance, the object is classified as a main-belt comet, in other words, an activated asteroid from the main asteroid belt. Comet P/2010 A2s orbit is the nearest to the Sun known so far, for this kind of object (semi-major axis of 2.29 AU)

A versatile new high-throughput imager and spectrograph, ACAM, was successfully commissioned on the William Herschel Telescope in June 2009, and is now available for use by the astronomical community.