Observations

Nov 11, 2018

Surface Chemistry of Peculiar Hot Subdwarfs

2018-2-SCI-033

Stars approaching the end of their lives expand and, in many cases, exchange material with close companions. This has a radical effect on their evolution and surface composition, producing a zoo of rare but highly exotic stars. By exploring the propertiesof thes pathological cases, we are endeavouring to understand the ways in which stars exhange matter and evolve towardstheir final fate as white dwarfs or supernovae. The stars in this programme are perfect examples — many of them have completelylost their surface hydrogen, for reasons still to be explained. These observations will tell us about the abundances of otherelements — previously we have discovered huge overabundances of exotic species such as lead and zirconium, and will explore how some of these stars may vary over time.

Dark energy tests with quasar monitoring XII

2018-1-MLT-004

Cosmological measurements show that only 5% of the Universe is made up of the well-known atomic matter, while the rest consists of exotic dark matter and even more exotic dark energy. The nature of this dark energy is unknown, physicists proposed hundreds of theories what it might be but the current observational constraints are still consistent with the cosmological constant proposed by Einstein. This is not enough to constrain the physical nature of the dark energy. Thus the goal of the present day cosmology is to detect the departure of the dark energy properties from this constant value. This requires further progress in the currently adopted methods, like the study of the Cosmic Microwave Background, or the Supernova Ia. But it also requires designing new cosmological tools to verify the results, and to achieve even greater accuracy.We propose that quasars can be as good probes of dark energy as Supernova Ia and provide independent distance estimates. Quasars are very luminous centres of active galaxies, which are observed from very large distances. Thanks to the powerful SALT telescope we are able to carry out very accurate observations of quasar emission lines, and from their behaviour, combined with the model of the line emission we developed, we can measure directly the absolute luminosity of every observed quasar, and subsequently to measure distances which are next used in cosmological studies. This in turn constraints the history of the Universe expansion, and the properties of the dark energy which is responsible for accelerated expansion.

Monitoring the line emission in Southern Galactic Be/X-ray binaries

2017-1-MLT-004

Lines arising from the disc of material around Be/X-ray binaries are highly variable on multiple timescales. The variability seen is intimately linked to the mass transfer and resulting X-ray emission seen in such systems, though the details of this link are still not well understood. We are monitoring these lines with SALT/RSS to see how they change during periods of differing X-ray activity and at different points around their orbits.

Asymmetry is Destiny: Wolf-Rayet Binary Stars as GRB Progenitors

2018-2-MLT-005

This program aims to use the recently-commissioned high-precision spectropolarimetry mode of RSS to probe the prodigious mass-loss from certain massive evolved stars known as Wolf-Rayet stars which are in binary systems. These objects are possible progenitors of Gamma-Ray Bursts, which are the most energetic explosions yet known, and can be seen across the entire known universe.

Optical Spectroscopy for the NuSTAR Serendipitous Survey with SALT

2018-2-MLT-006

The cosmic X-ray background (CXB) was first discovered in the early 1960’s, several years before the detection of the cosmic microwave background (CMB). However, unlike the CMB, which is truly diffuse in origin, the CXB is dominated by the emission from high-energy distant point sources: Active Galactic Nuclei (AGNs), the sites of intense black-hole growth. Surveys with Chandra and XMM-Newton have resolved ≈ 70–90% of the CXB at low energies ( 10 keV observatory with focusing optics. We focus our study on NuSTAR serendipitous sources to identify spectral features in order to measure the distances to these sources (redshifts), as well as to establish their classification and characteristics. In order to achieve our goals we aim to obtain longslit spectra with the Robert Stobie Spectrograph (RSS), mounted at prime focus of SALT, of 17 NuSTAR serendipitous sources.

THE SALT GRAVITATIONAL LENSING LEGACY SURVEY

2015-2-MLT-006

Everything in the universe warps space – even you, right now, are warping the space around you. This is too tiny to see in everyday objects but entire galaxies are big enough for the warps to be measurable. You can see the warps if you have a chance alignment of a foreground and a background galaxy: the background looks warped and stretched and magnified because of the warped space around the foreground galaxy. However, finding these alignments of foreground and background galaxies has been tricky. We have made a breakthrough and discovered an extremely efficient method of finding these chance alignments of galaxies using the Herschel infrared space telescope. Some galaxies appear to be unexpectedly bright in infrared light, and this is because of the magnification from a foreground galaxy. Our project on SALT aims to measure the distances to these foreground galaxies, so we can work out the geometry of the lenses and make inferences about the geometry of the Universe, the shape of the invisible dark matter, and shed light on why the expansion of the Universe is accelerating.

Interaction history of the LMC and SMC: spectroscopic observations of Cepheids in the Magellanic Bridge

2018-2-MLT-001

Interaction history of the LMC and SMC

Observing the Transient Universe

2018-2-LSP-001

This large SALT program is aimed at studying “things that go bang in the night”, namely transient objects in the Universe which either are newly discovered objects, or known objects who suddenly change their appeatance. Such things include binary stars with accreting compact companions, many of them X-ray or gamma ray sources, eruptive stars which suddenly brighten, black holes systems, including active galaxies powered by them, and all manner of explosions including the most energetic of all, gamma ray bursts.

Nov 10, 2018

Surface Chemistry of Peculiar Hot Subdwarfs

2018-2-SCI-033

Stars approaching the end of their lives expand and, in many cases, exchange material with close companions. This has a radical effect on their evolution and surface composition, producing a zoo of rare but highly exotic stars. By exploring the propertiesof thes pathological cases, we are endeavouring to understand the ways in which stars exhange matter and evolve towardstheir final fate as white dwarfs or supernovae. The stars in this programme are perfect examples — many of them have completelylost their surface hydrogen, for reasons still to be explained. These observations will tell us about the abundances of otherelements — previously we have discovered huge overabundances of exotic species such as lead and zirconium, and will explore how some of these stars may vary over time.

Optical Spectroscopy for the NuSTAR Serendipitous Survey with SALT

2018-2-MLT-006

The cosmic X-ray background (CXB) was first discovered in the early 1960’s, several years before the detection of the cosmic microwave background (CMB). However, unlike the CMB, which is truly diffuse in origin, the CXB is dominated by the emission from high-energy distant point sources: Active Galactic Nuclei (AGNs), the sites of intense black-hole growth. Surveys with Chandra and XMM-Newton have resolved ≈ 70–90% of the CXB at low energies ( 10 keV observatory with focusing optics. We focus our study on NuSTAR serendipitous sources to identify spectral features in order to measure the distances to these sources (redshifts), as well as to establish their classification and characteristics. In order to achieve our goals we aim to obtain longslit spectra with the Robert Stobie Spectrograph (RSS), mounted at prime focus of SALT, of 17 NuSTAR serendipitous sources.