2021 MSc and PhD Research Opportunities at SAAO

1. Shazrene Mohamed: 3D simulations of stellar explosions and interactions

Special qualifications: Strong computational and theoretical background. Previous experience with (magneto)hydrodynamic, N-body or radiative transfer modelling would be an advantage.

In their final stages of evolution, stars lose copious amounts of mass and momentum via powerful, dense stellar winds. Enriched in dust and heavy elements forged in the cores of stars, these outflows not only provide the raw material for planetary systems, but also play a central role in chemical evolution of galaxies. In binary systems, where the winds impinge upon a close companion, a wide range of phenomena result, from bipolar outflows in planetary nebulae to violent nova and supernova explosions.

This project aims to fundamentally improve our understanding of the complex outflows and explosions of evolved stars, and their impact on their environments. With the recent tremendous improvement in the sensitivity and resolution of observational facilities, and the continuously upgraded computational capabilities, this goal is now within reach.

Possible project topics include supercomputer models of:

• Star-planet interactions
• Radio emission from stellar explosions
• Stellar collisions and mergers
• Mass transfer in (semi-)detached binaries
• Bow shocks from runaway stars

2. Retha Pretorius: The Galactic low mass X-ray binary population

Low-mass X-ray binaries (LMXBs) are compact binary systems in which a neutron star or stellar-mass black hole accretes material from a close, low-mass stellar companion. The interest in LMXBs has revolved mainly around accretion and relativistic jets, the neutron star equation of state, and strong-field gravity. Most studies of these systems have focused on individual sources. However, the overall population properties, and formation and evolution of these systems, also have wide-ranging consequences in many areas of astrophysics.

Data such as the orbital period distribution, observationally inferred mass transfer rates, and duty cycles of their transient X-ray behaviour, provide constraints on the theory of how LMXBs form and evolve. Ideally, one wants a complete, uniformly-selected sample of systems, for which the observational
selection effects can be quantified, in order to compare it to population synthesis models. A suitably well-defined sample can be constructed using wide-field hard X-ray data from Swift. The astrometric Gaia mission is also already providing distances and proper motions, leading to powerful new constraints on the properties of the Galactic LMXB population (the next Gaia data release will be in the second half of 2020).

Project goals

This PhD project will focus on the observed properties of the Galactic LMXB population, and the constraints that they place on the evolution of these systems. The details of the research to be undertaken will be defined by the successful applicant, with guidance from the supervisor. The project will use mainly existing data, from e.g. Gaia and Swift/BAT, but there is scope to propose for additional observations, especially with the SAAO telescopes and SALT.

Skills

Basic programming skills and demonstrated research ability are required. Experience in observational or computational astrophysics will be an advantage.

3. Rosalind Skelton: The evolution of Brightest Cluster Galaxies with BEAMS

Other collaborators:
Matt Hilton (UKZN), Ilani Loubser (NWU), Daniél Groenewald (SAAO), Moses Mogotsi (SAAO)

Project Description:
We are carrying out a large SALT programme called BEAMS (PI: Matt Hilton) to explore the evolution of brightest cluster galaxies (BCGs) from 0.3 < z < 0.8. The galaxies are selected from the Advanced ACT survey, which finds clusters using the Sunyaev-Zeldovich (SZ) effect, with a well-defined selection function that is relatively independent of cluster mass across a wide range of redshifts. We are using SALTspectroscopy to target the central galaxy in approximately 150 of these clusters, and data for a third of the sample is already in hand. The clusters will also be observed by MeerKAT. By stacking the optical spectra in mass and redshift bins we will explore the evolution of the stellar populations and AGN feedback in massive galaxies in dense environments. We will determine what fraction of BCGs have nearby companions, with the aim of measuring the merger fraction and how much they grow in mass through mergers (see Groenewald et al. 2017). The SALT spectroscopy will help constrain what fraction of these companions are bound to the BCGs rather than projected as pairs, and together with the available multi-wavelength data, will allow us to study the properties of the BCGs in detail, correlating merger activity with star formation histories, the characteristics of the central AGN and the cluster environment.

Useful links:
ACT clusters, Hilton et al. 2018 http://adsabs.harvard.edu/abs/2018ApJS..235…20H
BCG growth through mergers, Groenewald et al. 2017
http://adsabs.harvard.edu/abs/2017MNRAS.467.4101G

4. David Buckley: Transients in the LSST Era

Supervisor:
Dr David Buckley (DB), SAAO (dibnob@saao.ac.za).

Potential Co-supervisors:
Professor Patrick Woudt, UCT (pwoudt@ast.uct.ac.za)
Dr Magaretha Pretorius, SAAO (retha@saao.ac.za)
Dr Stephen Potter, SAAO (sbp@saao.ac.za)
In addition, there also exists the possibility for co-supervisors from other South African institutions.

Overview
The activities proposed for this programme involve various activities supporting followup studies of optical transients discovered by the Large Synoptic Survey Telescope (LSST). When completed in 2022, LSST, with its 10 square degree field and 3.2 gigapixel camera, will embark on its 10 year mission to continuously survey the southern sky, in multiple filters, every few days. This will be a game-changer in terms of the number discoveries of transient or variable objects, leading to the discovery of new types of objects and phenomena. South Africa will be heavily involved in followup of these LSST-discovered transient.

The supervisor is the South African PI Affiliate for LSST transient science, leading a team currently consisting of 8, including the 3 named potential co-supervisors, and three graduate students. Most of the activities will involve existing and new international collaborations. Our programme focuses primarily on the various object classes, science drivers and task force activities within the LSST Transients and Variable Stars (TVS) science collaboration, plus related projects within the Stars, Milky Way and Local Volume (SMWLV) collaboration.

Planned Activities
Some of the activities within this programme, for which students could potentially become involved, cover the following areas:
• participation in existing transient science projects within the scope of the SALT and MeerKAT (i.e. ThunderKAT) transient programmes, focusing on specific object classes of interest
• multi-wavelength and multi-messenger transient followup of gravitational wave and neutrino events
• involvement in the new KMTNet Synoptic Survey of Southern Sky (KS4), in collaboration with Korean and Australian colleagues, as an LSST precursor
• developing automatic followup systems at SAAO/SALT to react to triggers from LSST observing brokers
• developing optimal cadencing strategies for Galactic transient from simulations of various compact binaries populations in the Galaxy and Magellanic Clouds
• undertaking mini-surveys with facilities like MeerLICHT (e.g. in twilight), MONET-South or KMTNet to test detection algorithms and automated light curve classifications
• assisting with various task force activities within the science collaborations, some of which were recently (Nov 2018) discussed in a series of science White Papers

The final choice of topics will depend on the student’s interests and the requirements of the programme.

5. Prof. M. Bershady (Instrumentation/Observational analysis)

SALT Slit-Mask IFU for Nearby Galaxy Studies: Design, development and
commissioning of a fibre slit-mask integral-field unit for SALT
prime-focus spectrograph.

Requirement: Masters program in astronomy or a closely aligned field.

Key words: astronomical instrumentation; slit-mask integral-field unit
lead.

Description: We seek applicants to undertake a three-year
Ph.D. program with Prof. M. Bershady, co-leading the design,
construction and commissioning of a two-dimensional fibre array
(integral field unit, or IFU) for the Southern African Large Telescope
prime-focus spectrograph. The IFU will be designed to achieve the
highest possible spectral resolution while delivering photon-limited
performance for the mapping and study of galaxy kinematics traced by
stars and ionized gas. The specific design will be driven by a science
case developed by the Ph.D. candidate and Bershady. The instrument
will be suited for follow-up of relatively nearby galaxies observed in
HI-imaging surveys with MeerKAT for analyzing their stellar
populations, dark-matter content, and dynamics. This relatively simple
and small instrument is ideal for candidates who wish to learn about
instrumentation and who have plans for a career path in industry or a
research institution.

Project scope: The Ph.D. project will include (1) high-level design of
the fibre slit-mask IFU based on specific science requirements
established by the candidate and their supervisor; (2) implementation
and fabrication of opto-mechanical assemblies, mounts and fixtures
based on an existing design for a companion IFU being built at the
University of Wisconsin (UWisc); (3) establishing a fibre-polishing
protocol to ensure high throughput and low focal-ratio degradation;
(4) procurement, assembly and termination of fibres in the slit-mask,
including their alignment and bonding fibres to micro-prisms; (5)
designing the interface between the IFU and the fibre-optic test
facility (FTF); (6) co-mentoring the honors/bursary student and
masters student on the development and calibration of the FTF; (7)
commissioning the instrument on-sky in the Robert Stobie Spectrograph
on SALT to complete a pilot program demonstrating science performance;
(8) completing a written dissertation describing both instrument and
pilot observations suitable for publication.

The student will work closely with Prof M. Bershady (SAAO SARChI), his
research team of observers and instrumentalists, members of the SAAO
Machine Shop, as well as other members of the SAAO technical and
science staff. The student will have the opportunity to travel to
UWisc where the companion slit-mask IFU is being made and observe with
existing IFUs.

Requirements: Applicants need not have a background in astronomical
instrumentation or fibre optics; knowledge of astronomy and geometric
optics at the undergraduate level is required; completion of a Masters
program in astronomy or a closely aligned field is required; an
interest to learn laboratory skill with fibre-optics
and opto-mechanics is required.

1. Steve Potter: Transient and time domain astronomy

This would be an observational project using the facilities in Sutherland: SAAO and SALT. Experience in observational astronomy would be an advantage.

2. Steve Potter:  African Intelligent Observatory (AIO)

This project would involved working in the AIO development team. Experience in either observational astronomy and/or data reductions and/or software development would be an advantage.

3. Encarni Romero Colmenero: Reverberation Mapping of AGN, using LCO and SALT

The postdoc should already have some AGN research experience, including photometry and spectroscopy, and of course publication(s).

4. Shazrene Mohamed: 3D simulations of stellar explosions and interactions

Special qualifications: Strong computational and theoretical background, as well as previous experience with (magneto)hydrodynamic, N-body or radiative transfer modelling.

In their final stages of evolution, stars lose copious amounts of mass and momentum via powerful, dense stellar winds. Enriched in dust and heavy elements forged in the cores of stars, these outflows not only provide the raw material for planetary systems, but also play a central role in chemical evolution of galaxies. In binary systems, where the winds impinge upon a close companion, a wide range of phenomena result, from bipolar outflows in planetary nebulae to violent nova and supernova explosions.

This project aims to fundamentally improve our understanding of the complex outflows and explosions of evolved stars, and their impact on their environments. With the recent tremendous improvement in the sensitivity and resolution of observational facilities, and the continuously upgraded computational capabilities, this goal is now within reach.

Possible project topics include supercomputer models of:

• Star-planet interactions
• Radio emission from stellar explosions
• Stellar collisions and mergers
• Mass transfer in (semi-)detached binaries
• Bow shocks from runaway stars

5. Retha Pretorius: Mini-trackers on SALT

Project description: The Southern African Large Telescope has a spherical primary mirror, implying a very large field of view (35 degrees in diameter), of which only a very small fraction is corrected by the current spherical aberration corrector (SAC) on the SALT tracker, and hence available for science observations. The mini-racker concept involves adding a number of smaller SACs, on mini-trackers that can be positioned anywhere in the large telescope field of view. A successful implementation of mini-trackers on SALT will greatly increase the scientific productivity of the telescope, and turn it into a uniquely powerful facility for a range of science cases.

This project involves in the first 6 months a technical feasibility study to determine whether a concept design phase will go ahead. The postdoc will work as a member of the project team of astronomers and engineers, investigating several science related problems that will drive the design of the mini-trackers. If the result of this study is that mini-trackers are not technically feasible, the postdoc will have the opportunity to work on other instrumentation projects. The position also allows for the postdoc to pursue their personal research program, for up to 60% of their time, either independently, or in collaboration with the supervisor or any SAAO astronomers.

Special qualifications: a background in observational optical astronomy

6. Rosalind Skelton: The evolution of Brightest Cluster Galaxies with BEAMS

Other collaborators:
Matt Hilton (UKZN), Ilani Loubser (NWU), Daniél Groenewald (SAAO), Moses Mogotsi (SAAO)

Project Description:
We are carrying out a large SALT programme called BEAMS (PI: Matt Hilton) to explore the evolution of brightest cluster galaxies (BCGs) from 0.3 < z < 0.8. The galaxies are selected from the Advanced ACT survey, which finds clusters using the Sunyaev-Zeldovich (SZ) effect, with a well-defined selection function that is relatively independent of cluster mass across a wide range of redshifts. We are using SALTspectroscopy to target the central galaxy in approximately 150 of these clusters, and data for a third of the sample is already in hand. The clusters will also be observed by MeerKAT. By stacking the optical spectra in mass and redshift bins we will explore the evolution of the stellar populations and AGN feedback in massive galaxies in dense environments. We will determine what fraction of BCGs have nearby companions, with the aim of measuring the merger fraction and how much they grow in mass through mergers (see Groenewald et al. 2017). The SALT spectroscopy will help constrain what fraction of these companions are bound to the BCGs rather than projected as pairs, and together with the available multi-wavelength data, will allow us to study the properties of the BCGs in detail, correlating merger activity with star formation histories, the characteristics of the central AGN and the cluster environment.

Useful links:
ACT clusters, Hilton et al. 2018 http://adsabs.harvard.edu/abs/2018ApJS..235…20H
BCG growth through mergers, Groenewald et al. 2017
http://adsabs.harvard.edu/abs/2017MNRAS.467.4101G

7. David Buckley Observing the Transient Universe

Dr David Buckley, SAAO (dibnob@saao.ac.za), Principal Investigator of the SALT transient programme, on behalf of a large team of local and international collaborators.

Overview
This postdoctoral position is to support the on-going SALT Large Science Programme on transients, which has been running since 2016 and involves studies of astrophysical transients across a broad range of object classes,
including high energy (X-ray, γ-ray) and multi-messenger (gravitational wave, neutrino) sources and, since 2018, MeerKAT radio transients. In addition, with the 2019 launch of the Spektrum-RG X-ray observatory (with the eROSITA and ART-XC instruments), an expansion of transient followup of X-ray sources from this survey is anticipated. Finally, there are also opportunities for involvement in the South African LSST transient programme, which involves preparatory work ahead of LSST, which begins commissioning in 2022/23.

Potential research topics
Due the wide scope of the programme, there is ample opportunity for participation in a number of areas of observational multi-wavelength astronomy, working with various collaborators and international teams. Some
of the major topic areas currently under investigation, together with relevant publication outputs from the programme, are listed below:

1. Transitional millisecond pulsars: multi-wavelength observations, particularly radio and X-ray (de Martino et al. 2014, MNRAS 444, 3004; Coti Zelati et al. 2019, A&amp;A 622, 21).
These are rare but interesting systems for which SALT (and recently MeerKAT) has been making significant contributions Plans are afoot for MeerKAT timing mode observations of one new candidate system which was detected during Open Time observations in 2019.

2. Unusual supernovae: optical spectroscopy, spectropolarimetry (e.g. Vallely et al. 2019, MNRAS 487, 2372)
Recent work, particularly on core collapse and super-luminous supernovae, has been led by our Chinese and Indian collaborators and has involved followup on ASASSN-discovered sources. We aim to expand the South African involvement in this area.

3. High energy transients, including GRBs and Gravitational Wave events: optical spectroscopy (e.g. Abbott et al. 2017, ApJL, 848, L12; Buckley et al. 2018, MNRAS Letters 474, L71).
The first electromagnetic counterpart of a GW event was strongly supported by observations at SALT and SAAO, with results featuring in 8 refereed papers. We are currently actively involved in efforts to identify new counterparts of aLIGO/Virgo NS-NS and NS-BH events during the current O3 campaign
and this will continue.

4. Novae and related objects: optical spectroscopy, multi-wavelength observations (e.g. Aydi et al. 2018, MNRAS 474, 2679; Aydi et al. 2018, MNRAS 480, 572).
Synoptic multi-wavelength monitoring has resulted in a number of significant new discoveries which is changing our view point, particularly for those which emit at γ-rays.

5. Cataclysmic variable and related objects: spectroscopy, polarimetry, high speed photometry (e.g.Buckley et al. 2017, Nat Ast 1, 29; Maccarone et al. 2018, Nat Ast 3, 173; Breytenbach et al. 2018, MNRAS 484, 3831; Hakala et al. 2018, MNRAS 486, 2549). Some of these were transient followup of discoveries made from ASASSN, MASTER and TESS.

6. Compact binary X-ray transients (Low Mass X-ray Binaries, High Mass X-ray Binaries): time resolvedoptical spectroscopy, high-speed spectroscopy (e.g. Paice et al. 2019, MNRAS 488, 512; Charles et al.2019, MNRAS Letters 489, L47; Monageng et al. 2019, MNRAS 485, 4617).
Both neutron star and black hole accretors are the subject of multi-wavelength time domain studies revealing both new objects and phenomena never seen before. This work has been particularly productive due to the ability of SALT to react fast to targets of opportunity and to undertake high time resolution observations.

8. Prof. M. Bershady Instrumentation/Observational analysis

Spatial Heterodyne Spectrometer to Search for Missing Baryons: Design,
development and commissioning of a Spatial Heterodyne Spectrometer for
SAAO’s Sutherland telescopes to detect diffuse nebular emission around
galaxies.

Requirement: Ph.D. in astronomy a closely aligned field.

Key words: astronomical instrumentation; interferometric techniques in
spectroscopy; nebular spectroscopy

Description: We seek applicants to undertake a two-year postdoctoral
program with Prof. M. Bershady co-leading the design, construction and
commissioning of a spatial-heterodyne spectrometer (SHS) for
telescopes at Sutherland, including the Southern African Large
Telescope (SALT). The instrument will be used to detect and
characterize diffuse nebular emission around nearby galaxies, thereby
contributing to our understanding of where the missing cosmic baryons
are located.

The SHS is a grating-dispersed Michelson interferometer with no moving
parts; it generates a spectral interferogram yielding high spectral
resolution for a much larger entrance aperture than a conventional
spectrograph. SHS instruments are competitive for observations of
diffuse nebular emission over narrow spectral band-pass but wide
field-of-view. The SHS to be designed will be shoe-box in size, yet
capable of achieving resolutions comparable to SALT’s high-resolution
spectrograph with an entrance aperture of 40 arcsec^2 (on SALT). The
instrument will be optimized to detect specific nebular spectral
diagnostics to determine the chemical content and the physical
conditions of the ionized gas. This instrument will enable new
discoveries with SALT and it will be a path-finder for future
instruments that include high multiplex, wide-field coverage as well
as compact payloads for future space missions in the ultraviolet and
infrared.

Project scope: The postdoctoral program will include (1) high-level
design of the SHS instrument based on specific science requirements
established by the scholar and their supervisor; (2) procurement,
fabrication and alignment of optics, opto-mechanical assemblies,
mounts and fixtures based on this instrument design; (3) development
of the data-analysis tools to transform the spectral interferogram
into a spectrum; (4) laboratory calibration of the instrument; (5)
packaging the instrument for use on SALT and/or other telescopes at
SAAO; (6) commissioning the instrument on-sky to complete a pilot
program demonstrating science performance; (7) publishing both
technical and scientific results in peer-reviewed journals.

The postdoctoral scholar will work closely with Prof M. Bershady (SAAO
SARChI), his research team of observers and instrumentalists
(including a team building a fibre-optic test facility and a fibre
integral-field unit for SALT), members of the SAAO Machine Shop, as
well as other members of the SAAO technical and science staff.

Requirements: Applicants should have some background in astronomical
instrumentation. Knowledge of astronomy and geometric optics at the
undergraduate and graduate levels is required. Completion of a
Ph.D. in astronomy a closely aligned field (such as physics or
atmospheric science) is required. An interest to learn laboratory
skills and undertake instrument development with optics and imaging
detectors is required.

9. Prof. M. Bershady – Observational analysis

Vertical Population Gradients as Galaxy Evolutionary Probes of Disk
Formation

Requirements: Ph.D. in astronomy a closely aligned field.

Key words: galaxies; galaxy evolution; stellar populations;
integral-field spectroscopy

Description: We seek applicants to undertake a two-year postdoctoral
program working with Prof. M. Bershady to measure the vertical stellar
age, metallicity and abundance gradients as well as the kinematics in
nearby, edge-on galaxy disks with public integral-field spectroscopic
data from SDSS-IV/MaNGA. The scientific aim of this program will be to
determine if the Milky Way is a typical spiral galaxy in terms of its
stellar age and metallicity gradients, and more broadly to provide
constraints on the possible ways in which stars are formed and
assembled in galaxy disks. The successful applicant will have the
opportunity to travel to the University of Wisconsin for a time period
to be determined.

The program analysis will include the following elements and time-line:

Define the sample from SDSS-IV Data-Release(DR)-15. [1 month] DR15
includes 4706 MaNGA galaxies. Our sub-sample will be selected visually
from the subset of galaxies with b/a<0.3 that are truly edge-on to
within a few degrees. For more massive spirals, this is
well-determined by the symmetry in the central dust-lane. Selection
will become more subjective at lower mass where the central dust lane
is less pronounced. The goal is to identify several 10’s of candidates
in 6 stellar-mass bins in the range 9<log(M*)<11, with a total sample
of order 100 galaxies.

Define radial and vertical apertures with adequate S/N from existing
flux- and wavelength-calibrated data-cubes [3 months] that are
well-tailored for studying vertical and radial gradients. The DR15
MaNGA Data Analysis Pipeline (DAP) has defined apertures at S/N~10
based on Voronoi binning, but in general these will not be
well-optimized for studying vertical and radial gradients. We will
define bins of constant vertical thickness at a given height, with
increasing radial width as required to achieve continuum S/N~10 pix-1
bin-1. The vertical thickness may increase with height such that there
are at least 3 radial bins at a given height. The vertical thickness
will be no smaller than 2 arcsec (of order the spatial resolution).

Derive line-of-sight velocities and velocity dispersions for gas and
stars [2 months] using pPXF in apertures where values do not already
exist from the MaNGA Data Analysis Pipeline (DAP).

Derive light- and mass-weighted stellar ages, metallicities ([Fe/H]),
and abundances ([alpha/Fe]) [2 months] in these apertures using
Starlight and an agreed-upon set of stellar or SSP templates.

Compare results to measures from Pipe3D [2 months], also released in
DR15.

Analyze the trends in the vertical and radial gradients [6 months] and
how they depend on galaxy mass and star-formation history. Analysis
will include applying a simple dynamical model with different
star-formation histories to match both the observed distribution of
mass and the vertical stratification of stellar populations.

Write and submit two papers to a peer-reviewed journal [8 months]
(MNRAS, AJ, ApJ, or A&A) describing the salient results in the context
of a simple model for the stratification of stellar populations in
spiral disks.