Fall Quarter 2017 (current)
The flow of gas through the circumgalactic medium (CGM) regulates galaxy growth over cosmic time. Observations have recently revealed a complex multi-phase structure in the CGM that has challenged many of the established theories—highlighting significant gaps in our understanding of this critical aspect of galaxy formation. The spatial scales relevant to the CGM span a huge range with its structure and evolution determined by small-scale processes, such as the launching of galactic winds by clustered supernovae and thermal instability in the hydrostatic halo, and large-scale processes, such as cosmological accretion. I will describe my attempts to understand the details and interplay of these multi-scale processes in order to develop a coherent picture of the CGM that is consistent with observations.
The Origin of Stellar Species: constraining stellar evolution scenarios with Local Group galaxy surveys
Current mainstream theories of stellar evolution make simple approximations for fundamental processes like convective mixing or mass transfer in close binaries. These approximations can lead to systematic errors in our understanding of the physical properties of galaxies, both local and at high-redshifts. A critical reappraisal of stellar evolution theories is in order. In this talk, I will discuss a method to recover delay-time distributions (DTDs), which can pose powerful observational constraints on stellar evolution scenarios for many classes of stellar objects. To calculate DTDs, one needs a catalog of objects and a map of the star-formation histories of the host galaxy. The technique is particularly effective in the Local Group, where reliable star-formation histories from resolved stellar populations, and high quality surveys are available. I will discuss the application of this method to pulsating variable stars like RR Lyrae and Cepheids. I will also discuss the progress of my group towards the calculation of a DTD from Local Group supernova remnants, with the hope of constraining the long-standing progenitor problem of thermonuclear and core-collapse supernovae.
At UNSW we have built the world’s most sensitive astronomical polarimeter, capable of measuring stellar polarisation down to levels of a few parts per million. I will describe the instrument and the research we have done with it since its commissioning in 2014. One of the main goals of such instruments has been to contribute to the characterisation of exoplanet atmospheres by detecting polarised light reflected from hot-Jupiter type planets. However, we can also learn much about stars using these techniques. We have made some of the first polarimetric observations that directly probe stellar atmospheres and allow us to constrain stellar properties. In order to interpret these observations we have developed methods for modelling the atmospheres of both planets and stars including full polarisation in the radiative transfer. I will also describe future plans including a version of the instrument we are developing for Gemini North.
Spring Quarter 2017
Astronomers are entering a new era of exoplanet imaging with the Gemini Planet Imager (GPI), an extreme adaptive optics system at Gemini South. I will present some highlights of the achievable science with high contrast imaging instruments, including the GPI Exoplanet Survey (GPIES), an ongoing 890 hour survey of 600 young nearby stars. I will also present an overview of the technical limitations that prevent GPI from reaching planet masses and separations below ~2 Jupiter masses and ~10 AU, namely contrast and resolution, respectively. To further improve sensitivity to lower exoplanet masses and smaller separations, I will also discuss my ongoing work on new data processing algorithms, as well as possible future upgrades to the instrument in between leaving Gemini South in mid-2018 (when GPIES is planned to finish) and a possible move to Gemini North. For the former, I present an analysis from a new PSF subtraction algorithm that can improve contrast by up to ~45% at angular separations near the diffraction limit, while for the latter I present simulations showing that upgrading GPI with a new focal plane wavefront sensing technique, called the Self-Coherent Camera, could improve contrast by up to a factor of ~20, reaching ~Saturn mass sensitivity.
I will present an overview of Synthetic UniveRses For Surveys (SURFS), the next generation of mock observations, following in the footsteps of Millennium and Bolshoi simulations. The SURFS simulation set consists of N-body/Hydro simulations in the Planck concordance LCDM cosmology, sampling scales & halo masses down to 1 kpc and 100 million solar masses in 210 Mpc/h cosmological volumes. These simulation parameters are optimised to understand the galaxy formation physics governing satellite galaxies and chosen so as to produce synthetic analogues to upcoming surveys like WAVES and WALLABY. We use state-of-the-art Halo Finders, Trackers and Semi-Analytic Models (SAM) of galaxy formation to follow not just the evolution of central galaxies/haloes but the active lives of satellites/subhaloes spanning group to low cluster mass scales. I will present preliminary results on the evolution on the cosmic growth and gas accretion history of haloes and how the cosmic web ties into it.
Anchoring the distance scale and providing new insights into stellar physics using high-precision observations of classical Cepheids
Classical Cepheid variable stars (henceforth: Cepheids) are best-known for their crucial role in calibrating the cosmic distance scale, and thus, for investigating dark energy. Yet, Cepheids continue to be objects of high interest for stellar physics and rank among the most-studied types of variable stars.
This talk presents recent observational work aimed at increasing the accuracy of extragalactic distance measurements as well as providing new insights into stellar pulsations via highly precise observations obtained with state-of-the-art instrumentation from the ground and from space. Specifically, I present how high-precision radial velocity measurements of Cepheids a) support unprecedented parallax accuracy, b) reveal systematic uncertainties of Baade-Wesselink-type distances, and c) have enabled the discovery of atmospheric velocity field perturbations that are presently not understood. Related irregular variability patterns discovered via high-precision photometric and interferometric observations are also discussed.
The ongoing ESA mission Gaia is expected to revolutionize stellar astrophysics and provide a highly accurate anchor for the extragalactic distance scale. As this talk shows, high-precision observations can expose secrets of seemingly well-understood stars and play a crucial role for leveraging Gaia’s full potential.
Winter Quarter 2017
I will present the first coronagraphic spectroscopy of the AU Mic debris disk system obtained with HST/STIS as part of GO-12512. Spectra of the system were taken by placing a long slit in the disk direction while blocking out the central star with an occulting bar. A naked star of similar spectral type was likewise observed for a PSF subtraction. This procedure results in a two dimensional spectrum as a function of disk position between 5200 and 10,200 angstroms for the system. I will report the results of these AU Mic spectra, which can be used to help determine the dust grain composition of the system by characterizing the disk’s color as a function of radial distance along the its midplane. In addition, I compare the spectra on either side of the disk in order to probe the presence of any compositional and structural asymmetries. This reveals the dynamical perturbations and chemical processing occurring within the disk and traces the potential composition and architecture of any planetary bodies in the system.
I will present an overview of the identification and investigation of the handful of “young solar system analogs” — star/disk systems — that lie within a mere ~100 pc of Earth. I describe advances in our understanding of protoplanetary disk structure and evolution enabled by these systems, with particular emphasis on the new discovery space that is now being opened by high-resolution imaging with ALMA as well as extreme AO cameras on large ground-based optical/IR telescopes.
I will review a few recent results on theoretical models of galaxy formation in non standard DM models, with a focus on Warm Dark Matter and Self Interacting DM.
Galactic chemical evolution is a multidisciplinary topic that involves nuclear physics, stellar evolution, galaxy evolution, and cosmology. Observations, experiments, and theories need to work together in order to build a comprehensive understanding of how the chemical elements synthesized in astronomical events are ejected and spread inside galaxies and recycled into new generations of stars. Nuclear physics provides nuclear reaction rates, stellar models provide the composition of stellar ejecta, galaxy models follow the evolution of chemical species driven by multiple stellar populations, cosmological simulations dictate how galaxies form and evolve in general, and observations provide constraints to test and improve numerical recipes driven by theories. During this talk, I will address the topic of galactic chemical evolution and present our efforts to create permanent connections between different fields of research (including nucleosynthesis and gravitational wave physics). Our ultimate goal is to better understand the origin of the elements in the universe and to explain the diverse chemical evolution patterns observed in nearby galaxies.
Autumn Quarter 2016
After briefly reviewing what is known and what we still need to know in order to correctly identify the supernovae Ia progenitors in different populations, I will talk about massive white dwarfs that are accreting mass in binary systems and are burning hydrogen in shell. I will review what we know about symbiotics and Be+white dwarf systems as possible progenitors of type Ia supernovae, and I will present new observational data about some of the hottest and massive white dwarf binaries in the Local Group.
Spring Quarter 2016
Rotation and Activity in Low-mass Hyades and Praesepe Members, and the Implications for Gyrochronology
Winter Quarter 2016
Galactic winds blow through galaxies of all shapes and sizes, but they are particularly ubiquitous in high-redshift star-forming galaxies, where they may be driving galactic evolution by regulating the baryon cycle. Due to recent advances in the modeling of stellar feedback, cosmological simulations of galaxy formation can now generate galactic winds explicitly, while also matching many observed properties of galaxies at various epochs. We can therefore study simulated winds as an emergent phenomenon, and derive insights into galaxy evolution to compliment current observational knowledge. In my talk, I will discuss my progress in characterizing galactic outflows in the Feedback in Realistic Environments (FIRE) simulations. I will quantify the overall prevalence and intensity of galactic winds, their connection to physical galactic properties, and the observational implications of wind-driven evolution for galaxies and the circumgalactic medium.
Please join us in the reading room on Tuesday Jan 12 at 4pm for a general meeting about APO, including new instrumentation on the 3.5m telescope, planning that is starting now for the 2.5m Sloan telescope in the 2020’s time frame (“After Sloan 4”), and current usage and availability of ARCSAT, the 0.5m photometric telescope.
You are particularly encouraged to participate if you have input about the new spectrograph (currently in planning stage) to replace DIS on the 3.5m. A committee is actively soliciting input from the users community for science requirements to determine design goals.
Join us for 10 min talks by Chris Laws, Nicole Silvestri Kelly, Toby Smith, Oliver Fraser, Ana Larson, and Joe Huehnerhoff!
10 min astro lunch talks by graduate students.
The Fluctuating UV Background Across Cosmic Time
10 min astro lunch talks by graduate students.
Autumn Quarter 2015
Oscillating stars in eclipsing binaries are powerful tools for testing stellar models because binarity allows for independent computation of physical stellar parameters. Thanks to advances in asteroseismology, red giants have become astrophysical laboratories for studying stellar evolution and probing the Milky Way. In this talk, I highlight an interesting pair of oscillating red giants in the eclipsing binary KIC 9246715, and I discuss work underway to characterize the 20 known red giants with eclipsing companions observed by Kepler. These are rapidly becoming some of the best-studied stars and an important benchmark for asteroseismology.
This is the first of a series of astro lunches featuring short (10 minute) talks by the faculty in October. This event will contain talks by Julianne, Matt, Emily, Fabio, and Paula. See you there!
I will discuss my work to determine the compositions of small planets. The density-radius distribution of 72 exoplanets smaller than 4 Earth radii peaks at 1.5 Earth radii. Planets smaller than 1.5 Earth radii usually increase in density with increasing planet radius, suggesting that planets up to 1.5 Earth radii can have rocky surfaces. However, planets larger than 1.5 Earth radii typically decrease in density with increasing planet radius, suggesting that at around 1.5 Earth radii, planets begin to accrete volatile envelopes that reduce their bulk density. This trend is exemplified in two systems for which I present updated planet masses. By simultaneously fitting radial velocities and transit timing variations with TTVFast, I determined that (1) Kepler-11 has six planets with volatile envelopes; and (2) Kepler-10 has one rocky planet, one planet with a volatile envelope, and one non-transiting planet
10 minute faculty research talks at noon in the reading room. Join us!
10 minute post-doc/research scientist research talks (+ 1 faculty member).
10 minute post-doc/research scientist research talks (+ 1 faculty member)
10 minute post-doc/research scientist research talks