Zhongtian “Jack” Hu

MRK 477: Peeking Through the Veil

 Zhongtian Hu

Most Active-Galactic-Nuclei (AGN) studied so far are anticipated to have a dusty torus structure surrounding their central engines. While there has been a steady improvement in the understanding of this torus structure’s role in shaping the AGN’s emission on various wavelengths, the actual details concerning the structure of these tori remain shrouded. My undergraduate research project with Dr. Marco Ajello at Clemson University involves trying to understand better the AGN torus structure using data collected on the Seyfert 2 galaxy MRK 477. In particular, given a new, clumpy AGN torus model developed by Dr. Ajello’s team in 2019, how changes in the line-of-sight column density can hint at the shape of the torus surrounding the super-massive black hole at the center of MRK 477.

Jessica Anderson

The puzzle of accretion disks and thermal stability

Jessica Anderson

For years, there has been a discrepancy between theory and observation of properties of low mass X-ray binary systems (LMXRB).The Shakura-Sunyaev thin disk model proposes a radiation-pressure dominated, thermally unstable, inner region. In this region, heating and cooling depend on midplane temperature at different exponential rates, leading to thermal instability, a thermal runaway, and the expansion or collapse of the disk. However, observers see a stable disk, and the question of what stabilizes these disks arises. Strong magnetic fields are proposed to thermally support the disk as radiation pressure is overcome by magnetic pressure. We simulate three different magnetic field configurations: 1) a zero-net-flux, multiple-loop configuration; 2) a net-flux, vertical-field configuration; 3) and a zero-net-flux, radial-field configuration. The results from these simulations help us answer the question of the discrepancy between thin disk theory and observation, giving us more insight on the properties of black hole X-ray binary systems.

Adam Vendransco

High-redshift blazars through NuSTAR eyes

Adam Vendrasco

MeV Blazars are some of the most luminous and powerful sources in the known Uni-verse. Located at the center of galaxies and at high redshift (z>2), these Active Galactic Nuclei (AGN) can produce relativistic jets releasing a vast amount of energy. Finding more such sources and studying their broadband emission enables us to unveil the properties of these jets and the supermassive black holes powering them. In this work we analysed four high-redshift blazars using NuSTAR and Swift-XRT to precisely characterize their high-energy emission. These four sources are some of the few blazars to date that have both NuSTAR, Swift-XRT and Fermi-LAT data. Analysing the sources in both hard x-rays and gamma-rays will allow us to constrain the jet power of these objects. In this talk I will present the most recent results on this work.

Tri Nguyen

Simulating Tilted Black Hole Accretion Disk and Their Effects on Astrophysical Jets

This presentation provides an update on our efforts to simulate precession of tilted accretion disks in orbit about a rotating black hole using the cubed-sphere grid. The main motivation for this research is to assess what impact a precessing disk has on the orientation and power of relativistic jets associated with it. Precession, in this case, is caused by relativistic torques from a rotating black hole acting on the tilted disk. Since jets are an important instrument of feedback of accreting black holes on their environments, it is important to study them at their source. We used the cubed-sphere grid, as it eliminates one of the most troubling features of a spherical-polar grid, i.e., the pole, while retaining an approximately spherical symmetry. We found correlations between the disk and jet twist, indicating that our jets follow the precession of the disk over time. Interestingly enough, the disk seems to align with the black hole throughout the simulation while the jets became more tilted. However, this is probably due to fluctuations In jet matter and the tilt angle stays relatively similar. The power plots show the jets pushing to massive outer radius but decreasing in power until they seemingly die out at a later time. Our next step will be to help further sustain the jets and utilize additional parameters.

Ken Brandt

Planethunters Activity and a Perseverance Update

Ken Brandt

We will do an update of the Perseverance mission, to include resources useful in teaching about Mars exploration that I’ve developed.

Brad Barlow

A TESS Survey of Candidate Variable Hot Subdwarf Stars Identified from Anomalous Gaia Flux Errors

Barlow Brad

Hot subdwarf stars are known to exhibit photometric oscillations due to stellar pulsations, eclipses, the reflection effect, ellipsoidal modulation, and even Rossby waves. Detailed studies of their light curves can constrain stellar parameters through asteroseismological analyses or binary light curve modeling and generally improve our capacity to draw a statistically meaningful picture of this enigmatic stage of stellar evolution. Additionally, they can reveal orbiting exoplanets through timing analyses, SN Ia progenitors, and even gravitational wave verification sources for LISA. While several members are known for all classes of binary and pulsating hot subdwarfs, they would each benefit from additional members. From an analysis of Gaia DR2 flux errors, we have identified nearly 800 hot subdwarf stars with inflated flux errors for their magnitudes, strongly indicative of variability. We obtained 2-min cadence TESS Cycle 2 observations of 250 of these hot subdwarfs to both find new variables and collect high signal-to-noise light curves of known systems. We find that more than 90% of the targets with anomalously-high Gaia DR2 flux errors show significant photometric variations in their TESS light curves. Although the majority of new systems found are cataclysmic variables, we also report the discovery of one new HW Vir binary, several new reflection effect systems, and one potential Type 1a supernova progenitor. This material is based in part upon work supported by NASA Award Number 80NSSC19K1720.

Núria Torres-Albà

The Hunt for Compton-thick AGN

Nuria Torres-Alba

Accretion onto a supermassive black hole can result into the triggering of an active galactic nuclei (AGN). According to the different models of Cosmic X-ray Background (CXB) the diffuse X-ray emission observed in the 1 to ∼200-300 keV band is mainly caused by AGN. Particularly, at the peak of the CXB a significant fraction of emission is expected to be produced by heavily obscured (Compton-thick) AGN. In fact, current models estimate that between 20-50% of all AGN in the local Universe should be Compton thick, while the observed fraction is 5-10%.The goal of the Clemson Compton thick AGN project is to have a complete census of the heavily obscured active galactic nuclei in the local Universe, in order to derive the true Compton-thick AGN fraction. In this talk, I will present our strategy for targeting new Compton-thick AGN candidates in the local Universe, as well as our results regarding the detailed characterization of the properties of obscured AGN within redshift z < 0.05 (d < 200 Mpc).

Jordan Eagle

Hunting pulsar wind nebulae (PWNe) with the Fermi-LAT

Jordan Eagle

Pulsar wind nebulae (PWNe) are some of the brightest sources in the very high energy sky and their gamma-ray emission, powered by relativistic electrons, provides a direct view of some of the most extreme Galactic environments. Even though PWNe like the Crab are some of the most well-known and widely studied objects in the high energy sky, little is understood about their nature. In particular, we lack clear characterizations of the injected particles and their consequent evolution once inside the nebula. The recent event reconstruction and instrumental response function upgrades to the Fermi-LAT Gamma-ray Space Telescope have significantly improved the spatial resolution and sensitivity of the instrument. Furthermore, systematic pulsation searches have greatly increased the number of detected gamma-ray pulsars to well over 200. Using Fermi observations with over 11.5 years of data, we are performing a systematic search for MeV – GeV PWNe. This systematic effort targets both Fermi pulsars, in search of their PWN companions, as well as the gamma-ray counterparts of PWNe detected at other wavelengths. For new discoveries, we will characterize the broadband emission in order to determine the underlying relativistic particle spectrum. Studies of the PWN emission structure over the entire electromagnetic spectrum offer the best way to understand the particle injection spectrum, its evolution, and the nature of the particle population that is eventually injected into the ISM. A combination of these observational studies with semi-analytic modeling efforts and multi-wavelength observations, will provide an intimate view of the nature of the PWN and its evolution inside its host SNR.

Varsha Kulkarni

Properties and Evolution of the Gas in and Around Galaxies

Varsha Kulkarni

Element abundances in distant galaxies are an important probe of the star formation and feedback processes in galaxies. Gas-rich absorbers detected in quasar spectra offer important probes of the chemistry of distant galaxies. Especially important for determining dust-free metallicity measurements are the abundances of volatile elements such as S, O, Zn that do not deplete much on interstellar dust grains. I will describe results of our recent and ongoing work on the measurements of these elements at redshifts 2 < z < 5 using observations obtained with the MIKE spectrograph on the Magellan telescope and the X-shooter spectrograph on the Very Large Telescope. I will also describe our results for dust depletions, electron density and the gas cooling rate in the absorbing galaxies. Finally, I will discuss the metallicity versus velocity dispersion relation in these distant galaxies.

Chris Fragile

Computational Astrophysics at the College of Charleston

Chris Fragile

In this talk, I will review the development of some of the cutting edge computational techniques in use in astrophysical numerical simulations today. For each technique, I will provide an illustrative example of the use of that technique. I will cover a range of phenomena from jet-induced star formation to tidal disruption events.

Syeda Nasim

Aligning nuclear cluster orbits with an active galactic nucleus accretion disk

Syeda Nasim

Active galactic nuclei (AGN) are powered by the accretion of discs of gas on to supermassive black holes (SMBHs). Stars and stellar remnants orbiting the SMBH in the nuclear star cluster (NSC) will interact with the AGN disc. Orbiters plunging through the disc experience a drag force and, through repeated passage, can have their orbits captured by the disc. A population of embedded objects in AGN discs may be a significant source of binary black hole mergers, supernovae, tidal disruption events, and embedded gamma-ray bursts. For two representative AGN disc models, we use geometric drag and Bondi–Hoyle–Littleton drag to determine the time to capture for stars and stellar remnants. We assume a range of initial inclination angles and semimajor axes for circular Keplerian prograde orbiters. Capture time strongly depends on the density and aspect ratio of the chosen disc model, the relative velocity of the stellar object with respect to the disc, and the AGN lifetime. We expect that for an AGN disc density ρ ≳ 10⁻¹¹ g cm⁻³ and disc lifetime ≥ 1 Myr, there is a significant population of embedded stellar objects, which can fuel mergers detectable in gravitational waves with LIGO-Virgo and LISA.

Ken Brandt

Perseverance and ingenuity

ken brandt cropped

Currently en route to Mars, NASA’s next robotic explorers will attempt to discover remains of past life on Mars. This provides many possible teaching opportunities, and I’ll discuss a few, and provide some examples of past activities I’ve done in the virtual environment based on Mars exploration.

Dan Reichart

Robotic Telescope-Based Labs for Survey-Level Astronomy Students

me Dan Reichart

For the past decade we have been developing robotic telescope-based introductory astronomy labs for survey-level undergraduates, making use of our Skynet robotic telescopes distributed around the world, including at CTIO. Introduction of these labs at UNC-Chapel Hill led to >100% enrollment increases in our introductory astronomy courses, and to >300% increases in our number of astro-track majors and minors. The curriculum has now been adopted by ~2 dozen institutions, and we have just received $1.85M from NSF’s IUSE program to expand it nationwide, with funding for participating instructors. The curriculum works equally well online as in person. I will briefly demo some of the key tools and point interested instructors to key resources.

Brad Meyer

Insights into the Building Blocks of the Solar System

meyer photo Bradley Meyer

Planetary bodies in our Solar System formed from the initial gas and dust in the proto-planetary disk surrounding the forming Sun. Nearly all traces of the initial dust have been erased since those dust grains mixed in the disk, accumulated into larger objects, and melted and resolidified to form solid planets and asteroids. Nevertheless, subtle isotopic variations among the planets show that the mixing of the grains in the proto-planetary disk was not complete and gives clues as to composition of the initial dust grains. From a compilation of isotopic anomaly data in a wide variety of planetary and asteroid samples (through meteorites), I and collaborators Katherine Berminingham of Rutgers University and Klaus Metzger of the Universitaet Bern are inferring the initial composition of the Solar System dust and its provenance. The isotopic effects seen in meteorites seem to be largely governed by the relative proportion of silicon carbide dust grains, which have been isolated from primitive meteorites, and yet to be discovered carriers that we propose are perovskite and spinel grains that condensed in the outflows from rare thermonuclear supernovae that produced large quantities of neutron-rich iron-group isotopes like calcium-48 and titanium-50.