Bulletin of the American Physical Society
2021 Virtual Conference for Undergraduate Women in Physics
Friday–Sunday, January 22–24, 2021; Virtual
Session U11: Astrophysics and Cosmology VInteractive Live
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Chair: Leah Dodson, University of Maryland |
Sunday, January 24, 2021 12:00PM - 12:10PM |
U11.00001: Cloud Formation on Titan Julia Garver, Yue Yu, Xinting Yu, Xi Zhang Titan's atmosphere is composed of mainly nitrogen and methane. Photochemically produced hydrocarbon and nitrile species in the upper atmosphere may further react and aggregate to produce the complex organic particles that form the atmospheric haze layers. The particles may serve as cloud condensation nuclei (CCN) in the process of cloud formation for organic ices and liquids. Our goal is to better understand the cloud formation processes on Titan using wetting and nucleation theories. The surface energy of Titan’s haze analogs was measured, enabling us to evaluate the wetting scheme between the Titan haze particles and possible cloud condensates. The wetting scheme (contact angle) between haze-cloud condensates has consequences on whether heterogeneous nucleation can occur efficiently. Using the surface energies, we can calculate the contact angle between them. We found that most condensates form small contact angles on the haze particles ($\theta < 30 \degree $), implying that the haze particles are good CCN for most clouds to nucleate and grow to form visible clouds. From the estimated contact angle, we calculated the nucleation rates, the rates at which clouds form, for individual condensates. Nucleation rates provide us with a deeper understanding of cloud formation on Titan. [Preview Abstract] |
Sunday, January 24, 2021 12:10PM - 12:20PM |
U11.00002: Analysis of Te-REX Sources using HAWC Observatory Data Erica Heller, Maya Debski, Miguel Mostafa TeV-emitting Radio-emitting X-Ray (Te-REX) sources are a sample of high-energy peaked BL Lac (HBL) objects selected from the larger REX catalogue that are thought to be TeV-emitting. Four of these Te-REX sources are identified as being seen by Fermi-LAT (Large Area Telescope) and are within the field of view of the High-Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory. Using data collected with the HAWC Observatory, we calculate the upper limits of each source. We aim to get a better picture of the highest energy emissions of these sources, allowing us to get a more complete idea of the overall emissions of these specific sources. [Preview Abstract] |
Sunday, January 24, 2021 12:20PM - 12:30PM |
U11.00003: X-ray observations of 4U1957$+$11: potentially the fastest spinning Kerr black hole in the galactic halo Erin Barillier, Michael Nowak The black hole candidate 4U1957$+$11 is part of an X-ray binary exhibiting peculiar behavior. The measured high temperature and low normalization (disk area relative to its distance) of the disk lead to an inferred low mass and extremely high angular momentum, challenging our current understanding of black holes. We analyzed 10 observations from the NuSTAR X-ray telescope to obtain precise measurements of flux and color temperature (a measure of the energy at which the spectrum of the source peaks). As the color temperature depends on the accretion rate, spin, and inclination of the disk while the flux depends on the inclination, mass, and distance, we hope to constrain those parameters. Relativistic effects of the system allow for strong measurements of the spin and inclination of the disk, thereby constraining the mass and distance. We studied simultaneous observations on the NICER telescope with precise timing and found low variability and no evidence of a pulsar, which would have been evidence that 4U1957$+$11 was a mis-identified neutron star. This low variability places constraints on the luminosity of the system (and therefore the accretion rate, mass, and distance). [Preview Abstract] |
Sunday, January 24, 2021 12:30PM - 12:40PM |
U11.00004: Effects of Turbulence on the Circumnuclear Disk Cuc Dinh, Jesus Salas, Mark Morris, Smadar Naoz A Circumnuclear Disk (CND) of molecular gas occupies the central few parsecs of the Galactic Center. It is likely subject to turbulent disruptions from violent events in its surrounding environment, but the effect of such perturbations has not yet been investigated in detail. Here we perform N-body/smoothed particle hydrodynamic (SPH) simulations with an adapted general turbulence driving method to investigate the CND's structural evolution, in particular its reaction to varied scales of turbulence. We find that because of shear flow in the disk, transient arcs of gas (streams) naturally arise when turbulence is driven on large scales (up to about 4 pc), as might occur when a supernova blast wave encounters the CND. Because energetic events arise naturally and often in the central parsecs of our Galaxy, this result suggests that the transient structures that characterize the CND do not imply that the CND itself is a transient structure. We also note that features similar to the clumps detailed in literature emerge when we account for the actual orientation of the disk as well as the resolution of observations. As such, clumps could be an artifact from observational limitations [Preview Abstract] |
Sunday, January 24, 2021 12:40PM - 12:50PM |
U11.00005: Analyzing Abundances of R-process Elements in Metal Poor Stars Utilizing GTC Spectra Victoria Moore The r-process involves a heavy atomic nucleus seed undergoing rapid neutron capture to create a heavier element. This can only be achieved in environments of high free neutron density and high temperature. The site(s) of the r-process have been debated for a long time. Theoretical investigations have suggested neutron star mergers, collapsars and magneto-rotational supernovae as possible contenders. The electromagnetic counterpart of the first ever observed neutron star merger, GW170817, has confirmed the presence of r-process rich ejecta. However, no detailed r-process abundance measurements could be made. Evidence of the r-process can be seen in metal-poor stars such as those in the halo of the Milky Way. We present chemical abundance analysis of metal-poor stars observed using the 10m Gran Telescopio Canarias (GTC) in the Canary Islands, Spain. This is the first set of data to be analyzed for r-process from the high resolution optical echelle spectrograph HORuS on the GTC. I have used the spectroscopic analysis tool Spectroscopy Made Hard to determine the abundances of neutron capture elements from the high resolution spectra of a sample of r-process enhanced stars. The results of our analysis are used to better constrain the origins of the r-process and its sites. [Preview Abstract] |
Sunday, January 24, 2021 12:50PM - 1:00PM |
U11.00006: Membership selection in the Alpha Persei Cluster Lou Baya Ould Rouis The nearby Alpha Persei is a youthful cluster of stars, born roughly at the same time, and sharing similar chemical composition. As such, star clusters give essential information on stellar evolution. In order to study the members of the Alpha Persei cluster, we use the latest data release from the Gaia Satellite Mission which measures distances, positions, and motions of stars. With these data it has been possible to detect thousands of new Alpha Per candidates, an increase by a factor of 10 or more over pre-Gaia studies. We identify the likely membership of Alpha Persei stars within dynamical parameters such as the core and tidal radius of the cluster. We use additional photometric data from surveys at infrared wavelengths to assess the presence (or lack) of excess infrared emission that is characteristic of circumstellar dust related to planetary system formation. [Preview Abstract] |
Sunday, January 24, 2021 1:00PM - 1:10PM |
U11.00007: Active Galactic Nuclei and Stellar kinematics Sana Elgamal, Andrea Maccio Cosmological numerical simulations have greatly contributed to our understanding of the physical processes governing galaxy formation and evolution. In this work, I will present a new analysis of the NIHAO (Numerical Investigation of Hundred Astrophysical Objects) suite, the largest collection of high-resolution simulations of galaxy formation, to investigate the internal kinematics of the stellar component of massive galaxies. Observations, namely the SAURON and the ATLAS$^{\mathrm{3D}}$ surveys, have established the dichotomy between fast and slow rotating galaxies. I will present a detailed comparison with the results of the ATLAS$^{\mathrm{3D}}$ survey, aimed to understand the abundance and formation pathway for fast and slow rotators. The NIHAO galaxies are able to reproduce the observed relative frequency of fast and slow rotators only in the presence of vigorous feedback from Active Galactic Nuclei (AGN). Such feedback is key to prevent the formation of new fast rotating (disk-like) component after major mergers, thereby increasing the occurrence of slow rotators. Our results highlight the importance of non-stellar feedback in shaping the stellar kinematics of massive galaxies. [Preview Abstract] |
Sunday, January 24, 2021 1:10PM - 1:20PM |
U11.00008: Search for Extragalactic Tev-Emitting Sources Kara Whitaker, Miguel Mostafa Although charged cosmic rays have been observed up to energiesexceeding 10 20 eV, their origin and acceleration mechanisms remainunknown. The study of gamma rays is an excellent opportunity tostudy cosmic rays because photons have no electric charge, andtherefore come straight to us from their original sources. Havingdetected galactic sources beyond 100 TeV, the High Altitude WaterCherenkov (HAWC) Observatory is currently the gamma-ray detectorwith the highest energy reach. Beyond our own galaxy, photons sufferattenuation in the extragalactic background light. Thus, by observingmulti-TeV emission from extragalactic sources we would be identifyingthe most powerful accelerators in the universe. We start our studyfrom a predefined list of relatively nearby extragalactic radio-emittingX-ray sources and search for very-high-energy emissions using datafrom the HAWC Observatory. If no significant excess is found, we usethe HAWC data to determine upper limits at TeV energies for eachextragalactic candidate allowing for constraints on the physicalparameters of the sources (e.g., energy cutoff, spectral index, etc.). Wealso identify possible interesting candidates for further studies. [Preview Abstract] |
Sunday, January 24, 2021 1:20PM - 1:30PM |
U11.00009: Bayesian inference of neutron star crust properties using neutron skin constraints Rebecca Preston, Dr. William Newton It is known that the thickness of neutron skins - the layer of excess neutrons at the surface of neutron rich isotopes - is correlated with certain neutron star properties. Using a Bayesian analysis of neutron skin measurements 208Pb, 48Ca and tin isotopes, we constrain values for the nuclear symmetry energy at nuclear saturation density. Using the posterior distribution of symmetry energy parameters we then model the neutron star crust and infer ranges for the location of the crust-core transition and the amount of nuclear “pasta” - non-spherical nuclear geometries - at the base of the crust. [Preview Abstract] |
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