Oral Presentations

Atomic hydrogen (HI) in galaxies is measured with its 21cm line emission that can be detected using telescopes like the 100m Green Bank Telescope, a single dish radio telescope. This signal has a large wavelength so detections are spatially unresolved, but the Doppler shift spreads the 21cm line across a range of observable frequencies. These are HI global profiles. In this work we aim to explore their shapes, and then attempt to recover HI radial profiles in galaxies with measured rotation curves from the HI-MaNGA survey. We present a model HI global profile, in an idealized situation, which can be used for symmetric HI global profiles pulled from the HI-MaNGA data. We use the correlation between HI flux and HI radius, and model the dependence of HI surface density with radius as a truncated exponential with a scale length set by the total HI mass in the given galaxy. We use fits to the rotation from MaNGA. Future work will investigate further how well our model can be used to find the best for HI radial profile in real, raw data that is not idealized.

Astronomical observations of neutral atomic hydrogen (HI) are an important tracer of several key processes of galaxy evolution, but face significant difficulties with terrestrial telescopes. Among these is source confusion, or the inability to distinguish between emission from multiple nearby sources separated by distances smaller than the telescope’s spatial resolution. Confusion can compromise the data for the primary target if the extra flux from the secondary galaxy is sufficient. This paper presents an assessment of the confusion-flagging methods of the HI- MaNGA survey, using higher-resolution HI data from the WRST-Apertif survey. We find that removing potentially confused observations using a confusion probability metric—calculated from the relationship between galaxy color, surface brightness, and HI content—successfully eliminates all significantly confused observations in our sample, but also eliminates some insignificantly confused observations.

The factors that influence bar formation in galaxies and the effects bars have on their hosts form a complex web of causally interrelated astrophysical phenomena. While previous studies have investigated the relationship between star formation and environment or morphological properties (e.g. Scudder et al. 2012, Cheung et al. 2013), this work conducts an inquiry into the interplay between all three by introducing the use of a quantified net tidal strength parameter. From our sample of 16,607 morphologically classified disk galaxies with spectroscopic and tidal measurements, we find that galaxies lie in two behaviorally distinct populations, split by specific star formation rate. In low tidal strength environments, star-forming galaxies are found to host bars at comparable or slightly lower rates compared to the overall population. Conversely, bar formation is enhanced among quiescent galaxies in similar environments. In more tidally dense areas, this trend dissipates and the quiescent population lowers in bar likelihood, converging with star-forming galaxies. This may suggest that the effect of bar-induced quenching is reduced when closely interacting with other galaxies, a concept further evidenced by a greater relative increase in total star formation than central star formation in barred galaxies compared to unbarred galaxies when experiencing high tidal forces. We additionally find a slight decrease in overall bar population at high tidal forces, although complications regarding major merger disruptions and delays in the formation of post-flyby features prevent us from associating this trend with either the tidal triggering or suppression of bars.

Between about 400 million and one billion years after the Big Bang, ionizing radiation from the first galaxies reionized the intergalactic medium. Given the high redshifts of these galaxies, rest-frame ultraviolet spectroscopy is an essential tool for understanding their prop- erties. Observations of low-redshift analogues of these reionization era galaxies, characterized by their high star formation rate, low mass, low metallicity, and highly ionized interstellar medium, are essential for understanding those ultraviolet spectra, since the rest-frame optical spectrum is also available for those galaxies. I analyzed complete rest-frame ultraviolet spec- tra of low-redshift, Lyman continuum (LyC) leaking galaxies taken with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope (HST), and compared these spectra with photoionization model predictions and observations in the literature. I found C III] equivalent widths ranging from 5-20 Å, detected O III] 𝜆𝜆1661, 1666 in 2/3 galaxies for which I had full spectra, and detected He II 𝜆1640, C IV 𝜆𝜆1548, 1551, and N III] 𝜆𝜆1747, 1749 in one galaxy each. The measured C III] equivalent widths are consistent with galaxies of similar metallicities at both low and high redshift, but Cloudy photoionization models struggled to reproduce the C III] equivalent widths of the most extreme emitters at their inferred metallicities and starburst ages. Moreover, the Cloudy models significantly under-predict He II 𝜆1640 in one of the galaxies. The broadness of the He II line (1300 km/s) suggests that it’s stellar emission. The Cloudy models also predict C III] emission to decrease as the LyC escape fraction increases, but this sample doesn’t conclusively support that prediction. This suggests that the systems aren’t uniformly optically thin, but rather that the LyC photons escape through optically thin channels.

The Neutron Star Interior Composition Explorer (NICER) mission has been conducting observations of fast rotating and highly magnetized neutron stars known as pulsars since its launch in 2017. Specifically designed to observe neutron stars, it collects photons at X-rays, ranging from 0.2 to 12.0 keV. With its unique capabilities like the possibility to time tag X-ray events with a resolution higher than 300 ns and a higher effective area than previous X-ray missions, it can perform complementary high-time resolution observations of pulsars, enabling a new generation of multi-wavelength studies. In this study we analyzed NICER observations of the first millisecond pulsar discovered known as PSR B1937+21. We used the NICERsoft software package to parse and clean NICER data of PSR B1937+21. The NICERsoft calibration and filtration procedures allowed us to subtract extraneous background events, both cosmic and non-cosmic events, in order to filter out the X-ray pulse profile of PSR B1937+21. Since NICER determines the pulsed emission from a celestial source like a pulsar statistically, we combined over a year of data to analyze the finer distinctions of its X-ray pulse profile, and to take note of any possible hints at potential correlations that could be made with occurrences of so called giant pulses (GPs), which are irregular and very bright individual pulses observed at radio wavelengths from this pulsar.

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has become the leading instrument for detecting Fast Radio Bursts (FRBs). With CHIME as the primary telescope for detecting FRBs, CHIME/FRB Outriggers will use very-long-baseline interferometry (VLBI) in order to localize these events. Localization errors due to internal clock delay must be minimized in order to stay true to CHIME/FRB Outrigger’s goal of milliarcsecond precision. This paper discusses the techniques used to decide which clocks will be installed at outrigger stations. Additionally, the resulting pipeline significantly improves clock performance and provides calibration methods for clocks that do not initially meet CHIME/FRB Outriggers’ stability requirements for VLBI.

1308+326 is a well-studied BL Lacertae object most-often cited for its high luminosity optical burst spanning the late 1970s into the early 1980s. Observations became less frequent as the brightness decreased in the 1990s. The Foggy Bottom Observatory at Colgate University started observing the object at that time and has continued up through the present, providing invaluable data on 1308+326 at times when few other observatories watched it. At the Foggy Bottom Observatory, preliminary photometric measurements are made each night from unre- duced images of each quasar as we are observing it, but formal reductions to produce reliable magnitude measurements are made afterwards with AstroImageJ, using object images, darks, and skyflats, including biases when necessary. We performed a thorough literature search to find every source referencing 1308+326. These data were used to supplement observations made at FBO to create the most complete optical light curve to date. Using this long-term light curve, we were able to analyze the periodicity of this object, primarily through Lomb-Scargle and Structure Function analyses. From this, we found a relatively strong period of 22 years, which is promising, but also necessitates further research and analysis on this object.

Using data from the rapidly-rotating and highly magnetized neutron stars (pulsars) PSR B1937+21 and B0531+21, this paper calculates and constrains scintillation parameters of both pulsars as well as the relative distances to the screens causing the scattering effects, assuming a thin screen model and a homogeneous Kolmogorov electron density spectrum. These values are obtained in the hopes of better understanding the large- and small-scale structure of the interstellar medium and searching for areas of improvement in current Galactic electron density models in order to further the efforts of pulsar timing arrays.

Total Solar Eclipses (TSEs) are our best opportunity to observe the solar corona in its entirety. However, due to the combination of varying location and observing constraints due to the nature of TSEs, eclipse data have the potential to be impacted by data collection variables that are different from those of typical astronomical data. The flattening index of the white light corona is particularly susceptible to these variables, and we believe it is one of the main sources of scattering within the flattening index values from 1851-2020. We decided to focus on the types of photography equipment used, differences between individual photographer’s techniques, particularly their exposure times, and weather conditions during totality. We used data taken in 2016, 2017, 2019, and 2020 to compare flattening indices from multiple data sets and determine how these variables alter the value of the flattening index.

We present a multi-epoch spectroscopic study of LkCa 4, a Weak-line T Tauri Star, and DQ Tau and LkCa 15, both Classical T Tauri Star systems, finding new evidence for a correlation between the observed low amplitude photospheric variability characteristic of T Tauri Stars and the presence of large, inhomogeneously distributed cool spots on the stellar surface. Simultaneously, we examine their accretion variability through common infrared accretion indicators (Ca II infrared triplet, the Paschen and Brackett H I lines and the He I line at 1.083𝜇m). Our findings suggest that the surface of LkCa 4 is mostly covered by large spots with filling factors between 𝑓 ≈ 0.6 − 0.9% where the minimum and maximum spot coverage coincide with the photometric maximum and minimum for the stellar light curve phased with the rotational period of the star. This provides an explanatory basis for the observed spectral type discrepancies between infrared and optically determined spectral types as well as for the low amplitude variability. Additionally, we find evidence for orbitally-modulated accretion in the DQ Tau system, with the intensity of accretion increasing towards the periastron passage of the system.

Protoplanetary disks are disks of gas and dust that surround newly-formed stars. The structure and evolution of these objects determine how planet formation proceeds; studying how protoplanetary disks vary with age, structure, and region will provide us with clues to the origin and properties of planets around other stars and within our own solar system. The goal of our research was to uniformly model protoplanetary disks in the star-forming regions Chameleon II and Taurus in order to complete a database of disk structure that can be used to study planet formation across star-forming regions. The disks in Chameleon II (n=24) and Taurus (n=49) were imaged using observations from the Atacama Large Millimeter/sub- millimeter Array (ALMA) at 􏰟 1.33 mm wavelength and the Submillimeter Array (SMA) at 0.869 mm, respectively, with angular resolution for most disks being approximately 0′.′35. An affine invariant Markov chain Monte Carlo (MCMC) algorithm was used to fit the disks for 8 parameters: flux, characteristic radius, inclination, position angle, and offset position (right ascension and declination), as well as the slope of a power law γ1 and exponential tail γ2 which describe the flux as a function of radius in the inner and outer disk, respectively. This database will be used to study the conditions that influence planet formation to help us better understand the evolution of planetary systems.

Previous observations of CARMA-7, a low mass Class 0 protostar in the Serpens South cluster region, detected episodic ejection events traced by 12CO. Other than carbon monoxide isotopologues, however, little is known about the abundances and morphologies of molecular lines around the source. We present Band 6 observations of 9 molecular emission lines near CARMA-7 using the Atacama Large Millimeter/sub-millimeter Array (ALMA). We confirm the presence of a bipolar outflow extending in the north-south direction (P.A. 4◦) as traced by 12CO and H2CO. Further investigation of the H2CO line uncovered a low-velocity emission feature extending to the southwest (P.A. 72◦). We interpret this feature as a potential accretion flow, but further analysis via modeling is necessary. The C18O emission line shows early signs of Keplerian rotation in the disk/envelope. However, other known disk and envelope tracers such as 13CO and N2D+ fail to show signs of rotation. We find that CARMA-7 does not hold a disk larger than 305 AU and that the detection of a strong outflow is not a clear indicator of an evolved rotating disk.

The goal of this research is to look for exoplanets orbiting white dwarf stars. This project serves as a jumping off point for future research using the 24” telescope at the Van Vleck Observatory. We narrow down a large data release to look at just the white dwarf stars that have heavy metals observed in their spectra, are visible from the Van Vleck Observatory, and have not already been observed in depth by other survey telescopes. As of now, 93% of the white dwarf stars in the latest Gaia release have been observed for substantial periods of time by TESS, Kepler, or K2. Of the remaining 52 unobserved stars that also have polluted spectra, we focus mainly on the star LB 1188 and are able to conclude with 100% confidence that LB 1188 does not have a transit with a period less than 5.3 hours and 70% confidence out to half a day. Future work will focus on expanding observations to new stars and continuing observations on the stars covered by this project.

This project has found evidence of trends in known 3-planet systems with inner planets in a Mean Motion Resonance (MMR) in an effort to construct a predictive model with the ability to detect planets in currently known 2-planet MMR systems. Using light curve data collected over long cadences from the Kepler/K2 mission, periodograms and transit curves can be constructed and analyzed to develop such a model as to provide ranges for outer extant planets’ periods. With the known 3-planet systems as the training dataset, we apply the model to all known 2-planet MMR systems. The distribution of period ratios in known 3-planet systems are examined individually, noting the trend within some MMRs for period ratios to group together. This model creates a framework for further mass-based analyses of orbital trends, as well as laying the foundation for future prospective n-body dynamical simulations in systems with known classified period relationships and MMRs. This may serve as a mode to find new exoplanets in currently known and classified transiting systems and provide a broader sample to investigate the gravitational interactions and evolution of planetary systems that lead to mean motion resonances. As such, this model should be applied to all Kepler/K2 and TESS 2-planet systems exhibiting an inner-planet MMR to use these trends and find new exoplanets in such known systems.

We catalogue and analyze Gale crater’s diagenetic concretions–features created during its post-lacustrine aqueous events–from MSL Curiosity Rover MAHLI and Mastcam observations, Sols 1900-3049. Notably, we observe few to no concretions in the clay-rich Glen Torridon region, and a correlation between concretion presence and geomorphic unit. Moreover, Mast- cam multispectral data from Sols 2850-3049 may indicate a correlation between concretion morphology and spectral properties.

Super-Earth and Sub-Neptune size planets show a lot of diversity and can be very different from the Earth. A subset of small planets have very different (less dense) compositions than the Earth that may be explained by a surface water envelope. To evaluate water-rich composition scenarios and determine how much water these worlds could have, software tools are needed to compare the measured masses and radii of exoplanets to water world interior structure models. We develop a tool that interpolates within a grid of water world interior structure models, which predict the radii of planets for a specified mass, compositions, age, and irradiation. We apply this to TOI-763 b, a newly-discovered transiting exoplanet. We show with our water world model that TOI-763 b has a water mass fraction of 30% ± 10%. The methods developed in this work will be crucial for making robust inferences about water world compositions from transit and radial velocity observations.