CCAPP Fellows Symposium 2024

1:00 pm -- Session 1: Astronomy I

Michael Tucker: "Merging or Colliding White Dwarfs Produce Type Ia Supernovae in Elliptical Galaxies"

Manami Roy: "Unveiling the Complex Temperature Structure of the Galactic Atmosphere"

Amber Malpas: "Gaussian Process Regression in Microlensing"

Alison Crisp: "New Constraints on the Giant Planet Occurrence Rate in 47 Tucanae"

2:20 pm – Snack break and graduate student e-posters

2:50 pm – Session 2: Cosmology

Molly Wolfson: "Constraining Reionization with the z > 5 Lyman-α forest"

Naim Goksel Karacayli: "Cross correlations between CMB lensing and Lyman-alpha forest"

Charuhas Shiveshwarkar: "Local Primordial Non-Gaussianity from Large-scale Galaxy Surveys"

12:00 pm – Session 3: Astronomy II

Lucy Lu: "Evidence of Truly Young high-α Dwarf Stars"

Maddy Howell: "Measuring RGB Mass Loss in Globular Clusters with Asteroseismology"

Jung-Tsung Li: "The Solar Gamma Rays as A New Probe of Solar Magnetism"

1:00 pm – Snack break and graduate student e-posters

1:30 pm – Session 4: Astroparticle

Lucas Beaufore: "The PUEO Balloon Experiment: Searching for Ultrahigh Energy Neutrinos"

Paramita Dasgupta: "Searching Ultra High Energy Neutrinos with in-ice Askaryan Radio Array in South Pole"

William Luszczak "Astroparticle Fill-in-the-Blank: Using Atmospheric Muons to Study Tornadoes"

Michael Tucker

Title : Merging or Colliding White Dwarfs Produce Type Ia Supernovae in Elliptical Galaxies

I show that merging or colliding white dwarf binaries almost exclusively produce Type Ia supernovae in old stellar populations. These low-luminosity merger or collision driven explosions account for ~1/3 of all Type Ia supernovae and readily explain correlations between host-galaxy environment and explosion luminosity discovered over the past decade. Moreover, this requires at least 2 independent progenitor channels for Type Ia supernovae. Implications are discussed. 

Manami Roy

Title: Unveiling the Complex Temperature Structure of the Galactic Atmosphere

The circumgalactic medium (CGM), the gaseous halo enveloping galaxies, plays a crucial role in shaping the evolution of galaxies by providing the fuel for star formation. This medium is multiphase and exhibits a vast temperature structure, ranging from the cool 10^4 K gas to super-virial 10^7 K gas. The presence and enigmatic location of the newly discovered super-virial gas is an intriguing question. In this talk, I aim to shed light on this enigma by leveraging simulations and observational studies.

Amber Malpas

Title: Gaussian Process Regression in Microlensing

Recent implementations of Gaussian process (GP) regression aim to mitigate time-domain correlated noise in microlensing data. Significant sources of correlated noise in microlensing events include long-time-scale events (e.g., black-hole lenses), variable nearby (blend) stars, and systematic photometric errors (e.g., those in Spitzer microlensing data). I will discuss the application of a GP in lightcurve modeling within the context of Spitzer microlensing events, the microlensing-model-specific degeneracies with GP hyperparameters, and the implications of this modeling for physical inferences about the lens and population inference in general. Additionally, I will comment on the role of such modeling in the era of the Nancy Grace Roman Space Telescope. 

Alison Crisp

Title: New Constraints on the Giant Planet Occurrence Rate in 47 Tucanae

To date, searches for planets in the globular cluster 47 Tucanae with Hubble and other telescopes have not resulted in the detection of hot Jupiters. However, recent reanalysis considering Kepler occurrence rates (e.g., Masuda & Winn 2017) has shown that if 47 Tuc’s hot Jupiter population matched that of Kepler’s field stars, these searches could only have expected to find ~2 planets given their sample sizes, and thus the non-detections were inconclusive. To establish more interesting constraints, we have been observing 47 Tuc using the Dark Energy Camera (DECam) at CTIO as part of the Multiband Image Survey for High-Alpha PlanetS. DECam’s 3 degree field of view allows us to simultaneously monitor the entire extent of 47 Tuc, obtaining a sample size of over 53,000 stars with 17.0 ⩽ r ⩽ 21.0. Its photometric precision allows us to probe a larger magnitude range and smaller planet radii than previous searches were able, greatly increasing the statistical significance of our results. Here we present new constraints on the giant planet occurrence rate of 47 Tuc obtained with the survey and discuss the implications of our results for hot Jupiter formation mechanisms in crowded, low-metallicity stellar populations. We will also give an overview of our work on other MISHAPS targets.

Molly Wolfson

Title: Constraining Reionization with the z > 5 Lyman-α forest

One of the most important open problems in cosmology is understanding the reionization of the intergalactic medium (IGM) by the first luminous sources. This happened during a time period now known as Reionization and is generally believed to be complete at z > 5. During Reionization ionization fronts propagate through the IGM, heating the reionized gas. This heat injection can be observed over a redshift interval of ∆z ∼ 1 due to the long cooling times in the low-density IGM. Simultaneously, the mean free path of ionizing photons (λmfp) describing the ultraviolet background (UVB) rapidly evolves as bubbles of reionized gas, where the UVB is stronger, merge. Thus, constraining the thermal state of the IGM and the evolution of λmfp can, in turn, be used to constrain Reionization. Transmission in the Lyman-a (Lya) forest, the ubiquitous Lya absorption lines produced by residual neutral hydrogen in the IGM along quasar sightlines, is sensitive to both of these phenomena. I will discuss my work showing that the Lya forest flux auto-correlation function can be used to constrain the thermal state of the IGM as well as λmfp. In addition, I will introduce my measurements of the flux auto-correlation functions at z > 5 from the XQR-30 extended data set.

Naim Goksel Karacayli

Title: Cross correlations between CMB lensing and Lyman-alpha forest

The gravitational collapse that forms the large-scale structure is faster in overdense regions due to the presence of more matter. This makes that region of the Universe clumpier and amplifies the local small-scale power spectrum. The Lyman-alpha (Lya) forest and Cosmic Microwave Background (CMB) lensing maps provide a rare opportunity to observe this effect. We can measure multiple “local” power spectra using the Lya forest data and cross-correlate them with the “local” density estimates from the CMB lensing maps. I will present the detection of this signal from DESI’s first-year quasar sample and a model to extract cosmological information.

Charuhas Shiveshwarkar

Title: Local Primordial Non-Gaussianity from Large-scale Galaxy Surveys

With increased control over observational systematics, large-scale structure (LSS) surveys have emerged as a promising probe of the physics of cosmic inflation. Proposed and upcoming large-scale galaxy surveys are poised to be particularly useful in constraining primordial non-Gaussianity (PnG) -- which is an important distinguishing feature of many inflationary models. In particular, Local Primordial non-Gaussianity (LPnG) is a signature of the existence of an additional light field during inflation and is particularly amenable to detection by observations of large-scale galaxy clustering. On the other hand, post-inflationary effects can also modulate the observed clustering of galaxies at near-horizon scales thereby introducing theoretical systematics which can prove to be a limiting factor in the accuracy and precision of PnG measurements. In this talk, I will give an overview of previous work exploring the potential of the upcoming SPHEREx all-sky survey in constraining LPnG in the face of the aforementioned theoretical challenges.

Lucy Lu

Title: Evidence of Truly Young high-α Dwarf Stars

The existence of high-α stars with age measurements < 6 Gyr has been confirmed recently with large spectroscopic and photometric surveys. However, it is still unclear whether they are truly young or were rejuvenated through past mass-transfer or merger events. Many studies involving looking for anomalies in abundances, binary fractions, stellar activity, and rotation suggest young high-α giants and subgiants are likely products of binary interactions. For dwarf and subgiant stars, lithium is a strong indicator of whether a star has gone through mass transfer or stellar mergers. In this study, we provide strong evidence that truly young high-α stars exist by studying high-α rotators in the Kepler and K2 field with abundance measurements from GALAH and APOGEE. 

Maddy Howell

Title: Measuring RGB Mass Loss in Globular Clusters with Asteroseismology

Mass loss remains a major uncertainty in stellar modelling. In low-mass stars, mass loss is most significant on the red giant branch, and will impact the star's evolutionary path and final stellar remnant. Directly measuring the mass difference of stars in various phases of evolution represents one of the best ways to quantify mass loss. Globular clusters are ideal objects for this, because they contain stars with essentially identical initial masses and metallicities, and hence easily distinguishable evolutionary phases. The advent of space-based photometric missions has provided the opportunity to measure stellar masses with unprecedented accuracy using asteroseismology. 

Using photometry from the K2 mission, we report asteroseismic mass loss estimates in four globular clusters: M4, M80, M9 and M19. This is the largest asteroseismic sample of globular clusters stars to date. Mass loss is thought to scale with metallicity, which we confirm by deriving a model-independent mass loss-metallicity relation. 

We also investigate whether there are mass differences between the sub-populations in each cluster. In M80, we detect a distinct bimodality in the (early) AGB mass distribution, which could be a signature of sub-population membership. If confirmed with spectroscopy, it would be the first direct measurement of a mass difference between sub-populations. We also report strong evidence for mass loss differences between the sub-populations. Differing mass loss rates on the RGB has been proposed as the second parameter that could explain the horizontal branch morphology variations between GCs. 

Jung-Tsung Li

Title: The Solar Gamma Rays as A New Probe of Solar Magnetism

The Sun is a bright, continuous source of gamma rays in the GeV-TeV range. Emissions from the solar disk are primarily attributed to hadronic interactions of Galactic cosmic rays (GCRs) with solar gas at the chromosphere and photosphere layers. These GeV-TeV gamma rays from the Sun provide indirect measurements of solar-surface magnetism, which is otherwise inaccessible through in situ measurements. In this talk, I will provide an overview of the observations from Fermi-LAT and HAWC. I will identify the crucial scientific questions that gamma-ray data can resolve in solar research. I will conclude by discussing how future gamma-ray observation could advance our understanding of photospheric magnetism and GCR transport in the solar atmosphere.

Lucas Beaufore

Title: The PUEO Balloon Experiment: Searching for Ultrahigh Energy Neutrinos

The Payload for Ultrahigh Energy Observations (PUEO) is a balloon-borne experiment that is designed to measure ultrahigh energy (>1 EeV) astrophysical and cosmic neutrinos at world-leading sensitivities. These measurements will allow us to probe distribution and nature of the sources of the highest energy particles in the universe. To do this, PUEO monitors for radio signals generated via the Askaryan effect by neutrino interactions in the Antarctic ice. Improvements implemented in PUEO’s design following the Antarctic Impulsive Transient Antenna (ANITA) balloon program include the use of a phased-array trigger, real-time digital filtering, more antennas with longer baselines, and a dedicated low-frequency instrument, amongst others. PUEO is scheduled to fly over Antarctica in late 2025. This talk will give a brief overview of the PUEO experiment, with special attention given to its data acquisition system.

Paramita Dasgupta 

Title: Searching Ultra High Energy Neutrinos with in-ice Askaryan Radio Array in South Pole

The Askaryan Radio Array (ARA) is an in-ice ultra high energy (UHE, >10 PeV) neutrino experiment at the South Pole that aims to detect UHE-neutrino induced radio emission in ice. ARA consists of five independent stations each consisting of a cubical lattice of in-ice antenna clusters with side length of ~10 m buried at about 200 m below the ice surface. All five independent ARA stations have collectively accumulated about 310 TB of data over the last decade. The fifth station of ARA (A5) is special as this station has an additional central string, the phased array (PA), which provides an interferometric trigger that enables ARA to trigger on weak signals that are otherwise buried in noise. Leveraging the low threshold phased array trigger, ARA was the first radio neutrino experiment to demonstrate significant improvement in sensitivity to weak signals. In this talk, I will present initial results from a neutrino search on A5 combining information from both the traditional station antennas and the phased array antennas. This analysis is the paradigmatic representation of future neutrino searches with the next generation of in-ice neutrino experiments. 

I will also present the current state of the first array-wide diffuse neutrino search using data from all five independent stations of ARA. We anticipate that this analysis will result in the first UHE neutrino observation or world-leading limits from a radio neutrino detector below 100 EeV. Additionally, this analysis will demonstrate the feasibility of multi-station in-ice radio arrays to successfully conduct an array-wide neutrino search, paving the way for future, large detector arrays such as RNO-G and IceCube-Gen2 Radio.

William Luszczcak

Title: Astroparticle Fill-in-the-Blank: Using Atmospheric Muons to Study Tornadoes

Tornadoes are severe weather phenomena characterized by a violently rotating column of air connecting the ground to a parent storm. Within the United States, hundreds of tornadoes occur every year. Despite this, the dynamics of tornado formation and propagation are not particularly well understood, in part due to the challenge of instrumentation. Many existing instruments are in-situ detectors, making deployment in or near an active or developing tornado difficult. Atmospheric muons may present a partial solution to this problem, as their flux has been shown to be affected by local atmospheric conditions, allowing for measurements of atmospheric parameters at a range. While this technique has been used in the past on larger, more stable weather systems, tornadic supercells present a unique challenge due to their transience and relatively small size. This talk explores prospects for remote measurement of the pressure field surrounding tornadic supercells by combining simulation of supercell thunderstorms and cosmic ray showers to quantify the local effect of these storms on the atmospheric muon flux.