Recent discoveries of faint satellite systems challenge the distinction between star clusters and dwarf satellites.Classifying these systems are pivotal for understanding the physics of dark matter (DM) on smaller scales and constraining the number of DM sub-halos in larger galaxies. With more satellite systems than the Milky Way, Andromeda (M31) offers a unique environment for this investigation. We present three ultra-faint dwarf (UFD) galaxy candidates in the halo of M31, initially discovered in the Pan-Andromeda Archaeological Survey (PAndAS). Hubble Space Telescope (HST) follow-up imaging indicates that these candidates lie in the boundary between the largest and most diffuse star clusters and the smallest UFD galaxies in the luminosity-size plane, making classification challenging. We derived the structural parameters of the three faint systems using an elliptical exponential density profile through a Markov Chain Monte Carlo Maximum Likelihood algorithm. The candidates have half-light radii ranging from about 28 to 50 parsecs and ellipticities around 0.3. Finally, we estimated the absolute V-band magnitudes of the candidates (between -5.8 to -5.0) based on distance estimates from horizontal branch magnitudes. Further spectroscopic analysis will allow us to confirm or deny the presence of dark matter or a metallicity dispersion and properly classify these systems. 

A T Tauri star typically is a young star with an accretion disk, which has potential for forming planets, but this is hard to detect due to the disk’s optical thickness at this stage in the star’s life. An indicator of the presence of planets in the disk is a depletion of refractory materials at the accretion flows onto the star, which is due to refractory materials such as calcium and magnesium being added to an accreting planet somewhere in the disk and never making it to the central star. In this work, we calculated the flux of the Hα and Ca II K spectral lines of 16 stars in the Taurus region to find their calcium abundance relative to hydrogen and see if any of them had any calcium depletion relative to solar values. The flux of a line is determined by multiplying the equivalent width of the line with the flux of the continuum at the line. Equivalent widths were determined in a previous work with MIKE spectra. We used two methods to determine the continuum flux. For stars with DAO spectra taken by HST covering the optical range, the continuum flux was determined through line fitting and interpolation at the site of the spectral line. An additional number of stars’ continuum spectra were reconstructed using previously published photometric measurements. We found that some of the stars in the Taurus region showed significant calcium depletion, though most did not. Additionally, the Taurus population follows a linear relationship between [Ca/H] and the log of mass accretion rate, which is similar to that  found in other young stellar population

Galaxy cluster masses are important for constraining cosmological parameters like the matter density of the universe. We can infer galaxy cluster masses from observables like their weak lensing profiles. Traditionally, one would use MCMC to infer cluster parameters from observables, but computing the analytic likelihood function can be expensive. In this work, we're investigating an alternative approach called Simulation Based Inference which uses a trained inferrer instead of the likelihood function and comparing the results to what we'd infer from MCMC.

Large, energetic accretion events have been observed in the inner disks of young stars and protostars. Modeling of these “FU Ori” outbursts predicts the presence of an infrared precursor before the optical peak, caused by the inwards movement of a high-temperature, high-density accretion wave which begins at approximately 1 AU. Whether or not these infrared precursors can be detected depends on the degree of extinction of the accretion disk from the dusty, infalling protostellar envelopes commonly found around FU Ori objects. To explore this question, we combined these outburst models with a disk and envelope component, using the radiative transfer simulation RADMC3D, in order to determine the viability of observing the spectra of these infrared precursors with realistic density distributions. We find that, for envelope mass infall rates typical of protostars, the infrared precursor is only conclusively apparent when viewed along an outflow cavity. At other inclinations, the precursor is difficult to distinguish from the thermal emission of the dusty envelope.

We present equivalent widths, model atmosphere parameters and abundances for 14 species of 11 elements derived from high resolution optical spectroscopy of 311 metal-poor stars. All of these stars were previously published by Roederer et al. 2014. We use color-Teff relationships calibrated previously for Gaia and 2MASS photometry to calculate improved effective temperatures (Teff). We calculate log of surface gravity (log g) values using measurements derived from Gaia parallaxes and other fundamental stellar properties. We then rederive microturbulence values, metallicities and abundances for O I, Na I, Mg I, Si I, K I, Ca I, Ti I, Ti II, Cr I, Cr II, Fe I, Fe II, Ni I and Zn I elements based on the previously published equivalent widths. On average, the new \teff values are 310 K warmer, the new log g values are higher by 0.64 dex, and the new [Fe/H] values are higher by 0.26 dex. We perform a standard LTE abundance analysis using MARCS model atmospheres and the MOOG line analysis software. We apply NLTE corrections for elements of O I, Na I, Mg I, Si I, K I, Fe I, and Fe II. Our sample contains 6 stars with [Fe/H] < −3.5, 28 stars with [Fe/H] < −3.0, and 113 stars with [Fe/H] < −2.5.

The launch and subsequent employment of JWST has made it possible to characterize exoplanet atmospheres in exquisite detail. However, when astronomers fit observations of exoplanet spectra using atmospheric retrieval (a Bayesian technique), it is common to assume that the chemical composition does not vary with pressure. Yet, in fact, myriad chemical and physical processes may cause large vertical deviations in molecular abundances.

     In this poster, we explore the ability to directly measure vertical chemical gradients from exoplanet transmission spectra. We present a new parameterization for atmospheric retrievals including vertical chemical gradients and demonstrate its viability using simulated JWST observations for a warm Neptune atmosphere. Our improved retrieval model opens the prospect to measure the impact of important physical and chemical processes—such as photochemistry—from JWST spectra of exoplanets.

Ultra-faint dwarf (UFD) satellite galaxies are believed to have the oldest, most dark-matter dominated, and least chemically evolved stellar populations. Therefore, UFDs serve as effective cosmological probes for the early stage of the Universe. In this study, we applied unsupervised machine learning (DBSCAN & OPTICS) to search for potential UFDs by analyzing spatial overdensities of the tip of red giant branch (TRGB) stars in the DELVE survey. Our objective is to complement the current catalog of UFDs in the local volume while exploring the potential of using modern statistical density searching tools in UFD studies. We have focused on searching for M31 UFDs and recovered all 10 M31 satellite galaxies in the DELVE DR2 coverage. This work provides tools to identify UFDs in large sky surveys, which helps to test cosmological constraints of the Lambda Cold Dark Matter (ΛCDM ) model. 

Comparing model spectra to observation is one of the predominant ways we learn about exoplanets and their atmospheres. In the new age of JWST, how those model spectra are calculated may have greater implications than previously assumed. In this project, we evaluate the impacts of two different radiative transfer geometries commonly used in calculating spectra from 3D models: line-of-sight geometry (“ray tracing”), and radial geometry. To do this, we examine the dayside emission spectra of two test cases. We preliminarily find that the two geometries produce noticeably different simulated JWST spectra. These differences are on the scale of a few percent, and correlate to how the ray tracing calculation captures limb effects while the radial calculation does not. These results show that the geometry used in model spectra calculation must be considered when evaluating the similarity of models to data.

Though future wide-field telescopes promise to revolutionize our understanding of dark matter subhalos and dwarf galaxy systems, we still have years to wait for large-scale upheaval. In the interim, we have prepared a project to run clustering algorithms on HST data in the halo of M31, to check for UFD satellites caught in the Hubble footprint. Though we lack a wide field of view, we are encouraged by the high resolution of data and relevant location of many HST observations. We intend to conduct a comprehensive search of all images with potential satellites, in the interest of either identifying new M31 satellites, or ruling out Hubble observations as home to UFD satellite candidates.

Orbits have a tendency to gravitate towards resonances, integer combinations of their fundamental frequencies. Orbital resonances have shown the ability to support features of galaxies, such as the boxy-peanut bulge, and be the driving mechanism behind vertical heating in orbits. We develop an algorithm to automatically detect and classify resonances in orbital frequency maps to obtain a more comprehensive resonance distribution in galactic models. We also investigate the differences in resonance distributions across galactic models, examining shifts in resonant populations over time and resonance trapping ability. Further analysis will involve identifying key resonances that drive the boxy-peanut bulge that form in certain galactic models, and the repopulating mechanism that keeps certain resonance populations constant over time. 

Small close-in exoplanets can be separated into two distinct populations: super-Earths at approximately 1.0-1.4 Earth radii and sub-Neptunes at approximately 2.3-3.9 Earth radii (Fulton et al., 2017; Luque & Pallé 2022). Since our Solar System lacks analogs of such worlds, we possess a fundamental lack of understanding of planets in this regime. While small super-Earths are likely rocky/iron in composition and sub-Neptunes are likely dominated by an H2/He atmosphere, planets approximately within the 1.5-2.2 Earth radii regime could also be explained by a third ‘water-world’ scenario, with a volatile-rich envelope in a supercritical state above a rocky/iron core. To resolve the ambiguous composition of such planets, we are measuring the atmospheric compositions of 5 potential water worlds as part of a Large Cycle 2 JWST Program via transmission spectroscopy. Here, we present our initial results for two of these planets, TOI-270d and GJ-9827d, from an atmospheric retrieval analysis. Based on these results, we introduce a new classification for the composition of sub-Neptunes: a “miscible envelope sub-Neptune.” We finally compare the atmospheric compositions of TOI-270d and GJ-9827d and discuss implications for future studies of water worlds with JWST. 

Globular clusters (GCs) are useful signposts of the accretion of satellite galaxies and kinematic probes that reach far out into the dark matter-dominated galactic potentials. However, GCs are challenging to distinguish from foreground stars and background galaxies, and thus very little is known about their distribution very far from their host. The Andromeda Galaxy (M31) is an excellent example for studying GCs, with an exceptionally complete GC catalog within a projected radius of 150 kpc; yet, only two GCs are known beyond this radius. Our goal is to determine if more GCs lie past a projected radius of 150 kpc. Using archival data from Pan-STARRS DR1, WISE, and Gaia, we were able to recover 111 confirmed GCs within 150 kpc with only 2 background galaxies contaminating our sample. 70% of these GCs were not in our training set and illustrate the effectiveness of the selections. We have searched to a projected radius of around 600 kpc, finding 255 candidates. Visual inspection and previous spectroscopy show that many candidates were background galaxies or foreground stars. We discovered 8 GC candidates up to projected radii of around 500 kpc from the center of M31. We have work underway to calculate radial velocities of these candidates, allowing us to confirm or deny if they are true GCs.   

We carry out a study of the dust composition in the disk of the T Tauri star BP Tau, employing the DIAD model, which features various free parameters, to generate spectral energy distributions (SEDs) aiming to replicate Vizier IRS spectra obtained from the Spitzer Space Telescope, and photometry to construct the SED with the aid of Avalon Litwiller's code. Baseline parameters, informed by Ritlinger et al.'s 2022 and Sargent et al. 2009 work was initially utilized, and the key parameters–Amorphous Pyroxene, Amorphous Olivine, Crystalline Enstatite, and Crystalline Forsterite–were adjusted accordingly to more accurately match IRS spectra data. The primary objective presently is to gain proficiency in DIAD modeling and SED fitting, while investigating the influence of different refractory materials on the SED. Future endeavors aim to leverage MCMC fitting to sample extensive datasets and discern trends indicative of planetesimal formation.

Scaling relations are a key aspect to understanding galaxy evolution, especially the co-evolution between galaxies and their central supermassive black holes (SMBHs). The tight correlations between black hole mass (M_BH) and quantities like velocity dispersion, stellar mass (M_*), and dark matter halo mass (M_halo) are strongly suggestive of a causal connection between black hole growth and galaxy evolution. M_BH has also been shown to correlate strongly with star formation rate (SFR), with quiescent galaxies hosting more massive SMBHs for a given stellar mass than ones actively forming stars.

One important limiting factor in the analysis of scaling relations between M_BH, M_*, M_halo, and SFR is the relative rarity of high-quality M_halo measurements using consistent methodology. With this in mind, we used the globular cluster mass-halo mass relationship (eta = (3.9 +- 0.9) x 10^(-5) = M_GCS/M_halo) to expand the number of available M_halo estimates. Using this, we recreate existing scaling relations as well as explore SFR in different regimes of parameter space. We find that the stellar masses of star forming galaxies and the SMBH masses of quiescent galaxies follow the same power law trend across four orders of magnitude in halo mass (with different offsets). This suggests that galaxies fundamentally self-regulate energetically through feedback, with stellar feedback providing the requisite energy until M_halo~10^12, and AGN feedback dominating afterwards. This result has great potential for providing an understanding of the fundamentals of galaxy evolution.

Mergers of and interactions between galaxies imprint a wide diversity of morphological, dynamical, and chemical characteristics in stellar halos and tidal streams. Measuring these characteristics elucidates aspects of the progenitors of the galaxies we observe today. The M81 group is the perfect galaxy group to understand the past, present, and future of a group of galaxies in the process of merging. Here we measure the end of star formation (t_90) and metallicity ([M/H]) of the stellar halo of M82 and the eastern tidal stream of NGC 3077 to: 1) test the idea that M82 possesses a genuine stellar halo, formed before any interaction with M81, 2) determine if NGC 3077's tidal disruption caused the end to star formation in its tails, and 3) create a timeline of the assembly history of the central trio in the M81 group. We find that M82 possesses a genuine, metal poor ([M/H] ~ -1.5 dex) stellar halo, formed from the merger of a small satellite galaxy roughly 6.5 Gyr ago. We also find that the stars present in NGC 3077's tails formed well before tidal disruption, and possesses a roughly uniform metallicity as shown in Okamoto et. al. 2023. Finally, we present a timeline of the central trio's merger/interaction history.

We measure the projected half-light radii of young stellar clusters in 36 galaxies from the Physics at High Angular resolution in Nearby GalaxieS - Hubble Space Telescope (PHANGS-HST) distribution. We modify and update the pipeline developed for the Legacy Extragalactic UV Survey (LEGUS) in Brown and Gnedin (2021). With this updated pipeline and dataset, we have measured the radii for 29,287 clusters. This makes this the new largest sample of young stellar cluster radii currently available. Using these radii, we investigate the mass-radius relation and density distribution to investigate cluster evolution as well as the completeness of our sample. Finally, we compare these results to those from the LEGUS distribution measured by Brown and Gnedin (2021).

In our research, we tested the traditional approach of identifying OBe star candidates by using Hα-continuum subtracted images. Specifically, we compared the candidates detected through this method in the Large Magellanic Cloud (LMC) with known OBe stars listed in an established catalog. To do this, we extracted star-shaped objects from the Hα-continuum subtracted images and then evaluated how this group matched up with the cataloged OBe stars in the same region of the LMC. we find that this method results in false positives and is thus insufficient in identifying OBe stars.

We also measure the proper motions of OBe stars within the LMC using data from Gaia DR3. We then combine these findings with the proper motion characteristics of OBe stars in the Small Magellanic Cloud (SMC) region. We find that the velocity distributions of OBe stars in the LMC and the SMC are very similar. However, the velocity of OBe stars in the LMC is slightly higher than in the SMC.