Posters

The galaxies which contributed most to the reionization of the universe (z ∼ 6) are uncertain. It is currently impossible to observe the ionizing Lyman continuum (LyC) emission from high- redshift galaxies due to absorption by neutral gas in the intergalactic medium (IGM). Thus, it is essential to study LyC-leaking galaxies at low redshift, because they are the only galaxies for which we can detect LyC emission. LyC detections are used to determine some of the physical properties of galaxies that could be analogous to ionizing galaxies during the Epoch of Reionization. Previous LyC diagnostics rely on strong emission lines; therefore, we will investigate faint emission lines such as [O I], as the strength of certain faint emission lines may be more sensitive to LyC radiation. Using low-redshift (z ∼ 0.3) galaxy spectra taken with the visible-wavelength Echellete Spectrograph and Imager (ESI) at the Keck Observatory, we will try to search for faint emission lines as their properties are under-explored.

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Between stars there lie the clouds of gas and dust that make up the Interstellar Medium (ISM). The Local Interstellar Medium (LISM) includes the ISM directly surrounding our solar system out to a distance of approximately 100 pc. Observing stars whose light is shrouded by the surrounding LISM allows us to understand the properties of such clouds and dust. We used spectra collected by the Hubble Space Telescope using the Space Telescope Imaging Spectrograph (STIS). We had a sample size of eight stars, all within 100 pc, each exhibiting one ISM component indicative of the sight line traversing a single LISM cloud. STIS observes a target star and measures the flux with respect to wavelength. We focused on six elements, SiII, CII, DI, OI, NI, and AlII. The clearest absorption profiles came from DI and CII. To fit our spectra we use an IDL program that models the ISM absorption profile. We looked for interruptions in these absorption features which indicate that ISM is blocking the light. In five of our stars, DI and CII had significant LISM absorption. We successfully modeled the single component LISM absorption in DI for 3 sight lines, and in CII for 3 sight lines. From this point, we plan on using the widths of the LISM absorption to calculate the temperature and turbulent velocity of the clouds. The absorption of these ions as shown in our data gives us a more well rounded image of our LISM that we can use to further understand our place in the universe.

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The Low-Redshift Lyman Continuum Survey (LzLCS) investigates galaxies with Lyman continuum escape in order to understand the Epoch of Reionization, and it obtains some of its data from spectra of galaxies taken by the Sloan Digital Sky Survey (SDSS). However, for some of the galaxies in the survey, the values for the H𝛼/H𝛽 emission line flux ratios are lower than expected, even if there were no intervening dust. This paper presents the H𝛼/H𝛽 ratios calculated from new spectra taken at the MDM Observatory and compares them to the ratios calculated from the SDSS spectra. Ultimately, the new spectra support the conclusion that the low H𝛼/H𝛽 ratio values from SDSS were due to SDSS processing errors or the emission lines being saturated rather than physical properties of the galaxies. However, examinations of the measurements from the SDSS spectra of the galaxies with low H𝛼/H𝛽 ratios do not indicate how these galaxies differ significantly from the rest of the LzLCS galaxies, leaving the reason unknown as to why some of the H𝛼/H𝛽 ratios from the SDSS spectra were low.

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Bars are a common structure found at the center of about half of the spiral galaxies. They are linear structures of stars which can cross large fractions of the galaxy disc. They are understood to affect the motion of stars and gases within their host galaxy. Previous studies (Stark et al. 2018) have examined the possible correlations between the existence of bars in galaxies and distortions in their velocity field with data from the MaNGA IFU survey. This paper continues working on this correlation using a sample of galaxies with both SDSS IV MaNGA and Galaxy Zoo data, to create a filtered sample of galaxies that are spiral, face-on, and would have visible bars if present. We then employed the Radon transform calculation tool (Stark et al. 2018) to derive their Radon profiles and uncertainty. These information describe how symmetric velocity fields are and allow us to detect non-circular motions. These images then go into crowd-sourcing to classify the shape of their profiles into categories of constant, inner-bend, out-bend, inner+outer-bend, and asymmetrical. From the crowd-sourcing results, we will be able to seek for further correlations of barred galaxies and their classified profiles.

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Galactic bars are extended linear structures crossing the center of a substantial fraction of disc galaxies (Masters et al. 2011). These structures have various impacts on their host galaxy, for example regulating star formation rates (Masters et al. 2012), varying stellar orbits (Contopoulos & Papayannopoulos 1980), driving radial inflow (Fraser-McKelvie et al. 2019), all examples of secular evolution of galaxies (Lin et al. 2020) driven by large-scale kinematic influence of the bar. The length and axis ratio of bars are useful quantities to measure their strength. Previous works have used different methods to measure these bar dimensions, such as using interactive and robust crowd-sourcing interfaces (Hoyle et al. 2011), Fourier analysis (Elmegreen & Elmegreen 1985) and elliptical Petrosian photometric analysis (Krishnarao et al. 2020). We make use of Galaxy Zoo: 3D (Masters et al. 2021), a Galaxy Zoo style analysis which identifies in detail the locations of internal structures seen in galaxies targeted by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA), an optical fiber-bundle integral-field unit (IFU) spectroscopic survey that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). We perform elliptical isophote analysis on the crowd sourced bar masks from GZ3D. We select a sample of 1,355 barred face-on disc galaxies to test the code with 656 (48%) successful outputs. The results presented are preliminary, however, drawing comparisons with bar measurements from Krishnarao et al. (2020), also based on GZ3D but using a bounding box technique, we conclude that performing elliptical isophote analysis with Photutils on GZ3D bar masks is relatively accurate and provides a useful novel approach to generate bar dimensions.

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In the classic Hubble spiral sequence, it is implicitly assumed that spiral arm windiness correlates with bulge size, such that spiral galaxies with larger bulges have more tightly wound spiral arms. We use crowd-sourced galaxy morphologies from Galaxy Zoo participants along- side measurements from the NASA Sloan Association (NSA) catalogue to explore the impact of different galaxy properties upon the correlation between arm windiness and bulge size. Selecting a low redshift volume limited subset of galaxies with distinctly observable features, particularly spiral arms, we have a total sample of 7,982 galaxies. We find that the correlation between arm windiness and bulge size shows a significant mass and color dependence. While the correlation is negligible for the entire data sample (as reported in Masters et al. 2019), this correlation is more evident for subsets of bluer galaxies and becomes negative for subsets of redder galaxies. Furthermore, we observe that more massive galaxies tend to have a negative correlation - in this sample, we find increasingly tightly wound arms for decreasing bulge size. We also compare Galaxy Zoo arm windiness with pitch angle measured using a Fourier technique (by Yu and Ho 2021) in a sample of 2,679 galaxies with both measurements. We find only a weak correlation between arm windiness determined by Galaxy Zoo and pitch angle measured by Yu and Ho. These are quite different methods of calculating the windiness of spiral arms, and we suggest several possible reasons for the observed disparity of results.

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The types of galaxies that dominated the reionization of the universe in the Epoch of Reionization are debated greatly. Radiation called Lyman Continuum (LyC) radiation ionizes neutral hydrogen and is produced by stars and galaxies. However, measuring any of the LyC emission from the galaxies at the redshift of the Epoch of Reioniation (z>6) is impossible due to it getting absorbed by intervening neutral hydrogen gas in the intergalactic medium. Thus we look at nearby galaxies (0.2<z<0.5), in order to understand what properties of galaxies signify LyC leakage. NASA’s SPRITE Mission will help observe and gather data about these nearby galaxies with new technology which is very sensitive to the UV. We are choosing galaxies for this mission to measure LyC in previously unexplored galaxies. The galaxies span a range of masses, metallicities, and ionization. We optimized which galaxies we chose based on lower required exposure times for LyC detection with SPRITE and higher signal-to-noise in key emission lines for follow-up measurements in the future.

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In preparation for the upcoming Laser Interferometer Space Antenna (LISA) mission, the LISA Data Challenges pose a series of open questions on how to extract gravitational wave (GW) signals from simulated LISA data. Solving these challenges is essential to demonstrating effective analysis methods for the mission in the mid-2030s. As the LISA mission will detect GW signals in a new frequency range, a variety of previously undetected GW source types will be present in the LISA data. One such source type is that of extreme mass ratio inspirals (EMRIs), inspiraling binary systems where a stellar mass object is orbiting a supermassive black hole. This project seeks to use Markov Chain Monte Carlo (MCMC) algorithms to develop a reliable method for identifying EMRI signals and extracting their source parameters, using the NANOGrav collaboration’s PTMCMCSampler.

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Early warning gravitational wave detection pipelines are extremely important tools that could alert astronomers to a gravitational wave event before the event has occurred, facilitating a new frontier for multi-messenger astronomy. The aims of this project were to study the early warning pipeline, specifically GstLAL, and run the pipeline using data from Advanced LIGO and Advanced Virgo’s third observing run colored to projected O4 sensitivities. This project involved varying the upper frequency bounds, which correspond to different early warning times, and using these different runs to test a new process of calculating the false alarm rate for events. The false alarm rate is a measure of how often we expect LIGO noise to produce a gravitational wave event. By decreasing the significance of noise events through this process, we are aiming to reduce the number of false alarms, and therefore retractions, for the next LIGO observing run.

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Radio telescopes are the optimal method for observing many astronomical objects due to their flexibility compared to optical telescopes. Radio telescopes are not affected by optical light pollution, which maximizes their usable time over a given period. Radio waves are also less affected by dust clouds and our atmosphere than visible light. However, radio telescopes still face a barrier to collecting clean data: Radio Frequency Interference (RFI). This is a phenomenon similar to light pollution where radio signals from human-made objects are in the path of the signals from the astronomical object. GPS satellites are one of the most frequent cause for RFI, and their impact on astronomical data is difficult to remove. We analyzed the rate of GPS interference from the Green Bank Telescope in West Virginia as a function of time of day and location in the sky to determine whether there are optimal combinations of time and location where GPS interference is minimized allowing astronomers to design observing plans to maximize data. We found that there was an overall increase in GPS interference as time since midnight increased. From the hours of midnight to 05:00 UTC, around 8.5 percent of scans have GPS interference, while the GPS interference rate was as high as 13 percent after 20:00 UTC. We also found that observations directed at an altitude of 80 degrees or higher were far more likely to suffer from GPS interference than observations directed at other altitudes. This is especially true for scans directed at between an azimuth of 160 and 170 degrees and an altitude greater than 80 degrees. Nearly 80 percent of observations in that azimuth and altitude range returned scans with GPS interference. In addition, we calculated the overall rate of scans with GPS interference by year from 2016 to 2021 and found an increase in GPS interference each year. These findings will be used to develop strategic observing plans and increase usable data for astronomers working with the Green Bank Telescope and possibly others in the future.

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The Epoch of Reionization Spectrometer (EoR-Spec) is an instrument module for the Prime-Cam receiver of the 6 meter Fred Young Submillimeter Telescope located on Cerro Chajnantor at 5600 m altitude on the Atacama plateau in northern Chile. EoR-Spec will investigate the structural evolution of reionization of the universe due to star formation in galaxies by performing 158 µm [CII] line intensity mapping between redshifts 3.5 and 8 (210 - 420 GHz). This project is centered around EoR-Spec’s cryogenic, silicon substrate-based Fabry-Perot Interferometer (FPI) with a resolving power (𝜆/𝛥𝜆) of 100. The FPI acts as a resonant filter, transmitting selected frequencies of light to the detector array based on the spacing between its parallel silicon mirrors. The current design employs capacitive sensors to measure the distance between the mirrors. Additionally, the frequencies of off-axis beams passing through the FPI will be blue-shifted with respect to the on-axis beam, thereby enabling spectral multiplexing at pixels that are radially offset from the optical axis. The first goal of this study was to perform and analyze initial measurements from the capacitive sensors to identify sources of noise; the second was to simulate observations using the Time Ordered Astrophysics Scalable Tools (TOAST) software framework to determine the efficiency of a particular scanning strategy, taking into account the frequency spread. Preliminary analysis of capacitive sensor measurements show very good stability and low noise of the metrology system. The Python scripts for TOAST simulations have been modified successfully and now allow investigating combined telescope and FPI scanning strategies and will help to optimize the observing efficiency. These results increase confidence in the current instrument design and application while also laying the foundation for more complex tests in the future. This work was supported by the NSF REU program at Cornell University, and in part by NSF grant ATI-2009767.

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Our team is developing a novel atom-counting instrument capable of spaceflight and in-situ Rb-Sr geochronology of planetary specimens, especially on the Moon and Mars. Since 87𝑅𝑏 decays into 87𝑆𝑟 at a known rate, determination of their relative abundance within a sample enables an estimate of its age. Having been sputtered from the sample, these atoms travel down a beam intersected by lasers tuned to resonantly excite either Rb or Sr. The resonating atoms fluoresce as they cross the laser beam, with each expected to emit a burst of hundreds of photons within ≈3500ns. Such bursts are detected as multiple flashes, termed multiplets, in temporal coincidence. This work focuses on optimizing their detection in two computational projects: (1) Modeling the angular distribution and polarization of Sr fluorescence, given the polarization of incoming laser light, and (2) writing an algorithm for identifying bursts of photons against a background of stray light. The former was accomplished through the use of angular momentum conservation and quantum state rotations, with which we expressed the excited state of the Sr atom along an arbitrary quantization axis. We found that the probability of emission was zero along the axis in which the incoming light is polarized, but maximum in the plane perpendicular to it. Modifications to the instrument accounting for this result has led to >50% improvement in signal. While a “brute-force” algorithm may identify all multiplets within a dataset in a matter of days, our algorithm achieves this in ≈5 seconds by subsampling the data in 3500ns windows. It additionally evaluates the observed multiplet abundances against predictions by Poisson statistics—a proxy for noise—to discern photon bursts from the background. Further research is required to aid our ongoing quest to enhance the instrument’s signal-to-noise ratio.

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Through the study of impact craters, a ubiquitous surface feature on rocky and icy worlds in our Solar System and beyond, we can draw conclusions about the history and evolution of a given world. In particular, studying the depth (d) to diameter (D) ratio (d/D) of a population of impact craters yields information about the evolution of the planet’s surface overall, including rates of erosion and burial. Given that impact crater data is obtained largely via satellite images, the goal of this project is to develop a quick and easy way to determine d/D from satellite images of impact craters for which stereo information is not available. To accomplish this goal, we set out to develop and train a machine learning algorithm to extract d/D from a dataset of synthetic impact crater satellite images (for which model d/D is known). In order to train the algorithm, we developed a Python script to create a training dataset of mock impact crater models consistent with the range of commonly-occurring parameters. The models also account for factors that may affect actual satellite images, such as crater-center offset, background noise, and lighting and shadows determined by the position of the Sun relative to the Martian surface. The models were developed using Python and POV-ray (a ray-tracing scene-renderer), with the goal of simulating an actual Martian landscape accurately enough for a proof of concept. The machine learning algorithm itself makes use of the Support Vector Regression (SVR) algorithm. Support Vector Machines (SVMs) are valued throughout the machine learning community for their straightforward implementation and versatility in solving both classification and regression problems. Due to technical and time-based difficulties, we were only able to train and test the algorithm on a small dataset (thousands rather than tens or hundreds of thousands of mock craters). However, even these results were encouragingly successful, as we achieved r-squared values as high as 0.865. We consider these results to be a solid proof of concept, and moving forward we hope to achieve further milestones such as training and testing on a dataset of actual non-stereo satellite images.

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Debris disks are collections of dust around main sequence stars, formed through collisions of planetesimals such as comets and asteroids. Although debris disks are common, only a handful of systems include a disk as well as a directly imaged planet. HD 106906 is a short-period stellar binary, host to an 11 M𝑗𝑢𝑝 planet, HD 106906b, at a separation of 735 au and a debris disk, which has been resolved at optical and radio wavelengths. We resolve the structure in the disk at a wavelength of 1.3 mm with the Atacama Large Millimeter/submillimeter Array (ALMA) at a resolution of .31" (30 au). An analysis of our data supports a disk that is symmetrical in surface brightness at this wavelength, with moderate evidence for an offset between the center of the disk and the expected position of the stellar binary (𝛿𝑥 = 19 ± 6 au). We then use dynamical theory to compare astrometric constraints on the planet’s orbit (Nguyen et al. 2021) and scattered light morphology (Krotts et al. 2021) with the observed disk morphology. The stellar offset in the ALMA data might indicate an eccentric disk, consistent with studies by HST and the Gemini Planet Image (GPI). However, a truly eccentric disk would result in asymmetrical surface brightness as well which is not observed in the ALMA data. In addition, a planet eccentric enough to induce disk eccentricity, as previously suggested by dynamical analysis, would induce inclination in disk particles as well, resulting in a vertically puffy or warped disk. In constrast, GPI observations indicate a vertically thin disk, with a scale height of 0.052 ± 0.0005. Finally, comparisons of simulated disks with ALMA observations prefer an unperturbed disk to disks with induced eccentricity within the parameter space allowed by the astrometric constraints on the planet’s orbit

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The composition of comets has remained largely unchanged compared with other planetary bodies in our Solar System since their formation in the protoplanetary disk. Studying their compositions can therefore provide insights into the chemical and physical processes that occurred during planet formation. Carbon dioxide (CO2) is an abundant volatile in comets and can be an important driver of cometary activity. Thus, CO2 abundances are a key aspect of cometary chemical composition. However, direct ground-based observations of CO2 are not possible owing to complete telluric absorption. While CO2 is observable from space-borne facilities, available observing time on these facilities is limited. Proxy observations that can be obtained from the ground are needed to overcome these barriers. Forbidden oxygen ([OI]) lines have been proposed as a candidate for such a proxy (specifically the flux ratio of the [OI]5577 Å line to the sum of the [OI]6300 Å and [OI]6364 Å lines, hereafter referred to as the oxygen line ratio). However, our understanding of the photochemistry responsible for the release of OI into the coma is still incomplete. We present analysis of narrowband OH imaging and high- resolution optical spectroscopy (acquired using facilities at McDonald Observatory) and IR imaging (obtained using the Spitzer Space Telescope and from the NEOWISE mission) of comet C/2013 X1 (PanSTARRS) to test [OI] as a proxy for the CO2 abundance. We utilize our OH observations as a proxy for the H2O production, while the spectroscopic observations sample [OI] emission and the Spitzer and NEOWISE observations are sensitive to CO2 emission. By comparing the inferred CO2 abundances from our oxygen line ratios to measured values based on the narrowband OH and Spitzer/NEOWISE imaging, we will test and calibrate the use of ground-based [OI] observations as a proxy for CO2 observations. This work was supported by NASA’s Summer Undergraduate Program for Planetary Research and the NASA Solar System Workings Program through grant 80NSSC20K0140.

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Carbonate minerals have been detected in several locations on Mars, including Nili Fossae, Jezero Crater, and the Comanche outcrops of the Columbia Hills. Carbonates are intriguing for what they could reveal about habitability of past environments; however, their exact formation mechanisms remain ambiguous. Observations support a range of formation mechanisms involving the hydrous alteration of the igneous mineral olivine to carbonate and serpentine. The minerals found alongside the carbonates, like serpentine, can help constrain their origins. This study examines high-resolution satellite images of serpentine and carbonate deposits in Nili Fossae and Jezero Crater to identify common characteristics of serpentine-carbonate terrains. The morphologies of serpentine- and carbonate-bearing terrains in Nili Fossae and Jezero are then compared to carbonate deposits in the Columbia Hills. By combining these analyses, this study explores the extent to which the carbonates’ histories are analogous and probes into previous serpentine detections in Jezero and Nili Fossae.

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Circumstellar disks are flat structures of gas and dust around main sequence stars, analogous to the Kuiper belt in our own solar system. Younger disks tend to be gas-rich, while older disks, called debris disks, tend to be gas-poor. However, gas has been detected in an increasing number of debris disks, such as the one around 49 Ceti. The origin of this gas is poorly understood. If it has primordial origins, then the gas must survive the dissipation of initial disk dust. If it has second generation origins, then it is released by collisions between icy planetesimals. Understanding the origin of the gas is important to understanding more about giant planet formation timescales, composition, and mass limits. One way to differentiate between primordial and second generation gas is to determine the scale height, h, which is a measure of the disk’s vertical puffiness. Disks with primordial gas are dominated by light molecules like H2 and will have a greater scale height than disks with second generation gas, since this gas is mostly C and O. We used 12CO(J=3-2) emission data from the Atacama Large Millimeter/submillimeter Array (ALMA) to model the gas in the debris disk around 49 Ceti. We then used a Markov Chain Monte Carlo (MCMC) algorithm to constrain the scale height by finding a best fit model. Initial results suggest consistency with second generation origins of the gas.

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Sub-mm observations show medium binaries (15-100 AU) to have a destructive influence on their protoplanetary disk material compared to single star systems. The occurrence rate of planets around tight binaries (<15 AU) and single stars is similar and distinctly larger than around medium binaries, suggesting that the same destructive effect is not present around tight binaries. Previous sub-mm studies of tight binaries, however, have been limited to a handful of objects. Here we examine sub-mm observations of 129 known tight binaries in Orion A, building on the sparse statistics around these systems, and investigate the mass budget of tight binaries compared those of other system types. Our analysis reveals a higher mass budget around tight binaries compared to medium binaries, while infrared color-color diagrams indicate that a significant proportion of our tight binary sources possess gaps in the inner regions of their disks. This indicates that many tight binaries possess the raw materials necessary for planet formation, consistent with the frequency of planets in these systems.

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Young protostars that undergo episodic accretion can provide insight into the effects of stellar evolution and impact on their circumstellar environments. L1251 VLA 6 is a four protostar system with one of those being a fading outbursting protostar. Here we resolve structure in the disk around L1251 VLA 6 at a wavelength of 33 GHz with the Very Long Array (VLA). Given the rarity of YSOs undergoing this type of accretion, L1251 VLA 6 can provide insight into the fading post-outburst process. We summarize key observations of the star outburst, and review the latest thinking on outburst triggering mechanisms, the propagation of outbursts from star/disk and disk/jet systems, and the relation between EXors and FUors.

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Current models that describe how young, low-mass stars evolve before they reach the main sequence diverge from one another and are inconsistent with measured stellar properties. A larger sample of young, low-mass stars with well-determined properties is needed in order to constrain these models and make them more accurate. Since properties of eclipsing binary systems can be determined through observations alone – without assumptions based on models – they are vital for building such a sample. In this project, we searched TESS data for previously unstudied young, low-mass eclipsing binary systems. Using cutouts of TESS full-frame images, we created and examined light curves for 398 targets flagged as young, low-mass spectroscopic binaries or radial velocity variables. From this initial search, we identified nine eclipsing binary candidates. We have begun the process of modeling these nine systems. The next steps for this project include taking additional ground-based observations of each target in our current sample and expanding our search for young, low-mass eclipsing binaries to greater numbers of targets.

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Due to their very hot temperatures and high luminosities, supergiants like the O-type star 𝜁 Puppis eject material from their surfaces at high speeds in radiation-driven stellar winds. Here we present broadband spectral modeling of the X-rays produced by shocks embedded in these stellar winds to investigate changes in the properties of 𝜁 Puppis over an 18 year period. In particular, we aim to deduce the star’s mass-loss rate, which was unexpectedly found to increase by 40% in previous research using individual emission line profiles. We verify this surprising result with an independent analysis of the same set of 22 separate Chandra observations taken in 2000 and 2018-19, to which we fit a multi-temperature thermal emission and wind absorption spectral model. We find a 36% increase in the wind mass-loss rate, as well as an increase in X-ray luminosity of a similar magnitude (38%). Furthermore, the multi-temperature emission component of the model provides an estimate of the differential emission measure, which describes the hot plasma’s temperature distribution. The emission measure appears to almost double over the period of study – a change consistent with the increased wind strength we found.

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Dusty debris disks that orbit main sequence stars are comparable to our Solar System’s Kuiper belt. While debris disks have less gas than their younger counterparts, a surprising, recent discovery by the Atacama Large Millimeter/submillimeter Array (ALMA) is that many of these debris disks do in fact have substantial reservoirs of molecular gas. This facet provides the opportunity to utilize spectroscopic methods to analyze the Keplerian rotation curve of these types of disks and therefore obtain novel methods to ascertain the mass of the host star. Doing so involves imaging and data cleaning techniques standard to the field, as well as iteratively creating models and comparing those models to the real data in line with a Bayesian approach to find best fit parameters. This project combines archival ALMA data with new Gaia (European Space Agency’s space-based telescope) data that provides precise stellar distances which are crucial for determining more accurate host star masses. We will compare the dynamical masses that we derive with stellar evolution models to test our understanding of these isolated young stars. The broader implication of this research will contribute to the field by testing predictions made by stellar evolution and it has the potential to re-define development outcomes of how these unique systems evolve.

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Turbulence in protoplanetary disks is a very important factor in planet formation and evolution, from promoting collisional growth of small dust grains, to limiting settling of larger dust grains near the disk midplane. However, disks for which we have turbulence estimates are limited in number and skewed towards brighter disks with more disk mass surrounding a more massive star, and with high signal to noise ratios. To address this, we explore fitting disk models to data using a new statistical method(MultiNest), which may be more accurate at lower signal to noise ratios. We have used MultiNest to replicate results obtained for a disk previously studied using the Markov Chain Monte Carlo method EMCEE. Initial tests indicate that MultiNest can effectively identify models with the highest likelihood in a two-parameter space. We have found that the number of live points (e.g., 20 vs 400) strongly influences the sampling of the posterior. In the future we will use MultiNest to obtain new turbulence estimates for a new sample of disks that are more representative of the disk population than the current sample.

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X-ray emission line analysis from new long Chandra grating observations taken during 2018 and 2019 indicates a surprising 40 per cent increase in 𝜁 Pup’s wind mass-loss rate as compared to data taken in Chandra’s first observation cycle in 2000. X-ray emission lines from shock-heated wind plasma are Doppler-broadened due to high wind speeds, and are made asymmetric by absorption from the cool bulk of the wind. Modeling the asymmetry of the emission lines serves as a diagnostic of the mass-loss rate. We found a mass-loss rate of 2.47 ± 0.09 × 10−6 M⊙ yr−1, representing a significant increase since the first observing cycle. This is accompanied by a flux increase especially in the short-wavelength lines, which are subject to less wind absorption, since the cycle 1 observation. Both these changes could be explained by a presumed increase in wind strength that affects the level of X-ray emission uniformly across the spectrum and affects X-ray absorption in a wavelength-dependent fashion.

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