Michigan Astronomy
Undergraduate Research Symposium 2022

Title: Circumstellar disks: An exponential relationship between disk lifetimes and stellar mass

Anneliese Ardizzone¹ and Michael Meyer¹

¹ University of Michigan

Abstract: Circumstellar disks are quite common around young stars, as they are thought to be a result of conservation of angular momentum as stars form (Meyer et al. 2007). The properties of circumstellar disks are dependent on stellar mass (Ansdell et al. 2016) and accretion rates of materials onto the star (Hartmann et al. 2016). Circumstellar disks tend to dissipate as stars age, especially so around higher mass stars (Yao et al. 2018; Ribas et al. 2015, Yasui et al. 2014; Kennedy & Kenyon, 2009). Utilizing data from published literature, we determined an exponential best fit for circumstellar disk lifetimes as a function of stellar mass.

Exploring High-Resolution Emission Spectra from Ultra-hot Jupiters using 1D and 3D Models

Mireya Arora¹, Hayley Beltz¹, Emily Rauscher¹

¹ University of Michigan

A large part of studying exoplanets involves analyzing their spectra to detect atmospheric species. By observing a series of emission and absorption lines, we can compare their shapes and intensity to spectra produced by atmospheric models. If the observed data and models match strongly, we know that the species is present in the exoplanet atmosphere. This project uses High Resolution Spectroscopy (HRS) which resolves spectral features of species to a dense series of lines. To ensure astronomers collect the data they desire with telescopes, they need to know which species are present at the wavelengths of their instruments. In this study, I used simulated data of what an exoplanet’s emission spectra would look like with and without 6 species. I worked with a 1D model of WASP-76b, an ultra-hot Jupiter, for this project. With this, I isolated the features of each species and then combined them to create a figure showing the expected spectral features for 6 species in the 0.95-5.5 micron wavelength range. Taking this work a step further by utilizing 3D models, with more detailed measurements it is possible to look at spectra from the planet throughout its orbit around its host star (also described as different phases of orbit). By comparing the spectra at different phases, I created a plot showing the relation between phase and amount of emission or absorption in the spectrum — which varies based on the temperature structure of the planet. This project helps astronomers get a better understanding of emission spectra from ultra-hot Jupiters they should expect to receive from an exoplanet, and how it varies with phase.

An Exploration of Constraining Chemistry in Three-Dimensional Eclipse Mapping

Lucas Brefka¹, Ryan Challener¹, Emily Rauscher¹

¹ University of Michigan

Abstract: Eclipse mapping is a useful tool for understanding the composition, temperature, and dynamics of the atmospheres of transiting extrasolar planets, by measuring the flux emitted by the planet as it passes behind its star, subsequently mapping its temperature as a function of longitude and latitude. The open source Three-dimensional Exoplanet Retrieval from Eclipse Spectroscopy of Atmospheres (ThERESA) code utilizes these spectral observations, building two-dimensional maps at individual wavelengths, stacking and interpolating them to create a fully three-dimensional temperature-pressure model of the atmosphere. In this work, we relax ThERESA’s assumption of solar atomic abundances by allowing metallicity to vary as a free parameter, comparing the results of our atmospheric retrieval with the known input model. We expect true planetary atmospheres to be in disequilibrium, existing with varying compositions and complexities; this work is thus a step toward more robust exoplanet atmospheric characterization, and will be a powerful tool for studying observations from JWST in the near future, as well as planning observations for exoplanet characterization.

Accretion Outburst events in Protoplanetary Disks

Jacob Cleaver¹, Lee Hartmann¹, Jaehan Bae².

¹ University of Michigan, ² University of Florida

Abstract: We compute model light curves and spectral energy distributions of accretion outburst events from protoplanetary disks. We input variable initial disk properties in order to make predictions on the amplitude and timescale of the outbursts. From previous observations in the optical (Gaia) and infrared (WISE), we anticipate an earlier observation of the outburst in the infrared than in the optical spectrum. Using this knowledge, our goal is to then constrain the location at which the outburst started in the disk and attempt to determine the level of mass and angular momentum transport that lead to the observed phenomena.

The Binary Origins of OBe Stars in the Small Magellanic Cloud

Matthew Dallas¹, Sally Oey¹

¹ University of Michigan

Abstract: Classical OBe stars are rapidly rotating OB stars with emission lines produced in a decretion disk. The origins of the fast rotation and subsequent disk are not yet well understood. In this work we add to the growing evidence that OBe stars form from massive binary systems. The model proposes that OBe stars gain angular momentum if their massive binary companion evolves to fill its Roche lobe. These close binary interactions should result in OBe stars residing farther into the field on average than OB stars, because mass transfer can prolong the life of the OBe star, allowing it to drift longer in the field; or, the companion & subsequent supernova can impart a runaway velocity on the OBe star. To test for this effect, we analyse the distances between OBe stars and their nearest O stars in the Small Magellanic Cloud. These distances serve as an effective measure of how far into the field each star resides. We find that OBe stars reside at a median distance of 36 ± 3.3 pc into the field vs 22 ±1.8 pc for OB stars, consistent with the expectation that post-mass-transfer objects are more isolated. Furthermore, the Oe and Be populations themselves are equally isolated in the field, with Oe stars residing at 34 ± 9.4 pc into the field and 39 ± 5.0 for Be stars. This is to be expected if their birth masses are obscured by mass transfer. We note that OBe stars and high-mass X-ray binaries (HMXBs) are closely related, with 39/49 HMXBs in the sample being OBe stars. These HMXBs have a median distance of 48 ± 6.5 pc, which further supports the scenario that most OBe stars are post-binary supernova objects released into the field. Finally, we show that supergiant OBe stars, which are known to not have formed via binary interactions, have a spatial distribution consistent with OB supergiants rather than non-supergiant OBe stars. Our analysis therefore finds multiple lines of evidence supporting the binary formation model of OBe stars, which has implications ranging from binary population models to gravitational wave astronomy.

Complex dusty envelopes and disks around forming protostars

Fiona Han¹, Lee Hartmann¹, Manuel Zamora², Shangjia Zhang³

¹ University of Michigan, ² INOAE, Mexico, ³ Univ. Nevada-Las Vegas

Abstract: We calculate the mm-wave emission predicted by theoretical simulations of protostar formation and compare them to ALMA and VLA observations of highly extincted, and probably extremely young, protostars in the Orion B molecular cloud. These Orion protostars are unusually bright at 0.87mm and 8mm, suggesting that they have very large dust (and gas) masses on scales <~ 100 AU. The masses and sizes suggest protostellar disks, but the observations show complex structure. Using computer simulations, we compute images from the simulated protostars to see whether we can explain the morphology by a combination of infalling streams and complex non-equilibrium disk structure.

Aperture Photometry on Exoplanet Host Stars in the Near-UV

Aleck Hernandez¹, George King¹, Lia Corrales¹

¹ University of Michigan

Abstract: The near-UV is a relatively under-explored region of the electromagnetic spectrum for a large number of exoplanet systems. To remedy this, we compiled a catalog of the results of performing aperture photometry on 56 nearby exoplanet host stars in the near-UV using the Ultraviolet Optical Telescope (UVOT) on the Swift Observatory. We made use of the UVOT software package in making a pipeline of bash and python scripts that streamlined the processes of collecting, aggregating, and tabulating all of our data. The data in this catalog includes count rates, fluxes, and AB magnitudes, as well as the filters used, and the exposure time of each observation. The importance of this catalog is that measuring the UV brightness of these stars will help optimize which systems are targeted for later UV transit observations. Though the catalog is our main result, we also include figures that serve as examples of the different types of analysis that can be done using the data we collected.

Globular cluster candidates in the M83 group, using the GHOSTS HST survey.

Karthik V. Ganti¹, Eric F. Bell¹, Jiaming Pan¹

¹ University of Michigan

Abstract: We have identified four candidate globular clusters (hereafter GCs) in the archival GHOSTS HST survey of the M83 group (specifically, 1 candidate in Field 4 and 3 candidates in Field 5) by visual inspection. We used the Subaru HSC data for the M83 group to search for GCs using Spitzer/IRAC catalog data to constrain colors, cognizant that previous efforts to find GCs have benefitted from combining optical and IR imaging data, through which we obtained 5 candidates, 1 of which matches within tolerance the position of one of the GHOSTS Field 5 candidates. We also observed that the Subaru GCs in conjunction with IRAC do not show clear trends in color-color diagrams. Upon using the IRAC [3.6㎛] imaging at the GHOSTS candidate positions, we observe that only the one GC’s position in IRAC is clearly resolved. The flux at the predicted positions of the other 2 Field 5 GCs is dominated by neighboring bright objects and the SNR (signal-to-noise ratio) at the predicted position of the Field 4 GC is not enough for detecting a candidate. Therefore, we conclude that the existing archival IRAC data is probably too shallow and suffers from crowding that limits its ability to be used as a tool for detecting GC candidates in the stellar stream of M83.

Space-Based Formation Flying Interferometry

Prachet Jain¹, John D. Monnier¹

¹ University of Michigan

Abstract: Conventional ground-based interferometer arrays are hindered by atmospheric disturbances and telescope thermal emissions. Additionally, the lack of reconfigurable baselines limits angular resolutions to certain ranges. A suitable alternative to a conventional ground-based interferometer array would be a space-based array of formation-flying satellites, free of atmospheric turbulence and reconfigurable to adjust baselines for any required angular resolution. This interferometer will particularly improve exoplanet detection and characterization, allowing astronomers to study exoplanet atmospheres for habitability criteria and biomarkers. We propose developing a technology demonstrator for such a space-based array through the use of smallsats. This mission would utilize two satellites to demonstrate various key technologies for a larger concept, such as reflection of starlight from one satellite to another, inter-satellite metrology, and the ability to “re-form” the geometry of the formation to acquire new stars. Currently, an optical testbed is being developed to be used on a drone to demonstrate actively-controlled light acquisition mechanisms on a moving platform. Successful testing of this platform will prompt further development work on satellite-based light reflection and acquisition mechanisms. Additionally, we continue to explore initial mission architecture design choices, including potentially suitable orbits and requirements on path length control.

Modeling the O K shell photoabsorption spectrum of GX 339-4

Sanjana Kerkar¹, Ioanna Psaradaki¹, Lia Corrales¹

¹ University of Michigan

Abstract: X-ray telescopes can study the gas and dust content of the interstellar medium by studying the absorption spectra of low mass X-ray binaries. We use observations from XMM-Newton, an X-ray space observatory, to study the spectrum of the black hole binary GX 399-4. Once we identify the Oxygen K-edge, the absorption spectrums of GX 339-4 are fitted using pyXspec and SPEX. By setting the oxygen contributions to zero and calculating the residuals, we separate the O K edge absorption features from the underlined continuum. This allows the modeling of the gas and dust absorption to be continuum independent.

The use of two point correlation estimators in star-galaxy separation

Michaela Landman¹, Eric Bell¹

¹ University of Michigan

Abstract: Two point correlation functions characterize the distribution of galaxies across the sky by describing the excess probability of two objects in a dataset having the same classification. Star-galaxy separation is the process through which objects in a dataset are identified as either stars or galaxies. Classifying data in this way is a necessary step. Higher numbers of background galaxies that can be mistaken for stars poses a problem when investigating galaxy formation. Information about the formation of galaxies can be inferred from the ages and colors of the stars that compose the galaxy, as well as other artifacts in the galaxy from interactions like collisions between systems. The two point correlation function can be used to characterize objects of the same type in small regions of space. The excess probabilities of similarity derived from the on-sky clustering of objects can be used to identify further differences between objects, as background galaxies tend to demonstrate a uniform distribution where stars do not. The following poster details the construction of the two point correlation function, and its potential application to identifying objects in star-galaxy separation.

Constraining the Features of the Low-mass Stellar Multiple Population in the Orion Nebula Cluster

Christopher Liu¹, Matthew De Furio¹, Michael Meyer¹

¹ University of Michigan

Abstract: We describe the multiple population of low mass stars (0.1-0.6Msun) in the Orion Nebula Cluster (ONC), exploring orbital separations from 10-200 AU and mass ratios down to 0.2. Young star clusters such as the ONC are an important laboratory to study star formation. Low mass, low density stellar associations like Taurus have been shown to contain a companion frequency roughly twice that of the Galactic field, from 3-5000 AU over all mass ratios. High mass, higher density clusters like the ONC do not exhibit an excess of multiples relative to the field, but are less well studied. If clusters like the ONC were to have multiplicity properties (e.g., companion frequency, mass ratios, and separations) similar to the field, we might conclude that low density regions do not contribute significantly to the galactic stellar population. Alternatively, if ONC-like clusters also show an excess of binaries, environmental factors such as dynamical interactions could be an important future process to shape the companion population in dense clusters. Based on the work of De Furio et al. (2022), we applied a double point-spread function (PSF) fitting procedure using empirical PSF models to archival Hubble Space Telescope (HST) images from the Advanced Camera for Surveys (ACS) in multiple filters. Our sample consists of low-mass M-type stars for which we are sensitive to companions ≥ 10 AU (0.025”) for high signal-to-noise sources, roughly 0.5*λ/D. We have identified 44 candidate companions with projected separations as low as 13 AU, and calculated the mass ratios of 30 of these candidates. With these detections, we will place constraints on the companion frequency, orbital separation distribution and the companion mass ratio distribution of the ONC, and search for environmental impacts on the multiple population.

Tidal HI gas and star formation efficiency in the M81 group

Miranda McCarthy¹ Eric Bell¹, Adam Smercina², Richard D'Souza³, Roelof de Jong⁴ , Insung Jang⁴, Antonela Monachesi⁵, Jeremy Bailin⁶, Colin Slater⁷, Paul Price⁸, David Nidever⁹

¹ University of Michigan, ² University of Washington, ³ Vatican Observatory, ⁴ Leibniz-Institut für Astrophysik Potsdam (AIP), ⁵ Universidad de La Serena, ⁶ University of Alabama, Tuscaloosa, ⁷University of Washington, ⁷University of Washington, ⁸ Princeton University, ⁹ Montana State University

Abstract: In the M81 group of galaxies, large tidal regions of neutral HI comprise a vast gas debris field between the members of the group. Within this debris field, although the number of high mass main sequence stars generally tracks the gas density with significant scatter, other areas have far less star formation for their gas content. Using wide-field resolved star data from Subaru along with HI data from the VLA, we calculate the spatially-resolved ratio of gas density to high-mass main sequence stars, finding a ridge of prominent star formation along the majority of the tidal bridge between M81 and NGC 3077. Despite having similar amounts of HI gas, the areas to either side of this ridge have few to no main sequence stars, implying that some other factor is inducing this long strip of recent star formation down the bridge. To understand potential factors driving this strip of activity, we compare our data with simulations of similar large galaxy mergers from the Illustris project.

Global Rotation Rate in the Pleiades Star Cluster

Sanil Mittal¹, Michael Meyer¹

¹ University of Michigan

Abstract: We computed an estimate of the total rotational energy of the Pleiades Star Cluster and compared it with gravitational binding energy and kinetic energy. A project with an analysis of rotational velocities has not been done before in a way that analyzes the internal cluster dynamics for the Pleiades star cluster as a whole. Measuring the rotation rate of clusters can inform models of giant molecular cloud formation (the origin sites of the clusters) as well as models of cluster evolution. An in-depth analysis with astrometry and data obtained from GAIA would give insight into how complex systems such as star clusters interact.

The analysis revealed that the rotational kinetic energy was very low compared to the total kinetic energy and the potential energy, which suggests that the Pleiades star cluster may be rotating on an axis with a very small overall rotational velocity. A plot of radial velocities with the distance from the center had a least-squares line fit with a positive slope of 0.372 which suggests a strong case for a small rotation of the Pleiades star cluster about an axis.

To perform statistical analysis on radial velocities of the Pleiades star cluster, we obtained data from a previous research paper. The statistical inferences were performed using Python for the least-squares fit and gaussian and histogram plots and to find the most probable axis of rotation in the plane of the sky (under the assumption that the axis for rotation lies in the plane of the sky).

Effects of Magnetic Drag on Doppler Shifts of High Resolution Emission Spectra of Ultrahot Jupiter WASP-76b

Grace Ochs¹, Hayley Beltz¹, Emily Rauscher¹

¹ University of Michigan

This poster examines how different magnetic drag models affect the Doppler shifts of high resolution emission spectra of the ultrahot Jupiter WASP-76b. The magnetic drag changes the temperature structure of the planet, so spectra will differ as the magnetic drag differs. Three models were used: magnetic drag from a 0 G magnetic field, magnetic field from a 3 G magnetic field, and a uniform global magnetic drag. From here, we had one spectra with Doppler effects turned off, and one spectra with Doppler effects turned on. We cross-correlated these spectra to find the relative velocity shift of the spectra from the peak of the cross-correlation. This method allows us to determine the net Doppler shift for each spectra. We compare these three models with relative velocity shifts versus phase. All models were run in two different wavelength regimes, the first of which is primarily driven by carbon monoxide and the second of which is primarily driven by water. Because of this, the different wavelength regimes will present at different heights, and therefore different wind speeds and shifts. Both wavelengths are shown together on the three model plots, with an additional plot to show the relative velocity difference between the two wavelength regimes. This work helps to show the need for fully 3D models, especially in the case of high resolution spectra.

Studying Mg II absorption within quasar halos to improve our understanding of quasar fueling and feedback

Priscilla Pitiak¹, Jasper VanHorn¹, Dr. Sean Johnson¹

¹ University of Michigan

Abstract: Although quasar fueling has been extensively studied in the past, this research was restricted primarily to focusing on signs of recent mergers in star light. However, quasars are fueled by gas reservoirs, not stars. For this project, we used Mg II absorption in 4256 foreground/background quasar pairs from the Sloan Digital Sky Survey (SDSS) to study gas in the halos of the foreground quasars. The light from a background quasar reaches us by passing nearby the foreground quasar, and if there is a cool (10,000 K), metal-enriched cloud along the line-of-sight, a Mg II absorption spectrum is produced. For each pair, we inspected the quasar spectra to visually verify if they were actually quasars, and verified the SDSS redshift measurement. Using Python Graphical User Interfaces, we zoomed in on the background quasar spectrum at the observed wavelength of Mg II at the foreground quasar redshift. We then fit the continuum and searched for Mg II absorption, which we classified as either confident, single-line, or non-detection. For confident and single-line detections, we fit a Gaussian profile to the absorption which provided us with a measurement of the line strength (equivalent width). Two of us made independent measurements for each pair and then compared them, resulting in a final confirmed sample of 300 confident absorbers, 155 single-line absorbers, and 3590 non-detections. We measured the covering fraction (total number of confident absorbers over sample size) and plotted it against projected distance between the foreground and background quasars. This provided us with a measurement of how common Mg II is at different distances. We found that as projected distance increases, covering fraction decreases. Our next steps involve stratifying our sample by redshift and luminosity, and observing whether these divisions produce changes in the covering fraction vs. distance trends.

SPORK That Spectrum: Increasing Detection Significances from High-Resolution Exoplanet Spectroscopy with Novel Smoothing Algorithms

Fahin Rahman, Kaitlin C. Rasmussen, Matteo Brogi, Hayley Beltz, Miles Currie, Emily Rauscher, Alexander P. Ji

Abstract: Studying Extrasolar planets allows us to not only understand the worlds many light-years away but ones in our own solar system as well. In particular, high-resolution cross-correlation spectroscopy reveals information about their structure, composition, formation, and much more. However, exoplanet signals are buried in stellar and telluric features, meaning that clever statistical methods are necessary to obtain information about them. We show that, with better

normalization and smoothing algorithms, the detection of molecular species in exoplanet atmospheres can be dramatically increased. We introduce the normalization routine SPORK (SPectral cOntinuum Refinement for telluriKs) and the smoothing function iterative smoothing and demonstrate that for hot Jupiters HD 209458 b and HD 179949 b, we retrieve detection significances 2-4 sigma higher than previously published values. These methods have a wide variety of applications to exoplanet spectroscopy, from obtaining previously-impossible detections in archival datasets to enabling stronger signals in the ELT spectra of the future.

Investigating Galactic Superwind-Triggered Star Formation in M82

Marlee Rapp¹, Adam Smercina², Eric Bell¹

¹ University of Michigan, ² University of Washington

Abstract: The objective of this study is to investigate past tidal interactions between the M82 and NGC 3077 galaxies in the M81 Group, by looking at the apparent tidal bridge between the two galaxies, discovered by Messere et al. (2022) (unpublished). We are focusing on a region of stars closer to M82, in which there is an apparent outflow of young stars trailing behind M82. Using data collected in this region by the Hubble Space Telescope’s WFC3 and ACS instruments in the F475W and F814W filters, we are examining the age distribution of this stellar outflow. We expect to find an age gradient along the trail of stars through which we can reveal more about M82’s past movement and tidal interactions with NGC 3077, as well as its future trajectory. With this study, we hope to gain a stronger understanding of M81’s history and future, as well as a more thorough understanding of starburst-driven galactic outflows.

Constraining Three-dimensional Cloud Properties with Spectroscopic Exoplanet Eclipse Mapping

Derek Still, Ryan Challener, Emily Rauscher

Abstract: Instrumentation aboard the recently launched James Webb Space Telescope will soon allow for the characterization of three-dimensional exoplanet atmospheres by utilizing spectroscopic eclipse mapping techniques. We expect the formation of clouds in cold and warm exoplanetary atmospheres to change observed pressures and temperatures, thereby incentivizing a method to account for the clouds' opacity in planetary emission models. The following is an extension of ThERESA’s, a three-dimensional exoplanet mapping code, to incorporate clouds into the 3D model by adding parameters for cloud properties like particle size and cloud deck depth. Employing the use of clear and cloudy general circulation models of HD209458b, we generate synthetic spectroscopic light curves that include the opacity of clouds at varying pressure levels, with wavelength dependence based on the molecular composition of the cloud species. Applying ThERESA to these light curves, we test a basic cloud model parameterization, with a single horizontally homogeneous cloud deck and single particle size, recovering 3D temperature maps and estimated cloud properties, and comparing them with the input general circulation models. ThERESA is open-source and publicly available as a tool for the community.

Examining Fluxes of Mg II Lines in T Tauri Stars

Trinity Thelen¹, Nuria Calvet¹, Marbely Micolta Calderon¹, Thanawuth Thanathibodee²

¹ University of Michigan, ² Boston University

Abstract: We analyze a sample of Mg II line profiles from the Disks, Accretion, and Outflows of T Tauri stars sample, obtained with Hubble Space Telescope instrument Space Telescope Imaging Spectrograph, using the high resolution e230m grating with a resolution of 10 km/s. We test the Mg II lines for a magnetospheric origin, finding that the line profiles are a few hundred km/s broad and centered at a velocity of zero, which is expected from magnetospheric accretion. We also find blueshifted absorption components in the line profiles coming from the disk winds. We calculate the line luminosities, and find that the values correlate with the mass accretion rate and the accretion luminosity, as well as with the luminosities of other lines that are known to form in the magnetosphere.

Investigating Tidal Processing in M81’s Ultra-Diffuse Galaxy, F8D1

Benjamin Velguth¹, Adam Smercina², Eric Bell¹

¹ University of Michigan, ² University of Washington

Abstract: Ultra diffuse galaxies (UDGs) are a relatively new classification of low surface brightness galaxies, with certain features that make them distinct. UDGs have low surface brightness, (> 24 mag arcsec^-2) large physical size ( > 2kpc) and low stellar mass (<10^8 M_sun). They also exhibit a high population of old stars, suggesting that their star formation was abruptly halted at some point in their evolution. Tidal processing explains all of these special characteristics, and a more in-depth look at this population of galaxies is crucial to filling in a hole in the knowledge surrounding galaxy formation. The purpose of this research is to take a closer look at the M81 group’s F8D1, the closest UDG to Earth, and determine if tidal processing played a role in its formation. Recent studies have simulated UDGs forming from normal galaxies undergoing tidal interactions, (L. Sales et al. 2020) and observations done on distant galaxy clusters have found evidence of tidal streams emanating from satellite UDGs (P. Bennet et al. 2018). However, other recent studies (Mowla et. al 2017, Carleton et al. 2019) have shown that UDG formation may occur under different initial conditions and through different processes. The origin of these galaxies is still up for debate, but the results of this research have shown that F8D1 does in fact show evidence of tidal disruption, with tidal arms around 20 kpcs long.