Circumbinary planets, those that orbit two stars, are a unique challenge for traditional ideas of planetary habitability. Due to orbital considerations and different stellar properties for the two host stars, these planets receive sunlight that continuously varies in time and as a function of wavelength. These changes could result in time-dependent changes to atmospheric composition and climate. Earlier theoretical studies of circumbinary planets indicate that there is likely a habitable zone where liquid water could exist on these planets, and that climate variations may not be extreme. However, these models did not take into account the effects of atmospheric photochemical reactions, which can alter planetary composition, including the abundance of greenhouse gases, and so also the climate as well. We have developed a new time-dependent coupled photochemical-climate model which allows for exploration of these effects. Here we describe the model, validate it against prior results, and present initial results on the impact of photochemistry in binary star systems.

The life and death of a galaxy is inextricably linked to the gaseous supply of its circumgalactic medium (CGM). Using the Hubble Space Telescope’s Cosmic Origins Spectrograph (HST/COS), we carry out quasar spectroscopy to probe this diffuse, extended gas. To characterize these galaxies, we supplement COS UV spectroscopy with optical spectroscopy from the Gemini North and South Telescopes. In total, 2,207 galaxy spectra were collected, all within 2.5 arcminutes of the quasar that have COS spectra. Of this initial group, 1,607 galaxies were classified as star-forming, elliptical, or some combination of the two based on the detected spectral lines. This study focuses on metal-line transitions in both galaxy and quasar spectra which track billions of years of supernova metal pollution. Absorption signatures from Ionized metals trace the physical conditions within the CGM of galaxies at the same redshift (+/- 500 km s-1) as the metal absorbers. We tie the metallicity of the CGM based on absorption-line measurements to the metal content of the host galaxies, as measured using strong emission lines. To date, no correlation exists between galactic metallicity and the metal content of the CGM. This finding indicates that the feedback processes within the CGM are complex and varied.

I have led a study of over 13 years of optical and near-ultraviolet spectropolarimetric observations of the famous Luminous Blue Variable (LBV), P Cygni. LBVs are a critical transitional phase in the lives of the most massive stars, and achieve the largest mass-loss rates of any group of stars. Using spectropolarimetry, I am able to learn about the geometry of the near circumstellar environment surrounding P Cygni and gain insights into LBV mass-loss. Using data from the HPOL and WUPPE spectropolarimeters, I have estimated the interstellar polarization contribution to P Cygni's spectropolarimetric signal, analyzed the variability of the polarization across the Hα emission line, searched for periodic signals in the data, and introduced a statistical method to search for preferred position angles in deviations from spherical symmetry which is novel to astronomy. 

Our research project aims to find red supergiant stars (RSGs) among the starburst galaxy IC10. Using stellar evolutionary theory, estimates can be made about how many RSGs are expected, based upon analyzation of known facts such as size, age, and metal content. The research conducted will allow for a comparison between observational data to theoretical expectations. RSGs are massive stars with a supergiant luminosity class; they are the coolest of the supergiants and have spectral types of K and M; hence temperatures below 4,100 K. Typically, they can be up to a thousand times the radius of the sun, and are therefore highly luminous. We began our search for these stars in IC10 by collecting the Two Micron All-Sky Survey and United Kingdom Infrared Telescope (UKIRT) J and K photometry. We then transformed the colors to luminosity and temperature allowing us to create an HR Diagram and identify candidate RSGs. Our next step was to continue to refine our results in order to remove foreground stars that aren't in the IC10 galaxy. We cross-matched our IC10 photometry with data from the GAIA satellite to obtain a list of proper motions and parallax values of all potential RSG candidates. From this we plotted the proper motion values vs. parallax to visually select stars in IC10. Our resulting list brings us closer to identifying RSGs in the starburst galaxy IC10.

The ocean under Europa’s crust has the possibility of harboring life. Using the available energy, I have made an estimation of the possible biomass on Europa. The available energy was calculated using the available oxidants (O₂ and SO₄^2-) and reductants in the system (H₂). This was then compared to estimates for the amount of energy life needs to survive. The estimated biomass would result in a much smaller cell density in Europa’s oceans than in Earth’s oceans; however, it is most likely that any biomass on Europa would be concentrated where there is available energy instead of being evenly spread throughout.

The prospect of life on the icy ocean world of Europa is an exciting one. A common theory is that hydrothermal vents could produce the necessary reductants for chemosynthesis to take place on the ocean bottom. However, future missions to probe for life will initially focus on the icy surface and the ocean just below the ice. We propose a ‘viral elevator’, a mechanism which functions similarly to the ‘viral shunt’ in Earth’s oceans, which could create and shuttle dissolved organic matter (DOM) to the surface through viral carriers. Current studies model Europa’s ocean with a system of currents and a sub-ice freshwater layer (Soderlund et al. 2014, Zhu et al. 2017). Our calculations demonstrate that the viral elevator could feasibly move DOM through a combination of the ocean currents and diffusion through the freshwater layer. The end goal of this research is to create a functioning model for virus-bacteria dynamics in Europa’s ocean, based on the influx rate of DOM from the viral elevator. We have modified an existing closed-system model (Max Showalter, UW) for viral and bacterial populations in Earth’s sea ice to fit the open-system environment of Europa’s surface ocean. Our new model shows how the virus-bacteria ratio changes given likely parameters for Europa’s ocean.

Debris Disk Stars are stars that are surrounded by dust and diffuse gas. Certain elements in the gas and dust absorb the light from the star and show up as an absorption-line spectrum. Our goal was to find trends in the elemental abundance patterns of similar debris disk stars. We took 30 debris disk stars that are similar in mass and surface temperature and measured their elemental abundances. Using Spectroscopy through IRAF’s s-plot tool we found accurate abundances of certain elements. We found abundances of metals including Iron, Nickel, Sodium, Carbon, and Oxygen. Comparing their Metallicities ([x/Fe]) we can find certain trends between the abundance of the elements and their condensation temperatures. From the 30 stars in the data-set, we chose 3 of the most interesting objects. The first star we chose, HD162826, is the closest in terms of motion and chemical abundances to the Sun. The second star, HD187691, has a small debris disk. The third star, HD122652, has a large debris disk. For HD162826, we found the metallicity of the refractory elements (high condensation temperature, >1200 K) to be spread around the 0 metallicity marker ([x/Fe]=0), for HD187691 we found most of the refractory elements above [x/Fe]=0 with the rest being very close to zero, and for HD122652 we found that the metallicities of most of the refractory elements were negative. The trends we found are small and could be explained by observational uncertainty, therefore further analysis of our data set would be required to make stronger conclusions. By accurately measuring more absorption lines from our dataset, possibly more connections can be made about the properties of Debris Disk Stars.

 Mid galaxy merger, a process called dynamical friction allows collided galaxies’ central massive black holes (MBHs) to spiral into the center of the system. Dynamical friction (DF) is a result of interactions between background material of small masses and one larger mass, such as a MBH. This creates a wake of particles behind the MBH, causing a gravitational pull opposite to its velocity, slowing it down. This process controls the orbit of non-central black holes in a galaxy and drives the creation of massive black hole binaries, prospective gravitational wave sources for current and future low-frequency detectors. The standard equation used to estimate DF, the Chandrasekhar DF formula, assumes that a galaxy has a uniform density profile, and all small particles have the same mass with Maxwellian velocity distribution. With this formula, many scenarios such as density fluctuations, large mass interactions, and perpendicular force are ignored. These conditions are not representative of realistic galactic environments and thus provide an incomplete look at dynamical friction. Taking a Monte-Carlo approach, we developed a numerical formula, to create an accurate and computationally efficient method to calculate the dynamical friction. Our method allows for density fluctuations and a range of particle masses and velocities to be accounted for.

Martian regolith is very different from Earth soil. In order to colonize, or have an extended stay on Mars, agriculture must be established. The purpose of this experiment was to investigate growing plants in Martian regolith in a manner that would be fuel-efficient, by using the existing soil of Mars with minimal interference and minimal materials brought from Earth. The regolith used was Mojave Mars Simulant-2 (MMS-2), developed by The Martian Garden. MMS-2 is more than a 90% match to the chemical composition of the regolith on Mars. Plant growth was compared between Earth soil (control), 50% Martian regolith MMS-2/50% Earth soil mixture (Mars Mix A), and 50% Mars regolith MMS-2/25% coffee grounds/12.5% Earth soil/12.5% vermiculite mixture (Mars Mix B). Plants were grown in all three mixtures and growth was measured during three month cycles. Although several plant species were planted, only kale produced any significant measurable data. Plant growth decreased with decreased percentages of Earth compost additive as measured by plant length and robustness. Efforts to reduce the mass of additives required to support plant growth include an exploration of acidifying Martian regolith MMS-2 prior to planting. Acids have been chosen for their ability to add critical nutrients of nitrogen and phosphorus. Nitric acid and phosphoric acid have both effectively lowered the pH to 6, similar to the optimal pH range for plant growth. The implications of this study indicate that Martian regolith and Earth soils on their own will not be sufficient to begin agriculture on Mars. Further research on chemical soil amendments will be needed for sustainable agricultural development on Mars.