Introduction

Curriculum Vitae (Last Updated: June 2020)

Hello! You have arrived at the website of Andrew Couperus, me! (You know... in case the giant banner and site name didn't make it clear...) I am a third year graduate student in the astronomy PhD program at the Georgia State University Department of Physics and Astronomy. I work with Dr. Todd Henry as part of the RECONS group, investigating the photometric variability and magnetic activity of nearby M dwarf stars.

Research

REsearch Consortium On Nearby Stars (RECONS)

I lead two projects as a graduate student working with Dr. Todd Henry and RECONS. The first of these efforts is a comprehensive endeavor to investigate stellar cycles in nearby M dwarfs, using more than two decades of data obtained by RECONS. The RECONS volume complete sample consists of 455 M dwarfs within 16.7 pc in the southern sky, with a median coverage of approximately 10 years. My efforts so far have yielded one of the largest existing collections of stellar cycles for fully convective M dwarfs. My second project examines a sample I have constructed of 36 M dwarf binaries with nearly identical components. These ‘twin’ wide binaries are comprised of stars with similar masses, ages, and compositions based on (a) astrometry confirming that they are part of the same, presumably coeval system, and (b) optical/infrared photometry from 0.5-2.2 µm that match within 0.1 mag. Evolutionary models and conventional thinking suggest that such twin stars should evolve co-equally, resulting in similar rotation rates and magnetic activity. However, this has not been rigorously examined for M dwarfs, which host complex and poorly understood magnetic activity. These binaries are being studied with several ongoing observational programs, including spectroscopy, speckle imaging, and long and short duration optical photometry. Early results indicate notable differences in the magnetic activity between components for several systems.

Figure 1 - An H-R diagram of the RECONS volume complete M dwarf sample I am studying, which spans the entire M dwarf spectral range, and is comprised of subgroups that divide the different mass regimes. The current number of objects in the sample totals 455. A black dashed line has been added at MV = 11.33, which corresponds to the modeled 0.35 Solar mass transition between partially and fully convective stars, based on the mass-luminosity relation by Benedict et al. (2016). The sample is dominated by mid and late M dwarfs, which have been critically understudied to date in regards to stellar cycle activity.
Figure 2 - Selected results for the prominent stellar cycle observed in WT 460AB, a nearby M dwarf observed as part of RECONS efforts. The all-frames differential photometry light curve is shown, with a dashed line at 0 defined by the mean of all the points. The grey number on the top right is the mean MAD of all reference stars, weighted by brightness, and is shown visually as the grey shaded region spanning the value above and below 0. The red line shows the Lomb-Scargle based fit, and the period and peak-to-peak delta magnitude of the cycle fit are shown in red at the bottom. The y-axis is inverted, so that the stellar brightness increases moving upward on the plot. Open circles represent one frame epochs that are excluded from all quantitative analysis.
Figure 3 - Here I show a plot of Gaia Bp−Rp color versus absolute Gaia G mag for two sets of stars. Black circles represent the 36 members of my twin binary sample, with components in each binary connected by a red line. Under plotted in grey is a partly cleaned sample of Gaia DR2 sources, showing the main sequence for comparison. My binaries span the range from partially convective early-type M dwarfs to mid and late M dwarfs that are fully convective, with this transition occurring around Bp − Rp = 2.5 (Jao et al. 2018).

Interests

Fantasy Novels - Favorites include: Kingkiller Chronicles, The Stormlight Archive, Riyria Chronicles
Video Games - Favorites include: Breath of the Wild, Skyrim, Borderlands 2, Don't Starve
Arbitrary passionate rants about random things.


Fun Images and Plots

Four false-color composite images of the Orion Nebula, made by me using multi-filter images I acquired using Reynolds Observatory at Clarkson University.
Figure 1 - The semi-major axis versus inclination for the known moons of Jupiter (Fall 2018). Made using data from the JPL Small-Body Database and Scott Sheppard at the Carnegie Institution for Science.
Figure 2 - The semi-major axis versus inclination for the known moons of Saturn (Fall 2018). Made using data from the JPL Small-Body Database and Scott Sheppard at the Carnegie Institution for Science.