135 research outputs found
Hawai‘i Supernova Flows: A Peculiar Velocity Survey Using Over a Thousand Supernovae in the Near-Infrared
No full textPh.D
Discovering and Exploring Extreme Black Holes and their Environments in the Transient Universe
No full textSupermassive black holes (SMBHs) at the centers of galaxies are some of the most luminous objects in the universe when feeding on surrounding material. This occurs when the SMBH is continuously accreting, called an active galactic nuclei (AGN). Or, a star can wander too close to the SMBH and becomes destroyed by the tidal forces, called a tidal disruption event (TDE), and the SMBH feeds on the stellar debris. The current landscape of astrophysics is rich with missions and telescopes ideal for exploring the transient universe, including AGNs and TDEs. Surveys, which image the entire night sky on various timescales ranging from minutes to days, provide crucial data to discover and characterize these nuclear transients. After developing a large sample of highly variable AGN observed by the ASAS-SN survey, I discovered a new, unique nuclear transient that undergoes periodic flares called ASASSN-14ko. One flare in 2014 was mistakenly classified as a supernova and the periodic behavior went undetected until my discovery. ASASSN-14ko is located within AGN ESO 253-G003 with optical flares present in the ASAS-SN light curve since 2014, and after modeling the peak times I find their timings are well-modeled with a period of 115.2 +1.3 -1.2 days and period derivative of -0.0026 +/- 0.0006. I organized, led, carried out, and analyzed data in an intensive multi-wavelength observing campaign to understand this unique object, and obtained X-ray, UV, and optical photometry and spectroscopy with numerous space- and ground-based facilities since 2020. All flares are characterized by a concurrent brightening in the UV and optical. The X-ray luminosities consistently decrease and the spectra become harder during the UV/optical rise but apparently without changes in absorption. The flares' photometric and spectroscopic signatures evolve rapidly. With the current suite of data, ASASSN-14ko is observationally consistent with a repeating partial tidal disruption event. This is the only such object ever discovered that has strongly periodic flares across X-ray, UV, and optical wavelengths, and provides a new laboratory to model TDEs and refine their theoretical frameworks.Ph.D
Messy eaters: A diversity of supermassive black hole accretion behaviors revealed by nuclear transients
No full textPh.D
The Golden Era of Transient Astronomy
No full textAstronomy has seen a massive increase in the discovery and classification of astrophysical transients, which are fleeting celestial events such as supernovae, flaring black holes, and tidal disruption events. The proliferation of sky surveys has produced an unprecedented data deluge, transforming how the astronomical community approaches research in the digital era. I have worked on various types of transients and how they shape their environment, or vice versa. The first 4 chapters discuss unique transients which provided special insight into the physical mechanisms governing their formation and evolution. Next, I take an in-depth look at how and why white dwarf stars explode as Type Ia supernovae. Finally, I present an overview of the Spectroscopic Classification of Transients (SCAT) survey. SCAT is a spectrophotometric transient survey designed to study the myriad of transient phenomena discovered by photometric sky surveys. I conclude by summarizing the current status of the survey, describing the data reduction pipeline, and highlighting preliminary results.Ph.D
Total eclipse of the heart: : the AM CVn Gaia14aae/ASSASN-14cn
No full textWe report the discovery and characterization of a deeply eclipsing AM CVn-system, Gaia14aae (=ASSASN-14cn). Gaia14aae was identified independently by the All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al.) and by the Gaia Science Alerts project, during two separate outbursts. A third outburst is seen in archival Pan-STARRS-1 (PS1; Schlafly et al.; Tonry et al.; Magnier et al.) and ASAS-SN data. Spectroscopy reveals a hot, hydrogen-deficient spectrum with clear double-peaked emission lines, consistent with an accreting double-degenerate classification. We use follow-up photometry to constrain the orbital parameters of the system. We find an orbital period of 49.71 min, which places Gaia14aae at the long period extremum of the outbursting AM CVn period distribution. Gaia14aae is dominated by the light from its accreting white dwarf (WD). Assuming an orbital inclination of 90° for the binary system, the contact phases of the WD lead to lower limits of 0.78 and 0.015 M⊙ on the masses of the accretor and donor, respectively, and a lower limit on the mass ratio of 0.019. Gaia14aae is only the third eclipsing AM CVn star known, and the first in which the WD is totally eclipsed. Using a helium WD model, we estimate the accretor's effective temperature to be 12 900 ± 200 K. The three outburst events occurred within four months of each other, while no other outburst activity is seen in the previous 8 yr of Catalina Real-time Transient Survey (CRTS; Drake et al.), Pan-STARRS-1 and ASAS-SN data. This suggests that these events might be rebrightenings of the first outburst rather than individual events.Peer reviewe
Comparing Optical Variability of Type 1 and Type 2 AGN from the BAT 9 Month Sample Using ASAS-SN and TESS Surveys
No full textWe present an optical variability analysis and comparison of the samples of Seyfert 1 (Sy1) and Seyfert 2 (Sy2) galaxies, selected from the Swift 9 month BAT catalog, using the light curves from Transiting Exoplanet Survey Satellite (TESS) and All-Sky Automated Survey for SuperNovae (ASAS-SN). We measured the normalized excess variance of TESS and ASAS-SN light curves for each target and performed a Kolmogorov–Smirnov test between the two samples, where our results showed significant differences. This is consistent with predictions from the unification model, where Seyfert 2s are obscured by the larger scale dust torus and their variability is suppressed. This variability difference is independent of the luminosity, Eddington ratio, or black hole mass, further supporting geometrical unification models. We searched the dependence of the normalized excess variance of Sy1s on absolute magnitudes, Eddington ratio, and black hole mass, where our results are consistent with relations found in the literature. Finally, a small subsample of changing-look (CL) active galactic nuclei (AGNs) that transitioned during the time frame of the ASAS-SN light curves, with their variability amplitudes changing according to the classification, have larger variability as type 1s and smaller as 2s. The change of variability amplitudes can be used to better pinpoint when the type transition occurred. The consistency trend of the variability amplitude differences between Sy1s and Sy2s and between CL AGNs in 1 or 2 stages suggests that variability can be a key factor in shedding light on the CL AGN or the dichotomy between Sy1 or Sy2 populations
Digital Content Curation
No full textThe author introduces two tools—Flipgrid and Pearltrees—for digital content curation to share information with colleagues without overwhelming them with social media messaging
Instructional designers\u27 roles and the pandemic
No full textThe author describes the criticality of instructional designers in enabling universities to shift from face-to-face learning to effective online learning during the sudden pandemic. She cites her own experiences wearing multiple hats at Kansas State University-Salina, as Director of Instructional Design and Faculty Support/Associate Professor
A NEW CEPHEID DISTANCE TO THE GIANT SPIRAL M101 BASED ON IMAGE SUBTRACTION OF<i>HUBBLE SPACE TELESCOPE</i>/ADVANCED CAMERA FOR SURVEYS OBSERVATIONS
No full text- …
