Doctor of Philosophy, University of Toledo, 2020, Physics

Be stars are rapidly rotating B stars whose spectra contain Balmer emission lines originating from circumstellar decretion disks. The decretion disks also produce in- frared (IR) excesses in their spectral energy distributions, and the slope of the excess reveals information about the density of the disk. The decretion disks serve as medi- ums through which mass and angular momentum are transported away from the star. Be stars rotate at or near the critical rotation rate, and the angular momentum lost through the disks prevents them from breaking up. Determinations of the amount mass and angular momentum lost through the decretion disks are model dependent. The best accepted model describing the decretion disk is the Viscous Decretion Disk (VDD) model. However, there is a discrepancy between the current measurements of mass-loss rates and those predicted by stellar evolutionary models. The projects in this thesis were chosen to better constrain the models in an effort to reconcile this discrepancy. First, it has been suggested that Be stars are spun up through previous mass- transfer from a binary companion. Also, binary companions are observed to be common. However, the VDD model assumes an isolated Be star. In this thesis, I investigate the density structure of the disks in the presence of binary companions. The Be disk is truncated by the companion, and while most of the disk material accretes onto the binary companion, we find that a portion flows past the binary in what is likely a wind-like outflow. Second, the radiation from the central Be star can launch a line-driven ablation wind that flows radially outward along the surface of the disk. This disk wind is an additional source of mass and angular momentum loss from the central star. I investigate how the disk wind would be observed in the ultraviolet (UV) wind line profiles. I find that the disk wind can be seen as a low velocity narrow absorption component in the UV wind line when the observing geome (open full item for complete abstract)

Committee: Jon Bjorkman (Committee Chair); Alex Carciofi (Committee Member); Michael Cushing (Committee Member); Scott Lee (Committee Member); Tom Megeath (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, The Ohio State University, 2017, Astronomy

I conducted a search for binary companion stars around 10 stars hosting hot Jupiter exoplanets from the KELT survey and a large comparison sample of stars shown by KELT to not host transiting hot Jupiters. The goal of the survey was to determine whether hot Jupiter hosts are more likely to have stellar companions than the general population of stars. The primary stars are bright (7.5 < V < 11) and of similar distance from Earth (100 < d < 300 pc). In this dissertation, I present the results of my observations using the Differential Speckle Survey Instrument (DSSI) on the 3.5-meter WIYN telescope and LMIRCam on the Large Binocular Telescope Interferometer (LBTI), on the 2x8.4-meter Large Binocular Telescope. Across both instruments, I observed 10 of the 16 KELT planet hosts which are visible from the Northern Hemisphere and 71 comparison stars, discovering seven new potential companions and re-observing four previously known possible binary systems, as well as one confirmed binary system. I estimate the distances and masses of each binary system, as well as place lower limits on their orbital periods. I also provide an estimate of the chance alignment probability for our observed candidate binaries. I find that the KELT planet hosts have a stellar companion fraction of 50+-8:1% compared to 36.8+-6.3% for the comparison sample. This is a 1.6-sigma excess, indicating that hot Jupiter hosts are slightly more likely to have stellar binary companions.

Committee: Scott Gaudi (Advisor); Richard Pogge (Advisor); Paul Martini (Committee Member) Subjects: Astronomy

Doctor of Philosophy, University of Toledo, 2009, Physics

The subject of this thesis is the time-series analysis of 130 echelle spectra of ε Ori obtained at Ritter Observatory on the campus of the University of Toledo. These data were acquired over seven observing seasons between 1998 and 2006. The spectra include the Hα line, which is formed mainly in the inner wind region, and the He I λ5876 triplet, which is mostly a photospheric absorption line with weak wind features present in the wings. The equivalent widths of Hα (net) and the He I were measured and radial velocity measurements were obtained from the central absorption of the He I line.Temporal variance spectra were computed in order to quantify the variability and revealed significant wind variability in both Hα and He I. The He I TVS had a double-peaked profile consistent with radial velocity oscillations due to pulsations. Periodicity searches were carried out on the equivalent width, radial velocity and wavelength-binned spectral time series. A method developed by Bretthorst (2001) which applies Bayesian inference to the Lomb-Scargle (Lomb, 1976; Scargle, 1982) periodogram has been used in the period search on all data. The CLEAN algorithm (Roberts, Lehar, and Dreher, 1987) was also applied to the equivalent width time series. The Bayesian technique was used to construct 2D periodograms from the wavelength-binned spectra. This research has uncovered several apparently real periods. Signals with time scales on the order of the rotational period, which may be due to rotationally modulated structure, were detected in data from two seasons. Many periods with time scales of 2-8 d are present in the data. A photospheric origin is suspected for periods present in He I and radial velocity data but a wind origin cannot be ruled out. The periods detected in the Hα data are likely due to wind variability. A period of 4.4 d, was detected in nearly every season. This period was found in both Hα and He I and may indicate a persistent or recurring phenomenon. A 2.2 d period (open full item for complete abstract)

Committee: Nancy Morrison PhD (Advisor); Jon Bjorkman PhD (Committee Member); Karen Bjorkman PhD (Committee Member); Thomas Kvale PhD (Committee Member); Douglas Gies PhD (Committee Member) Subjects: Astronomy; Astrophysics

Doctor of Philosophy, University of Toledo, 2013, Physics

A time series analysis of spectroscopic and photometric observables of the A0Ia supergiant HR 1040 has been performed. The data, obtained from 1993 through 2007, include 152 spectroscopic observations from the Ritter Observatory and 269 Stromgren photometric observations from the Four College Automated Photoelectric Telescope (FCAPT). A number of spectroscopic and photometric features have been analyzed and compared, including line equivalent width, radial velocities and Stromgren photometric indices. Typical of late B- and early A-type supergiants, HR 1040 has a highly variable stellar wind including High Velocity Absorption (HVA) events. The star was found to have an active phase with large variation in the physical characteristics of the wind and with the potential for HVAs. During the active phase, correlation between the H¿¿ absorption equivalent width and blue-edge radial velocity was observed. If an HVA was present, the active phase was found to begin before the onset of the HVA and continue after the end of the event by as much as several weeks. This active phase alternated with a more common quiescent phase marked by little variability and equivalent width - radial velocity correlation and no HVAs. The active phase and HVAs were found to exhibit important connections to photospheric activity. Increases in H¿¿ absorption and blue-edge radial velocity at the onset of HVAs was preceded by correlated increases in Si II equivalent width and second moment, with the atmospheric changes indicated by the H¿¿ line lagging the photospheric changes seen in Si II by an interval of 13 to 23 days. The observed HVAs were found to be preceded by Si II radial velocity oscillations by an interval of 19 to 42 days. The equivalent width and second moment of the photospheric Si II ¿¿¿¿ 6347, 6371 lines were found to be highly variable and strongly correlated throughout the two active phases when an HVA is observed but not during the quiescent phase or in the one active phase whe (open full item for complete abstract)

Committee: Nancy Morrison PhD (Committee Chair); Jon Bjorkman PhD (Committee Member); John-David Smith PhD (Committee Member); Scott Lee PhD (Committee Member); David Cinabro PhD (Committee Member) Subjects: Astrophysics