Observations of the ß Cephei star 12 Lacertae have been made at both high time and spectral resolution with an Image Isocon television camera. The observations cover complete cycles of the pulsation on two consecutive nights in October 1972. The spectral region covered includes the two Si III inclines at λ 4553 and λ 4568. The line profile variations have been studied in detail; in particular the line doubling at certain phases of the pulsation. Wavelength shifts of the separate components were measured and a discontinuous radial velocity curve was obtained. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

We examine the precise radial velocities and chromospheric emission and derive the fundamental parameters of eight K stars - 36 Ophiuchi A, B (K0 V, K1 V), 61 Cygni A, B (K5 V, K7 V), β Geminorum (K0 IIIb ), δ Sagittarii (K2.5 IIIa), α Tauri (K5 III), and ϵ Pegasi (K2 Ib) - through analyses of high quality (S/N > 1000) near-infrared (864-878 nm) spectra. The spectra were obtained as part of the hydrogen fluoride precise (≈ 15 — 30 m s-1) radial velocity (RV) program at the Canada-France-Hawaii 3.6-m telescope (1981- 1992) and the Dominion Astrophysical Observatory 1.22-m telescope (1991- 1995). We define the ∆EW 866.2 index used to quantify changes in the core flux of the Ca II 866.214 nm line and show the index is a sensitive measure of changes in chromospheric emission. We compare the “reference” spectrum for each star with synthetic spectra of the 864.7-867.7 nm region and derive the fundamental parameters: effective temperature [special characters omitted] surface gravity [special characters omitted], metallicity ([M/H]), and microturbulence (ξ). We describe an efficient, time-saving method which identifies and eliminates insignificant lines. Through our comparisons of the narrow spectral region for these “well-known” stars and through our development of a rapid synthesis method, we demonstrate a solid foundation for a broader, more comprehensive study of this region of the H-R diagram. The nearly identical stars 36 Oph A and B have dissimilar chromospheric activity. For these stars, we derived [special characters omitted] = 5125 K, log g = 4.67, [M/H] = -0.25, and ξ = 1.4 km s-1, in excellent agreement with relationships predicted by stellar interior models for [special characters omitted] ≈ 0.75 and [Fe/H] = -0.3. For 61 Cyg A, we detect a rotation period of 36.2 days in the ∆EW 866.2 index and of 37.8 days in the radial velocities, implying that active regions are spatially and temporally coherent over long time scales for this star. For 61 Cyg A, we derived [special characters omitted] = 4545 K, log g = 4.55, [M/H] = -0.40, and ξ = 1.5 km s-1; for 61 Cyg B, [special characters omitted] = 4150 K, log g = 4.55, [M/H] = -0.40, and ξ = 0.7 km s-1. These parameters are in excellent agreement with relationships predicted by stellar interior models for [Fe/H] = -0.4 and [special characters omitted] ≈ 0.65 for 61 Cyg A, and [special characters omitted] ≈ 0.55 for 61 Cyg B. Low-amplitude RV variability is a ubiquitous characteristic of the K giants. For β Gem, we find similar RV {K = 46.23 ± 3.9 m s-1, P = 584.65 ± 3.3 dy) and ∆EW 866.2 index (K = 0.583 ± 1.9 pm, P = 587.7 ± 12 dy) periods. If due to rotation modulation of some surface feature, this period is inconsistent with the most reliable ν sin i value for this star. We detect a long-term (> 12 yr) change in the ∆EW 866.2 index for this star, reminiscent of a solar-type magnetic cycle. For δ Sgr, we find significant long-term trends in the radial velocities and ∆EW 866.2 index, and significant, but aliased, RV periods at 1.98 days (K = 82.1 ± 9.1 m s-1) and 293 days {K = 68.8 ± 9.8 m s-1). α Tauri has a 647.93-dy period (K = 114.9±10.6 m s-1) in the radial velocities, but no corresponding period in the ∆EW 866.2 index. From 1.22- m telescope observations, we find a 1.8358-dy RV period (K = 32.0 ± 5.0 m s-1) consistent with theoretical granulation-driven acoustic modes or a fundamental overtone (n ≈ 4). The supergiant ϵ Peg resembles a semi-regular RV variable. We find multiple RV periods (not aliases) of 65.2 days (K = 415.8 ± 59.0 m s-1), 46.3 days (K = 559.1 ± 57.0 m s-1), perhaps both fundamental overtones, and 10.7 days (K = 410.3 ± 66.0 m s-1), perhaps related to solar-type spicules. The 10.7-dy period is present in the ∆EW866.2 index for this star. / Graduate

Ultraviolet spectra obtained with Hubble Space Telescope (HST) of two Mira-type variable stars, R Leo and R Hya, are presented, along with analysis providing information on their outer atmospheres. These high-dispersion spectra were taken with the Goddard High Resolution Spectrograph (HRS) in two spectral regions: 2320-2368 Å to record the C II] (UV0.01) multiplet and 2785-2835 Å to obtain the Mg II h and k lines. The R Hya spectrum was obtained at visual light phase 0.26 and shows a Mg II spectrum that is very clean, showing clear evidence for the overlying circumstellar absorption from Fe I (UV3) and Mn I (UV1) over the k line. The fluoresced Fe I (UV44) feature at 2824 Å is plainly visible in this spectrum, whereas past International Ultraviolet Explorer (IUE) observations of Mira variables at high dispersion were unable to record this feature. Remarkably, the newly identified fluoresced Fe I (UV45) feature near 2807 Å is seen in this spectrum. Until now, this line has been seen only in cool carbon stars with HST/HRS. This line is pumped by the thin C II] (UV0.01) emission line at 2325.5 Å. Two of the strongest C II] (UV0.01) lines near 2325 Å are plainly seen in this spectrum. This region of the spectrum, however, is dominated by the Si II] (UV0.01) line near 2335 Å, in contrast to that observed in the carbon stars and the non-Mira oxygen-rich red giant stars. Very weak Mg II lines are seen in the R Leo spectrum at phase 0.12. At this phase, these lines are typically absent in IUE spectra. Velocity shifts of emission features in the UV spectra of Mira variables are consistent with previously published hydrodynamic models of these stars. These velocities indicate, however, that the C II] (UV0.01) emission lines are not formed in the same atmospheric layers as the Mg II emission. The electron density deduced from the C II] (UV0.01) multiplet is ∼109 cm-3. Finally, the temperature-density structure of the semi-regular variable carbon stars is similar to the oxygen-rich Mira variables-both are hydrodynamic in nature; however, the carbon stars macroscopic velocity fields are not identical to the Mira stars in the atmosphere layers between the Mg II emission region and the circumstellar shell.

The B0.2 V magnetic star τ Sco stands out from the larger population of massive magnetic OB stars due to its remarkable, superionized wind, apparently related to its peculiar magnetic field - a field which is far more complex than the mostly-dipolar fields usually observed in magnetic OB stars. τ Sco is therefore a puzzling outlier in the larger picture of stellar magnetism - a star that still defies interpretation in terms of a physically coherent model. Recently, two early B-type stars were discovered as τ Sco analogues, identified by the striking similarity of their UV spectra to that of τ Sco, which was - until now - unique among OB stars. We present the recent detection of their magnetic fields by the MiMeS collaboration, reinforcing the connection between the presence of a magnetic field and a superionized wind. We will also present ongoing observational efforts undertaken to establish the precise magnetic topology, in order to provide additional constrains for existing models attempting to reproduce the unique wind structure of τ Sco-like stars.

The stellar winds of hot stars have an important impact on both stellar and galactic evolution, yet their structure and internal processes are not fully understood in detail. One of the best nearby laboratories for studying such massive stellar winds is the O4I(n)fp star ζ Pup. After briefly discussing existing X-ray observations from Chandra and XMM, we present a simulation of X-ray emission line profile measurements for the upcoming 840 kilosecond Chandra HETGS observation. This simulation indicates that the increased S/N of this new observation will allow several major steps forward in the understanding of massive stellar winds. By measuring X-ray emission line strengths and profiles, we should be able to differentiate between various stellar wind models and map the entire wind structure in temperature and density. This legacy X-ray spectrum of ζ Pup will be a useful benchmark for future X-ray missions.

The following thesis has been undertaken primarily as an observational study. Accordingly, theoretical discussion and speculations have been kept to a minimum, formulas in most case being early quoted and references given for their derivations. Since the observational techniques used are nearly all in standard practice, they have not been fully described, while descriptions of their reductions have been relegated to appendices.

Comets and Centaurs are icy remnants from the formation of the solar system. Analyzing the physical properties of their nuclei and their production rates can serve as powerful tools for tracing primitive solar system material. The four research projects in this dissertation examine these properties in comets and Centaurs. The first project focuses on observations of main belt comet 176P/LINEAR that were obtained with the Kepler space telescope. Optical lightcurves were used to constrain models of the nucleus's spin pole axis, shape and activity level. The second project used millimeter-wavelength spectra from the Arizona Radio Observatory Submillimeter Telescope and infrared photometry of Spitzer images to derive production rates of CO and CO2 from Oort Cloud comet C/2016 R2 (PANSTARRS). The third project is a compendium of CO, CO2, and H2O production rates in more than 25 comets and Centaurs that were obtained with a variety of space-based and ground-based telescopes and which were analyzed to test models of comet formation and evolution. CO, CO2, and H2O are the most abundant molecules observed in comets. The combination of these three molecules are likely the largest sources of elemental oxygen in the gas comae of comet and therefore a close approximation of the oxygen released in the comae. One key result of the survey is that CO/CO2 production rate ratios appear largely heliocentric dependent, with more CO produced the farther the comet is from the Sun. One exception is dynamically new comets which typically produce more CO2 than CO which is in predicted by models of significant cosmic-ray processing over time. The fourth project produced the first CO2 detection in a Centaur (39P/Oterma), which shows significant differences between the CO/CO2 in 39P and 29P, another Centaur, which may be partly due to different heating and processing histories.

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