Population Dynamics In Active Galactic Nuclei,
2015
University of Arkansas, Fayetteville
Population Dynamics In Active Galactic Nuclei, Jon Bessler
Graduate Theses and Dissertations
The goal of this thesis is to present an approach to understanding the dynamics that govern the evolution of active galactic nuclei (AGN) in general, and those associated with spiral galaxies in particular. This approach starts with the continuity equation governing the mass function for a population of supermassive black holes (SMBHs). This approach is then extended to the luminosity function for AGN. Where the dynamical parameters that govern accretion are fairly well known, those values are adopted. The values that are not as well known are constrained by comparing evolved luminosity functions with observed luminosity functions. Boundary conditions for …
Constraining The Progenitor And Central Engine Of Gamma-Ray Bursts With Observational Data,
2015
University of Nevada, Las Vegas
Constraining The Progenitor And Central Engine Of Gamma-Ray Bursts With Observational Data, Lu Houjun
UNLV Theses, Dissertations, Professional Papers, and Capstones
Gamma-ray bursts (GRBs) are extremely energetic explosions at cosmological distances. We have made great progress in understanding the mysteries of these events since they were discovered more than forty years ago. However, some open questions still remain, e.g. how many classes of GRBs are there, what are the progenitors of these classes, and what is the central engine powering these huge explosions? Thanks to the NASA missions Swift and Fermi, which are used to detect the multi-wavelength emission from these transients, our understanding of GRBs has been greatly advanced. In this dissertation, I use multi-wavelength data to constrain the progenitor …
Stellar Spectroscopy: New Methods And Insights,
2015
The University of Western Ontario
Stellar Spectroscopy: New Methods And Insights, Sanaz S. Golriz
Electronic Thesis and Dissertation Repository
The study of the chemical evolution of stars is of crucial importance since they play a major role in the enrichment of the chemistry of the universe. Throughout their lifetime, stars undergo several processes that can alter their chemistry. Gradually, the nucleosynthesis products from the interior of the star are radiatively and convectively levitated and mixed with the upper layers of the atmosphere. In the later stages of their evolution, low to intermediate mass stars (0.8-8.0~M☉) eject a significant fraction of these nucleosynthesis products, resulting in a circumstellar envelope of gas and dust around the central star with a very …
Sdss J14584479+3720215: A Benchmark Jhks Blazar Light Curve From The 2mass Calibration Scans,
2015
Western Washington University
Sdss J14584479+3720215: A Benchmark Jhks Blazar Light Curve From The 2mass Calibration Scans, James R. A. Davenport, John J. Ruan, Andrew C. Becker, Chelsea L. Macleod, Roc M. Cutri
Physics & Astronomy
Active galactic nuclei (AGNs) are well-known to exhibit flux variability across a wide range of wavelength regimes, but the precise origin of the variability at different wavelengths remains unclear. To investigate the relatively unexplored near-IR (NIR) variability of the most luminous AGNs, we conduct a search for variability using well sampled JHKs-band light curves from the Two Micron All Sky Survey (2MASS) calibration fields. Our sample includes 27 known quasars with an average of 924 epochs of observation over three years, as well as one spectroscopically confirmed blazar (SDSS J14584479+3720215) with 1972 epochs of data. This is the …
Methods And Results Toward Measuring Magnetic Fields In Star-Forming Regions,
2015
The University of Western Ontario
Methods And Results Toward Measuring Magnetic Fields In Star-Forming Regions, Scott C. Jones
Electronic Thesis and Dissertation Repository
Star formation is a fundamental process in the evolution of the cosmos. Yet given the abundance of stellar constituents, it remains prescient as to why the number of stars is not correspondingly large. If we cannot satisfactorily explain how stars are formed, then many further avenues of research are hindered. This thesis makes claims about one of the foremost theories as to the relative lack of stars, interstellar magnetic fields. These fields have been observationally verified on multiple scales. I will use the most direct method to probe magnetic fields in known star-forming regions, polarization, at millimetre/submillimetre wavelengths. In particular …
Ultracool White Dwarfs And The Age Of The Galactic Disc,
2015
University of Oklahoma
Ultracool White Dwarfs And The Age Of The Galactic Disc, A. Gianninas, B. Curd, John R. Thorstensen, Mukremin Kilic
Dartmouth Scholarship
We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool (Teff < 4000 K) white dwarfs (WDs) in the solar neighbourhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21 pc to >100 pc, and include five stars within 30 pc. Contrary to expectations, all but two of them have tangential velocities smaller than 150 km s−1 thus suggesting Galactic disc membership. The oldest WDs in this sample have WD cooling ages of 10 Gyr, providing a firm lower limit to the age of the thick disc population. Many of our targets have uncharacteristically large radii, indicating that they are low mass WDs. It appears that we have detected the brighter population of cool and ultracool …
A Connection Between Obscuration And Star Formation In Luminous Quasars,
2015
Dartmouth College
A Connection Between Obscuration And Star Formation In Luminous Quasars, Chien-Ting J. Chen, Ryan C. Hickox, Stacey Alberts, Chris M. Harrison
Dartmouth Scholarship
We present a measurement of the star formation properties of a uniform sample of mid-IR selected, unobscured and obscured quasars (QSO1s and QSO2s) in the Bo\"otes survey region. We use an spectral energy distribution (SED) analysis for photometric data spanning optical to far-IR wavelengths to decompose AGN and host galaxy components. We find that when compared to a matched sample of QSO1s, the QSO2s have higher far-IR detection fractions, far-IR fluxes and infrared star formation luminosities (LSFIR) by a factor of ∼2. Correspondingly, we show that the AGN obscured fraction rises from 0.3 to 0.7 between 4−40×10 …
Spectroscopic Orbital Periods For 29 Cataclysmic Variables From The Sloan Digital Sky Survey,
2015
Dartmouth College
Spectroscopic Orbital Periods For 29 Cataclysmic Variables From The Sloan Digital Sky Survey, John R. Thorstensen, Cynthia J. Taylor, Christopher S. Peters, Julie N. Skinner
Dartmouth Scholarship
We report follow-up spectroscopy of 29 cataclysmic variables from the Sloan Digital Sky Survey (SDSS), 22 of which were discovered by SDSS and seven of which are previously known systems that were recovered in SDSS. The periods for 16 of these objects were included in the tabulation by Gänsicke et al. While most of the systems have periods less than 2 hr, only one has a period in the 80–86 minutes "spike" found by Gänsicke et al., and 11 have periods longer than 3 hr, indicating that the present sample is skewed toward longer-period, higher-luminosity objects. Seven of the objects …
Stellar Activity And Its Implications For Exoplanet Detection On Gj 176,
2015
Pennsylvania State University
Stellar Activity And Its Implications For Exoplanet Detection On Gj 176, Paul Robertson, Michael Endl, Gregory W. Henry, William D. Cochran, Phillip J. Macqueen, Michael H. Williamson
Information Systems and Engineering Management Research Publications
We present an in-depth analysis of stellar activity and its effects on radial velocity (RV) for the M2 dwarf GJ 176 based on spectra taken over 10 yr from the High Resolution Spectrograph on the Hobby–Eberly Telescope. These data are supplemented with spectra from previous observations with the HIRES and HARPS spectrographs, and V- and R-band photometry taken over six years at the Dyer and Fairborn observatories. Previous studies of GJ 176 revealed a super-Earth exoplanet in an 8.8-day orbit. However, the velocities of this star are also known to be contaminated by activity, particularly at the 39-day stellar rotation …
The Small Binary Asteroid (939) Isberga,
2015
Institut de Mecanique Celeste et de Calcul des Ephemerides
The Small Binary Asteroid (939) Isberga, B. Carry, A. Matter, P. Scheirich, P. Pravec
University Faculty Publications and Creative Works
In understanding the composition and internal structure of asteroids, their density is perhaps the most diagnostic quantity. We aim here at characterizing the surface composition, mutual orbit, size, mass, and density of the small main-belt binary asteroid (939) Isberga. For that, we conduct a suite of multi-technique observations, including optical lightcurves over many epochs, near-infrared spectroscopy, and interferometry in the thermal infrared. We develop a simple geometric model of binary systems to analyze the interferometric data in combination with the results of the lightcurve modeling. From spectroscopy, we classify Ibserga as a Sq-type asteroid, consistent with the albedo of 0.14-0.06+0.09 …
Bayesian Investigation Of Isochrone Consistency Using The Old Open Cluster Ngc 188,
2015
Queen's University - Kingston, Ontario
Bayesian Investigation Of Isochrone Consistency Using The Old Open Cluster Ngc 188, Shane Hills, Ted Von Hippel, Stéphane Courteau, Aaron M. Geller
Publications
This paper provides a detailed comparison of the differences in parameters derived for a star cluster from its color– magnitude diagrams (CMDs) depending on the filters and models used. We examine the consistency and reliability of fitting three widely used stellar evolution models to 15 combinations of optical and near-IR photometry for the old open cluster NGC 188. The optical filter response curves match those of theoretical systems and are thus not the source of fit inconsistencies. NGC 188 is ideally suited to this study thanks to a wide variety of high-quality photometry and available proper motions and radial velocities …
Polarimetric Modeling Of Corotating Interaction Regions (Cirs) Threading Massive-Star Winds.,
2015
East Tennessee State University
Polarimetric Modeling Of Corotating Interaction Regions (Cirs) Threading Massive-Star Winds., Richard Ignace, Nicole St-Louis, Felix Proulx-Giraldeau
ETSU Faculty Works
Massive star winds are complex radiation-hydrodynamic (sometimes magnetohydrodynamic) outflows that are propelled by their enormously strong luminosities. The winds are often found to be structured and variable, but can also display periodic or quasi-periodic behavior in a variety of wind diagnostics. The regular variations observed in putatively single stars, especially in UV wind lines, have often been attributed to corotating interaction regions (CIRs) like those seen in the solar wind. We present light curves for variable polarization from winds with CIR structures. We develop a model for a time-independent CIR based on a kinematical description. Assuming optically thin electron scattering, …
Polarimetric Modeling Of Corotating Interaction Regions (Cirs) Threading Massive-Star Winds.,
2015
East Tennessee State University
Polarimetric Modeling Of Corotating Interaction Regions (Cirs) Threading Massive-Star Winds., Richard Ignace, N. St-Louis, F. Proulx-Giraldeau
Richard Ignace
Massive star winds are complex radiation-hydrodynamic (sometimes magnetohydrodynamic) outflows that are propelled by their enormously strong luminosities. The winds are often found to be structured and variable, but can also display periodic or quasi-periodic behavior in a variety of wind diagnostics. The regular variations observed in putatively single stars, especially in UV wind lines, have often been attributed to corotating interaction regions (CIRs) like those seen in the solar wind. We present light curves for variable polarization from winds with CIR structures. We develop a model for a time-independent CIR based on a kinematical description. Assuming optically thin electron scattering, …
Hd 207651: A Composite Spectrum Triple System,
2015
Tennessee State University
Hd 207651: A Composite Spectrum Triple System, Francis C. Fekel
Information Systems and Engineering Management Research Publications
From numerous radial velocities obtained at KPNO and Fairborn Observatory, we have determined the orbital elements of the composite spectrum triple system HD 207651. This system consists of a broad-lined A8 V star and an unseen M dwarf companion in a 1.470739 days orbit. Variations of the center-of-mass velocity of this short-period system and velocity variations of a narrow-lined F7: V star have an orbital period of 724.1 days or 1.98 yr and an eccentricity of 0.39. The revised Hipparcos parallax, corresponding to a distance of 255 pc, appears to be too small to yield consistent properties. Instead, we adopt …
New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. Ix. Hd 54371, Hr 2692, And 16 Ursa Majoris,
2015
Tennessee State University
New Precision Orbits Of Bright Double-Lined Spectroscopic Binaries. Ix. Hd 54371, Hr 2692, And 16 Ursa Majoris, Francis C. Fekel, Michael H. Williamson, Matthew W. Muterspaugh, Dimitri Pourbaix, Daryl W. Willmarth, Jocelyn Tomkin
Information Systems and Engineering Management Research Publications
With extensive sets of new radial velocities we have determined orbital elements for three previously known spectroscopic binaries, HD 54371, HR 2692, and 16 UMa. All three systems have had the lines of their secondaries detected for the first time. The orbital periods range from 16.24 to 113.23 days, and the three binaries have modestly or moderately eccentric orbits. The secondary to primary mass ratios range from 0.50 to 0.64. The orbital dimensions (a1 sin i and a2 sin i) and minimum masses (m1 sin3 i and m2 sin3 i) of the binary components all have accuracies of $\leqslant $1%. …
The Broad-Lined Type Ic Sn 2012ap And The Nature Of Relativistic Supernovae Lacking A Gamma-Ray Burst Detection,
2015
Harvard-Smithsonian Center for Astrophysics
The Broad-Lined Type Ic Sn 2012ap And The Nature Of Relativistic Supernovae Lacking A Gamma-Ray Burst Detection, D. Milisavljevic, R. Margutti, J. T. Parrent, A. M. Soderberg, R. A. Fesen
Dartmouth Scholarship
We present ultraviolet, optical, and near-infrared observations of SN 2012ap, a broad-lined Type Ic supernova in the galaxy NGC 1729 that produced a relativistic and rapidly decelerating outflow without a gamma-ray burst signature. Photometry and spectroscopy follow the flux evolution from –13 to +272 days past the B-band maximum of –17.4 ± 0.5 mag. The spectra are dominated by Fe II, O I, and Ca II absorption lines at ejecta velocities of v ≈ 20,000 km s–1 that change slowly over time. Other spectral absorption lines are consistent with contributions from photospheric He I, and hydrogen may also …
Absolute Properties Of The Eclipsing Binary Star Im Persei,
2015
University of Arkansas, Fayetteville
Absolute Properties Of The Eclipsing Binary Star Im Persei, Claud H. Sandberg Lacy, Guillermo Torres, Francis C. Fekel, Matthew W. Muterspaugh, John Southworth
Information Systems and Engineering Management Research Publications
IM Per is a detached A7 eccentric eclipsing binary star. We have obtained extensive measurements of the light curve (28,225 differential magnitude observations) and radial velocity curve (81 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.7831 ± 0.0094 and 1.7741 ± 0.0097 solar masses, and radii of 2.409 ± 0.018 and 2.366 ± 0.017 solar radii. The orbital period is 2.25422694(15) days and the eccentricity is 0.0473(26). A faint third component was detected in the analysis of the light curves, and also directly observed in the spectra. …
New Multiwavelength Observations Of The Of?P Star Cpd -28◦ 2561.,
2015
Leibniz-Institut f¨ur Astrophysik Potsdam (AIP)
New Multiwavelength Observations Of The Of?P Star Cpd -28◦ 2561., S. Hubrig, M. Schöller, A. Kholtygin, H. Tsumura, A. Hoshino, S. Kitamoto, L. Oskinova, Richard Ignace, H. Todt, I. Ilyin
ETSU Faculty Works
A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD −28° 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent …
New Multiwavelength Observations Of The Of?P Star Cpd -28◦ 2561.,
2015
East Tennessee State University
New Multiwavelength Observations Of The Of?P Star Cpd -28◦ 2561., S. Hubrig, M. Schöller, A. F. Kholtygin, H. Tsumura, A. Hoshino, S. Kitamoto, L. Oskinova, R. Ignace, H. Todt, I. Ilyin
Richard Ignace
A rather strong mean longitudinal magnetic field of the order of a few hundred gauss was detected a few years ago in the Of?p star CPD −28° 2561 using FORS2 (FOcal Reducer low dispersion Spectrograph 2) low-resolution spectropolarimetric observations. In this work, we present additional low-resolution spectropolarimetric observations obtained during several weeks in 2013 December using FORS 2 mounted at the 8-m Antu telescope of the Very Large Telescope (VLT). These observations cover a little less than half of the stellar rotation period of 73.41 d mentioned in the literature. The behaviour of the mean longitudinal magnetic field is consistent …
The Critical Parameters Of A Slowly Rotating Neutron Star,
2015
Yanbikov Vildyan Shavkyatovich
The Critical Parameters Of A Slowly Rotating Neutron Star, Vildyan Yanbikov
Vildyan Yanbikov
A model of unstable conditions of a slowly rotating neutron star. The formulas for calculating the mass and diameter of a neutron star. As well as the pressure and temperature in the center of the star. At the time of its unstable condition before it exploded.
