Talks & Events
Ph.D. Thesis Defenses: 1999
Evolution in the space density of clusters of galaxies from the Palomar distant cluster survey
We present the first dynamical study of the Palomar Distant Cluster Survey (PDCS). We measured redshifts for seventeen clusters of galaxies in that survey and velocity dispersions for a subset of eleven. Using our new cluster redshifts, we re-determine the X-ray luminosities and upper limits. We show that eleven out of twelve PDCS we observed are real over-densities of galaxies and most have velocity dispersions appropriate for clusters of galaxies. However, we find a fraction (~⅓) of objects in the PDCS which have velocity dispersions in the range of groups of galaxies but have richnesses appropriate for clusters of galaxies. We describe a subsample of our data for which we can compute a survey volume. With this subsample, we then measure the richness function, X-ray luminosity function using both the detections and upper limits, and the mass function derived from the velocity dispersions. We confirm that the space density of clusters of galaxies in the PDCS as a function of richness is significantly higher than expected based on the Abell catalog, though it is in agreement with other optically selected surveys. Our X-ray luminosity function is in agreement with other measurements based on both X-ray and optically selected samples, so we find that the PDCS does not miss clusters of galaxies that would be found in an X-ray selected survey. Our resulting mass function agrees with the expectations from such surveys as the Canadian Network for Observational Cosmology cluster survey but our mass measurements are too large to constrain cosmological parameters. Nonetheless, we show that future machine- based, optically selected surveys can be used to constrain cosmological parameters.
The sodium laser guide star experiment for adaptive optics and the development of a high bandwidth tracking system for the University of Chicago Adaptive Optics System
This dissertation consists of two parts. The first part describes the generation and observation of the laser guide star for adaptive optics (AO). The second part describes the development of a tracking system with high bandwidth for the Chicago Adaptive Optics System (ChAOS). A requirement for the laser guide star (LGS) from the point of view of the wavefront sensor of an adaptive optics system is discussed. The design and characteristics of a diode pumped sum-frequency laser designed for astronomical AO system is described. The experiment using this laser to generate and observe the sodium LGS undertaken on the National Solar Observatory's R. B. Dunn Solar Telescope is described and the result data presented. LGS as bright as 9.5 magnitude and as small as a natural star with FWHM size of 1 arcsecond has been formed with about 1.1 watts of laser power incident at the mesosphere. Experimental data has indicated that the optical pumping effect has enhanced the LGS, return by about 40% to 50%. The laser has shown to be an efficient and robust as a facility instrument for the astronomical adaptive optics system. Analysis using the returned flux and LGS spot profile has shown that the wavefront measurement error would be 0.155 rad2 with current ChAOS system at the winter (maximum) sodium abundance level and 0.208 rad2 with the improved ChAOS and laser system at the summer (minimum) sodium abundance level. ChAOS is a high order adaptive optics system designed for the 3.5-meter telescope at the Apache Point Observatory. High frequency jitter from the secondary mirror mount of the telescope has limited the performance of the original tracking system of ChAOS. A high bandwidth tracking system with the sampling frequency of more than 700 Hz was developed to overcome the problems of telescope jitter and the excess power of the high frequency atmospheric turbulence. An upgrade of the sensor will be needed for the tracking system to be able to track on the fainter objects and further reduce the power of the high frequency tilt.
Medium-scale microwave background anisotropy: Measurement and detectors design
This thesis describes three areas of research, all of them closely related to measuring the anisotropy in cosmic microwave background (CMB). In the first part of the thesis the results of analysis of the third flight of MSAM1 (Medium Scale Anisotropy Measurement) telescope are reported. The instrument is balloon-borne telescope with a 28' beam and 3 position chopper with +/-40' throw. It has radiometer with bands centered at 5.6, 9.2, 16.5, and 22.5 cm-1. The data from all channels are used to simultaneously fit the major foreground source-thermal emission from interstellar dust. The first flight in 1992 yielded a detection of anisotropy confirmed by second 1994 flight. The third flight measured a new region giving 1σ limits for CMB fluctuations bandpower amplitude dTl=50+16- 11 mK for single difference demodulation at mean l = 160 and dTl=65+18-13 mK for double difference demodulation at mean l = 270 with calibration errors included. The results of the analysis of all three MSAM1 flights are also reported. The second part is the analysis of the observation of Mars, Jupiter and Saturn cross-calibrated in four bands are reported. This cross-calibration improves the understanding of Jupiter as calibrator using the better understood Mars flux. The measured temperatures of Jupiter are 169 +/- 2, 165 +/- 2, 133 +/- 2 and 129 +/- 2 Kelvin in our bands without taking into account closely correlated for all bands Mars emission model uncertainty +/-10 K. This is the most precise measurement of Jupiter microwave brightness temperature at these frequencies to date. The last part describes ongoing work on new generation multifrequency bolometric radiometer for far infrared astronomy. The design promises much better optical efficiency compared to traditional multifrequency radiometers and, because of its compactness, makes multipixel bolometric cameras with many frequency channels much easier to design. Such an instrument can be useful in next generation CMB or Far Infrared Background (FIRB) experiment.
The evolution of MHD modes through recombination
We study the distribution and evolution of magnetohydrodynamic (MHD) modes generated by a primordial magnetic field. We follow linear MHD modes through recombination as they are significantly affected by two cosmological processes: the damping of modes by the viscosity of the decoupling photons, and the sharp drop in the speed of sound. A magnetic field generated in the early universe sets up MHD oscillations as its modes enter the growing horizon scale. We find that before recombination most of the magnetic energy in the cosmological magnetic field is transferred to those MHD modes that are driven by the tension in the magnetic field. These modes do not damp as efficiently through recombination as sound waves and consequently preserve energy in magnetic field fluctuations, b~(k), in the range of comoving scales from l~=0.1(B0/6×10- 9G) Mpc to 20 Mpc, where B0 is the magnitude of the background cosmological magnetic field today. We also find that for magnetic fields with present strengths between 4 × 10-11 G and 6 × 10-9 G on the scale of the horizon at recombination, magnetic perturbations dominate the evolution of the baryonic fluid on small scales after recombination and before the onset of gravitational collapse by cold dark matter perturbations. As photon decoupling ends after recombination, the surviving fluctuations act as a source of new density perturbations in the baryonic fluid with linear amplitude dr(k) /rb~=b( k) B0 , and fluid velocities on the order of the Alfvén speed at recombination, cA=B0(t) /
High-resolution far-infrared observations of star-forming regions
We present new 60 and 100 μm observations of the massive star formation regions in the Orion Nebula (M42), M17, and NGC 6334, and of the bipolar nebula S106. Due to improvements in instrumentation and data reduction techniques, our images have the highest resolutions ever achieved at these wavelengths: 17'-18' at 60 μm and 27 '-29' at 100 μm. Compact objects are found in each region which were unresolved in previous studies; we estimate the luminosity and comment upon the nature of each of these sources.
Galaxy spectral type and star formation as a function of density
The 15R-North galaxy survey is a sample of 3149 optical spectra (3650-7400Å), with median redshift 0.05. The sample is 90% complete to RC = 15.4. I use spectral features including Hα 6563Å to classify the galaxies spectroscopically, and measure local density and synthetic colors. The main results are (1)>=22% of the galaxies are star- forming, >=16% have AGN-like emission, and an additional >=14% have emission that cannot be classified with the available data; (2)the unclassified 14% may include a ``hybrid'' population of galaxies with both star-formation and AGN activity; (3)when estimating star-formation rates from the [OII] 3727Å line (in cases where Hα is unavailable), a luminosity correction gives a better estimate than the [OII] line alone; (4)spectral type is correlated with local density much as galaxy morphology correlates with density; and (5)the star-formation rate (estimated from Hα) is only weakly correlated with local density.
Data reduction and analysis of the Python V cosmic microwave background anisotropy experiment
Observations of the microwave sky using the Python telescope in its fifth season of operation at the Amundsen-Scott South Pole Station in Antarctica are presented. The system consists of a 0.75 m off-axis telescope instrumented with a HEMT amplifier-based radiometer having continuum sensitivity from 37-5 GHz in two frequency bands. With a 0.91° × 1.02° beam the instrument fully sampled 598 deg2 of sky, including fields measured during the previous four seasons of Python observations. Interpreting the observed fluctuations as anisotropy in the cosmic microwave background, we place constraints on the angular power spectrum of fluctuations in eight multipole bands up to l ~ 260. The observed spectrum is consistent with both the COBE experiment and previous Python results. Total-power Wiener-filtered maps of the CMB are also presented. There is no significant contamination from known foregrounds. The results show a discernible rise in the angular power spectrum from large (l ~ 40) to small (l ~ 200) angular scales.
Reconstruction of stellar surface features via matrix lightcurve inversion
Matrix Lightcurve Inversion (MLI) is a technique for deducing the surface brightness distributions of rapidly rotating spotted stars or the surface albedo distributions of planets (in particular Pluto) from their rotational lightcurves. When applied to the stellar problem it has the significant advantage over ``spot models'' that it makes no a priori assumptions about the number of spots on the stellar surface or their shapes. We demonstrate the viability of the method for determining the shapes and locations of dark spots on stellar surfaces and explore its potential and its limitations by presenting the results of inversions of synthetic lightcurves corresponding to model stars with known surface features. We show that when lightcurves acquired through different photometric filters are simultaneously inverted, significant improvements can be achieved compared to when only a single filter is used. In particular, it becomes possible to more reliably deduce the presence of high-latitude activity, presenting the possibility of corroborating Doppler images which imply high-latitude spots. We apply MLI to the inversion of V and B lightcurves of the RS CVn binary II Pegasi acquired from September 1995 to January 1996, and show that two major spots or active regions were present. Initially they were separated by almost 180° in longitude, but over time the larger spot drifted forward in longitude in the direction of rotation relative to the orbital ephemeris while the smaller spot remained nearly stationary. This may be due to differential rotation. There is evidence that the larger spot was at a higher latitude than the smaller spot, which would imply that the differential rotation has the opposite sense of that on the Sun.