The brightness and variability of the atmosphere in the thermal infrared poses obstacles to precision photometry measurements. The need to remove atmospheric effects calls for the use of a comparison star, but it is usually impossible to fit both science and comparison targets on current long-wavelength (> 2 mu m) detectors. We present a new pointing mode at the Large Binocular Telescope, which has twin 8.4-m primary mirrors that can be pointed up to similar to 2 arcminutes apart and allow the placement of both targets on a small-field infrared detector. We present an observation of the primary transit of an exoplanet in front of its host star, and use it to provide preliminary constraints on the attainable photometric precision.

Chung, Hin Shun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 40-43). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Lambertian photometric stereo --- p.1 / Chapter 1.2 --- Non-Lambertian photometric stereo --- p.3 / Chapter 1.3 --- Large specular lobe problems --- p.4 / Chapter 2 --- Related Work --- p.9 / Chapter 2.1 --- Lambertian photometric stereo --- p.9 / Chapter 2.2 --- Non-Lambertian photometric stereo --- p.9 / Chapter 2.2.1 --- Analytic models to reconstruct non-Lambertian surface --- p.9 / Chapter 2.2.2 --- Reference object based --- p.10 / Chapter 2.2.3 --- Highlight removal before shape reconstruction --- p.11 / Chapter 2.2.4 --- Polarization based method --- p.12 / Chapter 2.2.5 --- Specularity fitting method --- p.12 / Chapter 2.2.6 --- Photometric stereo with shadow --- p.12 / Chapter 3 --- Our System --- p.13 / Chapter 3.1 --- Estimation of global parameters --- p.14 / Chapter 3.1.1 --- Shadow separation --- p.16 / Chapter 3.1.2 --- Separation edges of shadow and edges of foreground object --- p.16 / Chapter 3.1.3 --- Normal estimation using shadow boundary --- p.20 / Chapter 3.1.4 --- Global parameter estimation and refinement --- p.22 / Chapter 3.2 --- Surface shape and texture reconstruction --- p.24 / Chapter 3.3 --- Single material results --- p.25 / Chapter 4 --- Comparison between Our Method and Direct Specularity Fitting Method --- p.29 / Chapter 4.1 --- Summary of direct specularity fitting method [9] --- p.29 / Chapter 4.2 --- Comparison results --- p.31 / Chapter 5 --- Reconstructing Multiple-Material Surfaces --- p.33 / Chapter 5.1 --- Multiple material results --- p.34 / Chapter 6 --- Conclusion --- p.38 / Bibliography --- p.39 / Chapter A --- Proof of Surface Normal Projecting to Gradient of Cast Shadow Boundary --- p.43

Thesis (Ph. D.)--Texas Christian University, 2007. / Title from dissertation title page (viewed Dec. 10, 2007). Includes abstract. Includes bibliographical references.

Point source extraction is critical to proper analysis of images containing point sources obtained by focal plane array cameras. Two popular methods of extracting the intensity of a point source are aperture photometry and point spread function fitting. Digital aperture photometry encompasses procedures utilized to extract the intensity of an imaged point source. It has been used by astronomers in various forms for calculating stellar brightness. It is also useful for doing analysis of data associated with other unresolved radiating objects. The various aperture photometry methods include the two-aperture method, aperture correction, and growth curve method. The growth curve method utilizes integrated irradiance within an aperture versus growing aperture size. Signal to noise ratio, imperfect backgrounds, moving and off centered targets, and noise structure are just a few of the items that can cause problems with point source extraction. This thesis presents a study of how best to apply the growth curve method. Multiple synthetic image sets were produced to replicate real world data. The synthetic images contain a Gaussian target of known intensity. Noise was added to the images, and various image related parameters were altered. The growth curve method is then applied to each data set using every reasonable aperture size combination to calculate the target intensity. It will be shown that for different types of data, the most optimal application of the growth curve method can be determined. An algorithm is presented that can be applied to all data sets that fall within the scope of this study will be presented.

Point source extraction is critical to proper analysis of images containing point sources obtained by focal plane array cameras. Two popular methods of extracting the intensity of a point source are aperture photometry and point spread function fitting. Digital aperture photometry encompasses procedures utilized to extract the intensity of an imaged point source. It has been used by astronomers in various forms for calculating stellar brightness. It is also useful for doing analysis of data associated with other unresolved radiating objects. The various aperture photometry methods include the two-aperture method, aperture correction, and growth curve method.The growth curve method utilizes integrated irradiance within an aperture versus growing aperture size. Signal to noise ratio, imperfect backgrounds, moving and off centered targets, and noise structure are just a few of the items that can cause problems with point source extraction. This thesis presents a study of how best to apply the growth curve method.Multiple synthetic image sets were produced to replicate real world data. The synthetic images contain a Gaussian target of known intensity. Noise was added to the images, and various image related parameters were altered. The growth curve method is then applied to each data set using every reasonable aperture size combination to calculate the target intensity. It will be shown that for different types of data, the most optimal application of the growth curve method can be determined. An algorithm is presented that can be applied to all data sets that fall within the scope of this study will be presented.

This thesis presents observational studies of long-term and extreme variability of stars with the Digital Access to a Sky Century@Harvard (DASCH) project. Stellar variations over decades are poorly explored. With the unique 100 years coverage of DASCH, for the first time, we are able to study the variable sky over long timescales in a systematic way. I have developed photometric calibration and variable search algorithms for DASCH. I have discovered exciting new types of long-term variables, which do not match any of the common classes, and studied the physical processes involved. Following a brief introduction on variable stars and DASCH in the first chapter, I describe my work on DASCH pipeline, including photometric development and defect filtering in chapter 2. I present our discovery of a group of peculiar long-term K giant variables with \(\sim1\) mag variations over decades in chapter 3. Follow-up observations show that they consist of two subgroups, including a subgroup of RS CVn binaries with strong magnetic activity, and another subgroup of single stars. In both cases, the variation amplitudes and timescales are abnormal, and may be related to either ultra strong star spots, or novel dust formation processes. In chapter 4, I present the discovery of a 5 yr dip around 1900 in the eclipsing binary KU Cyg consisting of a F star and a K giant, which is related to the accretion disk surrounding the F star. It showed a slow fading \((\sim 4 yr)\), which is probably caused by increases in dust extinction in the disk, and a relatively fast brightening \((\sim 1 yr)\), which may be due to the evaporation of dust transported inward through the disk. The extinction excess which caused the fading may arise from an increased mass transfer rate in the system or from dust clump ejections from the K giant, in accordance with K giant “dimming” as discussed above. In chapter 5, I present a 10 yr nova-like outburst in a peculiar symbiotic system. With P = 119 days, it is interestingly located in the period gap region between classical novae and symbiotic novae. The most probable explanation of the outburst is hydrogen shell-burning on the white dwarf (WD) without significant mass loss, which suggests a promising new channel for Type Ia Supernovae (SNe). In chapter 6, I present the DASCH light curves of Kepler planet-candidate host stars. We found no variation for these host stars. In chapter 7, I present my variable search algorithms and the resulting DASCH variable catalog for the Kepler field. The conclusion is presented in chapter 8. / Astronomy

The objective of this project is to design a facility that will characterize the electrical and optical properties of both tubular and the more recent compact fluorescent tubes. The first stage of this project, which is the subject of this dissertation, was to design, build, test, and model a cylindrical light integrating chamber. An integrating chamber capable of measuring 2-metre long fluorescent tubes was built at the University of KwaZulu-Natal, South Africa. To approximate an infinitely long tube, precisely mounted planar mirrors were placed at opposite ends of the cylinder. The reflectance of diffusive reflective paint and mirrors enter into calculations and were investigated experimentally using a Jarrel-Ash optical spectrometer. The light flux was finally measured for various chamber lengths and compared with a mathematical model. Total light power output from the lamp was calculated and compared with the electrical power input, and the lamp efficiency deduced. Accurate calculations required that the light field surrounding a cylindrical diffuse source be modeled mathematically. The reflection coefficients of the mirrors were not unity and the equations had to be modified to include this effect. The mathematical model was solved using a combination of analytical and numerical techniques. The model results were compared with measurements. The final result includes a mathematical description of the integrating chamber, and a flux-density plot of the space surrounding the fluorescent tube. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2008.

We have used broad-band near infrared photometry in combination with optical Johnson-Cousins photometry to study the dust properties in the line of sight to the Galactic globular cluster M4. These data have been used to investigate the reddening effects in terms of absolute strength, distribution and variations across the cluster field, as well as the shape of the reddening law defined by the type of dust. All three aspects were poorly defined for this system and therefore there has been controversy about the absolute distance to the globular cluster which is closest to the sun. Here, we introduce a new method to determine the ratio of absolute to selective extinction (RV ) in the line of sight toward resolved stellar populations, which is known to be a useful indicator for the type of dust and therefore characterizes the applicable reddening law. This method is independent of age assumptions and appears to be significantly more precise and accurate than existing approaches. In a first application, we determine AV /E(B − V ) = 3.76 ± 0.07 (random error) for the dust in the line of sight to M4 for our set of filters. That corresponds to a dust-type parameter RV = 3.62 ± 0.07 in the Cardelli, Clayton & Mathis (1989) reddening law. With this value, the distance to M4 is found to be d = 1.80 ± 0.05 kpc, corresponding to a true distance modulus of (m − M)0 = 11.28 ± 0.06. These uncertainties do not include possible systematic errors in the theoretical isochrones. A reddening map for M4 has been created which reveals a spatial differential reddening of δE(B − V ) ≥ 0.2 mag across the field within 10′ around the cluster centre; this is about 50% of the total mean reddening, which has been determined to be E(B − V ) = 0.37 ± 0.01. In order to provide accurate zero points for the extinction coefficients of our photometric filters, a computer code has been written to investigate the impact of stellar parameters such as temperature, surface gravity and metallicity on the extinction properties and the necessary corrections in different bandpasses. Using both synthetic ATLAS9 spectra and observed spectral energy distributions, we found similar sized effects for the range of temperature and surface gravity typical of globular cluster stars: both cause a change of about 3% in the necessary correction factor for each filter combination. Interestingly, variations in the metallicity cause effects of the same order when the assumed value is changed from the solar metallicity ([Fe/H] = 0.0) to [Fe/H]=-2.5. Our analysis showed that the systematic differences between the flux of a typical main-sequence turnoff star in a metal poor globular cluster and a Vega-like star are even stronger (∼ 5%). We compared the results from synthetic spectra to those obtained with observed spectral energy distributions and found significant differences in detail for temperatures lower than 5 000 K. We have attributed these discrepancies to the inadequate treatment of molecular bands in the B filter within the ATLAS9 models. Accordingly, for those cooler temperatures we obtained corrections for temperature, gravity and metallicity primarily from the observed spectra. Fortunately, these differences do not affect our principal astrophysical conclusions in this study, which are based on stars hotter than 5 000 K. / Graduate

In this thesis, I explore the star formation histories of both spiral and elliptical galaxies. In Part 1,1 present an in-depth study of the star formation histories of spiral galaxies with a wide range of properties. Optical and near-infrared colours are used in conjunction with up-to-date stellar population synthesis models to constrain the ages and metallicities of my sample galaxies. I find that age and metallicity gradients are common in spiral galaxies of all types. The age of a spiral galaxy correlates mainly with its surface brightness, and its metallicity correlates strongly with both its surface brightness and absolute magnitude. Using simple models, I demonstrate that the correlations observed in this thesis show that the star formation history of a region within a galaxy depends primarily on its surface density, and possibly on the dynamical time. Metal- enriched outflow from low mass galaxies seems to be required to reproduce a reasonably strong metallicity-magnitude correlation. These variations in star formation history are a continuous function of the physical parameters: in particular, I find no evidence for a bimodal spiral galaxy surface brightness distribution. In Part 2, I present a short study on the formation epoch of early-type galaxies. I developed a photometric redshift estimator optimised for redshifts z ~ 1. The redshift estimator provides redshifts accurate to ~ 10 per cent. This redshift estimator is then applied to a sample of morphologically-selected early-type galaxies in the northern Hubble Deep Field. Comparison of their colour-magnitude relation with a passively evolved Coma cluster colour-magnitude relation indicates that over half of the sample must form at redshifts greater than two.

Thesis (Ph. D.)--McMaster University, 2006. / Supervisor: William E. Harris.