Phased Light Curves Research Articles

Nova V5116 Sagittarii and searching for superhumps in nova remnants

Aims. We present the period analysis of unfiltered photometric observations of V5116 Sgr (Nova Sgr 2005 #2) and search for superhump candidates in novae remnants. Methods. The PDM method for period analysis was used. The masses of the novae componets we are estimated from the secondary mass – orbital period and primary mass – decline time relations. Results. We find that 13 nights of V5116 Sgr observations in the year 2006 are modulated with a period of 0.1238 ± 0.0001 d (2.9712 ± 0.0024 h). Following the shape of the phased light curves and no apparent change in the value of the periodicity in different subsamples of the data, we interpreted the period as orbital in nature. The binary system then falls within the period gap of the orbital period distribution of cataclysmic variables. From the maximum magnitude – rate of decline relation, we estimated a maximum absolute visual magnitude of MVmax = −8.85 ± 0.04 mag using the measured value of decline t2 = 6.5 ± 1.0 d. The mass-period relation for cataclysmic variables yields a secondary mass estimate of about 0.26 ± 0.05 M� . We propose that V5116 Sgr is a high inclination system showing an irradiation effect of the secondary star. No fully developed accretion disc up to the tidal radius with the value lower than 3.5 × 10 10 cm is probable. The mass ratio was estimated in a few novae and the presence or absence of superhumps in these systems was compared with the mass ratio limit for superhumps of about 0.35. We find that, in the majority of novae with expected superhumps, this variability has not been found yet. Therefore, more observations of these systems is encouraged.

X‐Ray Hardness Variations as an Internal/External Shock Diagnostic

The early, highly time-variable X-ray emission immediately following gamma-ray bursts (GRBs) exhibits strong spectral variations that are unlike the temporally smoother emission that dominates after t ~ 103 s. The ratio of hard-channel (1.3-10.0 keV) to soft-channel (0.3-1.3 keV) counts in the Swift X-ray telescope provides a new measure delineating the end time of this emission. We define TH as the time at which this transition takes place and measure for 59 events a range of transition times that spans 10 2 to 104 s, on average 5 times longer than the prompt T90 duration observed in the gamma-ray band. It is very likely that the mysterious light-curve plateau phase and the later power-law temporal evolution, both of which typically occur at times greater than TH and hence exhibit very little hardness ratio evolution, are both produced by external shocking of the surrounding medium and not by the internal shocks thought responsible for the earlier emission. We use the apparent lack of spectral evolution to discriminate among proposed models for the plateau phase emission. We favor energy injection scenarios with a roughly linearly increasing input energy versus time for six well-sampled events with nearly flat light curves at t ≈ 103-104 s. Also, using the transition time TH as the delineation between the GRB and afterglow emission, we calculate that the kinetic energy in the afterglow shock is typically a factor of 10 lower than that released in the GRB. Three very bright events suggest that this presents a missing X-ray flux problem rather than an efficiency problem for the conversion of kinetic energy into the GRB. Lack of hardness variations in these three events may be due to a very highly relativistic outflow or due to a very dense circumburst medium. There are a handful of rare cases of very late time t > 104 s hardness evolution, which may point to residual central engine activity at very late time.

Eclipsing Binaries in the MACHO Database: New Periods and Classifications for 3031 Systems in the Large Magellanic Cloud

Eclipsing binaries offer a unique opportunity to determine fundamental physical parameters of stars by using the constraints on the geometry of the systems. Here we present a reanalysis of publicly available two-color observations of about 6800 stars in the Large Magellanic Cloud obtained by the MACHO Project between 1992 and 2000 and classified as eclipsing variables. Of these, fewer than half are genuine eclipsing binaries. We determined new periods and classified the stars, 3031 in total, using the Fourier parameters of the phased light curves. The period distribution is clearly bimodal, reflecting separate groups of more massive blue main-sequence objects and low-mass red giants. The latter resemble contact binaries and obey a period-luminosity relation. Using evolutionary models, we identified foreground stars. The presented database has been cleaned of artifacts and misclassified variables, thus allowing searches for apsidal motion, tertiary components, pulsating stars in binary systems, and secular variations with timescales of several years.

Photometric Stellar Variability in the Galactic Center

We report the results of a diffraction-limited, photometric variability study of the central 5'' × 5'' of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W. M. Keck I 10 m telescope. Within our limiting magnitude of mK < 16 mag for images made from a single night of data, we find a minimum of 15 K[2.2 μm]-band variable stars out of 131 monitored stars. The only periodic source in our sample is the previously identified variable IRS 16SW, for which we measure an orbital period of 19.448 ± 0.002 days. In contrast to recent results, our data on IRS 16SW show an asymmetric phased light curve with a much steeper fall time than rise time, which may be due to tidal deformations caused by the proximity of the stars in their orbits. We also identify a possible wind colliding binary (IRS 29N) based on its photometric variation over a few year timescale, which is likely due to episodic dust production. None of the four luminous blue variable (LBV) candidates in our sample show the characteristic large increase or decrease in luminosity. However, our time baseline is too short to rule them out as LBVs. Among the remaining variable stars, the majority are early-type stars, and three are possibly variable due to line-of-sight extinction variations. For the seven OB stars at the center of our field of view that have well-determined three-dimensional orbits, we see no evidence of flares or dimming of their light, which limits the possibility of a cold, geometrically thin, inactive accretion disk around the supermassive black hole, Sgr A*.

Terrestrial Consequences of Spectral and Temporal Variability in Ionizing Photon Events

Gamma-Ray Bursts (GRBs) directed at Earth from within a few kpc may have damaged the biosphere, primarily though changes in atmospheric chemistry which admit greatly increased Solar UV. However, GRBs are highly variable in spectrum and duration. Recent observations indicate that short (~0.1 s) burst GRBs, which have harder spectra, may be sufficiently abundant at low redshift that they may offer an additional significant effect. A much longer timescale is associated with shock breakout luminosity observed in the soft X-ray (~10^3 s) and UV (~10^5 s) emission, and radioactive decay gamma-ray line radiation emitted during the light curve phase of supernovae (~10^7 s). Here we generalize our atmospheric computations to include a broad range of peak photon energies and investigate the effect of burst duration while holding total fluence and other parameters constant. The results can be used to estimate the probable impact of various kinds of ionizing events (such as short GRBs, X-ray flashes, supernovae) upon the terrestrial atmosphere. We find that the ultimate intensity of atmospheric effects varies only slightly with burst duration from 10^-1 s to 10^8 s. Therefore, the effect of many astrophysical events causing atmospheric ionization can be approximated without including time development. Detailed modeling requires specification of the season and latitude of the event. Harder photon spectra produce greater atmospheric effects for spectra with peaks up to about 20 MeV, because of greater penetration into the stratosphere.

Photometric Stellar Variability in the Galactic Center

We report the results of a diffraction-limited, photometric variability study of the central 5′′ × 5′′ of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W.M. Keck I 10 m telescope. Within our limiting magnitude of mK < 16 for maps made from a single night of data, we find a minimum of 25 variable stars out of 131 monitored stars. Among 46 stars brighter than mK < 14 which have roughly uniform photometric uncertainties, there are 16 variable stars. This suggests a minimum variable star frequency of 34%. We see no evidence of fares or dimming of the 7 stars that have known 3-dimensional orbits in our study, which greatly limits the possibility of a cold, geometrically-thin, inactive accretion disk around the supermassive black hole, Sgr A*. While large populations of binaries have been posited to exist in this region both to explain the presence of young stars in the vicinity of a black hole and because of the high stellar densities, only one eclipsing binary is identiffed. The only periodic source in our sample is the previously identiffed variable IRS 16SW (P = 19.448 ± 0.002 days). In contrast to recent results, our data show an asymmetric phased light curve with a much steeper fall-time than rise-time. IRS 29N shows variability on time scales of ≈ 5 years and has a known spectral type of WC9. This variation is likely due to episodic dust production, which may suggest that this source is a binary star system. Only 2 of the LBV candidates in our sample (16NW, 16SW) show variability and none of the 4 show the characteristic large increase or decrease in luminosity. However, our time baseline is too short to rule them out as LBVs. Our study has shown that photometric variability provides a useful handle on the unusual massive star population surrounding our Galaxy's supermassive black hole and its local environment.

2MASS J05162881+2607387: A New Low‐mass Double‐lined Eclipsing Binary

We show that the star known as 2MASS J05162881+2607387 (hereafter J0516) is a double-lined eclipsing binary with nearly identical low-mass components. The spectroscopic elements derived from 18 spectra obtained with the High Resolution Spectrograph on the Hobby-Eberly Telescope during the fall of 2005 are K1 = 88.45 ± 0.48 and K2 = 90.43 ± 0.60 km s-1, resulting in a mass ratio of q = K1/K2 = 0.978 ± 0.018 and minimum masses of M1 i = 0.775 ± 0.016 M☉ and M2 i = 0.759 ± 0.012 M☉, respectively. We have extensive differential photometry of J0516 obtained over several nights between 2004 January and March (epoch 1) and between 2004 October and 2005 January plus 2006 January (epoch 2) using the 1 m telescope at the Mount Laguna Observatory. The source was roughly 0.1 mag brighter in all three bandpasses during epoch 1 when compared to epoch 2. Also, phased light curves from epoch 1 show considerable out-of-eclipse variability, presumably due to bright spots on one or both stars. In contrast, the phased light curves from epoch 2 show little out-of-eclipse variability. The light curves from epoch 2 and the radial velocity curves were analyzed using our ELC code with updated model atmospheres for low-mass stars. We find the following: M1 = 0.787 ± 0.012 M☉, R1 = 0.788 ± 0.015 R☉, M2 = 0.770 ± 0.009 M☉, and R2 = 0.817 ± 0.010 R☉. The stars in J0516 have radii that are significantly larger than model predictions for their masses, similar to what is seen in a handful of other well-studied low-mass double-lined eclipsing binaries. We compiled all recent mass and radius determinations from low-mass binaries and determine an empirical mass-radius relation of the form R(R☉) = 0.0324 + 0.9343M(M☉) + 0.0374M2(M☉).

V4745 Sgr - a nova above the period gap and an intermediate polar candidate

A period analysis of CCD unfiltered photometry of V4745 Sgr (Nova Sgr 2003 #1) performed during 23 nights in the years 2003 - 2005 is presented. The photometric data are modulated with a period of 0.20782 +- 0.00003 d ($4.98768 +- 0.00072 h). Following the shape of the phased light curve and the presence of the periodicity in all data sets with no apparent change in its value, we interpret this periodicity as orbital in nature and this is consistent with a cataclysmic variable above the period gap. We found a probable short-term periodicity of 0.017238 +- 0.000037 d (24.82272 +- 0.05328 m) which we interpret as the probable spin period of the white dwarf or the beat period between the orbital and spin period. Therefore, we propose that nova V4745 Sgr should be classified as an intermediate polar candidate, supporting the proposed link between transition-oscillation novae and intermediate polars. The mass-period relation for cataclysmic variables yields a secondary mass of about 0.52 +- 0.05 M_solar.

Photometric studies of three multiperiodic β Cephei stars: β CMa, 15 CMa and KZ Mus

We have carried out single and multisite photometry of the three β Cephei stars β and 15 CMa as well as KZ Mus. For the two stars in CMa, we obtained 270 h of measurement in the Stromgren uvy and Johnson V filters, while 150 h of time-resolved Stromgren uvy photometry was acquired for KZ Mus. All three stars are multiperiodic variables, with three (β CMa) and four (15 CMa, KZ Mus) independent pulsation modes. Two of the mode frequencies of 15 CMa are new discoveries and one of the known modes showed amplitude variations over the last 33 yr. Taken together, this fully explains the diverse behaviour of the star reported in the literature. Mode identification by means of the amplitude ratios in the different passbands suggests one radial mode for each star. In addition, β CMa has a dominant l= 2 mode while its third mode is non-radial with unknown l. The non-radial modes of 15 CMa, which are l≤ 3, form an almost equally split triplet that, if physical, would imply that we see the star under an inclination angle larger than 55°. The strongest non-radial mode of KZ Mus is l= 2, followed by the radial mode and a dipole mode. Its weakest known mode is non-radial with unknown l, confirming previous mode identifications for the pulsations of the star. The phased light curve for the strongest mode of 15 CMa has a descending branch steeper than the rising branch. A stillstand phenomenon during the rise to maximum light is indicated. Given the low photometric amplitude of this non-radial mode this is at first sight surprising, but it can be explained by the aspect angle of the mode.

The possible orbital period of the nova V1493 Aquilae

Period analysis of CCD photometry of V1493 Aql (Nova Aql 1999 no. 1) performed during 12 nights through I and R filters a few weeks after maximum is presented. The PDM method for period analysis (Stellingwerf 1978) is used. The photometric data is modulated with a period of 0.156 +- 0.001 d. Following the sinusoidal shape of the phased light curve, we interpret this periodicity as possibly orbital in nature which is consistent with a cataclysmic variable above the period gap.

Eclipsing binaries in the Galactic bulge: candidates for distance estimates

The 222~000 I-band light curves of variable stars detected by the OGLE-II survey in the direction of the Galactic Bulge have been searched for eclipsing binaries (EBs). A previously developed code to analyze lightcurve shapes and identify long period variables (LPVs) has been adapted to identify EBs. The parameters in the modified code have been optimised to recover a list of about 140 detached EBs in the Small Magellanic Cloud previously identified in the literature as particularly well suited for distance estimates (and wich have periods \more 0.85 days). The power of the code is demonstrated by identifying 16 and 178 previously uncatalogued EBs in the SMC and LMC, respectively. Among the 222~000 variable stars in the direction of the Galactic Bulge 3053 EBs have been identified. Periods and phased lightcurves are presented.

Phase Functions and Light Curves of Wide‐Separation Extrasolar Giant Planets

We calculate self-consistent extrasolar giant planet (EGP) phase functions and light curves for orbital distances ranging from 0.2 to 15 AU. We explore the dependence on wavelength, cloud condensation, and Keplerian orbital elements. We find that the light curves of EGPs depend strongly on wavelength, the presence of clouds, and cloud particle sizes. Furthermore, the optical and infrared colors of most EGPs are phase-dependent, tending to be reddest at crescent phases in V - R and R - I. Assuming circular orbits, we find that at optical wavelengths most EGPs are 3-4 times brighter near full phase than near greatest elongation for highly inclined (i.e., close to edge-on) orbits. Furthermore, we show that the planet/star flux ratios depend strongly on the Keplerian elements of the orbit, particularly inclination and eccentricity. Given a sufficiently eccentric orbit, an EGP's atmosphere may make periodic transitions from cloudy to cloud-free, an effect that may be reflected in the shape and magnitude of the planet's light curve. Such elliptical orbits also introduce an offset between the time of the planet's light-curve maximum and the time of full planetary phase, and for some sets of orbital parameters, this light-curve maximum can be a steeply increasing function of eccentricity. We investigate the detectability of EGPs by proposed space-based direct-imaging instruments.

New near-aphelion light curves of Comet 2P/Encke

We present new, near-aphelion, time series of photometry of Comet 2P/Encke in Cousins-R band. With these light curves we find that the dominant, synodic rotational periodicity is either P 0 = 11.079 ± 0.009 h or 2 P 0 = 22.158 ± 0.012 h . This is in contrast to data from the 1980s published by others that are consistent with 15.08- and 22.6-h periods. Those periods do not satisfy our phased light curves, and also the 1980s data are not easily reconciled with our periods. This could be due to P/Encke having non-principal axis rotation or due to a drift in the rotation period caused by outgassing torques. We observed the comet at five epochs: July, August, September, and October 2001, and September 2002, and the comet was at times intrinsically brighter than expected for a bare nucleus, due to an apparent contribution from an unresolved coma. Three-quarters of the data were obtained in the second and fifth epochs, and we analyzed these two time series using both the phase-dispersion minimization and “WindowCLEAN” techniques. At both epochs and with both techniques strong periodicities were found near frequencies f 0 = 2.16 d −1 and f 1 = 4.35 d −1 . By then using visual inspection of the phased light curves to corroborate these frequencies, and by using the data from the other three epochs to properly align light curve features, we were able to derive P 0 and 2 P 0 as the only solutions that satisfy all our observations. The periodicity due to f 1 is clearly seen in our data, but we cannot tell from our data alone whether it is a manifestation of the nucleus's shape, non-principal axis rotation, or both.

Phase Light Curves for Extrasolar Jupiters and Saturns

We predict how a remote observer would see the brightness variations of giant planets similar to Jupiter and Saturn as they orbit their central stars. We model the geometry of Jupiter, Saturn and Saturn's rings for varying orbital and viewing parameters. Scattering properties for the planets and rings at wavelenghts 0.6-0.7 microns follow Pioneer and Voyager observations, namely, planets are forward scattering and rings are backward scattering. Images of the planet with or without rings are simulated and used to calculate the disk-averaged luminosity varying along the orbit, that is, a light curve is generated. We find that the different scattering properties of Jupiter and Saturn (without rings) make a substantial difference in the shape of their light curves. Saturn-size rings increase the apparent luminosity of the planet by a factor of 2-3 for a wide range of geometries. Rings produce asymmetric light curves that are distinct from the light curve of the planet without rings. If radial velocity data are available for the planet, the effect of the ring on the light curve can be distinguished from effects due to orbital eccentricity. Non-ringed planets on eccentric orbits produce light curves with maxima shifted relative to the position of the maximum planet's phase. Given radial velocity data, the amount of the shift restricts the planet's unknown orbital inclination and therefore its mass. Combination of radial velocity data and a light curve for a non-ringed planet on an eccentric orbit can also be used to constrain the surface scattering properties of the planet. To summarize our results for the detectability of exoplanets in reflected light, we present a chart of light curve amplitudes of non-ringed planets for different eccentricities, inclinations, and the viewing azimuthal angles of the observer.

Orbital Parameters for the Black Hole Binary XTE J1650−500

We present R-band photometry of the X-ray transient and candidate black hole binary XTE J1650-500 obtained between 2003 May and August with the 6.5 m Clay telescope. A timing analysis of these data reveals a photometric period of 0.3205 ± 0.0007 days (i.e., 7.63 hr) with a possible alias at 0.3785 days (9.12 hr). Our photometry completely rules out the previously published spectroscopic period of 0.212 days (5.09 hr). Consequently, we reanalyzed the 15 archival ESO VLT spectra (obtained 2002 June by Sanchez-Fernandez et al.) that were the basis of the previously published spectroscopic period. We used a "rest-frame search" technique that is well suited for cases in which the signal-to-noise ratio of individual spectra is low. For each of roughly 1.1 million binary ephemerides, we summed all of the spectra in a trial rest frame of the secondary star, and each rest-frame spectrum was cross-correlated against a template spectrum. We then searched for the set of orbital parameters that produced the strongest cross-correlation value. The results confirmed the photometric period of 0.3205 days and ruled out the alias period near 0.38 days. The best value for the velocity semiamplitude of the companion star is K2 = 435 ± 30 km s-1, and the corresponding optical mass function is f(M) = 2.73 ± 0.56 M☉. The spectral type of the companion star is not well constrained because we only have six template spectra available to us. The K4 V template provides the best match; next-best matches are provided by the G5 V and K2 III templates. We also find that the accretion disk dominates the light in the R band where the disk fraction is 80% or higher, although this value should be treated with caution owing to the poor signal-to-noise ratio and the limited number of templates. The amplitude of the phased R-band light curve is 0.2 mag, which gives a lower limit to the inclination of 50° ± 3° in the limiting case of no contribution to the R-band light curve from the accretion disk. If the mass ratio of XTE J1650-500 is similar to the mass ratios of other black hole binaries, such as A0620-00 or GRS 1124-683 (e.g., Q ≳ 10), then our lower limit to the inclination gives an upper limit to the mass of the black hole in XTE J1650-500 of M1 ≲ 7.3 M☉. However, the mass can be considerably lower if the R-band flux is dominated by the accretion disk. For example, if the accretion disk does contribute 80% of the flux, as our preliminary results suggest, then the black hole mass would be only about 4 M☉.

A rotational light curve for the Kuiper belt object 1997 CV 29

We present R- and V-band rotational light curves for classical Kuiper belt object 1997 CV 29. The imaging data was obtained from the Canada–France–Hawaii Telescope (CFHT) archive located at the Canadian Astronomical Data Center (CADC). The data consist of one nights observations of a series of 42, 8 minute exposures in R band followed by 33, 8 minute exposures in V band acquired on the following night. Using relative photometry we determined a highly significant variation in the brightness of 1997 CV 29. Using phase-dispersion-minimization we find 8.0, 11.2, and 15.8 hrs to be the most likely, periods of rotation and we argue that the ∼16 hr period is the most likely based on our limited observing window. The phased light curve has a peak-to-peak range of Δ m≳0.4±0.1 mag suggesting an axial ratio of a/ b≳1.45.

Photometric Variability at the L/T Dwarf Boundary

We have monitored the photometric variability of nine field L and T brown dwarfs for 10 nights during the course of 1 month. Observations were obtained in the K_s band with the Palomar 60 inch (1.5 m) telescope Near-Infrared Camera. Results of statistical analyses indicate that at least three of the nine targets show significant evidence for variability, and three more are possibly variable. Fractional deviations from the median flux vary from 5% to 25%. Two of the variable targets, 2MASS 0030-14 (L7) and SDSS 0151+12 (T1), have marginally significant peaks in their periodograms. The phased light curves show evidence for periodic behavior on timescales of 1.5 and 3.0 hr, respectively. No significant correlations between variability amplitude and spectral type or J-K_s color are found. While it is clear that variability exists in objects near the L/T dwarf boundary, we find no evidence that variability near the L/T boundary is more likely than it is for early L dwarfs.

Time Series Photometry of Variable Stars in the Globular Cluster NGC 6397

Time series BVI photometry is presented for 16 short-period variables located in the central region of the globular cluster NGC 6397. The sample includes 9 newly detected variables. The light curve of cataclysmic variable CV6 shows variability with a period of 0.2356 days. We confirm an earlier reported period of 0.472 days for cataclysmic variable CV1. Phased light curves of both CVs exhibit sine-like light curves, with two minima occurring during each orbital cycle. The secondary component of CV1 has a low average density of 0.83 g/cm^{3} indicating that it cannot be a normal main sequence star. Variables among the cluster blue stragglers include a likely detached eclipsing binary with orbital period of 0.787 days, three new SX Phe stars (one of which has the extremely short period of 0.0215 days), and three low amplitude variables which are possible gamma Doradus variables.

The Puzzling Optical Light Curve of the Polar QQ Vulpeculae

About 10.5 yr of V-band photometry of QQ Vul allows the examination of systematic changes in orbital light curve features of the system. The photometry is generally limited to one or two data points each clear night at a random orbital phase; however, the orbital light curve and its slower changes can be studied when the data are grouped into intervals of 1 to 2 months. We have isolated four main distinguishing behaviors in the optical light curve of the system. In type 1 the phased light curve has a single broad primary dip. In type 2 the primary dip retains its shape but becomes dimmer and is accompanied by a secondary dip about 0.5 phase units away. As part of the type 2 behavior there is a decrease in the overall brightness level of the phased light curve by ~0.5 mag. This correlation between the morphology of the orbital light curve and the brightness of the system is shown to hold not only for our new data but also for light curves obtained during 1982–1986. Type 3 behavior is an unresolved mixture of types 1 and 2, whereas type 4 appears to be an extreme bright case of type 1. We find a highly significant correlation between the depth of the secondary dip and the system brightness. The implications of this correlation in the context of one- or two-pole accretion are discussed.

A Search for Eclipsing Binaries in Galactic Globular Clusters

Variable stars have historically served as tools and laboratories in our understanding of stellar formation and evolution, the formation of star clusters, the calibration of distance determination methods, and a variety of other areas. In particular, the study of eclipsing binaries (EBs) in globular clusters (GCs) can provide direct distance estimates to clusters as well as constraints for the turnoff masses of GC stars. Knowing precise distances to GCs would constitute an independent check of widely used distance determination methods in astronomy. Obtaining masses of GC turnoff stars provides a fundamental test of low-metallicity stellar models that calculate ages for these stars—and thus the GCs themselves—and thereby allow a lower limit estimate of the age of the universe. My dissertation research with M. Mateo at the University of Michigan consists of a monitoring survey of 10 Galactic GCs with the aim of identifying photometrically variable EBs around or below the main-sequence turnoff (MSTO). My thesis work comprises the results of our research on the GCs NGC 3201, M10, and M12. Our observing strategy is aimed at detecting variables with periods between 0.2 and around 5 days and , thereby optimizing our chance to find the 16.5 ! V ! 20 valuable detached EBs in the target clusters. In addition, we correct for differential reddening variations across the cluster fields of up to several tenths of magnitudes in V by internally creating a differential extinction map with an arcminute resolution from our cluster photometry data and calculate the additional reddening zero point using isochrone fitting. The resulting improvement in the appearance of the color-magnitude diagrams (CMDs) of the clusters is considerable (see K. von Braun & M. Mateo 2001, AJ, 121, 1522). We obtained approximately 200 VI epochs with about 20,000 stars per image for each of the three clusters. Analysis of these data revealed the existence of 14 variable stars (11 EBs) in the field of NGC 3201, three variables (one EB) in the field of M10, and two EBs in the field of M12. Spectroscopic followup work showed that only one variable (a blue straggler W Ursa Majoris contact EB) in the field of NGC 3201 is associated with the cluster. Another W UMa EB is most likely a member of M12, based on its location in M12’s CMD and its empirically calculated absolute magnitude. The rest of the variable stars we detected are members of the Galactic disk (see K. von Braun & M. Mateo 2002, AJ, 123, 279; and K. von Braun et al. 2002, AJ, 124, 2067 for details). We thus calculate a ratio of observable, short-period, main-sequence binaries to main-sequence stars of around 1/500 for the Galactic disk (consistent with literature estimates) and 1/9000 for GC members. The latter value is considerably smaller than the commonly quoted value of 1/1000. While the discrepancy may be due to small number statistics, we attribute it to the fact that we lose about 20% of our fields to crowding toward the cluster center where the binary fraction should be highest after a few cluster relaxation times. In my dissertation, I show the cluster fields and CMDs (before and after dereddening) with the locations of the variable stars and our differential extinction maps, as well as the phased light curves and spectra (wherever applicable) of the variable stars. For additional information or to obtain a copy of the dissertation, please contact me or visit http://www.ciw.edu/vonbraun.