Matt A. Wood

Texas A&M University - Commerce, Commerce, Texas, United States

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Publications (24)83 Total impact

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    ABSTRACT: BOKS 45906 was found to be a blue source in the Burrell-Optical-Kepler-Survey which showed a 3 mag outburst lasting ~5 d. We present the Kepler light curve of this source which covers nearly 3 years. We find that it is in a faint optical state for approximately half the time and shows a series of outbursts separated by distinct dips in flux. Using data with 1 min sampling, we find clear evidence that in its low state BOKS 45906 shows a flux variability on a period of 56.5574+/-0.0014 min and a semi-amplitude of ~3 percent. Since we can phase all the 1 min cadence data on a common ephemeris using this period, it is probable that 56.56 min is the binary orbital period. Optical spectra of BOKS 45906 show the presence of Balmer lines in emission indicating it is not an AM CVn (pure Helium) binary. Swift data show that it is a weak X-ray source and is weakly detected in the bluest of the UVOT filters. We conclude that BOKS 45906 is a cataclysmic variable with a period shorter than the `period-bounce' systems and therefore BOKS 45906 could be the first helium-rich cataclysmic variable detected in the Kepler field.
    Monthly Notices of the Royal Astronomical Society 11/2013; · 5.52 Impact Factor
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    ABSTRACT: We present the results of an analysis of data covering 1.5 years of the dwarf nova V447 Lyr. We detect eclipses of the accretion disk by the mass donating secondary star every 3.74 hrs which is the binary orbital period. V447 Lyr is therefore the first dwarf nova in the Kepler field to show eclipses. We also detect five long outbursts and six short outbursts showing V447 Lyr is a U Gem type dwarf nova. We show that the orbital phase of the mid-eclipse occurs earlier during outbursts compared to quiescence and that the width of the eclipse is greater during outburst. This suggests that the bright spot is more prominent during quiescence and that the disk is larger during outburst than quiescence. This is consistent with an expansion of the outer disk radius due to the presence of high viscosity material associated with the outburst, followed by a contraction in quiescence due to the accretion of low angular momentum material. We note that the long outbursts appear to be triggered by a short outburst, which is also observed in the super-outbursts of SU UMa dwarf novae as observed using Kepler.
    Monthly Notices of the Royal Astronomical Society 07/2012; 425(2). · 5.52 Impact Factor
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    ABSTRACT: We examine the Kepler light curves of V1504 Cyg and V344 Lyr, encompassing ~736 d at 1 min cadence. During this span each system exhibited ~64-65 outbursts, including six superoutbursts. We find that, in both systems, the normal outbursts between two superoutbursts increase in duration over time by a factor ~1.2-1.9, and then reset to a small value after the following superoutburst. In both systems the trend of quiescent intervals between normal outbursts is to increase to a local maximum about half way through the supercycle - the interval from one superoutburst to the next - and then to decrease back to a small value by the time of the next superoutburst. This is inconsistent with Osaki's thermal-tidal model, which predicts a monotonic increase in the quiescent intervals between normal outbursts during a supercycle. Also, most of the normal outbursts have an asymmetric, fast-rise/slower-decline shape, consistent with outbursts triggered at large radii. The exponential rate of decay of the plateau phase of the superoutbursts is 8 d/mag for V1504 Cyg and 12 d/mag for V344 Lyr. This time scale gives a direct measure of the viscous time scale in the outer accretion disk given the expectation that the entire disk is in the hot, viscous state during superoutburst. The resulting constraint on the Shakura-Sunyaev parameter, alpha_{hot} ~ 0.1, is consistent with the value inferred from the fast dwarf nova decays. By looking at the slow decay rate for superoutbursts, which occur in systems below the period gap, in combination with the slow decay rate in one long outburst above the period gap (in U Gem), we infer a steep dependence of the decay rate on orbital period for long outbursts. This implies a steep dependence of alpha_{cold} on orbital period, consistent with tidal torquing as being the dominant angular momentum transport mechanism in quiescent disks in interacting binary systems.
    The Astrophysical Journal 12/2011; 747(2). · 6.73 Impact Factor
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    ABSTRACT: We report on the analysis of the Kepler short-cadence (SC) light curve of V344 Lyr obtained during 2009 June 20 through 2010 Mar 19 (Q2--Q4). The system is an SU UMa star showing dwarf nova outbursts and superoutbursts, and promises to be a touchstone for CV studies for the foreseeable future. The system displays both positive and negative superhumps with periods of 2.20 and 2.06-hr, respectively, and we identify an orbital period of 2.11-hr. The positive superhumps have a maximum amplitude of ~0.25-mag, the negative superhumps a maximum amplitude of ~0.8 mag, and the orbital period at quiescence has an amplitude of ~0.025 mag. The quality of the Kepler data is such that we can test vigorously the models for accretion disk dynamics that have been emerging in the past several years. The SC data for V344 Lyr are consistent with the model that two physical sources yield positive superhumps: early in the superoutburst, the superhump signal is generated by viscous dissipation within the periodically flexing disk, but late in the superoutburst, the signal is generated as the accretion stream bright spot sweeps around the rim of the non-axisymmetric disk. The disk superhumps are roughly anti-phased with the stream/late superhumps. The V344 Lyr data also reveal negative superhumps arising from accretion onto a tilted disk precessing in the retrograde direction, and suggest that negative superhumps may appear during the decline of DN outbursts. The period of negative superhumps has a positive dP/dt in between outbursts.
    The Astrophysical Journal 08/2011; 741(2). · 6.73 Impact Factor
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    ABSTRACT: We discuss modifications we made to the public domain N -body/SPH code VINE in order to model accretion disks in cataclysmic variable systems.
    Journal of the Southeastern Association for Research in Astronomy. 07/2010;
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    ABSTRACT: The timing capabilities and sensitivity of Kepler, NASA's observatory to find Earth-sized planets within the habitable zone of stars, are well matched to the timescales and amplitudes of accretion disk variability in cataclysmic variables. This instrumental combination provides an unprecedented opportunity to test and refine stellar accretion paradigms with high-precision, uniform data, containing none of the diurnal or season gaps that limit ground-based observations. We present a 3-month, 1 minute cadence Kepler light curve of V344 Lyr, a faint, little-studied dwarf nova within the Kepler field. The light curve samples V344 Lyr during five full normal outbursts and one superoutburst. Surprisingly, the superhumps found during superoutburst continue to be detected during the following quiescent state and normal outburst. The fractional excess of superhump period over the presumed orbital period suggests a relatively high binary mass ratio in a system where the radius of the accretion disk must vary by less than 2% in order to maintain tidal precession throughout the extended episode of superhumping. Disk radius is less restricted if the quiescent signal identified tentatively as the orbital period is a negative superhump, generated by a retrograde-precessing accretion disk, tilted with respect to the binary orbital plane. Comment: ApJL, in press, 5 pages, 3 figures
    The Astrophysical Journal Letters 06/2010; · 6.35 Impact Factor
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    ABSTRACT: Negative superhumps in cataclysmic variable systems result when the accretion disc is tilted with respect to the orbital plane. The line of nodes of the tilted disc precesses slowly in the retrograde direction, resulting in a photometric signal with a period slightly less than the orbital period. We use the method of smoothed particle hydrodynamics to simulate a series of models of differing mass ratio and effective viscosity to determine the retrograde precession period and superhump period deficit $\varepsilon_-$ as a function of system mass ratio $q$. We tabulate our results and present fits to both $\varepsilon_-$ and $\varepsilon_+$ versus $q$, as well as compare the numerical results with those compiled from the literature of negative superhump observations. One surprising is that while we find negative superhumps most clearly in simulations with an accretion stream present, we also find evidence for negative superhumps in simulations in which we shut off the mass transfer stream completely, indicating that the origin of the photometric signal is more complicated than previously believed. Comment: 14 pages, 15 figures. Accepted for publication in MNRAS
    Monthly Notices of the Royal Astronomical Society 06/2009; · 5.52 Impact Factor
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    Matt A. Wood, D. Oswalt
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    ABSTRACT: Observationally, white dwarf stars are a remarkably homogeneous class with a minimum observed Teff ~ 4000 K. Theoretically, the physics that determines their cooling timescales is relatively more straightforward than that which determines main-sequence evolutionary timescales. As a result, the white dwarf luminosity function has for the last decade been used as a probe of the age and star formation rate of the Galactic disk, providing an estimated local disk age of ~10 Gyr with estimated total uncertainties of roughly 20%. A long-standing criticism of the technique is that the reality of the reported downturn in the luminosity function (LF) hinges on just a handful of stars and on statistical arguments that fainter (older) objects would have been observed were they present. Indeed, the likely statistical variations of these small-number samples represent one of the primary uncertainties in the derived Galactic age, and the behavior of Schmidt's 1/Vmax estimator in this limit is not well understood. In this work, we explore these uncertainties numerically by means of a Monte Carlo population synthesis code that simulates the kinematics and relative numbers of cooling white dwarfs. The "observationally selected" subsamples are drawn using typical proper motion and V-magnitude limits. The corresponding 1/Vmax LFs are then computed and compared to the input-integrated LFs. The results from our (noise-free) data suggest that (1) Schmidt's 1/Vmax technique is a reliable and well-behaved estimator of the true space density with typical uncertainties of ~50% for 50 point samples and 25% for 200 point samples; (2) the age uncertainties quoted in previously published observational studies of the LF are consistent with uncertainties in the Monte Carlo results—specifically, there is a ~15% and 10% observational uncertainty in the ages inferred from 50 point and 200 point samples, respectively; and (3) the large statistical variations in the bright end of these LFs—even in the large-N limit—preclude using the white dwarf LF to obtain an estimate of the recent star formation rate as a function of time.
    The Astrophysical Journal 01/2009; 497(2):870. · 6.73 Impact Factor
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    Matt A. Wood
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    ABSTRACT: The interacting binary white dwarf (AM CVn) systems HM Cnc and V407 have orbital periods of 5.4 min and 9.5 min, respectively. The two systems are characterized by an "on/off" behaviour in the X-ray light curve, and optical light curves that are nearly sinusoidal and which lead the X-ray light curves in phase by about 0.2 in both systems. Of the models that have been proposed to explain the observations, the one that seems to require the least fine tuning is the direct impact model of Marsh & Steeghs (2002). In this model, the white dwarf primary is large enough relative to the semi-major axis that the accretion stream impacts the surface of the primary white dwarf directly without forming an accretion disc. Marsh & Steeghs proposed that in this situation there could be a flow set up around the equator with a decreasing surface temperature the further one measured from the impact point. In this study, we estimate the light curves that might result from such a temperature distribution, and find them to be reasonable approximations to the observations. One unexpected result is that two distinct X-ray spots must exist to match the shape of the X-ray light curves. Comment: 9 Pages, 7 figures, MNRAS accepted for publication
    Monthly Notices of the Royal Astronomical Society 01/2009; · 5.52 Impact Factor
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    Matt A. Wood, Christopher J. Burke
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    ABSTRACT: It has been suspected for over 20 years that the observed negative superhumps in cataclysmic variables are due to the retrograde precession of a tilted disk. We present new smooth particle hydrodynamics simulation results that demonstrate that the source of the modulation of the luminosity of the light in a negatively superhumping cataclysmic variable is the transit of the bright spot across the face of an accretion disk that is tilted out of the orbital plane. In an untilted disk the bright spot is always located on the outer edge of the disk, and the intrinsic brightness of the accretion spot is constant for a disk at equilibrium. However, if the accretion disk is tilted out of the orbital plane and only slowly precessing in the inertial frame, then the bright spot will have this luminosity just twice per orbit as the accretion stream impacts the disk edge at the line of nodes. At other times, however, the accretion spot will transit across one face or the other of the tilted disk as the secondary star moves in orbit. Because the impact point is then deeper in the gravitational potential well of the primary white dwarf, the bright spot luminosity is correspondingly higher. Because only one face of the disk is visible in these optically thick disk systems, only one brightening per orbit is observed, and the slow retrograde precession of the tilted disk results in a period slightly shorter than the orbital period. We present simulation light curves and an animation to demonstrate these results.
    The Astrophysical Journal 12/2008; 661(2):1042. · 6.73 Impact Factor
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    Joshua Dolence, Matt A. Wood, Isaac Silver
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    ABSTRACT: The ultracompact binary systems V407 Vul (RX J1914.4+2456) and HM Cnc (RX J0806.3+1527) - a two-member subclass of the AM CVn stars - continue to pique interest because they defy unambiguous classification. Three proposed models remain viable at this time, but none of the three is significantly more compelling than the remaining two, and all three can satisfy the observational constraints if parameters in the models are tuned. One of the three proposed models is the direct impact model of Marsh & Steeghs (2002), in which the accretion stream impacts the surface of a rapidly-rotating primary white dwarf directly but at a near-glancing angle. One requirement of this model is that the accretion stream have a high enough density to advect its specific kinetic energy below the photosphere for progressively more-thermalized emission downstream, a constraint that requires an accretion spot size of roughly 1.2x10^5 km^2 or smaller. Having at hand a smoothed particle hydrodynamics code optimized for cataclysmic variable accretion disk simulations, it was relatively straightforward for us to adapt it to calculate the footprint of the accretion stream at the nominal radius of the primary white dwarf, and thus to test this constraint of the direct impact model. We find that the mass flux at the impact spot can be approximated by a bivariate Gaussian with standard deviation \sigma_{\phi} = 164 km in the orbital plane and \sigma_{\theta} = 23 km in the perpendicular direction. The area of the the 2\sigma ellipse into which 86% of the mass flux occurs is roughly 47,400 km^2, or roughly half the size estimated by Marsh & Steeghs (2002). We discuss the necessary parameters of a simple model of the luminosity distribution in the post-impact emission region. Comment: 24 pages, 5 figures, Accepted for publication in ApJ
    The Astrophysical Journal 05/2008; · 6.73 Impact Factor
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    Joshua V. Cardenzana, Matt A. Wood
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    ABSTRACT: Cataclysmic variable (CV) stars are close binary systems withtypically a white dwarf primary accreting from a low-mass main-sequencesecondary star. One useful technique to study these systemsobservationally is through time-series spectroscopy. We presentin this paper a method by which synthetic line profiles can be producedusing our CV modeling program FITDisk, which implements the method ofsmoothed particle hydrodynamics. Because we compute thevelocities and instantaneous energy dissipation (``luminosity'') of allthe particles in a simulation, it is relatively simple to synthesizeline profiles as a function of simulation time. In this work, wesimulated the accretion disk of a negatively superhumping CV, where theaccretion stream bright spot migrates in turn across the two faces of atilted, slowly-precessing accretion disk. We are then able toformat these data to observe how the emission line profiles change as afunction of viewing angle.
    Journal of the Southeastern Association for Research in Astronomy. 04/2008; 2:35-38.
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    ABSTRACT: We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 M. This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average Teff ~ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf stars tend to have a bimodal distribution with a second mass peak at ~1.0 M, which skews the mean toward a higher mass. Both the mean and individual white dwarf masses we report here are in better agreement with those determined from model atmosphere spectroscopic fits to line profiles than with most previous gravitational redshift studies of cool white dwarfs. Our results indicate that measurement biases and weak geocoronal emission lines in the observed spectra may have affected previous gravitational redshift measurements. These have been minimized in our study. We present measurements for some previously unobserved white dwarfs, as well as independent new measurements for some that have been reported in the literature. A list of complete space motions for 50 wide binary white dwarfs is presented, derived from radial velocity measurements of their nondegenerate companions. We find that the UVW space motions and dispersions of the common proper motion binaries that contain white dwarf components are consistent with those of old, metal-poor disk stars.
    The Astronomical Journal 12/2007; 121(1):503. · 4.97 Impact Factor
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    ABSTRACT: We report on two intermediate polar star systems, RX J1730-06 and RX J1803+40. We analyze a total of 97.4 hours of data for RX J1730-06 and 17.5 hours for the system RX J1803+40. We confirm previously reported spin periods (128 s and 25.4 min, respectively) and give a best-fit non-linear least-squares ephemeris for each.
    Journal of the Southeastern Association for Research in Astronomy. 08/2007; 1:24-27.
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    ABSTRACT: We present the software tool FITDisk, a precompiled-binary Windows GUI version of our smoothed particle hydrodynamics cataclysmic variable accretion disk research code. Cataclysmic variables are binary star systems in which a compact stellar remnant, typically a white dwarf star, is stripping mass from a lower-main-sequence companion star by way of an accretion disk. Typically the disk is the brightest component of the system, because the plasma is heated dramatically as it spirals down in the gravitational well of the primary white dwarf star. The shortest-period systems can display disk "superhump" oscillations driven by the rotating tidal field of the secondary star. FITDisk models these accretion disk phenomena using a fully three-dimensional hydrodynamics calculation, and data can be visualized as they are computed or stored to hard drive for later playback at a fast frame rate. Simulations are visualized using OpenGL graphics and the viewing angle can be changed interactively. Pseudo light curves of simulated systems can be plotted along with the associated Fourier amplitude spectrum. FITDisk is available for free download at www.astro.fit.edu/cv/fitdisk.html. Comment: 16 pages, 4 color figures, one line figure. Accepted for March 2006 issue of Publ. Ast. Soc. Pacific. v2: fixed a typo in the references
    Publications of the Astronomical Society of the Pacific 11/2005; · 3.69 Impact Factor
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    International Amateur-Professional Photoelectric Photometry Communications. 01/2005; 101:32-37.
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    International Amateur-Professional Photoelectric Photometry Communications. 01/2005; 101:11-17.
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    ABSTRACT: We report on the discovery of a 25.5-min superhump period for the suspected helium dwarf nova system KL Draconis in a high state. The presence of superhumps combined with the previously observed helium spectrum and large-amplitude photometric variations confirm that KL Dra is an AM CVn system similar to CR Bootis, V803 Cen and CP Eridani. We also find a low-state photometric period at 25.0 min that we suggest may be the orbital period. With this assumption, we estimate q=0.075, M1=0.76 M⊙ and M2=0.057 M⊙.
    Monthly Notices of the Royal Astronomical Society 06/2002; 334(1):87 - 93. · 5.52 Impact Factor
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    ABSTRACT: We present preliminary results from a three-dimensional smoothed particle hydrodynamics (SPH) simulation of an accretion disk in a low mass-ratio cataclysmic variable system representative of the SU UMa and AM CVn subclasses of dwarf novae. Using a simple ray-tracing scheme to identify ``surface'' particles as a function of viewing angle, we use the relative temperature distribution of these particles to estimate the particles' luminosities at a given timestep by convolving blackbody energy distributions with UBVRI filter response functions. These values are then corrected for limb-darkening and summed to produce pseudo-lightcurves and Fourier amplitude spectra which may be directly compared with observations. We find that the resulting amplitude spectra for inclination angles ila 45(deg) are dominated by the superhump frequency, but that linear combination frequencies of the superhump and orbital periods begin to dominate the amplitude spectrum for systems with higher inclination angles. These preliminary calculations suggest that the observed harmonic structure of superhump light curves may provide independent constraints on SU UMa and AM CVn system inclinations.
    Baltic Astronomy. 02/1998; 7:255-267.

Publication Stats

273 Citations
83.00 Total Impact Points

Institutions

  • 2013
    • Texas A&M University - Commerce
      • Department of Physics and Astronomy
      Commerce, Texas, United States
  • 1998–2011
    • Florida Institute of Technology
      • Department of Physics and Space Sciences
      Melbourne, Florida, United States
  • 2010
    • National Optical Astronomy Observatory
      Tucson, Arizona, United States
  • 2008
    • University of Illinois, Urbana-Champaign
      • Department of Astronomy
      Urbana, Illinois, United States