Lewis M. Cook
A5003912605- Astrophysical Phenomena and Observations
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Stellar, planetary, and galactic studies
- Pulsars and Gravitational Waves Research
- High-pressure geophysics and materials
- Astronomy and Astrophysical Research
- Astrophysics and Cosmic Phenomena
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Mechanics and Biomechanics Studies
- Particle Accelerators and Free-Electron Lasers
- earthquake and tectonic studies
- Laser-Plasma Interactions and Diagnostics
- Adaptive optics and wavefront sensing
- Galaxies: Formation, Evolution, Phenomena
- Earthquake Detection and Analysis
- Astro and Planetary Science
- Pharmaceutical Practices and Patient Outcomes
- Health Systems, Economic Evaluations, Quality of Life
- Magnetic confinement fusion research
- Radioactivity and Radon Measurements
- Particle physics theoretical and experimental studies
- Pelvic and Acetabular Injuries
- Environmental Monitoring and Data Management
American Association of Variable Star Observers
2004-2022
Helix (United States)
2000-2019
Concord Hospital
2018
Backyard Brains (United States)
2002-2016
Catholic Biblical Association
2002-2003
Texas Department of State Health Services
1975
United States Department of State
1975
We report on successes and failures in searching for positive superhumps cataclysmic variables, show the superhumping fraction as a function of orbital period. Basically, all short-period systems do, long-period don't, 50% success rate is found at P_orb=3.1+-0.2 hr. can use this to measure critical mass ratio creation superhumps. With mass-radius relation appropriate an assumed mean white-dwarf 0.75 M_sol, we find q_crit=0.35+-0.02. also superhump studies several stars independently known...
Abstract We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution superhump is found to be composed three distinct stages: an early evolutionary stage with a longer period, middle varying periods, final shorter, stable period. During stage, systems periods less than 0.08 d show positive derivatives. present observational characteristics these stages give greatly improved...
We report the results of a worldwide campaign to observe WZ Sagittae during its 2001 superoutburst. After 23 yr slumber at V = 15.5, star rose within 2 days peak brightness 8.2, and showed main eruption lasting 25 days. The return quiescence was punctuated by 12 small eruptions, ∼1 mag amplitude day recurrence time; these "echo outbursts" are uncertain origin, but somewhat resemble normal outbursts dwarf novae. 52 days, began slow decline quiescence.
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 102 SU UMa-type dwarf novae observed mainly during 2014-2015 season and characterized these objects. Our has greatly improved statistics distribution orbital periods, which is a good approximation cataclysmic variables at terminal evolutionary stage, confirmed presence period minimum 0.053 d spike just above this period. The number density monotonically decreased toward longer...
We report on time-series photometric observations in the earliest stages of superoutbursts extreme dwarf novae, AL Com and WZ Sge, which started 2001 May after 6 years quiescence July 23 quiescence, respectively. detected growth "early superhumps" during each rising stage. Our reject mass transfer instability for trigger superoutburst Sge stars, show existence some relations between spiral structure, gives a hint origin superhumps."
Abstract Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 128 SU UMa-type dwarf novae observed mainly during 2015–2016 season and characterized these objects. The data have improved distribution orbital periods, relation between period variation superhumps, variations rebrightening type in WZ Sge-type Coupled with new measurements mass ratios using growing stages now a clearer statistically greatly evolutionary path near...
We report the results of long observing campaigns on two novalike variables: V442 Ophiuchi and RX J1643.7+3402. These stars have high‐excitation spectra, complex line profiles signifying mass loss at particular orbital phases, similar periods (respectively, 0.12433 0.12056 days). They are well‐credentialed members SW Sex class cataclysmic variables. Their light curves also quite complex. Oph shows periodic signals with 0.12090(8) 4.37(15) days, J1643.7+3402 0.11696(8) 4.05(12) days....
Abstract Since its discovery in 2008, the Andromeda galaxy nova M31N 2008-12a has been observed eruption every single year. This unprecedented frequency indicates an extreme object, with a massive white dwarf and high accretion rate, which is most promising candidate for single-degenerate progenitor of Type Ia supernova known to date. The previous three eruptions have displayed remarkably homogeneous multiwavelength properties: (i) from faint peak, optical light curve declined rapidly by two...
We report precise measures of the orbital and superhump period in twenty more dwarf novae. For ten stars, we new confirmed spectroscopic periods - signifying P_o as well P_sh. These are GX Cas, HO Del, HS Vir, BC UMa, RZ Leo, KV Dra, KS TU Crt, QW Ser, Sge. remaining ten, a medley P_sh measurements from photometry; most new, with some confirmations previous values. And, LL WX Cet, MM Hya, AO Oct, V2051 Oph, NY KK Tel, HV RX J1155.4-5641. Periods, usual, can be measured to high accuracy,...
Abstract We discovered an optical counterpart of about 13 mag a soft X-ray transient, XTE J1118+480 on 2000 March 30. performed astrometry and provided accurate position R.A. = 11h18m10s.85, Decl. +48°02′12″.9. The outbursting object has been identified with 18.8 star in the USNO catalog. Our pre-discovery data shows another outburst during January, again coinciding detected X-rays. Through CCD time-series photometry, we found presence periodic variation amplitude 0.055 period 0.17078 ±...
We present optical photometry of six intermediate polars that exhibit transitions to a low-flux state. For four these systems, DW Cnc, V515 And, V1223 Sgr and RX J2133.7+5107, we are able perform timing analysis in out the low states. find that, for Cnc dominant periodicities light curves change as flux decreases, indicating sources' accretion properties they transition variability is almost completely quenched at lowest flux, but do not evidence changing geometry. temporal state, see period...
We report the results of a long campaign time series photometry on nova-like variable UX Ursae Majoris during 2015. It spanned 150 nights, with ∼ 1800 h coverage 121 separate nights. The star was in its normal 'high state' near magnitude V = 13, slow waves light curve and eclipses every 4.72 h. Remarkably, also showed nearly sinusoidal signal full amplitude 0.44 mag period 3.680 ± 0.007 d. interpret this as signature retrograde precession (wobble) accretion disc. same is manifest ±33 s...
We observed the 2015 July-August long outburst of V1006 Cyg and established this object to be an SU UMa-type dwarf nova in period gap. Our observations have confirmed that is second showing three types outbursts (normal, normal superoutbursts) after TU Men. succeeded recording growing stage superhumps (stage A superhumps) obtained a mass ratio 0.26-0.33, which close stability limit tidal instability. This identification demonstrated indeed slowly grow systems near limit, idea first...
We report photometry of the helium‐dominated cataclysmic variable HP Librae during 1995–2001. The main photometric signal varies between 1118.89 and 1119.14 s, on a timescale few years, displays waveform characteristic "superhumps." After subtracting signal, we found weak residual at 1102.70 ± 0.05 which interpret as underlying orbital period binary. full amplitude this putative variation is just 0.005 mag, weakest yet in (CV). 1119 s Lib superb match to well‐studied 1051 superhump AM CVn,...
YY Draconis (likely the same variable called DO Draconis) is one of a small number intermediate polars (IPs) that show outburst behavior. We report results from Target Opportunity observations with Rossi X-Ray Timing Explorer, together ground-based optical photometry during outbursts in 1999 September and 2000 November. Similar behavior was evident both outbursts. At outburst, X-ray flux increased by more than factor 12, spectrum became hotter absorbed compared to quiescence. While spin...
We present an analysis of photometric observations the eclipsing novalike variable DW UMa made by CBA consortium between 1999 and 2015. Analysis 372 new 260 previously published eclipse timings reveals a 13.6 yr period or quasi-period in times minimum light. The seasonal light curves show complex spectrum periodic signals: both positive negative 'superhumps', likely arising from prograde apsidal precession retrograde nodal accretion disc. These signals appear most prominently famously as...
The cataclysmic variable ASAS J002511+1217.2 was discovered in outburst by the All‐Sky Automated Survey (ASAS) 2004 September, and intensively monitored AAVSO observers through following 2 months. Both photometry spectroscopy indicate that this is a very short period system. Clearly defined superhumps with of 0.05687 ± 0.00001 (1 σ) days (81.9 minutes) are present during superoutburst, 5 to 18 detection. We observe change superhump profile similar transition "late superhumps" observed other...
We report photometric and spectroscopic observations of the nova‐like variable V751 Cygni. The radial velocities indicate an underlying binary period 0.1445(2) day; long‐term cycle count is not firmly decided, but best choice implies a 0.144464(1) day. star shows moderately low excitation spectrum with transient P Cygni absorption suggestive wind origin, occasionally seen in cataclysmic variables accreting at high rate. Curiously, appears correlated phase our two most extensive data sets. A...
An intensive photometric-observation campaign of the recently discovered SU UMa-type dwarf nova, Var73 Dra was conducted from 2002 August to 2003 February. We caught three superoutbursts in October, December and The recurrence cycle superoutburst (supercycle) is indicated be ~60 d, shortest among values known so far UMa stars close those ER stars. superhump periods measured during first two were 0.104885(93) 0.10623(16) respectively. A 0.10424(3)-d periodicity detected quiescence. change...
We present optical multi-colour photometry of V404 Cyg during the outburst from December, 2015 to January, 2016 together with simultaneous X-ray data. This occurred less than 6 months after previous in June-July, 2015. These two outbursts were a slow rise and rapid decay-type showed large-amplitude ($\sim$2 mag) short-term ($\sim$10 min-3 hours) variations even at low luminosity (0.01-0.1$L_{\rm Edd}$). found correlated $\sim$1 hour time intervals performed Bayesian delay estimations between...
After 10 years of quiescence, HV Vir underwent a superoutburst in January 2002. We report time-series observations clearly revealing the period change ordinary superhumps during superoutburst. derived mean superhump 0.058260 d and positive derivative $7 \times 10^{-5}$. These results are good agreement with value obtained from 1992 also detected early superhumps, which were not recognized past outburst, possible rebrightening. Both them common characteristics WZ Sge-type stars.
DV Ursae Majoris is a deeply eclipsing dwarf nova which shows very powerful superhumps when it attains superoutburst. We report detailed observations of the 1997 and 1999 eruptions. Some results reproduce what has been learned from other novae: that disk becomes large in outburst, develop few days, remain strong even after shrunk by more than 30%. The mean superhump period was 0.08870(8) day, but both eruptions decreased with P˙ ≈ -6 × 10-5. Globally distributed coverage eruption revealed...
Continuing the project described by Kato et al. (2009, arXiv:0905.1757), we collected times of superhump maxima for 127 SU UMa-type dwarf novae observed mainly during 2016--2017 season and characterized these objects. We provide updated statistics relation between orbital period variation superhumps, variations rebrightening type in WZ Sge-type obtained minimum 0.05290(2)d confirmed presence gap above ~0.09d. note that four objects (NY Her, 1RXS J161659.5+620014, CRTS J033349.8-282244 SDSS...