Whole Earth Telescope Observations of the Helium Interacting Binary PG 1346+082 (CR Bootis)

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670 ± 0.004 μHz and 669.887 ± 0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency power\u27s amplitude and frequency structure on overall system magnitude. We discuss these findings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity

Diffuse glioma growth: a guerilla war

In contrast to almost all other brain tumors, diffuse gliomas infiltrate extensively in the neuropil. This growth pattern is a major factor in therapeutic failure. Diffuse infiltrative glioma cells show some similarities with guerilla warriors. Histopathologically, the tumor cells tend to invade individually or in small groups in between the dense network of neuronal and glial cell processes. Meanwhile, in large areas of diffuse gliomas the tumor cells abuse pre-existent “supply lines” for oxygen and nutrients rather than constructing their own. Radiological visualization of the invasive front of diffuse gliomas is difficult. Although the knowledge about migration of (tumor)cells is rapidly increasing, the exact molecular mechanisms underlying infiltration of glioma cells in the neuropil have not yet been elucidated. As the efficacy of conventional methods to fight diffuse infiltrative glioma cells is limited, a more targeted (“search & destroy”) tactic may be needed for these tumors. Hopefully, the study of original human glioma tissue and of genotypically and phenotypically relevant glioma models will soon provide information about the Achilles heel of diffuse infiltrative glioma cells that can be used for more effective therapeutic strategies

Astronomical Photoelectric Photometry for Undergraduate Research

Many college physics departments would welcome the opportunity to initiate a modest research program which could involve their undergraduate students. Astronomical photoelectric phot.ometry is a field in which it is possible to int'tiale a 'IJ.$ef ul undergradoote oriented research program with relatively modest equiprnent, some of which can commcmly be found in a college phyl>ics department. A sketch of the equipment necessary, opportunities, and challenges in this work are presented

Impact of Space Weather on the Natural Night Sky

In 2018, Solar Cycle 24 entered a deep solar minimum. During this period, we collected night sky brightness data at Cosmic Campground International Dark Sky Sanctuary (CCIDSS) in the USA (2018 September 4-2019 January 4) and at Aotea/Great Barrier Island International Dark Sky Sanctuary (AGBIIDSS) in New Zealand (2018 March 26-August 31. These sites have artificial-light-pollution-free natural night skies. The equipment employed are identical Unihedron SQM-LU-DL meters, used as single-channel differential photometers, to scan the sky as Earth rotates on its axis. We have developed new analysis techniques which select those data points which are uninfluenced by Sun, Moon, or clouds to follow brightness changes at selected points on the celestial sphere and to measure the brightness of the airglow above its quiescent level. The 2018 natural night sky was measured to change in brightness by approximately 0.9 mag arcsec(-2) at both locations. Preliminary results indicate the modulations of the light curves (brightness versus R.A.) we observed are related in complex ways to elements of space weather conditions in the near-Earth environment. In particular, episodes of increased night sky brightness are observed to be contemporaneous with geomagnetic activity, increases in mean solar wind speed, and some solar proton/electron fluence events. Charged particles in the solar wind take days to reach near-Earth environment after a coronal hole is observed to be facing in our direction. Use of this information could make it possible to predict increases in Earth's natural night sky brightness several days in advance. What we have learned during this solar minimum leads us to search for other solar driven changes in night sky brightness as the Sun begins to move into solar maximum conditions.12 month embargo; published online: 10 October 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Whole Earth Telescope observations of the helium interacting binary PG 1346+082 (CR bootis)

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670±0.004 μHz and 669.887±0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency powerÏs amplitude and frequency structure on overall system magnitude. We discuss these Ðndings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity

Whole earth telescope observations of the interacting binary white dwarf v803 cen in its low state

Using a network of observatories in the southern hemisphere, high-speed photometry of the interacting binary white dwarf (IBWD) V803 Cen in its low state is presented. Because of the faintness of the system, the 1611-s oscillation, reported in previous studies when V803 Cen was near maximum, was difficult to distinguish from the noise in many of the individual high-speed photometric runs; it was, however, unambiguously detected in combinations of runs. No evidence for the presence of either its harmonics or the previously observed 175-s oscillation was found. Low state optical spectroscopy of V803 Cen confirmed the presence of weak He emission lines which had been suspected in an earlier study. The line profiles showed evidence of doubling, typical of an accretion disc, and varied in strength, possibly correlated with system luminosity. The breadths of the emission lines were similar to those of the He absorption lines seen near maximum, suggesting that the same mechanism, Stark broadening, is responsible. The He emission-line strengths indicate that the lines are optically thick and their weakness at times suggests that the continuum is nearly optically thick; the construction of detailed hydrogen-deficient disc models to account for these properties is urged

Whole earth telescope observations of the interacting binary white dwarf v803 cen in its low state

Using a network of observatories in the southern hemisphere, high-speed photometry of the interacting binary white dwarf (IBWD) V803 Cen in its low state is presented. Because of the faintness of the system, the 1611-s oscillation, reported in previous studies when V803 Cen was near maximum, was difficult to distinguish from the noise in many of the individual high-speed photometric runs; it was, however, unambiguously detected in combinations of runs. No evidence for the presence of either its harmonics or the previously observed 175-s oscillation was found. Low state optical spectroscopy of V803 Cen confirmed the presence of weak He emission lines which had been suspected in an earlier study. The line profiles showed evidence of doubling, typical of an accretion disc, and varied in strength, possibly correlated with system luminosity. The breadths of the emission lines were similar to those of the He absorption lines seen near maximum, suggesting that the same mechanism, Stark broadening, is responsible. The He emission-line strengths indicate that the lines are optically thick and their weakness at times suggests that the continuum is nearly optically thick; the construction of detailed hydrogen-deficient disc models to account for these properties is urged

Whole Earth Telescope observations of the helium interacting binary PG 1346+082 (CR bootis)

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670±0.004 μHz and 669.887±0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency powerÏs amplitude and frequency structure on overall system magnitude. We discuss these Ðndings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity