Search Publications
The fundamental parameters of the roAp star HD 24712. A rapidly oscillator at the red edge of the instability strip
Shulyak, D.; ten Brummelaar, T. A.; Perraut, K. +4 more
Context. There is still a debate about the nature of the mechanism that causes the pulsation excitation of the rapidly oscillating Ap stars that oscillate above the highest theoretically acoustic frequency. HD 24712 is a good test case for such a study because it is bright, its parallax accurately determined, and its frequency spectrum is well kno…
Stellar twins determine the distance of the Pleiades
Casey, Andrew R.; Hawkins, Keith; Jofré, Paula +5 more
Since the release of the Hipparcos catalogue in 1997, the distance to the Pleiades open cluster has been heavily debated. The distance obtained from Hipparcos and those by alternative methods differ by 10 to 15%. As accurate stellar distances are key to understanding stellar structure and evolution, this dilemma puts the validity of some stellar e…
On improving the accuracy of electron density profiles obtained at high altitudes by the ionospheric sounder on the Mars Express spacecraft
Gurnett, D. A.; Němec, F.; Morgan, D. D.
We attempt to improve the standard inversion routine used to obtain electron density profiles from the data measured by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) topside radar sounder on board the Mars Express spacecraft. Artificial ionospheric traces corresponding to how the MARSIS instrument would see model electro…
Solar Energetic Particle Event Associated with the 2012 July 23 Extreme Solar Storm
Wang, Rui; Yang, Zhongwei; Liu, Ying D. +3 more
We study the solar energetic particle (SEP) event associated with the 2012 July 23 extreme solar storm, for which Solar Terrestrial Relations Observatory (STEREO) and the spacecraft at L1 provide multi-point remote sensing and in situ observations. The extreme solar storm, with a superfast shock and extremely enhanced ejecta magnetic fields observ…
Hemispheric asymmetry in the near-Venusian magnetotail during solar maximum
Zhang, T. L.; Baumjohann, W.; Xiao, S. D.
During solar minimum the near-Venusian magnetotail exhibits a hemispheric asymmetry in the cross-tail field distribution. It implies that the magnetic field lines in the -E hemisphere are wrapped more tightly around Venus than in the +E hemisphere. Therefore, a strong field reversal region occurs in the magnetotail, which is prone to the magnetic …
Multi-wavelength Study of a Delta-spot. I. A Region of Very Strong, Horizontal Magnetic Field
Jaeggli, S. A.
Active region NOAA 11035 appeared in 2009 December, early in the new solar activity cycle. This region achieved a delta sunspot (δ spot) configuration when parasitic flux emerged near the rotationally leading magnetic polarity and traveled through the penumbra of the largest sunspot in the group. Both visible and infrared imaging spectropolarimetr…
Decay of Activity Complexes, Formation of Unipolar Magnetic Regions, and Coronal Holes in Their Causal Relation
Golubeva, E. M.; Mordvinov, A. V.
The peculiar development of solar activity in the current cycle resulted in an asynchronous reversal of the Sun's polar fields. The asymmetry is also observed in the formation of polar coronal holes. A stable coronal hole was first formed at the South Pole, despite the later polar-field reversal there. The aim of this study is to understand the pr…
Coronal magnetic field profiles from shock-CME standoff distances
Gopalswamy, N.; Cairns, Iver H.; Yashiro, S. +1 more
Coronagraphs observe coronal mass ejections (CMEs) and driven shocks in white light images. From these observations the shock's speed and the shock's standoff distance from the CME's leading edge can be derived. Using these quantities, theoretical relationships between the shock's Alfvénic Mach number MA and standoff distance, and empirical radial…
Investigating the Origin of Hot Gas Lines in Herbig Ae/Be Stars
Johns-Krull, Christopher M.; Cauley, P. Wilson
We analyze high-resolution UV spectra of a small sample of Herbig Ae/Be stars (HAEBESs) in order to explore the origin of the T ∼ 105 K gas in these stars. The C IV λ λ1548, 1550 line luminosities are compared to nonsimultaneous accretion rate estimates for the objects showing C IV emission. We show that the correlation between L C…
CO2 pressure broadening and shift coefficients for the 2-0 band of 12C16O
Vandaele, A. C.; Vander Auwera, J.; Hashemi, R. +3 more
Fourier transform absorption spectra of the 2-0 band of 12C16O mixed with CO2 have been recorded at total pressures from 156 to 1212 hPa and at 4 different temperatures between 240 K and 283 K. CO2 pressure-induced line broadening and line shift coefficients, and the temperature dependence of the former …