53608040
Characteristics of Magnetohydrodynamic Oscillations Observed with the Michelson Doppler Imager
We report on the spatial distribution of the magnetogram oscillatory power and the phase angles between velocity and magnetogram signals as observed with the Michelson Doppler Imager. The data set is 15125 × 15125, containing the sunspot from 1997 December 2 with a temporal sampling interval of 60 s and spatial sampling of 0605. The simultaneously observed continuum intensity and surface velocity accompany the magnetic information. We focus on three frequency regimes: 0.5-1.0, 3.0-3.5, and 5.5-6.0 mHz, corresponding roughly to timescales of magnetic evolution, p-modes, and the 3 minute resonant sunspot oscillation. Significant low-frequency magnetogram power is found in lower flux pixels, 100-300 G, in a striking ring with filamentary structure surrounding the sunspot. The 5 minute magnetogram power peaks in extended regions of flux that measure 600-800 G. The 3 minute oscillation is observed in the sunspot umbra in pixels whose flux measures 1300-1500 G. Phase angles of approximately -90° between velocity and magnetic flux in the 3.0-3.5 and 5.5-6.0 mHz regimes are found in regions of significant cross amplitude.
15630684
The Solar Oxygen Crisis: Probably Not the Last Word
In this work we present support for recent claims that advocate a downward revision of the solar oxygen abundance. Our analysis employs spatially resolved spectropolarimetric observations including the Fe I lines at 6302 A and the O I infrared triplet around 7774 A in the quiet Sun. We used the Fe I lines to reconstruct the three-dimensional thermal and magnetic structure of the atmosphere. The simultaneous O I observations were then employed to determine the abundance of oxygen at each pixel, using both LTE and non-LTE (NLTE) approaches to the radiative transfer. In this manner, we obtain values of log O = 8.63 (NLTE) and 8.93 (LTE) dex. We find an unsettling fluctuation of the oxygen abundance over the field of view. This is likely an artifact indicating that, even with this relatively refined strategy, important physical ingredients are still missing in the picture. By examining the spatial distribution of the abundance, we estimate realistic confidence limits of approximately 0.1 dex.
119279122
Recovering Joy’s Law as a Function of Solar Cycle, Hemisphere, and Longitude
Bipolar active regions in both hemispheres tend to be tilted with respect to the East–West Equator of the Sun in accordance with Joy’s law, which describes the average tilt angle as a function of latitude. Mt. Wilson Observatory data from 1917 – 1985 are used to analyze the active-region tilt angle as a function of solar cycle, hemisphere, and longitude, in addition to the more common dependence on latitude. Our main results are as follows: i) We recommend a revision of Joy’s law towards a weaker dependence on latitude (slope of 0.13 – 0.26) and without forcing the tilt to zero at the Equator. ii) We determine that the hemispheric mean tilt value of active regions varies with each solar cycle, although the noise from a stochastic process dominates and does not allow for a determination of the slope of Joy’s law on an 11-year time scale. iii) The hemispheric difference in mean tilt angles, 1.1∘±0.27, over Cycles 16 to 21 was significant to a three-σ level, with average tilt angles in the Northern and Southern hemispheres of 4.7∘±0.26 and 3.6∘±0.27, respectively. iv) Area-weighted mean tilt angles normalized by latitude for Cycles 15 to 21 anticorrelate with cycle strength for the southern hemisphere and whole-Sun data, confirming previous results by Dasi-Espuig et al. (Astron. Astrophys.518, A7, 2010). The Northern Hemispheric mean tilt angles do not show a dependence on cycle strength. v) Mean tilt angles do not show a dependence on longitude for any hemisphere or cycle. In addition, the standard deviation of the mean tilt is 29 – 31∘ for all cycles and hemispheres, indicating that the scatter is due to the same consistent process even if the mean tilt angles vary.
121498142
Observation of charmed D meson production in pp collisions
Abstract Evidence for the forward production of D + mesons has been found in pp collisions at a c.m. energy of 52.5 GeV. A signal of 92 ± 18 events above background has been observed in the decay channel D + → K ∗ o π + → K − π + π + . The cross section in the phase space region of our experiment is given and implications for the total cross section for charmed D meson production are discussed.
125139127
Proposal to measure the rare decay K+ ---> pi+ nu anti-nu at the CERN SPS
61490538
Data acquisition using the 168/E
Event sizes and data rates at the CERN i>p collider compose a formidable environ- ment for a high level trigger. A system using three 168/~ processors for experiment UAl real-time event selection is described. With 168/E data memory expanded to 512K bytes, each processor holds a complete event allowing a FORTRAN trigger al- gorithm access to data from the entire detector. A smart CAMAC interface reads five Remus branches in parallel transferring one word to the target processor every 0.5 ps. The NORD host computer can simultaneously read an accepted event from another processor.
116379925
RECENT RESULTS FROM THE UA1 COLLABORATION AT THE CERN PROTON - ANTI-PROTON COLLIDER