14930266
Evidence for Polar Jets as Precursors of Polar Plume Formation
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI are utilized to study polar coronal jets and plumes. The study focuses on the temporal evolution of both structures and their relationship. The data sample, spanning 2007 April 7-8, shows that over 90% of the 28 observed jet events are associated with polar plumes. EUV images (STEREO/SECCHI) show plume haze rising from the location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV jets, with the plume haze appearing minutes to hours after the jet was observed. The remaining jets occurred in areas where plume material previously existed, causing a brightness enhancement of the latter after the jet event. Short-lived, jetlike events and small transient bright points are seen (one at a time) at different locations within the base of preexisting long-lived plumes. X-ray images also show instances (at least two events) of collimated thin jets rapidly evolving into significantly wider plumelike structures that are followed by the delayed appearance of plume haze in the EUV. These observations provide evidence that X-ray jets are precursors of polar plumes and in some cases cause brightenings of plumes. Possible mechanisms to explain the observed jet and plume relationship are discussed.
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.
119207648
SOLIS vector spectromagnetograph: status and science
The Vector Spectromagnetograph (VSM) instrument has recorded photospheric and chromospheric magnetograms daily since August 2003. Full-disk photospheric vector magnetograms are observed at least weekly and, since November 2006, area-scans of active regions daily. Quick-look vector magnetic images, plus X3D and FITS formated files, are now publicly available daily. In the near future, Milne-Eddington inversion parameter data will also be available and a typical observing day will include three full-disk photospheric vector magnetograms. Besides full-disk observations, the VSM is capable of high temporal cadence area-scans of both the photosphere and chromosphere. Carrington rotation and daily synoptic maps are also available from the photospheric magnetograms and coronal hole estimate images.
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.
118533577
Solar-Cycle Characteristics Examined in Separate Hemispheres: Phase, Gnevyshev Gap, and Length of Minimum
According to research results from solar-dynamo models, the northern and southern hemispheres may evolve separately throughout the solar cycle. The observed phase lag between the northern and southern hemispheres provides information regarding how strongly the hemispheres are coupled. Using hemispheric sunspot-area and sunspot-number data from Cycles 12 – 23, we determine how out of phase the separate hemispheres are during the rising, maximum, and declining period of each solar cycle. Hemispheric phase differences range from 0 – 11, 0 – 14, and 2 – 19 months for the rising, maximum, and declining periods, respectively. The phases appear randomly distributed between zero months (in phase) and half of the rise (or decline) time of the solar cycle. An analysis of the sunspot cycle double peak, or Gnevyshev gap, is conducted to determine if the double-peak is caused by the averaging of two hemispheres that are out of phase. We confirm previous findings that the Gnevyshev gap is a phenomenon that occurs in the separate hemispheres and is not due to a superposition of sunspot indices from hemispheres slightly out of phase. Cross hemispheric coupling could be strongest at solar minimum, when there are large quantities of magnetic flux at the Equator. We search for a correlation between the hemispheric phase difference near the end of the solar cycle and the length of solar-cycle minimum, but found none. Because magnetic flux diffusion across the Equator is a mechanism by which the hemispheres couple, we measured the magnetic flux crossing the Equator by examining Kitt Peak Vacuum Telescope and SOLIS magnetograms for Solar Cycles 21 – 23. We find, on average, a surplus of northern hemisphere magnetic flux crossing during the mid-declining phase of each solar cycle. However, we find no correlation between magnitude of magnetic flux crossing the Equator, length of solar minima, and phase lag between the hemispheres.
123436253
First running experience with the laser calibration system of the UA1 central detector
Abstract We report on a UA1 technical run made with four nitrogen lasers mounted on the UA1 Central Detector during the 1987 proton-antiproton collider run. With only moderate laser power ( 2 ) and the help of gas seeding (1 ppb of tetra-methyl-phenylene-diamine [TMPD]) straight 2 m calibration tracks can be produced. The unexpected effect of track fading under high luminosity conditions was observed. A model is presented explaining this phenomenon, which is based on the removal of neutral TMPD molecules from the drift volume via positive ion charge exchange.
123150136
Observation of jet structure in high pT events at the ISR and the importance of parton transverse momentum
Abstract Events with a charged particle of high transverse momentum were studied in pp collisions at √s = 52.5 GeV with the Split Field magnet (SFM) at the CERN-ISR, triggering on a charged particle of pT > 2 GeV/c, in the c.m. angular region θ ≅ 20° and θ ≅ 45°. The results provide further evidence for jet-like structure in high pT reactions. One of two produced jets is associated with the triggering hadron whereas the other is produced at an azimuthal angle that differs from that of the trigger by roughly 180°. The main features of the data are found to agree with the predictions of a simple parton-parton hard scattering model with vector gluon exchange, provided that one allows for partons in the proton to have transverse momentum. The ingredients of the model are all derived from data on deep inelastic lepton-proton scattering and from hadron production in e+e− annihilation. The model retains a simple pT−4 dependence for the parton-parton scattering. However, for pT ≲ 4GeV/c, the transverse movement of partons yields an approximate pT−8 scaling for the inclusive hadron distribution in agreement with observations. For the understanding of our data, it is found to be essential to take into account the soft component arising from the fragmentation of the spectator partons into hadrons.
119928689
A measurement of the inclusive cross section of charged pions at very high transverse momenta
Abstract The inclusive cross sections for the production of high transverse momentum π + and π − mesons in proton-proton interactions have been measured at the highest ISR energy √ s = 63 GeV and at a c.m. production angle of 50°. The cross sections for π + and π − mesons are compared as a function of transverse momentum. It is shown that the inclusive cross section of π − mesons decreases faster than the π + cross section. particle σ ( π ± )/ σ (charged particles) are presented as a function of transverse momentum.
122138775
Further investigation of beauty baryon production at the ISR
Abstract A recent publication by Basile et al. claims evidence for a hadronic state with beauty flavour, Λ b → D 0 p π − , produced in pp collisions at √ s =63 GeV. We report a negative result from an experiment which has used the same detector and has a significantly higher sensitivity. In addition we show that neither experiment can observe such a signal, the data available being about two orders of magnitude below the minimum required.
117842992
Quantum Number Effects in Events With a Charged Particle of Large Transverse Momentum. Part 2. Charge Correlations in Jets
Abstract Charge correlations of particles in an event with a large p T triggering particle have been investigated applying a new method, which has been developed for non-diffractive inelastic hadronic events. The correlation length for charge compensation of the fragments of the hard scattered partons and of the spectators, respectively, are equal to that one in normal inelastic events. Part of the charge of the high p T trigger particle is compensated by the soft particles of the “away jet”. These results support the idea that the rearrangement of quantum numbers in quark fragmentation shows a universal behaviour.