8 research outputs found
Thermal constraints on the reionisation of hydrogen by population-II stellar sources
Measurements of the intergalactic medium (IGM) temperature provide a
potentially powerful constraint on the reionisation history due to the thermal
imprint left by the photo-ionisation of neutral hydrogen. However, until
recently IGM temperature measurements were limited to redshifts 2 < z < 4.8,
restricting the ability of these data to probe the reionisation history at z >
6. In this work, we use recent measurements of the IGM temperature in the
near-zones of seven quasars at z ~ 5.8 - 6.4, combined with a semi-numerical
model for inhomogeneous reionisation, to establish new constraints on the
redshift at which hydrogen reionisation completed. We calibrate the model to
reproduce observational constraints on the electron scattering optical depth
and the HI photo-ionisation rate, and compute the resulting spatially
inhomogeneous temperature distribution at z ~ 6 for a variety of reionisation
scenarios. Under standard assumptions for the ionising spectra of population-II
sources, the near-zone temperature measurements constrain the redshift by which
hydrogen reionisation was complete to be z > 7.9 (6.5) at 68 (95) per cent
confidence. We conclude that future temperature measurements around other high
redshift quasars will significantly increase the power of this technique,
enabling these results to be tightened and generalised.Comment: 15 pages, 8 figures, accepted for publication in MNRA
A copper-benzotriazole based coordination polymer catalyzes the efficient one-pot synthesis of (N'-substituted)-hydrazo-4-aryl-1,4-dihydropyridines from azines
A series of new (N’-substituted)-hydrazo-4-aryl-1,4 dihydropyridines were successfully synthesized via a facile one pot catalytic pathway utilizing azines and propiolate esters as starting materials and 1D Cu benzotriazoles based coordination polymer as catalyst. In the absence of catalyst, the corresponding 5-substituted 4,5-dihydro pyrazoles were formed in moderate to high yields. Fine-tuning the catalysts allowed us to gain more insights regarding the plausible reaction mechanism
Solar parameters for modeling interplanetary background
The goal of the Fully Online Datacenter of Ultraviolet Emissions (FONDUE)
Working Team of the International Space Science Institute in Bern, Switzerland,
was to establish a common calibration of various UV and EUV heliospheric
observations, both spectroscopic and photometric. Realization of this goal
required an up-to-date model of spatial distribution of neutral interstellar
hydrogen in the heliosphere, and to that end, a credible model of the radiation
pressure and ionization processes was needed. This chapter describes the solar
factors shaping the distribution of neutral interstellar H in the heliosphere.
Presented are the solar Lyman-alpha flux and the solar Lyman-alpha resonant
radiation pressure force acting on neutral H atoms in the heliosphere, solar
EUV radiation and the photoionization of heliospheric hydrogen, and their
evolution in time and the still hypothetical variation with heliolatitude.
Further, solar wind and its evolution with solar activity is presented in the
context of the charge exchange ionization of heliospheric hydrogen, and in the
context of dynamic pressure variations. Also the electron ionization and its
variation with time, heliolatitude, and solar distance is presented. After a
review of all of those topics, we present an interim model of solar wind and
the other solar factors based on up-to-date in situ and remote sensing
observations of solar wind. Results of this effort will further be utilised to
improve on the model of solar wind evolution, which will be an invaluable asset
in all heliospheric measurements, including, among others, the observations of
Energetic Neutral Atoms by the Interstellar Boundary Explorer (IBEX).Comment: Chapter 2 in the planned "Cross-Calibration of Past and Present Far
UV Spectra of Solar System Objects and the Heliosphere", ISSI Scientific
Report No 12, ed. R.M. Bonnet, E. Quemerais, M. Snow, Springe