18035202
Dust emissivity in the submm/mm SCUBA and SIMBA observations of Barnard 68
We have observed the dark cloud Barnard 68 with SCUBA at 850  μ m and with SIMBA at 1.2 mm. The submillimetre and millimetre dust emission correlate well with the extinction map of Alves et al. (2001). The A V /850  μ m correlation is clearly not linear and suggests lower temperatures for the dust in the inner core of the cloud. Assuming a model for the temperature gradient, we derive the cloud-averaged dust emissivities (normalised to the V -band extinction efficiency) at 850  μ m and 1.2 mm. We find $\kappa_{850~\mu{\rm m}}/\kappa_{\rm V}=4.0\pm 1.0\times 10^{-5}$ and $\kappa_{1.2~{\rm mm}}/\kappa_{\rm V}=9.0\pm 3.0\times 10^{-6}$. These values are compared with other determinations in this wavelength regime and with expectations for models of diffuse dust and grain growth in dense clouds.
14748555
Possible signature of hypernova nucleosynthesis in a beryllium‐rich halo dwarf★
As part of a large survey of halo and thick disc stars, we found one halo star, HD 106038, exceptionally overabundant in beryllium. In spite of its low metallicity, [Fe/H]=−1.26, the star has log(Be/H) =−10.60, which is similar to the solar meteoritic abundance, log(Be/H) =−10.58. This abundance is more than 10 times higher the abundance of stars with similar metallicity and cannot be explained by models of chemical evolution of the Galaxy that include the standard theory of cosmic ray spallation. No other halo star exhibiting such a beryllium overabundance is known. In addition, overabundances of Li, Si, Ni, Y and Ba are also observed. We suggest that all these chemical peculiarities, excepting the Ba abundance, can be simultaneously explained if the star was formed in the vicinity of a hypernova.
119561246
Formation of OB associations in galaxies
We consider the formation of OB associations from two perspectives: (1) the fractional gas consumption in star formation, , per dynamical timescale tdyn in a galaxy, and (2) the origin of the so-called Kennicutt-Schmidt law, that the rate of star formation per unit area is proportional to a power, α, of the surface density in H I and H2 gas when certain thresholds are crossed. The empirical findings that ≈ 10-2 and α ≈ 1.4 or 1.5 have simple explanations if the rate of star formation is magnetically regulated. An empirical test of the ideas resides in an analysis of why giant OB associations are "strung out like pearls along the arms" of spiral galaxies.
15769380
Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A
Context. Magnetic fields are believed to play a crucial role in the process of star formation. Aims. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores. Methods. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response. Results. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 M� ,o f age 9× 10 4 yr, formed in a cloud with an initial mass-to-flux ratio ∼2 times the critical value. Conclusions. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields control the evolution and collapse of the molecular cloud cores from which stars form.
18590
The Chemistry of the early universe
The process of molecule formation in the primor- dial gas is considered in the framework of Friedmann cosmo- logical models from redshift z =1 0 4 to z =0 . First, a com- prehensive analysis of 87 gas phase reaction rates (both col- lisional and radiative) relevant in the physical environment of the expanding universe is presented and critically discussed. On this basis, calculations are carried out of the abundance of 21 molecular species as function of redshift, for different values of the cosmological parameters 0, and H0, evaluating con- sistently the molecular heating and cooling due to H2 ,H D and LiH molecules. One of the major improvements of this work is the use of a better treatment of H recombination that leads to a reduction of a factor 2-3 in the abundance of electrons and H + at freeze-out, with respect to previous studies. The lower residual ionization has a negative effect on the chemistry of the primordial gas in which electrons and protons act as cat- alysts in the formation of the first molecules. We find that in the standard model (h =0 :67, 10 =4 :5, 0 =1 and (D/H) =4 :3 10 5 ), the residual fractional ionization at z =1 is (e= H) =3 :0210 4 , and the main molecular species fractional abundances (H2= H) =1 :1 10 6 , (HD=H 2 )=1 :1 10 3 , (HeH + = H) =6 :2 10 13 , (LiH + = H) =9 :4 10 18 and (LiH=LiH + )=7 :6 10 3 . We devise a reduced chemical network that reproduces with excellent accuracy the numerical results of the complete model and allows to follow the chemical compositions and the thermal properties of a primordial gas in the presence of an external radiation field. Finally, we provide accurate cooling functions of H2, HD and LiH in a wide range of density and temperature that can be conveniently used in a variety of cosmological applications.
53662238
MAGNETIC INTERACTIONS IN PRE-MAIN-SEQUENCE BINARIES
Young stars typically have strong magnetic fields, so that the magnetospheres of newly formed close binaries can interact, dissipate energy, and produce synchrotron radiation. The V773 Tau A binary system, a pair of T Tauri stars with a 51 day orbit, displays such a signature, with peak emission taking place near periastron. This paper proposes that the observed emission arises from the change in energy stored in the composite magnetic field of the system. We model the fields using the leading order (dipole) components and show that this picture is consistent with current observations. In this model, the observed radiation accounts for a fraction of the available energy of interaction between the magnetic fields from the two stars. Assuming antisymmetry, we compute the interaction energy E int as a function of the stellar radii, the stellar magnetic field strengths, the binary semimajor axis, and orbital eccentricity, all of which can be measured independently of the synchrotron radiation. The variability in time and energetics of the synchrotron radiation depend on the details of the annihilation of magnetic fields through reconnection events, which generate electric fields that accelerate charged particles, and how those charged particles, especially fast electrons, are removed from the interaction region. However, the major qualitative features are well described by the background changes in the global magnetic configuration driven by the orbital motion. The theory can be tested by observing a collection of pre-main-sequence binary systems.
110639465
The LHCb Run Control
LHCb has designed and implemented an integrated Experiment Control System. The Control System uses the same concepts and the same tools to control and monitor all parts of the experiment: the Data Acquisition System, the Timing and the Trigger Systems, the High Level Trigger Farm, the Detector Control System, the Experiment's Infrastructure and the interaction with the CERN Technical Services and the Accelerator. LHCb's Run Control, the main interface used by the experiment's operator, provides access in a hierarchical, coherent and homogeneous manner to all areas of the experiment and to all its sub-detectors. It allows for automated (or manual) configuration and control, including error recovery, of the full experiment in its different running modes. Different instances of the same Run Control interface are used by the various sub-detectors for their stand-alone activities: test runs, calibration runs, etc. The architecture and the tools used to build the control system, the guidelines and components provided to the developers, as well as the first experience with the usage of the Run Control will be presented
109848273
The high-voltage monitor system for the calorimeter of the OBELIX experiment
Abstract We describe the monitor system developed to manage the high voltage power supply for the electromagnetic calorimeter of the OBELIX experiment, installed on the LEAR facility at CERN. The hardware and software characteristics of the system are discussed, as well as the performance of the same.
121570479
Compatibility and possible implications of the experimental results on solar neutrinos
Abstract The effect of varying the assumed value of the cross-section for the proton-proton fusion weak reaction of the solar cycle on the solar neutrino problem is discussed. It is shown that an increase of about 20% of the relevant astrophysical factor fields compatibility (within the present experimental accuracy) of the available results with theory and among themselves.
67702235
The Task Manager for the LHCb On-Line Farm
119804456
Multiplicity and energy trigger for a sampling electromagnetic calorimeter
Abstract We describe the trigger system for the electromagnetic calorimeter of the OBELIX experiment operating at the LEAR ring at CERN. The system has been studied mainly for multiplicity trigger on gamma rays, but energy and angular selections can also be performed. The designing criteria, the electronics performances, as well as the measured trigger capability to select some exclusive reactions are reported.