First measurement of interference fragmentation on a transversely polarized hydrogen target

The HERMES experiment has measured for the first time single target-spin asymmetries in semi-inclusive two-pion production using a transversely polarized hydrogen target. These asymmetries are related to the product of two unknowns, the transversity distribution function and the interference fragmentation function. In the invariant mass range 0.51 GeV < M_inv < 0.97 GeV the measured asymmetry deviates significantly from zero, indicating that two-pion semi-inclusive deep-inelastic scattering can be used to probe transversity.Comment: 6 pages, 6 figures, contribution to the proceedings of the International Workshop on Transverse Polarisation Phenomena in Hard Processes (Transversity 2005), Como, Italy, Sep 7 - 10, 200

Spatially Resolved Stellar Kinematics of Field Early-Type Galaxies at z=1: Evolution of the Rotation Rate

We use the spatial information of our previously published VLT/FORS2 absorption line spectroscopy to measure mean stellar velocity and velocity dispersion profiles of 25 field early-type galaxies at a median redshift z=0.97 (full range 0.6<z<1.2). This provides the first detailed study of early-type galaxy rotation at these redshifts. From surface brightness profiles from HST imaging we calculate two-integral oblate axisymmetric Jeans equation models for the observed kinematics. Fits to the data yield for each galaxy the degree of rotational support and the mass-to-light ratio M/L_Jeans. S0 and Sa galaxies are generally rotationally supported, whereas elliptical galaxies rotate less rapidly or not at all. Down to M(B)=-19.5 (corrected for luminosity evolution), we find no evidence for evolution in the fraction of rotating early-type (E+S0) galaxies between z=1 (63+/-11%) and the present (61+/-5%). We interpret this as evidence for little or no change in the field S0 fraction with redshift. We compare M/L_Jeans with M/L_vir inferred from the virial theorem and globally averaged quantities and assuming homologous evolution. There is good agreement for non-rotating (mostly E) galaxies. However, for rotationally supported galaxies (mostly S0) M/L_Jeans is on average ~40% higher than M/L_vir. We discuss possible explanations and the implications for the evolution of M/L between z=1 and the present and its dependence on mass.Comment: To appear in ApJ 683 (9 pages, 7 figures). Minor changes included to match published versio

Lessons from the Milky Way: the Kapteyn Universe

Jacobus Cornelius Kapteyn (1851-1922) presented a model for the distribution of stars in space together with a dynamical interpretation in terms of an equilibrium between the gravitational field of the stars and their random motion and rotation. In the vertical direction Kapteyn's results are substantially correct. Usually the Kapteyn Universe is described as being flawed due to neglect of interstellar absorption. Kapteyn was led to adopt this on the basis of widely accepted evidence by Shapley on an absence of reddening of stars in globular clusters. But another, equally important misconception was Kapteyn's interpretation of the two Star Streams as manifestations of two groups of stars rotating around a center in opposite directions. This was supported by the observation of very different mixes in stellar types in the two streams. Had Kapteyn adopted the absorption as he himself had determined it he would not have been able to arrive at a consistent picture.Comment: To appear in LESSONS FROM THE LOCAL GROUP: A Conference in Honour of David Block and Bruce Elmegreen, eds. Freeman, K.C., Elmegreen, B.G., Block, D.L.and Woolway, M., Springer: New Yor

The stars and gas in outer parts of galaxy disks: Extended or truncated -- flat or warped?

I review observations of truncations of stellar disks and models for their origin, compare observations of truncations in moderately inclined galaxies to those in edge-on systems and discuss the relation between truncations and HI-warps and their systematics and origin. Truncations are a common feature in edge-on stellar disks, but the relation of truncations in face-on to those in edge-on galaxies needs further clarification. The origin of truncations is most likely related to a maximum in the specific angular momentum in the material that formed the stellar disks, but this model does probably require some redistribution of angular momentum. HI-warps start just beyond the truncation radius and disks and warps appear distinct components. This suggests that inner disks form initially and settle as rigid, very flat structures, while HI-warps result from later infall of gas with a different orientation of the angular momentum.Comment: Invited Review at the Vatican Symposium: Formation and Evolution of Galaxy Disks, October 2007, proceeding editors Jose G. Funes, SJ and Enrico M. Corsin

Design of a 30 GHz bragg reflector for a Raman FEL

A design of a Bragg reflector for a Raman FEL is described. It is shown that mode conversion occurs whenever the axial wavenumbers of the two modes fulfil the Bragg condition. With a constant ripple of the corrugation it is shown that the reflected radiation also contains higher order modes, assuming that the incident radiation consists only of a TE11 mode. The mode purity can be increased by increasing the length of the reflector at the expense of a smaller reflection bandwidth. A more flexible method is by applying a Hamming window to the corrugation of the reflector. Contributions of other modes to the reflected radiation can in that case be neglected. The reflector will be installed in a Raman laser to be able to compare the amplifier with the oscillator configuration. Therefore some preliminary results are also presented about the start-up of the Raman laser