123499216
New silicon microstrip detectors optimized for tracker alignment
The resolution of tracking systems based on layers of silicon microstrips is comparable to the stability of the structures on which they are mounted. Environmental changes during operation will misalign the modules out of their nominal positions. A straight laser beam that sequentially traverses consecutive layers of microstrips can be used as an artificial track to align them. For such a laser track to reach the last sensor, high transmittance of microstrips to infrared (IR) light is needed. We have simulated the passage of a coherent beam of light through a microstrip detector and identified the minimum set of changes to the design that boosts its transmittance. The simulation has been validated against real microstrip detector samples.
26141595
First investigation of a novel 2D position-sensitive semiconductor detector concept
This paper presents a first study of the performance of a novel 2D position-sensitive microstrip detector, where the resistive charge division method was implemented by replacing the metallic electrodes with resistive electrodes made of polycrystalline silicon. A characterization of two proof-of-concept prototypes with different values of the electrode resistivity was carried out using a pulsed Near Infra-Red laser. The experimental data were compared with the electrical simulation of the sensor equivalent circuit coupled to simple electronics readout circuits. The good agreement between experimental and simulation results establishes the soundness of resistive charge division method in silicon microstrip sensors and validates the developed simulation as a tool for the optimization of future sensor prototypes. Spatial resolution in the strip length direction depends on the ionizing event position. The average value obtained from the protype analysis is close to 1.2% of the strip length for a 6 MIP signal.
120425236
Effect of neutron and gamma-ray irradiation on the transmittance power of glasses and glues
Abstract LHC, working at the expected nominal luminosity, will induce an extremely high irradiation in the CMS experiment. The CMS alignment system uses optical elements to build the laser beams paths. Optical properties of basic components such as glasses and glues may result affected and their transmission power may degrade significantly. We have proceeded to a first test of various glasses and glues and identified some of them that can stand up to 150 kGy of gamma-rays plus 5×10 14 neutrons / cm 2 .
120520890
Silicon microstrip detectors for future tracker alignment systems
Abstract The next experiments at particles colliders will demand stability of the tracking systems to the level of few microns. The available technology cannot provide a supporting structure able to guarantee this degree of stability in working condition, when environmental changes will misalign the detectors out of their nominal position. Based on the successful experience of AMS and CMS tracker systems, we propose to use infrared laser beams traversing consecutive layers of silicon detectors to align them with respect to the beams. For such a laser track to reach the last sensor, high transmittance of microstrip sensors to infrared (IR) light is needed. We simulated the passage of a coherent beam of light through a microstrips detector and we identified the minimum set of changes to the design and technology that boost its transmittance while still respecting its tracking capabilities. The first prototypes are in process at IMB-CNM clean room facilities. We held the fabrication process at an intermediate step and we performed the first measurements of transmittance and reflectance on the sensors.
27640748
Radiation resistance of double-type double-sided 3D pixel sensors
The proposed high-luminosity upgrade of the Large Hadron Collider is expected to increase the instantaneous luminosity at the experiments' interaction points by a factor of ten. The vertex detector will be the subsystem most affected by the luminosity increase, raising substantially their occupancy and radiation-induced damage. To preserve the vertex physics performance under these new conditions, current pixel technologies have to be improved. Hybrid pixel sensors with double-sided double-type vertical electrodes (3D sensors) are becoming a mature technology for the detector layers closest to the interaction point due to their intrinsic radiation hardness. In addition, the double-sided implementation of the 3D pixel technology provides some additional technical advantages with respect to the singlesided implementation. For this study, 3D pixel sensors manufactured at the Centro Nacional de Microelectronica of Barcelona (IMB-CNM) have been bonded to the PSI46 readout chip currently used by the Compact Muon Solenoid vertex detector. Detector performance before and after irradiation up to fluences of 5 � 10 15 neq=cm2 is presented.
123257317
PERFORMANCE TEST OF THE CMS LINK ALIGNMENT SYSTEM
Abstract A first global test of the CMS Alignment System was performed at the I4 hall of the CERN ISR tunnel. Positions of the network, reproducing a set of points in the CMS detector monitored by the Link System, were reconstructed and compared to survey measurements. Spatial and angular reconstruction precisions reached in the present experimental set-up are already close to the CMS requirements.
15140780
Eclipses by circumstellar material in the T Tauri star AA Tau II. Evidence for non-stationary magnetospheric accretion ?
We report the results of a synoptic study of the photometric and spectroscopic variability of the classical T Tauri star AA Tau on timescales ranging from a few hours to several weeks. The AA Tau light curve had been previously shown to vary with a 8.2 d period, exhibiting a roughly constant brightness level, interrupted by quasi-cyclic fading episodes, which we interpreted as recurrent eclipses of the central star by the warped inner edge of its accretion disk (Bouvier et al. 1999). Our observations show the system is dynamic and presents non-stationary variability both in the photometry and spectroscopy. The star exhibits strong emission lines that show substantial variety and variability in their profile shapes and fluxes. Emission lines such as H and H show both infall and outflow signatures and are well reproduced by magnetospheric accretion models with moderate mass accretion rates (10 8 10 9 M yr 1 ) and high inclinations (i 60). The veiling shows variations that indicate the presence of 2 rotationally modulated hot spots corresponding to the two magnetosphere poles. It correlates well with the Hei line flux, with B V and the V excess flux. We have indications of a time delay between the main emission lines (H ,H and Hei) and veiling, the lines formed farther away preceding the veiling changes. The time delay we measure is consistent with accreted material propagating downwards the accretion columns at free fall velocity from a distance of about 8 R?. In addition, we report periodic radial velocity variations of the photospheric spectrum which might point to the existence of a 0.02 M object orbiting the star at a distance of 0.08 AU. During a few days, the eclipses disappeared, the variability of the system was strongly reduced and the line fluxes and veiling severely depressed. We argue that this episode of quiescence corresponds to the temporary disruption of the magnetic con- figuration at the disk inner edge. The smooth radial velocity variations of inflow and outflow diagnostics in the H profile yield further evidence for large scale variations of the magnetic configuration on a timescale of a month. These results may provide the first clear evidence for large scale instabilities developping in T Tauri magnetospheres as the magnetic field lines are twisted by dierential rotation between the star and the inner disk.The interaction between the inner accretion disk and the stellar magnetosphere thus appears to be a highly dynamical and time dependent process.
10656237
Rotation periods of Post-T Tauri stars in Lindroos systems
We present a rotational study of Post-T Tauri stars (PTTSs) in Lindroos systems, defined as binaries with early type primaries on the main-sequence (MS) and late-type secondaries on the pre-main-sequence (PMS) phase. The importance of this study in comparison with previous ones is that the Lindroos sample is not X-ray selected so we avoid a possible bias towards fast rotators. In this preliminary study we have monitored eleven stars in the UBVRI bands during two campaigns of ten consecutive nights each. Eight of the observed PTTSs show periodic modulations in their lightcurves and the derived periods range from 1.9 d to 8.0 d. The comparison of these results with theoretical rotational tracks based on disk-star locking theory shows that star-disk decoupling times of 1−20 Myr could reproduce the rotational properties of the targets, assuming an initial rotation period of ∼ 8d and a mass of 1M� . We have studied the rotation-activity relations of Lindroos PTTSs and compared them with those found in other groups of PMS and zero-age main-sequence (ZAMS) ∼1 Mstars. The Lindroos sample displays activity-rotation relations very similar to those found in TTSs. It contains a mixture of very active stars, with LX/Lbol ratios close to the saturation level of -3, and less active (unsaturated) stars. This could be the result of different star-disk decoupling times. Future monitoring of a larger and unbiased sample of PTTS will be important to confirm the significance of these results.
118556816
The stellar content of the young open cluster Trumpler 37
With an apparent cluster diameter of 1.5° and an age of 4 Myr, Trumpler 37 is an ideal target for photometric monitoring of young stars as well as for the search of planetary transits, eclipsing binaries and other sources of variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and 2011 to obtain a comprehensive view of variable phenomena in this region. In this first paper we present the cluster properties and membership determination as derived from an extensive investigation of the literature. We also compared the coordinate list to some YETI images. For 1872 stars we found literature data. Among them 774 have high probability of being member and 125 a medium probability. Based on infrared data we re-calculate a cluster extinction of 0.9–1.2 mag. We can confirm the age and distance to be 3–5 Myr and870 pc. Stellar masses are determined from theoretical models and the mass function is fitted with a power-law index of α = 1.90 (0.1–0.4 M⊙) and α = 1.12 (1–10 M⊙). (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
17255900
CONSTRAINTS ON A SECOND PLANET IN THE WASP-3 SYSTEM*
There have been previous hints that the transiting planet WASP-3b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity (RV) measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The RV data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period.
119477379
The weak-line T Tauri star V410Tau I. A multi-wavelength study of variability
We present the results of an intensive coordinated monitoring campaign in the optical and X-ray wavelength ranges of the low-mass, pre-main sequence star V410Tau carried out with the aim to study the relation between various indicators for magnetic activity that probe emission from different atmospheric layers: optical photometric star spot (rotation) cycle, chromospheric Halpha emission, and coronal X-rays. Two X-ray pointings were carried out with the Chandra satellite simultaneously with the optical observations, and centered near the maximum and minimum levels of the optical lightcurve. A relation of their different count levels to the rotation period of the dominating spot is not confirmed by a third Chandra observation carried out some months later, during another minimum of the 1.87d cycle. Similarly we find no indications for a correlation of the Halpha emission with the spots' rotational phase. The extraordinary stability of the largest spot is confirmed by long-term photometric and radial velocity measurements. Joining our optical photometry with previous data we provide a new estimate for the dominant periodicity of V410Tau. This updated value removes systematic offsets of the time of minimum observed in data taken over the last decade. Furthermore, the combination of the new data with published measurements taken during the last decade allows us to examine long-term changes in the mean light level of the photometry of V410Tau. A variation on the timescale of 5.4yr is suggested. Assuming that this behavior is truely cyclic V410Tau is the first pre-main sequence star on which an activity cycle is detected.