15555548
Alignment of Silicon tracking systems R&D on Semitransparent Microstrip Sensors
We summarize the R&D activities on a novel semitransparent microstrip sensor to be used on laser-based alignment systems for silicon trackers. The new sensor is used both for particle tracking and laser detection. The aim of this research line is to increase the optical transmittance (T) of Silicon microstrips detectors to infrared light, introducing minor modifications to the sensor design still suitable for its industrial production. The optical simulations used in the sensor design have been experimentally validated against several patterned material samples. This activities have been carried out in the context of SiLC collaboration for the next International Linear Collider.
139842026
Test Results of the Semi-transparent Amorphous Silicon Sensors for the Link System of CMS
119795166
2D position sensitive microstrip sensors with charge division along the strip: Studies on the position measurement error
Abstract Position sensitivity in semiconductor detectors of ionizing radiation is usually achieved by the segmentation of the sensing diode junction in many small sensing elements read out separately as in the case of conventional microstrips and pixel detectors. Alternatively, position sensitivity can be obtained by splitting the ionization signal collected by one single electrode amongst more than one readout channel with the ratio of the collected charges depending on the position where the signal was primary generated. Following this later approach, we implemented the charge division method in a conventional microstrip detector to obtain position sensitivity along the strip. We manufactured a proof-of-concept demonstrator where the conventional aluminum electrodes were replaced by slightly resistive electrodes made of strongly doped poly-crystalline silicon and being readout at both strip ends. Here, we partially summarize the laser characterization of this first proof-of-concept demonstrator with special emphasis on the study on how the different noise sources are affecting the device position error along the strip.
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.
122960849
Gamma irradiation of semitransparent amorphous silicon sensors
Abstract Semitransparent amorphous silicon sensors are the key elements for laser light 2D position reconstruction in the CMS alignment system. Some of them have to work in very extreme radiation environment. We have irradiated with gammas, up to 10 MRad, two different sensors and measured their change in performance.
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.
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.
18775872
TW Hydrae: evidence of stellar spots instead of a Hot Jupiter
Context. TW Hya is a classical T Tauri star that shows significant radial-velocity variations in the optical regime. These variations have been attributed to a 10 MJup planet orbiting the star at 0.04 AU. Aims. The aim of this letter is to confirm the presence of the giant planet around TW Hya by (i) testing whether the observed RV variations can be caused by stellar spots and (ii) analyzing new optical and infrared data to detect the signal of the planet companion. Methods. We fitted the RV variations of TW Hya using a cool spot model. In addition, we obtained new high-resolution optical & infrared spectra, together with optical photometry of TW Hya and compared them with previous data. Results. Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54 ◦ can reproduce the reported RV variations. The model also predicts a bisector semi-amplitude variation <10 m s −1 , which is less than the errors of the RV measurements discussed in Setiawan et al. (2008, Nature, 451, 38). The analysis of our new optical RV data, with typical errors of 10 m s −1 , shows a larger RV amplitude that varies depending on the correlation mask used. A slight correlation between the RV variation and the bisector is also observed although not at a very significant level. The infrared H-band RV curve is almost flat, showing a small variation (<35 m s −1 ) that is not consistent with the published optical orbit. All these results support the spot scenario rather than the presence of a hot Jupiter. Finally, the photometric data shows a 20% (peak to peak) variability, which is much larger than the 4% variation expected for the modeled cool spot. The fact that the optical data are correlated with the surface of the cross-correlation function points towards hot spots as being responsible for the photometric variability. Conclusions. We conclude that the best explanation for the RV signal observed in TW Hya is the presence of a cool stellar spot and not an orbiting hot Jupiter.
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.
119545603
Astrometric confirmation of a wide low‐mass companion to the planet host star HD 89744
In our ongoing deep infrared imaging search for faint wide secondaries of planet-candidate host stars we have confirmed astrometrically the companionship of a low-mass object to be co-moving with HD 89744, a companion-candidate suggested already by Wilson et al. (2000). The derivation of the common proper motion of HD 89744 and its companion, which are separated by 62.996±0.035 arcsec, is based on about 5 year epoch difference between 2MASS and our own UKIRT/UFTI images. The companion effective temperature is about 2200K and its mass is in the range between 0.072 and 0.081M⊙, depending on the evolutionary model. Therefore, HD 89744 B is either a very low mass stellar or a heavy brown dwarf companion. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
55465692
Isotropy and Marginally Trapped Surfaces in a Spacetime
In this paper we shall study the notions of an isotropic and marginally trapped surface in a spacetime by using a differential geometric approach. We first consider spacelike isotropic surfaces in a Lorentzian manifold and, in particular, in a four-dimensional spacetime, where the isotropy function appears to be determined by the mean curvature vector field of the surface. Explicit examples of isotropic marginally outer trapped surfaces are given in the standard four-dimensional space forms: Minkowski, de Sitter and anti-de Sitter spaces. Then we prove rigidity theorems for complete spacelike 0-isotropic surfaces without flat points in these standard space forms. As a consequence, we also obtain characterizations of complete spacelike isotropic marginally trapped surfaces in these backgrounds.