This paper describes a series of experiments which were carried out during the main operations of LISA Pathfinder. These experiments were performed by modulating the power of the measurement and ...reference beams. In one series of experiments the beams were sequentially switched on and off. In the other series of experiments the powers of the beams were modulated within 0.1% and 1% of the constant power. These experiments use recordings of the total power measured on the photodiodes to infer the properties of the Optical Metrology System (OMS), such as reflectivities of the test masses and change of the photodiode efficiencies with time. In the first case the powers are back propagated from the different photodiodes to the same place on the optical bench to express the unknown quantities in the measurement with the complimentary photodiode measurements. They are combined in the way that the only unknown left is the test mass reflectivities. The second experiment compared two estimates of the force applied to the test masses due to the radiation pressure that appears because of the beam modulations. One estimate of the force is inferred from the measurements of the powers on the photodiodes and propagation of this measurement to the test masses. The other estimation of the force is done by calculating it from the change in the main scientific output of the instrument - differential displacement of the two test masses.
On board LISA Pathfinder spacecraft the test mass displacement along the main measurement axis is sensed in two different ways: optically and electrostatically. We have monitored the relative ...calibration between the two measurements during the mission science phase. The trend sensitivity of the relative calibration has been computed for different physical parameters, such as temperature, magnetic field, test mass bias voltage and current.
Low-power, ultra-high-vacuum compatible, non-contacting position sensors with nanometer resolution and centimeter dynamic range have been developed, built and tested. They have been designed at Virgo ...as the sensors for low-frequency modal damping of Seismic Attenuation System chains in Gravitational Wave interferometers and sub-micron absolute mirror positioning. One type of these linear variable differential transformers (LVDTs) has been designed to be also insensitive to transversal displacement thus allowing 3D movement of the sensor head while still precisely reading its position along the sensitivity axis. A second LVDT geometry has been designed to measure the displacement of the vertical seismic attenuation filters from their nominal position
. Unlike the commercial LVDTs, mostly based on magnetic cores, the LVDTs described here exert no force on the measured structure.
Seismic isolation by mechanical filters at very low frequencies Bougleux, E; Braccini, S; Bradaschia, C ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/1998, Letnik:
409, Številka:
1-3
Journal Article
Recenzirano
The VIRGO SuperAttenuator is a complex six-degrees of freedom remote-controlled mechanism that isolates a 80kg payload from environmental perturbations, such as the seismic noise. It consists of a ...Pre-Isolator stage, a chain of mechanical filters and a last stage, holding the payload. The Pre-Isolator and the filters are essentially harmonic oscillators with a low resonant frequency. The filters are designed to work below 500mHz in all degrees of freedom. During the last year, a Pre-Isolator with resonant frequencies of 30mHz in three degrees of freedom has been engineered and built. Intensive studies on the long-term spring behaviour have been performed to find a metal suitable to be stressed up to 1kN/mm2 with no evidence of creep.
Infrared spectroscopy of T Tauri stars GIOVANARDI, C; GENNARI, S; NATTA, A ...
The Astrophysical journal,
01/1991, Letnik:
367, Številka:
1
Journal Article
Recenzirano
The hydrogen-sodium diagnostic method is applied to a sample of 134 T Tauri stars of low luminosity, and the luminosity of Pa-beta, Br-gamma, and Br-alpha are measured. This method permits the ...physical conditions in the inner regions of winds to be determined with useful accuracy. The results show that a restricted range of T(g), between 5000 and 7000 K, and of mass loss rate, between 10 to the -8th and 10 to the -7th solar mass/yr, is populated by several luminous T Tauri stars. It seems likely that the ejection of cold and neutral atomic winds represents a common phase of the premain sequence evolution of low-mass stars. 36 refs.
Narrow-band H-alpha images and long-slit spectroscopy of the Seyfert galaxy NGC 985 are presented. Large-scale extended ionized zones are seen to cover a significant fraction of the ring of this ...object. These ionized zones are responsible for a considerable fraction (greater than 35 percent) of the far-infrared emission of NGC 985. These ionized zones are interpreted as giant H II region complexes, formed in a recent burst of star formation. It is also argued that that starburst was triggered by a galaxy interaction. 41 refs.
Modeling an accretion disk in NGC 985 STANGA, R. M; RODRIGUEZ ESPINOSA, J. M; MANNUCCI, F
The Astrophysical journal,
10/1991, Letnik:
379, Številka:
2
Journal Article
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