169 research outputs found
Transfer of autocollimator calibration for use with scanning gantry profilometers for accurate determination of surface slope and curvature of state of the art x ray mirrors
X ray optics, desired for beamlines at free electron laser and diffraction limited storage ring x ray light sources, must have almost perfect surfaces, capable of delivering light to experiments without significant degradation of brightness and coherence. To accurately characterize such optics at an optical metrology lab, two basic types of surface slope profilometers are used the long trace profilers LTPs and nanometer optical measuring NOM like angular deflectometers, based on electronic autocollimator AC ELCOMAT 3000. The inherent systematic errors of the instrument s optical sensors set the principle limit to their measuring performance. Where autocollimator of a NOM like profiler may be calibrated at a unique dedicated facility, this is for a particular configuration of distance, aperture size, and angular range that does not always match the exact use in a scanning measurement with the profiler. Here we discuss the developed methodology, experimental set up, and numerical methods of transferring the calibration of one reference AC to the scanning AC of the Optical Surface Measuring System OSMS , recently brought to operation at the ALS Xray Optics Laboratory. We show that precision calibration of the OSMS performed in three steps, allows us to provide high confidence and accuracy low spatial frequency metrology and not print into measurements the inherent systematic error of tool in use. With the examples of the OSMS measurements with a state of the art x ray aspherical mirror, available from one of the most advanced vendors of X ray optics, we demonstrate the high efficacy of the developed calibration procedure. The results of our work are important for obtaining high reliability data, needed for sophisticated numerical simulations of beamline performance and optimization of beamline usage of the optics. This work was supported by the U. S. Department of Energy under contract number DE AC02 05CH1123
Interference of an array of atom lasers
We report on the observation of interference of a series of atom lasers. A
comb-like array of coherent atomic beams is generated by outcoupling atoms from
distinct Bose-Einstein condensates confined in the independent sites of a
mesoscopic optical lattice. The observed interference signal arises from the
spatial beating of the overlapped atom laser beams, which is sampled over a
vertical region corresponding to 2 ms of free fall time. The average relative
de Broglie frequency of the atom lasers was measured.Comment: 3 figure
Development of a new generation of optical slope measuring profiler
A collaboration, including all DOE synchrotron labs, industrial vendors of x-ray optics, and with active participation of the HBZ-BESSY-II optics group has been established to work together on a new slope measuring profiler -- the optical slope measuring system (OSMS). The slope measurement accuracy of the instrument is expected to be<50 nrad for the current and future metrology of x-ray optics for the next generation of light sources. The goals were to solidify a design that meets the needs of mirror specifications and also be affordable; and to create a common specification for fabrication of a multi-functional translation/scanning (MFTS) system for the OSMS. This was accomplished by two collaborative meetings at the ALS (March 26, 2010) and at the APS (May 6, 2010)
Detection of orbital and superhump periods in Nova V2574 Ophiuchi (2004)
We present the results of 37 nights of CCD unfiltered photometry of nova
V2574 Oph (2004) from 2004 and 2005. We find two periods of 0.14164 d (~3.40 h)
and 0.14773 d (~3.55 h) in the 2005 data. The 2004 data show variability on a
similar timescale, but no coherent periodicity was found. We suggest that the
longer periodicity is the orbital period of the underlying binary system and
that the shorter period represents a negative superhump. The 3.40 h period is
about 4% shorter than the orbital period and obeys the relation between
superhump period deficit and binary period. The detection of superhumps in the
light curve is evidence of the presence of a precessing accretion disk in this
binary system shortly after the nova outburst. From the maximum magnitude -
rate of decline relation, we estimate the decay rate t_2 = 17+/-4 d and a
maximum absolute visual magnitude of M_Vmax = -7.7+/-1.7 mag.Comment: 6 pages, 6 figures, 2 .sty files, AJ accepted, minor change to one of
reference
Ontology: Use and abuse
The final publication is available at Springer via http://dx.doi.org/110.1007/978-3-540-79860-6_2Revised Selected Papers of 5th International Workshop, AMR 2007, Paris, France, July 5-6, 2007This paper is a critical analysis of the use of ontology as an instrument to specify the semantics of a document. The paper argue that not only is a logic of the type used in ontology insufficient for such a purpose, but that the very idea that meaning is a property of a document that can be expressed and stored independently of the interpretation activity is misguided.
The paper proposes, in very general lines, a possible alternative view of meaning as modification of context and shows that many current approaches to meaning, from ontology to emergent semantics, can be seen as spacial cases of this approach, and can be analyzed from a very general theoretical framework
X-Ray Emission and Optical Polarization of V1432 Aquilae: An Asynchronous Polar
A detailed analysis of X-ray data from ROSAT, ASCA, XMM and RXTE for the
asynchronous polar V1432 Aql along with Stokes polarimetry data from SAAO, is
presented. Power spectra from long-baseline ROSAT data show a spin period of
12150s along with several system related frequency components. However, the
second harmonic of the spin period dominates power spectrum in the XMM data.
For the optical circular polarization, the dominant period corresponds to half
the spin period. The ROSAT data can be explained as due to accretion onto two
hot spots that are not anti-podal. The variations seen in the optical
polarization and the ASCA and XMM data suggest the presence of at least three
accretion foot prints on the white dwarf surface. Two spectral models, a
multi-temperature plasma and a photo-ionized plasma model, are used for
spectral study. The RXTE PCA data are used to constrain the white dwarf mass to
1.20.1 M_odot using the multi-temperature plasma model. A strong soft
X-ray excess (<0.8 keV) in the XMM MOS data is well modeled by a blackbody
component having a temperature of 80-90 eV. The plasma emission lines seen at
6.7 and 7.0 keV are well fitted using the multi-temperature plasma model,
however an additional Gaussian is needed for the 6.4 keV line. The
multi-temperature plasma model requires a homogeneous absorber fully covering
the source and a partial absorber covering 65% of the source. The photo-ionized
plasma model, with a range of Fe column densities, gives a slightly better
overall fit and fits all emission lines. The presence of a strong blackbody
component, a spin period of 12150s, modulation of the 6.4 keV line flux with
spin period, and a very hard X-ray component suggest that V1432 Aql is a polar
with X-ray spectral properties similar to that of a soft intermediate polar.Comment: 46 pages, including 13 figures and 4 tables, To appear in The
Astrophysical Journal, 20 May 2005 issue, vol. 625, Added Report-no and
Journal-ref, no change in the text of the pape
An alternative model of the magnetic cataclysmic variable V1432 Aquilae (=RX J1940.1-1025)
V1432 Aql is currently considered to be an asynchronous AM Her type system,
with an orbital period of 12116.3 s and a spin period of 12150 s. I present an
alternative model in which V1432 Aql is an intermediate polar with disk
overflow or diskless accretion geometry, with a spin period near 4040 s. I
argue that published data are insufficient to distinguish between the two
models; instead, I provide a series of predictions of the two models that can
be tested against future observations.Comment: 10 pages LaTeX including 3 Postscript Figures, to be published in Ap
Time-Resolved HST Spectroscopy of Four Eclipsing Magnetic Cataclysmic Variables
Time-resolved HST UV eclipse spectrophotometry is presented for the magnetic
CVs V1309 Ori, MN Hya, V2301 Oph, and V1432 Aql. Separation of the light curves
into wavebands allows the multiple emission components to be distinguished.
Photospheric hot spots are detected in V1309 Ori and V2301 Oph. The emission-
line spectra of V1309 Ori and MN Hya are unusual, with the strength of N V 1240
and N IV 1718 suggesting an overabundance of nitrogen. Three epochs of
observation of the asynchronous V1432 Aql cover ~1/3 of a 50-day lap cycle
between the white dwarf spin and binary orbit. The light curves vary from epoch
to epoch and as a function of waveband. The dereddened UV spectrum is extremely
bright and the spectral energy distribution coupled with the duration of
eclipse ingress indicate that the dominant source of energy is a hot
(T~35,000K) white dwarf. Undiminished line emission through eclipse indicates
that the eclipse is caused by the accretion stream, not the secondary star. The
hot white dwarf, combined with its current asynchronous nature and rapid
timescale for relocking, suggests that V1432 Aql underwent a nova eruption in
the past 75-150 yr. The reversed sense of asynchronism, with the primary star
currently spinning up toward synchronism, is not necessarily at odds with this
scenario, if the rotation of the magnetic white dwarf can couple to the ejecta
during the wind phase of the eruption.Comment: To appear in ApJ Part 1; 25 pages, 12 figure
Idling Magnetic White Dwarf in the Synchronizing Polar BY Cam. The Noah-2 Project
Results of a multi-color study of the variability of the magnetic cataclysmic
variable BY Cam are presented. The observations were obtained at the Korean
1.8m and Ukrainian 2.6m, 1.2m and 38-cm telescopes in 2003-2005, 56
observational runs cover 189 hours. The variations of the mean brightness in
different colors are correlated with a slope dR/dV=1.29(4), where the number in
brackets denotes the error estimates in the last digits. For individual runs,
this slope is much smaller ranging from 0.98(3) to 1.24(3), with a mean value
of 1.11(1). Near the maximum, the slope becomes smaller for some nights,
indicating more blue spectral energy distribution, whereas the night-to-night
variability has an infrared character. For the simultaneous UBVRI photometry,
the slopes increase with wavelength from dU/dR=0.23(1) to dI/dR=1.18(1). Such
wavelength dependence is opposite to that observed in non-magnetic cataclysmic
variables, in an agreement to the model of cyclotron emission. The principal
component analysis shows two (with a third at the limit of detection)
components of variablitity with different spectral energy distribution, which
possibly correspond to different regions of emission. The scalegram analysis
shows a highest peak corresponding to the 200-min spin variability, its quarter
and to the 30-min and 8-min QPOs. The amplitudes of all these components are
dependent on wavelength and luminosity state. The light curves were fitted by a
statistically optimal trigonometrical polynomial (up to 4-th order) to take
into account a 4-hump structure. The dependences of these parameters on the
phase of the beat period and on mean brightness are discussed. The amplitude of
spin variations increases with an increasing wavelength and with decreasing
brightnessComment: 30pages, 11figures, accepted in Cent.Eur.J.Phy
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