Search results for "Spectral"
showing 10 items of 3116 documents
Wavelength dependence of multiphoton ionization of xenon
2004
We have studied the multiphoton ionization of xenon atoms by $160\phantom{\rule{0.3em}{0ex}}\mathrm{fs}$ pulses at intensities of $5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ and $1.3\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ and present photoelectron kinetic energy and angular distribution spectra measured with a photoelectron imaging spectrometer. A noncollinear optical parametric amplifier allows us to tune the wavelength of the laser pulse over a range between 500 and $700\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. Resonant and nonresonant processes as well as channel switching effects have been observed in this intensity and wavel…
The Origin of T Tauri X-ray Emission: New Insights from the Chandra Orion Ultradeep Project
2005
We use the data of the Chandra Orion Ultradeep Project (COUP) to study the nearly 600 X-ray sources that can be reliably identified with optically well characterized T Tauri stars (TTS) in the Orion Nebula Cluster. We detect X-ray emission from more than 97% of the optically visible late-type (spectral types F to M) cluster stars. This proofs that there is no ``X-ray quiet'' population of late-type stars with suppressed magnetic activity. All TTS with known rotation periods lie in the saturated or super-saturated regime of the relation between activity and Rossby numbers seen for main-sequence (MS) stars, but the TTS show a much larger scatter in X-ray activity than seen for the MS stars. S…
Results from Droxo
2007
AIMS. We study the variability of the Fe 6.4 KeV emission line from the Class I young stellar object Elias 29 in the Rho-Oph cloud. METHODS. We analysed the data from Elias 29 collected by XMM during a nine-day, nearly continuous observation of the Rho-Oph star-forming region (the Deep Rho-Oph X-ray Observation, named Droxo). The data were subdivided into six homogeneous time intervals, and the six resulting spectra were individually analysed. RESULTS. We detect significant variability in the equivalent width of the Fe 6.4 keV emission line from Elias 29. The 6.4 keV line is absent during the first time interval of observation and appears at its maximum strength during the second time inter…
Chandra X-ray observations of the stellar group near the Herbig Be star MWC 297
2006
We present a Chandra ACIS-I X-ray observation of the region near the Herbig early-Be star MWC 297, where we detect a tight group of point X-ray sources. These are probably physically associated to MWC 297, because of their obvious clustering with respect to the more scattered field-source population. These data are compared to earlier ASCA data with much poorer spatial resolution, from which the detection of strong quiescent and flaring emission from MWC 297 itself was claimed. We argue that this star, contributing only 5% to the total X-ray emission of the group, was probably not the dominant contributor to the observed ASCA emission, while the X-ray brightest star in the group is a much b…
How does environmental variation translate into biological processes?
2001
Birth and death rates, as so many other biological processes, are usually not linearly related to environmental variation. Common examples of non-linear response forms include unimodal ‘‘optimum-type’’ responses and various saturating responses. These responses filter the signal coming from the environment to a corresponding biological process. We explored how different types of environmental signal may be transformed to a biological process. We were interested in the effect of the filter on modulation of (1) the variance of the signal, on (2) the variance-covariance structure between the signal and the filtered signal, and on (3) the match between the power spectra of the signal and the fi…
Coherent population oscillations with nitrogen-vacancy color centers in diamond
2015
We present results of our research on two-field (two-frequency) microwave spectroscopy in nitrogen-vacancy (NV-) color centers in a diamond. Both fields are tuned to transitions between the spin sublevels of the NV- ensemble in the 3A2 ground state (one field has a fixed frequency while the second one is scanned). Particular attention is focused on the case where two microwaves fields drive the same transition between two NV- ground state sublevels (ms=0 -> ms=+1). In this case, the observed spectra exhibit a complex narrow structure composed of three Lorentzian resonances positioned at the pump-field frequency. The resonance widths and amplitudes depend on the lifetimes of the levels in…
NaK Λ doubling and permanent electric dipoles in low-lying1Πstates: Experiment and theory
1998
The paper presents \ensuremath{\Lambda} splittings and q factors in the NaK $D{}^{1}\ensuremath{\Pi}$ state, directly measured from the electric radio-frequency-optical double resonance (RF-ODR) in laser-induced fluorescence (LIF) for a number of vibrational states $v=1--22$ with definite rotational levels J between 7 and 46. Permanent electric dipole moment values (d) have been obtained by measuring in LIF spectra the relative intensities of ``forbidden'' lines caused by dc Stark effect induced $e/f$ mixing in the ${}^{1}\ensuremath{\Pi}$ state, with their subsequent processing, which allowed us to obtain the $q/d$ ratio. A possible influence of the hyperfine structure on the RF-ODR signal…
Observation of an Intense Quasicontinuum of Superdeformed Rotational Transitions inEu143
1996
Quasicontinuum spectra in coincidence with transitions belonging to the different potential wells of {sup 143}Eu are studied with an increasing number of coincidence folds. An intense bump of rotationally correlated transitions is observed to develop in the high spin region. Fold distributions, angular anisotropies, moment of inertia determinations, and lower limits of lifetimes as a function of the rotational frequency show that the bump originates from highly collective rotationally damped {ital E}2 transitions generated by superdeformed states. {copyright} {ital 1996 The American Physical Society.}
SPECTROSCOPY AND NON-EQUILIBRIUM DISTRIBUTION OF VIBRATIONALLY EXCITED METHANE IN A SUPERSONIC JET
1998
Abstract High-resolution spectra of supersonic jets of vibrationally excited methane have been recorded by diode laser in the 8 μm region. A formalism for the description of energy distribution is proposed. It allows to estimate populations of vibrational polyads. Under these non-equilibrium conditions, translational temperature is also measured from line profiles. For relaxation, it is shown that vibrational relaxation between polyads is negligible whereas strong redistribution of population arises inside each polyad. Spectroscopically, observed lines involving the first four excited polyads allows cross-checked tests for energy level analysis.
On coronal structures and their variability in active stars: The case of Capella observed with Chandra/LETGS
2003
In this paper we present a detailed analysis of two X-ray spectra of Capella, taken eleven months apart with the Low Energy Transmission Grating Spectrometer (LETGS) of the Chandra Observatory. We have studied variability of the coronal emission over different time scales, both in the whole X-ray band and in narrow temperature ranges identified by lines. The comparison of the two observations shows that the whole coronal emission of Capella in March 2000 was 3% higher than in February 2001; there also appears to be a tendency, albeit a marginal one, for the hottest lines to show the largest changes between the two observations. A detailed search for short-term variability (on time scales ra…