112,136 research outputs found
Laser diagnostics and minor species detection in combustion using resonant four-wave mixing
Peer reviewedPostprin
Rotational CARS application to simultaneous and multiple-point temperature and concentration determination in a turbulent flow
Coherent anti-Stokes Raman scattering (CARS) from the pure rotational Raman lines of N2 is employed to measure the instantaneous (approximately 10 ns) rotational temperature of N2 gas at room temperature and below with good spatial resolution (0.2 x 0.2 x 3.0 cu mm). A broad bandwidth dye laser is used to obtain the entire rotational spectrum from a single laser pulse; the CARS signal is then dispersed by a spectrograph and recorded on an optical multichannel analyzer. A best fit temperature is found in several seconds with the aid of a computer for each experimental spectrum by a least squares comparison with calculated spectra. The model used to calculate the theoretical spectra incorporates the temperature and pressure dependence of the pressure-broadened rotational Raman lines, includes the nonresonant background susceptibility, and assumes that the pump laser has a finite linewidth. Temperatures are fit to experimental spectra recorded over the temperature range of 135 to 296 K, and over the pressure range of .13 to 15.3 atm
Confirmation of simultaneous p and g mode excitation in HD 8801 and Gamma Peg from time-resolved multicolour photometry of six candidate "hybrid" pulsators
We carried out a multi-colour time-series photometric study of six stars
claimed as "hybrid" p and g mode pulsators in the literature. Gamma Peg was
confirmed to show short-period oscillations of the Beta Cep type and
simultaneous long-period pulsations typical of Slowly Pulsating B (SPB) stars.
From the measured amplitude ratios in the Stromgren uvy passbands, the
stronger of the two short period pulsation modes was identified as radial; the
second is l=1. Three of the four SPB-type modes are most likely l=1 or 2.
Comparison with theoretical model calculations suggests that Gamma Peg is
either an 8.5 solar mass radial fundamental mode pulsator or a 9.6 solar mass
first radial overtone pulsator. HD 8801 was corroborated as a "hybrid" Delta
Sct Gamma Dor star; four pulsation modes of the Gamma Dor type were detected,
and two modes of the Delta Sct type were confirmed. Two pulsational signals
between the frequency domains of these two known classes of variables were
confirmed and another was newly detected. These are either previously unknown
types of pulsation, or do not originate from HD 8801. The O-type star HD 13745
showed small-amplitude slow variability on a time scale of 3.2 days. This
object may be related to the suspected new type of supergiant SPB stars, but a
rotational origin of its light variations cannot be ruled out at this point. 53
Psc is an SPB star for which two pulsation frequencies were determined and
identified with low spherical degree. The behaviour of 53 Ari and Iota Her is
consistent with non-variability during our observations, and we could not
confirm light variations of the comparison star 34 Psc previously suspected.
The use of signal-to-noise criteria in the analysis of data sets with strong
aliasing is critically discussed.Comment: 14 pages, 10 figures, accepted by MNRA
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