We present the observation of line doubling absorption in the spectra of the RR Lyrae variable star on the metal lines of FeII (λ = 4923.921Å) as well as of D1 and D2 lines of sodium. For the ...emission, we observed the lines of hydrogen Hα and Hβ with a very high intensity and the two lines of HeI (λ = 5875.66 Å and λ = 6678.15Å). This transmission/helium I remission 1, 2 is directly related to the intensity of the shock wave through the atmosphere of the star during the phase of maximum Blazhko cycle 3. During the expansion phase of the photosphere of the star and during the passage of the shock wave we witnessed a disappearance of the absorption lines of neutral FeI (λ = 4934.006Å and λ = 4920.503Å) and their reappearance in phase 1.00. These observations were made with a spectrograph resolution scale of about 12,000 installed on the C14 telescope at the Oukaimeden observatory (J43) during the different star pulsation cycle. We noticed that some of them almost coincide with the maximum Blazhko cycle. The doubling line were interpreted by Schwarzschild 4 on the basis of a two-layer atmosphere. This interpretation could measure the speed of the shock wave derived from the difference between the two red and blue spectral components on Hα hydrogen lines, D3 helium, D1 and D2 lines of sodium and FeII during the observed doubling of lines. At phase 1.00, the shock wave reached the maximum speed of 160 km.s−1 confirming the hypersonic regime occur during this maximum Blazhko cycle.
In this paper, we study the behavior of atmospheric turbulence in the boundary layer and free atmosphere using balloon-born radiosondes. The data measurements were carried out with 168 balloons ...launched from 9 sites. Profiles of various parameters (C super(2) sub(N), M super(2) and L sub(o)) characterizing atmospheric turbulence are established. We work out statistical models of atmospheric turbulence in the boundary layer, and we checked their coherence by comparing them with other models. In the free atmosphere, the C super(2) sub(N) profile is coherent with those of the models of Hufnagel and of Brown-Beland. A complete behavior of the outer scale L sub(o) is given from the ground up to 30 km which fits with partial models of Coulman-Vernin and Beland-Brown.
In this paper we describe a two-dimensional apodization of a circular aperture produced by interferometry. The light that is diffracted by a circular aperture is split into two beams of different ...amplitudes, where one of them has undergone a homothety to change its radial dimensions using an afocal optical system. The two beams are then combined coherently to form an apodized point-spread function (PSF). This procedure allows us to reduce the diffraction wings of the PSF, with different reduction factors depending on the combination of parameters.
Context. In the framework of the European Extremely Large Telescope project (E-ELT), a survey of prospective sites was launched by the European Southern Observatory (ESO) to select a site to host the ...next generation of optical telescopes of 42 m diameter, i.e., the E-ELT. The Moroccan Anti-Atlas (Jbel Aklim) was selected as one of these sites. Aims. We present an analysis of meteorological parameters and seeing measurements at Aklim, the Moroccan prospective site of the E-ELT project. Methods. We initiated a preliminary campaign to measure the astronomical seeing at Jbel Aklim using a differential image motion monitor (DIMM) instrument. We installed a weather station 2 m above the ground level to measure meteorological parameters such as temperature, relative humidity, pressure, wind speed, and wind direction. Results. We present data obtained by the DIMM monitor during 105 nights. The median and mean values of the seeing for the entire period of observation are 0.72′′ and 0.79′′, respectively, with a standard deviation of 0.31′′. The best value of the seeing obtained during this period is 0.30′′. A seasonal analysis of meteorological parameters are presented. We also used data from the National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis database (NCEP/NCAR) to derive more information about the long-term evolution of atmospheric parameters at Aklim site. Conclusions. Our preliminary results indicate that Aklim has indeed good conditions for conducting astronomical observations and could be a site to host a future astronomical observatory, even of E-ELT dimensions.
In order to complete characterization of the Oukaïmeden site and hoping to prospect other sites in the Moroccan High Atlas, we constructed a seeing monitor. We named the instrument DIMMAR for ...Differential Image Motion Monitor of Marrakesh. After more than one year of operation, we can conclude that the DIMMAR is quite reliable and that it can be a prototype for other similar low-cost instruments. In this work, the seeing measured at Oukaïmeden site using the DIMMAR on top of a 5 meters high tower is presented. Statistics from fifteen months seeing's are treated (from July 19, 2003 up to September 26, 2004). The median and mean zenith seeing for the entire period of observations are 0.84´´ and 0.92´´, respectively, at 0.5 $\mu\rm m$ (or 0.96´´ and 1.05´´, if corrected for exposure-time bias). The best seeing value measured is 0.32´´.
Context.
Although spectroscopic observations of RR Lyrae stars have been underway for almost a century, the fact that the hydrogen line exhibits three successive emissions in each pulsation cycle is ...still a very recent discovery.
Aims.
The purpose of the present study is to clarify the physical origin of these three emissions and their connection to atmospheric dynamics and to examine the influence of Blazhko modulation on their intensity.
Methods.
We used 2437 high-resolution spectra over a total of 81 nights taken by the ELODIE spectrograph (Haute Provence Observatory, France) in the years 1994–1997, rounded out with a 2015 run from Oukaïmeden Observatory (Morocco). We performed a detailed analysis of the line profile variations over the whole pulsation cycle.
Results.
Based on the blueshift of the main H
α
emission, the velocity of the hypersonic shock front was estimated at between 100 and 150 ± 10 km s
−1
(Mach number between 10 and 15). It has been established that the shock velocity increases from the minimum Blazhko to its maximum and afterward, it gradually decreases to the Blazhko minimum to start growing again. This observational result is consistent with the shock model proposed in 2013 to explain the Blazhko effect. The intensity of the H
α
emission increases with the shock velocity up to a maximum value around 137 km s
−1
and then decreases as the shock velocity increases further. This effect would be the consequence of the increasingly important ionization of the atoms in the radiative shock wake. The second (blueshifted) H
α
emission is the consequence of an approximately constant supersonic compression (Mach number between 2 and 3) of the upper atmosphere falling onto the photospheric layers, during 3 to 16% of the pulsation period. Finally, the third H
α
emission (P-Cygni profile) would be the consequence of the expansion of the high atmosphere induced by the shock wave during its final weakening.
Interferential seeing monitor Habib, A.; Sabil, M.; Benkhaldoun, Z. ...
Astronomy and astrophysics (Berlin),
04/2008, Letnik:
482, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Context. This work is a part of the development of observational instruments for the study of optical turbulence in the atmosphere. These instruments are developed for the optimization of high ...angular resolution and adaptive optics techniques. Aims. We present a new approach to estimate the astronomical seeing which is a fundamental parameter in high angular resolution, in adaptive optics and site testing. Based on this approach, we developed a simple low-cost seeing monitor, called Interferential Seeing Monitor (hereafter ISM). Methods. The principle of the ISM is based on the study of the diffraction-interference pattern produced by a Young's double-slit in a telescope focus. From the shape of that pattern, we determine the phase difference between the diffracted light rays that meet on the image plane. Then, the phase structure function is calculated which leads to the seeing value. Results. Two seeing measurement campaigns were carried out at Oukaimden observatory and the ENS de Marrakech site using this new seeing monitor and a DIMM monitor. The two results are in good agreement, which makes the ISM a reliable instrument.
Here we analyze 168 optical turbulence profiles made at nine different locations worldwide by means of free flight balloons equipped with instrumentation. Seeing $\varepsilon_{{\rm FWHM}}$, optical ...turbulence outer scales Lo, and wavefront outer scales $\pounds_{\rm o}$ are derived for the different locations and taking into account the contribution of the surface layer 0, 50 m, the boundary layer 0, 1 km and the free atmosphere 1 km, 30 km. Noticeable changes are found between the different locations, mainly due to the boundary layer contribution as well as the surface layer contribution. The free atmosphere contribution seems almost the same for each site. There is a very good coherence between the outer scale derived by us and that measured using the Generalized Seeing Monitor (GSM) technique.
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