1,720,978 research outputs found
NEW OBSERVATIONS OF 5 MINUTE OSCILLATIONS IN THE OPPOSITE FLANKS OF SOLAR FRAUNHOFER LINES .1. THE EFFECT OF VARYING THE SPECTRAL AND TEMPORAL RESOLUTION
No full textResults of an investigation of the rms wavelength fluctuations in the 5-min range, at fixed intensity levels, in the opposite flanks of 15 Fe I and two Fe II lines, selected from the range 6200-6400 A are presented. Critical values for these quantities are evaluated. The number of used lines makes it possible to analyze the height dependence of the oscillations within the photosphere, and a clear correlation between the formation height of the emergent intensity and the ratio of the oscillation power in the two flanks of the lines is found. The existence of a unique relationship, independent of the characteristics of the single lines, confirms the diagnostic value of this ratio to investigate the variations of the wave properties throughout the solar atmosphere. The effect is argued to be due to radiative damping, which produces a height-dependent phase shift between velocity and thermodynamic perturbations within the line-forming region
New observations of 5-minutes oscillations in the opposite flanks of solar Fraunhofer lines
No full textThe importance of colour-colour loops in the determination of the physical parameters of pulsating variables
No full textAttention is drawn to the importance of studying the surface brightness of pulsating stars as a function of two colors, in order to disentangle the contributions of temperature and gravity variations to the observed curve from that due to the simultaneous variation of the emitting surface of the star. The area of the observed color-color loops obtained with different colors is compared with the area delta B of the surface-brightness color loop, inferred from calibrations. The existence of the color-color loops and the dependence of the loop area on the pulsation period, very similar to that of delta B, is easily explained, under the assumption of quasi-static approximation, by the existence of a loop in the plane of effective temperature and effective gravity, the area of which varies with the period. The consistency and adequacy of the whole picture on which the CORS method (used to determine the radius of classical Cepheids) is based are strongly supported by the experimental evidence
Radii and masses of Cepheids and RR Lyrae variables
No full textA reliable determination of absolute luminosities of RR Lyrae variables would provide a crucial test of stellar evolution and a mean to determine the distance and age of globular clusters. The authors have developed a modification of the classical Baade-Wesselink method, aimed at exploiting the possibilities offered by multicolor photometric systems, by taking into proper account metallicity and gravity effects. Here the authors present the fundamental aspects of the method, emphasizing the importance of a self-consistent bidimensional approach to multicolor photometry, and give preliminary results of a first application to five field variables (SW And, RR Lyr, X Ari, SU Dra, VY Ser)
The sensitivity of the C I 538.0 nm Fe I 537.9 nm and Ti II 538.1 nm lines to solar active regions
No full textUsing spectroscopy to probe stellar global parameters, such as effective temperature, is much exploited in the literature. In the solar case it can be used as an indicator of magnetic cycle variations.
In this work we study the sensitivity to bright active regions of three photospheric lines (Fe I 537.9 nm, C I 538.0 nm and Ti II 538.1 nm), which have been monitored on the sun for more than twenty years.
In our analysis we compare our experimental results, from observations with the THEMIS telescope, with theoretical results, obtained by spectral synthesis with FAL semi empirical models
(Fontenla et al. [CITE], ApJ, 518, 480). We demonstrate the inappropriateness of using these lines (full disk integrated) as indicators of quiet sun irradiance modifications without considering their intrinsic variations due to active regions. Instead, their different sensitivity to the presence of active regions can be exploited in order to discriminate the background quiet sun variations from the magnetic region contributions
Performances of THEMIS-IPM and first analyses of 1999 observations
No full textThe results of preliminary analyses of the images acquired at Themis with the Italian Panoramic Monochromator (IPM) during the 1999 campaign of observations, after the replacement of the telescope mirror ape presented. The overall performances of the whole system (telescope + IPM) for spectroscopic studies of solar granulation are evaluated
A Generalization of the Cors Method to Determine Cepheid Radii: Theory and Application
No full textThe CORS method for the empirical determination of the radii of pulsating variables (Caccin et al., 1981; Sollazzo et al., 1981) is discussed in the framework of the quasistatlc approximation to the variations of the atmospheric parameters (Unno, 1965) and reformulated in a way that does not make direct use of theoretical calibrations of the photometric system in terms of model atmospheres. The radii calculated with this approach are in good agreement with those previously obtained by means of Pel's calibrations of the VBLUW system (Sollazzo et al.,1981) which lead to a period-radius relation coinciding, within the errors, with the theoretical one (Cogan, 1978) and, consequently, mass determinations consistent with pulsational masses (Cox, 1979). The method can be immediately applied to any other multicolour system, and very promising preliminary results are obtained by using recent UBV data by Gieren (1982)
2-D multiline spectroscopy of the solar photosphere
No full textThe structure and dynamics of the photosphere are investigated, with time series of broadband and monochromatic images of quiet granulation, at the solar disk center. Images were acquired with the IPM observing mode at the THEMIS telescope. Velocity and line center intensity fields, derived from the observation of three different photospheric lines, are used to study velocity and intensity patterns at different heights in the photosphere. Automatic segmentation procedures are applied to velocity and intensity frames to extract solar features, and to investigate the dependence of their properties at different scales and heights. We find a dependence of the statistical properties of upflow and downflow regions on the atmospheric height. Larger granules, passing through a great part of the photosphere, are used to investigate the damping of convective motions in stably stratified layers. The results suggest the occurrence of an intense braking in the deep photosphere (first ~ 120 km). Furthermore, we investigate the temporal and spatial evolution of velocity fields, deriving typical time scales of dynamical processes relative to different solar features. In particular, for two selected isolated exploders, we reveal a velocity deceleration in the central region since the early phase of their fragmentation. Based on observations made with THEMIS-CNRS/INSU-CNR operated on the island of Tenerife by THEMIS S.L. in the Spanish Observatorio del Teide of the Instituto de Astrofisica de Canarias
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