Exploring short period oscillations in filaments

The authors analyse sources of false Doppler velocity signals of high frequencies (10 mHz and higher) in observations of filaments. In ground-based observations, spectrograph noise and image shifting at the spectrograph entrance slit are the main causes of the false signal. It is shown that using differential methods and telluric lines as reference lines significantly reduces the influence of the first factor. Periodical image shifting along the spectrograph slit can be compensated for during data reduction. In some cases detected high-frequency oscillations appear to be real.

Antarctica – a case for 3D-spectroscopy

DS or Integral-Field Spectroscopy (IFS) provides multiple spectra for each point of a 2-D field, rather than along a narrow, 1-D spectrograph slit only. Therefore, IFS does not require very accurate telescope pointing, nor do pre-assumptions about slit or aperture sizes have to be made. It avoids any ‘slit-losses’ due to seeing or atmospheric dispersion, which eliminates the need for any parallactic alignment or a dispersion compensator (see Fig. 1).

A Modelling of Expansion Velocities of Planetary Nebulae

Recently written model of photoionization structure of planetary nebula has been used to calculate the emissivities of different nebular lines. With these values the line profiles have been modelled. The profiles can be obtained for different size and position of the spectrograph slit on the nebula image. The prepared computer code allows for estimation of the expansion velocities (Vexp) in the way consistent with the methods used by observers, i.e. defined as the half-width of the line profile (when nebula is not resolved, “whole neb.” in the Figure) or defined as the half of the emission peaks separation (when the nebula can be resolved — “rectangle” in the Figure — and the line can be observed in the central part of the nebula). The real matter velocity at the radius where the observed surface brightness of Hβ falls below 20 % of the maximal value is shown for comparison (“model” in the Figure).

Opacity Broadening as a Density Diagnostic for Spot Spectroscopy

Recently, a novel technique known as spot spectroscopy has been developed for use in diagnosis of laser-produced plasmas. This method involves the implantation of tracer microdots (circular or rectangular) of material in laser targets whose composition and size (typically about 100 μm) are known. Aluminum has been a popular choice since its K-shell lines are readily produced; however, any element appropriate to the experiment may be chosen. A major advantage of this technique is that the plasma produced from each microdot is generally homogeneous in the direction parallel to the plane of the original target. Since the dots can be distinguished spectroscopically, the diagnosis of each spot is not subject to the ambiguities created by the presence of gradients. Gradients do exist in each blowoff tracer perpendicular to the target plane; however, it is possible to resolve spatially the cylindrical blowoff created by each dot with appropriate orientation of the spectrograph slit.

On the Rotational Velocity of Fine Solar Structures Deduced from the Inclination to the Direction of Dispersion of Their Spectral Streaks

Observational material indicates that matter in some streamers and knots of prominences rotates (Rompolt, 1975a). We would like to propose a method which enables evaluation of the rate of rotation of such structures from their spectral streaks inclined to the direction of dispersion. These considerations concern fine prominence structures, the image of which is comparable with the width of the spectrograph slit. The matter in these structures is assumed to rotate as in a solid rod.

Spatial and Spectral Structure of Chromospheric Lines

We are reducing a set of spectra covering the region from 3400 to 4330 Å that show both spatial and spectral structure in chromospheric emission lines from many elements and ions. The spectra were taken with the vacuum tower telescope at the Sacramento Peak Observatory with the spectrograph slit tangent to and touching the limb. Thus some height resolution in the chromosphere is present. Many of the lines show doubly-reversed emission, often asymmetric either for the whole line or for fine structure. The quality of the data is such as to improve our understanding of line blends. The spectral structure can be compared with the well-known structure in the H and K lines of Ca II and in the resonance lines of MgII in order to deduce a model for the lower chromosphere.

Spectroscopic Observations of Visual Double Stars

There are certain visual double stars which, when close to a node of their relative orbit, should have enough radial velocity difference (10-20 km/s) that the spectra of the two component stars will appear resolved on high-dispersion spectrograms (5 Å/mm or less) obtainable by use of modern coude and solar spectrographs on bright stars. Both star images are then recorded simultaneously on the spectrograph slit, so that two stellar components will appear on each spectrogram.

The Measurement of Radial-Velocity Differences Between the Components of Close Visual Binary Systems

The value obtained for the difference in radial velocity between components of a visual binary that is unresolved on the spectrograph slit appears to depend, sometimes, on whether the measurement is made visually with a microscope or by means of an oscilloscopic setting device. This apparent dependence has been confirmed by measurement of artificially produced doublelined spectrograms, and disappears for line pairs separated by more than 1.5 or 2 times the half-widths of their components. The dependence arises from blending of the two line profiles. There is some evidence that the results obtained from visual measures are affected by the scale of the image being measured. For this reason, oscilloscope measures are probably to be preferred; although their errors are sometimes larger, they seem to be more consistent. Errors arising from this sort of blending are not sufficient to explain measures of relative radial velocity of the components of some visual binaries, that differ widely from the predictions made from the visual orbits.