On the fine structure of the evershed effect

The fine structure of the Evershed effect was studied using spectrograms obtained on 3 July 1969 at the Pulkovo Observatory. The results of the study of Fei and Cai lines show that the outward motion in the penumbra is concentrated only in dark filaments. It is supposed that interfilamentary spaces are parts of the photosphere not covered by dark filaments. The velocity variation along a few dark filaments shows that maximum velocity is at a distance 0.8 Rs from the center of the sunspot. The mean velocity in the interfilamentary elements is of the same order as that in the photosphere directly adjoining the penumbra. The results of measurement in Ti ii, Fe ii and CH lines show that in the colder upper part of the penumbra (CH) the velocity is greater than the velocity measured in the deeper layers (Feii and Tiii). The mean velocity at the outer boundaries of the dark filaments (Tii) is 1.5–2.0 km/s.     

The radial velocity variations of certainOii,Siiii, andNii lines — A confirmation of the shell ejection in the P cygni stellar wind

The radial velocity variations of the components of someOii, Siiii, andNii lines in P Cyg spectrum are investigated during the period 1981–1983. All data are analyzed in terms of a model which implies a multiple ejection of shells in the stellar wind. It is shown that the observed phenomenon is not periodic, but it occurs on a time-scale between 110 and 160 days with the most frequently observed length of the cycle of about 110 days. The shells move away from the star with an acceleration that is greater at low velocities than at high ones. The radial velocity variations ofOii, Siiii, andNii lines agree with these of hydrogen lines if we assume velocity and excitation condition differences inside the shell.     

Shifts of the Caii K line in Hei 10830 dark points

We investigate the velocity field of the solar chromosphere at the location of 65 He i 10830 dark points (DP's). We have obtained spectra of such points in the vicinity of the Ca II K line. As a measure of differential chromospheric velocity, we use the shift of the K line center relative to a nearby photospheric Fe i line. We find that in He i DP's, the distribution of K line shifts is skewed towards the blue: the blueward skewing is more pronounced in He i DP's located in coronal holes. To the extent that He i DP's are proxies of coronal bright points, our study is relevant to previous reports of outflows from such bright points.     

Four southern A-type supergiants

Measures of line intensities from high-dispersion spectrograms of HD 92207, 100262, 125835 and 161912 are presented. Analysis with a theoretical curve of growth leads to the selection of parameters for excitation temperature and microturbulence. The turbulent velocity in the atmosphere of HD 92207 varies through a factor of two in approximately one month, in phase with a similar change in the equivalent width of H. The spectra of the other three stars do not appear to vary, but the turbulent velocity is much less for Fei than for Feii and Crii.     

Radial velocity and profile variations of the ultraviolet circumstellar lines in ζ tauri

The radial velocity and profile variations of UV lines of the shell star Tau have been examined in the IUE spectra obtained in 1978–1982. The neutral atoms, and once or twice-ionized ions (exceptCii, Aliii, Siiii resonance lines) follow the same velocity variations as in the visual spectra, while the Siiv andCiv resonance lines show a constant negative velocity (–50 km s^–1 at the core). The Aliii,Cii resonance lines and probably Feiii (mult. No. 34) are formed in both regions, i.e., in lowly-ionized and highly-ionized regions and the Siiii resonance line is formed in a highly-ionized region.Paper presented at the Lembang-Bamberg IAU Colloquium No. 80 on Double Stars: Physical Properties and Generic Relations, held at Bandung, Indonesia, 3–7 June, 1983.     

Emission spectrum of hot R OB star MV Sgr

The new spectroscopic observation of MV Sgr obtained at ESO in 1987 July shows enhanced emission lines of He I λ3889, [SII] λ4068 relative to the observations discussed by Jeffreyet al. (1988). The presence of [SII] λ4068 indicates the presence of planetary-nebulae-like envelope around the star. Although the radial velocity of the absorption lines and Fe II emission lines do agree with the velocity given by Jeffreyet al., the [SII] λ4068 and probably He I emission lines appear to behave differently. Based on observations collected at the European Southern Observatory, La Silla, Chile.     

Somef-values for transitions in ZrII,ZrIII and SrI

Transition probabilities were calculated for certain transitions in ZrII, ZrIII and SrI. For these allowed transitions Hartree-Fock wavefunctions were calculated for use in determining the absolute line strength. The methods developed by C. Froese-Fischer and Mayers and O'Brien for calculating the wavefunctions were used in determining those for the transitions in ZrII, ZrIII and SrI. Theoretical and experimentalf-values were compared in the case of SrI, and the results were in reasonable agreement for transition probabilities based on dipole velocity calculations.     

A Contribution to the Understanding of Chromospheric Oscillations

We present SUMER/SOHO UV measurements of chromospheric oscillations of intensity, velocity, and linewidth observed in C i, S i, O i, and C ii lines, which are formed in the altitude range from 1000 km to 2000 km above τ ₅₀₀=1. Oscillations in lines originating at similar altitudes exhibit different behaviors which we discuss in terms of the formation of the lines.     

LU Vel (GJ 375): A M3.5Ve Flare and Double-Lined Spectroscopic Binary

High resolution echelle spectroscopic observations taken with the FEROS spectrograph at the 2.2 m telescope ESO confirm the binary nature of the flare M3.5V star LU Vel (GJ 375, RE J0958-462) previously reported by Christian and Mathioudakis (2002). Emission of similar intensity from both components is detected in the Balmer, Na i D₁&D₂, He i D₃, Ca ii H&K, and Ca ii IRT lines. We have determined precise radial velocities by cross correlation with radial velocity standard stars, which have allowed us to obtain for the first time the orbital solution of the system. The binary consists of two near-equal M3.5V components with an orbital period shorter than 2 days. We have analyzed the behaviour of the chromospheric activity indicators (variability and possible flares). In addition, we have determined its rotational velocity and kinematics.     

Relation between element depletion and interstellar reddening in the direction of OB Stars

We have studied the interstellar column densities of Alii, Siii,Sii, Feii, Niii, and Znii in the direction of 18 O- and 6 B-type stars so as to improve the relations of element depletions withE(B-V), and to look for other possible relations with two stellar parameters: namely, the rate of mass loss and rotational velocity. The stars were chosen in order to cover several directions in the Galaxy, as well as a wide range in interstellar reddening. We found a clear inverse trend relating the abundance of elements to interstellar reddening.     

A systematic radial velocity survey of the HII regions IC 1318a and HS 191

The results of a systematic radial velocity survey of two Hii regions in the Cygnus-X complex are presented. The [Nii] emission line components obtained at many positions over each object have been compared and correlated with other phenomena. It is suggested that they are probably connected objects and may be part of a giant shell or cylinder.     

O VI (λ = 1032 Å) profiles in and above an active region prominence,compared to quiet Sun center and limb profiles

O vi ( = 1032 Å) profiles have been measured in and above a filament at the limb, previously analyzed in H i, Mg ii, Ca ii resonance lines (Vial et al., 1979). They are compared to profiles measured at the quiet Sun center and at the quiet Sun limb.Absolute intensities are found to be about 1.55 times larger than above the quiet limb at the same height (3); at the top of the prominence (15 above the limb) one finds a maximum blue shift and a minimum line width. The inferred non-thermal velocity (29 km s^–1) is about the same as in cooler lines while the approaching line-of-sight velocity (8 km s^–1) is lower than in Ca ii lines.The O vi profile recorded 30 above the limb outside the filament is wider (FWHM = 0.33 Å). It can be interpreted as a coronal emission of O vi ions with a temperature of about 10⁶ K, and a non-thermal velocity (NTV) of 49 km s^–1. This NTV is twice the NTV of quiet Sun center O vi profiles. Lower NTV require higher temperatures and densities (as suggested by K-coronameter measurements). Computed emission measures for this high temperature regime agree with determinations from disk intensities of euv lines.     

The velocity structure of S54 and S142

The velocity structures of two extended, low-density and low-temperature Hii, regions S54 and S142, have been examined. Both exhibit an ionized sheet structure.     

Velocity effects on the profiles of Hα and two FeI lines

Profiles are computed for Ha and two Fei lines for a differentially moving atmosphere. The results show that the profiles are asymmetric and that velocity measurements made in the Doppler cores will often lead to erroneous results when the velocity gradient is significant in the regions of the atmosphere where the core forms.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Ultraviolet studies of the interstellar gas in the direction of the stars AE Aur (09.5V) andθ 2 Ori A (09.0V)

We have studied high-resolution SWP spectra of AE Aur and ² Ori A, obtained from the International Ultraviolet Explorer Satellite; and derived curve of growth and column densities ofCii,Cii ^*, Alii, Siii, Siii ^*,Sii, Crii, Feii, Niii, and Znii. It has been possible to fit these ions on one empirical curve of growth with a velocity parameterb=13 km s^–1 for both stars.Based on the observations made by the International Ultraviolet Explorer (IUE), and collected at the Villafranca Satellite Tracking Station of the European Space Agency.     

The velocity field associated with the birth of sunspots

A velocity field is found to occur prior to the birth of sunspots or during the rapidly developing phase of new spots. Fraunhofer lines are always shifted redwards in the observed active regions which are situated at various distances from the disk center. The velocity amplitude derived from Na i D1-line, 5895.940, amounts to, at maximum, 1.5 km s^–1 which is always a little larger than that derived from the weaker line, NI i 5892.883. The velocity field disappears when the spot ceases to grow. The lifetime of the velocity is, at least, 1 hr. The velocity field is interpreted in terms of the continuous downward flow in the process of formation of sunspots.Bray and Loughhead (1964) regard the disturbance in the granulation pattern accompanying the birth and growth of sunspot pores as an evidence of the existence of rising loops of magnetic flux. In view of the similarity of the phase of development of active regions and the lifetime in the observations by Bray and Loughhead and by us, we suggest that the velocity field may be a spectroscopic feature accompanying the rising magnetic loops in the photosphere and the chromosphere. We briefly discuss the observed mode of penetration of the magnetic flux to the solar surface before and after the appearance of AFS's.     

Critical ionization velocity interaction: Some unsolved problems

Different problems of current interest regarding the critical ionization velocity (Civ) phenomenon are discussed. The article is divided into five sections corresponding to different aspects of the interaction: velocity, magnetic field strength, geometry, neutral gas density, and time duration. In each section, experiments and theories — microscopic and macroscopic — are discussed.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988     

Steady flows in active regions observed with the HeI 10830 Å line

We show that the He i 10830 A line gives reliable Doppler shift measurements in the upper chromosphere above active regions. Persistent flow patterns in active regions observed near the solar limb show features previously noted in Dopplergrams using the Civ transition region ultraviolet emission line. Unlike the Civ measurements, however, the He i absorption shows a strong correlation with the line-of-sight velocity images in certain regions of some active regions.Operated by the Association of Universities for Research in Astronomy, Inc., under contract AST 78-17292 with the United States National Science Foundation.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation.Visiting Astronomers, Sacramento Peak Observatory.     

The effect of a non-maxwellian electron velocity distribution on Be-like ion diagnostics in the Sun

Non-Maxwellian collision rates of the Be-sequence ions Ciii and Ov in the solar transition region are derived for quiet Sun and flare conditions using the electron velocity distribution functions of Shoub. The rates are found to be enhanced relative to the Maxwellian values but only at low temperatures where the fractional abundances of these species is very small. This implies that the electron density and temperature diagnostics used by previous authors for the transition region will be unchanged by non-Maxwellian effects. It is noted that such effects will only be important for species that are formed at low temperatures and have large transition energies such as Hei.     

The small scale velocity field of a quiescent prominence

The small scale velocity field of a large quiescent prominence is studied from simultaneous filtergrams in the red and violet wings of the Ca ii K-line.The average spatial separation of peak velocities is about 3000 km. The duration of individual velocity elements appears to increase with increasing area of the elements. In some positions of the prominence the direction of the velocity persists through the 5 hrs of observations. It is suggested that emitting elements of gas, which flow along the magnetic lines of force, produce peak velocities when they pass through particular locations of the prominence region.There is no clear evidence in the data for oscillations or waves.