Analysis of spectra of α CMi and α Cen A observed with the orbiting stellar ultraviolet spectrophotometer S59 in ESRO's TD1A satellite

Ultraviolet spectra of CMi and Cen A taken with moderate spectral resolution (approx. 1.8 Å) are used to analyse whether a determination of stellar chemical abundances of Fe and Cr and of the photospheric parameters is possible. For CMi, for which good spectral data are available, we findT _eff=7660±110 K; logg _eff=3.05±0.1. Further, log(Fe)=–0.06±0.09; log (Cr)=–0.01±0.09 with regard to standard (solar) abundances. For Cen A the resulting data — particularly the photospheric ones — are less certain, but it seems that the Fe abundance may be smaller than the standard value.     

Analysis of the solar low-ℓ p-mode asymmetries using wavelets

It is presently widely accepted that the solar low p modes show asymmetric profiles when their power spectrum is analysed and that the fact of fitting symmetric profiles yields systematic effects in the obtained frequencies which could affect the results of inversions. In this paper the low p-mode profiles are analysed using wavelets to denoise the power spectra of the modes. This denoising method is applied both to artificial data generated by Kosovichev (the Hare and Hound exercise) and to real data obtained with the GOLF instrument. The asymmetries as well as the frequencies obtained are studied in both cases. The results show that although the obtained p-mode profiles present a slightly negative asymmetry, the use of symmetric profiles to fit the power spectra does not introduce any systematic effect in the obtained frequencies.     

Measurements of radial velocities of α and: A spotted HgMn star?

Measurements of radial velocities from the SiII 6347A and 6371Alines and the HeI 6678A line based on observations of 1989–1994 are examined. The variability of the line shapes over the 96.6-day orbital period is analyzed. Evidence for a second component is found from lines in the spectrum of And which correspond to the silicon lines 6347 and 6371A. The preliminary value for the rotational velocity of the secondary component is 100–120 km/sec. Analysis of the variability of the radial velocities of the HeI 6678A line during the night has given the rotational period of the star of P_rot=I^d.012344 and indicates an inhomogeneous distribution either of the helium abundance or of the physical conditions over the surface. Thus, we have the first evidence for the existence of spots on the surface of an HgMn star.Translated fromAstrofizika, Vol. 39, No. 3, pp. 375–384, July–September, 1996.     

Solar-like Oscillations of the Red Giant ɛ Ophiuchi

Solar-like oscillations have recently been observed in the red giant ? Ophiuchi (G9.5III). The large frequency separation is found to be 4.8 μHz, non-radial oscillation mode has been shown to exist. Based on the observed frequency of oscillations and the position of ? Ophiuchi on the Hertzsprung-Russell diagram and by adopting a method of combined calculation of stellar evolution and oscillations, some preliminary constraints on the mass, metal abundance, age and radius of this star have been obtained.     

Sunspot Oscillations: A Review – (Invited Review)

The current state of our knowledge, and ignorance, of the nature of oscillations in sunspots is surveyed. An effort is made to summarize the robust aspects of both the observational and theoretical components of the subject in a coherent, and common, conceptual framework. Detailed discussions of the various controversial issues are avoided except in instances where new viewpoints are advanced. Instead, extensive references are made to the growing literature on the subject, and generous explanatory remarks are made to guide the reader who wishes to delve more deeply into the underpinnings of the subject matter.     

The Effect of Flows on Transverse Oscillations of Coronal Loops

In this paper we study kink oscillations of coronal loops in the presence of flows. Using the thin-tube approximation we derive the general governing equation for kink oscillations of a loop with the density varying along the loop in the presence of flows. This equation remains valid even when the density and flow are time dependent. The derived equation is then used to study the effect of flows on eigenfrequencies of kink oscillations of coronal loops. The implication of the obtained results on coronal seismology is discussed.     

Oscillations of the Hα emission in solar prominences

The time dependence of Doppler shift and line-center intensity is simultaneously observed for the H emission of three solar prominences, each one during about two hours. Doppler oscillations with periods near one hour and amplitudes between 1 and 2 km s^–1 are conspicuously visible in the recordings of all three prominences. Fourier analysis yields periods of 50, 60, and 64 min, as well as slight indications of short periods near 3 and 5 min. No oscillations are found in the line-center brightness.     

Detection of Hα Intensity Oscillations in Solar Flares

We report here the first direct evidence for detection of H intensity oscillations in two extended flares of 15 November 1989 and 20 April 1991. The relative intensity variations measured with time at 18 different flare and chromospheric locations were analysed to obtain the oscillation modes. The analysis shows prominent 5- and 3-min modes in flares in addition to their existence in the chromosphere. However, there exists a frequency difference between the flare and chromospheric modes. This frequency deviation of about 300 µHz is proposed as an influence of higher magnetic field, location of the measurements (height) in chromosphere, and high temperature in the flare.     

Oscillations of the Sun: Results of observations in 1974–2007

Doppler measurements of the photosphere of the entire Sun carried out at the Crimean Astrophysical Observatory (CrAO) in 1974–2007 by the differential technique showed the presence of an enigmatic periodicity of P ₁ = 159.967(4) min. The phase of this oscillation was constant over the entire 34-year of surveys and interval. The true nature of this phenomenon is unknown. Pulsation with the former period P ₀ = 160.0101(15) min has been reliably detected only in the first nine years, from 1974 to 1982. It is noted that (a) the average amplitude of the P ₁ oscillation in the first half of the data was nearly 34% higher than in the second half and (b) the beat period of 400(14) d of these two pulsations is equal within error to the Jovian synodic period (399 d). A hypothesis is discussed relating the P ₁ oscillation to the superfast rotation of the inner solar core.     

Chromospheric Internetwork Oscillations at Various Locations of the Quiet Sun

We analyze oscillation behaviours in chromospheric internetwork regions using spectral observations of the CⅡ1334 A line obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) aboard Solar and Heliospheric Observatory (SOHO). Three areas, 26 ×120arcsec2 each, at the various latitudes from the disk center to the north polar coronal hole, were rastered with a cadence of about 40-60 s in the solar minimum year. We obtained the time evolution of two-dimensional (2D) line intensity, continuum and line core shift. The continuum and the line shift show -3 min chromospheric oscillations in the internetwork regions underlying the coronal hole as well as at the disk center. We find that the CⅡ1334A line shift oscillates with an average speed of -1.7 km s-1, independent of the latitude, while its coherent scale decreases with latitude. On the other hand, the oscillation amplitude of the continuum around the 1334 A and the phase delay between the Doppler shift and continuum sli     

Quasi-Biennial Oscillations in the North – South Asymmetry of Solar Activity

The north – south (N – S) asymmetry of solar activity is investigated by using the data on coronal green-line brightness and total number and total area of sunspots over the period of 1939  –  2001. Typical time variations of the N – S asymmetry are found to be consonant in these indices. Quasi-biennial oscillations (QBO) of solar activity are well recognizable in the N – S asymmetry of the examined indices. Moreover, the QBO are much better manifested in the N – S asymmetry of the individual indices than in the original (N plus S) indices. The time variations of relative QBO power are synchronous for the N – S asymmetry of various solar activity indices whereas such a synchronization is weaker for the indices themselves. It is revealed that the relative QBO power found in the N – S asymmetry of the studied indices has a negative correlation with the value of the N – S asymmetry itself. The findings indicate that the N – S asymmetry should be regarded as a fundamental phenomenon of solar activity similarly manifested in different activity indices. These findings should be taken into account when any dynamo theory of solar activity is constructed.     

Spectroscopic Analysis of the Eclipsing Binary α CrB

The eclipsing binary α CrB, is a well-known double-lined spectroscopic binary. The system is considered unique among main-sequence systems with respect to its small mass ratio and large magnitude difference between the components. Our aim in the present paper is to compute the orbital parameters and to model the atmospheric parameters of the system. Synthetic spectral analysis of both the individual and disentangled spectra has been performed and yielded effective temperatures T _eff?=?10000±250 K, surface gravities logg?=?4±0.25 and projected rotational velocities $\emph{v}$ sini?=?110±5 km/sec for the primary component, and T _eff?=?6000±250 K and logg?=?4.5±0.25 for the secondary component. Evolutionary state of the system is investigated using stellar models.     

Physical mechanisms of the spectral variability of α Orionis with IUE

We present a spectroscopic study of Mg II k&h emission lines in the 2000–3000 Å region of 91 high resolution IUE spectra of α Orionis obtained during the period 1978–1996. There are absorption and emission components on the blue sides of the k&h emission lines, these components may be coming from the dust envelope located inside the extended atmosphere of α Orionis. A set of 91 Mg II k&h emission lines have been identified and measured to determine their fluxes and widths. We found that there is a spectral variability for these physical parameters with phase, similar to that found for the light curve, which we attribute to the changes of density and temperature of the regions from which these emission lines are coming, as a result of the semi-regular pulsation and the variability of mass loss of the red supergiant.Also we present a study of C II and Fe II emission features in the 2000–3000 Å region of 55 high resolution IUE spectra during the period 1978–1996. A set of 55 C II and Fe II emission lines have been identified and measured to determine their fluxes and widths. We found the same result as with the Mg II emission lines.     

The Intensity–Velocity Phase Spectra of Evanescent Oscillations and Acoustic Sources

There are three major issues in modeling solar evanescent oscillations: the variation of the intensity [I]–velocity [V] phase difference of p-modes close to the base of photosphere; the existence of a plateau of negative I–V phase differences below and between the ridges of the low-frequency p-modes; the explanation of the I–V cross-spectra of the evanescent oscillations. We present new interpretations for the first two issues, based on modeling intensity fluctuations taking steep temperature gradients, opacity, and non-adiabatic cooling into account. We also discuss consequences of our model for the explanation of power spectra and cross-power spectra of p-modes. In particular, we present evidence that the acoustic sources that generate evanescent waves produce a coherent background that explains the plateau–interridge regime of negative I–V phase difference.     

Damping of Longitudinal Magneto–Acoustic Oscillations in Slowly Varying Coronal Plasma

We investigate the propagation of MHD waves in a magnetised plasma in a weakly stratified atmosphere, representative of hot coronal loops. In most earlier studies, a time-independent equilibrium was considered. Here we abandon this restriction and allow the equilibrium to develop as a function of time. In particular, the background plasma is assumed to be cooling due to thermal conduction. The cooling is assumed to occur on a time scale greater than the characteristic travel times of the perturbations. We investigate the influence of cooling of the background plasma on the properties of magneto–acoustic waves. The MHD equations are reduced to a 1D system modelling magneto–acoustic modes propagating along a dynamically cooling coronal loop. A time-dependent dispersion relation that describes the propagation of the magneto–acoustic waves is derived using the WKB theory. An analytic solution for the time-dependent amplitude of waves is obtained, and the method of characteristics is used to find an approximate analytical solution. Numerical calculations of the analytically derived solutions are obtained to give further insight into the behaviour of the MHD waves in a system with a variable, time-dependent background. The results show that there is a strong damping of MHD waves and the damping also appears to be independent of the position along the loop. Studies of MHD wave behaviour in a time-dependent backgrounds seem to be a fundamental and very important next step in the development of MHD wave theory that is applicable to a wide range of situations in solar physics.     

Line variability in the spectrum of supergiant α Cam

CCD spectra taken with the PFES and CEGS echelle spectrographs attached to the 6-m Special Astrophysical Observatory (Russian Academy of Sciences) telescope and the 2-m Shamakha Astrophysical Observatory (National Academy of Sciences of Azerbaijan) telescope, respectively, were used to study the line-profile variations in the spectrum of the hot supergiant α Cam. No fast (≤1.5 h) line-profile and radial-velocity variations were found. Some of the systematic effects that cause spurious variability are considered. The Hα-profile variability appears symmetric relative to the radial velocity of the star’s center of mass and is attributable to variable blueshifted and redshifted emission and/or absorption components superimposed on a variable photospheric profile. The Hα line shows evidence of a large-scale mass ejection from the stellar surface, which is also traceable in other spectral lines. The He II 4686 line exhibits an inverse P Cyg profile, while the red wing of the He I 5876 line shows weak and variable emission. The fast (on characteristic time scales of shorter than an hour) variability of the He II 4686 profile that was previously revealed by our observations (Kholtygin et al. 2000) is called into question. A comparison of the observational data on the variability of ultraviolet and optical line profiles for the supergiant αCam suggests that nonradial motions are mainly responsible for the radial-velocity and line-profile variability.