Space-time profile variations of some spectral lines and their influence upon doppler velocity measurements

A technique for high-sensitivity measurements of spectral line profile fluctuations is suggested. Observations with spectral lines most commonly used to study the oscillations have been carried out. It is found that 5-min and 3-min fluctuations of Fei 5123, 5250, 5434 and NaDi 5896 line profiles are able to produce signals equivalent to line-of-sight velocities of 1–5 m s^–1 at a spatial resolution of 5 and 10–35 m s^–1 at 1.5 × 4 resolution. Such observations permit a better understanding of the particular physical factors responsible for the oscillations of line-of-sight velocity signals and the magnetic field which are the subject of study of helioseismology.     

The imaging vector magnetograph at Haleakala

We describe an instrument we have built and installed at Mees Solar Observatory on Haleakala, Maui, to measure polarization in narrow-band solar images. Observations in Zeemansensitive photospheric lines have been made for nearly all solar active regions since the instrument began operations in 1992. The magnetograph includes a 28-cm aperture telescope, a polarization modulator, a tunable Fabry-Pérot filter, CCD cameras and control electronics. Stokes spectra of a photospheric line are obtained with 7 pm spectral resolution, 1 arc sec spatial resolution over a field 4.7 arc min square, and polarimetric precision of 0.1%. A complete vector magnetogram observation can be made every eight minutes. The flexibility of the instrument encourages diverse observations: besides active region magnetograms we have made, for example, composite vector magnetograms of the full solar disk, and H polarization movies of flaring regions.     

Quantitative analysis and spectral variation of the Ap star HD 151 199

The radial velocity, intensity variations of the Caii line and chemical composition of the suspected magnetic star HD 151 199 have been studied using three 9.6 A/mm and twenty-one 40 A/mm dispersion spectrograms which were taken at St. Michel and Asiago Observatories respectively. The radial velocity and the intensity of the Caii K line suggest a variation with a 6.143 day period. The range is about 40 km/sec for the radial velocity and the K line changes in intensity by 50%. Preliminary results of the photometric data in the Geneva system show a similar trend of variation in (B ₂–B ₁) with the same period. H and H contours and the Balmer discontinuity give _eff=0.50 and logg=4. The most probable microturbulence is found to be 6.4 km/sec. The excitation temperature, _exc=0.50, is derived from the Fe lines and adopted for the other elements as well. A quantitative analysis by curve of growth and weighting function method, using Mihalas and Conti's atmospherical models was made. HD 151 199 shows an overabundance of Ca, Sr, Ba, by factors of 2, 40, and 5 with respect to 30 L Mi. Euii is probably overabundant also but it is not possible to give this element a numerical value. The other elements seem to be normal.     

Motions in arch filament systems

A new analysis of H filtergrams and H spectra of arch filament systems (AFS) shows that material flows downwards in both branches of the arch filaments (v 50 km/sec) while the top of the arches ascends (v 10 km/sec). It is suggested that AFS are produced by the magnetic field which expands, between growing spots, into higher levels carrying material with it that subsequently slides down along the magnetic field following gravity.AFS are also visible in the K line of Caii; however, there they appear less pronounced than in H and they are less conspicuous than the K-line quiescent filaments. There is some indication that AFS just cover a supergranulum (Ca network cell) with material streaming down at the border of the cell.No indication was found for a close relationship between AFS and flares.Mitteilung aus dem Fraunhofer Institut Nr. 91.     

The He i 10 830 Å chromosphere and filament associated structures

Full disk, He I 10 830 Å solar spectroheliograms have been generated using the Haleakala Stokes polarimeter-spectrometer. The spectroheliograms, with spatial resolution of 10 × 16 arc sec and wavelength bandpass of 0.53 Å, were developed for the detection of coronal holes, and have been compared with nearly simultaneous H and Ca K flltergrams.Areas of reduced helium absorption have been noted in the neighborhood of filaments and neutral zones in the longitudinal solar magnetic field. The existence of these helium lanes is discussed in terms of their relationship to H filament channels or to the coronal cavities which surround prominences.     

High n emission and absorption lines of the Sun

The analysis of three Ca ii K-spectra with spatial resolution of 1 is described and its results presented. The comparison of the observed single peak line profiles with model computation leads to some conclusions regarding the non-uniform large-scale velocity fields in the chromosphere.Mitteilungen aus dem Fraunhofer Institut No. 128.     

Center limb observations of inhomogeneities in the solar atmosphere

High resolution Ca II K-line spectra obtained at Kitt Peak National Observatory in September 1970 at a dispersion of 20 mm/Å and a spatial resolution approaching 1 arc sec are described.We first investigate the claim made by Zirin, Pasachoff and others that, at high spatial resolution, the K₂ emission occurs either in the red wing or the blue but not both. In fact, it is shown that although some spectra exhibit predominantly singly-peaked emission features, other spectra, at equally high spatial resolution, show mainly doubly-peaked structures. We suggest that both types of spectra may be regarded as normal.Secondly, time series studies reveal at least two cases in which features exhibiting single emission peaks in either the red or the blue wings evolve into doubly-peaked structures in a time scale of 15sec.Finally, two features on the slit are observed to separate in a manner which implies velocities of order 50 km/sec. Other alternative explanations of the phenomena are discussed but are found to be even more implausible than velocities of this magnitude. Nevertheless, we urge the need for independent confirmation of this result.The implications of these observations for inhomogeneous models for the formation of the Caii K-line are discussed.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

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.     

The temperature and internal kinematics of M8

A photoelectric Fabry-Pérot spectrometer is used to record the line profiles of H and [Nii] at 22 points in the nebula. The ratio of intensity H/[Nii] is used to derive an electron temperature distribution with values between 5700° and 9100° showing a peak at the centre of density. These temperatures are compared with the H Doppler temperatures to estimate excess velocities of mass motion. Together with the shifts of the H line centres, these lead to an evaluation of the velocity field in the nebula.It is suggested that the nebula consists of a core expanding at about ±10 km/sec^–1 surrounded by a thick peripheral shell in which large scale mass motions are small. Non-thermal broadening suggesting turbulent velocities at about the speed of sound is observed in this shell and is attributed to small scale dynamic effects in a non-smooth density distribution. The effect of such expanding cores on heliocentric velocities of galacticHii regions is discussed.     

On the chromospheric velocity field in sunspot regions

The wavelength shifts of approximately 8000 absorption elements in the H-line from spectra of 66 different sunspot regions have been measured.The average velocity field in the chromosphere close to sunspots is determined. Inside 15000 km from the spot's penumbral rim the average velocity vector is directed towards the spot and downwards in the chromosphere; the angle with the horizontal direction is on the average equal to 20°. The magnitude of the average velocity vector shows a maximum of 6.8 ± 1.2 km/sec just outside the penumbral rim and decreases quickly with increasing distance from the spot. Outside 15000 km from the penumbral rim the average velocity vector is small (-0.7 km/sec) and directed nearly vertically outwards from the sun. No significant tangential component of the average velocity field is found.The deviations of the individual elements from the average velocity field are on the average larger than the value of the average velocity. The total rms deviation in the line of sight velocity is equal to 6.8 km/sec. Thus, a large number of elements, as used in this investigation, is required to give significant values of the average velocity vector.We have also observed velocities in the penumbra. The average velocity vector is here probably small and its direction uncertain. The rms deviation in the line of sight velocities observed in the penumbra is equal to 7.5 km/sec.     

Temporal variations of the magnetic field in sunspots

We obtained simultaneous spectra with a spatial resolution of 1/2 and a temporal resolution of 15 s in H, Ca ii-K, Caii 8542 Å, and three Fei lines of the sunspot group responsible for the large flares of August, 1972 (McMath No. 11976). A time series taken 1972, August 3 in the Fei 6173 Å Zeeman sensitive line was analyzed for oscillations of field strength and the angle between the field and the line of sight, and for changes of the field associated with the Ca ii-K umbral flashes discovered by Beckers and Tallant (1969). The power spectra show no significant peaks, conflicting with the results of Mogilevskii et al. (1972) who reported oscillations in the longitudinal component of the field strength with periods of 56, 90, and 150 s. Changes in the field were not observed to be correlated with the occurrence of umbral flashes. These results place restrictions on magnetic modes of energy transport between the photospheric layers and the chromospheric layers where the umbral flashes are observed.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Preliminary results from the spectra of V471 tauri

The findings about this unusual eclipsing variable which possesses a white-dwarf component are reported. It was found that the H and K absorption lines of Caii are strongly pressure-broadened, and exhibit two double-reversal emission components. The radial velocities derived from the central strong emission components of Caii (H and K) are in agreement with the mean radial velocity curve obtained from the metallic absorption lines of the existing elements, whereas H (4340.47 Å) does not conform with the mean radial velocity curve. In certain orbital phases the H (6562.82 Å) line occurs in emission.     

Power spectra of Hα Doppler shifts

The temporal characteristics of the chromospheric velocity field in a quiet region are studied by means of a carefully guided sequence of 215 H spectra of the disk centre lasting 54 min. The Doppler shifts of each frame at = 0.4 Å are measured and the velocity history of each position on the sun is reconstructed. The velocity power spectrum is found for each of 256 points along the total slit length of 280000 km.A steady downward velocity is associated with places where the amplitude of the fluctuating velocity is high. The average velocity power spectrum exhibits three main features: (1) A peak at 287 sec, (2) A group of high frequency peaks in the range 150–210 sec, and (3) A low frequency peak with a period of 900 sec.The relationship of these features to the Ca K network is discussed.Member of the High Altitude Observatory Solar Project at Sacramento Peak, on leave from Dunsink Observatory, Ireland.     

Studies of granular velocities

Continuum brightness and Doppler velocity fluctuations in the lines 6301.5 and 6302.5 Å of Fei, measured in two selected spectrograms, are analysed by standard statistical (power- and coherence spectrum) methods. It is shown qualitatively that the oscillatory component of the velocity fluctuations (at spatial wavelengths > 4) decreases, while the supposedly granular component (at spatial wavelengths < 4) as well as the coherence between brightness and velocity fluctuations increases with optical depth.The spatial resolution of the spectrograms is estimated by comparing the observed power spectrum of brightness fluctuations with spectra found in the literature, assuming the combined instrumental and seeing spread function to be Gaussian. The resolution thus determined is = 1.24 ± 0.07. If the measured values are corrected accordingly, we obtain a true brightness rms of 10 to 14%, depending upon the shape of the power spectrum chosen for comparison, and a velocity rms at continuum optical depth of 1.3 km/sec. It is shown, however, that using the same correction function for the velocity power spectrum as for the brightness possibly gives rise to misestimating the velocity rms.Mitteilungen aus dem Fraunhofer Institut Nr. 100.     

High-dispersion spectroscopy of the symbiotic star AX Per: A binary model with rapid mass accretion

Results of high-dispersion spectroscopy (10 Å mm^–1) of the symbiotic star AX Per carried out in the years from 1979 to 1987 are reported. The emission line [FeVII] 6086 consists of a narrow and a broad component; the radial velocity of the narrow one varies according to the photometric period 681.6 days. This variation (K=30.6±1.5 km s^–1) seems to be due to the orbital motion of the hot star. The radial velocity of absorption lines varies with an inverse phase dependence and a much smaller amplitude (K=5.6±2 km s^–1), which may reflect the orbital motion of the red giant. The variation of the radial velocity of the emission lines of FeII, ect. (K=6.7±1.5 km s^–1) might be due to the rotation of the red giant. The profile of H emission line suddenly changed around the phase of the photometric minimum, which could be explained as a result of an eclipse of the emitting region by the red giant. On the other hand, some problems remain open in the behaviour of the radial velocities of H and HeI 5876.The observed results support a binary model of AX Per consisting of a rather massive (3M ) M-type giant and a Main-Sequence star (0.6M ). AX Per seems to be in an early stage of the Case C mass transfer, and the estimated very high mass accretion rate (10^–4 M yr^–1) is consistent with the theoretical models. The narrow component of the emission line of [FeVII] 6086 might be emitted in radiatively driven polar jets on the hot star of which luminosity is close to the Eddington limit.A new identification as ZrII at 6106.47 Å is proposed for the emission line at 6106 Å.     

Persistent 1.5 s oscillations superimposed to a solar burst observed at two mm-wavelengths

Long-enduring quasi-periodic oscilations (1.5s) superimposed upon a solar burst have for the first time been observed simultaneously at two different mm-wavelengths (22 GHz and 44 GHz). The oscillations were present throughout the burst duration (about 10 min), and were delayed at 44 GHz with respect to 22 GHz by 0.3 s. The relative amplitude of the oscillation was of about 20% at 44 GHz and of about 5% at 22 GHz. Interferometer measurements at 10.6 GHz indicated the burst source position stable within 1 arc sec. An He i D₃ line flare showed two persistent small spots separated by about 10 arc sec. The 22/44 GHz burst position corresponds well with the location of the He i D₃ spots. The oscillations display features which distinguish them from ultrafast time structures found in other bursts. One possible interpretation is a modulation of the synchrotron emission of trapped electrons by a variable magnetic field on a double burst source, optically thin at 44 GHz and with optical thickness 0.3 at 22 GHz.     

The High Altitude Observatory Coronagraph/Polarimeter on the Solar Maximum Mission

The High Altitude Observatory Coronagraph/Polarimeter, to be flown on the National Aeronautics and Space Administration's Solar Maximum Mission satellite, is designed to produce images of the solar corona in seven wavelength bands in the visible spectral range. The spectral bands have been chosen to specifically exclude or include chromospheric spectral lines, so as to allow discrimination between ejecta at high (coronal) and low (chromospheric) temperatures, respectively. In addition, the instrument features spectral filters designed to permit an accurate color separation of the F and K coronal components, and a narrow band (5.5 Å) filter to observe the radiance and polarization of the Fe xiv 5303 Å line. The effective system resolution is better than 10 arc sec and the instrument images a selected quadrant (or smaller field) on an SEC vidicon detector. The total height range that may be recorded encompasses 1.6 to more than 6.0R (from Sun center). The instrument is pointed independently of the SMM spacecraft, and its functions are controlled through the use of a program resident within the onboard spacecraft computer. Major experimental goals include: (a) Observation of the role of the corona in the flare process and of the ejecta from the flare site and the overlying corona; (b) the study of the direction of magnetic fields in stable coronal forms, and, perhaps, ejecta; and (c) examination of the evolution of the solar corona near the period of solar maximum activity.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

A two-dimensional multi-band spectroheliograph

The present paper describes a two-dimensional multi-band spectrograph which is located at Yunnan Observatory (25° N 103° E), Kunming. The instrument consists of a coelostat system with an aperture of 40 cm, and spatial resolution better than 1 under excellent seeing, and a spectrograph equipped with a plane reflecting grating. It can simultaneously obtain spectral data in ten bands, including the Balmer lines, metallic lines [Fei 6173 ,D _{1, 2, 3}, Mg, and Caii (H + K)] and Heii 4686 . We are able to control the observational processes by means of a computer and obtain the following data synchronously or quasi-synchronously: multi-band spectra, H filtergrams, magnetic field, and white light. With the aid of H slit-jaw filtergrams, we can determine where and when the spectral data are obtained and, on the basis of analysing the spectral line profiles, we can understand the physical characteristics of an active region and derive the fields of physical parameters. For the line-of-sight velocities, the values measured are as high as hundreds of kilometers per second and as low as a few kilometers per second.     

Chromospheric inhomogeneities in sunspot umbrae

The properties of rapidly changing inhomogeneities visible in the H and K lines above sunspot umbrae are described. We find as properties for these ‘Umbral Flashes’:

1. A lifetime of 50 sec. The light curve is asymmetrical, the increase is faster than the decrease in brightness.
2. A diameter ranging from the resolution limit up to 2000 km.
3. A tendency to repeat every 145 sec.
4. A ‘proper motion’ of 40 km/sec generally directed towards the penumbra.
5. A Doppler shift of 6 km/sec.
6. A magnetic field of 2100 G.
7. A decrease in this field of 12 G/sec. This decrease is probably related to the flash motion.
8. At any instant an average of 3–5 flashes in a medium-sized umbra. A weak feature often persists in the umbra after the flash. This post-flash structure initially shows a blue shift, but 100–120 sec after the flash, it shows a rapid red shift just before the flash repeats.

     

Profiles of Hi (La), Mgii (h and k), Caii (H and K) Lines of an active filament at the limb,with the LPSP instrument aboard the OSO-8 Satellite

We scanned the H i L, Mg ii h and k, Ca ii K and H lines simultaneously with the LPSP instrument on OSO-8, to investigate the low and moderate temperature regions of an active region filament. The L line is not reversed except for the innermost position in the prominence. Intensity (k/h), (K/H) ratios are respectively 2 and 1.1, indicating that the Mg ii lines are optically thin, and that Ca ii K is saturated, although not clearly reversed. The results obtained during the second sequence of observations (K saturated before L for example) indicate that within the size of the slit (1 × 10) we are not observing the same emitting features in the different lines.We also observe an important line-of-sight velocity at the outer edge of the feature, increasing outwards from a few km s^–1 to 20 km s^–1 within 2. Less than half an hour later, this velocity is reduced to 15 km s^–1 while the intensities increase. Full width at half maximum intensities for this component indicate turbulence variations from 22 to 30 km s^–1. The observed high velocities at the top of the prominence can be compared with radial velocities that Mein (1977) observed in H at the edges of an active filament and interpreted as velocity loops slightly inclined on the axis of the filament.