The fraunhofer lines classifications by asymmetry changes inside the profiles in the spectrum of the Sun

The method of asymmetry change inside Fraunhofer lines profiles is proposed. New digital spectra with high resolution were used. It was shown that asymmetry may change repeatedly by value and a sign inside the spectral line profile. The lines can be classified in three groups on asymmetry changes inside the profiles.     

On the asymmetry of selected fraunhofer lines,II

The asymmetry of 11 absorption lines of neutral iron was determined from observations made with the double-pass system on the horizontal solar telescope Asu-5. An attempt was made to interpret this asymmetry in terms of progressive sound waves. The value of asymmetry computed theoretically was shown to be on average only 20 % of the observed value.     

Solar rotation from a number of fraunhofer lines

Solar differential rotation for 1982–83 obtained at the double pass spectrograph of the McMath telescope at Kitt Peak, are presented for lines of Fe, Mg, Na, K, Si, and O in the wavelength interval 3820–10827. The results are analyzed by representations in Legendre polynominals and a power series. The differential rotation is very close to the result obtained by Howard and Harvey in 1966–68 at Mt. Wilson but with a slightly greater amplititude. We find a mean equatorial rate of rotation of 1.977 km s^-1. Day to day variations are observed in the equatorial zone; a stable rate of rotation is observed outside of the sunspot zone.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

Computation and observation of Zeeman multiplet polarization in fraunhofer lines

Solar Physics - From an analysis of Stokes parameter profiles measured in a unipolar sunspot, properties of its large-scale magnetic field structure have been derived. With due allowance for our...     

A systematic method for the analysis of high-resolution fraunhofer line profiles

A fraunhofer line profile depends on various parameters, partly related to the photospheric structure (T, P _g, P _e, v _conv, v _turb), partly to the atom or ion involved (such as oscillator strength, energy levels), partly also resulting from the interaction of the relevant kind of particles with the photosphere, and the photospheric radiation field. In this paper we shall mainly pay attention to the determination of: the macroturbulent (convective) velocities, v _conv (); the damping constant (); the abundance, A _el; the distribution function (v _conv, ) of the convective velocities at each depth ; the source function, S (); the microturbulent velocities, v _turb ().The particular difficulty with these unknowns is that they are, as a rule, coupled in the resulting line profiles, that is: the shapes and intensities in these profiles are determined by the combined influence of these unknowns (together with the other above-given parameters).In this paper we describe a method to determine these six unknowns empirically by separating them, in analysing accurate high-resolution observations of line profiles of a multiplet. The unknown functions and quantities are consecutively determined in the above given succession. For each determination another, appropriate part of the line profile is used. In some cases the influence of the mutual coupling of the various parameters cannot be completely eliminated, and an iterative method has to be used.The method is summarized in Table II and section 2, and is further explained in sections 3 to 8. It is applied to an infrared Ci multiplet. The main results are the following:     

Source functions of infrared fraunhofer lines from equivalent widths

A method for obtaining the source function and value of r ₀ k _c/k _L,0 from the variation of equivalent width across the solar disk has been applied to several infrared Fraunhofer lines. The results indicate that most of the lines investigated have non-L.T.E. source functions which are less than or equal to the mean continuum intensity. De Jager and Neven (1968) appear to have underestimated the departures from L.T.E. in a number of cases.     

Solar oscillations in strong and weak fraunhofer lines over a quiet region

We have analysed a 35-min-long time sequence of spectra in the Caii H line, Nai D1 and D2 lines, and in a large number of strong and weak Fei lines taken over a quiet region at the center of the solar disk. The time series of these spectra have been observed simultaneously in these lines under high spatial, spectral, and temporal resolution at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory. We have derived the line profiles and their central intensity values at the sites of the chromospheric bright points, which are visible in the H line for easy identification. We have done a power spectrum analysis for all the lines, using their central intensity values to determine the period of oscillations. It is shown that the 3 Fei lines, present 23 Å away from the core of the H line representing the pure photospheric lines, Nai D1 and D2 lines, 6 Fei lines at the wings of H line, and Can H line exhibit 5-min, 4.05-min, 3.96-min, and 3.2-min periodicity in their intensity oscillations, respectively. Since all these lines form at different heights in the solar atmosphere from low photosphere to middle chromosphere and show different periodicities in their intensity oscillations, these studies may give an idea about the spatial and temporal relation between the photospheric and chromospheric intensities. Therefore these studies will help to better understand the physical mechanisms of solar oscillations. It is clearly seen that the period of intensity oscillations decreases outward from the low photosphere to the middle chromosphere. Since we have studied a single feature at a time on the Sun (i.e., bright points seen in the H line) in all these spectral lines simultaneously, this may explain about the footpoints of the bright points, the origin of 3-min oscillations, and the relation to other oscillations pertaining to these locations on the Sun. We have concluded that 80% of the bright points are associated with dark elements in the true continuum, and they may seem to have a relationship with the dark intergranular lanes of the photosphere, after carefully examining the brightness (bright threads) extending from the core to the far wings of the H line at the locations of a large number of bright points, using their time sequence of spectra.NRC Resident Research Associate, on leave from Indian Institute of Astrophysics, Bangalore 560034, India.     

On the depth dependence of the solar rotation velocity determined from fraunhofer lines

From 63 mostly unblended Fraunhofer lines measured along the solar east-west diameter the rotation velocity has been determined. The mean value is 1986 km s^#X2212;1. The velocity decreases with the optical depth in the photosphere. Over a range of 700 km the difference of the velocities is 41 m s^#X2212;1 for the Holweger-Müller atmosphere or 34 m s^#X2212;1 for the Harvard Smithsonian reference atmosphere.     

Zeeman splitting of molecular lines in sunspot spectra

The presence of magnetic splitting in a line of MgH (first discovered by Wöhl) is confirmed by photo-electric observations. The umbral magnetic field deduced from the line splitting was 3150 ± 200 G against 2360 ± 200 G given by FeI 5250. This difference is opposite in sign to that found by Wöhl. Lines from the B ² —X ² transition of CaH are also shown to be broadened by Zeeman splitting.     

Non-LTE profiles of the Ali autoionization lines

A non-LTE formulation is given for the transfer of radiation in the autoionizing lines of neutral aluminum at λ1932 and λ1936 through both the Bilderberg and Harvard-Smithsonian model atmospheres. Numerical solutions for the common source function of these lines and their theoretical line profiles are calculated and compared with the corresponding LTE profiles. Our results show that the non-LTE profiles provide a better match with the observations. They also indicate that the continuous opacity of the standard solar models should be increased in this wavelength region if the center-limb variations of observed and theoretical profiles of these lines are to be in reasonable agreement.

     

The formation of asymmetric Stokes V profiles in the presence of a magnetopause

A magnetopause that separates two regimes of different flow, additional to the separation of a magnetic field from a field-free plasma, gives rise to the formation of asymmetric Stokes profiles. Using a simple two-layer model atmosphere, where one layer comprises a magnetic field, the other being field-free, it is shown by analytical derivation that a wide variety of Stokes V profiles can be produced, having amplitude asymmetries a in the range –a. These include two-humped V profiles, which have two lobes of equal sign. For the most simple models, the asymmetry depends on the ratio of continuum intensity to the Planck radiation intensity of the magnetic layer at the wavelength of the spectral line under consideration, and on the line depth. Two-humped profiles (|a|>1) require the temperature of the magnetic layer to surpass the temperature of the line-core forming region, implying a temperature inversion, so that the V profile is partially in emission. The confrontation of this formation scenario with properties of observed one-lobe profiles of quiet-Sun network regions is inconclusive due to insufficient spatial resolution and lack of a sufficient sample of simultaneously recorded Stokes spectral lines of varying line depths. It seems, however, to be in good agreement with the observed frequent occurrence of abnormal V profiles of the very strong Nai D ₂ and D ₂ spectral line. A possible observational verification for the present formation scenario of abnormal Stokes V profiles and a novel method of Stokes inversion are discussed.     

The possible presence of C2 lines in sunspot spectra

Indirect evidence against the presence of C₂ lines in umbral spectra is discussed. The dominant role of CO in the molecular equilibrium of C at umbral temperatures ensures that CN, CH and C₂ lines are formed in the same atmospheric regions. Observations of CN and CH umbral lines are in good accord with predictions based on accepted umbral model atmospheres. This implies that C₂ must follow the predictions and that it is too weak to contribute to the umbral spectrum. C₂ lines in the photosphere and penumbrae are in excellent quantitative agreement with predictions. Additional tests are proposed.     

The forbidden line [Ca ii] λ7323 in the fraunhofer spectrum

New observations of the [Caii] 7323 Fraunhofer line are reported. The blending H₂O line was weak at the time of observation. Accurate estimates of the centre-limb variation of the equivalent width of the [Caii] transition are obtained and shown to be consistent with the calcium abundance log N(Ca) = 6.33.     

Flare-related changes in the profiles of six photospheric spectral lines

The profiles of six photospheric absorption spectral lines (Fei 5250 Å, Fei 5324 Å, Fei 5576 Å, Cai 5590 Å, Cai 6103 Å and Fei 6165 Å), measured in the kernel of a 2N solar flare and in a quiet-Sun area, were compared. The observations were carried out with an echelle spectrograph of the Crimean Astrophysical Observatory. It was shown that, compared to the quiet-Sun profiles, the flare profiles are shallower in the line core and are less steep in the wings. Therefore, measurements of the longitudinal magnetic field made with a magnetograph system which uses the Cai 6103 Å  spectral line, can be underestimated by 18–25% in areas of bright H ribbons of a moderate solar flare. Modeling of the solar photosphere performed by using a synthesis method showed that, in a solar flare, the enhanced core emission seems to be related to heating of the photosphere by the flare, whereas the decrease of the slope of the wings was presumably caused by the inhomogeneity of the photospheric magnetic field.     

The profiles of polarized broad Hα lines in radio galaxies

We present spectropolarimetric observations of seven broad-line radio galaxies. We find significantly polarized broad Hα emission in four objects including two, Arp 102B and 3C 390.3, which have double-peaked line profiles. In these objects the prominent redshifted and blueshifted peaks of the broad Hα line have no clear counterparts in polarized flux. This conflicts with theoretical predictions for a relativistic line-emitting disc with an electron scattering atmosphere, one of the leading models advanced to account for the double-peaked lines. The shapes and widths of the polarized line profiles can be explained if, as expected in unified schemes, the scattering occurs near the poles of an obscuring torus. However, the observed polarization position angles favour geometries in which the scattering plane is perpendicular to the radio jet. A configuration in which Hα photons emitted by a biconical flow are scattered off the inner wall of the torus has this property, and would also produce a single-peaked scattered line profile. With the exception of 3C 227, the sample as a whole conforms to the general trend in powerful radio galaxies for the optical polarization to be aligned with the radio source axis, favouring toroidal rather than polar scattering.     

Spatial profiles of lines in active region loops

From the statistical treatment of magnetohydrodynamically turbulent plasma, a steady-state density, temperature and magnetic field structure is derived for a coronal loop emitting in UV and EUV range. Spatial variation of line flux is presented for the lines C ii, C iii, O iv, O vi, Ne vii, and Mgx. It is found that the hotter lines which are emitted near the surface of the loop have larger spatial extents compared to the lines originating in the cool core of the loop, in agreement with the observations.     

Center-to-limb profiles of the aluminum autoionization lines in the solar spectrum

The rotation of the solar corona has been studied using recurrence properties of the green coronal line (5303 Å) for the interval 1947–1970. Short-lived coronal activity is found to show the same differential rotation as short-lived photospheric magnetic field features. Long-lived recurrences show rigid rotation in the latitude interval ±57°.5. It is proposed that at least part of the variability of rotational properties of the solar atmosphere may be understood as a consequence of coexistence of differential and rigid solar rotation.On leave from Torino University, Italy, as an ESRO-NASA Fellow.     

The first and second order moments of the polarization profiles of hydrogen lines

The main properties of the first- and second-order moments of polarized hydrogen lines, forming in the presence of stationary electric and magnetic fields, are reviewed. The analytical results presented here apply directly to the case of optically-thin emission lines in the LTE regime. Some applications of such results to electric- and magnetic-field diagnostics in (solar) plasmas are then briefly considered.On leave from the Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Largo E. Fermi 5, I-50125 Firenze, Italy     

Correction of observational profiles of spectral lines

The profiles obtained from radial-velocity observations of the Rosette Nebula with a Fabry-Pérot (F.P.) interferometer (Meaburn andSmith, 1968) had to be corrected, for the spreading action of the instrumental function, and for motion of the observer. Two current methods are compared and a method devised for fitting a sum of Gaussians to a noisy output profile.     

The influence of a photospheric spectrum of turbulence on the profiles of weak Fraunhofer lines

We assume that the motion field in the solar photosphere is described by a spectrum of turbulence, defined by suitably chosen parameters. For various values of the spectral parameters we compute average (i.e. averaged over a sufficiently large part of the photosphere) profiles of weak Fraunhofer lines. The resulting profiles which represent the distribution function of line-of-sight velocity components as modified by the transfer of radiation through the atmosphere, are thereupon still broadened by a function representing the influence of the distribution function of the granulation cell sizes. The resulting functions should be compared with the distribution function of line-of-sight velocity components as derived from observations, in order to arrive at an observational derivation of the parameters of the photospheric spectrum of turbulence.