The Fe xii 195.1 Å/1242 Å emission line ratio in the solar corona

Recent R-matrix calculations of electron impact excitation rates in Fe xii are used to derive the theoretical emission line ratio R ₁ = I(195.1 Å)/I(1242 Å), which is potentially a useful electron density diagnostic for the solar inner corona (r 1.05 61-01). These results are found to be significantly different from the earlier estimates of Withbroe and Raymond (1984), but are in good agreement with the observed values of R ₁, for the quiet Sun and an active region. Adoption of the R-matrix atomic data for the 1242 Å line in the coronal iron abundance determination removes an existing discrepancy between results derived from the EUV transition and other iron lines in the solar XUV spectrum. The R-matrix calculations confirm the prediction of Withbroe and Raymond that the earlier discrepancies in R ₁ and the iron abundance were due to the 1242 Å line excitation rates being underestimated by a factor of ~2. Withbroe and Raymond's paper is, therefore, an excellent example of how astronomical observations can be used to accurately predict atomic physics data.     

The 3410 Å band of the PH molecule in the solar photospheric spectrum

Some weak unidentified solar photospheric lines in the wavelength range: (3400–3465) Å may be due to PH lines of the (0, 0) band of the PH(A ³ _i - X ^{3 -})system. These faint PH molecular lines have resulted an excitation temperature of the order of 4500 K. Using experimental lifetime data for PH in the A ³ _i state, an absorption oscillator strength f ₀₀ = 0.0075 is derived for the 3410 Å band of the PH (A ³ _i - X ^{3 -})system. Accurate line positions, oscillator strength and transition probability for the 4.4 fundamental rotation-vibration band of the PH molecule are obtained. A comparison of positions of some lines of the 4.4 band with those obtained on new tracings of high resolution solar spectra shows many coincidences with weak solar lines.     

Soft X-ray emission lines of Ni XVIII in the solar spectrum

R-matrix calculations of electron impact excitation rates in Nixviii are used to derive theoretical electron-temperature-sensitive emission line ratios involving 3s–4p,3p–4d,3p –4s, and 3d–4f transitions in the 41–53 Å wavelength range. A comparison of these with solar flare observations from a rocket-borne X-ray spectrograph (XSST) reveals generally excellent agreement between theory and experiment (within the experimental and theoretical uncertainties), which provides support for the atomic data adopted in the analysis. However the 3s 2S–4p 2P1/2 line of Nixviii at 41.22 Å appears to be blended with the Fexix 13.74 Å feature observed by XSST in third order. In addition, the measured Nixviii intensity ratio I(3p 2P3/2– 4s 2S)/I(3p 2P1/2–4s 2S)=I(51.02 Å)/I(50.26 Å)=0.56, a factor of 3.8 smaller than the theoretical (temperature and density-insensitive) value of 2.1. The reason for this discrepancy is currently unexplained, but is unlikely to be due to blending of the 50.26 Å line, as the intensity of this feature is consistent with that expected from the other Nixviii lines in the XSST spectrum. Future observations of the Nixviii lines by the Advanced X-ray Astrophysics Facility (AXAF) should allow this problem to be resolved, and may also permit the use of the lines as electron-temperature diagnostics.     

Periodic variations of the Ba II 4554 Å and Ca II 8542 Å line profiles in coronal holes

The oscillations of the half-width of the Ba II 4554 ? and Ca II 8542 ? spectral lines have been analyzed using observations at the base of solar coronal holes (CHs). The observed variations (~50 m ? for Ca II and ~4 m ? for Ba II) exceed considerably the thermal broadenings of these lines calculated from the measured intensity oscillations, suggesting their nonthermal nature. We point out a number of observational facts that hamper an unambiguous interpretation of the periodic Ba II and Ca II profile variations solely by the manifestation of torsional Alfve´ n waves in the lower solar atmosphere.     

Identification of peculiar A-stars. I. Analysis of the equivalent width of the 2786–2810 Å spectral band and the MgII 4481 Å line for 137 A-stars

The dependence of the equivalent widths of the 2786–2810 Å spectral band and the MgII 4481 Å line on the basic parameters (T_eff, logg and [M/H]) for 137 bright A-stars shows that 60 of them are candidate peculiar stars. Given the similar behavior of W(2800) and W(4481), it can be assumed that 34 of the stars are chemically peculiar stars. The anomalous values of W(2800), W(4481), and [M/H] vary over wide limits for the rest of the stars, possibly because they are binary. Translated from Astrofizika, Vol. 51, No. 4, pp. 577–593 (November 2008).     

Variability of the spectrum of β CrB in the region of the lithium line Li I λ6708Å

Some results of observations of the spectrum of the spectroscopic-binary Ap star CrB in the region of the lithium line Li I 6708Å are presented. The observations were made at the Crimean Astrophysical Observatory over the period 1993–1995 with the coudé spectrograph equipped with a CCD camera on the 2.6-m telescope. Several factors which can affect the behavior of the lithium blend are examined: stellar rotation, magnetic field, isotopic shift, the binary system, and blending by unidentified elements. The principal result of this work is the detection of variability of the lithium blend Li I 6708Å over the period of rotation of the star. The variations of the radial velocity V_r, and the FWHM of the lithium blend are reported here for the first time. They indicate either a nonuniform distribution of lithium or a nonuniform distribution of conditions for excitation of the lithium resonance doublet in the complex structure of the strong surface magnetic field. Similar variations are also shown by the lines of the rare-earth elements Gd II 6702.10 Å, Gd II + Ce II 6704.3Å, and Ce II + Fe I 6706.0 Å.Translated fromAstrofizika, Vol. 39, No. 1, pp. 19–30, January–March, 1996.     

Properties of flares observed in the Mg i b2 line at 5172 Å

Observations of emission in the Mgi b₂ line at 5172 Å are presented for 13 flares. Also discussed are 3 flares which occurred in regions under observation but which showed no Mg emission. The Mg flare kernels resemble white-light flare kernels in their general morphology and location. Comparison of Mg filtergrams with magnetograms indicates that the Mg kernels occur at the feet of magnetic arches across neutral lines. Time-lapse Mg filtergram films indicate photospheric shearing motions near flare sites for several hours before flare onset. We have compared flare Mg emission with microwave and both hard and soft X-ray flare emissions. Examination at the time development of the 1981, July 27 flare shows that the microwave and X-ray bursts may be clearly related to the appearance of successive Mg flare kernels. We have also compared subjective, relative Mg flare importances with other flare emission measurements. For the full sample of flares, Mg importance is significantly correlated with hard and soft X-ray emission peaks, with X-ray ‘hardness’ (ratio of hard to soft peaks) and with the rise slope of soft X-ray bursts. The Mg importance does not correlate with the microwave peaks when the full sample of flares is used, but for the subset showing Mg emission there is significant correlation. No correlation with Hα importance was found. Our results suggest that Mg emission is associated with an impulsive component which may be absent from some flares. The San Fernando Observatory magnesium etalon filter system is described.     

New satellite structure of the solar and laser plasma spectra in vicinity of the Lα (mg xii) line

Spectra in the narrow vicinity of the Mg xii resonance line at = 8.42 Å were obtained aboard the satellites Intercosmos-4, -7 and the rocket Vertical-2, as well as from laser-produced plasma. The high resolution in solar and laboratory spectra made it possible to reveal a new spectral structure close to the L (Mg xii) line from both short and long wavelength sides. The main features were observed in all the spectra and were interpreted as a single or group of dielectronic satellite lines due to 2l3l 1s3l transitions in the He-like ions according to theoretical calculations which were carried out by means of relativistic Z-expansion technique. The derived electron temperature of the emitting volumes seemed to be 3 × 10⁶ K for laser plasma and about 6 × 10⁶ K for the solar flares studied. The latter value is in good agreement with the temperature estimated with the help of the resonance line-to-continuum intensity ratios.Polish Academy of Science, Solar-Terrestrial Relations Laboratory, Wroclaw, Poland.     

The Dynamics of High-Temperature Plasma in the Solar Corona according to SPIRIT Observations in Mg XII 8.42 Å Line

The spatial-distribution dynamics of the hot coronal plasma with T ～ 10 MK during a period of high solar activity is studied. We analyze images of the NOAA 9830 active region and its surroundings obtained during the second half of February 2002 with the SPIRIT spectroheliograph in the Mg XII 8.42-Å line and simultaneously on the SOHO satellite with the EIT instrument and on the TRACE satellite in the 195-Å channel. As shown by a multiwavelength analysis, a high-temperature plasma is concentrated in the corona near the apices of magnetic loops, it has long lifetimes (up to several days), and its dynamics is complex and bears no direct relation to flare activity. During the flares, conspicuous increases are observed in the X-ray flux and the emission measure for temperatures of ～5–15 MK. Our analyses of the time variations in emission during a flare suggest that hot plasma is heated by fluxes of accelerated electrons.     

The Formation of MgI 4571 Å in the solar atmosphere

The two-dimensional equation of transfer is solved for the case of locally-controlled source function (LTE) and radiationally-controlled ionization. Horizontal fluctuations in electron temperature and macroscopic velocity fields are superposed on the basic one-dimensional model (cf. Altrock and Cannon, 1972). Output intensities are compared with observed rms intensity fluctuations and spatially-averaged intensities in Mg i 4571 Å. We find that at least one model (with a height-independent temperature fluctuation T/T=±0.02 in the range 0h450 km) can predict the magnitude of the intensity fluctuations in both the continuum and 4571 Å. The asymmetry of the line can be explained by adding a height-independent, temperature-correlated flow of amplitude 1 to 2 km s^–1. The relationship between these results and other multi-dimensional analyses is discussed.On leave from Department of Applied Mathematics, University of Sydney, Sydney, Australia.     

On the fine structure of the Fe I λ532.4185-nm line profile in the spectrum of the solar disk center

Based on the digital spectra taken with double monochromators of high spectral resolution, we have constructed the profile of the Fe I λ532.4185-nm line in the spectrum of the solar disk center. Basic spectrophotometric characteristics of the line profile have been determined with a high accuracy. The fine structure of the line profile is studied in detail. The profile asymmetry parameters have been determined.     

Irradiance observations of the 1–8 Å solar soft X-ray flux from goes

The solar 0.5–8 soft X-ray flux was monitored by the NOAA Geostationary Operational Environmental Satellites (GOES) from 1974 to the present, providing a continuous record over two solar activity cycles. Attempts have been made to determine a soft X-ray (SXR) background flux by subtracting out solar flares (using the daily lowest flux level). The SXR background flux represents the quiescent SXR flux from heated plasma in active regions, and reflects similar (intermediate-term) variability and periodicities (e.g. 155-day period) as the SXR or hard X-ray (HXR) flare rate, although it is determined in non-flaring time intervals. The SXR background flux peaks late in Solar Cycle 21 (2–3 years after the sunspot maximum), similar to the flare rate measured in SXR, HXR, or gamma rays, possibly due the increasing complexity of coronal magnetic structures in the decay phase of the solar cycle. The SXR background flux appears to be dominated by postflare emission from the dominant active regions, while the contributions from the quiet Sun are appreciable in the Solar Minimum only (A1-level). Comparisons with full-disk integrated images from YOHKOH suggest that the presence of coronal holes can decrease the quietest SXR irradiance level by an additional order of magnitude, but only in the rare case of absence of active regions.Presented at IAU Colloquium No. 143, The Sun as a Variable Star: Solar and Stellar Irradiance Variations, Boulder, CO, June 20–25, 1993     

Hα line in the spectrum of the WW Vul star

Investigations in the line H_α of the spectrum of UX Ori WW Vul are presented. Comparison with the data of other researchers has shown that the regime of variable matter ejection of the star WW Vul is retained for a long time. The spectra of two nights (July 18 and 23, 2006) showed an increased intensity of red emission component without noticeable change in the radial velocity. On the other hand, radial velocity of the central absorption considerably changed to negative values with decreasing V/R. During the night on July 8, 2006, we found doubling of the blue emission component for these two spectra.     

Measurement of the relative intensities of Heζ-H8 lines λ3889Å in the spectrum of the chromospheric spicules at various heights above the limb

A series of 31 large scale spectra of the spicules near H8-He lines 3889 Å has been photographed at different heights (1500–5000 km) with 53-cm coronagraph. The solar image was 121 mm in diameter, dispersion and spatial resolution were respectively 0.647 Å mm^–1 and 1–2. Equivalent widths of both lines have been measured and ratio R = EW_He/EW_H8 was obtained. T _e(h) distribution in the averaged spicule deduced differs from that in the recent spicule model by Beckers (1972): the spicules are colder greatly than it was accepted hitherto (T _e 10000 K). The electron temperature in the quiescent prominence which occurred in the spectra was also estimated: T _e 6000 K at h = 4000 and 5000 km.     

Optical spectrum of the post-AGB Star HD56126 in the wavelength interval 4010-8790 Å Å

The optical spectrum of the post-AGB star HD56126 identified with the infrared source IRAS07134+1005 is studied in detail using high spectral resolution observations (R = 25000 and 60000) performed with the echelle spectrographs of the 6-m telescope. A total of about one and a half thousand absorptions of neutral atoms and ions, absorption bands of C₂, CN, and CH molecules, and interstellar bands (DIBs) are identified in the 4012 to 8790 Å Å wavelength interval, and the depths and radial velocities of these spectral features are measured. Differences are revealed between the variations of the radial velocities measured from spectral features of different excitation. In addition to the well-known variability of the Hα profile, we found variations in the profiles of a number of FeII, YII, and BaII lines. We also produce an atlas of the spectrum of HD56126 and its comparison star α Per. The full version of the Atlas is available in electronic form from: http://www.sao.ru/hq/ssl/Atlas/Atlas.html.     

Changes of the CaI λ6102.7 Å line profile and the magnetic field structure during the August 12, 1981 solar flare

We study the changes of the CaI λ6102.7 Å line profile and the magnetic field structure during the 1B/M2.2 while-light flare of August 12, 1981. The two brightest flare knots located in the penumbra of a sunspot with a δ configuration are investigated. The 1 ± V line profiles are analyzed. The reduction and analysis of our observations have yielded the following results. (1) The line profiles changed significantly during the flare, especially at the time of optical continuum emission observed near the flare maximum. In addition to the significant decrease in the depth, a narrow polarized emission whose Zeeman splitting corresponded to a longitudinal magnetic field strength of 3600 Gs was observed. This is much larger than the magnetic field strength in the underlying sunspot determined from the Zeeman splitting of absorption lines. (2) The largest changes of the CaI λ6102.7 Å line profile observed during the flare can lead to an underestimation of the longitudinal magnetic field strength measured with a video magnetograph by a factor of 4.5, but they cannot be responsible for the polarity reversal. (3) A sharp short-term displacement of the neutral line occurred at a time close to the flare maximum, which gave rise to a reversed-polarity magnetic field on a small area of the active region, i.e., a magnetic transient. This can be interpreted as a change in the inclination of the magnetic field lines to the line of sight during the flare. The short-term depolarization of the CaI λ6102.7 Å line emission observed at the other flare knot can also be the result of a change in the magnetic field structure. (4) These fast dynamic changes of the magnetic field lines occurred after the maximum of the impulsive flare phase and were close in time to the appearance of type II radio emission.     

High resolution observations of the 6300 Å oxygen line in the day airglow

Ground based high resolution (R ～ 120,000) spectra of the zenith day sky near 6300 Å were obtained with a PEPSIOS. When compared with the solar spectrum taken with the same spectrometer, the 6300.3 Å line of atomic oxygen was clearly present in emission. The apparent emission rate averaged 6 to 8 kR for solar zenith angles of 50 to 60 deg and decreased smoothly to about 1 kR as the solar zenith angle increased to 95 deg. The average emission line is somewhat different in width than the thermal line width expected with the Jacchia (1971) model for a 250 km altitude.     

The effects of solar and ionospheric parameters on seasonal variation of 6300 Å line emission at Calcutta

The purpose of this paper is to find correlation between OI 6300 Å line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained:

Hα emission line profiles of solar flares with turbulent velocity fields

The H line profile in a flare atmospheric model superposed by a spatially correlated velocity field is studied in detail in this paper. The computations are carried out with the assumption that the velocity field is represented by a Kubo-Anderson process. It is found that the shape and the intensity of the H line profile depend greatly on the parameters of the velocity field. The variation of the profile and its relative deviation with respect to different correlation lengths is more complex than in the case of absorption lines. It is also shown that such a profile cannot be matched by those produced in the usually-used micro- and macro-turbulent approaches, especially for the velocity field with an intermediate correlation length. The results imply that the flare atmosphere should be highly turbulent in order to explain the observed H line profile with only weak central reversal in the flare spectra. Particularly, the effects of meso-turbulent fields should be taken into account in order to improve the spectral diagnostics and modelling of the flare atmosphere.     

The helium 10830 Å line in the undisturbed chromosphere

A study of the solar spectrum near helium 10 830 Å has shown that, where the line is very weak, the anomalous ratio of the two components is due almost certainly to faint blends. The centre-limb intensity variation over supergranule centres is in good agreement with an optically-thin law. The line is stronger over supergranule boundaries, and the ratio of the two components can be understood only if the absorbing elements have been resolved incompletely (as is probable); using centre-limb intensity variations, we have been unable to distinguish between unresolved horizontal platelets or inclined slabs.The integrated absorption in 10 830 Å over supergranule centres is double that at the boundaries. An analysis of the extension of 10 830 Å beyond the limb has failed to reveal the relative contributions from these two regions or their variations with height (though the supergranule-centre emission should be located relatively low). Line profiles in 10 830 Å, hydrogen Pa and Caii 8542 Å indicate that, out to at least 5000 km, line broadening is effectively non-thermal, with horizontal rms velocities of about 20 km s^–1.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.