The lithium content in sunspots: Observations of 2007

The spectra of sunspots were observed in the region of the LiI 6708 Å lines and several FeI and CaI lines. The observations were carried out with a CCD camera in May, June, and July 2007 using the BST-2 telescope of the Crimean Astrophysical Observatory. The spot models were calculated using the observed profiles of FeI and CaI lines. The lithium content was estimated at log(NLi) = 1.20, 1.15, and 1.00 (at the scale of logA(H) = 12.0) using the calculated spot models and observed LiI 6708 Å line profiles.     

Determination of lithium abundance in sunspots: Observations in 1973

Spectra of sunspots in the region of the lithium 6708 ? line, as well as certain CaI, AlI, FeI, YI, ScI, VI lines, were studied. The observations were performed on July 8, 1973 using a BST-2 telescope at the Crimean Astrophysical Observatory. A sunspot model was developed based on the observed profiles of CaI, AlI, FeI, YI, ScI, and VI lines. Using the developed model and observed profile of the Li 6708 ? line, the abundance of lithium was determined. The obtained result is log(N_Li) = 0.95.     

Structure of a simple sunspot from the inversion of IR spectral data

Analysis of spectral data of two neighboring infrared lines, Fe I 15648.5 Å (g = 3) and FeI 15652.9 Å (g_eff = 1.53) are carried out for a simple sunspot when it was near the solar disk center (μ = 0.92), to understand the basic structure of sunspot magnetic field. Inversions of Stokes profiles are carried out to derive different atmospheric parameters both as a function of location within the sunspot and height in the atmosphere. As a result of the inversion we have obtained maps of magnetic field strength, temperature, line‐of‐sight velocity, field inclination and azimuth for different optical depth layers between log(τ₅) = 0 and log(τ₅) = –2.0. In this paper we present few results from our inversion for a layer averaged between log(τ5) from 0.0 to –0.5.     

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.     

Observational evidences for multi-component magnetic field structure in solar flares

Two solar flares of 25 July 1981 and 5 November 2004 of importance 2N and M4.1/1B, respectively, were investigated using observational data obtained with the Echelle spectrograph of the Kyiv University Astronomical Observatory. Stokes I and V profiles of the FeI lines 5233, 5247.1, 5250.2, 5250.6, 5576.1 and of CrI 5247.6 Å have been analyzed. We found several evidences for the existence of spatially unresolved magnetic field structures with kG strengths. In particular, the values of the measured average longitudinal field B _∥ depend on the Lande factors g of the lines: in general, B _∥ increases with increasing factor g. Analogously, the observed line ratio B _∥(5250.2)/B _∥(5247.1) is increasing with increasing distance Δλ from the line center. The observed Stokes V profiles show some deviations from that of an assumed homogeneous field, presented by the Stokes I gradient, dI/dλ. A comparison with the non-split line FeI 5576.1 Å shows that some of these deviations are real and indicate the presence of subtelescopic magnetic elements with discrete field strengths of several kG. The lines with large Lande factors have considerable broadenings of the Stokes I profiles, indicating a strong background magnetic field of mixed polarity. On the basis of all these data we conclude that a four-component magnetic field structure is a possible explanation. The field strengths are about ±1.05 kG in the background field, and 1.3?1.5, 3.9?4.0, and 7.4?7.8 kG at level of middle photosphere (h ≈ 300 km) in the spatially unresolved, small-scale magnetic elements.     

Spectral observations using a BTA telescope of chemically peculiar stars in the spectral region near the Li I (6708 Å) resonance doublet

New spectral observations of chemically peculiar (CP) magnetic stars were obtained using an NES echelle spectrometer with a BTA telescope in the Special Astrophysical Observatory (Russian Academy of Sciences). Several stars were shown to have anomalous Li abundances. Testing and monitoring the stars with Doppler shifts Vsini > 10 km/s indicated that the lithium 6708 Å line was variable in the spectra of some roaAP-CP stars. To distinguish variable features in the spectra, the dispersogram technique was used. The most peculiar among the stars studied is HD 12098. The strong and variable lithium 6708 Å line was detected in the spectrum of this star. The star has been shown to have greatly different lithium abundances in two rotation phases corresponding to opposite surface areas. As mentioned earlier, a similar behavior of the Li blend was found in the spectra of HD 83368 and HD 60435 which have lithium spots on their surface. Spectral observations of slowly rotating CP stars with the Doppler shifts Vsini < 10 km/s revealed the strong and nonvariable lithium 6708 Å line in the spectra of these stars. Quantitative spectral analysis using the Li I 6708 Å resonance doublet and the Li I 6103 Å line shows the lithium abundance, as determined by the 6103 Å line, to be somewhat greater than that determined by the 6708 Å line. A higher ratio of ⁶Li/⁷Li amounting to ～0.3–0.5 was found in these stars. ⁶Li production is assumed to be due to spallation reactions on the surface of magnetic CP stars; this isotope ratio remained in strong magnetic fields.     

Lithium abundance in the sunspot from the observational data of August 1981

A spectrum of a sunspot in the range of the Li I ?? 670.8 nm line and some lines of Ca I, Ti I, Al I, and Na I was measured. Observations were carried out with the TST-2 telescope of the Crimean astrophysical observatory on August 21, 1981. A model of the spot was calculated from the observed profiles of the Ca I, Ti I, Al I, and Na I lines. From the calculated model and the observed profile of the Li I ?? 670.8 nm line, the lithium abundance was estimated as log(N _Li) = 0.78 (in the scale of logA(H)= 12.0).     

Fine structure of solar magnetic fields

The problem of inequality of results of longitudinal magnetic fields measured in the magnotosensetive lines FeI 5250 and FeI 5247 is investigated. The observed ratio of longitudinal components of magnetic field H ₁₁(5250)/H ₁₁(5247) is compared to the calculated for different combinations of magnetic field elements. The calculations have been made with standard model photosphere for quiet regions. It was concluded that the underestimated value of magnetic field obtained with the FeI 5250 line is explained by the presence of unresolved elements with kilogauss magnetic fields.     

Magnetic and velocity fields of active regions

We have observed about 15 active regions on the Sun, with the Advanced Stokes Polarimeter and Dick Dunn Telescope at NSO/SP to map the Stokes parameters in the photospheric Fe 6302.5 Å and chromospheric Mg I 5173 Å lines, during 1999‐2002. The observations are corrected for dark current, gain, instrumental polarization and cross‐talk using ASP pipeline. The wavelength calibration is carried out using the O₂ telluric line 6302 Å which is also present in the observations. The photospheric and chromospheric longitudinal magnetograms are made from the Stokes V profiles, which were intercalibrated with the Kitt Peak magnetograms. The plasma motions are inferred from the line bisector measurements at different positions of the spectral line. In this paper we present the height dependence of Doppler velocity scatter plots of a sunspot in the photospheric Fe I 6302 Å line.     

Alfven waves and sunspot line profiles

We investigate the effect of Alfven waves on the profile of the g = 0 lines FeI 5691.505 and FeI 5434.534. We find nonnegligible oscillation and distortion of the profile and vastly different lines. We calculate the theoretical profiles of these two lines under the action of Alfven waves, compare them with observations and hence verify preliminarily that sunspots are cooled by the propagation of Alfven waves.     

Detection of lithium in the spectrum of the symbiotic Mira star V407 Cygni

We detected the resonance lithium doublet, ⁷LiI λ6708, in the spectra of the symbiotic Mira V407 Cyg (P≈763^d) obtained with a resolution R = λ/Δλ ≈ 18 500. The line equivalent width is ～0.34 Å. The presence of lithium in the atmosphere of the Mira, which, judging by its period, appreciably ascended the asymptotic giant branch (AGB), can be explained by the penetration of its convective envelope into the hot-bottom-burning (HBB) hydrogen-shell source. At the same time, the spectrum of V407 Cyg does not reveal the ZrO λ5551, 6474 absorption bands, which are used to classify S-type stars from low-resolution spectra. We found only weak ZrO λ5718, 6412 bands, which are, however, invisible in low-resolution spectra. Thus, the Mira star V407 Cyg should be classified as being of the spectral type M. In general, the spectrum of V407 Cyg is similar to the spectrum of the red giant in the symbiotic star CH Cyg, but the latter exhibits no lithium lines. The switch-on of the HBB process without any significant enrichment of the atmosphere of an AGB star with s-process elements implies that the third dredge-up is not efficient for some of these stars.     

Measurement and study of the rotations of RS canum venaticorum binaries

We measured the rotations of all the primaries and 5 of the secondaries in 33 RS CVn binary systems, using the three lines in the red region, FeI 6663, FeI 6678 and CaI 6718. A comparison with synchronous rotation shows that none of the systems observed (some with P > 14 d) contradicts the assumption of synchronous rotation, contrary to a previous view.     

The potassium abundance in the solar photosphere

High precision center-limb spectrograms of the K i resonance doublet line at λ 7699 Å were used to study the line formation and to determine the abundance of potassium in the solar atmosphere. The LTE assumption is not valid for these lines. Synthetic profiles computed in NLTE reproduce very well the observed center-limb line behaviour and yield log? _K = 5.14±0.10 for the solar abundance of potassium (on the scale of log? _H = 12 for Hydrogen).     

Interstellar and circumstellar medium in the direction to IR source IRAS 01005+7910

Using the high-resolution spectra obtained at the 6-meter telescope of the SAO RAS over 2002–2013, we studied the spectral features of the lines of interstellar medium. The radial velocities of the Na I 5890 Å, Na I 5896 Å, Ca II 3934 Å and Ca II 3968 Å absorption lines were analyzed. Seven diffuse interstellar bands 4964, 5780, 5797, 6196, 6203, 6379 Å were identified in the optical spectrum of IRAS01005+7910. Radial velocities V_r and equivalent widths W_λ of these DIBs were measured, for which the values of the interstellar reddening E_B?V and column density of neutral hydrogen log [N(H)] were calculated.     

Anomalous abundance of lithium in the roAp star HD 12098 recently discovered in the northern hemisphere of the sky

Spectral observations of Ap-CP stars with the BTA (Special Astronomical Observatory, Russian Academy of Sciences) using the NES echelle spectrometer have revealed several stars with an anomalous lithium abundance. The oscillating star HD 12098, which is the first roAp star in the northern hemisphere of the sky, merits special attention. Strong, variable LiI 6708 Å line was observed in the spectrum of this star. There are not enough observations for a reliable analysis by Doppler mapping, but there are enough to indicate the presence of lithium spots on the surface of this star similar to the roAp stars HD 83368 and HD 60435, on whose surfaces spots with a high lithium abundance have been reliably detected. Parameters for a model of its atmosphere have been chosen using the method of synthetic spectra based on atmospheric models including lines from the VALD list and several additional blended REE lines calculated by the authors. The profile of the lithium LiI 6708 Å blend has been calculated taking the magnetic field into account using the SYNTHM code. A lithium abundance has been determined for two phases of the rotation of HD 12098 that is anomalously high compared to the solar and meteoritic abundances. The large difference in the lithium abundance in the two phases (in two different regions on the star's surface) exceeds 0.5 dex and is very close to that which we have found by analyzing the spectra of the roAp stars HD 83368 and HD 60435. Thus, we have discovered yet another roAp star, HD 12098, with lithium spots on its surface. Translated from Astrofizika, Vol. 51, No. 4, pp. 607–616 (November 2008).     

Sunspot and stray light observations during the 1971, February 25 partial solar eclipse

Observations of a sunspot during and after a partial solar eclipse are described. The amount of scattered light confirms the existence of a spread function component with a half width of 10″. The observations also indicate the possibility of severely underestimating this component by aureole measurements. Umbral continuum intensities of 0.10 I _⊙ in the red spectral region were directly measured, the correction for scattered light amounts to 0.02 I _⊙. Intensities calculated with four umbral models are larger than the observed values, indicating this sunspot to be cooler by some 100 K. The wings of two strong Ca i lines are equally explained by the models of Henoux, Kneer, and Stellmacher/Wiehr. Yun's model can be ruled out because of too high a temperature.     

An Estimate for the Size of Sunspot Cycle 24

For the sunspot cycles in the modern era (cycle?10 to the present), the ratio of R _Z(max)/R _Z(36th month) equals 1.26±0.22, where R _Z(max) is the maximum amplitude of the sunspot cycle?using smoothed monthly mean sunspot number and R _Z(36th month) is the smoothed monthly mean sunspot number 36 months after cycle?minimum. For the current sunspot cycle?24, the 36th month following the cycle?minimum occurred in November 2011, measuring?61.1. Hence, cycle?24 likely will have a maximum amplitude of about 77.0±13.4 (the one-sigma prediction interval), a value well below the average R _Z(max) for the modern era sunspot cycles (about 119.7±39.5).     

The wilson effect and the transparency of sunspot models

Hydrostatic models of sunspot penumbra and umbra are evaluated using Bode's tables of monochromatic absorption coefficients andT-τ-relations given by Makita and Morimoto (1960) and by Zwaan (1965). These models are placed side by side to simulate a complete sunspot corresponding to an area of 480×10^?6 of a hemisphere. Intensity profiles are evaluated for aspect angles up to 85° and compared to observations. The primary aim was to study the influence of spot transparency, which is closely related to the gas-pressure, on the Wilson-effect and on other changes in the intensity profile that appear close to the solar limb. The gas-pressures at the zero-level in the geometrical depth (z=0) corresponding to optical depth, τ=10^?3, both in the umbra,P ₀ ^u , and in the penumbra,P ₀ ^p , appear as adjustable parameters. When curvature is taken into account, the Wilson-effect cannot be reproduced without depressing the zero-point in the geometrical scale in the umbra relative to the same layer in the photosphere. A depression of 400 km will give a reasonably good fit for the Wilson-effect providedP ₀ ^u <P ₀ ^P <P ₀ ^Ph . The model we found to give the best fit is based on Makita and Morimoto'sT-τ-relations withP ₀ ^P =3200 andP ₀ ^u =800. We have here chosen an umbra pressure that gives a small limb-side intensity peak at the penumbra border, assuming that the bright points described by Bray and Loughhead (1964) may be interpreted in terms of a transparency effect. Other parameters measured by Wilson and Cannon (1968) are evaluated, and for some a good agreement was obtained, while for others only a qualitative effect in the same direction could be found. Surfaces along which the optical path is constant (isodiaphanous surfaces) are functions of aspect angle and well suited for visualizing the transparency in spots. It is shown how for a wide range of models the isodiaphanous surfaces get asymmetric close to the limb. This has consequences for the interpretation of the Evershed-effect. In fact, under certain conditions, a ‘masking’ effect may take place because the greater transparency in the penumbra will allow observations of a deep laying flow, which will not be visible through the more opaque photosphere. Due to the asymmetry this effect is different on the limb side and the center side. We also found the spot to show an apparent displacement away from the limb, which at a heliocentric distance of 85° amounts to about one second of arc. Intensity profiles in the near infrared at 8206 Å and at 16482 Å are evaluated, and the importance of observations in these spectral regions is emphasized.     

Physical conditions in the chromosphere of a two-strand solar flare with ejection

Chromosphere layers of solar flares were investigated according to the observed profiles of the H_α line. A two-strand flare was observed on September 4, 1990. Spectra were obtained with the ATsU-26 solar horizontal telescope at Terskol Peak Observatory (3100 m). Spectra photometry is performed for two bright nodes of one strand of the flare. Some profiles are superposed to the ejection. The observed profiles are characterized by high emissions in the wings of the H_α line (up to 10–12 Å) under relatively low intensity in the center of H_α (r = 0.35–0.6). To explain such profile behavior we calculated flare models with two or three components. Separate components of the model correspond to unresolved details in the flare area and therefore the averaged profile is calculated. Emission in the far wings is explained by model components with deep heating of chromosphere layers. These occupy 5–12% of the total area. Noticeable emission asymmetry is explained by ray velocities of up to 70 km/s and more. The models are determined by agreement of the observed and calculated profiles. We processed several photometric profiles for seven observations. The temperature in the models with deep heating in the lower cromosphere is increased by 1000–2500 K with respect to the model with an undisturbed chromosphere VAL-C. The second feature of the observed profiles is their high asymmetry and shift with respect to the undisturbed profiles. This can be explained by the opposite motion of the material. We revealed that for the most of the profiles the line-of-sight velocities were directed to the observer in the upper chromosphere (10–100 km/s) and from the observer in the lower chromosphere (5–20 km/s).     

Analysis of HST ultraviolet spectra for T Tauri stars: RU Lup

The ultraviolet spectra of the star RU Lup obtained with the Hubble Space Telescope are analyzed. Emission lines are identified. The presence of absorption components with a nearly zero residual intensity in the Mg II resonance doublet lines is indicative of mass outflow with a velocity V _∞?300 km s^?1. These lines also exhibit a broad (?1400 km s^?1 at the base) component originating in the star itself. The profiles of the (optically thin) Si II] and Si III]1892 Å lines for the first time unequivocally prove that these lines originate in an accretion shock wave rather than in the chromosphere, with the gas infall velocity being V ₀?400 km s^?1. The intensity ratio of the C IV 1550 Å and Si IV 1400 Å resonance doublet components was found to be close to unity, suggesting a high accreted-gas density, logN ₀>12.5. Molecular H₂ Lyman lines formed in the stellar wind were detected. The H I Lα luminosity of RU Lup was found from their intensities to exceed 10% of L _bol. Radiation pressure in the Lα line on atomic hydrogen may play a significant role in the initial acceleration of stellar-wind matter, but the effect of Lα emission on the dynamics of molecular gas is negligible.