One- and multi-component models of the upper photosphere based on molecular spectra

Non-LTE synthetic spectra derived from a detailed analysis of the formation of the CN (0, 0) λ13883 Å spectrum are compared with center-limb photoelectric spectra taken at Kitt Peak National Observatory. Kitt Peak National Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. Significant non-LTE effects are found and the Kurucz, Altrock-Cannon, Mount-Linsky II, and HSRA models are compared. We derive a solar carbon abundance of A _c =8.30±0.10 for the Mount-Linsky model and A _c =8.40±0.10 for the Altrock-Cannon model, compared to the HSRA value of A _c =8.55±0.10, assuming a nitrogen abundance of logA _N=7.93. In addition we specify the regions of formation for the CN(0, 0) 3883.35 Å bandhead at disc center and limb.     

Horizontal velocities in the solar photosphere

Horizontal macroscopic velocities V _hor in the photosphere are studied. High-resolution spectrograms of quiet regions are analyzed for center-limb variation of rms Doppler shifts. The data are treated to assure that the observed velocities refer to constant size volumes on the Sun (800 × × 3000 × 250 km), independent of μ. Using known height variation of vertical velocities and calculated line formation heights, the height dependence of 〈V _hor〉 is obtained. From a value around 450 m s^?1 it decreases rapidly with increasing height. To study also small-scale velocities, the time evolution of subarcsecond size elements in the photospheric network (solar filigree) is studied on filtergrams. It is concluded that they show proper motions implying 〈V _hor〉 about 1 km s^?1.     

Atmospheric iron abundance in the primary component of υ Sgr

Based on the observed energy distribution and line spectrum of the primary component of the binary υ Sgr, we computed blanketed model atmospheres. The atmospheric iron abundance in the primary component of υ Sgr was derived from photographic and CCD spectra. Our analysis confirmed the previously inferred T _eff = 13500 ± 150 K and logg = 2.0 ± 0.5. The microturbulent velocity was found from spectral lines in different spectral ranges to be V _t = 8–12 km s^?1. We refined the mass fractions of light elements: 10^?4 for H, 0.91 for He, 0.013 for C, 0.049 for N, and 0.008 for O. The iron abundance was determined with a high accuracy from Fe I, Fe II, and Fe III lines in the spectral range 4000–7000 Å: log (N(Fe)/∑N _i ) = ?3.80±0.20.     

The ability of current micro-velocity models to represent center-limb line profiles

We present results on the ability of microturbulence, LTE line formation, and a homogeneous thermal model to realistically represent the center-limb variation of temporally and spacially averaged solar line profiles. We have used three somewhat similar semi-empirical thermal models in combination with five current microturbulence models which cover the gamut of homogeneous-isotropic to nonhomogeneous-anisotropic. From high resolution photoelectric data for λ λ5000–6000 at five μ-values (1, 0.63, 0.4, 0.25, 0.16) obtained at KPNO, we selected 17 Fe i and 5 Fe ii line profiles to unblend and symmetrize for study. An iterative scheme has been developed to calculate theoretical profiles for the various combination of models and compare them to the observed profile using the abundance at each limb position and the magnitude of the pressure broadening at the center of the disc as parameters. We find that a microturbulence model, for which the radial and tangential components increase into deeper layers with ξ_tan>ξ_rad, produces a reasonable good center-limb fit for lines less than 100 mÅ. However, for lines stronger than 140 mÅ, microturbulence models with no depth dependence produce the best match between theory and observation. Thus, there is reason to question the uniqueness of the microturbulence concept.     

The solar abundance of germanium

The solar abundance of germanium, deduced from two relatively unblended Ge i lines, λ3039.06 and λ3269.50 is found to be log N(Ge) = 3.50 ± 0.05 on the scale log N(H) = 12.00 in good agreement with Cameron's recent solar system abundance logN(Ge) = 3.56 (on assumption log N(Si) = 7.50).     

Atomic-beam study of the solar 7699 Å potassium line and the solar gravitational red-shift

The shape and red-shift of the solar potassium resonance line (4² P _1/2→4² S _1/2) at 7699 Å have been studied by an atomic-beam resonant scattering technique. Light from the central 10% of the solar image fell on a potassium atomic beam whose scattering wavelength was shifted in a known way by a magnetic field. The line profile was obtained by measuring the scattered light intensity as a function of magnetic field. The time required for a single profile of the line core was 30–40 min. Most of the observed profiles were asymmetrical and the character of the asymmetry varied in an erratic way from profile to profile. The mean red-shift of the 40 profiles which showed small or no asymmetry was: (δλ)_mean = 10 ± 1 mÅ = (0.61±0.06)(δλ)_gravwhere (δλ _grav) is the gravitational red-shift predicted on the basis of the principle of equivalence. This result, together with those of other recent experiments, is consistent with the previously observed correlation between the red-shift of a solar line and its strength. Various checks of the experimental method are discussed, including preliminary measurements on the solar sodium D1 line.     

Forbidden Ca ii in the Sun unmasked by way of Venus

Eleven high-dispersion spectra of Venus, taken with blue Doppler shifts have enabled us to unmask the 7323.88 Å forbidden line of Ca ii from terrestrial absorption. We obtain an equivalent width of 7.4±0.4 mÅ for this line in integrated sunlight. Our value of W _λ is smaller than previous values and much more accurate. The HSRA solar model gives a solar calcium abundance of A _Ca = 6.21.     

Influence of departures from LTE on oxygen abundance determination in the atmospheres of A-K stars

We have performed non-LTE calculations for O I with a multilevel model atom using currently available atomic data for a set of parameters corresponding to stars of spectral types from A to K. Departures from LTE lead to a strengthening of O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The non-LTE correction does not exceed 0.05 dex in absolute value for visible O I lines for main-sequence stars in the entire temperature range. For the infrared O I 7771 Å line, the non-LTE correction can reach ?1.9 dex. The departures from LTE are enhanced with increasing temperature and decreasing surface gravity. We have derived the oxygen abundance for three A-type mainsequence stars with reliably determined parameters (Vega, Sirius, HD 32115). For each of the stars, allowance for the departures from LTE leads to a decrease in the difference between the abundances from infrared and visible lines, for example, for Vega from 1.17 dex in LTE to 0.14 dex when abandoning LTE. In the case of Procyon and the Sun, inelastic collisions with HI affect the statistical equilibrium of OI, and agreement between the abundances from different lines is achieved when using Drawin’s classical formalism. Based on the O I 6300, 6158, 7771-5, and 8446 Å lines of the solar spectrum, we have derived the mean oxygen abundance log ? = 8.74 ± 0.05 using a classical plane-parallel model solar atmosphere and log ? _+3D = 8.78 ± 0.03 by applying the 3D corrections taken from the literature.     

Computation of oscillator strengths by a semiempirical method for some elements of the iron group and their solar photospheric abundance

Absolute oscillator strengths are computed by the STF method for selected lines of Sci.The lifetimes deduced from these values are in satisfactory agreement with recent beam-foil measurements. From a study of 10 selected lines, a new value of the solar photospheric abundance is derived (logN _sc = 3.04) in agreement with the meteoritic value.     

The solar photospheric abundance of iron

A new value of the solar photospheric abundance of iron, independent of line-shape parameters, is derived. Our analysis is based on a study of 40 weak infrared lines (0.85<λ<2.5 μ) for which theoretical oscillator strengths (calculated with configuration interactions taken into account) have recently been computed by Kurucz (1974). The abundance obtained, A _Fe = 7.57±0.11 (in the usual scale where log N _H = 12.00) is in agreement with the ‘high’ solar values recently reported in the literature and with the meteoritic abundance.     

A spectroscopic study of V1016 Ori

Two CCD spectra of the star V1016 Ori were obtained with the echelle spectrograph of the 6-m (BTA) telescope. An analysis of these spectra allowed us to estimate the star's atmospheric parameters (T _eff=29700 K, logg=4.4) and projected rotational velocity (Vsini=60 km s^?1) and to determine its chemical composition. Chemical anomalies were found. The Fe abundance is nearly solar; He, C, O, Mg, Al, Si are underabundant; and Ne, S, Zn are overabundant. The “spectroscopic” radius of the primary is in satisfactory agreement with its radius determined from the light and radial-velocity curves if the small star is assumed to lie in front of the giant star during an eclipse. The paradox of the primary's anomalous radius is thus resolved. A table of line equivalent widths and a portion of the star's spectrum are given in Appendices 1 and 2.     

Calculation of coronal line intensities for boron-like ions

New atomic data (Saha and Trefftz, 1982a) have been used to calculate line intensities of S xii for the physical conditions found in the solar corona. They are compared with similar calculations for S ix (Saha and Trefftz, 1982b) and with published work. For the density sensitive intensity ratio I ₂₂₇/I2₂₁₈ the new values give the observed ratio (Malinovski and Heroux, 1973) for an electron density of logN _e = 8.5 which is more likely than the density deduced from the values of Flower and Nussbaumer (1975), logN _e ? 7.     

Determination of galactic rotation parameters and the solar galactocentric distance R 0 from 73 masers

We have determined the Galactic rotation parameters and the solar Galactocentric distance R ₀ by simultaneously solving Bottlinger’s kinematic equations using data on masers with known line-of-sight velocities and highly accurate trigonometric parallaxes and proper motions measured by VLBI. Our sample includes 73 masers spanning the range of Galactocentric distances from 3 to 14 kpc. The solutions found are Ω₀ = 28.86 ± 0.45 km s^?1 kpc^?1, Ω′₀ = ?3.96 ± 0.09 km s^?1 kpc^?2, Ω″₀ = 0.790 ± 0.027 km s^?1 kpc^?3, and R ₀ = 8.3 ± 0.2 kpc. In this case, the linear rotation velocity at the solar distance R ₀ is V = 241 ± 7 km s^?1. Note that we have obtained the R ₀ estimate, which is of greatest interest, from masers for the first time; it is in good agreement with the most recent estimates and even surpasses them in accuracy.     

Altitude profile of H in the atmosphere of Venus from Lyman α observations of Venera 11 and Venera 12 and origin of the hot exospheric component

Two extreme ultraviolet (EUV) spectrophotometers flown in December 1978 on Venera 11 and Venera 12 measured the hydrogen Lyman α emission resonantly scattered in the atmosphere of Venus. Measurements were obtained across the dayside of the disk, and in the exosphere up to 50,000 km. They were analyzed with spherically symmetric models for which the radiative transfer equation was solved. The H content of the Venus atmosphere varies from optically thin to moderately thick regions. A shape fit at the bright limb allows one to determine the exospheric temperature T_c and the number density n_c independently of the calibration of the instrument or the exact value of the solar flux. The dayside exospheric temperature was measured for the first time in the polar regions, with T_c = 300 ± 25°K for Venera 11 (79°S) and T_c = 275 ± 25°K (59°S) for Venera 12. At the same place, the density is n_c = 4_?2⁺³ × 10⁴ atom.cm^?3, and the integrated number density N_t from 250 to 110 km (the level of CO₂ absorption) is 2.1 × 10¹² atom.cm^?2, a factor of 3 to 6 lower than that predicted in aeronomical models. This probably indicates that the models should be revised in the content of H-bearing molecules and should include the effect of dynamics. Across the disk the value of N_t decreases smoothly with a total variation of two from the morning side to the afternoon side. Alternately it could be a latitude effect, with less hydrogen in the polar regions. The nonthermal component if clearly seen up to 40,000 km of altitude. It is twice as abundant as at the time of Mariner 10 (solar minimum). Its radial distribution above 4000 km can be simulated by an exospheric distribution with T = 10³⁰K and n = 10³ atom.cm^?3 at the exobase level. However, there are less hot atoms between 2000 and 4000 km than predicted by an ionospheric source. A by-product of the analysis is a determination of a very high solar Lyman α flux of 7.6 × 10¹¹ photons (cm² sec Å)^?1 at line center (1 AU) in December 1978.     

Kinematics of the galaxy from Cepheids with proper motions from the Gaia DR1 catalogue

A sample of classical Cepheids with known distances and line-of-sight velocities has been supplemented with proper motions from the Gaia DR1 catalogue. Based on the velocities of 260 stars, we have found the components of the peculiar solar velocity vector (U, V, W)_⊙ = (7.90, 11.73, 7.39) ± (0.65, 0.77, 0.62) km s^?1 and the following parameters of the Galactic rotation curve: Ω₀ = 28.84 ± 0.33 km s^?1 kpc^?1, Ω′₀ = ?4.05 ± 0.10 km s^?1 kpc^?2, and Ω″₀ = 0.805 ± 0.067 km s^?1 kpc^?3 for the adopted solar Galactocentric distance R ₀ = 8 kpc; the linear rotation velocity of the local standard of rest is V ₀ = 231 ± 6 km s^?1.     

A method for the determination of the lithium abundance in sunspots: Observations for 2011

Sunspot spectra for LiI 6708Å lines and for several FeI and CaI lines were obtained. Observations were performed in January and in August, 2011 using the TST-2 telescope with a charge-coupled camera at the Crimean Astrophysical Observatory. The sunspot models were calculated by using the observing profiles of FeI and CaI lines. Lithium abundance was determined by using the calculated sunspot models and LiI 6708Å observed profiles; this equals log(N _Li) = 0.98 and 0.95 (in the scale logA(H) = 12.0).     

Remarks concerning Ward's ‘the latitudinal motion of sunspots and solar meridional circulations’

Oscillator strengths are calculated for 259 lines of Ti i by taking configuration interaction into account in a somewhat simplified treatment. Radial integrals are obtained by an adaptation of the scaled Thomas-Fermi method. The great majority of selected lines originate from slightly perturbed terms. From a satisfactory comparison of our g \({\text{f}}\) -values with recent experimental data and with solar results in the visible region, we have been able to extend the work for some infrared lines. Very few transition probabilities were known for Ti i in that spectral range. On the basis of our oscillator strengths, a mean value logN _ti = 4.88 ± 0.12 (in the usual scale), is proposed for the solar photospheric abundance, in agreement with the meteoritic value.     

The solar abundance of thulium

The solar spectrum contains one relatively unblended line λ 3131.258 Tm ii which yields a thulium abundance of log N(Tm)/N(H) + 12 = {Tm} = 0.80 ± 0.10, with the Corliss and Bozman f-value. A recent beam-foil experiment suggests that the thulium abundance may be reduced to {Tm} = 0.30.     

Isotopes of samarium in the sun

Terrestrial samarium consists of seven isotopes. Some spectral lines from Sm have isotope shifts and hyperfine structures that will modify the profile of the absorption lines in the Fraunhofer spectrum. The photospheric spectrum around the Sm ii lines at 4467 and 4519 Å has been studied. Although it is impossible to derive the solar abundance of each individual isotope, it is shown that a terrestrial isotopic composition can account for the anomal line width and asymmetry of the observed solar lines. The solar abundance found from the two lines is A(Sm) = 1.54 in the logarithmic A(H) = 12.00 scale.     

Interpretation of the 6818.9-Å methane line in terms of inhomogeneous scattering models for Uranus and Neptune

We have obtained high-resolution spectra of Uranus and Neptune in the methane transition near 6800 Å, and in particular, the 6818.9Å feature. Calculated equivalent widths for this line using recently proposed models of the atmospheres of these two planets indicate that the C/H ratio is greater than or equal to 5 × 10^?3 below the CH₄ saturation level. This value is 12 times the solar mixing ratio. The half-widths of the computed line profiles are in agreement with the observed half-widths. Therefore, it is unnecessary to introduce an unidentified constituent with an abundance comparable to H₂, postulated recently by Belton and Hayes, and by Bergstrahl, to account for the observed line broadening.