Line Blanketing in Vega and Sirus

A theoretical model and spectrum calculation for Vega is discussed. The abundance of carbon is approximately -3.8, which is 0.3 lower than the old solar value and supports Mount and Linsky's newer value. The oxygen abundance is approximately -3.5. Assuming that Vega has solar abundances, the solar oxygen abundance appears to have been overestimated by 0.3 in the log. Other abundances appear to be solar. For Sirius the calculations do not agree with the observed spectrum. Line opacity is considerably underestimated, notably in third-spectrum iron group lines. Carbon is underabundant relative to Vega by 0.2 in the log. Nitrogen is unchanged. Oxygen is enhanced by 0.3. Heavier elements are enhanced by 1.0 in the log. Calibration yields 1.3E-10 ergs/sq cm/s/nm for each U1 Copernicus count at 130 nm

The fourth positive system of carbon monoxide

Tables of energy levels, Franck-Condon factors, r-centroids, transition moments, line wavelengths, and gf values are presented for the fourth positive system of CO

A matrix method for calculating the source function, mean intensity, and flux in a model atmosphere

Matrix method for calculating source function, mean intensity, and flux in model stellar atmospher

New Fe II energy levels from stellar spectra

The spectra of B-type and early A-type stars show numerous unidentified lines in the whole optical range, especially in the 5100 - 5400 A interval. Because Fe II transitions to high energy levels should be observed in this region, we used semiempirical predicted wavelengths and gf-values of Fe II to identify unknown lines. Semiempirical line data for Fe II computed by Kurucz are used to synthesize the spectrum of the slow-rotating, Fe-overabundant CP star HR 6000. We determined a total of 109 new 4f levels for Fe II with energies ranging from 122324 cm^-1 to 128110 cm^-1. They belong to the Fe II subconfigurations 3d^6(^3P)4f (10 levels), 3d^6(^3H)4f (36 levels), 3d^6(^3F)4f (37 levels), and 3d^6(^3G)4f (26 levels). We also found 14 even levels from 4d (3 levels), 5d (7 levels), and 6d (4 levels) configurations. The new levels have allowed us to identify more than 50% of the previously unidentified lines of HR 6000 in the wavelength region 3800-8000 A. Tables listing the new energy levels are given in the paper; tables listing the spectral lines with loggf>/=-1.5 that are transitions to the 4f energy levels are given in the Online Material. These new levels produce 18000 lines throughout the spectrum from the ultraviolet to the infrared.Comment: Paper accepted by A&A for publicatio

New Mn II energy levels from STIS-HST spectrum of the HgMn star HD 175640

The NIST database lists several Mn II lines that were observed in the laboratory but not classified. They cannot be used in spectrum synthesis because their atomic line data are unknown. These lines are concentrated in the 2380-2700 A interval. We aimed to assign energy levels and log gf values to these lines. Semi-empirical line data for Mn II computed by Kurucz were used to synthesize the ultraviolet spectrum of the slow-rotating, HgMn star HD 175640. The spectrum was compared with the high-resolution spectrum observed with the HST-STIS equipment. A UVES spectrum covering the 3050-10000 A region was also examined. We determined a total of 73 new energy levels, 58 from the STIS spectrum of HD 175640 and another 15 from the UVES spectrum. The new energy levels give rise to numerous new computed lines. We have identified more than 50% of the unclassified lines listed in the NIST database and have changed the assignement of another 24 lines. An abundance analysis of the star HD 175640, based on the comparison of observed and computed ultraviolet spectra in the 1250-3040 A interval, is the by-product of this study on Mn II.Comment: Paper accepted by Astronomy & Astrophysic

Modelling the incomplete Paschen-Back effect in the spectra of magnetic Ap stars

We present first results of a systematic investigation of the incomplete Paschen-Back effect in magnetic Ap stars. A short overview of the theory is followed by a demonstration of how level splittings and component strengths change with magnetic field strength for some lines of special astrophysical interest. Requirements are set out for a code which allows the calculation of full Stokes spectra in the Paschen-Back regime and the behaviour of Stokes I and V profiles of transitions in the multiplet 74 of FeII is discussed in some detail. It is shown that the incomplete Paschen-Back effect can lead to noticeable line shifts which strongly depend on total multiplet strength, magnetic field strength and field direction. Ghost components (which violate the normal selection rule on J) show up in strong magnetic fields but are probably unobservable. Finally it is shown that measurements of the integrated magnetic field modulus $H_s$ are not adversely affected by the Paschen-Back effect, and that there is a potential problem in (magnetic) Doppler mapping if lines in the Paschen-Back regime are treated in the Zeeman approximation.Comment: 8 pages, 10 figures, to appear in MNRA

HST Spectrophotometry and Models for Solar Analogs

Absolute flux distributions for seven solar analog stars are measured from 0.3 to 2.5 \mu m by HST spectrophotometry.In order to predict the longer wavelength mid-IR fluxes that are required for JWST calibration, the HST SEDs are fit with Castelli & Kurucz model atmospheres; and the results are compared with fits from the MARCS model grid. The rms residuals in 10 broad band bins are all <0.5% for the best fits from both model grids. However, the fits differ systematically: The MARCS fits are 40-100 K hotter in T_{eff}, 0.25-0.80 higher in log g, 0.01-0.10 higher in log z, and 0.008-0.021 higher in the reddening E(B-V), probably because their specifications include different metal abundances. Despite these differences in the parameters of the fits, the predicted mid-IR fluxes differ by only ~1%; and the modeled flux distributions of these G stars have an estimated ensemble accuracy of 2% out to 30 \mu m.Comment: 19 pages, 2 tables, 7 figures; to appear in AJ 2010 Apri