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

A refined analysis of the remarkable Bp star HR 6000

UVES spectra of the very young (~10^7 years) peculiar B-type star HR 6000 were analyzed in the near-UV and visual spectral regions (3050-9460 A) with the aim to extend to other spectral ranges the study made previously in the UV using IUE spectra. Stellar parameters Teff=12850K, logg=4.10, and xi=0km/s, as determined from H_beta, H_gamma, H_delta Balmer profiles and from the Fe I, Fe II ionization equilibrium, were used to compute an individual abundances ATLAS12 model. We identified spectral peculiarities and obtained final stellar abundances by comparing observed and computed equivalent widths and line profiles. The adopted model fails to reproduce the (b-y) and c color indices. The spectral analysis has revealed: the presence of emission lines for Mn II, Cr II, and Fe II; isotopic anomalies for Hg, Ca; the presence of interstellar lines of Na I at lambda lambda 3302.3, 3302.9, 5890, 5896 A, and of K I at 7665, 7699 A; the presence of a huge quantity of unidentified lines, which we presume to be mostly due to Fe II transitions owing to the large Fe overabundance amounting to [+0.7]. The main chemical peculiarities are an extreme overabundance of Xe, followed by those of Hg, P, Y, Mn, Fe, Be, and Ti. The most underabundant element is Si, followed by C, N, Al, S, Mg, V, Sr, Co, Cl, Sc, and Ni. The silicon underabundance [-2.9] is the lowest value for Si ever observed in any HgMn star. The observed lines of He I can not be reproduced by a single value of the He abundance, but they require values ranging from [-0.8] to [-1.6]. Furthermore, when the observed and computed wings of He I lines are fitted, the observed line cores are much weaker than the computed ones. From the present analysis we infer the presence of vertical abundance stratification for He, Mn, and possibly also P.Comment: 14 pages, 8 figures, 6 tables, accepted for publication in A&

High resolution spectroscopy of HgMn stars: a time of surprises

We present the results of a high spectral resolution study of a few spectroscopic binaries with HgMn primary stars. We detect for the first time in the spectra of HgMn stars that for many elements the line profiles are variable over the rotation period. The strongest profile variations are found for the elements Pt, Hg, Sr, Y, Zr, Mn, Ga, He and Nd. The slight variability of He and Y is also confirmed from the study of high resolution spectra of another HgMn star, alpha And.Comment: 2 pages, 2 figures, to appear in "Precision Spectroscopy in Astrophysics

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

Stellar populations in the dwarf spheroidal galaxy Leo I

We present a detailed study of the color magnitude diagram (CMD) of the dwarf spheroidal galaxy Leo I, based on archival Hubble Space Telescope data. Our photometric analysis, confirming previous results on the brighter portion of the CMD, allow us to obtain an accurate sampling of the stellar populations also at the faint magnitudes corresponding to the Main Sequence. By adopting a homogeneous and consistent theoretical scenario for both hydrogen and central helium-burning evolutionary phases, the various features observed in the CMD are interpreted and reliable estimations for both the distance modulus and the age(s) for the main stellar components of Leo I are derived. More in details, from the upper luminosity of the Red Giant Branch and the lower luminosity of the Subgiant Branch we simultaneously constrain the galaxy distance and the age of the oldest stellar population in Leo I. In this way we obtain a distance modulus (m-M)_V=22.00$\pm$0.15 mag and an age of 10--15 Gyr or 9--13 Gyr, adopting a metallicity Z=0.0001 and 0.0004, respectively. The reliability of this distance modulus has been tested by comparing the observed distribution of the Leo I anomalous Cepheids in the period-magnitude diagram with the predicted boundaries of the instability strip, as given by convective pulsating models.Comment: 19 pages, 3 tables, 14 figures To be published in A