7,024 research outputs found
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=22.000.15 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
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