29,933 research outputs found
Abundances of Baade's Window Giants from Keck/HIRES Spectra: I. Stellar Parameters and [Fe/H] Values
We present the first results of a new abundance survey of the Milky Way bulge
based on Keck/HIRES spectra of 27 K-giants in the Baade's Window (, ) field. The spectral data used in this study are of much higher resolution
and signal-to-noise than previous optical studies of Galactic bulge stars. The
[Fe/H] values of our stars, which range between -1.29 and , were used to
recalibrate large low resolution surveys of bulge stars. Our best value for the
mean [Fe/H] of the bulge is . This mean value is similar to the
mean metallicity of the local disk and indicates that there cannot be a strong
metallicity gradient inside the solar circle. The metallicity distribution of
stars confirms that the bulge does not suffer from the so-called ``G-dwarf''
problem. This paper also details the new abundance techniques necessary to
analyze very metal-rich K-giants, including a new Fe line list and regions of
low blanketing for continuum identification.Comment: Accepted for publication in January 2006 Astrophysical Journal. Long
tables 3--6 withheld to save space (electronic tables in journal paper). 53
pages, 10 figures, 9 table
New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy
Aims: We define the relationship between the double-mode pulsation of
Cepheids and metallicity in a more accurate way, determine the empirical
metallicities of double-mode Cepheids from homogeneous, high-resolution
spectroscopic data, and study of the period-ratio -- metallicity dependence.
Methods: The high S/N echelle spectra obtained with the FEROS spectrograph were
analyzed using a self-developed IRAF script, and the iron abundances were
determined by comparing with synthetic spectra assuming LTE. Results: Accurate
[Fe/H] values of 17 galactic beat Cepheids were determined. All these stars
have solar or slightly subsolar metallicity. Their period ratio P1/P0 shows
strong correlation with their derived [Fe/H] values. The corresponding period
ratio -- metallicity relation has been evaluated.Comment: 10 pages, 7 figures, accepted in A&
The metallicity range of variables in M3
The recently published spectroscopic metallicities of RR Lyrae stars in M3
(Sandstrom, K., Pilachowski, C. A., and Saha, A. 2001, AJ 122, 3212) though
show a relatively wide range of the [Fe/H] values, the conclusion that no
metallicity spread is real has been drawn, as no dependence on either minimum
temperature or period was detected. Comparing these spectroscopic metallicities
with [Fe/H] calculated from the Fourier parameters of the light curves of the
variables a correlation between the [Fe/H] values appears. As a consequence of
the independence of the spectroscopic and photometric metallicities, this
correlation points to the reality of a metallicity spread. The absolute
magnitudes of these stars follow a similar trend along both the spectroscopic
and photometric metallicities as the general relation
predicts, which strengthens that the detected metallicity range is real.Comment: 5 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Metallicity Evolution in the Early Universe
Observations of the damped Lya systems provide direct measurements on the
chemical enrichment history of neutral gas in the early universe. In this
Letter, we present new measurements for four damped Lya systems at high
redshift. Combining these data with [Fe/H] values culled from the literature,
we investigate the metallicity evolution of the universe from z~1.5-4.5.
Contrary to our expectations and the predictions of essentially every chemical
evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal
evolution over this epoch. For the individual systems, we report tentative
evidence for an evolution in the unweighted [Fe/H] mean and the scatter in
[Fe/H] with the higher redshift systems showing lower scatter and lower typical
[Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex.
Finally, we discuss the potential impact of small number statistics and dust on
our conclusions and consider the implications of these results on chemical
evolution in the early universe.Comment: 6 pages, 2 encapsulated figures, Latex2e, uses emulateapj.sty and
onecolfloat.sty. Accepted for publication in ApJ Letters: Feb 28, 200
A High Deuterium Abundance at z=0.7
Of the light elements, the primordial abundance of deuterium, (D/H)_p,
provides the most sensitive diagnostic for the cosmological mass density
parameter Omega_B. Recent high redshift (D/H) measurements are highly
discrepant, although this may reflect observational uncertainties. The larger
(D/H) values, which imply a low Omega_B and require the Universe to be
dominated by non-baryonic matter (dynamical studies indicate a higher total
density parameter), cause problems for galactic chemical evolution models since
they have difficulty in reproducing the large decline down to the lower
present-day (D/H). Conversely, low (D/H) values imply an Omega_B greater than
derived from ^7Li and ^4He abundance measurements, and may require a deuterium
abundance evolution that is too low to easily explain. Here we report the first
measurement at intermediate redshift, where the observational difficulties are
smaller, of a gas cloud with ideal characteristics for this experiment. Our
analysis of the z = 0.7010 absorber toward 1718+4807 indicates (D/H) = 2.0 +/-
0.5 x 10^{-4} which is in the high range. This and other independent
observations suggests there may be a cosmological inhomogeneity in (D/H)_p of
at least a factor of ten.Comment: 6 pages, 1 figur
The connection between the Galactic halo and ancient Dwarf Satellites
We explore the hypothesis that the classical and ultra-faint dwarf spheroidal
satellites of the Milky Way have been the building blocks of the Galactic halo
by comparing their [O/Fe] and [Ba/Fe] versus [Fe/H] patterns with the ones
observed in Galactic halo stars. Oxygen abundances deviate substantially from
the observed abundances in the Galactic halo stars for [Fe/H] values larger
than -2 dex, while they overlap for lower metallicities. On the other hand, for
the [Ba/Fe] ratio the discrepancy is extended at all [Fe/H] values, suggesting
that the majority of stars in the halo are likely to have been formed in situ.
Therefore, we suggest that [Ba/Fe] ratios are a better diagnostic than [O/Fe]
ratios. Moreover, we show the effects of an enriched infall of gas with the
same chemical abundances as the matter ejected and/or stripped from dwarf
satellites of the Milky Way on the chemical evolution of the Galactic halo. We
find that the resulting chemical abundances of the halo stars depend on the
assumed infall time scale, and the presence of a threshold in the gas for star
formation.Comment: To appear in Proceeding of Science: Frontier Research in Astrophysics
- II 23-28 May 2016 Mondello (Palermo), Ital
The Color-Magnitude Relation in Coma: Clues to the Age and Metallicity of Cluster Populations
We have observed three fields of the Coma cluster of galaxies with a narrow
band (modified Stromgren) filter system. Observed galaxies include 31 in the
vicinity of NGC 4889, 48 near NGC 4874, and 60 near NGC 4839 complete to
M_5500=-18 in all three subclusters. Spectrophotometric classification finds
all three subclusters of Coma to be dominated by red, E type (ellipticals/S0's)
galaxies with a mean blue fraction, f_B, of 0.10. The blue fraction increases
to fainter luminosities, possible remnants of dwarf starburst population or the
effects of dynamical friction removing bright, blue galaxies from the cluster
population by mergers. We find the color-magnitude (CM) relation to be well
defined and linear over the range of M_5500=-13 to -22. After calibration to
multi-metallicity models, bright ellipticals are found to have luminosity
weighted mean [Fe/H] values between -0.5 and +0.5, whereas low luminosity
ellipticals have [Fe/H] values ranging from -2 to solar. The lack of CM
relation in our continuum color suggests that a systematic age effect cancels
the metallicity effects in this bandpass. This is confirmed with our age index
which finds a weak correlation between luminosity and mean stellar age in
ellipticals such that the stellar populations of bright ellipticals are 2 to 3
Gyrs younger than low luminosity ellipticals.Comment: 26 pages AAS LaTeX, 6 figures, accepted for publication in A
Carbon Nitrogen, and Oxygen Galactic Gradients: A Solution to the Carbon Enrichment Problem
Eleven models of Galactic chemical evolution, differing in the carbon,
nitrogen,and oxygen yields adopted, have been computed to reproduce the
Galactic O/H values obtained from H II regions. All the models fit the oxygen
gradient, but only two models fit also the carbon gradient, those based on
carbon yields that increase with metallicity due to stellar winds in massive
stars (MS) and decrease with metallicity due to stellar winds in low and
intermediate mass stars (LIMS). The successful models also fit the C/O versus
O/H evolution history of the solar vicinity obtained from stellar observations.
We also compare the present day N/H gradient and the N/O versus O/H and the
C/Fe, N/Fe, O/Fe versus Fe/H evolution histories of the solar vicinity
predicted by our two best models with those derived from H II regions and from
stellar observations. While our two best models fit the C/H and O/H gradients
as well as the C/O versus O/H history, only Model 1 fits well the N/H gradient
and the N/O values for metal poor stars but fails to fit the N/H values for
metal rich stars. Therefore we conclude that our two best models solve the C
enrichment problem, but that further work needs to be done on the N enrichment
problem. By adding the C and O production since the Sun was formed predicted by
Models 1 and 2 to the observed solar values we find an excellent agreement with
the O/H and C/H values of the solar vicinity derived from H II regions O and C
recombination lines. One of the most important results of this paper is that
the fraction of carbon due to MS and LIMS in the interstellar medium is
strongly dependent on time and on the galactocentric distance; at present about
half of the carbon in the interstellar medium of the solar vicinity has been
produced by MS and half by LIMS.Comment: 34 pages, 6 tables, 7 figures. Accepted for publication in Ap
High orders of the perturbation theory for hydrogen atom in magnetic field
The states of hydrogen atom with principal quantum number and zero
magnetic quantum number in constant homogeneous magnetic field are
considered. The coefficients of energy eigenvalues expansion up to 75th order
in powers of are obtained for these states. The series for energy
eigenvalues and wave functions are summed up to values of the order
of atomic magnetic field. The calculations are based on generalization of the
moment method, which may be used in other cases of the hydrogen atom
perturbation by a polynomial in coordinates potential.Comment: 16 pages, LaTeX, 6 figures (ps, eps
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