No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The peculiarities of chemical elements abundances in the atmosphere of PMMR23 – red supergiant of Small Magellanic Cloud, as a result of interstellar gas accretion
... We have previously investigated possible accretion features in several binary stellar systems [16][17][18][19], in Magellanic Cloud supergiants RM_1-390 and PMMR23 [20,21], in barium stars [22,23], in the supergiant BL138 of the Fornax dwarf spheroidal galaxy [24], in the pulsating variable star V1719 Cyg [25], in F-K giants of the Local region of the Galaxy [26], and in the planetary host halo giant HD47536 [27]. ...
The relationships between the relative abundances of chemical elements and their second ionization potentials, as well as their condensation temperatures, were analyzed using four published homogeneous abundance surveys of halo and thin disk stars. We selected 932 stars with effective temperatures ranging from 4900 K to 5900 K and used the abundances of 10 chemical elements common across all surveys: Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, and Ni. The correlation coefficients between the relative abundances of these elements and their second ionization potentials and condensation temperatures were investigated in relation to metallicity and the stars' location in the Galaxy. The observed correlations may result from certain physical processes, such as the accretion of interstellar gas onto stellar atmospheres. We also analyzed the dependencies of relative abundances on second ionization potentials based on published abundance patterns in five halo stars. Evidence of charge-exchange reactions in the atmospheres of these stars was found. For more accurate determination of stellar ages from the abundance ratios of radioactive and stable chemical elements in stellar atmospheres, processes such as charge-exchange reactions and dust-gas separation should be considered in future detailed investigations. Additionally, changes in the chemical abundances in the atmospheres of halo stars after crossing the Galactic plane were found to be possible.
In this study, we conduct a pilot program aimed at the red supergiant
population of the Magellanic Clouds. We intend to extend the current known
sample to the unexplored low end of the brightness distribution of these stars,
building a more representative dataset with which to extrapolate their
behaviour to other Galactic and extra-galactic environments. We select
candidates using only near infrared photometry, and with medium resolution
multi-object spectroscopy, we perform spectral classification and derive their
line-of-sight velocities, confirming the nature of the candidates and their
membership to the clouds. Around two hundred new RSGs have been detected,
hinting at a yet to be observed large population. Using near and mid infrared
photometry we study the brightness distribution of these stars, the onset of
mass-loss and the effect of dust in their atmospheres. Based on this sample,
new a priori classification criteria are investigated, combining mid and near
infrared photometry to improve the observational efficiency of similar programs
as this.
We investigated the chemical composition of. Pup using high-resolution spectral observations taken from the Very Large Telescope and the IUE archives and also spectra obtained at the 1.8 m telescope of the Bohyunsan observatory in Korea. The abundances of 56 chemical elements and the upper limits of Li and Be abundances were determined. The abundance pattern of. Pup was found to be similar to that of Am-type stars. The possibility of the influence of the accretion of interstellar gas and dust on the abundance patterns of B-F-type stars is discussed. The plots of the relative abundances of chemical elements in the atmospheres of. Pup and delta Sct versus the second ionization potentials of these elements show the correlations. The discontinuities at 13.6 and 24.6 eV-the ionization potentials of hydrogen and helium, respectively, are also exhibited in these plots. These discontinuities can be explained by interaction of the atoms of interstellar gas, mainly hydrogen and helium atoms, with the atoms of stellar photospheres (so-called charge-exchange reactions). Note that only the jumps near 13.6 and 24.6 eV were pointed out in previous investigations of relative abundances versus the second ionization potentials for Am-type stars. The dependencies of the relative abundances of chemical elements on the second ionization potentials of these elements were investigated using the published abundance patterns of B-F-type stars. The correlations of relative and absolute abundances of chemical elements, second ionization potentials, and projected rotational velocities are clearly detected for stars with effective temperatures between 7,000 and 12,000 K. If the correlation of relative abundances and second ionization potentials can be explained by the accretion of interstellar gas on the stellar surfaces, the investigation of these correlations can provide valuable information on the density and velocities of interstellar gas in different regions of the Galaxy and also on the influence of this phenomenon on stellar evolution. The dependencies of the relative abundances of chemical elements on the condensation temperatures of these elements were also found in the atmospheres of. Pup, d Sct, and other B-F-type stars. Ten possible. Boo-type stars were detected. The effective temperatures of these objects are between 10,900 and 14,000 K.
We re-evaluate the abundances of the elements in the Sun from copper (Z = 29) to thorium (Z = 90). Our results are mostly based on neutral and singly-ionised lines in the solar spectrum. We use the latest 3D hydrodynamic solar model atmosphere, and in a few cases also correct for departures from local thermodynamic equilibrium (LTE) using non-LTE (NLTE) calculations performed in 1D. In order to minimise statistical and systematic uncertainties, we make stringent line selections, employ the highest-quality observational data and carefully assess oscillator strengths, hyperfine constants and isotopic separations available in the literature, for every line included in our analysis. Our results are typically in good agreement with the abundances in the most pristine meteorites, but there are some interesting exceptions. This analysis constitutes both a full exposition and a slight update of the relevant parts of the preliminary results we presented in Asplund et al. (2009, ARA&A;, 47, 481), including full line lists and details of all input data that we have employed.Tables 1-3 are available in electronic form at http://www.aanda.org
We provide APASS photometry in the Landolt BV and Sloan g'r'i' bands for all
the 425,743 stars included in the latest 4th RAVE Data Release. The internal
accuracy of the APASS photometry of RAVE stars, expressed as error of the mean
of data obtained and separately calibrated over a median of 4 distinct
observing epochs and distributed between 2009 and 2013, is 0.013, 0.012, 0.012,
0.014 and 0.021 mag for B, V, g', r' and i' band, respectively. The equally
high external accuracy of APASS photometry has been verified on secondary
Landolt and Sloan photometric standard stars not involved in the APASS
calibration process, and on a large body of literature data on field and
cluster stars, confirming the absence of offsets and trends. Compared with the
Carlsberg Meridian Catalog (CMC-15), APASS astrometry of RAVE stars is accurate
to a median value of 0.098 arcsec. Brightness distribution functions for the
RAVE stars have been derived in all bands. APASS photometry of RAVE stars,
augmented by 2MASS JHK infrared data, has been chi2 fitted to a densely
populated synthetic photometric library designed to widely explore in
temperature, surface gravity, metallicity and reddening. Resulting Teff and
E(B-V), computed over a range of options, are provided and discussed, and will
be kept updated in response to future APASS and RAVE data releases. In the
process it is found that the reddening caused by an homogeneous slab of dust,
extending for 140 pc on either side of the Galactic plane and responsible for
E(B-V,poles)=0.036 +/- 0.002 at the galactic poles, is a suitable approximation
of the actual reddening encountered at Galactic latitudes |b|>=25 deg.
We present spectroscopic observations of LX Per carried out using the Korean Bohyunsan Observatory Echelle Spectrograph (BOES) with spectral resolving power R = 80, 000. The spectrograph was attached to the 1.8 m telescope. The fit of synthetic spectra to the observed spectrum of the system allowed us to find the component parameters and the abundances of chemical elements in the atmospheres of the components. The strong Ca II H&K emissions are confirmed; we also found emission lines in the Ca II reversals' triplet absorptions at the wavelengths of 8498, 8542, and 8662 Å in the spectrum of the cooler component of LX Per. A unique photometric solution using the distorted light curves of three different epochs was made. The spot model light curves were fitted to the 1981, 1982, and 1983 observations successfully by adjusting only spot parameters. We could infer that the variation of spot location and size was the main reason for the changing shape of light curves. The main feature of the abundance patterns of both components was the apparent deficiency of heavy (Z > 30) elements. Only elements with strong lines, namely Y and Ba, were detected. Correlations of relative abundances of chemical elements with condensation temperatures and second ionization potentials of these elements, which can be explained by the accretion of dust and gas, were found.
The "Vienna Atomic Line Data Base" (VALD) consists of a set of
critically evaluated lists of astrophysically important atomic
transition parameters and supporting extraction software. VALD contains
about 600000 entries and is one of the largest collections of accurate
and homogeneous data for atomic transitions presently available. It also
includes specific tools for extracting data for spectrum synthesis and
model atmosphere calculations. The different accuracies of data
available in the literature made it necessary to introduce a ranking
system and to provide a flexible method for extracting the best possible
set of atomic line parameters for a given transition from all the
available sources. The data base is presently restricted to spectral
lines which are relevant for stars in which the LTE approximation is
sufficient and molecular lines do not have to be taken into account. The
provision was made that these requirements should not restrict the
general design of VALD and the possibility of future expansion. In this
paper we describe the structure of VALD, the available data sets and
specific retrieval tools. The electronic-mail interface (VALD-EMS)
created to allow remote access to VALD is also described. Both users and
producers of atomic data are invited to explore the database, and to
collaborate in improving and extending its contents.
We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE-SMC survey database, for which we present uniform photometry from 0.3to24 μm in the UBVIJHKs +IRAC+MIPS24 bands. We compare the color-magnitude diagrams and color-color diagrams to those of stars in the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 μm in the SMC are a few very luminous hypergiants, four B-type stars with peculiar, flat spectral energy distributions, and all three known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in our SMC catalog, respectively, when compared to the LMC catalog, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A & F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust.
From newly obtained high-resolution, high signal-to-noise ratio spectra the abundances of the elements La and Eu have been determined over the stellar metallicity range -3 < [Fe/H] < +0.3 in 159 giant and dwarf stars. Lanthanum is predominantly made by the s-process in the solar system, while Eu owes most of its solar system abundance to the r-process. The changing ratio of these elements in stars over a wide metallicity range traces the changing contributions of these two processes to the Galactic abundance mix. Large s-process abundances can be the result of mass transfer from very evolved stars, so to identify these cases we also report carbon abundances in our metal-poor stars. Results indicate that the s-process may be active as early as [Fe/H] = -2.6, although we also find that some stars as metal-rich as [Fe/H] = -1 show no strong indication of s-process enrichment. There is a significant spread in the level of s-process enrichment even at solar metallicity.
We present a catalog of 1750 massive stars in the Large Magellanic Cloud (LMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 1268 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer SAGE survey database, for which we present uniform photometry from 0.3 to 24 μm in the UBVIJHKs +IRAC+MIPS24 bands. The resulting infrared color-magnitude diagrams illustrate that the supergiant B[e], red supergiant, and luminous blue variable (LBV) stars are among the brightest infrared point sources in the LMC, due to their intrinsic brightness, and at longer wavelengths, due to dust. We detect infrared excesses due to free-free emission among ~900 OB stars, which correlate with luminosity class. We confirm the presence of dust around 10 supergiant B[e] stars, finding the shape of their spectral energy distributions (SEDs) to be very similar, in contrast to the variety of SED shapes among the spectrally variable LBVs. The similar luminosities of B[e] supergiants (log L/L ☉ ≥ 4) and the rare, dusty progenitors of the new class of optical transients (e.g., SN 2008S and NGC 300 OT), plus the fact that dust is present in both types of objects, suggests a common origin for them. We find the infrared colors for Wolf-Rayet stars to be independent of spectral type and their SEDs to be flatter than what models predict. The results of this study provide the first comprehensive roadmap for interpreting luminous, massive, resolved stellar populations in nearby galaxies at infrared wavelengths.
We have very recently re-determined the abundances of nearly all the available chemical elements in the solar photosphere, from lithium to thorium (Asplund et al. Annu. Rev. Astron. Astrophys. 47, 481 (2009)). This new complete and homogeneous analysis results from a very careful selection of spectral lines of all the indicators of the abundances present in the solar photospheric spectrum, from a discussion of the atomic and molecular data, and from an analysis of these lines based on a new 3D model of the solar outer layers, taking non-LTE effects into account when possible. We present these new results, compare them with other recent solar data as well as with recent results for the solar neighborhood, and discuss some of their most important implications as well as some of the atomic data we still urgently need.
The evolutionary status of the chemically peculiar class of λ Boo stars has been intensely debated. It is now agreed that the λ Boo phenomenon affects A stars of all ages, from star formation to the terminal age main sequence, but the cause of the chemical peculiarity is still a puzzle.We revisit the debate of their ages and temperatures in order to shed light on the phenomenon, using the new parallaxes in Gaia Data Release 1 with existing Hipparcos parallaxes and multicolour photometry.We find that no single formation mechanism is able to explain all the observations, and suggest that there are multiple channels producing λ Boo spectra. The relative importance of these channels varies with age, temperature and environment.
We present Hubble Space Telescope imaging confirming the optical disappearance of the failed supernova candidate identified by Gerke et al. (2015). This red supergiant experienced a weak optical outburst in 2009 and is now at least 5 magnitudes fainter than the progenitor in the optical. The mid-IR flux has slowly decreased to the lowest levels since the first measurements in 2004. There is faint () near-IR emission likely associated with the source. We find the late-time evolution of the source to be inconsistent with obscuration from an ejected, dusty shell. Models of the spectral energy distribution indicate that the remaining bolometric luminosity is times fainter than that of the progenitor and is decreasing as . We conclude that the transient is unlikely to be a SN impostor or stellar merger. The event is consistent with the ejection of the envelope of a red supergiant in a failed supernova and the late-time emission could be powered by fallback accretion onto a newly-formed black hole. Future IR and X-ray observations are needed to confirm this interpretation of the fate for the star.
Over the last 15 years, the supernova community has endeavoured to identify
progenitor stars of core-collapse supernovae in high resolution archival images
of their galaxies.This review compiles results (from 1999 - 2013) in a distance
limited sample and discusses the implications. The vast majority of the
detections of progenitor stars are of type II-P, II-L or IIb with one type Ib
progenitor system detected and many more upper limits for progenitors of Ibc
supernovae (14). The data for these 45 supernovae progenitors illustrate a
remarkable deficit of high luminosity stars above an apparent limit of Log L ~=
5.1 dex. For a typical Salpeter IMF, one would expect to have found 13 high
luminosity and high mass progenitors. There is, possibly, only one object in
this time and volume limited sample that is unambiguously high mass (the
progenitor of SN2009ip). The possible biases due to the influence of
circumstellar dust and sample selection methods are reviewed. It does not
appear likely that these can explain the missing high mass progenitor stars.
This review concludes that the observed populations of supernovae in the local
Universe are not, on the whole, produced by high mass (M > ~18Msun) stars.
Theoretical explosions of model stars also predict that black hole formation
and failed supernovae tend to occur above M > ~18Msun. The models also suggest
there are islands of explodability for stars in the 8-120Msun range. The
observational constraints are quite consistent with the bulk of stars above M >
~18Msun collapsing to form black holes with no visible supernovae. (Abridged).
We are monitoring 27 galaxies within 10 Mpc using the Large Binocular
Telescope to search for failed supernovae (SNe), massive stars that collapse to
form a black hole without a SN explosion. This sample yielded 3 successful SNe
during the 4 year survey period. We search for stars that have "vanished" over
the course of our survey, by examining all stars showing a decrease in
luminosity of from the first to the last
observation. We also search for the low luminosity, long duration transients
predicted by \citet{lovegrove2013} for failed explosions of red supergiants.
After analyzing the first 4 years of data in this first direct search for
failed SNe, we are left with three candidates requiring further study. Only one
candidate approaches the luminosity needed to address the absence of higher
mass red supergiant SN progenitors. Under the assumption that further
observations show that 1, 2 or 3 candidates are failed SN, the median fractions
are , , and respectively with
symmetric 90\% confidence limits of , , and . If follow up data eliminates these
candidates, we find an upper limit on the fraction of core collapses leading to
a failed SN of at 90% confidence. As the duration of the survey
continues to increase, it will have no difficulty constraining the
20-30% failure rates needed to explain the absence of massive SN progenitors.
Moderately r-process-enriched stars (r-I) are at least four times as common
as those that are greatly enriched in r-process elements (r-II), and the
abundances in their atmospheres are important tools for obtaining a better
understanding of the nucleosynthesis processes responsible for the origin of
the elements beyond the iron peak. The main aim of this work is to derive
abundances for a sample of seven metal-poor stars with classified as r-I stars,
to understand the role of these stars for constraining the astrophysical
nucleosynthesis event(s) that is(are) responsible for the production of the
r-process, and to investigate whether they differ, in any significant way, from
the r-II stars. We carried out a detailed abundance analysis based on
high-resolution spectra obtained with the VLT/UVES spectrograph. The OSMARCS
LTE 1D model atmosphere grid was employed, along with the spectrum synthesis
code Turbospectrum. We have derived abundances of light elements Li, C, and N,
alpha-elements, odd-Z elements, iron-peak elements, and the trans-iron elements
from the first peak, the second peak, the third peak, and the actinides
regions. The results are compared with values for these elements for r-II and
normal very and extremely metal-poor stars reported in the literature, ages
based on radioactive chronometry are explored using different models, and a
number of conclusions about the r-process and the r-I stars are presented.
Hydrodynamical models were used for some elements, and general behaviors for
the 3D corrections were presented.
This paper presents a brief discussion of the apparent underdepletion of the heavy neutron-capture elements (elements heavier than Ba), compared with Fe in the Magellanic Clouds. The s-process appears to have been only effective in forming elements in the light neutron-capture group (Sr, Y, Zr) in the Magellanic Clouds, but to have much reduced effectiveness in forming the heavy neutron-capture group. The abundances of the elements heavier than Ba have a distribution that indicates that they were produced by the r-process alone.
We determine the atmospheric chemical composition of the components of
the CP SB2 system 66 Eri with approximately equal masses (M_A / M_B =
0.97) by using two CCD echelle spectra of the star. These spectra have
been taken with the 1-m telescope at Special Astrophysical Observatory
with a spectral resolution of 36 000 and a signal-to-noise ratio no less
than 100 in the wavelength range 4385-6695 A. The model-atmosphere
parameters for the components are estimated by analyzing all available
photometric and spectrophotometric data and the equivalent widths of
iron lines. For components A and B, we have obtained Teff_A =
11 100 K, Teff_B = 10 900 K, lg(g_A) = 4.25, lg(g_B)= 4.25,
Vturb_A = 0.9 km/s, Vturb_B = 0.7 km/s, and v
sin(i_{A,B}) = 17 km/s. The derived projected rotational velocities of
the components, together with the HIPPARCOS parallax and photometric
observations, show that their rotation may be synchronized with the
orbital period. The star exhibits a considerable infrared excess at
wavelengths longer than 25 micrometers. The synthetic-spectrum and
model-atmosphere methods are used to determine the atmospheric
abundances of 26 chemical elements in component B and 15 chemical
elements in component A. The components differ markedly in chemical
composition. The peculiar component B exhibits no chemical anomalies
that are typical of the Hg-Mn group, such as an underabundance of He and
Al and an enhancement of P and Ga, but shows large heavy-element
overabundances reaching 4-5 dex. The atmosphere of component A also
exhibits moderate overabundances of Mn and Ba, but no lines of other
heavy elements have been found in its spectrum. However, an estimate of
the upper limit on their abundances does no rule out small heavy-element
overabundances in the atmosphere of component A either. 66 Eri is the
first and the only close SB2 system with CP non-Hg-Mn components studied
to date.
We present the results of the analysis of thorium absorption lines in the spectra of metal-deficient stars: the thorium-rich Galactic halo star HD 221170 and some supergiants in the Magellanic Clouds. For all the analyzed stars, the Th II lines were identified by comparing the synthetic and observed spectra. The Th II 6044.433 Å line and the weaker Th II 6619.943 Å line were identified in the spectra of red supergiants in the Magellanic Clouds.
We investigated ZZ Boo using a high-resolution (R = 80,000) spectrum obtained at the BOES echelle spectrograph attached to a 1.8 m telescope at the Bohuynsan observatory in Korea. The atmospheric parameters of the components were found using the published photometrical observations and the abundance analysis of iron lines: the flux ratio of the components F{sub A} /F{sub B} = 1.12 {+-} 0.15, the effective temperatures of the components T{sub eff} = 6860 {+-} 20 K and 6930 {+-} 20 K, the surface gravities log g = 3.72 {+-} 0.10 and 3.84 {+-} 0.10, the metallicities [Fe/H] = -0.10 {+-} 0.08 and -0.03 {+-} 0.10, and the projected rotation velocities vsin i = 11.9 {+-} 0.4 km s{sup -1} and 19.3 {+-} 0.8 km s{sup -1} for the primary and secondary components, respectively. The pointed errors are the formal errors of the methods used; the systematic errors of the temperatures, gravities, metallicities, and projected rotational velocities can be as high as 250-300 K, 0.3 dex, 0.15 dex, and 4 km s{sup -1}, respectively. The abundances of 24 and 22 chemical elements were determined in the atmospheres of the components. The abundance pattern of the primary component shows the solar or slightly undersolar abundances of all elements. CNO abundances are close to solar values. The abundance pattern of this component resembles those of {lambda} Boo type stars. The abundances of light elements, except oxygen, in the atmosphere of the secondary component are practically solar. The abundances of barium and two detected lanthanides are close to the solar values; the overabundance of oxygen is 0.9 dex. The abundances of two components are evidently different. The comparison of relative abundances with the condensation temperatures and second ionization potentials of the elements confirms the difference in abundance patterns and allows discussion of the different accretion scenarios for two components of this binary system.
Using fully self-consistent N-body models for the dynamical evolution of the
Large Magellanic Cloud (LMC) in the Galaxy, we show that if the LMC initially
has an extended old stellar halo before its commencement of tidal interaction
with the Galaxy, physical properties of the stars stripped from the LMC stellar
halo can have fossil information as to when and where the LMC was accreted onto
the Galaxy for the first time. If the epoch of the first LMC accretion onto the
Galaxy from outside its viriral radius is more than ~4 Gyr ago (i.e., at least
two pericenter passages), the stars stripped from the stellar halo of the LMC
can form an irregular polar ring or a thick disk with a size of ~100 kpc and
rotational kinematics. On the other hand, if the LMC was first accreted onto
the Galaxy quite recently (~ 2 Gyr ago), the stripped stars form shorter
leading and trailing stellar stream at R=50-120 kpc. Also distributions of the
stripped stars in phase space between the two cases can be significantly
different. The derived differences in structure and kinematics of the stripped
stars therefore suggest that if we compare the observed three-dimensional (3D)
distribution and kinematics of the outer Galactic stellar halo along the
polar-axis, then we can give strong constraints on the past orbit of the LMC.
We find that the orbital properties of the LMC in the successful formation
models of the Magellanic Stream (MS) are consistent with those predicted from
recent LambdaCDM cosmological simulations. We conclude that the LMC was
accreted onto the Galaxy more than ~4 Gyr ago so that interaction between the
LMC, the Small Magellanic Cloud (SMC), and the Galaxy could form the MS and its
Leading Arms (LAs).
We present the results of identifications of the Th II lines in the spectra of four stars in the Small Magellanic Cloud: PMMR 23, PMMR 39,PMMR144, and PMMR 145. We report about detection of the lines of Th II in the visible part of spectra of K-supergiants. Thorium lines in the spectra of these stars are stronger than the thorium lines in the spectra of HD221170 and Arcturus. The thorium abundances in the atmospheres of four SMC stars are scattered from +0.05 to -0.69 in the scale where logN(H)=12.
In the puzzle of the metallic line (Am) stars, there still seem to be missing pieces. While the ``normal'' A stars have elemental abundances close to solar, the classical Am stars show stronger absorption lines for most heavy elements in their spectra. Elements with ionization potentials that nearly agree with those of hydrogen or helium have reduced abundances. The Ca II and Sc II lines are especially weak. The Am stars have no ultraviolet emission lines. They are binaries that, with very few exceptions, have rotational velocities vsini lower than 100 km s-1. Of the main-sequence A stars, 20% to 30% are Am stars. Here we rediscuss previous suggestions that tried to explain the peculiar line strengths in the Am star spectra. In particular, we compare the well-studied properties of Hyades A and Am stars in order to identify reasons that can or cannot explain the differences. We find that accretion of interstellar material by A stars with distorted magnetic fields, which are weaker than those in peculiar A (Ap) stars, has the best chance of explaining the main characteristics of the peculiar heavy-element abundances in Am star photospheres. Charge-exchange reactions also seem to be important.
Our re-examination of the neutral hydrogen gas in the Small Magellan Cloud has led to four important results. Firstly, we find that Hindman’s (1967) total content HI map is a satisfactory representation of the gas in the line of sight. Secondly, we find that the HI gas in the SMC exists in four distinct large masses separated from one another in radial velocity by 20 to 30 km s −1 . Thirdly, having made this division of the gas we show that there is good correlation between the radial velocities of HII regions, supergiant stars and HI. Finally, we believe that our observations reveal that the SMC is associated with an extremely large trailing halo of HI gas which forms the major component of the inter-cloud bridge region.
This compilation is aimed at providing a general catalog of atomic lines for comparatively low-ionized species, laying emphasis on their transition probabilities. Please refer to file "explain" for a detailed description. (2 data files).
Among 25 spectroscopically confirmed M supergiants in the SMC, none are classified later than M1. Except for one M1-type supergiant, all of these stars have spectral types M0 or earlier. The two-color diagrams, V-I versus B-V and V-R versus B-V, for the red stars without spectra show the same phenomenon. Except for one M2-type candidate all of the remaining red stars are probably M0--M1 or earlier in spectral type. This is significantly different from the spectral types for the M supergiants in the Milky Way or the LMC.It is suggested that the lower metallicities in the SMC produce lower opacities in the atmospheres of these cool stars. Consequently the spectra come from somewhat warmer layers resulting in earlier spectral types.
Oscillator strengths for 57 U II lines in the region 3500-6700 Å have been derived by combining new branching fraction measurements with recently measured lifetimes. The lines combine six upper levels with numerous low levels having excitation energies of 0-1.5 eV. The data include the U II line at 3859 Å, which is used for cosmochronology.
The results of a spectrum synthesis analysis of elemental abundances derived from the high-resolution CCD-spectrograms of the SMC red supergiant stars PMMR23 and PMMR39 (stars 23 & 39 in the catalogue Prevot et al. 1983) are presented. The abundances of 35 elements in the atmosphere of PMMR23 have been obtained. Elements with atomic numbers Z<56 are deficient with respect to the solar abundances. The mean underabundance is about -0.7 dex. The abundances of elements heavier than barium are close to the solar value. In the case of PMMR23, the atmosphere is enriched in elements heavier than barium which show abundances close to the solar value. These abundances can be explained as a combination of r- and s-processes. In PMMR39, all the 20 studied elements present abundances deficient with respect to solar values The abundances of 31 elements with Z>30 are determined in the atmosphere of Arcturus.
This compilation is the first in a series of updates to a critical compilation published in 1969 [W. L. Wiese, M. W. Smith, and B. M. Miles, Atomic Transition Probabilities, Vol. II: Sodium through Calcium, NSRDS-NBS Vol. 2 (U.S. GPO, Washington, D.C., 1969)]. Atomic transition probabilities have been critically evaluated and compiled for about 11 400 spectral lines of sodium and magnesium (nuclear charge Z=11-12, respectively). The cited values and their estimated uncertainties are based on our consideration of all available theoretical and experimental literature sources. All ionization stages (except for hydrogenic) are covered, and the data are presented in separate tables for each atom and ion. Separate listings are given for ``allowed'' (electric dipole) transitions, on the one hand, and for ``forbidden'' (magnetic dipole plus electric and magnetic quadrupole) transitions, on the other. In each spectrum, lines are grouped into multiplets which are arranged in order of ascending lower and upper-level energies, respectively. For each line, the emission transition probability Aki, the line strength S, and (for allowed lines) the absorption oscillator strength fik are given, together with the spectroscopic designation, the wavelength, the statistical weights, and the energy levels of the lower and upper states. The estimated relative uncertainties of the line strength are also indicated, as are the source citations. We introduce a statistical method that we use to estimate these uncertainties for most of the cited transition rates. We only include those lines whose transition rates are deemed sufficiently accurate to qualify as reference values. Short introductions precede the tables for each ion. The general introduction contains a discussion of the principal criteria for our judgments and our method of data selection and evaluation.
We have carried out a new, expanded tabulation of the atomic transition probabilities for allowed and forbidden lines of Fe I and Fe II, based on the critical evaluation of all available literature sources. The compiled data are taken mainly from recent experimental and theoretical results that became available after the publication of our first compilation in 1988. The data are arranged in multiplet format and are ordered according to increasing excitation energies. © 2006 by the U.S. Secretary of Commerce on behalf of the United States. All rights reserved.
This compilation is the second in a series of updates to Atomic Transition Probabilities, Sodium through Calcium, published in 1969 by Wiese et al. [Atomic Transition Probabilities, Vol. II, Vol. II: Sodium through Calcium, NSROS-NBS Vol. 2 (U.S. GPO, Washington, D.C., 1969)]. Atomic transition probabilities have been critically evaluated and compiled for about 5000 spectral lines of aluminum (nuclear charge Z=13). The cited values and their estimated uncertainties are based on our consideration of all available theoretical and experimental literature sources. All ionization stages (except for hydrogenic) are covered, and the data are presented in separate tables for each atom and ion. Separate listings are given for ``allowed'' (electric dipole) and ``forbidden'' (magnetic dipole plus electric and magnetic quadrupole) transitions. In each spectrum, lines are grouped into multiplets which are arranged in order of ascending lower- and upper-level energies, respectively. For each line, the emission transition probability Aki, the line strength S, and (for allowed lines) the absorption oscillator strength fik are given, together with the spectroscopic designation, the wavelength, the statistical weights, and the energy levels of the lower and upper states. The estimated relative uncertainties of the line strength are also indicated, as are the source citations. We include only those lines whose transition rates are deemed sufficiently accurate to qualify as reference values. Short introductions precede the tables for each ion.
We reexamine closely the solar photospheric line at 6300 A û , which is attributed to a forbidden line of neutral oxygen and is widely used in analyses of other late-type stars. We use a three-dimensional time-dependent hydrodynamical model solar atmosphere that has been tested successfully against observed granulation patterns and an array of absorption lines. We show that the solar line is a blend with a Ni i line, as previously suggested but oftentimes neglected. Thanks to accurate atomic data on the (O i) and Ni i lines, we are able to derive an accurate oxygen abundance for the Sun: dex, a value at the lower end of the distribution log e(O) p 8.69 0.05 of previously published abundances but in good agreement with estimates for the local interstellar medium and hot stars in the solar neighborhood. We conclude by discussing the implication of the Ni i blend on oxygen abundances derived from (O i) l6300 in disk and halo stars.
Galaxies in the Local Group span a factor of 15 in metallicity, ranging from
the super-solar M31 to the Wolf-Lundmark-Melotte (WLM) galaxy, which is the
lowest-metallicity (0.1xZsun) Local Group galaxy currently forming stars.
Studies of massive star populations across this broad range of environments
have revealed important metallicity-dependent evolutionary trends, allowing us
to test the accuracy of stellar evolutionary tracks at these metallicities for
the first time. The RSG population is particularly valuable as a key
mass-losing phase of moderately massive stars and a source of core-collapse
supernova progenitors. By reviewing recent work on the RSG populations in the
Local Group, we are able to quantify limits on these stars' effective
temperatures and masses and probe the relationship between RSG mass loss
behaviors and host environments. Extragalactic surveys of RSGs have also
revealed several unusual RSGs that display signs of unusual spectral
variability and dust production, traits that may potentially also correlate
with the stars' host environments. I will present some of the latest work that
has progressed our understanding of RSGs in the Local Group, and consider the
many new questions posed by our ever-evolving picture of these stars.
The probability is evaluated that peculiar A and B stars show abundance
anomalies from nuclear processes which occurred in companions. The mass
accreted from supernova ejecta and the frequency of the accretion both
in binary systems and in associations are evaluated. The results show
that only one A or B star in a few thousand is likely to show abundance
anomalies caused by a nearby supernova. The possibility that the process
causing Ba stars would lead to main-sequence counterparts is discussed
in detail. The radius stars must reach to produce s-process elements is
large and is the likely reason for the period distribution of Ba stars.
It is then estimated that only 1.5 percent of all and B stars could have
been affected by accretion of s-process material during the AGB phase of
their companions. It is also found that at most 1.5 percent of Am-Fm
stars formed by a process other than mass accretion could have had their
abundances modified by the accretion of s-processed materials.
Carbon, nitrogen and oxygen abundances were derived from high-resolution
spectra of 6 cool supergiants of the Small Magellanic Cloud.
Oxygen-to-iron ratios (mean value <[O/Fe]>=~-0.18dex) are found to
be similar to those found in young objects in the LMC and the Galaxy.
This result is discussed in terms of chemical evolution. A mean
deficiency of the carbon-to-iron ratio of <[C/Fe]>=~-0.3dex and a
nitrogen-to-iron ratio <[N/Fe]>=~+0.22dex might imply a mixing
signature, which is confirmed by the low ^12^C/^13^C ratio measured in
three stars. In terms of chemical evolution, carbon plus nitrogen
abundances have to be considered: in our sample, a mean value of
<[(C+N)/Fe]>=~-0.15dex indicates a slight deficiency in carbon
plus nitrogen with respect to the Sun, similar to the deficiencies found
in Galactic supergiants and Orion. Lithium has been detected in all the
program stars, reaching ɛ(Li)=0.6dex for two stars.
The differences in metal abundances between the Milky Way, Large
Magellanic Cloud (LMC), and Small Magellanic Cloud (SMC) affect most of
the observable properties of the M supergiants in these galaxies; those
in the SMC (which has the lowest metal abundance) have the earliest mean
spectral type, while those of the Milky Way exhibit the latest mean
spectral type. This is presently interpreted as a combination of two
effects of differing metal abundance on the supergiant atmospheres:
first, lower abundance stars of a given effective temperature have
earlier MK spectral types due to reduced TiO abundance; second, the
Hayashi track is shifted to hotter effective temperature at reduced
metal abundance, thereby shifting the mean spectral type still earlier.
The fact that the 10-micron excess decreases linearly with metal
abundance suggests that mass loss rates are roughly the same for stars
in all three galaxies, with the dust-to-gas ratio proportional to metal
abundance.
Abundance analyses are reported for three certain members (Lambda Boo,
29 Cyg, Pi1 Ori) of the class of rapidly rotating, metal-poor A-type
stars known as Lambda Bootis stars. Model atmosphere analysis of
high-resolution, high signal-to-noise spectra shows that the metal
deficiencies are more severe than previously reported: Fe/H = -2.0,
-1.8, -1.3 for Lambda Boo, 29 Cyg, and Pi1 Ori, respectively. Other
metals (Mg, Ca, Ti, and Sr) are similarly underabundant, with Na often
having a smaller underabundance. C, N, O, and S have near-solar
abundances. Vega is shown to be a mild Lambda Boo star. The abundance
anomalies of the Lambda Boo stars resemble those found for the
interstellar gas in which the metals are depleted through formation of
interstellar grains. It is suggested that the Lambda Boo stars are
created when circumstellar (or interstellar) gas is separated from the
grains and accreted by the star. The bulk of the interstellar grains
comprises a circumstellar cloud or disk that is detectable by its
infrared radiation.
An objective-prism survey of the Small Magellanic Cloud has been made on
IIIaJ plates taken with the 1 m ESO Schmidt telescope and has resulted
in the detection of nearly 200 late K and M supergiant stars. Most of
these are new probable members of the SMC which do not appear in
previous catalogues. The mean visual absolute magnitude of -6.0 agrees
with the visual absolute magnitude of lab-lb galactic supergiants of
spectral types M0 to M4. The fraction of known variable stars found in
this catalogue is barely 10 percent; this is 2.5 times less than the
value found for the corresponding stars in the LMC. The catalogue
provides accurate 1975 coordinates, finding charts, spectral types, V
magnitudes, indications concerning radial velocities when available and
designations of the stars in other catalogues.
A sample of six SMC cool stars (K supergiants) are analysed by high
resolution spectroscopy in order to investigate their chemical content,
which should reflect that of the current interstellar medium within the
SMC. The abundance of Na, Al, α-elements, Fe peak and heavy
elements are derived through an LTE analysis of the lines, compared to a
Galactic "standard" (the well-studied K giant Arcturus) and discussed in
terms of chemical evolution of the SMC. The following results were
obtained: 1.) All the stars from this sample are metal deficient ([Fe/H]
ranges from -0.59 to -0.89dex). The abundance varies little from
star-to-star (0.10dex rms, comparable with the expected error due to
uncertainties on the effective parameters of the stars), in agreement
with the very small chemical composition variations among the H II
regions within the SMC found by Pagel et al. (1978MNRAS.184..569P). 2.)
Sodium is not strongly enhanced in these stars, and the star-to-star
scatter is larger than expected. 3.) At variance with metal-poor stars
in our Galaxy, the so-called α-elements do not seem to be
enhanced. 4.) Nickel displays a noticeable depletion with respect to
iron ([Ni/Fe]=~-0.3dex), at variance with what is found in the SMC F
supergiants and in Arcturus. 5.) Except for PMMR 144, the s and r
process elements heavier than Ba are enhanced in all of our stars by
=~+0.4dex.
The structure of the SMC is investigated using previous H-I data,
accurate radial velocities of 307 young stars and 35 H-II regions, and
high-spectral-resolution profiles of interstellar absorption lines. It
is found that 224 stars and 30 H-II regions of the main body of the SMC
are associated with four H-I components, and that 54 of the objects are
not associated with H I. Two main complexes of gas, stars, and H-II
regions are found, one with a velocity of about -28 km/s and the other
with a velocity of about +9 km/s. Most of the young stars are shown to
lie within a depth smaller than 10 kpc, in agreement with recent
Magellanic Cepheid data.
I am attempting to produce line lists for all atoms and diatomic molecules
that are important in stars. I collect all published data on spectrum analysis
and oscillator strengths. I compute the energy levels, wavelengths, gf
values, and damping constants that are not available from the
literature. Line lists have been computed for diatomic molecules H2,
CII, NH, OH, MgH, SiH, CN, C2, CO, SiO, and TiO, and for the iron group
atoms Ca 1-IX to Ni 1-IX. These lists total 58 million lines. These
calculations are being revised as new laboratory data become available.
The work is being extended to other diatomic molecules, to lighter and
heavier elements, and to higher stages of ionization. Key words: ATOMIC
PROCESSES - MOLECULAR PROCESSES - TRANSITION PROBABILITIES
This compilation extends the 1991 listing of atomic data by Morton to the heavier stable elements from germanium to bismuth. Technetium, thorium, and uranium are added because they can live long enough to be astrophysically detectable. The tabulation emphasizes resonance lines, i.e., lines the lower level of which is the ground state, or an excited fine-structure state of the ground term, and is restricted to wavelengths longward of the H I Lyman limit at 911.75 Å. This paper has attempted to review all data published by mid-1999 and includes some later material. The tables contain the best data available to the author on level designations, ionization potentials, vacuum and air wavelengths, lower and upper energy levels, statistical weights, transition probabilities, natural damping constants (reciprocal lifetimes), oscillator strengths, and the often-used combinations of log gf and log λf. All ion stages with classified lines are included. Individual components resulting from isotope shift and hyperfine structure are listed explicitly for Rb I, Cs I, Hg I and Hg II, Ti II, and Pb II. The accompanying text provides references, explanations for the critical selection of data, and notes indicating where new measurements or calculations are needed. This compilation should be particularly useful in the analysis of interstellar and quasar absorption lines and other astrophysical sites where the density of particles and radiation is low enough to excite only the lowest atomic levels. The data also are relevant to the study of stellar atmospheres, particularly those with enhanced abundances of heavy elements.
Extragalactic transient searches have historically been limited to looking for the appearance of new sources such as supernovae. It is now possible to carry out a new kind of survey that will do the opposite, that is, search for the disappearance of massive stars. This will entail the systematic observation of galaxies within a distance of 10 Mpc in order to watch ~106 supergiants. Reaching this critical number ensures that something will occur yearly, since these massive stars must end their lives with a core collapse within ~106 yr. Using deep imaging and image subtraction, it is possible to determine the fates of these stars, whether they end with a bang (supernova) or a whimper (fall out of sight). Such a survey would place completely new limits on the total rate of all core collapses, which is critical for determining the validity of supernova models. It would also determine the properties of supernova progenitors, better characterize poorly understood optical transients (such as η Carina-like mass ejections), find and characterize large numbers of Cepheids, luminous blue variables, and eclipsing binaries, and allow the discovery of any new phenomena that inhabit this relatively unexplored parameter space.
Radiative lifetimes, accurate to AE5%, have been measured for 168 odd-parity levels of Nd ii using laser-induced fluorescence. The lifetimes are combined with branching fractions measured using Fourier-transform spectrometry to determine transition probabilities for over 700 lines of Nd ii. This work is the largest-scale laboratory study to date of Nd ii transition probabilities using modern methods. This improved data set is used to determine Nd abundances for the Sun and three metal-poor giant stars with neutron-capture enhancement: CS 22892À052, HD 115444, and BD +17 3248. In all four stars the line-to-line scatter is considerably reduced from earlier published results. The solar photospheric abundance is determined to be log ðNdÞ ¼ 1:45 AE 0:01ð ¼ 0:05Þ, which is in excellent agreement with meteoric data. The ratio of Nd/Eu is virtually identical in all three metal-poor Galactic halo stars. Furthermore, the newly determined stellar Nd abundances, in comparison with other heavy neutron-capture elements, are consistent with an r-process–only origin early in the history of the Galaxy. These more accurate Nd abundance determinations might help to constrain the predicted solar system r-process abundances, and suggest other elements for further neutron-capture abundance studies.