3,986 research outputs found
Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
Infrared observations of the dusty, massive Homunculus Nebula around the
luminous blue variable Carinae are crucial to characterize the mass-loss
history and help constrain the mechanisms leading to the Great Eruption. We
present the 2.4 - 670 m spectral energy distribution, constructed from
legacy ISO observations and new spectroscopy obtained with the {\em{Herschel
Space Observatory}}. Using radiative transfer modeling, we find that the two
best-fit dust models yield compositions which are consistent with CNO-processed
material, with iron, pyroxene and other metal-rich silicates, corundum, and
magnesium-iron sulfide in common. Spherical corundum grains are supported by
the good match to a narrow 20.2 m feature. Our preferred model contains
nitrides AlN and SiN in low abundances. Dust masses range from 0.25 to
0.44 but 45 in both cases due to an
expected high Fe gas-to-dust ratio. The bulk of dust is within a 5
7 central region. An additional compact feature is detected at 390 m.
We obtain = 2.96 10 , a 25\% decline from
an average of mid-IR photometric levels observed in 1971-1977. This indicates a
reduction in circumstellar extinction in conjunction with an increase in visual
brightness, allowing 25-40\% of optical and UV radiation to escape from the
central source. We also present an analysis of CO and CO through lines, showing that the abundances are consistent with
expectations for CNO-processed material. The [C~{\sc{ii}}] line is
detected in absorption, which we suspect originates in foreground material at
very low excitation temperatures.Comment: Accepted in Ap
On Infrared Excesses Associated With Li-Rich K Giants
Infrared (IR) excesses around K-type red giants (RGs) have previously been
discovered using IRAS data, and past studies have suggested a link between RGs
with overabundant Li and IR excesses, implying the ejection of circumstellar
shells or disks. We revisit the question of IR excesses around RGs using higher
spatial resolution IR data, primarily from WISE. Our goal was to elucidate the
link between three unusual RG properties: fast rotation, enriched Li, and IR
excess. We have 316 targets thought to be K giants, about 40% of which we take
to be Li-rich. In 24 cases with previous detections of IR excess at low spatial
resolution, we believe that source confusion is playing a role, in that either
(a) the source that is bright in the optical is not responsible for the IR
flux, or (b) there is more than one source responsible for the IR flux as
measured in IRAS. We looked for IR excesses in the remaining sources,
identifying 28 that have significant IR excesses by ~20 um (with possible
excesses for 2 additional sources). There appears to be an intriguing
correlation in that the largest IR excesses are all in Li-rich K giants, though
very few Li-rich K giants have IR excesses (large or small). These largest IR
excesses also tend to be found in the fastest rotators. There is no correlation
of IR excess with the carbon isotopic ratio, 12C/13C. IR excesses by 20 um,
though relatively rare, are at least twice as common among our sample of
Li-rich K giants. If dust shell production is a common by-product of Li
enrichment mechanisms, these observations suggest that the IR excess stage is
very short-lived, which is supported by theoretical calculations. Conversely,
the Li-enrichment mechanism may only occasionally produce dust, and an
additional parameter (e.g., rotation) may control whether or not a shell is
ejected.Comment: 73 pages, 21 figures (some of which substantially degraded to meet
arXiv file size requirements), accepted to AJ. Full table 1 (and full-res
figures) available upon request to the autho
Chlorine-bearing molecules in molecular absorbers at intermediate redshifts
We use observations of chlorine-bearing species in molecular absorbers at intermediate redshifts to investigate chemical properties and Cl-35/Cl-37 isotopic ratios in the absorbing sightlines. Chloronium (H2Cl+) is detected along three independent lines of sight in the z = 0.89 and z = 0.68 molecular absorbers located in front of the lensed quasars PKS 1830-211 and B 0218+357, respectively. Hydrogen chloride (HCl) was observed only toward PKS 1830-211, and is found to behave differently from H2Cl+. It is detected in one line of sight with an abundance ratio [H2Cl+]/[HCl] similar to 1, but remains undetected in the other, more diffuse, line of sight, with a ratio [H2Cl+] / [HCl] > 17. The absorption profiles of these two chlorine-bearing species are compared to other species and discussed in terms of the physical properties of the absorbing gas. Our findings are consistent with the picture emerging from chemical models where different species trace gas with different molecular hydrogen fraction. The Cl-35/Cl-37 isotopic ratios are measured in the different lines of sight and are discussed in terms of stellar nucleosynthesis
HERSCHEL OBSERVATIONS OF EXTRA-ORDINARY SOURCES: H2S AS A PROBE OF DENSE GAS AND POSSIBLY HIDDEN LUMINOSITY TOWARD THE ORION KL HOT CORE
We present Herschel/HIFI observations of the light hydride H2S obtained from the full spectral scan of the Orion Kleinmann-Low nebula (Orion KL) taken as part of the Herschel Observations of EXtra-Ordinary Sources GT (guaranteed time) key program. In total, we observe 52, 24, and 8 unblended or slightly blended features from H2 32S, H2 34S, and H2 33S, respectively. We only analyze emission from the so-called hot core, but emission from the plateau, extended ridge, and/or compact ridge are also detected. Rotation diagrams for ortho and para H2S follow straight lines given the uncertainties and yield T rot = 141 ± 12 K. This indicates H2S is in local thermodynamic equilibrium and is well characterized by a single kinetic temperature or an intense far-IR radiation field is redistributing the population to produce the observed trend. We argue the latter scenario is more probable and find that the most highly excited states (E up gsim 1000 K) are likely populated primarily by radiation pumping. We derive a column density, N tot(H2 32S) = 9.5 ± 1.9 × 1017 cm–2, gas kinetic temperature, T kin = 120 K, and constrain the H2 volume density, gsim 9 × 10 7 cm–3, for the H2S emitting gas. These results point to an H2S origin in markedly dense, heavily embedded gas, possibly in close proximity to a hidden self-luminous source (or sources), which are conceivably responsible for Orion KL's high luminosity. We also derive an H2S ortho/para ratio of 1.7 ± 0.8 and set an upper limit for HDS/H2S of <4.9 × 10 –3
Search for Interstellar Water in the Translucent Molecular Cloud toward HD 154368
We report an upper limit of 9 x 10^{12} cm-2 on the column density of water
in the translucent cloud along the line of sight toward HD 154368. This result
is based upon a search for the C-X band of water near 1240 \AA carried out
using the Goddard High Resolution Spectrograph of the Hubble Space Telescope.
Our observational limit on the water abundance together with detailed chemical
models of translucent clouds and previous measurements of OH along the line of
sight constrain the branching ratio in the dissociative recombination of H_3O+
to form water. We find at the level that no more than 30% of
dissociative recombinations of H_3O+ can lead to H_2O. The observed spectrum
also yielded high-resolution observations of the Mg II doublet at 1239.9 \AA
and 1240.4 \AA, allowing the velocity structure of the dominant ionization
state of magnesium to be studied along the line of sight. The Mg II spectrum is
consistent with GHRS observations at lower spectral resolution that were
obtained previously but allow an additional velocity component to be
identified.Comment: Accepted by ApJ, uses aasp
Sports mega-events – three sites of contemporary political contestation
This article discusses the contemporary politics of sports mega-events, involving the Olympic Games and Fédération Internationale de Football Association (FIFA) Men’s Football World Cup Finals as well as other lower ‘order’ sports megas, taking two main forms: the promotional and the protest. There is a politics in, and a politics of, sports mega-events. The former focuses on the internal politics of the organizing bodies, such as the International Olympic Committee and FIFA. This form of politics has been written about elsewhere, and hence, there is no detailed discussion in this article about it. Instead this article offers a brief discussion of the range and number of sports mega-events since 2000, an assessment of the contemporary politics of sports mega-events, a focus on three main sites of political contestation – rights, legacy and labour, and finally, it offers conclusions about research into the politics of sports mega-events
Primordial Star Formation under Far-ultraviolet radiation
Thermal and chemical evolution of primordial gas clouds irradiated with
far-ultraviolet (FUV; < 13.6 eV) radiation is investigated. In clouds
irradiated by intense FUV radiation, sufficient hydrogen molecules to be
important for cooling are never formed. However, even without molecular
hydrogen, if the clouds are massive enough, they start collapsing via atomic
hydrogen line cooling. Such clouds continue to collapse almost isothermally
owing to successive cooling by H^{-} free-bound emission up to the number
density of 10^{16} cm^{-3}. Inside the clouds, the Jeans mass eventually falls
well below a solar mass. This indicates that hydrogen molecules are dispensable
for low-mass primordial star formation, provided fragmentation of the clouds
occurs at sufficiently high density.Comment: 32 pages and 9 figures. ApJ, in pres
Carinae's Dusty Homunculus Nebula from Near-Infrared to Submillimeter Wavelengths: Mass, Composition, and Evidence for Fading Opacity
Infrared observations of the dusty, massive Homunculus Nebula around the luminous blue variable Carinae are crucial to characterize the mass-loss history and help constrain the mechanisms leading to the great eruption. We present the 2.4-670 m spectral energy distribution, constructed from legacy Infrared Space Observatory observations and new spectroscopy obtained with the Herschel Space Observatory. Using radiative transfer modeling, we find that the two best-fit dust models yield compositions that are consistent with CNO-processed material, with iron, pyroxene and other metal-rich silicates, corundum, and magnesium-iron sulfide in common. Spherical corundum grains are supported by the good match to a narrow 20.2 m feature. Our preferred model contains nitrides AlN and Si3N4 in low abundances. Dust masses range from 0.25 to 0.44 M, but M(sub tot) 45 M in both cases, due to an expected high Fe gas-to-dust ratio. The bulk of dust is within a 5" x 7" central region. An additional compact feature is detected at 390 m. We obtain L = 2.96 x 10(exp 6) Lunar mass, a 25% decline from an average of mid-IR photometric levels observed in 1971-1977. This indicates a reduction in circumstellar extinction in conjunction with an increase in visual brightness, allowing 25%-40% of optical and UV radiation to escape from the central source. We also present an analysis of 12CO and 13CO J = 5-4 through 9-8 lines, showing that the abundances are consistent with expectations for CNO-processed material. The [12CII] line is detected in absorption, which we suspect originates in foreground material at very low excitation temperatures
Observational tests of interstellar methanol formation
Context. It has been established that the classical gas-phase production of interstellar methanol (CH3OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces.
Aims: While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs).
Methods: We have observed the rotational transition quartets J = 2K - 1K of 12CH3OH and 13CH3OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1-0 transitions of 12C18O and 13C18O were observed towards some of these sources. We use the 12C/13C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH3OH and CO. If not, the ratio should be higher in CH3OH due to 13C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative over-abundance of A-methanol.
Results: We show that the 12C/13C isotopic ratio is very similar in gas-phase CH3OH and C18O, on the spatial scale of about 40", towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity.
Conclusions: While the 12C/13C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive
Development of antigen-specific ELISA for circulating autoantibodies to extracellular matrix protein 1 in lichen sclerosus
Lichen sclerosus is a common, acquired chronic inflammatory skin disease of unknown etiology, although circulating autoantibodies to the glycoprotein extracellular matrix protein 1 (ECM1) have been detected in most patients’ sera. We have examined the nature of ECM1 epitopes in lichen sclerosus sera, developed an ELISA system for serologic diagnosis, and assessed clinicopathological correlation between ELISA titer and disease. Epitope-mapping studies revealed that lichen sclerosus sera most frequently recognized the distal second tandem repeat domain and carboxyl-terminus of ECM1. We analyzed serum autoantibody reactivity against this immunodominant epitope in 413 individuals (95 subjects with lichen sclerosus, 161 normal control subjects, and 157 subjects with other autoimmune basement membrane or sclerosing diseases). The ELISA assay was highly sensitive; 76 of 95 lichen sclerosus patients (80.0%) exhibited IgG reactivity. It was also highly specific (93.7%) in discriminating between lichen sclerosus and other disease/control sera. Higher anti-ECM1 titers also correlated with more longstanding and refractory disease and cases complicated by squamous cell carcinoma. Furthermore, passive transfer of affinity-purified patient IgG reproduced some histologic and immunopathologic features of lichen sclerosus skin. This new ELISA is valuable for the accurate detection and quantification of anti-ECM1 autoantibodies. Moreover, the values may have clinical significance in patients with lichen sclerosus
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