345 research outputs found
The Nature of the Variable Galactic Center Source IRS16SW
We report measurements of the light curve of the variable Galactic Center
source IRS16SW. The light curve is not consistent with an eclipsing binary or
any other obvious variable star. The source may be an example of a high mass
variable predicted theoretically but not observed previously.Comment: 11 pages, 2 figures. Accepted by Ap
On the Excitation and Formation of Circumstellar Fullerenes
We compare and analyze the Spitzer mid-infrared spectrum of three
fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds;
Tc1, SMP SMC16, and SMP LMC56. The three planetary nebulae share many
spectroscopic similarities. The strongest circumstellar emission bands
correspond to the infrared active vibrational modes of the fullerene species
C60 and little or no emission is present from Polycyclic Aromatic Hydrocarbons
(PAHs). The strength of the fullerene bands in the three planetary nebulae is
very similar, while the ratio of the [NeIII]15.5um/[NeII]12.8um fine structure
lines, an indicator of the strength of the radiation field, is markedly
different. This raises questions about their excitation mechanism and we
compare the fullerene emission to fluorescent and thermal models. In addition,
the spectra show other interesting and common features, most notably in the
6-9um region, where a broad plateau with substructure dominates the emission.
These features have previously been associated with mixtures of
aromatic/aliphatic hydrocarbon solids. We hypothesize on the origin of this
band, which is likely related to the fullerene formation mechanism, and compare
it with modeled Hydrogenated Amorphous Carbon that present emission in this
region.Comment: 13 pages, 2 tables, 7 figures, Accepted for publication in Ap
Infrared photometry of the semistellar nucleus of M31
New broad-band infrared JHK data and narrow-band CO and H_2O indices for the semistellar nucleus of M31 are presented. The data were obtained specifically to test a prediction of a recent synthesis model by Faber and French in which the ratio of dwarf-to-giant light increases strongly in going from the bulge to the nucleus of M31. The new infrared data do not support such a model. Some alternative explanations for the behavior of the various indices are given, but the apparent conflict between the Faber-French interpretation of the strength of the Na i λ8190 feature and our data is not satisfactorily resolved
A mid-infrared survey of the inner 2 Ă— 1.5 degrees of the Galaxy with Spitzer/IRAC
We present a survey of Spitzer Space Telescope/IRAC observations of the central 2 Ă— 1.5 degrees (265 Ă— 200 pc) of the Galaxy at 3-8 ÎĽm. These data represent the highest spatial resolution and sensitivity large-scale map made to date of the Galactic Center (GC) at mid-infrared wavelengths. The IRAC data provide a census of the optically obscured stellar sources as well as a detailed map of the highly filamentary structure in the interstellar medium. The diffuse emission is dominated by PAH emission from small grains in star-forming regions. Dark clouds displaying a large variety of sizes and morphologies are imaged, many of which remain opaque at IRAC wavelengths. Using a multiwavelength comparison, we determine which objects are likely to be in the foreground and which are located at the GC. We find no counterparts at IRAC wavelengths to the unique system of linear, nonthermal radio filaments present at the GC
The mid-infrared colors of the interstellar medium and extended sources at the Galactic center
A mid-infrared (3.6–8 μm) survey of the Galactic center has been carried out with the IRAC instrument on the Spitzer Space Telescope. This survey covers the central 2º x 1.4º (~280 x 200 pc) of the Galaxy. At 3.6 and 4.5 μm the emission is dominated by stellar sources, the fainter ones merging into an unresolved background. At 5.8 and 8 μm the stellar sources are fainter, and large-scale diffuse emission from the ISM of the Galaxy's central molecular zone becomes prominent. The survey reveals that the 8-to-5.8 μm color of the ISM emission is highly uniform across the surveyed region. This uniform color is consistent with a flat extinction law and emission from polycyclic aromatic hydrocarbons (PAHs). Models indicate that this broadband color should not be expected to change if the incident radiation field heating the dust and PAHs is ~10^4 times that of the solar neighborhood. Other regions of very red emission indicate cases where thick dust clouds obscure deeply embedded objects or very early stages of star formation
Genome-wide study of immune biomarkers in cerebrospinal fluid and serum from patients with bipolar disorder and controls.
Bipolar disorder is a common, chronic psychiatric disorder. Despite high heritability, there is a paucity of identified genetic risk factors. Immune biomarkers are under more direct genetic influence than bipolar disorder. To explore the genetic associations with immune biomarker levels in cerebrospinal fluid (CSF) and blood serum which previously showed differences in bipolar disorder, we performed a study involving 291 individuals (184 bipolar disorder patients and 107 controls). The biomarkers assayed in both CSF and serum were: chitinase-3-like protein-1 (YKL-40), monocyte chemoattractant protein-1 (MCP-1), soluble cluster of differentiation (sCD14), tissue inhibitor of metalloproteinases-1 and 2 (TIMP-1 and TIMP-2). C-reactive protein (CRP) was only quantified in serum, and interleukin 8 (IL-8) measures were only available in CSF. Genome-wide association studies were conducted using PLINK for each of three genotyping waves and incorporated covariates for population substructure, age, sex, and body mass index (BMI). Results were combined by meta-analysis. Genome-wide significant associations were detected for all biomarkers except TIMP-1 and TIMP-2 in CSF. The strongest association in CSF was found for markers within the CNTNAP5 gene with YKL-40 (rs150248456, P = 2.84 × 10-10). The strongest association in serum was also for YKL-40 but localized to the FANCI gene (rs188263039, P = 5.80 × 10-26). This study revealed numerous biologically plausible genetic associations with immune biomarkers in CSF and blood serum. Importantly, the genetic variants regulating immune biomarker levels in CSF and blood serum differ. These results extend our knowledge of how biomarkers showing alterations in bipolar disorder are genetically regulated
The abundances of polyacetylenes towards CRL618
We present a mid-infrared high spectral resolution spectrum of CRL618 in the
frequency ranges 778-784 and 1227-1249 cm^-1 (8.01-8.15 and 12.75-12.85 um)
taken with the Texas Echelon-cross-Echelle Spectrograph (TEXES) and the
Infrared Telescope Facility (IRTF). We have identified more than 170
ro-vibrational lines arising from C2H2, HCN, C4H2, and C6H2. We have found no
unmistakable trace of C8H2. The line profiles display a complex structure
suggesting the presence of polyacetylenes in several components of the
circumstellar envelope (CSE). We derive total column densities of 2.5 10^17,
3.1 10^17, 2.1 10^17, 9.3 10^16 cm^-2, and < 5 10^16 cm^-2 for HCN, C2H2, C4H2,
C6H2, and C8H2, respectively. The observations indicate that both the
rotational and vibrational temperatures in the innermost CSE depend on the
molecule, varying from 100 to 350 K for the rotational temperatures and 100 to
500 K for the vibrational temperatures. Our results support a chemistry in the
innermost CSE based on radical-neutral reactions triggered by the intense UV
radiation field.Comment: 9 pages, 4 figures, 1 table; accepted for publication in The
Astrophysical Journa
The Infrared Spectra of Very Large Irregular Polycyclic Aromatic Hydrocarbons (PAHs): Observational Probes of Astronomical PAH Geometry, Size and Charge
The mid-IR spectra of six large, irregular PAHs with formulae (C84H24 -
C120H36) have been computed using Density Functional Theory (DFT). Trends in
the dominant band positions and intensities are compared to those of large,
compact PAHs as a function of geometry, size and charge. Irregular edge
moieties that are common in terrestrial PAHs, such as bay regions and rings
with quartet hydrogens, are shown to be uncommon in astronomical PAHs. As for
all PAHs comprised solely of C and H reported to date, mid-IR emission from
irregular PAHs fails to produce a strong CCstr band at 6.2 um, the position
characteristic of the important, class A astronomical PAH spectra. Earlier
studies showed inclusion of nitrogen within a PAH shifts this to 6.2 um for PAH
cations. Here we show this band shifts to 6.3 um in nitrogenated PAH anions,
close to the position of the CC stretch in class B astronomical PAH spectra.
Thus nitrogenated PAHs may be important in all sources and the peak position of
the CC stretch near 6.2 um appears to directly reflect the PAH cation to anion
ratio. Large irregular PAHs exhibit features at 7.8 um but lack them near 8.6
um. Hence, the 7.7 um astronomical feature is produced by a mixture of small
and large PAHs while the 8.6 um band can only be produced by large compact
PAHs. As with the CCstr, the position and profile of these bands reflect the
PAH cation to anion ratio.Comment: accepted by Ap
Near-Infrared Spectroscopy of Molecular Filaments in the Reflection Nebula NGC 7023
We present near-infrared spectroscopy of fluorescent molecular hydrogen (H_2)
emission from molecular filaments in the reflection nebula NGC 7023. We derive
the relative column densities of H_2 rotational-vibrational states from the
measured line emission and compare these results with several model
photodissociation regions covering a range of densities, incident UV-fields,
and excitation mechanisms. Our best-fit models for one filament suggest, but do
not require, either a combination of different densities, suggesting clumps of
10^6 cm^{-3} in a 10^4 - 10^5 cm^{-3} filament, or a combination of fluorescent
excitation and thermally-excited gas, perhaps due to a shock from a bipolar
outflow. We derive densities and UV fields for these molecular filaments that
are in agreement with previous determinations.Comment: ApJ accepted, 26 pages including 5 embedded figures, uses AASTEX.
Also available at http://www-astronomy.mps.ohio-state.edu/~martini/pubs.htm
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