Aromatic Hydrocarbons, Diamonds, and Fullerenes in Interstellar Space: Puzzles to be Solved by Laboratory and Theoretical Astrochemistry

New research is presented, and previous research is reviewed, on the emission and absorption of interstellar aromatic hydrocarbons. Emission from aromatic hydrocarbons dominate the mid-infrared emission of many galaxies, including our own Milky Way galaxy. Only recently have aromatic hydrocarbons been observed in absorption in the interstellar medium, along lines of sight with high column densities of interstellar gas and dust. Much work on interstellar aromatics has been done, with astronomical observations and laboratory and theoretical astrochemistry. In many cases the predictions of laboratory and theoretical work are confirmed by astronomical observations, but in other cases clear discrepancies exist which provide problems to be solved by a combination of astronomical observations, laboratory studies, and theoretical studies. The emphasis of this paper will be on current outstanding puzzles concerning aromatic hydrocarbons which require further laboratory and theoretical astrochemistry to resolve. This paper will also touch on related topics where laboratory and theoretical astrochemistry studies are needed to explain astrophysical observations, such as a possible absorption feature due to interstellar "diamonds" and the search for fullerenes in space.Comment: Spectrochimica Acta A, Feb. 2001, in press. 33 pages including 11 postscript figures, AASTeX format. Full postscript paper also available at http://www.astronomy.ohio-state.edu/~sellgren/saa.htm

The Roberta Mitchell Lecture: Structuring Responsibility in Securitization Transactions

In this Lecture, Professor Schwarcz examines how complex securitization transactions may have created a “protection gap,” the conundrum that transaction parties may be unable to purchase or might not want to pay the price for full protection. As a result, they sometimes choose or are forced to assume the good faith of the other parties to the transaction and the consistency and completeness of protections provided in the transaction documents

Fullerenes and proto-fullerenes in interstellar carbon dust

Laboratory spectra of hydrogenated amorphous carbon (HAC) particles prepared under a variety of conditions show spectral features at 7.05, 8.5, 17.4 and 18.9 {\mu}m (1418, 1176, 575 & 529 cm-1) that have been associated with emission from C60 molecules. These lines occur in the spectra even though C60 molecules as such are not present in our samples. It appears that these four spectral lines in HAC can instead be associated with precursor molecules or "proto-fullerenes" that subsequently react to yield C60. We develop a model tracing the evolution and de-hydrogenation of HAC dust and show that the observation of an emission feature at 16.4 {\mu}m (610 cm-1) in astronomical spectra signals the presence of the pentagonal carbon rings required for the formation of fullerenes. We suggest that the set of four IR emission lines previously identified with C60 in many objects that also show the 16.4 {\mu}m feature and other polycyclic aromatic hydrocarbon bands arise from proto-fullerenes rather than C60. Tc1 is an example of a source in which de-hydrogenation has proceeded to the point where only fullerenes are present.Comment: 17 pages, 2 figures, accepted ApJ Letter

On neuroinflammation in psychotic disorders

Neuroinflammation has been implicated in several psychiatric conditions. Based on experimental studies, the glia-derived tryptophan metabolite kynurenic acid (KYNA) may be especially relevant for positive psychotic symptoms and impaired executive functioning. The first two studies (I and II) of this thesis translate these experimental findings to bipolar disorder patients. Rooted in a genome-wide association study against cerebrospinal fluid (CSF) concentrations of KYNA, we used a multi-pronged approach and linked the identified genetic risk marker not only with other CSF biomarkers in bipolar patients, but also with specific symptoms such as delusions, hallucinations, and impaired executive functioning. We conducted cell studies, postmortem analyses, and clinical association studies that together suggested a sorting nexin 7 driven activation of caspase-8/IL-1ß as a mechanism underlying increased CSF concentration of KYNA in psychotic bipolar patients. Caspase-1 is activated by the purinergic ionotropic receptor P2X7R. This receptor is suggested to be internalized by a G-protein coupled receptor kinase 3 (GRK-3)-dependent mechanism. Decreased protein levels of GRK-3 have been observed in postmortem studies of schizophrenia and psychotic bipolar patients. In study III, we used a mouse with a targeted deletion for GRK3. These mice displayed impaired P2X7R internalization, increased brain levels of IL-1ß, increased immunoreactivity for the astrocytic marker glial fibrillary acidic protein (GFAP), a more pronounced accumulation of hippocampal KYNA, as well as an accentuated dopaminergic response to amphetamine. In behavior models, these animals displayed disrupted pre-pulse inhibition, as well as impaired contextual fear conditioning with spared cue-specific fear conditioning. Taken together, these findings suggest that the GRK3-/-mouse is a novel genetic animal model of schizophrenia that may prove useful in exploring the actions of the emerging immunomodulatory drugs in psychotic disorders. Study IV was a validation study aiming at defining an algorithm that identifies bipolar disorder patients in Swedish national registries as accurate as possible, a pre-requisite for study V. In the last study V of this thesis, we studied the association between psychotic disorders and rheumatoid arthritis (RA). We found that the previously reported inverse association is likely to have been confounded by underreporting and/or underdiagnosis of RA. However, an inverse association between schizophrenia and seronegative RA may be real, tentatively due to shared genetic underpinnings involving glia functioning. In conclusion, this thesis suggests an important role of glial mechanisms in the pathophysiology of the two main psychiatric disorders, schizophrenia and bipolar disorder. Our results add to growing evidence that cytokine and kynurenine metabolite signaling is tied to psychotic and cognitive symptoms. These findings open up for novel drug targets and imply that contemporary glia research can provide a rewarding foundation for investigations into pathology of psychiatric disorders

On the band-to-continuum intensity ratio in the infrared spectra of interstellar carbonaceous dust

Published interpretations of the relative intensity variations of the Unidentified Infrared Bands (UIBs) and their underlying continuum are discussed. An alternative model is proposed, in which a single carrier for both emits a) mostly a continuum when it is electronically excited by photons (visible or UV), or b) exclusively the UIBs, when only chemical energy is deposited by H capture on its surface, inducing only nuclear vibrations. The bands will dominate in atomic H regions but will be overcome by thermal continuum radiation when the ambient field is strong but lacks dissociating photons (900-1100 Angstroms). The model applies to PDRs as well as to limbs of molecular clouds in the ISM and agrees quantitatively with recent satellite observations. It gives indications on atomic H density and UIB intensity provided the ambient radiation field is known. It invokes no chemical, electronic, structural or size change in order to interpret the observed intensity variations.Comment: 18 pages, 2 figure

Moderate spectral resolution observations of 3 micron absorption features in highly obscured objects

The 3 micron absorption spectra of sources seen in or behind molecular clouds generally show a variety of absorption features. Three separate absorptions are used to explain these features. The cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility was used to obtain spectra of the late-type mass-loss star OH 0739-12 and the protostars MonR2 IRS-2 and IRS-3 (solid circles). The differences between the spectra are discussed

Really Cool Stars and the Star Formation History at the Galactic Center

We present R=550 to 1200 near infrared H and K spectra for a magnitude limited sample of 79 asymptotic giant branch and cool supergiant stars in the central ~ 5 pc (diameter) of the Galaxy. We use a set of similar spectra obtained for solar neighborhood stars with known Teff and Mbol that is in the same range as the Galactic center (GC) sample to derive Teff and Mbol for the GC sample. We then construct the Hertzsprung--Russell (HRD) diagram for the GC sample. Using an automated maximum likelihood routine, we derive a coarse star formation history of the GC. We find (1) roughly 75% of the stars formed in the central few pc are older than 5 Gyr; (2) the star formation rate (SFR) is variable over time, with a roughly 4 times higher star formation rate in the last 100 Myr compared to the average SFR; (3) our model can only match dynamical limits on the total mass of stars formed by limiting the IMF to masses above 0.7 M$_\odot$. This could be a signature of mass segregation or of the bias toward massive star formation from the unique star formation conditions in the GC; (4) blue supergiants account for 12 % of the total sample observed, and the ratio of red to blue supergiants is roughly 1.5; (5) models with isochrones with [Fe/H] = 0.0 over all ages fit the stars in our HRD better than models with lower [Fe/H] in the oldest age bins, consistent with the finding of Ramirez et al. (2000) that stars with ages between 10 Myr and 1 Gyr have solar [Fe/H].Comment: ApJ, accepted. Latex, 65 pages including 19 figure