[en] Before, during, and after 19 courses of chemotherapy given to patients with disseminated malignant melanoma plasma spermidine levels were determined with a radioimmunoassay. Baseline values were normal in 17 courses, a doubling of plasma levels following chemotherapy occurred in 13 courses. There was no relation between the occurrence of a tumor response and an increase in spermidine levels nor between hematological toxicity or digestive tract toxicity and spermidine levels. (orig.)

[en] This paper describes a near-UV/VIS study of a pyrene:H₂O interstellar ice analogue at 10 K using optical absorption spectroscopy. A new experimental approach makes it possible to irradiate the sample with vacuum ultraviolet (VUV) light (7-10.5 eV) while simultaneously recording spectra in the 240-1000 nm range with subsecond time resolution. Both spectroscopic and dynamic information on VUV processed ices are obtained in this way. This provides a powerful tool to follow, in situ and in real time, the photophysical and photochemical processes induced by VUV irradiation of a polycyclic aromatic hydrocarbon containing inter- and circumstellar ice analogue. Results on the VUV photolysis of a prototype sample-strongly diluted pyrene in H₂O ice-are presented. In addition to the pyrene cation (Py⁺), other products-hydroxypyrene (PyOH), possibly hydroxypyrene cation (PyOH⁺), and pyrene/pyrenolate anion (Py^-/PyO^-)-are observed. It is found that the charge remains localized in the ice, also after the VUV irradiation is stopped. The astrochemical implications and observational constraints are discussed.

[en] The spectral region around 10 μm, showing prominent emission bands from various dust species is commonly used for the evaluation of the chemical composition of protoplanetary dust. Different methods of analysis have been proposed for this purpose, but so far, no comparative test has been performed to test the validity of their assumptions. In this paper, we evaluate how good the various methods are in deriving the chemical composition of dust grains from infrared spectroscopy. Synthetic spectra of disk models with different geometries and central sources were calculated, using a two-dimensional radiative transfer code. These spectra were then fitted in a blind test by four spectral decomposition methods. We studied the effect of disk structure (flared versus flat), inclination angle, size of an inner disk hole, and stellar luminosity on the fitted chemical composition. Our results show that the dust parameters obtained by all methods deviate systematically from the input data of the synthetic spectra. The dust composition fitted by the new two-layer temperature distribution method, described in this paper, differs the least from the input dust composition and the results show the weakest systematic effects. The reason for the deviations of the results given by the previously used methods lies in their simplifying assumptions. Due to the radial extent of the 10 μm emitting region there is dust at different temperatures contributing to the flux in the silicate feature. Therefore, the assumption of a single averaged grain temperature can be a strong limitation of the previously used methods. The continuum below the feature can consist of multiple components (e.g., star, inner rim, and disk midplane), which cannot simply be described by a Planck function at a single temperature. In addition, the optically thin emission of 'featureless' grains (e.g., carbon in the considered wavelength range) produces a degeneracy in the models with the optically thick emission of the disk. The effect of different noise levels on the results has also been tested. We find that for a signal-to-noise ratio (S/N) of 100 one can expect an absolute uncertainty in the value of the crystallinity of about 11% using ground-based observations (8-13 μm). For space-based observations (7-17 μm) the expected uncertainty is about 5% for the same S/N value. Moreover, the average value of the estimated crystallinity increases toward lower S/N in general. On the basis of our results, we propose a recipe for the analysis and interpretation of dust spectroscopy data in the mid-infrared which should be especially valuable for analyzing Spitzer spectroscopy data and ground-based infrared spectroscopy data in the 10 μm window.

[en] Highlights: • Ro-vibrational spectrum of C3H4 recorded in 3060–3080 cm⁻¹ region by cw-CRDS. • First detection of the ${\nu }_3+{\nu }_5$ combination band. • Perturbation analysis of the ${\nu }_3+{\nu }_5$ combination band is given. We present the first detection of the high-resolution ro-vibrational spectrum of the ${\nu }_3+{\nu }_5$ combination band of propyne around 3070 cm⁻¹. The fully resolved spectrum is recorded for supersonically jet-cooled propyne using continuous wave cavity ring-down spectroscopy (cw-CRDS). The assignments are supported with the help of accurate ab initio vibration-rotation interaction constants (${\alpha }_i$) and anharmonic frequencies. A detailed analysis of the rotationally cold spectrum is given.

[en] Up to now, no laboratory-based study has investigated polycyclic aromatic hydrocarbon (PAH) species as potential carriers of both the diffuse interstellar bands (DIBs) and the 2175 Å UV bump. We examined the proposed correlation between these two features by applying experimental and theoretical techniques on two specific medium-sized/large PAHs (dibenzorubicene C₃₀H₁₄ and hexabenzocoronene C₄₂H₁₈) in their neutral and cationic states. It was already shown that mixtures of sufficiently large, neutral PAHs can partly or even completely account for the UV bump. We investigated how the absorption bands are altered upon ionization of these molecules by interstellar UV photons. The experimental studies presented here were realized by performing matrix isolation spectroscopy with subsequent far-UV irradiation. The main effects were found to be a broadening of the absorption bands in the UV combined with slight redshifts. The position of the complete π-π* absorption structure around 217.5 nm, however, remains more or less unchanged, which could explain the observed position invariance of the interstellar bump for different lines of sight. This favors the assignment of this feature to the interstellar PAH population. As far as the DIBs are concerned, neither our investigations nor the laboratory studies carried out by other research groups support a possible connection with this class of molecules. Instead, there are reasonable arguments that neutral and singly ionized cationic PAHs cannot be held responsible for the DIBs.

[en] Planet formation is profoundly impacted by the properties of protoplanetary disks and their central star. However, how disk properties vary with stellar parameters remains poorly known. Here, we present the first comprehensive, comparative Spitzer/IRS study of the dust and gas properties of disks around young Sun-like stars (K1-M5) and cool stars/brown dwarfs (M5-M9). The comparison of these two large samples of over 60 sources reveal major differences in the evolution of both the dust and gas components. We report the first detection of organic molecules in disks around brown dwarfs. The detection rate statistics and the line flux ratios of HCN and C₂H₂ show a striking difference between the two samples, demonstrating a significant underabundance of HCN relative to C₂H₂ in the disk surface of cool stars. We propose this to originate from the large difference in the UV irradiation around the two types of sources. The statistical comparison of the 10 μm silicate emission features also reveals a difference between the two samples. Cool stars and brown dwarfs show weaker features arising from more processed silicate grains in the disk atmosphere. These findings complement previous indications of flatter disk structures and longer disk lifetimes around cool stars. Our results highlight important differences in the chemical and physical evolution of protoplanetary disks as a function of stellar mass, temperature, and radiation field which should be taken into account in planet formation models. We note that the different chemistry of preplanetary materials in the disk may also influence the bulk composition and volatile content of the forming planets. In particular, if exogenous HCN has played a key role in the synthesis of prebiotic molecules on Earth as proposed, then prebiotic chemistry may unfold differently on planets around cool stars.

[en] The chemistry of astronomical hydrocarbons, responsible for the well-known infrared emission features detected in a wide variety of targets, remains enigmatic. Here we focus on the group of young intermediate-mass Herbig Ae stars. We have analyzed the aliphatic and polycyclic aromatic hydrocarbon (PAH) emission features in the infrared spectra of a sample of 53 Herbig Ae stars, obtained with the Infrared Spectrograph aboard the Spitzer Space Telescope. We confirm that the PAH-to-stellar luminosity ratio is higher in targets with a flared dust disk. However, a few sources with a flattened dust disk still show relatively strong PAH emission. Since PAH molecules trace the gas disk, this indicates that gas disks may still be flared, while the dust disk has settled due to grain growth. There are indications that the strength of the 11.3 μm feature also depends on dust disk structure, with flattened disks being less bright in this feature. We confirm that the CC bond features at 6.2 and 7.8 μm shift to redder wavelengths with decreasing stellar effective temperature. Moreover, we show that this redshift is accompanied by a relative increase of aliphatic CH emission and a decrease of the aromatic 8.6 μm CH feature strength. Cool stars in our sample are surrounded by hydrocarbons with a high aliphatic/aromatic CH ratio and a low aromatic CH/CC ratio, and vice versa for the hot stars. We conclude that, while the overall hydrocarbon emission strength depends on the dust disk's geometry, the relative differences seen in the IR emission features in disks around Herbig Ae stars are mainly due to chemical differences of the hydrocarbon molecules induced by the stellar UV field. Strong UV flux reduces the aliphatic component and emphasizes the spectral signature of the aromatic molecules in the IR spectra.

[en] We present Spitzer Space Telescope low-resolution spectroscopy of the protoplanetary disk around the M4 star RECX 5, a low-mass member of the ∼8 Myr old η Chamaeleontis star cluster. Two features of the disk around RECX 5 set it apart from other young, low-mass stars with protoplanetary disks: its mineralogy and its disk geometry. Band strengths of the crystalline silicate forsterite are a factor of two higher than that typically observed in T Tauri star disks, indicative of a high forsterite mass fraction. Continuum fluxes of the disk are inconsistent with either a flaring or flattened structure, suggesting a complex disk geometry. Radiative transfer modeling of the spectrum suggests that the disk has a gap at a radius of r = 0.6 AU, and that the disk density at r < 33 AU is a factor of 100 lower than that of a continuous disk. A second disk gap might be centered at r = 24 AU. The RECX 5 disk has properties that are remarkably similar to the disk surrounding the Herbig Be star HD 100546, which is noted for having extreme mineralogy and geometry among Herbig star disks. Similar to a solution proposed for HD 100546, we speculate that the clearance of the RECX 5 disk at r < 33 AU is a consequence of the formation of a Saturn-mass planet, with the planet being responsible for the striking difference in both the spectral energy distribution and chemical composition of the dust around RECX 5.

[en] In this paper, we present mid-infrared spectra of a comprehensive set of Herbig Ae/Be stars observed with the Spitzer Space Telescope. The signal-to-noise ratio of these spectra is very high, ranging between about a hundred and several hundreds. During the analysis of these data we tested the validity of standardized protoplanetary dust models and studied grain growth and crystal formation. On the basis of the analyzed spectra, the major constituents of protoplanetary dust around Herbig Ae/Be stars are amorphous silicates with olivine and pyroxene stoichiometry, crystalline forsterite, and enstatite and silica. No other solid-state features, indicating other abundant dust species, are present in the Spitzer spectra. Deviations of the synthetic spectra from the observations are most likely related to grain shape effects and uncertainties in the iron content of the dust grains. Our analysis revealed that larger grains are more abundant in the disk atmosphere of flatter disks than in that of flared disks, indicating that grain growth and sedimentation decrease the disk flaring. We did not find, however, correlations between the value of crystallinity and any of the investigated system parameters. Our analysis shows that enstatite is more concentrated toward the warm inner disk than forsterite, in contrast to predictions of equilibrium condensation models. None of the three crystal formation mechanisms proposed so far can alone explain all our findings. It is very likely that all three play at least some role in the formation of crystalline silicates.

[en] EX Lup is the prototype of the EXor class of eruptive young stars. These objects show optical outbursts which are thought to be related to runaway accretion onto the star. In a previous study we observed in situ crystal formation in the disk of EX Lup during its latest outburst in 2008, making the object an ideal laboratory to investigate circumstellar crystal formation and transport. This outburst was monitored by a campaign of ground-based and Spitzer Space Telescope observations. Here we modeled the spectral energy distribution (SED) of EX Lup in the outburst from optical to millimeter wavelengths with a two-dimensional radiative transfer code. Our results showed that the shape of the SED at optical wavelengths was more consistent with a single-temperature blackbody than a temperature distribution. We also found that this single-temperature component emitted 80%-100% of the total accretion luminosity. We concluded that a thermal instability, the most widely accepted model of EXor outbursts, was likely not the triggering mechanism of the 2008 outburst of EX Lup. Our mid-infrared Spitzer spectra revealed that the strength of all crystalline bands between 8 and 30 μm increased right after the end of the outburst. Six months later, however, the crystallinity in the 10 μm silicate feature complex decreased. Our modeling of the mid-infrared spectral evolution of EX Lup showed that, although vertical mixing should be stronger during the outburst than in the quiescent phase, fast radial transport of crystals (e.g., by stellar/disk wind) was required to reproduce the observed mid-infrared spectra.