Rotational spectroscopy of the HCCO and DCCO radicals in the millimeter and submillimeter range

The ketenyl radical, HCCO, has recently been detected in the ISM for the first time. Further astronomical detections of HCCO will help us understand its gas-grain chemistry, and subsequently revise the oxygen-bearing chemistry towards dark clouds. Moreover, its deuterated counterpart, DCCO, has never been observed in the ISM. HCCO and DCCO still lack a broad spectroscopic investigation, although they exhibit a significant astrophysical relevance. In this work we aim to measure the pure rotational spectra of the ground state of HCCO and DCCO in the millimeter and submillimeter region, considerably extending the frequency range covered by previous studies. The spectral acquisition was performed using a frequency-modulation absorption spectrometer between 170 and 650 GHz. The radicals were produced in a low-density plasma generated from a select mixture of gaseous precursors. For each isotopologue we were able to detect and assign more than 100 rotational lines. The new lines have significantly enhanced the previous data set allowing the determination of highly precise rotational and centrifugal distortion parameters. In our analysis we have taken into account the interaction between the ground electronic state and a low-lying excited state (Renner-Teller pair) which enables the prediction and assignment of rotational transitions with $K_a$ up to 4. The present set of spectroscopic parameters provides highly accurate, millimeter and submillimeter rest-frequencies of HCCO and DCCO for future astronomical observations. We also show that towards the pre-stellar core L1544, ketenyl peaks in the region where $c$-$\mathrm{C_3H_2}$ peaks, suggesting that HCCO follows a predominant hydrocarbon chemistry, as already proposed by recent gas-grain chemical models

Rotational and high-resolution infrared spectrum of HC3_3N: global ro-vibrational analysis and improved line catalogue for astrophysical observations

HC$_3$N is an ubiquitous molecule in interstellar environments, from external galaxies, to Galactic interstellar clouds, star forming regions, and planetary atmospheres. Observations of its rotational and vibrational transitions provide important information on the physical and chemical structure of the above environments. We present the most complete global analysis of the spectroscopic data of HC$_3$N. We have recorded the high-resolution infrared spectrum from 450 to 1350 cm$^{-1}$, a region dominated by the intense $\nu_5$ and $\nu_6$ fundamental bands, located at 660 and 500 cm$^{-1}$, respectively, and their associated hot bands. Pure rotational transitions in the ground and vibrationally excited states have been recorded in the millimetre and sub-millimetre regions in order to extend the frequency range so far considered in previous investigations. All the transitions from the literature and from this work involving energy levels lower than 1000 cm$^{-1}$ have been fitted together to an effective Hamiltonian. Because of the presence of various anharmonic resonances, the Hamiltonian includes a number of interaction constants, in addition to the conventional rotational and vibrational l-type resonance terms. The data set contains about 3400 ro-vibrational lines of 13 bands and some 1500 pure rotational lines belonging to 12 vibrational states. More than 120 spectroscopic constants have been determined directly from the fit, without any assumption deduced from theoretical calculations or comparisons with similar molecules. An extensive list of highly accurate rest frequencies has been produced to assist astronomical searches and data interpretation. These improved data, have enabled a refined analysis of the ALMA observations towards Sgr B2(N2).Comment: 35 pages, 14 figures, accepted for pubblication in ApJ Supplemen

A new approach to electromagnetic wave tails on a curved spacetime

We present an alternative method for constructing the exact and approximate solutions of electromagnetic wave equations whose source terms are arbitrary order multipoles on a curved spacetime. The developed method is based on the higher-order Green's functions for wave equations which are defined as distributions that satisfy wave equations with the corresponding order covariant derivatives of the Dirac delta function as the source terms. The constructed solution is applied to the study of various geometric effects on the generation and propagation of electromagnetic wave tails to first order in the Riemann tensor. Generally the received radiation tail occurs after a time delay which represents geometrical backscattering by the central gravitational source. It is shown that the truly nonlocal wave-propagation correction (the tail term) takes a universal form which is independent of multipole order. In a particular case, if the radiation pulse is generated by the source during a finite time interval, the tail term after the primary pulse is entirely determined by the energy-momentum vector of the gravitational field source: the form of the tail term is independent of the multipole structure of the gravitational source. We apply the results to a compact binary system and conclude that under certain conditions the tail energy can be a noticeable fraction of the primary pulse energy. We argue that the wave tails should be carefully considered in energy calculations of such systems.Comment: RevTex, 28 pages, 5 eps figures, http://www.tpu.ee/~tony/texdocs/, 4 changes made (pp. 2, 4, 22, 24), 2 references adde

The puzzling temporally variable optical and X-ray afterglow of GRB 101024A

Aim: To present the optical observations of the afterglow of GRB 101024A and to try to reconcile these observations with the X-ray afterglow data of GRB 101024A using current afterglow models Method: We employ early optical observations using the Zadko Telescope combined with X-ray data and compare with the reverse shock/forward shock model. Results: The early optical light curve reveals a very unusual steep decay index of alpha~5. This is followed by a flattening and possibly a plateau phase coincident with a similar feature in the X-ray. We discuss these observations in the framework of the standard reverse shock/forward shock model and energy injection.We note that the plateau phase might also be the signature of the formation of a new magnetar.Comment: 5 pages, 2 figures. Accepted for publication in Astronomy and Astrophysic

Wind and trophic status explain within and among‐lake variability of algal biomass

Phytoplankton biomass and production regulates key aspects of freshwater ecosystems yet its variability and subsequent predictability is poorly understood. We estimated within‐lake variation in biomass using high‐frequency chlorophyll fluorescence data from 18 globally distributed lakes. We tested how variation in fluorescence at monthly, daily, and hourly scales was related to high‐frequency variability of wind, water temperature, and radiation within lakes as well as productivity and physical attributes among lakes. Within lakes, monthly variation dominated, but combined daily and hourly variation were equivalent to that expressed monthly. Among lakes, biomass variability increased with trophic status while, within‐lake biomass variation increased with increasing variability in wind speed. Our results highlight the benefits of high‐frequency chlorophyll monitoring and suggest that predicted changes associated with climate, as well as ongoing cultural eutrophication, are likely to substantially increase the temporal variability of algal biomass and thus the predictability of the services it provides

A study of methyl formate in astrochemical environments

Several complex organic molecules are routinely detected in high abundances towards hot cores and hot corinos. For many of them, their paths of formation in space are uncertain, as gas phase reactions alone seem to be insufficient. In this paper, we investigate a possible solid-phase route of formation for methyl formate (HCOOCH3). We use a chemical model updated with recent results from an experiment where simulated grain surfaces were irradiated with 200 keV protons at 16 K, to simulate the effects of cosmic ray irradiation on grain surfaces. We find that this model may be sufficient to reproduce the observed methyl formate in dark clouds, but not that found in hot cores and corinos.Comment: 6 pages, 2 figures, 2 tables Accepted by MNRA

A High Spatial Resolution Study of the λ=3 mm Continuum of Orion-KL

Recent interferometric observations have called into question the traditional view of the Orion-KL region, which displays one of the most well-defined cases of chemical differentiation in a star-forming region. Previous, lower-resolution images of Orion-KL show emission signatures for oxygen-bearing organic molecules toward the Orion Compact Ridge, and emission for nitrogen-bearing organic molecules toward the Orion Hot Core. However, more recent observations at higher spatial resolution indicate that the bulk of the molecular emission is arising from many smaller, compact clumps that are spatially distinct from the traditional Hot Core and Compact Ridge sources. It is this type of observational information that is critical for guiding astrochemical models, as the spatial distribution of molecules and their relation to energetic sources will govern the chemical mechanisms at play in star-forming regions. We have conducted millimeter imaging studies of Orion-KL with various beam sizes using CARMA in order to investigate the continuum structure. These \lambda;=3mm observations have synthesized beam sizes of ~0.5"-5.0". These observations reveal the complex continuum structure of this region, which stands in sharp contrast to the previous structural models assumed for Orion-KL based on lower spatial resolution images. The new results indicate that the spatial scaling previously used in determination of molecular abundances for this region are in need of complete revision. Here we present the results of the continuum observations, discuss the sizes and structures of the detected sources, and suggest an observational strategy for determining the proper spatial scaling to accurately determine molecular abundances in the Orion-KL region.Comment: 20 pages, 5 figures, accepted for publication in the Astrophysical Journa