- ID:
- ivo://CDS.VizieR/J/ApJ/852/7
- Title:
- Theoretical charge exchange X-ray cross sections
- Short Name:
- J/ApJ/852/7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fundamental collisional process of charge exchange (CX) has been established as a primary source of X-ray emission from the heliosphere, planetary exospheres, and supernova remnants. In this process, X-ray emission results from the capture of an electron by a highly charged ion from a neutral atom or molecule, to form a highly excited, high-charge state ion. As the captured electron cascades down to the lowest energy level, photons are emitted, including X-rays. To provide reliable CX-induced X-ray spectral models to realistically simulate these environments, line ratios and spectra are computed using theoretical CX cross sections obtained with the multi-channel Landau-Zener (MCLZ), atomic-orbital close-coupling (AOCC), molecular-orbital close-coupling (MOCC), and classical trajectory Monte Carlo methods for various collisional velocities relevant to astrophysics. X-ray spectra were computed for collisions of bare and H-like C to Al ions with H, He, and H_2_ with results compared to available experimental data. Using these line ratios, XSPEC models of CX emission in the northeast rim of the Cygnus Loop supernova remnant and the heliosphere are shown as examples with ion velocity dependence.
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- ID:
- ivo://CDS.VizieR/J/A+A/595/A130
- Title:
- Thermodynamic quantities of molecular hydrogen
- Short Name:
- J/A+A/595/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hydrogen is the most abundant molecule in the Universe. Its thermodynamic quantities dominate the physical conditions in molecular clouds, protoplanetary disks, etc. It is also of high interest in plasma physics. Therefore thermodynamic data for molecular hydrogen have to be as accurate as possible in a wide temperature range. We here rigorously show the shortcomings of various simplifications that are used to calculate the total internal partition function. These shortcomings can lead to errors of up to 40 percent or more in the estimated partition function. These errors carry on to calculations of thermodynamic quantities. Therefore a more complicated approach has to be taken. Seven possible simplifications of various complexity are described, together with advantages and disadvantages of direct summation of experimental values. These were compared to what we consider the most accurate and most complete treatment (case 8). Dunham coefficients were determined from experimental and theoretical energy levels of a number of electronically excited states of H2. Both equilibrium and normal hydrogen was taken into consideration.
- ID:
- ivo://CDS.VizieR/J/A+A/659/A111
- Title:
- The rotational spectrum of acrylamide
- Short Name:
- J/A+A/659/A111
- Date:
- 15 Mar 2022 06:07:15
- Publisher:
- CDS
- Description:
- Numerous complex organic molecules have been detected in the universe and among them are amides, which are considered as prime models for species containing a peptide linkage. In its backbone, acrylamide (CH_2_CHC(O)NH_2_) bears not only the peptide bond, but also the vinyl functional group that is a common structural feature in many interstellar compounds. This makes acrylamide an interesting candidate for searches in the interstellar medium. In addition, a tentative detection of the related molecule propionamide (C_2_H_5_C(O)NH_2_) has been recently claimed toward Sgr B2(N). The aim of this work is to extend the knowledge of the laboratory rotational spectrum of acrylamide to higher frequencies, which would make it possible to conduct a rigorous search for interstellar signatures of this amide using millimeter wave astronomy. We measured and analyzed the rotational spectrum of acrylamide between 75 and 480GHz. We searched for emission of acrylamide in the imaging spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array toward Sgr B2(N). We also searched for propionamide in the same source. The astronomical spectra were analyzed under the assumption of local thermodynamic equilibrium. We report accurate laboratory measurements and analyses of thousands of rotational transitions in the ground state and two excited vibrational states of the most stable syn form of acrylamide. In addition, we report an extensive set of rotational transitions for the less stable skew conformer. Tunneling through a low energy barrier between two symmetrically equivalent configurations has been revealed for this higher-energy species. Neither acrylamide nor propionamide were detected toward the two main hot molecular cores of Sgr B2(N). We did not detect propionamide either toward a position located to the east of the main hot core, thereby undermining the recent claim of its interstellar detection toward this position. We find that acrylamide and propionamide are at least 26 and 14 times less abundant, respectively, than acetamide toward the main hot core Sgr B2(N1S), and at least 6 and 3 times less abundant, respectively, than acetamide toward the secondary hot core Sgr B2(N2). A comparison with results of astrochemical kinetics model for related species suggests that acrylamide may be a few hundred times less abundant than acetamide, corresponding to a value that is at least an order of magnitude lower than the observational upper limits. Propionamide may be as little as only a factor of two less abundant than the upper limit derived toward Sgr B2(N1S). Lastly, the spectroscopic data presented in this work will aid future searches of acrylamide in space.
- ID:
- ivo://CDS.VizieR/J/A+A/657/A99
- Title:
- The rotational spectrum of glycinamide
- Short Name:
- J/A+A/657/A99
- Date:
- 21 Mar 2022 09:35:44
- Publisher:
- CDS
- Description:
- Glycinamide (NH_2_CH_2_C(O)NH_2_) is considered to be one of the possible precursors of the simplest amino acid glycine. Its only rotational spectrum reported so far has been in the cm-wave region on a laser-ablation generated supersonic expansion sample. The aim of this work is to extend the laboratory spectrum of glycinamide into the millimetre wave region to support its searches in the interstellar medium and to perform the first check for its presence in the high-mass star forming region Sagittarius B2(N). Glycinamide was synthesised chemically and was studied with broadband rotational spectroscopy in the 90-329 GHz region with the sample in slow flow at 50{deg}C. Tunneling across a low energy barrier between two symmetry equivalent configurations of the molecule resulted in splitting of each vibrational state and many perturbations in associated rotational energy levels, requiring careful coupled state fits for each vibrational doublet. We searched for emission of glycinamide in the imaging spectral line survey ReMoCA performed with the Atacama Large Millimetre/submillimetre Array toward Sgr B2(N). The astronomical spectra were analysed under the assumption of local thermodynamic equilibrium. We report the first analysis of the mm-wave rotational spectrum of glycinamide, resulting in fitting to experimental measurement accuracy of over 1200 assigned and measured transition frequencies for the ground state tunneling doublet, of many lines for tunneling doublets for two singly excited vibrational states, and determination of precise vibrational separation in each doublet. We did not detect emission from glycinamide in the hot molecular core Sgr B2(N1S). We derived a column density upper limit of 1.5x10^16^cm^-2^, which implies that glycinamide is at least seven times less abundant than aminoacetonitrile and 1.8 times less abundant than urea in this source.
- ID:
- ivo://CDS.VizieR/J/ApJS/207/13
- Title:
- The spectrum and term analysis of V II
- Short Name:
- J/ApJS/207/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spectrum and extended term analysis of V II are presented. Fourier transform spectrometry was used to record high resolution spectra of singly ionized vanadium in the region 1492-5800 {AA} (67020-17260/cm) with vanadium-neon and vanadium-argon hollow cathode lamps as sources. The wavenumber uncertainty for the center of gravity of the strongest lines is typically 0.002/cm, an improvement of an order of magnitude over previous measurements. Most of the lines exhibit partly resolved hyperfine structure. The V II energy levels in the 1985 compilation of Sugar and Corliss have been confirmed and revised, with the exception of the high-lying 4f levels and eight of the lower levels. Thirty-nine of the additional eighty-five high levels published by Iglesias et al. (1988, Publicaciones del Instituto Optica Daza de Valdes Madrid, 47, 1) have also been confirmed and revised, and three of their missing levels have been found. The energy uncertainty of the revised levels has been reduced by about an order of magnitude. In total, 176 even levels and 233 odd levels are presented.
- ID:
- ivo://CDS.VizieR/J/ApJ/723/845
- Title:
- The submillimeter spectrum of glycolaldehyde
- Short Name:
- J/ApJ/723/845
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Glycolaldehyde (HOCH_2_CHO) is a sugar-related interstellar prebiotic molecule that has been detected in two star-forming regions, Sgr B2(N) and G31.41+0.31. Glycolaldehyde is suspected to form from photodissociation-driven ice chemistry, and therefore can be used to trace complex organic chemistry in interstellar environments. The relative abundance of glycolaldehyde to its structural isomers, methyl formate (HCOOCH_3_) and acetic acid (CH_3_COOH), can be used to constrain astrochemical models. Given its central role in the complex chemistry of the interstellar medium, glycolaldehyde has been suggested as a prime molecular target for upcoming high-frequency molecular line searches using new far-infrared observatories. In particular, glycolaldehyde is a target for the Herschel Space Observatory HEXOS Key Program, which is conducting spectral line surveys of the Sgr B2(N) and Orion KL star-forming regions across the entire HIFI band. Laboratory investigation of glycolaldehyde in the HIFI frequency range is required before its lines can be identified in these spectra. We have therefore acquired the laboratory spectrum of glycolaldehyde in selected frequency ranges across the submillimeter range. We present here the laboratory spectral analysis of the ground vibrational state of glycolaldehyde up to 1.2THz.
- ID:
- ivo://CDS.VizieR/J/A+A/468/1115
- Title:
- Thorium and argon lines in the visible
- Short Name:
- J/A+A/468/1115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new list of thorium and argon emission lines in the visible obtained by analyzing high-resolution (R=110000) spectra of a ThAr hollow cathode lamp. The aim of this new line list is to allow significant improvements in the quality of wavelength calibration for medium- to high-resolution astronomical spectrographs. We use a series of ThAr lamp exposures obtained with the HARPS instrument (High Accuracy Radial-velocity Planet Searcher) to detect previously unknown lines, perform a systematic search for blended lines and correct individual wavelengths by determining the systematic offset of each line relative to the average wavelength solution.
708. Thorium line list
- ID:
- ivo://CDS.VizieR/J/A+A/648/A103
- Title:
- Thorium line list
- Short Name:
- J/A+A/648/A103
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The solar telescope connected to HARPS-N has observed the Sun since the summer of 2015. Such high-cadence, longbaseline data set is crucial for understanding spurious radial-velocity signals induced by our Sun and by the instrument. Aims. This manuscript describes the data reduction performed to obtain unprecedented radial-velocity precision for the three years of solar data released along with this paper. The nearly continuous observation of our Sun has allowed us to detect sub-m/s systematics in the HARPS-N solar data reduced by the current data reduction software. To improve the radial-velocity precision of the solar data, we reduced them using the new ESPRESSO data reduction software and developed new recipes to mitigate the detected systematics. The most significant improvement brought by the new data reduction is a strong decrease in the day-to-day radial-velocity scatter, from 1.28 to 1.09m/s; this is thanks to a more stable method to derive wavelength solutions, but also to the use of calibrations closer in time. We also demonstrate that the current HARPS-N data reduction software induces a long-term drift of 1.2m/s, due to the use of non-stable thorium lines. As a result, the old solar RVs are weakly correlated to the solar magnetic cycle, which is not expected. On the contrary, the newly derived radial velocities are much more correlated, with a Pearson correlation coefficient of 0.93. We also discuss a special correction for ghost contamination, to extract a calcium activity index free from instrumental systematics. Our work leads toward a better understanding of the instrumental and data reduction systematics affecting the HARPSN spectrograph. The new solar data released, representing an unprecedented time-series of 34550 high-resolution spectra and precise radial velocities will be crucial to understanding stellar activity signals of solar-type stars, with the goal of enabling the detection of other Earths.
- ID:
- ivo://CDS.VizieR/J/ApJS/211/4
- Title:
- Thorium spectrum from 250nm to 5500nm
- Short Name:
- J/ApJS/211/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have made precise observations of a thorium-argon hollow cathode lamp emission spectrum in the region between 350nm and 1175nm using a high-resolution Fourier transform spectrometer. Our measurements are combined with results from seven previously published thorium line lists to re-optimize the energy levels of neutral, singly, and doubly ionized thorium (Th I, Th II, and Th III). Using the optimized level values, we calculate accurate Ritz wavelengths for 19874 thorium lines between 250nm and 5500nm (40000/cm to 1800/cm). We have also found 102 new thorium energy levels. A systematic analysis of previous measurements in light of our new results allows us to identify and propose corrections for systematic errors in Palmer & Engleman (1983ats..book.....P) and typographical errors and incorrect classifications in Kerber et al. (2008ApJS..178..374K). We also found a large scatter with respect to the thorium line list of Lovis & Pepe (Cat. J/A+A/468/1115). We anticipate that our Ritz wavelengths will lead to improved measurement accuracy for current and future spectrographs that make use of thorium-argon or thorium-neon lamps as calibration standards.
- ID:
- ivo://CDS.VizieR/J/A+A/541/A121
- Title:
- Three conformers of n-butyl cyanide
- Short Name:
- J/A+A/541/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The saturated n-propyl cyanide has recently been detected in Sagittarius B2(N). The next larger unbranched alkyl cyanide is n-butyl cyanide. We want to provide accurate rest frequency predictions beyond the millimeter wave range to search for this molecule in the Galactic center source Sagittarius B2(N) and facilitate its detection in space. The laboratory rotational spectrum of n-butyl cyanide has been investigated between 75 and 348GHz. We have searched for emission lines caused by the molecule in our sensitive IRAM 30m molecular line survey of Sagittarius B2(N). More than one thousand rotational transitions have been identified in the laboratory for each of the three conformers for which limited data had been obtained previously in a molecular beam microwave study. The quantum number range has been greatly extended to J~120 or more and Ka>35, resulting in accurate spectroscopic parameters and accurate rest frequency calculations up to about 500GHz for strong to moderately weak transitions of the two lower energy conformers. Upper limits of the column densities of N<=3x10^15^cm^-2^ and 8x10^15^cm^-2^ were derived towards Sagittarius B2(N) for the two lower energy conformers, anti-anti and gauche-anti, respectively. The present data will be helpful to identify n-butyl cyanide at millimeter or longer wavelengths with radio telescope arrays such as ALMA, NOEMA, or EVLA. In particular, its detection in Sagittarius B2(N) with ALMA seems feasible.
