- ID:
- ivo://CDS.VizieR/J/A+A/635/A104
- Title:
- Chemical abundance analysis of HD 20
- Short Name:
- J/A+A/635/A104
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Metal-poor stars with available detailed information about their chemical inventory pose powerful empirical benchmarks for nuclear astrophysics. Here we present our spectroscopic chemical abundance investigation of the metal-poor ([Fe/H]=-1.60dex), r-process-enriched ([Eu/Fe]=0.73dex) halo star HD 20 using novel and archival high-resolution data at outstanding signal-to-noise ratios (up to 1000 per Angstroem). By combining one of the first asteroseismic gravity measurements in the metal-poor regime from a TESS light curve with the spectroscopic analysis of iron lines under non-local thermodynamic equilibrium conditions, we derive a set of highly accurate and precise stellar parameters. These allow us to delineate a reliable chemical pattern that is comprised of solid detections of 48 elements, including 28 neutron-capture elements. Hence, we establish HD 20 among the few benchmark stars that have almost complete patterns and possess low systematic dependencies on the stellar parameters. Our light-element (Z<30) abundances are representative of other, similarly metal-poor stars in the Galactic halo with contributions from core-collapse supernovae of type II. In the realm of the neutron-capture elements, our comparison to the scaled solar r-pattern shows that the lighter neutron-capture elements (Z<60) are poorly matched. In particular, we find imprints of the weak r-process acting at low metallicities. Nonetheless, by comparing our detailed abundances to the observed metal-poor star BD +17 3248, we find a persistent residual pattern involving mainly the elements Sr, Y, Zr, Ba, and La. These are indicative of enrichment contributions from the s-process and we show that mixing with material from predicted yields of massive, rotating AGB stars at low metallicity considerably improves the fit. Based on a solar ratio of heavy- to light-s elements -- at odds with model predictions for the i-process -- and a missing clear residual pattern with respect to other stars with claimed contributions from this process, we refute (strong) contributions from such astrophysical sites providing intermediate neutron densities. Finally, nuclear cosmochronology is used to tie our detection of the radioactive element Th to an age estimate for HD 20 of 11.0+/-3.8Gyr.
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- ID:
- ivo://CDS.VizieR/J/A+AS/125/149
- Title:
- CHIANTI - An Atomic Database For Emission Lines I.
- Short Name:
- J/A+AS/125/149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comprehensive set of accurate atomic data is required for analyses of astrophysical and solar spectra. CHIANTI provides a database of atomic energy levels, wavelengths, radiative data and electron excitation data for ions which are abundant in cosmic plasmas. The most recent electron excitation data have been assessed and stored following the method of Burgess & Tully (1992A&A...254..436B). The current version is essentially complete for specifying the emission spectrum at wavelengths greater than 50{AA}. A list of observed lines in the spectral region between 50 and 1100{AA} has been compiled and compared with the lines predicted by the CHIANTI database. The CHIANTI database reproduces the vast majority of lines observed at these wavelengths. CHIANTI includes IDL (Interactive Data Language) routines to calculate optically thin synthetic spectra for equilibrium conditions. IDL routines to calculate theoretical line intensities required for electron density or temperature diagnostics and emission measure studies are also included. The CHIANTI atomic database and supporting IDL routines are available by anonymous FTP.
- ID:
- ivo://CDS.VizieR/J/ApJ/812/L5
- Title:
- CH_3_NCO (methyl isocyanate) transition frequencies
- Short Name:
- J/ApJ/812/L5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A new interstellar molecule, CH_3_NCO (methyl isocyanate), has been detected using the 12m telescope of the Arizona Radio Observatory (ARO). CH_3_NCO was identified in spectra covering 48GHz (68-116GHz) in the 3mm segment of a broadband survey of Sgr B2(N). Thirty very favorable rotational lines (K_a_=0 and K_a_=1 only; E_u_<60K) originating in five consecutive transitions (J=8->7, 9->8, 10->9, 11->10, and 12->11) in both the A and E internal rotation species are present in this frequency range. Emission was observed at all of the predicted frequencies, with 17 lines appearing as distinct, uncontaminated spectral features, clearly showing the classic a-type, asymmetric top pattern, with T_R_^*^~20-70mK. The CH_3_NCO spectra also appear to exhibit two velocity components near V_LSR_~62 and 73km/s, both with {Delta}V_1/2_~10km/s --typical of molecules such as CH_2_CHCN, HNCO, and HCOOCH_3_ in Sgr B2(N). The column density of CH_3_NCO in Sgr B2(N) was determined to be N_tot_~2.3x10^13^ and 1.5x10^13^/cm^2^ for the 62 and 73km/s components, corresponding to fractional abundances, relative to H_2_, of f~7.6x10^-12^ and 5.0x10^-12^, respectively. CH_3_NCO was recently detected in volatized material from comet 67P/Churyumov-Gerasimenko by Rosetta's Philae lander, with an abundance ~1.3% of water; in Sgr B2(N), CH_3_NCO is roughly ~0.04% of the H_2_O abundance.
- ID:
- ivo://CDS.VizieR/J/A+A/544/A19
- Title:
- CH_2_NH accurate rotational rest frequencies
- Short Name:
- J/A+A/544/A19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Methanimine (CH_2_NH) has been detected in different astronomical sources, both galactic (as in several "hot cores", the circumstellar enevolope IRC+10216, and the L183 pre-stellar core) and extragalactic, and is considered a pre-biotic interstellar molecule. Its ground-state rotational spectrum has been studied in the laboratory up to 172GHz, well below the spectral ranges covered by Herschel/HIFI and the ALMA bands 9 and 10. In this laboratory study, we extend into the submillimetre-wave region the detection of the rotational spectrum of CH_2_NH in its vibrational ground state.
- ID:
- ivo://CDS.VizieR/J/A+A/601/A49
- Title:
- CH_3_NHCHO rotational spectroscopy
- Short Name:
- J/A+A/601/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- N-methylformamide, CH_3_NHCHO, may be an important molecule for interstellar pre-biotic chemistry because it contains a peptide bond, which in terrestrial chemistry is responsible for linking amino acids in proteins. The rotational spectrum of the most stable trans conformer of N-methylformamide is complicated by strong torsion-rotation interaction due to the low barrier of the methyl torsion. For this reason, the theoretical description of the rotational spectrum of the trans conformer has up to now not been accurate enough to provide a firm basis for its interstellar detection. In this context, as a prerequisite for a successful interstellar detection, our goal is to improve the characterization of the rotational spectrum of N-methylformamide. We use two absorption spectrometers in Kharkiv and Lille to measure the rotational spectra over the frequency range 45-630 GHz. The analysis is carried out using the Rho-axis method and the RAM36 code. We search for N-methylformamide toward the hot molecular core Sagittarius (Sgr) B2(N2) using a spectral line survey carried out with the Atacama Large Millimeter/submillimeter Array (ALMA). The astronomical spectra are analyzed under the assumption of local thermodynamic equilibrium. The astronomical results are put into a broader astrochemical context with the help of a gas-grain chemical kinetics model. The new laboratory data set for the trans conformer of N-methylformamide consists of 9469 distinct line frequencies with J<=62, including the first assignment of the rotational spectra of the first and second excited torsional states. All these lines are fitted within experimental accuracy for the first time. Based on the reliable frequency predictions obtained in this study, we report the tentative detection of N-methylformamide towards Sgr B2(N2). We find N-methylformamide to be more than one order of magnitude less abundant than formamide (NH_2_CHO), a factor of two less abundant than the unsaturated molecule methyl isocyanate (CH_3_NCO), but only slightly less abundant than acetamide (CH_3_CONH_2_). We also report the tentative detection of the 15N isotopologue of formamide (^15^NH_2_CHO) toward Sgr B2(N2). The chemical models indicate that the efficient formation of HNCO via NH + CO on grains is a necessary step in the achievement of the observed gas-phase abundance of CH_3_NCO. Production of CH_3_NHCHO may plausibly occur on grains either through the direct addition of functional-group radicals or through the hydrogenation of CH_3_NCO. Conclusions. Provided the detection of N-methylformamide is confirmed, the only slight underabundance of this molecule compared to its more stable structural isomer acetamide and the sensitivity of the model abundances to the chemical kinetics parameters suggest that the formation of these two molecules is controlled by kinetics rather than thermal equilibrium.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A120
- Title:
- CH_3_OCHD_2_ experimental frequencies
- Short Name:
- J/A+A/651/A120
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- In 2013, we have published the first rotational analysis and detection of mono-deuterated dimethyl ether in the solar-type protostar IRAS 16293-2422 with the IRAM 30m telescope. Dimethyl ether is one of the most abundant complex organic molecules (COMs) in star-forming regions and their D-to-H (D/H) ratios is important to understand its chemistry and trace the source history. We present the first analysis of doubly-deuterated dimethyl ether (methoxy-d2-methane, 1,1-dideuteromethylether) in its ground- vibrational state, based on an effective Hamiltonian for an asymmetric rotor molecules with internal rotors. The analysis covers the frequency range 0.15-1.5THz. The laboratory rotational spectrum of this species was measured between 150 and 1500GHz with the Lille's submillimeter spectrometer. For the astronomical detection, we used the Atacama Large Millimeter/submillimeter Array (ALMA) observations from the Protostellar Interferometric Line Survey, PILS. New sets of spectroscopic parameters have been determined by a least squares fit with the ERHAM code for both symmetric and asymmetric conformers. As for the mono-deuterated species, these parameters have permitted the first identification in space of both conformers of a doubly-deuterated dimethyl ether via detection near the B component of the Class 0 protostar IRAS 16293-2422.
- ID:
- ivo://CDS.VizieR/J/ApJ/851/L46
- Title:
- CH_3_OCH_2_OH ALMA detection in NGC 6334I
- Short Name:
- J/ApJ/851/L46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of interstellar methoxymethanol (CH_3_OCH_2_OH) in Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 7 toward the MM1 core in the high-mass star-forming region NGC 6334I at ~0.1-1" spatial resolution. A column density of 4(2)x10^18^cm^-2^ at T_ex_=200K is derived toward MM1, ~34 times less abundant than methanol (CH_3_OH), and significantly higher than predicted by astrochemical models. Probable formation and destruction pathways are discussed, primarily through the reaction of the CH_3_OH photodissociation products, the methoxy (CH_3_O) and hydroxymethyl (CH_2_OH) radicals. Finally, we comment on the implications of these mechanisms on gas-phase versus grain-surface routes operative in the region, and the possibility of electron-induced dissociation of CH3OH rather than photodissociation.
- ID:
- ivo://CDS.VizieR/J/A+A/423/235
- Title:
- C_5_H_2_ Radiatively allowed transitions
- Short Name:
- J/A+A/423/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Laboratory detection of four isomers of C_5_H_2_ molecule have been reported by Travers et al. (1997ApJ...483L.135T), McCarthy et al. (1997, Science, 275, 518), and Gottlieb et al. (1998ApJ...509L.141G). They suggested for detection of the ring-chain isomer of C_5_H_2_ (c-C_5_H_2_) in cosmic objects, as it is the most stable one in comparison to the others. Two transitions 3_13_-2_12_ and 3_03_-2_02_ at 19.147GHz and 19.606GHz, respectively, of c-C_5_H_2_ have been detected in TMC-1. We suggest that the c-C_5_H_2_ may be identified in cool cosmic objects through its transition 3_13_-4_04_ at 4.3GHz in absorption against the cosmic microwave background. Since in absence of availability of the collisional rates, we have used scaled values for them, we have checked the sensitivity of the lines on the rates by enhancing the rate for the transitions with {Delta}k_a_=0 by a factor of 10. Though the transitions are not found sensitive, our results ma y be treated as qualitative in nature. This absorption line may play an important role for identification of c-C_5_H_2_ in cosmic objects.
- ID:
- ivo://CDS.VizieR/J/A+A/644/A102
- Title:
- CH3SC(O)H observed line frequencies and strengths
- Short Name:
- J/A+A/644/A102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- S-methyl thioformate CH_3_SC(O)H is a monosulfur derivative of methyl formate, a relatively abundant component of the interstellar medium (ISM). S-methyl thioformate being, thermodynamically,the most stable isomer, it can be reasonably proposed for detection in the ISM. This work aims to experimentally study and theoretically analyze the ground and first torsional excited states for CH_3_SC(O)H in a large spectral range for astrophysical use. S-methyl thioformate was synthesized as a result of a reaction of methyl mercaptan with acetic-formic anhydride. The millimeter-wave spectrum was then recorded for the first time from 150 to 660GHz with the solid-state-based spectrometer at Lille. A set of 3545 lines is determined and combined with 54 previously measured lines in the microwave region, belonging to ground state vt=0 as well as 1391 transitions in the first excited state of torsion v18=1. Some 164 lines were also assigned to vt18=2 for the A-species. A global fit was performed using the BELGI-Cs code taking into account the large splitting of A and E lines due to methyl internal rotation motion with a relatively low barrier, V3=127.4846(15)cm^-1^. Using our spectroscopy work, a deep search of S-methyl thioformate was carried out in the IRAM 30m and ALMA data of different high-mass star-forming regions (Orion KL and Sgr B2). We derived an upper limit to the CH_3_SC(O)H column density in these regions.
- ID:
- ivo://CDS.VizieR/J/A+A/623/A167
- Title:
- C2H3SH observed experimental transitions
- Short Name:
- J/A+A/623/A167
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New laboratory investigations of the rotational spectrum of postulated astronomical species are essential to support the assignment and analysis of current astronomical surveys. In particular, considerable interest surrounds sulfur analogs of oxygen-containing interstellar molecules and their isomers. To enable reliable interstellar searches of vinyl mercaptan, the sulfur-containing analog to the astronomical species vinyl alcohol, we investigated its pure rotational spectrum at millimeter wavelengths. We extended the pure rotational investigation of the two isomers syn and anti vinyl mercaptan to the millimeter domain using a frequency-multiplication spectrometer. The species were produced by a radiofrequency discharge in 1,2-ethanedithiol. Additional transitions were remeasured in the centimeter band using Fourier-transform microwave spectroscopy to better determine rest frequencies of transitions with low-J and low-Ka values. Experimental investigations were supported by quantum chemical calculations on the energetics of both the [C_2_,H_4_,S] and [C_2_,H_4_,O] isomeric families. Interstellar searches for both syn and anti vinyl mercaptan as well as vinyl alcohol were performed in the EMoCA spectral line survey carried out toward Sgr B2(N2) with ALMA. Results. Highly accurate experimental frequencies (to better than 100kHz accuracy) for both syn and anti isomers of vinyl mercaptan are measured up to 250GHz; these deviate considerably from predictions based on extrapolation of previous microwave measurements. Reliable frequency predictions of the astronomically most interesting millimeter-wave lines for these two species can now be derived from the best-fit spectroscopic constants. From the energetic investigations, the four lowest singlet isomers of the [C2,H4,S] family are calculated to be nearly isoenergetic, which makes this family a fairly unique test bed for assessing possible reaction pathways. Upper limits for the column density of syn and anti vinyl mercaptan are derived toward the extremely molecule-rich star-forming region Sgr B2(N2) enabling comparison with selected complex organic molecules.
