اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدLaboratory spectroscopic study of isotopic thioformaldehyde, H$_{2}$CS, and determination of its equilibrium structure
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Thioformaldehyde is an abundant molecule in various regions of the interstellar medium. However, available laboratory data limit the accuracies of calculated transition frequencies in the submillimeter region, in particular for minor isotopic species. We aim to determine spectroscopic parameters of isotopologs of H2CS that are accurate enough for predictions well into the submillimeter region. We investigated the laboratory rotational spectra of numerous isotopic species in natural isotopic composition almost continuously between 110 and 377 GHz. Individual lines were studied for most species in two frequency regions between 566 and 930 GHz. Further data were obtained for the three most abundant species in the 1290-1390 GHz region. New or improved spectroscopic parameters were determined for seven isotopic species. Quantum-chemical calculations were carried out to evaluate the differences between ground state and equilibrium rotational parameters to derive semi-empirical equilibrium structural parameters. The spectroscopic parameters are accurate enough for predictions well above 1 THz with the exception of H2(13)C(34)S where the predictions should be reliable to around 700 GHz.
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We present the analysis of 34 light curves in $V$ and $I$ of 17 giant stars in the globular cluster NGC 3201, to check if such stars are variable and if their variability has some kind of impact on the iron abundance as obtained from spectroscopic me
asurements. First, we computed the Generalized Lomb-Scargle and Phase Dispersion Minimization periodograms on the sample to check if the stars were variables. In this way, 7 stars of the sample were found to be non-variable, 2 stars are considered as possible variables, and 8 stars were found to be variable, with periods ranging from $0.0881pm0.0001$ to $0.5418pm0.0027$ days. According to the literature, the variables have distinct values of $text{[Fe I/H]}$: the 3 most metal-rich stars are in the RGB stage, one has an $text{[Fe I/H]}=-1.37$ dex, while the other two have $text{[Fe I/H]}=-1.31$ dex. The two most metal-poor variables have $text{[Fe I/H]}=-1.61$ dex and $text{[Fe I/H]}=-1.62$ dex, and are AGB stars; the remaining variables have $text{[Fe I/H]}=-1.44$, $-1.48$, and $-1.50$ dex, the first two being RGB while the last is AGB star. On the other hand, stars that appear to be non-variables have $-1.56leqtext{[Fe I/H]}leq-1.40$. We conclude that variability somehow affects the spectroscopic determination of the iron content of giant stars in NGC 3201 increasing the iron spread of the cluster. If variability is not taken into account, this spread could be wrongly interpreted as due to an intrinsic iron spread affecting the stars of the cluster.
Cyanamide is one of the few interstellar molecules containing two chemically different N atoms. It was detected recently toward the solar-type protostar IRAS 16293-2422 B together with H$_2$N$^{13}$CN and HDNCN in the course of the Atacama Large Mill
emeter/submillimeter Array (ALMA) Protostellar Interferometric Line Survey (PILS). The detection of the 15N isotopomers or the determination of upper limits to their column densities was hampered by the lack of accurate laboratory data at the frequencies of the survey. We wanted to determine spectroscopic parameters of the $^{15}$N isotopomers of cyanamide that are accurate enough for predictions well into the submillimeter region and to search for them in the PILS data. We investigated the laboratory rotational spectra of H$_2^{15}$NCN and H$_2$NC$^{15}$N in the selected region between 192 and 507~GHz employing a cyanamide sample in natural isotopic composition. Additionally, we recorded transitions of H$_2$N$^{13}$CN. We obtained new or improved spectroscopic parameters for the three isotopic species. Neither of the $^{15}$N isotopomers of cyanamide were detected unambiguously in the PILS data. Two relatively clean lines can be tentatively assigned to H$_2^{15}$NCN. If confirmed, their column densities would imply a low $^{14}$N/$^{15}$N ratio for cyanamide toward this source. The resulting line lists should be accurate enough for observations up to about 1 THz. More sensitive observations, potentially at different frequencies, may eventually lead to the astronomical detection of these isotopic species.
Aims: To trace the radial and vertical spatial distribution of H2CS, a key species of the S-bearing chemistry, in protoplanetary disks. To analyse the observed distributions in light of the H2CS binding energy, in order to discuss the role of thermal
desorption in enriching the gas disk component. Methods: In the context of the ALMA chemical survey of Disk-Outflow sources in the Taurus star forming region (ALMA-DOT), we observed five Class I or early Class II sources with the o-H2CS(7_1,6-6_1,5) line on a 40 au scale. We estimated the binding energy (BEs) of H2CS using quantum mechanical calculations, for the first time, for an extended, periodic, crystalline ice. Results: We imaged H2CS in two rotating molecular rings in the HL Tau and IRAS04302+2247 disks. The outer radii are about 140 au (HL Tau), and 115 au (IRAS 04302+2247). The edge-on geometry of IRAS 04302+2247 reveals that H2CS emission peaks, at radii of 60-115 au, at z = +- 50 au from the equatorial plane. The column densities are about 10^14 cm^-2. For HL Tau, we derive, for the first time, the [H2CS]/[H] abundance in a protoplanetary disk (about 10^-14). The BEs of H2CS computed for extended crystalline ice and amorphous ices is 4258 K and 3000-4600 K, respectively, implying a thermal evaporation where dust temperature is larger than 50-80 K. Conclusions: H2CS traces the so-called warm molecular layer, a region previously sampled using CS, and H2CO. Thioformaldehyde peaks closer to the protostar than H2CO and CS, plausibly due to the relatively high-excitation level of observed 7_1,6-6_1,5 line (60 K). The H2CS BEs implies that thermal desorption dominates in thin, au-sized, inner and/or upper disk layers, indicating that the observed H2CS emitting up to radii larger than 100 au is likely injected in the gas due to non-thermal processes.
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