D. Torres-Díaz, R. Basalgète, L. Amiaud, L. Philippe, X. Michaut, J.-H. Fillion, A. Lafosse, M. Bertin
{"title":"氨冰对 NH3 和 N2 的 X 射线光解吸:原行星盘中的机制和产量","authors":"D. Torres-Díaz, R. Basalgète, L. Amiaud, L. Philippe, X. Michaut, J.-H. Fillion, A. Lafosse, M. Bertin","doi":"10.1051/0004-6361/202450883","DOIUrl":null,"url":null,"abstract":"<i>Context<i/>. Ammonia is detected both in the gas phase and in the ices of protoplanetary disks. However, its gas phase abundances are still difficult to reproduce via chemical modelling when only the thermal-, UV photon-, and cosmic ray-induced processes are considered. Among other non-thermal mechanisms, X-ray photo-desorption is a relevant pathway to maintaining a budget of molecules in the gas of disks. However, no quantitative data are available to constrain its efficiency in the case of ammonia-containing ices.<i>Aims<i/>. We studied the desorption induced by soft X-rays from ammonia ices to determine the photo-desorption yields of neutral molecules that can be applied to the conditions of protoplanetary disks. We also aim to identify the desorption mechanisms at play.<i>Methods<i/>. Pure ammonia ices were deposited at 23 or 75 K and irradiated between 395 and 435 eV, with monochromatic synchrotron light. Desorption of neutral molecules and fragments was detected using a quadrupole mass spectrometer, calibrated to obtain des-orption yields. These values were extrapolated and the spectrum of a protoplanetary disk was used to extract average astrophysical desorption yields.<i>Results<i/>. Photo-desorption from NH<sub>3<sub/> ices is dominated by the desorption of neutral NH<sub>3<sub/> and N<sub>2<sub/> molecules. The desorption mechanism mostly involves the thermalisation of Auger electrons in the ice, although resonant phenomena also contribute near the N 1s ionisation edge. The NH<sub>3<sub/> photo-desorption is independent of ice morphology and irradiation temperature. Contrary to NH<sub>3<sub/> desorption, N<sub>2<sub/> desorption is sensitive to the photon fluence received by the ice. Average photo-desorption yields derived using the TW Hya X-ray spectrum reveal that the NH<sub>3<sub/> photo-desorption would be four to six times more efficient than that of H<sub>2<sub/>O. This could be at the origin of unexplained high NH<sub>3<sub/>/H<sub>2<sub/>O abundance ratios predicted in the disk around TW Hya. This result ought to be confirmed by the study of mixed water-ammonia ices.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":null,"pages":null},"PeriodicalIF":5.4000,"publicationDate":"2024-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"X-ray photo-desorption of NH3 and N2 from ammonia ices: Mechanisms and yields in protoplanetary disks\",\"authors\":\"D. Torres-Díaz, R. Basalgète, L. Amiaud, L. Philippe, X. Michaut, J.-H. Fillion, A. Lafosse, M. Bertin\",\"doi\":\"10.1051/0004-6361/202450883\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<i>Context<i/>. Ammonia is detected both in the gas phase and in the ices of protoplanetary disks. However, its gas phase abundances are still difficult to reproduce via chemical modelling when only the thermal-, UV photon-, and cosmic ray-induced processes are considered. Among other non-thermal mechanisms, X-ray photo-desorption is a relevant pathway to maintaining a budget of molecules in the gas of disks. However, no quantitative data are available to constrain its efficiency in the case of ammonia-containing ices.<i>Aims<i/>. We studied the desorption induced by soft X-rays from ammonia ices to determine the photo-desorption yields of neutral molecules that can be applied to the conditions of protoplanetary disks. We also aim to identify the desorption mechanisms at play.<i>Methods<i/>. Pure ammonia ices were deposited at 23 or 75 K and irradiated between 395 and 435 eV, with monochromatic synchrotron light. Desorption of neutral molecules and fragments was detected using a quadrupole mass spectrometer, calibrated to obtain des-orption yields. These values were extrapolated and the spectrum of a protoplanetary disk was used to extract average astrophysical desorption yields.<i>Results<i/>. Photo-desorption from NH<sub>3<sub/> ices is dominated by the desorption of neutral NH<sub>3<sub/> and N<sub>2<sub/> molecules. The desorption mechanism mostly involves the thermalisation of Auger electrons in the ice, although resonant phenomena also contribute near the N 1s ionisation edge. The NH<sub>3<sub/> photo-desorption is independent of ice morphology and irradiation temperature. Contrary to NH<sub>3<sub/> desorption, N<sub>2<sub/> desorption is sensitive to the photon fluence received by the ice. Average photo-desorption yields derived using the TW Hya X-ray spectrum reveal that the NH<sub>3<sub/> photo-desorption would be four to six times more efficient than that of H<sub>2<sub/>O. This could be at the origin of unexplained high NH<sub>3<sub/>/H<sub>2<sub/>O abundance ratios predicted in the disk around TW Hya. 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引用次数: 0
摘要
背景在原行星盘的气相和冰相中都能探测到氨。然而,如果只考虑热、紫外光子和宇宙射线诱导的过程,其气相丰度仍然难以通过化学建模再现。在其他非热机制中,X 射线光解吸是维持星盘气体中分子预算的一个相关途径。然而,对于含氨的冰来说,目前还没有定量数据来确定其效率。我们研究了氨冰在软 X 射线诱导下的解吸,以确定中性分子的光解吸产率,并将其应用到原行星盘的条件中。我们的目的还在于确定起作用的解吸机制。纯氨冰沉积在 23 或 75 K 的温度下,在 395 至 435 eV 之间用单色同步辐射光照射。使用四极质谱仪检测中性分子和碎片的解吸,并进行校准以获得解吸产率。对这些值进行外推,并利用原行星盘的光谱来提取平均天体物理解吸率。NH3 冰的光解吸主要是中性 NH3 和 N2 分子的解吸。解吸机理主要涉及冰中奥杰电子的热化,不过在 N 1s 电离边附近也存在共振现象。NH3 光解吸与冰的形态和辐照温度无关。与 NH3 的解吸相反,N2 的解吸对冰接收到的光子通量很敏感。利用 TW Hya X 射线光谱得出的平均光解吸率显示,NH3 的光解吸效率是 H2O 的四到六倍。这可能是无法解释的 TW Hya 周围圆盘中 NH3/H2O 丰度比过高的原因。这一结果应该通过对水氨混合冰的研究得到证实。
X-ray photo-desorption of NH3 and N2 from ammonia ices: Mechanisms and yields in protoplanetary disks
Context. Ammonia is detected both in the gas phase and in the ices of protoplanetary disks. However, its gas phase abundances are still difficult to reproduce via chemical modelling when only the thermal-, UV photon-, and cosmic ray-induced processes are considered. Among other non-thermal mechanisms, X-ray photo-desorption is a relevant pathway to maintaining a budget of molecules in the gas of disks. However, no quantitative data are available to constrain its efficiency in the case of ammonia-containing ices.Aims. We studied the desorption induced by soft X-rays from ammonia ices to determine the photo-desorption yields of neutral molecules that can be applied to the conditions of protoplanetary disks. We also aim to identify the desorption mechanisms at play.Methods. Pure ammonia ices were deposited at 23 or 75 K and irradiated between 395 and 435 eV, with monochromatic synchrotron light. Desorption of neutral molecules and fragments was detected using a quadrupole mass spectrometer, calibrated to obtain des-orption yields. These values were extrapolated and the spectrum of a protoplanetary disk was used to extract average astrophysical desorption yields.Results. Photo-desorption from NH3 ices is dominated by the desorption of neutral NH3 and N2 molecules. The desorption mechanism mostly involves the thermalisation of Auger electrons in the ice, although resonant phenomena also contribute near the N 1s ionisation edge. The NH3 photo-desorption is independent of ice morphology and irradiation temperature. Contrary to NH3 desorption, N2 desorption is sensitive to the photon fluence received by the ice. Average photo-desorption yields derived using the TW Hya X-ray spectrum reveal that the NH3 photo-desorption would be four to six times more efficient than that of H2O. This could be at the origin of unexplained high NH3/H2O abundance ratios predicted in the disk around TW Hya. This result ought to be confirmed by the study of mixed water-ammonia ices.
期刊介绍:
Astronomy & Astrophysics is an international Journal that publishes papers on all aspects of astronomy and astrophysics (theoretical, observational, and instrumental) independently of the techniques used to obtain the results.