IBEX已经对星际中性气体（包括氢和氘）进行了超过一个太阳活动周期的直接采样观测。IBEX的观测方向仅限于垂直于航天器—太阳连线的方向，这使观测每年只能进行几个月。即将到来的星际测绘与加速探测器（Interstellar Mapping and Acceleration Probe）任务消除了这一限制。IMAP-Lo仪器将具备调整其视轴与航天器旋转轴之间夹角的能力。我们继续开展一系列关于由此产生的科学机遇的研究。我们采用Kubiak等人2023年建议的视轴角度调整方案，并聚焦于太阳极大期阶段的星际氢和氘。基于大量模拟，我们确定了在日历年中的哪些时间以及视轴的哪些伸长角可用于测量终止激波处的D/H丰度，并无歧义地观测星际H而不受星际He的贡献干扰。此外，IMAP-Lo将能够分辨主群和次群粒子，特别是在主群贡献很小的情况下观测次群粒子。我们表明，预期信号对辐射压力的细节（尤其是其随原子径向速度的依赖关系）以及对日球层顶处主群和次群分布函数行为的细节都很敏感。因此，IMAP-Lo将能够提供解决日球层物理学乃至普通天体物理学中紧迫问题所需的观测。
英文摘要：
Direct-sampling observations of interstellar neutral gas, including hydrogen and deuterium, have been performed for more than one cycle of solar activity by IBEX. IBEX viewing is restricted to directions perpendicular to the spacecraft--Sun line, which limits the observations to several months each year. This restriction is removed in a forthcoming mission Interstellar Mapping and Acceleration Probe. The IMAP-Lo instrument will have a capability of adjusting the angle of its boresight with the spacecraft rotation axis. We continue a series of studies of resulting science opportunities. We adopt a schedule of adjusting the boresight angle suggested by Kubiak et al. 2023 and focus on interstellar hydrogen and deuterium during solar maximum epoch. Based on extensive set of simulations, we identify the times during calendar year and elongation angles of the boresight needed to measure the abundance of D/H at the termination shock and unambiguously observe interstellar H without contribution from interstellar He. Furthermore, IMAP-Lo will be able to resolve the primary and secondary populations, in particular to view the secondary population with little contribution from the primary. We show that the expected signal is sensitive to details of radiation pressure, particularly its dependence on radial speed of the atoms, and to details of the behavior of the distribution function of the primary and secondary populations at the heliopause. Therefore, IMAP-Lo will be able to provide observations needed to address compelling questions of the heliospheric physics, and even general astrophysics.
Local Interstellar Flow Parameters from the First Intersection of IMAP-Lo's Parameter Tubes
Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；University of New Hampshire（新罕布什尔大学）；Princeton University（普林斯顿大学）；Space Research Centre PAS (CBK PAN)（波兰科学院太空研究中心）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Southwest Research Institute（西南研究院）；University of Texas at San Antonio（得克萨斯大学圣安东尼奥分校）
We analyze the reasons for the correlation between the temperature, direction, and speed of the interstellar neutral gas inflow into the heliosphere, obtained in analyzes of observations performed by the IBEX-Lo instrument onboard Interstellar Boundary Explorer (IBEX). We point out that this correlation is the combined result of the inability to measure the speed of the atoms that enter the instrument and the restriction of the observations to a short orbital arc around the Sun performed by the instrument during observation. We demonstrate that without the capability to measure the speed, but …
The abundance of deuterium in the interstellar gas in front of the Sun gives insight into the processes of filtration of neutral interstellar species through the heliospheric interface and potentially into the chemical evolution of the Galactic gas. We investigate the possibility of detection of neutral interstellar deuterium at 1 AU from the Sun by direct sampling by the Interstellar Boundary Explorer (IBEX). We simulate the flux of neutral interstellar D at IBEX for the actual measurement conditions. We assess the number of interstellar D atom counts expected during the first three years of …
Organic material found in meteorites and interplanetary dust particles is enriched in D and 15N. This is consistent with the idea that the functional groups carrying these isotopic anomalies, nitriles and amines, were formed by ion-molecule chemistry in the protosolar nebula. Theoretical models of interstellar fractionation at low temperatures predict large enrichments in both D and 15N and can account for the largest isotopic enrichments measured in carbonaceous meteorites. However, more recent measurements have shown that, in some primitive samples, a large 15N enrichment does not correlate …
In situ measurements of the heliospheric particle populations by the Voyager spacecraft can only be put in an appropriate context with remote-sensing observations of energetic and interstellar neutral atoms (ENAs and ISN, respectively) at 1 au when the time delay between the production and the observation times is taken into account. ENA times of flight from the production regions in the heliosheath are relatively easy to estimate because these atoms follow almost constant speed, force-free trajectories. For the ISN populations, dynamical and ballistic selection effects are important, and time…
Despite low elemental abundance of atomic deuterium in interstellar medium (ISM), observational evidences suggest that several species in gas-phase and in ices could be heavily fractionated. We explore various aspects of deuterium enrichment by constructing a chemical evolution model in gas and grain phases. Depending on various physical parameters, gas and grains are allowed to interact with each other through exchange of their chemical species. It is known that HCO+ and N2H+ are two abundant gas phase ions in ISM and their deuterium fractionation are generally used to predict degree of ioniz…
The interstellar neutral (ISN) gas enters the heliosphere and is detected at a few au from the Sun, as demonstrated by Ulysses and the nterstellar Boundary Explorer (IBEX) missions. Ulysses observed ISN gas from different vantage points in a polar orbit from 1994 to 2007, while IBEX has been observing in an Earth orbit in a fixed direction relative to the Sun from 2009. McComas et al. 2018 reported about an IMAP-Lo detector on board the Interstellar Mapping and Acceleration Probe (IMAP), with an ability to track the ISN flux in the sky. We present observation geometries for ISN gas for a detec…
The deuterium fractionation of gas-phase molecules in hot cores is believed to reflect the composition of interstellar ices. The deuteration of methanol is a major puzzle, however, because the isotopologue ratio [CH2DOH]/[CH3OD], which is predicted to be equal to 3 by standard grain chemistry models, is much larger (~20) in low-mass hot corinos and significantly lower (~1) in high-mass hot cores. This dichotomy in methanol deuteration between low-mass and massive protostars is currently not understood. In this study, we report a simplified rate equation model of the deuterium chemistry occurri…
Deuterium-to-hydrogen (D/H) enrichments in molecular species provide clues about their original formation environment. The organic materials in primitive solar system bodies have generally higher D/H ratios and show greater D/H variation when compared to D/H in solar system water. We propose this difference arises at least in part due to 1) the availability of additional chemical fractionation pathways for organics beyond that for water, and 2) the higher volatility of key carbon reservoirs compared to oxygen. We test this hypothesis using detailed disk models, including a sophisticated, new d…
The IBEX-Lo instrument on board the Interstellar Boundary Explorer (IBEX) mission samples interstellar neutral (ISN) helium atoms penetrating the heliosphere from the very local interstellar medium (VLISM). In this study, we analyze the IBEX-Lo ISN helium observations covering a complete solar cycle, from 2009 through 2020 using a comprehensive uncertainty analysis including statistical and systematic sources.W e employ the Warsaw Test Particle Model to simulate ISN helium fluxes at IBEX, which are subsequently compared with the observed count rate in the three lowest energy steps of IBEX-Lo. …
Aim. We investigate the role of PAHs as a sink for deuterium in the interstellar medium and study UV photolysis as a potential process in the variations of the deuterium fractionation in the ISM. Methods. The UV photo-induced fragmentation of various isotopologues of D-enriched, protonated anthracene and phenanthrene ions was recorded in a FTICR mass spectrometer. IRMPD spectroscopy using FELIX provided the IR spectra that were compared to DFT vibrational spectra; reaction barriers and rates were also calculated and related to the product abundances. Results. The mass spectra for both UV and I…
Water D/H in 3I/ATLAS as a Probe of Formation Conditions in Another Planetary System
University of Michigan（密歇根大学）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；The Catholic University of America（美利坚天主教大学）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Case Western Reserve University（凯斯西储大学）；University of California, Berkeley（加利福尼亚大学伯克利分校）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）
Understanding water deuterium fractionation is important for constraining the mechanisms of water formation in interstellar clouds. Observations of HDO and H$_2^{18}$O transitions were carried out towards the high-mass star-forming region G34.26+0.15 with the HIFI instrument onboard the Herschel Space Observatory, as well as with ground-based single-dish telescopes. Ten HDO lines and three H$_2^{18}$O lines covering a broad range of upper energy levels (22-204 K) were detected. We used a non-LTE 1D analysis to determine the HDO/H$_2$O ratio as a function of radius in the envelope. Models with …
Identifying the source of Earth's water is central to understanding the origins of life-fostering environments and to assessing the prevalence of such environments in space. Water throughout the solar system exhibits deuterium-to-hydrogen enrichments, a fossil relic of low-temperature, ion-derived chemistry within either (i) the parent molecular cloud or (ii) the solar nebula protoplanetary disk. Utilizing a comprehensive treatment of disk ionization, we find that ion-driven deuterium pathways are inefficient, curtailing the disk's deuterated water formation and its viability as the sole sourc…
Observations of deuterium fractionation in the solar system, and in interstellar and circumstellar material, are commonly used to constrain the formation environment of volatiles. Toward protoplanetary disks, this approach has been limited by the small number of detected deuterated molecules, i.e. DCO$^+$ and DCN. Based on ALMA Cycle 2 observations toward the disk around the T Tauri star AS 209, we report the first detection of N$_2$D$^+$ (J=3-2) in a protoplanetary disk. These data are used together with previous Submillimeter Array observations of N$_2$H$^+$ (J=3-2) to estimate a disk-averag…
Formamide (NH$_2$CHO) has previously been detected in several star-forming regions and is thought to be a precursor for different prebiotic molecules. Its formation mechanism is still debated, however. Observations of formamide, related species and their isopotologues may provide useful clues to the chemical pathways leading to their formation. The Protostellar Interferometric Line Survey (PILS) represents an unbiased high angular resolution and sensitivity spectral survey of the low-mass protostellar binary IRAS 16293-2422 with the Atacama Large Millimeter/submillimeter Array (ALMA). We detec…
Only recently, OD, the deuterated isotopolog of hydroxyl, OH, has become accessible in the interstellar medium; spectral lines from both species have been observed in the supra-Terahertz and far infrared regime. Here we study rotational lines of OD and OH towards 13 Galactic high-mass star forming regions, with the aim to constrain the OD abundance and infer the deuterium fractionation of OH in their molecular envelopes. We used the Stratospheric Observatory for Infrared Astronomy (SOFIA) to observe the $^2Π_{3/2}$ $J=5/2-3/2$ ground-state transition of OD at 1.3 THz ($215~μ$m) and the rotatio…
