Journal articles: 'Hydrogène interstellaire'

1

Lin, Ching Yeh, Andrew T. B. Gilbert, and Mark A. Walker. "INTERSTELLAR SOLID HYDROGEN." Astrophysical Journal 736, no. 2 (July 12, 2011): 91. http://dx.doi.org/10.1088/0004-637x/736/2/91.

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Etim, Emmanuel E., Prasanta Gorai, Ankan Das, Sandip K. Chakrabarti, and Elangannan Arunan. "Interstellar hydrogen bonding." Advances in Space Research 61, no. 11 (June 2018): 2870–80. http://dx.doi.org/10.1016/j.asr.2018.03.003.

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Whang, Y. C. "Ionization of Interstellar Hydrogen." Astrophysical Journal 468 (September 1996): 947. http://dx.doi.org/10.1086/177749.

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Shull, J. Michael. "Observing interstellar molecular hydrogen." Physics Today 75, no. 12 (December 1, 2022): 12. http://dx.doi.org/10.1063/pt.3.5132.

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Balm, S. P., and H. W. Kroto. "Possible assignment of the 11.3-μm UIR feature to emission from carbonaceous microparticles with internal hydrogens." Monthly Notices of the Royal Astronomical Society 245, no. 2 (July 15, 1990): 193. http://dx.doi.org/10.1093/mnras/245.2.193.

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Summary The carriers of the UIR bands seen in many galactic and extragalactic objects have previously been assigned to emission from polycyclic aromatic hydrocarbons (PAHs). However, the match between laboratory spectra of typical PAHs with the interstellar features in the structurally sensitive 11-15-μm (909-667-cm-1) region remains unsatisfactory. In particular, it has been difficult to explain, considering that a PAH mixture is undoubtedly involved, why only one strong band is seen at 11.3 μm (885 cm-1) and why this has the same position in all sources. We discuss here the possibility that a hitherto unrecognized class of molecule containing a novel type of hydrogen functional group, the internal hydrogen, may provide important new clues to the origin of the 11.3-μm (885 cm-1) feature. This type of grouping is typified by the molecule kekulene which contains six such internal hydrogens and exhibits bands in its IR absorption spectrum which coincide with the interstellar feature. This structural unit is likely to be common in soot-like microparticles which simulations suggest are present in the cool carbon-rich outflows of red giant stars and hence should contribute to the 11.3-μm (885-cm-1) emission.

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Irvine, William M. "Microwave Spectroscopy of Astrophysical Molecules." Highlights of Astronomy 8 (1989): 339–44. http://dx.doi.org/10.1017/s1539299600007966.

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ABSTRACTRecent detections of new molecules in dense interstellar clouds, first detections of certain chemical elements in interstellar molecules, and new information on isotopic fractionation of hydrogen in the interstellar medium are discussed in the context of the need for new laboratory data on transition rest frequencies, reaction rates, and branching ratios.

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Neufeld, David A., and Sheldon Green. "Excitation of interstellar hydrogen chloride." Astrophysical Journal 432 (September 1994): 158. http://dx.doi.org/10.1086/174557.

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Bergman, P., B. Parise, R. Liseau, B. Larsson, H. Olofsson, K. M. Menten, and R. Güsten. "Detection of interstellar hydrogen peroxide." Astronomy & Astrophysics 531 (June 20, 2011): L8. http://dx.doi.org/10.1051/0004-6361/201117170.

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Neufeld, David A., Jonas Zmuidzinas, Peter Schilke, and Thomas G. Phillips. "Discovery of Interstellar Hydrogen Fluoride." Astrophysical Journal 488, no. 2 (October 20, 1997): L141—L144. http://dx.doi.org/10.1086/310942.

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Prieto, Jorge Enrique Bueno. "PP - Organic synthesis of uracil from interstellar organic molecules." Proceedings of the International Astronomical Union 4, S251 (February 2008): 475–76. http://dx.doi.org/10.1017/s1743921308022217.

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AbstractIt is important to say that the formaldehyde and hydrogen cyanide have been detected in the interstellar medium through resonance spectrum emission. Here I describe a way to produce uracil in interstellar space.

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Sivaram, C., Kenath Arun, and O. V. Kiren. "Alternative standard frequencies for interstellar communication." International Journal of Astrobiology 18, no. 3 (October 2, 2017): 209–10. http://dx.doi.org/10.1017/s1473550417000350.

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AbstractThe 21 cm hydrogen line is considered a favourable frequency by the SETI programme in their search for signals from potential extraterrestrial (ET) civilizations. The Pioneer plaque, attached to the Pioneer 10 and Pioneer 11 spacecraft, portrays the hyperfine transition of neutral hydrogen and used the wavelength as a standard scale of measurement. Although this line would be universally recognized and is a suitable wavelength to look for radio signals from ETs, the presence of ubiquitous radiation from galactic hydrogen could make searches a little difficult. In this paper, we suggest several alternate standard frequencies, which are free of interference from atomic or molecular sources and is independent of any bias.

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Bzowski, M., M. A. Kubiak, M. Strumik, I. Kowalska-Leszczynska, C. Porowski, and E. Quémerais. "The Direction of the Flow of Interstellar Neutral H Based on Photometric Observations from SOHO/SWAN." Astrophysical Journal 952, no. 1 (July 1, 2023): 2. http://dx.doi.org/10.3847/1538-4357/acda8c.

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Abstract Interstellar neutral hydrogen flows into the heliosphere as a mixture of the primary and secondary populations from two somewhat different directions due to splitting occurring in the magnetized outer heliosheath. The direction of the inflow of interstellar neutral H observed in the inner heliosphere, confronted with that of the unperturbed flow of interstellar neutral helium, is important for understanding the geometry of the distortion of the heliosphere from axial symmetry. It is also needed for facilitating remote-sensing studies of the solar wind structure based on observations of the helioglow, such as those presently performed by SOHO/SWAN, and in the near future by IMAP/GLOWS. In the past, the only means to measure the direction of the flow of interstellar hydrogen were spectroscopic observations of the helioglow. Here, we propose a new method to determine this parameter based on a long series of photometric observations of the helioglow. The method is based on purely geometric considerations and does not depend on any model and absolute calibration of the measurements. We apply this method to sky maps of the helioglow available from the SOHO/SWAN experiment and derive the mean longitude of the flow of interstellar hydrogen. We obtain 253.°1 ± 2.°8, which is in perfect agreement with the previously obtained results based on spectroscopic observations.

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Katushkina, O. A., A. Galli, V. V. Izmodenov, and D. B. Alexashov. "Analysis of the IBEX-Lo interstellar hydrogen fluxes collected in 2009–2018 as a tool for sensing of the solar radiation pressure and the hydrogen ionization rate." Monthly Notices of the Royal Astronomical Society 501, no. 2 (December 8, 2020): 1633–43. http://dx.doi.org/10.1093/mnras/staa3780.

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ABSTRACT The Interstellar Boundary Explorer (IBEX) has been measuring interstellar hydrogen fluxes at 1 au since 2009. In this paper, we analysed all available data obtained with the IBEX-Lo instrument at energies 11–41 eV using our numerical kinetic model of the interstellar hydrogen distribution in the heliosphere. We performed a fitting of the data to find independently the model parameters: the ratio of the solar radiation pressure to the solar gravitation (μ0), ionization rate of hydrogen atoms at 1 au (β0), parameters of the secondary interstellar atoms at 70 au from the Sun, which provide the best agreement with the data by minimization of metric χ2. We also analysed temporal variations of the ratio of the fluxes measured in a fixed direction at energy bin 1 and energy bin 2. It is found that in 2009–2011 and 2017–2016 the ratio provided by the model is smaller than in the IBEX-Lo data, while in 2012–2015, oppositely, the model ratio is larger compared to the data. This might be caused by the incorrect separation of the measured fluxes between energy channels in the data, or by some additional physical factors that are omitted in the model. Understanding this issue may be important for the preparation of future Interstellar Mapping and Acceleration Probe mission. At this stage, we relied on the sum of the fluxes measured in energy bins 1 and 2 for comparison to model predictions.

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Katushkina, O. A., I. I. Baliukin, V. V. Izmodenov, and D. B. Alexashov. "Imprints of the secondary interstellar hydrogen atoms at 1 au." Monthly Notices of the Royal Astronomical Society 504, no. 2 (April 6, 2021): 2501–8. http://dx.doi.org/10.1093/mnras/stab944.

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ABSTRACT In this paper, we search for the possible imprints of the secondary interstellar hydrogen atoms created at the heliospheric boundary in the full-sky maps of the hydrogen fluxes at the Earth orbit. By using our three-dimensional time-dependent kinetic model, the maps of the hydrogen fluxes are calculated for different phases of the solar cycle and different energy ranges. It is shown that the flux maps obtained during the solar minimum conditions for the energy range 1–20 eV have specific features such as blobs and tails, which are pronounced due to a signal of the secondary component of the interstellar atoms. We investigate how these features depend on parameters of the secondary atoms far away from the Sun and found that the geometry and shape of the tails depend on the averaged velocity and kinetic temperatures of the secondary population. The results of the paper provide a strategy where and when we need to look in order to detect the secondary component of the interstellar hydrogen separately from the primary component at 1 au. This can be important for future space missions devoted to the exploration of the heliospheric boundary.

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15

Verschuur, Gerrit L. "Interstellar Neutral Hydrogen Emission Profile Structure." Astronomical Journal 127, no. 1 (January 2004): 394–407. http://dx.doi.org/10.1086/379957.

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Sidharth, B. G. "Interstellar hydrogen and cosmic background radiation." Chaos, Solitons & Fractals 12, no. 8 (June 2001): 1563–64. http://dx.doi.org/10.1016/s0960-0779(00)00158-2.

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17

Gatley, Ian, and Norio Kaifu. "Infrared Observations of Interstellar Molecular Hydrogen." Symposium - International Astronomical Union 120 (1987): 153–66. http://dx.doi.org/10.1017/s0074180900153963.

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Emission from vibrationally excited molecular hydrogen has been detected from a wide range of astronomical targets during the last decade (e.g. Shull and Beckwith 1982). in all cases the H2has been shock excited, and we have grown accustomed to the idea that H2is a useful tracer of interstellar shocks.

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18

Whang, Y. C. "Interstellar neutral hydrogen in the heliosphere." Advances in Space Research 19, no. 6 (January 1997): 941–44. http://dx.doi.org/10.1016/s0273-1177(97)00308-6.

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19

Schaefer, J. "Spectroscopic evidence of interstellar solid hydrogen." Chemical Physics 332, no. 2-3 (February 2007): 211–24. http://dx.doi.org/10.1016/j.chemphys.2006.11.031.

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20

Whang, Y. C. "Moment equation description of interstellar hydrogen." Space Science Reviews 78, no. 1-2 (October 1996): 387–92. http://dx.doi.org/10.1007/bf00170824.

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21

Gruntman, Mike. "Interstellar hydrogen ionization in the heliosheath." Journal of Geophysical Research: Space Physics 120, no. 8 (August 2015): 6119–32. http://dx.doi.org/10.1002/2015ja021539.

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22

Pirronello, Valerio. "On the Mechanism of H2 Formation in the Interstellar Medium." Symposium - International Astronomical Union 120 (1987): 167–69. http://dx.doi.org/10.1017/s0074180900153975.

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The problem of the formation of molecular hydrogen in interstellar clouds is revisited. the role played by cosmic ray bombardment under certain circumstances is considered mainly in the light of the low formation rate of H2 on grains due to the reduced mobility of adsorbed H atoms on their amorphous surfaces at interstellar temperatures.

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23

Gredel, R., S. Lepp, A. Dalgarno, and E. Herbst. "Cosmic Ray Induced Photodestruction of Interstellar Molecules." International Astronomical Union Colloquium 120 (1989): 32–37. http://dx.doi.org/10.1017/s0252921100023459.

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AbstractUltraviolet photons are created in the interior of dense interstellar clouds by the impact excitation of molecular hydrogen by secondary electrons generated by cosmic ray ionization. The resulting photodissociation and photoionization rates of a wide range of interstellar molecules are calculated. The effects on the equilibrium chemical composition of dense clouds are briefly discussed.

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Wu, Junjun, Hongbo Ning, Liuhao Ma, and Wei Ren. "Pressure-dependent kinetics of methyl formate reactions with OH at combustion, atmospheric and interstellar temperatures." Physical Chemistry Chemical Physics 20, no. 41 (2018): 26190–99. http://dx.doi.org/10.1039/c8cp04114h.

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25

Sarre, P. J., and T. R. Kendall. "Diffuse Interstellar Bands." Symposium - International Astronomical Union 197 (2000): 343–48. http://dx.doi.org/10.1017/s0074180900164927.

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The unidentified diffuse interstellar bands are observed in near-UV, visible and near-IR spectra recorded towards stars which are partially obscured by interstellar dust. Their origin is the longest standing problem in astronomical spectroscopy and dates back to the 1930s when systematic study of the bands first started. Proposals for the carriers range from molecular hydrogen to porphyrins and from colour centres to species adsorbed on grain surfaces. This paper contains a short review of the problem and a discussion of recent possible assignments of some of the bands to transitions of the H2, and molecules. Observations of ultra-high resolution spectra of diffuse absorption bands, optical diffuse emission bands from the Red Rectangle, and complementary studies of the 3.3 μm ‘unidentified’ infrared (UIR) emission band are described.

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Vallerga, J. V., and B. Y. Welsh. "ϵ Canis Majoris and the Ionization of the Local Cloud." International Astronomical Union Colloquium 152 (1996): 277–82. http://dx.doi.org/10.1017/s0252921100036095.

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Using the EUV (70 – 730 Å) spectrum of the brightest EUV source, ϵ CMa taken with the Extreme Ultraviolet Explorer Satellite (EUVE) and simple models that extrapolate this spectrum to the Lyman edge at 912 Å, we have determined the local interstellar hydrogen photoionization parameter, Г, solely from this B2 II star to be 1.1 × 10−15 s−1. This figure is a factor of 7 greater than previous estimates of Г calculated for all nearby stars combined (Bruhweiler & Cheng 1988). Using measured values of the density and temperature of neutral interstellar hydrogen gas in the Local Cloud, we derive a particle density of ionized hydrogen, n(H+), and electrons, ne, of 0.015 – 0.019 cm−3 assuming ionization equilibrium and a helium ionization fraction of less than 20%. These values correspond to a hydrogen ionization fraction, XH from 19% to 15%, respectively.

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Puyoo, Olivia, and Lotfi Ben Jaffel. "The Intrinsic Properties of the Local Interstellar Medium." International Astronomical Union Colloquium 166 (1997): 29–32. http://dx.doi.org/10.1017/s0252921100070664.

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AbstractWe propose a new method to constrain the actual state of the interstellar cloud that surrounds the solar system. Using Voyager UVS Lyman-α sky maps and the powerful principle of invariance, we derive the H distribution all along the spacecraft path. Provided current models of the heliopause interface between the solar and the interstellar winds, we extrapolate this distribution to farther distances from the Sun and infer in a self consistent way key parameters of the local cloud. Our findings are a high interstellar hydrogen density of ~ 0.24 cm−3 and a weak ionization .

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Reynolds, R. J. "Ionized Disk/Halo Gas: Insight from Optical Emission Lines and Pulsar Dispersion Measures." Symposium - International Astronomical Union 144 (1991): 67–76. http://dx.doi.org/10.1017/s0074180900088914.

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Warm (≈ 104 K), diffuse H+ is a significant component of the interstellar medium within the Galactic disk and lower halo. This gas accounts for about one quarter of the interstellar atomic hydrogen, consumes a large fraction of the interstellar power budget, and appears to be the dominant state of interstellar matter 1 kpc above the midplane. The origin of this ionized gas is not yet established; however, of the known sources of ionization only 0 stars and perhaps supernovae produce enough power to balance the “cooling” rate of the gas. If 0 stars are the source of the ionization, then the interstellar HI, including the extended “Lockman layer”, must have a morphology that allows about 14% of the Lyman continuum photons emitted by the stars to travel hundreds of parsecs within the Galactic disk and up into the lower halo.

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Kurt, Vladimir G., and Jean-Loup Bertaux. "Neutral component of the outerstellar medium in the vicinity of the Sun." Symposium - International Astronomical Union 122 (1987): 389–91. http://dx.doi.org/10.1017/s0074180900156839.

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Optical observations of the solar radiation resonance scattering in the hydrogen and helium lines (λ1216Å and 584Å) provide a unique opportunity for determining numerous parameters of the local interstellar medium closest to the Sun (LISM). The distance exceeds 10 to 102 AU where the interstellar medium is no longer perturbed by the gravity field, and the hard and corpuscular radiation of the Sun.

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Dartois, E., E. Charon, C. Engrand, T. Pino, and C. Sandt. "Mechanochemical synthesis of aromatic infrared band carriers." Astronomy & Astrophysics 637 (May 2020): A82. http://dx.doi.org/10.1051/0004-6361/202037725.

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Context. Interstellar space hosts nanometre- to micron-sized dust grains, which are responsible for the reddening of stars in the visible. The carbonaceous-rich component of these grain populations emits in infrared bands that have been observed remotely for decades with telescopes and satellites. They are a key ingredient of Galactic radiative transfer models and astrochemical dust evolution. However, except for C60 and its cation, the precise carriers for most of these bands are still unknown and not well reproduced in the laboratory. Aims. In this work, we aim to show the high-energy mechanochemical synthesis of disordered aromatic and aliphatic analogues provides interstellar relevant dust particles. Methods. The mechanochemical milling of carbon-based solids under a hydrogen atmosphere produces particles with a pertinent spectroscopic match to astrophysical observations of aromatic infrared band (AIB) emission, linked to the so-called astrophysical polycyclic aromatic hydrocarbon hypothesis. The H/C ratio for the analogues that best reproduce these astronomical infrared observations lies in the 5 ± 2% range, potentially setting a constraint on astrophysical models. This value happens to be much lower than diffuse interstellar hydrogenated amorphous carbons, another Galactic dust grain component observed in absorption, and it most probably provides a constraint on the hydrogenation degree of the most aromatic carbonaceous dust grain carriers. A broad band, observed in AIBs, evolving in the 1350–1200 cm−1 (7.4–8.3 μm) range is correlated to the hydrogen content, and thus the structural evolution in the analogues produced. Results. Our results demonstrate that the mechanochemical process, which does not take place in space, can be seen as an experimental reactor to stimulate very local energetic chemical reactions. It introduces bond disorder and hydrogen chemical attachment on the produced defects, with a net effect similar to the interstellar space very localised chemical reactions with solids. From the vantage point of astrophysics, these laboratory interstellar dust analogues will be used to predict dust grain evolution under simulated interstellar conditions, including harsh radiative environments. Such interstellar analogues offer an opportunity to derive a global view on the cycling of matter in other star forming systems.

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31

Haupa, Karolina Anna, Wei-Siong Ong, and Yuan-Pern Lee. "Hydrogen abstraction in astrochemistry: formation of ˙CH2CONH2 in the reaction of H atom with acetamide (CH3CONH2) and photolysis of ˙CH2CONH2 to form ketene (CH2CO) in solid para-hydrogen." Physical Chemistry Chemical Physics 22, no. 11 (2020): 6192–201. http://dx.doi.org/10.1039/c9cp06279c.

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The amide bond of acetamide is unaffected by hydrogen exposure, but the hydrogen abstraction on its methyl site activates this molecule to react with other species to extend its size as a first step to form interstellar complex organic molecules.

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32

Geballe, T. R. "Infrared spectroscopy of molecular hydrogen in astrophysical environments." Canadian Journal of Physics 72, no. 11-12 (November 1, 1994): 782–85. http://dx.doi.org/10.1139/p94-102.

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Forty-five years ago Gerhard Herzberg became the first person to observe lines of the infrared rotation–vibration bands of molecular hydrogen; 20 years ago astronomers first found some of these lines in the interstellar medium. Examples are given of astrophysical environments in which H2 has been detected, with emphasis on their growing importance to astronomy. The rotation–vibration spectrum has been observed in emission following both collisional and radiative excitation processes. Recent detections of absorption by cold interstellar molecular hydrogen, both in the gaseous and the solid states, have expanded knowledge of physical properties of molecular clouds and the physical and chemical processes occurring within them.

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L. Linsky, Jeffrey, and Brian E. Wood. "Deuterium Abundance in the Local ISM." Symposium - International Astronomical Union 187 (2002): 75–79. http://dx.doi.org/10.1017/s0074180900113762.

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Excellent HST/GHRS spectra of interstellar hydrogen and deuterium Lyman-α absorption toward nearby stars allow us to identify systematic errors that have plagued earlier work and to measure accurate values of the D/H ratio in local interstellar gas. Analysis of 12 sightlines through the Local Interstellar Cloud leads to a mean value of D/H = (1.50 ± 0.10) x 10−5 with all data points lying within ±1σ of the mean. Deciding whether or not the D/H ratio has different values elsewhere in the Galaxy and beyond will be one of the major objectives of the FUSE mission.

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34

Larsson, Mats. "H3+: the initiator of interstellar chemistry." International Journal of Astrobiology 7, no. 3-4 (August 7, 2008): 237–41. http://dx.doi.org/10.1017/s1473550408004230.

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AbstractSecond only to H2, protonated molecular hydrogen, H3+, is the most abundantly produced interstellar molecule. Owing to its high reactivity and acidity, it plays the pivotal role in initiating interstellar chemical reactions, something which also reduces its steady-state concentration. Interstellar H3+ is not only destroyed in chemical reactions but also in dissociative recombination with electrons. The rate constant and mechanism of recombination have long been controversial, but great advances have been made during recent years, with the important consequence that the cosmic ray ionization rate in diffuse clouds is now believed to be higher by an order of magnitude than previously assumed.

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35

Slavin, Jonathan D., and Priscilla C. Frisch. "The Influence of the Local Bubble on the Ionization of the Local Interstellar Cloud." International Astronomical Union Colloquium 166 (1997): 305–8. http://dx.doi.org/10.1017/s0252921100071165.

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AbstractThe ionization of the the Local Interstellar Cloud (LIC) is quite unusual compared with most warm (T ~ 104 K) interstellar gas. Hydrogen and helium are both partially ionized with helium surprisingly more ionized than hydrogen. Directly observed ionization sources including nearby stellar EUV sources and the diffuse emission of the Soft X-ray Background (SXRB), do not provide enough ionization and heating to account for both the ionization state and temperature of the LIC. We propose that an evaporative boundary between the LIC and the hot gas of the Local Bubble can provide the necessary ionizing radiation. Results of detailed models of the emission from the interface are presented and shown to be adequate to explain the observations.

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36

Lee, Dae-Hee, Kwang-Il Seon, and Kyoung-Wook Min. "ORFEUS SURVEYS OF THE INTERSTELLAR MOLECULAR HYDROGEN." Publications of The Korean Astronomical Society 20, no. 1 (December 31, 2005): 11–20. http://dx.doi.org/10.5303/pkas.2005.20.1.011.

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37

Somerville, W. B., and C. A. Smith. "Estimating molecular hydrogen in diffuse interstellar clouds." Monthly Notices of the Royal Astronomical Society 238, no. 2 (May 1, 1989): 559–65. http://dx.doi.org/10.1093/mnras/238.2.559.

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38

Clark, David B. "Very large hydrogen atoms in interstellar space." Journal of Chemical Education 68, no. 6 (June 1991): 454. http://dx.doi.org/10.1021/ed068p454.

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39

Cazaux, S., and A. G. G. M. Tielens. "Molecular Hydrogen Formation in the Interstellar Medium." Astrophysical Journal 575, no. 1 (August 10, 2002): L29—L32. http://dx.doi.org/10.1086/342607.

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40

Ratajczak, A., E. Quirico, A. Faure, B. Schmitt, and C. Ceccarelli. "Hydrogen/deuterium exchange in interstellar ice analogs." Astronomy & Astrophysics 496, no. 2 (March 2009): L21—L24. http://dx.doi.org/10.1051/0004-6361/200911679.

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41

Swaczyna, Paweł, Nathan A. Schwadron, Eberhard Möbius, Maciej Bzowski, Priscilla C. Frisch, Jeffrey L. Linsky, David J. McComas, et al. "Mixing Interstellar Clouds Surrounding the Sun." Astrophysical Journal Letters 937, no. 2 (September 28, 2022): L32. http://dx.doi.org/10.3847/2041-8213/ac9120.

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Abstract On its journey through the Galaxy, the Sun passes through diverse regions of the interstellar medium. High-resolution spectroscopic measurements of interstellar absorption lines in spectra of nearby stars show absorption components from more than a dozen warm partially ionized clouds within 15 pc of the Sun. The two nearest clouds—the Local Interstellar Cloud (LIC) and Galactic (G) cloud—move toward each other. Their bulk heliocentric velocities can be compared with the interstellar neutral helium flow velocity obtained from space-based experiments. We combine recent results from Ulysses, IBEX, and STEREO observations to find a more accurate estimate of the velocity and temperature of the very local interstellar medium. We find that, contrary to the widespread viewpoint that the Sun resides inside the LIC, the locally observed velocity of the interstellar neutral helium is consistent with a linear combination of the velocities of the LIC and G cloud, but not with either of these two velocities. This finding shows that the Sun travels through a mixed-cloud interstellar medium composed of material from both these clouds. Interactions between these clouds explain the substantially higher density of the interstellar hydrogen near the Sun and toward stars located within the interaction region of these two clouds. The observed asymmetry of the interstellar helium distribution function also supports this interaction. The structure and equilibrium in this region require further studies using in situ and telescopic observations.

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Kreckel, H., O. Novotný, and A. Wolf. "Astrochemical studies at the Cryogenic Storage Ring." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2154 (August 5, 2019): 20180412. http://dx.doi.org/10.1098/rsta.2018.0412.

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The new Cryogenic Storage Ring at the Max Planck Institute for Nuclear Physics (Heidelberg, Germany) has recently become operational. One of the main research areas foreseen for this unique facility is astrochemical studies with cold molecular ions. The spontaneous radiative cooling of the prototype interstellar molecule CH + to its lowest rotational states has been demonstrated by photodissociation spectroscopy, paving the way for experiments under true interstellar conditions. To this end, a low-energy electron cooler and a neutral atom beam set-up for merged beams studies have been constructed. These experiments have the potential to provide energy-resolved rate coefficients for fundamental astrochemical processes involving state-selected molecular ions. The main target reactions include some of the key processes of interstellar chemistry, such as the electron recombination of H 3 + , charge exchange between H 2 + and H, or the formation of CH + in collisions of triatomic hydrogen ions and C atoms. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.

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Kubiak, M. A., M. Bzowski, E. Möbius, and N. A. Schwadron. "Science Opportunities for IMAP-Lo Observations of Interstellar Neutral Hydrogen and Deuterium during a Maximum of Solar Activity." Astrophysical Journal Supplement Series 271, no. 2 (March 22, 2024): 43. http://dx.doi.org/10.3847/1538-4365/ad23e9.

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Abstract Direct-sampling observations of interstellar neutral gas, including hydrogen and deuterium, have been performed for more than one cycle of solar activity by IBEX. The 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 the forthcoming mission called Interstellar Mapping and Acceleration Probe. The IMAP-Lo instrument will have the capability of adjusting the angle of its boresight with the spacecraft rotation axis. We continue a series of studies of the resulting science opportunities. We adopt the schedule of adjusting the boresight angle suggested by Kubiak et al. and focus on interstellar hydrogen and deuterium during solar maximum. Based on an extensive set of simulations, we identify the times during the calendar year and the elongation angles of the boresight needed to measure the abundance of D/H at the termination shock and to unambiguously observe interstellar H without a 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 the 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 the observations needed to address compelling questions in heliospheric physics and even in general astrophysics.

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44

Oueslati, Ichraf, Boutheïna Kerkeni, and Stefan T. Bromley. "Trends in the adsorption and reactivity of hydrogen on magnesium silicate nanoclusters." Physical Chemistry Chemical Physics 17, no. 14 (2015): 8951–63. http://dx.doi.org/10.1039/c4cp05128a.

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Mac Low, Mordecai-Mark. "Atomic and Molecular Phases of the Interstellar Medium." Proceedings of the International Astronomical Union 11, S315 (August 2015): 1–8. http://dx.doi.org/10.1017/s174392131600716x.

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AbstractThis review covers four current questions in the behavior of the atomic and molecular interstellar medium. These include whether the atomic gas originates primarily in cold streams or hot flows onto galaxies; what the filling factor of cold gas actually is in galactic regions observationally determined to be completely molecular; whether molecular hydrogen determines or merely traces star formation; and whether gravity or turbulence drives the dynamical motions observed in interstellar clouds, with implications on their star formation properties.

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Campisi, Dario, Frederik Doktor S. Simonsen, John D. Thrower, Rijutha Jaganathan, Liv Hornekær, Rocco Martinazzo, and Alexander G. G. M. Tielens. "Superhydrogenation of pentacene: the reactivity of zigzag-edges." Physical Chemistry Chemical Physics 22, no. 3 (2020): 1557–65. http://dx.doi.org/10.1039/c9cp05440e.

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Studies of pentacene hydrogenation reveal a preferential hydrogenation sequence. The guiding concepts apply more broadly to aromatic carbonaceous systems and may be crucial in catalytic formation of molecular hydrogen in interstellar space.

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Lang, Kenneth R. "A Historical Review of Star Formation: Observation and Theory." Symposium - International Astronomical Union 115 (1987): 57. http://dx.doi.org/10.1017/s0074180900094833.

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We present a historical review of evidence for ongoing star formation in our Galaxy beginning with the discovery that interstellar space is not empty. The discoveries of interstellar dust, interstellar hydrogen and molecular clouds are reviewed. Observational investigations of dark clouds are then traced from the photographs of Edward Emerson Barnard to contemporary studies of their molecular constituents. A historical overview of observational evidence for new-born stars includes T-Tauri stars, young stellar clusters, sequential star birth and infrared stars beginning with Alfred Joy, Merle Walker, Becklin, and Neugebauer, and Adrian Blaauw and continuing to giant molecular clouds and IRAS. Theoretical studies of gravitational collapse and the early stages of stellar evolution are also placed within a historical context.

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Clark, S. E. "Galactic neutral hydrogen and the magnetic ISM foreground." Proceedings of the International Astronomical Union 12, S333 (October 2017): 146–50. http://dx.doi.org/10.1017/s1743921317011462.

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AbstractThe interstellar medium is suffused with magnetic fields, which inform the shape of structures in the diffuse gas. Recent high-dynamic range observations of Galactic neutral hydrogen, combined with novel data analysis techniques, have revealed a deep link between the morphology of neutral gas and the ambient magnetic field. At the same time, an observational revolution is underway in low-frequency radio polarimetry, driven in part by the need to characterize foregrounds to the cosmological 21-cm signal. A new generation of experiments, capable of high angular and Faraday depth resolution, are revealing complex filamentary structures in diffuse polarization. The relationship between filamentary structures observed in radio-polarimetric data and those observed in atomic hydrogen is not yet well understood. Multiwavelength observations will enable new insights into the magnetic interstellar medium across phases.

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Kowalska-Leszczynska, I., M. A. Kubiak, M. Bzowski, and M. Strumik. "Sensitivity of the Helioglow to Variation of the Total Ionization Rate and Solar Lyα Emission." Astrophysical Journal 965, no. 1 (April 1, 2024): 30. http://dx.doi.org/10.3847/1538-4357/ad2a55.

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Abstract Direct observations of solar wind are mostly limited to the vicinity of the ecliptic plane. Retrieving the latitudinal structure of solar wind indirectly based on observations of the backscatter glow of interstellar neutral hydrogen is complex and requires support from theoretical models. The GLOWS instrument, to operate on the planned IMAP mission, will scan the helioglow along circumsolar rings with an angular distance of ∼75°. Its objective is to retrieve the latitudinal structure of the ionization rate of interstellar hydrogen and with this the structure of the solar wind. In preparation for the future analysis, we studied the sensitivity of the light curves to temporal and latitudinal variation of the ionization rate of interstellar hydrogen and the solar Lyα illumination. Based on carefully planned numerical experiments, we analyze the time delay and relaxation time of the system for variations of the ionization rate and solar illumination in heliolatitude and with time. We found that variations in the solar illumination are reflected in the helioglow without delay, but relaxation takes longer than the variation rise time. By contrast, variations in the ionization rate are anticorrelated with the helioglow brightness with a delay of several months. We also found that the helioglow is not sensitive to variations in the ionization rate at the solar poles, so retrieving the ionization rate and solar wind at the poles requires approximation of the ionization rate profiles with appropriate parametric functions.

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Michael, A. T., M. Opher, G. Tóth, V. Tenishev, and D. Borovikov. "The Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) Code: A Self-consistent Kinetic–Magnetohydrodynamic Model of the Outer Heliosphere." Astrophysical Journal 924, no. 2 (January 1, 2022): 105. http://dx.doi.org/10.3847/1538-4357/ac35eb.

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Abstract Neutral hydrogen has been shown to greatly impact the plasma flow in the heliosphere and the location of the heliospheric boundaries. We present the results of the Solar Wind with Hydrogen Ion Exchange and Large-scale Dynamics (SHIELD) model, a new, self-consistent, kinetic–MHD model of the outer heliosphere within the Space Weather Modeling Framework. The charge exchange mean free path is on the order of the size of the heliosphere; therefore, the neutral atoms cannot be described as a fluid. The numerical code SHIELD couples the MHD solution for a single plasma fluid to the kinetic solution for neutral hydrogen atoms streaming through the system. The kinetic code is based on the Adaptive Mesh Particle Simulator, a Monte Carlo method for solving the Boltzmann equation. The numerical code SHIELD accurately predicts the increased filtration of interstellar neutrals into the heliosphere. In order to verify the correct implementation within the model, we compare the results of the numerical code SHIELD to those of other, well-established kinetic–MHD models. The numerical code SHIELD matches the neutral hydrogen solution of these studies as well as the shift in all heliospheric boundaries closer to the Sun in comparison with the multi-fluid treatment of neutral hydrogen atoms. Overall the numerical code SHIELD shows excellent agreement with these models and is a significant improvement to the fluid treatment of interstellar hydrogen.

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Journal articles on the topic 'Hydrogène interstellaire'

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