26 results on '"Linsky, Jeffrey"'
Search Results
2. The local ISM in three dimensions: kinematics, morphology and physical properties
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Linsky, Jeffrey L. and Redfield, Seth
- Published
- 2014
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3. Voyagers of Discovery
- Author
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Linsky, Jeffrey L.
- Published
- 2011
- Full Text
- View/download PDF
4. Local Interstellar Medium : Summary of Working Group VI
- Author
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Linsky, Jeffrey L., Wilson, T. L., Rood, R. T., Prantzos, Nikos, editor, Tosi, Monica, editor, and Von Steiger, Rudolf, editor
- Published
- 1998
- Full Text
- View/download PDF
5. Deuterium Abundance in the Local ISM and Possible Spatial Variations
- Author
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Linsky, Jeffrey L., Prantzos, Nikos, editor, Tosi, Monica, editor, and Von Steiger, Rudolf, editor
- Published
- 1998
- Full Text
- View/download PDF
6. GHRS Observations of the LISM
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Linsky, Jeffrey L., Von Steiger, R., editor, Lallement, R., editor, and Lee, M. A., editor
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- 1996
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- View/download PDF
7. Deuterium in the Local Interstellar Medium: Its Cosmological Significance
- Author
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Linsky, Jeffrey L., Diplas, Athanassios, Savage, Blair, Andrulis, Catherine, Brown, Alex, Wamsteker, W., editor, Longair, M. S., editor, and Kondo, Y., editor
- Published
- 1994
- Full Text
- View/download PDF
8. Understanding physical processes in the diffuse ISM using high-resolution UV spectroscopy
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Linsky, Jeffrey L.
- Published
- 2011
- Full Text
- View/download PDF
9. Astrospheres of Planet-Hosting Cool Stars and Beyond ⋅ When Modeling Meets Observations.
- Author
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Herbst, Konstantin, Baalmann, Lennart R., Bykov, Andrei, Engelbrecht, N. Eugene, Ferreira, Stefan E. S., Izmodenov, Vladislav V., Korolkov, Sergey D., Levenfish, Ksenia P., Linsky, Jeffrey L., Meyer, Dominique M.-A., Scherer, Klaus, and Strauss, R. Du Toit
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GALACTIC cosmic rays ,EARLY stars ,INTERSTELLAR medium ,SOLAR wind ,EXTRASOLAR planets ,STELLAR winds ,NEUTRON stars - Abstract
Thanks to dedicated long-term missions like Voyager and GOES over the past 50 years, much insight has been gained on the activity of our Sun, the solar wind, its interaction with the interstellar medium, and, thus, about the formation, the evolution, and the structure of the heliosphere. Additionally, with the help of multi-wavelength observations by the Hubble Space Telescope, Kepler, and TESS, we not only were able to detect a variety of extrasolar planets and exomoons but also to study the characteristics of their host stars, and thus became aware that other stars drive bow shocks and astrospheres. Although features like, e.g., stellar winds, could not be measured directly, over the past years several techniques have been developed allowing us to indirectly derive properties like stellar mass-loss rates and stellar wind speeds, information that can be used as direct input to existing astrospheric modeling codes. In this review, the astrospheric modeling efforts of various stars will be presented. Starting with the heliosphere as a benchmark of astrospheric studies, investigating the paleo-heliospheric changes and the Balmer H α projections to 1 pc , we investigate the surroundings of cool and hot stars, but also of more exotic objects like neutron stars. While pulsar wind nebulae (PWNs) might be a source of high-energy galactic cosmic rays (GCRs), the astrospheric environments of cool and hot stars form a natural shield against GCRs. Their modulation within these astrospheres, and the possible impact of turbulence, are also addressed. This review shows that all of the presented modeling efforts are in excellent agreement with currently available observations. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
10. Inhomogeneity in the Local ISM and Its Relation to the Heliosphere.
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Linsky, Jeffrey, Redfield, Seth, Ryder, Diana, and Moebius, Eberhard
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HELIOSPHERE , *INTERSTELLAR medium , *SOLAR temperature , *ABSORPTION spectra , *SPATIAL variation - Abstract
This paper reviews past research and new studies underway of the local interstellar environment and its changing influence on the heliosphere. The size, shape, and physical properties of the heliosphere outside of the heliopause are determined by the surrounding environment – now the outer region of the Local Interstellar Cloud (LIC). The temperature, turbulence, and velocity vector of neutral atoms and ions in the LIC and other partially ionized interstellar clouds are measured from high-resolution spectra of interstellar absorption lines observed with the STIS instrument on the HST. Analysis of such spectra led to a kinematic model with many interstellar clouds defined by velocity vectors derived from radial velocity measurements. This analysis identified fifteen clouds located within about 10 pc of the Sun and their mean temperatures, turbulence, and velocity vectors. With the increasing number of sight lines now being analyzed, we find that temperatures and turbulent velocities have spatial variations within the LIC and other nearby clouds much larger than measurement uncertainties, and that these spatial variations appear to be randomly distributed and can be fit by Gaussians. The inhomogeneous length scale is less than 4,000 AU, a distance that the heliosphere will traverse in less than 600 years. The temperatures and turbulent velocities do not show significant trends with stellar distance or angle from the LIC center. If/when the Sun enters an inter-cloud medium, the physical properties of the future heliosphere will be very different from the present. For the heliosheath and the very local interstellar medium (VLISM) just outside of the heliopause, the total pressures are approximately equal to the gravitational pressure of overlying material in the Galaxy. The internal pressure in the LIC is far below that in the VLISM, but there is an uncertain ram pressure term produced by the flow of the LIC with respect to its environment. [ABSTRACT FROM AUTHOR]
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- 2022
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11. Intrinsic Lyα Profiles of High-velocity G, K, and M Dwarfs.
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Youngblood, Allison, Pineda, J. Sebastian, Ayres, Thomas, France, Kevin, Linsky, Jeffrey L., Wood, Brian E., Redfield, Seth, and Schlieder, Joshua E.
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STELLAR chromospheres ,COOL stars (Astronomy) ,INTERSTELLAR medium ,INTERSTELLAR gases ,DEUTERIUM ,SOLAR atmosphere ,SOLAR chromosphere - Abstract
Observations of H i Lyman α, the brightest UV emission line of late-type stars, are critical for understanding stellar chromospheres and transition regions, modeling photochemistry in exoplanet atmospheres, and measuring the abundances of neutral hydrogen and deuterium in the interstellar medium. Yet Lyα observations are notoriously challenging owing to severe attenuation from interstellar gas, hindering our understanding of this important emission line's basic morphology. We present high-resolution far- and near-UV spectroscopy of five G, K, and M dwarfs with radial velocities large enough to Doppler-shift the stellar Lyα emission line away from much of the interstellar attenuation, allowing the line core to be directly observed. We detect self-reversal in the Lyα emission-line core for all targets, and we show that the self-reversal depth decreases with increasing surface gravity. Mg ii self-reversed emission-line profiles provide some useful information to constrain the Lyα line core, but the differences are significant enough that Mg ii cannot be used directly as an intrinsic Lyα template during reconstructions. We show that reconstructions that neglect self-reversal could overestimate intrinsic Lyα fluxes by as much as 60%–100% for G and K dwarfs and 40%–170% for M dwarfs. The five stars of our sample have low magnetic activity and subsolar metallicity; a larger sample size is needed to determine how sensitive these results are to these factors. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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12. New Observational Constraints on the Winds of M dwarf Stars.
- Author
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Wood, Brian E., Müller, Hans-Reinhard, Redfield, Seth, Konow, Fallon, Vannier, Hunter, Linsky, Jeffrey L., Youngblood, Allison, Vidotto, Aline A., Jardine, Moira, Alvarado-Gómez, Julián D., and Drake, Jeremy J.
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DWARF stars ,CORONAL mass ejections ,INTERSTELLAR medium ,MAIN sequence (Astronomy) ,STELLAR winds ,SOLAR flares ,STELLAR spectra ,SOLAR corona - Abstract
High-resolution UV spectra of stellar H i Lyα lines from the Hubble Space Telescope (HST) provide observational constraints on the winds of coronal main-sequence stars, thanks to an astrospheric absorption signature created by the interaction between the stellar winds and the interstellar medium. We report the results of a new HST survey of M dwarf stars, yielding six new detections of astrospheric absorption. We estimate mass-loss rates for these detections and upper limits for nondetections. These new constraints allow us to characterize the nature of M dwarf winds and their dependence on coronal activity for the first time. For a clear majority of the M dwarfs, we find winds that are weaker than or comparable in strength to that of the Sun, i.e.,. However, two of the M dwarfs have much stronger winds: YZ CMi (M4 Ve;) and GJ 15AB (M2 V+M3.5 V;). Even these winds are much weaker than expectations if the solar relation between flare energy and coronal mass ejection (CME) mass extended to M dwarfs. Thus, the solar flare/CME relation does not appear to apply to M dwarfs, with important ramifications for the habitability of exoplanets around M dwarfs. There is evidence for some increase in with coronal activity as quantified by X-ray flux, but with much scatter. One or more other factors must be involved in determining wind strength besides spectral type and coronal activity, with magnetic topology being one clear possibility. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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13. Reconstructing the Extreme Ultraviolet Emission of Cool Dwarfs Using Differential Emission Measure Polynomials.
- Author
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Duvvuri, Girish M., Pineda, J. Sebastian, Berta-Thompson, Zachory K., Brown, Alexander, France, Kevin, Kowalski, Adam F., Redfield, Seth, Tilipman, Dennis, Vieytes, Mariela C., Wilson, David J., Youngblood, Allison, Froning, Cynthia S., Linsky, Jeffrey, Loyd, R. O. Parke, Mauas, Pablo, Miguel, Yamila, Newton, Elisabeth R., Rugheimer, Sarah, and Schneider, P. Christian
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PLANETARY atmospheres ,SPECTRAL energy distribution ,INTERSTELLAR medium ,X-ray spectra ,PLANETARY orbits ,SPACE telescopes - Abstract
Characterizing the atmospheres of planets orbiting M dwarfs requires understanding the spectral energy distributions of M dwarfs over planetary lifetimes. Surveys like MUSCLES, HAZMAT, and FUMES have collected multiwavelength spectra across the spectral type's range of T
eff and activity, but the extreme ultraviolet (EUV, 100–912 Å) flux of most of these stars remains unobserved because of obscuration by the interstellar medium compounded with limited detector sensitivity. While targets with observable EUV flux exist, there is no currently operational facility observing between 150 and 912 Å. Inferring the spectra of exoplanet hosts in this regime is critical to studying the evolution of planetary atmospheres because the EUV heats the top of the thermosphere and drives atmospheric escape. This paper presents our implementation of the differential emission measure technique to reconstruct the EUV spectra of cool dwarfs. We characterize our method's accuracy and precision by applying it to the Sun and AU Mic. We then apply it to three fainter M dwarfs: GJ 832, Barnard's star, and TRAPPIST-1. We demonstrate that with the strongest far-ultraviolet (FUV, 912–1700 Å) emission lines, observed with the Hubble Space Telescope and/or Far Ultraviolet Spectroscopic Explorer, and a coarse X-ray spectrum from either the Chandra X-ray Observatory or XMM-Newton, we can reconstruct the Sun's EUV spectrum to within a factor of 1.8, with our model's formal uncertainties encompassing the data. We report the integrated EUV flux of our M dwarf sample with uncertainties of a factor of 2–7 depending on available data quality. [ABSTRACT FROM AUTHOR]- Published
- 2021
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14. The Interface between the Outer Heliosphere and the Inner Local ISM: Morphology of the Local Interstellar Cloud, Its Hydrogen Hole, Strömgren Shells, and 60Fe Accretion.
- Author
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Linsky, Jeffrey L., Redfield, Seth, and Tilipman, Dennis
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HELIOSPHERE , *INTERSTELLAR medium , *IONIZED gases , *HYDROGEN , *SUPERNOVAE - Abstract
We describe the interface between the outer heliosphere and the local interstellar medium (LISM) surrounding the Sun. The components of the inner LISM are the four partially ionized clouds (the Local Interstellar Cloud (LIC), G cloud, Blue cloud, and Aql cloud) that are in contact with the outer heliosphere, and ionized gas produced by EUV radiation primarily from ϵ CMa. We construct the three-dimensional shape of the LIC based on interstellar line absorption along 62 sightlines and show that in the directions of ϵ CMa, β CMa, and Sirius B the neutral hydrogen column density from the center of the LIC is a minimum. We call this region the "hydrogen hole." In this direction, the presence of Blue cloud absorption and the absence of LIC absorption can be simply explained by the Blue cloud lying just outside the heliosphere. We propose that the outer edge of the Blue cloud is a Strömgren shell driven toward the heliosphere by high pressures in the H ii region. We find that the vectors of neutral and ionized helium flowing through the heliosphere are inconsistent with the LIC flow vector, and that the nearby intercloud gas is consistent with ionization by ϵ CMa and other stellar sources without requiring additional sources of ionization or million-degree plasma. In the upwind direction, the heliosphere is passing through an environment of several LISM clouds, which may explain the recent influx of interstellar grains containing 60Fe from supernova ejecta measured in Antarctic snow. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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- View/download PDF
15. Structure, Dynamics, and Physical Properties of the Warm LISM Within the Local Bubble.
- Author
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Linsky, Jeffrey L. and Redfield, Seth
- Subjects
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COSMIC ripples , *SOLAR wind , *INTERSTELLAR medium , *RADIO sources (Astronomy) , *SPECTRUM analysis - Abstract
We describe our empirical model of warm gas in the local interstellar medium. High-resolution absorption-line spectra of 157 stars provide radial-velocity and physical parameter data for 270 interstellar velocity components. This extensive data set allowed us to piece together a detailed model of the partially ionized warm gas within the Local Bubble. We have identified velocity vectors and projected morphologies of 15 warm gas clouds located within 15 parsecs of the Sun. These clouds have diverse gas temperatures, turbulent velocities, and metal depletions. Cloud-cloud collisions may be responsible for the filamentary morphologies found in about 1/3 of the clouds. We explain the large-amplitude intraday and annular scintillation variability of several quasars seen at radio wavelengths by turbulent scattering screens located at cloud boundaries. Collisions between the clouds could produce the turbulence and ionization at the cloud boundaries. A nearby cold dense cloud is likely compressed and shielded by surounding warm clouds. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
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16. Results from the ISSI Workshop: “From the Outer Heliosphere to the Local Bubble: Comparison of New Observations with Theory”.
- Author
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Linsky, Jeffrey L.
- Subjects
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HELIOSPHERE , *COSMIC ripples , *SOLAR wind , *INTERSTELLAR medium , *STELLAR winds , *SOLAR activity - Abstract
On 15–19 October 2007, the International Space Science Institute (ISSI) in Bern, Switzerland, hosted a workshop that brought together scientists studying various aspects of the interaction of the solar wind with the local interstellar medium and the Local Bubble. Recent results from the Voyager missions and other space-based observatories have stimulated new understanding and theories concerning phenomena in these environments. Important questions discussed at the workshop included the structure and dominant physical processes in the outer heliosphere and the properties, structures, and origin of the local interstellar medium. A focus of the workshop was the many roles that magnetic fields play in the outer heliosphere and Local Bubble. This review summarizes the important topics discussed at the workshop and lists some of the important conclusions. [ABSTRACT FROM AUTHOR]
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- 2009
- Full Text
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17. Provocative Questions for the Deuterium Session.
- Author
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Linsky, Jeffrey L.
- Subjects
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DEUTERIUM , *ASTRONOMY , *INTERSTELLAR medium , *ULTRAVIOLET spectra , *ASTRONOMICAL instruments - Abstract
Analyses of spectra obtained with the Far Ultraviolet Spectrograph Explorer (FUSE) satellite, together with spectra from the Copernicus, Hubble Space Telescope (HST), and Interstellar Medium Absorption Profile Spectrograph (IMAPS) instruments reveal a very wide range in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond the Local Bubble. For gas located beyond the Local Bubble but within several hundred parsecs, the observed D/H ratios differ by a factor of 4–5. A critically important question is what value or values of D/H in the local region of our Galaxy should be compared with chemical evolution models of the Galaxy and with the primordial deuterium abundance. Linsky et al. [Astrophys. J. 647, 1106 (2006)] argued that spatial variations in the depletion of deuterium onto dust grains can explain these local variations in the observed gas-phase D/H ratios. In this provacative introduction to the deuterium session, I ask six questions concerning analysis techniques and proposed results from the FUSE D/H program in the hope that the speakers and participants in this conference will give serious thought to the robustness of our present understanding of this important topic. In particular, is the deuterium depletion model valid? Is it only part of the explanation? [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
18. COMPUTING INTRINSIC LYα FLUXES OF F5 V TO M5 V STARS.
- Author
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LINSKY, JEFFREY L., FRANCE, KEVIN, and AYRES, TOM
- Subjects
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ULTRAVIOLET spectra , *PHOTODISSOCIATION , *MOLECULES , *EXTRASOLAR planets , *INTERSTELLAR medium ,SPECTRA of cool stars - Abstract
The Lyα emission line dominates the far-ultraviolet spectra of late-type stars and is a major source for photodissociation of important molecules including H2O, CH4, and CO2 in exoplanet atmospheres. The incident flux in this line illuminating an exoplanet's atmosphere cannot be measured directly as neutral hydrogen in the interstellar medium (ISM) attenuates most of the flux reaching the Earth. Reconstruction of the intrinsic Lyα line has been accomplished for a limited number of nearby stars, but is not feasible for distant or faint host stars. We identify correlations connecting the intrinsic Lyα flux with the flux in other emission lines formed in the stellar chromosphere, and find that these correlations depend only gradually on the flux in the other lines. These correlations, which are based on Hubble Space Telescope spectra, reconstructed Lyα line fluxes, and irradiance spectra of the quiet and active Sun, are required for photochemical models of exoplanet atmospheres when intrinsic Lyα fluxes are not available. We find a tight correlation of the intrinsic Lyα flux with stellar X-ray flux for F5 V to K5 V stars, but much larger dispersion for Mstars. We also show that knowledge of the stellar effective temperature and rotation rate can provide reasonably accurate estimates of the Lyα flux for G and K stars, and less accurate estimates for cooler stars. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
19. NEAR-ULTRAVIOLET EXCESS IN SLOWLY ACCRETING T TAURI STARS: LIMITS IMPOSED BY CHROMOSPHERIC EMISSION.
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Ingleby, Laura, Calvet, Nuria, Bergin, Edwin, Herczeg, Gregory, Brown, Alexander, Alexander, Richard, Edwards, Suzan, Espaillat, Catherine, France, Kevin, Gregory, Scott G., Hillenbrand, Lynne, Roueff, Evelyne, Valenti, Jeff, Walter, Frederick, Johns-Krulli, Christopher, Brown, Joanna, Linsky, Jeffrey, McClure, Melissa, Ardila, David, and Abgrall, Hervé
- Subjects
ULTRAVIOLET stars ,STARS ,CIRCUMSTELLAR matter ,INTERSTELLAR medium - Abstract
Young stars surrounded by disks with very low mass accretion rates are likely in the final stages of inner disk evolution and therefore particularly interesting to study. We present ultraviolet (UV) observations of the ~5-9 Myr old stars RECX-1 and RECX-11, obtained with the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph on the Hubble Space Telescope, as well as optical and near-infrared spectroscopic observations. The two stars have similar levels of near-UV emission, although spectroscopic evidence indicates that RECX-11 is accreting and RECX-1 is not. The line profiles of Hα and HeI λ10830 in RECX-11 show both broad and narrow redshifted absorption components that vary with time, revealing the complexity of the accretion flows. We show that accretion indicators commonly used to measure mass accretion rates, e.g., U-band excess luminosity or the Ca II triplet line Inminosity, are unreliable for low accretors, at least in the middle K spectral range. Using RECX-1 as a template for the intrinsic level of photospheric and chromospheric emission, we determine an upper limit of 3 x 10
-10 M⊙ yr-1 for RECX-11. At this low accretion rate, recent photoevaporation models predict that an inner hole should have developed in the disk. However, the spectral energy distribution of RECX-11 shows fluxes comparable to the median of Taurus in the near-infrared, indicating that substantial dust remains. Fluorescent H2 emission lines formed in the innermost disk are observed in RECX-11, showing that gas is present in the inner disk, along with the dust. [ABSTRACT FROM AUTHOR]- Published
- 2011
- Full Text
- View/download PDF
20. Solving the mysteries of the diffuse interstellar medium with high-resolution UV spectroscopy.
- Author
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Linsky, Jeffrey L.
- Subjects
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ULTRAVIOLET spectroscopy , *INTERSTELLAR medium , *IONIZATION of gases , *GAS dynamics , *PHYSICAL & theoretical chemistry , *SPECTROMETERS - Abstract
Understanding the complex structure, dynamics, and ionization of gas in the nearby interstellar medium is required before one can realistically model interstellar gas in other galaxies. High-resolution ultraviolet spectra provide the essential data for such studies because the resonance lines of most important atoms, ions, and molecules are located in the ultraviolet, and high spectral resolution is needed to resolve line profiles and determine the velocity structure along a line of sight. I list ten important physical questions concerning interstellar gas that require a more sensitive spectrometer than STIS and the desired spectral resolution to answer these questions. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
21. UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets.
- Author
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Castro, Ana, Lecavelier, Alain, D'Avillez, Miguel, Linsky, Jeffrey, and Cernicharo, José
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ULTRAVIOLET astronomy ,STAR formation ,INTERSTELLAR medium ,PLANETS ,WINDS ,JETS (Fluid dynamics) - Abstract
Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medium (ISM) mass. The structure, properties and lifetimes of molecular clouds are determined by the overall dynamics and evolution of a very complex system – the ISM. Understanding the physics of the ISM is of prime importance not only for Galactic but also for extragalactic and cosmological studies. Most of the ISM volume (∼ 65%) is filled with diffuse gas at temperatures between 3000 and 300 000 K, representing about 50% of the ISM mass. The physics of accretion and outflow. Powerful outflows are known to regulate angular momentum transport during star formation, the so-called accretion–outflow engine. Elementary physical considerations show that, to be efficient, the acceleration region for the outflows must be located close to the star (within 1 AU) where the gravitational field is strong. According to recent numerical simulations, this is also the region where terrestrial planets could form after 1 Myr. One should keep in mind that today the only evidence for life in the Universe comes from a planet located in this inner disk region (at 1 AU) from its parent star. The temperature of the accretion–outflow engine is between 3000 and 10
7 K. After 1 Myr, during the classical T Tauri stage, extinction is small and the engine becomes naked and can be observed at ultraviolet wavelengths. The physics of planet formation. Observations of volatiles released by dust, planetesimals and comets provide an extremely powerful tool for determining the relative abundances of the vaporizing species and for studying the photochemical and physical processes acting in the inner parts of young planetary systems. This region is illuminated by the strong UV radiation field produced by the star and the accretion–outflow engine. Absorption spectroscopy provides the most sensitive tool for determining the properties of the circumstellar gas as well as the characteristics of the atmospheres of the inner planets transiting the stellar disk. UV radiation also pumps the electronic transitions of the most abundant molecules (H2 , CO, etc.) that are observed in the UV. Here we argue that access to the UV spectral range is essential for making progress in this field, since the resonance lines of the most abundant atoms and ions at temperatures between 3000 and 300 000 K, together with the electronic transitions of the most abundant molecules (H2 , CO, OH, CS, S2 , CO2 + , C2 , O2 , O3 , etc.) are at UV wavelengths. A powerful UV-optical instrument would provide an efficient mean for measuring the abundance of ozone in the atmosphere of the thousands of transiting planets expected to be detected by the next space missions (GAIA, Corot, Kepler, etc.). Thus, a follow-up UV mission would be optimal for identifying Earth-like candidates. [ABSTRACT FROM AUTHOR]- Published
- 2006
- Full Text
- View/download PDF
22. Atomic Deuterium/Hydrogen in the Galaxy.
- Author
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Linsky, Jeffrey L.
- Subjects
COSMOCHEMISTRY ,DEUTERIUM ,HYDROGEN ,INTERSTELLAR medium ,SPACE sciences ,INTERSTELLAR molecules - Abstract
An accurate value of the D/H ratio in the local interstellar medium (LISM) arid a better understanding of the D/H variations with position in the Galactic disk and halo arc vitally important questions as they provide in formation on the primordial D/H ratio in the Galaxy at the time of the protosolar nebula, and the amount of astration and mixing in the Galaxy over time. Recent measurements have been obtained with UV spectrographs on FUSE, HST, and IMAPS using hot white dwarfs, OB stars, and late-type stars as background light sources against which to measure absorption by D and H in the interstellar medium along the lines of sight. Recent analyses of FUSE observations of seven white dwarfs and subdwarfs provide a weighted mean value of D/H = (1 .52 ± 0.08) × 10
-5 (15.2 ± 0.8 ppm), consistent with the value of (1.50 ± 0.10) × 10-5 (15.0 ± 1.0 ppm) obtained from analysis of lines of sight toward nearby late-type stars. Both numbers refer to the ISM within about 100 pc of the Sun, which samples warm clouds located within the Local Bubble. Outside of the Local Bubble at distances of 200 to 500 pc, analyses of far-UV spectra obtained with the IMAPS instrument indicate a much wider range of D/H ratios between 0.8 to 2.2 ppm. This portion of the Galactic disk provides information on inhomogeneous astration in the Galaxy. [ABSTRACT FROM AUTHOR]- Published
- 2003
- Full Text
- View/download PDF
23. Deuterium Abundance in the Local ISM and Possible Spatial Variations.
- Author
-
Linsky, Jeffrey
- Abstract
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) × 10-5 with all data points lying within ± 1σ of the mean. Whether or not the D/H ratio has different values elsewhere in the Galaxy and beyond is a very important open question that will be one of the major objectives of the Far Ultraviolet Spectroscopic Explorer (FUSE) mission. [ABSTRACT FROM AUTHOR]
- Published
- 1998
- Full Text
- View/download PDF
24. Local Interstellar Medium Summary of Working Group VI.
- Author
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Linsky, Jeffrey, Wilson, T., and Rood, R.
- Abstract
This report summarizes the issues discussed in Working Group VI concerning the accuracy of measurements of D/H and 3He/H in the local interstellar medium, possible systematic errors, and emerging trends in the results. [ABSTRACT FROM AUTHOR]
- Published
- 1998
- Full Text
- View/download PDF
25. GHRS observations of the LISM.
- Author
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Linsky, Jeffrey
- Abstract
The GHRS has obtained high-resolution spectra of interstellar gas toward 19 nearby stars. These excellent data show that the Sun is located inside the Local Interstellar Cloud (LIC) with other warm clouds nearby. I will summarize the physical properties of these clouds and the three-dimensional structure of this warm interstellar gas. There is now clear evidence that the Sun and other late-type stars are surrounded by hydrogen walls in the upwind direction. The D/H ratio probably has a constant value in the LIC, (1.6 ± 0.2) × 10, consistent with the measured values for all LIC lines of sight. [ABSTRACT FROM AUTHOR]
- Published
- 1996
- Full Text
- View/download PDF
26. THE STRUCTURE OF THE LOCAL INTERSTELLAR MEDIUM. VI. NEW Mg II, Fe II, AND Mn II OBSERVATIONS TOWARD STARS WITHIN 100 pc.
- Author
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Malamut, Craig, Redfield, Seth, Linsky, Jeffrey L., Wood, Brian E., and Ayres, Thomas R.
- Subjects
INTERSTELLAR medium ,STARS ,SPECTRUM analysis ,ASTROPHYSICS research - Abstract
We analyze high-resolution spectra obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope toward 34 nearby stars (⩽100 pc) to record Mg II, Fe II, and Mn II absorption due to the local interstellar medium (LISM). Observations span the entire sky, probing previously unobserved regions of the LISM. The heavy ions studied in this survey produce narrow absorption features that facilitate the identification of multiple interstellar components. We detected one to six individual absorption components along any given sight line, and the number of absorbers roughly correlates with the pathlength. This high-resolution near-ultraviolet (NUV) spectroscopic survey was specifically designed for sight lines with existing far-UV (FUV) observations. The FUV spectra include many intrinsically broad absorption lines (i.e., of low atomic mass ions) and are often observed at medium resolution. The LISM NUV narrow-line absorption component structure presented here can be used to more accurately interpret the archival FUV observations. As an example of this synergy, we present a new analysis of the temperature and turbulence along the line of sight toward ε Ind. The new observations of LISM velocity structure are also critical in the interpretation of astrospheric absorption derived from fitting the saturated H I Lyα profile. As an example, we reanalyze the spectrum of λ And and find that this star likely does have an astrosphere. Two stars in the sample that have circumstellar disks (49 Cet and HD141569) show evidence for absorption due to disk gas. Finally, the substantially increased number of sight lines is used to test and refine the three-dimensional kinematic model of the LISM and search for previously unidentified clouds within the Local Bubble. We find that every prediction made by the Redfield & Linsky kinematic model of the LISM is confirmed by an observed component in the new lines of sight. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
- View/download PDF
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