arXiv subjects

P. C. Frisch

Publications and source records attributed to P. C. Frisch.

36 records · Page 2Linked to original sources

arXiv2008

Is the Sun Embedded in a Typical Interstellar Cloud?

The physical properties and kinematics of the partially ionized interstellar material near the Sun are typical of warm diffuse clouds in the solar vicinity. The interstellar magnetic field at the heliosphere and the kinematics of nearby clouds are naturally explained in terms of the S1 superbubble shell. The interstellar radiation field at the Sun appears to be harder than the field ionizing ambient diffuse gas, which may be a consequence of the low opacity of the tiny cloud surrounding the heliosphere. The spatial context of the Local Bubble is consistent with our location in the Orion spur.

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arXiv2008

Multi-Cycle HST Treasury Program for STIS: Mapping the Galactic Environment of the Sun

Interstellar clouds form the cosmic "ecosystem" through which the Sun moves. Understanding the physical properties of nearby interstellar material, in sufficient detail to evaluate historical variations in the solar galactic environment, requires a survey of ultraviolet interstellar absorption lines towards stars within 20 pc with the STIS spectrometer. A complete survey would yield ionization, temperature, density and velocity for nearby interstellar clouds, and would require a large number of Hubble Space Telescope orbits spaced over several cycles. This note was submitted as a "white paper" to the Space Telescope Science Institute in support of multi-cycle treasury programs.

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arXiv2008

Implications of Interstellar Dust and Magnetic Field at the Heliosphere

Tiny interstellar dust grains causing the polarization of light from the nearest stars are deflected sideways in the outer heliosheath regions, along with the interstellar magnetic field. Observations of optical polarization of stars beyond the heliosphere nose, suggest the direction of the upwind interstellar magnetic field is relatively constant. The polarizations of nearby stars and offset angle between HeI and HeI flowing into the heliosphere have position angles in galactic coordinates of 30- 40 deg, indicating a local magnetic field direction inclined by ~55 deg and ~65 deg, respectively, with respect to the galactic and ecliptic planes. The hot and cold poles of the measured Cosmic Microwave Background (CMB) dipole moment are nearly symmetric around the heliosphere nose direction, and the v^{22} quadrupole vector is directed towards the heliosphere nose. The area vectors of the CMB quadrupole and ocotopole moments are directed towards the band perpendicular to the ecliptic plane formed by the alternate locations for the 3 kHz emissions detected by Voyagers 1 and 2. In the upwind direction, the position angle of the null plane separating the CMB dipole hot and cold poles is nearly aligned with the interstellar magnetic field direction at the Sun. Heliospheric foreground contamination of the low-$\ell$ CMB modes now requires detailed study.

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arXiv2007

The Local Bubble and Interstellar Material Near the Sun

The properties of interstellar matter (ISM) at the Sun are regulated by our location with respect to the Local Bubble (LB) void in the ISM. The LB is bounded by associations of massive stars and fossil supernovae that have disrupted natal ISM and driven intermediate velocity ISM into the LB interior void. The Sun is located in such a driven ISM parcel. The Local Fluff has a bulk velocity of 19 km/s in the LSR, and an upwind direction towards the center of the gas and dust ring formed by the Loop I supernova remnant interaction with the LB. When the ram pressure of the LIC is included in the total LIC pressure, and if magnetic thermal and cosmic ray pressures are similar, the LIC appears to be in pressure equilibrium with the local hot bubble plasma.

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arXiv2006

The Heliosphere as a Probe of Small Scale Structure

The heliosphere serves as a probe of interstellar material (ISM) close to the Sun. Measurements of ISM inside and outside of the heliosphere show that we reside in typical warm partially ionized ISM that can be successfully modeled using equilibrium photoionization models. The heliosphere wake leaves a ~200 X 1000 AU trail in space of low density, n<0.05 /cc, cooling plasma comingled with ISM. The closest ISM flows through the solar vicinity at V_LSR ~20 km/s, with an upwind direction towards the Scorpius-Centaurus Association. Clouds in this flow have thicknesses typically <1 pc. The flow is decelerating, with velocity variations of ~3-4 km/s /pc. The alpha Oph sightline shows evidence of a cold, possibly tiny, cloud.

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arXiv2006

The Sun's Journey Through the Local Interstellar Medium: The PaleoLISM and Paleoheliosphere

Over the recent past, the galactic environment of the Sun has differed substantially from today. Sometime within the past ~130,000 years, and possibly as recent as ~56,000 years ago, the Sun entered the tenuous tepid partially ionized interstellar material now flowing past the Sun. Prior to that, the Sun was in the low density interior of the Local Bubble. As the Sun entered the local ISM flow, we passed briefly through an interface region of some type. The low column densities of the cloud now surrounding the solar system indicate that heliosphere boundary conditions will vary from opacity considerations alone as the Sun moves through the cloud. These variations in the interstellar material surrounding the Sun affected the paleoheliosphere.

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arXiv2004

The Solar Galactic Environment

Combined heliosphere-astronomical data and models enrich our understanding both of effects the solar galactic environment might have on the inner heliosphere, and of interstellar clouds. Present data suggest that FeII/DI increases toward the upwind direction of the cluster of interstellar clouds (CLIC) flowing past the Sun. Cloud kinematics and abundances suggest an origin related to a supershell around the Scorpius-Centaurus Association. The solar space trajectory indicates the Sun entered the CLIC gas relatively recently.

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arXiv2003

Local Interstellar Matter: The Apex Cloud

Several nearby individual low column density interstellar cloudlets have been identified based on kinematical features evident in high-resolution CaII observations near the Sun. One of these cloudlets, the ``Aquila-Ophiuchus'' cloud, is within 5 pc of the Sun and located in the solar apex direction. The velocity vector of this Apex Cloud is reevaluated and components at this velocity are found towards 17 stars with distances 1--60 pc, and located primarily in the galactic center hemisphere. The Apex Cloud is the most likely candidate for the ``next'' interstellar cloud to be encountered by the Sun.

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arXiv2003

Why Study Interstellar Matter Very Close to the Sun?

Interstellar matter (ISM) sets the boundary conditions of the heliosphere and dominates the interplanetary medium. The heliosphere configuration has varied over recent history, as the Sun emerged from the Local Bubble and entered a turbulent outflow of cloudlets originating from the Scorpius-Centaurus Association direction. Several indicators suggest that the local interstellar magnetic field is weak and parallel to the galactic plane. Observations of the interaction products of the ISM with the heliosphere, such as pickup ions and anomalous cosmic rays, when combined with data on the ISM towards nearby stars, provide unique constraints on the composition and physical properties of nearby gas. These data suggest abundances in nearby ISM are subsolar, and that gas and dust are not well mixed at the solar location.

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arXiv2002

Galactic Environment of the Sun and Stars: Interstellar and Interplanetary Material

Interstellar material surrounding an extrasolar planetary system interacts with the stellar wind to form the stellar astrosphere, and regulates the properties of the interplanetary medium and cosmic ray fluxes throughout the system. Advanced life and civilization developed on Earth during the time interval when the Sun was immersed in the vacuum of the Local Bubble and the heliosphere was large, and probably devoid of most anomalous and galactic cosmic rays. The Sun entered an outflow of diffuse cloud material from the Sco-Cen Association within the past several thousand years. By analogy with the Sun and solar system, the Galactic environment of an extrasolar planetary system must be a key component in understanding the distribution of systems with stable interplanetary environments, and inner planets which are shielded by stellar winds from interstellar matter (ISM), such as might be expected for stable planetary climates.

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arXiv2002

Constraining the Heliosphere: The Need for High-Resolution Observations of Nearby Interstellar Matter

High-resolution ultraviolet observations of nearby bright and faint stars are required to evaluate changes in the past and future galactic environments of the Sun, and the possibly impact of these changes on the interplanetary environment at 1 AU (around the Earth). The boundary conditions of the heliosphere and interplanetary environments are constrained by the characteristics of the surrounding interstellar material (ISM), which changes on timescales of 10^3-10^5 years. An increase in the density of the interstellar cloud surrounding the solar system to 10 cm^-3 decreases the heliosphere radius by about an order of magnitude. UV observations of nearby stars at high spectral resolution (>300,000) and high signal-to-noise are required to evaluate future modifications to heliosphere properties by the ISM.

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arXiv2002

The Velocity Distribution of the Nearest Interstellar Gas

The bulk flow velocity for the cluster of interstellar cloudlets within about 30 pc of the Sun is determined from optical and ultraviolet absorption line data, after omitting from the sample stars with circumstellar disks or variable emission lines and the active variable HR 1099. Ninety-six velocity components towards the remaining 60 stars yield a streaming velocity through the local standard of rest of -17.0+/-4.6 km/s, with an upstream direction of l=2.3 deg, b=-5.2 deg (using Hipparcos values for the solar apex motion). The velocity dispersion of the interstellar matter (ISM) within 30 pc is consistent with that of nearby diffuse clouds, but present statistics are inadequate to distinguish between a Gaussian or exponential distribution about the bulk flow velocity. The upstream direction of the bulk flow vector suggests an origin associated with the Loop I supernova remnant. Groupings of component velocities by region are seen, indicating regional departures from the bulk flow velocity or possibly separate clouds. The absorption components from the cloudlet feeding ISM into the solar system form one of the regional features. The nominal gradient between the velocities of upstream and downstream gas may be an artifact of the Sun's location near the edge of the local cloud complex. The Sun may emerge from the surrounding gas-patch within several thousand years.

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arXiv1999

The Galactic Environments of Nearby Cool Stars

The definition of nearby star systems is incomplete without an understanding of the dynamical interaction between the stars and ambient interstellar material. The Sun itself has been immersed in the Local Bubble interior void for millions of years, and entered the outflow of interstellar material from the Scorpius-Centaurus Association within the past $\sim10^5$ years. Heliosphere dimensions have been relatively large during this period. A subset of nearby stars have similar recent histories, and astrosphere properties are predictable providing ambient interstellar matter and stellar activity cycles are understood. The properties of astrospheres can be used to probe the interstellar medium, and in turn outer planets are more frequently immersed in raw interstellar material than inner planets.

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arXiv1999

The galactic environment of the Sun

The interstellar cloud surrounding the solar system regulates the galactic environment of the Sun and constrains the physical characteristics of the interplanetary medium. This paper compares interstellar dust grain properties observed within the solar system with dust properties inferred from observations of the cloud surrounding the solar system. Properties of diffuse clouds in the solar vicinity are discussed to gain insight into the properties of the diffuse cloud complex flowing past the Sun. Evidence is presented for changes in the galactic environment of the Sun within the next 10$^4$--10$^6$ years. The combined history of changes in the interstellar environment of the Sun, and solar activity cycles, will be recorded in the variability of the ratio of large- to medium-sized interstellar dust grains deposited onto geologically inert surfaces. Combining data from lunar core samples in the inner and outer solar system will assist in disentangling these two effects.

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arXiv1999

The Galactic Environments of Cool Stars - part I: Modeling Interstellar Dust around the Sun and Nearby Cool Stars

We present a model of the interaction of interstellar dust grains with a stellar environment, that predicts the distribution of interstellar dust grains in the size range between $0.1 {\rm μm}$ and $1 {\rm μm}$ around a star for the whole stellar cycle. Comparisons of the model results with in-situ dust measurements by the Ulysses spacecraft in the Solar System validate the model. We show that in the case of the Sun, interstellar dust grains can produce large regions of infrared emission that can be confused with a circumsolar dust disk when observed from afar. Our model can determine the shape of interstellar dust concentrations close to nearby stars, if we have information on the relative velocty of the stars with respect to the surrounding interstellar medium, and the properties of the stellar wind.

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arXiv1999

Dust in the Local Interstellar Wind

The gas-to-dust mass ratios found for interstellar dust within the Solar System, versus values determined astronomically for the cloud around the Solar System, suggest that large and small interstellar grains have separate histories, and that large interstellar grains preferentially detected by spacecraft are not formed exclusively by mass exchange with nearby interstellar gas. Observations by the Ulysses and Galileo satellites of the mass spectrum and flux rate of interstellar dust within the heliosphere are combined with information about the density, composition, and relative flow speed and direction of interstellar gas in the cloud surrounding the solar system to derive an in situ value for the gas-to-dust mass ratio, $R_{g/d} = 94^{+46}_{-38}$. Hubble observations of the cloud surrounding the solar system yield a gas-to-dust mass ratio of Rg/d=551+61-251 when B-star reference abundances are assumed. The exclusion of small dust grains from the heliosheath and heliosphere regions are modeled, increasing the discrepancy between interstellar and in situ observations. The shock destruction of interstellar grains is considered, and comparisons are made with interplanetary and presolar dust grains.

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arXiv1997

One- vs. Two-Shock Heliosphere: Constraining Models with GHRS LyA Spectra toward alpha Cen

Redshifted L$α$ absorption toward $α$ Cen has been interpreted by Linsky & Wood (1996) and Frisch et al. (1996) as evidence for decelerated interstellar hydrogen piled up on the upstream side of the heliosphere. We utilize newly developed two-dimensional multi-fluid models of the solar wind interaction with the ISM to corroborate this interpretation by synthesizing the L$α$ absorption profile predicted for this ``hydrogen wall''. Both subsonic and supersonic inflow into the heliosphere are considered, corresponding to one-shock and two-shock global morphologies, respectively. It is found that these two extremes give observably different redward absorption characteristics in the L$α$ profiles, and our preliminary conclusion is that the L$α$ profiles seen toward $α$ Cen favor a barely subsonic model (Mach number 0.9). For such a model to hold, additional interstellar pressure terms, such as cosmic ray or magnetic pressures, must contribute. To make this conclusion more certain, an extended model-parameter survey is required, coupled with L$α$ data along other lines of sight.

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arXiv1997

The Journey of the Sun

An analysis of the distribution and kinematics of interstellar material within 500 pc of the Sun leads to the conclusion that the galactic environment of the Sun changes with time. Consideration of evidence for interstellar gas interacting with the solar wind implies that these variations may alter the interplanetary environment of the Earth. The events causing the 10Be spikes 33,000 years and 60,000 years ago in the Antarctic ice record must be associated with the Local Fluff cloud complex, possibly due to solar encounters with structures with subparsec scale sizes. An encounter with "dense" interstellar cloud material could attenuate the solar L-alpha flux by as much as 70%, modify mesospheric chemistry, modify the magnetosphere-solar wind coupling, and alter the global electrical circuit. Prior to the entry of the Sun into the Local Fluff cloud complex, within the past 200,000 years, the galactic environment of the Sun differed radically from the environment prevailing today and expected for the near future.

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