The Local Interstellar Medium

The Local Interstellar Medium in 3D

The space between the stars is filled with gas and dust. Spectacular displays of this interstellar medium (ISM) can be found in star-forming regions where new stars are being created from the ISM, as well as in planetary nebulae and supernova remnants where old stars are returing much of their mass back into space. I explore the region just around the Sun, within approximately 100 pc, which is home to the local interstellar medium (LISM). Here we find a suite of warm, modest density, partially ionized clouds (see figure below).

I use high-resolution spectra of nearby stars acquired from the Hubble Space Telescope, which show absorption lines caused by these LISM clouds. This tenuous material can only be detected by the strongest atomic transitions, which are predominately found in the ultraviolet. This explains the recent growth of this field and our need for a space-based telescope.

Recent Papers On This Topic:

1. Evaluating the Morphology of the Local Interstellar Medium: Using New Data to Distinguish Between Multiple Discrete Clouds and a Continuous Medium     Redfield, S., & Linsky, J.L. 2015, ApJ, 812, 125

We use a new sample of HST observations to test between a LISM morphology of a single LISM cloud that is kinematically deformed or a multiple cloud model. We find the multiple cloud model is preferred, even though it utilizes more parameters.

2. The Structure of the Local Interstellar Medium. VI. New Mg II, Fe II, and Mn II Observations toward Stars within 100 pc    Malamut, C., Redfield, S., Linsky, J.L., Wood, B.E., & Ayres, T.R. 2014, ApJ, 787, 75

Lead by Wesleyan BA/MA student Craig Malamut, we analyzed the absorption lines of a sample of >30 new sight lines through the LISM. We tested the Redfield & Linsky (2008) kinematic model, refined an astrospheric detection, and found absorption due to the odd debris disk of 49 Ceti.

3. The Interstellar Medium Surrounding the Sun   Frisch, P.C., Redfield, S., & Slavin, J.D. 2011, ARAA, 49, 237

A review of our current understanding of the Local Interstellar Medium.

4. The Structure of the Local Interstellar Medium IV: Dynamics, Morphology, Physical Properties, and Implications of Cloud-Cloud Interactions   Redfield, S., & Linsky, J.L. 2008, ApJ, 673, 283

A new kinematic model of the suite of 15 clouds within about 15 pc of the Sun. An online LISM Kinematic Calculator is available to predict the velocity of absorption along any given sight line.

5. What is the Total Deuterium Abundance in the Local Galactic Disk?   Linsky, J.L., Draine, B.T., Moos, H.W., Jenkins, E.B., Wood, B.E., Oliveira, C., Blair, W.P., Friedman, S.D., Gry, C., Knauth, D., Lacour, S., Lehner, N., Redfield, S., Shull, J.M., Sonneborn, G., & Williger,G.M. 2006, ApJ, 647, 1106

A detailed evaluation of deuterium abundances throughout the Galaxy. In the LISM, the ratio of deuterium to hydrogen is constant, arguing for a common origin or evolution.

6. The Three-dimensional Structure of the Warm Local Interstellar Medium. II. The Colorado Model of the Local Interstellar Cloud   Redfield, S., & Linsky, J.L. 2000, ApJ, 534, 825

My first paper on the LISM that I led, and the beginning of a long series of papers with my Ph.D. advisor, Jeff Linsky. We developed a model of the morphology of the Local Interstellar Cloud, the cloud that directly surrounds the solar system, and the material in which the Voyager spacecraft are speeding into. An online LIC Model Column Density Calculator is available to predict the amount of material associated with the LIC along any given sight line. This work was featured in Physics Today and Sky & Telescope.

Astrospheres: When Stars Meet ISM

Stars have outward moving winds (sometimes clumps in these winds hit the Earth and cause dramatic aurorae), while the surrounding ISM acts to confine this wind. This interaction creates the heliosphere, in the case of the Sun, and astrospheres, more generally around any star. A schematic of this interaction is shown below.

It is possible to measure the astrospheric interface in the strongest transtion of the most abundant element, hydrogen, specifically the Lyman-α line. If we know the properties of the LISM, we can then deduce the properties of the stellar wind. Because stellar winds have such a profound influence on planetary atmospheres, I am intrigued by this connection between my research areas of the LISM and exoplanetary atmospheres.

Recent Papers On This Topic:

1. The Interstellar Medium in the Kepler Search Volume   Johnson, M.C., Redfield, S., & Jensen, A.G. 2015, ApJ, 807, 162

Inspired by a trip to McDonald Observatory by myself and a senior undergraduate, Marshall Johnson. We analyzed the ISM properties in the Kepler volume and predicted the astrospheric properties for several planetary systems. This work was featured in New Scientist.

2. Evidence for a Weak Wind from the Young Sun   Wood, B.E., Müller, H.-R., Redfield, S., & Edelman, E. 2014, ApJL, 781, L33

We detected the astrosphere of a youthful solar analog. The ISM analysis was performed by BA/MA Eric Edelman.

3. A New Detection of LYα Absorption from the Heliotail   Wood, B.E., Izmodenov, V.V., Alexashov, D.B., Redfield, S., & Edelman, E. 2014, ApJ, 780, 108

We detected heliospheric absorption in the direction of the cometary-like tail of the heliosphere as it speeds through the LISM. The ISM analysis was perfored by BA/MA Eric Edelman.

4. Probing Our Heliospheric History. I. High-resolution Observations of Na I and Ca II along the Solar Historical Trajectory   Wyman, K., & Redfield, S. 2013, ApJ, 773, 96

We analyzed a large sample of ground-based ISM observations along the direction of that the Sun has traveled over the last 40 million years. This interstellar "ice-core" allows us to reconstruct the ISM environments that the Sun may have traversed over this time, and thereby predict the heliospheric response to these interstellar conditions. This was lead by MA student, Katherine Wyman.

5. New Mass Loss Measurements from Astrospheric Lyα Absorption   Wood, B.E., Müller, H.-R., Zank, G.P., Linsky, J.L., & Redfield, S. 2005, ApJL, 628, L143

We present several new astrospheric detections, bringing the total to around a dozen. This kind of measurement can only be done with high-resolution ultraviolet spectra observed from space.