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2 Planets, Star Formation, and the Interstellar Medium
Pages 10-20

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From page 10...
... KEY THEMES The fundamental scientific goal in studies of star formation and the interstellar medium is to understand how stars and planets form and how habitable environments might arise from the evolving interstellar medium in galaxies. This goal can be subdivided into three themes that link the formation of planets like Earth to the formation and evolution of galaxies: · Formation and evolution of planetary systems; · Formation of stars from the interstellar medium; and · Evolution of the interstellar medium in galaxies.
From page 11...
... Recent Progress in Understanding the Formation and Evolution of Planetary Systems The past 2 years have seen the culmination of a decades-long search for planets around normal, nearby stars. Nearly one dozen stars are now known to have planets with masses ranging from a few tenths to a few times the mass of Jupiter and with orbits at distances ranging from a few hundredths of an astronomical unit to a few
From page 12...
... It is preferable to attempt detection of extrasolar terrestrial planets around nearby stars by astrometry at the 1-microarc see level, so that follow-up observations can be made of the planets and their associated planetary systems. However, observations of more distant planets, by photometry or gravitational microlensing, might provide statistical evidence regarding the frequency of occurrence of terrestrial planets.
From page 13...
... The long-term dynamical evolution of planetary systems may also ' account for the debris disks observed around 15 to 20% of main sequence A-K stars, and for the 'formation and evolution of the Kuiper Belt in the solar system. ~O ~O FORMATION OF STARS FROM THE INTERSTELLAR MEDIUM Knowledge of how stars form is critical to understanding both the origin and evolution of systems of stars, such as galaxies, and the origin and evolution of planetary systems.
From page 14...
... Observers still have not achieved an unambiguous identification of a protostellar object. Key Questions About Star Formation important questions about the formation of stars from the interstellar medium include the following: Core Collapse · What are the properties of protostellar cores in giant molecular clouds?
From page 15...
... observations have also detected disks and gaseous globules around low-mass stars in regions of massive star formation, providing a new approach to the study of such disks (Figure 2.1~. Deep-infrared imaging of giant molecular clouds has revealed that star formation occurs exclusively in dense molecular cores and that a significant, and perhaps dominant, fraction of all stars form in rich stellar clusters generally embedded in the most massive molecular cores.
From page 16...
... On larger scales they need to understand the rate and extent of the dispersal of hot gas, ionizing photons, and nucleosynthetic products throughout the galactic disk and halo. Most generally, investigations of the interstellar medium of galaxies may answer fundamental questions such as the following: What triggers star formation in a galaxy?
From page 17...
... Physical Properties of the Diffuse Interstellar Medium · What are the physical properties of He different phases of the interstellar gas: the cold and warm neutral media, the warm ionized medium, and the hot ionized medium? · What is the spatial distribution of these components within the galaxy, on both the scale of clouds and the much larger scale of spiral arms?
From page 18...
... Similarly, mid-infrared spectroscopy from ISO shows the great value of measuring astrophysical conditions in diffuse atomic and molecular gas. Probes of the hot gas in the local interstellar medium have been provided by ROSAT, which measures soft xray emission from gas at 106 to 107 K
From page 19...
... Answering these questions presents a major technological challenge owing to the enormous range of scales involved from the size of galaxies to the size of planets and the range of wavelengths over which observations must be made, from x rays for the hot gas in galactic disks to millimeter and submillimeter radiation for the cold gas and dust in protostellar disks. The greatest gap in current knowledge is at the smallest scales, and motivates the long-term goals of developing systems that can obtain spectra of terrestrial planets around nearby stars and image protoplanetary disks in nearby star-formin~ regions.
From page 20...
... This project could be done by mapping the galaxy at high spectral resolution (<10 km/s) and moderate angular resolution (<30 arc min)


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