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Radio synchrotron emission, its polarization and its Faraday rotation are powerful tools to study the strength and structure of interstellar magnetic fields. The total intensity traces the strength and distribution of total magnetic fields. Total fields in gas-rich spiral arms and bars of nearby galaxies have strengths of 20–30 μGauss, due to the amplification of turbulent fields, and are dynamically important. In the Milky Way, the total field strength is about 6 μG near the Sun and several 100 μG in filaments near the Galactic Center. – The polarized intensity measures ordered fields with a preferred orientation, which can be regular or anisotropic fields. Ordered fields with spiral structure exist in grand-design, barred, flocculent and even in irregular galaxies. The strongest ordered fields are found in interarm regions, sometimes forming “magnetic spiral arms” between the optical arms. Halo fields are X-shaped, probably due to outflows. – The Faraday rotation of the polarization vectors traces coherent regular fields which have a preferred direction. In some galaxies Faraday rotation reveals large-scale patterns which are signatures of dynamo fields. However, in most galaxies the field has a complicated structure and interacts with local gas flows. In the Milky Way, diffuse polarized radio emission and Faraday rotation of the polarized emission from pulsars and background sources show many small-scale and large-scale magnetic features, but the overall field structure in our Galaxy is still under debate.
Organic compounds are ubiquitous in space: they are found in diffuse clouds, in the envelopes of evolved stars, in dense star-forming regions, in protoplanetary disks, in comets, on the surfaces of minor planets, and in meteorites and interplanetary dust particles. This brief overview summarizes the observational evidence for the types of organics found in these regions, with emphasis on recent developments. The Stardust sample-return mission provides the first opportunity to study primitive cometary material with sophisticated equipment on Earth. Similarities and differences between the types of compounds in different regions are discussed in the context of the processes that can modify them. The importance of laboratory astrophysics is emphasized.
Forecasting the next 50 years of space research is a dangerous game and a somewhat irresponsible action. Fortunately, the past 50 years have evidenced what remains in the realm of realism and of the feasible and what definitely belongs to the realm of utopia. Nevertheless those who, like me today, take the risk of forecasting such a relatively long time trend are sure of one thing: to be wrong!
The first stars were key drivers of early cosmic evolution. We review the main physical elements of the current consensus view, positing that the first stars were predominantly very massive. We continue with a discussion of important open questions that confront the standard model. Among them are uncertainties in the atomic and molecular physics of the hydrogen and helium gas, the multiplicity of stars that form in minihalos, and the possible existence of two separate modes of metal-free star formation.
Division I provides a focus for astronomers studying a wide range of problems related to fundamental physical phenomena such as time, the inertial reference frame, positions and proper motions of celestial objects and precise dynamical computation of the motions of bodies in stellar or planetary systems in the Universe.
In this introductory review, I summarize the path from the initial 1995 radial-velocity discovery of hot Jupiters to the current rich panoply of investigations that are afforded when such objects are observed to transit their parent stars. Forty transiting exoplanets are now known, and the time for that population to double has dropped below one year. Only for these objects do we have direct estimates of their masses and radii, and can we (at the current time) undertake direct studies of the chemistries and dynamics of their atmospheres. Informed by the successes of hot Jupiter studies, I outline a path for the spectroscopic study of certain habitable exoplanets that obviates the need for direct imaging.
With ever changing solar abundances being reported the equation of state and opacities needed for stellar evolution models also change. A discussion of those changes in mean molecular opacities will be presented with a discussion on the effect on evolution models. Aside from changing the abundances of the base mixture the enrichment changes too. Traditionally mean opacity tables are produced for oxygen-rich mixtures, however stars will often become carbon-rich. A discussion of carbon-rich opacities tables will also be presented.
It is known that more than 140 interstellar and circumstellar molecules have so far been detected, mainly by means of the radio astronomy observations. Many organic molecules are also detected, including alcohols, ketons, ethers, aldehydes, and others, that are distributed from dark clouds and hot cores in the giant molecular clouds. It is believed that most of the organic molecules in space are synthesized through the grain surface reactions, and are evaporated from the grain surface when they are heated up by the UV radiation from adjacent stars.
On the other hand the recent claim on the detection of glycine have raised an important issue how difficult it is to confirm secure detection of weak spectra from less abundant organic molecules in the interstellar molecular cloud.
I will review recent survey observations of organic molecules in the interstellar molecular clouds, including independent observations of glycine by the 45 m radio telescope in Japan, and will discuss the procedure to securely identify weak spectral lines from organic molecules and the importance of laboratory measurement of organic species.
The star-formation histories of the main stellar components of the Milky Way constrain critical aspects of galaxy formation and evolution. I discuss recent determinations of such histories, together with their interpretation in terms of theories of disk galaxy evolution.
The sample of available Galactic pulsar rotation measures has proven an invaluable tool for measuring the direction and magnitude of the interstellar magnetic fields of our Galaxy. In this review, I present highlights of recent efforts to measure and map the Galactic magnetic field using pulsars. I give an overview of the analysis methods that were used by previous authors and underline the key results that have given us a clear picture of the magnetic field in certain regions of the Galaxy. This review also lays out the limitations of the present analysis methods and the observational difficulties that have so far hindered the study of the Galactic magnetic field with pulsars. Despite these difficulties, the continuous discovery of new pulsars in more and more sensitive surveys offer a continuous improvement on the existing knowledge of the Galactic magnetic field.
We study the formation of primordial proto-stars in a ΛCDM universe using ultra high-resolution cosmological simulations. Our approach includes all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to “stellar” densities. We describe the numerical implementation of the physics. We also show the result of a simulation of the formation of primordial stars in a reionized gas.
The solar chemical composition has recently undergone a drastic revision, in particular in terms of the C, N, O and Ne abundances that have been lowered by almost a factor of two. In this invited review I will describe the different compounding reasons for this change (3D model atmospheres, non-LTE line formation, improved atomic/molecular data) and discuss some astrophysical implications thereof, which fall under both good (solar neighborhood) and bad (helioseismology) news. The most recent literature regarding the solar O abundance is surveyed and a critical evaluation whether or not these support the low solar abundance scale is presented. Finally I venture to make some predictions to what the real solar O abundance may be.
The recycling of matter between the interstellar medium (ISM) and stars are key evolutionary drivers of a galaxy's baryonic matter. The Spitzer wavelengths provide a sensitive probe of circumstellar and interstellar dust and hence, allow us to study the physical processes of the ISM, the formation of new stars and the injection of mass by evolved stars and their relationships on the galaxy-wide scale of the LMC. Due to its proximity, favorable viewing angle, multi-wavelength information, and measured tidal interactions with the Small Magellanic Cloud (SMC), the LMC is uniquely suited for surveying the agents of a galaxy's evolution (SAGE), the ISM and stars. The SAGE-LMC project is measuring these key transition points in the life cycle of baryonic matter in the LMC. Here we present a connective view of the preliminary quantities estimated from SAGE-LMC for the total mass of the ISM, the galaxy wide star formation rate and the current stellar mass loss return. For context, we compare these numbers to the LMC's stellar mass.
JPL planetary ephemeris development has been very active assimilating measurements from current planetary missions and supporting future missions. The NASA Mars Science Laboratory (MSL) mission with launch in 2009 requires knowledge of the Earth and Mars ephemerides with 30m accuracy. By comparison, the accuracy of the Mars ephemeris in the widely used DE405 ephemeris was about 3 km. Meeting the MSL needs requires an ongoing program of range and very-long baseline interferometry measurements of Mars orbiting spacecraft. The JPL ephemeris DE421 was released three months before the landing of the Phoenix mission on Mars, and has met the 300m requirement. Continued measurements are planned to support the MSL landing.
Together with the discovery of the accelerated expansion of the present Universe and measurements of large-scale structure at low redshift, observations of the cosmic microwave background have established a standard paradigm in which all cosmic structure grew from small fluctuations generated at very early times in a flat universe which today consists of 72% dark energy, 23.5% dark matter and 4.5% ordinary baryons. The CMB sky provides us with a direct image of this universe when it was 400,000 years old and very nearly uniform. The galaxy formation problem is then to understand how observed galaxies with all their regularity and diversity arose from these very simple initial conditions. Although gravity is the prime driver, many physical processes appear to play an important role in this transformation, and direct numerical simulation has become the principal tool for detailed investigation of the complex and strongly nonlinear interactions between them.
The evolution of structure in the gravitationally dominant Cold Dark Matter distribution can now be simulated in great detail, provided the effects of the baryons are ignored, and there is general consensus for the results on scales relevant to the formation of galaxies like our own. The basic nonlinear units are so-called “dark matter halos”, slowly rotating, triaxial, quasi-equilibrium systems with a universal cusped density profile and substantial substructure in the form of a host of much less massive subhalos which are concentrated primarily in their outer regions.
Attempts to include the baryons, and so to model the formation of the visible parts of galaxies, have given much more diverse results. It has been known for 30 years that substantial feedback, presumably from stellar winds and supernovae, is required to prevent overcooling of gas and excessive star formation in the early stages of galaxy assembly. When realistic galaxy formation simulations first became possible in the early 1990's, this problem was immediately confirmed. Without effective feedback, typical halos produced galaxies which were too massive, too concentrated and had too little disk to be consistent with observation.
Simple models for disk formation from the mid 1990's show that the angular momentum predicted for collapsing dark halos is sufficient for them to build a disk population similar to that observed. Direct simulations have repeatedly failed to confirm this picture, however, because nonlinear effects lead to substantial transfer of angular momentum between the various components. In most cases the condensing baryonic material loses angular momentum to the dark matter, and the final galaxy ends up with a disk that is too compact or contains too small a fraction of the stars.
These problems have been reduced as successive generations of simulations have dramatically improved the numerical resolution and have introduced “better” implementations of feedback (i.e. more successful at building disks). Despite this, no high-resolution simulation has so far been able to produce a present-day disk galaxy with a bulge-to-disk mass ratio much less than one in a proper ΛCDM context. Such galaxies are common in the real Universe; our own Milky Way is a good example. The variety of results obtained by different groups show that this issue is very sensitive to how star formation and feedback are treated, and all implementations of these processes to date have been much too schematic to be confident of their predictions.
The major outstanding issues I see related to disk galaxies and their formation are the following: Do real disk galaxies have the NFW halos predicted by the ΛCDM cosmology? If not, could the deviations have been produced by the formation of the observed baryonic components, or must the basic structure formation picture be changed? How are Sc and later type galaxies made? Why don't our simulations produce them? What determines which galaxies become barred and which not? Can we demonstrate that secular evolution produces the observed population of (pseudo)bulges from pre-existing disks? How does the observed population of thin disks survive bombardment by substructure and the other transient potential fluctuations expected in ΛCDM halos? Is a better treatment of feedback really the answer? If so, can we demonstrate it using chemical abundances as fossil tracers? And how can we best use observations at high redshift to clarify these formation issues?
This paper reviews the basic technical characteristics of the ground-based photometric searches for transiting planets, and discusses a possible observational selection effect. I suggest that additional photometric observations of the already observed fields might discover new transiting planets with periods around 4–6 days. The set of known transiting planets supports the intriguing correlation between the planetary mass and the orbital period suggested already in 2005.
The structure of the Universe is determined primarily by the interplay of gravity which is dominant in condensed objects, and the magnetic force which is dominant in the rarefied medium between condensed objects. Each of these forces orders the matter into a set of characteristic structures each with the ability to store and release energy in response to changes in the external environment. For the most part, the storage and release of energy proceeds through a number of Universal Processes. The coordinated study of these processes in different settings provides a deeper understanding of the underlying physics governing Universal Processes in astrophysics.