To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure no-reply@cambridge.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
IAU Commission 5 deals with data management issues, and its working groups and task groups deal specifically with information handling, with data centres and networks, with technical aspects of collection, archiving, storage and dissemination of data, with designations and classification of astronomical objects, with library services, editorial policies, computer communications, ad hoc methodologies, and with various standards, reference frames, etc., FITS, astronomys Flexible Image Transport System, the major data exchange format, is controlled, maintained and updated by the Working Group FITS.
Division VIII provides a focus for astronomers studying a wide range of problems related to galaxies and cosmology. Objects of the study include individual galaxies, groups and clusters of galaxies, large scale structure, comic microwave background radiation and the universe itself. Approaches are diverse from observational one to theoretical one including computer simulations.
The Working Group was formed at the IAU XXV General Assembly in Sydney, 2003, as a joint initiative of Commissions 40 Radio Astronomy and Commission 41 History of Astronomy, in order to assemble a master list of surviving historically-significant radio telescopes and associated instrumentation found worldwide, and document the technical specifications and scientific achievements of these instruments. In addition, it would maintain an on-going bibliography of publications on the history of radio astronomy, and monitor other developments relating to the history of radio astronomy (including the deaths of pioneering radio astronomers).
The diversity of physical phenomena embraced by the study of Chemically Peculiar (CP) stars results in an associated research community with interests that are equally diverse. This fact became once more evident during the CP#Ap Workshop that took place in Vienna (Austria) in September 2007, and which gathered over 80 members of this research community. Besides the excellent scientific outcome of the meeting, during the workshop the community had the opportunity to discuss its organization and plans for the future. Following on those plans, the Working Group has submitted a proposal for a Joint Discussion during the IAU XXVII General Assembly, in Rio de Janeiro, which has meanwhile been accepted. Moreover, through an ApN newsletter forum, the Working Group has compiled requests from the community concerning atomic and related data. These requests have been put together and will be shared with Commission 14.
Division II of the IAU provides a forum for astronomers and astrophysicists studying a wide range of phenomena related to the structure, radiation and activity of the Sun, and its interaction with the Earth and the rest of the solar system. Division II encompasses three Commissions, 10, 12 and 49, and four Working Groups.
Research in atomic and molecular collision processes and spectral line broadening has been very active since our last report (Schultz & Stancil 2007, Allard & Peach 2007). Given the large volume of the published literature and the limited space available, we have attempted to identify work most relevant to astrophysics. Since our report is not comprehensive, additional publications can be found in the databases at the web addresses listed in the final section. Elastic and inelastic collisions among electrons, atoms, ions, and molecules are included and reactive processes are also considered, but except for charge exchange, they receive only sparse coverage.
Commission 21 consists of IAU members and consultants with expertise and interest in the study of the light of the night sky and its various diffuse components, at all accessible electromagnetic frequencies. In cosmic distance scales, the subjects of Commission 21 range from airglow and tropospheric scattering in Earth's atmosphere, through zodiacal light in the solar system, including thermal emission from interplanetary dust, integrated starlight in the Milky Way galaxy, diffuse galactic light due to dust scattering in the galactic diffuse interstellar medium, thermal emissions from interstellar dust and free free emission from ionized interstellar gas, to various diffuse extragalactic background sources, including the cosmologically important cosmic microwave background (CMB). Observations of the diffuse night sky brightness at any frequency typically include signals from several of these sources, and it has been the historic mandate of Commission 21 to foster the necessary collaboration of experts from the different astronomical sub-disciplines involved.
Star clusters are valuable tools for theoretical and observational astronomy across a wide range of disciplines from cosmology to stellar spectroscopy. For example, properties of globular clusters are used to constrain stellar evolutionary models, nucleosynthesis and chemical evolution, as well as the star formation and assembly histories of galaxies and the distribution of dark matter in present-day galaxies. Open clusters are widely used as stellar laboratories for the study of specific stellar phenomena (e.g., various emission-line stars, pulsating pre-MS stars, magnetic massive stars, binarity, stellar rotation, etc.). They also provide observational constraints on models of massive star evolution and of Galactic disk formation and chemical evolution.
This report is divided in four parts: the first part summarizes the activities of the Commission between September 2006 and June 2008; the second part reports on recent advances in the physical study of planets and satellites. However, instead of attempting to cover the large body of new knowledge gathered over the last three years, we have chosen to highlight just a few exciting results – on Mercury, the exploration of unchartered terrains with ground-based imaging and a new measurement of its libration parameters, some spectacular findings from the Cassini mission inside the Saturnian system, and the results of methane-band spectrophotometric monitoring of Saturn over the last 13 years; the third part summarizes future plans now being drawn by the various space agencies for the exploration of planets and satellites in the solar system; the last part tries to project the activities of the Commission over the period June 2008–August 2009, and to express a few thoughts concerning the future developments in the field, and the role of the Commission therein.
According to the IAU membership database, Commission 25 currently has 230 members from 40 countries. The Commission's membership represents 2.4% of the total IAU membership of 9658.
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.
During the period the Working Group had proposed and was granted renewed status by Division XI Space and High-Energy Astrophysics. Additionally the Working Group requested to be extended to Division IX Optical and Infrared Techniques, Division X Radio Astronomy, as well as Division XI.
Although we were happy to welcome over 20 new members at the Prague meeting, Commission 26 is still one of the smallest in the IAU. Notwithstanding its size, it continues to carry on an active and diversified program of activities. Our web site, maintained at the US Naval Observatory, contains further information on the Commission. The site includes links to other relevant sites, to databases and catalogues, an archive of our Information Circulars, a list of upcoming meetings of interest, as well as an extensive bibliography of recently published papers on double and multiple stars. The site can be accessed at <ad.usno.navy.mil/wds/dsl.html#iau>.
Our Working Group studies massive, luminous stars, with historical focus on early-type (OB) stars, but extending in recent years to include massive red supergiants that evolve from hot stars. There is also emphasis on the role of massive stars in other branches of astrophysics, particularly regarding starburst galaxies, the first stars, core-collapse gamma-ray bursts, and formation of massive stars.
In this contribution, we will take a broad view of active galactic nuclei (AGNs), but concentrating on emission-line phenonema. As a result, some interesting topics such as blazars and jets, connections with starbursts, and the environments of AGNs will receive little attention, although these are important topics and are discussed at length elsewhere.
It is useful to begin a discussion of AGNs with some history of the subject, partly because the history of how a scientific field is launched and develops over time is interesting and instructive, but primarily because it gives us some insight into the observed properties of AGNs, which is essential for distinguishing them from other objects in the sky. As we introduce the observational properties of these sources, at least the basis of the sometimes complicated taxonomy we use to describe active galaxies will become clear. An underlying theme throughout this discussion will be the principle of “AGN unification,” which posits that the diverse taxonomy of AGNs has more to do with observational circumstances, such as inclination and obscuration effects, than with intrinsic physical differences among various types of AGN. Considerable effort has been expended in attempts to explain the broadest range of phenomena with the most-limited range of physical mechanisms and structures.
The discovery and nature of active galaxies
The word “activity” in connection with phenomena in the nuclei of galaxies appears to have originated with Ambartsumian (1968).
The imaging method which uses narrow-band filters is the first and most direct way to obtain information about the emission lines. In contrast to broad-band photometry, in which several emission lines are integrated within one filter, the narrow-band filters are designed to transmit only one emission line (in ideal cases).
This method has considerable advantages over spectroscopic methods: we are able to obtain spatial resolution, i.e. several objects fit in only one exposure frame; the required time for an observation run is shortened; and lastly, the observation procedures and reduction are less complicated than those of a spectroscopic survey. Usually during a run information for only a few lines (three or four at best) can be obtained, in contrast to the full spectrum obtained in spectroscopy: see, for example, the works of Belley & Roy (1992), where hundreds of HII regions are presented with fluxes in three emission lines using direct imaging, and van Zee et al. (1998), with only about a dozen HII regions in ten different emission lines employing optical spectroscopy.
Narrow-band imaging is a powerful tool for characterizing the physical properties of the star-forming regions in nearby galaxies. With a few lines, we are able to determine, for example, the abundance, temperature, or initial mass function of the ionizing stars, thus obtaining clues to the physical processes that occur in the core of the HII regions; see, for example, Cedrés & Cepa (2002). This can be seen in Figure 8.1, where the composite broad-band image (with the B, R, and K bands) and an Hα image of the galaxy UCM 2325+2318 can be compared. The star-forming regions are clearly defined in the narrow-band image.
The goal of emission-line surveys is to identify a preselected class of astrophysical sources by means of emission lines in their spectral energy distribution. The techniques vary, depending on the sources, the spectral region and even the exact wavelength at which the observations are made, the desired sensitivity of the survey, and the volume of space that it aims to cover. But the basic methodology remains the same: exploiting the fact that emission lines in the spectrum of astronomical sources radiate significantly more luminosity over a relatively small wavelength interval than the continuum emission does over the same, or even larger, intervals in nearby portions of the spectrum. The excess luminosity, quantitatively expressed as the equivalent width of the line, enhances the signal-to-noise ratio of measures of the line flux for those sources whose emission lines satisfy the selection criteria of the survey, allowing the observer to cull them from otherwise similar sources.
Operationally, emission-line surveys exploit the presence of emission lines to substantially improve the detection rate of a particular class of astrophysical sources for which other methods of investigation would be significantly more inefficient or even outright impossible. The typical targets of these surveys are either sources that are too faint to detect by means of their continuum emission or sources that are rare and/or inconspicuous, and hence very difficult to recognize from all the other sources of similar apparent luminosity and/or morphology that crowd images made using the continuum emission.