Assuming that the extended emission (EE) with broad dynamic range is a common property ofshort duration bursts, we propose a two-jet model which can describe both short mainepisode of hard spectra emission, specific for short bursts, and softer spectra EE by thedifferent off axis position of the observer. The model involves a short-duration jet,which is powered by heating due to νν̅ annihilation, and a long-lived Blandford–Znajek (BZ)jet with a significantly narrow opening angle. We also discuss observational tests oftwo-jet model.

Large amounts of invisible matter have been discovered back in 1933 when the Swiss astronomer Fritz Zwicky measured for the first time the velocity dispersion of individual galaxies inside the Coma cluster. Since then, this pioneering observation has been confirmed on scales ranging from galactic radii to cosmological distances. The existence of the so–called astronomical dark matter is now well established. The puzzle lies in the fact that this essential component of the universe is not made of ordinary atoms and electrons. The astronomical dark matter is indeed non–baryonic. Its nature is still an unresolved issue. Many theoretical ideas and proposals have flourished in the past thirty years and yet none of them provides a definite answer. I have the challenging task to introduce the cohort of these dark matter candidates to you. They make up a bestiary of exotic species which have been recently proliferating. Instead of a liste à la Prévert, I will present a tentative classification of the various models.

Multi-epoch, high-resolution (R ∼ 50 000) optical spectrosco-py of the O-type (O9 III – IV) star HD 152246 suggests that it is a triple system where a close inner pair (Aa–Ab) with a circular orbit and a period of 6 days is in a 53–d eccentric orbit (e = 0.68) with a third component Ac. The mass ratios for the inner and outer system are 0.10 and 0.96, respectively. The strengths of various He lines classify Aa and Ac as late O-type stars while Ab is invisible in our spectra.

We present the results of an all sky survey for binary systems among the massive stars that we made with the HST Fine Guidance Sensors. The sample of 225 stars is comprised mainly of Galactic O- and B-type stars and Luminous Blue Variables, plus a few luminous stars in the LMC. The FGS TRANS mode observations are sensitive to detection of companions with an angular separation of 0.01–1 arcsec and brighter than △m = 5 mag. The FGS observations resolved 52 binary and 6 triple star systems and detected partially resolved binaries in 7 additional targets, yielding a companion detection frequency of 29%. We also gathered literature results on the numbers of close spectroscopic binaries and wider astrometric binaries among the sample. These results confirm the high multiplicity fraction. The period distribution is essentially flat in increments of log P, although there remains an observational gap in detections for periods of years and decades.

The Very Large Telescope (VLT) Observatory on Cerro Paranal (2635 m) in Northern Chile is approaching completion. After the four 8-m Unit Telescopes (UT) individually saw first light in the last years, two of them were combined for the first time on October 30, 2001 to form a stellar interferometer, the VLT Interferometer. The remaining two UTs will be integrated into the interferometric array later this year, so that any two UTs can be used for interferometry. In this article, we will describe the subsystems of the VLTI and the planning for the following years.

Spectral data reduction is a crucial step, as so important as the acquisition process. Rigor shall be as well applied at this stage to not degrade the quality of the data acquired. It is the last step before the computation of the astrophysical quantities. It is thus necessary to understand what is involved in each processing steps and the underlying limitations. Thus limitations or limit conditions are usually embedded and then hidden in a specific software command that everyone use without completely mastering what is really at stake. In this chapter we will introduced the different type of processing and spectral analysis which can dispose an amateur in several software packages. The first processing will treat about basic images correction which are linked to the CCD acquisition and the processes pipeline. We will then describe the different strategy to calibrate the spectral profile in wavelength and the few corrections driven by the earth environment to increase the accuracy of the future measurements. We will end with the description of few tools on quantitative spectral analysis and their limitations. The practice of spectral acquisition and processing is just at its beginning in amateur world. We hope that this section will demystify the essential step of spectral processing and will motivate the amateur to go beyond the contemplative watching of sky wonders.

Recent observations of broad-band afterglow of gamma-ray bursts (GRBs) suggest that thestandard external shock model cannot account for all the data. The observed “afterglow” ofsome GRBs includes the contributions from at least three emission components.Theoretically, there are naturally three emission sites. Besides the traditional externalforward shock, the existence of X-ray flares demands late central engine activities of theGRB central engine, so that an “internal dissipation” region of the late wind is anotheremission site. After dissipation, this late wind would inevitably catch up with theblastwave, giving rise to a third emission site at a long-lasting reverse shock. Somerecent efforts in understanding the broadband afterglow are reviewed.

The BATSE experiment on the Compton Gamma-ray Observatory was the first large detectorsystem designed for the study of gamma-ray bursts. The eight large-area detectors allowedfull-sky coverage and were optimized to operate in the primary energy region of emissionof most GRBs. BATSE provided detailed observations of the temporal and spectralcharacteristics of several thousand GRBs, and it was the first experiment to provide rapidnotifications of the coarse location of many them. It also provided strong evidence forthe cosmological distances to GRBs through the observation of the sky distribution andintensity distribution of numerous GRBs. The large number of GRBs observed with the high-sensitivity BATSE detectors continues to provide a database of GRB spectral and temporalproperties in the primary energy range of GRB emission that will likely not be exceededfor at least another decade. The origin and development of the BATSE experiment, somehighlights from the mission and its continuing legacy are described in this paper.

It has been claimed in the past that in low-metallicity Blue Compact Dwarf (BCDs) galaxies, the N/O value is independent of metallicity (O/H ratio), implying the need to invoke a primary production of nitrogen in intermediate-mass stars, in addition to the secondary nitrogen produced from the CNO cycle in high-mass stars. In order to better understand this controversial issue we undertook an integral field spectroscopic study of the nebular gas within a sample of BCDs previously thought to have anomalously high N/O values. Here we present the results of this study for 3 BCDs: two with anomalous N/O values (Mrk 996 and UM 420) and one with more normal N/O values (UM 462). We describe in detail how we derived the physical conditions (Te, Ne) as a function of position within the galaxy, and as a consequence, how this revealed both revised metallicities and normal N/O ratios and uncovered one of the first clear evidences of nitrogen self-enrichment of an H ii  region from WR stars.

A review of some of the most important studies of the past several decades pertaining to the study of atomic diffusion in stellar atmospheres is presented. A brief description of various studies of radiative accelerations and diffusion calculations in stellar atmospheres is given. Several physical phenomena such as ambipolar diffusion, light-induced drift and the effect of magnetic fields on diffusion are discussed. Results from recent self-consistent model atmospheres including elemental stratification are also reviewed. Particularities of radiative acceleration calculations in stellar atmospheres as well as difficulties and future challenges related to diffusion calculations in stellar atmospheres are also presented.

Because of their very red colours and intrinsic faintness, field browndwarfs will represent a small but valuable subset of the GAIAcatalogue. The return of the astrometric satellite is expected to beimportant because of the inherent difficulty of obtaining goodparallaxes in general and for this class of objects in particular. Ourfirst estimates show that, due to the photometric sensitivity of theastrometric CCD (ASM1) towards relatively blue objects, GAIA isunlikely to detect field brown dwarfs that have not been already seenis previous near-IR surveys, to the notable exception of the galacticplane region. The real advantage of GAIA over ground-based surveyswill be the very accurate (to within a few percents) astrometric datafor a few thousands brown dwarfs. These data should permit a detailedmapping of the transition region between stellar and substellarregimes, together with the kinematical and density patterns of theyoungest brown dwarfs in our neighbourhood.

We present a method for knowledge analysis in large astronomical spectrophotometric archives. The method is based on a type of unsupervised learning Artificial Neural Networks named Self-organizing maps (SOMs). SOMs are used to organize the information in clusters of objects, as homogeneously as possible according to their spectral energy distributions, and to project them onto a 2D grid where the data structure can be visualized.

Our algorithm has been tested by means of simulated Gaia spectrophotometry (150,000 objects), which is based on SDSS observations and theoretical spectral libraries covering a wide sample of astronomical objects. We demonstrate the usefulness of the method by analyzing over 10,000 objects, mostly fainted objects and unsuccessful observations, that were rejected by the SDSS spectroscopic classification pipeline and thus classified as “UNKNOWN”. This dataset was transformed to Gaia BP and RP format by the use of GOG simulator.

GUASOM provides a useful toolbox to study the data distribution in extense archives. Even more, the discovered neighbourhood relationships help to unveil the physical nature of objects never observed before. To this effect, we used the SIMBAD catalog to perform crossmatching with the SDSS astrometry, seeking for more identifications.

Type Ia supernovae are thought to be the outcome of the thermonuclear explosion of a carbon–oxygen white dwarf in a close binary system. In this review we discuss the observational background, the possible progenitors, the mechanisms leading to the instability and the development of the explosion itself as well as the remaining uncertainties.

The three instruments on the Herschel Space Observatory, HIFI, SPIRE, and PACS, cover together over a decade in frequency, from 450 GHz to 5000 GHz, with spectral resolutions δν/ν between 0.3 and 10-6. The equivalent temperature range, defined by T = hν/k is 21 K ≤ Teq ≤ 240 K, and thus for dust emission, Herschel will cover the peak of the Planck function in many sources associated with both quiescent and star-forming molecular clouds, both in the Milky Way and other galaxies. The temperature equivalence of the Herschel frequency range also means that essentially all portions of giant molecular clouds will be well probed by the many spectral lines in the Herschel wavelength range of 0.67 mm to 60 µm. My focus in this paper is on gas phase spectral lines of molecules, atoms, and ions, which will be well resolved with the heterodyne receivers on HIFI, but typically not resolved in Galactic sources with the other two instruments. Kinematic interpretation of spectral lines with HIFI is of great interest, along with determination of temperature, density, and column density. I briefly summarize in this review the most important species for Herschel observations, and discuss how one can derive important astronomical quantities from data obtained with the Herschel Space Observatory. Along with describing techniques for analyzing data from the Herschel instruments, I will cover briefly what supplementary ground–based observations are necessary to extract the most from the valuable observing time of the space–based facility.

This paper analyses cosmological observations within inhomogeneous and exact solutions of the Einstein equations. In some way the analyses presented here can be freed from assumptions such as small amplitude of the density contrast.The supernova observations are analysed using the Lemaître–Tolman model and the CMB observations are analysed using the quasispherical Szekeres model.The results show that it is possible to fit the supernova datawithout the cosmological constant. However ifinhomogeneities of sizes and amplitudes as observed in the local Universeare considered, their impact on cosmological observations is small.

We analyze two X-shooter spectra of the GRB 120327A afterglow, acquired    2.1 and    30hrs after the trigger. The ISM in the GRB host galaxy at z = 2.8145 isextremely rich in absorption features, with three components contributing to the lineprofiles. The hydrogen column density associated with GRB 120327A islog NHI / cm2 = 22.01 ± 0.09,and the metallicity of the host galaxy is in the range [X/H] =  − 1.7 to  − 1 with respectto the solar values, i.e., a typical value for a GRB host galaxy. Inaddition to the ground state lines, we detect in the first observation several excitedabsorption features, which disappeared in the second observation. Using these features, wederive that component I is at dI = 200+100-60 pc from the GRB, while component II is located closer,at dII = 100+4030 pc. These values are among the lowest found in GRBs.Comparing the abundances with star formation history models, we find that the GRB 120327Ahost galaxy abundances are compatible with a star formation efficiency of 10Gyr-1, typical of spheroids (elliptical or bulge).

We investigate the nature of the clumpy structures seen at high redshift.For this we use a 3D chemodynamical simulationincluding dark matter, stars and a multiphase interstellar medium aswell as feedback processes from the stars. The infall of baryonicmatter leads to the formation of a disk which later fragments anddevelops starforming sub-galactic clumps. Calculating U, B, V, Kcolors of the model including absorption by interstellar material wefind similar morphology and colors as for multiple clump and chaingalaxies in the HDF.

Based on my direct personal experience as an author, referee, editor, and PhD thesissupervisor, I present in this paper some advice and guidelines on writing scientificpapers. This article copes with the preparation of manuscripts, with the handling ofcopyrights and permissions to reproduce, with communicating with editors and referees, andwith avoiding common errors. More than two dozen FAQs are dealt with, among others: whoshould be coauthor, what is honorary authorship, how to settle the order of author names,may the list of authors change during the review process, who submits the manuscript tothe Editor, must one wait for coauthors’ consent to submit, when to submit a manuscript toastro-ph, how to communicate with the referee, with whom to share a referee report, canstudents be referee, how to cite and quote a straying paper, how to cope with writer’sblock, should others be allowed to completely rewrite a manuscript, how to review a paper,how to revise a multi-author paper, when to ask for another referee, why do Editors edit,and why do referees review?

Searches for planets around massive stars are essential for developing general understanding of planet formation and evolution of planetary systems. The main objective of the PSU-TCfA Search for Planets around Evolved Stars is detection of planets around G-K subgiants and giants through highly accurate radial velocity (RV) measurements using an iodine absorption cell on the HET HRS spectrograph. However, the long-period radial velocity variations of red giants may also have other causes than planets (e.g. non-radial pulsations or rotational modulation in the presence of starspots). In this work, for the second red giant with planets found in our survey, HD 102272, we present bisector analysis of cross-correlation functions (CCF) constructed from the spectra used for radial velocity determination but cleaned from the iodine lines.