Astrophysics in 2006

The fastest pulsar and the slowest nova; the oldest galaxies and the youngest stars; the weirdest life forms and the commonest dwarfs; the highest energy particles and the lowest energy photons. These were some of the extremes of Astrophysics 2006. We attempt also to bring you updates on things of which there is currently only one (habitable planets, the Sun, and the universe) and others of which there are always many, like meteors and molecules, black holes and binaries.Comment: 244 pages, no figure

Towards an Understanding of the Globular Cluster Over--abundance around the Central Giant Elliptical NGC 1399

We investigate the kinematics of a combined sample of 74 globular clusters around NGC 1399. Their high velocity dispersion, increasing with radius, supports their association with the gravitational potential of the galaxy cluster rather than with that of NGC 1399 itself. We find no evidence for rotation in the full sample, although some indication for rotation in the outer regions. The data do not allow us to detect differences between the kinematics of the blue and red sub-populations of globular clusters. A comparison between the globular cluster systems of NGC 1399 and those of NGC 1404 and NGC 1380 indicates that the globular clusters in all three galaxies are likely to have formed via similar mechanisms and at similar epochs. The only property which distinguishes the NGC 1399 globular cluster system from these others is that it is ten times more abundant. We summarize the evidence for associating these excess globulars with the galaxy cluster rather than with NGC 1399 itself, and suggest that the over-abundance can be explained by tidal stripping, at an early epoch, of neighboring galaxies and subsequent accumulation of globulars in the gravitational potential of the galaxy cluster.Comment: AJ accepted (March issue), 27 pages (6 figures included), AAS style, two columns. Also available at http://www.eso.org/~mkissle

The Panchromatic High-Resolution Spectroscopic Survey of Local Group Star Clusters - I. General Data Reduction Procedures for the VLT/X-shooter UVB and VIS arm

Our dataset contains spectroscopic observations of 29 globular clusters in the Magellanic Clouds and the Milky Way performed with VLT/X-shooter. Here we present detailed data reduction procedures for the VLT/X-shooter UVB and VIS arm. These are not restricted to our particular dataset, but are generally applicable to different kinds of X-shooter data without major limitation on the astronomical object of interest. ESO's X-shooter pipeline (v1.5.0) performs well and reliably for the wavelength calibration and the associated rectification procedure, yet we find several weaknesses in the reduction cascade that are addressed with additional calibration steps, such as bad pixel interpolation, flat fielding, and slit illumination corrections. Furthermore, the instrumental PSF is analytically modeled and used to reconstruct flux losses at slit transit and for optimally extracting point sources. Regular observations of spectrophotometric standard stars allow us to detect instrumental variability, which needs to be understood if a reliable absolute flux calibration is desired. A cascade of additional custom calibration steps is presented that allows for an absolute flux calibration uncertainty of less than ten percent under virtually every observational setup provided that the signal-to-noise ratio is sufficiently high. The optimal extraction increases the signal-to-noise ratio typically by a factor of 1.5, while simultaneously correcting for resulting flux losses. The wavelength calibration is found to be accurate to an uncertainty level of approximately 0.02 Angstrom. We find that most of the X-shooter systematics can be reliably modeled and corrected for. This offers the possibility of comparing observations on different nights and with different telescope pointings and instrumental setups, thereby facilitating a robust statistical analysis of large datasets.Comment: 22 pages, 18 figures, Accepted for publication in Astronomy & Astrophysics; V2 contains a minor change in the abstract. We note that we did not test X-shooter pipeline versions 2.0 or later. V3 contains an updated referenc

Процедура и результаты международных сличений эталона РЭМП и государственного эталона РФ

Описана методика процедури та висновки міжнародних двосторонніх звірень еталонів імпульсних електричних та магнітних полів України та Російської Федерації.The method of procedure and conclusions of international two-sided comparisons of standards the pulsed electrical and magnetic fields of Ukraine and Russian Federation is described

The Globular Cluster System of NGC 1399: III. VLT Spectroscopy and Database

Radial velocities of 468 globular clusters around NGC 1399, the central galaxy in the Fornax cluster, have been obtained with FORS2 and the Mask Exchange Unit (MXU) at the ESO Very Large Telescope. This is the largest sample of globular cluster velocities around any galaxy obtained so far. The mean velocity uncertainty is 50 km/sec. This data sample is accurate and large enough to be used in studies of the mass distribution of NGC 1399 and the properties of its globular cluster system. Here we describe the observations, the reduction procedure, and discuss the uncertainties of the resulting velocities. The complete sample of cluster velocities which is used in a dynamical study of NGC 1399 is tabulated. A subsample is compared with previously published values.Comment: 34 pages, 9 figures, 2 tables, accepted by A

M87, Globular Clusters, and Galactic Winds: Issues in Giant Galaxy Formation

New VRI photometry is presented for the globular clusters in the innermost 140'' of the M87 halo. The results are used to discuss several issues concerning the formation and evolution of globular cluster systems in supergiant ellipticals like M87. (1) we find no significant change in the globular cluster luminosity function (GCLF) with galactocentric radius, for cluster masses M < 10^5 solar masses, indicating that the main effects of dynamical evolution may be only on lower-mass clusters. (2) Within the core radius (1') of the globular cluster system, the metallicity distribution is uniform, but at larger radii the mean metallicity declines steadily as Z ~ r^-0.9. (3) The various options for explaining the existence of high specific frequency galaxies like M87 are evaluated, and scaling laws for the GCSs in these galaxies are given. Interpretations involving secondary evolution (formation of many globular clusters during mergers, intergalactic globular clusters, etc.) are unlikely to be the primary explanation for high-S_N galaxies. (4) We suggest that central-supergiant E galaxies may have formed in an exceptionally turbulent or high-density environment in which an early, powerful galactic wind drove out a high fraction of the protogalactic gas, thus artificially boosting the specificComment: 67 pages, 17 figures. To appear in Astronomical Journal, in press for May 1998. Preprints also available from W.Harris; send e-mail request to [email protected]

Horizontal-Branch Morphology and the Photometric Evolution of Old Stellar Populations

Theoretical integrated broad-band colors ranging from far-UV to near-IR have been computed for old stellar systems from our evolutionary population synthesis code. These models take into account, for the first time, the detailed systematic variation of horizontal-branch (HB) morphology with age and metallicity. Our models show that some temperature-sensitive color indices are significantly affected by the presence of `blue HB stars'. Our models are calibrated in the B-V, V-I, C-T1, and M-T1 vs. [Fe/H] planes, using low-reddened Galactic globular clusters (GCs) [E(B-V) < 0.2] and the relative age difference between the older inner halo Galactic GCs and younger outer halo counterparts is well reproduced. Several empirical linear color-metallicity transformation relations are assessed with our models and it is noted that they may not be safely used to estimate metallicity if there are sizable age differences amongst GCs within and between galaxies. It is anticipated that the detailed population models presented here coupled with further precise spectrophotometric observations of globular cluster systems in external galaxies from the large ground-based telescopes and space UV facilities will enable us to accurately estimate their ages and metallicities. (abridged)Comment: 40 pages, 14 figures, Tentatively scheduled for the November 2002 issue of The Astronomical Journa

Imaging of the Merging Galaxy NGC 3597 and its Population of Proto--Globular Clusters

We present wide field-of-view near-infrared imaging from the NTT and very deep optical imaging from the HST of the young merging galaxy NGC 3597. The morphology of the galaxy and the properties of the newly formed proto-globular clusters (PGCs) are examined. Our K band data reveals the presence of a second nucleus, which provides further evidence that NGC 3597 is the result of a recent merger. Combining new K band photometry with optical photometry, we are able for the first time to derive a unique age for the newly formed PGCs of a few Myrs. This is consistent with the galaxy starburst age of < 10 Myrs. From deep HST imaging, we are able to probe the luminosity function ~8 magnitudes fainter than normal, old globular clusters, and confirm that the PGCs have a power-law distribution with a slope of ~-2.Comment: 19 pages, Latex, 10 figures, 4 tables, accepted by MNRA