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It is a general belief that the starburst activity of a nearby galaxy M82 was triggered in a close encounter with its massive companion M81, a few tens of million years ago. Despite the lack of supernovae observed, multiwavelength radio observations of M82 discovered a considerable number of compact supernova remnant candidates. We use these remnants to estimate the supernova rate (SNR) and the enhanced star-formation (SFR) rate in M82, and compare them with rates in normal galaxies.
Accurate measurements of emission line properties are crucial to understand the physics of the broad line region in quasars. This region consists of warm gas that is closest to the quasar central engine and has not been spatially resolved for almost all sources. We present here an analysis of optical and IR data for a large sample of quasars, covering the Hi Hβ spectral region in the redshift range 0 ≲ z ≲ 2.5. Spectra were interpreted within the framework of the the so-called “eigenvector 1” parameter space, which can be viewed as a tentative H-R diagram for quasars. We stress the lack of spectral evolution in the low ionization lines of quasars, with prominent Fe ii emission also at z ≳ 2. We also show how selection effects influence the ability to find quasars radiating at low Eddington ratio in flux-limited surveys. The quasar similarity at different redshift is probably due to the absence of super-Eddington radiators (at least within the caveats of black hole mass and Eddington ratio determination discussed in this paper) as well as to the limited Eddington ratio range within which quasars seem to radiate.
We discuss observational evidence for sequential and triggered star formation in OB associations. We first review the star formation process in the Scorpius-Centaurus OB association, the nearest OB association to the Sun, where several recent extensive studies have allowed us to reconstruct the star formation history in a rather detailed way. We then compare the observational results with those obtained for other OB associations and with recent models of rapid cloud and star formation in the turbulent interstellar medium. We conclude that the formation of whole OB subgroups (each consisting of several thousand stars) requires large-scale triggering mechanisms such as shocks from expanding wind and supernova driven superbubbles surrounding older subgroups. Other triggering mechanisms, like radiatively driven implosion of globules, also operate, but seem to be secondary processes, forming only small stellar groups rather than whole OB subgroups with thousands of stars.
We perform the two-dimensional radiation-hydrodynamic simulations to study the radiation pressure-dominated accretion flows around a black hole (BH). Our simulations show that the highly supercritical accretion flow (mass accretion rate is much larger than the critical value) is composed of the disk region and the outflow region above the disk.
The radiation force supports the thick disk and drives the outflow. The photon trapping plays an important role within the disk, reducing the disk luminosity. On the other hand, in the case that mass accretion rate moderately exceeds the critical value, we find that the disk is unstable and exhibits the limit-cycle oscillations. The disk oscillations in our simulations nicely fit to the variation amplitude and duration of quasi-periodic luminosity variations observed in the GRS 1915+105 microquasar.
Two Moroccan sites have been selected to be characterized for the ELT telescopes. Those sites are in the Atlas, between Oukaïmeden (where the national observatory is situated) and the Canary Islands. For this preliminary study, we have used the Nimbus-7 TOMS aerosol index to derive the astronomical extinction. This work builds on the findings of an earlier study which established the link between these two parameters over the Canary Islands.
The NSF Science and Technology Center for Adaptive Optics (CfAO) is supporting a major scientific legacy project called the CfAO Treasury Survey (CATS). CATS is obtaining near-infrared AO data in deep HST survey fields, such as GEMS, GOODS-N, & EGS. Besides summarizing the main objectives of CATS, we highlight some recent imaging work on the study of distant field galaxies, AGNs, and a redshift z = 1.32 supernova. CATS plans the first data release to the community in early 2007 (check http://www.astro.ucla.edu/~irlab/cats/index.shtml for more details on CATS and latest updates).
Young massive star-forming regions are known to produce hot molecular gas cores (HMCs) with a rich chemistry. While this chemistry is interesting in itself, it also allows to investigate important physical parameters. I will present recent results obtained with high-angular-resolution interferometers disentangling the small-scale structure and complexity of various molecular gas components. Early attempts to develop a chemical evolutionary sequence are discussed. Furthermore, I will outline the difficulty to isolate the right molecular lines capable to unambiguously trace potential massive accretion disks.
We study solar irradiance variability. The current generation of models show that the irradiance since then has increased by between 0.9 and 1.5 W m−2.
The Committee on Space Research (COSPAR) Capacity-Building Programme introduces astronomers in the developing world to the rich resource of space research online archives. The programme consists of a series of regional workshops which each bring together about 30 developing world astronomers with around 8 teaching faculty for lectures and hands-on projects. Five workshops have been held so far with another two planned for next year and a budget which enables on average one workshop each year. Proposals for future workshops are encouraged.
This summary covers the first two days of the Symposium, in which the oral papers were primarily observational in nature. It also mentions several of the many observational posters associated with those discussions.
We present HI observations of the elliptical galaxy NGC 2974, obtained with the VLA. These observations reveal that the previously detected HI disc in this galaxy (Kim et al. 1988) is in fact a ring. Combining the flat rotation curve with the central kinematics of the ionised gas, obtained with the integral-field spectrograph SAURON, allows us to determine the mass-to-light ratio M/L as a function of radius, ranging from 100 pc in the centre to 10 kpc at the edges of the HI ring. A dark halo is required to explain the observed rotation: at the outer radii ~70% of the total mass is dark†.
Dome C, Antarctica is a prime site for astronomical observations in terms of climate, wind speeds, turbulence, and infrared and terahertz sky backgrounds (for example, see Aristidi et al. 2005; Storey et al. 2005). However, at present little is known about the optical sky brightness and atmospheric extinction. Using a variety of modelling techniques, together with data from the South Pole, the brightness of the night sky at Dome C is estimated in Kenyon & Storey (2006) including the contributions from scattered sunlight, moonlight,aurorae, airglow, zodiacal light, integrated starlight, diffuse Galactic light and artificial sources. The results are compared to Mauna Kea, Hawaii. We summarise the main conclusions.
We have obtained the first accurate determination of the albedo of (99942) Apophis, by means of polarimetric observations carried out at the VLT. The observations allowed us to obtain the slope of the polarization–phase curve of this object, from which an albedo estimate of 0.33 ± 0.04 could be obtained. From our observations we also obtained a new estimate of the absolute magnitude: H = 19.7 ± 0.2 (assuming G=0.25, which applies to S- and Q-type asteroids). Based on these results, we derive for the size of Apophis a value of 270 ± 30 meters. The accuracy of this size estimate is mostly related to uncertainties in H, whereas the obtained albedo value should be considered more robust. Our observations convincingly show that polarimetry is an effective and efficient tool to obtain accurate albedos and sizes for small and faint potentially hazardous asteroids.
We have redetermined the absolute dimensions of the mid B-type eclipsing binary U Oph from new light and radial-velocity curves, accounting for both the apsidal motion and the light-time orbit around the third star. The stars in U Oph have masses of 5.27 and 4.74 M⊙(±1.5%) and are located in the middle of the main-sequence band for an an age of ∼50 Myr. U Oph and three other systems (V760 Sco, MU, Cas and DI Her) all have components within 10% of 5M⊙ and ages below 100 Myr; we find significant heavy-element abundance differences between these young nearby stars.
We give estimates of the global mass-loss rate from bulge stars and show that this supply of gas is not negligible for the mass budget of the central kiloparsec in comparison with mass inflow rate predicted by N-body simulations of barred galaxies and mergers.
Disks of galaxies in clusters are deeply affected by interactions. We investigate the pattern speed of galaxies in cluster in order to detect a possible dependence with cluster environmental parameters, such as galaxies density. If the perturbation of cluster galaxies is mainly produced by the interaction with the cluster ambient, the pattern speed might well depend on the history of the galaxy orbit within the cluster. Tremaine & Weinberg (1984) method is applied to 2-D Hα velocity fields, reconstructed from the isovelocity contours published by Amram et al. (1992), and 2-MASS K–band images (Skrutskie 2001) to obtain spirals pattern angular speed. The use of K–band images and Hα velocity maps is justified by the fact that the perturbations imprinted in Hα velocity maps are produced by the old stellar population which emits most of its energy in the near-IR. We analyzed Pegasus I cluster galaxies NGC 7593, NGC 7631 and NGC 7643 (this one shown in Figure 1). Preliminary results indicates that NGC 7593 presents a pattern speed Ωp sin(i) = 18 ± 5km s−1 kpc−1, (inclination i = 51°) while NGC 7631 and NGC 7643 pattern speeds are Ωp sin(i) = 21 ± 4 km s−1 kpc−1 and Ωp sin(i) = 35 ± 3 km s−1 kpc−1 (inclinations i = 64° and 59° respectively). In the three successful cases the correlation coefficients in the 〈X〉 vs 〈V〉 plots are 0.94, 0.95 and 0.98 respectively. We are presently analyzing other galaxies in the cluster.
Results based on the deep imaging survey of the inner region (~300pc of the bulge within |ℓ| ~ 1.5°, |b| ~ 0.5°) of the Milky Way are reported in this communication. This survey is about 2.5 magnitude deeper than DENIS and 2MASS and is able to detect stars of the red clump at a distance of the Galactic center. Toward some directions we find extinction reaching AV = 50 mag. A catalog of the sources is in preparation.
We present VisIVO a software for the visualisation and analysis of astrophysical data which can be retrieved from the Virtual Observatory framework and for cosmological simulations. VisIVO is VO standards compliant and supports the most important astronomical data formats such as FITS, HDF5 and VOTables. Data can be retrieved directly connecting to an available VO service (i.e., VizieR WS), loaded in the local computer memory where they can be further selected, visualised and manipulated.