Structural Parameters of Star Clusters: Signal to Noise Effects

We study the impact of photometric signal to noise on the accuracy of derived structural parameters of unresolved star clusters using MCMC model fitting techniques. Star cluster images were simulated as a smooth surface brightness distribution following a King profile convolved with a point spread function. The simulation grid was constructed by varying the levels of sky background and adjusting the cluster's flux to a specified signal to noise. Poisson noise was introduced to a set of cluster images with the same input parameters at each node of the grid. Model fitting was performed using emcee algorithm. The presented posterior distributions of the parameters illustrate their uncertainty and degeneracies as a function of signal to noise. By defining the photometric aperture containing 80% of the cluster's flux, we find that in all realistic sky background level conditions a signal to noise ratio of $\sim$50 is necessary to constrain the cluster's half-light radius to an accuracy better than $\sim$20%. The presented technique can be applied to synthetic images simulating various observations of extragalactic star clusters.Comment: 9 pages, 5 figure

Compact Star Clusters in the M31 Disk

We have carried out a survey of compact star clusters (apparent size <3 arcsec) in the southwest part of the M31 galaxy, based on the high-resolution Suprime-Cam images (17.5 arcmin x 28.5 arcmin), covering ~15% of the deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V < 20.5 mag) was performed using frames of the Local Group Galaxies Survey. The final sample, containing 238 high probability star cluster candidates (typical half-light radius r_h ~ 1.5 pc), was selected by specifying a lower limit of r_h > 0.15 arcsec (>0.6 pc). We derived cluster parameters based on the photometric data and multiband images by employing simple stellar population models. The clusters have a wide range of ages from ~5 Myr (young objects associated with 24 um and/or Ha emission) to ~10 Gyr (globular cluster candidates), and possess mass in a range of 3.0 < log(m/M_sol) < 4.3 peaking at m ~ 4000 M_sol. Typical age of these intermediate-mass clusters is in the range of 30 Myr < t < 3 Gyr, with a prominent peak at ~70 Myr. These findings suggest a rich intermediate-mass star cluster population in M31, which appears to be scarce in the Milky Way galaxy.Comment: 16 pages, 8 figures, 1 table, accepted for publication in Ap

Modelling the spectral energy distribution of galaxies. V. The dust and PAH emission SEDs of disk galaxies

We present a self-consistent model of the spectral energy distributions (SEDs) of spiral galaxies from the ultraviolet (UV) to the mid-infrared (MIR)/far-infrared (FIR)/submillimeter (submm) based on a full radiative transfer calculation of the propagation of starlight in galaxy disks. This model predicts not only the total integrated energy absorbed in the UV/optical and re-emitted in the infrared/submm, but also the colours of the dust emission based on an explicit calculation of the strength and colour of the UV/optical radiation fields heating the dust, and incorporating a full calculation of the stochastic heating of small dust grains and PAH molecules. The geometry of the translucent components of the model is empirically constrained using the results from the radiation transfer analysis of Xilouris et al. on spirals in the middle range of the Hubble sequence, while the geometry of the optically thick components is constrained from physical considerations with a posteriori checks of the model predictions with observational data. These geometrical constraints enable the dust emission to be predicted in terms of a minimum set of free parameters: the central face-on dust opacity in the B-band tau^f_B, a clumpiness factor F for the star-forming regions, the star-formation rate SFR, the normalised luminosity of the old stellar population old and the bulge-to-disk ratio B/D. We show that these parameters are almost orthogonal in their predicted effect on the colours of the dust/PAH emission. The results of the calculations are made available in the form of a large library of simulated dust emission SEDs spanning the whole parameter space of our model, together with the corresponding library of dust attenuation calculated using the same model. (see full abstract in the paper)Comment: 39 pages; accepted for publication in Astronomy & Astrophysics; For a higher resolution version of Fig.1 and Fig.20 see http://www.star.uclan.ac.uk/~ccp/index.shtm

A study of the centrally produced pi0pi0pi0 channel in pp interactions at 450 GeV/c

The reaction pp -> pf (pi0pi0pi0) ps has been studied at 450 GeV/c. The pi0pi0pi0 effective mass spectrum shows clear eta(547) and pi2(1670) signals. Branching ratios for the eta(547) and pi_2(1670) are given as well as upper limits for the decays of the omega(782), a1(1260) and a2(1320) into 3pi0.Comment: 10 pages, Latex, 4 Figure

Orographic Disturbances in the Upper Atmosphere Stipulated by Air Currents Streamlining of Great Caucasus Range

Измерения температуры мезопаузы в северной подветренной области Кавказского хребта позволили получить уникальные сведения о характеристиках орографических возмущений на высотах мезопаузы и особенностях их генерации в приземной атмосфере. Температура на высотах ~ 90 км в подветренной области гор имеет максимум ~ 10 К на расстоянии ~ 150 км от хребта. Источники волновых возмущений возникают в тропосфере примерно на высотах 4 км над Кавказским хребтомMeasurements of mesopause temperature in northern leeward area of the Caucasian ridge have allowed to obtain unique data on characteristics of orographical disturbances at heights of mesopause and of their generation processes in a ground atmosphere. The temperature at heights ~ 90 km in leeward area of mountains has a maximum ~ 10 K on distance about 150 km from a ridge. Sources of wave disturbances arise in troposphere approximately at heights of 4 km above the Caucasian ridg

Interobserver Agreement between On-Call Radiology Resident and General Radiologist Interpretations of CT Pulmonary Angiograms and CT Venograms

Acute pulmonary embolism (PE) has long been recognized as a life-threatening emergency, and although the statistics vary widely depending on the clinical setting, associated mortality rates have been estimated at 100 000 deaths per year in the United States, including 15% of in-hospital deaths. Consequently, the ability to obtain rapid and accurate diagnosis of PE becomes critical for clinical management, namely, early initiation of anticoagulant therapy. Current clinical practice algorithms advocate use of computed tomographic pulmonary angiogram (CTPA) to reliably diagnose or exclude PE. Most commonly, PE results from deep venous thrombosis (DVT). Therefore, in addition to the diagnosis of PE, the evaluation of the lower limbs in order to detect the presence of DVT is important for appropriate patient management. Although DVT can be diagnosed or excluded via sonographic evaluation of the lower limbs with Doppler technique, the use of combined CTPA and computed tomographic venogram (CTV) for one-time imaging allows diagnosing both PE and DVT