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A Helium Spread among the Main-Sequence Stars in NGC 2808
D'Antona, F.; Bellazzini, M.; Galleti, S. +3 more
We have made a detailed study of the color distribution of the main sequence of the globular cluster (GC) NGC 2808, based on new deep HST WFPC2 photometry of a field in the uncrowded outskirts of the cluster. The observed color distribution of main-sequence stars is not Gaussian and is wider than expected for a single stellar population, given our…
The association of coronal mass ejections with their effects near the Earth
Schwenn, R.; Gonzalez, W. D.; Huttunen, E. +1 more
To this day, the prediction of space weather effects near the Earth suffers from a fundamental problem: The radial propagation speed of "halo" CMEs (i.e. CMEs pointed along the Sun-Earth-line that are known to be the main drivers of space weather disturbances) towards the Earth cannot be measured directly because of the unfavorable geometry. From …
The Centers of Early-Type Galaxies with Hubble Space Telescope. V. New WFPC2 Photometry
Filippenko, Alexei V.; Ho, Luis C.; Gebhardt, Karl +14 more
We present observations of 77 early-type galaxies imaged with the PC1 CCD of the Hubble Space Telescope (HST) WFPC2. ``Nuker-law'' parametric fits to the surface brightness profiles are used to classify the central structure into ``core'' or ``power-law'' forms. Core galaxies are typically rounder than power-law galaxies. Nearly all power-law gala…
The Mass Assembly Histories of Galaxies of Various Morphologies in the GOODS Fields
Conselice, Christopher J.; Ellis, Richard S.; Bundy, Kevin
We present an analysis of the growth of stellar mass with cosmic time partitioned according to galaxy morphology. Using a well-defined catalog of 2150 galaxies based, in part, on archival data in the Great Observatories Origins Deep Survey (GOODS) fields, we assign morphological types in three broad classes (ellipticals, spirals, peculiar/irregula…
Standard Photometric Systems
Bessell, Michael S.
Standard star photometry dominated the latter half of the twentieth century reaching its zenith in the 1980s. It was introduced to take advantage of the high sensitivity and large dynamic range of photomultiplier tubes compared to photographic plates. As the quantum efficiency of photodetectors improved and the wavelength range extended further to…
The nature and origin of Seyfert warm absorbers
Page, M. J.; Branduardi-Raymont, G.; Blustin, A. J. +2 more
We collate the results of recent high resolution X-ray spectroscopic observations of 23 AGN, and use the resulting information to try to provide answers to some of the main open questions about warm absorbers: where do they originate, what effect do they have on their host galaxies, and what is their importance within the energetics and dynamics o…
Imaging of Titan from the Cassini spacecraft
Dones, Luke; Porco, Carolyn C.; McEwen, Alfred +33 more
Titan, the largest moon of Saturn, is the only satellite in the Solar System with a substantial atmosphere. The atmosphere is poorly understood and obscures the surface, leading to intense speculation about Titan's nature. Here we present observations of Titan from the imaging science experiment onboard the Cassini spacecraft that address some of …
Deflection of the Interstellar Neutral Hydrogen Flow Across the Heliospheric Interface
Bertaux, J. L.; Lallement, R.; Quémerais, E. +3 more
Using an absorption cell, we measured the Doppler shifts of the interstellar hydrogen resonance glow to show the direction of the neutral hydrogen flow as it enters the inner heliosphere. The neutral hydrogen flow is found to be deflected relative to the helium flow by about 4°. The most likely explanation of this deflection is a distortion of the…
The all-sky distribution of 511 keV electron-positron annihilation emission
Knödlseder, J.; Schanne, S.; Schönfelder, V. +11 more
We present a map of 511 keV electron-positron annihilation emission, based on data accumulated with the SPI spectrometer aboard ESA's INTEGRAL gamma-ray observatory, that covers approximately ~95% of the celestial sphere. Within the exposed sky area, 511 keV line emission is significantly detected towards the galactic bulge region and, at a very l…
Decay of Planetary Debris Disks
Bryden, G.; Stapelfeldt, K. R.; Rieke, G. H. +9 more
We report new Spitzer 24 µm photometry of 76 main-sequence A-type stars. We combine these results with previously reported Spitzer 24 µm data and 24 and 25 µm photometry from the Infrared Space Observatory and the Infrared Astronomy Satellite. The result is a sample of 266 stars with mass close to 2.5 Msolar, all detec…