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| EAS Tycho Brahe Prize Lecture 2011 - Hipparcos: a Retrospective |
Preprint. Paper to appear in Astronomy and Astrophys Review, 2011. The Hipparcos satellite was launched in 1989. It was the first, and remains to date the only, attempt at performing large-scale astrometric measurements from space. Hipparcos marked a fundamentally new approach to the field of astrometry, revolutionising our knowledge of the positions, distances, and space motions of the stars in the solar neighbourhood. In this retrospective, I look back at the processes which led to the mission's acceptance, provide a short summary of the underlying measurement principles and the experiment's scientific achievements, and a conclude with a brief summary of its principal legacy - the Gaia mission. |
| Publication date: 30 Sep 2011 |
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| Euclid definition study report (Red Book) |
| Reference: ESA/SRE(2011)12
This report, the so-called Red Book, describes the outcome of the mission definition study (Phase A) for the Euclid mission. Euclid is a medium-size (M-class) mission of the ESA Cosmic Vision 2015-2025 programme, and competes for one of the two launch slots foreseen in 2017 and 2018. |
| Publication date: 29 Sep 2011 |
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| Evidence of Water Vapor in Excess of Saturation in the Atmosphere of Mars |
| The vertical distribution of water vapor is key to the study of Mars' hydrological cycle. To date, it has been explored mainly through global climate models because of a lack of direct measurements. However, these models assume the absence of supersaturation in the atmosphere of Mars. Here, we report observations made using the SPICAM (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) instrument onboard Mars Express that provide evidence of the frequent presence of water vapor in excess of saturation, by an amount far surpassing that encountered in Earth's atmosphere. This result contradicts the widespread assumption that atmospheric water on Mars cannot exist in a supersaturated state, directly affecting our long-term representation of water transport, accumulation, escape, and chemistry on a global scale. |
| Publication date: 29 Sep 2011 |
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| Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS |
| We present new Herschel/PACS images at 70, 100, and 160 micron of the well-known, nearby, carbon-rich asymptotic giant branch star IRC+10216 revealing multiple dust shells in its circumstellar envelope. For the first time, dust shells (or arcs) are detected until 320". The almost spherical shells are non-concentric and have an angular extent between ~40° and ~200°. The shells have a typical width of 5"-8", and the shell separation varies in the range of ~10"-35", corresponding to ~500 -1700 yr. Local density variations within one arc are visible. The shell/intershell density contrast is typically ~4, and the arcs contain some 50% more dust mass than the smooth envelope. The observed (nested) arcs record the mass-loss history over the past 16 000 yr, but Rayleigh-Taylor and Kelvin-Helmholtz instabilities in the turbulent astropause and astrosheath will erase any signature of the mass-loss history for at least the first 200 000 yr of mass loss. Accounting for the bowshock structure, the envelope mass around IRC+10216 contains >2 solar masses of gas and dust mass. It is argued that the origin of the shells is related to non-isotropic mass-loss events and clumpy dust formation. |
| Publication date: 20 Sep 2011 |
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| Removal of Titan's atmospheric noble gases by their sequestration in surface clathrates |
| A striking feature of the atmosphere of Titan is that no heavy noble gases other than argon were detected by the Gas Chromatograph Mass Spectrometer aboard the Huygens probe during its descent to Titan's surface in 2005 January. Here we provide an explanation of the mysterious absence or rarity of these noble gases in Titan's atmosphere: the thermodynamic conditions prevailing at the surface-atmosphere interface of the satellite allow the formation of multiple guest clathrates that preferentially store some species, including all heavy noble gases, over others. The clean water ice needed for the formation of these clathrates could be delivered by successive episodes of cryovolcanic lavas that have been hypothesized to regularly cover the surface of Titan. The formation of clathrates in the porous lavas and their propensity for trapping Ar, Kr, and Xe would progressively remove these species from the atmosphere of Titan over the course of its history. In some circumstances, a global clathrate crust with an average thickness not exceeding a few meters could be sufficient on Titan for a complete removal of the heavy noble gases from the atmosphere. |
| Publication date: 19 Sep 2011 |
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| GOODS-Herschel: an infrared main sequence for star-forming galaxies |
We present the deepest 100 to 500 micron far-infrared observations obtained with the Herschel Space Observatory as part of the GOODS-Herschel key program, and examine the infrared (IR) 3-500 micron spectral energy distributions (SEDs) of galaxies at 0 < z < 2.5, supplemented by a local reference sample from IRAS, ISO, Spitzer and AKARI data. We determine the projected star formation densities of local galaxies from their radio and mid-IR continuum sizes.
We find that the ratio of total IR luminosity to rest-frame 8 micron luminosity, IR8 (=LtotIR/L8), follows a Gaussian distribution centered on IR8=4 (sigma=1.6) and defines an IR main sequence for star-forming galaxies independent of redshift and luminosity. Outliers from this main sequence produce a tail skewed toward higher values of IR8. This minority population (<20%) is shown to consist of starbursts with compact projected star formation densities. IR8 can be used to separate galaxies with normal and extended modes of star formation from compact starbursts with high-IR8, high projected IR surface brightness (SigmaIR>3×1010 LSunkpc-2) and a high specific star formation rate (i.e., starbursts). The rest-frame, UV-2700 Angstrom size of these distant starbursts is typically half that of main sequence galaxies, supporting the correlation between star formation density and starburst activity that is measured for the local sample.
- The remainder of the abstract is truncated - |
| Publication date: 13 Sep 2011 |
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| Filaments and ridges in Vela C revealed by Herschel: from low-mass to high-mass star-forming sites |
| We present the first Herschel PACS and SPIRE results of the Vela C molecular complex in the far-infrared and submillimetre regimes at 70, 160, 250, 350, and 500 micron, spanning the peak of emission of cold prestellar or protostellar cores. Column density and multi-resolution analysis (MRA) differentiates the Vela C complex into five distinct sub-regions. Each sub-region displays differences in their column density and temperature probability distribution functions (PDFs), in particular, the PDFs of the "Centre-Ridge" and "South-Nest" sub-regions appear in stark contrast to each other. The Centre-Ridge displays a bimodal temperature PDF representative of hot gas surrounding the HII region RCW 36 and the cold neighbouring filaments, whilst the South-Nest is dominated by cold filamentary structure. The column density PDF of the Centre-Ridge is flatter than the South-Nest, with a high column density tail, consistent with formation through large-scale flows, and regulation by self-gravity. At small to intermediate scales MRA indicates the Centre-Ridge to be twice as concentrated as the South-Nest, whilst on larger scales, a greater portion of the gas in the South-Nest is dominated by turbulence than in the Centre-Ridge. In Vela C, high-mass stars appear to be preferentially forming in ridges, i.e., dominant high column density filaments. |
| Publication date: 07 Sep 2011 |
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| Herschel detects a massive dust reservoir in supernova 1987A |
| Published online in Science Express, 7 July 2011.
We report far-infrared and submillimeter observations of Supernova 1987A, the star that exploded on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160 000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 K at a rate of about 220 LSun. The intensity and spectral energy distribution of the emission suggests a dust mass of about 0.4 to 0.7 MSun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts. |
| Publication date: 02 Sep 2011 |
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| Diffuse emission measurement with the spectrometer on INTEGRAL as an indirect probe of cosmic-ray electrons and positrons |
Significant advances have been made in the understanding of the diffuse Galactic hard X-ray continuum emission using data from the INTEGRAL observatory. The diffuse hard power-law component seen with the SPectrometer on INTEGRAL (SPI) has been identified with inverse-Compton emission from relativistic (GeV) electrons on the cosmic microwave background and Galactic interstellar radiation field. In the present analysis, SPI data from 2003 to 2009, with a total exposure time of ~108 s, are used to derive the Galactic ridge hard X-ray spatial distribution and spectrum between 20 keV and 2.4 MeV. Both are consistent with predictions from the GALPROP code. The good agreement between measured and predicted emission from keV to GeV energies suggests that the correct production mechanisms have been identified. We discuss the potential of the SPI data to provide an indirect probe of the interstellar cosmic-ray electron distribution, in particular for energies below a few GeV. |
| Publication date: 01 Sep 2011 |
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| Spatium 27: Science First |
| This issue of Spatium is devoted to Professor Johannes Geiss, cofounder of PRO ISSI and spiritus
rector of ISSI, on the occasion of his 85th anniversary on 4 September 2011. |
| Publication date: 01 Sep 2011 |
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