European Southern Observatory

About: European Southern Observatory is a facility organization based out in Garching bei München, Germany. It is known for research contribution in the topics: Galaxy & Stars. The organization has 3594 authors who have published 16157 publications receiving 823095 citations. The organization is also known as: The European Southern Observatory，ESO & ESO.

Planck 2015 results - VIII. High Frequency Instrument data processing: Calibration and maps

Abstract: This paper describes the processing applied to the cleaned, time-ordered information obtained from the Planck High Frequency Instrument (HFI) with the aim of producing photometrically calibrated maps in temperature and (for the first time) in polarization. The data from the entire 2.5-year HFI mission include almost five full-sky surveys. HFI observes the sky over a broad range of frequencies, from 100 to 857 GHz. To obtain the best accuracy on the calibration over such a large range, two different photometric calibration schemes have been used. The 545 and 857 GHz data are calibrated using models of planetary atmospheric emission. The lower frequencies (from 100 to 353 GHz) are calibrated using the time-variable cosmological microwave background dipole, which we call the orbital dipole. This source of calibration only depends on the satellite velocity with respect to the solar system. Using a CMB temperature of TCMB = 2.7255 ± 0.0006 K, it permits an independent measurement of the amplitude of the CMB solar dipole (3364.3 ± 1.5 μK), which is approximatively 1σ higher than the WMAP measurement with a direction that is consistent between the two experiments. We describe the pipeline used to produce the maps ofintensity and linear polarization from the HFI timelines, and the scheme used to set the zero level of the maps a posteriori. We also summarize the noise characteristics of the HFI maps in the 2015 Planck data release and present some null tests to assess their quality. Finally, we discuss the major systematic effects and in particular the leakage induced by flux mismatch between the detectors that leads to spurious polarization signal.

A 10 μm spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization

Abstract: We present spectroscopic observations of a large sample of Herbig Ae stars in the 10 µm spectral region. We perform compositional fits of the spectra based on properties of homogeneous as well as inhomogeneous spherical particles, and derive the mineralogy and typical grain sizes of the dust responsible for the 10 µm emission. Several trends are reported that can constrain theoretical models of dust processing in these systems: i) none of the sources consists of fully pristine dust comparable to that found in the interstellar medium; ii) all sources with a high fraction of crystalline silicates are dominated by large grains; iii) the disks around more massive stars (M > 2.5 M� , L > 60 L� ) have a higher fraction of crystalline silicates than those around lower mass stars, iv) in the subset of lower mass stars (M < 2.5 M� ) there is no correlation between stellar parameters and the derived crystallinity of the dust. The correlation between the shape and strength of the 10 micron silicate feature reported by van Boekel et al. (2003) is reconfirmed with this larger sample. The evidence presented in this paper is combined with that of other studies to present a likely scenario of dust processing in Herbig Ae systems. We conclude that the present data favour a scenario in which the crystalline silicates are produced in the innermost regions of the disk, close to the star, and transported outward to the regions where they can be detected by means of 10 micron spectroscopy. Additionally, we conclude that the final crystallinity of these disks is reached very soon after active accretion has stopped.

X-shooter spectroscopy of young stellar objects. IV. Accretion in low-mass stars and substellar objects in Lupus

Abstract: We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2 M ⊙ , but mostly with 0.1 M ⊙ ⋆ ⊙ . Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (L acc ), and in turn the accretion rate (Ṁ acc ), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (L line ) of many emission lines of H , He , and Ca ii, observed simultaneously in the range from ~330 nm to 2500 nm. The luminosity of all the lines is well correlated with L acc . We provide empirical relationships between L acc and the luminosity of 39 emission lines, which have a lower dispersion than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to L acc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring L acc and Ṁ acc yield significantly different results: Hα line profile modelling may underestimate Ṁ acc by 0.6 to 0.8 dex with respect to Ṁ acc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships between Ṁ acc and other YSOs properties reported in the literature. We derived Ṁ acc in the range 2 × 10-12 –4 × 10-8 M ⊙ yr-1 and conclude that Ṁ acc ∝ M ⋆ 1.8(±0.2) , with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Ṁ acc , confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star.

Global collapse of molecular clouds as a formation mechanism for the most massive stars

Abstract: The relative importance of primordial molecular cloud fragmentation versus large-scale accretion still remains to be assessed in the context of massive core/star formation. Studying the kinematics of the dense gas surrounding massive-star progenitors can tell us the extent to which large-scale flow of material impacts the growth in mass of star-forming cores. Here we present a comprehensive dataset of the 5500(±800) M⊙ infrared dark cloud SDC335.579-0.272 (hereafter SDC335), which exhibits a network of cold, dense, parsec-long filaments. Atacama Large Millimeter Array (ALMA) Cycle 0 observations reveal two massive star-forming cores, MM1 and MM2, sitting at the centre of SDC335 where the filaments intersect. With a gas mass of 545(-385+770) M⊙ contained within a source diameter of 0.05 pc, MM1 is one of the most massive, compact protostellar cores ever observed in the Galaxy. As a whole, SDC335 could potentially form an OB cluster similar to the Trapezium cluster in Orion. ALMA and Mopra single-dish observations of the SDC335 dense gas furthermore reveal that the kinematics of this hub-filament system are consistent with a global collapse of the cloud. These molecular-line data point towards an infall velocity Vinf = 0.7( ± 0.2) km s-1, and a total mass infall rate Ṁinf ≃ 2.5(±1.0) × 10-3 M⊙ yr-1 towards the central pc-size region of SDC335. This infall rate brings 750(±300) M⊙ of gas to the centre of the cloud per free-fall time (tff = 3 × 105 yr). This is enough to double the mass already present in the central pc-size region in 3.5-1.0+2.2 × tff. These values suggest that the global collapse of SDC335 over the past million year resulted in the formation of an early O-type star progenitor at the centre of the cloud’s gravitational potential well.

The ATLAS3D project - XXIX. The new look of early-type galaxies and surrounding fields disclosed by extremely deep optical images

Abstract: Galactic archaeology based on star counts is instrumental to reconstruct the past mass assembly of Local Group galaxies. The development of new observing techniques and data reduction, coupled with the use of sensitive large field of view cameras, now allows us to pursue this technique in more distant galaxies exploiting their diffuse low surface brightness (LSB) light. As part of the ATLAS^(3D) project, we have obtained with the MegaCam camera at the Canada–France–Hawaii Telescope extremely deep, multiband images of nearby early-type galaxies (ETGs). We present here a catalogue of 92 galaxies from the ATLAS^(3D) sample, which are located in low- to medium-density environments. The observing strategy and data reduction pipeline, which achieve a gain of several magnitudes in the limiting surface brightness with respect to classical imaging surveys, are presented. The size and depth of the survey are compared to other recent deep imaging projects. The paper highlights the capability of LSB-optimized surveys at detecting new prominent structures that change the apparent morphology of galaxies. The intrinsic limitations of deep imaging observations are also discussed, among those, the contamination of the stellar haloes of galaxies by extended ghost reflections, and the cirrus emission from Galactic dust. The detection and systematic census of fine structures that trace the present and past mass assembly of ETGs are one of the prime goals of the project. We provide specific examples of each type of observed structures – tidal tails, stellar streams and shells – and explain how they were identified and classified. We give an overview of the initial results. The detailed statistical analysis will be presented in future papers.