Sensitivity of a Bolometric Interferometer to the CMB power spectrum

Context. The search for B-mode polarization fluctuations in the Cosmic Microwave Background is one of the main challenges of modern cosmology. The expected level of the B-mode signal is very low and therefore requires the development of highly sensitive instruments with low systematic errors. An appealing possibility is bolometric interferometry. Aims. We compare in this article the sensitivity on the CMB angular power spectrum achieved with direct imaging, heterodyne and bolometric interferometry. Methods. Using a simple power spectrum estimator, we calculate its variance leading to the counterpart for bolometric interferometry of the well known Knox formula for direct imaging. Results. We find that bolometric interferometry is less sensitive than direct imaging. However, as expected, it is finally more sensitive than heterodyne interferometry due to the low noise of the bolometers. It therefore appears as an alternative to direct imagers with different and possibly lower systematic errors, mainly due to the absence of an optical setup in front of the horns.Comment: 5 pages, 3 figures. This last version matches the published version (Astronomy and Astrophysics 491 3 (2008) 923-927). Sensitivity of Heterodyne Interferometers modified by a factor of tw

Porphyrin-Assisted Docking of a Thermophage Portal Protein into Lipid Bilayers : Nanopore Engineering and Characterization

Nanopore-based sensors for nucleic acid sequencing and single-molecule detection typically employ pore-forming membrane proteins with hydrophobic external surfaces, suitable for insertion into a lipid bilayer. In contrast, hydrophilic pore-containing molecules, such as DNA origami, have been shown to require chemical modification to favor insertion into a lipid environment. In this work, we describe a strategy for inserting polar proteins with an inner pore into lipid membranes, focusing here on a circular 12-subunit assembly of the thermophage G20c portal protein. X-ray crystallography, electron microscopy, molecular dynamics, and thermal/chaotrope denaturation experiments all find the G20c portal protein to have a highly stable structure, favorable for nanopore sensing applications. Porphyrin conjugation to a cysteine mutant in the protein facilitates the protein's insertion into lipid bilayers, allowing us to probe ion transport through the pore. Finally, we probed the portal interior size and shape using a series of cyclodextrins of varying sizes, revealing asymmetric transport that possibly originates from the portal's DNA-ratchet function

Planck early results. VI. The High Frequency Instrument data processing

We describe the processing of the 336 billion raw data samples from the High Frequency Instrument (HFI) which we performed to produce six temperature maps from the first 295 days of Planck-HFI survey data. These maps provide an accurate rendition of the sky emission at 100, 143, 217, 353, 545 and 857GHz with an angular resolution ranging from 9.9 to 4.4 . The white noise level is around 1.5 μK degree or less in the 3 main CMB channels (100–217 GHz). The photometric accuracy is better than 2% at frequencies between 100 and 353 GHz and around 7% at the two highest frequencies. The maps created by the HFI Data Processing Centre reach our goals in terms of sensitivity, resolution, and photometric accuracy. They are already sufficiently accurate and well-characterised to allow scientific analyses which are presented in an accompanying series of early papers. At this stage, HFI data appears to be of high quality and we expect that with further refinements of the data processing we should be able to achieve, or exceed, the science goals of the Planck project

Planck early results: first assessment of the High Frequency Instrument in-flight performance

The Planck High Frequency Instrument (HFI) is designed to measure the temperature and polarization anisotropies of the Cosmic Microwave Background and galactic foregrounds in six wide bands centered at 100, 143, 217, 353, 545 and 857 GHz at an angular resolution of 10' (100 GHz), 7' (143 GHz), and 5' (217 GHz and higher). HFI has been operating flawlessly since launch on 14 May 2009. The bolometers cooled to 100 mK as planned. The settings of the readout electronics, such as the bolometer bias current, that optimize HFI's noise performance on orbit are nearly the same as the ones chosen during ground testing. Observations of Mars, Jupiter, and Saturn verified both the optical system and the time response of the detection chains. The optical beams are close to predictions from physical optics modeling. The time response of the detection chains is close to pre-launch measurements. The detectors suffer from an unexpected high flux of cosmic rays related to low solar activity. Due to the redundancy of Planck's observations strategy, the removal of a few percent of data contaminated by glitches does not affect significantly the sensitivity. The cosmic rays heat up significantly the bolometer plate and the modulation on periods of days to months of the heat load creates a common drift of all bolometer signals which do not affect the scientific capabilities. Only the high energy cosmic rays showers induce inhomogeneous heating which is a probable source of low frequency noise.Comment: Submitted to A&A. 22 pages, 6 tables, 21 figures. One of a set of simultaneous papers for the Planck Missio

Planck early results. VI. The High Frequency Instrument data processing

We describe the processing of the 336 billion raw data samples from the High Frequency Instrument (HFI) which we performed to produce six temperature maps from the first 295 days of Planck-HFI survey data. These maps provide an accurate rendition of the sky emission at 100, 143, 217, 353, 545 and 857 GHz with an angular resolution ranging from 9.9 to 4.4^2. The white noise level is around 1.5 {\mu}K degree or less in the 3 main CMB channels (100--217GHz). The photometric accuracy is better than 2% at frequencies between 100 and 353 GHz and around 7% at the two highest frequencies. The maps created by the HFI Data Processing Centre reach our goals in terms of sensitivity, resolution, and photometric accuracy. They are already sufficiently accurate and well-characterised to allow scientific analyses which are presented in an accompanying series of early papers. At this stage, HFI data appears to be of high quality and we expect that with further refinements of the data processing we should be able to achieve, or exceed, the science goals of the Planck project.Comment: Replaced by the accepted version for publication, as part of a package of papers describing first results of the Planck mission The paper with figures at full resolution and full color tables can also be downloaded from the ESA site http://www.rssd.esa.int/Planc

Stability of the HgS molecule and spectroscopy of its low lying electronic states

International audienceLarge scale Multireference Configuration Interactions (MRCI) and energy consistent relativistic pseudopotential (for the Hg atom) have been used to investigate the electronic structure, stability and spectroscopy of the low lying electronic states of the HgS molecule. The relative position of the two lowest electronic states, X-1 Sigma(+) and a(3)Pi, was found to be very sensitive to the quality of the basis set. Spin-orbit effects were taken into account leading to accurate spectroscopic data useful for the identification of the molecule. T-0 between the lowest components of the two states, X-1 Sigma(+)(0) and a(3)Pi(2), has been evaluated to be 0.142eV (3.5 kcal mol(-1)). Dipole moment functions were calculated for the lowest states; the rather large dipole moment of the X-1 Sigma(+) state makes possible the detection of vibrational transitions with a calculated ! e equal to 364cm(-1). Transitions between the X-1 Sigma(+) and the A(1)Pi states are predicted in the far IR domain with a T-0 = 5794cm(-1). The predissociation of the X-1 Sigma(+) and A(1)Pi states has been analysed and it has been shown that for the X-1 Sigma(+)(0) state only the vibrational levels below v = 11 are stable; higher levels are predissociated by the a(3)Pi(0) state. The effective dissociation energy of the X-1 Sigma(+)(0) state of HgS can thus be estimated to be 0.47eV (6.5 kcal mol(-1)). For the A(1)Pi state, the levels with v > 8 are predissociated by the dissociative b(3)Sigma(-) state

The BRAIN project: looking for B-mode from Dome-C

Texte integral disponible sur http://proc.sf2a.asso.fr/sf2a06.phpInternational audienceThe detection and characterisation of Cosmic Microwave Background B-mode polarization is one of the next challenges in observational cosmology. This primordial polarization mode is only due to tensor perturbations of the metric produced by primordial gravitational waves, which could have been generated during the inflation epoch. With a signal of less than 0.1? K, B-mode measurement requires very sensitive experiments and also an extremely good control of instrumental effects. In this paper we present the BRAIN experiment, a bolometric interferometer devoted to B-mode detection. This new detection architecture allows to directly measure the Fourier modes of the Stokes parameters. High sensitivity is obtained by using low temperature bolometers while systematic effects are reduced by using the interferometric technique

A five-dimensional potential-energy surface for the rotational excitation of SO2 by H2 at low temperatures

9 pags., 8 figs., 7 tabs.The SO2 molecule is detected in a large variety of astronomical objects, notably molecular clouds and star-forming regions. An accurate modeling of the observations needs a very good knowledge of the collisional excitation rates with H2 because of competition between collisional and radiative processes that excite and quench the different rotational levels of SO2. We report here a five-dimensional, rigid-body, interaction potential for SO2 - H2. As a first application, we present rate constants for excitation/de-excitation of the 31 first levels of SO 2 by para- H2 at low temperatures. Propensity rules are discussed. © 2009 American Institute of Physics.The calculations of ab initio PES were performed at the Centro de Supercomputación de Galicia, CESGA, and on the parallel machine MPOPM of Paris Observatory. The scattering calculations were performed at the IDRIS-CNRS French National Computing Center Institut de Développement et des Ressources en Informatique Scientifique du Centre National de la Recherche Scientifique under Project No. 060883 and on local work stations of the Centre Informatique of Paris Observatory. L.C.-V. was supported in 2006- 2008 by the FP6 Research Training Network “Molecular Universe” under Contract No. MCRTN-CT-2004-512302 and in 2008-2009 by a grant of the Lavoisier Program of the french Foreign Office Ministry. M.-L. Senent acknowledges the MEC Spain for the Grant No. AYA2005-00702

Rotational excitation of SO2 by collision with H2: a collaborative work

The SO2 molecule is detected in a large variety of objects, notably cold dark clouds and star-forming regions. An accurate modeling of the observations requires a very good knowledge of the collisional excitation rates with H2 due to competition between collisional and radiative processes that excite and quench the different rotational levels of the molecule. The results of our recent collisional calculations are summarized. Pierre was associated to all steps of this collaborative work that was a key project in the Molecular Universe European FP6 network