Electric Dipole Radiation from Spinning Dust Grains

We discuss the rotational excitation of small interstellar grains and the resulting electric dipole radiation from spinning dust. Attention is given to excitation and damping of rotation by: collisions with neutrals; collisions with ions; plasma drag; emission of infrared radiation; emission of microwave radiation; photoelectric emission; and formation of H_2 on the grain surface. We introduce dimensionless functions F and G which allow direct comparison of the contributions of different mechanisms to rotational drag and excitation. Emissivities are estimated for dust in different phases of the interstellar medium, including diffuse HI, warm HI, low-density photoionized gas, and cold molecular gas. Spinning dust grains can explain much, and perhaps all, of the 14-50 GHz background component recently observed in CBR studies. It should be possible to detect rotational emission from small grains by ground-based observations of molecular clouds.Comment: 59 pages, 19 eps figures, uses aaspp4.sty . Submitted to Ap.

Multi-stage four-quadrant phase mask: achromatic coronagraph for space-based and ground-based telescopes

Less than 3% of the known exoplanets were directly imaged for two main reasons. They are angularly very close to their parent star, which is several magnitudes brighter. Direct imaging of exoplanets thus requires a dedicated instrumentation with large telescopes and accurate wavefront control devices for high-angular resolution and coronagraphs for attenuating the stellar light. Coronagraphs are usually chromatic and they cannot perform high-contrast imaging over a wide spectral bandwidth. That chromaticity will be critical for future instruments. Enlarging the coronagraph spectral range is a challenge for future exoplanet imaging instruments on both space-based and ground-based telescopes. We propose the multi-stage four-quadrant phase mask that associates several monochromatic four-quadrant phase mask coronagraphs in series. Monochromatic device performance has already been demonstrated and the manufacturing procedures are well-under control since their development for previous instruments on VLT and JWST. The multi-stage implementation simplicity is thus appealing. We present the instrument principle and we describe the laboratory performance for large spectral bandwidths and for both pupil shapes for space- (off-axis telescope) and ground-based (E-ELT) telescopes. The multi-stage four-quadrant phase mask reduces the stellar flux over a wide spectral range (30%) and it is a very good candidate to be associated with a spectrometer for future exoplanet imaging instruments in ground- and space-based observatories.Comment: 7 pages, 11 figures, 4 tables, accepted in A&

The four-quadrant phase-mask coronagraph: white light laboratory results with an achromatic device

Achromatic coronagraphs are the subject of intensive research since they will be mandatory for many programs which aim at detecting and characterizing exoplanets. We report a laboratory experiment assessing the performance of the Four-Quadrant Phase-Mask coronagraph (FQPM) over a broadband wavelength range (R≈2). The achromatization of the FQPM is provided by achromatic halfwave plates (HWP). These phase shifters combine birefringent plates made of different materials with properly chosen thicknesses. The HWP thickness control is relaxed by two orders of magnitudes with respect to the classical (non-birefringent) dispersive plate approach. In our experiment we used a two stage stack of Quartz and MgF_2. This combination allows to cover a large spectral range in the visible (500-900nm) with a small phase error residual around π(≈0.12 rad rms). With this achromatization, we obtained an attenuation of 755 on the white light PSF peak. This solution is directly applicable to ground-based telescopes using high order adaptive optics such as the ESO's VLT-Planet Finder project and could easily be transposed in the mid-infrared domain for future space-based missions like DARWIN/TPF

Sequence structure emission in The Red Rectangle Bands

We report high resolution (R~37,000) integral field spectroscopy of the central region (r<14arcsec) of the Red Rectangle nebula surrounding HD44179. The observations focus on the 5800A emission feature, the bluest of the yellow/red emission bands in the Red Rectangle. We propose that the emission feature, widely believed to be a molecular emission band, is not a molecular rotation contour, but a vibrational contour caused by overlapping sequence bands from a molecule with an extended chromophore. We model the feature as arising in a Polycyclic Aromatic Hydrocarbon (PAH) with 45-100 carbon atoms.Comment: 13 pages, 9 figures, accepted for publication in ApJ. A version of the paper with full resolution figures is available at: http://www.aao.gov.au/local/www/rgs/Sequence-Structure

Pharmacokinetics and dosage adjustment of cefotiam in renal impaired patients

The pharmacokinetics of cefotiam were investigated after intravenous administration of 1 g to 2 healthy volunteers with normal renal function and to 16 patients whose creatinine clearance ranged from 4.7 to 0.11/h (78 to 1.66 ml/min). The elimination half-life varied from 1.1 h in normal subjects to 13 h in patients and the total plasma clearance from 21 to 0.6 1/h (350 to 10 ml/min). The urinary recovery decreased from 62% of the dose in normal subjects to 1.1% in patients, and the renal clearance from 15 to 0.03 l/h (250 to 0.5 ml/min). Plasma and renal clearances of cefotiam correlated well with the creatinine clearance. The dosage schedule for cefotiam in patients with normal renal function can be used in the presence of renal failure when the creatinine clearance is equal to or greater than 1 1/h (16.6 ml/min). For patients whose creatinine clearance is less than 1 1/h, the dose must be decreased to 75% of that for a patient with normal renal function only when it is given every 6 or 8

Interviews from Scratch: Individual Differences in Writing Interview Questions

Against best practice recommendations, interviewers prefer unstructured interviews where they are not beholden to regimentation. In cases where interviews are less structured, the interviewer typically generates his or her own set of interview questions. Even in structured interviews though, the initial interview content must be generated by someone. Thus, it is important to understand the different factors that influence what types of questions individuals generate in interview contexts. The current research aims to understand the types of interview questions individuals generate, factors that affect the quality of those questions, how skill in generating interview questions relates to skill in evaluating existing interview questions, and how individual traits relate to skill in generating interview questions. Results show that respondents who are skilled in evaluating existing interview questions are also skilled in writing interview questions from scratch, and these skills relate to general mental ability and social intelligence. Respondents generated questions that most commonly assessed applicant history and self-perceived applicant characteristics, whereas only 30% of questions generated were situational or behavioral

A probable giant planet imaged in the Beta Pictoris disk

Since the discovery of its dusty disk in 1984, Beta Pictoris has become the prototype of young early-type planetary systems, and there are now various indications that a massive Jovian planet is orbiting the star at ~ 10 AU. However, no planets have been detected around this star so far. Our goal was to investigate the close environment of Beta Pic, searching for planetary companion(s). Deep adaptive-optics L'-band images of Beta Pic were recorded using the NaCo instrument at the Very Large Telescope. A faint point-like signal is detected at a projected distance of ~ 8 AU from the star, within the North-East side of the dust disk. Various tests were made to rule out with a good confidence level possible instrumental or atmospheric artifacts. The probability of a foreground or background contaminant is extremely low, based in addition on the analysis of previous deep Hubble Space Telescope images. The object L'=11.2 apparent magnitude would indicate a typical temperature of ~1500 K and a mass of ~ 8 Jovian masses. If confirmed, it could explain the main morphological and dynamical peculiarities of the Beta Pic system. The present detection is unique among A-stars by the proximity of the resolved planet to its parent star. Its closeness and location inside the Beta Pic disk suggest a formation process by core accretion or disk instabilities rather than a binary-like formation process.Comment: 5 pages, 3 figures, 1 table. A&A Letters, in pres

Infrared emission from interstellar dust cloud with two embedded sources: IRAS 19181+1349

Mid and far infrared maps of many Galactic star forming regions show multiple peaks in close proximity, implying more than one embedded energy sources. With the aim of understanding such interstellar clouds better, the present study models the case of two embedded sources. A radiative transfer scheme has been developed to deal with an uniform density dust cloud in a cylindrical geometry, which includes isotropic scattering in addition to the emission and absorption processes. This scheme has been applied to the Galactic star forming region associated with IRAS 19181+1349, which shows observational evidence for two embedded energy sources. Two independent modelling approaches have been adopted, viz., to fit the observed spectral energy distribution (SED) best; or to fit the various radial profiles best, as a function of wavelength. Both the models imply remarkably similar physical parameters.Comment: 17 pages, 6 Figures, uses epsf.sty. To appear in Journal of Astronophysics & Astronom

The Photophysics of the Carrier of Extended Red Emission

Interstellar dust contains a component which reveals its presence by emitting a broad, unstructured band of light in the 540 to 950 nm wavelength range, referred to as Extended Red Emission (ERE). The presence of interstellar dust and ultraviolet photons are two necessary conditions for ERE to occur. This is the basis for suggestions which attribute ERE to an interstellar dust component capable of photoluminescence. In this study, we have collected all published ERE observations with absolute-calibrated spectra for interstellar environments, where the density of ultraviolet photons can be estimated reliably. In each case, we determined the band-integrated ERE intensity, the wavelength of peak emission in the ERE band, and the efficiency with which absorbed ultraviolet photons are contributing to the ERE. The data show that radiation is not only driving the ERE, as expected for a photoluminescence process, but is modifying the ERE carrier as manifested by a systematic increase in the ERE band's peak wavelength and a general decrease in the photon conversion efficiency with increasing densities of the prevailing exciting radiation. The overall spectral characteristics of the ERE and the observed high quantum efficiency of the ERE process are currently best matched by the recently proposed silicon nanoparticle (SNP) model. Using the experimentally established fact that ionization of semiconductor nanoparticles quenches their photoluminescence, we proceeded to test the SNP model by developing a quantitative model for the excitation and ionization equilibrium of SNPs under interstellar conditions for a wide range of radiation field densities.Comment: 42 p., incl. 8 fig. Accepted for publication by Ap

On-sky observations with an achromatic hybrid phase knife coronagraph in the visible

CONTEXT: The four-quadrant phase mask stellar coronagraph, introduced by D. Rouan et al., is capable of achieving very high dynamical range imaging and was studied in the context of the direct detection of extra-solar planets. Achromatic four-quadrant phase mask is currently being developed for broadband IR applications. AIMS: We report on laboratory and on-sky tests of a prototype coronagraph in the visible. This prototype, the achromatic hybrid phase knife coronagraph, was derived from the four-quadrant phase mask principle. METHODS: The instrumental setup implementing the coronagraph itself was designed to record the pre- and post-coronagraphic images simultaneously so that an efficient real-time image selection procedure can be performed. We describe the coronagraph and the associated tools that enable robust and repeatable observations. We present an algorithm of image selection that has been tested against the real on-sky data of the binary star HD80081 (* 38 Lyn). RESULTS Although the observing conditions were poor, the efficiency of the proposed method is proven. From this experiment, we derive procedures that can apply to future focal instruments associating adaptive optics and coronagraphy, targeting high dynamic range imaging in astronomy, such as detecting extra-solar planets