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A Geant4 based simulation platform of the Holland Proton Therapy Centre (HollandPTC, Netherlands) R&D beamline (G4HPTC-R&D) was developed to enable the planning, optimisation and advanced dosimetry for radiobiological studies. It implemented a six parameter non-symmetrical Gaussian pencil beam surrogate model to simulate the R&D beamline in both a pencil beam and passively scattered field configuration. Three different experimental proton datasets (70 MeV, 150 MeV, and 240 MeV) of the pencil beam envelope evolution in free air and depth-dose profiles in water were used to develop a set of individual parameter surrogate functions to enable the modelling of the non-symmetrical Gaussian pencil beam properties with only the ProBeam isochronous cyclotron mean extraction proton energy as input. This refined beam model was then benchmarked with respect to three independent experimental datasets of the R&D beamline operating in both a pencil beam configuration at 120 and 200 MeV, and passively scattered field configuration at 150 MeV. It was shown that the G4HPTC-R&D simulation platform can reproduce the pencil beam envelope evolution in free air and depth-dose profiles to within an accuracy on the order of $\pm$5% for all tested energies, and that it was able to reproduce the 150 MeV passively scattered field to the specifications need for clinical and radiobiological applications.

HollandPTC is an independent outpatient center for proton therapy, scientific research, and education. Patients with different types of cancer are treated with Intensity Modulated Proton Therapy (IMPT). In addition, the HollandPTC R&D consortium conducts scientific research into the added value and improvements of proton therapy. To this end, HollandPTC created clinical and pre-clinical research facilities including a versatile R&D proton beamline for various types of biologically and technologically oriented research. In this work, we present the characterization of the R&D proton beam line of HollandPTC. Its pencil beam mimics the one used for clinical IMPT, with energy ranging from 70 up to 240 MeV, which has been characterized in terms of shape, size, and intensity. For experiments that need a uniform field in depth and lateral directions, a dual ring passive scattering system has been designed, built, and characterized. With this system, field sizes between 2x2 cm2 and 20x20 cm2 with 98% uniformity are produced with dose rates ranging from 0.5 Gy/min up to 9 Gy/min. The unique and customized support of the dual ring system allows switching between a pencil beam and a large field in a very simple and fast way, making the HollandPTC R&D proton beam able to support a wide range of different applications.

We present a comprehensive examination of interstellar P and Cl abundances based on an analysis of archival spectra acquired with the Space Telescope Imaging Spectrograph of the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. Column densities of P II, Cl I, and Cl II are determined for a combined sample of 107 sight lines probing diffuse atomic and molecular gas in the local Galactic interstellar medium (ISM). We reevaluate the nearly linear relationship between the column densities of Cl I and H$_2$, which arises from the rapid conversion of Cl$^+$ to Cl$^0$ in regions where H$_2$ is abundant. Using the observed total gas-phase P and Cl abundances, we derive depletion parameters for these elements, adopting the methodology of Jenkins. We find that both P and Cl are essentially undepleted along sight lines showing the lowest overall depletions. Increasingly severe depletions of P are seen along molecule-rich sight lines. In contrast, gas-phase Cl abundances show no systematic variation with molecular hydrogen fraction. However, enhanced Cl (and P) depletion rates are found for a subset of sight lines showing elevated levels of Cl ionization. An analysis of neutral chlorine fractions yields estimates for the amount of atomic hydrogen associated with the H$_2$-bearing gas in each direction. These results indicate that the molecular fraction in the H$_2$-bearing gas is at least 10% for all sight lines with $\log N({\rm H}_2)\gtrsim18$ and that the gas is essentially fully molecular at $\log N({\rm H}_2)\approx21$., Comment: 44 pages, 21 figures, accepted for publication in ApJ

Our understanding of radiation induced cellular damage has greatly improved over the past decades. Despite this progress, there are still many obstacles to fully understanding how radiation interacts with biologically relevant cellular components to form observable endpoints. One hurdle is the difficulty faced by members of different research groups in directly comparing results. Multiple Monte Carlo codes have been developed to simulate damage induction at the DNA scale, while at the same time various groups have developed models that describe DNA repair processes with varying levels of detail. These repair models are intrinsically linked to the damage model employed in their development, making it difficult to disentangle systematic effects in either part of the modelling chain. The modelling chain typically consists of track structure Monte Carlo simulations of the physics interactions creating direct damages to the DNA; followed by simulations of the production and initial reactions of chemical species causing indirect damages. After the DNA damage induction, DNA repair models combine the simulated damage patterns with biological models to determine the biological consequences of the damage. We propose a new Standard data format for DNA Damage to unify the interface between the simulation of damage induction and the biological modelling of cell repair processes. Such a standard greatly facilitates inter model comparisons, providing an ideal environment to tease out model assumptions and identify persistent, underlying mechanisms. Through inter model comparisons, this unified standard has the potential to greatly advance our understanding of the underlying mechanisms of radiation induced DNA damage and the resulting observable biological effects.

Gibbs energy representations for ice III, V and VI are reported. These were constructed using new measurements of volumes at high pressure over a range of low temperatures combined with calculated vibrational energies grounded in statistical physics. The collection of representations including ice Ih and water (released as the open source SeaFreeze framework) allow accurate determinations of thermodynamics properties (phase boundaries, density, heat capacity, bulk modulus, thermal expansivity, chemical potentials) and seismic wave velocities over the entire range of conditions encountered in hydrospheres in our solar system (220 - 500K to 2300 MPa). These comprehensive representations allow exploration of the rich spectrum of thermodynamic behavior in the H2O system. Although the results are broadly applicable in science and engineering, their use in habitability analysis in water-rich planetary bodies of our solar system and beyond is particularly relevant.

Organ-specific, targeted Field-of-View (FoV) Positron Emission Tomography (PET)/Magnetic Resonance Imaging (MRI) inserts are viable solutions for a number of imaging tasks where whole-body PET/MRI systems lack the necessary sensitivity and resolution. To meet the required PET detector performance of these systems, high count-rates and effective spatial resolutions on the order of a few mm, a novel two-axis patterned reflector foil pixelated scintillator crystal array design is developed and its proof-of-concept illustrated in-silico with the Monte Carlo radiation transport modelling toolkit Geant4. It is shown that the crystal surface roughness and phased open reflector cross-section patterns could be optimised to maximise either the PET radiation detector's effective spatial resolution, or count rate before event pile up. In addition, it was illustrated that these two parameters had minimal impact on the energy and time resolution of the proposed PET radiation detector design. Finally, it is shown that a PET radiation detector with balance performance could be constructed using ground crystals and phased open reflector cross-section pattern corresponding to the middle of the tested range.

We present observations of highly frustrated quasi two-dimensional (2D) magnetic correlations in the honeycomb lattice layers of the S$_{eff}$ = 1/2 compound $\gamma$-BaCo$_2$(PO$_4$)$_2$ ($\gamma$-BCPO). Specific heat shows a broad peak comprised of two weak kink features at $T_{N1} \sim$ 6 K and $T_{N2} \sim$ 3.5 K, the relative weights of which can be modified by sample annealing. Neutron powder diffraction measurements reveal short range quasi-2D order that is established below $T_{N1}$ and $T_{N2}$, at which two separate, incompatible, short range magnetic orders onset: commensurate antiferromagnetic correlations with correlation length $\xi_c = 60\pm2$ \AA \ ($T_{N1}$) and in quasi-2D helical domains with $\xi_h = 350 \pm 11$ \AA \ ($T_{N2}$). The ac magnetic susceptibility response lacks frequency dependence, ruling out spin freezing. Inelastic neutron scattering data on $\gamma$-BCPO is compared with linear spin wave theory, and two separate parameter regions of the XXZ $J_1$-$J_2$-$J_3$ model with ferromagnetic nearest-neighbor exchange $J_1$ are favored, both near regions of high classical degeneracy. High energy coherent excitations ($\sim 10$ meV) persist up to at least 40 K, suggesting strong in-plane correlations persist above $T_N$. These data show that $\gamma$-BCPO is a rare highly frustrated, quasi-2D S$_{eff}$ = 1/2 honeycomb lattice material which resists long range magnetic order and spin freezing., Comment: 9 pages, 12 figures

The antiferromagnetic pyrochlore material NaCaCo$_2$F$_7$ is a thermal spin liquid over a broad temperature range (~ 140 K down to $T_F = 2.4 $K), in which magnetic correlations between Co$^{2+}$ dipole moments explore a continuous manifold of antiferromagnetic XY states. The thermal spin liquid is interrupted by spin freezing at a temperature that is ~ 2 % of the mean field interaction strength, leading to short range static XY clusters with distinctive relaxation dynamics. Here we report the low energy inelastic neutron scattering response from the related compound NaSrCo$_2$F$_7$, confirming that it hosts the same static and dynamic spin correlations as NaCaCo$_2$F$_7$. We then present the single-ion levels of Co$^{2+}$ in these materials as measured by inelastic neutron scattering. An intermediate spin orbit coupling model applied to an ensemble of trigonally distorted octahedral crystal fields accounts for the observed transitions. The single-ion ground state of Co$^{2+}$ is a Kramers doublet with a strongly XY-like $g$-tensor ($g_{xy}/g_{z}$ ~ 3). The local disorder inherent from the mixed pyrochlore $A$ sites (Na$^{+}$/Ca$^{2+}$ and Na$^{+}$/Sr$^{2+}$) is evident in these measurements as exaggerated broadening of some of the levels. A simple model that reproduces the salient features of the single-ion spectrum produces approximately 8.4 % and 4.1 % variation in the $z$ and $xy$ components of the $g$-tensor, respectively. This study confirms that an $S_{eff} =1/2$ model with XY antiferromagnetic exchange and weak exchange disorder serves as a basic starting point in understanding the low temperature magnetic behavior of these strongly frustrated magnets., Comment: 12 pages, 7 figures

The formation scenario of a gapped disk, i.e., transitional disk, and its asymmetry is still under debate. Proposed scenarios such as disk-planet interaction, photoevaporation, grain growth, anticyclonic vortex, eccentricity, and their combinations would result in different radial distributions of the gas and the small (sub-$\mu$m size) and large (millimeter size) dust grains as well as asymmetric structures in a disk. Optical/near-infrared (NIR) imaging observations and (sub-)millimeter interferometry can trace small and large dust grains, respectively; therefore multi-wavelength observations could help elucidate the origin of complicated structures of a disk. Here we report SMA observations of the dust continuum at 1.3~mm and $^{12}$CO~$J=2\rightarrow1$ line emission of the pre-transitional protoplanetary disk around the solar-mass star PDS~70. PDS~70, a weak-lined T Tauri star, exhibits a gap in the scattered light from its disk with a radius of $\sim$65~AU at NIR wavelengths. However, we found a larger gap in the disk with a radius of $\sim$80~AU at 1.3~mm. Emission from all three disk components (the gas and the small and large dust grains) in images exhibits a deficit in brightness in the central region of the disk, in particular, the dust-disk in small and large dust grains has asymmetric brightness. The contrast ratio of the flux density in the dust continuum between the peak position to the opposite side of the disk reaches 1.4. We suggest the asymmetries and different gap-radii of the disk around PDS~70 are potentially formed by several (unseen) accreting planets inducing dust filtration., Comment: Accepted by ApJ

Herschel/HIFI spectroscopic observations of CO J=10-9, CO J=16-15 and [CII] towards HD 100546 are presented. The objective is to resolve the velocity profile of the lines to address the emitting region of the transitions and directly probe the distribution of warm gas in the disk. The spectra reveal double-peaked CO line profiles centered on the systemic velocity, consistent with a disk origin. The J=16-15 line profile is broader than that of the J=10-9 line, which in turn is broader than those of lower J transitions (6-5, 3-2, observed with APEX), thus showing a clear temperature gradient of the gas with radius. A power-law flat disk model is used to fit the CO line profiles and the CO rotational ladder simultaneously, yielding a temperature of T_0=1100 \pm 350 K (at r_0 = 13 AU) and an index of q=0.85 \pm 0.1 for the temperature radial gradient. This indicates that the gas has a steeper radial temperature gradient than the dust (mean q_{dust} ~ 0.5), providing further proof of the thermal decoupling of gas and dust at the disk heights where the CO lines form. The [CII] line profile shows a strong single-peaked profile red-shifted by 0.5 km s-1 compared to the systemic velocity. We conclude that the bulk of the [CII] emission has a non-disk origin (e.g., remnant envelope or diffuse cloud)., Comment: Accepted for publication in ApJL

We introduce a new computational approach for femtosecond pulse propagation in the transparency region of gases that permits full resolution in three space dimensions plus time while fully incorporating quantum coherent effects such as high-harmonic generation and strong-field ionization in a holistic fashion. This is achieved by utilizing a one-dimensional model atom with a delta-function potential which allows for a closed-form solution for the nonlinear optical response due to ground-state to continuum transitions. It side-steps evaluation of the wave function, and offers more than one hundred-fold reduction in computation time in comparison to direct solution of the atomic Schr\"odinger equation. To illustrate the capability of our new computational approach, we apply it to the example of near-threshold harmonic generation in Xenon, and we also present a qualitative comparison between our model and results from an in-house experiment on extreme ultraviolet generation in a femtosecond enhancement cavity., Comment: 16 pages, 9 figures

A large set of Spitzer-selected transitional disks in the Ophiuchus molecular cloud was recently examined by Cieza et al (2010), and 4 of the targets were identified as (giant) planet-forming candidates based on the morphology of their Spectral Energy Distributions (SEDs), the apparent lack of stellar companions, and evidence for accretion. Here we characterize the structures of these disks modeling their optical, infrared and (sub)millimeter SEDs. We use the Monte Carlo radiative transfer package RADMC to construct a parametric model of the dust distribution in a flared disk with an inner cavity and calculate the temperature structure consistent with the density profile, in thermal equilibrium with the irradiating star. For each object, we conducted a Bayesian exploration of the parameter space generating Monte Carlo Markov Chains (MCMC) that allow the identification of the best fit parameters and to constrain their range of statistical confidence. Our calculations point to the presence of evacuated cavities with radii ~2-8 AU, consistent with having been carved by embedded giant planets. We found parameter values consistent with those previously given in the literature, indicating a mild degree of grain growth and dust settling, which deserves to be investigated with further modeling and follow up observations. Resolved images with (sub)millimeter interferometers are required to break some of the degeneracies of the models and better constrain the physical properties of these fascinating disks., Comment: Accepted for publication in Astronomy & Astrophysics

We develop a new comagnetometer using $^{21}$Ne atoms with nuclear spin $I=3/2$ and Rb atoms polarized by spin-exchange with K atoms to search for tensor interactions that violate local Lorentz invariance. We frequently reverse orientation of the experiment and search for signals at the first and second harmonics of the sidereal frequency. We constrain 4 of the 5 spatial Lorentz-violating coefficients $c^n_{jk}$ that parameterize anisotropy of the maximum attainable velocity of a neutron at a level of $10^{-29}$, improving previous limits by 2 to 4 orders of magnitude and placing the most stringent constrain on deviations from local Lorentz invariance., Comment: 5 pages

Circumstellar disks are thought to experience a rapid "transition" phase in their evolution that can have a considerable impact on the formation and early development of planetary systems. We present new and archival high angular resolution (0.3" = 40-75 AU) Submillimeter Array (SMA) observations of the 880 micron dust continuum emission from 12 such transition disks in nearby star-forming regions. In each case, we directly resolve a dust-depleted disk cavity around the central star. Using radiative transfer calculations, we interpret these dust disk structures in a homogeneous, parametric model framework by reproducing their SMA visibilities and SEDs. The cavities in these disks are large (R_cav = 15-73 AU) and substantially depleted of small (~um-sized) dust grains, although their mass contents are still uncertain. The structures of the remnant material at larger radii are comparable to normal disks. We demonstrate that these large cavities are common among the millimeter-bright disk population, comprising at least 20% of the disks in the bright half of the millimeter luminosity (disk mass) distribution. Utilizing these results, we assess some of the physical mechanisms proposed to account for transition disk structures. As has been shown before, photoevaporation models do not produce the large cavity sizes, accretion rates, and disk masses representative of this sample. It would be difficult to achieve a sufficient decrease of the dust optical depths in these cavities by particle growth alone: substantial growth (to meter sizes or beyond) must occur in large (tens of AU) regions of low turbulence without also producing an abundance of small particles. Given those challenges, we suggest instead that the observations are most commensurate with dynamical clearing due to tidal interactions with low-mass companions --young brown dwarfs or giant planets on long-period orbits., Comment: ApJ, in press

The transition between massive Class II circumstellar disks and Class III debris disks, with dust residuals, has not yet been clearly understood. Disks are expected to dissipate with time, and dust clearing in the inner regions can be the consequence of several mechanisms. Planetary formation is one of them that will possibly open a gap inside the disk. According to recent models based on photometric observations, T Cha is expected to present a large gap within its disk, meaning that an inner dusty disk is supposed to have survived close to the star. We investigate this scenario with new near-infrared interferometric observations. We observed T Cha in the H and K bands using the AMBER instrument at VLTI and used the MCFOST radiative transfer code to model the SED of T Cha and the interferometric observations simultaneously and to test the scenario of an inner dusty structure. We also used a toy model of a binary to check that a companion close to the star can reproduce our observations. The scenario of a close (few mas) companion cannot satisfactorily reproduce the visibilities and SED, while a disk model with a large gap and an inner ring producing the bulk of the emission (in H and K-bands) close to 0.1 AU is able to account for all the observations. With this study, the presence of an optically thick inner dusty disk close to the star and dominating the H and K- bands emission is confirmed. According to our model, the large gap extends up to ~ 7.5 AU. This points toward a companion (located at several AU) gap-opening scenario to explain the morphology of T Cha.

The study of warm molecular gas in the inner region (<10 AU) of circumstellar disks around young stars is of significant importance to understand how planets are forming. This inner zone of disks can now be explored in unprecedented detail with the high spectral (R=100000) and spatial resolution spectrometer CRIRES at the VLT. This paper investigates a set of disks that show CO ro-vibrational v=1-0 4.7 micron emission line profiles characterized by a single, narrow peak and a broad base extending to > 50 km/s, not readily explained by just Keplerian motions of gas in the inner disk. The line profiles are very symmetric, have high line/continuum ratios and have central velocity shifts of <5 km/s relative to the stellar radial velocity. The disks in this subsample are accreting onto their central stars at high rates relative to the parent sample. All disks show CO lines from v=2, suggesting that the lines are excited, at least in part, by UV fluorescence. Analysis of their spatial distribution shows that the lines are formed within a few AU of the central star. It is concluded that these broad centrally peaked line profiles are inconsistent with the double peaked profiles expected from just an inclined disk in Keplerian rotation. Alternative non-Keplerian line formation mechanisms are discussed, including thermally and magnetically launched winds and funnel flows. The most likely interpretation is that these profiles originate from a combination of emission from the inner part (< a few AU) of a circumstellar disk, perhaps with enhanced turbulence, and a slow moving disk wind, launched by either EUV emission or soft X-rays., Comment: 21 pages, 19 figures, accepted A&A

We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental band at 4.6-5.0 um. The observations were carried out at the VLT and the Subaru Telescope at six epochs from April to August 2008, covering the plateau of the outburst and the fading phase to a quiescent state. The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 um, but composed of two subcomponents that decay with different rates. The narrow line emission (50 km s-1 in FWHM) is near the systemic velocity of EX Lupi. These emission lines appear exclusively in v=1-0. The line widths translate to a characteristic orbiting radius of 0.4 AU. The broad line component (FWZI ~ 150 km s-1) is highly excited upto v<=6. The line flux of the component decreases faster than the narrow line emission. Simple modeling of the line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04-0.4 AU. The excitation state, the decay speed of the line flux, and the line profile, indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event., Comment: 13 pages, 7 figures, Accepted for publication in ApJ

We performed a search for neutron spin coupling to a Lorentz and CPT-violating background field using a magnetometer with overlapping ensembles of K and $^3$He atoms. The co-magnetometer is mounted on a rotary platform for frequent reversal of its orientation. We measure sidereal oscillations in the signal to search for anomalous spin coupling of extra-solar origin. We determine the equatorial components of the background field interacting with the neutron spin to be $\widetilde{b}^n_X = (0.1 \pm 1.6) \times 10^{-33}$ GeV and $\widetilde{b}^n_Y = (2.5 \pm 1.6) \times 10^{-33}$ GeV, improving on the previous limit by a factor of 30. This measurement represents the highest energy resolution of any spin anisotropy experiment.

We present far-infrared spectroscopic observations, taken with the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory, of the protoplanetary disk around the pre-main-sequence star HD 100546. These observations are the first within the DIGIT Herschel key program, which aims to follow the evolution of dust, ice, and gas from young stellar objects still embedded in their parental molecular cloud core, through the final pre-main-sequence phases when the circumstellar disks are dissipated. Our aim is to improve the constraints on temperature and chemical composition of the crystalline olivines in the disk of HD 100546 and to give an inventory of the gas lines present in its far-infrared spectrum. The 69 \mu\m feature is analyzed in terms of position and shape to derive the dust temperature and composition. Furthermore, we detected 32 emission lines from five gaseous species and measured their line fluxes. The 69 \mu\m emission comes either from dust grains with ~70 K at radii larger than 50 AU, as suggested by blackbody fitting, or it arises from ~200 K dust at ~13 AU, close to the midplane, as supported by radiative transfer models. We also conclude that the forsterite crystals have few defects and contain at most a few percent iron by mass. Forbidden line emission from [CII] at 157 \mu\m and [OI] at 63 and 145 \mu\m, most likely due to photodissociation by stellar photons, is detected. Furthermore, five H2O and several OH lines are detected. We also found high-J rotational transition lines of CO, with rotational temperatures of ~300 K for the transitions up to J=22-21 and T~800 K for higher transitions.

DK Cha is an intermediate-mass star in transition from an embedded configuration to a star plus disk stage. We aim to study the composition and energetics of the circumstellar material during this pivotal stage. Using the Range Scan mode of PACS on the Herschel Space Observatory, we obtained a spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program. Almost 50 molecular and atomic lines were detected, many more than the 7 lines detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37 (E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan matches the flux expected from a model consisting of a star, a surrounding disk of 0.03 Solar mass, and an envelope of a similar mass, supporting the suggestion that the object is emerging from its main accretion stage. Molecular, atomic, and ionic emission lines in the far-infrared reveal the outflow's influence on the envelope. The inferred hot gas can be photon-heated, but some emission could be due to C-shocks in the walls of the outflow cavity., Comment: 4 Page letter, To appear in A&A special issue on Herschel

We present a deep optical/near-infrared imaging survey of the Serpens molecular cloud. This survey constitutes the complementary optical data to the Spitzer "Core To Disk" (c2d) Legacy survey in this cloud. The survey was conducted using the Wide Field Camera at the Isaac Newton Telescope. About 0.96 square degrees were imaged in the R and Z filters, covering the entire region where most of the young stellar objects identified by the c2d survey are located. 26524 point-like sources were detected in both R and Z bands down to R=24.5 mag and Z=23 mag with a signal-to-noise ratio better than 3. The 95% completeness limit of our catalog corresponds to 0.04 solar masses for members of the Serpens star forming region (age 2 Myr and distance 260 pc) in the absence of extinction. Adopting the typical extinction of the observed area (Av=7 mag), we estimate a 95% completeness level down to 0.1 solar masses. The astrometric accuracy of our catalog is 0.4 arcsec with respect to the 2MASS catalog. Our final catalog contains J2000 celestial coordinates, magnitudes in the R and Z bands calibrated to the SDSS photometric system and, where possible, JHK magnitudes from 2MASS for sources in 0.96 square degrees in the direction of Serpens. This data product has been already used within the frame of the c2d Spitzer Legacy Project analysis in Serpens to study the star/disk formation and evolution in this cloud; here we use it to obtain new indications of the disk-less population in Serpens., Comment: 7 page, 5 figures

Mid-infrared spectrophotometric observations have revealed a small sub-class of circumstellar disks with spectral energy distributions (SEDs) suggestive of large inner gaps with low dust content. However, such data provide only an indirect and model-dependent method of finding central holes. Imaging of protoplanetry disks provides an independent check of SED modeling. We present here the direct characterization of three 33-47 AU radii inner gaps, in the disks around LkHa 330, SR 21N and HD 135344B, via 340 GHz (880 micron) dust continuum aperture synthesis observations obtained with the Submillimeter Array (SMA). The large gaps are fully resolved at ~0\farcs3 by the SMA observations and mostly empty of dust, with less than 1 - 7.5 x 10^-6 Msolar of fine grained solids inside the holes. Gas (as traced by atomic accretion markers and CO 4.7 micron rovibrational emission) is still present in the inner regions of all three disks. For each, the inner hole exhibits a relatively steep rise in dust emission to the outer disk, a feature more likely to originate from the gravitational influence of a companion body than from a process expected to show a more shallow gradient like grain growth. Importantly, the good agreement of the spatially resolved data and spectrophotometry-based models lends confidence to current interpretations of SEDs, wherein the significant dust emission deficits arise from disks with inner gaps or holes. Further SED-based searches can therefore be expected to yield numerous additional candidates that can be examined at high spatial resolution., Comment: 19 pages, 4 figures, published in ApJ

Dust grains in the planet forming regions around young stars are expected to be heavily processed due to coagulation, fragmentation and crystallization. This paper focuses on the crystalline silicate dust grains in protoplanetary disks. As part of the Cores to Disks Legacy Program, we obtained more than a hundred Spitzer/IRS spectra of TTauri stars. More than 3/4 of our objects show at least one crystalline silicate emission feature that can be essentially attributed to Mg-rich silicates. Observational properties of the crystalline features seen at lambda > 20 mu correlate with each other, while they are largely uncorrelated with the properties of the amorphous silicate 10 mu feature. This supports the idea that the IRS spectra essentially probe two independent disk regions: a warm zone (< 1 AU) emitting at lambda ~ 10 mu and a much colder region emitting at lambda > 20 mu (< 10 AU). We identify a crystallinity paradox, as the long-wavelength crystalline silicate features are 3.5 times more frequently detected (~55 % vs. ~15%) than the crystalline features arising from much warmer disk regions. This suggests that the disk has an inhomogeneous dust composition within ~10 AU. The abundant crystalline silicates found far from their presumed formation regions suggests efficient outward radial transport mechanisms in the disks. The analysis of the shape and strength of both the amorphous 10 mu feature and the crystalline feature around 23 mu provides evidence for the prevalence of micron-sized grains in upper layers of disks. Their presence in disk atmospheres suggests efficient vertical diffusion, likely accompanied by grain-grain fragmentation to balance the efficient growth expected. Finally, the depletion of submicron-sized grains points toward removal mechanisms such as stellar winds or radiation pressure.

A magnetometer using spin-polarized K and $^3$He atoms occupying the same volume is used to search for anomalous nuclear spin-dependent forces generated by a separate $^3$He spin source. We measure changes in the $^3$He spin precession frequency with a resolution of 18 pHz and constrain anomalous spin forces between neutrons to be less than $2 \times 10^{-8}$ of their magnetic or less than $2\times 10^{-3}$ of their gravitational interactions on a length scale of 50 cm. We present new limits on neutron coupling to light pseudoscalar and vector particles, including torsion, and constraints on recently proposed models involving unparticles and spontaneous breaking of Lorentz symmetry., Comment: 4 pages, 4 figures, latest version as appeared in PRL

Mid-infrared spectrophotometric observations have revealed a small sub-class of circumstellar disks with spectral energy distributions (SEDs) suggestive of large inner gaps with low dust content. However, such data provide only an indirect and model dependent method of finding central holes. We present here the direct characterization of a 40 AU radius inner gap in the disk around LkHa 330 through 340 GHz (880 micron) dust continuum imaging with the Submillimeter Array (SMA). This large gap is fully resolved by the SMA observations and mostly empty of dust with less than 1.3 x 10^-6 M_solar of solid particles inside of 40 AU. Gas (as traced by accretion markers and CO M-band emission) is still present in the inner disk and the outer edge of the gap rises steeply -- features in better agreement with the underlying cause being gravitational perturbation than a more gradual process such as grain growth. Importantly, the good agreement of the spatially resolved data and spectrophometry-based model lends confidence to current interpretations of SEDs with significant dust emission deficits as arising from disks with inner gaps or holes. Further SED-based searches can therefore be expected to yield numerous additional candidates that can be examined at high spatial resolution., Comment: 11 pages, 3 figures, accepted to ApJL

We compute opacities for the electronic molecular band systems A 6Sigma+ -- X 6Sigma+ of CrH and CrD, and A 2Pi -- X 2Sigma+ of MgH and MgD. The opacities are computed by making use of existing spectroscopic constants for MgH and CrH. These constants are adjusted for the different reduced masses of MgD and CrD. Frank-Condon factors are used to provide intensities for the individual vibronic bands. These results are used in the computation of synthetic spectra between Tef = 1800 and 1200 K with an emphasis on the realisation of ``deuterium test'', first proposed by Bejar et al. (1999) to distinguish brown dwarfs from planetary mass objects. We discuss the possible use of CrD and MgD electronic bands for the "deuterium test". We find CrD to be the more promising of the two deuterides, potentially, the most useful bands of CrH/CrD are the Delta v = +1 and Delta v = -1 at 0.795 and 0.968 micron., Comment: 11 pages, 4 figs, 4 tables, accepted by MNRAS, revised version with the new D_o = 1.285 eV (Shayesteh et al., in prep.) for MgH

We have identified four circumstellar disks with a deficit of dust emission from their inner 15-50 AU. All four stars have F-G spectral type, and were uncovered as part of the Spitzer Space Telescope ``Cores to Disks'' Legacy Program Infrared Spectrograph (IRS) first look survey of ~100 pre-main sequence stars. Modeling of the spectral energy distributions indicates a reduction in dust density by factors of 100-1000 from disk radii between ~0.4 and 15-50 AU, but with massive gas-rich disks at larger radii. This large contrast between the inner and outer disk has led us to use the term `cold disks' to distinguish these unusual systems. However, hot dust [0.02-0.2 Mmoon] is still present close to the central star (R ~0.8 AU). We introduce the 30/13 micron, flux density ratio as a new diagnostic for identifying cold disks. The mechanisms for dust clearing over such large gaps are discussed. Though rare, cold disks are likely in transition from an optically thick to an optically thin state, and so offer excellent laboratories for the study of planet formation., Comment: 13 pages, 3 figures, accepted to ApJL

A full spectral survey was carried out towards the Giant Molecular Cloud complex, Sagittarius B2 (Sgr B2), using the ISO Long Wavelength Spectrometer Fabry-Perot mode. This provided complete wavelength coverage in the range 47-196 um (6.38-1.53 THz) with a spectral resolution of 30-40 km/s. This is an unique dataset covering wavelengths inaccessible from the ground. It is an extremely important region of the spectrum as it contains both the peak of the thermal emission from dust, and crucial spectral lines of key atomic (OI, CII, OIII, NII and NIII) and molecular species (NH3, NH2, NH, H2O, OH, H3O+, CH, CH2, C3, HF and H2D+). In total, 95 spectral lines have been identified and 11 features with absorption depth greater than 3 sigma remain unassigned. Most of the molecular lines are seen in absorption against the strong continuum, whereas the atomic and ionic lines appear in emission (except for absorption in the OI 63 um and CII 158 um lines). Sgr B2 is located close to the Galactic Centre and so many of the features also show a broad absorption profile due to material located along the line of sight. A full description of the survey dataset is given with an overview of each detected species and final line lists for both assigned and unassigned features., Comment: Accepted for publication in MNRAS

We announce the discovery of SST-Lup3-1, a very low mass star close to the brown dwarf boundary in Lupus III with a circum(sub)stellar disk, discovered by the `Cores to Disks' Spitzer Legacy Program from mid-, near-infrared and optical data, with very conspicuous crystalline silicate features in its spectrum. It is the first of such objects with a full 5 to 35 micron spectrum taken with the IRS and it shows strong 10 and 20 micron silicate features with high feature to continuum ratios and clear crystalline features out to 33 micron. The dust in the disk upper layer has a crystalline silicate grain fraction between 15% and 33%, depending on the assumed dust continuum. The availability of the full Spitzer infrared spectrum allows an analysis of the dust composition as a function of temperature and position in the disk. The hot (~ 300 K) dust responsible for the 10 micron feature consists of a roughly equal mix of small (~ 0.1 micron) and large (~ 1.5 micron) grains, whereas the cold (~ 70 K) dust responsible for the longer wavelength silicate features contains primarily large grains (> 1 micron). Since the cold dust emission arises from deeper layers in the inner (< 3 AU) disk as well as from the surface layers of the outer (3-5 AU) disk, this provides direct evidence for combined grain growth and settling in the disk. The inferred crystalline mass fractions in the two components are comparable. Since only the inner 0.02 AU of the disk is warm enough to anneal the amorphous silicate grains, even the lowest fraction of 15% of crystalline material requires either very efficient mixing or other formation mechanisms., Comment: Accepted for publication in ApJ. 19 pages and 4 figures. V2 with correct references

Recent results indicate that the grain size and crystallinity inferred from observations of silicate features may be correlated with spectral type of the central star and/or disk geometry. In this paper, we show that grain size, as probed by the 10 um silicate feature peak-to-continuum and 11.3-to-9.8 um flux ratios, is inversely proportional to log L_star. These trends can be understood using a simple two-layer disk model for passive irradiated flaring disks, CGPLUS. We find that the radius, R_10, of the 10 um silicate emission zone in the disk goes as (L_star/L_sun)^0.56, with slight variations depending on disk geometry (flaring angle, inner disk radius). The observed correlations, combined with simulated emission spectra of olivine and pyroxene mixtures, imply a grain size dependence on luminosity. Combined with the fact that R_10 is smaller for less luminous stars, this implies that the apparent grain size of the emitting dust is larger for low-luminositysources. In contrast, our models suggest that the crystallinity is only marginally affected, because for increasing luminosity, the zone for thermal annealing (assumed to be at T>800 K) is enlarged by roughly the same factor as the silicate emission zone. The observed crystallinity is affected by disk geometry, however, with increased crystallinity in flat disks. The apparent crystallinity may also increase with grain growth due to a corresponding increase in contrast between crystalline and amorphous silicate emission bands., Comment: 6 pages, 3 figures, scheduled to appear in ApJ, vol 658 (April 1, 2007)

Aims: We search for PAH features towards T Tauri stars and compare them with surveys of Herbig Ae/Be stars. The presence and strength of the PAH features are interpreted with disk radiative transfer models exploring the PAH feature dependence on the incident UV radiation, PAH abundance and disk parameters. Methods: Spitzer Space Telescope 5-35 micron spectra of 54 pre-main sequence stars with disks were obtained, consisting of 38 T Tauri, 7 Herbig Ae/Be and 9 stars with unknown spectral type. Results: Compact PAH emission is detected towards at least 8 sources of which 5 are Herbig Ae/Be stars. The 11.2 micron PAH feature is detected in all of these sources, as is the 6.2 micron PAH feature where short wavelength data are available. However, the 7.7 and 8.6 micron features appear strongly in only 1 of these 4 sources. PAH emission is observed towards at least 3 T Tauri stars (8% detection rate). The lowest mass source with PAHs in our sample is T Cha (G8). All 4 sources in our sample with evidence for dust holes in their inner disk show PAH emission, increasing the feature/continuum ratio. Typical 11.2 micron line intensities are an order of magnitude lower than those observed for the more massive Herbig Ae/Be stars. Measured line fluxes indicate PAH abundances that are factors of 10-100 lower than standard interstellar values. Conversely, PAH features from disks exposed to stars with Teff<=4200K without enhanced UV are predicted to be below the current detection limit, even for high PAH abundances. Disk modeling shows that the 6.2 and 11.2 micron features are the best PAH tracers for T Tauri stars, whereas the 7.7 and 8.6 micron bands have low feature over continuum ratios due to the strongly rising silicate emission., Comment: 20 pages, 15 figures, accepted for publication in A&A

The frequencies and line strengths of the 2Pi3/2 J=5/2-3/2 rotational transition of 17OH have been calculated from an analysis of its far-infrared laser magnetic resonance spectrum. These results have been used to make the first detection of a pure rotational transition of 17OH in the ISM. Two resolved components of this transition appear in absorption towards the giant molecular cloud Sagittarius B2, which was observed at a spectral resolution of 33 km/s with the Fabry-Perot mode of the ISO Long Wavelength Spectrometer. The corresponding transition of 18OH was also observed and its line shape was modelled using HI measurements. The 18O/17O ratio of 3.5 was then used to compare this with the observed 17OH line shape., Comment: 4 pages, 3 figure, for associated ascii table see ftp://cdsarc.u-strasbg.fr/cats/J/A+A/406/L47/

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