Near-Infrared Imaging Polarimetry of Young Stellar Objects in rho-Ophiuchi

The results of a near-infrared (J H K LP) imaging linear polarimetry survey of 20 young stellar objects (YSOs) in rho Ophiuchi are presented. The majority of the sources are unresolved, with K-band polarizations, P_K < 6 per cent. Several objects are associated with extended reflection nebulae. These objects have centrosymmetric vector patterns with polarization discs over their cores; maximum polarizations of P_K > 20 per cent are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribution. K-band core polarizations >6 per cent are only observed in Class I YSOs. A 3D Monte Carlo model with oblate grains aligned with a magnetic field is used to investigate the flux distributions and polarization structures of three of the rho Oph YSOs with extended nebulae. A rho proportional to r^(-1.5) power law for the density is applied throughout the envelopes. The large-scale centrosymmetric polarization structures are due to scattering. However, the polarization structure in the bright core of the nebula appears to require dichroic extinction by aligned non-spherical dust grains. The position angle indicates a toroidal magnetic field in the inner part of the envelope. Since the measured polarizations attributed to dichroic extinction are usually <10 per cent, the grains must either be nearly spherical or very weakly aligned. The higher polarizations observed in the outer parts of the reflection nebulae require that the dust grains responsible for scattering have maximum grain sizes <=1.05 microns.Comment: 26 pages. Accepted by MNRAS. Available as online early versio

Seismic retrofitting and health monitoring of school buildings of Cyprus

The vulnerability of existing buildings to seismic forces and their retrofitting is an international problem. The majority of structures in seismic-prone areas worldwide are structures that have been designed either without the consideration of seismic forces, or with previous codes of practice specifying lower levels of seismic forces. In Cyprus, after the three earthquakes that occurred in 1995, 1996, and 1999, the Cyprus State, acting in a pioneering way internationally, has decided the seismic retrofitting of all school buildings, taking into account the sensitivity of the society towards these structures, which house the future generation of the society. In this paper the overall assessment methodology is presented, along with details of the over 10 year ongoing retrofitting program of the school buildings of Cyprus, with emphasis on the description of the program and the development of a wireless monitoring system. In addition, mathematical models of selected school buildings are presented and comparison is made with in-situ measurement

Dust-driven Dynamos in Accretion Disks

Magnetically driven astrophysical jets are related to accretion and involve toroidal magnetic field pressure inflating poloidal magnetic field flux surfaces. Examination of particle motion in combined gravitational and magnetic fields shows that these astrophysical jet toroidal and poloidal magnetic fields can be powered by the gravitational energy liberated by accreting dust grains that have become positively charged by emitting photo-electrons. Because a dust grain experiences magnetic forces after becoming charged, but not before, charging can cause irreversible trapping of the grain so dust accretion is a consequence of charging. Furthermore, charging causes canonical angular momentum to replace mechanical angular momentum as the relevant constant of the motion. The resulting effective potential has three distinct classes of accreting particles distinguished by canonical angular momentum, namely (i) "cyclotron-orbit", (ii) "Speiser-orbit", and (iii) "zero canonical angular momentum" particles. Electrons and ions are of class (i) but depending on mass and initial orbit inclination, dust grains can be of any class. Light-weight dust grains develop class (i) orbits such that the grains are confined to nested poloidal flux surfaces, whereas grains with a critical weight such that they experience comparable gravitational and magnetic forces can develop class (ii) or class (iii) orbits, respectively producing poloidal and toroidal field dynamos.Comment: 70 pages, 16 figure

UV Circular Polarisation in Star Formation Regions : The Origin of Homochirality?

Ultraviolet circularly polarised light has been suggested as the initial cause of the homochirality of organic molecules in terrestrial organisms, via enantiomeric selection of prebiotic molecules by asymmetric photolysis. We present a theoretical investigation of mechanisms by which ultraviolet circular polarisation may be produced in star formation regions. In the scenarios considered here, light scattering produces only a small percentage of net circular polarisation at any point in space, due to the forward throwing nature of the phase function in the ultraviolet. By contrast, dichroic extinction can produce a fairly high percentage of net circular polarisation (∼10%) and may therefore play a key role in producing an enantiomeric excessPeer reviewe

ISO observations toward the reflection nebula NGC 7023: A nonequilibrium ortho- to para-H2 ratio

We have observed the S(0), S(1), S(2), S(3), S(4) and S(5) rotational lines of molecular hydrogen (H2) towards the peak of the photodissociation region (PDR) associated with the reflection nebula NGC 7023. The observed H2 line ratios show that they arise in warm gas with kinetic temperatures ~300 - 700 K. However, the data cannot be fitted by an ortho- to para- (OTP) ratio of 3. An OTP ratio in the range ~1.5 - 2 is necessary to explain our observations. This is the first detection of a non-equilibrium OTP ratio measured from the H2 pure-rotational lines in a PDR. The existence of a dynamical PDR is discussed as the most likely explanation for this low OTP ratio.Comment: 4 pages, 3 figure

High Resolution Millimeter-Wave Mapping of Linearly Polarized Dust Emission: Magnetic Field Structure in Orion

We present 1.3 and 3.3 mm polarization maps of Orion-KL obtained with the BIMA array at approximately 4 arcsec resolution. Thermal emission from magnetically aligned dust grains produces the polarization. Along the Orion ``ridge'' the polarization position angle varies smoothly from about 10 degrees to 40 degrees, in agreement with previous lower resolution maps. In a small region south of the Orion ``hot core,'' however, the position angle changes by 90 degrees. This abrupt change in polarization direction is not necessarily the signpost of a twisted magnetic field. Rather, in this localized region processes other than the usual Davis-Greenstein mechanism might align the dust grains with their long axes parallel with the field, orthogonal to their normal orientation.Comment: AAS preprint:14 pages, 2 figures (3mm.eps and 1mm.eps); requires aaspp4.sty To be published in Astrophysical Journal Letter

HeI 1.083 micron emission and absorption in DG Tau: line excitation in jet, hot wind, and accretion flow

We present long-slit spectroscopy and spectro-astrometry of HeI 1.083 micron emission in the T Tauri star, DG Tau. We identify three components in the HeI feature: (1) a blueshifted emission component atv -200 km s^-1, (2) a bright emission component at zero-velocity with a FWZI of ~500 km s^-1, and (3) a blueshifted absorption feature at velocities between -250 and -500 km s^-1. The position and velocity of the blueshifted HeI emission coincide with a high-velocity component (HVC) of the [FeII] 1.257 micron emission, which arises from a jet within an arcsecond of the star. The presence of such a high excitation line (excitation energy ~ 20 eV) within the jet supports the scenario of shock heating. The bright HeI component does not show any spatial extension, and it is likely to arise from magnetospheric accretion columns. The blueshifted absorption shows greater velocities than that in H-alpha, suggesting that these absorption features arise from the accelerating wind close to the star.Comment: 10 pages including 2 figures, accepted for publication in the Astrophysical Journal Letter

A multiwavelength study of Galactic HII region Sh2-294

We present the observational results of Galactic HII region S294, using optical photometry, narrow-band imaging and radio continuum mapping at 1280 MHz, together with archival data from 2MASS, MSX and IRAS surveys. The stellar surface density profile indicates that the radius of the cluster associated with the S294 region is ~ 2.3 arcmin. We found an anomalous reddening law for the dust inside the cluster region and the ratio of total-to-selective extinction is found to be 3.8+-0.1. We estimate the minimum reddening E (B-V) = 1.35 mag and distance of 4.8+-0.2 kpc to the region from optical CC and CM diagrams. We identified the ionizing source of the HII region, and spectral type estimates are consistent with a star of spectral type ~ B0 V. The 2MASS JHKs images reveal a partially embedded cluster associated with the ionizing source along with a small cluster towards the eastern border of S294. The ionization front seen along the direction of small cluster in radio continuum and Halpha images, might be due to the interaction of ionizing sources with the nearby molecular cloud. We found an arc shaped diffuse molecular hydrogen emission at 2.12 micron and a half ring of MSX dust emission which surrounds the ionized gas in the direction of the ionization front. Self consistent radiative transfer model of mid- to far-infrared continuum emission detected near small cluster is in good agreement with the observed spectral energy distribution of a B1.5 ZAMS star. The morphological correlation between the ionised and molecular gas, along with probable time scale involved between the ionising star, evolution of HII region and small cluster, indicates that the star-formation activity observed at the border is probably triggered by the expansion of HII region.Comment: 50 pages, 21 figures: Accepted by The Astrophysical Journal; Also available at http://www.tifr.res.in/~ojha/S294.pd

A new era of wide-field submillimetre imaging: on-sky performance of SCUBA-2

SCUBA-2 is the largest submillimetre wide-field bolometric camera ever built. This 43 square arc-minute field-of-view instrument operates at two wavelengths (850 and 450 microns) and has been installed on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. SCUBA-2 has been successfully commissioned and operational for general science since October 2011. This paper presents an overview of the on-sky performance of the instrument during and since commissioning in mid-2011. The on-sky noise characteristics and NEPs of the 450 and 850 micron arrays, with average yields of approximately 3400 bolometers at each wavelength, will be shown. The observing modes of the instrument and the on-sky calibration techniques are described. The culmination of these efforts has resulted in a scientifically powerful mapping camera with sensitivities that allow a square degree of sky to be mapped to 10 mJy/beam rms at 850 micron in 2 hours and 60 mJy/beam rms at 450 micron in 5 hours in the best weather.Comment: 18 pages, 15 figures.SPIE Conference series 8452, Millimetre, Submillimetre and Far-infrared Detectors and Instrumentation for Astronomy VI 201

Multibeam Maser Survey of methanol and excited OH in the Magellanic clouds: new detections and maser abundance estimates

‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.12888.xPeer reviewe