ISO-LWS grating spectroscopy: the case of R CrA star forming region

We present the far infrared spectra of the R CrA star forming region obtained with ISO-LWS. We collected a pointed observation on the Herbig Ae star R CrA and a raster scan covering the surrounding region, where HH100 (with its exciting source) and the pre-Main Sequence star T CrA are located. The OI 63μm and the CII 158μm lines have been detected in all the pointed positions, with a ratio consistent with PDR excitation. CO rotational lines (between Jup=14 and Jup=19) are detected on R CrA; from their intensities we derived, using a LVG model, the density and temperature of the emitting region. Other molecular transitions (OH and H2O) have been detected on the investigated objects; the derived cooling of all the molecular species is in agreement with C-shock as the likely excitation mechanism. The continuum emission of R CrA peaks around 100μm (as expected for a Herbig star) while the other sources (T CrA, HH100) show increasing continua up to ~200μm, indicating that they are probably less evolved sources

Looking at the photon-dominated region in NGC 2024 through FIR line emission

We present the ISO-LWS spectra (45-200 μm) of both the molecular cloud NGC 2024 and its associated HII region. We observed the two Class 0 objects FIR3 and FIR5 and the infrared source IRS2. All the spectra appear quite similar, with approximately the same strength high-J CO rotational lines (from Jup=17 to Jup=14), and atomic and ionic lines from oxygen, carbon and nitrogen. This uniformity suggests the bulk of the emission is from the extended cloud, and is not related to the local source conditions. The molecular emission has been modelled with a large velocity gradient (LVG) code, and the results imply that the emission originates in a clumpy, extended PDR with a temperature T ~ 100 K and a density nH2 ~ 106 cm-3. CO column densities in excess of 1018 cm-2 are derived for this molecular component. A line intensity ratio I([O I] 63 μm)/I([O I] 145 μm) of about 5 is found through all the region, indicating either that these two lines are both optically thick at the same temperature of CO, or, more likely, that the 63 μm line is strongly absorbed by cold foreground gas. The ionised emission lines have been consistently modelled with CLOUDY; the lines arise from gas illuminated by an O9.5 star or its UV equivalent, representing the ionising capability of the whole OB cluster present in the region. From the intensity ratios of the ionic lines, relevant physical properties of the ionised gas (N/O abundance, electron density) are derived

Far infrared spectroscopy of FU Ori objects. ISO-LWS observations

We present the results of the first spectrophotometric observations of a sample of FU Ori objects obtained with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The [OI] (63 μm) and the [CII] (158 μm) lines are commonly observed in all spectra (both ON and OFF source). The observational novelty is the presence in most of the sources of the transition of ionised nitrogen [NII] (122 μm), which is not detected in other objects in a similar evolutionary phase. This line probes low ionisation and low density material not easily traced by other lines. Line intensities and intensity ratios are used along with model predictions to infer the prevailing mechanisms for line excitation. To reconcile our far-infrared spectroscopy with previous knowledge of these objects, the simultaneous presence of two components is required: well localised J-shocks, responsible for the [OI] emission, and an extended low density ionised medium produced by UV photons from the disc boundary layer, responsible for the [NII] and [CII] emission. A few molecular lines (CO, OH, H2O) associated with relatively cold and dense peaks are revealed and their intensities are in good agreement with the proposed scenario. Other ionic lines ([OIII] and [NIII]) are detected in two sources in the Cyg OB7 region and likely trace the presence of nearby HII regions

An infrared study of the L1551 star formation region

Spectroscopic observations using the Infrared Space Observatory are reported towards the two well known infrared sources and young stellar objects L1551 IRS 5 and L1551 NE, and at a number of locations in the molecular outflow. The ISO spectrum contains several weak gas-phase lines of O I, C II, [Fe II] and [Si II], along with solid state absorption lines of CO, CO2, H2O, CH4 and CH3OH. Hubble Space Telescope (HST) images with the NICMOS infrared camera reveal a diffuse conical shaped nebulosity, due to scattered light from the central object, with a jet emanating from L1551 IRS 5. The continuum spectral energy distribution has been modelled using a 2D radiative transfer model, and fitted for a central source luminosity of 45 L⊙, surrounding a dense torus extending to a distance of ~ 3x104 AU, which has a total mass of ~ 13 M⊙. The visual extinction along the outflow is estimated to be ≈ 10 and the mid-plane optical depth to L1551 IRS 5 to be ≈ 120. This model provides a good fit to the ISO spectral data, as well as to the spatial structures visible on archival HST/NICMOS data, mid-IR maps and sub-millimetre radio interferometry, and to ground-based photometry obtained with a range of different aperture sizes. On the basis of the above model, the extinction curve shows that emission at wavelengths shorter than ~ 2 μm is due to scattered light from close to L1551 IRS 5, while at wavelengths ≳ 4 μm, is seen through the full extinguishing column towards the central source. Several [Fe II] lines were detected in the SWS spectrum towards L1551 IRS 5. Although it would seem at first sight that shocks would be the most likely source of excitation for the [Fe II] in a known shocked region such as this, the line intensities do not fit the predictions of simple shock models. An alternative explanation has been examined where the [Fe II] gas is excited in hot ( ~ 4000 K) and dense (≳ 109 cm-3) material located close to the root of the outflow. The SWS observations did not detect any emission from rotationally excited H2. Observations with United Kingdom Infrared Telescope (UKIRT) of the vibrationally excited S- and Q-branch lines were however consistent with the gas having an excitation temperature of ~ 2500 K. There was no evidence of lower temperature ( ~ 500 K) H2 gas which might be visible in the rotational lines. Observations with UKIRT of the CO absorption bands close to 2.4 μm are best fit with gas temperatures ~ 2500 K, and a column density ~ 6x1020 cm-2. There is strong circumstantial evidence for the presence of dense (coronal and higher densities) and hot gas (at least 2500 K up to perhaps 5000 K) close to the protostar. However there is no obvious physical interpretation fitting all the data which can explain this

Silicon photonics in Pirelli

Silicon is the dominant material in the microelectronic industry and silicon photonics is rapidly gaining importance as a technological platform for a wide range of applications in telecom, and optical interconnect. It allows the implementation of many photonic functions through the use of wafer-scale technologies normally used for advanced CMOS-processing. In this paper some of the most important issues toward a practical implementation of Silicon photonics into an industrial device will be addressed: low loss waveguides, polarization handling, tunability, hitless switching. A tunable Add-Drop multiplexer has been chosen as a case Study of a fully integrated device

Gender differences in the use of cardiovascular interventions in HIV-positive persons; the D:A:D Study

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