101 research outputs found

    Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

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    International audienceIn this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We use gaussian-shaped filters as well as actual filter transmission curves to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. The moderate-resolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940 nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10?6 to 10?4, and typical response curves of commercially available silicon photodiodes are included into the calculations. It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is systematically underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. We apply published parameterized transmittance functions to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. Further investigations will use experimental data from field campaigns to validate these findings

    Technical Note: Improved total atmospheric water vapour amount determination from near-infrared filter measurements with sun photometers

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    International audienceIn this work we explore the effect of the contribution of the solar spectrum to the recorded signal in wavelengths outside the typical 940-nm filter's bandwidth. We employ gaussian-shaped filters as well as actual filter transmission curves, mainly AERONET data, to study the implications imposed by the non-zero out-of-band contribution to the coefficients used to derive precipitable water from the measured water vapour band transmittance. Published parameterized transmittance functions are applied to the data to determine the filter coefficients. We also introduce an improved, three-parameter, fitting function that can describe the theoretical data accurately, with significantly less residual effects than with the existing functions. The moderate-resolution SMARTS radiative transfer code is used to predict the incident spectrum outside the filter bandpass for different atmospheres, solar geometries and aerosol optical depths. The high-resolution LBLRTM radiative transfer code is used to calculate the water vapour transmittance in the 940-nm band. The absolute level of the out-of-band transmittance has been chosen to range from 10?6 to 10?4, and typical response curves of commercially available silicon photodiodes are included into the calculations. It is shown that if the out-of-band transmittance effect is neglected, as is generally the case, then the derived columnar water vapour is mainly underestimated by a few percents. The actual error depends on the specific out-of-band transmittance, optical air mass of observation and water vapour amount. Further investigations will use experimental data from field campaigns to validate these findings

    The kinematics of the bi-lobal supernova remnant G 65.3+5.7 - Paper II

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    Further deep, narrow-band images in the light of [O III] 5007 A have been added to the previous mosaic of the faint galactic supernova remnant G 65.3+5.7. Additionally longslit spatially resolved [O III] 5007 A line profiles have been obtained at sample positions using the Manchester Echelle Spectrometer at the San Pedro Martir observatory. The remnant is shown to be predominantly bi-lobal with an EW axis for this structure. However, a faint additional northern lobe has now been revealed. Splitting of the profiles along the slit lengths, when extrapolated to the remnant's centre, although uncertain suggests that the expansion velocity of this remnant is between 124 and 187 km/s ie much lower than the 400 km/s previously predicted for the forward shock velocity from the X-ray emission. An expansion proper motion measurement of 2.1+-0.4 arcsec in 48 years for the remnant's filamentary edge in the light of Halpha+[N II] has also been made. When combined with an expansion velocity of ~155 km/s, a distance of ~800 pc to G 65.3+5.7 is derived. Several possibilities are considered for the large difference in the expansion velocity measured here and the 400 km/s shock velocity required to generate the X-ray emission. It is also suggested that the morphology of the remnant may be created by a tilt in the galactic magnetic field in this vicinity.Comment: 10 pages, 5 figures, accepted for publication in A&

    Imaging and spectroscopy of the faint remnant G 114.3+0.3

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    We present the first calibrated CCD images of the faint supernova remnant G 114.3+0.3 in the emission lines of [OII], [OIII], Halpha+[NII] and [SII]. The deep low ionization CCD images reveal diffuse emission in the south and central areas of the remnant. These are correlated with areas of intense radio emission, while estimates of the [SII]/Halpha ratio suggest that the detected emission originates from shock heated gas. In the medium ionization image of [OIII] we discovered a thin filament in the south matching very well the outer radio contours. This filament is not continuous over its total extent but shows variations in the intensity, mainly in the south-west suggesting inhomogeneous interstellar clouds. Deep long-slit spectra were also taken along the [OIII] filament clearly identifying the observed emission as emission from shock heated gas. The Halpha emission is a few times 10^(-17) erg s^(-1) cm^(-2) arcsec^(-2), while the variations seen in the [OIII] flux suggest shock velocities into the interstellar clouds around or below 100 km/s. The sulfur line ratio approaches the low density limit implying electron densities less than ~500 cm^(-3).Comment: 6 pages, 4 figures, accepted for publication in A&

    The peculiar supernova remnant CTB 80

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    Deep CCD exposures of the peculiar supernova remnant CTB 80 in the light of major optical lines have been obtained. These images reveal significant shock heated emission in the area of the remnant. The sulfur line image shows emission in the north along the outer boundary of the IRAS and HI shells. The comparison between the [OIII] and [OII] line images further suggest the presence of significant inhomogeneities in the interstellar medium. The flux calibrated images do not indicate the presence of incomplete recombination zones, and we estimate that the densities of the preshock clouds should not exceed a few atoms per cm^3. The area covered by the optical radiation along with the radio emission at 1410 MHz suggest that CTB 80 occupies a larger angular extent than was previously known.Comment: 19 pages, 6 png figures. Submitted revised version to A &

    Candidates for giant lobes projecting from the LBV stars P Cygni and R 143

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    Deep, wide-field, continuum-subtracted, images in the light of the Halpha+[NII] 6548 & 6584 A and [O III] 5007 A nebular emission lines have been obtained of the environment of the Luminous Blue Variable (LBV) star P Cygni. A previously discovered, receding, nebulous filament along PA 50 deg has now been shown to extend up to 12' from this star. Furthermore, in the light of [O III] 5007 A, a southern counterpart is discovered as well as irregular filaments on the opposite side of P Cygni. Line profiles from this nebulous complex indicate that this extended nebulosity is similar to that associated with middle-aged supernova remnants. However, there are several indications that it has originated in P Cygni and is not just a chance superposition along the same sight-line. This possibility is explored here and comparison is made with a new image of the LBV star R 143 in the LMC from which similar filaments appear to project. The dynamical age of the P Cygni giant lobe of ~5x10^{4} yr is consistent with both the predicted and observed durations of the LBV phases of 50M stars after they have left the main sequence. Its irregular shape may have been determined by the cavity formed in the ambient gas by the energetic wind of the star, and shaped by a dense torus, when on the main sequence. The proper motion and radial velocity of P Cygni, with respect to its local environment, could explain the observed angular and kinematical shifts of the star compared with the giant lobe.Comment: 7 pages, 3 figures, accepted for publication in A&

    The faint supernova remnant G 116.5+1.1 and the detection of a new candidate remnant

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    The extended supernova remnant G 116.5+1.1 was observed in the optical emission lines of Halpha+[N II], [S II] and [O III]; deep long-slit spectra were also obtained. The morphology of the remnant's observed emission is mainly diffuse and patchy in contrast to the known filamentary emission seen along the western limb. The bulk of the detected emission in the region appears unrelated to the remnant but there is one area of emission in the south-east which is characterized by a [S II]/Halpha ratio of ~0.5, implying a possible relation to G 116.5+1.1. If this is actually the case, it would imply a more extended remnant than previously realized. Emission in the [O III] 5007 A line image is not detected, excluding moderate or fast velocity shocks running into ionized interstellar clouds. Our current estimate of the distance to G 116.5+1.1 of ~3 kpc is in agreement with earlier estimates and implies a very extended remnant (69 pc x 45 pc). Observations further to the north-east of G 116.5+1.1 revealed a network of filamentary structures prominent in Halpha+[N II] and [S II] but failed to detect [O III] line emission. Long-slit spectra in a number of positions provide strong evidence that this newly detected emission arises from shock heated gas. Typical Halpha fluxes lie in the range of 9 to 17 x10^{-17} erg/s/cm^2/ arcsec^2, while low electron densities are implied by the intensities of the sulfur lines. Weak emission from the medium ionization line at 5007 A is detected in only one spectrum. Cool dust emission at 60 and 100 microns may be correlated with the optical emission in a limited number of positions. Surpisingly, radio emission is not detected in published surveys suggesting that the new candidate remnant may belong to the class of "radio quiet" supernova remnants.Comment: 10 pages, 5 figures, accepted for publication in A&
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