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< < | The subtraction of the background observations has minimized the differences delivered by these various methods. Thus we choose removing the simple median of all data points outside the 600" radius around the center. | |||||||
> > | The subtraction of the background observations has minimized the differences delivered by these various methods. Visual inspection of the background subtracted maps shows that for the 1" resolution maps the useful area stops outside of 750" because of too many NaNs. Thus we choose subtracting the simple median of all data points between 600" and 750" radius around the center. | |||||||
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Figure 4: Overplot of Triton positions during the observation over PSW isophotes of the Neptune map as thick black trace. The levels are in Jy and the small tick marks on the side are arc seconds. | ||||||||
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> > | Radial Beam ProfilesSince the ellipticity of the beam is moderate a radial beam profile can be calculated to study the far field at a better S/N. The beam center is fitted with a Gaussian, and average map values within concentric annuli of 1" radial difference around that center are calculated. Plots of these profiles versus radius are shofn in Figure 5. | |||||||
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Solid AnglesAfter background tilt subtraction and background source removal the signal was averaged over concentric annuli around the source and this radialized beam profile was plotted against radius (Plot 1). To ensure symmetry, e.g. flatness of the background, the same was also plotted for three sectors (Plot 2 and 3). From the radialized beam profile a new background was determined and subtracted based on the necessity to have only positive flux within the errors (Plot 4). |
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Analysis Details of SPIRE Photmeter Beam Profiles( Bernhard Schulz, October 2014) | |||||||||||||||||||||||||||||||||||||||||
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Initial Beam ProfileThe beam profile was reconstructed from four fine scan maps with obsids: 1342186522, 1342186523, 1342186524, 1342186525, and two observations of the same sky region 1342255134 and 1342255135 three years later. The Neptune observations followed the small proper motion of the object. The scan pattern had, unlike standard scan map observations, very narrowly spaced scan legs. The maps scanning in spacecraft-y direction consisted of 150 scan legs separated by 3.9", the orthogonally scanning maps comprised of 210 scans at the same separation. There were actually two sets of each map, each starting in opposite directions to test for dependencies on scan direction. The second set of scans in Y-direction actually started mid-way between the previous +Y scan legs (2" offset), leading to an overall finer spacing of legs along the Z-coordinate. The +Z and -Z directions started with almost perfect overlap.Neptune moved about 6.1" between the mid-points of the first and last observation. The observations were special calibration observations that yielded a number of calibration results, for example the positions of all detector pixels, relative flatfields, and the ratio between integral and peak based flatfields, the so-called extended source gains. | |||||||||||||||||||||||||||||||||||||||||
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Table 1: Observation IDs, times and positions of all six maps. The last two "shadow" observations were made after Neptune had left the region 3 years later at about the same time of year to ensure the same observing geometry w.r.t the Zodiacal cloud. These were performed in a non-moving reference frame with the same narrow scan pattern as the Neptune observations. Each scan direction was executed only once. The duration of each map was equivalent to the corresponding ones on Neptune, i.e. spending a total of half the observing time that was used on Neptune. | |||||||||||||||||||||||||||||||||||||||||
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Figure 2: The reconstructed raw maps for array PSW at 1" pixel size and standard 6" pixel size. The standard pixel size maps offer higher signal to noise in exchange for poorer spatial resolution.
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< < | Although Neptune and shadow maps appear very consistent in its background features at first sight, a direct subtraction of the maps (see Fig. 3 left) shows a number of artifacts hinting at a small astrometric shift between both maps and a photometric difference. This is particularly obvious when using the maps at standard pixel size benefitting from higher S/N. The shadow map over-subtracts the sources by about 10%. Scaling down the shadow map by 10% gives a better removal, however the best background subtraction was achieved empirically by Gaussian smoothing of the shadow maps with sigmas = [0.10, 0.03, 0.10] for PSW, PMW PLW respectively and shifting the PSW and PMW by 1.8" in the spacecraft X-direction. The smoothing of the shadow map effectively accounts for the smearing of the background galaxies in the Neptune images that were made while the telescope tracked the proper motion of the planet. | ||||||||||||||||||||||||||||||||||||||||
> > | Although Neptune and shadow maps appear very consistent in its background features at first sight, a direct subtraction of the maps (see Fig. 3 left) shows a number of artifacts hinting at a small astrometric shift between both maps and a photometric difference. This is particularly obvious when using the maps at standard pixel size benefitting from higher S/N. The shadow map over-subtracts the sources by about 10%. Scaling down the shadow map by 10% gives a better removal, however the best background subtraction was achieved empirically by Gaussian smoothing of the shadow maps with sigmas = [0.10", 0.03", 0.10"] for PSW, PMW PLW respectively and shifting the PSW and PMW by 1.8" in the spacecraft X-direction. The smoothing of the shadow map effectively accounts for the smearing of the background galaxies in the Neptune images that were observed while the map center tracked the proper motion of the planet. | ||||||||||||||||||||||||||||||||||||||||
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< < | Figure 3: The . | ||||||||||||||||||||||||||||||||||||||||
> > | Figure 3: Difference maps of Neptune and shadow maps for PSW without any correction (left) and with a small shift by 1.8" in spacecraft X-direction and Gaussian smoothing of the shadow map with sigma=0.1" before the subtraction (right). | ||||||||||||||||||||||||||||||||||||||||
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> > | With the advent of the shadow maps, previous efforts involving detection and subtraction of point sources, and fitting of a warped background plane, became unnecessary. | ||||||||||||||||||||||||||||||||||||||||
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> > | Looking for "Triton Contamination" | ||||||||||||||||||||||||||||||||||||||||
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< < | Background fit and removalThe background was not flat at the level 0.1e-5 from the peak, most likely due to Zodiacal Light background variation, however galactic Cirrus could also be the reason. A two dimensional polynomial was fitted and removed. The removed background can be examined in the following files:
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< < | Overlaying the ecliptic coordinate system over the background fit (contours) shows that a an interpretation by a Zodiacal light gradient is at least qualitatively consistent. | ||||||||||||||||||||||||||||||||||||||||
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< < | Using IRSKY to obtain a rough estimate through extrapolation of its Zodiacal model to SPIRE wavelengths at the position of the observation and one degree towards the ecliptic pole, the following gradients were obtained. | ||||||||||||||||||||||||||||||||||||||||
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Background source removalA large number of extragalactic sources contaminated the maps. These were removed in HIPE using Sussextractor.
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Solid AnglesAfter background tilt subtraction and background source removal the signal was averaged over concentric annuli around the source and this radialized beam profile was plotted against radius (Plot 1). To ensure symmetry, e.g. flatness of the background, the same was also plotted for three sectors (Plot 2 and 3). From the radialized beam profile a new background was determined and subtracted based on the necessity to have only positive flux within the errors (Plot 4). |
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THIS PAGE IS UNDER CONSTRUCTIONAnalysis Details of SPIRE Photmeter Beam Profiles( Bernhard Schulz, October 2014) | |||||||||||||
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< < | --> Update!! | ||||||||||||
Initial Beam ProfileThe beam profile was reconstructed from four fine scan maps with obsids: 1342186522, 1342186523, 1342186524, 1342186525, and two observations of the same sky region 1342255134 and 1342255135 three years later. The Neptune observations followed the small proper motion of the object. The scan pattern had, unlike standard scan map observations, very narrowly spaced scan legs. The maps scanning in spacecraft-y direction consisted of 150 scan legs separated by 3.9", the orthogonally scanning maps comprised of 210 scans at the same separation. There were actually two sets of each map, each starting in opposite directions to test for dependencies on scan direction. The second set of scans in Y-direction actually started mid-way between the previous +Y scan legs (2" offset), leading to an overall finer spacing of legs along the Z-coordinate. The +Z and -Z directions started with almost perfect overlap.Neptune moved about 6.1" between the mid-points of the first and last observation. The observations were special calibration observations that yielded a number of calibration results, for example the positions of all detector pixels, relative flatfields, and the ratio between integral and peak based flatfields, the so-called extended source gains. | |||||||||||||
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> > | The data processing started with standard archival data reduced with HIPE 12.1 and HIPE 11.1. The differences between these versions are irrelevant for products at Level 1. HIPE 13.0.3221 was used for destriping and map-making. We had to resort to an, at the time, very new development version of HIPE to have newly discovered issues with the initial median timeline subtraction of the destriper fixed. Another issue causing cross-like "shadows" was avoided by excluding the central 5' around Neptune from the destriping procedure. | ||||||||||||
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> > | The reduction steps were as follows:
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< < | HIPE 9.0.1782 and SPIA 1.8 were used. The map reconstruction was performed after median subtraction excluding a radius of 4 arcmin around the source. The maps have 1 arcsec sky bin size. Pointing for Neptune proper motion was corrected. The resulting original files are: | ||||||||||||
> > | Background SubtractionAlthough Neptune and shadow maps appear very consistent in its background features at first sight, a direct subtraction of the maps (see Fig. 3 left) shows a number of artifacts hinting at a small astrometric shift between both maps and a photometric difference. This is particularly obvious when using the maps at standard pixel size benefitting from higher S/N. The shadow map over-subtracts the sources by about 10%. Scaling down the shadow map by 10% gives a better removal, however the best background subtraction was achieved empirically by Gaussian smoothing of the shadow maps with sigmas = [0.10, 0.03, 0.10] for PSW, PMW PLW respectively and shifting the PSW and PMW by 1.8" in the spacecraft X-direction. The smoothing of the shadow map effectively accounts for the smearing of the background galaxies in the Neptune images that were made while the telescope tracked the proper motion of the planet. | ||||||||||||
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< < | Complications that arise when using these maps directly for derivation of beam profiles and solid angles were discussed in a presentation![]() | ||||||||||||
Background fit and removal |
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Initial Beam Profile | ||||||||
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< < | The beam profile was reconstructed from four fine scan maps with obsids: 1342186522, 1342186523, 1342186524, 1342186525 Pointing for Neptune proper motion was corrected. HIPE 9.0.1782 and SPIA 1.8 were used. The map reconstruction was performed after median subtraction excluding a radius of 4 arcmin around the source. The maps have 1 arcsec sky bin size. | |||||||
> > | The beam profile was reconstructed from four fine scan maps with obsids: 1342186522, 1342186523, 1342186524, 1342186525, and two observations of the same sky region 1342255134 and 1342255135 three years later. The Neptune observations followed the small proper motion of the object. The scan pattern had, unlike standard scan map observations, very narrowly spaced scan legs. The maps scanning in spacecraft-y direction consisted of 150 scan legs separated by 3.9", the orthogonally scanning maps comprised of 210 scans at the same separation. There were actually two sets of each map, each starting in opposite directions to test for dependencies on scan direction. The second set of scans in Y-direction actually started mid-way between the previous +Y scan legs (2" offset), leading to an overall finer spacing of legs along the Z-coordinate. The +Z and -Z directions started with almost perfect overlap.Neptune moved about 6.1" between the mid-points of the first and last observation. The observations were special calibration observations that yielded a number of calibration results, for example the positions of all detector pixels, relative flatfields, and the ratio between integral and peak based flatfields, the so-called extended source gains.
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> > | HIPE 9.0.1782 and SPIA 1.8 were used. The map reconstruction was performed after median subtraction excluding a radius of 4 arcmin around the source. The maps have 1 arcsec sky bin size. Pointing for Neptune proper motion was corrected. | |||||||
The resulting original files are: |
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THIS PAGE IS UNDER CONSTRUCTIONAnalysis Details of SPIRE Photmeter Beam Profiles( Bernhard Schulz, October 2014) --> Update!!Initial Beam ProfileThe beam profile was reconstructed from four fine scan maps with obsids: 1342186522, 1342186523, 1342186524, 1342186525 Pointing for Neptune proper motion was corrected. HIPE 9.0.1782 and SPIA 1.8 were used. The map reconstruction was performed after median subtraction excluding a radius of 4 arcmin around the source. The maps have 1 arcsec sky bin size. The resulting original files are:
![]() Background fit and removalThe background was not flat at the level 0.1e-5 from the peak, most likely due to Zodiacal Light background variation, however galactic Cirrus could also be the reason. A two dimensional polynomial was fitted and removed. The removed background can be examined in the following files:
![]()
Background source removalA large number of extragalactic sources contaminated the maps. These were removed in HIPE using Sussextractor.
Solid AnglesAfter background tilt subtraction and background source removal the signal was averaged over concentric annuli around the source and this radialized beam profile was plotted against radius (Plot 1). To ensure symmetry, e.g. flatness of the background, the same was also plotted for three sectors (Plot 2 and 3). From the radialized beam profile a new background was determined and subtracted based on the necessity to have only positive flux within the errors (Plot 4). The average background outside a given radius was plotted for all radii (Plot 5). The integrated solid angle within a given radius was plotted for all radii (Plot 6). All the aforementioned diagrams are seen for the three detector arrays in files:
![]() ResultsThe diagrams showing solid angle vs. radius show a plateau around 600 arcsec which may signal the end of significant contribution from the beam profile. At different integration radii, the following values in arcsec^2 result:
![]() ErrorsAnother presentation![]() Correction between Isophotal and Reference WavelengthIt is important to point out that solid angles are color dependent. The FWHM of the beam varies with frequency proportional to nu^gamma. The most recent estimate from Griffin (priv. comm) for gamma is 0.78, 0.85, 0.85, respectively for PSW, PMW and PLW. As the beam profiles and the solid angles were derived from a map of Neptune, there is a discrepancy to the n*Fnu = const. spectrum that all photometry is color corrected for. To determine the magnitude of this variation, a radial beam profile model was derived from the final background subtracted 2D beam profiles, following the idea in Griffin et al. 2013![]()
![]() ![]() Normalized Beam Profile Products
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