Table3.2compiles the dereddened line intensity ratios with respect to I( Hα ) = 100. Table3.3 lists the results of the chemical abundance analysis for the HIIcomplex discovered in the galaxy GAMA J141103.98-003242.3 and the center of the galaxy. Table3.4compiles the oxygen abun- dances derived using the most commonly used strong emission-line methods.
3SAMI: http://sami-survey.org/
4KMOS: http://www.eso.org/sci/facilities/develop/instruments/kmos.html 5MaNGA: http://www.sdss3.org/future/manga.php
3.7 | Advancements in multi-object integral-field spectroscopy
Line f (λ) HIIcomplex Rest of the galaxy [OII] 3728 0.322 91.3± 5.6 352± 52 H11 3770 0.313 5.52± 0.42 ... [NeIII] 3869 0.291 60.4± 3.8 ... HeI 3889 + H8 0.286 20.9± 2.2 ... [NeIII] 3969 + H7 0.267 36.7± 3.6 ... Hδ 4101 0.230 26.1± 2.0 25.0 : Hγ4340 0.157 47.5± 2.3 43± 6.7 [OIII] 4363 0.150 11.4± 0.8 ... HeI4471 0.116 3.87± 0.45 ... HeII4686 0.050 0.51 : ... [ArIV] + HeI4712 0.043 1.72± 0.32 ... [ArIV] 4740 0.034 0.99 : ... Hβ 4861 0.000 100.0± 3.6 100± 14 [OIII] 4959 −0.025 234± 11 168± 23 [OIII] 5007 −0.037 695± 30 482± 58 [OI] 6300 −0.262 1.70± 0.46 ... [SIII] 6312 −0.264 1.73± 0.79 ... [OI] 6364 −0.271 0.78± 0.11 ... [NII] 6548 −0.295 1.75± 0.17 6.25 : Hα 6563 −0.297 279± 12 281± 34 [NII] 6583 −0.300 4.88± 0.29 16.7± 2.1 HeI6678 −0.312 3.17± 0.35 ... [SII] 6716 −0.318 7.67± 0.44 38.9± 4.7 [SII] 6731 −0.319 6.01± 0.35 24.6± 3.9 HeI7065 −0.364 2.74± 0.42 ... [ArIII] 7135 −0.373 10.33 ± 0.57 20.9± 3.8 EW(Hα) [Å] 451± 11 34.8± 3.2 EW(Hβ) [Å] 137± 4 6.8± 1.6 EW(Hγ) [Å] 44.2± 1.6 1.7± 0.4 EW(Hδ) [Å] 22.8± 0.9 1.1 : FHβ♢ 22.6± 6.3† 9.4± 2.6† c( Hβ) 0.34± 0.02 0.31± 0.04 Wabs[Å] 0.0± 0.1 0.8± 0.2 ♢Units of 10−16erg cm−2s−1
†Error is currently dominated by a 28 per cent error in SAMI’s absolute flux calibration, and in all values
derived from it (seeAllen et al.(2015a) for more details).
Table 3.2: Dereddened line intensity ratios with respect to I(Hβ)=100 for the HIIcomplex discovered in the galaxy GAMA J141103.98-003242.3. The ionized gas observed in the rest of the galaxy is also presented. At the bottom of the table we also give the Hβ flux, the reddening coefficient, c( Hβ ), the equivalent widths of the absorption in the hydrogen lines, Wabs, and the equivalent widths of the emission HIBalmer lines. The value of f (λ) considering the Cardelli, Clayton & Mathis(1989) extinction law and used for dereddening the line intensity ratios are also included. A colon denotes an error of larger than 40%.
3.7 | Advancements in multi-object integral-field spectroscopy
HIIcomplex Rest of the galaxy Te[OIII] [K] 14000± 650 12750± 1000 Te[OII] [K] 12800± 450 11930± 800 ne[cm−3] 140± 30 100 12+log(O+/H+) 7.16± 0.07 7.85± 0.13 12+log(O++/H+) 7.94± 0.05 7.90± 0.09 12+log(O/H) 8.01± 0.05 8.18± 0.11 log(O++/O+) 0.78± 0.09 0.05± 0.15 12+log(N+/H+) 5.74± 0.05 6.35± 0.08 12+log(N/H) 6.58± 0.09 6.67± 0.11 log(N/O) −1.43 ± 0.06 −1.51 ± 0.10 12+log(S+/H+) 5.27± 0.04 5.99± 0.07 12+log(S++/H+) 6.06± 0.18 ... 12+log(S/H) 6.27± 0.16 ... log(S/O) −1.74 ± 0.21 ... 12+log(Ne++/H+) 7.29± 0.06 ... 12+log(Ne/H) 7.36± 0.12 ... log(Ne/O) −0.65 ± 0.07 ... 12+log(Ar++/H+) 5.67± 0.06 6.06± 0.12 12+log(Ar+3/H+) 5.00± 0.11 ... 12+log(Ar/H) 5.77± 0.07 5.90± 0.20 log(Ar/O) −2.24 ± 0.12 −2.29 ± 0.22 c( Hβ) 0.34± 0.02 0.31± 0.04 Wabs[Å] 0.0± 0.1 0.8± 0.2
Table 3.3: Physical conditions and chemical abundances of the ionized gas for the HII complex discovered in the galaxy GAMA J141103.98-003242.3 and the rest of the galaxy when this region is not considered. In this latter case, the electron temperatures were estimated as those that best reproduce the oxygen abundance computed via the SEL methods based on Te. Bold values are those of most interest.
c( Hβ) Wabs[Å] Te M91 KD02 KK04 PT05 P01 PP04a PP04c Adopted Branch
Parameters R23, y R23, y R23, y R23, P R23, P N2 N2O3 MKD PPP HIIcomplex 0.34± 0.02 0.0 ± 0.1 8.01 ± 0.05 8.17 8.33 8.35 7.99 7.88 7.90 7.90 8.28 7.92 Low Rest of the galaxy 0.31± 0.04 0.8 ± 0.2 ... 8.35 8.51 8.52 8.25 8.13 8.20 8.12 8.45 8.18Intermediate
Difference ... ... ... 0.18 0.18 0.17 0.26 0.25 0.30 0.22 0.18 0.26 ...
Table 3.4: Oxygen abundances derived using the most commonly used strong emission-line methods. The strong emission-line calibrations are: M91:McGaugh(1991); KD02:Kewley & Dopita(2002); KK04:Kobulnicky & Kewley (2004) PT05:Pilyugin & Thuan(2005); P01:Pilyugin(2001a,b); PP04a: Pettini & Pagel(2004), using a linear fit to the N2parameter; PP04c: Pettini & Pagel(2004), using the O3N2 parameter. The last two columns list the average abundance value using all the empirical methods, the Temethod is not considered here. We provide two results: PPP, which considers the average value obtained with the PT05, P01, PP04a and PP04c calibrations and MKD, which assumes the average value of the M91, KD02, and KK04 calibrations. The typical uncertainty in these values is
4
|
Polymer Imaging Bundles
In Astronomy
Preamble
The motivation of this work came from the need to find an alternative solution to the guiding system on SAMI. At that time, SAMI had an inconvenient guide camera suspended above the field plate, which set undesirable constraints on SAMI’s target selection. Moving to fibre bundles for field acquisition and guiding relieved these constraints, however current silica imaging bundles remain expensive with poor efficiency (limiting the observable magnitude of guide stars). New polymer imaging bundles made for industry applications such as endoscopy were found to be a novel alternative. They were considerably cheaper and had significantly higher throughput than the silica bundles over short lengths. Full laboratory characterisation to validate their use in SAMI led to discovering their other possible applications in astronomical instrumentation. This chapter is the content of the submitted paper listed below with minor changes to the formatting.
Title
Performance of a novel PMMA polymer imaging bundle for field acquisition and wavefront sensing
Abstract
Imaging bundles provide a convenient way to translate a spatially coherent image, yet conven- tional imaging bundles made from silica fibre optics typically remain expensive with large losses due to poor filling factors (∼ 40%). We present the characterisation of a novel polymer imaging bundle made from poly(methyl methacrylate) (PMMA) that is considerably cheaper and a better alternative to silica imaging bundles over short distances (∼ 1 m; from the middle to the edge of a telescope’s focal plane). The large increase in filling factor (92% for the polymer imaging bundle) outweighs the large increase in optical attenuation from using PMMA (1 dB/m) instead of silica (10−3dB/m). We present and discuss current and possible future multi-object applications of the polymer imaging bundle in the context of astronomical instrumentation including: field acquisi- tion, guiding, wavefront sensing, narrow-band imaging, aperture masking, and speckle imaging. The use of PMMA limits its use in low light applications (e.g. imaging of galaxies), however it is possible to fabricate polymer imaging bundles from a range of polymers that are better suited to the desired science.
S. N. Richards; S. Leon-Saval; M. Goodwin; J. Zheng; J. S. Lawrence; J. J. Bryant; J. Bland-Hawthorn; B. Norris; N. Cvetojevic; A. Argyros
4.1 | Advancements in multi-object integral-field spectroscopy
4.1
Introduction
Over the course of the past few decades, the act of bundling optical fibres together to translate an image in a spatially coherent manner has been optimised to increase the spatial resolution, yet retaining efficiency and flexibility. These devices are known as imaging fibre bundles (or coher- ent fibre bundles), and are widely used for remote sensing with applications such as biomedical endoscopy. Most fibre bundles are made using silica optical fibres, however the process used to make a∼ 1 mm diameter bundle that remains flexible sacrifices efficiency due to the fibre filling factor. This is because for most of the length, each fibre needs to be loose, otherwise a 1 mm bun- dle would be a solid rod with near zero flexibility. The SCHOTT Leached Image Bundles1are a good example of this, where the inter-core cladding material is etched down over the length of the fibre, leaving only the ends bundled together. The delicate process of making a flexible silica fibre bundle increases the cost to∼ US$1000 per metre. High filling factor silica fibre bundles do exist (e.g.Bland-Hawthorn et al.,2011;Bryant et al.,2014), though their large individual core diameters (∼ 100µm) results in a coarse spatial resolution, and with the bundle only being fixed at one end, they lack the ability to preserve a spatially coherent image and therefore are not classed as imaging bundles.
The use of polymer as an alternative to silica in fibre imaging bundles presents an attractive solution to many of the issues faced by using silica (e.g. the ability to obtain a high filling factor whilst retaining flexibility). One of the most common polymer fibre materials is poly(methyl methacrylate) (PMMA), however the use of PMMA (and most polymers) over silica comes at the cost of attenuation (on the order of 1 dB/m for PMMA versus 10−3dB/m for silica). This increase in attenuation limits the applications of polymer fibre to cases where fibre lengths on order of a metre are required (e.g. endoscopy, localised remote sensing). Albeit, longer lengths of these polymer imaging bundles can be used in applications where the source is of high enough power to overcome the attenuation loss.
An area where fibre optics continue to increase in their application is astronomy, where they have become the dominant method of translating the light of thousands of galaxies and stars from the telescope focal plane to nearby spectrographs. Most focal planes of current large (4-10 m) telescopes are≲ 1 m in diameter, but there are soon to be focal planes of 1-2 m diameter upon the arrival of Extremely Large Telescopes (ELTs). These large focal planes require precise field acquisition and guiding, for which coherent imaging bundles are well suited. In this application, at one end, multiple imaging bundles are deployed over the focal plane targeting guide stars, and at the other end, all of the imaging bundles are brought together with one camera situated away from the focal plane imaging their end faces. This method has been adopted by the Sloan Digital Sky Survey multi-object spectrograph (SDSS;Smee et al.,2013) and the Sydney-AAO Multi-object Integral field spectrograph (SAMI;Bryant et al.,2015). SDSS use silica imaging bundles from Sumitomo2, and SAMI use polymer imaging bundles from ESKA3.
Basic characterisation of the Sumitomo silica image bundles has been performed byHaynes et al.(2006), who analysed the spatial fidelity, cross talk and scattering, and concluded that more investigation into imaging bundles is needed to assess their suitability in astronomical applica- tions. The Sumitomo bundle has 2µm cores spaced by 3 µm in a semi-regular hexagonal pattern, resulting in a filling factor of∼ 40% (Udovich et al.,2008). This immediate substantial loss from the filling factor is detrimental in astronomical applications of these spatially coherent imaging bundles, where every photon counts. In addition to the filling factor, core sizes of 2µm are very
1http://www.schott.com/lightingimaging/english/medical/ medical-products/transmitting-images_leached-image-bundle.html
2Sumitomo Electric Lightwave Corp., http://www.sumitomoelectric.com
4.2 | Advancements in multi-object integral-field spectroscopy
Figure 4.1: (left) Back-illuminated microscope image of a coherent polymer bundle showing the entire face of the bundle. (middle) a magnified image of (left) showing the hexagonal structure of the cores. There are 7095 cores hexagonally packed, with each core being 16µm (full-diagonal) resulting in an overall diameter of 1.5 mm. Dust in the microscope imaging system gives the appearance of damaged cores. (right) a projected Hα map of a spiral galaxy by butt-coupling the input end of the bundle to a 1.5 mm grayscale printout of the galaxy.
close to being purely single-moded at optical wavelengths resulting in an even greater loss due to very poor modal coupling (Horton & Bland-Hawthorn, 2007). In the case of the Sumitomo bundle, the outer diameter is only 800µm, meaning that even without separating the individual cores along the length of the fibre, the bundle retains some flexibility.
More recently, SCHOTT have developed a Wound Fibre Bundle4for the Defense sector, that creates a spatially coherent array of smaller 6× 6 fibre arrays with each fibre being 10µm in diameter. Its efficiency over the wavelength range 400− 1500 nm is typically 40-50%, including attenuation, fill-factor and Fresnel surface reflection losses. Detailed characterisation on its optical performance has yet to be carried out.
Our interest then lies with the ESKA polymer imaging bundles (PMMA), which have a larger filling fraction than silica imaging bundles, yet retain spatial resolution and flexibility. In Section 4.2we present the results of laboratory characterisations of two different sizes of polymer imag- ing bundles. In Section4.3we explore their various applications in the context of astronomical instrumentation, presenting recent on-sky demonstrations, and concluding our work in Section 4.4.