spectrograph for transients a low-resolution multi-object...optical fiber positioning system...
TRANSCRIPT
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A Low-resolution Multi-Object Spectrograph for Transients
Documentation: http://bit.ly/2tH1Zzi 1
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Instrument team
Anne Normann Hansen
César Íñiguez
Emir Karamehmetoglu
Petr Kobrle
Bikram Pradhan
Antonio de Ugarte Postigo
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Overview● The problem● The solution● Science cases & requirements● Instrument specs● Instrument design● Telescope & spectrograph● Efficiency● Mechanical design● Electronics software & pipeline● Risk & costs
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Problem● The era of the transient
universe is now.● Optical surveys will
discover millions of candidates.
● Existing single object spectrographs unable to keep up.
● Transient density.
● Wide-field multi-object spectrograph to classify & categorize transients.
● Needs to be fast.
Solution
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Science Cases & Requirements
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Meeting The Spectral Classification Challenge● Current classification
efforts will not scale.● Classification is
important for almost all transient science.
Examples:
● Rates● Rare transients● Progenitor-transient
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EM-counterparts to Gravitational Waves● LIGO localization huge!● NS-NS, NS-BH pairs are
predicted to be seen across EM-spectrum.
● Thousands of transients will be discovered in localization.
● Need to eliminate false transients.
● Could enable first EM-counterpart to GW detection!
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Additional Science CasesGRB Afterglows
AGN reverberation mapping
Variable star characterization
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Science requirements● Wide-field multi-object spectrograph (MOS) in the
range 4000-8000 Å, resolution ~ 800 down to magnitude 20-21 with SNR 5-10.
● Large enough FOV to observe extragalactic transients in sparse fields ~0.5/sq degree
● Observe ~30 transients per field to meet classification challenge.
● Fast telescope, live ingestion of transients, “on-the-fly” acquisition of candidates.
● Center and take spectrum of targets with ~1’’ PSF.● Increase classification speed to >300 transients per
night.
● Integral field unit (IFU) with a FoV ~ 15’’’ for GRB follow-up.
● On target in <30 s
MOS
IFU
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Instrument requirement
Optical fiber
positioning system
Telescope
Integral Field Unit
(IFU)CCD detector
Guiding camera
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- 2K X 2K- Resolution ~ 800- Efficiency > 85 %
- Fast slew (~ 20°/ sec)
- Large field of view (> 3° wide)
- > 30 Fibers- > 25 Robotic arms- Positioning accuracy <
40 µm- Each fiber covering ~
3 “ FOV
- Multiple Guiding cameras
- > 1’ of FOV to achieve sub arc- second accuracy
- FOV > 15 “ ( ideal for GRB and SN observation
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Instrument Specs
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- 2K x 2K CCD- Pixel size 15 µm- RON 5 e-/pixels at 1 MHz- QE ~ 0.9 for a band from 4000 A° to 6000 A°
- Cassegrain - Alt-Az- 2.55 m diameter- f/3.4- 3° FOV diameter
- 4 cameras , 1’ X 1’ FOV- 13 µm pixel size- RON of 5 e-- /pixel- Peak QE = 80 % at 600
nm wavelength
- 217 fiber cables forming a hexagon
- 15” wide FOV
- 34 robotic arms- Each carries a fiber
bundle of 7 fibers- 30 (target) + 4 (sky)- Position accuracy of
25 µm
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MOS/IFU Fiber design
Concept
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Fibers
IFU● Bundle of 217 fibers in hexagonal arrangement● 21 fibers feeding spectrograph for calibration
Arms● Bundles of 7 for arms with microlenses to collect
light from the whole surface● 30 bundles for science, 4 for sky● Possibility to input calibration lamp light
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Positioning arms
● Step motors to enable movement
● 2 DoF: radial and angular movement
● Ring to enable radial movement and supporting bowl for stability
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All together
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Telescope & Spectrograph
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JST/T250● It has the F.o.V that we need● The IQ is also good 0.5 -1.2 ’’● It is NOT telecentric, that will be a problem
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Optical design changes
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Light into the optical fiber
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Autoguide and Image Quality control● 4 small Frame Transfer CCD for autoguide
control at the edges of the F.o.V
● 8 small Frame Transfer CCD, 4 for Intra and 4 for 8 focal images to control 2 hexapods at M2 and FP
● High pointing precision
● M2 and FP situated with a precisión < 40 µm X-Y-Z & 30’’ rX rY
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Efficiency
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Optical efficiency
Effective collecting area:3.89 m²
M2 blocks 21% of the light !
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Mechanical design
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Telescope attachment
Spectrograph + Support
Cooling unit
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Electronics and Software
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Software and Pipeline
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PIPELINE
ShcedulingFiber
Positioning
Data-reduction
MOS and IFU Data reduction
- Bias subtraction- Flat field correction- Wavelength calibration- Cosmic ray removal- Sky subtraction- Flux calibration
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Costs
The cost for the engineering team is based on a 7 people team over a time period of 2 years.
Rough estimate of project costs
The most uncertain cost at the moment is the positioners, since some R/D is needed to make them work.
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Risks
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PositionersFunding
● Attract more established PI’s
● Reduce scope
● Build onto existing telescope
● Increase size of fibers
● Increase number of fibers in each bundle
● Inherit technology from KMOS
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ALMOST there ...
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