A Low-resolution Multi-Object Spectrograph for Transients

Documentation: http://bit.ly/2tH1Zzi 1

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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