The Magellan f/15 SecondaryScience Case

Laird CloseVictor GashoMIRAC4 team

(Steward Observatory)

Why A New Secondary For Magellan

• The current f/11 has high (~15%?) emissivity – same as ~5m scope with lower emissivity

• This cannot complete with Gemini redwards 2.3 um

• However exciting science is now being done at ~5” resolution in Mid-IR with Spitzer – “bright” objects (>1 mJy) can be followed up at Magellan

• Almost all GLIMPSE & WISE sky survey detections can be done from Magellan for follow-up at 10x better angular resolution with a new Mid-IR optimized secondary.

What Magellan Needs to enable effective Mid-IR Science

• System Emissivity <5% – Sky baffled secondary (at inner and outer edge)– Tip-tilt (100Hz @ 0dB) and >90” chopping (>2 Hz)– IR optimized coating (Gemini Silver ?)– Direct Cass. Focus & active optics

• Must feed MIRAC4 Magellan’s facility Mid-IR (~3-25 um) 256x256 camera (need f/15 beam)

• Should open new areas of Mid-IR science: Wide field diffraction-limited imaging – large chopping throws plus tip-tilt correction over all sky. For example, wide field Mid-IR is critical to understand the interactions of young massive stars and their dusty envelopes, outflows, etc. How is the dust from what we are made distributed?

• Wide chops allow one to get dark skies and study dusty structures at the faintest levels. Until now star formation clusters dust structures not understood at high resolutions due to small chops.

Predicted system performance at 10μm (left, Phase I – funded by NSF MRI) and 2.2μm (right, Phase II – not funded by MRI). Seeing of 0.73" at V, a wind of 6 m/s, 21 mag/sq arcsec sky brightness, and a sensor with readnoise of 2 electrons sampled at 330 Hz have been assumed in these simulations (our Andor gain CCD should have 1e RON and 500 Hz rates).

Note that tip-tilt alone is adequate for diffraction-limited imaging at Magellan at >8 microns. We should have nearly full sky coverage with the Andor tip-tilt/speckle camera as the fast guider.

We should have Strehls of 75% at 10um with a Tip-tilt Secondary & Active Optics

Technical Summary (MIRAC4 & f/15)Wavelength ~3-25 m

Resolution 0.3” at 10 m (R~100 Grism 8-13 m)

Strehl with tip-tilt 75% in 0.73” seeing at 10 m

FOV 49.4x49.4” and 24.7x24.7”

Nyquist lambda 11.9 m and 5.9 m

Sensitivity ~1 mJy @ 5 in 1 hour at N (10 m) good conditions

Chop throw +/-45” any direction @ 0.5 Hz

Active Tip-tilt field size 24x24” (~12” object can always stay on chip with full tilt correction and chop-nod pattern – unlike Gemini)

Tip-tilt acquisition field size & lim. Mag

90” diameter to find star <18th mag @ V

Sky coverage for tip-tilt correction

Nearly 100% for fields <30% off galactic plane~50% galactic poles

Tilt bandwidth (0 dB) ~100 Hz (max update 500 Hz)

Speckle (optical) FOV 1.05x1.05”

Speckle resolution 0.016” (diffraction limited at V band)

Speckle lim. mag V=14th mag (2600 speckles @ 40 Hz -- 0.8” seeing)

What Science is enabled?• We would have the ONLY Mid-IR facility that could

chop 90” – First mid-ir images of extended Comet Nuclei– First mid-ir images of crowed fields like M31, M33– Optimal coverage of the warm dust at the Galactic Center– Imaging of the dusty cores of star formation sites– hundreds of high mass star formation cores could be

resolved– Imaging of the surface of Mars, Venus etc.– Imaging of the Trapezium core – Imaging of new crowded fields discovered by Spitzer & WISE – etc

Why is 90” chopping important?• A typical 120s, 11.6 um

image of the central pc (~25”x25”) of our Galaxy, N’ image, from UKIRT (Bertero et al. 2000, PASP 112, 1121)

• Note how the rather small chop throws of 10” (north-south ---with a 10” nod also north-south) are not sufficient to move the crowded field off the array for the sky frame. Hence the final image is badly corrupted.

• This chop throw is typical for all big IR telescopes today.

Why is 90” chopping important: Star Formation

• typical N-band images of the Orion Nebulae (~25”x25”) proplyd left, trapezium ionization front right .

• Note how the rather small chop throws of 10” & 5” (north-south ---with a 10” nod also north-south) are not sufficient to move the crowded field off the array for the sky frame. Hence the final image is badly corrupted (spatially and photometrically).

• These 10” max chop throws are typical for all big IR telescopes today, but fail to work well in star formation or crowded galactic fields.

Why is 90” chopping important: FOV

• Here are 3 different observations: (a) Chop/Nod throw of 7”; (b) 13”; and (c) 25”.

• Note how the larger throws allow more accurate sky subtraction.

• Note how the final image produced by the 25” chop (f) is ~75x25” in size, but it is also the best background subtracted.

• But note the loss in resolution of image (c) due to the large chop.

7” chop25” chop

13” chop

Planetary Science is enabled with MIRAC4’s large FOV

• By chopping >50” enables planetary science (NOTE: images from the MegaMIR proposal – MIRAC4 has a 49.4” FOV with the f/15 secondary that samples >11.9 microns

- size of Mirca4 field with a future MegaMIR 1k chip ~82”)

MIRAC4 50” FOV

@ f/15

MIRAC4 50” FOV

@ f/15

What Follow-up Survey Science is enabled?GLIMPSE - the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire - is a fully sampled, confusion limited, 4-band near- to mid-infrared survey of the inner two-thirds of the Galactic disk with a spatial resolution of ~2". The Infrared Array Camera (IRAC) imaged 220 square degrees at wavelengths centered on 3.6, 4.5, 5.8, and 8.0 microns in the Galactic longitude range 10 deg to 65 deg on both sides of the Galactic center and in Galactic latitude +/- 1 deg.

The area covered by GLIMPSE contains most of the star formation activity in the Galaxy and ~70% of the molecular gas in the Galaxy. The inner cutoff at |l| = 10 deg permits adequate sampling of both ends of the purported ~3 kpc central bar and possibly some of the nuclear bulge stellar population. They expect to determine the asymmetry of the bar (brighter at l>0 deg) with high accuracy. The outer cutoff at |l| = 65 deg includes all of the 5 kpc molecular ring, the Sagittarius spiral arm tangent, and the Norma spiral arm tangent. The Galactic center region is not included because of its extreme background brightness and high confusion limits. These confusion-limited areas in the center could be uniquely well probed by MIRAC4 @ f/15.

How Does MIRAC4 compare to the sky surveys

• Ground based 10 m imaging is similar to spitzer’s miky way disk survey (Glimpse) and the all-sky Wise mission.

• Note the significantly better resolution on a 6.5 m

• (modified from the MegaMIR paper)

Sensitivity of Mirac4

0.35” 0.7”Magellan f/15

What Science is enabled?

• Spitzer is discovering countless new 10um sources in the plane of the galaxy in the Glimpse survey many of which are only visible from the south and would benefit from ~10x better 10um resolutions.

• The most crowded regions require >50” chops.

What Science is enabled?

Newly discovered Extragalactic regions are also prime targets for study.

What Science is enabled?• Images of

galactic center would greatly benefit from larger chop throws and FOVs > 25”

• Note the poor sky subtraction.

MIRAC4 50” FOV

@ f/15

What Science is enabled?• Nearby

brown dwarfs could also be detected that are discovered by WISE

What Science is enabled?• We would enable fast tilt correction: 10 um Images would

have ~75% Strehl an FWHM~0.3”– First mid-ir images of crowed fields like M31, M33. How is the dust

in OB ass. In other galaxies?– Optimal coverage of the warm dust at the Galactic Center: How is

the dust in core of our galaxy distributed? Effect of the mini-spiral?– Imaging of the dusty cores of star formation sites. What is the

mass IMF, binarity, disk faction. How does large scale high mass star formation work?

– Imaging & spectra of Mars, Venus, Jupiter. Thermal chemistry of gas giants, extra solar planet models.

– Imaging of the Trapezium core. Understanding ionization fronts and dust, high mass star formation.

– Imaging of the millions new crowed fields discovered by Spitzer

What Science is enabled?• With fast tilt correction & speckle camera: 0.55

um diffraction-limited resolutions of 0.016” – Highest angular resolution of any telescope?– Binarity studies down to V=14 in 0.75” seeing (fainter

than multi-aperture interferometry)– Relatively high dynamic range due to low noise Andor

camera– Studies of binaries at record resolutions.– Orbits of young high mass stars, IMF etc– Halpha image reconstruction etc.

The future:1024x1024 arrays (like the MegaMIR Chip) will require very large chops (~82”) to utilize these new chips. No large telescope has >+/-10” chop. Our proposed secondary would be the largest chopping 10 um facility on a large telescope.

The Future: New instruments will likely eliminate US astronomers access to Gemini south Mid-IR observations past 2008 (the only US southern Mid-IR facility).

T-ReCS will likely not make the required 16 night semester minimum. NICI alone will use ~30% of the bright time, and FLAMINGOS-2 and GSAOI with MCAO will use up the rest of the bright time. Hence T-ReCS will likely not be used from 2008 onwards.

Magellan Mid-IR could be the leading (only?) US southern Mid-IR facility from 2008 on. And with its 82” FOV and 90” chopper the only large telescope location for the MegaMIR chips.

CONCLUSIONS: What Science is enabled?• We would enable fast tilt correction: 10 um Images would have 75%

Strehl an FWHM~0.3”• Very high res. 0.016” optical (V band) speckle imaging• MIRAC4’s wide 50” FOV (and possible future 82” FOV) would be unique

in the world for a large telescope• A few examples of what wide-field Mid-IR imaging would be very

important for:– First mid-ir images of crowed extra-galactic fields like M31, M33– Imaging of dense star formation clusters in other galaxies like M81– Optimal coverage of the warm dust at and around the Galactic Center– Imaging of the dusty cores of galactic high-mass star formation sites– Imaging of the surface of Mars, Venus, Jupiter, Saturn, Neptune etc.– Imaging the Nuclei of Comets– Imaging of the Trapezium core and other OB associations – Imaging of the high extinction protostar class 0 fields and cloud cores.– Imaging of the thousands of new crowed fields discovered by Spitzer– Follow-up of the GLIMPSE and WISE surveys at ~10x higher resolution.