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The Magellan f/15 Secondary
Science Case
Laird Close
Victor Gasho
MIRAC4 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 followup 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 diffractionlimited 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.
We should have Strehls of 75% at 10um with a Tip-tilt Secondary & Active Optics
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.
Technical Summary (MIRAC4 & f/15)
Wavelength
~3-25 mm
Resolution
0.3” at 10 mm (R~100 Grism 8-13 mm)
Strehl with tip-tilt
75% in 0.73” seeing at 10 mm
FOV
49.4x49.4” and 24.7x24.7”
Nyquist lambda
11.9 mm and 5.9 mm
Sensitivity
~1 mJy @ 5s in 1 hour at N (10 mm) 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” (northsouth ---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
7” chop
13” chop
• Here are 3 different
observations: (a)
Chop/Nod throw of 7”; (b)
25” chop
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.
Planetary Science is enabled with MIRAC4’s large
FOV
MIRAC4
50” FOV
@ f/15
MIRAC4
50” FOV
@ f/15
• 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 l>11.9 microns
- size of Mirca4 field with a future MegaMIR 1k chip ~82”)
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
Sensitivity of
Mirac4
• Ground based
10 mm 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
•
Magellan f/15
0.35”
0.7”
(modified from the
MegaMIR paper)
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?
MIRAC4
50” FOV
@ f/15
• Images of
galactic
center
would
greatly
benefit from
larger chop
throws and
FOVs > 25”
• Note the
poor sky
subtraction.
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:
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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.