SOFIA: First Light to First Science Terry Herter

October 14, 2013

FORCAST Team members:

Joe Adams (Project Scientist, now at USRA), George Gull (Lead

Engineer), Justin Schoenwald (Software Engineer), Chuck Henderson

(Mechanical Eng), Luke Keller (Ithaca College, Co-I)

Ryan Lau (Grad. Student); Jason Wang & Lea Hirsch (Undergrads)

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Outline

The FORCAST Instrument

FORCAST Science

SOFIA and FORCAST

Preparation and First light – truly a once in a

lifetime experience

First Light

Science Images & Discussion

Summary

Instrument Overview Facility Instrument

Delivered to NASA / USRA

Dual-Channel 256x256 Camera w/ Si

BIB arrays

5-25 m with Si:As array (SWC)

25-40 m with Si:Sb array (LWC)

Selectable filters in 5-40 m range

Grism modes now available

Field of View

0.75''/pixel giving a 3.2'3.2'

Designed for diffraction-limited

imaging for > 15 µm

Able to observe with the SWC and

LWC simultaneously

But with some penalty in sensitivity in

the LWC

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FORCAST Filters

FORCAST filter transmissions (black) overlaid on atmospheric

transmission from SOFIA (blue) and from Mauna Kea (red)

Roughly 10 m vs. 1 mm precipitable water vapor

Except for very limited bands, transmission for ground based

observatories is poor over the 5 – 40 m region

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FORCAST Detects “Dirt”

FORCAST is sensitive to emission from dust in the

interstellar medium

UV and optical photons heat the dust which radiates in the

“thermal” infrared

Dust composition, heating sources, geometry, and optical

depth all affect the observed spectrum.

“Large” particles

Emitted power in equilibrium with absorbed radiation

Have a well-defined temperature

“Small” particles

Temperature significantly affected by single photon

Depends on heat capacity of grain

e.g. PAH’s (Polycyclic Aromatic Hydrocarbons)

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A day in

the life of

a dust

particle in

the ISM

A day in the life of four carbonaceous grains, heated by the local interstellar radiation field. tabs is the mean time between photon absorptions. (see Draine and Li 2003, ApJ, 551, 807)

ISM = Interstellar Medium

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Orion: A Different View

Infrared (IRAS) Visible Light

The IR affords a complementary view of the Universe relative to other wavelengths –

The bright extended regions in IRAS view are due to thermal emission from small

grains (dust) heated by stellar radiation. Complex molecules emit in the IR and

submillimeter regions of the spectrum

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FORCAST Uniqueness

Complement Spitzer & Herschel

Both out of cryogen

Increased spatial resolution

Additional wavelength coverage

Spectroscopy upgrade for current proposal cycle

e.g. dust composition, ionic and molecular diagnostics

But … sensitivity far lower than space based observatories

For instance, use FORCAST to

Investigate source morphology (vs. wavelength)

Separate sources (such as in a young stellar cluster)

Fill in spectral energy distribution (get total luminosity, derive

dust temperatures)

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“Original” Team Science Objectives

The galactic center region

Nature of circumnuclear ring (CNR)

Excitation of “arches” (long structures)

Star formation

Census of “protostars” in nearby molecular clouds

Spiral arms of nearby galaxies

Circumstellar disks

Spatially resolve Vega phenomena

Spectral energy distribution of Young Stellar

Objects

Start of FORCAST funding: 1997 !

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NASA Lear Jet Observatory

1967

30-cm telescope

NASA Kuiper Airborne Observatory (KAO)

1974

91-cm telescope

NASA/DLR Stratospheric Observatory for Infrared Astronomy (SOFIA)

2010

2.5-m telescope 1975 until 1996

(shut down in

prep for SOFIA) Early 70’s

until 1980.

Started operations

in 2010

Evolution of Airborne Astronomy

Cornell has been a part of airborne astronomy

since its inception (Martin Harwit & Jim Houck)

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SOFIA

Instrumentation: wide variety, rapidly interchangeable, state-of-the art – SOFIA is a new observatory every few years

Mobility: anywhere, anytime Deployments to the Southern Hemisphere

and elsewhere

Twenty year design lifetime >120 8-10 hour flights per year

Flight altitude 41,000 – 45,000 ft

Collaboration between

NASA and DLR (Germany)

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The SOFIA Observatory

open cavity

(door not shown)

2.5m telescope

pressure bulkhead

scientific instrument

scientist stations, telescope

and instrument control, etc.

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Primary Mirror Installed Oct. 8, 2008

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Telescope and aperture assembly

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Installation on the plane

Installing PI rack & getting FORCAST into the plane

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Cryogen transfers on the plane

George and Luke in their LN2 transfer “costumes”

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Flight Log ….

Preparation and flights consisted of the following:

LineOps

Park plane on tarmac and look at stars, allowed end-to-end testing

of H/W & S/W, and practice!

Observatory characterization flights

25-May-2010 <= First light for SOFIA !!

10-Nov-2010, 18-Nov-2010

Observatory operation and performance checkout

Short Science flights

30-Nov-2010, 03-Dec-2010, 07-Dec-2010

Observed Jupiter, Comet Hartley 2, M42, W3, M82 + calibrators

Basic Science flights (support of guest investigations)

10 flights: 05-May through 07-Jun-2011

Commissioning and onward

May & Jun-2013, September 2013

On the Tarmac

for LineOps

Left: Setting up the

plane for a “LineOp”

(line operation)

Right: Door open,

looking at an alignment

and calibration star

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In flight operations

Holgar, Randy, Andy, and

Uli at work

Jim and Joe (foreground),

Alan (background)

TACFL (Telescope Assembly

Characterization and First Light) = OCF#1

(Observatory Characterization Flight #1)

First photons ever collected on

a SOFIA flight! (May 25, 2010)

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It’s the plane that’s moving

Apparent motion of telescope as plane pitches, rolls, and yaws.

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IR Background Removal In mid-infrared backgrounds

can be as large as 109 photons/second/pixel

“Chop” rapidly between to sky positions and difference Removes 1/f noise

“Nod” telescope and repeat “Double” difference removes

non-common path effects of chopping

Chopping & Nodding

CHOP

ON OFF

CHOP

ON OFF

NOD

Chopping

secondary

Telescope

nods

Chop frequency: 1 – 5 Hz

Nod frequency: 0.2 – 0.02 Hz

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Nod-Subtracted

Mid-infrared Data Acquisition

FORCAST data from OCF#3 on calibration star Alpha Cet at 37.1 micron. The integration time in a single image is 30 seconds. The features in the chop-subtracted image likely dominated by the dewar window but involve all off the optical system on either side of the secondary mirror.

Raw Image

rms ~ 350 DN

Chop-Subtracted

rms ~ 1.4 DN rms ~ 0.49 DN

The thermal emission from the atmosphere and warm optics (telescope,

etc.) create a background which we must look through (generating photon

noise)

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4 6 8 10 12

-40

-30

-20

-10

0

10

utcstart

tem

psec1, te

mp

pri

1

Telescope Temperature vs. time

TA primary (red) and secondary (blue) temperatures vs. UT for short

science flight #1

Primary mirror

Secondary mirror

10

0

-10

-20

-30

-40

Tem

pera

ture

(C

)

4 6 8 10 12

Time (hr)

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TACFL: First “Science” Integration

M82 – first chop-nod sequence: 24 m (left) and 37 m (right)

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FORCAST Science Observations

Short Science sample images

Jupiter and W3

Sample Science

Pistol/Sickle region of Galactic Center

Circumnuclear disk around Sgr A*

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Jupiter

Multi-wavelength imaging of Jupiter with FORCAST

Peter Gierasch along with Barney Conrath and Jason Wang (CU undergrad) are

analyzing and modeling the data (to look at H2 ortho to para ratio, etc.)

“Raw” 11.1 m Jupiter

images – right image has

been rescaled to show

Callisto and Io (and noise

level)

11.1 m

5.4 11.1 19.7 24.2 31.5 37.1

W3: from previous

to the present

Above left: Spitzer composite image at 3.6, 4.5, and 8.0 m of W3 (Ruch et al. 2007). Middle: 20 m image from Wynn-Williams, et al. 1972 and FIR images from Werner et al. 1980. Right: Images from SOFIA

20 m (Mt Wilson)

30 m (KAO)

50 m (KAO)

19.7 m

31.5 m

37.1 m

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W3 Main

Left: FORCAST image in 7.7 m PAH feature

Right: FORCAST image at 37.1 m

37.1 microns 7.7 microns, PAH

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Experiences flying on SOFIA

It has been both challenging and rewarding

We are part of a making a highly complex system

work

But, of course, that is the point (to push new

boundaries)

At every stage things have worked better than

(I personally) expected

Observatory performance is quite good

Would like continued image quality improvement

Great team effort by everyone

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Summary

Science flights have been highly successful.

Lots of publishable results

Science breadth

Wide range of programs covering planetary

science, star formation, stellar evolution, the

interstellar medium, and others.

FORCAST niche will be

Spatial resolution & wavelength coverage

Grisms spectroscopy (to be commissioned the

next time FORCAST flies)