Surace Cal Summit III Jason Surace April 19, 2007 Spitzer-IRAC/Akari-IRC Cross-Calibration With figures by Ohyama, Wada, and Tanabe

Surace Cal Summit III

Jason Surace

April 19, 2007

Spitzer-IRAC/Akari-IRCCross-Calibration

With figures by Ohyama, Wada, and Tanabe


Our Interest in Akari (formerly Astro-F, formerly IRIS)

• It is in the overall interest of IRAC to ensure that the calibration of Akari is consistent with IRAC’s. This will allow direct comparison between datasets on both satellites, and along the way ensure we haven’t made any major errors.

• IRC has capabilities Spitzer doesn’t. It has more broadband filters, and spectroscopic capabilities down to 1.5 µm.


Brief Akari Overview

Much like Spitzer:

68 cm telescope, this satellite is not small! 4m long, 960kg!

Imaging and Spectroscopy


Sun-synchronous Earth orbit

68cm telescope

3.7m, 960kg

170l He, 1.8 yrs

1.8-160µm

Primarily all-sky survey

Earth-trailing Solar orbit

86cm telescope

4.4m, 950 kg

350l He, 5.5 yrs

3.6-160µm

Primarily pointed observations


IRC and FIS

10x10’ imaging

2,3,4,7,9,11,15,18,24,60,160µm

Low-res slit and slitless spectroscopy over entire wavelength range

IRAC, IRS, and MIPS

5x5’ imaging

~4,5,6,8,24,70,160 µm, plus some minimal 16µm

Low and high-res slit spectroscopy over 5-40µm

Low-res spectroscopy 50-100µm


Post-Cryo!

Spitzer: IRAC 3.6 and 4.5µm channels will continue working. Passive cooling.

Akari: IRC NIR channel, with 2, 3, 4µm filters plus spectroscopy will continue to work. Passive cooling plus cryo-coolers.


Equivalent of JPL+Goddard

Runs all space science missions (I.e. everything).

Development, assembly, operations, research, etc.

250 total people.

Akari looks to be operated by 10-20 people, total.



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Summary on IRC Spectroscopy Capability

Camera Disperser

Nam

e ArrayFOV

(arcmin2)

Pix scale(arcse

c/pix)

ID

Typ

e

(µm)

dSpec.Lengt

h

NIR

InSb

512X412

9.5'X10.0'

1.46”

NPprism

1.8–5.5

22@

3.5µm

81 pix

NG

grism

2.5–5.0

135@

3.6µm261

MIR

-S

Si:As

256X256

9.1'X10.0'

2.34”

SG1

grism

5.3–8.3

47@

6.6µm85

SG2

grism

7.5–13.5

34@

10.6µm

91M

IR-L

Si:As

256x256

10.3'X10.2'

2.51”x2.39”

LG1

grism

11–19

19@

14.4µm

---

LG2

grism

17.7–

25.0

27@

20.2µm

79

IRC Spectroscopic Capabilities


NIR N2 (1.7-2.7µm)

single1-min observation ~10 min stack


NIR (InSb) NP Prism (2-6µm)


MIR-L Si:As LG2 Grism (17-25µm)


Akari Calibrator Stars

Akari calibration methodology identical to IRAC’s. Martin Cohen generates predicted fluxes based on instrument throughput and templates. Broad-band imaging and spectroscopy both calibrated in this fashion. Almost all Akari calibrators already observed by IRAC. Mostly A & K-stars. Deliberate overlap with IRAC to extent allowed by pointing constraints.


Some Difficulties

Difficult to use the slits due to pointing issues.

Advantages to using slitless (easier to handle slit loss), but there are confusion problems at short wavelengths.

Also, wavelength calibration not fixed and leads to problems near spectrum ends.


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Black is Cohen template, blue is IRC data.

2MASS 1757132

KF06T2 - K-star

Note - calibration is set by this object at short end.

Near-IR Prism








BP +66 1073 - K-star

HD 42525 A-star

(calibrator)

KF09T1 K-star

Near-IR Grism


<NP>K vs. A

(in mJy*um^2 unit)

<base>

K A

KF06T22MASS

1757132


<NG>K vs. A

(in mJy*um^2 unit)

<base>

K A


Unfortunately, this is confused by the fact that we don’t have the raw spectra, only the flux-calibrated ones which already have the standard star response in them.

But you can see the absorption trough in channel 2 easily!


<SG1>K vs. A

(in mJy*um^2 unit)

<base>

K A


Mid-IR Short Grism 1







BP +66 1073

K-star

HD 42525

A-star

(calibrator)

NPM 1p67 536

K-star




Mid-IR Short Grism 2



BP +66 1073

K-star

HD 42525

A-star

(calibrator)


Are We Learning Anything?

• For at least some K-stars, Martin’s templates have too deep troughs. But they work well for other stars. Inadequacy of optical spectral typing?

• No obvious surprise features.

• Still need to get raw data. Getting any data has been tricky.


Akari Calibration Locations

• Akari CVZ within 0.6 degrees of ecliptic pole (similar to WISE), vs. 4-5 for Spitzer.

• All Akari cal stars located within their northern and southern CVZ.

• Deep survey at ecliptic caps. Ideal for general cross-cal with IRAC.

• IRAC dark field outside the Akari CVZ, although it is being observed in a fashion as part of a mission project (Egami, PI).

• Observing Akari cal field as an IRAC cal activity.


“Deep” Component

Central 5x5’

Depth is 28x100 seconds

5-sigma = 0.6, 1.2, 7.5, and 9 µjy at 3.6, 4.5, 5.8, and 8 µm.

Confusion-limited at 3.6 and 4.5µm.

2 hours to execute.


“Shallow” Component

Coverage of a 10x10’ area with all 4 arrays.

8x30 seconds = 2x SWIRE integration time

5-sigma = 2.5, 4.2, 28, and 32µJy at 3.6, 4.5, 5.8, 8 µm.

High Dynamic Range Mode

50 minutes to execute


Akari NEP Cal Field Observed by IRAC

Ch.1 Entire Field, all exposures

Ch.

1C

h.4


IRAC vs. IRC Broadband Photometry


Early Results from Cross-Cal Field Encouraging

• Computed the expected slopes from Martin’s model calculations for specific stars.

• IRC/IRAC numbers match to within 5%, the limit I could measure them to.

• Somewhat circular, since Akari also calibrated to Cohen templates.

• Indicates no significant issues with system throughput measurements.

• Indicates that point source measurement and calibration methodology holds and agrees between missions.

Documents

Surace Cal Summit III Jason Surace April 19, 2007 Spitzer-IRAC/Akari-IRC Cross-Calibration With figures by Ohyama, Wada, and Tanabe