Observing the Galactic Center with SOFIA Mark Morris, UCLA

ABSRACT Many of the historical breakthroughs in Galactic center research were made with the Kuiper Airborne Observatory, observing in the far-infrared. This important capability will soon resume with the Stratospheric Observatory for Infrared Astronomy, and the Galactic center will be one of the primary targets. Early science observations now slated for mid-2010 will utilize two instruments -- the FORCAST imager and the GREAT spectrometer -- to study the physical conditions in Galactic center clouds over several tens of parsecs around Sgr A. This presentation will preview what is expected from these early observations, and will describe the complete suite of instruments that will be available in the first few years of operations, and that can be brought to bear on the Galactic center.

SOFIA is the successor to the Kuiper Airborne Observatory, a C141A transport stationed at NASA/Ames 1971 – SOFIA’s telescope has 7.5 times the collecting area of the KAO telescope, a conventional Cassegrain reflector with a 36-inch mirror.

The CircumNuclear Disk (the CND), discovered with the KAO (Becklin, Gatley & Werner 1982) J. Davidson et al 1992 (using KAO) 90 µm H 2 Yusef-Zadeh et al (HST) The clumpy disk is heated approximately equally by central stellar cluster of old stars and by the UV flux from the bright young stars in the central cluster. Total UV flux implied: ~10 7 L . A few KAO highlights, to make the case for airborne astronomy:

63 µm OI emission measured with the KAO: Jackson et al FWHM: 22” OI emission peaks in the interior of the CND, so the ionized gas there is mixed with atomic gas, presumably produced by photodissociation. An indication that there is far more gas inside the CND (300 M  ) than the ionized gas in Sgr A West (30 M  )

Latvakoski, H. M.; Stacey, G. J.; Gull, G. E.; Hayward, T. L KWIC on the KAO 31.5 µm37.7 µm Hot dust in the Arched Filaments, ionized & heated by the Arches Cluster

and 100 µm polarimetry from the KAO, and 350 µm polarimetry using the Hertz polarimeter on the CSO Dotson et al and Far-IR polarimetry !

Stratospheric Observatory for Infrared Astronomy: SOFIA This long-promised replacement for the KAO will carry the torch for the next 20 years. A Boeing 747SP aircraft modified to accommodate a 2.5-meter diameter reflecting telescope <> compare to Herschel – 3.5 m SOFIA is a joint NASA + DLR sub-orbital observatory –80% NASA –20% DLR -- Germany’s Aerospace Agency KAO experience  Airborne astronomy is exceptionally well suited for study of the Galactic center

USRA ( Universities Space Research Association ) will manage the science operations of SOFIA - science center: NASA/Ames Research Center - the German SOFIA science center is in Stuttgart NASA’s Dryden Flight Research Center will operate the aircraft Operating altitude: 37,000 – 45,000 ft.

Advantages of SOFIA:  Long duration, once it starts  Portable observatory  Flexibility of operation, and instrument swapping  Real-time observer participation  High spectral resolution  High spatial resolution in mid to far IR, compared to any other existing platform. Disadvantages: timing, with respect to Herschel cost of jet fuel

Telescope in Aircraft

Looking aft toward the pressure bulkhead & telescope assembly

Observatory Layout

FORCAST Faint Object Infrared Camera for the SOFIA Telescope A mid-IR camera, 256 x 256 pixels, operating at 5-40 µm First Science Instruments: GREAT German Receiver for Astronomy at Terahertz Frequencies A heterodyne spectrometer operating at µm other 1 st generation instruments: HAWC High-resolution Airborne Wideband Camera EXES Echelon-Cross-Echelle Spectrograph FIFI-LS Field Imaging Far-Infrared Line Spectrometer CASIMIR Caltech Submm Interstellar Medium Investigations Receiver FLITECAM First Light Infrared Test Experiment Camera SAFIRE Submillimeter and Far-Infrared Experiment HIPO High-speed Imaging Photometer for Occultations

SOFIA spectroscopy. EXES: [S III] 18.7 µm, [S I] 25.2 um, [O IV] 25.9 µm; H 17 & 28 µm R~20,000 (15 km/s) FIFI LS: [O III] 52, 88 µm, [O I] 63 µm, R~3000 (100 km/s) [O I] 145 µm, [C II] 158 µm, CO J=14-13, 17-16, 22-21, R~2000 GREAT: [OI] 63 um; R~20,000 (15 km/s) CASIMIR: CO 8-7, 9-8, 10-9, 12-11, HCN 6-5, 8-7, 9-8, 12-11, 13-12, HCN 14-13, 16-15, HCO

The Galactic Center from Spitzer

Galactic center issues that SOFIA can address: I. Thermal balance of GC clouds – what is the dominant heating source? Candidates: shocks, X-rays, dissipation of hydromagnetic waves Shock heating – investigate with the 63 and 149 µm fine structure lines of OI, produced in both shocks and PDRs. <> But compare to [CII] 158 µm line, which is much less affected by shocks. <> Use the intensity ratio of the two [OI] lines to control for density II. Heat flow through the GC ISM – dust and gas luminosities III. Magnetic field measurements <> equip the HAWC far-IR imager with a polarimeter to measure alignment direction of dust grains using the polarization vector of their thermal emission. IV. Chemistry – into the THz regime

SOFIA Schedule First open door flight: November 2009 First Science: August 2010 Full operations: flights per year, 8-hr flights Operation for 20 years Let’s go……

START, TAXI, TAKEOFF GW LBS TAXI FUEL TOTAL FUEL USED = 169,000 LBS. (24,708 Gallons) TOTAL CRUISE TIME = 7.05 HRS. TOTAL FLIGHT TIME = 8.05 HRS ASSUMPTIONS ZFW 381,000 LBS. ENGINES OPERATE AT 95% MAX CONT THRUST AT CRUISE 25,000 LBS. FUEL TO FIRST LEVEL OFF CLIMB TO FIRST LEVEL-OFF AT MAX CRUISE WT LANDING WITH 20,000 LBS. FUEL BASED ON NASA AMI REPORT: AMI 0423 IR BASED ON 747 SP FLIGHT MANUAL TABULATED DATA STANDARD DAY PLUS 10 DEGREES C CRUISE SPEED-MACH.84 CRUISE 84,000 LBS. FUEL F.F. 20,200 LBS/HR. CRUISE 52,000 LBS.FUEL F.F. 17,920 LBS/HR. FL410, 4.2 Hr GW FL430, 2.9 Hr GW DESCENT GW ,000 LBS. FUEL.5 HRS. LANDING GW ,000 LBS FUEL CLIMB 25,000 LBS. FUEL.5 HRS. Flight Profile 1 Performance with P&W JT9D-7J Engines: Observations - start FL410, duration 7.1 Hr

START,TAXI,TAKEOFF GW LBS TAXI FUEL TOTAL FUEL USED = 237,000 LBS. (34,650 Gallons) TOTAL CRUISE TIME = HRS. TOTAL FLIGHT TIME = HRS. CRUISE 68,000 LBS. FUEL F.F. 21,930 LBS/HR. CRUISE 84,000 LBS. FUEL F.F. 20,200 LBS/HR. CRUISE 52,000 LBS.FUEL F.F. 17,920 LBS/HR. FL390, 3.1 Hr GW FL410, 4.2 Hr GW FL430, 2.9 Hr GW DESCENT GW ,000 LBS. FUEL.5 HRS. LANDING GW ,000 LBS FUEL CLIMB 25,000 LBS. FUEL.5 HRS. Performance with P&W JT9D-7J Engines: Observations - start FL390, duration 10.2 Hr ASSUMPTIONS ZFW 381,000 LBS. ENGINES OPERATE AT 95% MAX CONT THRUST AT CRUISE 25,000 LBS. FUEL TO FIRST LEVEL OFF CLIMB TO FIRST LEVEL-OFF AT MAX CRUISE WT LANDING WITH 20,000 LBS. FUEL BASED ON NASA AMI REPORT: AMI 0423 IR BASED ON 747 SP FLIGHT MANUAL TABULATED DATA STANDARD DAY PLUS 10 DEGREES C CRUISE SPEED-MACH.84 Flight Profile 2