1. Millimetric observations of compact HII regions from Antarctica Lucia Sabbatini Astronomy PhD student - University “La Sapienza” OASI-COCHISE group – University of Roma Tre SNA - May 2007

2. HII Regions Interesting problems related to the physical properties of the dust (lack of information in the millimeter range) HII regions are non-variable, bright, compact sources: suitable candidates for calibration and pointing (es: PLANCK)

3. HII Regions: The structure Final stages of the birth of massive O and B stars (or cluster) Structure of compact HII regions: Central cavity (radius r 1 ) Ionized nebula HII (radius r S ) Neutral envelope HI (radius r 2 ) Typical dimensions of neutral envelope: r 2 ≈ 5 ± 50 pc Typical dimensions of the ionized nebula: equilibrium between ionization and recombination rates  Strömgren radius: r S ≈ 0.5 ± 10 pc

4. HII Regions: The spectrum The ionized nebula: Lines: Lyman (UV), Balmer (visible), Paschen (IR) Lower energy levels (radio: H109α  ν≈5 GHz) Continuum: bremsstrahlung emission Low frequencies: τ »1 High frequencies: τ «1 The neutral envelope: modified blackbody emission –Spectral index m (related to composition, grains dimensions, grains structure) –Dust temperature T d

5. OASI Osservatorio Antartico Submillimetrico e Infrarosso The O.A.S.I. telescope @ Terra Nova Bay –Coordinates: LAT. 74° 41’ 42” S LONG. 164° 07’ 23” E θ FWHM = 5.9 arcmin Detectors: 2 bolometers Operating temperature: T = 0.3 K ( 3 He refrigerator) ν 1 = 240 GHz (λ 1 =1.25mm) ν 2 = 150 GHz (λ 2 =2.0 mm) O.A.S.I. (Osservatorio Antartico Submillimetrico e Infrarosso) Optical configurationCassegrain Primary mirrorD = 2600mm Focal lengthf = 1300 mm Focal ratiof/D = 0.5 Secondary mirrord = 410 mm Equivalent focal lengthF = 10400 mm Equivalent focal ratioF/D = 4 Dall’Oglio et al., ExA 2, 275 (1992)

6. OFFON Observational techniques: ON-OFF Differential measurement: removal of atmospheric emission (first order). Tracking of the source during Δt: V ON (source + atmosphere) Tracking of the blank sky for Δt: V OFF (atmosphere only) The source signal is then the difference: V = V ON -V OFF Three fields modulation Double-differential measurement to allow the removal of the linear gradient of temperature in the atmospheric emission. The secondary mirror is modulated (ν  few Hz). The signal is then demodulated by a lock-in amplifier.

7. Data analysis: Baseline removal Right Ascension: evidence of the ON-OFF technique Modulated signal (pre-lockin) Demodulated signal (after lockin): offset varying with time (baseline) Polynomial fit of the OFF part of the data Removal of the baseline Peak signal for every cycle: S PEAK =V i ON -V i OFF

8. Data analysis: Source angular dimensions Estimation of sources diameters: gaussian fit along two main axis on IR and radio maps IR maps: IRAS (100, 60, 25 and 12 μm) G284.3 -0.3 (12 μm) G284.3 -0.3 (6 cm) Radio Maps: Parkes (6 cm) All Sky (408 MHz)

9. Data analysis: Flux calibration Observations of planets (Drift Scan) Rayleigh-Jeans approximation: Sabbatini et al., 2007, submitted

10. Results (1) G291.6 -0.5 Distance:7.6 ± 0.8 Kpc Strömgren radius: 3 ÷ 5 pc Angular dimensions: 10’ x 6.5’ Measured fluxes: F 1 =367 ± 59 Jy F 2 =208 ± 29 Jy G291.3 -0.7 Distance:3.6 ± 1.0 Kpc Strömgren radis: ≈ 0.5 pc Angular dimensions: 4.3’ x 4’ Measured fluxes: F 1 =97 ± 16 Jy F 2 =68 ± 10 Jy Sabbatini et al., A&A 439,595 (2005)

11. Results (2) G267.9 -1.1 Distance:2.0 ± 0.8 Kpc Strömgren radius: ≈ 0.4 pc Angular dimensions: 6.5’ x 1.8’ Measured fluxes: F 1 = 192 ± 23 Jy F 2 = 123 ± 15 Jy G284.3 -0.3 Distance:6.0 ± 1.2 Kpc Strömgren radius: 12 ÷ 15 pc Angular dimensions: 11.9’ x 9.0’ Measured fluxes: F 1 = 223 ± 27 Jy F 2 = 131 ± 16 Jy

12. Preliminary results (1)

14. Physical parameters Dust mass: Assuming that the dust cloud is optically thin: F ν : flux density due to dust d: distance from Sun B ν (T d ): blackbody at T d k v : dust mass absorption coefficient (@ λ =1.3 mm  k v =0.9 cm 2 g -1 cfr. Ossenkopf & Henning 1994) Bolometric luminosity: integrating fluxes over frequencies (using both literature and our results) Excitation parameter: calculating the linear dimensions from distance and our estimate of angular dimensions, and using electronic densities from literature: Lyman flux: number of photons needed to keep the excitation of the source: (Kurtz et al. 1994 ApJ 91, 659) Number of stars in the cluster: obtained by dividing N c for the tpical luminosity of a star (eg: O5 V  luminosity 4.9 10 49 sec -1 Panagia 1973)

15. COCHISE January 2007: Installation @ Dome C COCHISE (Cosmological Observations at Concordia with High sensitivity Instrument for Source Extraction) Optical configurationCassegrain Primary mirrorD = 2600mm Focal legthf = 1300 mm Focal ratiof/D = 0.5 Secondary mirrord = 410 mm Equivalent focal lengthF = 10400 mm Equivalent focal ratioF/D = 4 Angular resolutionFew arcmins in mm range

16. Thanks

18. HII Regions: Selection of sources HII Regions selected for dimensions and flux density (values extrapolated from radio to mm). Sources observed during the XX Campaign: SourceAR (hh mm ss)DEC (° ‘ “)Time of observations Drift ScanON-OFF G267.9 -1.108 59 15-47 32 2760 m145 m G279.4 -31.705 38 37-69 05 00--160 m G284.3 -0.310 24 26-57 48 29145 m260 m G287.4 -0.610 43 49-59 36 56105 m255 m G287.5 -0.610 44 58-59 40 36--245 m G291.3 -0.711 12 10-61 20 28220 m140 m G291.6 -0.511 15 18-61 17 18255 m115 m G298.2 -0.312 10 19-62 51 40--100 m G298.9 -0.412 15 42-63 03 0875 m200 m G305.2 +0.213 11 54-62 35 01--120 m RCW 3808 59 07-47 31 01135 m-- Paladini et al. A&A 397, 213 (2003)

19. Spectrometer characteristics Lamellar Grating scheme Resolution: 0.2 cm -1 Spectral coverage: 2 – 10 cm -1 Multi-pixel photometer Cryogen-free cooling system Designed to be (eventually) remotely operated

20. Atmospheric absorption Estimation of the atmospheric transmission in the mm-range Daily variability of the transmission Comparison to atmospheric transmission models  water vapour content pwv (precipitable water volume) Atmospheric composition: N 2 (78%), O 2 (21%) H 2 O, CO 2, O 3 Atmospheric absorption at millimeter wavelengths: O 2 : 60, 119 GHz H 2 O: 183, 325 GHz

21. PWV See also:Chamberlin, 2001(Typical PWV SP  0.7mm in January) Burova, 1986 Townes & Melnick, 1990 (as low as PWV Vostok  0.1 mm) Lawrence, 2004 Valenziano et al., 1997 Valenziano & Dall’Oglio, PASA, 1999 January 1997January 2007 Sabbatini et al., 2007, in prep

22. Spectral hygrometer Taking a pair of simultaneous direct solar irradiance measurements within two narrow spectral intervals centered at nearby wavelengths: -the first in the middle of an infrared water vapour absorption band -the second within a next transparency window of solar spectrum (reference) Prototype model designed by Tomasi and Guzzi (1974) Hygrometric ratio: R=QT 1 (x)/T 2 (x) T 1, T 2 : transmission in the two bands λ 1  0.940 μm (HBW=0.0122 μm, F(λ p )=53.5%) λ 2  0.870 μm (HBW=0.0116 μm, F(λ p )=55.0%) x: water vapour content R=V(0.940)/V(0.870) Calibration: using radiosoundings (provided by ENEA)  accuracy and reliability (better than radiosounding data)  Possibility of intraday measurements  low costs  easy to be operated at harsh sites  Only for antarctic summer…

23. Measurements of pwv (1997-2007) December 1996 – January 1997: about 80 intraday measurements (Valenziano et al. 1998) portable near-IR spectral hygrometers portable Volz (1974) sun-photometer for intercomparison tests New calibration (2007): using the monthly mean vertical profiles of pressure, temperature and humidity using 87 radiosoundings performed in 2003 and 2004 (Aristidi et al. 2005)  First attempt to characterize the site (pwv content)  First instrumental calibration specific for Dome C values (pwv < 1mm) January-February 2007: 16 days, every hour (day time)  More than 100 measurements of pwv  First systematic monitoring of daily variation of pwv  Calibration with radiosoundings of the same period  The instrument is still at Dome C: it is possible to have other measurements at the beginning of next summer season