Millimetric observations of compact HII regions

from Antarctica

Lucia SabbatiniAstronomy PhD student - University “La Sapienza”

OASI-COCHISE group – University of Roma Tre

SNA - May 2007

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)

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 r1)• Ionized nebula HII (radius rS)• Neutral envelope HI (radius r2)

Typical dimensions of neutral envelope: r2 ≈ 5 ± 50 pc

Typical dimensions of the ionized nebula: equilibrium between ionization and recombination rates Strömgren radius:rS ≈ 0.5 ± 10 pc

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HII Regions:

The spectrum

S S

deTBdIS e

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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

TdBSS

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TdBS 35.015.0

The neutral envelope:modified blackbody emission– Spectral index m (related to composition, grains dimensions, grains structure)– Dust temperature Td

)( dm TB

OASIOsservatorio Antartico Submillimetrico e Infrarosso

• The O.A.S.I. telescope @ Terra Nova Bay– Coordinates:

LAT. 74° 41’ 42” S

LONG. 164° 07’ 23” E

• θFWHM = 5.9 arcmin• Detectors: 2 bolometers • Operating temperature:

T = 0.3 K (3He refrigerator)

ν1 = 240 GHz (λ1=1.25mm)

ν2 = 150 GHz (λ2=2.0 mm)

O.A.S.I.(Osservatorio Antartico Submillimetrico e

Infrarosso)

Optical configuration Cassegrain

Primary mirror D = 2600mm

Focal length f = 1300 mm

Focal ratio f/D = 0.5

Secondary mirror d = 410 mm

Equivalent focal length F = 10400 mm

Equivalent focal ratio F/D = 4

Dall’Oglio et al., ExA 2, 275 (1992)

OFF ON

Observational techniques: ON-OFF

Differential measurement: removal of atmospheric emission (first order).

Tracking of the source during Δt: VON (source + atmosphere)

Tracking of the blank sky for Δt: VOFF (atmosphere only)

The source signal is then the difference: V = VON-VOFF

Three fields modulationDouble-differential measurement to allow the removal of the linear gradient of temperature in the atmospheric emission.

The secondary mirror is modulated (νfew Hz).The signal is then demodulated by a lock-in amplifier.

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 dataRemoval of the baselinePeak signal for every cycle:

SPEAK=ViON-Vi

OFF

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)

21 peaktot SS

Data analysis:

Flux calibrationObservations of planets (Drift Scan)

Rayleigh-Jeans approximation:

2

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Sabbatini et al., 2007, submitted

Results (1)

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G 291.6 -0.5 Letteratura Questo lavoro

G291.6 -0.5Distance: 7.6 ± 0.8 Kpc

Strömgren radius: 3 ÷ 5 pc

Angular dimensions: 10’ x 6.5’

Measured fluxes:

F1=367 ± 59 Jy

F2=208 ± 29 Jy

G291.3 -0.7Distance: 3.6 ± 1.0 Kpc

Strömgren radis: ≈ 0.5 pc

Angular dimensions: 4.3’ x 4’

Measured fluxes:

F1=97 ± 16 Jy

F2=68 ± 10 Jy

Sabbatini et al., A&A 439,595 (2005)

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G291.3 -0.7 Letteratura Questo lavoro

Results (2)

G267.9 -1.1Distance: 2.0 ± 0.8 Kpc

Strömgren radius: ≈ 0.4 pc

Angular dimensions: 6.5’ x 1.8’

Measured fluxes:

F1= 192 ± 23 Jy

F2= 123 ± 15 Jy

G284.3 -0.3Distance: 6.0 ± 1.2 Kpc

Strömgren radius: 12 ÷ 15 pc

Angular dimensions: 11.9’ x 9.0’

Measured fluxes:

F1= 223 ± 27 Jy

F2= 131 ± 16 Jy

Preliminary results (1)

Preliminary results (1)

Physical parameters• Dust mass:

Assuming that the dust cloud is optically thin: Fν: flux density due to dustd: distance from SunBν(Td): blackbody at Td

kv: dust mass absorption coefficient (@ λ=1.3 mm kv=0.9 cm2 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 Nc for the tpical luminosity of a star (eg: O5 V luminosity 4.9 1049 sec-1 Panagia 1973)

)(

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dd TBk

dFM

3/2 ernU

385.0461004.8 UTN ec

COCHISE

January 2007: Installation @ Dome C

COCHISE(Cosmological Observations at Concordia

with High sensitivity Instrument for Source Extraction)

Optical configuration Cassegrain

Primary mirror D = 2600mm

Focal legth f = 1300 mm

Focal ratio f/D = 0.5

Secondary mirror d = 410 mm

Equivalent focal length F = 10400 mm

Equivalent focal ratio F/D = 4

Angular resolution Few arcmins in mm range

Thanks

HII Regions:

Selection of sourcesHII Regions selected for dimensions and flux density (values

extrapolated from radio to mm).Sources observed during the XX Campaign:Source AR (hh mm ss) DEC (° ‘ “) Time of observations

Drift Scan ON-OFF

G267.9 -1.1 08 59 15 -47 32 27 60 m 145 m

G279.4 -31.7 05 38 37 -69 05 00 -- 160 m

G284.3 -0.3 10 24 26 -57 48 29 145 m 260 m

G287.4 -0.6 10 43 49 -59 36 56 105 m 255 m

G287.5 -0.6 10 44 58 -59 40 36 -- 245 m

G291.3 -0.7 11 12 10 -61 20 28 220 m 140 m

G291.6 -0.5 11 15 18 -61 17 18 255 m 115 m

G298.2 -0.3 12 10 19 -62 51 40 -- 100 m

G298.9 -0.4 12 15 42 -63 03 08 75 m 200 m

G305.2 +0.2 13 11 54 -62 35 01 -- 120 m

RCW 38 08 59 07 -47 31 01 135 m --

Paladini et al. A&A 397, 213 (2003)

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

Atmospheric absorption

Estimation of the atmospheric transmission in the mm-rangeDaily variability of the transmissionComparison to atmospheric transmission models

water vapour content

pwv (precipitable water volume)

Atmospheric composition: • N2 (78%), O2 (21%)• H2O, CO2, O3

Atmospheric absorption at millimeter wavelengths:

O2: 60, 119 GHzH2O: 183, 325 GHz

PWV

See also: Chamberlin, 2001(Typical PWVSP 0.7mm in January) Burova, 1986Townes & Melnick, 1990 (as low as PWVVostok 0.1 mm) Lawrence, 2004

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Valenziano et al. , 1997Valenziano & Dall’Oglio, PASA, 1999

January 1997 January 2007

Sabbatini et al., 2007, in prep

Spectral hygrometerTaking 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=QT1(x)/T2(x)T1, T2: transmission in the two bands

λ1 0.940 μm (HBW=0.0122 μm, F(λp)=53.5%)λ2 0.870 μm (HBW=0.0116 μm, F(λp)=55.0%)

x: water vapour contentR=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…

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