Title: Millimetric observations of compact HII regions from Antarctica
1Millimetric 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
2HII 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)
3HII 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
4HII RegionsThe spectrum
The ionized nebula Lines Lyman (UV), Balmer
(visible), Paschen (IR) Lower energy levels
(radio H109a ? ?5 GHz) Continuum
bremsstrahlung emission
5OASIOsservatorio Antartico Submillimetrico e
Infrarosso
DallOglio et al., ExA 2, 275 (1992)
- The O.A.S.I. telescope _at_ Terra Nova Bay
- Coordinates
- LAT. 74 41 42 S
- LONG. 164 07 23 E
- ?FWHM 5.9 arcmin
- Detectors 2 bolometers
- Operating temperature
- T 0.3 K (3He refrigerator)
- ?1 240 GHz (?11.25mm)
- ?2 150 GHz (?22.0 mm)
6Observational techniques ON-OFF
- Differential measurement removal of atmospheric
emission (first order). - Tracking of the source during ?t VON (source
atmosphere) - Tracking of the blank sky for ?t
VOFF (atmosphere only) - The source signal is then the difference V
VON-VOFF
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 (??few Hz). The signal is then
demodulated by a lock-in amplifier.
7Data analysisBaseline 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 SPEAKViON-ViOFF
8Data analysisSource 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)
Radio Maps Parkes (6 cm) All Sky (408 MHz)
9Data analysisFlux calibration
Observations of planets (Drift Scan)
Sabbatini et al., 2007, submitted
Rayleigh-Jeans approximation
10Results (1)
Sabbatini et al., AA 439,595 (2005)
G291.6 -0.5 Distance 7.6 0.8 Kpc Strömgren
radius 3 5 pc Angular dimensions 10 x
6.5 Measured fluxes F1367 59 Jy F2208
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 F197 16 Jy F268
10 Jy
11Results (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 F1 192 23 Jy F2 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 F1 223 27 Jy F2 131
16 Jy
12Preliminary results (1)
13Preliminary results (1)
14Physical parameters
- Dust mass
- Assuming that the dust cloud is optically thin
- F? flux density due to dust
- d distance from Sun
- B?(Td) blackbody at Td
- kv dust mass absorption coefficient
- (_at_ ?1.3 mm ? kv0.9 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
15COCHISE
January 2007 Installation _at_ Dome C
16Thanks
17(No Transcript)
18HII RegionsSelection of sources
- HII Regions selected for dimensions and flux
density (values extrapolated from radio to mm). - Sources observed during the XX Campaign
Paladini et al. AA 397, 213 (2003)
19Spectrometer 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
20Atmospheric absorption
- Atmospheric composition
- N2 (78), O2 (21)
- H2O, CO2, O3
- Atmospheric absorption at millimeter wavelengths
- O2 60, 119 GHz
- H2O 183, 325 GHz
- water vapour content
- pwv (precipitable water volume)
Estimation of the atmospheric transmission in the
mm-range Daily variability of the
transmission Comparison to atmospheric
transmission models
21PWV
January 1997
January 2007
Valenziano et al. , 1997 Valenziano DallOglio,
PASA, 1999
Sabbatini et al., 2007, in prep
- See also Chamberlin, 2001 (Typical PWVSP? 0.7mm
in January) - Burova, 1986
- Townes Melnick, 1990 (as low as PWVVostok ?
0.1 mm) - Lawrence, 2004
22Spectral 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 RQT1(x)/T2(x)
- T1, T2 transmission in the two bands
- ?1 ? 0.940 µm (HBW0.0122 µm, F(?p)53.5)
- ?2 ? 0.870 µm (HBW0.0116 µm, F(?p)55.0)
- x water vapour content
- RV(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
23Measurements 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 lt 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