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Millimetric observations of compact HII regions from Antarctica

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Title: Millimetric observations of compact HII regions from Antarctica


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 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

4
HII RegionsThe spectrum
The ionized nebula Lines Lyman (UV), Balmer
(visible), Paschen (IR) Lower energy levels
(radio H109a ? ?5 GHz) Continuum
bremsstrahlung emission
5
OASIOsservatorio 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)

6
Observational 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.
7
Data 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
8
Data 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)
9
Data analysisFlux calibration
Observations of planets (Drift Scan)
Sabbatini et al., 2007, submitted
Rayleigh-Jeans approximation
10
Results (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
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 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
12
Preliminary results (1)
13
Preliminary results (1)
14
Physical 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

15
COCHISE
January 2007 Installation _at_ Dome C
16
Thanks
17
(No Transcript)
18
HII 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)
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
  • 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
21
PWV
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

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 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

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 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
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