Download The infrared void in the Lupus dark clouds revisited: a

The infrared void in the Lupus
dark clouds revisited: a
polarimetric approach
(Alves & Franco, 2006)
F. O. Alves
G. A. P. Franco
Physics Departament, ICEX, UFMG, Belo Horizonte, Brazil
Lupus dark clouds and Lupus 1
Optical extinction: Cambresy, 1999
100 m IRAS emisison
Main purposes
 Starlight polarization by dust to improve the
distance to the low-mass star forming cloud
Lupus 1
 Confirm the existence of a low emission
region towards the cloud complex.
 Describe the solar neighborhood and,
particularly, the Loop 1-Local Bubble
interface
Instrumentation
B-band CCD polarimetry (8’ x 8’)
Polarimetric unit (Magalhães et al, 1996)
IAG 0.60m telescope
Observational technique
 44 nights from 2001 to 2005 at
Observatório do Pico dos Dias (LNA/MCT,
Brazil).
 131 Hipparcos stars with trigonometric
parallaxes H ≥ 4mas (≤ 250 pc).
 Selection criterion: /H ≤ 1/3
 Calibration targets: polarized and
unpolarized standart stars (<Q> ~ -0.007
and <U> ~ -0.006 per cent small
instrumental polarization).
Standart stars
The parallax-polarization diagram
Lupus 1 and surroundings
The parallax-polarization diagram
Low emission region (cavity)
The polarization map
Comparison to previous work
Colour excess data by Franco, 2002
Results
 Distribution of linear polarization as a function of
distance shows the same pattern found for the
reddening-distance diagram;
 Parallax-polarization diagram indicates low polarization
values up to 130-150 pc, where the dust associated to
Lupus 1 may be responsible for the sharp increasing in
the polarization values;
 Reddening- and polarization- distance diagrams
suggest the existence of a region cleaned from dust in
the Lupus dark clouds;
 Material associated to the Loop 1-Local Bubble
interface may be at 60-100 pc.
Pipe nebula
Distance from the Sun: 145 ± 16 pc (Alves & Franco, in preparation).