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 F. O. Alves G. A. P. Franco Physics Departament, ICEX, UFMG, Belo Horizonte, Brazil

Lupus dark clouds and Lupus 1 Optical extinction: Cambresy,  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  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 ( ~ and ~ per cent  small instrumental polarization).  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 ( ~ and ~ 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 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 pc.  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 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 pc.

Pipe nebula Distance from the Sun: 145 ± 16 pc (Alves & Franco, in preparation).