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Projeto Observacional para 2009A - OP2009A-045

Instituição: OBS.PARIS

Antônio M. Magalhães

Título: Multi-Scale Analysis of Magnetic Fieds in the CL04 MSX dark Cloud

Resumo: Polarimetry is a very good tool to study magnetic fields in our Galaxy by observing the radiation of stars absorbed by magnetically aligned dust grains in a preferential direction. Here we would like to use CAMIV in polarimetry mode to probe the magnetic field around the MSX dark cloud CL04 in a few fields around this cloud. Polarimetry in the visible is already available and allows to probe the magnetic field in the diffuse media surrounding the CL04 cloud. Submillimeter (submm) polarimetry already done at the JCMT allows to probe the magnetic field in the densests parts of the cloud. Polarimetry with CAMIV would greatly help by probing the magnetic field in intermediate regions and help to study possible variations of its orientations with column density. This aspect is important to understand the role that can be played by the magnetic fields in term of stellar formation since a variation of their orientation with density can be interpreted physically. This approach can also help to put constraint on star-forming and cloud evolution models. In a first step which is the main object of this proposal, four fields of 4'x4' on the 1.60 m telescope would be sufficient to cover the region observed in the submm and its neighbouring by observing during 4 to 5 nights (depending of the weather statistics during this period of the year) the faintest stars having H > 13 mag. The center positions of the four fields are given below: 1- RA(J2000)=18h37mn27.4s Dec(J2000):-7° 13' 21.9" 2- RA(J2000)=18h37mn27.4s Dec(J2000):-7° 09' 21.9" 3- RA(J2000)=18h37mn11.4s Dec(J2000):-7° 13' 21.9" 4- RA(J2000)=18h37mn11.4s Dec(J2000):-7° 09' 21.9" A second step would be to spent one night at the 60 cm to cover one field of 8'x8' in order to observe the 28 objects with 9.5 mag < H < 13 mag without saturation. The center position of this field is: RA(J2000)=18h37mn19.4s Dec(J2000):-7° 11' 21.9" Following Prof. AM Magalhães's recent proposal: Campo Magnético no Colapso Gravitacional: Polarimetria na banda H das Nuvens de Musca e Barnard 68: a mean of about 3 hours per field could be a good compromise to get a sufficient polarization signal to noise for stars up to H=13 mag at the 1.6 m. The same time of integration being good for stars up to 12 mag at the 60 cm. Since we have to deal with the polarization signal-to-noise ratio, our strategy will be to spent the more time possible per night (ideally 4-5 hours) on the four fields observed at the 1.6 m, with one given field position being observed during one given night. The necessary polarized and unpolarized standard stars will be observed each night. Since the CL04 region will be observable only a few hours during each night, strategic regions included in the Polarimetry Survey lead by AM Magalhães, and of particular interest for me in the framework of the COFECUB collaboration that myself, Prof. AM Magalhães and other collaborators have with people at the CESR in Toulouse in France, could be included in the project to complete the nights.