Dust Properties Towards Galactic Anti-Center Direction
Date & Time :
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The polarization of starlight is one among several properties manifested by interstellar dust grains. Polarization of background starlight through the interstellar medium (ISM) is a result of the dichroic extinction of starlight through the aligned grains. The alignment of ISM dust grains is such that the short axis of grains is parallel to the magnetic field direction. The polarimetric study will reveal the projected direction of the magnetic field at the region whether it is a macroscopic field in the Galaxy or the local magnetic fields of the cloud. The size distribution, shape, and alignment efficiency of dust grains can be investigated using the study. We are investigating the properties of ISM dust grains and their alignment towards the Galactic anti-center direction. Aiming this, we have selected open star clusters in the selected direction. The multi-wavelength polarimetric observations were taken from Aries imaging polarimeter (AIMPOL) mounted as a backend instrument of 1.04-m telescope of ARIES. The linear polarimetric study of 73 stars in the region of the cluster Alessi 1, 125 stars in NGC 1817, 197 stars in NGC 2345, and 72 stars in NGC 7380 in B, V, R, and I bands have been carried out. The polarization of the majority of stars is found to be ISM originated in all four clusters. Dust grains are found to be aligned possibly by the Galactic magnetic field towards the direction of the cluster Alessi 1, NGC 2345, and NGC 7380 while in the case of NGC 1817, the deviation of the polarization position angle from Galactic parallel is found indicating the dust perturbation at the place. The increment of wavelength for maximum polarization with extinction accompanied by its decrements with increasing polarizing efficiency could be a result of radiative torque alignment of grains, as found in the case of the cluster NGC 2345. The increasing polarizing efficiency and decreasing wavelength of maximum polarization towards the cluster center indicate about increasing local radiation field within the cluster. The average value of wavelength for maximum polarization near 0.54 - 0.59 micron reveals that the size distribution of dust grains towards all these clusters is similar to that of general ISM.
About Speaker :
Sadhana Singh is a Ph.D. student at ARIES. This is her pre Ph.D. thesis submission seminar.