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Measuring polarization in microlensing events


Ingrosso, G; Calchi Novati, S; De Paolis, F; Jetzer, P; Nucita, A A; Strafella, F (2015). Measuring polarization in microlensing events. Monthly Notices of the Royal Astronomical Society, 446(1):1090-1097.

Abstract

We re-consider the polarization of the star light that may arise during microlensing events due to the high gradient of magnification across the atmosphere of the source star, by exploring the full range of microlensing and stellar physical parameters. Since it is already known that only cool evolved giant stars give rise to the highest polarization signals, we follow the model by Simmons et al. (2002) to compute the polarization as due to the photon scattering on dust grains in the stellar wind. Motivated by the possibility to perform a polarization measurement during an ongoing microlensing event, we consider the recently reported event catalog by the OGLE collaboration covering the 2001-2009 campaigns (OGLE-III events), that makes available the largest and more comprehensive set of single lens microlensing events towards the Galactic bulge. The study of these events, integrated by a Monte Carlo analysis, allows us to estimate the expected polarization profiles and to predict for which source stars and at which time is most convenient to perform a polarization measurement in an ongoing event. We find that about two dozens of OGLE-III events (about 1 percent of the total) have maximum polarization degree in the range 0.1 < P_{\rm max} <1 percent, corresponding to source stars with apparent magnitude I < 14.5, being very cool red giants.This signal is measurable by using the FORS2 polarimeter at VLT telescope with about 1 hour integration time.

Abstract

We re-consider the polarization of the star light that may arise during microlensing events due to the high gradient of magnification across the atmosphere of the source star, by exploring the full range of microlensing and stellar physical parameters. Since it is already known that only cool evolved giant stars give rise to the highest polarization signals, we follow the model by Simmons et al. (2002) to compute the polarization as due to the photon scattering on dust grains in the stellar wind. Motivated by the possibility to perform a polarization measurement during an ongoing microlensing event, we consider the recently reported event catalog by the OGLE collaboration covering the 2001-2009 campaigns (OGLE-III events), that makes available the largest and more comprehensive set of single lens microlensing events towards the Galactic bulge. The study of these events, integrated by a Monte Carlo analysis, allows us to estimate the expected polarization profiles and to predict for which source stars and at which time is most convenient to perform a polarization measurement in an ongoing event. We find that about two dozens of OGLE-III events (about 1 percent of the total) have maximum polarization degree in the range 0.1 < P_{\rm max} <1 percent, corresponding to source stars with apparent magnitude I < 14.5, being very cool red giants.This signal is measurable by using the FORS2 polarimeter at VLT telescope with about 1 hour integration time.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Language:English
Date:October 2015
Deposited On:18 Feb 2016 16:10
Last Modified:05 Apr 2016 20:05
Publisher:Oxford University Press
ISSN:0035-8711
Additional Information:This article has been accepted for publication in MNRAS © 2015 The Authors Published by Oxford University Press Royal Astronomical Society. All rights reserved.
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1093/mnras/stu2161
Other Identification Number:arXiv:1410.3594v1

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