Bibcode
DOI
Wisniewski, J. P.; Bjorkman, K. S.; Magalhães, A. M.; Bjorkman, J. E.; Meade, M. R.; Pereyra, Antonio
Bibliographical reference
The Astrophysical Journal, Volume 671, Issue 2, pp. 2040-2058.
Advertised on:
12
2007
Journal
Citations
30
Refereed citations
23
Description
We present the first detailed imaging polarization observations of six
SMC and six LMC clusters, known to have large populations of B-type
stars that exhibit excess Hα emission from 2-CD photometric
studies, to constrain the evolutionary status of these stars and hence
better establish links between the onset of disk formation in classical
Be stars and cluster age and/or metallicity. We parameterize and remove
the interstellar polarization (ISP) associated with each line of sight,
thereby isolating the presence of any intrinsic polarization. We use the
wavelength dependence of this intrinsic polarization to discriminate
pure gas disk systems, i.e., classical Be stars, from composite
gas-plus-dust disk systems, i.e., Herbig Ae/Be or B[e] stars. Our
intrinsic polarization results, along with available near-IR color
information, support the suggestion of Wisniewski et al. that classical
Be stars are present in clusters of age 5-8 Myr and contradict
assertions that the Be phenomenon only develops in the second half of a
B star's main-sequence lifetime, i.e., no earlier than 10 Myr. The
prevalence of polarimetric Balmer jump signatures decreases with
metallicity; we speculate that either it is more difficult to form large
disk systems in low-metallicity environments or that average disk
temperatures are higher in low-metallicity environments. The
polarimetric signatures of ~25% of our sample appear unlikely to arise
from true classical Be star disk systems, suggesting one should proceed
with caution when attempting to determine the role of evolutionary age
and/or metallicity in the Be phenomenon purely via 2-CD results.