Spitzer observations of a circumstellar nebula around the candidate luminous blue variable MWC 930
Journal
Date Issued
2014
Author(s)
Cerrigone, L.
•
•
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Hora, J.L.
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•
LETO, PAOLO
•
Hart, A.
Abstract
MWC 930 is a star just ~2{\deg} above the Galactic plane whose nature is not
clear and that has not been studied in detail so far. While a post-Asymptotic
Giant Branch (AGB) classification was proposed in the past, studies of its
optical spectrum and photometry pointed toward strong variability, therefore
the object was reclassified as a Luminous Blue Variable (LBV) candidate. LBVs
typically undergo phases of strong mass loss in the form of eruptions that can
create shells of ejecta around the star. Our goal is to search for the presence
of such a circumstellar nebula in MWC 930 and investigate its properties. To do
so, we make use of space-based infrared data from our Spitzer campaign
performed with the InfraRed Array Camera (IRAC) and the InfraRed Spectrograph
(IRS) as well as data from optical and infrared (IR) surveys. In our Spitzer
images, we clearly detect an extended shell around MWC 930 at wavelengths
longer than 5 um. The mid-infrared spectrum is dominated by the central star
and mostly shows forbidden lines of [FeII], with an underlying continuum that
decreases with wavelength up to ~15 um and then inverts its slope, displaying a
second peak around 60 um, evidence for cold dust grains formed in a past
eruption. By modeling the SED, we identify two central components, besides the
star and the outer shell. These extra sources of radiation are interpreted as
material close to the central star, maybe due to a recent ejection. Features of
C-bearing molecules or grains are not detected.
Volume
562
Start page
A93
Issn Identifier
0004-6361
Ads BibCode
2014A&A...562A..93C
Rights
open.access
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