The properties of astrophysical masers are governed by the physical conditions
of circumstellar envelopes of evolved stars, implying a connection between
maser and mass-loss phenomena. Although similar studies to another type of
mass-losing star, Asymptotic Giant Branch (AGB) stars, have been conducted,
a quantitative understanding for the case of Red Supergiants (RSGs) is still
largely lacking. Recently, more and more galactic massive clusters are discovered
and studied, which provide a coeval environment to investigate the evolution
of cool massive evolved stars with similar distance and metallicity. Among
them, Westerlund 1 (Wd1) is one of the most massive open clusters, classified
as Super Star Clusters (SSCs), within the Milky Way harboring 4 RSGs.
We have 2 goals in this project. We aim to investigate the relationship between
SiO maser detection and mass-loss behavior of RSGs in massive clusters,
in order to explore the possibility of developing SiO maser as an evolutionary
indicator of RSGs. We also aim to determine the kinematic properties of Wd1
with the aid of SiO maser.
We report on observation of 43 GHz SiO (v = 1, J = 1–0) maser towards
Wd1 conducted with Australia Telescope Compact Array (ATCA). We also
make use of archival 22 GHz H2O maser (616–523) in help of studying kinematic
of Wd1. We derive the maser detection information and stellar velocities from
maser data. We also compile an extra sample of 36 RSGs, which surveyed in SiO
maser before, within massive clusters, e.g. Red Supergiant Cluster 1 (RSGC1),
Red Supergiant Cluster 2 (RSGC2), Perseus OB association 1 (Per OB 1) and
Mercer et al.’s #8 (Mc8), and organize their photometric data from 2MASS,
GLIMPSE, MSX, AKARI and WISE to derive their spectral energy distributions
(SEDs). Luminosity, effective temperature and mass-loss rate are derived
from fitting the SEDs with DUSTY model in order to search for correlations
between mass-loss rate, SiO maser properties and evolution of RSGs.
We detected SiO maser emission towards 2 RSGs (W 237 and W 26) in
Wd1. These 2 RSGs also emit H2O maser as revealed from archival H2O maser
observation data. We noticed that SiO masers tend to be detected towards RSGs
with higher luminosity and mass-loss rate. We also determined the kinematic
distance of Wd1 to be 3.3 kpc. From that result, we conclude that SiO maser
is an effective evolution indicator for RSGs, which traces RSGs with high massloss
rate. We also show that the age of RSGs in Wd1 is 10 ± 2 Myr which
support the multi-generation star formation scenario in Wd1. / published_or_final_version / Physics / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174485 |
| Date | January 2012 |
| Creators | Fok, Kai-tung., 霍啟東. |
| Contributors | Nakashima, J, Kwok, S |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47753055 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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