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Postgraduate Thesis: Maser and infrared properties of red supergiants embedded in the superstar cluster Westerlund 1
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TitleMaser and infrared properties of red supergiants embedded in the superstar cluster Westerlund 1
 
AuthorsFok, Kai-tung.
霍啟東.
 
Issue Date2012
 
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
 
AbstractThe 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.
 
AdvisorsNakashima, J
Kwok, S
 
DegreeMaster of Philosophy
 
SubjectSupergiant stars.
Stars - Clusters.
 
Dept/ProgramPhysics
 
DC FieldValue
dc.contributor.advisorNakashima, J
 
dc.contributor.advisorKwok, S
 
dc.contributor.authorFok, Kai-tung.
 
dc.contributor.author霍啟東.
 
dc.date.hkucongregation2012
 
dc.date.issued2012
 
dc.description.abstractThe 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.
 
dc.description.naturepublished_or_final_version
 
dc.description.thesisdisciplinePhysics
 
dc.description.thesislevelmaster's
 
dc.description.thesisnameMaster of Philosophy
 
dc.identifier.hkulb4775305
 
dc.languageeng
 
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)
 
dc.relation.ispartofHKU Theses Online (HKUTO)
 
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.
 
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License
 
dc.source.urihttp://hub.hku.hk/bib/B47753055
 
dc.subject.lcshSupergiant stars.
 
dc.subject.lcshStars - Clusters.
 
dc.titleMaser and infrared properties of red supergiants embedded in the superstar cluster Westerlund 1
 
dc.typePG_Thesis
 
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<item><contributor.advisor>Nakashima, J</contributor.advisor>
<contributor.advisor>Kwok, S</contributor.advisor>
<contributor.author>Fok, Kai-tung.</contributor.author>
<contributor.author>&#38669;&#21855;&#26481;.</contributor.author>
<date.issued>2012</date.issued>
<description.abstract>&#65279;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&#8211;0) maser towards

Wd1 conducted with Australia Telescope Compact Array (ATCA). We also

make use of archival 22 GHz H2O maser (616&#8211;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.&#8217;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 &#177; 2 Myr which

support the multi-generation star formation scenario in Wd1.</description.abstract>
<language>eng</language>
<publisher>The University of Hong Kong (Pokfulam, Hong Kong)</publisher>
<relation.ispartof>HKU Theses Online (HKUTO)</relation.ispartof>
<rights>The author retains all proprietary rights, (such as patent rights) and the right to use in future works.</rights>
<rights>Creative Commons: Attribution 3.0 Hong Kong License</rights>
<source.uri>http://hub.hku.hk/bib/B47753055</source.uri>
<subject.lcsh>Supergiant stars.</subject.lcsh>
<subject.lcsh>Stars - Clusters.</subject.lcsh>
<title>Maser and infrared properties of red supergiants embedded in the superstar cluster Westerlund 1</title>
<type>PG_Thesis</type>
<identifier.hkul>b4775305</identifier.hkul>
<description.thesisname>Master of Philosophy</description.thesisname>
<description.thesislevel>master&apos;s</description.thesislevel>
<description.thesisdiscipline>Physics</description.thesisdiscipline>
<description.nature>published_or_final_version</description.nature>
<date.hkucongregation>2012</date.hkucongregation>
<bitstream.url>http://hub.hku.hk/bitstream/10722/174485/1/FullText.pdf</bitstream.url>
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