Variability survey of massive stars in Milky Way star clusters
Date
2017-06-30
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Abstract
Massiivsete tähtede tekke- ja evolutsiooniteooriad on hetkel veel ebatäpsed, kuna mitmeid füüsikalisi protsesse massiivsete tähtede sees on vähe uuritud. Nende tähtede sisemusi on võimalik sondeerida asteroseismoloogiliste vaatluste kaudu, mõõtes tähe pinnal toimuvaid heledusmuutusi. Kuigi kosmosest on vaadeldud sadu päikesesarnaseid tähti, on massiivsete tähtede uurimine jäänud pidama väheste vaatlusandmete taha. Kuna asteroseismoloogilised vaatlused peavad olema tehtud tiheda ajasammuga pika perioodi jooksul, sobivad selleks paremini just maapealsed teleskoobid. Üldiselt jääb maa pealt mõõdetud heleduste täpsus asteroseismoloogia jaoks liiga väikeseks, kuid mõõtes suureamplituudilisi muutusi massiivsetes tähtedes, on võimalik täpsustada asteroseismoloogiliste parameetrite piire.
Uurides massiivseid tähti erinevate vanustega täheparvedes on võimalik vaadeldud tähtede muutlikkuse kaudu hinnata neis toimuvaid protsesse. Selleks viisime New Mexicos asuva kaugjuhitava teleskoobiga läbi 3-aastase vaatluskampaania Linnutee põhjataeva eri vanustega täheparvedes. Me leidsime oma vaatlusandmetest 354 muutlikku tähte ning kasutades nende perioodilisust ja spektraalset informatsiooni, klassifitseerisime neid muutlikkuse rühmadesse. 60% neist muutlikest tähtedest on potentsiaalsed uued avastused. Lisaks uurisime muutlike tähtede kuuluvust täheparvedess ning leidsime liikmemäära osakaalu ülempiiriks märgatavalt suurema väärtuse kui varasemates töödes.
Massiivse tähte evolutsioon sõltub tugevalt tema elu jooksul tähetuultena välja heidetud massist. Massikadu kaksiktähtedes on võimalik arvutada nende orbitaalse perioodi muutuse kaudu, mis viitab kas süsteemi kiirenemisele või aeglustumisele. Massikao detailsemaks uurimisteks valisime seitse massiivset kaksiktähte Luige tähtkujust. Bayesi analüüsi käigus kasutasime lisaks omaenda vaatlustele ka ajaloolisi vaatlusandmeid, et pikendada uuritavat ajabaasi. Kolme tähe jaoks leidsime esmakordselt perioodi muutuse. Kõikide tähtede jaoks modelleerisime nende stellaar- ja orbitaalparameetreid ning määrasime massikao väärtused.
The formation and evolution of massive stars is still an open question as many physical phenomena inside massive stars are poorly understood. The field of asteroseismology helps us explore these stellar interiors by observing the surface brightness variability of stars. Although, space missions have made asteroseismic observations of hundreds of solar-like stars, our knowledge of massive stars is relatively poor due to the small number of them observed from space. Ground-based observations can not achieve the precision for proper asteroseismic analysis but, for massive stars with suitably large brightness amplitudes, they can be used to expand on the known asteroseismic constraints. The availability of small-scale telescopes helps to study massive stars with good temporal coverage that is unachievable from space missions. In order to study massive stars in different evolutionary phases, we monitored 22 star clusters for three years and obtained light curves for over 3000 stars using a telescope in New Mexico, USA. We identified 354 variable stars of which 60% were first discoveries of variability. We used frequency analysis along with the pulsation HR diagram to classify our variable stars and determine multi-periodic stars. Analysing the probability density function of variable stars, we found the upper limit of cluster membership fraction to be higher than predicted from other works. Mass loss in massive stars determines the evolution of their temperature, luminosity, etc. Mass-loss rates in binary stellar systems can be measured from the change in their periods, indicating either a spin-up or slow-down of the system. To study mass-loss rates in eclipsing massive binaries, we used a Bayesian approach to determine the period change of seven selected binary systems. For this, we used archival data together with our own observations. For three stars, we reported the period change for the first time. In addition, we determined the origin and values of the mass-loss rates for all seven binaries as well as modelled their orbital and stellar parameters.
The formation and evolution of massive stars is still an open question as many physical phenomena inside massive stars are poorly understood. The field of asteroseismology helps us explore these stellar interiors by observing the surface brightness variability of stars. Although, space missions have made asteroseismic observations of hundreds of solar-like stars, our knowledge of massive stars is relatively poor due to the small number of them observed from space. Ground-based observations can not achieve the precision for proper asteroseismic analysis but, for massive stars with suitably large brightness amplitudes, they can be used to expand on the known asteroseismic constraints. The availability of small-scale telescopes helps to study massive stars with good temporal coverage that is unachievable from space missions. In order to study massive stars in different evolutionary phases, we monitored 22 star clusters for three years and obtained light curves for over 3000 stars using a telescope in New Mexico, USA. We identified 354 variable stars of which 60% were first discoveries of variability. We used frequency analysis along with the pulsation HR diagram to classify our variable stars and determine multi-periodic stars. Analysing the probability density function of variable stars, we found the upper limit of cluster membership fraction to be higher than predicted from other works. Mass loss in massive stars determines the evolution of their temperature, luminosity, etc. Mass-loss rates in binary stellar systems can be measured from the change in their periods, indicating either a spin-up or slow-down of the system. To study mass-loss rates in eclipsing massive binaries, we used a Bayesian approach to determine the period change of seven selected binary systems. For this, we used archival data together with our own observations. For three stars, we reported the period change for the first time. In addition, we determined the origin and values of the mass-loss rates for all seven binaries as well as modelled their orbital and stellar parameters.
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Keywords
Linnutee, täheparved, muutlikud tähed, Milky Way, variable stars