Circumstellar dust emission from nearby Solar-type stars
Doktorsavhandling, 2016

Far-infrared excess above the photosphere of a star indicates the presence of a circumstellar dust disc which is a sign-post for extrasolar planets, and was first detected in the mid 1980s. Dust discs are intricately connected to planets and planetesimals, give insights in the dynamics and evolution of the system, and are also useful for future exoplanet-observations. This thesis is aimed at modelling dust emission of nearby Solar-type stars, and is partly involved with the Herschel key programme DUNES (DUst around NEarby Stars). It includes detailed studies on a few nearby stars, and results from a coherent re-reduction of the combined datasets of the original DUNES catalogue and 55 DEBRIS-observed sources (Disc Emission via a Bias-free Reconnaissance in the Infrared/Sub-millimetre). Based on observations with Herschel and Spitzer of the nearby binary alpha Centauri (G2 V and K1 V), an upper limit on the fractional luminosity (dust-to-star) of circumstellar dust was determined to a few 10^-5 (Paper I). Both stars exhibit detectable temperature minima at wavelengths around 100-300um due to a chromospheric temperature inversion akin to that of the sun. The resulting flux difference, when compared to stellar photospheric models, is equivalent to dust emission with a fractional luminosity of <2*10^-7. The triple star 94 Ceti hosts known dust emission-features that are modelled in Paper II. The dust is constrained to a circumbinary disc around the companion stars, 94 Cet B and C (M dwarfs), which orbits the primary 94 Cet A (F8 V) on a 2000 yr orbit, with a fractional luminosity of 4.6+/-0.4*10^-6, and a disc radius of 40 AU. Tentative evidence for a circumtertiary disc is also found. The resolved emission at EP Eridani (K1 V) corresponds well with a face-on dust disc with the outer radius 110 AU, an inner hole of 5 to 10 AU, and fractional luminosity of $2.0+/-0.2*10^-5. The emission at Gliese 42 (K2 V) appears contaminated by background sources. Dust models with a flatter than normal grain size distribution fit the observations with a fractional luminosity of 8.7+/-1.0*10^-6. A wide range of far-infrared galaxy SEDs, with redshifts between 0.7 to 1.9, and IR luminosities of 0.4 to 8.3*10^12 Lsun, also fit these data. The DUNES catalogue, combined with 55 DEBRIS-observed sources, contains 188 nearby FGK stars (including resolved binaries). These data were previously reduced with older versions of the Herschel software and calibration, and have now been coherently re-reduced with more recent versions. There are 16 new marginal excess sources, and one new detected at delta Pavonis. We find a systematical 1sigma higher flux density for the 133 original DUNES sources, while the estimates for the additional 55 sources agree well with our results.

Stars: binaries - Stars: circumstellar matter - Infrared: stars - Infrared: planetary systems - Submillimeter: stars

HC1
Opponent: Pawel Artymowicz

Författare

Joachim Wiegert

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

94 Ceti: a triple star with a planet and dust disc

Monthly Notices of the Royal Astronomical Society,; Vol. 462(2016)p. 1735-1748

Artikel i vetenskaplig tidskrift

How dusty is alpha Centauri? Excess or non-excess over the infrared photospheres of main-sequence stars

Astronomy and Astrophysics,; Vol. 563(2014)p. A102-

Artikel i vetenskaplig tidskrift

I solsystemet finns asteroidbältet mellan Mars och Jupiter, samt Edgeworth-Kuiperbältet utanför Neptunus, som också Pluto tillhör. Dessa bälten består av planetesimaler, oregelbundna himlakroppar som vardagligt kallas för asteroider. Kollisioner inom bältena ger upphov till två stycken stoftskivor runt solen, ett inre som kallas för zodiakalmolnet, och ett yttre som sträcker sig mer än dubbelt så långt från solen än Neptunus. Andra stjärnor har också stoftskivor. Eftersom skivorna är så stora kan man ibland observera dem direkt. Men i många fall måste man leta efter deras infraröda signatur. Stoftet i skivorna är bra på att absorbera ljus ifrån sin stjärna, vilket det sen sänder ut igen i form av infrarött ljus, värmestrålning. Värmestrålningens temperatur beror på storleken på stoftskivan och kan berätta om ifall det finns gap i skivan som jätteplaneter kan ha gröpt ur. För skivor som liknar solsystemets Kuiperbälte innebär det att stoftet lyser med våglängder som Herschel Space Observatory var byggt för att observera. Denna avhandling sammanfattar studier av fyra stycken närbelägna, solliknande stjärnor. Jag har också gjort om datanalysen av de 188 stycken stjärnor som ingår i det internationella projektet DUNES. Studier av stoftskivor som dessa ger ledtrådar om stjärnornas planetsystems historia och utveckling. Dessutom ger de värdefull information som behövs i framtida projekt där man ämnar att direkt avbilda närbelägna, extrasolära planeter.

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

Infrastruktur

Onsala rymdobservatorium

ISBN

978-91-7597-443-9

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4124, ISSN 0346-718X

HC1

Opponent: Pawel Artymowicz

Mer information

Skapat

2017-10-08