THESIS FOR THE DEGREE OF DOCTORATE OF PHILOSOPHY Circumstellar dust emission from nearby Solar-type stars JOACHIM WIEGERT Department of Earth and Space Sciences CHALMERS UNIVERSITY OF TECHNOLOGY Goteborg,¨ Sweden 2016 Circumstellar dust emission from nearby Solar-type stars JOACHIM WIEGERT ISBN 978-91-7597-443-9 c Joachim Wiegert, 2016 Doktorsavhandlingar vid Chalmers tekniska hogskola¨ Ny serie nr 4124 ISSN 0346-718X Radio Astronomy & Astrophysics Group Department of Earth and Space Sciences Chalmers University of Technology SE–412 96 Goteborg,¨ Sweden Phone: +46 (0)31–772 1000 Contact information: Joachim Wiegert Onsala Space Observatory Chalmers University of Technology SE–439 92 Onsala, Sweden Phone: +46 (0)31–772 5542 E-mail:[email protected] Cover image: Composite images showing the Herschel Space Observatory (right) and the Atacama Pathfinder EX- periment (bottom left) together with particle simulation results of circumstellar discs around α Centauri, and Herschel/PACS observations of α Centauri and 94 Ceti at 100 µm. Image credits: ESA/AOES Medialab, and DUNES: DUst around NEarby Stars. Printed by Chalmers Reproservice Chalmers University of Technology Goteborg,¨ Sweden 2016 Circumstellar dust emission from nearby Solar-type stars JOACHIM WIEGERT Department of Earth and Space Sciences Chalmers University of Technology Abstract 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 DUst around NEarby Stars (DUNES). 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 α 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 100-300 µm 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 lumi- nosity 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 year 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 12 0.4 to 8:3 10 L , 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 Her- schel 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 δ Pavonis. We find a systematical 1σ higher flux density for the 133 original DUNES sources, while the estimates for the additional 55 sources agree well with our results. Keywords: Stars: binaries - Stars: circumstellar matter - Infrared: stars - Infrared: planetary systems - Submillimeter: stars i ii Research contributions This thesis is based on the work contained in the following papers. I J. Wiegert, R. Liseau, P. Thebault,´ G. Olofsson, A. Mora, G. Bryden, J. P. Marshall, C. Eiroa, B. Montesinos, D. Ardila, J. C. Augereau, A. Bayo Aran, W. C. Danchi, C. del Burgo, S. Ertel, M. C. W. Fridlund, M. Hajigholi, A. V. Krivov, G. L. Pilbratt, A. Roberge, G. J. White, and S. Wolf: How dusty is α Centauri? Excess or non-excess over the infrared photospheres of main-sequence stars Astronomy & Astrophysics, 563, A102 (2014) DOI: 10.1051/0004-6361/201321887 II J. Wiegert, V. Faramaz, F. Cruz-Saenz de Miera: 94 Ceti: a triple star with a planet and dust disc Monthly Notices of the Royal Astronomical Society, 462 (2), 1735-1748 (2016) DOI: 10.1093/mnras/stw1682 III J. Wiegert: Nearby debris discs: a second look at DUNES’ observations of nearby Solar-like stars In preparation for publication in Astronomy & Astrophysics I have also contributed to the following publications (not appended). i Alessandro B. Romeo and Joachim Wiegert: −1 −1 −1 The effective stability parameter for two-component galactic discs: is Q Qstars + Qgas? Monthly Notices of the Royal Astronomical Society, 416, 1191-1196 (2011)/ DOI: 10.1111/j.1365-2966.2011.19120.x ii R. Liseau, B. Montesinos, G. Olofsson, G. Bryden, J. P. Marshall, D. Ardila, A. Bayo Aran, W. C. Danchi, C. del Burgo, C. Eiroa, S. Ertel, M. C. W. Fridlund, A. V. Krivov, G. L. Pilbratt, A. Roberge, P. Thebault,´ J. Wiegert, and G. J. White: α Centauri A in the far infrared. First measurement of the temperature minimum of a star other than the Sun Astronomy & Astrophysics, 549, L7 (2013) DOI: 10.1051/0004-6361/201220776 iii F. Taddia, J. Sollerman, E. Gafton, G. Micheva, E. Freeland, A. Macchiavello, T. Mansson, J. Wiegert: NOT spectroscopic classifications of optical transients The Astronomer’s Telegram, 5087 (2013) iii iv R. Amanullah, J. Johansson, A. Goobar, R. Ferretti, S. Papadogiannakis, T. Petrushevska, P. J. Brown, Y. Cao, C. Contreras, H. Dahle, N. Elias-Rosa, J. P. U. Fynbo, J. Gorosabel, L. Guaita, L. Hangard, D. A. Howell, E. Y. Hsiao, E. Kankare, M. Kasliwal, G. Leloudas, P. Lundqvist, S. Mattila, P. Nugent, M. M. Phillips, A. Sandberg, V. Stanishev, M. Sullivan, F. Taddia, G. Ostlin,¨ S. Asadi, R. Herrero-Illana, J. J. Jensen, K. Karhunen, S. Lazarevic, E. Varenius, P. Santos, S. Seethapuram Sridhar, S. H. J. Wallstrom,¨ and J. Wiegert: Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 µm Monthly Notices of the Royal Astronomical Society, 453, 3300-3328 (2015) DOI: 10.1093/mnras/stv1505 iv Acknowledgements Astronomy is one of the most ancient natural sciences, with roots all the way back to those who, with their eyes only, were able to map the stars and the movement of the planets in Mesopotamia, some 4000 years ago. It has been a humbling experience to carry on this tradition. I have spent the last years trying to contribute with a small piece of a puzzle to help the humanity to understand its place in the Universe. There are many people I would like to thank for being around during this time. But first I must of course thank my supervisor, Rene´ Liseau, who introduced me to this specific field in astronomy and to the fantastic people in the DUNES collaboration. My co-supervisors have also always been available, Magnus Thomasson and John Black. I have also appreciated the help from Tuomas Lunttila, Kalle Torstensson, Alessandro Romeo, and Wouter Vlemmings. I would like to thank the whole DUNES team for amazing workshops and a healthy cooperation. I want to especially mention Carlos Eiroa, Philippe Thebault,´ Virginie Faramaz, Fernando Cruz-Saenz de Miera (thanks for showing me around Madrid), Jonathan “Jonty” Marshall, Alexander “Sasha” Krivov, and Grant Kennedy. The fantastic people at the department of Earth and Space Sciences at Chalmers, and at the Onsala Space Observatory deserves to be mentioned also. In the administrative and technical staff, thanks to Camilla, Glenn, Katarina K., Katarina N., Maria, Paula, Paulina, Per B., Roger, Simon, and Sofie! Those taking care of us PhD-students, Donal Murtagh and Susanne Aalto. And I’m name-dropping here because I think all of these are worth mentioning; the fantastic postdocs, (former) PhD-students et al., Boy, Daniel, Daria, Elvire, Eskil, Eva, Fabien, Francesco, Grzegorz, JB, Joakim, Johan, Judit, Lukas, Maryam, Matthias, Mitra, Niko, Niklas, Ole Martin, Per Bj., Robert, Robin, Sabine, Sofia, Suzy, and Ta¨ıssa. And a big thanks for the staff at APEX, working there has always been a pleasure, even during the long night shifts. Finally I want to thank friends and family. Those living in the Hilbert room, at Goteborg¨ Univer- sity, which it seems I can’t stop visiting. My parents, Lars and Monica who has always been very supportive and also helped me to proofread this thesis. My sister Theresa who is an inspiration and has done a marvellous detailed job with proofreading this thesis. My brothers, Benjamin, and Daniel plus his wife Jennifer (thanks for letting me and Theresa toast your wedding), who are fun as always, and of course our dachshund Cassie. I want to thank my lovely girlfriend, Beata, who is always there and supportive. I thank her family also, who have accepted me into their company. I’m so thankful that you want to be with me, Beata, even though I sometimes travel halfway across the world to steer a telescope or to sit at lectures.