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- PostCircumstellar Envelopes of Stars on the Asymptotic Giant Branch:The determination of gas mass-loss rates, identification of molecules and detection of dust(2019) Alm, Marcus; Angerd, Gabriel; Lundberg, Tomas; Wölfinger, Alexander; Oleszko, Sebastian; Chalmers tekniska högskola / Institutionen för fysik (GU); Chalmers University of Technology / Department of Physics (GU)Using data observed in Band 6 (211-275 GHz) and Band 7 (275-373 GHz) with the interferometer ACA (part of ALMA) from the DEATHSTAR project [1] we have analysed the CSEs of 5 AGB stars; three carbon-rich (Y Hya, U Hya and R For) and two oxygen-rich (R Hya and R Crt). The analysis was comprised of three main areas: determining the gas mass-loss rates, ˙M , identifying molecules and investigating the presence of dust, where the analysis of M was the most extensive. Using the CO lines J = 2 ! 1 and J = 3 ! 2 we determined ˙M with an equation from Ramstedt et al. 2008 [2] based on CO radiative transfer, as well as the expansion velocities of the CSEs. All calculated values of ˙M , ranging 2.2-22 · 10−7 M yr−1 (+79%/ − 66%), were within the equations stated error margin of a factor of three[2] and consistently higher, compared to values in the literature obtained with CO radiative transfer modelling[3, 4]. Due to the equation used for ˙M being based on single-dish telescopes, conversions for our data had to be made. Therefore, a systematic error in the conversion could account for the higher values. Furthermore, the expansion velocities were significantly higher than those in the literature[4] for all stars except Y Hya. However, the data used by us had a higher signal to noise ratio and overall lower uncertainty in comparison[5], indicating that our values may be more accurate. All molecules identified from the frequency spectra in Band 6 (215.4 - 217.4, 217.3-219.3, 230.2-231.2, 231.1-233.1 GHz) and Band 7 (330.3-331.3, 331.3-333.3, 342.5-344.5, 345.1-346.1 GHz), 15 in total with 11 in the carbon stars and 10 in the oxygen stars, were common for the respective spectral type except the recently (2016) discovered AlO [6], which was identified in R Crt. The spectral index, , was calculated from the flux in continuum emission in Band 6 (224.3-241.9 GHz) and band 7 (338.2-354.0 GHz). The temperature was calculated for the stars with 2 (Y Hya and R Crt) and agreed with the temperatures in the literature [3, 4]. For the stars with 6= 2 (U Hya, R For and R Hya) the dust mass, MD, and the dust mass-loss rate, ˙MD, was calculated with an assumed dust temperature of Tdust =100 K if the measured flux was 10% higher than expected (R For and R Hya), giving the uncertain values (due to Tdust having an exponential relation) MD = 10−5M for both stars and ˙MD = 10−8M yr−1 and ˙MD = 10−7M yr−1 for R For and R Hya respectively.
- PostSimulering av Oorts moln och nära planeter(2014) Strömbeck, Frida; Bore, Alexander; Rizk, Charbel; Ekdahl, Calle; Chalmers tekniska högskola / Institutionen för teknisk fysik; Chalmers University of Technology / Department of Applied PhysicsAbstract To examine the influence of different surroundings on cometary orbits we used computer simulations. They showed that there are at least two different sources for the comets that make up the Oort cloud. They also showed that the galactic tide and star passages can send comets of the Oort cloud into the solar system. Comets inside the solar system were also simulated, to determine whether or not Jupiter could catch them, and also to examine which way to preferably avert a comet on a collision course towards Earth.