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The outer rings of SN 1987A
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
Stockholm University, Faculty of Science, Department of Astronomy.
2010 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 527, no 14, 35-49 p.Article in journal (Refereed) Published
Abstract [en]

Aims: We investigate the physical properties and structure of the outer rings of SN 1987A to understand their formation and evolution. Methods: We used low resolution spectroscopy from VLT/FORS1 and high resolution spectra from VLT/UVES to estimate the physical conditions in the outer rings, using nebular analysis for emission lines such as [O II], [O III], [N II], and [S II]. We also measured the velocity at two positions of the outer rings to test a geometrical model for the rings. Additionally, we used data from the HST science archives to check the evolution of the outer rings of SN 1987A for a period that covers almost 11 years. Results: We measured the flux in four different regions, two for each outer ring. We chose regions away from the two bright neighbouring stars and as far as possible from the inner ring and created light curves for the emission lines of [O III], Hα, and [N II]. The light curves display a declining behaviour, which is consistent with the initial supernova-flash powering of the outer rings. The electron density of the emitting gas in the outer rings, as estimated by nebular analysis from the [O II] and [S II] lines, is ≲ 3 × 103 cm-3, has not changed over the last ~15 years, and the [N II] temperature remains also fairly constant at ~1.2 × 104 K. We find no obvious difference in density and temperature for the two outer rings. The highest density, as estimated from the decay of Hα, could be ~5 × 103 cm-3 however, and because the decay is somewhat faster in the southern outer ring than it is in the northern, the highest density in the outer rings may be found in the southern outer ring. For an assumed distance of 50 kpc to the supernova, the distance between the supernova and the closest parts of the outer rings could be as short as ~1.7 × 1018cm. Interaction between the supernova ejecta and the outer rings could therefore start in less than ~20 years. We do not expect the outer rings to show the same optical display as the equatorial ring when this happens. Instead soft X-rays should provide a better way of observing the ejecta - outer rings interaction.

Place, publisher, year, edition, pages
2010. Vol. 527, no 14, 35-49 p.
Keyword [en]
line: profiles, ISM: supernova remnants, ISM: individual objects: SN 1987A
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:su:diva-58325DOI: 10.1051/0004-6361/201015576OAI: oai:DiVA.org:su-58325DiVA: diva2:420157
Available from: 2011-05-31 Created: 2011-05-31 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Observations of young core collapse supernova remnants
Open this publication in new window or tab >>Observations of young core collapse supernova remnants
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Studies of young remnants offer an opportunity to test theoretical models of stellar evolution, explosion models and nucleosynthesis, as well as our understanding of the compact objects in the centre of the exploded stars.

The first part of the thesis involves observations of the Crab nebula. We have used photometric and spectroscopic observations to search for a faint halo around the visible nebula, that could carry the missing mass and kinetic energy of the nebula. No halo was found. In the photometric data due to psf contamination, and in the spectroscopic no fast velocity components were present. We have also used optical and IR photometry to check for variation in the emissivity and dynamic structure of the Crab pulsar wind nebula (PWN), to try to understand the nature of plerionic PWNe. There, we measured flux variations up to 20% in the IR and also shifting of the wisps with velocities up to 0.2c. We also showed that the nearby red knot moves in tandem with the Crab pulsar.

The second part of the thesis, deals with photometric &  spectroscopic observations of SN 1987A in the LMC. The aim of the project was to monitor the evolution of the outer rings (ORs) of SN 1987A. The fading of the ORs is consistent with recombination and cooling after the initial flash ionization by the supernova. From the spectroscopic data we measured the density and temperature in the ORs where we found temperatures of ~ 12,000 K for the [N II] gas, and ~ 25,000 K for the [O III]. Finally, from the [O II], and [S II] ratios we estimated electron densities of ~ 1,000 cm-3 and ~ 2,500 cm-3, respectively. From the evolution of Hα, we argue that the highest density in the ORs could be 5,000 cm-3.

Place, publisher, year, edition, pages
Stockholm: Department of Astronomy, Stockholm University, 2011. 63 p.
Keyword
supernova remnants, Crab, SN 1987A
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:su:diva-58319 (URN)978-91-7447-319-3 (ISBN)
Public defence
2011-10-05, FA32, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Submitted.

Available from: 2011-09-13 Created: 2011-05-31 Last updated: 2015-07-29Bibliographically approved

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