Karina Kjaer

Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, United States

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Publications (12)23.63 Total impact

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    ABSTRACT: We present a study of the morphology of the ejecta in Supernova 1987A based on images and spectra from the HST as well as integral field spectroscopy from VLT/SINFONI. The HST observations were obtained between 1994 - 2011 and primarily probe the outer hydrogen-rich zones of the ejecta. The SINFONI observations were obtained in 2005 and 2011 and instead probe the [Si I]/[Fe II] emission from the inner regions. We find a strong temporal evolution of the morphology in the HST images, from a roughly elliptical shape before ~5,000 days, to a more irregular, edge-brightened morphology thereafter. This transition is a natural consequence of the change in the dominant energy source powering the ejecta, from radioactive decay before ~5,000 days to X-ray input from the circumstellar interaction thereafter. The [Si I]/[Fe II] images display a more uniform morphology, which may be due to a remaining significant contribution from radioactivity in the inner ejecta and the higher abundance of these elements in the core. Both the H-alpha and the [Si I]/[Fe II] line profiles show that the ejecta are distributed fairly close to the plane of the inner circumstellar ring, which is assumed to define the rotational axis of the progenitor. The H-alpha emission extends to higher velocities than [Si I]/[Fe II] as expected. There is no clear symmetry axis for all the emission and we are unable to model the ejecta distribution with a simple ellipsoid model with a uniform distribution of dust. Instead, we find that the emission is concentrated to clumps and that the emission is distributed somewhat closer to the ring in the north than in the south. This north-south asymmetry may be partially explained by dust absorption. We compare our results with explosion models and find some qualitative agreement, but note that the observations show a higher degree of large-scale asymmetry.
    The Astrophysical Journal 12/2012; 768(1). · 6.73 Impact Factor
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    ABSTRACT: We present observations with VLT and HST of the broad emission lines from the inner ejecta and reverse shock of SN 1987A from 1999 until 2012 (days 4381 -- 9100 after explosion). We detect broad lines from H-alpha, H-beta, Mg I], Na I, [O I], [Ca II] and a feature at 9220 A. We identify the latter line with Mg II 9218, 9244,most likely pumped by Ly-alpha fluorescence. H-alpha, and H-beta both have a centrally peaked component, extending to 4500 km/s and a very broad component extending to 11,000 km/s, while the other lines have only the central component. The low velocity component comes from unshocked ejecta, heated mainly by X-rays from the circumstellar ring collision, whereas the broad component comes from faster ejecta passing through the reverse shock. The reverse shock flux in H-alpha has increased by a factor of 4-6 from 2000 to 2007. After that there is a tendency of flattening of the light curve, similar to what may be seen in soft X-rays and in the optical lines from the shocked ring. The core component seen in H-alpha, [Ca II] and Mg II has experienced a similar increase, consistent with that found from HST photometry. The ring-like morphology of the ejecta is explained as a result of the X-ray illumination, depositing energy outside of the core of the ejecta. The energy deposition in the ejecta of the external X-rays illumination is calculated using explosion models for SN 1987A and we predict that the outer parts of the unshocked ejecta will continue to brighten because of this. We finally discuss evidence for dust in the ejecta from line asymmetries.
    The Astrophysical Journal 12/2012; 768(1). · 6.73 Impact Factor
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    ABSTRACT: Twenty years after the explosion of SN 1987A, we are now able to observe the three-dimensional spatially resolved inner ejecta. Detailed mapping of newly synthesised material and its radioactive decay daughter products sheds light on the explosion mechanism. This may reveal the geometry of the explosion and its connection to the equatorial ring and the outer rings around SN 1987A. We have used integral field spectroscopy to image the supernova ejecta and the equatorial ring in the emission lines of [Si I]+[Fe II] and He I. The spectral information can be mapped into a radial velocity image revealing the expansion of the ejecta both as projected onto the sky and perpendicular to the sky plane. The inner ejecta are spatially resolved in a North-South direction and are clearly asymmetric. We argue that the bulk of the ejecta is situated in the same plane as defined by the equatorial ring and does not form a bipolar structure as has been suggested. The exact shape of the ejecta is modelled and we find that an elongated triaxial ellipsoid fits the observations best. From our spectral analyses of the ejecta spectrum we find that most of the He I, [Si I] and [Fe I-II] emission originates in the core material which has undergone explosive nucleosynthesis. The He I emission may be the result of alpha-rich freeze-out if the positron energy is deposited locally. Our observations clearly indicate a non-symmetric explosion mechanism for SN 1987A. The elongation and velocity asymmetries point towards a large-scale spatial non-spherical distribution as predicted in recent explosion models. The orientation of the ejecta in the plane of the equatorial ring argues against a jet-induced explosion through the poles due to stellar rotation. Comment: Above abstract is abridged. 11 pages, 9 figures. Accepted July 1st 2010 by Astronomy and Astrophysics
    Astronomy and Astrophysics 03/2010; · 5.08 Impact Factor
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    ABSTRACT: We discuss high resolution VLT/UVES observations (FWHM ~ 6 km s$^{-1}$) from October 2002 (day ~5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A large number of narrow emission lines from the unshocked ring, with ion stages from neutral up to Ne V and Fe VII, have been identified. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (~1.5-5.0)$\times$10$^3$ cm$^{-3}$ and temperatures of ~6.5$\times$10$^3$-2.4$\times$10$^4$ K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4$\times$10$^6$-10$^7$ cm$^{-3}$. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [ Fe X-XIV] , with the latter extending up to ~-390 km s$^{-1}$ in the blue wing for [Fe XIV], while the low ionization lines extend to typically ~-260 km s$^{-1}$. For H$\alpha$ a faint extension up to ~-450 km s$^{-1}$ can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ~510 km s$^{-1}$. We expect the maximum width of especially the low ionization lines to increase with time.
    http://dx.doi.org/10.1051/0004-6361:20077604. 01/2008;
  • K. Kjær, B. Leibundgut
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    ABSTRACT: SN 1987A is located in the Large Magellanic Cloud and thus close enough to study the very late time evolution of a supernova and its transition to a supernova remnant. After almost two decades the supernova ejecta have now reached the pre-explosion circumstellar ring and started to interact with it. The system presents a complex structure involving forward and reflected shocks with highly diferent physical conditions in close spatial proximity. The supernova ring system is currently observed in X-rays (Park et al. 2004,2005), optical (Graves et al. 1996, Michael et al. 2003), mid-infrared (Bouchet et al. 2004) and radio (Manchester et al. 2005). The near-infrared data presented here complement all this. Based on science verification observations with SINFONI we present the supernovaring interaction as it appears in the near-infrared. SINFONI’s adaptive optics supported integral field spectrograph spatially resolves the ring and the data thus provide new information and details for this unique object.
    12/2007: pages 333-337;
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    ABSTRACT: SN 1987A in the Large Magellanic Cloud is close enough for a study of the very late time evolution of a supernova and its transition to a supernova remnant. Nearly two decades after explosion we are witnessing the supernova shock wave engaging the inner circumstellar ring, which had been fluorescing since being ionised by the soft X‐ray flash from shock breakout. We present in the following observations of the SN‐ring interaction obtained in November 2004 with SINFONI on the VLT. SINFONI's adaptive optics supported integral field spectrograph spatially resolves the equatorial ring and we obtain a better spatial understanding of the spectrum in difi"erent emission regions. With a dynamical map of the shock interaction around the ring we determine parameters for its geometry. Since most of the IR emission lines originate behind the shock front, we obtain an indication of the expansion velocity of the shocked material. The ring geometry is consistent with a circle and we also derive a new, independent measurement of the systemic ring, and presumably also supernova, velocity.
    AIP Conference Proceedings. 10/2007; 937(1):76-80.
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    ABSTRACT: We discuss high resolution VLT/UVES observations (FWHM ~ 6 km/s) from October 2002 (day ~5700 past explosion) of the shock interaction of SN 1987A and its circumstellar ring. A nebular analysis of the narrow lines from the unshocked gas indicates gas densities of (1.5-5.0)E3 cm-3 and temperatures of 6.5E3-2.4E4 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to [Fe XIV]. From a nebular analysis we find that the density in the low ionization region is 4E6-1E7 cm-3. There is a clear difference in the high velocity extension of the low ionization lines and that of lines from [Fe X-XIV], with the latter extending up to ~ -390 km/s in the blue wing for [Fe XIV], while the low ionization lines extend to typically ~ -260 km/s. For H-alpha a faint extension up to ~ -450 km/s can be seen probably arising from a small fraction of shocked high density clumps. We discuss these observations in the context of radiative shock models, which are qualitatively consistent with the observations. A fraction of the high ionization lines may originate in gas which has yet not had time to cool down, explaining the difference in width between the low and high ionization lines. The maximum shock velocities seen in the optical lines are ~ 510 km/s. We expect the maximum width of especially the low ionization lines to increase with time.
    04/2007;
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    ABSTRACT: SN 1987A in the Large Magellanic Cloud is close enough for a study of the very late time evolution of a supernova and its transition to a supernova remnant. Nearly two decades after explosion we are witnessing the supernova shock wave engaging the inner circumstellar ring, which had been fluorescing since being ionised by the soft X-ray flash from shock breakout. We follow the interaction of the supernova shock with the ring material. The spatially resolved information provides us with insight into the individual shock regions around the ring. Near-infrared integral field spectroscopy observations with SINFONI/VLT of the SN-ring interaction is presented. SINFONI's adaptive optics supported integral field spectrograph spatially resolves the ring and the data thus we obtain a better spatial understanding of the spectrum in different regions of the object. With a dynamical map of the interacting ring we determine parameters for its geometry. Since most of the IR emission lines originate behind the shock front we obtain an indication of the radial velocity of the shocked material after deconvolving the geometry. The ring geometry is consistent with a circle and we also derive a new, independent measurement of the systemic ring, and presumably also supernova, velocity. We find from the spatial distributions of the flux in the different emission lines the degree of cooling in the shocked material and follows the increases observed in the radio and X-rays. Emission from the ejecta is detected only in the strongest [Fe II] lines.
    Astronomy and Astrophysics 04/2007; · 5.08 Impact Factor
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    ABSTRACT: The unique supernova SN 1987A has been a bonanza for astrophysicists. It provided several observational 'firsts', like the detection of neutrinos from the core collapse, the observation of the progenitor star on archival photographic plates, the signatures of a non-spherical explosion and mixing in the ejecta, the direct observation of supernova nucleosynthesis, including accurate masses of 56Ni, 57Ni and 44Ti, observation of the formation of dust in the supernova, as well as the detection of circumstellar and interstellar material. Now, after 20 years, it continues to be an extremely exciting object as we will be able to observe the supernova shock interacting with the circumstellar ring in real time.
    The Messenger. 03/2007;
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    ABSTRACT: After nearly two decades at least five emission mechanisms can be found in SN 1987A. The ejecta continue to glow as a result of the radioactive decay of long-lived nuclei (mostly 44Ti), but is fading continuously because of the expansion and the reduced opacity. The nearly stationary rings around SN 1987A are still fluorescing from the recombination of matter originally excited by the soft X-ray emission from the shock breakout at explosion. The supernova shock reached the inner circumstellar ring about ten years ago and the forward shock is moving through the inner ring and leaves shocked material behind. This material is excited and accelerated. The reverse shock illuminates the fast-moving supernova ejecta as it catches up. And, finally light echoes in nearby interstellar matter can still be observed. We present here high resolution spectroscopy in the optical and integral-field spectroscopy in the near infrared of SN 1987A and its rings.
    01/2007;
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    ABSTRACT: Since the beginning of 2005 another success story has gone into regular operation at the ESO facilities on Paranal. On UT4 (Yepun) an adaptive optics assisted near infrared integral field spectrometer makes an astronomer's dream come true: obtaining a diffraction-limited image of which each pixel contains a full spectrum. In fact, such data are best thought of as a cube rather than a flat image. SINFONI is the name of the new instrument and a whole symphony of exciting science results has been obtained already.
    The Messenger. 05/2005; 120:26-32.
  • The ESO Messenger, v.120, 26-32 (2005).

Publication Stats

22 Citations
23.63 Total Impact Points

Institutions

  • 2012
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2010
    • Queen's University Belfast
      • Astrophysics Research Centre (ARC)
      Béal Feirste, N Ireland, United Kingdom
  • 2007
    • European Southern Observatory
      Arching, Bavaria, Germany