The Line Emission from the Circumstellar Gas around SN 1987A (original) (raw)
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Time evolution of the line emission from the inner circumstellar ring of SN 1987A and its hot spots
Astronomy and Astrophysics, 2008
high resolution VLT/UVES echelle spectra of the ejecta-ring collision of SN 1987A. The fluxes of most of the narrow lines from the unshocked gas decreased by a factor of 2 − 3 during this period, consistent with the decay from the initial ionization by the shock break-out. However, [O III] in particular shows an increase up to day ∼ 6800. This agrees with radiative shock models where the pre-shocked gas is heated by the soft X-rays from the shock. The evolution of the [O III] line ratio shows a decreasing temperature of the unshocked ring gas, consistent with a transition from a hot, low density component which was heated by the initial flash ionization to the lower temperature in the pre-ionized gas ahead of the shocks. The line emission from the shocked gas increases rapidly as the shock sweeps up more gas. We find that the neutral and high ionization lines follow the evolution of the Balmer lines roughly, while the intermediate ionization lines evolve less rapidly. Up to day ∼ 6800, the optical light curves have a similar evolution to that of the soft Xrays. The break between day 6500 and day 7000 for [O III] and [Ne III] is likely due to recombination to lower ionization levels. Nevertheless, the evolution of the [Fe XIV] line, as well as the lines from the lowest ionization stages, continue to follow that of the soft X-rays, as expected. There is a clear difference in the line profiles between the low and intermediate ionization lines, and those from the coronal lines at the earlier epochs. This shows that these lines arise from regions with different physical conditions, with at least a fraction of the coronal lines coming from adiabatic shocks. At later epochs the line widths of the low ionization lines, however, increase and approach those of the high ionization lines of [Fe X-XIV]. The Hα line profile can be traced up to ∼ 500 km s −1 at the latest epoch. This is consistent with the cooling time of shocks propagating into a density of (1 − 4) × 10 4 cm −3. This means that these shocks are among the highest velocity radiative shocks observed.
Abundances and Density Structure of the Inner Circumstellar Ring Around SN 1987A
The Astrophysical Journal, 2010
We present optical spectroscopic data of the inner circumstellar ring around SN 1987A from the Anglo-Australian Telescope (AAT) and the Very Large Telescope (VLT) between ∼1400 and ∼5000 days post-explosion. We also assembled the available optical and near-infrared line fluxes from the literature between ∼300 and ∼2000 days. These line light curves were fitted with a photoionization model to determine the density structure and the elemental abundances for the inner ring. We found densities ranging from 1×10 3 to 3×10 4 atoms cm −3 and a total mass of the ionized gas of ∼5.8 × 10 −2 M ⊙ within the inner ring. Abundances inferred from the optical and near-infrared data were also complemented with estimates of Lundqvist & Fransson (1996) based on ultraviolet lines. This way we found an He/H-ratio (by number of atoms) of 0.17 ± 0.06 which is roughly 30% lower than previously estimated and twice the solar and the Large Magellanic Cloud (LMC) value. We found an N/O-ratio of 1.5 ± 0.7, and the total (C+N+O)/(H+He) abundance about 1.6 times its LMC value or roughly 0.6 times the most recent solar value. An iron abundance of 0.20 ± 0.11 times solar was found which is within the range of the estimates for the LMC. We also present late time (∼5000-7500 days) line light curves of [O III], [Ne III], [Ne IV], [Ar III], [Ar IV], and [Fe VII] from observations with the VLT. We compared these with model fluxes and found that an additional 10 2 atoms cm −3 component was required to explain the data of the highest ionization lines. Such low density gas is expected in the H II-region interior to the inner ring which likely extends also to larger radii at higher latitudes (out of the ring plane). At epochs later than ∼5000 days our models underproduce the emission of most of these lines as expected due to the contribution from the interaction of the supernova ejecta with the ring.
2007
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.
The Astrophysical Journal, 2002
We report and interpret Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) long-slit observations of the optical and ultraviolet (1150-10270 Å) emission line spectra of the rapidly brightening spot 1 on the equatorial ring of SN 1987A between 1997 September and 1999 October (days 3869-4606 after outburst). The emission is caused by radiative shocks created where the supernova blast wave strikes dense gas protruding inward from the equatorial ring. We measure and tabulate line identifications, fluxes, and, in some cases, line widths and shifts. We compute flux correction factors to account for substantial interstellar line absorption of several emission lines. Nebular analysis shows that optical emission lines come from a region of cool (T e % 10 4 K) and dense (n e % 10 6 cm À3) gas in the compressed photoionized layer behind the radiative shock. The observed line widths indicate that only shocks with shock velocities V s < 250 km s À1 have become radiative, while line ratios indicate that much of the emission must have come from yet slower (V s d135 km s À1) shocks. Such slow shocks can be present only if the protrusion has atomic density ne3 Â 10 4 cm À3 , somewhat higher than that of the circumstellar ring. We are able to fit the UV fluxes with an idealized radiative shock model consisting of two shocks (V s ¼ 135 and 250 km s À1). The observed UV flux increase with time can be explained by the increase in shock surface areas as the blast wave overtakes more of the protrusion. The observed flux ratios of optical to highly ionized UV lines are greater by a factor of $2-3 than predictions from the radiative shock models, and we discuss the possible causes. We also present models for the observed H line widths and profiles, which suggest that a chaotic flow exists in the photoionized regions of these shocks. We discuss what can be learned with future observations of all the spots present on the equatorial ring.
Physical Conditions in Circumstellar Gas surrounding SN 1987A 12 Years After Outburst
Astrophysical Journal, 2000
Two-dimensional spectra of Supernova 1987A were obtained on 1998 November 14-15 (4282 days after outburst) with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). The slit sampled portions of the inner circumstellar ring at the east and west ansae as well as small sections of both the northern and southern outer rings. The temperature and density at these locations are estimated by nebular analysis of [N II], [O III], and [S II] emission line ratios, and with time-dependent photoionization/recombination models. The results from these two methods are mutually consistent. The electron density in the inner ring is ~ 4000 cm-3 for S II, with progressively lower densities for N II and O III. The electron temperatures determined from [N II] and [O III] line ratios are ~11,000 K and \~22,000 K, respectively. These results are consistent with evolutionary trends in the circumstellar gas from similar measurements at earlier epochs. We find that emission lines from the outer rings come from gas of lower density (n_e \la 2000 cm-3) than that which emits the same line in the inner ring. The N/O ratio appears to be the same in all three rings. Our results also suggest that the CNO abundances in the northern outer ring are the same as in the inner ring, contrary to earlier results of Panagia et al. (1996). Physical conditions in the southern outer ring are less certain because of poorer signal-to-noise data. The STIS spectra also reveal a weak Ha emission redshifted by ~100 km s-1 at p.a. 103\arcdeg that coincides with the recently discovered new regions that are brightening (Lawrence et al. 2000). This indicates that the shock interaction in the SE section of the inner ring commenced over a year before it became apparent in HST images.
The evolution of ultraviolet emission lines from circumstellar material surrounding SN 1987A
2009
The presence of narrow high-temperature emission lines from nitrogen-rich gas close to SN 1987A has been a principal observational constraint on the evolutionary status of the supernova's progenitor. A new analysis of the complete five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A (1987.2-1992.3) provide fluxes for the N V λ1240, N IV] λ1486, He II λ1640, O III] λ1665, N III] λ1751, and C III] λ1908 lines with significantly reduced random and systematic errors and reveals significant short-term fluctuations in the light curves. The N V , N IV] , and N III] lines turn on sequentially over 15 to 20 days and show a progression from high to low ionization potential, implying an ionization gradient in the emitting region. The line emission turns on suddenly at 83 ± 4 days after the explosion, as defined by N IV]. The N III] line reaches peak luminosity at 399 ± 15 days. A ring radius of (6.24 ± 0.20) × 10 17 cm and inclination of 41. • 0 ± 3. • 9 is derived from these times, assuming a circular ring. The probable role of resonant scattering in the N V light curve introduces
Coronal emission from the shocked circumstellar ring of SN 1987A
Astronomy & Astrophysics, 2006
High resolution spectra with UVES/VLT of SN 1987A from December 2000 until November 2005 show a number of high ionization lines from gas with velocities of roughly 350 km/s, emerging from the shocked gas formed by the ejecta-ring collision. These include coronal lines from [Fe X], [Fe XI] and [Fe XIV] which have increased by a factor of about 20 during the observed period. The evolution of the lines is similar to that of the soft X-rays, indicating that they arise in the same component. The line ratios are consistent with those expected from radiative shocks with velocity 310-390 km/s, corresponding to a shock temperature of (1.6-2.5) x 10^6 K. A fraction of the coronal emission may, however, originate in higher velocity adiabatic shocks.
High resolution spectroscopy of the inner ring of SN 1987A
Astronomy and Astrophysics, 2008
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) × 10 3 cm −3 and temperatures of ∼6.5 × 10 3 −2.4 × 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 × 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 Hα 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.
Astronomy and Astrophysics, 2011
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 × 10 3 cm −3 , has not changed over the last ∼15 years, and the [N II] temperature remains also fairly constant at ∼1.2 × 10 4 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 × 10 3 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 × 10 18 cm. 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.
Mapping the Physical and Chemical Conditions of the Ring Nebula
Proceedings of the International Astronomical Union, 2016
We observed the Planetary Nebula NGC 6720 with the Gemini Telescope and the Gemini Multi-Object Spectrographs. We obtained spatial maps of 36 emission-lines in the wavelength range between 3600 Å and 9400 Å. We derived maps of c(Hβ), electronic densities, electronic temperatures, ionic and elemental abundances, and Ionization Correction Factors (ICFs) in the source and investigated the mass-loss history of the progenitor. The elemental abundance results indicate the need for ICFs based on three-dimensional photoionization models.