We report results from high resolution optical spectroscopy of three non-radiative galactic supernova remnants, RCW 86, Kepler's supernova remnant and SN 1006. We have measured the narrow component ...Hα line widths in Balmer-dominated filaments in RCW 86 and SN 1006, as well as the narrow component width in a Balmer-dominated knot in Kepler's SNR. The narrow component line widths measured in RCW 86 and Kepler's SNR show FWHM of $30{-}40$ km s-1, similar to what has been seen in other Balmer-dominated remnants. Of the remnants in our sample, SN 1006 is the fastest shock (~3000 km s-1). The narrow component Hα and Hβ lines in this remnant have a FWHM of merely 21 km s-1. Comparing the narrow component widths measured in our sample with those measured in other remnants shows that the width of the narrow component does not correlate in a simple way with the shock velocity. The implications for the pre-heating mechanism responsible for the observed line widths are discussed.
The current work discusses means to utilize low-grade small-scale energy in vehicle exhaust gases, to reduce the vehicle’s fuel consumption and to make it run more environmental friendly. To utilize ...the energy in the exhaust gas, a CO
2 bottoming system in the vehicle’s engine system is proposed. Several basic cycles—according to the different design concepts—are presented, and the efficiencies are calculated using Engineering Equation Solver (EES).
1
The thermodynamic properties for carbon dioxide in EES are calculated by the fundamental equation of state developed by Span and Wagner, A new equation of state for carbon dioxide covering the fluid region form the triple-point temperature to 1100
K at pressures up to 800
MPa, J. Phys. Chem, Ref. Data, Vol. 25, No. 6, 1996.
http://www.fchart.com/ees/ees.shtml.
1
Several thermodynamic models in EES show that after system optimization, in CO
2 Transcritical power cycle with a gas heater pressure of 130
bars and 200
°C expansion inlet temperature, about 20% of energy in the exhaust gas can be converted into useful work. Increasing the pressure in the gas heater to 300 bars and with same expansion inlet temperature, about 12% of exhaust gas energy can be converted. When raising the pressure both in the gas cooler and in the gas heater, the cycle runs completely above the critical point, and the efficiency is about 19%. Besides, in the CO
2 combined cycle, the system COP is 2.322 and about 5% of exhaust gas energy can be converted.
We present and discuss new visual wavelength-range observations of the inner regions of the supernova remnant SNR 0540−69.3 that is located in the Large Magellanic Cloud (LMC). These observations ...provide us with more spatial and spectral information than were previously available for this object. We use these data to create a detailed three-dimensional model of the remnant, assuming linear expansion of the ejecta. With the observations and the model, we study the general three-dimensional structure of the remnant, and the influence of an active region in the remnant - a 'blob' - that we address in previous papers. We used the fibre-fed integral-field Visual Multi-Object Spectrograph at the Very Large Telescope of the European Southern Observatory. The observations provide us with three-dimensional data in O iii λ5007 and S ii λλ6717, 6731 at a 0.33 arcsec × 0.33 arcsec spatial sampling and a velocity resolution of about 35 km s− 1. We decomposed the two, partially overlapping, sulphur lines and used them to calculate electron densities across the remnant at a high signal-to-noise ratio. In our study, we recover results of previous studies, but we are more importantly able to obtain more detailed information than before. Our analysis reveals a structure that stretches from the position of the 'blob', and into the plane of the sky at a position angle of PA 60°. Assuming a remnant age of 1000 yr and the usual LMC distance, the structure has an inclination angle of about 65° to the line of sight. The position angle is close to the symmetry axis with present and past activity in the visual and the X-ray wavelength ranges. We speculate that the pulsar is positioned along this activity axis, where it has a velocity along the line of sight of a few hundred km s− 1. The 'blob' is most likely a region of shock activity, as it is mainly bright in S ii; future observations of O ii λλ3726, 3729 would be useful to test whether the S/O abundance ratio is higher than average for that location in the remnant. The striking resemblance in X-rays between the pulsar wind nebula (PWN) of SNR 0540−69.3 and the Crab, in combination with our findings in this paper, suggests that the symmetry axis is part of a torus in the PWN. This is in agreement with the original suggestion by Gotthelf & Wang.
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$103 cm-3 and temperatures of ~6.5$\times$103-2.4$\times$104 K. This is consistent with the thermal widths of the lines. From the shocked component we observe a large range of ionization stages from neutral lines to Fe XIV. From a nebular analysis we find that the density in the low ionization region is 4$\times$106-107 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.
The outer rings of SN 1987A Tziamtzis, A.; Lundqvist, P.; Gröningsson, P. ...
Astronomy and astrophysics (Berlin),
03/2011, Letnik:
527, Številka:
14
Journal Article
Recenzirano
Odprti dostop
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 × 1018 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.
ABSTRACT We present high spatial resolution optical imaging and polarization observations of the PSRB0540-69.3 and its highly dynamical pulsar wind nebula (PWN) performed with Hubble Space Telescope, ...and compare them with X-ray data obtained with the Chandra X-ray Observatory. In particular, we have studied the bright region south-west of the pulsar where a bright 'blob' is seen in 1999. In a recent paper by De Luca et al. it was argued that the 'blob' moves away from the pulsar at high speed. We show that it may instead be a result of local energy deposition around 1999, and that the emission from this then faded away rather than moved outward. Polarization data from 2007 show that the polarization properties show dramatic spatial variations at the 1999 blob position arguing for a local process. Several other positions along the pulsar-'blob' orientation show similar changes in polarization, indicating previous recent local energy depositions. In X-rays, the spectrum steepens away from the 'blob' position, faster orthogonal to the pulsar-'blob' direction than along this axis of orientation. This could indicate that the pulsar-'blob' orientation is an axis along where energy in the PWN is mainly injected, and that this is then mediated to the filaments in the PWN by shocks. We highlight this by constructing an Sii-to-Oiii-ratio map, and comparing this to optical continuum and X-ray emission maps. We argue, through modelling, that the high Sii/Oiii ratio is not due to time-dependent photoionization caused by possible rapid X-ray emission variations in the 'blob' region. We have also created a multiwavelength energy spectrum for the 'blob' position showing that one can, to within 2σ, connect the optical and X-ray emission by a single power law. The slope of that power law (defined from ) would be αν= 0.74 ± 0.03, which is marginally different from the X-ray spectral slope alone with αν= 0.65 ± 0.03. A single power law for most of the PWN is, however, not be possible. We obtain best power-law fits for the X-ray spectrum if we include 'extra' oxygen, in addition to the oxygen column density in the interstellar gas of the Large Magellanic Cloud and the Milky Way. This oxygen is most naturally explained by the oxygen-rich ejecta of the supernova remnant. The oxygen needed likely places the progenitor mass in the 20-25M range, i.e. in the upper mass range for progenitors of Type IIP supernovae. PUBLICATION ABSTRACT
We present and analyse spectra of the Type IIn supernova (SN) 1994W obtained between 18 and 203 d after explosion. During the luminous phase (first 100 d) the line profiles are composed of three ...major components: (i) narrow P-Cygni lines with the absorption minima at −700 km s−1; (ii) broad emission lines with blue velocity at zero intensity ∼4000 km s−1; and (iii) broad, smooth wings extending out to at least ∼5000 km s−1, most apparent in Hα. These components are identified with an expanding circumstellar (CS) envelope, shocked cool gas in the forward post-shock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P-Cygni lines from the SN is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the density (n≈ 109 cm−3), radial extent ∼(4–5) × 1015 cm and Thomson optical depth (τT≳ 2.5) of the CS envelope during the first month. The plateau-like SN light curve is reproduced by a hydrodynamical model and is found to be powered by a combination of internal energy leakage after the explosion of an extended pre-SN (∼1015 cm) and subsequent luminosity from CS interaction. The pre-explosion kinematics of the CS envelope is recovered, and is close to homologous expansion with outer velocity ∼1100 km s−1 and a kinematic age of ∼1.5 yr. The high mass (∼0.4 M⊙) and kinetic energy (∼2 × 1048 erg) of the CS envelope, combined with low age, strongly suggest that the CS envelope was explosively ejected ∼1.5 yr prior to the SN explosion.
We report a supernova discovery in K sub(s)-band images from the NAOS CONICA adaptive optics (AO) system on the ESO Very Large Telescope. The images were obtained as part of a near-infrared search ...for highly obscured supernovae in the nuclear regions of luminous and ultraluminous infrared galaxies. SN 2004ip is located within a circumnuclear starburst at 1.4" (or 500 pc) projected distance from the K-band nucleus of the luminous infrared galaxy IRAS 18293-3413. The supernova luminosity and light curve are consistent with a core-collapse event suffering from a host galaxy extinction of up to about 40 mag in the V band, which is as expected for a circumnuclear starburst environment. This is the first supernova to be discovered making use of AO correction and demonstrates the potential of the current 8 m-class telescopes equipped with AO in discovering supernovae from the innermost nuclear regions of luminous and ultraluminous infrared galaxies.
We present contemporary optical and infrared spectroscopic observations of the type IIn SN 1998S covering the period between 3 and 127 days after discovery. During the first week the spectra are ...characterized by prominent broad H, He and C iii/N iii emission lines with narrow peaks, superimposed on a very blue continuum (T∼24 000 K). In the following two weeks the C iii/N iii emission vanished, together with the broad emission components of the H and He lines. Broad, blueshifted absorption components appeared in the spectra. The temperature of the continuum also dropped to ∼14 000 K. By the end of the first month the spectrum comprised broad, blueshifted absorptions in H, He, Si ii, Fe ii and Sc ii. By day 44, broad emission components in H and He reappeared in the spectra. These persisted to as late as days ∼100–130, becoming increasingly asymmetric. We agree with Leonard et al. that the broad emission lines indicate interaction between the ejecta and circumstellar material (CSM) emitted by the progenitor. We also agree that the progenitor of SN 1998S appears to have gone through at least two phases of mass-loss, giving rise to two CSM zones. Examination of the spectra indicates that the inner zone extended to ≤90 au, while the outer CSM extended from 185 au to over 1800 au. We also present high-resolution spectra obtained at days 17 and 36. These spectra exhibit narrow P Cygni H i and He i lines superimposed on shallower, broader absorption components. Narrow lines of N ii, O iii, Ne iii and Fe iii are also seen. We attribute the narrow lines to recombination and heating following ionization of the outer CSM shell by the UV/X-ray flash at shock breakout. Using these lines, we show that the outer CSM had a velocity of 40–50 km s−1. Assuming a constant velocity, we can infer that the outer CSM wind commenced more than 170 years ago, and ceased about 20 years ago, while the inner CSM wind may have commenced less than 9 years ago. During the era of the outer CSM wind the outflow from the progenitor was high — at least ∼2×10−5 M⊙ yr−1. This corresponds to a mass-loss of at least ∼0.003 M⊙, suggesting a massive progenitor. The shallower, broader absorption is of width ∼350 km s−1, and may have arisen from a component of the outer CSM shell produced when the progenitor was going through a later blue supergiant phase. Alternatively, it may have been produced by the acceleration of the outer CSM by the radiation pressure of the UV precursor. We also describe and model first-overtone emission in carbon monoxide observed in SN 1998S. We deduce a CO mass of ∼10−3 M⊙ moving at ∼2200 km s−1, and infer a mixed metal/He core of about 4 M⊙, again indicating a massive progenitor. Only three core-collapse supernovae have been observed in the K band at post-100 days, and all three have exhibited emission from CO.
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