Nebular Remnant Research Articles

Spatiokinematic models of five nova remnants: correlations between nova shell axial ratio, expansion velocity, and speed class

ABSTRACT We present long-slit intermediate-dispersion spectroscopic observations and narrow-band direct imaging of four classical nova shells, namely T Aur, HR Del, DQ Her, and QU Vul, and the nova-like source CK Vul. These are used to construct models of their nebular remnants using the morphokinematic modelling tool shape to reveal their 3D shape. All these nova remnants but CK Vul can be described by prolate ellipsoidal shells with different eccentricity degree, from the spherical QU Vul to the highly elongated shell with an equatorial component HR Del. On the other hand, CK Vul shows a more complex structure, with two pairs of nested bipolar lobes. The spatiokinematic properties of the ellipsoidal nova shells derived from our models include their true axial ratios. This parameter is expected to correlate with the expansion velocity and decline time t3 (i.e. their speed class) of a nova as the result the interaction of the ejecta with the circumstellar material and rotation speed and magnetic field of the white dwarf. We have compared these three parameters including data available in the literature for another two nova shells, V533 Her and FH Ser. There is an anticorrelation between the expansion velocity and the axial ratio and decline time t3 for nova remnants with ellipsoidal morphology, and a correlation between their axial ratios and decline times t3, confirming theoretical expectations that the fastest expanding novae have the smallest axial ratios. We note that the high expansion velocity of the nova shell HR Del of 615 km s−1 is inconsistent with its long decline time t3 of 250 d.

SALT observations of southern post-novae

We report on recent optical observations of the stellar and the nebular remnants of 22 southern post-novae. In this study, for each of our targets, we obtained and analysed long-slit spectra in the spectral range 3500-6600 A and in H$\alpha$+NII narrow-band images. The changes in the emission lines' equivalent widths with the time since the outburst agree with earlier published results of other authors. We estimated an average value $\alpha$=2.37 for the exponent of the power law fitted to the post-novae continua. Our observations clearly show the two-component structure of the V842 Cen expanding nebulae, owing to the different velocities of the ejected matter. We discovered an expanding shell around V382 Vel with an outer diameter of about 12 arcsec.

Modelling the Late-time Hubble Space Telescope Imaging of the Outburst of the Recurrent Nova RS Ophiuchi (2006)

AbstractThe nebular remnant of RS Ophiuchi was modelled using combined HST/ACS imaging and ground-based spectroscopy on day 155 after outburst as a two component bipolar expansion with a low velocity innermost hour-glass over density and a more extended high velocity dumbbell structure. The model was evolved to a much later date, day 455 after outburst, when second epoch HST images were secured. However, due to the lack of simultaneous ground-based spectroscopy the evolved model was much harder to constrain. One suggestion put forward was that the dumbbell structure expanded linearly while the inner hour-glass showed signs of deceleration. Archival data in the form of ground-based spectroscopy on day 415 were subsequently obtained. These new data suggest indeed that a non-linear expansion of the system occurred.

THE EXPANDING NEBULAR REMNANT OF THE RECURRENT NOVA RS OPHIUCHI (2006). II. MODELING OF COMBINEDHUBBLE SPACE TELESCOPEIMAGING AND GROUND-BASED SPECTROSCOPY

We report Hubble Space Telescope imaging, obtained 155 and 449 days after the 2006 outburst of the recurrent nova RS Ophiuchi, together with ground-based spectroscopic observations, obtained from the Observatorio Astron\'omico Nacional en San Pedro M\'artir, Baja California, M\'exico and at the Observatorio Astrof\'isico Guillermo Haro, at Cananea, Sonora, M\'exico. The observations at the first epoch were used as inputs to model the geometry and kinematic structure of the evolving RS Oph nebular remnant. We find that the modeled remnant comprises two distinct co-aligned bipolar components; a low-velocity, high-density innermost (hour glass) region and a more extended, high-velocity (dumbbell) structure. This overall structure is in agreement with that deduced from radio observations and optical interferometry at earlier epochs. We find that the asymmetry observed in the west lobe is an instrumental effect caused by the profile of the HST filter and hence demonstrate that this lobe is approaching the observer. We then conclude that the system has an inclination to the line of sight of 39$^{+1}_{-10}$ degrees. This is in agreement with the inclination of the binary orbit and lends support to the proposal that this morphology is due to the interaction of the outburst ejecta with either an accretion disk around the central white dwarf and/or a pre-existing red giant wind that is significantly denser in the equatorial regions of the binary than at the poles. The second epoch HST observation was also modeled. However, as no spectra were taken at this epoch, it is more difficult to constrain any model. Nevertheless, we demonstrate that between the two HST epochs the outer dumbbell structure seems to have expanded linearly.

Hubble Space Telescope Imaging of the Expanding Nebular Remnant of the 2006 Outburst of the Recurrent Nova RS Ophiuchi

We report Hubble Space Telescope imaging obtained 155 days after the 2006 outburst of RS Ophiuchi. We detect extended emission in both [O III] λ5007 and [Ne V] λ3426 lines. In both lines, the remnant has a double ring structure. The east-west orientation and total extent of these structures (580 ± 50 AU at d = 1.6 kpc) is consistent with that expected due to expansion of emitting regions imaged earlier in the outburst at radio wavelengths. Expansion at high velocity appears to have been roughly constant in the east-west direction (vexp = 3200 ± 300 km s-1 in the plane of the sky), with tentative evidence of deceleration north-south. We present a bipolar model of the remnant whose inclination is consistent with that of the central binary. The true expansion velocities of the polar components are then v = 5600 ± 1100 km s-1. We suggest that the bipolar morphology of the remnant results from interaction of the outburst ejecta with a circumstellar medium that is significantly denser in the equatorial regions of the binary than at the poles. This is also consistent with observations of shock evolution in the X-ray and the possible presence of dust in the infrared. Furthermore, it is in line with models of the shaping of planetary nebulae with close binary central systems, and also with recent observations relating to the progenitors of Type Ia supernovae, for which recurrent novae are a proposed candidate. Our observations also reveal more extended structures to the south and east of the remnant whose possible origin is briefly discussed.

Granitization of Paleoproterozoic high-pressure metagabbro-norites of the Belomorian Group in Gorelyi Island, Kandalaksha Bay area, Baltic Shield

The process of granitization was studied in a small massif of high-pressure Paleoproterozoic (2.45–2.36 Ga) metagabbro-norites (coronites) of the Belomorian Group at contacts with Bt-Hbl-Kfs-Pl-Qtz gneiss-granites. The granitization process occurred at the culmination of Svecofennian metamorphism, at T = 660–700°C and P = 9.5–10.5 kbar. The process affected the marginal portion (15–20 m thick) of the massif and proceeded under the effect of silicic-alkaline H2O-Cl-CO2 fluids related to the gneiss-granites and was of infiltration nature. The metagabbroids became enriched in Na, K, Si, Cl, CO2, and H2O and depleted in Ca, Mg, Fe, and Cr, which were removed outside the reaction zone. The debasified metabasites underwent melting during the final stages of the process. The changes in the bulk-rock compositions became more intense closer to the contact with the gneiss-granite, as can be clearly seen in the variation diagrams. Before their transformations, the metagabbroids contained magmatic minerals: pigeonite, pigeonite-augite, high-Ti biotite, and labradorite-bytownite, which are partly replaced by metamorphic minerals (sometimes in the form of reaction coronas): garnet, clinopyroxene, orthopyroxene, magnesian hornblende, anthophyllite, biotite, and andesine. According to the changes in the phase relations and the composition of the rocks, the contact-reaction interval can be subdivided into the following four zones: (I) weakly amphibolized metagabbro-norite; (II) apogabbro Hbl-Pl±Scp ± Qtz plagioamphibolites with rims, and then with pseudomorphs, after magmatic and corona minerals; (III) K-feldspathized Hbl-Bt-Pl-Kfs ± Scp-Qtz apogabbro amphibolites; and (IV) gneiss-granites with skialiths of bleached Bt-Hbl-Pl-Kfs ± Scp-Qtz amphibolites. Zone I contains newly formed embryonic Hbl, Opx, and Ath reaction rims around magmatic and coronitic minerals. In zone II, Pig, Pig-Aug, and Grt are completely replaced by hornblende and anthophyllite, and Lbr is replaced by andesine and scapolite with a calcite admixture. In zone III, Hbl is further replaced by biotite; andesine is replaced by oligoclase, potassic feldspar, and quartz; and Ath and Opx are decomposed. Biotitization becomes more intense in zone IV, where Hbl and Bt are partly replaced by feldspars and quartz, which mark the maximum of the debasification and enrichment in alkalis of the metagabbro-norites. The paper presents descriptions of reaction textures and mineral reactions that mark the transitions between the zones and considers the stability conditions of Ath and Opx in zones I and II and the causes of the disappearance of these minerals from zones III and IV. Equilibria of the Pl-Scp pair are discussed. The variations in the compositions of minerals from zone I through zone IV are systematic and display clearly pronounced tendencies. The hornblende becomes progressively more ferrous (its iron mole fraction increases from 0.31 to 0.69), along with an increase in the concentrations of alkalis and the K/Na ratio. The biotite also becomes more ferrous (from 0.28 to 0.61) and depleted in Ti in comparison with magmatic biotite. The anorthite content in plagioclases decreases from 60–80 to 20–22%. The content of the meionite end member in the scapolite varies from 30 to 50% but depends not on the zone but on the CO2 and Cl concentrations in the fluid. The distribution of the Me and An end members between Scp and Pl is equilibrium. Calculations indicate that the fluid in the most strongly transformed rear zone IV was a highly concentrated carbon dioxide-chloride brine rich in alkalis and silica. The transformations of the gabbroids in zones I–III was of metasomatic character. Zone IV is marked by the onset of the fragmentation of the amphibolized and bleached metagabbronorites, their transformation into skialiths submerged into gneiss-granite, and their further debasification and enrichment in alkalis. This process ends with the progressively more intense melting and dissolution of the nebular remnants of the metabasites in the anatectic granite migma or magma. The aureole described in this publication makes it possible to trace all granitization stages in metagabbroids in compliance with the known model proposed by D.S. Korzhinskii.

A multiwavelength study of the remnant of nova GK Persei

We present new observations of the nebular remnant of the old nova GK Persei 1901 in the optical using the Himalayan Chandra Telescope (HCT) and at low radio frequencies using the Giant Metrewave Radio Telescope (GMRT). The dimensions of the shell in the optical emission lines of [NII], [OIII] and [OII] are arcsec2, arcsec2 and arcsec2, respectively. The evolution of the nova remnant indicates shock interaction with the ambient medium, especially in the southwest quadrant. Application of a simple model for the shock and its evolution to determine the time dependence of the radius of the shell in the southwest quadrant indicates that the shell is now expanding into an ambient medium that has a density of 0.12 cm-3, compared to the density of the ambient medium of 0.8 cm-3 ahead of the shock in 1987. There are indications of a recent interaction of the nova remnant with the ambient medium in the northeast quadrant. There is a distinct flattening of the shell, as well as an increase in the number and brightness of the knots in the region. The brightest optical knots in this region are also detected in the radio images. The nova remnant of GK Per is detected at all the observed radio frequencies and is of a similar extent to the optical remnant. Putting together our radio observations with VLA archival data on GK Per from 1997, we obtain three interesting results: 1. the spectrum above 1.4 GHz follows a power law with an index -0.7 () and below 1.4 GHz follows a power law with an index ∼-0.85. This could be due to the presence of at least two populations of electrons dominating the global emission at different frequencies; 2. we record an annual secular decrease of 2.1% in the flux density of the nova remnant at 1.4 and 4.9 GHz between 1984 and 1997 which has left the spectral index unchanged at -0.7. No such decrease is observed in the flux densities below 1 GHz; 3. we record an increase in the flux density at 0.33 GHz compared to the previous estimate in 1987. We conclude that the remnant of nova GK Per is similar to supernova remnants and in particular to the young supernova remnant Cas A.

Optical Imaging of Old Nova Shells

AbstractA deep, predominantly Ha, imaging survey of 37 classical nova remnants has just been completed using the William Herschel and Anglo-Australian Telescopes. This has resulted in the detection of new nebular remnants and the resolution of detailed structure in previously known remnants. These data indicate a correlation between nova speed class and the ellipticity of the resulting remnants – those of faster novae tend to comprise randomly distributed clumps of ejecta superposed on spherically symmetric diffuse material, whilst slower novae produce more structured ellipsoidal remnants with at least one, and sometimes several, rings of enhanced emission.

A deep optical imaging study of the nebular remnants of classical novae

An optical imaging study of old nova remnants has revealed previously unobserved features in the shells of 13 classical novae – DQ Her, FH Ser, HR Del, GK Per, V1500 Cyg, T Aur, V533 Her, NQ Vul, V476 Cyg, DK Lac, LV Vul, RW UMi and V450 Cyg. These data indicate a possible correlation between nova speed class and the ellipticity of the resulting remnants – those of faster novae tend to comprise randomly distributed clumps of ejecta superposed on spherically symmetric diffuse material, whilst slower novae produce more structured ellipsoidal remnants with at least one and sometimes several rings of enhanced emission. By measuring the extent of the resolved shells and combining this information with previously published ejection speeds, we use expansion parallax to estimate distances for the 13 novae. Whilst we are able to deduce new information about every nova, it is notable that these observations include the first detections of shells around the old novae V450 Cyg and NQ Vul, and that velocity-resolved images of FH Ser and DQ Her have enabled us to estimate their orbital inclinations. Our observations of DQ Her also show that the main ellipsoidal shell is constricted by three rings and surrounded by a faint halo; this halo contains long tails extending outwards from bright knots, perhaps indicating that during or after outburst a fast inner wind has broken through the fractured principal shell.

The nebular remnant and quiescent spectrum of Nova GK Persei

CCD images of the nebular shell of the old nova GK Per in [N II] and [O III] emission lines, and also the quiescent spectrum in the optical region, are presented. Proper motion measurements of the knots in [N II] over the baseline 1984–90 give a mean expansion rate of 0.31 ± 0.07 arcsec yr -1 . This value agrees with models of the expansion of the ejecta into the ambient circumstellar medium. A correction for projection effects indicates that the ratio of the mass of the shell to the density of the circumstellar medium is a factor of 2 – 3 higher than estimated previously. The optical spectrum is decomposed into those of the secondary and the accretion disc. The estimate of M V = + 4.9 for the accretion disc implies a mass transfer rate of 3.5 × 10 -9 M☉ yr -1 in the steady state. The H and He emission-line fluxes are used to infer that (i) the line-emitting region has a high density, (ii) the He/H abundance is near-solar, and (iii) the ionizing source has a Zanstra temperature of 1.3 × 10 5 K and an effective radius of 0.01 R☉, which are consistent with its being a white dwarf.

A sharpened H-alpha + forbidden N II image of the nebula surrounding nova V1500 Cygni (1975)

An image of the resolved nebular remnant of Nova Cygni 1975 (V1500 Cygni), obtained in 1987 July, is presented. The image has been enhanced by sharpening techniques, with the central star both retained and removed by point-spread-function subtraction. The median nebular radius at thyat time was 1.90″ ± 0.10″, and the structure in projection was essentially that of a circular annulus. Blob and ring models of the ejected material, previously proposed, do not seem to match well with the actual image. If the ejection was roughly spherical, our observations coupled with the expansion velocity derived from the principal absorption spectrum imply a distance of 2.11 ± 0.10 kpc for the nova

Optical Imagery of Nova Remnants

AbstractResolved nebular remnants of classical novae are discussed in terms of size, surface brightness, and shape. A list of 26 known resolved remnants is given. The conditions necessary for visibility of a resolved remnant are discussed. The structure of remnants can be studied at optical wavelengths by direct imaging and by long-slit or otherwise spatially resolved spectroscopy of emission lines. Based on recent spatiokinematic studies, most nebular remnants are prolate in outline, with sub-structure that has been characterized as consisting of “polar blobs” and “equatorial rings”. The mechanism that shapes the remnants is not yet known with certainty. There is room for much additional work in discovering new remnants and in characterizing those that are known.

Ultraviolet spectroscopy of the shell of RR Pic

Spectroscopy of the nebular (as opposed to the stellar) remnants of old novae can be a powerful diagnostic of physical conditions in, and mode of excitation of, nova shells. While optical spectroscopy of nova shells has been widely used in this way, few are sufficiently well resolved, and sufficiently bright, to be observed with IUE.Combined optical and ultraviolet spectroscopy of only two nova remnants–those of GK Per and DQ Her–have been reported to date. Ferland et al. (1984) demonstrated that the shell of DQ Her is extremely cool (Te ≃ 500 K) and is excited by a hot central source. Bode et al. (1988) showed that the ultraviolet and optical lines in the spectrum of the GK Per nebula can best be understood in terms of shock excitation, consistent with its observed properties at radio wavelengths (Seaquist et al. 1989).

Direct photography of the nebular remnant of nova Delphini 1967

Direct photographs of N Del 1967 taken in the light of the [O III] 5007 Å line show an oval nebular remnant: angular size 3.7 × 2.5 arcsec, the position angle of the large (probably equatorial) axis is 43°. The nebular expansion method yields a distance of 850 ± 50 pc.

An X-ray model for the nebula of nova DQ Herculis 1934

view Abstract Citations (65) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An X-ray model for the nebula of nova DQ HER 1934. Ferland, G. J. ; Truran, J. W. Abstract A model for the nebula of DQ Her is presented which is built upon the assumption that the power is provided by an X-ray source. The X-ray and UV energy spectra recently calculated by Kylafis and Lamb for the case of spherical accretion onto degenerate dwarfs are modified to take account of the geometry of the system. The influence of a low frequency cutoff is considered: the column density we find to be consistent with our model falls nicely in the range inferred for nova systems by recent observations of Cordova, Mason, and Nelson. The effects of the radiation field upon the envelope ejected in the 1934 outburst were determined with a photoionization program which includes all X-ray heating and ionization processes known to be important (Compton recoil by both bound and free electrons, the Auger effects, and secondary ionization by suprathermal electrons). Our calculations show that many observed features of the nebula follow as a very natural consequence of this model. Specifically, the nebula is expected to be very cool, ∼300 K, and to show extremely strong recombination lines of ionized carbon, nitrogen, and oxygen, as previously reported by Williams et al. Time variations of the inferred nebular composition are to be expected, as the reestablishment of accretion flows, formation of a disk, and the ensuing emergence of an X-ray flux must follow upon the turnoff of the underlying white-dwarf nova remnant. Scrutiny of the spectroscopic data for DQ Her suggests that this turnoff occurred in the late 1940s, and that the nebula cooled rapidly in this stage. The relevance of our results to studies of other nova nebular remnants is briefly examined. Publication: The Astrophysical Journal Pub Date: March 1981 DOI: 10.1086/158773 Bibcode: 1981ApJ...244.1022F Keywords: Astronomical Models; Dwarf Stars; Nebulae; Novae; X Ray Sources; X Ray Spectra; Emission Spectra; Line Spectra; Photoionization; Stellar Mass Accretion; Ultraviolet Astronomy; Ultraviolet Spectra; Astrophysics full text sources ADS | data products SIMBAD (2)

THE MASS OF THE NOVA HR DELPHINI NEBULA.

ABSTRACT The Wisconsin low-resolution spectrophotometer was used to measure the absolute H flux from HR Del in August 1975. Using nebular temperatures from earlier measurements, the mass of the nebula is about 10- ')) . This is in reasonable agreement with results from other methods of estimating the mass of ejecta from HR Del, and is consistent with nova models in which radiation pressure drives mass loss. Key words: nebular remnant- spectrophotometry

Supernova Remnants and Hidden Pulsars.

view Abstract Citations (19) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Supernova Remnants and Hidden Pulsars. Cavaliere, A. ; Pacini, F. Abstract If a supernova remnant draws its energy from a rotating neutron star, the total luminosity should decrease about 4 times faster than the rotation period of the central star. Parameters for the pulsar in Cas A (if there is one) are derived as a function of the luminosity and luminosity change. The same considerations could have given the parameters of the neutron star in the Crab before the discovery of the pulsar NP 0531. Some general remarks are made concerning the coupling of the stellar rotation with the nebular remnant. Publication: The Astrophysical Journal Pub Date: January 1970 DOI: 10.1086/180470 Bibcode: 1970ApJ...159L..21C full text sources ADS |