ABSTRACT The spectral evolution of V407 Cyg during the outburst in 2010 is reported. The coronal emission lines Fe x 6374, Ar x 5535, and Ar xi 6919 strengthened rapidly around day 20 of the ...outburst, which coincided with the growth of soft X-ray flux. On the other hand, the non-coronal forbidden lines O i, N ii, O iii, etc. strengthened between days 40 and 60, which coincided with the fading of the soft X-rays. The luminosities in the UV and optical regions also decreased in the same period, and were seen as bends on the light curves. Our observations suggest that the fading of the soft X-rays and the bends on the light curves were likely related to a rapid decreasing of the emission measure of the nebulosity, and may not have been due to the cessation of the hydrogen burning in the system. It seems that the coronal emission lines were emitted by the collision of the ejecta with the circumstellar envelope as well as the soft X-rays. Intensities of the emission lines of He i relative to Hβ probably increased in the first 3 days of the outburst and decreased in the successive 10 days and then recovered, while no other line showed a similar variation. The variations in intensity of the He i emission lines coincided with that of the γ-ray flux in the first two weeks of the outburst. The helium abundance derived from the intensities of the He i and He ii emission lines relative to Hβ appeared to have decreased from N(He) = 0.17 to 0.076 according to the fading of the He i lines, and then increased to 0.20 when the intensities recovered in the later stage of the outburst. It is unlikely that the helium abundance really changed so much during the outburst. There might have been an unknown mechanism that weakened the He i emission lines. The distance to V407 Cyg is estimated to be kpc. The absolute V mag at maximum light of the outburst was probably fainter by about 0.6 mag than that expected from the time for a 2 mag decline.
High- and low-resolution optical spectra of CI Aql were obtained during the outburst in 2000. Multiple absorption components of H I and Fe II lines were detected at the early decline stage. Their ...radial velocities were roughly −2500 km s-1, −2200 km s-1, −1700 km s-1, and −1400 km s-1, among which only the last components were likely still accelerating during the early decline stage. Prominent emission lines of O III and N II appeared about one month after light maximum. The duration of the nebular stage, however, was only one month and a few weeks. The ejected gas shells seem to have started to shrink about 70 days after light maximum. The amount of interstellar extinction is estimated to be E(B − V) = 0.92 ± 0.15 from the equivalent widths of the diffuse interstellar absorption bands. The helium abundance in the ejecta is estimated to be N(He) = 0.19 ± 0.05 and the mass of the ejecta to be about 2 × 10-6 M⊙. This object has been classified as a U Sco type recurrent nova, but its spectral evolution during the outburst resembled those of T Pyx type recurrent novae. It is doubtful whether the peak of mV ≅ 9 mag on 2000 May 5 was the true light maximum or an earlier brighter peak had been overlooked, because the spectral data suggest that the ejections of gas shells occurred prior to the discovery of the outburst on 2000 April 28.
Industrial-grade pure nickel, NI-201, was tensile tested in high-pressure hydrogen gas at various testing temperatures and strain rates. The degree of hydrogen embrittlement (HE) was strongly ...affected by the testing temperature and strain rate, and elevating the strain rate and lowering the temperature result in suppressed HE. While hydrogen trapped at GBs via local equilibrium dominated the HE degree in hydrogen-charged cases, hydrogen supply to GBs during the tests was required in gaseous hydrogen cases. Although hydrogen–dislocation interaction was one of candidates for the hydrogen supply, the lattice hydrogen, which can interact with dislocations, hardly existed and related behaviors such as increase in flow stress and serrated yielding were not observed in the gaseous hydrogen cases; therefore, the contribution of the hydrogen–dislocation interaction was speculated to be minor. Alternatively, we proposed an HE model considering hydrogen diffusion along grain boundaries (GBs) from the crack tip, which successfully demonstrated the experimental results.
•Hydrogen effect on ductility in nickel is studied in gaseous hydrogen environment.•Impact of temperature and strain is discussed in terms of hydrogen uptake.•Hydrogen supply process is substantially different from hydrogen-charged case.•Hydrogen short-circuit diffusion along GBs is a major mechanism.•Hydrogen–dislocation interaction is a minor mechanism to supply hydrogen.
Spectral evolution in the optical region of the recurrent nova RS Oph during the 2006 outburst was monitored at the Asiago Astrophysical Observatory. A short-lived flare-up of He I emission lines, ...which was clearly different from the helium flash of classical novae, was observed on March 7, that is 22 days after the outburst and 3.8 mag below maximum luminosity. The coronal emission line Fe XIV 5303 was first detected 35 days after the outburst. Its maximum intensity relative to Hβ was observed 80 days after the outburst, then the intensity declined rapidly. Another coronal line Ar XI 6919 showed a similar variation, while Fe X 6374 faded more slowly. When the former two coronal lines started to fade about 90 days after the outburst, the emission lines of O I, N II, S II, and O III started to strengthen rapidly. Probably, the collisional shock front on the high velocity ejecta reached the outer boundary of the circumstellar envelope and a free expansion started at that time. The variations in intensity of the coronal lines Fe XIV and Ar XI coincided with that of the flux of super-soft X-rays, suggesting that also the latter originated in the collisional shock front. Many prominent emission lines were composed of a central narrow component, blue- and red-shifted wings, and a very broad component. Unidentified emission lines at 6105.5 and 6181.2 Å are identified as O IV 4s2P0–4p2S, 6105.9 and 6183.4 Å, respectively. On the other hand, new unidentified, probably coronal, emission lines are found at 7711 ± 2 Å and 7774 ± 2 Å. A weak trace of the Raman emission band at 6830 Å was detected when the emission lines of Fe VII were not seen. It seems that the lines of O IV at about 1033 Å contributed, in the place of O VI 1032 Å, to the Raman scattering in a low ionization condition. Splittings in two parts of the narrow emission components of H I, He I, and the coronal lines were observed. The splittings were largest on April 8, when the separations between the two peaks were 48 km s-1 for Fe XIV 5303, 37 km s-1 for Hβ, and 33 km s-1 for He I 5876. On the other hand, the narrow emission components of Fe II, N II, O III, O IV, and Fe VII did not show any splitting.
Context. CH Cyg is one of the most studied symbiotic stars. Its properties, however, are still not well known. Two main periods, about 15 years and 750 days, are known in the photometric and ...spectroscopic variations, and two models are proposed for these origins. One is a binary system with an orbital period of 15 years consisting of a hot component and pulsating red giant with a 750-day period. The other is a triple system consisting of an inner symbiotic binary with an orbital period of about 750 days and third component with an orbital period of 15 years. Several active stages have been observed since the 1970s during which the object brightened up by ΔU = 3−5 mag and prominent emission lines appeared. Large mass outflows were observed at some active stages. Aims. The spectral variation of CH Cyg has been monitored at Asiago Observatories to understand the problems mentioned above. We have analysed spectra obtained in the time period from 1995 to 2004 which covers an active stage during the years 1998−2000. Methods. High- and low-resolution optical spectra obtained at the Asiago Observatories are used. Results. Narrow absorption lines of Fe I, Cr I, Ti I, and so on appeared in 1998 at an early phase of the active stage. These lines are clearly distinguished from those of the M-type giant and are typically found on the spectrum of early A-type dwarfs. They were redshifted by about 30 km s−1 with respect to the absorption lines of the M-type giant. Assuming that their radial velocities represent the orbital motion of the hot component, its semi-amplitude is estimated to be 37.0 ± 0.5 km s−1. The masses of the hot component and the M-type giant are estimated to be 0.32 ± 0.02 M⊙ and 4.6 ± 0.2 M⊙, respectively, where a circular orbit with a period of 756 days is adopted. If the inner binary system has an elliptical orbit, e = 0.33, and a period of 750.1 days, the masses of the two components are 0.21 ± 0.01 M⊙ and 2.2 ± 0.1 M⊙, respectively. Our results lend support to the triple system model, because if the period of the symbiotic binary were 15 years, the mass of the hot component would be expected to exceed the Chandrasekhar limit. Highly blueshifted absorption components of H I and He I lines appeared at a later phase of the active stage. Mass ejections with velocities on the order of 1000 km s−1 seem to have occurred along the orbital plane from December 1998 to March 1999. The highest outflow velocity, − 2383 km s−1, was observed on 1999 February 26. Narrow absorption components of Na I D1, D2, and Fe II lines redshifted by 10−15 km s−1 coexisted with the highly blueshifted broad absorption components of H I and He I lines. This phenomenon might have been related to an inner disc inflow expected in wind-compressed discs. In contrast to the bipolar mass outflows at the past active stages, high-velocity equatorial mass ejections likely occurred at the active stage during the years 1998−2000. There should have been an eclipse of the hot component by the M-type giant in the inner binary system in the time period of December 1998 to January 1999. A clear light curve of the eclipse, however, was not detected. Possibly, the luminosity of the hot component was due mainly to free-free emission from the ejected circumstellar matter which was likely more extended than the M-type giant. On the other hand, another eclipse by the third component with the period of 15 years began at the end of May 1999 during which the hot component as well as the emitting regions of Hβ and Fe II lines were well eclipsed. The obscuring matter around the third component should have been much more extended than the M-type giant, and it was likely semi-transparent, because the spectrum of the M-type giant was well seen during the eclipse. The third component appears to be similar to the invisible secondary component in the long-period eclipsing binary ϵ Aur.
Context. The outburst of the symbiotic recurrent nova V407 Cyg in 2010 has been studied by numerous authors. On the other hand, its spectral variations in the quiescent stage have not been well ...studied yet. This paper is probably the first report for the relation between the pulsation of the secondary Mira variable and the temperature of the primary hot component for V407 Cyg. Aims. The spectral variation in the post-outburst stage has been monitored to study the properties of this object. In the course of this work, we found some unexpected spectral variations around the light maximum of the secondary Mira variable in 2012. The relation between the mass transfer in the binary system and the pulsation of the secondary Mira variable is studied. Methods. High- and low-resolution optical spectra obtained at the Astronomical Observatories at Asiago were used. The photometric data depend on the database of the VSNET. Results. The secondary Mira variable reached its light maximum in 2012, when an absorption spectrum of a late-M-type giant developed and the emission line of Hδ became stronger than those of Hβ and Hγ, which are typical spectral features of Mira variables at light maxima. On the other hand, intensity ratios to Hβ of the emission lines of He I, He II, Fe VII, etc., which obviously depended on the temperature of the hot component, rapidly varied around the light maximum. The intensity ratios started to decrease at phase about 0.9 of the periodical light variation of the Mira variable. This phenomenon suggests that the mass transfer rate, as well as the mass accretion rate onto the hot component, decreased according to the contraction of the Mira variable. However, these intensity ratios somewhat recovered just on the light maximum: phase 0.99. There might have occurred a temporal mass loss from the Mira variable at that time. The intensity ratios decreased again after the light maximum, then recovered and returned to the normal level at phase about 0.1. Since the mass transfer rate seems to have been closely related to the pulsation of the secondary component, the mass transfer in this binary system was likely due to a normal Roche-lobe overflow. If this is the case, the orbital period should be shorter than five years. Each of the Na I D1 and D2 lines had five emission and one absorption components around the light maximum. It seems that there were two pairs of mass outflows from the Mira variable with velocities of ± 79 km s-1 and ± 44 km s-1. These velocities were much higher than those of mass loss from usual Mira variables.
We present the one-year long observing campaign of SN 2012A which exploded in the nearby (9.8 Mpc) irregular galaxy NGC 3239. The photometric evolution is that of a normal Type IIP supernova, but the ...plateau is shorter and the luminosity not as constant as in other supernovae of this type. The absolute maximum magnitude, with M
B
= −16.23 ± 0.16 mag, is close to the average for SN IIP. Thanks also to the strong UV flux in the early phase, SN 2012A reached a peak luminosity of about 2 × 1042 erg s−1, which is brighter than those of other SNe with a similar 56Ni mass. The latter was estimated from the luminosity in the exponential tail of the light curve and found to be M(56Ni) = 0.011 ± 0.004 M, which is intermediate between standard and faint SN IIP. The spectral evolution of SN 2012A is also typical of SN IIP, from the early spectra dominated by a blue continuum and very broad (∼104 km s−1) Balmer lines, to the late-photospheric spectra characterized by prominent P-Cygni features of metal lines (Fe ii, Sc ii, Ba ii, Ti ii, Ca ii, Na i D). The photospheric velocity is moderately low, ∼3 × 103 km s−1 at 50 d, for the low optical depth metal lines. The nebular spectrum obtained 394 d after the shock breakout shows the typical features of SNe IIP and the strength of the O i doublet suggests a progenitor of intermediate mass, similar to SN 2004et (∼15 M). A candidate progenitor for SN 2012A has been identified in deep, pre-explosion K
′-band Gemini North Near-InfraRed Imager and Spectrometer images, and found to be consistent with a star with a bolometric magnitude −7.08 ± 0.36 (log L/L = 4.73 ± 0.14 dex). The magnitude of the recovered progenitor in archival images points towards a moderate-mass
star as the precursor of SN 2012A. The explosion parameters and progenitor mass were also estimated by means of a hydrodynamical model, fitting the bolometric light curve, the velocity and the temperature evolution. We found a best fit for a kinetic energy of 0.48 foe, an initial radius of 1.8 × 1013 cm and ejecta mass of 12.5 M. Even including the mass for the compact remnant, this appears fully consistent with the direct measurements given above.
The spectral evolution of an extremely slow nova V723 Cas was monitored at Asiago Observatory for seven years. Observations in the long pre-maximum stage, which lasted more than four months, were ...reported in our previous paper. Here, we report the spectral evolution in the decline stage from January 1996 to December 2001. The spectra just after maximum luminosity showed prominent emission lines of H I, He I, Fe II, Ti II, Si II, Na I, etc. P Cygni type absorption components appeared on H I, He I, and Fe II lines about two months after maximum when the nova performed the second brightening. The radial velocities of the absorption components of H I and He I lines varied from -600 km s-1 in February to -1600 km s-1 in June 1996. Broad emission wings of H I and He I lines that were red-shifted by about 1000 km s-1 were detected in the same season. When the third brightening began in July 1996, a new absorption system of H I and He I appeared in which the blue-shift changed from -1000 km s-1 in July 1996 to -1600 km s-1 in February 1997. Prominent emission lines of highly ionized ions such as Fe VI, Fe VII, and Ca V emerged in the period between May 30 and July 1, 1997. This nova probably entered the nebular stage in this period. The interval from maximum luminosity to the beginning of nebular stage is about 18 months, which is still longer than those of the other extremely slow novae: 10 months of RR Pic or 8 months of HR Del. Some emission lines of Fe IV, which were not found on the spectra of usual classical novae, were detected on the spectra in the nebular stage. The ionization state grew with time to have a coronal emission line Fe X λ6375 in November 1999 and later. The interstellar extinction is estimated at $E(B-V) = 0.57\pm 0.05$ and the distance to the nova at about $d = 2.8$ kpc, while the mass of the ejecta may be about $5\times 10^{-6}$ $M_{\odot}$. The abundance of helium is estimated at N(He)/N(H) = $0.18\pm 0.01$. The abundance of oxygen is not so different from those of usual classical novae, while a rather low abundance of nitrogen is noticed. The abundance of neon is roughly comparable to that of a neon nova QU Vul.
At Asiago Astrophysical Observatory, we observed the peculiar, explosive object Nova (V445) Puppis 2000 during its early decline stage between January and April 2001. We acquired both high and medium ...dispersion spectra for the optical wavelengths $3900{-}7000$ Å. The most remarkable properties of the spectra were an absence of hydrogen lines and unusually strong carbon-ion, emission lines. We identified the most prominent emission line in the optical region at 6585 Å to be due to C II 2, 6578 and 6583 Å. The second strongest emission line at 5900 Å may be due to Na I D1 and D2, blended by C II 5, 5900 and 5902 Å. Prominent emission lines of Fe II, Ti II, Cr II, Si II, Mg II, Fe II, Ti II, C I, C II, C III, Ca I, He I, and probably of O II, N II, N III, and S II were in addition detected. Some emission lines of Fe II, Ti II, Cr II, Na I, and Mg II were accompanied by P Cygni type absorption components blue-shifted by about -500 km s-1. Our first spectrum obtained on January 14, 2001 showed an absorption band of CN (cyanogen) molecule at 4215 Å. The overall spectral features resembled those of classical slow novae, apart from the absence of hydrogen lines. The appearance of some Ti II lines, and a rather high intensity of the emission line of Mg II 23, 6545.8 Å, were additional peculiar spectral features of this object. This object may be located in or beyond the Orion arm, because two sets of interstellar absorption components of Na I D1 and D2 were detected. Their radial velocities in the local standard of rest are +16.0 ± 0.4 km s-1 and +73.5 ± 1.0 km s-1. The radial velocity of this object is estimated to be +224 ± 8 km s-1, which suggests that this object belongs to the old disk population. The distance and the interstellar extinction to the object are estimated to be 3.5 ≤ d ≤ 6.5 kpc and $E(B-V) = 0.51$ mag, respectively. The derived absolute magnitude at light maximum is -5.8 ≤ MV ≤ -7.1 mag. Our results support the classification of this object as a helium nova.
Ultraviolet, optical and near-infrared observations of the Type IIP supernova (SN) 2007od, covering from maximum light to late phases, allow detailed investigation of different physical phenomena in ...the expanding ejecta. These data turn this object into one of the most peculiar SNe IIP ever studied. The early light curve of SN 2007od is similar to that of a bright IIP, with a short plateau, a bright peak (MV
=−18 mag), but a very faint late-time optical light curve. However, with the inclusion of mid-IR observations during the radioactive tail, we derive an ejected mass of 56Ni of M(56Ni) ∼2 × 10−2 M⊙. By modelling the bolometric light curve, ejecta expansion velocities and blackbody temperature, we estimate a total ejected mass of 5-7.5 M⊙ with a kinetic energy of at least 0.5 × 1051 erg. The early spectra reveal a boxy Hα profile and high-velocity features of the Balmer series that suggest the possible interaction of the ejecta with a close circumstellar matter (CSM). The interaction with the CSM and the presence of dust formed inside the ejecta are evident in the late-time spectra. The episodes of mass-loss shortly before explosion, the bright plateau, the relatively small amount of 56Ni and the faint O i emission observed in the nebular spectra are consistent with a super-asymptotic giant branch progenitor (M∼ 9.7-11 M⊙).
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