arXiv subjects

Hiroyuki Naito

Publications and source records attributed to Hiroyuki Naito.

22 records · Page 2Linked to original sources

arXiv2009

Discovery of Multiple High-Velocity Narrow Circumstellar Na I D Lines in Nova V1280 Sco

We discovered multiple high-velocity (ranging from -900 to -650 km/s) and narrow (FWHM = 15 km/s) absorption components corresponding to both the D2 and the D1 lines of Na I on a high dispersion spectrum of V1280 Sco observed on 2009 May 9 (UT), 814 d after the V-band maximum. Subsequent observations carried out on 2009 June and July confirmed at least 11 distinct absorption components in both systems. Some components had deepened during the two months period while their HWHMs and wavelengths remained nearly constant. We suggest these high velocity components originate in cool clumpy gas clouds moving on the line of sight, produced in interactions between pre-existing cool circumstellar gas and high velocity gas ejected in the nova explosion. The optical region spectrum of V1280 Sco in 2009 is dominated by the continuum radiation and exhibits no forbidden line characterizing the nebular phase of typical novae. Permitted Fe II lines show doubly peaked emission profiles and some strong Fe II lines are accompanied by a blue shifted (about -255 km/s) absorption component. However, no high-velocity and narrow components corresponding to those of Na I could be detected in Fe II lines nor in the Balmer lines. The 255 km/s low velocity absorption component is most probably originating in the wind from the nova.

astro-ph.SR↗

arXiv2009

Spectroscopic Observations of the WZ Sge-Type Dwarf Nova GW Librae during the 2007 Superoutburst

We carried out an international spectroscopic observation campaign of the dwarf nova GW Librae (GW Lib) during the 2007 superoutburst. Our observation period covered the rising phase of the superoutburst, maximum, slowly decaying phase (plateau), and long fading tail after the rapid decline from the plateau. The spectral features dramatically changed during the observations. In the rising phase, only absorption lines of H$α$, H$β$, and H$γ$ were present. Around the maximum, the spectrum showed singly-peaked emission lines of H$α$, He I 5876, He I 6678, He II 4686, and C III/N III as well as absorption lines of Balmer components and He I. These emission lines significantly weakened in the latter part of the plateau phase. In the fading tail, all the Balmer lines and He I 6678 were in emission, as observed in quiescence. We find that the center of the H$α$ emission component was mostly stable over the whole orbital phase, being consistent with the low inclination of the system. Comparing with the observational results of WZ Sge during the 2001 superoutburst, the same type of stars as GW Lib seen with a high inclination angle, we interpret that the change of the H$α$ profile before the fading tail phase is attributed to a photoionized region formed at the outer edge of the accretion disk, irradiated from the white dwarf and inner disk.

astro-ph.SR↗

arXiv2009

Early Spectral Evolution of the Rapidly Expanding Type Ia SN 2006X

We present optical spectroscopic and photometric observations of Type Ia supernova (SN) 2006X from --10 to +91 days after the $B$-band maximum. This SN exhibits one of the highest expansion velocity ever published for SNe Ia. At premaximum phases, the spectra show strong and broad features of intermediate-mass elements such as Si, S, Ca, and Mg, while the O{\sc i}$λ$7773 line is weak. The extremely high velocities of Si{\sc ii} and S{\sc ii} lines and the weak O{\sc i} line suggest that an intense nucleosynthesis might take place in the outer layers, favoring a delayed detonation model. Interestingly, Si{\sc ii}$λ$5972 feature is quite shallow, resulting in an unusually low depth ratio of Si{\sc ii}$λ$5972 to $λ$6355, $\cal R$(Si{\sc ii}). The low $\cal R$(Si{\sc ii}) is usually interpreted as a high photospheric temperature. However, the weak Si{\sc iii}$λ$4560 line suggests a low temperature, in contradiction to the low $\cal R$(Si{\sc ii}). This could imply that the Si{\sc ii}$λ$5972 line might be contaminated by underlying emission. We propose that $\cal R$(Si{\sc ii}) may not be a good temperature indicator for rapidly expanding SNe Ia at premaximum phases.

astro-ph.HE↗

arXiv2008

Photometric and Spectroscopic Observations of V1280 Sco

Photometries of B, V, Rc, Ic, y, J, and Ks bands and low dispersion optical spectroscopic observations of Nova V1280 Sco, started soon after the outburst, are reported. We show that V1280 Sco is an Fe II nova and it is going through the historically slowest spectroscopic evolution. The rapid decline observed in the early phase was caused by formation of a dust shell. We estimate the abundances of CNO using the absorption lines on a spectrum at pre-maximum, and find over-abundances by [C/Fe] ~ 1.4, [N/Fe] > 2.0 and [O/Fe] ~ 1.1.

astro-ph↗