Entity

Time filter

Source Type


Iijima T.,Astronomical Observatory of Padua
Astronomy and Astrophysics | Year: 2012

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 m V ≅ 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. © 2012 ESO. Source


Naito H.,Nagoya University | Mizoguchi S.,Sendai Astronomical Observatory | Arai A.,Kyoto Sangyo University | Tajitsu A.,Japan National Astronomical Observatory | And 9 more authors.
Astronomy and Astrophysics | Year: 2012

We present optical (B, V, R c, I c and y) and near-infrared (J, H, and K s) photometric and spectroscopic observations of a classical nova V1280 Scorpii for five years from 2007 to 2011. Our photometric observations show a declining event in optical bands shortly after the maximum light, which took about 250 days to recover. This event was most probably caused by dust formation. The event was accompanied by a short (∼30 days) re-brightening episode (∼2.5 mag in V), which suggests that there had been some re-ignition of the surface nuclear burning. After 2008, the y band observations show a very long plateau at around y = 10.5 for more than 1000 days until April 2011 (∼1500 days after the maximum light). The nova had taken a very long time (∼50 months) to enter the nebular phase, according to a clear detection of both [O III] 4959 and 5007 and is still continuing to generate the wind caused by H-burning. This finding suggests that historically V1280 Sco is evolving at its slowest ever measured rate. The interval from the maximum light (2007 February 16) to the beginning of the nebular phase is longer than any previously known slow novae: V723 Cas (18 months), RR Pic (10 months), or HR Del (8 months). It suggests that the mass of a white dwarf in the V1280 Sco system might be 0.6 M ⊙ or lower. The distance, based on our measurements of the expansion velocity combined with the directly measured size of the dust shell, is estimated to be 1.1 ± 0.5 kpc. © 2012 ESO. Source


Cavuoti S.,National institute for astrophysics | Brescia M.,National institute for astrophysics | Tortora C.,National institute for astrophysics | Longo G.,University of Naples Federico II | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We have estimated photometric redshifts (zphot) for more than 1.1 million galaxies of the public European Southern Observatory (ESO) Kilo-Degree Survey (KiDS) data release 2. KiDS is an optical wide-field imaging survey carried out with the Very Large Telescope (VLT) Survey Telescope (VST) and the OmegaCAM camera, which aims to tackle open questions in cosmology and galaxy evolution, such as the origin of dark energy and the channel of galaxy mass growth. We present a catalogue of photometric redshifts obtained using the Multi-Layer Perceptron with Quasi-Newton Algorithm (MLPQNA) model, provided within the framework of the DAta Mining and Exploration Web Application REsource (DAMEWARE). These photometric redshifts are based on a spectroscopic knowledge base that was obtained by merging spectroscopic data sets from the Galaxy and Mass Assembly (GAMA) data release 2 and the Sloan Digital Sky Survey III (SDSS-III) data release 9. The overall 1s uncertainty on Δz = (zspec - zphot)/(1 + zspec) is ~0.03, with a very small average bias of ~0.001, a normalized median absolute deviation of ~0.02 and a fraction of catastrophic outliers (|Δz| > 0.15) of ~0.4 per cent. © 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Iijima T.,Astronomical Observatory of Padua | Cassatella A.,National institute for astrophysics | Cassatella A.,Complutense University of Madrid
Astronomy and Astrophysics | Year: 2010

Spectral evolution of nova V838 Her 1991 was monitored at Asiago Astrophysical Observatory from 1991 March 31 to July 2. The spectra in the early decline stage showed emission lines of H I, He I, He II, N II, N III, C II, C III, C IV, Si II, [S III], [Ne III], and Fe II, where some identifications are different from those reported in the previous works. The emission lines of [Ne III] and carbon ions were unusually intense. New emission peaks appeared at the blue-ward edges of the emission lines of H I and He I about one week after maximum luminosity. It seems that a new clump of gas was ejected at that time along the line of sight towards us. The helium abundance is estimated at N(He) = 0.11 ± 0.01. © 2010 ESO. Source


Kubota K.,Kyoto University | Ueda Y.,Kyoto University | Kawai N.,Tokyo Institute of Technology | Kotani T.,Aoyama Gakuin University | And 8 more authors.
Publications of the Astronomical Society of Japan | Year: 2010

We report on results of the 2006 April multiwavelength campaign of SS 433, focusing on X-ray data observed with Suzaku at two orbital phases (in- and out-of-eclipse phases) and on simultaneous optical spectroscopic observa-tions. Analyzing the Fexxv Kα lines originating from the jets, we detected a rapid variability of the Doppler shifts, dz/dt ≈ 0.019/0.33 d-1, which is larger than those expected from the precession and/or nodding motion. This phenomenon probably corresponds to "jitter" motions observed for the first time in X-rays, for which significant variabilities in both the jet angle and the intrinsic speed are required. From time lags between optical Doppler curves and X-ray ones, we estimated a distance between the optical jets and the base to be ̃ (3-4) x 1014cm. Based on the radiatively cooling jet model, we determined that the innermost temperatures of the jets are T0 = 13 ±2 ke V for the out-of-eclipse phase and 16±3 ke V for the in-eclipse (the average of the blue and red jets) from the line intensity ratio of Fexxv Kα and FexxvI Kα. While the broad-band-continuum spectra over the 5-40 ke V band in eclipse is consistent with a multitemperature-bremsstrahlung emission expected from the jets and its reflection component from cold matter, the out-of-eclipse spectrum is harder man the jet emission with the base temperature determined above, implying the presence of an additional hard component. © 2010. Astronomical Society of Japan. Source

Discover hidden collaborations