Search Publications
Seimei/KOOLS-IFU mapping of the gas and dust distributions in Galactic PNe: Unveiling the origin and evolution of the Galactic halo PN H4-1
Ueta, Toshiya; Otsuka, Masaaki; Tajitsu, Akito
H4-1 is a planetary nebula (PN) located in the Galactic halo, and is notably carbon-rich and one of the most metal-deficient PNe in the Milky Way. To unveil its progenitor evolution through accurate measurement of the gas mass, we conducted a comprehensive investigation of H4-1, using the newly obtained Seimei/KOOLS-IFU spectra and multiwavelength…
Near-Infrared Spectra of 21 Wolf-Rayet Stars: Wind Clumping and Mass-Loss Rates
Miyata, Takashi; Motohara, Kentaro; Nishimaki, Yuichirou +2 more
We present 0.9-2.4µm spectra of 21 galactic Wolf-Rayet (WR) stars that were obtained by using an echelle spectrograph attached to the 1.5m infrared telescope in Tokyo. The observed Wolf-Rayet stars contain 12WNE, 3WNL, and 6WC stars. The near-infrared continuum spectra can be fitted by the superposition of stellar blackbody radiation with a …
A NewModel for the Structure of the DACs and SACs Regions in the Oe and Be Stellar Atmospheres
Antoniou, A.; Danezis, E.; Lyratzi, E. +4 more
In this paper we present a new mathematical model for the density regions where a specific spectral line and its SACs/DACs are created in the Oe and Be stellar atmospheres. In the calculations of final spectral line function we consider that the main reasons of the line broadening are the rotation of the density regions creating the spectral line …
The Complex Structure of the Mg II λλ 2795.523, 2802.698 Å Regions of 64 Be Stars
Lyratzi, Evaggelia; Danezis, Emmanouel; Popovic, Luka C. +3 more
Here we consider the presence of absorption components shifted to the violet or red side of the main spectral line (satellite or discrete absorption components, i.e., SACs or DACs) in the regions of the Mg II resonance lines in Be stars as well as their kinematical characteristics. Namely, our objective is to check whether there exists a common ph…
The Be Star Gamma Cassiopeiae: X-Ray, Far-UV, and Optical Observations in Early 1989
Murakami, Toshio; Kawai, Nobuyuki; Matsuoka, Masaru +12 more
The state of gamma Cas in early 1989 is presented as the result of joint observations in the X-ray, far-UV, and optical regions. Particular attention has been paid to short- and long-term variations within these spectral ranges. In X-ray observations with the Ginga satellite we have found no specific periodic variabilities in the 64 to 13,000 s ra…
Spectroscopic Determinations of Stellar Parameters and Photospheric Helium Abundances for Alpha Cygni and Beta Orionis
Takeda, Yoichi
A detailed non-LTE analysis of neutral helium lines was carried out for two early A--late B supergiants alpha Cyg and beta Ori in order to obtain information concerning the abundance of helium in their photospheres, the key element for studying evolution-induced mixing in the envelope of such massive stars. To minimize the systematic errors caused…
X-ray spectrum of the BL Lacertae object PKS 2155-304.
Koyama, K.; Warwick, R. S.; Makishima, K. +4 more
The BL Lacertae object PKS 2155-304 was observed with Ginga for two days in May 1987. The 2-35 keV intensity showed a significant variability, the most rapid change being a 30 percent increase in 3 hr. The X-ray spectrum was described by a single power-law model with photon spectral index ranging between 2.7 and 2.9, but the power-law slope showed…
Analysis of the ultraviolet spectrum (2000 A to 3000 A) of Vega.
Sadakane, K.; Hirata, R.; Nishimura, M.
A high-dispersion spectrum of Vega between 2000 and 3000 A is analyzed. The continuum level is determined by searching for line-free windows, comparing the observed spectrum with a synthesized one. The damping constant of the Fe II lines arising from low-excitation levels is found to be very close to the classical value. The microturbulence parame…
Spectroscopic analysis of the suspected AM star 15 Vulpeculae.
Takeda, Y. -I.
The suspected Am star 15 Vul is characterized using the ATLAS-6 model-atmosphere program of Kurucz (1979) and spectrograms (resolution 10 and 4 A/mm) obtained with the coudespectrograph of the 1.88-m reflector at Okayama Astrophysical Observatory during September and October 1981; comparison stars are 28 And and 9 Aur. The data and calculated abun…
Radial velocity of HD 77581 (Vela X-1) in the period of 1972 - 1983.
Matsuoka, M.; Sadakane, K.; Jugaku, J.
The radial velocity of HD 77581 (Vela X-1 = 4U 0900-40) was derived from photospheric Fe Iv and Fe II lines observed by the International Ultraviolet Explorer (IUE) satellite in the period 1978-1983. No long-term variation in the radial velocity of 30 km/s was observed. It is shown that the absence of variation effectively rules out the possibilit…