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71.
L. J. Hadfield S. D. Van Dyk P. W. Morris J. D. Smith A. P. Marston D. E. Peterson 《Monthly notices of the Royal Astronomical Society》2007,376(1):248-262
We report the discovery of 15 previously unknown Wolf–Rayet (WR) stars found as part of an infrared (IR) broad-band study of candidate WR stars in the Galaxy. We have derived an empirically based selection algorithm which has selected ∼5000 WR candidate stars located within the Galactic plane drawn from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (mid-IR) and Two-Micron All-Sky Survey (near-IR) catalogues. Spectroscopic follow-up of 184 of these reveals 11 nitrogen-rich (WN) and four carbon-rich (WC) WR stars. Early WC subtypes are absent from our sample and none shows evidence for circumstellar dust emission. Of the candidates which are not WR stars, ∼120 displayed hydrogen emission-line features in their spectra. Spectral features suggest that the majority of these are in fact B supergiants/hypergiants, ∼40 of these are identified Be/B[e] candidates.
Here, we present the optical spectra for six of the newly detected WR stars, and the near-IR spectra for the remaining nine of our sample. With a WR yield rate of ∼7 per cent and a massive star detection rate of ∼65 per cent, initial results suggest that this method is one of the most successful means for locating evolved, massive stars in the Galaxy. 相似文献
Here, we present the optical spectra for six of the newly detected WR stars, and the near-IR spectra for the remaining nine of our sample. With a WR yield rate of ∼7 per cent and a massive star detection rate of ∼65 per cent, initial results suggest that this method is one of the most successful means for locating evolved, massive stars in the Galaxy. 相似文献
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Rosemary A. Mardling 《Monthly notices of the Royal Astronomical Society》2007,382(4):1768-1790
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The results of the high-resolution long-term spectral monitoring of the Herbig Ae star HD 31648 in the regions of emission
Hα line, Na I D resonance lines and OI 7774 lines are presented.
We confirmed the conclusion, made in previous papers, that the spectral variability of the star in the region of Hα line have
a cyclic character. It is manifested itself as the changing of the equivalent width and intensity of Hα line of the time scale
of about 1200d.
It is shown, that the stellar wind is non-homogeneous and consists of several components, which are differed each other by
their velocities. They are observed as in the H line as in Na I D resonance lines. The component’s parameters are changed
during the cycle of stellar activity (in the maximum of activity the velocity and density of the wind are taken the largest
values and then they are gradually decreased).
The investigation of rapid variability of the He I 5876 line on the time scale of a few hours allows find the correlation
between the variability of the blue and the red wings of the line. It points at the connection between the accretion and the
outflows. Such connection, in particularly, is predicted by the modeling of the wind from young stars made in the frame of
the magneto-centrifugal model, the accordance of which for the HD 31648 was shown in the previous papers. In the present work
we confirmed this conclusion on the basis of the new data.
We found the weak variability of the stellar brightness (about 0.2m), which is agree with the spectral variability (the brightness
of the star becomes lower in the maximum of the activity). These changes are well explained by the process of the dust transfer
from CS disk by the stellar wind. This process is likely to be more effective in the maximum of activity.
An analysis of the variability of other spectral lines shows the agreement between the changing of the Hα line, the Na I D
resonance doublet lines and KI 7698 line. The weak connection between the He I 5876 and the Na I D lines is also found. Since
the formation regions of He I 5876 and Na I D lines are essentially different, we can conclude that the phenomena, responsible
for the observed cyclic variability, take place in a spacious region of the CS envelope.
We believe that the most plausible reason of found cyclic variability is the reconstruction of the inner structure of the
CS gas envelope, caused by the presence around the star a low mass companion or planet.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 565–588 (November 2007). 相似文献
77.
Daniel Malmberg Francesca De Angeli Melvyn B. Davies Ross P. Church Dougal Mackey Mark I. Wilkinson 《Monthly notices of the Royal Astronomical Society》2007,378(3):1207-1216
The stars that populate the solar neighbourhood were formed in stellar clusters. Through N -body simulations of these clusters, we measure the rate of close encounters between stars. By monitoring the interaction histories of each star, we investigate the singleton fraction in the solar neighbourhood. A singleton is a star which formed as a single star, has never experienced any close encounters with other stars or binaries, or undergone an exchange encounter with a binary. We find that, of the stars which formed as single stars, a significant fraction is not singletons once the clusters have dispersed. If some of these stars had planetary systems, with properties similar to those of the Solar System, the planets' orbits may have been perturbed by the effects of close encounters with other stars or the effects of a companion star within a binary. Such perturbations can lead to strong planet–planet interactions which eject several planets, leaving the remaining planets on eccentric orbits. Some of the single stars exchange into binaries. Most of these binaries are broken up via subsequent interactions within the cluster, but some remain intact beyond the lifetime of the cluster. The properties of these binaries are similar to those of the observed binary systems containing extrasolar planets. Thus, dynamical processes in young stellar clusters will alter significantly any population of Solar System-like planetary systems. In addition, beginning with a population of planetary systems exactly resembling the Solar System around single stars, dynamical encounters in young stellar clusters may produce at least some of the extrasolar planetary systems observed in the solar neighbourhood. 相似文献
78.
Roland Walter 《Astrophysics and Space Science》2007,309(1-4):5-9
INTEGRAL is operational since more than three years and producing high quality data that allows to detect fainter new hard
X-ray sources. The new sources, identified until now, are mostly active galactic nuclei and absorbed or transient high mass
X-ray binaries. TeV emission could be expected from the new high mass X-ray binaries accreting dense clumps of stellar wind.
INTEGRAL sources with TeV counterparts are discussed.
Based on observations with INTEGRAL, an ESA project with instruments and science data centre funded by ESA member states (especially
the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation
of Russia and the USA. 相似文献
79.
80.