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We present first observations of Mira stars obtained at the Very Large Telescope Interferometer (VLTI) at 2 microns, equipped
with the VINCI instrument, using different baselines with both the test siderostats and the 8.2 m unit telescopes. These observations,
collected in the course of the VLTI commissining program, have targeted so far about sixty cool giant stars. In this talk,
we list and describe the measurements obtained for 14 Mira stars, many of them representing first-time determinations of the
visibility. In particular, we devote special attention to a study of Mira itself, for which very accurate determinations of
the visibility at several baseline lenghts and orientations could be obtained. We find that a two-component model is more
consistent with the data than a single stellar disc. Further observations are needed for a better understanding of this source.
The VLTI will constitute an ideal instrument for such studies in the future. In particular it will permit detailed investigations
of southern AGB stars, such as accurate measurements of surface structureparameters (diameters, diameter variations, asymmetries,
center-to-limbvariations, special features like hot spots) and of circumstellar envelopes.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Near infrared measurements in the J, H and K bands have been carried out for a number of symbiotic stars with the 1.5 m telescope
at the Rothney Astrophysical Observatory (RAO). A comparison with the earlier observations shows that the S-type symbiotic
stars do not have any significant variation in the infrared flux over the past five years. However a small variation ∼ 0.3
magnitude in the infrared flux has been detected for CH Cygni. The observations of HM Sagittae show large decreases in the
infrared flux compared to the previous measurements. The variability in the infrared fluxes of both these objects could be
attributed to a variation in the temperature due to the cooling of the dust shell. The variability observed for V1016 Cygni
is found consistent with the previous measurements. 相似文献
3.
俞志尧 《中国天文和天体物理学报》1989,(1)
许多Mira变星具有轴对称转动的膨胀拱星包层。因此研究有轴对称转动的膨胀拱星包层的速度流场是十分必要的。我们研究了Mira变星的有轴对称转动的膨胀的拱星包层的速度流场,得到了它的严格形式解。所得到的结果与观测给出的事实是相一致的。最后,还讨论了恒星的质量损失率。 相似文献
4.
The absolute K-band magnitude determined for the object FBS 0137+400 is typical for Asymptotic Giant Branch (AGB) carbon stars. The large J - K color index as well as large amplitude variability (K > 0.4) and the presence of H in the emission indicate also that this star is a mass-losing long-period Carbon Mira variable with thick circumstellar shell. The IRAS LRS spectrum indicates the presence of a dust shell surrounding this object. Monitoring of the K-band magnitude is necessary for the determination of the pulsation period of FBS 0137+400. 相似文献
5.
Guo-Liang Lü 《中国天文和天体物理学报》2007,7(1):101-110
1 INTRODUCTION Symbiotic stars (SSs) are interacting binaries consisting of a cool giant, a hot compact companion and an H II region (Berman 1932; Boyarchuk 1967; Boyarchuk 1968). The cool component is a red giant (RG) that belongs either to the first gia… 相似文献
7.
Anodonta cygnea is a freshwater clam, belonging to the Unionidae family, which can be found in rivers and lagoons all over Europe and Northern America. As they appear as important case studies for ecological damage assessments, the various species of the Unionidae family have been submitted to a sort of recent studies on their chromosomal or cytogenetic status. In this study we confirmed the diploid chromosome number of 2n = 38 for this species, and established for the first time the karyotype, which comprised six metacentric, 12 submetacentric and one subtelocentric chromosome pairs. We also found a high percentage of cells with an abnormal number of chromosomes. Considering that karyotype disturbances in Unionids have been previously related with exposure to chemicals, either natural or produced by human activity, we determined the aneuploidy index for our population. The aneuploidy index is an excellent marker for pollutant presence/effect. The animals acclimatized in tap water and in natural water from the lake where the individuals were collected showed different levels of aneuploidy. The higher values were found in tap water. Chromosome analysis techniques seem a suitable tool to study the impact of contaminants referred above, and making A. cygnea a suitable organism for assessment of an eugenic damage in aquatic systems. On the other hand, our results also point out to the importance of doing the acclimatizing process of the collected animals in their own natural water. 相似文献
8.
C. Travaglio S. Randich D. Galli C. Abia J. Lattanzio 《Astrophysics and Space Science》2002,281(1-2):219-220
Different stellar sources may have contributed to the 7Li enrichmentof the Galaxy: type-II supernovae, novae, and AGB stars. In the latter case, the interplay between the Hot Bottom
Burning (HBB) process (via the Cameron-Fowler mechanism) and a very high mass-loss rate before the evolution off the AGB (the
so-called ‘superwind’ phase), can lead to a significant production of 7Li from low- and intermediate-mass AGB stars (Travaglio et al., 2001). We have now undertaken an observational campaign aimed
at constraining our stellar and Galactic models, with a twofold goal: (i) to assemble a compilation of high-resolution spectra of Galactic, unevolved (i.e. dwarfs), warm(spectral type F) stars,
in a selected metallicity range (-1.0 ≤>[Fe/H] ≤ -0.3), using the ESO 1.5m telescope and the FEROS spectrograph; (ii) to carry out a Li survey among a sample of selected AGB stars, to investigate the possible correlation between7Li abundance (when detected) and mass-loss rate.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
9.
Very red optical and IR-color indices indicate the presence of a dense circumstellar shell around object FBS 2213+421. The
estimated total mass-loss rate is typical for dust-enshrouded oxygen-rich Asymptotic Giant Branch (AGB) Long-Period Mira-type
variables. K-band monitoring is necessary to determine the pulsation period, the absolute bolometric luminosity, and the distance
to this object.
Published in Astrofizika, Vol. 49, No. 1, pp. 91–96 (February 2006). 相似文献
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