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The results of a spectrophotometric study of 13 carbon stars in the wavelength range from 4000 Å to 6800 Å with 2.75 Å resolution are given. The observed energy distributions for these stars relative to the flux at λ0 = 5556 Å, represented in graphic form, were determined. Their color temperatures were determined from the [5710] ? [6680] color index. A dust shell is assumed to exist around U Cyg. The indices of the C2’ MS, and CaCl molecular bands and the D2,1 line were also determined. 相似文献
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Mahendra Singh 《Astrophysics and Space Science》1986,120(1):133-138
The continuum energy distribution of six Be stars, namely 25 Cyg, 31 Peg, HR 8758, 14 Lac, 12 Vul, and Psc, in the wavelength region 3200–7800 Å, are presented. Comparing the observed energy distributions with those of theoretical models given by Kurucz (1979), their effective temperatures are determined.A near-infrared excess emission at wavelengths above 6000 Å is seen in most of the stars. 相似文献
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Manjari Bagchi Subharthi Ray Mira Dey † Jishnu Dey 《Monthly notices of the Royal Astronomical Society》2006,368(2):971-975
From recent reports on terrestrial heavy ion collision experiments it appears that one may not obtain information about the existence of asymptotic freedom (AF) and chiral symmetry restoration (CSR) for quarks of QCD at high density. This information may still be obtained from compact stars – if they are made up of strange quark matter (SQM).
Very high gravitational redshift lines (GRL), seen from some compact stars, seem to suggest high ratios of mass and radius ( M / R ) for them. This is suggestive of strange stars (SS) and can in fact be fitted very well with SQM equation of state (EOS) deduced with built in AF and CSR. In some other stars broad absorption bands (BAB) appear at about ∼0.3 keV and multiples thereof, that may fit in very well with resonance with harmonic compressional breathing mode frequencies of these SS. Emission at these frequencies are also observed in six stars.
If these two features of large GRL and BAB were observed together in a single star, it would strengthen the possibility for the existence of SS in nature and would vindicate the current dogma of AF and CSR that we believe in QCD. Recently, in 4U 1700 − 24 , both features appear to be detected, which may well be interpreted as observation of SS – although the group that analyzed the data did not observe this possibility. We predict that if the shifted lines, that has been observed, are from neon with GRL shift z = 0.4 – then the compact object emitting it is a SS of mass 1.2 M⊙ and radius 7 km. In addition the fit to the spectrum leaves a residual with broad dips at 0.35 keV and multiples thereof, as in 1E 1207 − 5209 which is again suggestive of SS. 相似文献
Very high gravitational redshift lines (GRL), seen from some compact stars, seem to suggest high ratios of mass and radius ( M / R ) for them. This is suggestive of strange stars (SS) and can in fact be fitted very well with SQM equation of state (EOS) deduced with built in AF and CSR. In some other stars broad absorption bands (BAB) appear at about ∼0.3 keV and multiples thereof, that may fit in very well with resonance with harmonic compressional breathing mode frequencies of these SS. Emission at these frequencies are also observed in six stars.
If these two features of large GRL and BAB were observed together in a single star, it would strengthen the possibility for the existence of SS in nature and would vindicate the current dogma of AF and CSR that we believe in QCD. Recently, in 4U 1700 − 24 , both features appear to be detected, which may well be interpreted as observation of SS – although the group that analyzed the data did not observe this possibility. We predict that if the shifted lines, that has been observed, are from neon with GRL shift z = 0.4 – then the compact object emitting it is a SS of mass 1.2 M
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P. S. Goraya 《Astrophysics and Space Science》1985,112(1):1-11
We present new measurements of the distribution of energy in the continuum for eight Be stars in the optical region (3200-7600 Å). The effective temperatures of these stars have been estimated from their observed fluxes. It is found that, in general, pole-on stars show near-infrared excess emission. It is interesting to note that the Balmer jumps for stars having an infrared excess are systematically smaller than for those lacking the infrared excess.Variability of ultraviolet and infrared excess emissions in these stars has been discussed. The stars 59 Cyg, 66 Cyg, 28 CMa, and 27 CMa show large variations in their continuum at ultraviolet (UV) and infrared (IR) regions. 相似文献
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Takashi Tsuji 《Journal of Astrophysics and Astronomy》1981,2(1):95-113
It is shown that the infrared flux method for determining stellar effective temperatures (Blackwell and Shallis 1977; Blackwell,
Petford and Shallis 1980) can be applied to cool carbon stars. Although the spectra of cool carbon stars are highly line blanketed,
the spectral region between 3 and 4 μm (L-band in the infrared photometry system) is found to be relatively free from strong
line absorption. The ratioR
L of bolometric flux toL flux can then be used as a measure of effective temperature. On the basis of the predicted line-blanketed flux based on model
atmospheres, with an empirical correction for the effect of 3 μm absorption due to polyatomic species (HCN, C2H2), it is shown thatR
L is roughly proportional to T3
eff. The high sensitivity ofR
L to Teff makes it a very good measure of effective temperature, and the usual difficulty due to differential line blanketing effect
in the analyses of photometric indices of cool carbon stars can be minimized.
It is found that the majority of N-type carbon stars with small variability (SRb and Lb variables) are confined to the effective
temperature range between 2400 and 3200 K, in contrast to M-giant stars (M0 III - M6 III, including SRb and Lb variables)
that are confined to the effective temperature range between 3200 and 3900 K. The effective temperatures based on the infrared
flux method show good agreement with those derived directly from angular diameter measurements of 5 carbon stars. On the basis
of the new effective temperature scale for carbon stars, it is shown that the well known C-classification does not represent
a temperature sequence. On the other hand, colour temperatures based on various photometric indices all show good correlations
with our derived effective temperatures.
An erratum to this article is available at . 相似文献
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A continued search for emission objects in three new fields within the association Cyg OB7 yielded eight new emission stars
in one of these fields. No emission stars were detected in the other two fields, apparently because we have come to the boundary
of the T association on this side. Two UV Cet-type flare stars have been detected in this region for the first time. 相似文献
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K. S. Gigoyan D. Engels N. Mauron V. V. Hambaryan C. Rossi R. Gualandi 《Astrophysics》2008,51(2):209-217
We present new observations of seven late-type stars previously discovered in the First Byurakan Survey (FBS). These observations
prove that they belong to the family of carbon (C) stars. Seventy-nine similar FBS C stars were previously known. The seven
objects under analysis were presented in the FBS lists as M or C star candidates. Among the seven objects, six objects are
confirmed by low-resolution spectra of the Hamburg Quasar Objective-Prism Survey. We also present for five of them moderate-resolution
spectra obtained at optical wavelengths with a spectrograph equipped with a CCD detector. Three objects can be classified
as N-type C stars. One object is an early CH-type C star. Most likely, the star FBS 1339+117 belongs to the group of carbon
dwarfs. We estimate distances of these seven new C stars either by using their red-band magnitudes, or by using their near-infrared
2MASS J-KS color and KS-band magnitudes.
Published in Astrofizika, Vol. 51, No. 2, pp. 255–265 (May 2008). 相似文献
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Takashi Tsuji 《Journal of Astrophysics and Astronomy》1981,2(3):253-276
On the basis of the effective temperature scale proposed previously for cool carbon stars (Paper I), other intrinsic properties
of them are examined in detail. It is shown that the major spectroscopic properties of cool carbon stars, including those
of molecular bands due to polyatomic species (SiC2, HCN, C2H2
etc.), can most consistently be understood on the basis of our new effective temperature scale and the theoretical prediction of
chemical equilibrium. Various photometric indices of cool carbon stars also appear to be well correlated with the new effective
temperatures. Furthermore, as effective temperatures of some 30 carbon stars are now obtained, the calibration of any photometric
index is straightforward, and some examples of such a calibration are given. In general, colour index-effective temperature
calibrations for carbon stars are quite different from those for K-M giant stars. It is found that the intrinsic (R —I)0 colour is nearly the same for N-irregular variables in spite of a considerable spread in effective temperatures, and this
fact is used to estimate the interstellar reddening of carbon stars.
An observational HR diagram of red giant stars, including carbon stars as well as K-M giant stars, is obtained on the basis
of our colour index-effective temperature calibrations and the best estimations of luminosities. It is shown that carbon stars
and M giant stars are sharply divided in the HR diagram by a nearly vertical line at aboutT
eff = 3200 K (logT
eff = 3.50) and the carbon stars occupy the upper right region of M giant stars (except for some high luminosity, high temperature
J-type stars in the Magellanic Clouds; also Mira variables are not considered). Such an observational HR diagram of red giant
stars shows rather a poor agreement with the current stellar evolution models. Especially, a more efficient mixing process
in red giant stars, as compared with those ever proposed, is required to explain the formation of carbon stars. 相似文献