共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
R. & R. Griffin 《Journal of Astrophysics and Astronomy》1986,7(3):195-223
Composite-spectrum binary stars generally consist of a late-type giant and a main-sequence star of type A or B. Their spectra
are therefore rather confusing; but by a technique of digital subtraction of the spectra of appropriate single late-type giants,
composite spectra can be split into their individual components. In favourable cases the radial velocities of both components
can be measured and the mass ratio determined. The procedures are illustrated by reference to HR 6902, a fifth-magnitude composite-spectrum
binary. Its components are shown to have spectral types of G9 II and B8 V, with a mass ratio of 1.31, and its orbit is determined.
There is some evidence that the system shows eclipses. If it does, the masses of the components are 3.9 and 3.0M⊙ respectively, and HR 6902 becomes the sixth known member of the important class ofζ Aur binaries. 相似文献
3.
R. E. M. Griffin † R. F. Griffin † 《Monthly notices of the Royal Astronomical Society》2009,394(3):1393-1408
We analyse 81 optical spectra of the composite-spectrum binary HD 216572, and show that the primary is a cool giant of type G8 III while the secondary is a double-lined binary consisting of two nearly identical B9 dwarfs in a 1.18-d orbit. The inner system undergoes partial eclipses, whose photometry we model to derive the physical parameters of both secondary stars. The outer system does not eclipse. We isolate the combined spectrum of the secondary by spectral subtraction, and from 48 separate radial-velocity measurements of both secondary components we obtain a triple-lined orbit solution from which we determine the individual masses of all three stars and the inclinations of both the inner and the outer orbits. The period of the outer system is 55 d, which is surprisingly short for a giant star, and our detection of small but non-negligible amounts of variable chromospheric emission in the Ca ii K line is not unlike that detected in other systems with comparably short periods. The secondary components are in a circular orbit and are rotating at about 95 ± 10 km s−1 ; although their surface-to-surface separation is only 4 R⊙ the stars are not noticeably distorted geometrically by such close proximity. All three stars appear to be in synchronous rotation in their respective orbits. We derive fairly accurate Hertzsprung–Russell diagram positions for all three stars and compare them to evolutionary tracks calculated for the respective stellar masses, but cannot reconcile the age of the cool giant with that of the B stars. 相似文献
4.
N. T. Kaltcheva 《Astrophysics and Space Science》1993,206(1):103-110
Photographic intermediate banduvb observations of RGB and some AGB stars in 7 × 7 arcmin fields centered on the globular clusters M 15 and NGC 6712 are obtained. The photometric data is not fully reduced to the standard system but it is converted in an unique instrumental system. The photometry confirms the existence of the gaps in the giant branch of M 15. For NGC 6712 the Stromgren colors show a bimodal distribution and point at a bimodal carbon abundance for the bright giants from the central part. The possibilities of theuvby system for a classification of RGB and AGB stars are briefly discussed. 相似文献
5.
As part of a long‐term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high‐precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial‐velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E (B –V) colour excesses were determined from combined B – V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities. The derived DDO metallicities range between values typical of moderately metal‐poor clusters ([Fe/H] = –0.19) to moderately metal‐rich ([Fe/H] = 0.25) ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
Millimetre observations of three southern carbon stars, IRAS 07454-7112, IRAS 15082-4808 and IRAS 15194-5115 detected 14 molecular species and some of their isotopomers. The12C/13C ratio was found to vary between sources. 相似文献
7.
A series of our and McAlisteret al.'s speckle observations of spectroscopic binaries show that certain fractions of them are triple systems. A typical configuration of those systems is that of two stars separated by about 0.1 AU with a third component in an orbit at a distance about 10 AU from the central stars. These results suggest that the third star was formed from the outer circumstellar envelope after forming the central double. 相似文献
8.
A total of 704 previously published photoelectricB colour observations of the multiple system HR 4560 are analyzed by means of the light curve models NDE (Popper and Etzel, 1981) and WINK (Wood, 1972) in an iterative procedure. As a result, we have found that componentC of the multiplpe system ADS 8347 is the most probable origin of the observed eclipses. Some relevant astrophysical parameters of the component stars which indicate a normal Main-Sequence binary star have also been estimated. 相似文献
9.
Preliminary results are given for seven Ap components of spectroscopic double stars in the B, V system. In all cases the amplitudes are smaller than 0.025 mag. For no system of these seven Ap stars there was found a light variation with the period of the orbit. 相似文献
10.
Jeremy Heyl † 《Monthly notices of the Royal Astronomical Society》2007,382(2):915-920
Recent observations of white dwarfs in globular clusters indicate that these stars may get a velocity kick during their time as giants. This velocity kick could originate naturally if the mass loss while on the asymptotic giant branch is slightly asymmetric. If white dwarfs get a kick comparable to the orbital velocity of the binary, the initial Runge–Lenz vector (eccentricity vector) of the orbit is damped to be replaced by a component pointing toward the cross-product of the initial angular momentum and the force. The final eccentricity may be of the order of unity and if the kick is sufficiently large, the system may be disrupted. These results may have important ramifications for the evolution of binary stars and planetary systems. 相似文献
11.
K. G. Strassmeier 《Solar physics》1994,152(1):314-314
Observations of rotational modulation of continuum brightness and photospheric and chromospheric spectral-line profiles of late-type stars indicate the presence of very inhomogeneous surface temperature distributions. We present three stellar examples (VY Ari, HR 7275, HU Vir) where time-series photometry is used to trace the evolution of spotted regions. Simultaneous spectroscopy and Doppler imaging for one of the three stars (HU Virgo, Fig. 1) makes it possible to compute the temperature distribution of the photosphere and the relative intensity distribution of parts of the chromosphere (from CaII K and H line profiles). The combination of time-series spot modeling and Doppler imaging enabled us to determine thesign and amount of differential surface rotation on HU Vir. We found a big, cool polar spot (see figure below) and a differential (surface) rotation law where higher-latitude regions rotate faster than lower-latitude regions (opposite to what we see on the Sun). Currently, this ensemble of techniques - time-series photometry and photospheric and chromospheric Doppler imaging - is only applicable to stars overactive by approximately a factor of 100 as compared to the active Sun, e.g. the evolved components in RS CVn-type binaries and some rapidly-rotating, single, pre-main sequence stars or giant stars. Stellar rotation is a fundamental parameter for (magnetic) activity. Starspots, or any other surface inhomogeneities, allow one to derive very precise stellar rotation rates and, if coupled with seismological observations of solar-type stars, could provide information on the internal angular momentum distribution in overactive late-type stars.To be published in Astronomy & Astrophysics. 相似文献
12.
From accurate radial‐velocity measurements covering 11 circuits of the orbit of the composite‐spectrum binary 45 Cnc, together with high‐resolution spectroscopy spanning nearly 3 circuits, we have (i) isolated cleanly the spectrum of the early‐type secondary, (ii) classified the component spectra as G8 III and A3 III, (iii) derived the first double‐lined orbit for the system and a mass ratio (M1/M2) of 1.035 ± 0.01, and (iv) extracted physical parameters for the component stars, deriving the masses and (log) luminosities of the G star and A star as 3.11 and 3.00 M⊙, and 2.34 and 2.28 L⊙, respectively, with corresponding uncertainties of ±0.10 M⊙ and ±0.09 L⊙. Since the mass ratio is close to unity, we argue that the more evolved component is unlikely to have been a red giant long enough to have made multiple ascents of the RGB, an argument that is supported somewhat by the rather high eccentricity of the orbit (e = 0.46) and the evolutionary time‐scales of the two components, but chiefly by the presence of significant Li I in the spectrum of the cool giant. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
A star will become brighter and brighter with stellar evolution, and the distance of its habitable zone will become larger
and larger. Some planets outside the habitable zone of a host star during the main sequence phase may enter the habitable
zone of the host star during other evolutionary phases. A terrestrial planet within the habitable zone of its host star is
generally thought to be suitable for the existence of life. Furthermore, a rocky moon around a giant planet may be also suitable
for life to survive, provided that the planet–moon system is within the habitable zone of its host star. Using Eggleton’s
code and the boundary flux of the habitable zone, we calculate the habitable zone of our Solar system after the main sequence
phase. It is found that Mars’ orbit and Jupiter’s orbit will enter the habitable zone of the Solar system during the subgiant
branch phase and the red giant branch phase, respectively. And the orbit of Saturn will enter the habitable zone of Solar
during the He-burning phase for about 137 million years. Life is unlikely at any time on Saturn, as it is a giant gaseous
planet. However, Titan, the rocky moon of Saturn, may be suitable for biological evolution and become another Earth during
that time. For low-mass stars, there are similar habitable zones during the He-burning phase as our Solar, because there are
similar core masses and luminosities for these stars during that phase. 相似文献
14.
H.C. Ferguson 《Astrophysics and Space Science》1999,267(1-4):263-272
The hot stellar component in elliptical galaxies offers clues to both stellar evolution and galaxy evolution. Current observations
suggest that extreme horizontal branch (EHB) stars dominate the far-UV emission from galaxies with the strongest "UV upturns,"
while post asymptotic giant branch (PAGB) stars are probably significant contributors for weaker galaxies. Spectra near the
Lyman limit indicate that a rather narrow range of temperature (and hence EHB star mass) is required. However, other arguments
suggest that most of the helium-burning stars in elliptical galaxies are in the red clump. The HB star mass distribution therefore appears
to be strongly bimodal. Such bimodality is qualitatively reproduced by two radically different stellar population models,
(those of Lee and Bressan et al., 1994), both of which require that the galaxies be very old. However, the Galactic open cluster NGC 6791 also contains EHB
stars and exhibits strong bimodality, indicating that old age may not necessarily be a requirement for the UV upturn phenomenon.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
M. M. Zakirov 《Kinematics and Physics of Celestial Bodies》2009,25(3):115-144
Eclipsing variables in visual binary and multiple stars are searched using data from GCVS, WDS, and CCDM catalogs. The list of 421 eclipsing variables is obtained. The masses of components of multiple systems from the list are estimated using the mass-luminosity relation for the main sequence stars. It is shown that, for 85% multiple systems from the list, the mass of visual components is smaller by a factor of 2 than the total mass of close binary systems. The distributions of orbital elements of visual binary systems are constructed and used for calculation of orbit semi-major axes for star from the list. The distributions of orbit semi-major axes and periods obtained from observations are approximated by Gaussian curves. The maxima of the curves correspond to a = 800 a.u. and P = 7600 years, respectively. The distribution of orbit semi-major axes larger than 800 a.u. is better described by Opik’s law; it is expected that this law describes the real a distribution in the region of small values as well. The frequency of eclipsing variables in multiple stars makes 12% of the total number of stars of this type in GCVS. 相似文献
16.
K. K. Ghosh 《Astrophysics and Space Science》1989,155(2):311-317
Rapid spectrophotometric observations of two Be stars were carried out on several nights between November 1984 and December 1985. During the interval of our observations we could not detect any ultra-rapid variations in the spectra of the studied stars except a few flare-like events. The flare-like event of HR 7403 was recorded only at H and that for HR 8762 (o And) was observed (two events) from H photometric observations. Time-scales of these emission events were around few minutes and the total energy liberated by the events were of the order of 1034 to 1037 ergs. 相似文献
17.
M. A. Fardal P. Guhathakurta A. Babul A. W. McConnachie 《Monthly notices of the Royal Astronomical Society》2007,380(1):15-32
Published maps of red giant stars in the halo region of M31 exhibit a giant stellar stream to the south of this galaxy, as well as a giant 'shelf' to the northeast of M31's centre. Using these maps, we find that there is a fainter shelf of comparable size on the western side as well. By choosing appropriate structural and orbital parameters for an accreting dwarf satellite within the accurate M31 potential model of Geehan et al., we produce a very similar structure in an N -body simulation. In this scenario, the tidal stream produced at pericentre of the satellite's orbit matches the observed southern stream, while the forward continuation of this tidal stream makes up two orbital loops, broadened into fan-like structures by successive pericentric passages; these loops correspond to the north-eastern and western shelves. The tidal debris from the satellite also reproduces a previously observed 'stream' of counterrotating planetary nebulae and a related stream seen in red giant stars. The debris pattern in our simulation resembles the shell systems detected around many elliptical galaxies, though this is the first identification of a shell system in a spiral galaxy and the first in any galaxy close enough to allow measurements of stellar velocities and relative distances. We discuss the physics of these partial shells, highlighting the role played by spatial and velocity caustics in the observations. We show that kinematic surveys of the tidal debris will provide a sensitive measurement of M31's halo potential, while quantifying the surface density of debris in the shelves will let us reconstruct the original mass and time of disruption of the progenitor satellite. 相似文献
18.
The orbital elements of three red‐giant single‐lined spectroscopic binaries, HR 1304, HR 1908 and HD 126947, are presented. They are obtained from observations made with two photoelectric spectrometers of CORAVEL type, the first located at the Observatoire de Haute‐Provence and the second at the Cambridge Observatories. HR 1304 and HR 1908 are known to be chromospherically active stars and to have high spatial velocities; HD 126947 is an intrinsic variable newly detected by Hipparcos. The three systems have long orbital periods: 1.9, 3.2 and 7.7 yr for HR 1304, HR 1908 and HD 126947, respectively. From the orbital elements that we determined and other data available in the literature, we deduce some information about the unseen companions and their separations with respect to the primaries. Finally we discuss the rotation–revolution synchronism and conclude that one star, HR 1908, may have reached the state of pseudo‐synchronism, despite of its long orbital period. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
The Hipparcos mission discovered a few dozen M giant stars with periods P shorter than 10 d. Similar stars may be found in other large data bases of new variables (e.g., OGLE). The three possible sources of the magnitude variations – pulsation, starspots and ellipsoidal deformation – are discussed in general terms. The parallaxes and V − I colour indices are used to calculate radii and temperatures for all M giant variables with P <100 d. Masses are estimated from the positions of the stars in a Hertzsprung–Russell (HR) diagram, using evolutionary tracks. Using these data, it is shown that starspots can be ruled out as a variability mechanism in almost all cases, and ellipsoidal variations in about half of the stars. Pulsation in very high-overtone modes appears to be the only viable explanation for the stars with P <10 d. Many of the stars may be multiperiodic. IRAS data are used to deduce information about reddening and circumstellar dust. The apparently low level of mass-loss, as well as the kinematics and the spatial distribution of the stars, indicates that they are from a relatively young (i.e., thin disc) giant star population. 相似文献
20.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1991,12(3):265-268
Photoelectric radial-velocity measurements show that HD 111068 is a spectroscopic binary with a period of 206 days. The primary star is probably about type K5 III; the secondary, only detected through the photometric compositeness of the system, may well be an F dwarf. The orbit is circular within observational uncertainty; it is near the upper limit of periods for which tidal circularization operates for giant stars. 相似文献