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1.
Published photometry in Sgri is used to derive the period-luminosity relation for Mira variables in yellow and in blue light. The observed dispersion about the adopted relation is comparable to that of RR Lyrae-stars around their mean luminosity. This suggests that the Mira star period-luminosity relation has a relatively small dispersion and is, therefore, a powerful tool for astronomical distance determination. The calibration of the Mira period-luminosity relation indicates that Glass and Feast may have overestimated the absorption in the direction of Sgri and NGC 6522. 相似文献
2.
This paper presents observations of SiO maser emission from 161 Mira variables distributed over a wide range of intrinsic
parameters like spectral type, bolometric magnitude and amplitude of pulsation. The observations were made at 86.243 GHz,
using the 10-4 m millimeter-wave telescope of the Raman Research Institute at Bangalore, India. These are the first observations
made using this telescope. From these observations, we have established that the maser emission is restricted to Miras having
mean spectral types between M6 and M10. The infrared period-luminosity relation for Mira variables is used to calculate their
distances and hence estimate their maser luminosities from the observed fluxes. The maser luminosity is found to be correlated
with the bolometric magnitude of the Mira variable. On an H-R diagram, the masing Mira variables are shown to lie in a region
distinct from that for the non-masing ones. 相似文献
3.
Chun-Hua Zhu Chao-Zheng Zha Department of Physics Xinjiang University Urumqi 《中国天文和天体物理学报》2005,5(4):419-425
By means of a population synthesis code, we investigate the Mira variables. Their birth rate (over 0.65 yr-1) and their number (-130000) in the Galaxy are estimated. For all possible Mira variables, ranges of their initial masses, pulsating periods, mass losses and lifetimes are given. We check our model with the observed Mira variables near the Sun and our results prove to be valid. 相似文献
4.
C. Ye?ilyaprak S.K. YerliB.B. Güçsav N. Aksaker E. Dikicio?luM. Helvac? D. ÇokerM.E. Ayd?n B. DinçelN. Uzun 《New Astronomy》2012,17(5):504-513
We have studied the long-term variations of Mira type variables observed with Robotic Optical Transient Search Experiment telescope (ROTSE-IIId) between 2004 and 2009 located at TÜB?TAK National Observatory (TUG) in Antalya, Turkey. The actual pulsation periods, variability amplitudes, epochs of maximums and light curves of selected 70 Mira type variables already defined in the SIMBAD database were investigated. In these variables, 17 periods are identified for the first time. 相似文献
5.
T. R. Bedding Albert A. Zijlstra A. Jones & G. Foster 《Monthly notices of the Royal Astronomical Society》1998,301(4):1073-1082
We discuss visual observations spanning nearly 70 years of the nearby semiregular variable R Doradus. Using wavelet analysis, we show that the star switches back and forth between two pulsation modes having periods of 332 d and about 175 d, the latter with much smaller amplitude. Comparison with model calculations suggests that the two modes are the first and third radial overtone, with the physical diameter of the star making fundamental-mode pulsation unlikely. The mode changes occur on a time-scale of about 1000 d, which is too rapid to be related to a change in the overall thermal structure of the star and may instead be related to weak chaos. The Hipparcos distance to R Dor is 62.4 ± 2.8 pc which, taken with its dominant 332-d period, places it exactly on the period–luminosity (P–L) relation of Miras in the Large Magellanic Cloud. Our results imply first-overtone pulsation for all Miras which fall on the P–L relation. We argue that semiregular variables with long periods may largely be a subset of Miras and should be included in studies of Mira behaviour. The semiregulars may contain the immediate evolutionary Mira progenitors, or stars may alternate between periods of semiregular and Mira behaviour. 相似文献
6.
Current periods and new epochs are presented for 40 very poorly studied Mira variables. The average periods of these stars were also determined using earlier epochs found in the literature. The current period differs significantly from the average period value in 4 cases. The importance of the period variation study of Mira stars is also briefly discussed. 相似文献
7.
A list of comparatively faint late M and Carbon type stars detected on the Digitized First Byurakan Survey (DFBS) spectral
plates in the zone with +45° ≤ δ ≤ +49° covering 684 deg2 is presented. Accurate DSS2 positions, USNO-B1.0 B and R magnitudes, 2MASS near-infrared J, H, and Ks photometry, IRAS PSC/FSC fluxes (when available), approximate spectral types, and luminosity class estimates are given for
72 objects. Nine of them are newly confirmed carbon stars and 63 are M-type stars. For seven Mira variables with known pulsation
periods we determined distances of 2 ÷ 8 kpc using a period-luminosity relation. Distances of 17 ÷ 115 pc for five M dwarfs,
classified on the base of detected proper motions, were estimated using a color-luminosity relation. The object FBS 0845+466
is classified as a candidate carbon dwarf with distance r ≈ 72 pc. 相似文献
8.
H. V. Abrahamyan 《Astrophysics》2003,46(4):455-464
BVIJHK period-luminosity relations for classical cepheids in the galaxy and magellanic clouds which pulsate in the fundamental mode are obtained on the basis of four samples. The period-luminosity relations for the BVI bands obtained here are more accurate than the analogous relations existing up to the present. Period-luminosity relations in terms of W functions are also obtained for these samples and have the same accuracy as the currently existing analogous relations. 相似文献
9.
《Chinese Astronomy and Astrophysics》1986,10(1):62-66
Results of infrared photometry in J, H, and K bands for 24 stellar maser sources are given. On the colour-colour diagram, nearly all the Mira variable masers are closer to the black body line than the normal M giants, which also have brighter H magnitudes. The main reason for the location of the Mira masers is the strong H2O absorption bands at 1.4 and 1.9 μm. The dust envelopes for maser sources have temperature of 600 – 700 K, so the radiation shorter than 3μm may be expected to be close to black body. The physical conditions in M supergiants are such that a peak intensity near 1 – 6 μm (the H band) may be expected.Maser-associated Mira variables have longer periods and redder colours than normal Mira stars and M giants, suggesting greater amount of mass ejection from the central stars. 相似文献
10.
M. A. T. Groenewegen P. A. Whitelock C. H. Smith F. Kerschbaum 《Astrophysics and Space Science》1997,251(1-2):89-96
The spectral energy distributions and mid-infrared spectra of 44 carbon Mira variables are fitted using a dust radiative transfer
model. The periods cover the entire range observed for carbon Miras. The luminosities are calculated from a period-luminosity
relation. Parameters derived are the distance, the dust mass loss rate and the ratio of silicon carbide to amorphous carbon
dust. The total mass loss rate is derived from a modified relation between the photon momentum (L/c) and the momentum in the
wind (M υ∞). Mass loss rates between 1 × 10−8 and 4 × 10−5 M⊙ yr−1 are found. We find good correlations between mass loss rate and pulsation period, and mass loss rate and luminosity. The
dust-to-gas ratio appears to be almost constant up to periods of about 500 days, corresponding to about 7900 L⊙, and then to increase by a factor of 5 towards longer periods and higher luminosities. A comparison is made with radiation-hydrodynamical
calculations including dust formation. The mass loss rates predicted by these models are consistent with those derived in
this paper. The main discrepancy is in the predicted expansion velocities for models with luminosities below ∼5000 L⊙. The radiation-hydrodynamical calculations predict expansion velocities which are significantly too large. This is related
to the fact that these models need to be calculated with a large C/O ratio to get an outflow in the first place. This is contrary
to observations. It indicates that a principle physical ingredient in these radiation-hydrodynamical calculations is still
missing. Possibly the winds are ‘clumpy’ which may lead to dust formation on a local scale, or there is an additional outwards
directed force, possibly radiation pressure on molecules.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
11.
Ts. G. Tsvetkov 《Astrophysics and Space Science》1985,117(1):137-149
On the basis of observational data (Breger, 1979), a radial pulsation mode of 83 Delta Scuti stars is estimated in two ways. These stars can pulsate in four lowest modes—F, 1H, 2H, 3H— and, perhaps, in 4H and 5H. Our earlier suggestion—that the apparent heterogeneity of these objects in both the period-luminosity plane and the period-frequency distribution may be explained by means of pulsations in various modes—is confirmed. Semi-empirical period-luminosity relations for the four lowest modes are derived and the semi-empirical period ratios are compared with the theoretical ones. 相似文献
12.
Both linear and nonlinear calculations of the 331 day, long period variable star Mira have been undertaken to see what radial pulsation mode is naturally selected. Models are similar to those considered in the linear nonadiabatic stellar pulsation study of Ostlie and Cox (1986). Models are considered with masses near one solar mass, luminosities between 4000 and 5000 solar luminosities, and effective temperatures of approximately 3000 K. These models have fundamental mode periods that closely match the pulsation period of Mira. The equation of state for the stellar material is given by the Stellingwerf (1975ab) procedure, and the opacity is obtained from a fit by Cahn that matches the low temperature molecular absorption data for the Population I Ross-Aller 1 mixture calculated from the Los Alamos Astrophysical Opacity Library. For the linear study, the Cox, Brownlee, and Eilers (1966) approximation is used for the linear theory variation of the convection luminosity. For the nonlinear work, the method described by Ostlie (1990) and Cox (1990) is followed. Results showing internal details of the radial fundamental and first overtone modes behavior in linear theory are presented. Preliminary radial fundamental mode nonlinear calculations are discussed. The very tentative conclusion is that neither the fundamental or first overtone mode is excluded from being the actual observed one. 相似文献
13.
Michael W. Feast Patricia A. Whitelock 《Monthly notices of the Royal Astronomical Society》2000,317(2):460-487
The space motions of Mira variables are derived from radial velocities, Hipparcos proper motions and a period–luminosity relation. The previously known dependence of Mira kinematics on the period of pulsation is confirmed and refined. In addition, it is found that Miras with periods in the range 145–200 d in the general Solar neighbourhood have a net radial outward motion from the Galactic Centre of 75±18 km s−1 . This, together with a lag behind the circular velocity of Galactic rotation of 98±19 km s−1 , is interpreted as evidence for an elongation of their orbits, with their major axes aligned at an angle of ∼17° with the Sun–Galactic Centre line, towards positive Galactic longitudes. This concentration seems to be a continuation to the Solar circle and beyond of the bar-like structure of the Galactic bulge, with the orbits of some local Miras probably penetrating into the bulge. These conclusions are not sensitive to the distance scale adopted. A further analysis is given of the short-period (SP) red group of Miras discussed in companion papers in this series. In Appendix A the mean radial velocities and other data for 842 oxygen-rich Mira-like variables are tabulated. These velocities were derived from published optical and radio observations. 相似文献
14.
Patricia Whitelock Michael Feast 《Monthly notices of the Royal Astronomical Society》2000,319(3):759-770
This paper concerns the calibration of the K period–luminosity relation for Mira variables using Hipparcos parallaxes. K magnitudes are available for 255 Mira-like variables which were observed by Hipparcos . Period–luminosity zero-points are evaluated for various subgroups of data. The best solution for oxygen-rich Miras, which uses 180 stars, omitting the short-period red group (which had different kinematics from the short-period blue stars) and the low-amplitude variables, provides a zero-point of which implies a distance modulus for the Large Magellanic Cloud of or perhaps slightly greater if a metallicity correction is required, in good agreement with the value derived from Cepheids. The zero-point of the period–luminosity relation for carbon stars is briefly discussed.
Linear diameters are derived for red variables with measured angular diameters and parallaxes, and are used to examine the long-standing question of the pulsation mode(s) of these stars. Evidence is presented to suggest that most of them are pulsating in the same mode and, if published model atmospheres are correct, this is probably the first overtone. Some discussion is given of sequences in the period–luminosity and period–colour diagrams and their bearing on the pulsation mode problem. 相似文献
Linear diameters are derived for red variables with measured angular diameters and parallaxes, and are used to examine the long-standing question of the pulsation mode(s) of these stars. Evidence is presented to suggest that most of them are pulsating in the same mode and, if published model atmospheres are correct, this is probably the first overtone. Some discussion is given of sequences in the period–luminosity and period–colour diagrams and their bearing on the pulsation mode problem. 相似文献
15.
Mira变星拱星包层的温度结构 总被引:1,自引:0,他引:1
俞志尧 《中国天文和天体物理学报》1988,(3)
我们研究了Mira变星拱星包层的温度结构。假设Mira变星拱星包层由气体和尘埃颗粒两种成分组成,气体为理想气体,并有稳定的和球对称的径向向外流动;我们研究了拱星包层气体的加热机制和致冷原因,根据拱星包层气体的质量、动量和能量守恒方程及多方膨胀过程方程,通过计算得到了拱星包层气体温度所满足的温度方程。这个温度方程对于Mira变星拱星包层有普遍意义。对于典型的Mira变星我们进行了数值计算,得到了温度曲线。与观测得到的温度曲线比较表明,理论模型与观测事实相一致。 相似文献
16.
We discuss our JHKLM photometry for nine carbon Mira stars, eighteen carbon semiregular variables, and two oxygen Mira stars. For fourteen carbon stars, we present and analyze their infrared light and color curves. For all of the observed objects, we have estimated the optical depths of the circumstellar dust envelopes, the angular diameters of the stars, and their temperatures. 相似文献
17.
N. D. Melikian 《Astrophysics》1999,42(4):408-418
Based on an analysis of light curves of 223 long-period variables of the Mira Ceti type, recorded using the HIPPARCOS space
telescope, it is shown that all the light curves of these stars can be divided by outward form into two groups: stars exhibiting
simple light curves of sinusoidal shape and stars with complicated light curves, with hump-shaped formations on the ascending
branch of the curve. Some observational parameters of the investigated stars display a tendency to separation into groups
of stars with complicated and simple light curves. Stars with complicated light curves have longer periods, they are brighter
in absolute bolometric magnitude, and there is a greater probability of detecting polarization in their light.
Translated from Astrofizika, Vol. 42, No. 4, pp. 541–554, October–December, 1999. 相似文献
18.
We have investigated the IRAS LRS spectra of a sample of 56 Semiregular (SR) variables with silicate dust features (class 2 n) and existing near infrared photometry. We compare our results to similar work that has been done on Mira variables by Little-Marenin & Little (1990).This work is supported by the Austrian Science Fund Project P9638-AST. 相似文献
19.
S. Nishida T. Tanabé Y. Nakada S. Matsumoto K. Sekiguchi I. S. Glass 《Monthly notices of the Royal Astronomical Society》2000,313(1):136-140
We report on the light variations of the infrared stars that were discovered recently in the Magellanic clusters NGC 419, 1783 and 1978. Their periods, of 528, 458 and 491 days, are among the longest known for carbon-rich Mira variables in the Clouds. All three IR stars were found to lie on the extension of the period– M bol relation derived from the shorter-period C-rich Miras while they were 0.45–0.70 mag fainter than the extension of the period– M K relation. Their main sequence masses were determined by isochrone fitting to be 1.5–1.6 M⊙ , consistent with the prediction of the evolutionary models of Vassiliadis & Wood. 相似文献
20.
Factors contributing to the scatter around the ridge-line period-luminosity relationship are listed, followed by a discussion how to eliminate the adverse effects of these factors (mode of pulsation, crossing number, temperature range, reddening, binarity, metallicity, non-linearity of the relationship, blending), in order to reduce the dispersion of the P-L relationship. 相似文献