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1.
We introduce a novel technique, called the double wavelet analysis (DWA), for the determination of stellar rotation periods from time serial data. This first paper aims narrowly at the discussion, introduction and application of the DWA technique to records of surface magnetism in solar-type (relatively old) lower main sequence stars that are obtained by the Mount Wilson Observatory (MWO) HK Project. The technique takes a series of careful steps that seek to optimize wavelet parameters and normalization schemes, ultimately allowing fine-tuned, arguably more accurate, estimates of rotation-modulated signals (with, e.g., periods of days to months) in records that contain longer periodicities such as stellar magnetic activity cycles (with, e.g., period of years). The apparent rotation periods estimated from the DWA technique are generally consistent with results from both “first-pass” (i.e., ordinary) global wavelet spectrum and earlier classical periodogram analyses. But there are surprises as well. For example, the rotation period of the ancient subdwarf Goombridge 1830 (HD 103095), previously identified as ≈31 days, suggests under the DWA technique a significantly slower period of 60 days. DWA spectra also generally reveal a shift in the cycle period toward high frequencies (hence shorter periods) compared to the first-pass wavelet spectrum. For solar-type stars analyzed here, the character of the DWA spectrum and slope of the first-pass global wavelet spectrum produce a classification scheme that allows a star's record to be placed into one of three categories.  相似文献   

2.
我们用美国McDonald天文台2.1米反光镜Coude Reticon观测,对31个RS CVn型双星系统的37颗子星的自转进行了测量。并结合以前测得的38颗子星的数据,对RS CVn型星是否同步作了统计分析,结果表明,绝大多数都显示出同步自转性质;但无论是短周期、正常周期还是长周期组的,都有少数与同步自转不一致的例子。这与过去认为短周期和正常周期的呈同步自转,而长周期的呈非同步自转的结论不一致。  相似文献   

3.
We present a spectroscopic and photometric follow-up of binary stars, discovered in a sample of X-ray sources, aimed at a deep characterization of the stellar X-ray population in the solar neighborhood and in Star Forming Regions (SFRs). The sources have been selected from the RasTyc sample, obtained by the cross-correlation between the ROSAT all-sky survey and Tycho catalogues (Guillout et al., 1999). Thanks to the high resolution spectroscopy, we have obtained good radial velocity curves, whose solutions provided us with the mass ratios and minimum masses of the components. We have also obtained an accurate spectral classification with codes specifically developed by us. In addition, we could obtain information on the age of the sources through the Lii-6708 line and on the chromospheric activity level through the Hα line.We show also some results on very young pre-main sequence (PMS) binaries discovered as optical counterparts of X-ray sources in SFRs. The spectroscopic and photometric monitoring has allowed us to determine the orbital and physical parameters and the rotation periods, that are of great importance for testing the models of PMS evolution.  相似文献   

4.
Evolutionary model calculations of 44 Tau, a δ-Scuti star, have been carried out. The star in question is a slow rotator (vsini = 6.8 kms-1).However small it may be, the effect of rotation on the oscillation properties of the star was thought to be worth of studying. Models were evolved with uniform rotation. Radial and non-radial adiabatic oscillation frequencies were calculated. In determining oscillation frequencies rotation has been treated as a perturbation. First order effect has been considered. The possible rotational splittings, due to two rotation speeds, have been calculated. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

5.
The variations of the orbital periods of two nearly neglected W UMa-type eclipsing binaries, EK Comae Berenices and UX Eridani, are presented through a detailed analysis of the O–C diagrams. It is found that the orbital period of EK Com is decreasing and the period of UX Eridani is increasing, and several sudden jumps have occurred in the orbital periods of both binaries. We analyze the mechanism(s), which might underlie the changes of the orbital periods of both systems, and obtain some new results. The long-term decrease of the orbital period of EK Comae Berenices might be caused by the decrease of the orbital angular momentum due to a magnetic stellar wind (MSW) or by mass transfer from the more massive to the less massive component. The secular increase in the orbital period of UX Eridani might be caused by mass transfer from the less massive to the more massive star. The possible mechanisms, which underlie the sudden changes in the orbital periods of the close binary systems are as the followings: (1) the variations of the structure due to the variation of the magnetic field; (2) the rapid mass exchange between the close binaries and their circumstellar matter. Finally, the evolutionary status of the systems EK Comae Berenices and UX Eridani is discussed.  相似文献   

6.
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   

7.
This paper presents charge-couple device (CCD) photometric observations for the eclipsing binary AW UMa. The V-band light curve in 2007 was analyzed using the 2003 version of the Wilson–Devinney code. It is confirmed that AW UMa is a total eclipsing binary with a higher degree of contact f=80.2% and a lower mass ratio of q=0.076. From the (O−C) curve, the orbital period shows a continuous period decrease at a rate of dP/dt=−2.05×10−7 d yr−1. The long-term period decrease suggested that AW UMa is undergoing the mass transfer from the primary component to the secondary one, accompanied by angular momentum loss due to mass outflow L 2. Weak evidence indicates that there exists a cyclic variation with a period of 17.6 yr and a small amplitude of A=0. d 0019, which may be attributed to the light-time effect via the third body. If the existence of an additional body is true, it may remove a great amount of angular momentum from the central system. For this kind of contact binary, as the orbital period decreases, the shrinking of the inner and outer critical Roche lobes will cause the contact degree f to increase. Finally, this kind of binary will merge into a single rapid-rotation star.  相似文献   

8.
Two CCD epochs of light minimum and a complete R light curve of SS Ari are presented. The light curve obtained in 2007 was analyzed with the 2003 version of the W-D code. It is shown that SS Ari is a shallow contact binary system with a mass ratio q=3.25 and a degree of contact factor f=9.4%(±0.8%). A period investigation based on all available data shows that there may exist two distinct solutions about the assumed third body. One, assuming eccentric orbit of the third body and constant orbital period of the eclipsing pair, results in a massive third body with M 3=1.73M ⊙ and P 3=87.0 yr. On the contrary, assuming continuous period changes of the eclipsing pair the orbital period of tertiary is 37.75 yr and its mass is about 0.278M ⊙. Both of the cases suggest the presence of an unseen third component in the system.  相似文献   

9.
Ultraviolet spectra of FK Comae and V1794 Cygni observed with the Hubble Space Telescope Cosmic Origins Spectrograph (HST COS) and the International Ultraviolet Explorer (IUE) satellites were analyzed for the period 1981–2011. Temporal variations of line fluxes of the O I 1306 Å, C II 1336 Å, C IV 1550 Å, He II 1640 Å and Mg II k & h 2800 Å, produced in the transition regions and chromospheres of these stars, imply variations in density and temperature changes in the line emitting regions as a result of the rapid rotation and magnetic fields responsible for stellar activity. Results are consistent with the models of Ramsey et al. (1981), Oliveira and Foing (1999), and Korhonen et al. (2000).  相似文献   

10.
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11.
In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M⊙, and the semi-major axis of its orbit is 10.75 AU.  相似文献   

12.
We present the discovery of OB type absorption lines superimposed to the emission line spectrum and the first double-lined orbital elements for the massive Wolf–Rayet binary HDE 318016 (=WR 98), a spectroscopic binary in a circular orbit with a period of 47.825 days. The semiamplitudes of the orbital motion of the emission lines differ from line to line, indicating mass ratios between 1 and 1.7 for .  相似文献   

13.
Starspots     
Starspots are created by local magnetic fields on the surfaces of stars, just as sunspots. Their fields are strong enough to suppress the overturning convective motion and thus block or redirect the flow of energy from the stellar interior outwards to the surface and consequently appear as locally cool and therefore dark regions against an otherwise bright photosphere (Biermann in Astronomische Nachrichten 264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots are observable tracers of the yet unknown internal dynamo activity and allow a glimpse into the complex internal stellar magnetic field structure. Starspots also enable the precise measurement of stellar rotation which is among the key ingredients for the expected internal magnetic topology. But whether starspots are just blown-up sunspot analogs, we do not know yet. This article is an attempt to review our current knowledge of starspots. A comparison of a white-light image of the Sun (G2V, 5 Gyr) with a Doppler image of a young solar-like star (EK Draconis; G1.5V, age 100 Myr, rotation 10 × Ω Sun) and with a mean-field dynamo simulation suggests that starspots can be of significantly different appearance and cannot be explained with a scaling of the solar model, even for a star of same mass and effective temperature. Starspots, their surface location and migration pattern, and their link with the stellar dynamo and its internal energy transport, may have far reaching impact also for our understanding of low-mass stellar evolution and formation. Emphasis is given in this review to their importance as activity tracers in particular in the light of more and more precise exoplanet detections around solar-like, and therefore likely spotted, host stars.  相似文献   

14.
We present a photometric study of a weak-contact binary V873 Per. New observations in BVR filter bands showed asymmetric light curves to be a negative type of the O’Connell effect, which can be described by magnetic activity of a cool spot on the more massive component. Our photometric solutions showed that V873 Per is a W-type with a mass ratio of q = 2.504(±0.0029), confirming the results of Samec et al. (2009). The derived contact degree was found to be f = 18.10%(±1.36%). Moreover, our analysis found the cyclic variation with the period of about 4 yr that could be due to existence of the third companion in the system or the mechanism of magnetic activity cycle in the binary. While available data indicated that the long-term orbital period tends to be stable rather than decreasing.  相似文献   

15.
New photometry for the eclipsing binary BE Cephei was performed from 2008 to 2011. The light-curve synthesis indicates that it is a marginal-contact binary with a mass ratio of q = 2.340(±0.009) and a degree of contact of f = 6.9%(±2.3%). From the O − C curve, it is discovered that the orbital period changes show a sinusoidal curve superimposed on a downward parabola. The period and semi-amplitude of the cyclic variation are Pmod = 59.26(±0.52) yr and A = 0.d0067(±0.d0010), which may be possibly attributed to light-time effect via the presence of an unseen third body. The long-term period decreases at a rate of dP/dt = −4.84(±0.31) × 10−8 d yr−1, which may result from mass transfer from the more massive component to the less massive one, accompanied by angular momentum loss. With the period decreasing, the degree of contact will increase. Finally, the marginal-contact binary BE Cep may be evolving into a deep-contact configuration.  相似文献   

16.
We present multi-colour CCD observations of the low-temperature contact binaries, V453 Mon and V523 Cas. Their light curves are modelled to determine a new set of stellar and orbital parameters. Analysis of mid-eclipse times yields a new linear ephemeris for both systems. A period decrease (dP/dt=2.3×10−7 days/yr) in V453 Mon is discovered. V523 Cas, however, is detected to show a period increase (dP/dt=9.8×10−8 days/yr) because of the mass transfer of a rate of 1.1×10−7 M⊙ yr−1, from a less massive donor. Using these findings we can determine the physical parameters of the components of V523 Cas to be M 1=0.76 (3)M ⊙, M 2=0.39 (2)M ⊙, R 1=0.74 (2)R ⊙, R 2=0.55 (2)R ⊙, L 1=0.19 (3)L ⊙, L 2=0.14 (3)L ⊙, and the distance of system as 46(9) pc.  相似文献   

17.
A new orbital period analysis for U Geminorum is made by means of the standard O–C technique based on 187 times of light minima including the three newest CCD data from our observation. Although there are large scatter near 70,000 cycles in its O–C diagram, there is strong evidence (>99.9% confidence level) to show the secular increase of orbital period with a rate  s−1. Using the physical parameters recently derived by Echevarría et al. (Astron. J. 134:262, 2007), the range of mass transfer rate for U Geminorum is estimated as from −3.5(5)×10−9 M ⊙ yr−1 to −1.30(6)×10−8 M ⊙ yr−1. Moreover, the data before 60,000 cycles shows the obvious quasi-period variations. The least square estimation of a ∼17.4 yr quasi-periodic variation superimposed on secular orbital period increase is derived. Considering the possibility that solar-type magnetic activity cycles in the secondary star of U Geminorum may produce the quasi-period variations of the orbital period, Applegate’s mechanism is discussed and the results indicate such mechanism has difficulty explaining the quasi-period variation for U Geminorum. Hence, we attempted to apply the light-travel time effect to interpret the quasi-period variation and found the perturbation of ∼17.4 yr quasi-period may result from a brown dwarf. If the orbital inclination is assumed as i∼15°, corresponding to the upper limit of mass of a brown dwarf, then its orbital radii is ∼7.7 AU.  相似文献   

18.
The variability of period and amplitude of the high-amplitude δ Scuti star YZ Boo was thoroughly investigated based on a comprehensive analysis of new time-series photometry and other available data. Fourier analysis, O–Cdiagram, and wavelet analysis establish a clear picture for the star's time-dependent behavior in period and amplitude. We detected no additional frequencies being intrinsic to the variable or caused by amplitude/frequency modulation confirming its mono-periodicity. We reveal the pulsation of YZ Boo is quite stable in both period and amplitude over the past 50 years. Short-term variations at cycle level including “anomalous cycles” are present clearly, while long-term variations in period and amplitude at annual base are insignificant. However, we note an increment from 2000 to 2003 in both period and amplitude. In 2000 the amplitude reached the lowest. This is indicated by the Fourier and wavelet results. In the long term, O–Cfits and wavelet analysis agree with the Fourier results that the period change of YZ Boo is still inconclusive.  相似文献   

19.
We study eigenmodes of acoustic oscillations of high multipolarity l ∼ 100–1000 and high frequency (∼100 kHz), localized in neutron star envelopes. We show that the oscillation problem is self-similar. Once the oscillation spectrum is calculated for a given equation of state (EOS) in the envelope and given stellar mass M and radius R , it can be rescaled to a star with any M and R (but the same EOS in the envelope). For l ≳ 300, the modes can be subdivided into the outer and inner ones. The outer modes are mainly localized in the outer envelope. The inner modes are mostly localized near the neutron drip point, being associated with the softening of the EOS after the neutron drip. We calculate oscillation spectra for the EOSs of cold-catalyzed and accreted matter and show that the spectra of the inner modes are essentially different. A detection and identification of high-frequency pressure modes would allow one to infer M and R and determine also the EOS in the envelope (accreted or ground state) providing a new, potentially powerful method to explore the main parameters and internal structure of neutron stars.  相似文献   

20.
We collected 55 galactic extreme carbon stars from the published literature in this paper. Observational data from IRAS, 2MASS and ISO were analyzed. The results show that the infrared properties of extreme carbon stars are quite different to those for ordinary visual carbon stars. It is shown from IRAS and 2MASS photometric data that extreme carbon stars have much redder infrared colors not only in the far infrared, but also in the near infrared, hence they have much thicker ciucumstellar envelopes and mass loss. It is also indicated from IRAS Low-Resolution Spectra (LRS) and ISO Short Wavelength Spectra (SWS) that they have much redder infrared spectra from 2 μm to 45 μm. The above results are believed to be the signature of undergoing the last stages of AGB evolution for extreme carbon stars.  相似文献   

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