Activity and kinematics of members of the TW Hydrae association

We present high-resolution echelle spectroscopy of 20 stars in 16 systems catalogued as members of the TW Hydrae association, and 16 stars identified as possible new members. We have calibrated the range of coronal and chromospheric activity expected for such young stars as a function of spectral type by combining our observations with literature data for field and open cluster stars. We also compute space motions for TWA members and candidate members with proper motion measurements, using two techniques to estimate distances to stars lacking direct trigonometric parallax measurements. The mean space motion of the four TWA members with known parallaxes is  ( U , V , W : −10.0, −17.8, −4.6) km s⁻¹  . 14 of the candidates have properties inconsistent with cluster membership; the remaining two are potential new members, although further observations are required to confirm this possibility.     

Peculiarities of the UV continuum energy distribution for T Tauri stars

In the UV spectra of BP Tau, GW Ori, T Tau, and RY Tau obtained with the Hubble Space Telescope, we detected an inflection near 2000 Å in the F _λ ^c (λ) curve that describes the continuum energy distribution. The inflection probably stems from the fact that the UV continuum in these stars consists of two components: the emission from an optically thick gas with T<8000 K and the emission from a gas with a much higher temperature. The total luminosity of the hot component is much lower than that of the cool component, but the hot-gas radiation dominates at λ<1800 Å. Previously, other authors have drawn a similar conclusion for several young stars from low-resolution IUE spectra. However, we show that the short-wavelength continuum is determined from these spectra with large errors. We also show that, for three of the stars studied (BP Tau, GW Ori, and T Tau), the accretion-shock radiation cannot account for the observed dependence F _λ ^c (λ) in the ultraviolet. We argue that more than 90% of the emission continuum in BP Tau at λ>2000 Å originates not in the accretion shock but in the inner accretion disk. Previously, a similar conclusion was reached for six more classical T Tau stars. Therefore, we believe that the high-temperature continuum can be associated with the radiation from the disk chromosphere. However, it may well be that the stellar chromosphere is its source.     

Giant Vibrations in Dip

This work reports the discovery of solar-type oscillations in thegiant star Hydrae.     

The nature of TW Pictoris

The results of X-ray and optical observations of the candidate intermediate polar TW Pic are presented in an attempt to understand its nature. We find no sign of the previously proposed ∼2 h white-dwarf spin period and ∼6 h orbital period of TW Pic in its X-ray light curve. There is therefore no convincing evidence in support of its previous classification. The lack of X-ray pulsation could be the result of a low inclination angle, but in that case there would be no reason why an optical pulsation should have been seen previously. Negative results from polarimetry also preclude TW Pic from being a polar. One possibility may be that the shorter of the two periods is in fact the orbital period, whilst the longer one is a harmonic of a disc precession period. Alternatively, both the high accretion rate and period structure of TW Pic indicate that it may be a system that displays persistent negative superhumps. In this case the true orbital period of the binary may be around 6.36 h and the shorter of the two previously identified periods, 1.996 h, represents the (shifted) second harmonic of a negative superhump period of 6.06 h. Under this interpretation, it would be the longest period system to display such a phenomenon. Finally there is also evidence that TW Pic may be a VY Scl star, in which case it would be the longest period member of that subclass too.     

Improved astrophysical parameters for the overcontact binary FG Hydrae

Photometric data on FG Hya obtained in 2002 and 2004 are presented. Three data sets show the exchange between A-type, W-type and the variable O'Connell effects. The photometric mass ratio  ( q = 0.1115 ± 0.0003)  derived from B and V light curves is almost the same as the spectroscopic mass ratio  ( q _sp= 0.112 ± 0.004)  . The new photometric solutions reveal that FG Hya is a deep overcontact binary system  ( f = 85.6 ± 1.8 per cent)  with a spotted massive component. A period investigation, based on all available photoelectric or CCD times of light minimum, shows that the O–C curve of FG Hya can be explained as a combination of a secular period decrease and a cyclic variation with a period of 36.4 yr and an amplitude of 0.0289 d. By comparing the variation of the depth of the primary minimum with the change of the cyclic period, it is discovered that both of them may vary with the same cycle length of 36.4 yr and in the same phase. The variation of the light curve, the spotted primary component and the connection between the cyclic period change and the depth of the primary minimum, all may suggest that the G0-type component displays solar-type magnetic activity with a 36.4-yr cycle length. The long-time period decrease is interpreted by mass transfer from the more massive component to the less massive one or/and angular momentum loss due to mass outflow from the outer Lagrangian point.     

Light and period study of the ecipsing binary system TW Andromedae

Photoelectric light curve (LC) solutions of the close binary system TW And were obtained using the PHOEBE program (version 0.31a). Absolute parameters of the stellar components were then determined, enabling us to discuss the structure and evolutionary status of TW And. The configuration of the system based on the LCs solutions indicates that the secondary component is slightly detached from its critical Roche surface. In addition, times of minima data (“O –C curve”) were analyzed. Apart from an almost parabolic variation of the general trend of the O –C data, indicative of a secular increase in the orbital period with a rate 0.032 s yr^–1, which was attributed to a mass transfer with a rate of Δm₂ = –1.10 × 10^–10 M_⊙ yr^–1. Additionally, a sinusoidal variation with a period of 52.75 ± 1.80 yr, modulating the orbital period, was found, which we attribute to a third body orbiting the system. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

玛纳斯河流域绿洲区域经济差异分解研究

以县域为研究单元,运用崔王指数（TW）、经济增长指数和泰尔指数分解等方法,对1978—2007年新疆典型绿洲县域经济的增长及其差异进行了分析.结果表明：以崔王极化指数测度的绿洲县域经济极化态势呈波动性扩大的趋势,并大致可以分为2个不同的发展阶段;自1978年以来玛纳斯河流域各县域经济都得到了较快发展,绿洲平均经济增长率...