T Tauri Stars

The observable characteristics of young solar-mass stars (T Tauri stars) are reviewed. Modern theoretical concepts and models of these stars are discussed briefly.     

Photometry of meteorites

We have measured the bi-directional reflectance phase function on selected meteorite samples (1 howardite, 1 eucrite, 1 diogenite, Orgeuil (CI), Tagish Lake (CC), Allende (CV), Lunar meteorite (MAC 88105), Forest Vale (H4)) covering part of the geochemical and petrologic diversity expected for asteroid surfaces. Samples were measured as powders, for which we achieved reflectance measurements from phase angles down to 3°, and up to 150°, at five different wavelengths covering the VIS–NIR spectral region. The data were fitted by the photometric model of Hapke (Hapke, B. [1993]. Theory of reflectance and emittance spectroscopy. Cambridge University Press, Cambridge). The physical sense of the retrieved Hapke’s parameters seems unclear but they permit to interpolate the data to any observation geometry. Strong opposition effects were observed for all samples. The absolute intensity of this effect appears moderately variable among our sample suite, and is not correlated with the average sample reflectance. We interpret this observation as Shadow-Hiding Opposition Effect (SHOE). In the case of samples presenting intense absorption bands (the Fe crystal field band at 1 μm of HED and the ordinary chondrite), we observe significant dependence of band depth to phase angle, up to 70°, even for moderate variation of phase angle. In addition, a general trend of spectral reddening with phase angle is observed. This reddening, linear with phase angle, is present in all meteorites studied. This behavior is not predicted by classical radiative theories. We propose that small-scale roughness (of the order of or below the wavelength) may induce such a behavior.     

Photometry of Phoebe

Observatios of Phoebe (S9) in the V filter at small solar phase angles (0.2° to 1.2°) with the MIT SNAPSHOT CCD are presented. The value of Phoebe's sideral rotational period is refined to 9.282 ± 0.015hr. Assuming the Voyager-derived 110 km radius, Phoebe's observed mean opposition V magnitude of 16.176 ± 0.033 (extrapolated from small angles) corresponds to a geometric albedo of 0.084 ± 0.003. A strong opposition effect is indicated by the 0.180 ± 0.035 mag/deg solar phase coefficient observed at these small phase angles. The data are shown to be compatible with a phase function for C-type asteroids (K. Lumme and E. Bowell, 1981, Astron. J. 86, 1705–1721; K. Lumme, E. Bowell, and A. W. Harris, 1984, Bull. Amer. Astron. Soc. 16, 684), but give a poorer fit to the average asteroid phase relation of T. Gehrels and E.F. Tedesco (1979, Astron. J. 84, 1079–1087). Phoebe's rotational lightcurve in the V filter is roughly sinusoidal, with a 0.230-mag peak-to-peak amplitude and weaker higher order harmonics indicating primarily bimodal surface feature contrast. In addition to these photometric results, precise positions on 3 nights are given.     

Photometry of asteroids

Photometry is one of the most efficient investigation techniques. It provided a large body of data on albedos, sizes, shapes, rotation, optical properties, and structural characteristics of asteroids and other minor bodies of the solar system. The contribution of photometry to the determination of asteroid parameters was most crucial. This review summarizes main results of asteroid studies in three most important areas: i) determination of the shape and rotation parameters of asteroids, ii) investigation of optical properties of asteroid surfaces, and iii) detection and investigation of binary asteroid systems.     

A T Tauri Star Database

A T Tauri Star Database was set up with the purpose of designing a user-friendly, graphical database which would provide a quick look into the properties of T Tauri stars. This revised version was published online in July 2006 with corrections to the Cover Date.     

Rotation of T Tauri Stars Revisited

This paper reviews the rotation of T Tauri stars. It summarizes the results of a complete bibliographical survey of all photometric and spectroscopic data available in connection with rotation studies of these stars. It is shown that T Tauri stars are slow rotators. More than half of the stars in the sample have been found to have v sin i < 25 km/s. Furthermore, the histogram for the photometric periods of rotation is clearly bimodal, with a peak at approximately 3 days and another at around 8 days. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evolutionary status of T Tauri stars

The problem of determining the masses and ages of T Tauri star(TTS) using their evolutionary status is discussed. We test four pre-main sequence evolutionary models using well determined observational parameters of 12 binary TTSs and two binary red dwarfs. It is shown that the masses derived using the tracks of all models are in good agreement with the masses obtained from the observations of TTSs with masses M 0.7 M_⊙(mean error ε ~ 10%). Low-mass stars with M ≤ 0.7 M_⊙have significantly greater mean error: ε ~ 50% for the tracks of Bressan et al. and Chen et al., and ε ~ 30% for the other tracks. The isochrones of all tested evolutionary models diverge for stars with masses M ≤ 0.7 M_⊙. The difference increases with the mass decrease and can reach 10% of KelvinHelmholtz time for stars with mass M = 0.2 M_⊙. The ages of most of the considered TTSs are smaller than the Kelvin-Helmholtz time. This confirms their evolutionary status of being pre-main sequence stars.     

Spectrophotometry of V711 Tauri

Spectrophotometric observations of the RS CVn binary system V711 Tau (HR 1099), convering the wavelength interval 3300–7100 Å, have been presented. A comparison of the standard spectral scans of V711 Tau with the spectral scans of the stars of known spectral types and luminosity classes taken from the Breger (1976) catalogue shows that, at all phases shown in the diagram, the spectral-luminosity type of the star is K0IV or K0III. The magnitude of the system fluctuates from 5 ^m .71 to 5 ^m .79 average being 5 ^m .75 approximately, the faintest being near 0 ^p .43 and the brightest near 0 ^p .78. The region around Balmer jump and near H region is apparently variable.     

Spectral investigations of T Tauri stars

Basic ideas concerning the nature of young T Tauri stars (TTS) are briefly outlined and some examples of spectral investigations of those stars are considered. The photometric and spectral variability of TTS is believed to be due to circumstellar extinction, magnetic activity, and accretion of matter from the circumstellar disk onto the stellar surface. In the 1990s, a series of high resolution spectra of several TTS were obtained using the SOFIN echelle spectrograph with the Nordic Optical Telescope (NOT). In particular, the emission lines in the spectra of the star RW Aur A were shown to be rotationally modulated with a period of 2.7 days, which was interpreted in terms of the magnetospheric accretion model with an inclined magnetic rotator. The spectra of TTS obtained using the UVES spectrograph with the VLT demonstrated that the effect of veiling the photospheric spectrum, usually attributed to accretion, was largely due to chromospheric extinction. The accretion is suggested to be a complementary heating source in chromospheres of TTS.     

Photometry of TT Arietis

An analysis of data spanning 24 years shows that a secondary 20^m periodicity is a persistent feature in photometric observations of TT Ari. This period decreases from 27^m in 1961 to 17^m in 1985. The 4^d beat period of 3 _. ^h 2 photometric and 3 _. ^h 3 spectroscopic periods is also apparent in observations of 1966.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Photometry of AR Lac

Visible photometry of the RS CVn system AR Lac is presented. We find some interesting features in the light curves. Also a possible oscillation with period 1.05 hr arises from the data. A new determination of the geometrical parameters of the system is given.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.     

Photometry of EX Hya

Photometric observations of EX Hya inB andVfilters are reported. The 67 min modulation of the light curve also is found to be in good agreement with the results of earlier studies. The (B-V) colour variation with respect to the 67 min variation is found to be opposite to those of typical colour variation during hump/superhump activity in other dwarf novae. The model of an intermediate polar is discussed.     

施密特望远镜CCD BVRI测光系统的初步研究

本文利用Thomson CCD,在北京天文台兴隆站施密特望远镜上进行BVRI四色测光,得到了该测光系统的颜色转换方程,并对所得结果进行了分析探讨。同时论证了BAO-CCD系统在施密特望远镜上用于测光的可行性。     

The overcontact binary RZ Tauri

The first reliable radial velocity curves for RZ Tau have been obtained. Combined with new light curve (LC) data, simultaneous Roche-based light curve analyses have been carried out using the 2003 version of the Wilson-Devinney code. New values for the masses and radii have been obtained: M₁ = 1.53 (4) M_ʘ, M₂ = 0.57 (2) M_ʘ, and R₁ = 1.50 (4) R_ʘ, R₂ = 0.99 (2) R_ʘ. Although there is a multitude of spectral classifications listed in the literature, the classification of F0 from Struve et al. (1950) is shown to be the most reliable. On the basis of the latter, the most likely luminosities are L₁ = 4.97 (44) L_ʘ and L₂ = 2.11 (19) L_ʘ. Additional modelling was carried out using the same RV data, but with LC data (binned and unbinned) from Binnendijk (1963); the results were substantially the same except that they favoured slightly later spectral sub-classes.     

Extensive photometric study of V471 Tauri

The white-dwarf red-dwarf eclipsing binary V471 Tauri has been observed photoelectrically, in blue and yellow lights, from 1985 to 1989. The behaviour of the mean brightness variation has been re-examined. The mean brightness has decreased from 1982 to 1985 and thereafter it started to increase again. The amount of the variation of the light of the system has reached to 0.19 mag in both colours since 1973. On the other hand, the new timings of mid-eclipse deviate considerably from those linear and light-time effect fittings. Neither the third-body hypothesis, nor any other mechanism can explain the orbital period change of the system.     

Chromospheric Activity of Weak-Lined T Tauri Stars

A summary of our ongoing high and medium resolution optical observational program, devoted to the study of chromospheric activity of pre-main sequence stars, is reported here. The study is centered in bona-fid weak-lined T Tauri stars (WTTS) in Taurus with known rotational period, and in WTTS recently discovered by the ROSAT All-Sky Survey. It is our purpose to quantify the phenomenology of the chromospheric activity of each star determining stellar surface fluxes in the more important chromospheric activity indicators (Ca II H & K, Hβ, Hα, Ca II IRT) as well as to obtain the Li I abundance, a better determination of the stellar parameters, spectral type, and possible binarity. By using these chromospheric excess emissions we will study the flux-flux and rotation-activity relationships in order to get insights into the mechanisms which drive solar-like stellar activity in this kind of low mass pre-main sequence stars. This revised version was published online in July 2006 with corrections to the Cover Date.