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Few Skewed Disks Found in First Closure-Phase Survey of Herbig Ae/Be Stars
Using the three-telescope IOTA interferometer on Mount Hopkins, wereport results from the first near-infrared (λ=1.65 μm)closure-phase survey of young stellar objects (YSOs). These closurephases allow us to unambiguously detect departures from centrosymmetry(i.e., skew) in the emission pattern from YSO disks on the scale of ~4mas, expected from generic ``flared disk'' models. Six of 14 targetsshowed small, yet statistically significant nonzero closure phases, withlargest values from the young binary system MWC 361-A and the(pre-main-sequence?) Be star HD 45677. Our observations are quitesensitive to the vertical structure of the inner disk, and we confrontthe predictions of the ``puffed-up inner wall'' models of Dullemond,Dominik, & Natta (DDN). Our data support disk models with curvedinner rims because the expected emission appears symmetricallydistributed around the star over a wide range of inclination angles. Incontrast, our results are incompatible with the models possessingvertical inner walls because they predict extreme skewness (i.e., largeclosure phases) from the near-IR disk emission that is not seen in ourdata. In addition, we also present the discovery of mysterious H-band``halos'' (~5%-10% of light on scales 0.01"-0.50") around a few objects,a preliminary ``parametric imaging'' study for HD 45677, and the firstastrometric orbit for the young binary MWC 361-A.
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Polarimetric and spectroscopic study of the weak-emission T Tauri star V 410 Tauri
Results of the polarimetric and spectroscopic observations of the weakemission T Tauri star V 410 Tau are presented. The linear polarizationand position angle are found to show variability with a periodcorresponding to the star's rotational period. It is also found that thepolarization reaches a maximum near the light minimum. Modelling of theV and R light curves shows that two adjacent spots, occupying a totalfractional area of 0.23 and with a temperature 750 K cooler than thephotosphere, could account for the observed light variability. Weattribute the periodic variability in linear polarization to thevariable illumination of an optically thin circumstellar envelope by therotating spotted star. The Hα line is found to vary from shallowabsorption to emission with the maximum emission strength at the minimumlight, and vice versa. The \ion{Li} I 6708 Angstroms absorptionequivalent width, which is consistent with that of the other T Tauristars, is found to show no appreciable variation with the photometricphase.
| Doppler imaging of stellar surface structure. II. The weak-lined T Tauri star V410 Tauri.
We present a new Doppler image of the rapidly-rotating weak-lined TTauri star V410 Tauri and compare this new map with one previouslypublished from observations taken over a year earlier. We find coolspots at both equatorial latitudes and at high latitudes with the highlatitude spots being cooler and showing greater area and having greaterlongevity than the equatorial spots. A comparison of the two maps showslittle relative change in the positions of the equatorial spots comparedto the spots at high latitude suggesting very little differentialrotation and what there is appears to be in the same sense as the Sun.Global spot lifetime would appear to be on the order of the timeinterval between the two maps, that is about a year. There are severalhot features evident supporting the claim for the existence of suchfeatures based on our map of Nov. 1992.
| U, B, V, R, I stellar photometry in the field of the Taurus dark clouds
A program of photoelectric stellar photometry has been carried out inthe field of the Taurus dark clouds with a view to establishing thedistance of the clouds and the absorption law in that region of the sky.It is found that the distance of the dark clouds accompanying the Tau T1and Tau T3 associations is 132 plus or minus 10 pc. Within theabsorption region 0-4 m, the Taurus dark clouds are characterized by anearly normal absorption law (to within 5-10%). In the field of the darkclouds a group of F0-G0 stars close to the main sequence is found whosespace density is three to eight times that in the solar neighborhood.
| The polarization of T and RY Tau.
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