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Astron. Astrophys. 354, 537-550 (2000)

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2. Observations

2.1. Spectroscopy

The spectroscopic observations were made at the National Solar Observatory (NSO) with the McMath-Pierce telescope during 57 consecutive nights in November - December 1996. The stellar spectrograph with grating I and the 105-mm tranfer lens was used throughout the observations and resulted in a resolving power of 42,000. A resolution element consisted of 1.6 pixels. All observations utilized the 800[FORMULA]800-pixel TI CCD with a dispersion scale of 0.10 Å/pixel. The integrations on V711 Tau had a typical signal-to-noise ratio of about 200-250:1 in the continuum and were made in a 50-Å wide wavelength region centered at 6440 Å. This region contains the two Doppler imaging lines Fe I at 6430 Å and Ca I at 6439 Å. The radial-velocity standard star [FORMULA] Ari ([FORMULA] = -14.51 km s-1 , Scarfe et al. 1990) was measured nightly except for a few nights as indicated in Table 1. In the latter cases, we rely on the zero point from the Th-Ar wavelength calibration. Data reductions were carried out in the standard fashion with the NOAO/IRAF software package.


[TABLE]

Table 1. Observing log and radial velocities.
Notes:
a) Nights where no radial-velocity standards were observed. These velocities rely on a zeropoint from the Th-Ar comparison lamp.


2.2. Photometry

Johnson-Cousins [FORMULA] photometry was collected with the T7 0.75-m Amadeus telescope, one of the Vienna Observatory twin Automatic Photoelectric Telescopes (APT) at Fairborn Observatory in southern Arizona (Strassmeier et al. 1997) in the time between 1996 Nov. 7 - 1997 Feb. 10. Altogether, 134 new [FORMULA] measurements were obtained with respect to the usual comparison star HD 22484: V = [FORMULA], U-B = [FORMULA], B-V = [FORMULA], [FORMULA] = [FORMULA], [FORMULA] = [FORMULA]; Cutispoto (1992). The standard error of the observations was [FORMULA] in V and [FORMULA] in R and I. Our differential V observations are plotted in Fig. 1 together with data collected from the literature (for a recent summary see Henry et al. 1995). Fig. 1 shows the long-term photometric behavior of V711 Tau and is intended to put our new measurements in the long-term perspective. Also shown are the times of previous Doppler images as well as the time of the images from this paper.

[FIGURE] Fig. 1. The long-term V-light curve of V711 Tau. The filled dots are the data from this paper. The crosses are data collected from various literature sources. A sine-curve fit to the entire data emphasizes a 16.0-year periodicity. The dashes mark the times of previous Doppler images, while the arrow indicates the time from this paper.

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© European Southern Observatory (ESO) 2000

Online publication: February 9, 2000
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