Astron. Astrophys. 319, 535-546 (1997)

2. Observations

All spectroscopic observations were obtained at Kitt Peak National Observatory (KPNO) with the coudé feed telescope during March 1994 and again in February-March 1995. The Doppler-imaging data in this paper are from the March 1994 run while the H spectra are from 1995. A few more spectra at various wavelengths were taken in January 1996. The 1994 and 1995 data were obtained with a 800 800 TI CCD (TI-5 chip, 15µ pixels) with grating A, camera 5 and the long collimator giving a resolving power of 38,000 at 6420 Å . For the few 1996 spectra we used the new 3000 1000 CCD (Ford F3KB chip, 15µ pixels) with an otherwise identical spectrograph set up. Table 1 is a summary of the spectroscopic observations.

Table 1. Spectroscopic observations

All data were reduced in the same standard fashion using IRAF and included standard bias subtraction, flat fielding and aperture extraction. Frequent wavelength comparison spectra and spectra of bright radial-velocity standards were obtained several times throughout the night to ensure an accurate wavelength calibration. Radial velocities were derived from cross correlating the IN Vir spectra with the IAU velocity standard 16 Vir (K0.5III, km s^-1) and are listed in Table 1. The standard error of an observation of unit weight is 1.9 km s^-1. The exposure level is indicated in Table 1 in analog-to-digital units (ADU) corresponding to signal-to-noise ratios between 150:1 and 200:1 for the red wavelength observations and about 50:1 for the Ca II spectra. Usually twenty flat-field exposures with a tungsten reference lamp were taken at the beginning of the night and again at the end of the night. These fourty flat fields were co-added and used to remove the pixel-to-pixel variations in the stellar spectra. Neither the TI CCD nor the F3KB CCD show obvious signs of fringing near 6420 Å and no attempts were made to correct for it other than the standard flat-field division. Special care was also exercised during the continuum fitting but a very low-order polynomial was sufficient to find a satisfactory continuum solution. Several representative spectra are shown in Fig. 1.

Fig. 1. Representative spectra of chromospheric activity indicators for IN Virginis (thick lines). The respective thin lines are shifted and broadened spectra of the inactive star  Ser (HR 5940), classified also as K2-3IV. The individual panels show: Ca II H&K (panel a), Ca II 8542 (panel b), Ca II 8498 (panel c), H (panel d), and Li I 6708 (panel e). The insert in panel e is the residual spectrum of IN Vir after subtraction of the broadened and shifted  Ser spectrum and offset by -0.2. The LiI -6708 line is identified with a tick mark.

The new photometric data were obtained with the Fairborn Observatory T7 0.75-m automatic photoelectric telescope (APT) on Mt. Hopkins, Arizona. The 151 observations were made differentially with respect to HD 117635 as the comparison star ( mag, mag and mag) and HD 118330 as the check star. All photometry has been transformed to match the Johnson-Cousins system. Observations started on JD 2,449,441 on the basis of several observations per night and cover the entire observing seasons 1994 and 1995 until 2,449,870. This data and additional photometry for IN Virginis, combined with data from other stars, will be presented in a forthcoming paper (Strassmeier et al. 1997).

All line profiles and photometric data in this paper are consistently phased with our new photometric ephemeris,

where the period is the best-fit period from the combined 1994 and 1995 APT photometry that we interpret to be the rotation period of the star, and the initial epoch is just an arbitrary point in time. Although the orbital period is more precise than the photometric period we use the latter to phase the data because we regard the orbital period still as preliminary. Whenever given in this paper though, orbital phases were computed with the new elements in Table 2.

Table 2. Orbital elements for IN Virginis

Fig. 2 shows the V -light curve and the and color curves of IN Virginis in 1994 phased with the photometric period as well as the periodogram from the combined 1994-1995 V -band data.

Fig. 2a and b. Left: Periodogram from the 1994-1995 V -band APT data. Right: Light and color curves phased with and the ephemeris in Eq.(1). The upper left panel shows the window function for the APT data with strong aliasing towards multiples of one day. The largest reduction of the residuals is achieved with a period near the orbital period at 8.232 0.003 days (frequency ). The other indicated frequencies are just aliases of the true frequency. The right panels show the light and color curves phased with . Despite that these plots show all combined data from 1994 we see a clear asymmetry in the light curve as well as in the color curve with a maximum at around phase 0.2 and a minimum at around 0.8.

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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