2 New observations

  Our spectroscopic observations of the 10 program stars were obtained at several observatories including the McDonald Observatory of the University of Texas, the KPNO, and the National Solar Observatory (NSO), all in the northern hemisphere, as well as the European Southern Observatory (ESO) in the southern hemisphere. Table 1 lists basic data for our program stars, and Fig. 1 shows a sample spectrum of each star.

 

Table 1: Program stars 

Table 2 summarizes the telescope/detector configurations used. However, since the vast majority of the spectrograms were obtained between 1983 and 1998 at the KPNO with the coudé feed telescope, coudé spectrograph, a couple combinations of grating and camera, and several different CCD detectors, primarily a Texas Instruments (TI) or Ford (F3KB) CCD detector, those particular configurations are discussed in more detail below.

 

Table 2: Telescope-spectrograph-detector combinations 

From 1983 through 1987 the $800 \times 800$ TI CCD with $15\,\mu$ pixels was used with grating D and camera 5, to yield a resolving power, $R = 30\,000$. The spectra have a 90 Å wavelength range centered on 6430 Å with an effective wavelength resolution of 0.23 Å. Improved throughput was obtained when KPNO acquired grating A, which has been used from 1987 through 1998 with camera 5, the long collimator, and a TI CCD to obtained a slightly better resolution of 0.21 Å, while reducing the wavelength range to 82 Å. From 1995 through 1998 additional observations were obtained with the $3096 \times 1024$ F3KB CCD ($15\,\mu$ pixels) but an otherwise identical spectrograph setup. For this combination the wavelength range is 300 Å, the effective wavelength resolution is 0.27 Å, and the spectra were centered at 6480 Å.

Data from the coudé feed have recently been supplemented with observations obtained at two other observatories. The NSO observations were obtained with the McMath-Pierce solar telescope during a single 70-night observing run from November 1, 1996 through January 8, 1997. Another TI CCD was used in conjunction with Milton-Roy grating #1 to give an effective wavelength resolution of 0.15 Å and a usable wavelength range of 55 Å centered at 6435 Å.

For two stars, UZ Librae and HD 152178, observations also were obtained at ESO La Silla during seven nights, from May 18-23, 1996. The 1.4 m coudé auxiliary telescope (CAT) was used with the coudé echelle spectrograph (CES) operating in single-order mode. This spectrograph setup together with a 2688$\times$512 Loral CCD having $15\,\mu$ pixels resulted in $R = 70\,000$. The spectra have a wavelength range of about 70 Å and are centered at 6425 Å.

Bias subtraction, flat-field division, wavelength calibration, and continuum rectification were performed on the raw spectra with the programs in IRAF (distributed by NOAO) or MIDAS (distributed by ESO). Thorium-argon comparison spectra were obtained each night at intervals of one to two hours to ensure an accurate wavelength calibration.

 

Figure 1: Examples of spectra used in the analysis of this paper. The different wavelength coverages are due to different telescope/detector combinations and range from 55 Å for, e.g., LN Peg at NSO to 300 Å for most other stars