TCO observatory
Spectroscopic observations were obtained at the Three College Observatory (here after TCO), which is located ~12 km south of the city of Graham, Alamance county, North Carolina, USA. TCO has a 0.81 m telescope equipped with a fiber-fed échelle spectrograph from Shelyak Instruments. The spectrograph with an ATIK-460EX detector (2749 ✕ 2199 pixels, pixel size 4.54 μm ✕ 4.54 μm) provides a spectral resolving power of R ~ 12,000 in a spectral range from 3800 Å to 7900 Å without gaps between the spectral orders.
The Observatory was built at the end of the 1970s, while regular spectroscopic observations began at the end of 2011. The observational program includes a broad range of normal (with no emission lines) and emission-line stars, such as classical Be stars, objects with the B[e] phenomenon, Herbig Ae/Be stars, supergiants, etc. The described setup allows to take spectra of objects starting from the brightest stars (e.g., Sirius) to those of 10 visual magnitude. It takes a few seconds to reach a signal-to-noise ratio of 100–200 in the continuum for the brightest stars and 2–3 h to get it to 50 for the faintest. The highest signal-to-noise ratio (up to 300) is achieved in a spectral range between 4500 Å and 5500 Å.
Each spectrum typically consists of several individual exposures, which are summed up during the data reduction process that was done using the echelle package in IRAF. The latter includes bias subtraction, spectral order separation, and wavelength calibration using spectra of a ThAr lamp. Flat field images are not taken, because the detector has a pixel sensitivity difference of 1.5% and the flat field lamp does not cover the entire extracted spectral range.
The number of comparison lines identified in the calibration spectra ranged from 800 to over 1000. Typical scatter of the comparison line positions from a polynomial solution is 0.03 Å which results in a RV accuracy of 300 m/s-1. This allows us to reliably detect RVvariations of a few km/s-1.