Tests at the telescope
Since our project telescope is in construction, tests of the
spectrograph were performed using provisional setup with a borrowed
0.4m telescope and semi-professional camera with inadequate cooling.
Because of unsuitable CCD camera (Apogee AP8p) tests were performed in
two separate stages: (i) tests of long term spectrograph stability and
accuracy of radial velocities were performed with bright stars and the
camera in standard setup and (ii) tests of stellar magnitude range were
performed in provisional setup with a custom-developed deep cooling of
CCD. The latter configuration was performed with a borrowed cooler and
could not be continued over long time as it violated manufacturer
warranty and threatened the camera electronics.
Stability and velocity errorsOur test CCD camera is was the Apogee AP8p with SITe 003 1k x 1k chip and a 2 stage Peltier cooler with water assist. It can operate at 50 deg C below the cooling agent temperature which normally should not be lower than 10 deg C to avoid condensation at the camera box. This type of the cameras are acceptable for direct imaging, where sky noise dominates. In spectrograph the skylight is diluted by the resolution factor, in our case R=33000, hence detector noise dominates.
Working with the camera cooled down to -40 deg we had to choose a relatively bright star for our test observations. A SB1 optical binary Theta Dra (V=4.0 mag) with known good quality spectroscopic orbit (SB2 using IR spectra of the secondary) was ideal for our purpose. Its observations spanned several weeks. In Fig. 1 we demonstrate our RV curve for Theta Dra. The best available spectroscopic orbit is P= 3.0708216+/-0.0000069, K=25.1+/-0.3 km/s, e=0.039+/-0.012 and omega=63+/-15o (Mazeh et al., 2002, ApJ, 564, 1007, see also Slovak & Barnes, 2002, BAAS 34, 814). Our internal scatter of velocities corresponds to 0.7 km/s RMS.
Fig. 1. The radial velocity curve of Theta Draconis (V=4.0 mag) obtained with our spectrograph at the 0.4m test telescope. Circles correspond to velocities obtained from cross-correlation of 30 spectral orders unaffected by atmospheric bands. Dotted line corresponds to the best available orbit. Internal scatter of points corresponds to 0.7 km/s RMS, and is quite robust as it depends on scatter within two clusters of points. The curve was adjusted in both directions by 0.04P and 1.5 km/s, reflecting uncertainty respectively of the ephemeris propagation and of our radial velocity zero point.
|2 x 0.5 m
|2 x 0.5 m
|2 x 0.5 m
The 2 x 0.5 m telescope indicates a double mirror telescope
which is presently being constructed for the sepctrograph (see the
One of several Th/Ar frames taken during observations. Two arcs
exposed 4 hours during observations apart were cross-correlated and
revealed a negligible shift of 0.015 pixels corresponding to 0.06
Fig.2. An echelle spectrum of V454 Aur, exposed for 1800s at the 0.4m telescope. Dark spots at the top are traces of strong Th/Ar lines, which left their bright marks in the dark frames. After dark current correction they turned into black spots. Small white dots are hot/cold pixels and cosmic rays. A sodium doublet can be seen in the middle, with an H alpha line in the upper-right part of the frame, just below atmospheric lines.