Astrophysics

Calibration and Efficiency

The sensitivity curve for the 150 lines/mm grating is calculated based on the observations of standard stars Feige 15 and Feige 34 during December 1999. A slit width of 600 microns (5 arcsec) was used. Blue ([OII] to [SII]) and red ([OI] to [SIII]) spectra were obtained separately at grating angle 2^o40^' and 4^o00^' respectively. The combined curve is given below in units of AB magnitude that gives 1 count/s/Å at standard gain (1.85 e^-/ADU). The spectra had been corrected for atmospheric extinction using the curve for Kitt Peak and hence the following curve represents sensitivity of the telescope+spectrograph+CCD combination.

Based on the above curve, sensitivities at selected wavelengths are given in the following table. This table also includes the sensitivities obtained by RJT using a 1999 observation of the standard star BD2546. The latter values were not corrected for the atmspheric extinction and hence represent the sensitivities of the telescope+atmosphere+spectrograph+CCD combination. The last column in the table is the typical sky brightness at OAGH in units of AB mag/arcsec².

A complete sensitivity curve for all the gratings available at the telescope will be posted in this page shortly.

Sky Spectrum at OAGH

A typical sky spectrum at OAGH is shown below. This spectrum corresponds to December 1999 observations. Important atmosperic and city lines have been identified.