HIRES Calibration Data

To properly calibrate your data, it is recommended that you obtain the following calibration files during the evening or at the end of the night for every HIRES configuration setting:

Quartz Lamp Flat Field: Typically, about ten 10-30 sec exposures of the internal quartz illumination are sufficient, depending on the wavelength range. Longer exposure time is needed for bluer wavelengths. The ng3 (neutral density) filter is normally needed in the red to prevent saturation.

Arc Lamp for Wavelength Calibration: There are two available Thorium-Argon sources, ThAr1 and ThAr2, with ThAr1 being the brighter of the two. Again, the ng3 filter can be inserted to prevent the brightest lines from saturating. The exposure time is usually 1-2 sec. Only one good exposure at the beginning or end of night is needed. For improved precision, a ThAr exposure can be taken right before and after the scientific object exposure during the night.

Bias Frames: Several exposures of very short duration (0-1 sec) with the shutter closed are needed to derive the column-to-column bias pattern of the HIRES CCD.

Trace Star: This is an exposure of a bright point source that will be used to trace the echelle orders for spectrum extraction. Usually this is an observation of a bright standard star during the night. If the object itself is bright enough, it can also be used as a trace star. Alternatively, a quartz lamp exposure with the D5 pinhole decker can also be used.

The above files are considered to be the minimum standard set of calibrations needed to properly calibrate HIRES data. Additional calibration files may be necessary depending on your science goals:

To remove telluric absorption features from the object spectrum, you need to take at least one spectrum of a rapidly rotating hot star. A list of these commonly used telluric standards or "rapid rotators" is provided here. It is desirable, but not required, that the rapid rotator's spectrum be taken at airmass similar to the object's.

If you use the Iodine (I2) gas cell for your observations, it is essential that you also obtain a high S/N spectrum of the object without the I2 cell. Called the "template", this spectrum without the I2 cell needs to be taken only once for each target that you observe with the I2 cell during the run. If a telluric standard spectrum is observed, it too must also be taken with and without the I2 cell.