APF Levy

Overview

This file summarizes the APF high resolution spectrometer, called the Levy after the donors. The spectrometer is a cross-dispersed echelle spectrograph with a fixed position for the all of the dispersive elements. The only important characteristics from a data reduction perspective are the length the slit, which can be either 3 or 8 arc-seconds, and the binning used on the the detector which cab be either 1x1 or 2x2.

Frame Types

There are a set of standard cailibrations frames that are acquired each night. These include: - flat fields with the 8 arc-second long slit (WideFlat) - dark (Dark) - arc lamp (ThAr) - flat fields with the 3 arc-second long slit (NarrowFlat) - flat field images with the iodine cell in the beam (Iodine)

The arc frames are usually taken with the pinhole, 3 and 8 arc-second long slits. The wide flats are taken with the 8 arc-second long slit that are 2 arcseconds in width. This means they cover pretty much all of the detector. These can be use for the trace frames for the 8 arc-second and for pixel flats for all of the data. The narrow flats are taken with the 3 arc-second long slit. These should be used for the trace frames for the 3 arc-second long slit.

Currently the wide flats are used for the pixel flats for both the 3 and 8 arc-second long slit data. The narrow flats are only used for the trace frames for the 3 arc-second long slit data, while the wide flats are used for the trace frames for the 8 arc-second long slit data. This should be handled automatically by PypeIt.

Flat Fielding

For the flat fields, currently the nightly calibrations produce 50 “wide flats” but only 12 “narrow flats” for each calibration run, so there could be twice as many in total of each.

Slit tracing

Files labeled as narrow flats are used for the slit tracing for data taken with the 3 arc-second long slit.

The WideFlat images should also be used for slit tracing for data taken with the 8 arc-second long slit.

Wavelength Calibration

The wavelength calibration is done using ThAr lamps, which are also used to compute the Tilt frames.

The wavelength solution, as is standard for PypeIt, is in vacuum wavelengths. The wavelength solution is computed using the HARPS line list.

Iodine cell observations are not used for the wavelength calibration. To correctly use the iodine cell requires specialized software which is not supported by PypeIt.

Object detection

The sky subtraction is turned off by default during the object detection step. This can be turned by on by the user but is not recommend for 3 arc-second slits, only for 8 arc-second slits.

The pixel sampling is coarse, with the pixels having a size of 0.4” in the spatial direction. Typical object sizes are a full-width at half maximum of 4 pixels in the spectrum while a 3 arc-second long slit has only 8 pixels in the spatial direction.

For faint objects observed with the 8 arc-second long slit, turning on the sky subtraction in the object detection step may be helpful.