6.1. Example 3 - Datasets descriptions

6.1.1. Point Source Longslit Nod-and-Shuffle

This is a GMOS longslit nod-and-shuffle observation. The target is a quasar. We will use this observation to show how a basic longslit nod-and-shuffle sequence is reduced with DRAGONS. The sequence dithers along the dispersion axis. DRAGONS will subtract the sky using the two beams, align and stack the 2-D, extract and flux calibrate the spectrum.

The data uses the R400 grating on GMOS North equipped with the Hamamatsu CCDs. The central wavelengths are 700 nm and 710 nm. The sequence is:

[Flat, 3 x Science, Flat, Arc], [Arc, Flat, 3 x Science, Flat]

with the first group of four at 700nm and the second at 710 nm. The spectrophotometry standard was obtained about three weeks before the science observation.

The calibrations we use for this example are:

  • BPM. The bad pixel masks are now found in the Gemini Science Archive instead of being packaged with the software. They are associated like the other calibrations. Here we need the 1x2 binning GMOS-N Hamamatsu BPM valid for data taken in 2017. (The date in the name is the “valid from” date.)

  • Biases. The science and the standard observations are often taken with different Region-of-Interest (ROI) as the standard uses only the central area. Therefore we need two sets of biases, one for the science’s “Full Frame” ROI, and one for the standard’s “Central Spectrum” ROI. Here we use only 5 biases for each setting to minimize the amount of data needed. For a science reduction, please consider using 10 to 20 biases.

  • Spectroscopic flats taken with each of the science and standard observations.

  • Arcs, for both the science and the standard observations.

  • A spectrophotometric standard.

Warning

The Bad Pixel Masks (BPMs) are now found in the archive rather than packaged with the software. You must get the static BPM from the archive. See Getting Bad Pixel Masks from the archive in Tips and Tricks.

Here is the breakdown of the files. All the files are included in the tutorial data package. They can also be downloaded from the Gemini Observatory Archive (GOA).

Science
N20190926S0130-32 (700 nm)
N20190926S0137-39 (710 nm)

Science biases
N20190926S0230-234

Science flats
N20190926S0129,133 (700 nm)
N20190926S0136,140 (710 nm)

Science arcs
N20190926S0134 (700 nm)
N20190926S0135 (710 nm)

Standard (G191B2B)
N20190902S0046 (700 nm)

Standard biases
N20190902S0089-093

Standard flats
N20190902S0047 (700 nm)

Standard arc
N20190902S0062 (700 nm)

BPM
bpm_20170306_gmos-n_Ham_12_full_12amp.fits

Note

The nod-and-shuffle dark current in the Hamamatsu CCDs has been found to be low enough to be ignored. They can be requested if desired by the PI. DRAGONS will use a dark if there is one.

In contrast, for the EEV CCDs and the ee2vv CCDs, nod-and-shuffle darks are required, not optional.