Troubleshooting guide

V.Taking Spectra with FLAMINGOS

A. Overview

FLAMINGOS may be used for obtaining long slit or multi-object slit spectra; please see § I. FLAMINGOS +

KPNO 4-m Overview for resolving powers within selected passbands. As with imaging, the sky emission is

variable and bright, and there is additional background in the HK mode from the camera dewar window. It is

necessary to subtract this contribution from the target spectrum. This is accomplished by dithering the target up

and down the slit. Two possible techniques are walking up the slit at 5 to 7 different locations, and nodding the

telescope back and forth between two offset positions, A and B, in an ABBA pattern, symmetrically placed

about the target's initial alignment position. Dithering in an ABBA pattern can be done by hand, or

automatically with a script. Walking up or down the slit must be done by hand.

Telescope guiding is required, as the integration times are generally long, and the time to align a long slit or

MOS plate is also significant. The South Port guide probe (x, y) location is shown on the TCS Video unit. The

radius, r = (x

+ y

)

, from the center of the field of view must be ≥100 mm or else the guide probe will

vignette the FLAMINGOS field.

The default bias for spectroscopy is 0.75 V, where the array has lower dark current than at the imaging bias of

1.0 V. The current bias value may be obtained by hitting the Update All Items button on the UFSTATUS GUI.

NOTE: the MCE4 array controller automatically sets the bias to 0.776 V on boot, which is not a bias voltage

used in any configuration. The initialization script initflam.pl sets the bias to 1.0 V, and then queries whether

you wish to change the bias. If MCE4 crashes and you have to run initflam.pl, don't forget to reset the bias for

spectroscopy!

There are two types of slits which may be used for spectroscopy. There are a number of fixed long slits

installed in the MOS wheel, in between the MOS mask locations, with widths of 2, 3, 6, 8, 12, and 20 pixels.

Because of their proximity to the MOS masks, these must be used with the Decker wheel set to the slit position,

and it is necessary to carefully set up the Decker wheel to ensure that the narrow aperture does not vignette the

slit. There are also a number of custom slits which have been machined in MOS masks and can be used with

the much wider MOS decker, which can greatly facilitate acquisition of the target.

Commonly used slits in MOS masks are:

UF 3pix This is a single long slit 3 × 1680 pixels (0.95 × 530 arcsec at 4-m)

NOAO 2 pix The three NOAO slits are 2, 3, 4 pixels (0.63, 0.95, 1.26 arcsec) wide and

NOAO 3 pix consist of two slits each 60 arcsec long centered 60 arcsec on either side

NOAO 4 pix of a 10 arcsec square aperture which is used for acquisition

Unless the long slit length is required for science, the NOAO slit masks are more suitable for compact source

spectroscopy because the acquisition aperture greatly simplifies centering the target on the slit.

Since multislit MOS masks are functionally similar to the NOAO slit masks and are also used with the Decker

wheel in the mos position, the same alignment procedures can be used for both, although MOS masks may

require a small additional tweaking of the MOS wheel to adjust the position angle slightly.

We will outline two acquisition/alignment procedures. The first is potentially more efficient, but requires some

preliminary setup ahead of time. The second is a more laborious procedure using the ucsclris routine xbox

which can be used should the quick procedure not work.

FLAMINGOS@4-m, Ver. 2.39, 2013 April 23 Page 23 of 47