Calibration Exposures

This page describes the APOGEE calibration exposures:

There several types of calibration exposures:

  • darks

  • internal flats

  • quartz flats

  • dome flats

  • arcs (UNe and ThArNe)

  • FPI

  • sky flats (on sky, all stars offset by XX arcsec)

These calibrations can be taken in either the regular FullPak (illuminates all 300 fibers) or the SparsePak configuration (50 fibers, every 6th fiber). There is a separate gang cconnector port in the cal box for these two configurations.

These pages describe the current calibrations taken during SDSS-V.

Master calibrations

On a roughly annual basis, longer calibration sequences are taken (often during engineering time or before/after summer shutdown at APO) in order to generate master calibration files.

Darks

A sequence of 30x 100-read darks is taken. It’s best if there was a period of time with no light hitting the detectors to make sure there is minimal persistence in the darks.

Internal Flats

A sequence of 30x 30-read internal flats. This is only possible at APO now, since the internal lamps are not working at LCO anymore.

Sky flat

The idea is to get exposures where every fiber is on sky. The airglow lines in the sky spectra are used to generate a new LSF master calibration file.

This is done on-sky. Any design can be used, but the telescope needs to be offset by XX arcsec so that no fibers are on actual targets.

Daily Calibrations

Every afternoon and morning, a set of daily calibration exposures are taken.

FILENAME    UT      NREAD   EXPTYPE QRTZ    THAR    UNE     CONFIG  DESIGN  FIELD   SECZ    SEEING  OBSCMNT COMMENT COLLPIST        COLPITCH        DITHPIX TCAMMID TLSDETB
56510001    19:24:45.604    60      DARK    0       0       0       10022464        745387  110537  1.0000000       1.6     None            0.0     0.0     13.496  81.948  77.395
56510002    19:35:26.825    3       QUARTZFLAT      1       0       0       10022464        745387  110537  2.2400000       1.6                     0.0     0.0     13.496  81.949  77.396
56510003    19:36:04.588    20      ARCLAMP 0       1       0       10022464        745387  110537  2.2400000       1.6                     0.0     0.0     13.496  81.949  77.395
56510004    19:39:41.855    40      ARCLAMP 0       0       1       10022464        745387  110537  2.2400000       1.6                     0.0     0.0     13.496  81.949  77.395
56510005    19:46:59.362    20      ARCLAMP 0       1       0       10022464        745387  110537  2.2400000       1.6                     0.0     0.0     12.995  81.947  77.396
56510006    19:50:36.612    40      ARCLAMP 0       0       1       10022464        745387  110537  2.2400000       1.6                     0.0     0.0     12.995  81.949  77.398
56510007    19:57:51.935    60      DARK    0       0       0       10022464        745387  110537  2.2400000       1.6                     0.0     0.0     12.995  81.949  77.398
56510008    20:08:33.579    30      ARCLAMP 0       0       0       10022464        745387  110537  2.2400000       1.6     FPI A           0.0     0.0     12.995  81.949  77.399
56510009    20:13:56.439    30      ARCLAMP 0       0       0       10022464        745387  110537  2.2400000       1.6     FPI B           0.0     0.0     13.496  81.949  77.4
56510010    20:42:00.095    8       DOMEFLAT        0       0       0       10022464        745387  110537  1.0000000       1.6     None            0.0     0.0     13.496  81.947  77.402

The gang connector is connected to the full fiber cal box position for the calibration sequence.

Darks

One 60 read dark starts the sequence. Another 60 read dark is also taken between the lamp arcs and the FPI exposures.

Quartzflat

A 3-read quartz flat exposure is taken. The quartz lamp is bright and will quickly saturate the image with a longer exposure. Fowler sampling is used to process these images, not up-the-ramp. These illuminate 298 fibers (excluding the 2 decided FPI fibers) and the data are used to determine the PSF.

Arcs

UNe (Uranium-Neon) and ThArNe (Thorium-Argon-Neon) arclamp exposures are taken at both A and B dither positions.

FPI

Two 30 read full-frame FPI exposures are taken, A and B dithers. This is used to generate the daily wavelength solutions. It’s important that the final UNe exposure is at the same dither position as the first FPI exposure so that the two solutions are anchored.

Domeflat

The gang connector is connected to the FPS and the dome lamps are turned on. This exposure is used to determine the throughput of the fibers.