NIC-FPS - Users Guide

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This page last updated: Sept 27, 2007 - GS
This page last checked: October 27, 2004 - JMD

Contents

Basic Usage

Basic information to know...

NIC-FPS Quick Start Guide (PDF)

Offset directions for NIC-FPS

Correlated Double Sampling (CDS)/Fowler Sampling

NIR Standards

Advanced Usage

Basic information to know...

You should retrieve your science images off from APO computers within 7 days after they are taken, otherwise they will be deleted. We DO NOT back up data locally here. Data can be found here.

Basic User's Guide: NICFPS - 2007

NIC-FPS: Near Infrared Camera/Fabry-Perot Spectrometer

NIC-FPS is an instrument combining the capabilities of a near-infrared imaging camera with a cryogenic Fabry-Perot etalon currently under development at the Center for Space Astrophysics and Space Astronomy, University of Colorado with support from Rice University, Ball Aerospace and the Astrophysical Research Consortium. It is scheduled to begin operations on the ARC 3.5m telescope at Apache Point Observatory in 2004.

Draft NIC-FPS Quickstart Guide (PDF)

Offset Directions for NIC-FPS (Check these offsets!!!)

IRAF View

This is the orientation of the image as viewed in an image display via IRAF (e.g. ximtool, saoimage). Note: This is different from the orientation of the image as viewed on a Macintosh, via Remark. Scroll down the page for the Macintosh orientation.

A +X, +Y instrument offset will move a star in the direction indicated by the arrows. Directions of East and North are given for 0 degrees object rotation. Note: The offset direction depends upon which interface the offset command was issued in!

TCC                          MC                     Remark

Macintosh View

This is the orientation of the image as viewed on a Macintosh (i.e. as displayed by Remark). Note: This is different from the orientation of the image as viewed by IRAF. Scroll up the page for the IRAF orientation.

A +X, +Y instrument offset will move a star in the direction indicated by the arrows. Directions of East and North are given for 0 degrees object rotation. Note: The offset direction depends upon which interface the offset command was issued in!

TCC                          MC                     Remark

Correlated Double Sampling (CDS)/Fowler Sampling

A quick note to let everyone know about the new modes of operations for NICFPS.

We've added the Correlated Double Sampling (CDS) and more generally, the Fowler Sampling as part of the Detector TUI command.

Since the H1RG chip is read in a non-destructive manner, averaging multiple reads helps beat down the read noise.

The NFS=0 mode is the same as what has been in place from the start (clear-integrate-read).

In the CDS mode (selecting Number of Fowler Sampling (NFS) = 1), the chip is first cleared, then read a first time, the integration takes place and finally the chip is read again. The resulting FITS file will now consist of a primary data section and a single image extension. The primary section (extension=0) contains the data from the second read minus the first read. The data is stored in 32 bit signed integers. The FITS extension has the data from the second (last) read in its usual unsigned 16 bit integer format. The first read is not written since it is easy to reconstruct it from these two images. Saving the subtracted data in the primary section allows for quick view of the image (fixed pattern noise is removed). The observer has to be aware that the subtracted image will not tell him/her if the image is saturated (or passed its linear response). It is important for the observer to also take a look at the image from the second read to make sure it is not saturated.

In the Fowler Sampling mode, (NFS>1), the requested number of frames (NFS) will be read right after the clear and another series of NFS frames will be read after the exposure is completed. By later subtracting the corresponding frames in the two series, the observer gets NFS images that he/she can average together for noise reduction. The FITS now has in its primary section: the image resulting from subtracting the last frame from the first series, from the last frame of the second series. There is also a FITS extension for each frame read (except for the last frame of the first series which can be reconstructed). Again, the observer has to watch out for saturated/non-linear images by looking at the last image of the last series (FITS extension 1).

The size of the FITS file will depend on the NFS and the size of the window selected. For full frame images, the FITS file will result in a size of:

NFS=0 -> 2 MB
NFS=1 -> 6 MB
NFS=2 -> 10 MB
NFS=3 -> 14 MB
NFS=4 -> 18 MB
NFS=5 -> 22 MB
NFS=6 -> 26 MB
NFS=7 -> 30 MB
NFS=8 -> 36 MB

Again because of the non-destructive read nature of NICFPS chip (and the absence of a shutter), each pixel starts integrating as soon as it is done clearing. The clear and read of the chip is done pixel by pixel and row by row starting at the bottom. The time it takes to clear/ read depends on size of the window and the number of channels. The full window uses two channels, any other (smaller) image size will use a single channel. Taking a window of half the chip will clear/read in the same amount of time as a full window, but a 256x256 window will clear/read in 1/8 the time of the full image.

As of 9/21/2005, it takes 5.4 seconds to either clear or read the entire chip in two channel mode (it used to take 3.3 seconds before work done during this shutdown).

The exposure time is the time between the start of the clear and the start of the read for NFS=0. If the observer requests an exposure time smaller than the shortest exposure time, the image will have the corresponding shortest exposure time (reflected in the FITS keyword EXPTIME) according to the window/channel settings.

For NFS>0, the exposure time of the primary data (subtraction of the last frames of each series), is the time between the start of the read for each of these frames. As for the other FITS extensions, the keyword EXPTIME corresponds to the time between the start of the initial clear and the estimated start of the read for that specific frame. The idea is that when subtracting the corresponding frames together, the resulting images will all have the same exposure time. When considered separately, each frame's EXPTIME will represent its actual exposure time.

It is also necessary to take darks for the same requested exposure time, NFS and Window combination as was taken during the night.

- Stephane Beland (9/21/2005)

NIR Standards (TUI Catalog) from Persson et al. AJ 116, 2475 (1998)

6 second exposure times gave good counts for P-550C and P-177D without going into saturation - John Barentine