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ACS Instrument Handbook
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Advanced Camera for Surveys Instrument Handbook for Cycle 20 > Glossary

The following terms and acronyms are used in this Handbook.
2MASS: Two Micron All Sky Survey.
ABMAG: –2.5 log (Fν) – 48.60 where Fν is the flux from the source in erg cm–2 sec-1 Hz-1
ABν: Correction to ABMAG to account for the fact that the source spectrum is not constant in Fν (ABMAG=V+ABν)
ACS: Advanced Camera for Surveys
ACS-R: Repaired ACS from SM4
ADC: Analog to digital converter
Aladin: Interactive sky atlas (
APT: Astronomer’s Proposal Tool
ASIC: Application-Specific Integrated Circuit in CEB-R
aXe: Spectroscopic Data Extraction Software
BOP: Bright Object Protection
BOT: Bright Object Tools for SBC proposing
calacs: ACS calibration pipeline software
CCD: Charge Coupled Device. Solid-state, light detecting device
CDS: Correlated Double Sampling mode in CEB-R (dual-slope integration or clamp-and-sample)
CEB: CCD Electronics Box
CEB-R: New CCD Electronics Box installed during SM4
CMD: Color Magnitude Diagram
CP: Call for Proposals
CR: Cosmic ray
CR-SPLIT: Division of a CCD exposure into shorter exposures to be used for cosmic ray rejection
CS: Contact Scientist for a HST proposal
CTE: Charge transfer efficiency
CVZ: Continuous viewing zone
DN: Data number
DSI: Dual-Slope Integrator
DSS: Digital Sky Survey
ETC: Exposure Time Calculator. ETCs are Web-based tools which can be accessed through the ACS Web pages.
ERO: Early release observations
FGS: Fine Guidance Sensors
FOS: Faint Object Spectrograph
FOV: Field of view
FTP: File Transfer Protocol. Basic tool used to retrieve files from a remote system. Ask your system manager for information about using FTP.
FUV: Far ultraviolet (~912 to 2000 Å)
FWHM: Full width at half maximum
GALEX: Galaxy Evolution Explorer
GHRS: Goddard High-Resolution Spectrograph
GO: General Observer
GSC: Guide Star Catalog
GSC2: Guide Star Catalog II
GTO: Guaranteed Time Observer
Help Desk: Facility for getting help on HST related topics via e-mail.
HRC: High Resolution Channel
HST: Hubble Space Telescope
IDT: Investigation Definition Team
IR: Infrared
IRAF: Image Reduction and Analysis System. The environment in which ­STSDAS operates.
ISR: Instrument Science Report
IUE: International Ultraviolet Explorer Satellite
K: Degree Kelvin
L-flats: Low Frequency Variations Flats
LMC: Large Magellanic Cloud
LVPS-R: replacement Low Voltage Power Supply
MAMA: Multi-Anode Microchannel Array
MAST: STScI Multi-mission Archive
MCP: Microchannel Plate
MPP: Multi Pinned Phased, a CCD mode that reduces dark current rate
NICMOS: Near-Infrared Camera and Multi-Object Spectrograph
NIR: Near infrared
NUV: Near ultraviolet (~2000 to 4000 Å)
OTA: Optical Telescope Assembly
OTFR: On-the-fly re-calibration pipeline that has the ability to select the most up-to-date reference files for science images at the time of request.
PASP: Publications of the Astronomical Society of the Pacific
PC: Program Coordinator
Phase I proposal: A proposal for observing time on HST
Phase II program: An approved HST program; includes precise detail of how program is to be executed
PI: Principal investigator
P-flats: pixel-to-pixel high-frequency flats
POS TARG: POSition TARGet is used to move the sky in the FOV of the camera
PRF: Pixel Response Function
PSF: Point-spread function.
PyRAF: version of IRAF implemented in the Python language
QE: Quantum Efficiency
QEH: Quantum Efficiency Hysteresis
Quadrant: Section of detector that is read-out by an amplifier. For WFC, there are 4 amplifiers, two for each detector, so each amplifier reads one 2048 x 2048 pixel quadrant.
RA: Right Ascension
RAS: HST simulator used in ground tests to accurately simulate the full field OTA illumination, and is used to calibrate HST instruments. Also know as RAS/HOMS, the Refractive Aberrated Simulator/Hubble Opto-Mechanical Simulator.
reference file: data file containing ACS parameters or calibration information which is used by the calibration pipeline
rms: Root mean square
RQE: Responsive Quantum Efficiency
SAA: South Atlantic anomaly
SBC: Solar-Blind Channel
SDSS: Sloan Digital Sky Survey
SIDECAR: System Image, Digitizing, Enhancing, Controlling, And Retrieving
SITe: Scientific Image Technologies; company that designed the ACS CCDs
SLIM: Slitless Spectroscopy Simulator
SM4: Servicing Mission 4 to HST in May 2009
SMOV: Servicing Mission Observatory Verification
S/N: signal-to-noise ratio
SNAPSHOT: Short exposures taken during unused blocks of telescope time.
SSDR: Solid state data recorders
ST-ECF: Space Telescope European Coordinating Facility
STAN: Space Telescope Analysis Newsletter
STIS: Space Telescope Imaging Spectrograph
STScI: Space Telescope Science Institute
STSDAS: Space Telescope Science Data Analysis System. The complete suite of IRAF data analysis and calibration routines used to process HST data.
synphot1: STSDAS synthetic photometry (IRAF) software package
TAC: Telescope Allocation Committee
TECs: Thermal Electric Coolers
Tiny Tim: PSF simulation software developed by John Krist &
Richard Hook
TIR: Technical Instrument Report
URL: Uniform resource locator. Address for WWW.
UV: Ultraviolet
UVIS: Ultraviolet and Visual (CCD channel of WFC3)
WFC: Wide-Field Channel
WFC3: Wide Field Camera 3, new instrument installed during SM4
WFPC2: Wide Field Planetary Camera-2. Replacement for WF/PC installed during first servicing mission of December 1993.
WWW: World Wide Web. Hypertext-oriented method for finding and retrieving information over the Internet.

Synphot will soon be replaced by the pysynphot package, a significantly improved re-implementation of Synphot written in Python. Please visit the pysynphot Web page at

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