Hubble Space Telescope Primer for Cycle 11
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| Hubble Space Telescope Primer for Cycle 11 | |||
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4.1 Overview
Table 4.1 - 4.5 summarize the capabilities of the SIs. For some applications more than one instrument can accomplish a given task, but not necessarily with equal quality or speed. Note that there may be small differences between the numbers quoted here and those quoted in the Instrument Handbooks. In such cases the Handbook numbers take precedence.
Table 4.1: HST Instrument Capabilities: Direct1 Imaging
SI Field of View [arcsec] Projected Pixel Spacing on Sky [arcsec] Wavelength Range [Å] Magnitude Limita ACS/WFCb ACS/HRC ACS/SBC 202 x 202 29 x 26 35 x 31 ~0.05 ~0.025 ~0.030 3700-11,000 2000-11,000 1150-1700 28.8 28.1 22.6 NICMOS/NIC1 NICMOS/NIC2 NICMOS/NIC3 11 x 11 19 x 19 51 x 51 0.043 0.076 0.20 8000-19,000 8000-25,000 8000-25,000 22.7 24.1 25.0 STIS/CCD STIS/NUV STIS/FUV 52 x 52 25 x 25 25 x 25 0.05 0.024 0.024 2500-11,000 1650-3100 1150-1700 28.5 24.6 24.0 WFPC2c 150 x 150 35 x 35 0.10 0.0455 1200-11,000 1200-11,000 27.5 27.8
a. Limiting V magnitude for an unreddened A0 V star in order to achieve a signal-to-noise ratio of 5 in an exposure time of 1 hour assuming low-background conditions (LOW; see Section 5.5.1). The limiting magnitude for imaging in the visual is strongly affected by the sky background; under normal observing conditions, the limiting magnitude can be about 0.5 brighter than listed here. Please note that low-sky conditions limit flexibility in scheduling and are not compatible with observing in the CVZ. Single entries refer to wavelengths near the center of the indicated wavelength range. STIS direct imaging entries assume use of a clear filter for the CCD and the quartz filter for the UV (for sky suppression). STIS NUV and FUV limits assume the higher background rates (see Section 4.5.2) that will apply following SM3B. For STIS spectroscopy to achieve the specified signal-to-noise ratio per wavelength pixel with a 0.5" slit, multiple values are given corresponding to 1300, 2800 and 6000 Å, respectively (if in range). The ACS/WFC, ACS/HRC and WFPC2 entries in Table 4.1 assume filter F606W. The WFPC2 Charge Transfer Efficiency (CTE) losses are negligible for this filter, due to the significant sky background accumulated over 3600 sec in F606W. However, note that WFPC2 images of faint point sources with little sky background can experience significant CTE losses; please see the WFPC2 InstrumentHandbook for details. The ACS/SBC entry in Table 4.1 assumes filter F115LP. For NICMOS imaging, we assume filter F160W with a detector temperature of 78 K + dark current bump; the limiting H magnitude, in the Vega system, is given for a point source to reach S/N=5 in 1 hr exposure. Please see the NICMOS Instrument Handbook, Chapter 7, for details
b. With ramp filters, the FOV is much smaller for the ACS/WFC. Please see the ACS Instrument Handbook for details
c. The WFPC2 has four CCD chips that are exposed simultaneously. Three are "wide-field" chips, each covering a 75" x 75" field and arranged in an "L" shape, and the fourth is a "planetary" chip covering a 35" x 35" field
Table 4.2: HST Instrument Capabilities: Slit Spectroscopy
STISc 52" x (0.05-2)" [optical] (25-28)" x (0.05-2)"
[UV first order]
(0.1-0.2)" x (0.025-0.2)"
[UV echelle]
25" x (0.05-0.2)"
[NUV prism]
a. The resolving power is lambda/resolution; for STIS it is/2
b. Limiting V magnitude for an unreddened A0 V star in order to achieve a signal-to-noise ratio of 5 in an exposure time of 1 hour assuming low-background conditions (LOW; see Section 5.5.1). See footnote a in Table 4.1 for details
c. The 25" or 28" first order slits are for the MAMA detectors, the 52" slit is for the CCD. The R ~150 entry for the prism on the NUV-MAMA is given for 2300 Å. More accurate and up to date values for spectroscopic limiting magnitudes can be found in the STIS Instrument Handbook.
Table 4.3: HST Instrument Capabilities: Slitless Spectroscopy
SI Field of View [arcsec] Projected Pixel Spacing on Sky [arcsec] Resolving Power Wavelength Range [Å] Magnitude Limit1 ACS/WFC grism G800L ACS/HRC grism G800L ACS/HRC prism PR200L ACS/SBC prism PR130L NICMOS2 STIS3 WFPC23
1Limiting V magnitude for an unreddened A0 V star in order to achieve a signal-to-noise ratio of 5 in an exposure time of 1 hour assuming low-background conditions (LOW; see Section 5.5.1).
2NICMOS has three grisms (G096,G141,G206) for use in NIC3. We assume a detector temperature of 78 K + dark current bump and "average" zodiacal light; the limiting Vega system H magnitude for spectroscopy is given for a point source to reach S/N=5 in 1 hr exposure. The sensitivities of the grisms were multiplied with a correction factor corr = 1.696 - 0.227*
3 All STIS modes can be operated in a slitless manner by replacing the slit by a clear aperture. WFPC2 has a capability of obtaining low-resolution spectra by placing a target successively at various locations in the WFPC2 linear ramp filter. STIS also has a prism for use in the UV.
Table 4.4: HST Instrument Capabilities: Positional Astrometry
FGS1R 69 square arcmin 1-2 mas
3 mas4700-7100 <14.5
<17.0
Table 4.5: HST Instrument Capabilities: Binary Star Resolution and Measurements
FGS1R
1 WFPC2, ACS, and NICMOS have polarimetric imaging capabilities. STIS, ACS, and NICMOS have coronographic capabilities.
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