ALFOSC spectroscopy countrates
Below the observed peak wide-slit count rates in electrons per second in the extracted spectrum for an mV=10 star using NOT+ALFOSC+CCD#7.| grism | blue mV=10 star | red mV=10 star | peak efficiency |  peak a | resolution b | dispersion | ||||
|---|---|---|---|---|---|---|---|---|---|---|
| star ID | per pixel | per [Â] | star ID | per pixel | per [Â] | [Â] | [Â/15µ] | |||
| 3 | 1 | 4600 | 2100 | 5 | 2700 | 1150 | 22% | 4600 | 690 | 2.3 | 4 | 2 | 5600 | 1900 | 4 | 4100 | 1350 | 28% | 5200 | 710 | 3.0 | 5 | 3 | 3800 | 1250 | 6 | 4100 | 1350 | 27% | 6400 | 830 | 3.1 | 6 | 2 | 2900 | 2100 | 4 | 1600 | 1100 | 22% | 4600 | 980 | 1.5 | 7 | 2 | 2600 | 1800 | 4 | 1900 | 1300 | 26% | 5200 | 1300 | 1.5 | 8 | 2 | 1100 | 1050 | 4 | 1300 | 1150 | 24% | 6200 | 2000 | 1.3 | 10 | 1 | 15500 | 2400 | 5 | 8800 | 1350 | 26% | 4700 | 210 | 6.5 | 11 | 1 | 10600 | 2200 | 5 | 7500 | 1550 | 30% | 5200 | 380 | 4.8 | 12 | 1 | 14400 | 1100 | 5 | 15800 | 1200 | 27% | 6700 | 190 | 13 | 14 | 3 | 2700 | 1950 | 6 | 1600 | 1150 | 21% | 4600 | 1200 | 1.4 | 15 | 3 | 4800 | 1550 | 6 | 3400 | 1100 | 21% | 5200 | 650 | 3.1 |
| echelle mode | peak efficiency | peak a | resolution b | dispersion |
|---|---|---|---|---|
| [Â] | [Â/15µ] | |||
| g9 + g10 | 10% | 5200 | 4500 @ 5000Â 3900 @ 7500Â | 0.4 @ 5000Â 0.7 @ 7500Â | g13 + order sorter | 14% | 5400 | 3700 | 0.5 | g13 + g10 | 12% | 5200 | 4300 @ 4050Â 3700 @ 5250Â | 0.35 @ 4050Â 0.5 @ 5250Â |
Click on the star ID to obtain a curve of countrate per extracted pixel scaled to mV=10.
Click here to get detailed info on the available grisms.
Notes
a) Wavelength of peak in efficiency curve.
b) With a 0.5" slit. Note that CCD#7 suffers from charge smearing and that
consequently 2-pixel resolution cannot always be achieved.
Listed below are the
spectral standard stars used for determining the throughput and
system efficiency.
| star ID | blue stars | spectral type | visual magnitude |
|---|---|---|---|
| 1 | sp0644+375 | DA | 12.1 |
| 2 | sp1045+378 | O9V | 7.0 |
| 3 | sp2032+248 | DA | 11.6 |
| star ID | red stars | spectral type | visual magnitude |
|---|---|---|---|
| 4 | sp0305+261 | sdF | 8.0 |
| 5 | sp0946+139 | sdF | 8.3 |
| 6 | sp1446+259 | sdF | 9.7 |
Slit losses for point sources
Listed below is the expected slit transmission for point sources, as a function of the ratio of slit width over seeing FWHM.| slit width / seeing | 0.4 | 0.5 | 0.75 | 1.0 | 1.3 | 1.8 | 2.5 |
| slit transmission | 0.35 | 0.43 | 0.65 | 0.76 | 0.88 | 0.96 | 1.00 |
Spatial scale and read-out noise
The spatial scale for ALFOSC+CCD#7 is about 0.19 arcsec/pixel.The read-out noise of CCD#7 is 5 to 6 electrons.
Sky brightness
ING technical note 115: La Palma night-sky brightness Chris Benn (Isaac Newton Group) and Sara Ellison (Univ. of Kent), May 1998Darkest La Palma sky: U=22, B=22.7, V=21.9, R=21.0, I=20 (high elevation, high ecliptic and galactic latitude, at sunspot minimum). Moonlight brightens the sky by about 1 mag (first/last quarter) to 4 mag (full moon) in UBV. In I the full moon brightens the sky about 2 mag.
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