Low-resolution
Single Raw Frame
| Low-resolution Spectroscopy | ||||||||
| count rates (ADU/s/coadd) | ||||||||
| Filter | source | sp. type | mag. | itime (s) | slit (") | source | sky line | bkg |
| NIRSPEC-2 | HD 89239 | A0V | V=6.528 | 4 | 42 x 0.76 | 3500 | 9 | 2 |
| NIRSPEC-3 (J) | HD 129653 | A2 | J=6.980 | 3 | 42 x 0.76 | 3900 | 12 | - |
| NIRSPEC-5 (H) | FS 27 | G8IV/V | H=13.181 | 5 | 42 x 0.76 | 13 | 25 | 1 |
| NIRSPEC-7 | FS 27 | G8IV/V | K=13.123 | 5 | 42 x 0.76 | 14 | 16 | 1-5 |
- Notes
- source and sky line count rates are peak
- bkg count rates (between sky lines) are typical unless there was a large range (i.e. in NIRSPEC-7)
Background Subtracted Nod Pair (using positive beam only)
| Low-resolution Spectroscopy | ||||||
| Filter | source | sp. type | mag. | itime (s) x coadd | slit (") | SNR/pixel |
| NIRSPEC-5 (H) | FS 27 | G8IV/V | H=13.181 | 5 x 2 | 42 x 0.76 | 12 |
| NIRSPEC-7 ~2.0µm |
FS 27 | G8IV/V | K=13.123 | 5 x 2 | 42 x 0.76 | 12 |
| NIRSPEC-7 ~2.2µm |
FS 27 | G8IV/V | K=13.123 | 5 x 2 | 42 x 0.76 | 8 |
| NIRSPEC-7 ~2.4µm |
FS 27 | G8IV/V | K=13.123 | 5 x 2 | 42 x 0.76 | 3 |
- Notes
- by using the negative beam, one can increase SNR by root 2 (1.4) in the source noise-limited case.
- Decreasing source counts with increasing wavelength and increasing background noise with increasing wavelength conspire to drive down the SNR in NIRSPEC-7 at longer wavelengths.
High-resolution
Single Raw Frame
| High-resolution Spectroscopy | |||||||||
| count rates (ADU/s/coadd) | |||||||||
| Filter | source | sp. type | mag. | itime (s) x coadd | slit (") | seeing (") | source | sky line | bkg |
| NIRSPEC-7 | HR 3067 | A3V | K=4.362 | 4 x 1 | 0.576 x 12 | ˜0.5 | 1760 | n/a | 0 |
| NIRSPEC-7 | HR 1237 | A0V | K=6.074 | 15 x 1 | 0.576 x 12 | ˜0.5 | 410 | n/a | 0 |
| NIRSPEC-7 | HIP 53735 | A0V | K=8.856 | 150 x 1 | 0.576 x 12 | ˜0.5 | 32 | n/a | 0 |
- Notes
- seeing estimated from FWHM across spectrum of 3.5 pixels (x 0.144 "/pixel)
- source count rates are peak
- the few sky lines were not measured
- average backgrounds were near 0
Background Subtracted Nod Pair (using positive beam only)
| High-resolution Spectroscopy | |||||||
| Filter | source | sp. type | mag. | itime x coadd x frames | slit (") | typical counts | SNR/pixel |
| NIRSPEC-7 | HR 3027 | A3V | K=4.362 | 4 x 1 x 2 | 0.576 x 12 | 6000 | 150 |
| NIRSPEC-7 | HR 1237 | A0V | K=6.074 | 15 x 1 x 2 | 0.576 x 12 | 6000 | 150 |
| NIRSPEC-7 | HIP 53735 | A0V | K=8.856 | 150 x 1 x 2 | 0.576 x 12 | 4000 | 120 |
- Notes
- by using the negative beam, one can increase SNR by root 2 (1.4) in the source noise-limited case.
- typical counts is "St" in the below relation.
- rms in background (B) was 5-15 in all cases (assumed 10 ADU)
SNR/pixel values were determined by the relation:
Sgt S = source count rate (ADU/s)
SNR = ______________________ where B = rms in background (ADU); implicit time dependence
______________________ D = dark current (0.2 e-/s/pix)
/ g = gain (4 e-/ADU for SPEC)
/ Sgt + Bg + Dt + r^2 t = integration time (itime x coadds)
\/ r = read noise ( 2 x (25 e-)^2 = 1250 e- for nod pair)
The calculated values match a "by-eye" assessment using cuts through the spectra.
Last modified: Fri Mar 31 15:05:01 HST