Hokupa'a Sensitivity

For reference, the following table lists the magnitude zero points (for 1 ADU/s) and the sky brightnesses. For J, H, and Kp the zero-points were measured from data taken during the December 2000 run. Note the relatively bright sky background at Kp is due in part to the extra thermal emissivity in Hokupa'a.

Hokupa'a+QUIRC Zero-points and Sky Brightnesses
Filter	Magnitude Zero Pt.	Sky Background (mag/arcsec²)	Sky Background (ADU/s/pix)	Notes
J	25.3	15.4	4+-2	a
H	25.6	13.9	20+-5	a
K'	24.9	12.0	60+-20	a

Notes to table:
(a) Zero points were measured from data taken during the December 2000 run.

Point Source Sensitivities:

The limiting magnitudes for point sources were calculated for a 5-sigma detection for the flux within the 50% encircled energy diameter in a one hour integration (total on-source exposure time). Median seeing conditions and an on-axis bright guide star (R < 15 mag) were assumed. Magnitude zero points in J, H, and Kp were taken from the table above. Please use these sensitivities for S/N calculations.

Note that the sensitivity limits depend on the performance of the adaptive optics system. In particular under poorer performance conditions (e.g. operating in worse seeing or for when using an off-axis guide star), the limiting magnitude will be brighter. For example, in 0.85'' seeing the larger 50%EED diameter results in a limiting magnitude about 1 magnitude brighter.

(5 sigma, 1 hour, pt. source within 50% EED^b)
Filter	50% EED (arcsec)	limiting flux density (Magnitude)	limiting flux density (microJy)	Notes
J	0.30	23.9	0.4	a
H	0.24	23.1	0.6	a
K'	0.18	22.1	1.0	a

Notes to table:
(a) PSFs were simulated and matched (for K-band) to dedication images. The residual jitter and the aberrations in QUIRC were inferred (no high-order telescope aberrations are assumed). The table assumes a seeing of r0 = 23cm (0.5'' seeing). The magnitude zero points were measured from the 2000 December Hokupaa/QUIRC run.
(b) Using a 100 mas aperture improves the sensitivity in H, K, and K' by about 0.2 magnitudes.

Extended Source Sensitivities:

The limiting magnitudes for extended sources were calculated for a 5-sigma detection for the flux within one square arcsecond in a one hour integration (total on-source exposure time). Magnitude zero points in J, H, and Kprime were taken from the table above.

Note that the source is assumed to be isolated (e.g. not near a bright star). In cases where there is a bright star nearby, the limiting magnitude will be strongly affected by the distribution of light in the point spread function.

(5 sigma, 1 hour, ext. source within 1 sq. arcsec)
Filter	limiting flux density (mag/sq. arcsec)	limiting flux density (microJy/sq. arcsec)	Notes
J	22.8	1.2	a
H	20.7	6.0	a
K'	18.7	22	a

Notes to table:
(a) The magnitude zero points were measured from the 2000 December Hokupaa/QUIRC run.