4 Calibration for the CCD field of view

We adopt two theories, G5 (Arlot 1982) and the newest JUP204 (Jacobson 2002), for the four Galilean satellites. In order to compute equatorial coordinates for the satellites, we also use JPL DE405 (Standish 1998) for the Jupiter. While calibrating the CCD field of view, we calculate topocentric positions for the Jupiter and Galilean satellites. Besides, both atmospheric refractions and the central projection (projection of the celestial sphere on the tangential plane of the focal point) are also taken into account. However, no phase effect is corrected for the observations of Galilean satellites since they are made very close to the opposition.

As well known, a small field of view of a CCD ( $6\hbox{$.\mkern-4mu^\prime$ }4\times6\hbox{$.\mkern-4mu^\prime$ }4$) has no enough reference stars chosen for calibrating the CCD device. We prefer to use a specific technique ("Brighter Moon Calibration'' method), which has been used in the previous works (Harper et al. 1997; Shen et al. 2001; Vienne et al. 2001; and Paper I) for the calibration in our reduction. Strictly, the "Brighter Moon Calibration'' method should only be used to obtain observations of inner faint satellites whose observational errors are large enough not to be affected by systematic errors in the scale and orientation caused by errors in the ephemerides of the bright satellites. Here, this method is used only to test our image-processing techniques and to assess the internal precision.

Table 1 gives results for the CCD calibration derived by using the four Galilean satellites. We see almost the same parameters for different exp-time subsets when the same ephemeris is used. Besides, for the same exp-time subset a very small difference exists when JUP204 and G5 are used respectively. The scales and orientations solved from all 133 frames of CCD images are adopted in the following reduction.

 

 

Table 1: The calibration parameters for the scale and orientation of CCD chip are computed by the JUP204 and G5 ephemerides respectively. N gives the number of frames of CCD images.

JUP204	N	Scale	Orientation
Subset		(arcsec/pixel)	(degree)
1 s exp-time	43	0.373633	179.527
2 s exp-time	46	0.373631	179.529
3 s exp-time	44	0.373630	179.528
Total	133	0.373631	179.528
G5	N	Scale	Orientation
Subset		(arcsec/pixel)	(degree)
1 s exp-time	43	0.373657	179.521
2 s exp-time	46	0.373655	179.522
3 s exp-time	44	0.373654	179.522
Total	133	0.373655	179.522

 

 

Table 2: Statistics of the mean (O-C)s (Observed minus Computed) (unit: mas) of each satellite and Jupiter with respect to Ganymede. N gives the number of observations. JI, JII and JIV represent Io, Europa and Callisto, respectively. Calibration parameters from JUP204 and G5, respectively, are adopted.

	Calibrated by	JUP204
	referred theory			JUP204					G5
Subset	N	object	mean	s.e.	mean	s.e.		mean	s.e.	mean	s.e.
			$\Delta$$\alpha$cos$\delta$		$\Delta$$\delta$			$\Delta$$\alpha$cos$\delta$		$\Delta$$\delta$
1 s exp-time	43	JI	-47	13	-2	11		50	9	-4	12
	43	JII	41	33	-30	38		152	33	-31	37
	43	JIV	61	26	-49	23		198	26	-93	23
	43	Jupiter	-49	26	-62	33		48	26	-81	33
2 s exp-time	46	JI	-46	13	-3	12		50	8	-4	13
	46	JII	42	26	-33	31		153	26	-34	31
	46	JIV	61	16	-44	23		198	16	-88	23
	46	Jupiter	-46	24	-63	30		52	24	-83	30
3 s exp-time	44	JI	-46	12	-3	10		52	6	-4	10
	44	JII	47	21	-34	20		158	21	-34	19
	44	JIV	67	12	-47	19		204	12	-91	19
	44	Jupiter	-45	18	-63	17		53	18	-82	17
Total	133	JI	-46	13	-2	11		51	8	-4	11
	133	JII	44	27	-32	30		154	27	-33	30
	133	JIV	63	19	-46	22		200	19	-91	22
	133	Jupiter	-47	23	-63	27		51	23	-82	27
	Calibrated by	G5
	referred theory			JUP204					G5
Subset	N	object	mean	s.e.	mean	s.e.		mean	s.e.	mean	s.e.
			$\Delta$$\alpha$cos$\delta$		$\Delta$$\delta$			$\Delta$$\alpha$cos$\delta$		$\Delta$$\delta$
1 s exp-time	43	JI	-49	14	0	11		48	9	-2	11
	43	JII	50	33	-52	38		169	33	-53	37
	43	JIV	55	26	-33	23		192	26	-77	23
	43	Jupiter	-44	26	-77	32		53	26	-96	32
2 s exp-time	46	JI	-49	13	-1	12		48	8	-2	12
	46	JII	51	26	-56	31		162	26	-56	31
	46	JIV	54	16	-27	23		192	16	-72	23
	46	Jupiter	-41	24	-78	30		57	24	-98	30
3 s exp-time	44	JI	-48	12	-1	9		49	7	-3	10
	44	JII	57	21	-56	20		167	21	-57	19
	44	JIV	60	12	-30	19		198	12	-75	19
	44	Jupiter	-40	18	-78	17		58	18	-97	17
Total	133	JI	-49	13	-1	11		48	8	-2	11
	133	JII	53	27	-55	30		163	27	-56	30
	133	JIV	56	19	-30	22		194	19	-75	22
	133	Jupiter	-42	23	-78	27		56	23	-97	27