Table 2:

Observations summary.

ID		Observatory	Observing time		Number of frames					Precision (mmag)					PSF function
			(nights)	(hours)	U	B	V	I	Total	U	B	V	I	(mmag)
1		OAN-SPM	15	63.9	-	-	-	-	-	-	-	-	-	-	-
2	a	Baker	1	1.8	-	-	111	-	111	-	-	6.1	-	1.03	Penny 1
2	b		6	33.9	-	2558	2564	-	5122	-	7.5	7.0	-	0.25	Moffat 25
3	a	ORM	135	399.0	2969	2968	2997	2932	11 866	3.8/6. 6	3.6/5.0	3.9/5.4	4.1/5.4	0.18	Moffat 25
3	b		14	28.6	-	-	-	-	-	-	-	-	-	-	-
4		OFXB	12	64.5	-	1107	1133	1089	3329	-	5.4	5.1	7.5	0.27	Moffat 25
5		Michelbach	9	18.5	-	479	476	475	1430	-	7.8	4.8	5.7	0.39	Gaussian
6		Vienna	17	90.7	-	4301	2140	3255	9696	-	5.1	10 .7	4.8	0.41	Moffat 25
7		Biaków	71	287.7	-	2830	12 438	5405	20 673	-	2.6	3.0	3.8	0.05	Moffat 25
8		Athens	8	24.3	-	-	967	970	1937	-	-	6.8/5.3	6.8/4.8	0.35	Penny 2/Moffat 15
9		EUO	3	13.0	-	1244	1245	-	2489	-	5.7	6.3	-	0.32	Penny 2
10	a	TUG	2	8.8	106	101	105	-	312	5.8	4.4	4.4	-	0.76	Moffat 25
10	b		3	14.7	-	293	289	-	582	-	9.2	8.0	-	0.83	Penny 1
11		Xinglong	42	186.2	-	-	18 663	-	18 663	-	-	4.7	-	0.06	Moffat 15
12		SOAO	13	50.7	-	289	422	522	1233	-	3.6	4.1	4.0	0.35	Moffat 25
Total			351	1286.3	3075	16 170	43 550	14 648	77 443	5.3	6.9	5.7	5.0	0.05

Notes. For ORM and Athens Observatory two precision numbers are noted. For ORM, these values refer to the first observation season on the one hand and to the second and third season on the other hand. For Athens Observatory, the two numbers refer to non-binned and binned images, respectively.  = denotes the noise in the amplitude spectrum of the V light curve, and the PSF function in the table is the analytical function we used to calculate the PSF photometry in DAOPHOT.