Table 1 
Overview of Observations and Data Reduction


Date	Time	Telescope^a	Filter	Frames	Exposure	Read	Airmass	Moon	Comp.	Aperture^b	Scatter^c	
(UTC)	(UTC)				(s)	(s)		illum.	Stars	(pixels)	(mmag)	
2013 Dec 09	14:40:56-20:05:27	Schmidt	R	247	60, 80	4	$1.41\to 1.01\to 1.07$	0.51	5	10	2.0	
2014 Feb 27	10:54:42-18:21:57	$60\,\mathrm{cm}$	R	373	60, 70	3	$1.13\to 1.01\to 2.01$	0.04	3	11	2.0	
2014 Feb 27	11:01:37-17:54:05	Schmidt	R	295	60, 110	4	$1.12\to 1.01\to 1.75$	0.04	3	14	1.9	
2014 Mar 06	10:48:53-18:02:13	$60\,\mathrm{cm}$	R	397	60	3	$1.09\to 1.01\to 2.10$	0.32	2	10	1.6	
2014 Mar 06	11:09:38-17:27:35	Schmidt	R	251	80, 110	4	$1.06\to 1.01\to 1.76$	0.32	2	14	1.7	
2015 Jan 16	14:52:35-20:47:16	Schmidt	R	343	55	4	$1.03\to 1.01\to 1.81$	0.19	4	14	1.7	
2015 Jan 23	13:23:02-19:45:43	Schmidt	R	322	52	4	$1.12\to 1.01\to 1.56$	0.14	4	11	1.9	
2015 Jan 30	12:23:56-18:56:37	Schmidt	R	465	40, 50	4	$1.18\to 1.01\to 1.44$	0.84	4	10	1.9	
2015 Feb 13	10:40:54-16:35:31	Schmidt	R	353	45, 55	4	$1.34\to 1.01\to 1.15$	0.34	2	13	1.8	
2016 Jan 09	12:16:06-15:15:30	$60\,\mathrm{cm}$	R	695	10	3	$1.55\to 1.04$	0.00	3	10	3.0	
Notes.
^a The telescopes belong to the Xinglong Station operated by National Astronomical Observatories of China (NAOC).
^b The aperture indicates the aperture diameter around stars.
^c The scatter indicates the rms of residuals from our best-fitting model.
