An Apparent Second Plateau in the UBVRIJHK Eruption Light Curve of the Recurrent Nova U Sco

ATel #2507; Ashley Pagnotta, Bradley E. Schaefer (Louisiana State Univ.), Gerald Handler (Univ. Vienna), Bill Allen, Tut Campbell, Tom Krajci, Berto Monard, Robert D. Rea, Thomas Richards, George Roberts, William Stein, Chris Stockdale, Jennie McCormick (Center for Backyard Astrophysics), Shawn Dvorak, Tomas Gomez, Barbara G. Harris, Arne Henden, George Sjoberg, Thiam Guan Tan (AAVSO), Arto Oksanen (Caisey Harlingten Observatory)
on 24 Mar 2010; 21:49 UT
Credential Certification: Ashley Pagnotta (pagnotta@phys.lsu.edu)

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We report on the post-plateau (ATEL #2452, #2477) optical and IR behavior of the recurrent nova U Sco (IAUC # 9111 ). We present UBVRIJHK magnitudes from the SMARTS 1.3m telescope, the SAAO 0.5m, and 16,800 fast photometry magnitudes from many small telescopes worldwide.

After the relatively fast decline from V=15.1 on March 1.0 to V=16.9 on March 11.0, the decline has slowed noticeably and U Sco appears to be in a second plateau where its out-of-eclipse magnitude is fairly constant, varying between 17.1 and 16.8 in V. This is distinctly above the quiescence level of V=18.0. The BVIJK light curve (for phases outside eclipse) can be seen at the website linked below. The observed V-band light curve (with smoothing and interpolation) from Jan 23.5 to March 19.5 (with 0.01 day resolution) and the data used to construct the curve are also available at the linked website.

Across the eruption, the colors have changed very slowly, nearly-monotonically, and with moderate-to-small amplitude. A curious exception is B-V which started out significantly positive near peak, was significantly negative during the initial fast decline of U Sco (about 2 - 10 days after peak), and then returned to being positive. The following table gives colors on selected dates throughout the eruption, where the dates are given in UT, Heliocentric JD, and Days After Discovery (D.A.D., 2010 Jan 28.4385).

UT	HJD-2455000	D.A.D.	V	U-B	B-V	V-R	V-I	V-J	V-H	V-K
Jan 29.33	225.83	0.89	9.12	-0.89	0.35	0.73	1.30	..	..	..
Jan 30.38	226.88	1.94	9.93	-0.68	-0.02	0.92	1.03	..	..	..
Feb 1.36	228.86	3.92	10.99	-0.56	-0.20	0.74	0.66	1.18	1.43	2.06
Feb 6.35	233.85	8.91	13.14	-0.56	-0.27	0.45	0.63	1.08	1.46	2.17
Feb 9.34	236.84	11.90	13.95	-0.71	0.14	0.29	0.50	0.95	1.34	2.08
Feb 14.33	241.83	16.89	14.28	-0.69	0.19	0.24	0.48	0.87	1.24	1.78
Feb 23.34	250.84	25.90	14.72	..	0.21	0.23	0.51	0.82	1.13	1.90
Mar 3.33	258.83	33.90	15.54	..	0.25	0.20	0.48	0.82	1.13	1.37
Mar 9.32	264.82	39.88	16.50	..	0.35	0.20	0.52	0.95	1.26	..
Mar 13.28	268.78	43.84	16.88	..	0.28	0.15	0.42	1.00	1.10	..
Mar 18.34	273.84	48.90	17.00	..	0.30	0.17	0.47	0.90	1.10	..

BVIJK and Smoothed V-band Light Curves