On the rotation period of (90377) Sedna

We present precise, similar to 1%, r-band relative photometry of the unusual solar system object ( 90377) Sedna. Our data consist of 143 data points taken over eight nights in 2004 October and 2005 January 2005. The rms variability over the longest contiguous stretch of five nights of data spanning 9 days is only similar to 1.3%. This subset of data alone constrains the amplitude of any long-period variations with period P to be A less than or similar to 1%(P/20 days)(2). Over the course of any given similar to 5 hr segment, the data exhibit significant linear trends not seen in a comparison star of similar magnitude, and in a few cases these segments show clear evidence of curvature at the level of a few millimagnitudes per hour squared. These properties imply that the rotation period of Sedna is O(10 hr); it cannot be less than or similar to 5 hr nor can it be greater than or similar to 10 days, unless the intrinsic light curve has significant and comparable power on multiple timescales, which is unlikely. A sinusoidal fit yields a period of and a semiamplitude P = 10.273 +/- 0.002 hr and a semiamplitude of A = 1.1% +/- 0.1%. There are additional acceptable fits with flanking periods separated by similar to 3 minutes as well as another class of fits with, although these later fits appear less viable based on visual inspection. P similar to 18 hr Our results indicate that the period of Sedna is likely consistent with typical rotation periods of solar system objects, thus obviating the need for a massive companion to slow its rotation.