Spitzer Space Telescope Mid-Ir Light Curves of Neptune

Abstract

We have used the Spitzer Space Telescope in 2016 February to obtain high cadence, high signal-to-noise, 17 hr duration light curves of Neptune at 3.6 and 4.5 μm. The light curve duration was chosen to correspond to the rotation period of Neptune. Both light curves are slowly varying with time, with full amplitudes of 1.1 mag at 3.6 μm and 0.6 mag at 4.5 μm. We have also extracted sparsely sampled 18 hr light curves of Neptune at W1 (3.4 μm) and W2 (4.6 μm) from the Wide-feld Infrared Survey Explorer (WISE)/NEOWISE archive at six epochs in 2010-2015. These light curves all show similar shapes and amplitudes compared to the Spitzer light curves but with considerable variation from epoch to epoch. These amplitudes are much larger than those observed with Kepler/K2 in the visible (amplitude ∼0.02 mag) or at 845 nm with the Hubble Space Telescope (HST) in 2015 and at 763 nm in 2016 (amplitude ∼0.2 mag). We interpret the Spitzer and WISE light curves as arising entirely from reflected solar photons, from higher levels in Neptune's atmosphere than for K2. Methane gas is the dominant opacity source in Neptune's atmosphere, and methane absorption bands are present in the HST 763 and 845 nm, WISE W1, and Spitzer 3.6 μm filters.

Rotation of Late-type Stars in Praesepe with K2

“…Much of our current analysis is very similar to that we conducted in the Pleiades (Rebull et al 2016a(Rebull et al , 2016bStauffer et al 2016), and we often make comparisons to the Pleiades analysis and results. In Section 2, we present the observations and data reduction, as well as the range of data from the literature that we assembled, and define the final sample of members that we analyze in the rest of the paper.…”

“…Linear fits are also shown in the blue, yellow, and red+green regimes. For the Pleiades, colored points follow Stauffer et al (2016), Figure 24: blue is 1.1 < (V−Ks) 0 < 2.6 and yellow is 2.5 < (V -Ks) 0 < 3.7. The bulk of the distribution through both of these regions trace out the "slowly rotating sequence"; the transition to yellow is placed at the location of the "kink" in the slowly rotating sequence.…”

“…In each plot, the solid vertical lines denote different regions of the diagram defined in the discussion; the dotted vertical lines are the lines from the other cluster (the solid lines in the Praesepe plot are the dotted lines in the Pleiades plot and vice versa). Rebull et al (2016b) and Stauffer et al (2016). Obvious pulsators have been removed in both plots.…”

“…The vertical lines are the same as the prior figure. The curved black line is the fit to the Pleiades M stars from Stauffer et al (2016) and is the same in both panels. The M star relation is steeper in Praesepe.…”

“…Mann et al (2016a) similarly derive rotation periods while searching for exoplanet transits; they illustrate the distribution of rotation periods as a function of M k and color, but do not otherwise discuss the periods or LC morphology. Finally, our group plotted an early version of the Praesepe period distribution in Stauffer et al (2016) in the context of comparing the Pleiades rotation periods to those in other clusters. However, no paper has yet published a complete analysis of the K2 Praesepe rotational data nor a discussion of the LC morphologies shown by those stars.…”