J/AJ/152/142 Spitzer and WISE light curves of Neptune (Stauffer+, 2016)
Spitzer Space Telescope Mid-IR light curves of Neptune.
Stauffer J., Marley M.S., Gizis J.E., Rebull L., Carey S.J., Krick J.,
Ingalls J.G., Lowrance P., Glaccum W., Kirkpatrick J.D., Simon A.A.,
Wong M.H.
<Astron. J., 152, 142-142 (2016)>
=2016AJ....152..142S 2016AJ....152..142S (SIMBAD/NED BibCode)
ADC_Keywords: Planets ; Photometry, infrared
Keywords: planets and satellites: individual: Neptune
Abstract:
We have used the Spitzer Space Telescope in 2016 February to obtain
high cadence, high signal-to-noise, 17hr duration light curves of
Neptune at 3.6 and 4.5µm. 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 1.1mag at 3.6µm
and 0.6mag at 4.5µm. We have also extracted sparsely sampled 18hr
light curves of Neptune at W1 (3.4µm) and W2 (4.6µm) 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 ∼0.02mag) or
at 845nm with the Hubble Space Telescope (HST) in 2015 and at 763nm in
2016 (amplitude ∼0.2mag). 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 845nm, WISE W1, and
Spitzer 3.6µm filters.
Description:
Neptune was observed between UT 2016 February 21-23 in both of the
3.6µm (IRAC-1) and 4.5µm (IRAC-2) channels of the Infrared Array
Camera (IRAC) on Spitzer. The measurements were part of Director's
Discretionary Time Program 12125 (PI: Stauffer).
The Astronomical Observation Requests (AORs) were made in IRAC's
staring mode, where for each channel, the spacecraft is maneuvered so
that the target is placed on the well-calibrated peak-up pixel and
back-to-back frames taken for the total time of the AOR with no
dithering. For each channel, the total duration of the AOR was set to
cover a complete rotation of Neptune, or about 17.2hr. In channel 1
(3.6µm), frames with times of 100s were used (corresponding to
96.8s exposure times), resulting in 622 images (see table1); in
channel 2 (4.5µm), a frametime of 30s was used (corresponding to
26.8s exposure times), resulting in 2018 images (see table2). The
image files were dark-subtracted, linearized, flat-fielded, and
calibrated using the S19.2 version of the IRAC pipeline. We had
requested that the channel 2 observations be made immediately
following the channel 1 observations, but a time-critical exoplanet
transit observation was inserted between the two Neptune AORs,
resulting in the channel 2 light curve beginning about 2.3 days after
the start of the channel 1 observation.
Flux densities were measured with aperture photometry on the Spitzer
Basic Calibrated Data images. We converted aperture fluxes to
magnitudes using the in-band flux densities of Vega: 278Jy (3.6µm)
and 180Jy (4.5µm). The light curve data of Neptune measured with
Spitzer/IRAC are provided in Tables 1 and 2. These are the first
continuous Neptune light curves covering a full rotation at mid-IR
wavelengths.
WISE was launched on 2009 December 14 to survey the sky in four broad
wavelength bands referred to as W1 (3.4µm), W2 (4.6µm), W3
(12µm), and W4 (22µm). Neptune has been observed at six
different epochs in the currently available WISE and NEOWISE data
releases. Its magnitudes range from W1∼10.1-11.5mag, W2∼9.5-11.1mag,
W3∼2.8-3.1mag, and W4∼0.0-0.3mag. The light curve data at the WISE W1
and W2 bands are provided in Table3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 27 623 Spitzer 3.6µm light curve for Neptune
table2.dat 27 2018 Spitzer 4.5µm light curve for Neptune
table3.dat 38 82 WISE light curve data for Neptune
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See also:
II/311 : WISE All-Sky Data Release (Cutri+ 2012)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d BMJD Barycentric Modified Julian Date (G1)
13- 19 F7.4 mag [3.6] [10.9/12.2] Spitzer/IRAC 3.6µm band
magnitude (1)
21- 27 F7.4 mag e_[3.6] [0.0015/0.018] Uncertainty in [3.6]
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Note (1): The amplitude at 3.6µm is 1.06mag, corresponding to a
peak-to-trough flux variation of more than a factor of 2.5.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 F11.5 d BMJD Barycentric Modified Julian Date (G1)
13- 19 F7.4 mag [4.5] [9.4/10.8] Spitzer/IRAC 4.5µm band
magnitude (1)
21- 27 F7.4 mag e_[4.5] [0.0015/0.045] Uncertainty in [4.5]
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Note (1): The amplitude at 4.5µm is 0.59mag, corresponding to a
peak-to-trough flux variation of about 1.7.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 12 F12.6 d MJD Modified Julian Date of the observation
14- 19 F6.3 mag W1mag [10/11.6] WISE 3.4µm band magnitude
21- 25 F5.3 mag e_W1mag [0.014/0.052] Uncertainty in W1mag
27- 32 F6.3 mag W2mag [9.5/11.1] WISE 4.6µm band magnitude
34- 38 F5.3 mag e_W2mag [0.015/0.28] Uncertainty in W2mag
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Global Notes:
Note (G1): Of observation at the start of the 100s integration.
History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 03-Feb-2017