J/AJ/159/27 LCs of the Manwe-Thorondor eclipsing system (Rabinowitz+, 2020)
The complex rotational light curve of (385446) Manwe-Thorondor, a multicomponent
eclipsing system in the Kuiper Belt.
Rabinowitz D.L., Benecchi S.D., Grundy W.M., Verbiscer A.J., Thirouin A.
<Astron. J., 159, 27 (2020)>
=2020AJ....159...27R 2020AJ....159...27R
ADC_Keywords: Minor planets; Solar system; Photometry, ugriz;
Magnitudes, absolute
Keywords: Kuiper belt ; Light curves ; Small solar system bodies
Abstract:
Kuiper Belt Object (385446) Manwe-Thorondor is a multiobject system
with mutual events predicted to occur from 2014 to 2019. To detect the
events, we observed the system at 4 epochs (UT 2016 August 25 and 26,
2017 July 22 and 25, 2017 November 9, and 2018 October 6) in g, r, and
VR bands using the 4m SOAR and the 8.1m Gemini South telescopes at
Cerro Pachon, Chile, and Lowell Observatory's 4.3m Discovery Channel
Telescope at Happy Jack, Arizona. These dates overlap the uncertainty
range (±0.5 day) for four inferior events (Thorondor eclipsing
Manwe). We clearly observe variability for the unresolved system with
a double-peaked period 11.88190±0.00005hr and ∼0.5mag amplitude
together with much longer-term variability. Using a multicomponent
model, we simultaneously fit our observations and earlier photometry
measured separately for Manwe and Thorondor with the Hubble Space
Telescope. Our fit suggests Manwe is bilobed, close to the "barbell"
shape expected for a strengthless body with density ∼0.8g/cm3 in
hydrostatic equilibrium. For Manwe, we thereby derive maximum width to
length ratio ∼0.30, surface area equivalent to a sphere of diameter
190km, geometric albedo 0.06, mass 1.4x1018kg, and spin axis oriented
∼75deg from Earth's line of sight. Changes in Thorondor's brightness
by ∼0.6mag with a ∼300day period may account for the system's
long-term variability. Mutual events with unexpectedly shallow depth
and short duration may account for residuals to the fit. The system is
complex, providing a challenging puzzle for future modeling efforts.
Description:
The epoch 1 observations reported here were obtained in the Sloan
Digital Sky Survey (SDSS) r and g bands on two consecutive nights
(2016 August 25 and 26 UT) using the SOAR Optical Imager on the 4m
SOAR telescope at Cerro Pachon, Chile. The imager pixel scale was
0.154".
The epoch 2 observations were obtained in SDSS r and g bands on 2017
July 22 and 25 UT using the GMOS-S imager on the 8.1m Gemini South
telescope at Cerro Pachon, Chile. The imager pixel scale was 0.16".
The epoch 3 observations were obtained on 2017 November 9 UT in r band
using the Large Monolithic Imager (LMI) on Lowell Observatory's
Discovery Channel Telescope (DCT) at Happy Jack AZ. The LMI pixel
scale was 0.24".
The epoch 4 observations were obtained on 2018 October 6 UT in a wide
VR band, again using the LMI on the DCT.
Table2 lists the observing circumstances for each epoch.
Table 4 lists resolved photometry of Manwe and Thorondor previously
obtained with the HST Wide-Field Planetary Camera2 (WFPC2) in the
F606W band at seven different epochs from 2007 to 2013.
Grundy+ (2014Icar..237....1G 2014Icar..237....1G) report magnitudes for Manwe and
Thorondor derived from these data after transforming F606W to V band
and averaging the results from each epoch. Here we present the
measurements without transformation or averaging.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 75 1 *Binary orbital parameters for Manwe-Thorondor
table2.dat 64 6 Observing circumstances
table3.dat 41 225 Photometric observations of Manwe-Thorondor
table4.dat 64 25 F606W-band photometry of Manwe-Thorondor with HST
table6.dat 124 1 Multicomponent model parameters
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Note on table1.dat: Orbital elements are for Thorondor relative to Manwe
(Grundy+, 2014Icar..237....1G 2014Icar..237....1G ) and referred to the
J2000 equatorial frame.
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
B/astorb : Orbits of Minor Planets (Bowell+, 2014)
J/A+A/380/347 : BVRI photometry of 27 Kuiper Belt Objects (Delsanti+, 2001)
J/A+A/407/1139 : RVB photometry Kuiper-Belt obj. 1999 TD10 (Rousselot+, 2003)
J/AJ/127/3023 : R magnitudes Kuiper Belt object 2001QG298 (Sheppard+, 2004)
J/AJ/135/55 : NIR spectra Centaurs & Kuiper Belt objects (Barkume+, 2008)
J/A+A/509/A94 : Lightcurves of 14 NEAs (Kwiatkowski+, 2010)
J/A+A/511/A49 : Lightcurves of 12 NEAs (Kwiatkowski+, 2010)
J/ApJ/720/1691 : Observations of the distant Kuiper belt (Schwamb+, 2010)
J/A+A/546/A86 : R absolute magnitudes Kuiper Belt objects (Peixinho+, 2012)
J/ApJ/749/10 : SDSS observations of Kuiper belt objects (Ofek, 2012)
J/A+A/556/A8 : 100 asteroids rotational parameters (Lhotka+, 2013)
J/A+A/562/A48 : Light curves of asteroid (25143) Itokawa (Lowry+, 2014)
J/ApJS/227/20 : Rotation periods of asteroids using iPTF (Chang+, 2016)
J/AJ/154/62 : Orbital parameters of Kuiper Belt objects (Volk+, 2017)
J/AJ/154/241 : Photometry Kuiper Belt object: 2002 CC249 (Thirouin+, 2017)
J/A+A/627/A172 : Near-Earth asteroid (1917) Cuyo opt. & IR obs. (Rozek+,2019)
J/AJ/157/228 : Cold Classical TNOs LCs & rot. properties (Thirouin+,2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 F7.3 d Per Manwe-Thorondor orbital period
9- 13 F5.3 d e_Per Error on Per
15- 18 I4 km a Manwe-Thorondor semi-major axis
20- 21 I2 km e_a Error on a
23- 28 F6.4 --- e Manwe-Thorondor eccentricity
30- 35 F6.4 --- e_e Error on e
37- 44 E8.4 kg Msys System mass
46- 53 E8.4 kg e_Msys Error on M
55- 59 F5.2 deg inc Manwe-Thorondor inclination
61- 64 F4.2 deg e_inc Error on inc
66- 70 I5 deg Omega Manwe-Thorondor ascending node
72- 75 F4.2 deg e_Omega Error on Omega
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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 I1 --- Epoch [1/4] Epoch number
3- 13 A11 "date" Date UT observation date
15- 20 A6 --- Tel Telescope used: DCT, Gemini and SOAR,
2 occurrences for each
22- 25 A4 --- Filt Filter used: VR 1 occurrences, g 4 occurrences
and r 5 occurrences
27- 30 A4 "h:m" Obs.start UT start time of the observation
32- 36 A5 "h:m" Obs.end UT end time of the observation
38- 42 A5 "h:m" Midpt UT event midpoint (1)
44- 47 F4.2 mag Depth [0.05/0.66]? Event depth (1)
49- 52 F4.2 deg theta [0.4/1.1] Solar phase angle (Θ)
54- 58 F5.2 AU rhel [43.4/43.7] Heliocentric distance (rhel)
60- 64 F5.2 AU rgeo [42/43] Geocentric distance (rgeo)
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Note (1): Event midpoints and depths are predicted values assuming
spherical shaped bodies with Lambertian light-scattering properties
and nominal diameters 160 and 92km for Manwe and Thorondor,
respectively.
Event parameters are unlisted if no event was expected within 12hr of
the observation start or end time. Event midpoints are uncertain by
∼0.5day, and event durations are ∼0.5day.
All events listed are inferior events with Thorondor in front of
Manwe. See Grundy+, 2014Icar..237....1G 2014Icar..237....1G.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
-------------------------------------------------------------------------------
1- 6 A6 --- Tel Telescope used (1)
8- 17 F10.5 d JD [7625/8398] Julian Date of observation, JD-2450000
19- 20 A2 --- Filt Filter used: "VR" 34 occurrences,
"g" 43 occurrences or "r" 148 occurrences
22- 26 F5.2 mag omag [21.7/24.6] Observed magnitude in Filt
28- 31 F4.2 mag e_omag [0.02/0.25] Uncertainty in omag
33- 35 I3 s Exp [150/600] Exposure time
37- 41 F5.2 mag O-C [-0.28/0.31] Fit Residuals
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Note (1): Telescope used as follows:
DCT = The 4.3m Lowell Observatory's Discovery Channel Telescope,
at Happy Jack AZ (39 occurrences);
Gemini = the 8.1m Gemini South telescope at Cerro Pachon, Chile
(99 occurrences);
SOAR = the 4m SOAR telescope at Cerro Pachon, Chile (87 occurrences)
See the "Description" section above.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 4 I4 yr Obs.Y [2007/2013] Year of observation, UT
6- 8 A3 "month" Obs.M Month of observation, UT
10- 11 I2 d Obs.D [4/26] Day of observation, UT
13- 22 F10.5 d JD [4306/6618] Julian date of observation,
JD-2450000
24- 28 F5.2 mag Mmag [23.2/24.1] Manwe HST/WFPC2 F606W magnitude
29- 29 A1 --- f_Mmag [*] *: rejected measurement
31- 34 F4.2 mag e_Mmag [0.05/0.11] Uncertainty in Mmag
36- 40 F5.2 mag Tmag [24.2/26.1]? Thorondor HST/WFPC2 F606W magnitude
41- 41 A1 --- f_Tmag [*] *: rejected measurement
43- 46 F4.2 mag e_Tmag [0.05/0.69]? Uncertainty in Tmag
48- 52 F5.2 mag M*mag [22.9/23.5] Pseudo magnitude for
Manwe+Thorondor (1)
53- 53 A1 --- f_M*mag [*] *: rejected measurement
55- 58 F4.2 deg theta [0.08/1.21] Solar phase angle of the
Manwe/Thorondor system (Θ)
60- 64 F5.3 arcsec Sep [0.03/0.33] Separation (Δ)
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Note (1): Pseudo magnitude which is the F606W magnitude that would be observed
for Manwe+Thorondor (unresolved) if the magnitude of Thorondor were
fixed at its weighted mean value, Tmag=24.4mag, determined from all
the unrejected HST observations.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 3 I3 km DiamM Diameter of sphere with equivalent area as
Manwe
5- 7 I3 km DiamMVol Diameter of sphere with equivalent volume as
Manwe
9- 11 I3 km DiamT Diameter of Thorondor
13- 19 E7.3 kg MM Mass of Manwe
21- 24 F4.2 --- MT/MM Upper limit to Thorondor/Manwe mass ratio (1)
26- 29 F4.2 --- pM Albedo of Manwe
31- 34 F4.2 --- pT Albedo of Thorondor
36- 38 F3.1 mag/deg beta Linear dependence on solar phase angle (β)
40- 47 F8.5 h PerM Rotation period of Manwe
49- 57 F9.1 d t1 Reference Julian date for absolute magnitudes
59- 62 F4.2 g/m3 rho Average density of the Manwe/Thorondor system
(ρ)
64- 72 F9.1 --- epsT Julian date of minimum brightness for Thorondor
(εT)
74- 78 F5.1 deg OmegaM Ascending node of Manwe's equator (Ω) (2)
80- 83 F4.1 deg incM Inclination of Manwe's equator (2)
85- 87 F3.1 deg RotM Rotation angle of Manwe's long axis (µ) (3)
89- 92 F4.1 deg aM Average angle between Manwe's spin and
Manwe-Earth direction (<αM>)
94- 99 F6.2 d PerT Rotation period of Thorondor (single-peaked)
101-104 F4.2 mag AmpT Light-curve amplitude of Thorondor
(peak-to-peak)
106-109 F4.2 mag gMAG Absolute g-band magnitude of Manwe/Thorondor
(Hg) at epoch t1
111-114 F4.2 mag rMAG Absolute r-band magnitude of Manwe/Thorondor
(Hr) at epoch t1
116-119 F4.2 mag MMAG Absolute F606W-band magnitude of Manwe
(HM) at epoch t1
121-124 F4.2 mag TMAG Absolute F606W-band magnitude of Thorondor
(HT) at epoch t1
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Note (1): Assuming equal density, ρ, for Manwe and Thorondor.
Note (2): J2000 equatorial coordinates.
Note (3): Relative to the ascending node of Manwe's equator at JD 2454300.0.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS] 12-Mar-2020