J/AJ/146/12 Occultations through Saturn's C ring (Hedman+, 2013)
Kronoseismology: using density waves in Saturn's C ring to probe the planet's
interior.
Hedman M.M., Nicholson P.D.
<Astron. J., 146, 12 (2013)>
=2013AJ....146...12H 2013AJ....146...12H
ADC_Keywords: Planets ; Occultations
Keywords: planets and satellites: interiors - planets and satellites: rings
Abstract:
Saturn's C ring contains multiple spiral patterns that appear to be
density waves driven by periodic gravitational perturbations. In other
parts of Saturn's rings, such waves are generated by Lindblad
resonances with Saturn's various moons, but most of the wave-like
C-ring features are not situated near any strong resonance with any
known moon. Using stellar occultation data obtained by the Visual and
Infrared Mapping Spectrometer on board the Cassini spacecraft, we
investigate the origin of six unidentified C-ring waves located
between 80900 and 87200km from Saturn's center. By measuring
differences in the waves' phases among the different occultations, we
are able to determine both the number of arms in each spiral pattern
and the speeds at which these patterns rotate around the planet. We
find that all six of these waves have between two and four arms and
pattern speeds between 1660°/day and 1861°/day. These speeds
are too large to be attributed to any satellite resonance. Instead,
they are comparable to the predicted pattern speeds of waves generated
by low-order normal-mode oscillations within the planet. The precise
pattern speeds associated with these waves should therefore provide
strong constraints on Saturn's internal structure. Furthermore, we
identify multiple waves with the same number of arms and very similar
pattern speeds, indicating that multiple m=3 and m=2 sectoral (l=m)
modes may exist within the planet.
Description:
Between 2005 and 2009, Visual and Infrared Mapping Spectrometer (VIMS)
on board the Cassini spacecraft obtained a total of 27 occultation
cuts through the C ring with sufficient signal-to-noise and spatial
resolution to discern the relevant waves. The VIMS instrument is
described in detail in Brown et al. (2004SSRv..115..111B 2004SSRv..115..111B). Using
stellar occultation we investigate the origin of six unidentified
C-ring waves located between 80900 and 87200km from Saturn's center.
We have between 100 and 260 δφ estimates for each of the
waves (Table5).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars 31 8 Stars in the occultation pairs
table5.dat 58 1158 Time, longitude, and phase differences used to
determine pattern speeds
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See also:
J/A+A/493/1183 : Saturn major satellites observations (1874-2007)
(Desmars+, 2009)
J/AJ/136/2214 : Positions of Saturn and its satellites in 2002-2006
(Peng+, 2008)
J/A+A/485/293 : Events of Saturn satellites during 2009 equinox (Arlot+, 2008)
J/A+A/422/377 : 1997-2000 Saturn's satellites astrometry (Qiao+, 2004)
J/A+A/383/1054 : Astrometry of Pluto and Saturn in 1995-2001 (Rapaport+, 2002)
J/A+A/383/296 : Saturnian Satellites positions (1996-2000) (Peng+, 2002)
J/A+A/380/727 : 1995 Saturnian satellite observations (Vienne+, 2001)
J/A+AS/139/47 : 1995 Saturnian satellites mutual events (Emelianov+, 1999)
J/A+AS/139/305 : Position of Saturn's satellites (1982-1988) (Veiga+, 1999)
J/A+AS/136/257 : Saturn's satellites in 1995/97 (Harper+ 1999)
J/A+AS/121/65 : 1990-1994 Saturn's satellites astrometry (Harper+ 1997)
J/AJ/103/983 : Stellar occultation candidates of Saturn (Bosh+, 1992)
Byte-by-byte Description of file: stars
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Bytes Format Units Label Explanations
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1- 7 A7 --- Name Name of the star
9- 10 I2 h RAh Hour of Right Ascension (J2000) (1)
12- 13 I2 min RAm Minute of Right Ascension (J2000) (1)
15- 19 F5.2 s RAs Second of Right Ascension (J2000) (1)
21 A1 --- DE- Sign of the Declination (J2000) (1)
22- 23 I2 deg DEd Degree of Declination (J2000) (1)
25- 26 I2 arcmin DEm Arcminute of Declination (J2000) (1)
28- 31 F4.1 arcsec DEs Arcsecond of Declination (J2000) (1)
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Note (1): Positions from SIMBAD database (http://simbad.u-strasbg.fr/simbad/;
added at CDS)
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1 A1 --- --- [W]
2- 6 F5.2 Mm Wave Wave designation (1)
8- 14 A7 --- Name1 Name of the first star in the occultation pair (2)
15- 17 I03 --- Rev1 First "Rev" number of the occultation pair (3)
18 A1 --- C1 [ie] Cut obtained during ingress (i) or egress (e)
19 A1 --- --- [-]
21- 27 A7 --- Name2 Name of second star in the occultation pair (2)
28- 30 I03 --- Rev2 Second "Rev" number of the occultation pair (3)
31 A1 --- n_Rev2 [ie] Cut obtained during ingress (i) or egress (e)
33- 41 F9.5 d dt Observed time difference δt
43- 47 F5.1 deg dl Observed longitude difference δλ
49- 53 F5.1 deg dphi Phase difference δφ between waves
55- 58 F4.1 deg e_dphi Standard deviation of the phase difference
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Note (1): The radial location of the inward-propagating wave in thousands of
kilometers.
Note (2): RCas (=R Cas), RSCnc (=RS Cnc), alpAur (=α Aur),
alpSco (=α Sco), betGru (=β Gru), betPeg (=β Peg),
gamCru (=γ Cru), RHya (=R Hya).
Note (3): Cassini's orbit around Saturn (when the data were obtained).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 05-Jun-2014