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We observe Saturn and its ring system at wavelengths of 1.3 mm (220 GHz) using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) interferometric array. We study the intensity and polarisation structure of the planet and present the best polarisation data of Saturn at these frequencies. Observations using CARMA E-array configuration exhibited some anomalous polarisation pattern in the rings. We provide details of our analysis and discuss the possibility of self gravity wakes in Saturn's ring system resulting in this anomaly. We observe Venus in intensity and polarisation to cross-check the levels of polarisation signal detectable by CARMA. We also discuss how limitations in CARMA instrumental accuracy for observing weakly polarised sources, project this signature as an upper bound of polarisation measurements of Saturn using CARMA., Comment: 9 pages, 7 figures, Submitted to MNRAS

We present the Cassini Atlas Of Stellar Spectra (CAOSS), comprised of near-infrared low-resolution spectra of bright stars recovered from space-based observations by the Cassini spacecraft. The 65 stellar targets in the atlas are predominately M, K and S giants. However it also contains spectra of other bright nearby stars including carbon stars and main sequence stars from A to F. The spectra presented are free of all spectral contamination caused by the Earth's atmosphere, including the detrimental telluric molecular bands which put parts of the near-infrared spectrum out of reach of terrestrial observations. With a single instrument, a spectro-photometric dataset is recovered that spans the near-infrared from 0.8 to 5.1 microns with spectral resolution ranging from R=53.5 to R=325. Spectra have been calibrated into absolute flux units after careful characterisation of the instrumental spectral efficiency. Spectral energy distributions for most stars match closely with literature values. All final data products have been made available online., Comment: 10 emulateapj pages, 4 figures, 4 tables. Accepted by ApJS. Full atlas available at http://www.physics.usyd.edu.au/sifa/caoss/

High angular resolution images of IRC+10216 are presented in several near infrared wavelengths spanning more than 8 years. These maps have been reconstructed from interferometric observations obtained at both Keck and the VLT, and also from stellar occultations by the rings of Saturn observed with the Cassini spacecraft. The dynamic inner regions of the circumstellar environment are monitored over eight epochs ranging between January 2000 and July 2008. The system is shown to experience substantial evolution within this period including the fading of many previously reported persistent features, some of which had been identified as the stellar photosphere. These changes are discussed in context of existing models for the nature of the underlying star and the circumstellar environment. With access to these new images, we are able to report that none of the previously identified bright spots in fact contain the star, which is buried in its own dust and not directly visible in the near infrared., Comment: 9 pages, 6 figures, Accepted by MNRAS

We use solar occultations observed by the Visual and Infrared Mapping Spectrometer aboard the Cassini Spacecraft to extract the 1 to 5 micron transmission spectrum of Saturn, as if it were a transiting exoplanet. We detect absorption from methane, ethane, acetylene, aliphatic hydrocarbons, and possibly carbon monoxide with peak-to-peak features of up to 90 parts-per-million despite the presence of ammonia clouds. We also find that atmospheric refraction, as opposed to clouds or haze, determines the minimum altitude that could be probed during mid-transit. Self-consistent exoplanet atmosphere models show good agreement with Saturn's transmission spectrum but fail to reproduce a large absorption feature near 3.4 microns likely caused by gaseous ethane and a C-H stretching mode of an unknown aliphatic hydrocarbon. This large feature is located in one of the Spitzer Space Telescope bandpasses and could alter interpretations of transmission spectra if not properly modeled. The large signal in Saturn's transmission spectrum suggests that transmission spectroscopy of cold, long-period gaseous exoplanets should be possible with current and future observatories. Motivated by these results, we briefly consider the feasibility of a survey to search for and characterize cold exoplanets analogous to Jupiter and Saturn using a target-of-opportunity approach., Comment: 15 pages, 9 figures. Accepted to ApJ. Data available in the source files

We present a study of the behavior of Saturn's A ring outer edge, using images and occultation data obtained by the Cassini spacecraft over a period of 8 years from 2006 to 2014. More than 5000 images and 170 occultations of the A ring outer edge are analyzed. Our fits confirm the expected response to the Janus 7:6 Inner Lindblad resonance (ILR) between 2006 and 2010, when Janus was on the inner leg of its regular orbit swap with Epimetheus. During this period, the edge exhibits a regular 7-lobed pattern with an amplitude of 12.8 km and one minimum aligned with the orbital longitude of Janus, as has been found by previous investigators. However, between 2010 and 2014, the Janus/Epimetheus orbit swap moves the Janus 7:6 LR away from the A ring outer edge, and the 7-lobed pattern disappears. In addition to several smaller-amplitudes modes, indeed, we found a variety of pattern speeds with different azimuthal wave numbers, and many of them may arise from resonant cavities between the ILR and the ring edge; also we found some other signatures consistent with tesseral resonances that could be associated with inhomogeneities in Saturn's gravity field. Moreover, these signatures do not have a fixed pattern speed. We present an analysis of these data and suggest a possible dynamical model for the behavior of the A ring's outer edge after 2010.

Images obtained by the Cassini spacecraft between 2012 and 2015 reveal a periodic brightness variation in a region of Saturn's D ring that previously appeared to be rather featureless. Furthermore, the intensity and radial wavenumber of this pattern have decreased steadily with time since it was first observed. Based on analogies with similar structures elsewhere in the D ring, we propose that this structure was created by some event that disturbed the orbital motions of the ring particles, giving them finite orbital eccentricities and initially aligned pericenters. Differential orbital precession then transformed this structure into a spiral pattern in the ring's optical depth that became increasingly tightly wound over time. The observed trends in the pattern's radial wavenumber are roughly consistent with this basic model, and also indicate that the ring-disturbing event occurred in early December 2011. Similar events in 1979 may have generated the periodic patterns seen in this same region by the Voyager spacecraft. The 2011 event could have been caused by debris striking the rings, or by a disturbance in the planet's electromagnetic environment. The rapid reduction in the intensity of the brightness variations over the course of just a few years indicates that some process is either damping orbital eccentricities in this region or causing the orbital pericenters of particles with the same semi-major axis to become misaligned., Comment: 26 pages, 6 Figures, Accepted for publication in Icarus, modified to fix errors found in proofs

The appearance of debris disks around distant stars depends upon the scattering/phase function (SPF) of the material in the disk. However, characterizing the SPFs of these extrasolar debris disks is challenging because only a limited range of scattering angles are visible to Earth-based observers. By contrast, Saturn's tenuous rings can be observed over a much broader range of geometries, so their SPFs can be much better constrained. Since these rings are composed of small particles released from the surfaces of larger bodies, they are reasonable analogs to debris disks and so their SPFs can provide insights into the plausible scattering properties of debris disks. This work examines two of Saturn's dusty rings: the G ring (at 167,500 km from Saturn's center) and the D68 ringlet (at 67,600 km). Using data from the cameras onboard the Cassini spacecraft, we are able to estimate the rings' brightnesses at scattering angles ranging from 170 to 0.5 degrees. We find that both of the rings exhibit extremely strong forward-scattering peaks, but for scattering angles above 60 degrees their brightnesses are nearly constant. These SPFs can be well approximated by a linear combination of three Henyey-Greenstein functions, and are roughly consistent with the SPFs of irregular particles from laboratory measurements. Comparing these data to Fraunhofer and Mie models highlights several challenges involved in extracting information about particle compositions and size distributions from SPFs alone. The SPFs of these rings also indicate that the degree of forward scattering in debris disks may be greatly underestimated., Comment: 39 pages, 15 Figures, Published in ApJ

We present an advance in the use of Cassini observations of stellar occultations by the rings of Saturn for stellar studies. Stewart et al. (2013) demonstrated the potential use of such observations for measuring stellar angular diameters. Here, we use these same observations, and tomographic imaging reconstruction techniques, to produce two dimensional images of complex stellar systems. We detail the determination of the basic observational reference frame. A technique for recovering model-independent brightness profiles for data from each occulting edge is discussed, along with the tomographic combination of these profiles to build an image of the source star. Finally we demonstrate the technique with recovered images of the {\alpha} Centauri binary system and the circumstellar environment of the evolved late-type giant star, Mira., Comment: 8 pages, 8 figures, Accepted by MNRAS

The recent discovery of dense rings around the Centaur Chariklo (and possibly Chiron) reveals that complete dense planetary rings are not only found around Saturn and Uranus, but also around small bodies orbiting in the vicinity of those giant planets. This report examines whether there could be a physical process that would make rings more likely to form or persist in this particular part of the outer Solar System. Specifically, the ring material orbiting Saturn and Uranus appears to be much weaker than the material forming the innermost moons of Jupiter and Neptune. Also, the mean surface temperatures of Saturn's, Uranus' and Chariklo's rings are all close to 70 K. Thus the restricted distribution of dense rings in our Solar System may arise because icy materials are particularly weak around that temperature., Comment: 4 Pages, 1 Figure, Accepted for publication in APJL. Updated to fix small wording changes in proofs

Previous investigations of Saturn's outer D ring (73,200-74,000 km from Saturn's center) identified periodic brightness variations whose radial wavenumber increased linearly over time. This pattern was attributed to a vertical corrugation, and its temporal variability implied that some event --possibly an impact with interplanetary debris-- caused the ring to become tilted out the planet's equatorial plane in 1983. This work examines these patterns in greater detail using a more extensive set of Cassini images in order to obtain additional insights into the 1983 event. These additional data reveal that the D ring is not only corrugated, but also contains a time-variable periodic modulation in its optical depth that probably represents organized eccentric motions of the D-ring's particles. This second pattern suggests that whatever event tilted the rings also disturbed the radial or azimuthal velocities of the ring particles. Furthermore, the relative amplitudes of the two patterns indicate that the vertical motions induced by the 1983 event were 2.3+/-0.5 times larger than the corresponding in-plane motions. If these structures were indeed produced by an impact, material would need to strike the ring at a steep angle (more than 60 degrees from the ring plane) to produce such motions. Meanwhile, the corrugation wavelengths in the D ring are about 0.7% shorter than one would predict based on extrapolations from similar structures in the nearby C ring. This could indicate that the D-ring was tilted/disturbed about 60 days before the C ring. Such a timing difference could be explained if the material that struck the ring was derived from debris released when some object broke up near Saturn some months earlier. This debris would need to have a substantial initial velocity dispersion and have its orbital properties perturbed by solar tides prior to its collision with the rings., Comment: 53 Pages, 11 Figures, Accepted for publication in Icarus, Includes small corrections found in the proof stage

Image photometry reveals that the F ring is approximately twice as bright during the Cassini tour as it was during the Voyager flybys of 1980 and 1981. It is also three times as wide and has a higher integrated optical depth. We have performed photometric measurements of more than 4,800 images of Saturn's F ring taken over a five-year period with Cassini's Narrow Angle Camera. We show that the ring is not optically thin in many observing geometries and apply a photometric model based on single-scattering in the presence of shadowing and obscuration, deriving a mean effective optical depth tau = 0.033. Stellar occultation data from Voyager PPS and Cassini VIMS validate both the optical depth and the width measurements. In contrast to this decades-scale change, the baseline properties of the F ring have not changed significantly from 2004 to 2009. However, we have investigated one major, bright feature that appeared in the ring in late 2006. This transient feature increased the ring's overall mean brightness by 84% and decayed with a half-life of 91 days., Comment: 27 pages, 12 figures, 2 tables

We present an analysis of the VIMS solar occultations dataset, which allows us to extract vertically resolved information on the characteristics of Titan's atmosphere between 100-700 km with a characteristic vertical resolution of 10 km. After a series of data treatment procedures, 4 occultations out of 10 are retained. This sample covers different seasons and latitudes of Titan. The transmittances show clearly the evolution of the haze and detect the detached layer at 310 km in Sept. 2011 at mid-northern latitudes. Through the inversion of the transmission spectra with a line-by-line radiative transfer code we retrieve the vertical distribution of CH$_4$ and CO mixing ratio. The two methane bands at 1.4 and 1.7 {\mu}m are always in good agreement and yield an average stratospheric abundance of $1.28\pm0.08$%. This is significantly less than the value of 1.48% obtained by the GCMS/Huygens instrument. The analysis of the residual spectra after the inversion shows that there are additional absorptions which affect a great part of the VIMS wavelength range. We attribute many of these additional bands to gaseous ethane, whose near-infrared spectrum is not well modeled yet. Ethane contributes significantly to the strong absorption between 3.2-3.5 {\mu}m that was previously attributed only to C-H stretching bands from aerosols. Ethane bands may affect the surface windows too, especially at 2.7 {\mu}m. Other residual bands are generated by stretching modes of C-H, C-C and C-N bonds. In addition to the C-H stretch from aliphatic hydrocarbons at 3.4 {\mu}m, we detect a strong and narrow absorption at 3.28 {\mu}m which we tentatively attribute to the presence of PAHs in the stratosphere. C-C and C-N stretching bands are possibly present between 4.3-4.5 {\mu}m. Finally, we obtain the CO mixing ratio between 70-170 km. The average result of $46\pm16$ ppm is in good agreement with previous studies., Comment: 51 pages, 28 figures