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"Conn, B. C."
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The 67P/Churyumov–Gerasimenko observation campaign in support of the Rosetta mission
We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of the mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively 'well-behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit to orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends--in this paper, we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies. This article is part of the themed issue 'Cometary science after Rosetta'.
Journal Article
Ships Passing in the Night: Spectroscopic Analysis of Two Ultra-Faint Satellites in the Constellation Carina
We present Magellan/IMACS, Anglo-Australian Telescope/AAOmega+2dF, and Very Large Telescope/GIRAFFE+FLAMES spectroscopy of the CarinaII (Car II) & Carina III (Car III) dwarf galaxy candidates, recently discovered in the Magellanic Satellites Survey (MagLiteS). We identify 18 member stars in Car II, including 2 binaries with variable radial velocities and 2 RR Lyrae stars. The other 14 members have a mean heliocentric velocity \\(v_{\\rm hel} = 477.2 \\pm 1.2\\) km/s and a velocity dispersion of \\(\\sigma_v = 3.4^{+1.2}_{-0.8}\\) km/s. Assuming Car II is in dynamical equilibrium, we derive a total mass within the half-light radius of \\(1.0^{+0.8}_{-0.4} \\times 10^{6} M_\\odot\\), indicating a mass-to-light ratio of \\(369^{+309}_{-161} M_\\odot/L_\\odot\\). From equivalent width measurements of the calcium triplet lines of 9 RGB stars, we derive a mean metallicity of [Fe/H] = \\(-2.44 \\pm 0.09\\) with dispersion \\(\\sigma_{\\rm [Fe/H]} = 0.22 ^{+0.10}_{-0.07}\\). Considering both the kinematic and chemical properties, we conclude that Car II is a dark-matter-dominated dwarf galaxy. For Car III, we identify 4 member stars, from which we calculate a systemic velocity of \\(v_{\\rm hel} = 284.6^{+3.4}_{-3.1}\\) km/s. The brightest RGB member of Car III has a metallicity of [Fe/H] \\(= -1.97 \\pm 0.12\\). Due to the small size of the Car III spectroscopic sample, we cannot conclusively determine its nature. Although these two systems have the smallest known physical separation (\\(\\Delta d\\sim10~kpc\\)) among Local Group satellites, the large difference in their systemic velocities, \\(\\sim200\\) km/s, indicates that they are unlikely to be a bound pair. One or both systems are likely associated with the Large Magellanic Cloud (LMC), and may remain LMC satellites today. No statistically significant excess of \\(\\gamma\\)-rays emission is found at the locations of Car II and Car III in eight years of Fermi-LAT data.
Paper
Discovery of two neighboring satellites in the Carina constellation with MagLiteS
We report the discovery of two ultra-faint satellites in the vicinity of the Large Magellanic Cloud (LMC) in data from the Magellanic Satellites Survey (MagLiteS). Situated 18\\(^{\\circ}\\) (\\(\\sim 20\\) kpc) from the LMC and separated from each other by only \\(18^\\prime\\), Carina~II and III form an intriguing pair. By simultaneously modeling the spatial and the color-magnitude stellar distributions, we find that both Carina~II and Carina~III are likely dwarf galaxies, although this is less clear for Carina~III. There are in fact several obvious differences between the two satellites. While both are well described by an old and metal poor population, Carina~II is located at \\(\\sim 36\\) kpc from the Sun, with \\(M_V\\sim-4.5\\) and \\(r_h\\sim 90\\) pc, and it is further confirmed by the discovery of 3 RR Lyrae at the right distance. In contrast, Carina~III is much more elongated, measured to be fainter (\\(M_V\\sim-2.4\\)), significantly more compact (\\(r_h\\sim30\\) pc), and closer to the Sun, at \\(\\sim 28\\) kpc, placing it only 8 kpc away from Car~II. Together with several other systems detected by the Dark Energy Camera, Carina~II and III form a strongly anisotropic cloud of satellites in the vicinity of the Magellanic Clouds.
Paper
A stellar over-density associated with the Small Magellanic Cloud
We report the discovery of a stellar over-density 8\\(^{\\circ}\\) north of the center of the Small Magellanic Cloud (Small Magellanic Cloud Northern Over-Density; SMCNOD) using data from the first two years of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarly composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0.01). The SMCNOD has an elongated shape with an ellipticity of 0.6 and a size of \\(\\sim\\) 6x2 deg. It has an absolute magnitude of \\(M_V \\cong\\) -7.7, \\(r_h = 2.1\\) kpc, and \\(\\mu_V(r
Paper
The 67P/Churyumov-Gerasimenko observation campaign in support of the Rosetta mission
We present a summary of the campaign of remote observations that supported the European Space Agency's Rosetta mission. Telescopes across the globe (and in space) followed comet 67P/Churyumov-Gerasimenko from before Rosetta's arrival until nearly the end of mission in September 2016. These provided essential data for mission planning, large-scale context information for the coma and tails beyond the spacecraft, and a way to directly compare 67P with other comets. The observations revealed 67P to be a relatively `well behaved' comet, typical of Jupiter family comets and with activity patterns that repeat from orbit-to-orbit. Comparison between this large collection of telescopic observations and the in situ results from Rosetta will allow us to better understand comet coma chemistry and structure. This work is just beginning as the mission ends -- in this paper we present a summary of the ground-based observations and early results, and point to many questions that will be addressed in future studies.
Paper
An Ultra-Faint Galaxy Candidate Discovered in Early Data from the Magellanic Satellites Survey
We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644-5953 (Pictor II or Pic II) is a low surface brightness ({\\mu} = 28.5 mag arcsec\\(^{-2}\\) within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of 45 kpc. The physical size (r\\(_{1/2}\\) = 46 pc) and low luminosity (Mv = -3.2 mag) of this satellite are consistent with the locus of spectroscopically confirmed ultra-faint galaxies. MagLiteS J0644-5953 (Pic II) is located 11.3 kpc from the Large Magellanic Cloud (LMC), and comparisons with simulation results in the literature suggest that this satellite was likely accreted with the LMC. The close proximity of MagLiteS J0644-5953 (Pic II) to the LMC also makes it the most likely ultra-faint galaxy candidate to still be gravitationally bound to the LMC.
Paper
A portrait of the extreme Solar System object 2012 DR30
2012 DR30 is a recently discovered Solar System object on a unique orbit, with a high eccentricity of 0.9867, a perihelion distance of 14.54 AU and a semi-major axis of 1109 AU, in this respect outscoring the vast majority of trans-Neptunian objects. We performed Herschel/PACS and optical photometry to uncover the size and albedo of 2012 DR30, together with its thermal and surface properties. The body is 185 km in diameter and has a relatively low V-band geometric albedo of ~8%. Although the colours of the object indicate that 2012 DR30 is an RI taxonomy class TNO or Centaur, we detected an absorption feature in the Z-band that is uncommon among these bodies. A dynamical analysis of the target's orbit shows that 2012 DR30 moves on a relatively unstable orbit and was most likely only recently placed on its current orbit from the most distant and still highly unexplored regions of the Solar System. If categorised on dynamical grounds 2012 DR30 is the largest Damocloid and/or high inclination Centaur observed so far.
Paper
AGB stars as tracers of metallicity and mean age across M33
Wide-field JHKs near-infrared observations covering an area of 1.8x1.8 sq. deg. centred on M33 were obtained using WFCAM at UKIRT. These data show a large population of intermediate-age asymptotic giant branch stars (AGB). We have used both C-type and M-type AGB stars to determine spatial variations in metallicity and mean age across the galaxy. We distinguished between C-type and M-type AGB stars from their location in the colour-magnitude diagram (J-Ks, Ks). The distribution of these stars is supported by a cross-identification between our sample and a catalogue of optically confirmed, long-period variable stars, as well as with the list of sources detected by Spitzer in the mid-infrared. We calculated the C/M ratio and the orientation of the galaxy in the sky, and compared the Ks magnitude distribution with theoretical distributions spanning a range of metallicities and star formation rates (SFRs). The C/M ratio surface map confirms a metallicity gradient in the galaxy corresponding to a spread in [Fe/H]=0.6 dex with substructures in the inner and outer galaxy. Magnitude and colour variations suggest orientation and extinction effects on the galaxy disc. Maps showing the distribution of mean age and metallicity obtained from the Ks method suggest that: the outer galaxy disc/halo is metal poorer than the nuclear region and metal-rich clumps in the inner galaxy change location with time. The average outer ring and nuclear stellar population is ~6 Gyr old while central regions are a few Gyr younger.
Paper
Correcting the influence of an asymmetric line spread function in 2-degree Field spectrograph data
We investigate the role of asymmetries in the line spread function of the 2-degree field spectrograph and the variations in these asymmetries with the CCD, the plate, the time of observation and the fibre. A data-reduction pipeline is developed that takes these deformations into account for the calibration and cross-correlation of the spectra. We show that, using the emission lines of calibration lamp observations, we can fit the line spread function with the sum of two Gaussian functions representing the theoretical signal and a perturbation of the system. This model is then used to calibrate the spectra and generate templates by downgrading high resolution spectra. Thus, we can cross-correlate the observed spectra with templates degraded in the same way. Our reduction pipeline is tested on real observations and provides a significant improvement in the accuracy of the radial velocities obtained. In particular, the systematic errors that were as high as ~20 km/s when applying the AAO reduction package 2dfDR are now reduced to ~5 km/s. Even though the 2-degree Field spectrograph is to be decommissioned at the end of 2005, the analysis of archival data and previous studies could be improved by the reduction procedure we propose here.
Paper
Studies of Mira and semiregular variables using visual databases
We use wavelets to investigate period and amplitude changes in Mira and semiregular variables and found a variety of behaviours. Period and amplitude changes often go together, perhaps because changes in amplitude are causing period changes via non-linear effects.
Paper