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To help identify interplanetary coronal mass ejections (ICMEs) in New Horizons (NH) Solar Wind Around Pluto observations, we developed a method for determining the alpha to proton density ratio (nα/np). Many common ICME signatures are derived from plasma and field parameters with values inside transient ICMEs distinct from values in the background solar wind. As the solar wind propagates, the plasma parameters evolve with increasing heliocentric distance, and ICMEs interact with the background solar wind. Some ICME signatures are based on composition such as the alpha (He++) to proton (H+) number density ratio, which is frequently enhanced in ICMEs. Intervals with enhanced nα/np ratios persist into the outer heliosphere even though individual solar wind parameters evolve as solar wind propagates farther from the Sun. Overall, the solar wind expands as it propagates, but parcels of differing speeds dynamically interact, forming compressions and rarefactions, and altering the solar wind parameters. Both nα and np change in lock step during such dynamic interactions, keeping the nα/np ratio fixed. Our nα/np results are consistent with prior missions, and we find that enhanced levels of nα/np often occur within intervals of low proton temperature, which is the only other reliable ICME signature that NH can measure. Eventually, enhanced nα/np values will likely become the most reliable ICME indicator for NH if the ICME temperatures become indistinguishable from background levels. NH is heading toward the Energetic Neutral Atom ribbon, and should have enough power to reach the termination shock. [ABSTRACT FROM AUTHOR]

We use deep near-IR photometry of the VISTA Variables in the Vía Láctea (VVV) Survey and deep DECam Plane Survey (DECaPS) optical photometry to confirm the physical reality of the candidate globular cluster (GC) Minni 22, which is located in the Galactic bulge. This object, which was detected as a high density region in our maps of bulge red giants, is now confirmed as a real GC based on the optical and near-IR color–magnitude diagrams. We also recover three known fundamental mode (ab type) RR Lyrae stars within 2 arcmin of the cluster center. The presence of RR Lyrae stars also seems to confirm Minni 22 as a bonafide old and metal-poor GC. We estimate a cluster reddening mag and determine its heliocentric distance D = 7.4 ± 0.3 kpc. The optical and near-IR color–magnitude diagrams reveal well-defined red giant branches in all cases, including a red giant branch bump at Ks = 13.30 ± 0.05 mag. The comparison with theoretical isochrones yields a mean metallicity of [Fe/H] = −1.3 ± 0.3 dex, and age of t ∼ 11.2 Gyr. This is a good example of a new low-luminosity (MV = −6.2 mag) GC found in the central bulge of the Milky Way. After discussing the different ways to confirm the existence of bulge GC candidates, we find that one of the best methods is to use the CMDs from the combination of the DECaPS + VVV photometries. [ABSTRACT FROM AUTHOR]

We present a search for new members of the 300 km s−1 stream (300S) near the dwarf galaxy Segue 1 using wide-field survey data. We identify 11 previously unknown bright stream members in the APOGEE-2 and SEGUE-1 and 2 spectroscopic surveys. Based on the spatial distribution of the high-velocity stars, we confirm for the first time that this kinematic structure is associated with a 24°-long stream seen in SDSS and Pan-STARRS imaging data. The 300S stars display a metallicity range of −2.17 < [Fe/H] < −1.24, with an intrinsic dispersion of dex. They also have chemical abundance patterns similar to those of Local Group dwarf galaxies, as well as that of the Milky Way halo. Using the open-source code galpy to model the orbit of the stream, we find that the progenitor of the stream passed perigalacticon about 70 Myr ago, with a closest approach to the Galactic center of about 4.1 kpc. Using Pan-STARRS DR1 data, we obtain an integrated stream luminosity of 4 × 103L⊙. We conclude that the progenitor of the stream was a dwarf galaxy that is probably similar to the satellites that were accreted to build the present-day Milky Way halo. [ABSTRACT FROM AUTHOR]

Regular satellites of giant planets are formed by accretion of solid bodies in circumplanetary disks. Planetesimals that are moving on heliocentric orbits and are sufficiently large to be decoupled from the flow of the protoplanetary gas disk can be captured by gas drag from the circumplanetary disk. In the present work, we examine the distribution of captured planetesimals in circumplanetary disks using orbital integrations. We find that the number of captured planetesimals reaches an equilibrium state as a balance between continuous capture and orbital decay into the planet. The number of planetesimals captured into retrograde orbits is much smaller than that into prograde orbits, because the former experience a strong headwind and spiral into the planet rapidly. We find that the surface number density of planetesimals at the current radial location of regular satellites can be significantly enhanced by gas drag capture, depending on the velocity dispersions of the planetesimals and the width of the gap in the protoplanetary disk. Using a simple model, we examine the ratio of the surface densities of dust and captured planetesimals in the circumplanetary disk and find that solid material at the current location of regular satellites can be dominated by captured planetesimals when the velocity dispersion of those planetesimals is rather small and a wide gap is not formed in the protoplanetary disk. In this case, captured planetesimals in such a region can grow by mutual collision before spiraling into the planet and would contribute to the growth of regular satellites. [ABSTRACT FROM AUTHOR]

Observations of the sungrazing comet C/2012 S1 (ISON) were carried out using the Atacama Large Millimeter/submillimeter Array at a heliocentric distance of 0.58–0.54 au (pre-perihelion) on 2013 November 16–17. Temporally resolved measurements of the coma distributions of HNC, CH3OH, H2CO, and dust were obtained over the course of about an hour on each day. During the period UT 10:10–11:00 on November 16, the comet displayed a remarkable drop in activity, manifested as a >42% decline in the molecular line and continuum fluxes. The H2CO observations are consistent with an abrupt, ≈50% reduction in the cometary gas production rate soon after the start of our observations. On November 17, the total observed fluxes remained relatively constant during a similar period, but strong variations in the morphology of the HNC distribution were detected as a function of time, indicative of a clumpy, intermittent outflow for this species. Our observations suggest that at least part of the detected HNC originated from degradation of nitrogen-rich organic refractory material, released intermittently from confined regions of the nucleus. By contrast, the distributions of CH3OH and H2CO during the November 17 observations were relatively uniform, consistent with isotropic outflow and stable activity levels for these species. These results highlight a large degree of variability in the production of gas and dust from comet ISON during its pre-perihelion outburst, consistent with repeated disruption of the nucleus interspersed with periods of relative quiescence. [ABSTRACT FROM AUTHOR]

We report submillimeter 450 and 850 μm dust continuum observations for comet C/2012 S1 (ISON) obtained at heliocentric distances 0.31–0.08 au prior to perihelion on 2013 November 28 (rh = 0.0125 au). These observations reveal a rapidly varying dust environment in which the dust emission was initially point-like. As ISON approached perihelion, the continuum emission became an elongated dust column spread out over as much as 60″ (>105 km) in the anti-solar direction. Deconvolution of the November 28.04 850 μm image reveals numerous distinct clumps consistent with the catastrophic disruption of comet ISON, producing ∼5.2 × 1010 kg of submillimeter-sized dust. Orbital computations suggest that the SCUBA-2 emission peak coincides with the comet's residual nucleus. [ABSTRACT FROM AUTHOR]

The Arecibo Galaxy Environment Survey has detected a nearby H i source at a heliocentric velocity of +363 km s−1. The object was detected through its neutral hydrogen emission and has an obvious possible optical counterpart in Sloan Digital Sky Survey data (though it does not have an optical redshift measurement). We discuss three possible scenarios for the object: (1) it is within the Local Group, in which case its H i properties are comparable with recently discovered ultracompact high-velocity clouds; (2) it is just behind the Local Group, in which case its optical characteristics are similar to the newly discovered Leo P galaxy; (3) it is a blue compact dwarf galaxy within the local volume but not associated with the Local Group. We find the third possibility to be the most likely, based on distance estimates from the Tully–Fisher relation and its velocity relative to the Local Group. [ABSTRACT FROM AUTHOR]

We report the discovery of a narrow stellar stream crossing the constellations of Sculptor and Fornax in the Southern celestial hemisphere. The portion of the stream detected in the Data Release 1 photometry of the ATLAS survey is at least 12° long, while its width is ≈0 $_{.}^{\circ}$25. The colour–magnitude diagram of this halo sub-structure is consistent with a metal-poor [Fe/H] ≲ −1.4 stellar population located at a heliocentric distance of 20 ± 2 kpc. There are three globular clusters that could tentatively be associated with the stream: NGC 7006, NGC 7078 (M15) and Pyxis, but NGC 7006 and 7078 seem to have proper motions incompatible with the stream orbit. [ABSTRACT FROM AUTHOR]

Many competing models for the coronal heating and acceleration mechanisms of the high-speed solar wind depend on the solar magnetic field and plasma structure in the corona within heliocentric distances of 5 R☼. We report on sensitive Very Large Array (VLA) full-polarization observations made in 2011 August, at 5.0 and 6.1 GHz (each with a bandwidth of 128 MHz) of the radio galaxy 3C 228 through the solar corona at heliocentric distances of 4.6-5.0 R☼. Observations at 5.0 GHz permit measurements deeper in the corona than previous VLA observations at 1.4 and 1.7 GHz. These Faraday rotation observations provide unique information on the magnetic field in this region of the corona. The measured Faraday rotation on this day was lower than our a priori expectations, but we have successfully modeled the measurement in terms of observed properties of the corona on the day of observation. Our data on 3C 228 provide two lines of sight (separated by 46″, 33,000 km in the corona). We detected three periods during which there appeared to be a difference in the Faraday rotation measure between these two closely spaced lines of sight. These measurements (termed differential Faraday rotation) yield an estimate of 2.6-4.1 GA for coronal currents. Our data also allow us to impose upper limits on rotation measure fluctuations caused by coronal waves; the observed upper limits were 3.3 and 6.4 rad m–2 along the two lines of sight. The implications of these results for Joule heating and wave heating are briefly discussed. [ABSTRACT FROM AUTHOR]

On 2010 January 18-19 and June 28-29, the Wide-field Infrared Survey Explorer (WISE) spacecraft imaged the Rosetta mission target, comet 67P/Churyumov-Gerasimenko. We present a preliminary analysis of the images, which provide a characterization of the dust environment at heliocentric distances similar to those planned for the initial spacecraft encounter, but on the outbound leg of its orbit rather than the inbound. Broadband photometry yields low levels of CO2 production at a comet heliocentric distance of 3.32 AU and no detectable production at 4.18 AU. We find that at these heliocentric distances, large dust grains with mean grain diameters on the order of a millimeter or greater dominate the coma and evolve to populate the tail. This is further supported by broadband photometry centered on the nucleus, which yield an estimated differential dust particle size distribution with a power-law relation that is considerably shallower than average. We set a 3σ upper limit constraint on the albedo of the large-grain dust at ⩽0.12. Our best estimate of the nucleus radius (1.82 ± 0.20 km) and albedo (0.04 ± 0.01) are in agreement with measurements previously reported in the literature. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Dispelling myths and highlighting the history of the heliocentric mode," by Mano Singham in the December 2007 issue of "Physics Today."