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We present high resolution imaging observations of interstellar comet 2I/Borisov (formerly C/2019 Q4) obtained using the Hubble Space Telescope. Scattering from the comet is dominated by a coma of large particles (characteristic size 0.1 mm) ejected anisotropically. Convolution modeling of the coma surface brightness profile sets a robust limit to the spherical-equivalent nucleus radius r_n < 0.5 km (geometric albedo 0.04 assumed). We obtain an independent constraint based on the non-gravitational acceleration of the nucleus, finding r_n > 0.2 km (nucleus density 500 kg/m3 assumed). The profile and the non-gravitational constraints cannot be simultaneously satisfied if density < 25 kg/m3; the nucleus of comet Borisov cannot be a low density fractal assemblage of the type proposed elsewhere for the nucleus of 1I/'Oumuamua. We show that the spin-up timescale to outgassing torques, even at the measured low production rates, is comparable to or shorter than the residence time in the Sun's water sublimation zone. The spin angular momentum of the nucleus should be changed significantly during the current solar fly-by. Lastly, we find that the differential interstellar size distribution in the 0.5 mm to 100 m size range can be represented by power laws with indices < 4 and that interstellar bodies of 100 m size scale strike Earth every one to two hundred million years., 24 Pages, 5 Figures

Using Gaia data release 2 (DR2), we analyzed the distribution of stars in the close vicinity of the Sun in the full 3D position–velocity space. We have found no evidence of incomplete phase mixing in the vertical direction of the disk, which could have originated from external events. We show that the vertical phase-space spiral Z–V z is produced by the well-known moving groups (MGs), mainly by Coma Berenices, Pleiades–Hyades, and Sirius, when the statistical characteristics (mean, median, or mode) of the azimuthal velocity V are used to analyze the distribution in the vertical position–velocity plane. This result does not invoke external perturbations and is independent of the internal dynamical mechanisms from which the MGs originate. Our conclusions counterbalance current arguments in favor of short-lived (between 300 and 900 Myr) structures in the solar neighborhood. Contrarily, they support the hypothesis of a longer formation timescale (around a few gigayears) for the MGs.

The large-scale distribution of globular clusters in the central region of the Coma cluster of galaxies is derived through the analysis of Hubble Space Telescope/Advanced Camera for Surveys data. Data from three different HST observing programs are combined in order to obtain a full surface density map of globular clusters in the core of Coma. A total of 22,426 Globular cluster candidates were selected through a detailed morphological inspection and the analysis of their magnitude and colors in two wavebands, F475W (Sloan g) and F814W (I). The spatial distribution of globular clusters defines three main overdensities in Coma that can be associated with NGC 4889, NGC 4874, and IC 4051 but have spatial scales five to six times larger than individual galaxies. The highest surface density of globular clusters in Coma is spatially coincidental with NGC 4889. The most extended overdensity of globular clusters is associated with NGC 4874. Intracluster globular clusters also form clear bridges between Coma galaxies. Red globular clusters, which agglomerate around the center of the three main subgroups, reach higher surface densities than blue ones., Comment: STScI press release: https://media.stsci.edu/news_release/news/2018-44 contains beautiful HST images of the Coma cluster

We present a study of the bar fraction in the Coma cluster galaxies based on a sample of $\sim 190$ galaxies selected from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and observed with the Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The unprecedented resolution of the HST-ACS images allow us to explore the presence of bars, detected by visual classification, throughout a luminosity range of 9 magnitudes ($-23 \lesssim$ M$_{r} \lesssim -14$), permitting us to study the poor known region of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of both luminosities ($-22 \lesssim$ M$_{r} \lesssim -17$) and masses ($10^{9} \lesssim {\cal M_{*}}/{\cal M}_{\sun} \lesssim 10^{11}$). This result holds when comparing with a sample of bright/massive field galaxies. In addition, we find that the bar fraction does not vary significantly when going from the center to the cluster outskirts, implying that cluster environment plays a second order role in bar formation/evolution. The shape of the bar fraction distribution with respect to both luminosity and mass is well matched by the luminosity distribution of disk galaxies in Coma, indicating that bars are good tracers of cold stellar disks. We discuss the implications of our results for the formation and evolution scenarios of bars and disks., Comment: Accepted for publication in ApJL

The volatile abundances in comet 17P/Holmes were measured on three dates (UT 2007 October 27.6 and 31.3 and November 2.3) using high-dispersion (λ/Δ λ ~ 2.5 × 104) infrared spectroscopy with NIRSPEC at the W. M. Keck Observatory and CSHELL at the NASA Infrared Telescope Facility. Compared to other comets, the relative gas production rates in the coma show an enhancement of C2H6, HCN, and C2H2 with respect to H2O, by factors of ~2-3. CH3OH was also detected with an abundance relative to H2O that is similar to or perhaps slightly enhanced compared to the values observed in other comets. The apparent enrichment of some volatiles in the coma of 17P/Holmes does not necessarily imply an unusual composition for its nucleus because fractionation effects may be important at the relatively large heliocentric distance (Rh = 2.45 AU) at which our observations were performed. Rotational temperatures were determined for H2O, HCN, C2H6, and C2H2 in the coma on UT October 27.6 and found to be between 60 and 80 K. We used lines in both the ν5 and ν7 bands to obtain the best constraints yet achieved for the rotational temperature of C2H6. The spatial distributions of all measured volatiles in the coma are consistent with each other and suggest at most only a minor contribution from sublimating icy grains within our aperture. The overall gas production rate declined by approximately a factor of 7 between UT October 27.6 and November 2.3 with no significant change measured in the relative production rates of C2H6 and H2O during this time.

Evidence for non-thermal activity in clusters of galaxies is well established from radio observations of synchrotron emission by relativistic electrons. New windows in the Extreme Ultraviolet and Hard X-ray ranges have provided for more powerful tools for the investigation of this phenomenon. Detection of hard X-rays in the 20 to 100 keV range have been reported from several clusters of galaxies, notably from Coma and others. Based on these earlier observations we identified the relatively high redshift cluster 1E0657-56 (also known as RX J0658-5557) as a good candidate for hard X-ray observations. This cluster, also known as the bullet cluster, has many other interesting and unusual features, most notably that it is undergoing a merger, clearly visible in the X-ray images. Here we present results from a successful RXTE observations of this cluster. We summarize past observations and their theoretical interpretation which guided us in the selection process. We describe the new observations and present the constraints we can set on the flux and spectrum of the hard X-rays. Finally we discuss the constraints one can set on the characteristics of accelerated electrons which produce the hard X-rays and the radio radiation.

One of the goals of the Hubble Space Telescope program to observe periodic comet 9P/Tempel 1 in conjunction with NASA's Deep Impact mission was to study the generation and evolution of the gaseous coma resulting from the impact. For this purpose, the Solar Blind Channel of the Advanced Camera for Surveys was used with the F140LP filter which is sensitive primarily to the ultraviolet emission (>1400 A) from the CO Fourth Positive system. Following the impact we detected an increase in brightness, which if all due to CO corresponds to 1.5 x 10^31 molecules or a mass of 6.6 x 10^5 kg, an amount that would normally be produced by 7-10 hours of quiescent outgassing from the comet. This number is less than or equal to 10% of the number of water molecules excavated, and suggests that the volatile content of the material excavated by the impact did not differ significantly from the surface or near sub-surface material responsible for the quiescent outgassing of the comet., 10 pages, 4 postscript figures. Accepted for publication in ApJ (Letters)

We have performed a pilot Chandra survey of an off-center region of the Coma cluster to explore the X-ray properties and Luminosity Function of normal galaxies. We present results on 13 Chandra-detected galaxies with optical photometric matches, including four spectroscopically-confirmed Coma-member galaxies. All seven spectroscopically confirmed giant Coma galaxies in this field have detections or limits consistent with low X-ray to optical flux ratios (fX/fR < 10^-3). We do not have sufficient numbers of X-ray detected galaxies to directly measure the galaxy X-ray Luminosity Function (XLF). However, since we have a well-measured optical LF, we take this low X-ray to optical flux ratio for the 7 spectroscopically confirmed galaxies to translate the optical LF to an XLF. We find good agreement with Finoguenov et al. (2004), indicating that the X-ray emission per unit optical flux per galaxy is suppressed in clusters of galaxies, but extends this work to a specific off-center environment in the Coma cluster. Finally, we report the discovery of a region of diffuse X-ray flux which might correspond to a small group interacting with the Coma Intra-Cluster Medium (ICM)., Accepted for publication in the Astrophysical Journal

We report the results of 15 hr of Chandra observations of comet 2P/Encke 2003 on November 24. X-ray emission from comet Encke was resolved on scales of 500-40,000 km, with unusual morphology due to the presence of a low-density, collisionally thin (to charge exchange) coma. A light curve with peak-to-peak amplitude of 20% consistent with a nucleus rotational period of 11.1 hr was found, further evidence for a collisionally thin coma. We confirm emission lines due to oxygen and neon in the 800-1000 eV range but find very unusual oxygen and carbon line ratios in the 200-700 eV range, evidence for low-density, high effective temperature solar wind composition. We compare the X-ray spectral observation results to contemporaneous measurements of the coma and solar wind made by other means and find good evidence for the dominance of a postshock bubble of expanding solar wind plasma, moving at 600 km/s with charge state composition between that of the "fast" and "slow" solar winds.

A substantial number of processes have been suggested as possible contributors to the extragalactic γ-ray background (EGRB). Yet another contribution to this background will be emission produced in hadronic interactions of cosmic-ray protons with the cluster thermal gas; this class of cosmic rays (CRs) has been shown to be responsible for the EUV emission in the Coma Cluster of galaxies. In this paper we estimate this contribution. We first derive an improved estimate of the γ-ray emission produced by this population of CRs in the Coma Cluster. We consider the impact of different strength shocks in the production of this flux. We then assume the that CRs in the Coma Cluster are prototypical of all clusters and derive the contribution to the EGRB from all clusters over time. We examine two different possibilities for the scaling of the CR flux with cluster size: the number density of the CRs scales with the number density of the thermal plasma, and alternatively, the energy density of the CRs scales with the energy density of the plasma. We find that in all scenarios the EGRB produced by this process is sufficiently low that it will not be observable in comparison with other mechanisms that are likely to produce an EGRB. Nonetheless, it is quite likely that future missions will be able to detect emission produced by this process in large clusters of galaxies. In particular, a signature of this process should be observable in the Coma Cluster with instruments on the GLAST satellite. We show that the spectral shape of this emission in the Coma Cluster may well allow a determination as to whether strong or mild shocks are primarily responsible for the production of CRs in this cluster.

We present measurements of the CaII triplet and the Ca4227 Lick-index for a sample of early-type galaxies in the Coma cluster, deriving, for the first time, their corresponding relationships with velocity dispersion. Compared with a similar subsample of ellipticals in the field, Coma galaxies with velocity dispersions in the range ~ 180-270 km/s exhibit significant differences in the strengths of the Ca features, suggesting an influence of the environment on the star formation histories of these galaxies. We argue that the main scenarios previously proposed to explain the relatively low CaII triplet of galaxies are not able by themselves to simultaneously reconcile the strengths of the two Ca indices in both environments., 6 pages including 2 figures. Accepted for publication in ApJL. For associated data tables see http://www.ucm.es/info/Astrof/ellipt/CATRIPLET.html

We present the 10 μm silicate feature of the dynamically new Oort Cloud comet C/2001 Q4 (NEAT) 5 days prior to perihelion (rh = 0.97 AU, Δ = 0.35 AU, 2004 May 11.25 and 11.30 UT) observed with the NASA Ames HIFOGS spectrophotometer. The silicate feature of comet Q4 contains strong crystalline peaks at 10.0 and 11.2 μm, along with weaker peaks at 9.3, 10.5, and 11.8 μm, which are characteristic of crystalline olivine and crystalline orthopyroxene. The relative heights of the resonant peaks as well as the shape of the silicate feature in comet Q4 is the same as in comet C/1995 O1 (Hale-Bopp) preperihelion (rh = 1.21 AU). Thermal emission modeling shows Q4 and Hale-Bopp have similar relative abundances of the silicate minerals and high silicate crystalline-to-amorphous ratios. The silicate-to-amorphous carbon ratio derived for comet Q4, however, is lower than in Hale-Bopp and varies by a factor of ~2 in 2 hr, potentially sampling material from different jets in the coma. Owing to the similarity in the silicate mineralogy between Q4 and Hale-Bopp, either these two icy planetesimals formed in the same regime or crystalline silicates were widely distributed within the comet-forming zone.

A large spectroscopic survey is constructed of galaxies in the Coma cluster. The survey covers a wide area (1 deg$^2$) to deep magnitudes (R ~ 19.5), covering both the core (high density) and outskirts (intermediate to low density) of the cluster. The spectroscopic sample consists of a total of 1191 galaxies, of which, 760 galaxies are confirmed members of the Coma cluster. A statistical technique is developed to correct the spectroscopic sample for incompletness. The corrected sample is then used to construct R-band luminosity function (LF) spanning a range of 7 magnitudes (-23 < M_R < -16) both at the core and outskirts of the cluster. Dependence of the LF on local environment in Coma is explored. The LFs are found to be the same, within the errors, between the inner and outer regions and close to those from recent measurements for field galaxies. The total B-band LF for the Coma cluster, fitted to a Schecter form is also measured and shows a dip at M(B) = -18 mag., in agreement with previous studies. The implications of this feature are discussed. The LF is studied in B-R color intervals and shows a steep faint-end slope for red (B-R > 1.35) galaxies, both at the core and outskirts of the cluster. This population of low luminosity red galaxies has a higher surface density than the blue (B-R < 1.35) star-forming population, dominating the faint-end of the Coma cluster LF. It is found that relative number of high surface brightness galaxies is larger at the cluster core, implying destruction of low surface brightness galaxies in dense core environment., 42 pages, 11 Figures. Accepted for publication in Ap.J

We present results on the spectroscopic analysis of XMM-Newton EPIC data of the central 0.5/h_50 Mpc regions of the clusters of galaxies Coma, A1795 and A3112. The temperature of the hot intracluster gas as determined by modeling the 2 - 7 keV PN and MOS data is consistent with that inferred from the FeXXV-FeXXVI line ratio. A significant warm emission component at a level above the systematic uncertainties is evident in the data and confirmed by ROSAT PSPC data for Coma and A1795. The non-thermal origin of the phenomenon cannot be ruled out at the current level of calibration accuracy, but the thermal model fits the data significantly better, with temperatures in the range of 0.6 -- 1.3 keV and electron densities of the order of 10^{-4} -- 10^{-3} cm^{-3}. In the outer parts of the clusters the properties of the warm component are marginally consistent with the results of recent cosmological simulations, which predict a large fraction of the current epoch's bayons located in a warm-hot intergalactic medium (WHIM). However, the derived densities are too high in the cluster cores, compared to WHIM simulations, and thus more theoretical work is needed to fully understand the origin of the observed soft X-ray excess., ApJ in press, 14 pages, 4 color figures WHIM discussion modified

The study of both light elements Li and Be in open clusters of known properties can reveal the internal structure and the mechanisms of mixing in main-sequence stars as a function of age and composition. In previous work, we have investigated the older Hyades cluster and the younger Pleiades and α Per clusters. The Coma Berenices cluster and the UMa moving group are intermediate in age between the Hyades and Pleiades and provide a good linchpin for the influence of stellar age on light-element abundances; there are dips in the mid-F stars in both Li and Be in the Hyades but no Be dip and only a minor Li dip in the Pleiades. We have made observations of the resonance doublet of Be II near 3130 A in 13 Coma and six UMa stars with the Keck I telescope and the High Resolution Echelle Spectrometer. The Be abundances were determined by spectrum synthesis. In the F dwarfs in Coma, there are both Li and Be deficiencies, indicating that the depletions occur during the main-sequence phase of evolution but do not become evident until an age of 200-300 Myr. For both UMa and Coma stars, the Li depletion is greater than the Be depletion at all temperatures, but there is little, if any, Be depletion in stars with Teff < 6000 K. In the four clusters studied for Be, the mean Be abundance for stars with temperatures less than 6000 K is log N(Be/H) + 12.00 = 1.27, independent of age or metal content. For the hotter stars (5850-6680 K), the Li and Be abundances are correlated, indicating that the depletion probably occurs simultaneously; this matches the results for the field stars and the Hyades and the predictions of Li and Be depletion by rotationally induced mixing.

Use of the Sunyaev-Zeldovich effect as a precise cosmological probe necessitates a realistic assessment of all possible contributions to Comptonization of the cosmic microwave background in clusters of galaxies. We have calculated the additional intensity change due to various possible populations of energetic electrons that have been proposed in order to account for measurements of intracluster radio, nonthermal X-ray, and (possibly also) EUV emission. Our properly normalized estimates of (the highly model-dependent value of) the predicted intensity change due to these electrons are well below ~6% and ~35% of the usual Sunyaev-Zeldovich effect as a result of electrons in the hot gas in Coma and A2199, respectively. These levels constitute high upper limits since they are based on energetic electron populations whose energy densities are comparable to those of the thermal gas. The main impact of nonthermal Comptonization is a shift of the crossover frequency (where the thermal effect vanishes) to higher values. Such a shift would have important consequences for our ability to measure cluster peculiar velocities from the kinematic component of the Sunyaev-Zeldovich effect.

Using photometric and redshift data for the Virgo and Coma clusters, we present evidence for a correlation between the light concentration of elliptical galaxies (including dwarf ellipticals) and the local 3-D (i.e. non-projected) density of the clusters: more concentrated ellipticals are located in denser regions. The null hypothesis (i.e. the absence of any relation) is rejected at a significance level better than 99.9%. In order to explain the observed relation, a power law relating the galaxy light concentration and the cluster 3-D density is proposed. We study how the projection effects affect the form and dispersion of the data-points in the light concentration-projected density diagram. The agreement between our model and the observed data suggests that there is a paucity of dwarf elliptical galaxies in the cluster central regions., 7 pages, 2 figures, ApJL accepted

We report the detection of diffuse O VI λλ1032, 1038 emission in a 29 ks observation centered on the Coma Cluster (l = 57.6, b = +88.0) and an 11 ks observation toward Virgo (l = 284.2, b = +74.5) through the 30'' × 30'' aperture of the Far-Ultraviolet Spectroscopic Explorer (FUSE). The emission lines have a redshift near zero and are thus produced by gas in our own Galaxy. Observed surface brightnesses are 2000 ± 600 photons cm-2 s-1 sr-1 for each of the O VI components in the Coma spectrum and 2900 ± 700 and 1700 ± 700 photons cm-2 s-1 sr-1 for the 1032 and 1038 A lines, respectively, toward Virgo. These features are similar in strength to those recently observed in the southern Galactic hemisphere (l = 315.0, b = -41.3) in an ~200 ks FUSE observation. From a FUSE spectrum of M87, we find that N(O VI) toward Virgo is (1.4 ± 0.8) × 1014 cm-2. By combining emission- and absorption-line data for this sight line, we estimate the physical parameters of the emitting gas.

Excess soft X-ray emission in clusters of galaxies has so far been detected for sources that lie along lines of sight to very low Galactic H I column density [such as Coma, A1795, A2199, and Virgo; NH ~ (0.9-2.0) × 1020 cm-2]. We show that the cluster soft excess emission can be investigated even at higher NH, which provides an opportunity for investigating soft X-ray emission characteristics among a large number of clusters. The ROSAT Position Sensitive Proportional Counter analysis of some members of the Shapley concentration [A3571, A3558, A3560, and A3562 at NH ~ (4-4.5) × 1020 cm-2] bears evidence for excess emission in the keV band. We were able to confirm the finding for the case of A3571 by a pointed BeppoSAX observation. Within the current sample, the soft X-ray flux is again found to be consistently above the level expected from a hot virialized plasma. The data quality is, however, insufficient to enable a discrimination between alternative models of the excess low-energy flux.

Laboratory measurements of the interaction of low-energy, bare, and hydrogen-like ions with neutral gases are presented. The measurements demonstrate that charge-exchange-induced cometary K-shell X-ray spectra represent rich spectral diagnostics for determining the speed of the solar wind and the collision dynamics within the coma. We show that the K-shell spectrum observed from low-energy ion-neutral collisions (≤ 50 km s-1) has a distinct high-energy component that is suppressed in high-energy collisions (≥800 km s-1). As a result, the hardness ratio of the K-shell spectrum increases by as much as a factor of 4 as the ions decelerate in the coma. The change in spectral shape can be observed even with low-resolution energy dispersive solid-state detectors, opening the possibility of spatial imaging of the solar wind heavy-ion velocity profile in the coma. Our results clearly show that energy-dependent data are needed to fully describe charge-exchange-induced X-ray production in the heliosphere.

Using N-body numerical simulations, we examine possible mechanisms for the origin of the intracluster starlight features recently discovered in the Coma cluster of galaxies. We show that tidal interactions of a ``normal'' elliptical galaxy with a symmetrically distributed dark matter potential do not produce the observed intracluster starlight features. A head-on collision of two normal ellipticals does, however, explain the origin of the intracluster features with surface brightness about 26 mag/arcsec$^2$). Another possible explanation for the intracluster starlight features is galactic tidal interactions with massive intracluster substructures. The presence of substructures in Coma with a density of $\sim$ 0.1 times the density in the center of the galaxy, and with a total mass about three orders of magnitude larger than the mass of a normal elliptical galaxy, would account for the observations., Comment: 11 pages, including 5 figures / to appear in Astrophysical Journal (2001) vol. 548

Physics-based numerical coma models are desirable whether to interpret the spacecraft observations of the inner coma or to compare with the ground-based observations of the outer coma. In this work, we develop a multineutral-fluid model based on the BATS-R-US code of the University of Michigan, which is capable of computing both the inner and outer coma and simulating time-variable phenomena. It treats H₂O, OH, H-2, O, and H as separate fluids and each fluid has its own velocity and temperature, with collisions coupling all fluids together. The self-consistent collisional interactions decrease the velocity differences, re-distribute the excess energy deposited by chemical reactions among all species, and account for the varying heating efficiency under various physical conditions. Recognizing that the fluid approach has limitations in capturing all of the correct physics for certain applications, especially for very low density environment, we applied our multi-fluid coma model to comet 67P/Churyumov-Gerasimenko at various heliocentric distances and demonstrated that it yields comparable results to the Direct Simulation Monte Carlo (DSMC) model, which is based on a kinetic approach that is valid under these conditions. Therefore, our model may be a powerful alternative to the particle-based model, especially for some computationally intensive simulations. In addition, by running the model with several combinations of production rates and heliocentric distances, we characterize the cometary H₂O expansion speeds and demonstrate the nonlinear dependencies of production rate and heliocentric distance. Our results are also compared to previous modeling work and remote observations, which serve as further validation of our model.

We present a temperature map of the Coma Cluster of galaxies with an angular resolution of 8' corresponding to 320 kpc (H0 = 50 km s-1 Mpc-1) and an angular extent of 15. The temperature was derived from the hardness ratio of two energy bands, 0.5-3 and 3-10 keV. The X-ray image in the 0.5-10 keV band was also deconvolved from the observed data with the angular resolution of 2'. We have refined the complex response function of the ASCA telescope, taking into account the off-axis angle and the energy of incident X-rays in this analysis. The temperature map indicates that a hot region (kT = 11-14 keV) is largely extended to the northwest 15'-40' off from the cluster center, while a cool region (kT ~ 5 keV) is 20' off to the southeast. Another cool region is identified with the subcluster associated with the cD galaxy NGC 4839. These observational features can be interpreted in the context of the subcluster-cluster merging.

We report new EUV data on the cluster of galaxies Abell 1795. These data were taken well away from a detector defect which could have compromised earlier results on this cluster. Our new observations confirm the validity of the original data set. However, we find our results are strongly influenced by the variation of the telescope sensitivity over the field of view and upon the details of the subtraction of the EUV emission from the X-ray plasma. We investigate these effects using our new data and archival data on Abell 1795, Abell 2199, and the Coma Cluster. When we use the appropriate correction factors, we find there is no evidence for any excess EUV emission in Abell 1795 or Abell 2199. However, we do find extended EUV emission in the Coma Cluster using our new analysis procedures, confirming that in at least this cluster some as yet unidentified process is operative.

This completes a study of the evolution of binary systems in five open clusters of various ages. Among 21 stars observed in Praesepe, eight are found or confirmed to be spectroscopic binaries and orbital elements are derived, while one more shows long-term binary motion. Among 18 stars observed in the Coma Berenices cluster, five are found or confirmed to be spectroscopic binaries and orbital elements are derived, while a sixth has tentative elements. Among five clusters studied we searched for three expected evolutionary effects, namely an increase with age in the mass ratios, a decrease with age of the binary periods, and an increase in binary frequencies. We find that there is a progression (at the 3 σ level) from no binaries out of 10 with mass ratios greater than 0.5 in the youngest cluster (combined with the published results for NGC 6193) to 25% such stars in the intermediate-age clusters to 43% such stars in these two oldest clusters. There is no evidence for an increase in short-period binaries with age. And there is slight evidence (at the 1 σ level) for an increase with age from 15% to 28% in the fraction of large-amplitude binaries. These results are mostly consistent with the idea that most binaries are formed or modified in three-body interactions, and successive generations of formation and disruptions tend to form binaries with larger mass ratios. However, part of the initial generation of binaries is probably primordial.

Very high resolution (R~200,000) and high signal-to-noise echelle spectra were obtained of comet Hyakutake (C/1996 B2) using the 2D coude spectrograph on the 2.7 m telescope at W. J. McDonald Observatory during 1996 in late March and early April. Doppler resolved profiles are presented for individual lines of the major optical neutral species: CN, C2, NH2, O1D) at 6300 A, and H Balmer-α at 6563 A. They are consistent with the expected expansion of a water-dominated cometary coma. Because of the small aperture and the small geocentric distance of the comet, the profiles of CN, C2, and NH2 are totally shaped by the outflowing hydrodynamic coma. The NH2 is the narrowest of the group because of the very short lifetime of the NH2 parent (NH3. The profile of C2 is somewhat broadened, compared with NH2, because of the relatively larger contribution of C2 radicals farther from the nucleus where the bulk outflow speed is larger. Any exothermic ejection speed they receive upon their production would be quenched. Although the profile of CN is broader than C2, this is due to the fact that most of the CN lines are blends of two closely spaced but nearly equal strength components. Because O1D) atoms in the region samples are produced mainly by the photodissociation of water which results in a prompt emission photon, the line retains contributions of both the basic coma expansion velocity and the 1.6 km s-1 exothermal ejection speed of the O1D) atoms. The H Balmer-α line is complicated by a chance coincidence of a line of H2O+ and/or NH2 and by optical depth effects in solar Lyβ which are primarily responsible for the Balmer-α excitation. However, the width of the line wings is consistent with other comet observations, including Hyakutake itself, and the production by dissociation of H2O and OH and partial thermalization. We have successfully reproduced these data using a hybrid kinetic/hydrodynamic and Monte Carlo approach which include the important physical/chemical processes which can shape the spectral lines. Because the model includes no adjustable fitting parameters, the model-data agreement indicates that the underlying assumptions and calculated coma outflow speeds are quite reasonable.

Unidentified molecular emission bands first observed in optical spectra of the plasma tail of comet Halley (1P/1982 U1) have been discovered in pure ion tail spectra (Δλ~4700-6300 A, λ/Δλ~1000-4400) of comet Hyakutake (C/1996 B2) and three other recent comets (Nakamura-Nishimura-Machholz P/1994 N1, Austin C/1989 X1, and Brorsen-Metcalf 32P/1989 N1), but not in comet Hale-Bopp (C/1995 O1). The strengths of the bands near 4940, 5310, and 6000 A are correlated among the comets observed, indicative that the unidentified bands arise from a single molecular species. The bands have an asymmetric spatial distribution that extends in the antisolar direction, resembling molecular ions observed in comet plasma tails. Thus, the source of the unidentified bands is probably a single species of molecular ions. Of known laboratory molecular ion spectra, none can be attributed to the unidentified cometary emission bands. The absence of the unidentified ions in the tail of Hale-Bopp may be explained by a parent species of the unidentified ions that mimics the coma dynamics and photochemistry of H2O more closely than CO. This is inferred from the large tail CO+/H2O+ ratio observed in Hale-Bopp, which arises from the comet's large production rate that extends the ionopause and coma collision zone. Our observations provide evidence that the source region for the ions in plasma tails of comets lies external to the magnetic field-free ionopause.

The Coma Cluster was observed in 1996 for 90 ks by the PCA and HEXTE instruments aboard the Rossi X-ray Timing Explorer (RXTE) satellite?the first simultaneous, pointing measurement of Coma in the broad, 2-250 keV energy band. The high sensitivity achieved during this long observation allows precise determination of the spectrum. Our analysis of the measurements clearly indicates that in addition to the main thermal emission from hot intracluster gas at kT 7.5 keV, a second spectral component is required to best fit the data. If thermal, this component has a temperature 4.7 keV, and it contributes 20% of the total flux. Alternatively, the second component can be a power law, likely due to Compton scattering of relativistic electrons by the cosmic microwave background. This interpretation is based on the measurements of diffuse radio emission and the similar values of the radio and X-ray spectral indices. A Compton origin of the nonthermal component would imply that the volume-averaged magnetic field in the central region of Coma is B 0.2 ?G, a value that is free of the usual assumption of energy equipartition. The energy density of the emitting electrons would then be ~8 ? 10-14 ergs cm-3. Barring the presence of unknown systematic errors in the RXTE source or background measurements, our spectral analysis yields considerable evidence for Compton X-ray emission in the Coma Cluster.

We present 1.2-18.5 μm infrared (IR) photometric observations of comet Hyakutake (C/1996 B2) that define the temporal development of the spectral energy distribution (SED) of the comet during its passage toward the Sun. The characteristics of the SED on/and prior to 1996 April 10.1 UT when the comet was at a heliocentric distance r ≥ 0.69 AU were consistent with the interpretation that the optically important grains dominating the IR emission from the coma were larger than 1 μm. The sudden appearance of a strong 10 μm silicate emission feature and several other abrupt changes in the fundamental characteristics of the SED by 1996 April 22.1 UT suggest that thermal emission from grains with radii 0.5 μm began to dominate the IR emission from the coma for r 0.39 AU. We discuss the implications of these findings in terms of the structure of the comet nucleus and suggest that they imply that Sun-activated jets may be involved in the observed temporal changes of the IR SED.

We report observations of the He I λ5876 (D3) line in the late A- and early F-type stars in the Hyades, Praesepe, and Coma star clusters used to determine chromospheric activity levels. The average activity level in the early F-type stars is statistically identical in the three clusters and in field dwarfs, and the dispersion in activity levels in each sample is similar. The earliest star detected in each cluster ranges from B-V = 0.26 in the Hyades to B-V = 0.31 in Praesepe. However, four stars in the Hyades in the range 0.28-0.32 are not detected. The detection of Hyades star VB 84 at B-V = 0.26 represents the bluest star observed to date with a statistically nonzero chromospheric D3 equivalent width. In nine early F-type stars we compare D3 strength either during two different observing runs or in several individual integrations. In two stars we find evidence for short-term variability of a factor of 2 on timescales of 1 day or less. The timescale of the variability is consistent with rotational modulation. Finally, the similarity in chromospheric activity in the Hyades and Praesepe stars contrasts with the significant weakness of coronal X-ray emission of early F-type stars in Praesepe compared to Hyades. We have no explanation for this difference; however, this result suggests that the observed disappearance of D3 in the late A-type stars is not directly caused by the weak coronal emission of these stars.

Spectroscopic observations of comet Hyakutake (C/1996 B2) in the visible region was performed at Bisei Astronomical Observatory. The obtained spectrum covers the wavelengths from 5800 to 7300 A and includes several emissions of some NH2 bands, i.e., the (0, 7, 0), (0, 8, 0), and (0, 9, 0) bands. Comet Hyakutake was observed when it was fairly close to the Earth; the geocentric distance of the comet was Δ = 0.113 AU. The surface brightness profile of the inner coma in the vicinity of the nucleus was obtained at the sufficient spatial resolution. The collisions between the molecules are conspicuous in the region near the nucleus (where the nucleocentric distance is less than about 103 km). The random walk model, considering the collisions between molecules, is used to research the parent molecule of NH2 in this study. It is possible to examine whether each of the few candidates for the parent molecule of NH2 can explain the observed NH2 spatial profile. The result of our simulation supports the fact that NH3 is most likely to be the parent molecule of NH2.

Comet Hyakutake (C/1996 B2) provided a target of opportunity for performing a systematic study of water photodissociation products in which we obtained data from three instruments on the Hubble Space Telescope (HST). The HST Goddard High Resolution Spectrograph (GHRS) was used to measure the line profile of hydrogen Lyα (H Lyα) at six locations around the coma of the comet, ranging from the nucleus to a displacement of 100,000 km, and covering different directions compared with the comet-sun line. GHRS yielded line profiles with a spectral resolution (FWHM ~4 km s^(-1)) that was a factor of 2-3 better than any previous H Lyα or Hα ground-based measurements. The Wide Field Planetary Camera 2 (WFPC2) and the Woods filter were used to obtain H Lyα images of the inner coma. The faint object spectrograph (FOS) was used to determine the OH production rate and monitor its variation throughout the HST observing sequence. The GHRS H Lyα line profiles show the behavior of a line profile that is optically thick in the core for positions near the nucleus (

Evidence of clustering within the Coma Cluster is found by means of a multiscale analysis of the combined angular-redshift distribution. We have compiled a catalog of 798 galaxy redshifts from published surveys of the region of the Coma Cluster. We examine the presence of substructure and of voids at different scales ranging from ∼1 to ∼16 h-1 Mpc, using subsamples of the catalog ranging from cz = 3000 km s-1 to cz = 28,000 km s-1. Our substructure detection method is based on the wavelet transform and on segmentation analysis. The wavelet transform allows us to find structures at different scales, and the segmentation method allows a quantitative statistical and morphological analysis of the sample. From the whole catalog, we select a subset of 320 galaxies, with redshifts between cz = 5858 km s-1 and cz = 8168 km s-1, which we identify as belonging to the central region of Coma and upon which we have performed a deeper analysis, on scales ranging from 180 h-1 kpc to 1.44 h-1 Mpc. Our results are expressed in terms of the number of structures or voids and their sphericity for different values of the threshold detection and at all the scales investigated. According to our analysis, there is strong evidence of multiple hierarchical substructure, on scales ranging from a few hundreds of kilo-parsecs to about 4 h-1 Mpc. The morphology of these substructures is rather spherical. On a scale of 720 h-1 kpc we find two main subclusters that have been found before, but our wavelet analysis shows even more substructures, whose redshift position is approximately marked by the following bright galaxies: NGC 4934 and 4840, NGC 4889, NGC 4898 and 4864, NGC 4874 and 4839, NGC 4927, and NGC 4875.

We study the uncertainty in galaxy cluster mass estimates derived from X-ray data, assuming hydrostatic equilibrium for the intracluster gas. Using a Monte Carlo procedure, we generate a general class of mass models allowing very massive clusters. We then compute the corresponding temperature profiles through the equation of hydrostatic equilibrium and compare them to observational data for some clusters. We find several massive clusters that pass the observational constraints, with integrated masses varying over quite a wide range. The resulting accuracy of the mass estimates is rather poor, the uncertainties larger than what is generally claimed. Despite the fact that the mass profile can be exactly determined mathematically from the temperature and surface brightness profiles, we find that very accurate measurements of both quantities are required to determine the actual mass with moderate accuracy. We argue that the tight constraints on cluster masses previously obtained arise from the fact that a too restricted class of mass density profiles has been investigated so far, without serious physical justification. Applying our procedure to the Perseus and then to the Coma clusters, we find that an improvement of the observational constraints results in a quite modest improvement in the accuracy of the mass estimate. For Coma, using the best current available data, we end up with an uncertainty of a factor of 2 for the mass within the Abell radius. This uncertainty rapidly increases at further radius.

Deep CCD photometry and positions for a new sample of $\simeq 250$ dwarf elliptical (dE) galaxies in the Coma cluster core are analyzed. A significant color gradient is detected in their projected radial distribution, given by $\Delta (B$--$R)/\Delta (\log R_{\rm cc}) = -0.08\pm0.02$ mag. Calibrating these dE galaxies against Galactic globular clusters yields a corresponding metallicity gradient which goes as $Z \propto R_{\rm cc}^{-0.29}$. Simulations reveal that this gradient in the projected radial distribution corresponds to a true (three-dimensional) radial color gradient which goes as $\Delta (B$--$R)/\Delta (\log r) \simeq -0.20$ mag, or $Z \propto r^{-0.69}$, over the same radial range. If this radial gradient is a primordial one, it is consistent with a model in which the intracluster gas exerted a significant confinement pressure, impeding the outflow of supernovae-driven metal-rich gas from the young dE galaxies., Comment: To appear in ApJ Letters (Oct.1, 1996); LaTeX file, 13 pages (includes 2 eps figures), uses aaspp4.sty; also available from http://www.sci.wsu.edu/math/faculty/secker/secker.html

Remote observation of spectroscopic emissions is a potential tool for the identification and quantification of various species in comets. CO Cameron band (to trace \cod) and atomic oxygen emissions (to trace H$_2$O and/or CO$_2$, CO) have been used to probe neutral composition in the cometary coma. Using a coupled-chemistry emission model, various excitation processes controlling CO Cameron band and different atomic oxygen and atomic carbon have been modelled in comet 67P-Churyumov-Gerasimenko at 1.29~AU (perihelion) and at 3~AU heliocentric distances, which is being explored by ESA's Rosetta mission. The intensities of CO Cameron band, atomic oxygen and atomic carbon emission lines as a function of projected distance are calculated for different CO and CO$_2$ volume mixing ratios relative to water. Contributions of different excitation processes controlling these emissions are quantified. We assess how CO$_2$ and/or CO volume mixing ratios with respect to H$_2$O can be derived based on the observed intensities of CO Cameron band, atomic oxygen, and atomic carbon emission lines.The results presented in this work serve as base line calculations to understand the behaviour of low out-gassing cometary coma and compare them with the higher gas production rate cases (e.g. comet Halley). Quantitative analysis of different excitation processes governing the spectroscopic emissions is essential to study the chemistry of inner coma and to derive neutral gas composition., Comment: 46 pages, 12 figures, Accepted in The Astrophysical Journal

We observed Comet C/Siding Spring using the Hubble Space Telescope (HST) during its close approach to Mars. The high spatial resolution images obtained through the F689M, F775W, and F845M filters reveal the characteristics of the dust coma. The dust production rate of C/Siding Spring, quantified by $Af\rho$, is 590$\pm$30, 640$\pm$30, and 670$\pm$30 cm in a 420 km-radius aperture at 38$^\circ$ solar phase angle through the three filters, respectively, consistent with other observations at similar time and geometry, and with model predictions based on earlier measurements. The dust expansion velocity is ~150-250 m s$^{-1}$ for micron-sized dust grains, similar to the speeds found for other comets. The coma has a color slope of (5.5$\pm$1.5)%/100 nm between 689 and 845 nm, similar to previous HST measurements at comparable aperture sizes, consistent with the lack of color dependence on heliocentric distance for almost all previously observed active comets. The rotational period of the nucleus of C/Siding Spring is determined from the periodic brightness variation in the coma to be 8.00$\pm$0.08 hours, with no excited rotational state detected. The dust coma shows a broad and diffuse fan-shaped feature in the sunward direction, with no temporal morphological variation observed. The projected orientation of the dust feature, combined with the previous analysis of the coma morphology and other characteristics, suggests secular activity evolution of the comet in its inner solar system passage as one previously observed active region turns off whereas new regions exposed to sunlight due to seasonal illumination change., Comment: Accepted by ApJ Lett

(ABRIDGED) We use high resolution (~0.1") F814W ACS images from the HST ACS Treasury survey of the Coma cluster at z~0.02 to study bars in massive disk galaxies (S0s), and in dwarf galaxies in the Coma core. Our study helps constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. (1) We characterize the fraction and properties of bars in a sample of 32 bright (M_V 10^9.5 M_sun) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. Measuring the S0 bar fraction must be handled carefully, as the results depend on the method used: the bar fraction for bright S0s in the Coma core is 50%+/-11%, 65%+/-11%, and 60%+/-11% for three methods of bar detection: strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (Coma core, A901/902, Virgo). We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation across environments spanning two orders of magnitude in galaxy number density (n~300-10,000 gal/Mpc^3). We speculate that the S0 bar fraction is not significantly enhanced in rich clusters because S0s in rich clusters are less prone to bar instabilities as they are dynamically hot and gas poor due to ram pressure stripping and accelerated star formation. In addition, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We analyze a sample of 333 faint (M_V > -18) dwarf galaxies in the Coma core. Using unsharp-masking, we find only 13 galaxies with bar and/or spiral structure. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies, or that any disks present are too hot to develop instabilities., Accepted to ApJ; version with full-resolution figures can be found at http://www.as.utexas.edu/~marinova/COMA_bars.pdf

Consideration is given to the possible mechanisms responsible for the production of the atomic sodium tail of comet Hale-Bopp. It is shown that both photosputtering and ion sputtering of nonvolatile dust grains might not be the main driving force. Instead, the generation of impact vapor by collisional interaction between the cometary dust coma of micron-sized particles and the very small grains (VSGs) of 10-100 A size could possibly account for the observations if a large amount of VSGs existed in the coma region.

Using long-slit spectroscopy at the NASA Infrared Telescope Facility, we extracted H{sub 2}O production rates and spatial profiles of gas rotational temperature and molecular column abundance in comet C/2012 S1 ISON, observed at heliocentric distances of 0.53 and 0.35 AU. These measurements uniquely probed the physical environment in the inner collisional coma of this comet during its first (and last) approach to the Sun since being emplaced in the Oort Cloud some 4.5 billion years ago. Our observations revealed a comet evolving on various timescales, both over hours and days. At 0.35 AU, ISON showed a considerable decrease in water production rate in less than 2 hr, likely declining from a major outburst. Our measured temperature spatial distributions reflect the competition between the processes that cause heating and cooling in the coma, and also provide insight about the prevalent mechanism(s) of releasing gas-phase H{sub 2}O. The observed temperatures suggest that the comet was likely ejecting icy material continuously, which sublimated in the coma and heated the ambient gas, augmenting fast H-atoms produced by H{sub 2}O photolysis. ISON adds to the very limited sample of comets for which spatial-spectral studies of water temperatures have been conducted. These studies are now feasible and can bemore » extended to comets having a variety of gas production rates. Continued synergy of such observations with both space missions like Rosetta and with physical models is strongly encouraged in order to gain a deeper understanding of the processes in the inner collisional zone of the cometary coma.« less

We used the UltraViolet-Optical Telescope on board Swift to observe the dynamically young comet C/2009 P1 (Garradd) from a heliocentric distance of 3.5 AU pre-perihelion until 4.0 AU outbound. At 3.5 AU pre-perihelion, comet Garradd had one of the highest dust-to-gas ratios ever observed, matched only by comet Hale-Bopp. The evolving morphology of the dust in its coma suggests an outburst that ended around 2.2 AU pre-perihelion. Comparing slit-based measurements and observations acquired with larger fields of view indicated that between 3 AU and 2 AU pre-perihelion a significant extended source started producing water in the coma. We demonstrate that this source, which could be due to icy grains, disappeared quickly around perihelion. Water production by the nucleus may be attributed to a constantly active source of at least 75 km$^2$, estimated to be more than 20 percent of the surface. Based on our measurements, the comet lost $4x10^{11}$ kg of ice and dust during this apparition, corresponding to at most a few meters of its surface.Even though this was likely not Garradd's first passage through the inner solar system, the activity of the comet was complex and changed significantly during the time it was observed.

We present the results of far-ultraviolet observations of comet C/2001 Q4 (NEAT) that were made with the Far-Ultraviolet Imaging Spectrograph on board the Korean satellite STSAT-1. The observations were conducted in two campaigns during its perihelion approach between 2004 May 8 and 15. Based on the scanning mode observations in the wavelength band of 1400-1700 ?, we have constructed an image of the comet with an angular size of 5??5?, which corresponds to the central coma region. Several important fluorescence emission lines were detected including S I multiplets at 1429 and 1479 ?, C I multiplets at 1561 and 1657 ?, and the CO A1?-X1?+ Fourth Positive system; we have estimated the production rates of the corresponding species from the fluxes of these emission lines. The estimated production rate of CO was Q CO?= (2.65?? 0.63) ? 1028?s?1, which is 6.2%-7.4% of the water production rate and is consistent with earlier predictions. The average carbon production rate was estimated to be QC ?= ~1.59 ? 1028?s?1, which is ~60% of the CO production rate. However, the observed carbon profile was steeper than that predicted using the two-component Haser model in the inner coma region, while it was consistent with the model in the outer region. The average sulfur production rate was QS ?= (4.03?1.03) ? 1027?s?1, which corresponds to ~1% of the water production rate.

We present evidence for non-Gaussian velocity fields within the cores of luminous elliptical galaxies. This evidence is based upon high signal-to-noise, medium-resolution spectroscopy of the cores of early-type members of the Virgo and Coma clusters obtained with the WIYN 3.5-m telescope. The Virgo data were acquired using an integral-field unit (DensePak) allowing the velocity field to be sampled over a variety of spatial scales. The Coma data were obtained through single, 2-arcsec diameter fibers. The cross-correlation profiles of luminous ellipticals show considerable structure, often having several features with amplitudes as high as 10% that of the cross-correlation peak itself. This structure is most obvious within a radius of 1.5 arcsec (at Virgo), or < 100 pc, and is nearly undetectable when the data are binned over R < 15 arcsec, or < 1 kpc. Similar features are found in the single-fiber spectra of the luminous ellipticals in the Coma Cluster suggesting they are ubiquitous to giant ellipticals. Interesting, only the most luminous elliptical galaxies show this phenomena; the central regions of lower luminosity ellipticals have regular, Gaussian-like profiles. We interpret this kinematic structure as ``stellar streaming'' and suggest that this phenomena could be a relic signature of the merger history of luminous elliptical galaxies., Latex, 5 pages, 2 figures

We show that the circular character of continuum structures observed in the coma of comet Hale-Bopp around the perihelion passage is most likely due to a dust jet from a large extended active region on the surface. The coma morphology due to a wide jet is different from that due to a narrow jet. The latter shows foreshortening effects due to observing geometry; a wider jet produces more circular features. This circularization effect provides a self-consistent explanation for the evolution of near-perihelion coma morphology. No changes in the direction of the rotational angular momentum vector are required during this period, in contrast to the models of Schleicher et al. This circularization effect also enables us to produce near-circular coma features in the southeast quadrant in late February of 1997, and therefore it puts into question the basic premise on which Sekanina bases his morphological arguments for a gravitationally bound satellite nucleus.

The quasi-Hilda object, 212P/2000YN30 with a cometary-like orbit, was found to display a dust tail structure between January and March, 2009. From orbital calculations, it is shown that this object could have been an active comet in its past history before being transported to the current orbital configuration in quasi-stable 3:2 resonance with Jupiter.

We present observations of the evolution of a prominent spiral jet in the inner coma of comet Hale-Bopp (1995 O1). The observations, taken with the 82 cm IAC-80 telescope at the Teide Observatory, were made on 1995 August 25, 27, 28, and 31, and on September 4-7, as part of an ongoing program of monitoring the comet in Tenerife. The jet is observed to show a nearly, but not completely, constant position angle over the two weeks of observation. Although it is generally assumed that the jet is a dust event, some aspects of the morphology and behavior mean that the hypothesis that it is a gas jet cannot be ruled out. No single hypothesis is thought to be completely satisfactory. Between our first detection of the jet on August 25 and its disappearance on September 7, we see the point of inflection within the jet expand away from the nucleus at a highly constant velocity. At the same time, the jet fades considerably. This jet event seems different from others that have been observed later because the collimation of the beam is very tight, rather than the highly wound spiral structure shown by some later jets.

Comets often display narrow dust jets but more diffuse gas comae when their eccentric orbits bring them into the inner solar system and sunlight sublimates the ice on the nucleus. Comets are also understood to have one or more active areas covering only a fraction of the total surface active with sublimating volatile ices. Calculations of the gas and dust distribution from a small active area on a comet's nucleus show that as the gas moves out radially into the vacuum of space it expands tangentially, filling much of the hemisphere centered on the active region. The dust dragged by the gas remains more concentrated over the active area. This explains some puzzling appearances of comets having collimated dust jets but more diffuse gaseous atmospheres. Our test case is 67P/Churyumov-Gerasimenko, the Rosetta mission target comet, whose activity is dominated by a single area covering only 4% of its surface.

We report results based on mid-infrared photometry of 5 active main belt objects (AMBOs) detected by the Wide-field Infrared Survey Explorer (WISE) spacecraft. Four of these bodies, P/2010 R2 (La Sagra), 133P/Elst-Pizarro, (596) Scheila, and 176P/LINEAR, showed no signs of activity at the time of the observations, allowing the WISE detections to place firm constraints on their diameters and albedos. Geometric albedos were in the range of a few percent, and on the order of other measured comet nuclei. P/2010 A2 was observed on April 2-3, 2010, three months after its peak activity. Photometry of the coma at 12 and 22 {\mu}m combined with ground-based visible-wavelength measurements provides constraints on the dust particle mass distribution (PMD), dlogn/dlogm, yielding power-law slope values of {\alpha} = -0.5 +/- 0.1. This PMD is considerably more shallow than that found for other comets, in particular inbound particle fluence during the Stardust encounter of comet 81P/Wild 2. It is similar to the PMD seen for 9P/Tempel 1 in the immediate aftermath of the Deep Impact experiment. Upper limits for CO2 & CO production are also provided for each AMBO and compared with revised production numbers for WISE observations of 103P/Hartley 2., Comment: 32 Pages, including 5 Figures

The CN coma structure of the NASA EPOXI mission target, comet 103P/Hartley 2, was observed during 20 nights from 2010 September to December. These CN images probe the rotational state of the comet's nucleus and provide a ground-based observational context to complement the EPOXI observations. A dynamically excited cometary nucleus with a changing rotational rate is observed, a characteristic not seen in any comet in the past. The lack of rotational damping during the four-month observing interval places constraints on the interior structure of the nucleus.