Author name code: graham ADS astronomy entries on 2022-09-14 author:"Graham, David R." ------------------------------------------------------------------------ Title: Science Goals and Mission Architecture of the Europa Lander Mission Concept Authors: Hand, K. P.; Phillips, C. B.; Murray, A.; Garvin, J. B.; Maize, E. H.; Gibbs, R. G.; Reeves, G.; Martin, A. M. San; Tan-Wang, G. H.; Krajewski, J.; Hurst, K.; Crum, R.; Kennedy, B. A.; McElrath, T. P.; Gallon, J. C.; Sabahi, D.; Thurman, S. W.; Goldstein, B.; Estabrook, P.; Lee, S. W.; Dooley, J. A.; Brinckerhoff, W. B.; Edgett, K. S.; German, C. R.; Hoehler, T. M.; Hörst, S. M.; Lunine, J. I.; Paranicas, C.; Nealson, K.; Smith, D. E.; Templeton, A. S.; Russell, M. J.; Schmidt, B.; Christner, B.; Ehlmann, B.; Hayes, A.; Rhoden, A.; Willis, P.; Yingst, R. A.; Craft, K.; Cameron, M. E.; Nordheim, T.; Pitesky, J.; Scully, J.; Hofgartner, J.; Sell, S. W.; Barltrop, K. J.; Izraelevitz, J.; Brandon, E. J.; Seong, J.; Jones, J. -P.; Pasalic, J.; Billings, K. J.; Ruiz, J. P.; Bugga, R. V.; Graham, D.; Arenas, L. A.; Takeyama, D.; Drummond, M.; Aghazarian, H.; Andersen, A. J.; Andersen, K. B.; Anderson, E. W.; Babuscia, A.; Backes, P. G.; Bailey, E. S.; Balentine, D.; Ballard, C. G.; Berisford, D. F.; Bhandari, P.; Blackwood, K.; Bolotin, G. S.; Bovre, E. A.; Bowkett, J.; Boykins, K. T.; Bramble, M. S.; Brice, T. M.; Briggs, P.; Brinkman, A. P.; Brooks, S. M.; Buffington, B. B.; Burns, B.; Cable, M. L.; Campagnola, S.; Cangahuala, L. A.; Carr, G. A.; Casani, J. R.; Chahat, N. E.; Chamberlain-Simon, B. K.; Cheng, Y.; Chien, S. A.; Cook, B. T.; Cooper, M.; DiNicola, M.; Clement, B.; Dean, Z.; Cullimore, E. A.; Curtis, A. G.; Croix, J. -P. de la; Pasquale, P. Di; Dodd, E. M.; Dubord, L. A.; Edlund, J. A.; Ellyin, R.; Emanuel, B.; Foster, J. T.; Ganino, A. J.; Garner, G. J.; Gibson, M. T.; Gildner, M.; Glazebrook, K. J.; Greco, M. E.; Green, W. M.; Hatch, S. J.; Hetzel, M. M.; Hoey, W. A.; Hofmann, A. E.; Ionasescu, R.; Jain, A.; Jasper, J. D.; Johannesen, J. R.; Johnson, G. K.; Jun, I.; Katake, A. B.; Kim-Castet, S. Y.; Kim, D. I.; Kim, W.; Klonicki, E. F.; Kobeissi, B.; Kobie, B. D.; Kochocki, J.; Kokorowski, M.; Kosberg, J. A.; Kriechbaum, K.; Kulkarni, T. P.; Lam, R. L.; Landau, D. F.; Lattimore, M. A.; Laubach, S. L.; Lawler, C. R.; Lim, G.; Lin, J. Y.; Litwin, T. E.; Lo, M. W.; Logan, C. A.; Maghasoudi, E.; Mandrake, L.; Marchetti, Y.; Marteau, E.; Maxwell, K. A.; Namee, J. B. Mc; Mcintyre, O.; Meacham, M.; Melko, J. P.; Mueller, J.; Muliere, D. A.; Mysore, A.; Nash, J.; Ono, H.; Parker, J. M.; Perkins, R. C.; Petropoulos, A. E.; Gaut, A.; Gomez, M. Y. Piette; Casillas, R. P.; Preudhomme, M.; Pyrzak, G.; Rapinchuk, J.; Ratliff, J. M.; Ray, T. L.; Roberts, E. T.; Roffo, K.; Roth, D. C.; Russino, J. A.; Schmidt, T. M.; Schoppers, M. J.; Senent, J. S.; Serricchio, F.; Sheldon, D. J.; Shiraishi, L. R.; Shirvanian, J.; Siegel, K. J.; Singh, G.; Sirota, A. R.; Skulsky, E. D.; Stehly, J. S.; Strange, N. J.; Stevens, S. U.; Sunada, E. T.; Tepsuporn, S. P.; Tosi, L. P. C.; Trawny, N.; Uchenik, I.; Verma, V.; Volpe, R. A.; Wagner, C. T.; Wang, D.; Willson, R. G.; Wolff, J. L.; Wong, A. T.; Zimmer, A. K.; Sukhatme, K. G.; Bago, K. A.; Chen, Y.; Deardorff, A. M.; Kuch, R. S.; Lim, C.; Syvertson, M. L.; Arakaki, G. A.; Avila, A.; DeBruin, K. J.; Frick, A.; Harris, J. R.; Heverly, M. C.; Kawata, J. M.; Kim, S. -K.; Kipp, D. M.; Murphy, J.; Smith, M. W.; Spaulding, M. D.; Thakker, R.; Warner, N. Z.; Yahnker, C. R.; Young, M. E.; Magner, T.; Adams, D.; Bedini, P.; Mehr, L.; Sheldon, C.; Vernon, S.; Bailey, V.; Briere, M.; Butler, M.; Davis, A.; Ensor, S.; Gannon, M.; Haapala-Chalk, A.; Hartka, T.; Holdridge, M.; Hong, A.; Hunt, J.; Iskow, J.; Kahler, F.; Murray, K.; Napolillo, D.; Norkus, M.; Pfisterer, R.; Porter, J.; Roth, D.; Schwartz, P.; Wolfarth, L.; Cardiff, E. H.; Davis, A.; Grob, E. W.; Adam, J. R.; Betts, E.; Norwood, J.; Heller, M. M.; Voskuilen, T.; Sakievich, P.; Gray, L.; Hansen, D. J.; Irick, K. W.; Hewson, J. C.; Lamb, J.; Stacy, S. C.; Brotherton, C. M.; Tappan, A. S.; Benally, D.; Thigpen, H.; Ortiz, E.; Sandoval, D.; Ison, A. M.; Warren, M.; Stromberg, P. G.; Thelen, P. M.; Blasy, B.; Nandy, P.; Haddad, A. W.; Trujillo, L. B.; Wiseley, T. H.; Bell, S. A.; Teske, N. P.; Post, C.; Torres-Castro, L.; Grosso, C.; Wasiolek, M. Bibcode: 2022PSJ.....3...22H Altcode: Europa is a premier target for advancing both planetary science and astrobiology, as well as for opening a new window into the burgeoning field of comparative oceanography. The potentially habitable subsurface ocean of Europa may harbor life, and the globally young and comparatively thin ice shell of Europa may contain biosignatures that are readily accessible to a surface lander. Europa's icy shell also offers the opportunity to study tectonics and geologic cycles across a range of mechanisms and compositions. Here we detail the goals and mission architecture of the Europa Lander mission concept, as developed from 2015 through 2020. The science was developed by the 2016 Europa Lander Science Definition Team (SDT), and the mission architecture was developed by the preproject engineering team, in close collaboration with the SDT. In 2017 and 2018, the mission concept passed its mission concept review and delta-mission concept review, respectively. Since that time, the preproject has been advancing the technologies, and developing the hardware and software, needed to retire risks associated with technology, science, cost, and schedule. Title: A Perspective from Earths Deep Mantle Krypton and Xenon on Evolution of Planetary Interiors Authors: Peron, Sandrine; Mukhopadhyay, Sujoy; Kurz, Mark; Graham, David Bibcode: 2021AGUFMDI23A..05P Altcode: The volatile elemental and isotopic compositions of planetary mantles is key to understand the processes that shaped the terrestrial planets and their atmospheres. Due to their very low reactivity and high volatility, noble gases are invaluable tracers of the cycling of volatiles on Earth and other terrestrial planets. In particular, the non-radiogenic isotopes of krypton (78Kr, 80Kr, 82Kr, 83Kr, 84Kr, 86Kr) and xenon (124Xe, 126Xe, 128Xe, 130Xe) provide direct evidence on the initial sources and redistribution of volatiles on planets (the rate of fission production of 83, 84, 86Kr is negligible in the Earths mantle). However, there is very limited, high precise data for the krypton and xenon compositions of Earths mantle sources, in particular for deep mantle plumes. Here we used a new methodology, that combined a recently developed protocol of gas accumulation, a protocol of heavy noble gas (Ar, Kr, Xe) separation and noble gas mass spectrometry with a Noblesse HR (Nu instruments), to obtain high precision measurements of the full suite of Kr and Xe isotopes from the deep mantle Galapagos and Iceland plumes. These two hotspots show among the most primitive helium, neon and tungsten isotopic compositions, indicative of relatively primitive, undegassed reservoirs, and thus providing primordial Kr and Xe composition of the Earths mantle. In this presentation, we will show the Kr and Xe isotopic compositions of these two hotspots. Building on these new results, we will introduce a new approach combining isotopic and elemental ratios to bring new insights on the distribution and cycling of volatiles through time, including the timing of volatile depletion in the Earths deep interior. Title: Whistler waves observed by Solar Orbiter/RPW between 0.5 AU and 1 AU Authors: Kretzschmar, M.; Chust, T.; Krasnoselskikh, V.; Graham, D.; Colomban, L.; Maksimovic, M.; Khotyaintsev, Yu. V.; Soucek, J.; Steinvall, K.; Santolík, O.; Jannet, G.; Brochot, J. -Y.; Le Contel, O.; Vecchio, A.; Bonnin, X.; Bale, S. D.; Froment, C.; Larosa, A.; Bergerard-Timofeeva, M.; Fergeau, P.; Lorfevre, E.; Plettemeier, D.; Steller, M.; Štverák, Š.; Trávníček, P.; Vaivads, A.; Horbury, T. S.; O'Brien, H.; Evans, V.; Angelini, V.; Owen, C. J.; Louarn, P. Bibcode: 2021A&A...656A..24K Altcode: 2021arXiv211005080K Context. Solar wind evolution differs from a simple radial expansion, while wave-particle interactions are assumed to be the major cause for the observed dynamics of the electron distribution function. In particular, whistler waves are thought to inhibit the electron heat flux and ensure the diffusion of the field-aligned energetic electrons (Strahl electrons) to replenish the halo population.
Aims: The goal of our study is to detect and characterize the electromagnetic waves that have the capacity to modify the electron distribution functions, with a special focus on whistler waves.
Methods: We carried out a detailed analysis of the electric and magnetic field fluctuations observed by the Solar Orbiter spacecraft during its first orbit around the Sun, between 0.5 and 1 AU. Using data from the Search Coil Magnetometer and electric antenna, both part of the Radio and Plasma Waves (RPW) instrumental suite, we detected the electromagnetic waves with frequencies above 3 Hz and determined the statistical distribution of their amplitudes, frequencies, polarization, and k-vector as a function of distance. Here, we also discuss the relevant instrumental issues regarding the phase between the electric and magnetic measurements as well as the effective length of the electric antenna.
Results: An overwhelming majority of the observed waves are right-handed circularly polarized in the solar wind frame and identified as outwardly propagating quasi-parallel whistler waves. Their occurrence rate increases by a least a factor of 2 from 1 AU to 0.5 AU. These results are consistent with the regulation of the heat flux by the whistler heat flux instability. Near 0.5 AU, whistler waves are found to be more field-aligned and to have a smaller normalized frequency (f/fce), larger amplitude, and greater bandwidth than at 1 AU. Title: MMS Observations of Short-Period Current Sheet Flapping Authors: Richard, L.; Khotyaintsev, Y.; Graham, D.; Lindqvist, P. A.; Russell, C. T.; Le Contel, O.; Giles, B. L. Bibcode: 2020AGUFMSM0410017R Altcode: The current sheet kink-like flapping motions are commonly observed in the magnetotail propagating toward the flanks with periods of few minutes down to few seconds with different thicknesses. Here, we report a short period (T≈25 s) flapping event of a thin current sheet observed by the Magnetospheric Multiscale (MMS) mission in the duskside plasmasheet following a dipolarization jet. Using the spatiotemporal derivative and timing methods, we observe that the wavelike structure is propagating along the current density with a phase velocity one order of magnitude less than the ion thermal speed. The presence of a normal electric field and gradients of density associated with lower hybrid waves, suggest an ion scale current sheet which is confirmed by the breaking of the adiabacity condition for ions. We discuss the presence of the lower hybrid waves as a broadening process of the thin current sheet and the scaling of its thickness with the wavelength of the oscillating structure. Title: Secondary magnetic reconnection at Earth's flank magnetopause Authors: Tang, B.; Li, W.; Wang, C.; Khotyaintsev, Y.; Graham, D.; Zhang, Q. H.; Sun, T.; Li, H.; Giles, B. L.; Lindqvist, P. A.; Ergun, R.; Russell, C. T.; Burch, J. L. Bibcode: 2020AGUFMSM0200007T Altcode: The interaction between the solar wind and the Earth's magnetosphere is one of the most fundamental issues of magnetospheric physics, as it is key to understand various space weather phenomena. Although the framework of global plasma circulation in the magnetosphere has been established decades before, our understanding regarding to this process has been continuously improved, showing the complexity of the entire system. Here we report newly discovered secondary magnetic reconnection at Earth's flank magnetopause, where closed magnetic field lines in the magnetosphere reconnect with the open field lines, which are generated by the primary reconnection at dayside magnetopause, and then dragged to the flank region. We present evidence of the encounter of the electron diffusion region of reconnection, indicating a cross-scale process from a global scale to a small electron scale. The present secondary reconnection suggests a new pathway for the entry of the solar wind into geospace, providing an important modification to the classic magnetospheric plasma circulation. Title: DC/LF electric field and spacecraft potential measurements in the solar wind by RPW/BIAS on Solar Orbiter Authors: Khotyaintsev, Y. V.; Vaivads, A.; Graham, D.; Edberg, N. J. T.; Johansson, E. P. G.; Eriksson, A. I.; Maksimovic, M.; Bale, S. D.; Chust, T.; Krasnoselskikh, V.; Kretzschmar, M.; Lorfevre, E.; Plettemeier, D.; Soucek, J.; Steller, M.; Štverák; Travnicek, P.; Vecchio, A.; Horbury, T. S.; O'Brien, H.; Angelini, V.; Evans, V.; Owen, C. J.; Louarn, P.; Fedorov, A. Bibcode: 2020AGUFMSH0360022K Altcode: The BIAS subsystem is a part of the Radio and Plasma Waves (RPW) instrument on the ESA Solar Orbiter mission. It allows sending bias current to each of the three RPW antennas. By setting the appropriate bias current the antenna potential can be shifted closer to the local plasma potential. This allows us to measure the floating potential of the spacecraft, as well as the electric field in the DC/LF frequency range with higher accuracy and lower noise level. Here we present the first results on RPW/BIAS in-flight performance based on the operations during the instrument commissioning and first months of science operations. Title: Observations of lower hybrid drift waves in a disturbed electron diffusion region in Earth's magnetotail Authors: Cozzani, G.; Andre, M.; Khotyaintsev, Y. V.; Graham, D.; Alexandrova, A.; Egedal, J.; Vaivads, A.; Lindqvist, P. A.; Le Contel, O.; Torbert, R. B.; Ergun, R.; Giles, B. L.; Moore, T. E.; Russell, C. T.; Nakamura, R.; Fuselier, S. A.; Mauk, B.; Burch, J. Bibcode: 2020AGUFMSM008..02C Altcode: Magnetic reconnection is a fundamental energy conversion process in plasmas. The Electron Diffusion Region (EDR) is the key region in which both ions and electrons are demagnetized so that the topological rearrangement of field lines can take place, together with rapid heating and acceleration of plasma particles. A crucial question is whether the EDR has a laminar or turbulent structure. In particular, instabilities may be operating within the EDR and perturb its structure but observational evidences of these processes are still lacking.

We report MMS observations of an EDR encounter with weak guide field (13 % of the magnetic field in the inflow region in the lobes) in Earth's magnetotail when the inter-spacecraft separation was 20 km ∼ 1.5 de. We observe an extended region of clear electron demagnetisation and differences among the spacecraft indicating sharp gradients with characteristic scales comparable to the electron inertial length ( ∼ inter-spacecraft separation). These signatures observed at the EDR and its proximity deviate from the standard laminar picture of the diffusion region.

A peculiar feature of this EDR encounter is the presence of electromagnetic fluctuations peaking in the center of the current sheet. The magnetic field fluctuations are significant since they reach 20 % of upstream magnetic field in the plasma sheet. The properties of these waves are consistent with lower hybrid drift waves (LHDW) that could be related to the non-linear phase of lower hybrid drift instability (LHDI) or the modified two stream instability (MTSI) operating in the center of the current sheet. The presence of these fluctuations affects the structure of the EDR which becomes non-laminar and disturbed. Title: Probability Distributions of Langmuir Waves in Type II and III sources Authors: Trevett, W.; Cairns, I.; Graham, D. Bibcode: 2020AGUFMSH025..06T Altcode: Type II and III solar radio bursts involve streaming electrons that produce Langmuir waves that then couple wave energy into radio emission. These Langmuir waves can be driven to large enough amplitudes that they undergo electrostatic (ES) decay into a backward propagating Langmuir wave and forward propagating ion acoustic wave. The forward and backwards propagating Langmuir waves can then "beat" together to produce characteristic Langmuir waveforms and spectra, plus radio emission. Stochastic growth theory (SGT) predicts that the probability distribution of the Langmuir wave electric field strength should be lognormal, with known modifications if non-linear processes like ES decay are occurring. Other analyses suggest Pearson distributions may be relevant. Here, previous work on Langmuir waves in type II and III source regions is generalized and tested by analysing the probability distributions of the waveforms of Langmuir waves observed by the STEREO spacecraft. The focus is on a set of published events identified using spectral analyses to have or not have spectral evidence for ES decay. In general events for which spectral analyses provide evidence of ES decay also show probability distributions consistent with the combination of SGT and a nonlinear process like ES decay (∼ 86%), while those without spectral evidence for ES decay are well fitted by pure SGT (∼ 79%). Moreover, better fits with stronger statistical significance are obtained for pure and nonlinear SGT than for Pearson distributions in the majority of events (∼ 81%). These results provide strong evidence for SGT and ES decay proceeding in type II and III source regions. Title: The Effects of Upper-Hybrid Waves on Energy Conversion in the Electron Diffusion Region Authors: Dokgo, K.; Hwang, K. J.; Burch, J.; Yoon, P. H.; Graham, D.; Li, W. Bibcode: 2020AGUFMSM008..03D Altcode: Recently, the Magnetospheric Multiscale Mission (MMS) found that the agyrotropic electrons in the electron diffusion region (EDR) can generation upper-hybrid waves (UHW). It is believed that UHW play a significant role by heating electrons via the wave-particle interaction. Using a 2-dimensional Particle-in-Cell simulation (PIC), we investigate the effects and roles of UHW on the energy conversion process near the EDR.

We found that there are two effects of UHW. The first one is the local energy conversion and electron heating via the wave-particle interaction. The local energy conversion rate J·E measured by MMS in the July 3rd, 2017 event agrees with the heating rate in the PIC simulation. The other is that the UHW can change the large-scale energy conversion Jy·Ey in the EDR. The simulation result shows that the plasma quantities, such as pressure tensor, current, and the reconnection electric field, are changed as a result of UHW activities. The current Jy decreases, and the pressure tensor Pyz increases/ decreases when the beam density is lower/ higher than 13% of total density. When the beam density is 30% of the total density, Jy decreases by at most 5% from the initial value, and Pyz decreases by 26%. Considering the gradient of the pressure tensor generates the reconnection electric field, which is a dominant term in the EDR, our results mean that UHW can change the global profile of energy conversion Jy·Ey in the EDR. Title: Cold ionospheric ion dynamics inside an EMIC wave in the inflow region of dayside magnetopause reconnection Authors: Toledo Redondo, S.; Lee, J. H.; Vines, S. K.; Turner, D. L.; Allen, R. C.; Andre, M.; Boardsen, S. A.; Burch, J. L.; Denton, R. E.; Fu, H.; Fuselier, S. A.; Gershman, D. J.; Giles, B. L.; Graham, D.; Kitamura, N.; Khotyaintsev, Y.; Lavraud, B.; Le Contel, O.; Li, W.; Moore, T. E.; Vinas, A. F. Bibcode: 2020AGUFMSM0060005T Altcode: We report detailed observations, using the Magnetospheric Multiscale mission, of the ion dynamics inside an Alfvén branch wave that travels tangential to the reconnecting dayside magnetopause on the magnetospheric side of the magnetopause boundary. The measured wave properties are in excellent agreement with linear theory, showing that the wave corresponds to an electromagnetic ion cyclotron wave. The magnetospheric plasma is composed of plasma sheet-originating ions (several keV temperature) and cold, ionospheric-originating ions (~10 eV), which exhibit different dynamics inside the wavefront. The cold ions follow the magnetic field fluctuations and remain frozen-in, while the hot ions, owing to their large gyroradius, are partially demagnetized inside the wavefront. The energy source of the wave is the hot ion anisotropy, and the cold ions also exchange energy and momentum with the wave. The cold ion velocity fluctuations contribute to balance the Hall term of the Ohm's law. In this regime, the cold ions exchange energy back and forth with the fields. On the other hand, the hot ions are in a kinetic regime, allowing irreversible energy transfer with the wave electromagnetic fields. Since the wave is adjacent to the reconnecting magnetopause, the effects of the wave on the local plasma near the magnetopause preconditions the ion populations flowing into the magnetospheric reconnection inflow region. Title: Cherenkov Whistler Emission by Electron Holes Authors: Steinvall, K.; Khotyaintsev, Y.; Graham, D.; Vaivads, A.; Le Contel, O.; Russell, C. T. Bibcode: 2020AGUFMSH025..03S Altcode: Electron holes (EHs) are nonlinear, electrostatic, Debye scale, plasma waves where self-consistent electron trapping results in a localized positive potential. They are formed by various instabilities related to electron beams such as the Buneman and electron two stream instability. As such they are ubiquitous in most space plasmas, and have been found for example, in the solar wind, at Earth's magnetopause, and in Earth's auroral acceleration region. Simulations and recent spacecraft observations have shown that EHs propagating with speeds approaching half the electron Alfvén speed act as antennas radiating whistler waves via the classic Cherenkov mechanism. In a simulation of magnetic reconnection, the radiated whistlers were found to affect the reconnection process. Since the Cherenkov mechanism is independent of the particle distribution function, the waves may be generated in a plasma where they are damped, leading to strong wave-particle interaction. We present and discuss MMS data showing evidence of EHs Cherenkov radiating whistler waves in the Earth's magnetotail during ongoing magnetic reconnection. We also discuss how this process can be important in different regions of the heliosphere. Title: High-resolution observations of the solar photosphere, chromosphere, and transition region. A database of coordinated IRIS and SST observations Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson, M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.; Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques, V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.; Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.; Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.; Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski, M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P. Bibcode: 2020A&A...641A.146R Altcode: 2020arXiv200514175R NASA's Interface Region Imaging Spectrograph (IRIS) provides high-resolution observations of the solar atmosphere through ultraviolet spectroscopy and imaging. Since the launch of IRIS in June 2013, we have conducted systematic observation campaigns in coordination with the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides complementary high-resolution observations of the photosphere and chromosphere. The SST observations include spectropolarimetric imaging in photospheric Fe I lines and spectrally resolved imaging in the chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present a database of co-aligned IRIS and SST datasets that is open for analysis to the scientific community. The database covers a variety of targets including active regions, sunspots, plages, the quiet Sun, and coronal holes. Title: Lower-Hybrid Drift Waves Driving Electron Nongyrotropic Heating and Vortical Flows in a Magnetic Reconnection Layer Authors: Chen, L. -J.; Wang, S.; Le Contel, O.; Rager, A.; Hesse, M.; Drake, J.; Dorelli, J.; Ng, J.; Bessho, N.; Graham, D.; Wilson, Lynn B.; Moore, T.; Giles, B.; Paterson, W.; Lavraud, B.; Genestreti, K.; Nakamura, R.; Khotyaintsev, Yu. V.; Ergun, R. E.; Torbert, R. B.; Burch, J.; Pollock, C.; Russell, C. T.; Lindqvist, P. -A.; Avanov, L. Bibcode: 2020PhRvL.125b5103C Altcode: We report measurements of lower-hybrid drift waves driving electron heating and vortical flows in an electron-scale reconnection layer under a guide field. Electrons accelerated by the electrostatic potential of the waves exhibit perpendicular and nongyrotropic heating. The vortical flows generate magnetic field perturbations comparable to the guide field magnitude. The measurements reveal a new regime of electron-wave interaction and how this interaction modifies the electron dynamics in the reconnection layer. Title: Spectral Signatures of Chromospheric Condensation in a Major Solar Flare Authors: Graham, David R.; Cauzzi, Gianna; Zangrilli, Luca; Kowalski, Adam; Simões, Paulo; Allred, Joel Bibcode: 2020ApJ...895....6G Altcode: 2020arXiv200405075G We study the evolution of chromospheric line and continuum emission during the impulsive phase of the X-class SOL2014-09-10T17:45 solar flare. We extend previous analyses of this flare to multiple chromospheric lines of Fe I, Fe II, Mg II, C I, and Si II observed with the Interface Region Imaging Spectrograph, combined with radiative-hydrodynamical (RHD) modeling. For multiple flaring kernels, the lines all show a rapidly evolving double-component structure: an enhanced emission component at rest, and a broad, highly redshifted component of comparable intensity. The redshifted components migrate from 25 to 50 km s-1 toward the rest wavelength within ∼30 s. Using Fermi hard X-ray observations, we derive the parameters of an accelerated electron beam impacting the dense chromosphere, using them to drive an RHD simulation with the RADYN code. As in Kowalski et al. (2017), our simulations show that the most energetic electrons penetrate into the deep chromosphere, heating it to T ∼ 10,000 K, while the bulk of the electrons dissipate their energy higher, driving an explosive evaporation, and its counterpart condensation—a very dense (ne ∼ 2 × 1014 cm-3), thin layer (30-40 km thickness), heated to 8-12,000 K, moving toward the stationary chromosphere at up to 50 km s-1. The synthetic Fe II 2814.45 Å profiles closely resemble the observational data, including a continuum enhancement, and both a stationary and a highly redshifted component, rapidly moving toward the rest wavelength. Importantly, the absolute continuum intensity, ratio of component intensities, relative time of appearance, and redshift amplitude are sensitive to the model input parameters, showing great potential as diagnostics. Title: High-density O+ in Earth's outer magnetosphere and its effect on dayside magnetopause magnetic reconnection Authors: Fuselier, S. A.; Mukherjee, J.; Denton, M. H.; Petrinec, S. M.; Trattner, K. J.; Toledo-Redondo, S.; André, M.; Aunai, N.; Chappell, C. R.; Glocer, A.; Haaland, S.; Hesse, M.; Kistler, L. M.; Lavraud, B.; Li, W. Y.; Moore, T. E.; Graham, D.; Tenfjord, P.; Dargent, J.; Vines, S. K.; Strangeway, R. J.; Burch, J. L. Bibcode: 2019JGRA..12410257F Altcode: The warm plasma cloak is a source of magnetospheric plasma that contain significant O+. When the O+ density in the magnetosphere near the magnetopause is >0.2 cm-3 and the H+ density is <1.5 cm-3, then O+ dominates the magnetospheric ion mass density by more than a factor of 2. A survey is conducted of such O+-rich warm plasma cloak intervals and their effect on reconnection at the Earth's magnetopause. The survey uses data from the Magnetospheric Multiscale mission (MMS) and the results are compared and combined with a previous survey of the warm plasma cloak. Overall, the warm plasma cloak and the O+-rich warm plasma cloak reduce the magnetopause reconnection rate by >20% due to mass-loading only about 2% to 4% of the time. However, during geomagnetic storms, O+ dominates the mass density of the warm plasma cloak and these mass densities are very high. Therefore, a separate study is conducted to determine the effect of the warm plasma cloak on magnetopause reconnection during geomagnetically disturbed times. This study shows that the warm plasma cloak reduces the reconnection rate significantly about 25% of the time during disturbed conditions. Title: Electron mixing in the exhaust of asymmetric magnetic reconnection with a guide field Authors: Tang, B.; Li, W. Y.; Le, A.; Graham, D.; Wang, C.; Khotyaintsev, Y.; Egedal, J. Bibcode: 2019AGUFMSM21B3157T Altcode: In this study, we investigate an exhaust crossing of asymmetric guide-field reconnection observed by Magnetospheric Multiscale (MMS) spacecraft at the dayside magnetopause. One MMS spacecraft (MMS4) observed multi-component electron distributions: (1) an anti-parallel sheath-inflow electron beam at lower-energies (30 - 70 eV); (2) a parallel electron beam at middle-energies (150 -250 eV) after acceleration and reflection; and (3) a high-energy electron population perpendicular to the magnetic field (450 - 700 eV), while all other three MMS spacecraft, with a separation of Title: Observation and theory of waves driven by agyrotropic beam near the electron diffusion region Authors: Dokgo, K.; Hwang, K. J.; Burch, J. L.; Yoon, P. H.; Graham, D. Bibcode: 2019AGUFMSM21C3194D Altcode: We study waves driven by agyrotropic beams near the electron diffusion region comparing MMS observations and analytical theory. We investigate two events in which MMS spacecraft observed high-frequency wave activities near the electron diffusion region (EDR). In a July 3, 2017 event, a single-beam type of waves near the electron plasma frequency is observed, and in a December 24, 2016 event discrete Bernstein-like modes at integer multiples of electron gyro-frequency were detected. In previous studies of each event, it is known that those waves are generated by electron crescent or agyrotropic beams near the EDR. However, two different types of assumptions were applied to explain wave generation mechanisms, respectively; one was an unmagnetized beam, the other was a symmetric ring-type distribution. We derive analytical dispersion relations including effects of the ambient magnetic field and the agyrotropic beam. The frequency ranges of growing modes agree with both MMS observation and both types of waves so that this dispersion relation can explain general wave instabilities by agyrotropic beams. We further analyze the wave dispersion curves and growth rate by changing several plasma parameters; beam density, speed, temperature, and the intensity of the ambient magnetic field. We found that waves driven by agyrotropic beams are fundamentally discrete Bernstein-like modes. As their growth rates increase, they overlap with adjacent modes. As a result, they become a beam-like mode. Title: Diagnostics of nanoflare heating in active region core loops from chromospheric and transition region observations and modeling Authors: Testa, P.; Polito, V.; De Pontieu, B.; Reale, F.; Graham, D. Bibcode: 2019AGUFMSH13B..07T Altcode: Rapid variability at the footpoints of active region coronal loops has been observed (Testa et al. 2013, 2014), and provides powerful diagnostics of the properties of coronal heating and energy transport (e.g., Testa et al. 2014, Polito et al. 2018, Reale et al. 2019, Testa et al. 2019).

We will present results of our detailed analysis of a dozen of IRIS/AIA observations of footpoints brightenings associated with coronal heating, and will present the distribution of the observed properties (e.g., duration of brightenings, intensity ratios, Doppler shifts, non-thermal broadening,..). We will discuss the properties of coronal heating as inferred from the coupling of these high spatial, spectral, and temporal resolution chromospheric/transition region/coronal observations, with modeling.

We will also present results of a new algorithm we have developed for an automatic detection of these footpoint brightenings in AIA observations (Graham et al. 2019), which will allow us, in our next step, to significantly expand the number of events detected, and build more robust statistics of the properties of nanoflares in active region loops. Title: Electrostatic Potential and Ion Reflection at a Rippled Perpendicular Shock Authors: Khotyaintsev, Y. V.; Johlander, A.; Vaivads, A.; Graham, D.; Dimmock, A. P. Bibcode: 2019AGUFMSH23B3397K Altcode: Ramps of quasi-perpendicular shocks often contain large-amplitude electric field fluctuations. Such electric fields can significantly affect electron and ion dynamics at the ramp. However, the properties of such electric field structures (apart from amplitude) are an open question in many cases (e.g. scale, potential). We use multi-spacecraft MMS observations to investigate electric fields observed at the ramp of a perpendicular shock with Ma=6. MMS spacecraft are separated by 10 km, which is of the order of the ramp thickness. We find that the ramp is rippled as evidenced by the characteristic signatures in the ion phase space. We also identify sub-proton scale (5-10 electron inertial lengths) large amplitude normal electric field structures. We suggest that the shock non-stationarity (rippling) leads to the formation of such electric fields, as the structures exist only at a certain phase of the ripples. Such normal electric fields are primarily balanced by the Hall term (JxB/ne). The corresponding potential is comparable to the energy of the incident solar wind ions, and thus has a major contribution to ion reflection. Title: Electron acceleration and thermalization at reconnection separatrices Authors: Norgren, C.; Graham, D.; Argall, M. R.; Khotyaintsev, Y.; Vaivads, A.; Hesse, M.; Steinvall, K.; Gershman, D. J.; Lindqvist, P. A.; Burch, J.; Plaschke, F.; Tenfjord, P. Bibcode: 2019AGUFMSM23B..02N Altcode: During magnetic reconnection, electrons can be accelerated to large energies. This acceleration is known to take place in several steps, both before, during, and after the electrons have passed the separatrices or X line. In this study we use the Magnetospheric MultiScale (MMS) mission to investigate the electron acceleration, and subsequent beam thermalization occurring along the separatrices at magnetotail separatrices. Here, initially cold electron populations are accelerated towards the X line forming beams with energies of one to a few keV's, corresponding to a substantial fraction of the electron thermal energy inside the exhaust. The accelerated population interacts with the exhaust population and leads to a two-stream instability and the formation of electrostatic waves. The wave's amplitudes are large enough to trap the accelerated electrons, leading to electron phase space holes, and aids in thermalising the beam. Title: Electromagnetic Electron Holes and Evidence of Cherenkov Whistler Emission Authors: Steinvall, K.; Khotyaintsev, Y. V.; Graham, D.; Vaivads, A.; Le Contel, O.; Lindqvist, P. A.; Russell, C. T.; Webster, J.; Burch, J. L.; Torbert, R. B. Bibcode: 2019AGUFMSM51H3264S Altcode: Electron holes (EHs) are Debye scale, positively charged, nonlinear plasma structures frequently observed in space plasmas. By trapping, scattering and heating electrons, EHs have an important effect on plasma dynamics. Though typically considered electrostatic, electromagnetic EHs have occasionally been reported, and simulations of magnetic reconnection have revealed EHs Cherenkov radiating whistler waves, modulating the reconnection rate.

We use Magnetospheric Multiscale (MMS) observations of EHs in the magnetotail plasma sheet boundary layer to investigate three mechanisms that generate the EHs' magnetic field (δB). First, the Lorentz transform of the EH electric field δE; second, δE×B drifting electrons inside the EH; third, Cherenkov emission of whistler waves. The high time-resolution and electron-scale spacecraft separation of MMS enables us to apply multi-spacecraft methods to analyze these mechanisms in unprecedented detail and distinguish their magnetic field contributions. Our results show that the δE×B drifting electrons are responsible for δB||, whereas the main source of δB varies with EH speed relative to the electron Alfvén speed. We discuss the different mechanisms and present the first observational evidence of whistler waves being Cherenkov radiated from EHs. Title: Electron vorticity observed during fundamental physical processes in near-Earth space Authors: Hwang, K. J.; Choi, E.; Dokgo, K.; Burch, J. L.; Sibeck, D. G.; Goldstein, M.; Giles, B. L.; Pollock, C. J.; Hasegawa, H.; Khotyaintsev, Y.; Graham, D.; Shi, Q.; Fu, H.; Toledo-Redondo, S.; Escoubet, C. P.; Gershman, D. J.; Ergun, R.; Torbert, R. B.; Russell, C. T. Bibcode: 2019AGUFMSM21C3185H Altcode: While vorticity, defined as the curl of the velocity, has been broadly used in fluid and plasma physics, the lack of multipoint measurements with spacecraft separations on small scales (e.g., less than tens electron inertial lengths) and the usual relatively low time resolution of particle data have hindered addressing electron vorticity in near-Earth space before the launch of the MMS spacecraft. We present MMS observations of electron vorticity observed 1) around reconnecting current sheets, 2) within a flux rope, and 3) in the magnetosheath. Using these events, we show 1) how enhancements of the electron vorticity (greater than the electron gyrofrequency) in the vicinity of the electron diffusion region (EDR) delineate the multi-scale reconnection boundaries , 2) how the electron vortex is associated with intense electric fields (hundreds mV/m) inside the flux rope, and 3) how the electron-only vortices form in the turbulent magnetosheath. We discuss the origins of enhanced electron vorticity in these events to distinguish generation mechanisms either invoking the electron Kelvin-Helmholtz instability or wave activity in the lower-hybrid band. Effects of the enhanced electron vorticity on the modification of magnetic field topology and evolution of related physical processes follow. Our study sheds new light on electron vorticity, a physical quantity that has been underutilized in space physics, its ubiquity and roles and effects on the diverse fundamental physical processes occurring in near-Earth space. Title: Impulsive Coronal Heating from Large-scale Magnetic Rearrangements: From IRIS to SDO/AIA Authors: Reale, Fabio; Testa, Paola; Petralia, Antonino; Graham, David R. Bibcode: 2019ApJ...882....7R Altcode: 2019arXiv190702291R The Interface Region Imaging Spectrograph (IRIS) has observed bright spots at the transition region footpoints associated with heating in the overlying loops, as observed by coronal imagers. Some of these brightenings show significant blueshifts in the Si IV line at 1402.77 Å ({log}T[{{K}}]≈ 4.9). Such blueshifts cannot be reproduced by coronal loop models assuming heating by thermal conduction only, but are consistent with electron beam heating, highlighting for the first time the possible importance of nonthermal electrons in the heating of nonflaring active regions. Here we report on the coronal counterparts of these brightenings observed in the hot channels of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. We show that the IRIS bright spots are the footpoints of very hot and transient coronal loops that clearly experience strong magnetic interactions and rearrangements, thus confirming the impulsive nature of the heating and providing important constraints for their physical interpretation. Title: Automated Detection of Rapid Variability of Moss Using SDO/AIA and Its Connection to the Solar Corona Authors: Graham, David R.; De Pontieu, Bart; Testa, Paola Bibcode: 2019ApJ...880L..12G Altcode: Active region moss—the upper transition region of hot loops—was observed exhibiting rapid intensity variability on timescales of order 15 s by Testa et al. in a short time series (∼150 s) data set from Hi-C (High-resolution Coronal Imager). The intensity fluctuations in the subarcsecond 193A images (∼1.5 MK plasma) were uncharacteristic of steadily heated moss and were considered an indication of heating events connected to the corona. Intriguingly, these brightenings displayed a connection to the ends of transient hot loops seen in the corona. Following the same active region, AR11520, for 6 days, we demonstrate an algorithm designed to detect the same temporal variability in lower resolution Atmospheric Imaging Assembly (AIA) data, significantly expanding the number of events detected. Multiple analogous regions to the Hi-C data are successfully detected, showing moss that appears to “sparkle” prior to clear brightening of connected high-temperature loops; this is confirmed by the hot AIA channels and the isolated Fe XVIII emission. The result is illuminating, as the same behavior has recently been shown by Polito et al. while simulating nanoflares with a beam of electrons depositing their energy in the lower atmosphere. Furthermore, the variability is localized mostly to the hot core of the region, hence we reinforce the diagnostic potential of moss variability as the driver of energy release in the corona. The ubiquitous nature of this phenomenon, and the ability to detect it in data with extended time series, and large fields of view, opens a new window into investigating the coronal heating mechanism. Title: Mass Loading the Earth's Dayside Magnetopause Boundary Layer and Its Effect on Magnetic Reconnection Authors: Fuselier, S. A.; Trattner, K. J.; Petrinec, S. M.; Denton, M. H.; Toledo-Redondo, S.; André, M.; Aunai, N.; Chappell, C. R.; Glocer, A.; Haaland, S. E.; Hesse, M.; Kistler, L. M.; Lavraud, B.; Li, W.; Moore, T. E.; Graham, D.; Alm, L.; Tenfjord, P.; Dargent, J.; Vines, S. K.; Nykyri, K.; Burch, J. L.; Strangeway, R. J. Bibcode: 2019GeoRL..46.6204F Altcode: When the interplanetary magnetic field is northward for a period of time, O+ from the high-latitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dual-lobe reconnection closes these field lines, which traps O+ and mass loads the boundary layer. This O+ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O+-rich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the high-shear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The high-latitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause. Title: High Resolution Observations of Chromospheric Condensation Authors: Cauzzi, Gianna; Graham, David; Zangrilli, Luca; Kowalski, Adam Bibcode: 2019shin.confE.180C Altcode: The chromospheric response to flaring can provide information on the coronal magnetic reconnection processes driving the flare. In particular, the evolution of the chromospheric condensation can trace the site and size of episodes of energy release in the corona, and inform on their duration. High resolution, spectrally resolved observations of chromospheric lines and continua are necessary to fully study this phenomenon.

High cadence observations of chromospheric condensation in small flaring kernels, derived from a multi-spectral analysis of IRIS UV lines in a well-studied X1 flare, put some hard constraints on these values. In particular, it is found that the chromospheric signatures occurr sequentially in multiple distinct positions, separated by only 0.3" Title: Near-Earth Supernova Explosions: Evidence, Implications, and Opportunities Authors: Fields, Brian; Ellis, John R.; Binns, Walter R.; Breitschwerdt, Dieter; deNolfo, Georgia A.; Diehl, Roland; Dwarkadas, Vikram V.; Ertel, Adrienne; Faestermann, Thomas; Feige, Jenny; Fitoussi, Caroline; Frisch, Priscilla; Graham, David; Haley, Brian; Heger, Alexander; Hillebrandt, Wolfgang; Israel, Martin H.; Janka, Thomas; Kachelreiß, Michael; Korschinek, Gunther; Limongi, Marco; Lugaro, Maria; Marinho, Franciole; Melott, Adrian; Mewaldt, Richard A.; Miller, Jesse; Ogliore, Ryan C.; Paul, Michael; Paulucci, Laura; Pecaut, Mark; Rauch, Brian F.; Rehm, Karl E.; Schulreich, Michael; Seitenzahl, Ivo; Sorensen, Mads; Thielemann, Friedrich-Karl; Timmes, Francis X.; Thomas, Brian C.; Wallner, Anton Bibcode: 2019BAAS...51c.410F Altcode: 2019arXiv190304589F; 2019astro2020T.410F Geological and lunar evidence of radioactive 60Fe implies that at least one supernova exploded within 100 pc of Earth within the last few Myr. The unique information provided by 60Fe to assess nearby supernovae make now a compelling time for the astronomy community to advocate for supporting multi-disciplinary, cross-cutting research programs. Title: Reconnection properties in Kelvin-Helmholtz instabilities Authors: Vernisse, Y.; Lavraud, B.; Eriksson, S.; Gershman, D. J.; Dorelli, J.; Pollock, C. J.; Giles, B. L.; Aunai, N.; Avanov, L. A.; Burch, J.; Chandler, M. O.; Coffey, V. N.; Dargent, J.; Ergun, R.; Farrugia, C. J.; Genot, V. N.; Graham, D.; Hasegawa, H.; Jacquey, C.; Kacem, I.; Khotyaintsev, Y. V.; Li, W.; Magnes, W.; Marchaudon, A.; Moore, T. E.; Paterson, W. R.; Penou, E.; Phan, T.; Retino, A.; Schwartz, S. J.; Saito, Y.; Sauvaud, J. A.; Schiff, C.; Torbert, R. B.; Wilder, F. D.; Yokota, S. Bibcode: 2017AGUFMSM13B2377V Altcode: Kelvin-Helmholtz instabilities are particular laboratories to study strong guide field reconnection processes. In particular, unlike the usual dayside magnetopause, the conditions across the magnetopause in KH vortices are quasi-symmetric, with low differences in beta and magnetic shear angle. We study these properties by means of statistical analysis of the high-resolution data of the Magnetospheric Multiscale mission. Several events of Kelvin-Helmholtz instabilities pas the terminator plane and a long lasting dayside instabilities event where used in order to produce this statistical analysis. Early results present a consistency between the data and the theory. In addition, the results emphasize the importance of the thickness of the magnetopause as a driver of magnetic reconnection in low magnetic shear events. Title: Magnetic Reconnection as Revealed by the Magnetospheric Multiscale Mission Authors: Burch, J. L.; Torbert, R. B.; Moore, T. E.; Giles, B. L.; Phan, T.; Le Contel, O.; Webster, J.; Genestreti, K.; Ergun, R.; Chen, L. J.; Wang, S.; Dorelli, J.; Rager, A. C.; Graham, D.; Gershman, D. J. Bibcode: 2017AGUFMSM21C..01B Altcode: The NASA Magnetospheric Multiscale (MMS) mission has completed its prime mission observations and has now entered an extended mission phase. During the two-year prime mission MMS made fundamental advances in our understanding of magnetic reconnection as enabled by its unprecedentedly high-resolution plasma and field measurements, which were made from 4 identical spacecraft in tetrahedral formations ranging down to 7 km. The primary objective of MMS is to understand reconnection at the electron scale, and this objective was accomplished by detailed analysis of 32 electron diffusion regions at the dayside magnetopause and a significant number in the magnetotail, which are still being captured and analyzed. Significant interplay between theory and experiment has occurred throughout the mission leading to the discovery of agyrotropic "crescent-shaped" electron velocity-space distributions, which carry the out-of-plane current; the electron pressure tensor divergence, which produces the reconnection electric field; standing oblique whistler waves, which produce intense dissipation in sub-gyroscale regions near the X-line and electron stagnation point; beam-plasma interactions leading to whistler-mode and Langmuir waves; electromagnetic drift waves leading to corrugated magnetopause current sheets, and numerous other new reconnection-related phenomena. In this talk the many new aspects of reconnection discovered by MMS will be placed into context and used to evaluate our current level of understanding of this universally important space plasma phenomenon. Title: Magnetospheric Multiscale observations of Flux Transfer Event signatures Authors: Lavraud, B.; Kacem, I.; Farrugia, C. J.; Oieroset, M.; Zhou, M.; Eastwood, J. P.; Dargent, J.; Dorelli, J.; Burch, J. L.; Giles, B. L.; Fuselier, S. A.; Gershman, D. J.; Coffey, V. N.; Ergun, R.; Avanov, L. A.; Pollock, C. J.; Chen, L. J.; Chandler, M. O.; Genot, V. N.; Eriksson, S.; Graham, D.; Grigorenko, E. E.; Hasegawa, H.; Jacquey, C.; Khotyaintsev, Y. V.; Marchaudon, A.; Moore, T. E.; Nakamura, R.; Paterson, W. R.; Rager, A. C.; Phan, T.; Russell, C. T.; Saito, Y.; Sauvaud, J. A.; Smith, S. E.; Schiff, C.; Strangeway, R. J.; Toledo Redondo, S.; Vernisse, Y.; Wang, S.; Yokota, S. Bibcode: 2017AGUFMSM11F..02L Altcode: Spatially and/or temporally variable reconnection at the Earth's magnetopause is thought to lead to the formation of structures called Flux Transfer Events (FTEs). We review new findings on FTE signatures, structure and dynamics recently obtained thanks to the very high-resolution measurements from the Magnetospheric Multiscale mission (MMS). We focus in particular on the detailed observations of (1) flux tube coalescence, (2) small-scale flux tubes in reconnection exhausts, (3) small-scale reconnecting current sheets within FTEs, and (3) larger-scale topology as implied from electron observations. Title: Influence of iron redox cycling on organo-mineral associations in Arctic tundra soil Authors: Herndon, Elizabeth; AlBashaireh, Amineh; Singer, David; Roy Chowdhury, Taniya; Gu, Baohua; Graham, David Bibcode: 2017GeCoA.207..210H Altcode: Arctic tundra stores large quantities of soil organic matter under varying redox conditions. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and release to the atmosphere as the greenhouse gases carbon dioxide (CO2) and methane (CH4). Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. The accumulation of iron (Fe) oxyhydroxides and organo-iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron [Fe(III)] species can enhance decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Here, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. Spectroscopic techniques, including micro-X-ray fluorescence (μXRF) mapping, micro-X-ray absorption near-edge structure (μXANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils.

Organic horizons were enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Minor amounts of ferrous iron [Fe(II)] were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Concentrations of organic carbon in the organic horizons (28 ± 5 wt.% C) were approximately twice the concentrations in the mineral horizons (14 ± 2 wt.% C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised <2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. Integrated over the entire depth of the active layer, soils contained 11 ± 4 kg m-2 low-density, particulate organic C and 19 ± 6 kg m-2 high-density, mineral-associated organic C, indicating that 63 ± 19% of organic C in the active layer was associated with the mineral fraction.

We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO2 and CH4 in these anoxic environments. Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions. Title: Spectral analysis and modeling of solar flares chromospheric condensation Authors: Cauzzi, Gianna; Graham, David; Kowalski, Adam; Zangrilli, Luca; Simoes, Paulo; Allred, Joel C. Bibcode: 2016SPD....47.0609C Altcode: We follow up on our recent analysis of the X1.1 flare SOL2014-09-10T17:45, where we studied the impulsive phase dynamics of tens of individual flaring "kernels", in both coronal (Fe XXI) and chromospheric (MgII) lines observed at high cadence with IRIS.We concentrate here on the chromospheric aspect of the phenomenon, extending the analysis to multiple spectral lines of Mg II, Fe II, Si I, C II. We show that many flaring kernels display high velocity downflows in the spectra of all these chromospheric lines, exhibiting distinct, transient and strongly redshifted spectral components.From modeling using RADYN with the thick-target interpretation, the presence of two spectral components appears to be consistent with a high flux beam of accelerated electrons, characterized by a hard spectrum. In particular the highest energy electrons heat the denser, lower layers of the atmosphere, while the bulk of the beam energy, deposited higher in the atmosphere, is sufficient to produce chromospheric evaporation with a corresponding condensation. Title: Currents and associated electron scattering and bouncing near the diffusion region at Earth's magnetopause Authors: Lavraud, B.; Zhang, Y. C.; Vernisse, Y.; Gershman, D. J.; Dorelli, J.; Cassak, P. A.; Dargent, J.; Pollock, C.; Giles, B.; Aunai, N.; Argall, M.; Avanov, L.; Barrie, A.; Burch, J.; Chandler, M.; Chen, L. -J.; Clark, G.; Cohen, I.; Coffey, V.; Eastwood, J. P.; Egedal, J.; Eriksson, S.; Ergun, R.; Farrugia, C. J.; Fuselier, S. A.; Génot, V.; Graham, D.; Grigorenko, E.; Hasegawa, H.; Jacquey, C.; Kacem, I.; Khotyaintsev, Y.; MacDonald, E.; Magnes, W.; Marchaudon, A.; Mauk, B.; Moore, T. E.; Mukai, T.; Nakamura, R.; Paterson, W.; Penou, E.; Phan, T. D.; Rager, A.; Retino, A.; Rong, Z. J.; Russell, C. T.; Saito, Y.; Sauvaud, J. -A.; Schwartz, S. J.; Shen, C.; Smith, S.; Strangeway, R.; Toledo-Redondo, S.; Torbert, R.; Turner, D. L.; Wang, S.; Yokota, S. Bibcode: 2016GeoRL..43.3042L Altcode: Based on high-resolution measurements from NASA's Magnetospheric Multiscale mission, we present the dynamics of electrons associated with current systems observed near the diffusion region of magnetic reconnection at Earth's magnetopause. Using pitch angle distributions (PAD) and magnetic curvature analysis, we demonstrate the occurrence of electron scattering in the curved magnetic field of the diffusion region down to energies of 20 eV. We show that scattering occurs closer to the current sheet as the electron energy decreases. The scattering of inflowing electrons, associated with field-aligned electrostatic potentials and Hall currents, produces a new population of scattered electrons with broader PAD which bounce back and forth in the exhaust. Except at the center of the diffusion region the two populations are collocated and appear to behave adiabatically: the inflowing electron PAD focuses inward (toward lower magnetic field), while the bouncing population PAD gradually peaks at 90° away from the center (where it mirrors owing to higher magnetic field and probable field-aligned potentials). Title: Impulsive Heating of Solar Flare Ribbons Above 10 MK Authors: Simões, P. J. A.; Graham, D. R.; Fletcher, L. Bibcode: 2015SoPh..290.3573S Altcode: 2015arXiv150503384S; 2015SoPh..tmp...62S The chromospheric response to the input of flare energy is marked by extended extreme ultraviolet (EUV) ribbons and hard X-ray (HXR) footpoints. These are usually explained as the result of heating and bremsstrahlung emission from accelerated electrons colliding in the dense chromospheric plasma. We present evidence of impulsive heating of flare ribbons above 10 MK in a two-ribbon flare. We analyse the impulsive phase of SOL2013-11-09T06:38, a C2.6 class event using data from Atmospheric Imaging Assembly (AIA) on board of the Solar Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to derive the temperature, emission measure and differential emission measure of the flaring regions and investigate the evolution of the plasma in the flaring ribbons. The ribbons were visible at all SDO/AIA EUV/UV wavelengths, in particular, at 94 and 131 Å filters, sensitive to temperatures of 8 MK and 12 MK. The time evolution of the emission measure of the plasma above 10 MK at the ribbons has a peak near the HXR peak time. The presence of hot plasma in the lower atmosphere is further confirmed by a RHESSI imaging spectroscopy analysis, which shows resolved sources at 11 - 13 MK that are associated with at least one ribbon. We found that collisional beam-heating can only marginally explain the power necessary to heat the 10 MK plasma at the ribbons. Title: Determining energy balance in the flaring chromosphere from oxygen V line ratios Authors: Graham, D. R.; Fletcher, L.; Labrosse, N. Bibcode: 2015A&A...584A...6G Altcode: 2014arXiv1411.4603G Context. The impulsive phase of solar flares is a time of rapid energy deposition and heating in the lower solar atmosphere, leading to changes in the temperature and density structure of the region.
Aims: We use an O v density diagnostic formed from the λ192 /λ248 line ratio, provided by the Hinode/EIS instrument, to determine the density of flare footpoint plasma at O v formation temperatures of ~2.5 × 105 K, giving a constraint on the properties of the heated transition region.
Methods: Hinode/EIS rasters from 2 small flare events in December 2007 were used. Raster images were co-aligned to identify and establish the footpoint pixels, multiple-component Gaussian line fitting of the spectra was carried out to isolate the density diagnostic pair, and the density was calculated for several footpoint areas. The assumptions of equilibrium ionisation and optically-thin radiation for the O v lines used were assessed and found to be acceptable. For one of the events, properties of the electron distribution were deduced from earlier RHESSI hard X-ray observations. These were used to calculate the plasma heating rate delivered by an electron beam for 2 semi-empirical atmospheres under collisional thick-target assumptions. The radiative loss rate for this plasma was also calculated for comparison with possible energy input mechanisms.
Results: Electron number densities of up to 1011.9 cm-3 were measured during the flare impulsive phase using the O v λ192 /λ248 diagnostic ratio. The heating rate delivered by an electron beam was found to exceed the radiative losses at this density, corresponding to a height of 450 km, and when assuming a completely ionised target atmosphere far exceed the losses but at a height of 1450-1600 km. A chromospheric thickness of 70-700 km was found to be required to balance a conductive input to the O v-emitting region with radiative losses.
Conclusions: Electron densities have been observed in footpoint sources at transition region temperatures, comparable to previous results but with improved spatial information. The observed densities can be explained by heating of the chromosphere by collisional electrons, with O v formed at heights of 450-1600 km above the photosphere, depending on the atmospheric ionisation fraction. Title: Hα Line Profile Asymmetries and the Chromospheric Flare Velocity Field Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski, A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P. Bibcode: 2015ApJ...813..125K Altcode: 2015arXiv151001877K The asymmetries observed in the line profiles of solar flares can provide important diagnostics of the properties and dynamics of the flaring atmosphere. In this paper the evolution of the Hα and Ca ii λ8542 lines are studied using high spatial, temporal, and spectral resolution ground-based observations of an M1.1 flare obtained with the Swedish 1 m Solar Telescope. The temporal evolution of the Hα line profiles from the flare kernel shows excess emission in the red wing (red asymmetry) before flare maximum and excess in the blue wing (blue asymmetry) after maximum. However, the Ca ii λ8542 line does not follow the same pattern, showing only a weak red asymmetry during the flare. RADYN simulations are used to synthesize spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. We show that the red asymmetry observed in Hα is not necessarily associated with plasma downflows, and the blue asymmetry may not be related to plasma upflows. Indeed, we conclude that the steep velocity gradients in the flaring chromosphere modify the wavelength of the central reversal in the Hα line profile. The shift in the wavelength of maximum opacity to shorter and longer wavelengths generates the red and blue asymmetries, respectively. Title: How Important Are Electron Beams in Driving Chromospheric Evaporation in the 2014 March 29 Flare? Authors: Battaglia, Marina; Kleint, Lucia; Krucker, Säm; Graham, David Bibcode: 2015ApJ...813..113B Altcode: 2015arXiv150909186B We present high spatial resolution observations of chromospheric evaporation in the flare SOL2014-03-29T17:48. Interface Region Imaging Spectrograph observations of the Fe xxi λ 1354.1 line indicate evaporating plasma at a temperature of 10 MK along the flare ribbon during the flare peak and several minutes into the decay phase with upflow velocities between 30 and 200 km s-1. Hard X-ray (HXR) footpoints were observed by the Ramaty High Energy Solar Spectroscopic Imager for two minutes during the peak of the flare. Their locations coincided with the locations of the upflows in parts of the southern flare ribbon but the HXR footpoint source preceded the observation of upflows in Fe xxi by 30-75 s. However, in other parts of the southern ribbon and in the northern ribbon, the observed upflows were not coincident with an HXR source in time or space, most prominently during the decay phase. In this case evaporation is likely caused by energy input via a conductive flux that is established between the hot (25 MK) coronal source, which is present during the whole observed time-interval, and the chromosphere. The presented observations suggest that conduction may drive evaporation not only during the decay phase but also during the flare peak. Electron beam heating may only play a role in driving evaporation during the initial phases of the flare. Title: First 230 GHz VLBI fringes on 3C 279 using the APEX Telescope Authors: Wagner, J.; Roy, A. L.; Krichbaum, T. P.; Alef, W.; Bansod, A.; Bertarini, A.; Güsten, R.; Graham, D.; Hodgson, J.; Märtens, R.; Menten, K.; Muders, D.; Rottmann, H.; Tuccari, G.; Weiss, A.; Wieching, G.; Wunderlich, M.; Zensus, J. A.; Araneda, J. P.; Arriagada, O.; Cantzler, M.; Duran, C.; Montenegro-Montes, F. M.; Olivares, R.; Caro, P.; Bergman, P.; Conway, J.; Haas, R.; Johansson, J.; Lindqvist, M.; Olofsson, H.; Pantaleev, M.; Buttaccio, S.; Cappallo, R.; Crew, G.; Doeleman, S.; Fish, V.; Lu, R. -S.; Ruszczyk, C.; SooHoo, J.; Titus, M.; Freund, R.; Marrone, D.; Strittmatter, P.; Ziurys, L.; Blundell, R.; Primiani, R.; Weintroub, J.; Young, K.; Bremer, M.; Sánchez, S.; Marscher, A. P.; Chilson, R.; Asada, K.; Inoue, M. Bibcode: 2015A&A...581A..32W Altcode: 2015arXiv150603244W
Aims: We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO).
Methods: We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5 h 230 GHz VLBI track with baseline lengths of 2800 Mλ to 7200 Mλ and a finest fringe spacing of 28.6 μas.
Results: Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy beam-1, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region ≲ 38 μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010 K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ~ 38 μas.
Conclusions: With APEX the angular resolution of 230 GHz VLBI improves to 28.6 μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed. Title: IRIS observations of chromospheric evaporation in multiple, individual flaring kernels Authors: Cauzzi, Gianna; Graham, David; Zangrilli, Luca Bibcode: 2015IAUGA..2257379C Altcode: We present new results from IRIS showing the dynamic evolution of chromospheric evaporation in a flare ribbon, with the highest temporal and spatial resolution to date. IRIS observed the entire duration of an X-class event using a 9 second cadence 'sit and stare' mode. As the ribbon brightened successively at new positions along the slit, a unique impulsive phase evolution was observed for about 80 individual spatial pixels in both coronal (Fe XXI) and chromospheric (MgII) lines.Each activation of a new footpoint kernel displays the same initial coronal up-flows of up to ~350 km/s, co-temporal and co-spatial with chromospheric downflows up to 40 km/s. This represents one of the most convincing examples of the development and evolution of chromospheric evaporation. Further, the temporal evolution of flows is remarkably similar between all slit pixel positions, leading to the conclusion that the time of energy deposition in any one footpoint is short - between 30-60 seconds - and occurs in an area of less than 2". Surprisingly the Fe XXI flows are sustained for several minutes, and significant line broadening beyond the thermal width is seen, which we interperet here as plasma above the equilibrium formation temperature. To understand these observations we compare them with a hydrodynamic flare model. Title: Temporal Evolution of Multiple Evaporating Ribbon Sources in a Solar Flare Authors: Graham, D. R.; Cauzzi, G. Bibcode: 2015ApJ...807L..22G Altcode: 2015arXiv150603465G We present new results from the Interface Region Imaging Spectrograph (IRIS) showing the dynamic evolution of chromospheric evaporation and condensation in a flare ribbon, with the highest temporal and spatial resolution to date. IRIS observed the entire impulsive phase of the X-class flare SOL2014-09-10T17:45 using a 9.4 s cadence “sit-and-stare” mode. As the ribbon brightened successively at new positions along the slit, a unique impulsive phase evolution was observed for many tens of individual pixels in both coronal and chromospheric lines. Each activation of a new footpoint displays the same initial coronal upflows of up to ∼300 km s-1 and chromospheric downflows up to 40 km s-1. Although the coronal flows can be delayed by over 1 minute with respect to those in the chromosphere, the temporal evolution of flows is strikingly similar between all pixels and consistent with predictions from hydrodynamic flare models. Given the large sample of independent footpoints, we conclude that each flaring pixel can be considered a prototypical, “elementary” flare kernel. Title: Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS, and RHESSI Authors: Simões, P. J. A.; Graham, D. R.; Fletcher, L. Bibcode: 2015A&A...577A..68S Altcode: 2015arXiv150301491S
Aims: We present direct evidence of the detection of the main energy release site in a non-eruptive solar flare, SOL2013-11-09T06:38 UT. This GOES class C2.6 event was characterised by two flaring ribbons and a compact, bright coronal source located between them, which is the focus of our study.
Methods: We use imaging from SDO/AIA, and imaging spectroscopy from RHESSI to characterise the thermal and non-thermal emission from the coronal source, and EUV spectroscopy from the Hinode/Extreme ultraviolet Imaging Spectrometer, which scanned the coronal source during the impulsive peak, to analyse Doppler shifts in Fe xii (log T = 6.2) and Fe xxiv (log T = 7.2) emission lines, and determine the source density.
Results: The coronal source exhibited an impulsive emission lightcurve in all SDO/AIA filters during the impulsive phase. RHESSI hard X-ray images indicate both thermal and non-thermal emission at the coronal source, and its plasma temperature derived from RHESSI imaging spectroscopy shows an impulsive rise, reaching a maximum at 12-13 MK about 10 s prior to the hard X-ray peak. High red-shifts associated with this bright source indicate downflows of 40-250 km s-1 at a broad range of temperatures, interpreted as loop shrinkage and/or outflows along the magnetic field. Outflows from the coronal source towards each ribbon are also observed by SDO/AIA images at 171, 193, 211, 304, and 1600 Å. The electron density of the source obtained from a Fe xiv line pair is 1011.50 cm-3 which is collisionally thick to electrons with energy up to 45-65 keV, responsible for the source's non-thermal X-ray emission.
Conclusions: Given the rich observational evidence, we conclude that the bright coronal source is the location of the main release of magnetic energy in this flare, with a geometry consistent with component reconnection between crossing, current-carrying loops. We argue that the energy that can be released via reconnection, based on observational estimates, can plausibly account for the non-thermal energetics of the flare. Title: Extreme ultraviolet spectroscopy of impulsive phase solar flare footpoints Authors: Graham, David Robert Bibcode: 2014PhDT.......327G Altcode: No abstract at ADS Title: DBBC3 - Full digital EVN and VLBI2010 Backend, Project Progress Authors: Tuccari, G.; Alef, W.; Wunderlich, M.; Buttaccio, S.; Graham, D.; Comoretto, G.; Bertarini, A.; Casey, S.; Roy, A.; Wagner, J.; Lindqvist, M. Bibcode: 2013evga.conf....3T Altcode: DBBC3 is a project to develop the third generation of a digital backend system for VLBI and other scientific applications. The development started about ten years ago and evolved in the course of time by improving all its components, hardware, firmware and software, passing from DBBC1 to DBBC2. Now the latest and third generation will allow to fully implement digitally all the functionality required of a complete VLBI backend for the EVN and VGOS (formerly named VLBI2010), with a maximum output data rate in the range from 32 Gbps to up to 128 Gbps. The architecture and adopted methods are described. Title: The Emission Measure Distribution of Impulsive Phase Flare Footpoints Authors: Graham, D. R.; Hannah, I. G.; Fletcher, L.; Milligan, R. O. Bibcode: 2013ApJ...767...83G Altcode: 2013arXiv1302.2514G The temperature distribution of the emitting plasma is a crucial constraint when studying the heating of solar flare footpoints. However, determining this for impulsive phase footpoints has been difficult in the past due to insufficient spatial resolution to resolve the footpoints from the loop structures, and a lack of spectral and temporal coverage. We use the capabilities of Hinode/Extreme Ultraviolet Imaging Spectrometer to obtain the first emission measure distributions (EMDs) from impulsive phase footpoints in six flares. Observations with good spectral coverage were analyzed using a regularized inversion method to recover the EMDs. We find that the EMDs all share a peak temperature of around 8 MK, with lines formed around this temperature having emission measures (EMs) peaking between 1028 and 1029 cm-5, indicating a substantial presence of plasma at very high temperatures within the footpoints. An EMD gradient of EM(T) ~ T is found in all events. Previous theoretical work on EM gradients shows this to be consistent with a scenario in which the deposited flare energy directly heats only the top layer of the flare chromosphere, while deeper layers are heated by conduction. Title: Investigating the Structure of Impulsive Phase Footpoints Authors: Graham, David; Hannah, I.; Fletcher, L.; Milligan, R. Bibcode: 2012AAS...22050903G Altcode: The location of flare heating in the solar atmosphere is imperative to understanding the heating mechanism. The differential emission measure is an important tool in understanding the properties of flaring plasma. However, determining the DEM of impulsive phase footpoints has been difficult in the past without sufficient spatial resolution to resolve footpoints from loop structures, and a lack of spectral and temporal coverage. We use the capabilities of Hinode/EIS to present the first DEMs from the impulsive phase of a number of flare footpoints. Observations were chosen from a period when EIS telemetry was at its best and analysed using a new regularised inversion method (Hannah & Kontar 2012). We find a peak temperature in the DEM of around 7 MK with emission measures peaking between 10^28 and 10^29 cm-5, indicating a substantial presence of plasma at 'coronal' temperatures within the footpoint. In addition to the DEM, we perform a wide range of density diagnostics from transition region to coronal temperatures, allowing us estimate where in the atmosphere the EUV emission originates. Title: The EVE Doppler Sensitivity and Flare Observations Authors: Hudson, H. S.; Woods, T. N.; Chamberlin, P. C.; Fletcher, L.; Del Zanna, G.; Didkovsky, L.; Labrosse, N.; Graham, D. Bibcode: 2011SoPh..273...69H Altcode: 2011SoPh..tmp..362H The Extreme-ultraviolet Variability Experiment (EVE; see Woods et al., 2009) obtains continuous EUV spectra of the Sun viewed as a star. Its primary objective is the characterization of solar spectral irradiance, but its sensitivity and stability make it extremely interesting for observations of variability on time scales down to the limit imposed by its basic 10 s sample interval. In this paper we characterize the Doppler sensitivity of the EVE data. We find that the 30.4 nm line of He II has a random Doppler error below 0.001 nm (1 pm, better than 10 km s−1 as a redshift), with ample stability to detect the orbital motion of its satellite, the Solar Dynamics Observatory (SDO). Solar flares also displace the spectrum, both because of Doppler shifts and because of EVE's optical layout, which (as with a slitless spectrograph) confuses position and wavelength. As a flare develops, the centroid of the line displays variations that reflect Doppler shifts and therefore flare dynamics. For the impulsive phase of the flare SOL2010-06-12, we find the line centroid to have a redshift of 16.8 ± 5.9 km s−1 relative to that of the flare gradual phase (statistical errors only). We find also that high-temperature lines, such as Fe XXIV 19.2 nm, have well-determined Doppler components for major flares, with decreasing apparent blueshifts as expected from chromospheric evaporation flows. Title: Hinode/EIS plasma diagnostics in the flaring solar chromosphere Authors: Graham, D. R.; Fletcher, L.; Hannah, I. G. Bibcode: 2011A&A...532A..27G Altcode: Context. The impulsive phase of solar flares is a time of rapid energy deposition and heating in the lower solar atmosphere, leading to changes in the temperature, density, ionisation and velocity structure of this region.
Aims: We aim to study the lower atmosphere during the impulsive phase of a flare using imaging and spectroscopic data from Hinode/EIS, RHESSI and TRACE. We place these observations in context by using a wide range of temperature observations from each instrument.
Methods: We analyse sparse raster data from the Hinode/EIS spectrometer to derive the density and line-of-sight velocity in flare footpoints, in a GOES C6.6 flare observed on 05-June-2007. The raster duration was 150s across the centre of a small active region, allowing multiple exposures of the flare ribbons and footpoints. Using RHESSI and Hinode/XRT we test both non-thermal and thermal models for the HXR emission.
Results: During the flare impulsive phase, we find evidence from XRT for flare footpoints at temperatures exceeding 7 MK. We measure the electron number density increasing up to a few ×1010 cm-3 in the footpoints, at temperatures of ~1.5-2 MK, accompanied by small downflows at temperatures below Fe XIII and upflows of up to ~140 km s-1 at temperatures above. This is reasonable in the context of HXR diagnostics of the flare electron beam. The electrons inferred have sufficient energy to affect the chromospheric ionisation structure.
Conclusions: EIS sparse raster data coupled with RHESSI imaging and spectroscopy prove useful here in studying the lower atmosphere of solar flares, and in this event suggest heat deposition relatively high in the chromosphere drives chromospheric evaporation while increasing the observed electron densities at footpoints. However, from RHESSI spectral fitting it is not possible to say whether the data are more consistent with a model including a non-thermal beam, or purely thermal model. Title: Doppler Signatures In EVE Spectra Authors: Hudson, Hugh S.; Chamberlin, P.; Woods, T.; Fletcher, L.; Graham, D. Bibcode: 2011SPD....42.2124H Altcode: 2011BAAS..43S.2124H The Extreme-ultraviolet Variability Experiment (EVE) on SDO is providing a comprehensive set of EUV spectra of the Sun as a star. The routine sampling is with 10 s integrations at a resolution of 0.1 nm. Although this resolution corresponds to only some 1000 km/s in velocity space, we demonstrate that the instrument is stable enough to detect the SDO orbital motion of a few km/s readily in the bright He II line at 30.4 nm. We find the random error in the centroid location of this line to be less than one pm (less than 1 km/s) per 10 s integration. We also note systematic effects from a variety of causes. For flare observations, the line centroid position depends on the flare position. We discuss the calibration of this effect and show that EVE can nonetheless provide clear Doppler signatures that may be interpreted in terms of flare dynamics. This information has some value in and of itself, because of EVE's sensitivity, but we feel that it will be of greatest importance when combined with imagery (e.g., via AIA) a modeling. We discuss flare signatures in several events, e.g. the gamma-ray flare SOL2010-06-12 and SOL2011-02-16T:07:44, taking advantage of AIA image comparisons. Title: Giant pulses with nanosecond time resolution detected from the Crab pulsar at 8.5 and 15.1 GHz Authors: Jessner, A.; Popov, M. V.; Kondratiev, V. I.; Kovalev, Y. Y.; Graham, D.; Zensus, A.; Soglasnov, V. A.; Bilous, A. V.; Moshkina, O. A. Bibcode: 2010A&A...524A..60J Altcode: 2010arXiv1008.3992J
Aims: We present a study of shapes, spectra, and polarization properties of giant pulses (GPs) from the Crab pulsar at the very high frequencies of 8.5 and 15.1 GHz. Studies at 15.1 GHz are performed for the first time. We probe GP emission at high frequencies and examine its intrinsic spectral and polarization properties with high time and spectral resolution. The use of high radio frequencies also alleviates the effects of pulse broadening caused by interstellar scattering, which masks the intrinsic properties of GPs at low frequencies.
Methods: Observations were conducted with the 100-m radio telescope in Effelsberg in Oct.-Nov. 2007 at the frequencies of 8.5 and 15.1 GHz as part of an extensive campaign of multi-station multi-frequency observations of the Crab pulsar. A selection of the strongest pulses was recorded with a new data acquisition system, based on a fast digital oscilloscope, providing nanosecond time resolution in two polarizations with a bandwidth of about 500 MHz. In total, 29 and 85 GPs at longitudes of the main pulse and interpulse were recorded at 8.5 and 15.1 GHz during 10 and 17 h of observing time respectively. We analyzed the pulse shapes, polarisation and dynamic spectra of GPs as well as the cross-correlations between their LHC and RHC signals.
Results: No events were detected outside the main pulse and interpulse windows. The GP properties were found to be very different for GPs emitted at longitudes of the main pulse and the interpulse. Cross-correlations of the LHC and RHC signals show regular patterns in the frequency domain for the main pulse, which are missing for the interpulse GPs. We consider the consequences of applying the rotating vector model to explain the apparent smooth variation in the position angle of linear polarization for main pulse GPs. We also introduce a new scenario of GP generation as a direct consequence of the polar cap discharge.
Conclusions: We find further evidence of strong nano-shot discharges in the magnetosphere of the Crab pulsar. The repetitive frequency spectrum seen in GPs at the main pulse phase is interpreted as a diffraction pattern of regular structures in the emission region. The interpulse GPs however have a spectrum that resembles that of amplitude modulated noise. Propagation effects may be the cause of the differences. Title: DBBC.2 Backend System: status report Authors: Tuccari, G.; Buttaccio, S.; Nicotra, G.; Alef, W.; Graham, D.; Roy, A.; Bertarini, A.; Neidhardt, A.; Zeitlhoefler, R. Bibcode: 2009evga.conf...71T Altcode: No abstract at ADS Title: Hf isotopic insights into mantle source contributions in Turkana East African Rift System Authors: Locke, J. A.; Bryce, J. G.; Furman, T.; Hanan, B.; Rooney, T.; Graham, D. Bibcode: 2008GeCAS..72R.566L Altcode: No abstract at ADS Title: Multi-component isotopic mixing in the Ethiopian Rift: Modeling plume contributions to recent magmatism Authors: Rooney, T.; Hanan, B.; Furman, T.; Graham, D. Bibcode: 2008GeCAS..72R.804R Altcode: No abstract at ADS Title: Assessing a plume contribution to the Galapagos Speading Center by Neon isotopes Authors: Colin, A.; Marty, P. Burnard B.; Graham, D. Bibcode: 2008GeCAS..72R.173C Altcode: No abstract at ADS Title: NRAO 150: A Recently Identified Quasar Revealing Extreme Non-Ballistic Motion Authors: Agudo, I.; Bach, U.; Krichbaum, T. P.; Marscher, A. P.; Gonidakis, I.; Diamond, P. J.; Alef, W.; Graham, D.; Witzel, A.; Zensus, J. A.; Bremer, M.; Acosta-Pulido, J. A.; Barrena, R. Bibcode: 2008ASPC..386..249A Altcode: NRAO 150 -- a compact and bright radio to mm source showing core/jet structure-- has been recently identified as a quasar at redshift 1.52 through a near-IR spectral observation. To compute quantitative estimates of the basic physical properties of the jet in the source, we have analysed the ultra-high-resolution images from a new sub-milliarcsecond-scale monitoring program of its structure at 86 GHz and 43 GHz with the GMVA and the VLBA, respectively. An additional archival and calibration 43 GHz-VLBA data set, covering from 1997 to 2007, has been used. Our data shows an extreme projected counter-clock-wise jet swing of up to ∼11°/yr within the inner ∼61 pc of the jet, which is associated with a non-ballistic superluminal motion of the jet within this region. We argue that the magnetic field might play an important role in the dynamics of the jet in NRAO 150, which is supported by the large values of the magnetic field strength obtained from our first estimates. The extreme characteristics of the jet swing make NRAO 150 a prime source to study the jet wobbling phenomenon. Title: Present and Future Millimeter VLBI Imaging of Jets in Agn: the Case of NRAO150 Authors: Agudo, I.; Krichbaum, T. P.; Bach, U.; Pagels, A.; Graham, D.; Alef, W.; Witzel, A.; Zensus, J. A.; Bremer, M.; Grewing, M.; Terasranta, H. Bibcode: 2007RMxAC..27..171A Altcode: 2007RMxAC..27S...1A No abstract at ADS Title: Interactive Visualization and Exploration of SPH Data. Authors: Biddiscombe, J.; Graham, D.; Maruzewski, P. Bibcode: 2007sphe.work...51B Altcode: No abstract at ADS Title: Book Review: SATURN AND HOW TO OBSERVE IT / Springer-Verlag, 2006 Authors: Graham, David Bibcode: 2006JBAA..116..147G Altcode: No abstract at ADS Title: Book Review: SATURN - OVERVIEW AND ABSTRACTS / Nova Science Publishers, through Gazelle, 2003 Authors: Graham, David Bibcode: 2006Obs...126...57G Altcode: No abstract at ADS Title: Absorbing re-reflected random waves in SPH Authors: Graham, D.; Hughes, J. Bibcode: 2006sphe.workE..13G Altcode: No abstract at ADS Title: Saturn observers at opposition are rewarded with a ringside view Authors: Graham, David Bibcode: 2005JBAA..115..309G Altcode: No abstract at ADS Title: The spectra of isotopic heterogeneities along the mid-Atlantic Ridge [rapid communication] Authors: Agranier, Arnaud; Blichert-Toft, Janne; Graham, David; Debaille, Vinciane; Schiano, Pierre; Albarède, Francis Bibcode: 2005E&PSL.238...96A Altcode: Due to the advent of large-throughput plasma source mass spectrometers, extensive sets of high-precision Pb, Nd, and Hf isotopic data can now be produced on mid-ocean ridge basalts. A first such set of isotopic results on the mid-Atlantic Ridge is examined here in combination with literature data. The spectra of the data vs. latitude are strongly colored. When combined with conventional scatter plots, they reveal two contrasting types of behavior. The signal of the Icelandic hot spot is clearly identifiable on the spectra of 206Pb/ 204Pb, 207Pb/ 204Pb, 208Pb/ 204Pb, the first principal component of Pb isotopes, 87Sr/ 86Sr, and 3He/ 4He, over length scales of 6-10° (type A spectrum). In contrast, the power decreases in a near-continuous manner for the isotopic signals of Nd and Hf, and for the second Pb isotope principal component (type B spectrum). We interpret type B spectra as a dynamic cascade, in which the size of mantle heterogeneities is continually reduced upon stretching and refolding of the mantle by convection. The power law coefficient of this spectrum has an exponent of - 1 indicative of a Batchelor regime and reflects a smooth, but chaotic, probably steady-state flow. Since the isotopic properties of the type B spectra also characterize the EM I + EM II mix of the Dupal anomaly, we infer that they depict the convective northward dispersal ('reeling off') of the Southern Hemisphere anomalous mantle. Title: Fractionation of noble gases (He, Ar) during MORB mantle melting: a case study on the Southeast Indian Ridge Authors: Burnard, Pete; Graham, David; Farley, Ken Bibcode: 2004E&PSL.227..457B Altcode: New measurements of the He, Ar and CO 2 abundances trapped in basaltic glasses from the Southeast Indian Ridge (SEIR) show that volatile concentrations in the SEIR magmas were controlled by fractional degassing. Fractionation between volatile species is consistent with their solubilities in silicate melts. As a result, there are linear relationships between (for example) ln( 4He/ 40Ar*) vs. ln[ 40Ar*] and between ln( 4He/ 40Ar*) vs. ln( 40Ar*/CO 2) (where 40Ar* is the 40Ar corrected for atmospheric contributions). The slopes of these correlations permit the relative He/Ar and Ar/CO 2 solubilities to be estimated; these are generally consistent with experimentally determined noble gas solubilities in basaltic melts. However, there are systematic differences in the degassing trajectories. For example, in a plot of ln( 4He/ 40Ar*) vs. ln( 40Ar*/CO 2), samples from the deepest portions of the ridge consistently plot at lower 4He/ 40Ar* for a given 40Ar*/CO 2, compared to shallower sections of ridge. These variations in 4He/ 40Ar* likely reflect variations in He/Ar in the primary melt, i.e. their relative abundances prior to degassing. We estimated the variation in 4He/ 40Ar* in the initial melts (i.e. the 4He/ 40Ar* prior to degassing) by extrapolating the degassing trend to a constant mantle-like 40Ar*/CO 2 ratio and assuming that the relative He-Ar-CO 2 solubilities do not vary between samples. The 4He/ 40Ar* corrected for degassing in this manner varies by a factor ≈10 and correlates positively with the 3He/ 4He ratio. It is possible that the correlation between "degassing corrected" 4He/ 40Ar* ratios and the 3He/ 4He ratio results from preferential diffusion of 3He relative to 4He and of 4He relative to 40Ar from the solid mantle into primary melts during melting. However, modeling this diffusive process fails to reproduce the comparatively large variations in 3He/ 4He found in the basalts; therefore, it seems likely that mantle heterogeneities, in combination with diffusive fractionation, resulted in coupled He isotope and He/Ar variations. Title: Operational Experience with the Mark 5 Recording System at the Bonn and USNO Correlator Authors: Müskens, Arno; Alef, Walter; Graham, David; Kingham, Kerry Bibcode: 2004ivsg.conf..115M Altcode: 2004ivs..confE..21M; 2004ivs..confE.115M No abstract at ADS Title: Saturn, 2003-'04 apparition: First interim report Authors: Graham, D.; Peach, D. Bibcode: 2004JBAA..114...65G Altcode: Saturn emerged from solar conjunction into the dawn sky during August, and the first good quality observations were received by the Section in 2003 September. This report covers the period from the first observations received, to the date of opposition. This occurred on the final day of 2003, when the planet reached its closest to Earth since 1974, and was favourably placed for Northern observers at +22° declination. Title: Spots on Saturn in visual wavelengths Authors: Graham, D.; Peach, D. Bibcode: 2003JBAA..113..322G Altcode: The 2002-'03 apparition of Saturn was one of the most active in several years, aided by the Earth's finally reaching its maximum angle south of the Saturnian ring plane, giving northern hemisphere observers their best view of the planet and its ring system since the early 1970s. The maximum southerly tilt of 27° occurred in late March, though by then Saturn had already begun its descent into evening twilight. This interim report provides details of small but definite white spots and other features recorded on the globe and rings of Saturn during the apparition. Title: The new 11 Jy radio outburst of NRAO 150: VLBI study at the resolution limit Authors: Agudo, I.; Bach, U.; Krichbaum, T. P.; Alef, W.; Graham, D.; Bremer, M.; Ungerechts, H.; Grewing, M.; Teräsranta, H.; Witzel, A.; Zensus, J. A. Bibcode: 2003enig.conf..114A Altcode: No abstract at ADS Title: The northern limit of the North Atlantic high-H2O mantle province Authors: Michael, P.; Matzen, A.; Langmuir, C.; Goldstein, S.; Graham, D.; Snow, J. Bibcode: 2003EAEJA....13298M Altcode: The H_2O that is dissolved in submarine basalt glasses can provide information about the H_2O content of the upper mantle. In the mantle that produces mid-ocean ridge basalts (MORB) and ocean island basalts (OIB), the relative incompatibility of H_2O is approximately like that of Cerium (Ce). H_2O/Ce is fairly constant for depleted and enriched MORB (N-MORB and E-MORB) from a given region, but there are interesting regional differences. The most distinctive regional variation of H_2O/Ce was found on the Mid-Atlantic Ridge, from around 35^oN to as far north as was previously sampled: 77^oN (Michael, 1995). Both N-MORB and E-MORB from this region have significantly higher H_2O/Ce compared to MORB and OIB from the rest of the globe: 210--350 versus 120--230. Here we report the discovery of the northern boundary of this high-H_2O province, on Gakkel Ridge in the high Arctic. MORB glasses were collected from over 1000 km of Gakkel Ridge during the Arctic Mid-ocean Ridge Expedition (AMORE 2001). H_2O/Ce declines from values typical of the northern MAR (310--360) at the western end (8^oW) of Gakkel Ridge to values typical of the rest of the globe by 60^oE on Gakkel Ridge (170--220). High H_2O/Ce coincides with enrichment in other incompatible trace elements, notably Ba (see Langmuir et al., this meeting). The fact that the western part of the Gakkel Ridge has MORB with high H_2O/Ce suggests that its mantle source shares some characteristics with North Atlantic mantle, and that they may have a similar history. The high-H_2O/Ce could reflect the influence of ancient subduction processes that might have affected this large region (Michael, 1995). Relatively high H_2O could also have an important influence on mantle melting, especially at the low extents of melting that characterize Gakkel Ridge. Michael, P.J., 1995, Earth Planet. Sci. Lett. 131, 301-320. Title: Occultations of Saturn and Jupiter - a call for observations Authors: Graham, D.; Gavin, M.; Foulkes, M.; Carter, P. Bibcode: 2002JBAA..112..229G Altcode: No abstract at ADS Title: Book Review: Jupiter Odyssey / Springer, 2000 Authors: Graham, D. Bibcode: 2001JBAA..111..169G Altcode: No abstract at ADS Title: Letters to the Editor: The visual/CCD debate Authors: Heath, A. W.; Rogers, J. H.; Graham, D. Bibcode: 2001JBAA..111...47H Altcode: No abstract at ADS Title: EVN Observations of GRS 1915+105 Authors: Giovannini, G.; Feretti, L.; Tordi, M.; Venturi, T.; Massaglia, S.; Bodo, G.; Trussoni, E.; Gliozzi, M.; Tavani, M.; Conway, J.; Foley, A.; Graham, D.; Kus, A.; Spencer, R.; Trigilio, C. Bibcode: 2001ApSSS.276..111G Altcode: New European VLBI Network observations are presented. Title: EVN Observations of GRS1915+105 Authors: Feretti, L.; Giovannini, G.; Tordi, M.; Venturi, T.; Massaglia, S.; Bodo, G.; Trussoni, E.; Gliozzi, M.; Tavani, M.; Conway, J.; Foley, A.; Graham, D.; Kus, A.; Spencer, R.; Trigilio, C. Bibcode: 2000astro.ph..9348F Altcode: We obtained EVN observations of the X-ray transient source GRS1915+105 in its radio-loud state. In 2 images obtained before a major flare, the source is resolved, showing two opposite asymmetric jets. This indicates that steady jets exist also before a major flare, with an estimated velocity of 0.2-0.6c. Title: EVN ad hoc observations of GRS1915+105 Authors: Feretti, L.; Giovannini, G.; Tordi, M.; Venturi, T.; Massaglia, S.; Bodo, G.; Trussoni, E.; Gliozzi, M.; Tavani, M.; Conway, J. E.; Foley, A.; Graham, D.; Kus, A.; Spencer, R.; Trigilio, C. Bibcode: 2000evn..conf..171F Altcode: No abstract at ADS Title: A colourful Saturn Authors: Graham, D. Bibcode: 1999JBAA..109..306G Altcode: No abstract at ADS Title: Clusters in collision. Authors: Graham, D. Bibcode: 1999Ast....27...58G Altcode: Collisions and merging in clusters of galaxies. Title: Saturn: rings within rings Authors: Graham, D. Bibcode: 1998JBAA..108..189G Altcode: Observations of Saturn and the ring system in 1997 are placed in a historical context. Title: S/1997 U 1 Authors: Cruikshank, D. P.; Gladman, B.; Smith, R. M.; Jones, J. B.; Windridge, D.; Hall, P.; Graham, D.; Kavelaars, J. J.; Williams, G. V.; Aksnes, K.; Marsden, B. G. Bibcode: 1998IAUC.6870....1C Altcode: 1998IAUC.6870A...1C; 1998IAUC.6870Q...1C Precovery and recovery observations of this satellite are reported: UT R.A. (2000) Decl. Observer 1984 June 1.5556 16 40 58.4 -22 03 56 Cruikshank 2.5410 16 40 48.5 -22 03 36 " 1998 Mar. 27.79254 20 57 08.27 -17 56 16.2 Smith 31.40380 20 57 41.27 -17 53 56.1 Hall D. P. Cruikshank (Mauna Kea). Measurer B. Gladman. Images found on plates taken with the Canada-France-Hawaii Telescope; uncertainty +/- 3". R. M. Smith, J. B. Jones and D. Windridge (Anglo-Australian Observatory). 4-m reflector + CCD. Measurer B. Gladman. P. Hall and D. Graham (Cerro Tololo Interamerican Observatory). 4-m reflector + CCD. Measurer J. J. Kavelaars. Orbit computations by G. V. Williams, K. Aksnes and the undersigned, show that the 1998 recovery observations, although some 3' from the prediction on IAUC 6833, confirm that this satellite has a low-e orbit (see also IAUC 6780 and 6765). They also clearly demonstrate the validity of correctness the 1984 candidate, already noted by Gladman prior to the 1998 recovery, but not previously announced. Epoch = 1998 July 6.0 TT T = 1998 Apr. 19.6463 TT Peri. = 339.4621 e = 0.082347 Node = 174.9928 2000.0 q = 0.043975 AU Incl. = 139.6813 a = 0.047921 AU n = 0.621291 P = 579 days 1998 TT R. A. (2000) Decl. Delta r_U Elong. dR.A. dDecl. Apr. 7 20 58.61 -17 50.0 20.243 0.044 65.0 329- 248- 17 20 59.76 -17 45.0 20.082 0.044 74.5 328- 215- 27 21 00.61 -17 41.2 19.913 0.044 84.1 322- 178- May 7 21 01.14 -17 38.7 19.742 0.044 93.7 311- 138- 17 21 01.35 -17 37.6 19.573 0.044 103.3 296- 95- 27 21 01.23 -17 37.8 19.411 0.044 112.9 277- 49- June 6 21 00.80 -17 39.4 19.261 0.045 122.6 253- 2- 16 21 00.07 -17 42.1 19.127 0.045 132.3 225- 46+ 26 20 59.07 -17 45.9 19.013 0.045 142.1 194- 93+ July 6 20 57.86 -17 50.6 18.922 0.045 151.9 160- 139+ 16 20 56.47 -17 56.0 18.858 0.046 161.8 124- 184+ 26 20 54.96 -18 01.8 18.822 0.046 171.7 85- 226+ Title: S/1997 U 2 Authors: Smith, R. M.; Jones, J. B.; Windridge, D.; Gladman, B.; Hall, P.; Graham, D.; Kavelaars, J. J.; Williams, G. V.; Aksnes, K.; Marsden, B. G. Bibcode: 1998IAUC.6869....1S Altcode: 1998IAUC.6869A...1S; 1998IAUC.6869Q...1S The recovery of the brighter of the new Uranian satellites is reported: 1998 UT R.A. (2000) Decl. Observer Mar. 27.79632 20 57 59.99 -17 46 15.5 Smith 31.40380 20 58 34.18 -17 44 03.4 Hall R. M. Smith, J. B. Jones and D. Windridge (Anglo-Australian Observatory). 4-m reflector + CCD. Measurer B. Gladman. P. Hall and D. Graham (Cerro Tololo Interamerican Observatory). 4-m reflector + CCD. Measurer J. J. Kavelaars. These recovery positions are fully 30" from the prediction on IAUC 6834. Computations by G. V. Williams, K. Aksnes and the undersigned show that the reason for this is that there is another orbital solution from the 1984-1997 observations, much more strongly perturbed by the sun, separated from the sequence of solutions previously mentioned and corresponding to N approximately 3.7. The 1998 recovery clearly shows that this high-e solution (see also IAUC 6780 and 6765) is the correct one. Epoch = 1998 July 6.0 TT T = 1997 June 16.0390 TT Peri. = 18.0055 e = 0.509386 Node = 255.8085 2000.0 q = 0.040055 AU Incl. = 152.6686 a = 0.081643 AU n = 0.279383 P = 1289 days 1998 TT R. A. (2000) Decl. Delta r_U Elong. dR.A. dDecl. Apr. 7 20 59.52 -17 40.4 20.181 0.096 64.8 456+ 327+ 17 21 00.72 -17 35.9 20.024 0.097 74.3 497+ 331+ 27 21 01.61 -17 32.6 19.860 0.099 83.8 538+ 335+ May 7 21 02.18 -17 30.8 19.693 0.100 93.4 577+ 339+ 17 21 02.41 -17 30.4 19.528 0.102 103.0 615+ 341+ 27 21 02.31 -17 31.3 19.370 0.103 112.6 652+ 342+ June 6 21 01.89 -17 33.6 19.222 0.105 122.3 687+ 342+ 16 21 01.17 -17 37.2 19.090 0.106 132.1 721+ 340+ 26 21 00.18 -17 41.9 18.977 0.107 141.8 753+ 338+ July 6 20 58.96 -17 47.4 18.888 0.108 151.7 783+ 334+ 16 20 57.56 -17 53.6 18.824 0.109 161.6 811+ 328+ 26 20 56.04 -18 00.2 18.788 0.111 171.5 836+ 322+ Aug. 5 20 54.45 -18 07.0 18.781 0.112 178.4 860+ 314+ 15 20 52.88 -18 13.6 18.804 0.113 168.6 881+ 306+ 25 20 51.37 -18 19.7 18.855 0.114 158.6 900+ 297+ Title: Corrigenda Authors: Graham, D.; Groom, D. Bibcode: 1998IAUC.6872....2G Altcode: 1998IAUC.6872B...1G; 1998IAUC.6872R...1G IAUC 6868, GRB 980329, line 5: for (see IAUC 6864) read [GRB Coordinates Network Circular No. 40 (GCN 40; URL given on IAUC 6864); see also http://gcn.gsfc.nasa.gov/gcn/gcn_main.html] IAUC 6869, S/1997 U 2, line 7, and IAUC 6870, S/1997 U 1, line 11: for D. Graham read D. Groom Title: MM-VLBI Monitoring of Broad-Band Active Blazars Authors: Krichbaum, T. P.; Witzel, A.; Graham, D.; Lobanov, A. P. Bibcode: 1997mvlb.work....3K Altcode: No abstract at ADS Title: Spring time on Saturn Authors: Graham, D. Bibcode: 1996JBAA..106..306G Altcode: The atmosphere of Saturn continues to produce storm systems on a scale large enough to be seen from Earth. The white spots which appear from time to time on the disk of Saturn are clouds of ammonia ice crystals that form when an upward current of warmer gases pushes its way through Saturn's frozen cloud decks. They have been likened to a terrestrial thunderhead. Title: Detection of HC_9_N (J=39-38) from CRL 2688. and CRL 618 and of NH_3_(5,4) toward CRL 618. Authors: Truong-Bach; Graham, D.; Nguyen-Q-Rieu Bibcode: 1996A&A...312..565T Altcode: Our previous discovery of the HC_9_N molecule in CRL 2688 via the J=43-42 transition has prompted us to search for other transitions. We report here our detection of the HC_9_N J=39-38 emission from the CRL 2688 and CRL 618 nebulae, using the 100-m Effelsberg telescope. Toward CRL 2688, the line is double peaked like the stronger J=43-42 one. Toward CRL 618, the line is tentatively detected; and a reversal ammonia line, non-metastable transition (5,4), appears in the spectrum. This absorption line is due to the ammonia emission in the west side of the fast wind which is absorbed by the cooler outer HII region emitting the radio continuum. We define the hot clump region extending from -30 to the systemic velocity -21 km/sand which emits non-metastable and metastable lines. Our previously described envelope model of CRL 2688 was applied to both HC_9_N J=39-38 and J=43-42 observed line profiles to derive the HC_9_N abundance and other physical parameters of the envelope. Title: Very long baseline interferometry of solar microwave radiation. Authors: Benz, A. O.; Graham, D.; Isliker, H.; Andersson, C.; Koehnlein, W.; Mantovani, F.; Umana, G. Bibcode: 1996A&A...305..970B Altcode: The solar 2.297 GHz radiation has been observed and investigated by very long baseline interferometry (VLBI). The radio observatories of Medicina, Noto, Onsala, and Weilheim were involved yielding baselines between 360km and 3800km and a nominal resolution of 0.09"to 0.008"or 70 to 6km on the Sun. This solar VLBI network operated successfully with at least one useful baseline for 167 hours during five campaigns at the maximum of the most recent activity cycle in 1989 and 1990. The Phoenix spectrometer at Zurich was used to detect and classify the radio bursts. A total of 59 solar radio bursts were observed at the VLBI frequency, of which 26 events were analyzed, including narrowband millisecond spikes, type III bursts, patches, pulsations, and diffuse broadband (gyrosynchrotron) emission. Neither during bursts nor in quiet times significant fringes were detected. All sources were well resolved including the narrowband spikes. We interpret the result in terms of relatively large radio sources and/or by scattering to apparent source sizes larger than the lowest resolution and by the lack of `speckles'. The results are consistent with scattering of the radio emission in the corona. The upper and lower limits of the source size of spikes are discussed. For the apparent source size, l_a_, we find 65km<l_a_<16000km, and for the original source size before scattering l<~200km. Title: The centi-arcsecond structure of 16 low-frequency variable sources at 92 cm. Authors: Altschuler, D. R.; Gurvits, L. I.; Alef, W.; Dennison, B.; Graham, D.; Trotter, A. S.; Carson, J. E. Bibcode: 1995A&AS..114..197A Altcode: We present results of global Mark 2 VLBI snapshot observations at 92cm of 16 low frequency variable sources. The sample contains 2 radio galaxies, 9 quasars, 4 BL Lac objects, and 1 source with an uncertain identification. The sources were selected from a five-year flux monitoring program using the 305-m radio telescope of the Arecibo Observatory and the 91-m radio telescope of the NRAO (Green Bank) at 1400, 880, 606, 430, and 318MHz. A comparison of our results with VLBI maps at higher frequencies and WSRT, VLA and MERLIN maps provides constraints on models of the structures of these sources. Our data show clear evidence that all sources are resolved at baselines longer than 2-6 Mλ. The results will enable us to look for possible correlations between flux density variability and source structure, aiming to distinguish between intrinsic variability of extragalactic radio sources and variability due to propagation phenomena. Finally, we identify a few particularly interesting sources for further investigation with higher dynamical range and at various frequencies. Title: Saturn Authors: O'Meara, S. J.; Sheehan, W.; Graham, D.; Dobbins, T. Bibcode: 1995IAUC.6204....1O Altcode: S. J. O'Meara, Sky & Telescope, reports that visual observa- tions by W. Sheehan, D. Graham, T. Dobbins, and himself with the Lick Observatory 0.91-m refractor show two white spots in the northern region of the equatorial zone. The larger, low-contrast spot of diameter about 4" transited the planet at Aug. 10.375 UT (corresponding to system-I longitude 333 deg). The smaller spot of diameter about 2" transited at Aug. 10.444 (longitude 31 deg). Observations made about 12 hr prior to crossing the ring plane on Aug. 10.5 showed the rings still visible to a distance from the planet of one Saturn diameter. Title: Book-Review - Atlas of Neptune Authors: Hunt, G.; Moore, P.; Graham, D. Bibcode: 1994JBAA..104..141H Altcode: No abstract at ADS Title: Disk brightness temperature of the planets at 43 GHz (and 43 GHz flux densities of some continuum sources). Authors: Greve, A.; Steppe, H.; Graham, D.; Schalinski, C. J. Bibcode: 1994A&A...286..654G Altcode: We have used the MPIfR 43 GHz (7 mm) Schottky receiver, installed in 1991 on the IRAM 30-m telescope for VLBI observations, for flux density measurements of several planets in comparison with several Galactic and extra-galactic continuum sources, using as calibration standards the sources W3OH and NGC 7027. The disk brightness temperatures of the planets are derived from these flux densities. Title: The milliarcsecond structure of four Seyfert galaxies at λ18 cm. Authors: Ghosh, T.; Schilizzi, R. T.; Miley, G. K.; Debruyn, A. G.; Kukula, M. J.; Pedlar, A.; Graham, D.; Saikia, D. J. Bibcode: 1994IAUS..159..426G Altcode: No abstract at ADS Title: 86 GHz Global VLBI Progress Report Authors: Doeleman, S.; Rogers, A. E. E.; Bååth, L.; Schalinski, C.; Krichbaum, T.; Inoue, M.; Zensus, A.; Padin, S.; Carlstrom, J.; Graham, D.; Predmore, C.; Moran, J.; Backer, D.; Wright, M.; Whyborn, N.; Nyman, L.; Standke, K.; Lerner, M.; Kameno, S. Bibcode: 1994vtpp.conf...89D Altcode: No abstract at ADS Title: Snapshot VLBI Mapping of Variable Extragalactic Sources at 327 MHz Authors: Gurvits, L. I.; Alef, W.; Altschuler, D. R.; Carson, J. E.; Dennison, B.; Graham, D.; Trotter, A. S. Bibcode: 1994vtpp.conf..141G Altcode: No abstract at ADS Title: Centiarcsecond structure and variability of AGN. Authors: Altschuler, D. R.; Gurvits, L. I.; Alef, W.; Graham, D.; Dennison, B.; Carson, J. E.; Trotter, A. S. Bibcode: 1994IAUS..159..389A Altcode: No abstract at ADS Title: Supernova 1993J in NGC 3031 Authors: Bartel, N.; Bietenholz, M.; Rupen, M.; Conway, J.; Beasley, T.; Sramek, R.; Romney, J.; Titus, M.; Graham, D.; Altunin, V.; Jones, D.; Rius, A.; Venturi, T.; Umana, G.; Francis, R.; McCall, M.; Richer, M.; Stevenson, C.; Weiler, K.; van Dyk, S.; Panagia, N.; Cannon, W.; Popelar, J.; Davis, R. Bibcode: 1993IAUC.5914....1B Altcode: N. Bartel and M. Bietenholz, York University; M. Rupen, J. Conway, T. Beasley, R. Sramek, and J. Romney, National Radio Astronomy Observatory; M. Titus, Haystack Observatory; D. Graham, Max-Planck-Institut fur Radioastronomie; V. Altunin and D. Jones, Jet Propulsion Laboratory; A. Rius, Instituto de Astronomia y Geodesia, Madrid; T. Venturi and G. Umana, Instituto di Radioastronomia, CNR; R. Francis, M. McCall, M. Richer, and C. Stevenson, York University; K. Weiler, Naval Research Laboratory; S. Van Dyk, Naval Research Laboratory and University of California at Berkeley; N. Panagia, Space Telescope Science Institute; W. Cannon, Institute for Space and Terrestial Science and York University; J. Popelar, Energy, Mines, and Resources, Ottawa; and R. Davis, Nuffield Radio Astronomy Laboratories, report: ''Global VLBI observations of SN 1993J during the first three months after the explosion, with 9 to 15 antennas for up to 18 hours, show a supernova consistent with being circularly symmetric and expanding uniformly. A selected set of 30 percent of the data is now correlated and analyzed. Following are epochs, observing frequencies, and the radii of circular uniform disk models used in fits to the visibility data: Apr. 27.2 UT, 22.2 GHz, 96 +/- 8 microarcsec; May 17.2, 22.2, 145 +/- 14; May 17.2, 8.4, 151 +/- 11; June 27.0, 14.9, 241 +/- 21; June 27.0, 8.4, 275 +/- 9; June 27.0, 4.9, 205 +/- 85. A weighted least-squares linear fit gives a zero-point of expansion of Mar. 25 +/- 4. With the more precise optically derived shock-breakout date of Mar. 28.0 +/- 0.1 (Wheeler et al. 1993, Ap.J. 417, L71), the expansion rate is 2.98 +/- 0.08 microarcsec per day. An equivalent power-law fit gives an index of 0.96 +/- 0.07, showing no evidence yet for deceleration of the shock front. Combining the angular expansion rate trigonometrically with the optically derived maximum expansion speed of the hydrogen gas, we obtain a value for the distance to M81 of 4.0 +/- 0.6 Mpc. All errors are 1-sigma uncertainties, with statistical and systematic contributions included. We have continued the observations at intervals of six weeks and should be able to obtain a sequence of detailed images of the expanding supernova." Title: VLBI Observations of Supernova 1993J in M81 Authors: Rupen, M.; Conway, J.; Bartel, N.; Bietenholz, M.; Beasley, T.; Sramek, R.; Romney, J.; Titus, M.; Graham, D.; Altunin, V.; Jones, D.; Rius, A.; Venturi, T.; Umana, G.; Francis, R.; McCall, M.; Richer, M.; Stevenson, C.; Weiler, K.; van Dyk, S.; Panagia, N.; Cannon, W.; Popelar, J.; Davis, R. Bibcode: 1993AAS...183.3104R Altcode: 1993BAAS...25.1339R Global VLBI observations of SN1993J with 9 to 14 antennas for up to 18 hours show clearly that the supernova is expanding in a way consistent with being uniform. The radii (HWHM in microarcseconds) of circular Gaussians used in model fits to the visibility data, together with the observing wavelengths and epochs are: 57+/-4 (1.3cm, Apr. 26), 91(+17}_{-10) (1.3cm, May 16), 82+/-7 (3.6cm, May 16), 165(+8}_{-17) (2cm, Jun. 26), 161(+5}_{-6) (3.6cm, Jun. 26). A weighted least-squares linear fit gives an angular expansion velocity of 1.74+/-0.22 microarcseconds per day and an explosion date of Mar. 27.0+/-3.5 UT, the latter in agreement with results from optical data. A power-law fit constrained to go through a more precise optical zero point of Mar. 28.0 (Traummell et al., 93 ApJL 414, L21) gives an exponent of 0.97+/-0.04. Early optical spectra, e.g. measured with the INT on La Palma and the DDO near Toronto, indicate maximum expansion velocities of 17,500+/-500 km/s (measured at the blue edge of the Hα absorption trough). With the assumptions that a) the transverse velocity of the radio emitting region is 10+/-15% larger than the above optical velocity and that b) the brightness distribution of the supernova can be approximated by any model between a uniform disk and a very thin shell, we obtain a distance to M81 of 4.3+/-0.8 Mpc. All uncertainties are 1 standard deviations. We have continued the observations in intervals of about 6 weeks and should later be able to obtain detailed images of the supernova. Title: Snapshot VLBI mapping at 92 CM of 16 low frequency variable extragalactic sources Authors: Carson, J. E.; Altschuler, D. R.; Gurvits, L. I.; Alef, W.; Graham, D.; Dennison, B.; Trotter, A. S. Bibcode: 1993AAS...183.7509C Altcode: 1993BAAS...25Q1410C We present the results of VLBI mapping at 92 cm of 16 of the most "active" sources from the Arecibo -- NRAO low frequency variability monitoring program. Typical resolution of the maps is a few centiarcseconds, and typical dynamical range is (50 - 100):1. Following is a list of the sources: \begin{tabular}{llll} 0116+319 & 0735+178 & 1422+202 & 2050+363 0235+164 & 0851+202 & 1611+343 & 2145+067 0333+321 & 1055+018 & 1633+382 & 2230+114 0723-008 & 1117+146 & 1901+319 & 2251+158 We note that the data show clear evidence of significant scattering at baselines of 2 -- 6 Mlambda and longer. Examination of structural information will enable us to: study the dependence of variability on source size choose the most relevant sources for further studies at different frequencies and with higher dynamical range. JEC and AST acknowledge, with thanks, the REU Summer Student program support. We are grateful for the support of the European and US VLBI networks. NAIC is operated by Cornell University under a cooperative agreement with the National Science Foundation. Title: Book Review: Sky watcher's handbook / W. H. Freeman, 1993 Authors: Graham, D. Bibcode: 1993JBAA..103..264G Altcode: 1993JBAA..103..264M No abstract at ADS Title: HC9N from the envelopes of IRC +10216 and CRL 2688. Authors: Truong-Bach; Graham, D.; Nguyen-Q-Rieu Bibcode: 1993A&A...277..133T Altcode: We report the detection of the highly-excited HC9N J = 43-42 emission from the circumstellar envelopes of IRC+t02t6 and CRL2688, using the 100-m Effelsberg telescope. This is the first detection of the HC9N molecule in CRL2688.

For IRC+ 102 t 6, our results together with lower- J transition data from Bell et al. (1992) are used to constrain the source size, the excitation temperature, and the column density. It turns out that the diameter of the HC9N envelope should be significantly larger than the value (50") assumed by Bell et al.. Using a spherical LTE envelope model, we derive a HC9N abundance by using the derived excitation temperature and main-beam brightness temperature. An unidentified line at rest frequency νU∼24991.3 MHz has been detected in this object.

For CRL2688, we develop a model of the molecular envelope, accounting for anisotropy of the slow and fast winds and the inclination of the equatorial plane. The calculated line profile is compared to the observations to derive the HC9N abundance.

The cyanopolyyne abundances obtained from observations and from chemical models are compared and discussed. Title: Book-Review - Proceedings of the 1ST Meeting of European Planetary and Cometary Observers Authors: Fischer, D.; Graham, D. Bibcode: 1993JBAA..103..136F Altcode: No abstract at ADS Title: Book Review: Worlds in the sky: planetary discovery from earliest times through Voyager and Magellan / U Arizona Press, 1992 Authors: Graham, D. Bibcode: 1993JBAA..103...41G Altcode: 1993JBAA..103...41S No abstract at ADS Title: The 86 GHz VLBI test with Pico Velat: first detection of quasar 3C454. 3 at 3 mm wavelength Authors: Schalinski, C.; Greve, A.; Grewing, M.; Steppe, H.; Graham, D.; Krichbaum, T.; Witzel, A.; Alberdi, A.; Baath, L.; Booth, R. S.; Colomer, F. Bibcode: 1993sara.conf..184S Altcode: No abstract at ADS Title: Centiarcsecond Structure of Low Frequency Variable Extragalactic Sources Authors: Trotter, A. S.; Alef, W.; Altschuler, D. R.; Dennison, B.; Graham, D.; Gurvits, L. I. Bibcode: 1992AAS...181.4110T Altcode: 1992BAAS...24.1185T The distinction between an intrinsic nature of the variability of extragalactic sources and propagation phenomena remains problematic. The low frequency variability monitoring program has been underway at Arecibo Observatory since 1980. In this program 33 extragalactic sources taken from complete samples searched for variability at 318 MHz were monitored at bi--monthly intervals at five frequencies (1400, 880, 606, 430, and 318 MHz). Sixteen of the most active sources from the Arecibo low frequency monitoring program were selected for VLBI observations at 327 MHz to search for the structure on the scale of tens of milliarcseconds. The observations were carried out with the Global VLBI network stretching from Crimea (USSR) to Owens Valley (California) in March 1986. The resolution lost comparably to higher frequencies is counterbalanced by the typically larger angular size of structure patterns at lower frequencies. Propagation effects are also more noticeable at longer wavelengths, as the degree of scattering of radiation in an ionized medium is proportional to the square of the wavelength. As a general statement we note, that the data show clear evidences of significant scattering at baselines 2 -- 6 Mlambda and longer. We present here VLBI maps at 327 MHz of 9 sources: 0116+319 (4C31.04), 0235+164, 0333+321 (NRAO 140), 0735+178, 1055+018, 1117+146 (4C14.41), 1611+343 (DA406), 1633+382 (4C38.41), 1901+319 (3C395). These maps are utilized both for search of intrinsic properties of sources (in particular, comparing with VLBI maps at higher frequencies) and for investigations of propagation phenomena. We acknowledge, with thanks, NSF and REU Summer Student program support, and the support of the European and US VLBI networks. NAIC is operated by Cornell University under Contract with the National Science Foundation. Title: VLBI studies of the complex core-jet structure of the compact steep spectrum source 3C 286. Authors: Zhang, Fujun; Chu, Hanshu; Schilizzi, R. T.; Spencer, R. E.; Wu, Shengyin; Graham, D.; Su, Bu-Mei Bibcode: 1992PBeiO..20...68Z Altcode: No abstract at ADS Title: 10-meter radiotelescope-VLBI network element. Authors: Dhavan, V.; Sarma, N. V. G.; Ganesas, R.; Matveyenko, L. I.; Kogan, L. R.; Molodjanu, A. P.; Graham, D. Bibcode: 1992SvAL...18..149D Altcode: 1992PAZh...18..391D A 10-m radio telescope of the Ranam Research Institute, Bangalore, India, has been equipped with a 22-GHz low-noise receiver, a coherent local oscillator, a hydrogen frequency standard, and an MK-2 terminal. The antenna's effective area is 50 sq m, and the system noise temperature is 60 K. VLBI observations of H2O maser sources were made in May 1990 at the Bangalore-EVN VLBI network. The angular sizes of the compact components and the coordinates of the radio telescope are determined. Title: Mercury: an interim report on the evening elongation 1991 March-April Authors: Graham, D. Bibcode: 1992JBAA..102...36G Altcode: No abstract at ADS Title: Book-Review - Wanderers in Space - Exploration and Discovery in the Solar System Authors: Lang, K. R.; Whitney, C. A.; Graham, D. Bibcode: 1991JBAA..101..239L Altcode: No abstract at ADS Title: Reply to comment by T.M. Gerlach on ``Mid-ocean ridge popping rocks: implications for degassing at ridge crests'' Authors: Graham, David; Sarda, Philippe Bibcode: 1991E&PSL.105..568G Altcode: No abstract at ADS Title: Comment on “A ten-year decrease in the atmospheric helium isotope ratio possibly caused by human activity”, by Y. Sano et al. Authors: Lupton, John; Graham, David Bibcode: 1991GeoRL..18..482L Altcode: No abstract at ADS Title: Astrometry of SiO masers Authors: Colomer, F.; Graham, D.; Krichbaum, T.; Ronnang, B. O.; de Vicente, P.; Barcia, A.; Booth, R. S.; Witzel, A.; Gomez-Gonzalez, J.; Baudry, A. Bibcode: 1991ASPC...19..338C Altcode: 1991IAUCo.131..338C The first detection of circumstellar SiO maser emission from the v = 12 J = 1-0 transition at 43122.027 MHz using a three-station VLBI interferometer in Europe is presented. Future observations are discussed. Title: Extreme temporal homogeneity of helium isotopes at Piton de la Fournaise, Réunion Island Authors: Graham, David; Lupton, John; Albarède, Francis; Condomines, Michel Bibcode: 1990Natur.347..545G Altcode: OCEAN island basalts (OIBs) have strontium, neodymium and lead isotopic compositions that are different from those of mid-ocean-ridge basalts, (MORBs), reflecting long-term differences in the chemical characteristics of the respective mantle source reservoirs. The high 3He/4He ratios at some islands such as Hawaii and Iceland1-7 indicate that these basalts come from sources that are less degassed than the source of MORB. Many islands exhibit considerable variability in Sr, Nd and Pb isotopes8-10, but detailed studies of temporal variations in helium isotopes have been restricted to Hawaiian volcanoes-at Mauna Loa, for example, significant variations in 3He/4He have been found for the past 30,000 years11. Here we report on 3He/4He ratios from Piton de la Fournaise volcano on Reunion Island. No variations are found over the long time of 360,000 years, indicating a remarkable uniformity of 3He/4He for the (large) mantle source region over this timescale. The He-Sr-Pb systematics at this island may reflect the simultaneous contribution of both recycled materials (perhaps subducted crust) and primitive components to the Réunion source. Title: Observations of Mercury: 1988 October to 1889 October Authors: Graham, D. Bibcode: 1990JBAA..100...55G Altcode: Drawings and observations are presented of Mercury during the 1988 to 1989 elongations. Title: Mid-ocean ridge popping rocks: implications for degassing at ridge crests Authors: Sarda, Philippe; Graham, David Bibcode: 1990E&PSL..97..268S Altcode: The vesicle size distribution (VSD) and rare gas abundances in popping rocks from 14°N on the Mid-Atlantic Ridge provide constraints on the behavior of volatiles during ridge crest volcanism. These popping rocks, which contain 16-18 volume percent vesicles, are rare mid-ocean ridge basalt (MORB) magmas which appear to have retained much of their volatile inventory. The logarithm of vesicle population density displays the same linear correlation with decreasing size in two of the samples studied. This implies that continuous and simultaneous nucleation and bubble growth have occurred during magma ascent, with no significant perturbations due to accumulation, coalescence or loss of bubbles. In contrast, most MORB magmas display low vesicularities and we suggest that they have suffered some degree of pre-eruptive vesicle loss. We tentatively propose that large vesicles are produced by coalescence when MORB melt is at rest in chambers and conduits, and may be lost during early gas-rich episodes. Most MORB would represent residual liquids which erupt after vesicle loss has occurred, whereas popping rocks would represent a rare case where physical sorting of vesicles from melt did not occur, because storage in a magma chamber did not occur. The rare gas concentrations in the studied popping rocks are the highest yet measured in glassy ridge basalts ([He] > 50 μccSTP/g). The rare gas abundance pattern of these popping rocks probably resembles the pattern for non-vesiculated MORB magma and potentially reflects that of the depleted mantle source. This pattern is similar to the "mean MORB" pattern (computed from MORB glasses with 40Ar/ 36Ar > 10,000) although a higher enrichment in He (and possibly Ne) compared to the heavier rare gases is observed in MORB. The overall similarity in abundance patterns for MORB and popping rocks indicates that vesiculation and vesicle loss do not fractionate the Ar sbnd Kr sbnd Xe relative abundances from those in non-vesiculated magma, and that the modern flux ratios of these gases at ridges are similar to their elemental ratios in the depleted mantle. The degassing flux of He at ridge crests estimated from the MORB He deficit relative to popping rocks is comparable to the flux derived from the 3He budget for the abyssal ocean. This suggests that degassing at ridges may be strongly influenced by the dynamics and style of submarine volcanism. Title: a Search for AN Anomalous Intermediate Range Composition Dependence in Gravity Authors: Graham, D.; Nelson, P.; Newman, R. Bibcode: 1989grg..conf..513G Altcode: No abstract at ADS Title: Your Views of Mars Authors: Graham, D. Bibcode: 1989PAst...36...17G Altcode: No abstract at ADS Title: Region of the outburst of H2O maser emission in Orion KL. Authors: Matveenko, L. I.; Graham, D.; Diamond, Ph. Bibcode: 1988PAZh...14.1101M Altcode: The fine structure of the H2O maser outburst in Orion KL was studied with VLBI methods in 1979 - 1986. The main emission is produced by a chain of the compact features oriented under the angle -80°. The size, velocity, polarization and position angles of the features are estimated. Brightness temperatures and profiles of the components are given, as well as the density of H2O molecules at the line of sight. The masers are unsaturated and their kinetic temperature is Tk ≤ 120K. It is supposed that the pumping energy is IR and anisotropic. The outburst region corresponds to expanding protoplanetary rings with radius 6 A.U., rotation velocity 5 km/s and expanding velocity 3.8 km/s. The mass of the protostar is 0.7 M_sun;. Title: First VLBI synthesis observations of the excited-state OH emission sources at 4765 MHz in W3 (OH). Authors: Baudry, A.; Diamond, P. J.; Booth, R. S.; Graham, D.; Walmsley, C. M. Bibcode: 1988A&A...201..105B Altcode: The 2π1/2 J = 1/2, F = 1 - 0 (4765.562 MHz) excited state OH emission from W3(OH) has been observed with four telescopes of the European VLBI network and successfully mapped with a three-element interferometer (Effelsberg-Westerbork Array-Jodrell Bank) having 0arcsec.018 resolution. The maps show three groups of sources with mean separation of the order of 0arcsec.9 to 1arcsec within a region whose total extent is roughly 1arcsec i.e. 0.011 pc at the 2.2 kpc distance of W3(OH). From the observed sizes of the sources the authors derive an apparent brightness temperature ⪆7×108K corresponding to a maser gain exceeding 105. The general properties of the 4765 MHz maser are similar to those of other OH transitions although it is the only OH maser without measurable polarization. Title: Observations of NH3, HC5N and HC7N toward AFGL 2688. Authors: Truong-Bach; Graham, D.; Rieu, N. Q. Bibcode: 1988A&A...199..291T Altcode: The authors report new detections toward AFGL 2688 (Egg nebula) of a series of metastable (3,3), (4,4), (5,5) and non-metastable (3,2) transitions of NH3 as well as the cyanopolyyne HC5N (J = 8-7 and 9-8) and HC7N (J = 22-21) lines, using the 100-m Effelsberg telescope. Using an LTE model and combining the data with those of NH3 (1,1) and (2,2) and HC7N (J = 21-20) obtained previously, the authors derive the temperature and the density of the molecular envelopes. The ammonia and cyanopolyyne spectra are interpreted in terms of an optically-thick circumstellar disk and an optically-thin sphere, respectively. The HC5N and HC7N emissions are found to be ≡3 times more extended than that of NH3, in agreement with recent results of interferometric (VLA) mapping. The NH3 abundance is higher than that of HC5N and HC7N by one and two orders of magnitude, respectively. Title: Book Review: Meteorites and their parent planets. / CUP, 1987. Authors: Graham, D. Bibcode: 1988Obs...108..101G Altcode: No abstract at ADS Title: First VLBI Observations of 6.3 CM OH Masers in Compact HII Regions Authors: Baudry, A.; Diamond, P. J.; Graham, D.; Walmsley, M.; Booth, R.; Brouillet, N.; Daigne, G. Bibcode: 1988IAUS..129..235B Altcode: VLBI synthesis observations of the 2Π1/2, J = 1/2 excited-state of OH at 6.3 cm have been made towards four compact H II regions. Detailed maps have been produced for W3(OH) where three groups of sources are distributed over a region ≡0.01 pc in size. The brightest sources are shown to be saturated masers with TB ⪆ 109K. In ON 1 a weak feature gives fringes with a ≡0.05arcsec lobe spacing. Title: Search for anomalous intermediate-range forces with a controlled local attracting mass. Authors: Nelson, P.; Graham, D.; Newman, R. Bibcode: 1988egp..conf..427N Altcode: A torsion balance experiment in preparation will search for a composition-dependent intermediate range force weaker than gravity ("fifth force"). The experiment uses a movable local attracting mass in the form of a ring to produce gravitational field changes with extreme spatial uniformity. This approach allows precise control of the composition and distribution of the attracting mass, and should yield information on the strength parameters of an anomalous force independent of assumptions about its range (for ranges greater than about 0.5 m). Title: A "fifth force" search using a controlled local mass. Authors: Nelson, P.; Graham, D.; Newman, R. Bibcode: 1988ffnp.conf..471N Altcode: The authors present a progress report on a search for composition dependence in the forces acting on lead and copper test masses on a torsion balance due to a copper or lead attracting mass. Title: VLBI research on OH-maser IN W33 Authors: Velikhov, V. Ye.; Graham, D.; Diamond, P. Bibcode: 1987RpScT.......53V Altcode: The OH maser source W33 was studied at a frequency 1665 MHz. In the continuous radio emission there is an extended region surrounding the compact W33 MAIN, in which star formation transpires. In W33 there are several discrete IR sources coinciding with the youngest HII zones. There are two regions with intermediate velocities of 36 km/s (W33A) and 56 km/s (W33B). A detailed knowledge of the horizontal structure of W33A is necessary for research on star formation. W33A observations were made using interferometers during 1983 and 1984. The image was constructed using a model with free parameters on the assumption that the source consists of a minimum number of components with a Gaussian spatial brightness distribution and that emission of no more than two components is received in each spectral channel. The spectral measurements revealed that the source spectrum consists of overlapping details with widths of about 2 kHz. The emission of the spectral lines is determined by several spatially separated regions. A map was constructed showing that the source is highly elongated and consists of six components which can be divided into three groups. The spectrum obtained in observations corresponds to the computed spectrum of the model. Title: VLBI-studies of OH-maser in W 33. Authors: Velichov, V. E.; Graham, D.; Diamond, Ph. Bibcode: 1987PAZh...13..399V Altcode: The OH maser in W33 was investigated at a frequency of 1665 MHz in left circular polarization by the Effelsberg-Onsala and Evapatoria-Simeiz-Pushchino radio interferometers. A map of the source was obtained; the angular sizes of the separate components were determined in the Gaussian approximation; and the flux densities and brightness temperatures of these components were measured. Title: Who's Watching Jupiter Tonight Authors: Graham, D. Bibcode: 1987PAst...34....7G Altcode: No abstract at ADS Title: VLBI at Seven-Millimeter Wavelength with 70μ Arcsec Resolution Authors: Dhawan, V.; Burke, B.; Bartel, N.; Shapiro, I.; Rogers, A.; Johnston, K.; Spencer, J.; Lawrence, C.; Readhead, A.; Graham, D.; Pauliny-Toth, I.; Booth, R.; Ronnang, B.; Hirabayashi, H. Bibcode: 1986BAAS...18R.970D Altcode: No abstract at ADS Title: Ammonia and Cyanotriacetylene in the EGG Nebula Authors: Rieu, N. -Q.; Graham, D.; Bujarrabal, V. Bibcode: 1985ASSL..117..311R Altcode: 1985mlrg.proc..311. No abstract at ADS Title: Ammonia and cyanotriacetylene in the Egg Nebula. Authors: Nguyen-Q-Rieu; Graham, D.; Bujarrabal, V. Bibcode: 1985mlrg.proc..311N Altcode: The authors report the first detection of the NH3 (1,1) and (2,2) inversion lines, and the rotational transition J = 21-20 of HC7N (at ≡23.7 GHz) in the Egg Nebula (CRL 2688). Title: Jupiter's Satellites Authors: Graham, D. Bibcode: 1985JBAA...95..167G Altcode: No abstract at ADS Title: Ammonia and cyanotriacetylene in the envelopes of CRL 2688 and IRC +10216. Authors: Nguyen-Q-Rieu; Graham, D.; Bujarrabal, V. Bibcode: 1984A&A...138L...5N Altcode: The first detection of the NH3 (1, 1) and (2, 2) inversion lines, and the rotational transition J = 21-20 of HC7N in the Egg nebula (CRL 2688) is reported. These lines have been reobserved in the envelope of IRC +10216, and the detection of the NH3 (2, 2) line which is centered approximately at the same velocity as the NH3 (1, 1) line has been confirmed. The ammonia lines detected in CRL 2688 are at least two times stronger than those observed in IRC +10216, while the HC7N line is about two times weaker, reflecting the difference in chemical processes operating in the two objects. The blueshifted wing in the HC7N spectrum of IRC +10216 is weaker than the redshifted wing, suggesting that self-absorption occurs in the circumstellar shell. The data have been interpreted in terms of a radiative transfer model, from which the source size, and the molecular abundance have been derived. Title: Experimental Test of the Role of Intrinsic Spin in Gravitation Authors: Graham, D.; Newman, R. Bibcode: 1983grg1.conf..981G Altcode: No abstract at ADS Title: VLBI of solar flares Authors: Tapping, K. F.; Kuijpers, J.; Kaastra, J. S.; van Nieuwkoop, J.; Graham, D.; Slottje, C. Bibcode: 1983A&A...122..177T Altcode: From April 28 to May 3, 1981, a VLBI experiment was carried out to observe small spatial scales in the initial energy release in solar flares. The 25 m radio telescope at Onsala (Sweden) and Dwingeloo (Netherlands) were used; the observing wavelength was 18 cm. Simultaneous observations were made using the Westerbork Synthesis Radio Telescope at a wavelength of 6 cm. The VLBI baseline was 619 km. During the observing period, three weak outbursts were observed, none yielding any strong correlated signals. However, the statistical behaviour of the correlator output over the range of delay channels shows significant indications of a correlated signal having a signal to noise ratio of order unity, during the impulsive spikes preceding the main phase of the event. Title: Very long baseline interferometry of solar flares Authors: Kuijpers, J.; Tapping, K. F.; Graham, D. Bibcode: 1983ASSL..102..339K Altcode: 1983ards.proc..339K; 1983IAUCo..71..339K An experimental VLBI search for the occurrence of subarcsecond microwave emission centers as tracers of the initial energy release in solar flares is discussed. The observations extended over the period April 28 to May 3, 1981, during which period three weak outbursts occurred. No large correlations were observed, but a strong indication of an unresolved source with a signal to noise ratio of order unity was found during the impulsive bursts preceding the main phase of one event. During the impulsive bursts the spread in number of the channel which showed the maximum correlation amplitude was reduced significantly below the value for random behavior. A clear reduction in the amount of scatter from the expectation value during impulsive bursts is shown. The derived brightness temperature is of the order 10 to the 12th K; the probable error box for the source position is shown. Title: Carbonate chemistry in marine pore waters: MANOP sites C and S Authors: Emerson, Steven; Grundmanis, Varis; Graham, David Bibcode: 1982E&PSL..61..220E Altcode: Calculations of the alkalinity and total CO 2 response to organic matter diagenesis in a closed system containing CaCO 3 indicate that the traditional stoichiometric reactions for organic matter degradation and the accompanying CaCO 3 reaction are approximations at the pH of seawater. These approximations are different from the true values by about 10% during oxygen and MnO 2 reduction and about 40% during denitrification. Intercalibration of in situ and ☐ core methods of pore water sampling from deep-sea carbonate-rich and carbonate-deficient sediments indicates that the sampling artifact on carbonate system measurements due to pressure change is variable in magnitude and apparently related to the carbonate content of the sediments. Previously proposed methods for predicting the effect are not general, implying that there is no alternative to in situ sampling for the evaluation of the carbonate system parameters. In situ results from a carbonate ooze sediment at MANOP site C reveal that the pore waters are slightly supersaturated with respect to calcite. Ion activity products fall within the range predicted for equilibrium with aragonite. The diagenetic model applied to an open system using molecular diffusion coefficients adequately predicts the pore water alkalinity and total CO 2 changes in response to organic matter degradation. This result provides clear evidence that the transport mechanism for dissolved species near the sediment-water interface at this location is by molecular diffusion and is not enhanced by biological or physical processes. At a siliceous ooze site, MANOP site S, the alkalinity increases in the pore waters in response to CaCO 3 rain to the sediment-water interface. Calcium carbonate is not preserved, and the stoichiometric model predicts a particulate CaCO 3/organic carbon rain ratio of 0.4-1.2. This ratio is in the same range as that measured in sediment traps deployed at this site as part of the MANOP program. Title: VLBI aperture synthesis observations of 1720-MHz OH in NGC 7538 /IRS1/ Authors: Forster, J. R.; Graham, D.; Goss, W. M.; Booth, R. S. Bibcode: 1982MNRAS.201P...7F Altcode: The 1720-MHz OH source in NGC 7358 (IRS1) has been observed with four telescopes in the European VLBI network. Aperture synthesis mapping with a beam of 0.03 arcsec shows six discrete maser positions concentrated in an elongated region of size 0.3 x 0.15 sq arcsec. The maser emission arises from two groups of unresolved spots, with apparent brightness temperatures greater than 10 billion K. The two separate spatial groups correspond to two distinct velocity groups. Title: Gastaufenthalt in Shanghai. Authors: Graham, D. Bibcode: 1982S&W....21..294G Altcode: No abstract at ADS Title: Mark-Iii VLBI Observations of the Nucleus of M81 at 2.3-GHZ and 8.3-GHZ Authors: Bartel, N.; Corey, B.; Shapiro, I.; Rogers, A.; Whitney, A.; Graham, D.; Romney, J.; Preston, R. Bibcode: 1982IAUS...97..387B Altcode: No abstract at ADS Title: Preliminary analysis of Shanghai-Effelsberg VLBI Experiment Authors: Wan, T. S.; Qian, Z. H.; Graham, D. Bibcode: 1982gari.conf...91W Altcode: No abstract at ADS Title: Summer Shutdowns at KPNO Authors: Graham, D. Bibcode: 1982KPNON..22...10G Altcode: No abstract at ADS Title: 6-cm VLBI observations of compact radio sources. Authors: Pauliny-Toth, I. I. K.; Preuss, E.; Witzel, A.; Graham, D.; Kellerman, K. I.; Ronnang, B. Bibcode: 1981AJ.....86..371P Altcode: VLBI observations made at 6-cm wavelength have been used to derive the brightness distribution of the radio emission from three galactic nuclei (M87, 3C 120, and NGC 1275), five quasars (4C 39.25, 3C 273, 3C 279, PKS 2134+004, and 3C 454.3), and two BL Lacertae objects (BL Lac and OJ 287). These observations have sufficient resolution and sensitivity to allow a wide range of surface brightness to be mapped. In four sources (3C 273, 3C 279, 3C 454.3, and BL Lac), the brightness distribution has an asymmetric structure, with one or more bright components and an elongated, jet-like feature. Two of these (3C 273 and 3C 279), as well as 3C 120, show superluminal expansion; in the case of 3C 279, the present data show an extremely high rate of component separation, with an apparent velocity of ∼45c. Comparison with observations at other wavelengths shows that the compact components have inverted or flat spectra, while the more extended ones have the "normal" spectra characteristic of trans- parent sources. Title: The radio fine structure of the BL Lac objects A0235+164, 0735+178, BL Lac, 1749+701, MK 421 and 3C 66 A at 5 GHz. Authors: Baath, L. B.; Elgered, G.; Lundqvist, G.; Graham, D.; Weiler, K. W.; Seielstad, G. A.; Tallqvist, S.; Schilizzi, R. T. Bibcode: 1981A&A....96..316B Altcode: Very long baseline interferometer observations at 4997 MHz (λ = 6 cm) on European and intercontinental baselines with lengths up to 1.35 108λ have been used to probe the milliarc s structure of the BL Lacertae objects AO 0235+164, 0735+178, BL Lac, 1749+701, Mk 421, and 3C 66A. Two sets of observations are reported, made in November 1978 and March 1979. AO 0235+164 and 0735+178 both showed structures consisting of a very bright, unresolved core and a jet-like component extending ∼5".4 10-3 along position angle ∼20° and ∼4".2 10-3 along position angle ∼45°, respectively. AO 0235+164 contained more than 98% of the total flux density within a diameter of ≲ 36" 10-3. BL Lac, 1749+701 and Mk 421 all showed evidence for a complex structure of several components, including an unresolved core. 3 C 66A was elongated along position angle ∼ -45°. Title: A new 1720 MHz OH outburst in V1057 Cyg. Authors: Winnberg, A.; Graham, D.; Walmsley, C. M.; Booth, R. S. Bibcode: 1981A&A....93...79W Altcode: An outburst of maser emission in the 1720MHz line of OH has been detected from the FU Orionis type variable V1057 Cyg (Winnberg and Walmsley, IAU Circular No. 3364). We have monitored the outburst over a two month period subsequent to the initial detection and find that the strength of the maser has diminished by more than a factor of two over this time span. The general characteristics are very similar to those of the maser detected in 1973 (Lo and Bechis, 1973). A VLBI experiment at 1720 MHz between Jodrell Bank and Effelsberg shows that the separation in position between the right and left circularly polarised velocity components is 0.03±0.01. However, the maser spots themselves appear to have an angular size of the same order as the separation between them. From these data, we conclude that we are observing a cloud of approximately 20 AU in size situated at a distance of about 200 AU from the star V1057 Cyg. The maser outbursts were probably triggered by collisions between expanding shells ejected during the 1969-70 optical flare-up (Herbig, 1977) and the OH cloud. The observed circular polarisation of the masering lines is likely to be due to Zeeman effect and a magnetic field of ∼2 mG in the OH cloud is inferred. We estimate that the gas density is ∼108 cm-3 and hence that the mass of the OH cloud is of the same order of magnitude as the mass of the earth. We discuss the possibility that the OH emitting region is the extended atmosphere of a protoplanet. Title: Summer Shutdowns of Telescopes - 4.M 2.1-M and Coude Feed Authors: Ott, L.; Bode, B.; Robinson, B.; Graham, D. Bibcode: 1981KPNON..17....7O Altcode: No abstract at ADS Title: Summer Shut-Down of the Coude Feed and 2.1-METER Coude Spectrograph Authors: Graham, D. Bibcode: 1981KPNON..17....7G Altcode: No abstract at ADS Title: Burrell Schmidt Improvements Authors: Graham, D. Bibcode: 1981KPNON..18....7G Altcode: No abstract at ADS Title: Alignment of a four meter Ritchey-Chrétien telescope. Authors: Simmons, J. E.; Schoening, W.; Graham, D.; Ott, L. Bibcode: 1980SPIE..251..138S Altcode: This paper describes the engineering steps taken to obtain best imagery across the field at the R-C focus of a 4m f/2.65 primary in combination with a secondary giving a final f/8 beam. Real life constraints, such as limited initial information, time available for testing, and manpower available, point to the importance of some factors which tend to be overlooked during the early mechanical design and optical manufacturing stages, as well as during the initial assembly of the telescope. Some of these factors are listed so that others may succeed in an operation which most likely will be performed under adverse conditions. Title: The compact radio sources in 4C 39. 25 and 3C 345. Authors: Shaffer, D. B.; Kellermann, K. I.; Purcell, G. H.; Pauliny-Toth, I. I. K.; Preuss, E.; Witzel, A.; Graham, D.; Schilizzi, R. T.; Cohen, M. H.; Moffet, A. T.; Romney, J. D.; Niell, A. E. Bibcode: 1977ApJ...218..353S Altcode: Long-baseline interferometry of the quasars 4C 39.25 and 3C 345 at 10.65 and 14.77 GHz shows that the centimeter radio source in each object is double, with component separations of 0.0020 arcsec (4C 39.25) and 0.0013 arcsec (3C 345 at 1974.5). For each source, the separation is the same at both frequencies, as well as similar to the structure observed at 7.85 GHz (and 5.0 GHz for 4C 39.25). The spectra of the individual components are derived and shown to vary with time approximately as expected for expanding self-absorbed synchrotron sources. The magnetic fields in the components are estimated to be as high as 0.1 gauss, but the structure of the sources appears to be unrelated to the magnetic-field orientation derived from low-resolution polarization measurements. The component separation in 4C 39.25 has not changed for several years, whereas 3C 345 shows rapid expansion. Title: Very high-resolution observations of the radio sources NRAO 150, OJ 287, 3C 273, M87, 1633+38, BL Lacertae, and 3C 454.3. Authors: Kellermann, K. I.; Shaffer, D. B.; Purcell, G. H.; Pauliny-Toth, I. I. K.; Preuss, E.; Witzel, A.; Graham, D.; Schilizzi, R. T.; Cohen, M. H.; Moffet, A. T.; Romney, J. D.; Niell, A. E. Bibcode: 1977ApJ...211..658K Altcode: Very long baseline interferometer observations made at a wavelength of 2 and 2.8 cm with baselines ranging from 54 to 291 million wavelengths show a number of radio sources with only slightly resolved components, even on the longest baselines; the quasars 1633 + 38 and 3C 454.3, the objects 0J 287 and BL Lac, and the nucleus of M87 (Virgo A, 3C 274) all contain components <% 0.4 milli-arcsec. The smallest component we have observed is in the core of 3C 454.3, which contains about 50% of the total flux density and is < 0.2 milli-arcsec in diameter. The compact component in the nucleus of M87 is <% 1.5 light-months across, and contains about one-third of the total flux density of the nucleus at 2.8 cm. NRA0 150 and BL Lac are double: the components of NRA0 150 are separated by 0.6 milliarcsec, while BL Lac has an elongated structure consisting of a large (1.4 milli-arcsec) component separated by 1.25 milli-arcsec from a smaller (0.5 milli-arcsec) variable one. The present data on 3C 273 are consistent with triple models similar to those we discussed previously, but with a somewhat greater apparent separation of components. Subject headings: BL Lacertae objects - galaxies: nuclei - interferometry - quasars - radio sources: general Title: Observations with a VLB array. I. Introduction and procedures. Authors: Cohen, M. H.; Moffet, A. T.; Romney, J. D.; Schilizzi, R. T.; Shaffer, D. B.; Kellermann, K. I.; Purcell, G. H.; Grove, G.; Swenson, G. W., Jr.; Yen, J. L.; Pauliny-Toth, I. I. K.; Preuss, E.; Witzel, A.; Graham, D. Bibcode: 1975ApJ...201..249C Altcode: Procedures and telescopes are discussed which have been used in a series of multibaseline VLB observations intended for investigating the small-scale structure and structural variation of compact extragalactic radio sources at a wavelength of 2.8 cm with a resolution of 0.001 sec. The system of antennas is described in detail, its sensitivity is determined, and the calibration procedures are outlined. Source-modeling techniques are briefly summarized, and ambiguities in the models are discussed. Title: Hochauflösende Interferometrie kompakter extragalaktischer Radioquellen Authors: Pauliny-Toth, I. I. K.; Preuss, E.; Witzel, A.; Graham, D. Bibcode: 1975MitAG..36..107P Altcode: Experiments were performed to determine the structures of compact extragalactic radio sources and the dependence of these structures on time. The measurements were made with synthetic-aperture antennas having their component antennas located in different continents. The maximum base line obtained was 8200 km long, or 280 million wavelengths (with lambda equals 2.8 cm); the resolution thus yielded was in the millisecond-of-arc range. Diameters of the measured objects were on the order of 0.1-10 pc. Structures derived were either complex, single, double, or nucleus/halo. The optical type (SEY, EO, or QSO), redshift, and priveleged direction of each of the sources observed are also given. Title: Binary pulsar. Authors: Taylor, J. H.; Hulse, R. A.; Margon, B.; Davidsen, A.; Mason, K.; Sanford, P.; Liller, W.; Bernacca, P. L.; Ciatti, F.; John, R. S.; Regener, V. H.; Papaliolios, C.; Pennypacker, C.; Canizares, C.; McClintock, J.; Jones, B.; Graham, D.; Wielebinski, R. Bibcode: 1974IAUC.2704....1T Altcode: No abstract at ADS Title: Observations at 11 cm of Recently Discovered Pulsars Authors: Graham, D.; Hunt, G. C. Bibcode: 1973NPhS..242...86G Altcode: 1973Natur.242...86G THE 100-m telescope at Effelsberg has been used to determine more accurate positions and periods for seven recently discovered pulsars, using a helium cooled parametric receiver at 11 cm, at which wavelength the telescope has a circular beam-width of 4.7 arc min to half-power. Positions were determined by taking an integration at every beam area within the published error rectangles1-4. The derived positions and other quantities determined are quoted in Table 1 where these represent an improvement over previous data. Title: On the Polarization of SCO X-1 Authors: Hiltner, W. A.; Mook, Delo E.; Ludden, D. J.; Graham, D. Bibcode: 1967ApJ...148L..47H Altcode: No abstract at ADS Title: Metis Authors: Cooper, E. J.; Graham Bibcode: 1850MNRAS..11...11C Altcode: No abstract at ADS