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Author name code: graham
ADS astronomy entries on 2022-09-14
author:"Graham, David R."
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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.
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.
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Title: A Perspective from Earths Deep Mantle Krypton and Xenon on
Evolution of Planetary Interiors
Authors: Peron, Sandrine; Mukhopadhyay, Sujoy; Kurz, Mark; Graham,
David
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.
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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.
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. <BR /> 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. <BR /> 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. <BR /> 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/f<SUB>ce</SUB>), larger amplitude, and greater
bandwidth than at 1 AU.
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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.
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.
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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.
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.
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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.
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.
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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.
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. <P
/>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 d<SUB>e</SUB>. 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. <P />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.
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Title: Probability Distributions of Langmuir Waves in Type II and
III sources
Authors: Trevett, W.; Cairns, I.; Graham, D.
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.
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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.
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. <P />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 3<SUP>rd</SUP>, 2017 event agrees with
the heating rate in the PIC simulation. The other is that the UHW can
change the large-scale energy conversion J<SUB>y</SUB>·E<SUB>y</SUB>
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 J<SUB>y</SUB>
decreases, and the pressure tensor P<SUB>yz</SUB> increases/ decreases
when the beam density is lower/ higher than 13% of total density. When
the beam density is 30% of the total density, J<SUB>y</SUB> decreases
by at most 5% from the initial value, and P<SUB>yz</SUB> 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 J<SUB>y</SUB>·E<SUB>y</SUB> in the EDR.
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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.
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.
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Title: Cherenkov Whistler Emission by Electron Holes
Authors: Steinvall, K.; Khotyaintsev, Y.; Graham, D.; Vaivads, A.;
Le Contel, O.; Russell, C. T.
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.
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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.
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.
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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.
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.
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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
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<SUP>-1</SUP> 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 (n<SUB>e</SUB> ∼ 2 × 10<SUP>14</SUP> cm<SUP>-3</SUP>), thin
layer (30-40 km thickness), heated to 8-12,000 K, moving toward the
stationary chromosphere at up to 50 km s<SUP>-1</SUP>. 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<SUP>+</SUP> 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.
2019JGRA..12410257F Altcode:
The warm plasma cloak is a source of magnetospheric plasma that
contain significant O<SUP>+</SUP>. When the O<SUP>+</SUP> density in
the magnetosphere near the magnetopause is >0.2 cm<SUP>-3</SUP>
and the H<SUP>+</SUP> density is <1.5 cm<SUP>-3</SUP>, then
O<SUP>+</SUP> dominates the magnetospheric ion mass density by more
than a factor of 2. A survey is conducted of such O<SUP>+</SUP>-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<SUP>+</SUP>-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<SUP>+</SUP> 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.
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.
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.
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). <P />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. <P />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.
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.
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.
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. <P />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<SUB>||</SUB>,
whereas the main source of δB<SUB>⊥</SUB> 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.
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.
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
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.
2019GeoRL..46.6204F Altcode:
When the interplanetary magnetic field is northward for a period of
time, O<SUP>+</SUP> 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<SUP>+</SUP> and mass loads the boundary layer. This O<SUP>+</SUP>
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<SUP>+</SUP>-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
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. <P />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
2019BAAS...51c.410F Altcode: 2019arXiv190304589F; 2019astro2020T.410F
Geological and lunar evidence of radioactive <SUP>60</SUP>Fe implies
that at least one supernova exploded within 100 pc of Earth within the
last few Myr. The unique information provided by <SUP>60</SUP>Fe 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.
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.
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.
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
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 (CO<SUB>2</SUB>)
and methane (CH<SUB>4</SUB>). 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. <P />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<SUP>-2</SUP>
low-density, particulate organic C and 19 ± 6 kg m<SUP>-2</SUP>
high-density, mineral-associated organic C, indicating that 63 ± 19%
of organic C in the active layer was associated with the mineral
fraction. <P />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 CO<SUB>2</SUB> and CH<SUB>4</SUB> 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.
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.
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.
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.
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. <BR /> 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 × 10<SUP>5</SUP> K, giving a constraint on the
properties of the heated transition region. <BR /> 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. <BR /> Results: Electron number densities of up
to 10<SUP>11.9</SUP> cm<SUP>-3</SUP> 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. <BR /> 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.
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
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<SUP>-1</SUP>. 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.
2015A&A...581A..32W Altcode: 2015arXiv150603244W
<BR /> 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). <BR /> 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. <BR /> 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<SUP>-1</SUP>, 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 10<SUP>10</SUP> K. Lastly,
we find an upper limit of 20% on the linear polarization fraction at a
fringe spacing of ~ 38 μas. <BR /> 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
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.
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<SUP>-1</SUP>
and chromospheric downflows up to 40 km s<SUP>-1</SUP>. 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.
2015A&A...577A..68S Altcode: 2015arXiv150301491S
<BR /> 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. <BR /> 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. <BR /> 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<SUP>-1</SUP> 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 10<SUP>11.50</SUP> cm<SUP>-3</SUP> which is collisionally
thick to electrons with energy up to 45-65 keV, responsible for the
source's non-thermal X-ray emission. <BR /> 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
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.
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.
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 10<SUP>28</SUP> and 10<SUP>29</SUP>
cm<SUP>-5</SUP>, 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.
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.
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<SUP>−1</SUP> 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<SUP>−1</SUP> 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.
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. <BR /> 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. <BR /> 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. <BR /> 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
×10<SUP>10</SUP> cm<SUP>-3</SUP> 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<SUP>-1</SUP> 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. <BR /> 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.
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.
2010A&A...524A..60J Altcode: 2010arXiv1008.3992J
<BR /> 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. <BR />
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. <BR /> 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. <BR /> 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.
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.
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.
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.
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.
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.
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.
2007sphe.work...51B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: SATURN AND HOW TO OBSERVE IT / Springer-Verlag,
2006
Authors: Graham, David
2006JBAA..116..147G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: SATURN - OVERVIEW AND ABSTRACTS / Nova Science
Publishers, through Gazelle, 2003
Authors: Graham, David
2006Obs...126...57G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Absorbing re-reflected random waves in SPH
Authors: Graham, D.; Hughes, J.
2006sphe.workE..13G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn observers at opposition are rewarded with a ringside
view
Authors: Graham, David
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
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 <SUP>206</SUP>Pb/
<SUP>204</SUP>Pb, <SUP>207</SUP>Pb/ <SUP>204</SUP>Pb, <SUP>208</SUP>Pb/
<SUP>204</SUP>Pb, the first principal component of Pb isotopes,
<SUP>87</SUP>Sr/ <SUP>86</SUP>Sr, and <SUP>3</SUP>He/ <SUP>4</SUP>He,
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
2004E&PSL.227..457B Altcode:
New measurements of the He, Ar and CO <SUB>2</SUB> 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(
<SUP>4</SUP>He/ <SUP>40</SUP>Ar*) vs. ln[ <SUP>40</SUP>Ar*] and between
ln( <SUP>4</SUP>He/ <SUP>40</SUP>Ar*) vs. ln( <SUP>40</SUP>Ar*/CO
<SUB>2</SUB>) (where <SUP>40</SUP>Ar* is the <SUP>40</SUP>Ar corrected
for atmospheric contributions). The slopes of these correlations
permit the relative He/Ar and Ar/CO <SUB>2</SUB> 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( <SUP>4</SUP>He/ <SUP>40</SUP>Ar*) vs. ln(
<SUP>40</SUP>Ar*/CO <SUB>2</SUB>), samples from the deepest portions of
the ridge consistently plot at lower <SUP>4</SUP>He/ <SUP>40</SUP>Ar*
for a given <SUP>40</SUP>Ar*/CO <SUB>2</SUB>, compared to shallower
sections of ridge. These variations in <SUP>4</SUP>He/ <SUP>40</SUP>Ar*
likely reflect variations in He/Ar in the primary melt, i.e. their
relative abundances prior to degassing. We estimated the variation
in <SUP>4</SUP>He/ <SUP>40</SUP>Ar* in the initial melts (i.e. the
<SUP>4</SUP>He/ <SUP>40</SUP>Ar* prior to degassing) by extrapolating
the degassing trend to a constant mantle-like <SUP>40</SUP>Ar*/CO
<SUB>2</SUB> ratio and assuming that the relative He-Ar-CO <SUB>2</SUB>
solubilities do not vary between samples. The <SUP>4</SUP>He/
<SUP>40</SUP>Ar* corrected for degassing in this manner varies by
a factor ≈10 and correlates positively with the <SUP>3</SUP>He/
<SUP>4</SUP>He ratio. It is possible that the correlation between
"degassing corrected" <SUP>4</SUP>He/ <SUP>40</SUP>Ar* ratios and the
<SUP>3</SUP>He/ <SUP>4</SUP>He ratio results from preferential diffusion
of <SUP>3</SUP>He relative to <SUP>4</SUP>He and of <SUP>4</SUP>He
relative to <SUP>40</SUP>Ar from the solid mantle into primary melts
during melting. However, modeling this diffusive process fails to
reproduce the comparatively large variations in <SUP>3</SUP>He/
<SUP>4</SUP>He 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
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.
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.
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.
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.
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.
2002JBAA..112..229G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: Jupiter Odyssey / Springer, 2000
Authors: Graham, D.
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.
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.
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.
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.
2000evn..conf..171F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A colourful Saturn
Authors: Graham, D.
1999JBAA..109..306G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Clusters in collision.
Authors: Graham, D.
1999Ast....27...58G Altcode:
Collisions and merging in clusters of galaxies.
---------------------------------------------------------
Title: Saturn: rings within rings
Authors: Graham, D.
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.
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.
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.
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.
1997mvlb.work....3K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spring time on Saturn
Authors: Graham, D.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
1993A&A...277..133T Altcode:
We report the detection of the highly-excited HC<SUB>9</SUB>N 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 HC<SUB>9</SUB>N molecule in CRL2688. <P />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 HC<SUB>9</SUB>N envelope should be significantly larger than the
value (50") assumed by Bell et al.. Using a spherical LTE envelope
model, we derive a HC<SUB>9</SUB>N abundance by using the derived
excitation temperature and main-beam brightness temperature. An
unidentified line at rest frequency ν<SUB>U</SUB>∼24991.3 MHz has
been detected in this object. <P />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 HC<SUB>9</SUB>N
abundance. <P />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.
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.
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.
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.
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
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.
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.
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.
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
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
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.
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
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
<SUP>3</SUP>He/<SUP>4</SUP>He ratios at some islands such as Hawaii and
Iceland<SUP>1-7</SUP> 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 isotopes<SUP>8-10</SUP>,
but detailed studies of temporal variations in helium isotopes
have been restricted to Hawaiian volcanoes-at Mauna Loa, for
example, significant variations in <SUP>3</SUP>He/<SUP>4</SUP>He
have been found for the past 30,000 years<SUP>11</SUP>. Here we
report on <SUP>3</SUP>He/<SUP>4</SUP>He 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
<SUP>3</SUP>He/<SUP>4</SUP>He 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.
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
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 <SUP>40</SUP>Ar/
<SUP>36</SUP>Ar > 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 <SUP>3</SUP>He 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.
1989grg..conf..513G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Your Views of Mars
Authors: Graham, D.
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.
1988PAZh...14.1101M Altcode:
The fine structure of the H<SUB>2</SUB>O 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 H<SUB>2</SUB>O molecules at the line
of sight. The masers are unsaturated and their kinetic temperature
is T<SUB>k</SUB> ≤ 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.
1988A&A...201..105B Altcode:
The <SUP>2</SUP>π<SUB>1/2</SUB> 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 ⪆7×10<SUP>8</SUP>K
corresponding to a maser gain exceeding 10<SUP>5</SUP>. 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.
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 NH<SUB>3</SUB> as well as the cyanopolyyne
HC<SUB>5</SUB>N (J = 8-7 and 9-8) and HC<SUB>7</SUB>N (J = 22-21)
lines, using the 100-m Effelsberg telescope. Using an LTE model and
combining the data with those of NH<SUB>3</SUB> (1,1) and (2,2) and
HC<SUB>7</SUB>N (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
HC<SUB>5</SUB>N and HC<SUB>7</SUB>N emissions are found to be ≡3
times more extended than that of NH<SUB>3</SUB>, in agreement with
recent results of interferometric (VLA) mapping. The NH<SUB>3</SUB>
abundance is higher than that of HC<SUB>5</SUB>N and HC<SUB>7</SUB>N
by one and two orders of magnitude, respectively.
---------------------------------------------------------
Title: Book Review: Meteorites and their parent planets. / CUP, 1987.
Authors: Graham, D.
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.
1988IAUS..129..235B Altcode:
VLBI synthesis observations of the <SUP>2</SUP>Π<SUB>1/2</SUB>,
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 T<SUB>B</SUB> ⪆ 10<SUP>9</SUP>K. 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.
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.
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.
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.
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.
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.
1986BAAS...18R.970D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ammonia and Cyanotriacetylene in the EGG Nebula
Authors: Rieu, N. -Q.; Graham, D.; Bujarrabal, V.
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.
1985mlrg.proc..311N Altcode:
The authors report the first detection of the NH<SUB>3</SUB> (1,1)
and (2,2) inversion lines, and the rotational transition J = 21-20 of
HC<SUB>7</SUB>N (at ≡23.7 GHz) in the Egg Nebula (CRL 2688).
---------------------------------------------------------
Title: Jupiter's Satellites
Authors: Graham, D.
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.
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.
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.
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.
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
1982E&PSL..61..220E Altcode:
Calculations of the alkalinity and total CO <SUB>2</SUB> response
to organic matter diagenesis in a closed system containing
CaCO <SUB>3</SUB> indicate that the traditional stoichiometric
reactions for organic matter degradation and the accompanying
CaCO <SUB>3</SUB> reaction are approximations at the pH of
seawater. These approximations are different from the true values by
about 10% during oxygen and MnO <SUB>2</SUB> 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 <SUB>2</SUB> 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
<SUB>3</SUB> rain to the sediment-water interface. Calcium carbonate
is not preserved, and the stoichiometric model predicts a particulate
CaCO <SUB>3</SUB>/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.
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.
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.
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.
1982gari.conf...91W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Summer Shutdowns at KPNO
Authors: Graham, D.
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.
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.
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
10<SUP>8</SUP>λ 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<SUP>-3</SUP> along position angle ∼20° and
∼4".2 10<SUP>-3</SUP> along position angle ∼45°, respectively. AO
0235+164 contained more than 98% of the total flux density within
a diameter of ≲ 36" 10<SUP>-3</SUP>. 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.
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 ∼10<SUP>8</SUP> cm<SUP>-3</SUP> 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.
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.
1981KPNON..17....7G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Burrell Schmidt Improvements
Authors: Graham, D.
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.
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.
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.
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.
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.
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.
1974IAUC.2704....1T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations at 11 cm of Recently Discovered Pulsars
Authors: Graham, D.; Hunt, G. C.
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 rectangles<SUP>1-4</SUP>. 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.
1967ApJ...148L..47H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Metis
Authors: Cooper, E. J.; Graham
1850MNRAS..11...11C Altcode:
No abstract at ADS
