Author name code: clark
ADS astronomy entries on 2022-09-14
=author:"Clark, T.A."
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Title: Detection of the H I n=22-21 Rydberg line in emission at the
solar submillimetre limb
Authors: Clark, T. A.; Naylor, D. A.; Davis, G. R.
Bibcode: 2000A&A...361L..60C
Altcode:
This letter reports the discovery of excess emission at the position of
the H I n=22-21 Rydberg transition in submillimetre solar spectra taken
at the extreme solar limb. This emission feature at 22.096+/-0.003
cm-1 shows significant limb brightening, reaching
intensities of 11% above the adjacent spectral continuum with line
shapes fitted best by Gaussian functions with widths of 0.018+/-0.004
cm-1. This measurement represents the highest-n Rydberg
line of H I detected to date in the solar spectrum.
Title: Atmospheric transmission at submillimetre wavelengths from
Mauna Kea
Authors: Naylor, D. A.; Davis, G. R.; Gom, B. G.; Clark, T. A.;
Griffin, M. J.
Bibcode: 2000MNRAS.315..622N
Altcode:
The submillimetre atmospheric transmission spectrum above Mauna Kea has
been measured at a resolution of 0.005cm-1 (150MHz) with a
Fourier transform spectrometer at the James Clerk Maxwell Telescope,
using the Sun as a source. Column abundances of O2,
H2O and O3 determined from these spectra are
found to be in excellent agreement with independent measurements. The
derived column abundances have been used as inputs to the atmospheric
spectral modelling program fascod. The synthetic transmission spectrum
is found to be in excellent agreement with the measured spectrum,
and provides a template for submillimetre observations from the JCMT.
Title: Detection and limb brightening of the H bt I n=20-19 Rydberg
line in the submillimetre spectrum of the Sun
Authors: Clark, T. A.; Naylor, D. A.; Davis, G. R.
Bibcode: 2000A&A...357..757C
Altcode:
Submillimetre spectra taken near to the solar limb with a polarizing
interferometer on the James Clerk Maxwell Telescope have been compared
with disk-centre spectra to reveal a limb-brightened feature whose
peak intensity occurs at the predicted frequency of the n=20-19 Rydberg
transition in H I at 29.622 cm-1. A shoulder on this peak, at
29.65 cm-1, has been tentatively assigned to the equivalent
transition in Mg I. The H I line exhibits limb brightening of up to
9% of the disk-centre continuum intensity. The intensity of the Mg
I line is about half of the H I line intensity across the observed
region near to the limb. Widths of the H I line are between 0.020
and 0.027 cm-1, smaller than predicted by current models
of this line in the Sun's spectrum. These measurements represent the
highest-n Rydberg lines detected to date in the solar spectrum. The
measured line intensity, line width, limb brightening and the relative
heights of the contributions from H I and Mg I place constraints upon
further modelling of the solar atmosphere.
Title: The Spatial Distribution of Molecules in Sunspots
Authors: Rabin, D. M.; Clark, T. A.; Bergman, M. W.
Bibcode: 2000SPD....31.0118R
Altcode: 2000BAAS...32..804R
We report preliminary results from a program to map the concentration
of H2O, OH, and SiO in the atmospheres of sunspots using
imaging infrared spectroscopy. The water molecule is confined to
the inner core of the umbra, whereas OH can sometimes be detected
in the penumbra. Plots of line depth against continuum intensity
show an abrupt onset of absorption at a different intensity for
each molecule. A larger sample is needed to decide to what extent
such features are characteristic. Evershed flow is seen in OH in the
penumbra of spots near the limb, with typical outward velocities of
1-2 km s-1. Spatial imaging of molecular concentrations in
sunspots should eventually provide new diagnostics for the temperature
structure of the umbral atmosphere, as yet poorly determined. This work
has been supported by the University of Calgary and by the National
Science Foundation through its support of NSO/NOAO.
Title: CORE: Continuous, High-Accuracy Earth Orientation Measurements.
Authors: McMillan, D. S.; Himwich, W. E.; Thomas, C. C.; Vandenberg,
N. R.; Bosworth, J. M.; Chao, B.; Clark, T. A.; Ma, C.
Bibcode: 1999evga.conf..166M
Altcode:
The international geodetic VLBI community will inaugurate during 1999
a new phase of the program called CORE (Continuous Observations of the
Rotation of the Earth). The capabilities of the new Mark IV correlators,
available as of mid-1999, will enable greater sensitivity, more frequent
observing sessions, and improved system throughput. The CORE program,
begun in 1996 with the CONT96 campaign, has gradually increased the
number of observing sessions per week. As of early 1999 the average is
2.5 24-hour sessions per week (including the NEOS sessions). This will
expand to 3.5 sessions per week beginning in the second half of 1999,
with the goal of continuous observing by the year 2001. The concept of
CORE requires that Earth orientation measurements will be made with
several networks, each operating on a different day. It is therefore
important to determine whether there are systematic differences between
EOP derived from different networks. We have been acquiring data from
different networks observing on the same day or on sequential days in
order to validate this concept. Recent analysis comparing data from
CORE-A, CORE-B, and NEOS sessions shows that there are systematic
differences in EOP, which are now under active investigation.
Title: Spectroscopic Observations of Jupiter from the Infrared to
the Millimetre
Authors: Davis, G. R.; Naylor, D. A.; Gom, B.; Griffin, M. J.;
Sidher, S. D.; Swinyard, B. M.; Burgdorf, M. J.; Irwin, P. G. J.;
Orton, G. S.; Encrenaz, Th.; Gautier, D.; Lellouch, E.; de Graauw,
Th.; Feuchtgruber, H.; Clark, T. A.
Bibcode: 1998BAAS...30Q1069D
Altcode:
We have measured the spectrum of Jupiter from 45 to 197mu m using the
Long Wavelength Spectrometer on ISO, and in the atmospheric windows
at 350mu m, 750mu m, 850mu m and 1.1mm using a Fourier transform
spectrometer on the James Clerk Maxwell Telescope. Absorption signatures
of tropospheric NH_3, PH_3, CH_4 and HD and emission features due to
stratospheric H_2O have all been detected. Tropospheric H_2S is also
a possible absorber at these wavelengths. Analysis of the spectra will
be presented.
Title: Broadband Submillimeter Spectroscopy of HCN, NH 3,
and PH 3in the Troposphere of Jupiter
Authors: Davis, G. R.; Naylor, D. A.; Griffin, M. J.; Clark, T. A.;
Holland, W. S.
Bibcode: 1997Icar..130..387D
Altcode:
We report measurements of the Jupiter brightness spectrum in the
850-μm and 1100-μm atmospheric windows with a spectral resolution
of 125 MHz, obtained with a Fourier transform spectrometer on the
James Clerk Maxwell Telescope. Three results were obtained. First,
the predicted absorption features due to the rotational lines of HCN
at 266 and 354 GHz were not detected within our error limits of less
than 1%. We establish new upper limits for the HCN abundance in the
jovian troposphere for five assumed abundance distributions and for
two assumed NH3abundances. The upper limits are 1.7 to 13
times smaller than the abundance value obtained in the only reported
detection of HCN in Jupiter prior to the impact of Shoemaker-Levy
9. Second, the continuum brightness temperature spectrum at 850
μm was determined and is in agreement with previous measurements,
but has large error bars due to uncertainties in the photometric
calibration. We estimate the ammonia abundance in the 1-2 bar region
to be 1.7 times solar, but this result is tentative since scattering by
NH3cloud particles and absorption by gaseous H2S
were neglected in our atmospheric model. Finally, the first rotational
line of PH3at 267 GHz was not detected, a result which we
demonstrate is consistent with the statistical noise level in these
measurements, with current values of the spectroscopic parameters,
and with phosphine measurements at other wavelengths.
Title: The First 25 Years of the Rothney Astrophysical Observatory
Authors: Milone, E. F.; Clark, T. A.
Bibcode: 1996AAS...189.0106M
Altcode: 1996BAAS...28.1272M
The RAO began as a twinkle in the eye of Sandy R. Cross, a local
rancher from a Calgary pioneering family. His generosity began with
an initial gift of a quarter section of land, continued with two
block grants to permit the construction of a building to house a
1.5-m telescope in 1981, and, finally, funding of a joint operation
with ARC to complete the figuring of a honeycomb 1.8-m mirror. The
summer of 1996 saw the completion of the 1.8-m replacement and the
restoration of all instrumental facilities formerly in use on the 1.5-m
telescope. NSERC of Canada provided the funding for the 1.8-m mounting,
and for infrastructure grants to assist development and instrumentation;
the University of Calgary has provided site support and development
and the Department of Physics and Astronomy the operating funds
and technical salary support to maintain the facility. The RAO was
formally opened by Margaret Burbidge in 1972, and the IRT (now named
the A.R. Cross Telescope) was dedicated by George Coyne and Harlan
Smith in 1987. In addition to the history, in which we describe the
parlay of a leased 1.5-m metal mirror into a million dollar facility,
we will highlight the RAO astronomical innovations, which include
the development of the Rapid Alternate Detection System and the use
of an alt-alt mounting for the 1.8-m telescope, and observational
accomplishments and plans for the future.
Title: Submillimetre Fourier Transform Spectroscopy of Jupiter,
Uranus and Neptune
Authors: Naylor, D. A.; Davis, G. R.; Griffin, M. J.; Clark, T. A.
Bibcode: 1996DPS....28.2235N
Altcode: 1996BAAS...28Q1148N
Planetary spectroscopy at submillimetre wavelengths is a potentially
rich field for the study of minor species because it is the region of
maximum intensity for the rotational lines of many potential atmospheric
constituents. Our previous attempts to measure submillimetre planetary
spectra from the JCMT were hindered by problems associated with the
facility bolometric detector which was not designed for broadband
astronomical spectroscopy. In this paper we present preliminary results
from the commissioning run of a new dual polarization detector system
which has been specifically developed for use with our Fourier transform
spectrometer at the JCMT. Following a brief review of the salient
features of the detector and spectrometer, we will present spectroscopic
observations of Jupiter, Uranus and Neptune obtained during August
1996 from the JCMT. The paper will conclude with an analysis of the
sensitivity of this technique and plans for future observations.
Title: The Sun in Submillimeter and Near-Millimeter Radiation
Authors: Lindsey, C.; Kopp, G.; Clark, T. A.; Watt, G.
Bibcode: 1995ApJ...453..511L
Altcode:
We examine the best solar submillimeter observations made on the James
Clerk Maxwell Telescope in 1991 and 1992. In these observations, the
solar disk was observed concurrently in pairs of wavelengths chosen
from 350, 850, and 1200 μm. Images at all of these wavelengths show
clear limb brightening of the quiet Sun. The observations clearly
resolve the chromospheric supergranular network in active and quiet
regions. The quiet Sun is characterized by large-scale variations in
brightness, particularly the occasion of anomalously dark regions that
tend to surround active regions. Sunspots are clearly resolved, with
large dark umbrae clearly distinguished from sometimes particularly
bright penumbrae.
Title: The Abundance of HCN on Jupiter
Authors: Davis, G. R.; Naylor, D. A.; Griffin, M. J.; Holland, W. S.;
Clark, T. A.
Bibcode: 1995DPS....27.3002D
Altcode: 1995BAAS...27.1138D
No abstract at ADS
Title: Precision measurements of the location of the VLBI Station
Simeiz
Authors: Clark, T. A.; Bosworth, J.; Vandenberg, N.; Gordon, D.;
Himwich, E.; Shaffer, D.; Whitney, A.; Corey, B.; Niel, A.; Tomas,
C.; Matveenko, L. I.; Musin, R. K.; Shevchenko, A. V.; Nesterov,
N. S.; Stepanov, A. V.; Nikitin, P. S.; Ipatov, A. V.; Mardyshkin,
V. V.; Ivanov, D. A.; Yatskiv, Y. S.; Medvedskii, M. M.
Bibcode: 1995AstL...21..116C
Altcode: 1995PAZh...21..129C
No abstract at ADS
Title: Eclipse Measurements of the Distribution of CO Emission Above
the Solar Limb
Authors: Clark, T. A.; Lindsey, C.; Rabin, D. M.; Livingston, W. C.
Bibcode: 1995itsa.conf..133C
Altcode:
No abstract at ADS
Title: Detection of the HI n = 20-19 Submillimeter Line in Emission
at the Solar Limb Using a Polarizing FT Spectrometer
Authors: Clark, T. A.; Naylor, D. A.; Davis, G. R.
Bibcode: 1995itsa.conf..139C
Altcode:
No abstract at ADS
Title: The Non-detection of HCN on Jupiter
Authors: Davis, G. R.; Naylor, D. A.; Griffin, M. J.; Holland, W. S.;
Clark, T. A.
Bibcode: 1994BAAS...26Q1549D
Altcode:
No abstract at ADS
Title: Eclipse Observations of the Extreme Solar Limb Profile of HI
Pfund beta Emission.
Authors: Clark, T. A.; Lindsey, C. A.; Rabin, D. M.; Livingston, W. C.
Bibcode: 1994AAS...185.4412C
Altcode: 1994BAAS...26.1378C
A region of the infrared solar spectrum (2147.7 - 2150.1 cm(-1)
) around the HI Pfund beta line (2148.79 cm(-1) ) was monitored
through 3 eclipse "contacts" with the Amber InSb array on the Main
spectrograph on the McMath-Pierce telescope during the 10 May 1994
partial solar eclipse over Kitt Peak National Observatory to produce
limb profiles of intensity and line width to an angular resolution
of 0.15 arc second. This line is broad (FWHM = 0.9 cm(-1) and shallow
(5.7%) in absorption at disk center but shows a narrow emission core
above the continuum envelope at 2 arc seconds inside the limb which
remains visible out to 4.5 arc seconds beyond the continuum limb. The
Pfund beta peak intensity appears to follow the continuum profile at
the limb but then intensifies again to reach a peak at about 1000 km
above the limb in a manner similar to that of the HeI D3 line. The line
width becomes narrower with height above the limb, reaching a FWHM of
0.22 cm(-1) at several arc seconds above the limb. These profiles will
be discussed in relation to those of other HI lines above the solar
limb. This work was supported by NSERC of Canada and by NSO, Tucson.
Title: Broad-band spectroscopic detection of the CO J=3-2 tropospheric
absorption in the atmosphere of Neptune.
Authors: Naylor, D. A.; Davis, G. R.; Griffin, M. J.; Clark, T. A.;
Gautier, D.; Marten, A.
Bibcode: 1994A&A...291L..51N
Altcode:
We report the first detection of the CO J=3->2 absorption feature
in Neptune. The broad tropospheric absorption line was measured in
May 1993 using a polarizing Fourier transform spectrometer on the
James Clerk Maxwell Telescope. The measured width and depth are in
general agreement with the model of Marten et al. (1993), supporting
their suggestion that carbon monoxide is transported upward into the
stratosphere from the deep Neptunian atmosphere.
Title: SEARCH'92 Campaign: AN Overview
Authors: Dickey, J. O.; Clark, T. A.; Eubanks, T. M.; Feissel,
M.; Melbourne, W. G.; Ray, J. R.; Salstein, D. A.; Schutz, B. E.;
Veillet, C.
Bibcode: 1994ITN....16a...1D
Altcode:
High time resolution measurements of Earth rotation and atmospheric
angular momentum and torque and their Interpretation can provide unique
insights into a variety of processes including dynamic coupling between
solid Earth and atmosphere, the effects of oceanic tides on the Earth's
rotational dynamics, excitation of the polar wobble, and fluid-core
resonance effects; hencc, an extensive campaign, SEARCH'92, has been
held through the coordination of the International Earth Rotation
Service (IERS) to obtain these measurements utilizing all space geodetic
techniques and to collect the best available complementary geophysical,
atmospheric and oceanographic data. This paper discusses its motivation
and planning; recent analysis results are highlighted.
Title: Detection of the H I n = 20→19 transition in emission in
the submillimeter solar spectrum.
Authors: Clark, T. A.; Naylor, D. A.; Davis, G. R.; Tompkins, G. J.
Bibcode: 1994JRASC..88Q.258C
Altcode:
No abstract at ADS
Title: Polarizing Fourier transform spectrometer for astronomical
spectroscopy at submillimeter and mid-infrared wavelengths
Authors: Naylor, David A.; Clark, T. A.; Davis, Gary R.
Bibcode: 1994SPIE.2198..703N
Altcode:
The design of a polarizing Fourier transform spectrometer, developed
for submillimeter and mid-infrared astronomical spectroscopy, is
presentd. Results from recent observing runs are used to illustrate
its performance.
Title: Observation of the N = 8-7 Rydberg Transition of Hydrogen in
Emission in the Solar Infrared Spectrum and the Search for Equivalent
Magnesium Lines
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.
Bibcode: 1994ASPC...64..608C
Altcode: 1994csss....8..608C
No abstract at ADS
Title: Solar Submillimeter Millimeter Spectroscopy between 7 30 cm1
from the James Clerk Maxwell Telescope
Authors: Naylor, D. A.; Tompkins, G. J.; Clark, T. A.; Davis, G. R.;
Duncan, W. D.
Bibcode: 1994IAUS..154..371N
Altcode:
No abstract at ADS
Title: Eclipse Observations of the Extreme Solar Limb at Submillimeter
Wavelengths
Authors: Clark, T. A.
Bibcode: 1994IAUS..154..139C
Altcode:
No abstract at ADS
Title: High-n Hydrogen Lines in Solar Infrared Spectra from
Balloon-borne; Mauna Kea; ATMOS Observations
Authors: Boreiko, R. T.; Clark, T. A.; Naylor, D. A.; Busler, J. R.
Bibcode: 1994IAUS..154..365B
Altcode:
No abstract at ADS
Title: Near IR Observations of the 11 July 1991 Total Solar Eclipse
from Mauna Kea; Hawaii
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Lindsey, C.
Bibcode: 1994IAUS..154..173C
Altcode:
No abstract at ADS
Title: The sky, the Moon and the tides: an observing exercise for
non-science introductory astronomy classes.
Authors: Clark, T. A.; Milone, E. F.; Wilson, W. J. F.
Bibcode: 1993JRASC..87Q.179C
Altcode:
No abstract at ADS
Title: Measurement of solar limb extension at CO fundamental band
wavelengths in a total eclipse: comparison with atmospheric model
predictions.
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Avrett, E. H.
Bibcode: 1993JRASC..87S.179C
Altcode:
No abstract at ADS
Title: An active solar prominence in 1.3 MM radiation
Authors: Harrison, R. A.; Carter, M. K.; Clark, T. A.; Lindsey, C.;
Jefferies, J. T.; Sime, D. G.; Watt, G.; Roellig, T. L.; Becklin,
E. E.; Naylor, D. A.; Tompkins, G. J.; Braun, D.
Bibcode: 1993A&A...274L...9H
Altcode:
We present new millimetre-wavelength observations of an active solar
prominence. Observations made over a two-day period with the James
Clerk Maxwell Telescope on Manna Kea, Hawaii, give a unique view in
1.3 mm radiation of the spectacular prominence that appeared on the
west solar limb in the total solar eclipse of 11 July 1991.
Title: Broad-band spectroscopy with the James Clerk Maxwell Telescope
using a polarizing Fourier transform spectrometer.
Authors: Naylor, D. A.; Clark, T. A.; Davis, G. R.; Duncan, W. D.;
Tompkins, G. J.
Bibcode: 1993MNRAS.260..875N
Altcode:
We report the first use of a polarizing Fourier transform
spectrometer on the James Clerk Maxwell Telescope. Solar spectra
have been measured through four of the submillimeter and millimeter
atmospheric windows. The repeatability is shown to be excellent,
with signal-to-noise ratios exceeding 100 per spectral element per
scan. The spectra also show good agreement with synthetic atmospheric
transmission spectra over most of the spectral range. As a demonstration
of the potential of this approach for astronomical spectroscopy, the
(C-12)O J= 6-5 and 7-6 emission lines from the Orion molecular cloud
have been detected for the first time using incoherent techniques.
Title: A UCSD-RAO Infrared Spectrometer
Authors: Milone, E. F.; Babott, F. M.; Clark, T. A.; Fry, D. J. I.;
Jones, B.; Puetter, R. C.; Pura, R. K.
Bibcode: 1993ASPC...41..403M
Altcode: 1993ais..conf..403M
No abstract at ADS
Title: Improvements in the Accuracy of Geodetic VLBI
Authors: Rogers, A. E. E.; Cappallo, R. J.; Corey, B. E.; Hinteregger,
H. F.; Niell, A. E.; Phillips, R. B.; Smythe, D. L.; Whitney, A. R.;
Herring, T. A.; Bosworth, J. M.; Clark, T. A.; Ma, C.; Ryan, J. W.;
Davis, J. L.; Shapiro, I. I.; Elgered, G.; Jaldehag, K.; Johansson,
J. M.; Ronnang, B. O.; Carter, W. E.; Ray, J. R.; Robertson, D. S.;
Eubanks, T. M.; Kingham, K. A.; Walker, R. C.; Himwich, W. E.; Kuehn,
C. E.; MacMillan, D. S.; Potash, R. I.; Shaffer, D. B.; Vandenberg,
N. R.; Webber, J. C.; Allshouse, R. L.; Schupler, B. R.; Gordon, D.
Bibcode: 1993csgg.conf...47R
Altcode:
No abstract at ADS
Title: The Consistency of the Scale of the Terrestrial Reference
Frames Estimated From SLR and VLBI Data
Authors: Himwich, W. E.; Watkins, M. M.; Ma, C.; MacMillan, D. S.;
Clark, T. A.; Eanes, R. J.; Ryan, J. W.; Schutz, B. E.; Tapley, B. D.
Bibcode: 1993csgg.conf..113H
Altcode:
No abstract at ADS
Title: On "Challenges of astronomy" as a broad-usage teaching tool.
Authors: Milone, E. F.; Clark, T. A.; Kwok, S.
Bibcode: 1992JRASC..86..287M
Altcode:
No abstract at ADS
Title: Broad band astronomical spectroscopy on the James Clerk
Maxwell Telescope with a polarizing Fourier transform spectrometer.
Authors: Naylor, D. A.; Moazzen-Ahmadi, N.; Tompkins, G. J.; Davis,
G. R.; Clark, T. A.; Griffin, M. J.; Duncan, W. D.
Bibcode: 1992JRASC..86..289N
Altcode:
No abstract at ADS
Title: Total solar eclipse measurement of the height of the CO layer
in the solar atmosphere.
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.
Bibcode: 1992JRASC..86..290C
Altcode:
No abstract at ADS
Title: Measurement of the Height of the Solar CO Layer During the
11 July 1991 Eclipse
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Lindsey, C. A.;
Becklin, E. E.; Jefferies, J. T.; Harrison, R. A.; Roellig, T. L.;
Carter, M.; Braun, D. C.; Watt, G.
Bibcode: 1992AAS...181.8108C
Altcode: 1992BAAS...24.1253C
No abstract at ADS
Title: Extension of the solar limb at sub-millimeter and millimeter
wavelengths
Authors: Clark, T. A.; Naylor, David A.; Tompkins, G. J.; Duncan, W. D.
Bibcode: 1992SoPh..140..393C
Altcode:
Solar limb scanning at 5 wavelengths from 0.35 to 2 mm on the JCMT
has revealed significant limb extension which increases rapidly with
wavelength, in agreement with other measurements. This appears to be
related to the increasing opacity of overlapping spicules which appear
to become optically thick at about 1mm.
Title: Extreme-infrared brightness profile of the solar chromosphere
obtained during the total eclipse of 1991
Authors: Lindsey, C.; Jefferies, J. T.; Clark, T. A.; Harrison, R. A.;
Carter, M. K.; Watt, G.; Becklin, E. E.; Roellig, T. L.; Braun, D. C.;
Naylor, D. A.
Bibcode: 1992Natur.358..308L
Altcode:
THE solar chromosphere is a thin layer of gas that is several thousand
degrees hotter than the underlying photosphere, and responsible for
most of the Sun's ultraviolet emission. The mechanism by which it is
heated to temperatures exceeding 10,000 K is not understood. Millimetre
and submillimetre radiometry can be used to obtain the chromospheric
temperature profile, but the diffraction-limited resolution for the
largest telescopes is at best 17 arcsec, or ~12,500 km at the Sun's
distance. This is greater than the thickness of the quiet chromosphere
itself. The total eclipse of July 1991, which passed over the Mauna
Kea Observatory in Hawaii, provided a rare opportunity to make limb
occultation observations with a large submillimetrewavelength telescope,
the 15-m James Clerk Maxwell Telescope, and in this way we obtained a
temperature profile in 1.3-mm radiation with ~300 km resolution at the
Sun. Our observations indicate that spicules (magnetically entrained
funnels of gas) reach a temperature of 8,000 K at 3,000-4,000 km above
the photosphere, a temperature lower than those of many spicule models.
Title: Position and morphology of the compact non-thermal radio
source at the Galactic Center.
Authors: Marcaide, J. M.; Alberdi, A.; Bartel, N.; Clark, T. A.; Corey,
B. E.; Elosegui, P.; Gorenstein, M. V.; Guirado, J. C.; Kardashev,
N.; Popov, M.; Preston, R.; Ratner, M. I.; Rioja, M. J.; Rogers,
A. E. E.; Shapiro, I. I.
Bibcode: 1992A&A...258..295M
Altcode:
We have determined with VLBI the position of the compact nonthermal
radio source at the Galactic Center, commonly referred to as SgrA*,
in the J2000.0 reference frame of extragalactic radio sources. We have
also determined the size of SgrA* at 1.3, 3.6 and 13 cm wavelengths and
found that the apparent size of the source increases proportionally
to the observing wavelength squared, as expected from source size
broadening by interstellar scattering and as reported previously by
other authors (e.g. Davies et al. 1976; Marcaide et al. 1985; Lo et
al. 1985; Jauncey et al. 1989). We have also established an upper limit
of about 8 mJy at 3.6 cm wavelength for any ultracompact component. The
actual size of the source is less than 15 AU. Fourier analysis of our
very sensitive 3.6 cm observations of this source shows no significant
variations of correlated flux density on time scales from 12 to 700 s.
Title: Infrared Variable Star Observing from the Rothney Astrophysical
Observatory
Authors: Milone, E. F.; Babott, F. M.; Clark, T. A.; Dougherty, S. M.;
Fry, D. J. L.; Himer, J. T.; Leahy, D. A.; Taylor, A. R.; Ananth, A. G.
Bibcode: 1992ASPC...28...49M
Altcode: 1992atpi.conf...49M
No abstract at ADS
Title: Near-IR Observations of 101 Be Stars
Authors: Dougherty, S. M.; Taylor, A. R.; Clark, T. A.
Bibcode: 1991AJ....102.1753D
Altcode:
Observations of 101 Be stars taken over a two year period in the near-IR
between 1 and 5 microns are presented and discussed. The near-IR color
excess of all program stars is derived, and found to increase with
wavelength for all these stars. The fraction of stars with color excess
doubles between 1.25 and 3.6 microns. There appears to be an upper
limit to the magnitude of the color excess as a function of stellar
type, with early-type stars having a higher upper limit than later
spectral types. No correlation of the presence or magnitude of color
excess with projected rotational velocity is evident. The spectral
index of the excess emission spectra is calculated for stars having
color excess. On average, the spectral index through the near-IR and
far-IR IRAS wavelength regimes is constant. There is evidence that
some stars have excess emission with spectral index values outside
the range expected for free-free and bound-free emission. This is
attributed to either dust emission or the effect of absorption of
photospheric emission by cool circumstellar material along the line
of sight to the star.
Title: Wide-band solar spectroscopy on the James Clerk Maxwell
telescope with a polarizing Fourier transform spectrometer.
Authors: Clark, T. A.; Naylor, D. A.; Tompkins, G. J.; Davis, G. R.;
Duncan, W. D.
Bibcode: 1991JRASC..85..190C
Altcode:
No abstract at ADS
Title: A polarizing Fourier transform spectrometer for intermediate
resolution spectroscopy at millimetre and sub-millimetre wavelengths
with the James Clerk Maxwell telescope.
Authors: Naylor, D. A.; Tompkins, G. T.; Clark, T. A.; Davis, G. R.;
Duncan, W. D.
Bibcode: 1991JRASC..85..185N
Altcode:
No abstract at ADS
Title: Wide-band planetary spectroscopy on the James Clerk Maxwell
telescope with a polarizing Fourier transform spectrometer.
Authors: Davis, G. R.; Naylor, D. A.; Tompkins, G. J.; Clark, T. A.;
Duncan, W. D.
Bibcode: 1991JRASC..85..190D
Altcode:
No abstract at ADS
Title: Atmospheric transmission at submillimetre wavelengths from
Mauna Kea
Authors: Naylor, David A.; Schultz, Arvid A.; Clark, T. A.; Davis,
Gary R.
Bibcode: 1991MNRAS.251..199N
Altcode:
Measurements of the submillimeter solar spectrum through the 350- and
450-micron windows of the atmosphere using a Michelson interferometer
on the James Clerk Maxwell Telescope have been used to determine the
transmission spectrum of the atmosphere above Mauna Kea, Hawaii. This
spectrum is shown to be in close agreement with that generated by
the FASCOD synthesis program using the HITRAN database. The majority
of absorption features can be attributed to H2O (which dominates the
overall window shape), O2 and O3, although several significant but so
far unassigned absorption features are noted. These results demonstrate
the feasibility, under drier and more stable atmospheric conditions,
of obtaining broad-band, intermediate resolution spectra from the JCMT
with a Fourier spectrometer.
Title: Comparison of VLBI and SLR geocentric site coordinates
Authors: Ray, J. R.; Ma, C.; Ryan, J. W.; Clark, T. A.; Eanes, R. J.;
Watkins, M. M.; Schutz, B. E.; Tapley, B. D.
Bibcode: 1991GeoRL..18..231R
Altcode:
The geocentric coordinates for 18 pairs of SLR and VLBI sites are
compared. After a seven-parameter frame adjustment, the two coordinate
sets have weighted rms differences of 15, 22, and 22 mm for X, Y, and
Z, respectively, consistent with the formal errors being too small by
a factor of about two.
Title: A New Transportable VLBI System
Authors: Clark, T. A.; Shaffer, D. B.; Allshouse, R. M.
Bibcode: 1991gvmg.conf..427C
Altcode:
No abstract at ADS
Title: The RF Bandwidth Upgrade: Doubling the X-Band Spanned Bandwidth
of Geodetic VLBI Receiving Systems
Authors: Corey, B. E.; Clark, T. A.
Bibcode: 1991gvmg.conf...15C
Altcode:
No abstract at ADS
Title: Progress to Millimeter Accuracy VLBI: Synergism of Many Factors
(Keynote Presentation)
Authors: Clark, T. A.
Bibcode: 1991gvmg.conf...98C
Altcode:
No abstract at ADS
Title: Search for infrared variability in Be stars.
Authors: Dougherty, S. M.; Taylor, A. R.; Clark, T. A.
Bibcode: 1990JRASC..84..424D
Altcode:
No abstract at ADS
Title: Solar limb scans at millimetre and submillimetre wavelengths
with the James Clerk Maxwell telescope.
Authors: Clark, T. A.; Naylor, D. A.; Duncan, W. D.
Bibcode: 1990JRASC..84..419C
Altcode:
No abstract at ADS
Title: Ultraviolet limb darkening in the eclipsing binary AI
Phoenicis.
Authors: Stagg, C. R.; Milone, E. F.; Clark, T. A.; Kjeldseth Moe, O.
Bibcode: 1990JRASC..84R.423S
Altcode:
No abstract at ADS
Title: Two new position sensors for telescope auto-guiding via
main beam.
Authors: Haslett, J. W.; Condon, R. J.; Gonnason, W. R.; Singaravelan,
S.; Trofimenkoff, F. N.; Milone, E. F.; Babott, F. M.; Clark, T. A.;
Taylor, A. R.
Bibcode: 1990JRASC..84..435H
Altcode:
No abstract at ADS
Title: Geodetic measurement of deformation in the Loma Prieta,
California Earthquake with very long baseline interferometry
Authors: Clark, T. A.; Ma, C.; Sauber, J. M.; Ryan, J. W.; Gordon,
D.; Shaffer, D. B.; Carprette, D. S.; Vandenberg, N. R.
Bibcode: 1990GeoRL..17.1215C
Altcode:
Following the Loma Prieta earthquake, two mobile Very Long Baseline
Interferometry (VLBI) systems operated by the NASA Crustal Dynamics
Project and the NOAA National Geodetic Survey were deployed at
three previously established VLBI sites in the earthquake area:
Fort Ord (near Monterey), the Presidio (in San Francisco) and Point
Reyes. From repeated VLBI occupations of these sites since 1983, the
pre-earthquake rates of deformation have been determined with respect
to a North American reference frame with 1σ formal standard errors of
∼1 mm/yr. The VLBI measurements immediately following the earthquake
showed that the Fort Ord site was displaced 49 ± 4 mm at an azimuth
of 11 ± 4° and that the Presidio site was displaced 12 ± 5 mm at
an azimuth of 148 ± 13°. No anomalous change was detected at Point
Reyes with 1σ uncertainty of 4 mm. The estimated displacements at
Ford Ord and the Presidio are consistent with the static displacements
predicted on the basis of a coseismic slip model in which slip on the
southern segment is shallower than slip on the more northern segment
of the fault rupture. We also give the Cartesian positions at epoch
1990.0 of a set of VLBI fiducial stations and the three mobile sites
in the vicinity of the earthquake.
Title: Rothney Astrophysical Observatory, Calgary, Alberta T2N 1N4,
Canada. 5. RAO report covering the period 1986 - 1989.
Authors: Milone, E. F.; Clark, T. A.
Bibcode: 1990BAAS...22..974M
Altcode:
No abstract at ADS
Title: VLBI Measurements of Earthquake Displacements in California
and Alaska
Authors: Clark, T. A.; Ryan, J. W.; Ma, C.; Sauber, J. M.; Vandenberg,
N. R.; Shaffer, D. B.; Gordon, D.
Bibcode: 1990BAAS...22..741C
Altcode:
No abstract at ADS
Title: The University of Calgary I. R. telescope: present status
and future developments.
Authors: Clark, T. A.; Milone, E. F.; Taylor, A. R.; Fry, D. J. I.;
Dougherty, S. M.; Naylor, D. A.; Babott, F. M.; Emard, T.; Griffiths,
S. C.; Robinson, K. G.; Zimmer, E.; Smith, G.
Bibcode: 1989JRASC..83Q.305C
Altcode:
No abstract at ADS
Title: Modelling of the IR to radio spectra of Be stars.
Authors: Dougherty, S. M.; Taylor, A. R.; Clark, T. A.; Waters,
L. B. F. M.
Bibcode: 1989JRASC..83Q.307D
Altcode:
No abstract at ADS
Title: Data acquisition at the RAO: light curves from the optical
and infrared telescopes.
Authors: Milone, E. F.; Clark, T. A.; Babott, F. M.; Fry, D. J. I.;
Griffiths, S. C.; Penfold, J. E.; Robinson, K. G.; Taylor, A. R.;
van Leeuwen, J.
Bibcode: 1989JRASC..83Q.317M
Altcode:
No abstract at ADS
Title: Models of Infrared Atmospheric Extinction
Authors: Volk, Kevin; Clark, T. A.; Milone, E. F.
Bibcode: 1989LNP...341...15V
Altcode: 1989ies..conf...15V
Computer simulations of the atmospheric extinction are presented for
the JHK filters. Comparison with observations show that the deviations
from linearity in a magnitude/air mass plot are small even though the
linear extrapolation to zero air mass produces a value much different
than the models predict. The cause of this effect is discussed. It
appears that direct verification of the non-linearity predicted by
the models will be difficult to obtain.
Title: Supernova 1987A: radiosphere resolved with VLBI five days
after the neutrino burst
Authors: Jauncey, D. L.; Kemball, A.; Bartel, N.; Whitney, A. R.;
Rogers, A. E. E.; Shapiro, I. I.; Preston, R. A.; Clark, T. A.; Harvey,
B. R.; Jones, D. L.; Nicolson, G. D.; Nothnagel, A.; Phillips, R. B.;
Reynolds, J. E.; Webber, J. C.
Bibcode: 1988Natur.334..412J
Altcode: 1988Nat...334..412J
Following the detection1 of radio emission from SN1987A
in the Large Magellanic Cloud, we conducted very-long-baseline
inter-ferometry (VLBI) observations with an interferometer composed of
a NASA Deep Space Network antenna (DSS42) at Tidbinbilla, Australia and
the antenna of the Hartebeesthoek Radio Astronomy Observatory, South
Africa2,3. We did not detect any emission from the supernova
above a level of ~20% of the supernova's total flux density, although
signals were detected from our two calibrator sources with amplitudes
roughly equal to those determined in earlier VLBI observations. We infer
that we resolved the supernova's radiosphere and estimate, for an epoch
5.2 days after the neutrino burst4,5, a lower bound on the
radiosphere's radius of 1.2 mas. Given the photometric data from the
supernova6,7, a distance to the Large Magellanic Cloud of
50 +/- 5 kpc (ref. 8), and an apparent expansion velocity that varied
systematically with time from 18-16 x 103 km s-1
(refs 9 and 10), as estimated from the blue-shifted Hα absorption
lines on the days preceding our observations, we conclude that 5.2 days
after the neutrino burst the supernova's radiosphere was at least 2.5
times larger than the inferred blackbody photosphere, and at least as
large as the Hα line-forming region.
Title: Constraints on North American-Pacific Plate Boundary
Deformation in Central California from VLBI and Ground-Based
Geodetic Data
Authors: Sauber, J.; Jordan, T. H.; Berosa, G. C.; Clark, T. A.;
Lisowski, M.
Bibcode: 1988IAUS..129..353S
Altcode:
No abstract at ADS
Title: Nasa/crustal Dynamics Project Results: Tectonic Plate Motion
Measurements with Mark-Iii VLBI (invited)
Authors: Ryan, J. W.; Clark, T. A.
Bibcode: 1988IAUS..129..339R
Altcode:
No abstract at ADS
Title: Consistency of CDP and IRIS VLBI Earth Orientation Results
Authors: Mallama, A.; Clark, T. A.; Ryan, J. W.
Bibcode: 1988IAUS..128..187M
Altcode:
This study compares the Earth orientation results obtained by the
NASA CDP and the NGS IRIS experiments. The results agree at about
one combined formal error (two milliarcseconds) after small biases
(one to three milliarcseconds) have been removed from each component.
Title: VLBI Observations of the O957 + 561 Gravitational Lens Systems
(review)
Authors: Gorenstein, M. V.; Bonometti, R. J.; Cohen, N. L.; Falco,
E. E.; Shapiro, I. I.; Bartel, N.; Rogers, A. E. E.; Marcaide, J. M.;
Clark, T. A.
Bibcode: 1988IAUS..129..201G
Altcode:
A series of VLBI observations of the gravitational lens system 0957 +
561 at a wavelength of 13 cm has yielded the positions of the A and B
images, the relative magnification of their largest discernible radio
structures, and the time variability of their smallest discernible
radio structures. These observations have also allowed upper limits
to be placed on the flux density of an expected third image. The
positions and relative magnification of the A and B images provide
new information with which to constrain models of the lens that forms
the images. The detection of variations in the flux densities of the
cores of A and B suggests that observations at shorter wavelengths
may reveal superluminal motion, which may in turn provide a means to
measure the relative time delay.
Title: Solar Brightness Temperature at Submillimeter Wavelengths
Authors: Boreiko, R. T.; Clark, T. A.
Bibcode: 1987ApJ...318..445B
Altcode:
Solar brightness temperature data obtained at 34.9 km during a balloon
flight from the Canadian Space Research Facility on August 28, 1982 are
analyzed. A servocontrolled telescope capable of solar image scanning,
a Michelson interferometer with 0.015/cm apodized resolution, and
an in-flight radiometric calibration source were used to obtain the
temperature data. Interferograms and spectra from the sun, the sky
background, and blackbody at its equilibrium temperature of 1165 K are
studied, and values of solar brightness temperature are derived from
the spectra. The relation between solar brightness temperature and
wave number is examined. The effects of systematic error on the solar
temperature data are investigated. An intrinsic temperature minimum
of 4170 K and an observable minimum of 4300 K were obtained. The
temperature values are compared with the predictions of Vernazza et
al. (1981), and good correlation is detected.
Title: Determination of site motions in the western United States
from Mark III VLBI measurements.
Authors: Gordon, D.; Clark, T. A.
Bibcode: 1987rpgb.rept....9G
Altcode:
The objective of the work is to determine site motions at 14 fixed
and mobile VLBI sites in the western continental United States using
a large data of Mark III VLBI measurements.
Title: Mark III VLBI technology: an evaluation of the new generation
water vapor radiometers.
Authors: Lundqvist, G. L.; Hayes, M. W.; Clark, T. A.
Bibcode: 1987rpgb.rept..201L
Altcode:
No abstract at ADS
Title: Radio-source positions from VLBI.
Authors: Ma, C.; Clark, T. A.; Ryan, J. W.; Herring, T. A.; Shapiro,
I. I.; Corey, B. E.; Hinteregger, H. F.; Rogers, A. E. E.; Whitney,
A. R.; Knight, C. A.; Lundqvist, G. L.; Shaffer, D. B.; Vandenberg,
N. R.; Pigg, J. C.; Schupler, B. R.; Ronnang, B. O.
Bibcode: 1986AJ.....92.1020M
Altcode:
Positions of 85 compact extragalactic radio sources and the Galactic
object Beta Persei (Algol) have been determined in the J2000.0
coordinate system for analysis of VLBI observations made with the
bandwidth-synthesis technique. Twenty-four of these sources were
observed with the Mark I VLBI system in 37 sessions distributed between
April 1972 and May 1978, and 82 of the sources were observed with the
Mark III system in 85 sessions distributed between August 1979 and
December 1982. Each session spanned at least 24 hr. Standard errors for
the estimated positions on the sky of the about 10 sources frequently
observed with the Mark I system are about 1 mas, except for the
declinations of nearly equatorial sources, where these errors approach
5 mas. Corresponding uncertainties for the about 20 sources frequently
observed with the Mark III system are 0.3 and 2 mas, respectively.
Title: Search for parent-molecule line-emission from comet Halley
with a high-resolution astronomical infrared Fourier-transform
spectrometer.
Authors: Naylor, D. A.; Schultz, A. A.; Clark, T. A.
Bibcode: 1986JRASC..80..278N
Altcode:
No abstract at ADS
Title: Balloon-borne measurements of solar brightness temperature
and high-nrecombination lines from hydrogen, magnesium, and silicon
at far I.R.wavelengths.
Authors: Boreiko, R. T.; Clark, T. A.
Bibcode: 1986JRASC..80..275B
Altcode:
No abstract at ADS
Title: The IRT and RADS-III - new developments at the Rothney
Astrophysical Observatory.
Authors: Milone, E. F.; Clark, T. A.; Emard, T.; Babott, F. M.
Bibcode: 1986JRASC..80..269M
Altcode:
No abstract at ADS
Title: Solar Brightness Temperature in the Region of the Temperature
Minimum from Radiometrically Calibrated Sub-Millimeter Spectra
Authors: Clark, T. A.; Boreiko, R. T.
Bibcode: 1986BAAS...18Q.991C
Altcode:
No abstract at ADS
Title: Geodesy by radio interferometry: Evidence for contemporary
plate motion
Authors: Herring, T. A.; Shapiro, I. I.; Clark, T. A.; Ma, C.; Ryan,
J. W.; Schupler, B. R.; Knight, C. A.; Lundqvist, G.; Shaffer, D. B.;
Vandenberg, N. R.; Corey, B. E.; Hinteregger, H. F.; Rogers, A. E. E.;
Webber, J. C.; Whitney, A. R.; Elgered, G.; Ronnang, B. O.; Davis,
J. L.
Bibcode: 1986JGR....91.8341H
Altcode:
Analysis of 211 very long baseline interferometry observing
sessions carried out between November 1979 and August 1984 has
yielded estimates of the distances between various radio telescopes
located in North America and Europe. The average rate of change of
the distances between four radio telescopes in North America (Haystack
Observatory, Massachusetts; Westford Radio Telescope, Massachusetts;
George R. Agassiz Station, Texas; and Owens Valley Radio Observatory,
California) and one in Europe (Onsala Space Observatory, Sweden)
obtained from the analysis of these data is 19+/-10 mm/yr, where the
(68% confidence interval) standard deviation is for the estimate
of the rate of change of the Haystack-Onsala baseline length, the
one determined most accurately from these data. This estimate of the
standard deviation is dominated by the effects of correlated systematic
errors due mostly to errors in the model used for the atmospheric delay
which we infer introduces errors in each baseline length estimate of
40 mm standard deviation and 60 days correlation time. (By contrast
the statistical standard deviation is only 2 mm/yr.) The estimated
geologic rates of change of these baseline lengths, averaged over
~106 years, are 15 to 17+/-3 mm/yr for the various North
American sites to Onsala. Improvements in our model of the atmosphere,
and continued monitoring of the distances between North American and
European telescopes, will allow the uncertainty of the rate estimates
to be reduced over the next few years to a value small compared to
our estimated rate of change of these baseline lengths. The use of
multiple radio telescopes in Europa will allow us also to separate
possible local site motions from plate motions.
Title: Far-IR solar emission lines form high N states of hydrogen
Authors: Boreiko, R. T.; Clark, T. A.
Bibcode: 1986A&A...157..353B
Altcode:
Emission lines arising from high n transitions (16-15 and 14-13)
in neutral hydrogen have been detected in high resolution solar
spectra obtained with a Michelson interferometer on a balloon-borne
telescope. Absolute intensities are close to the predicted values
of Hoang-Binh (1982) when pressure-broadening is included, with
observed line intensities of up to 10 percent above the solar
continuum. Equivalent emission from heavier elements, such as MgI and
SiI, which is dominant in the near infrared at lower n values, may be
present but is significantly weaker than that from HI transitions.
Title: Detection of Recombination Lines from Hydrogen, Magnesium
and Silicon in the Far Infrared Solar Spectrum
Authors: Clark, T. A.; Boreiko, R. T.
Bibcode: 1986BAAS...18..663C
Altcode:
No abstract at ADS
Title: Geodesy by radio interferometry: Determinations of baseline
vector, earth rotation, and solid earth tide parameters with the
Mark I very long baseline radio interferometry system
Authors: Ryan, J. W.; Clark, T. A.; Coates, R. J.; Ma, C.; Wildes,
W. T.; Gwinn, C. R.; Herring, T. A.; Shapiro, I. I.; Corey, B. E.;
Counselman, C. C.; Hinteregger, H. F.; Rogers, A. E. E.; Whitney,
A. R.; Knight, C. A.; Vandenberg, N. R.; Pigg, J. C.; Schupler, B. R.;
Rönnäng, B. O.
Bibcode: 1986JGR....91.1935R
Altcode:
We analyzed 37 very long baseline radio interferometry experiments
performed between 1972 and 1978 and derived estimates of baseline
vectors between six sites, five in the continental United States
and one in Europe. We found no evidence of significant changes in
baseline length. For example, with a statistical level of confidence
of approximately 85%, upper bounds on such changes within the United
States ranged from a low of 10 mm/yr for the 850 km baseline between
Westford, Massachusetts, and green Bank, West Virginia, to a high
of 90 mm/yr for the nearly 4000 km baseline between Westford and
Goldstone, California. We also obtained estimates for universal time
and for the x component of the position of the earth's pole. For the
last 15 experiments, the only ones employing wideband receivers, the
root-mean-square differences between our values and the corresponding
ones published by the Bureau International de l'Heure are 0.0012 s
and 0.018 arc sec respectively. The average value we obtained for the
radial Love number h for the solid earth is 0.62+/-0.02 (estimated
standard error).
Title: Quasar 4C39.25 is not contracting
Authors: Marcaide, J. M.; Bartel, N.; Gorenstein, M. V.; Shapiro,
I. I.; Corey, B. E.; Rogers, A. E. E.; Webber, J. C.; Clark, T. A.;
Romney, J. D.; Preston, R. A.
Bibcode: 1985Natur.314..424M
Altcode: 1985Nat...314..424M
The milli-arc second radio structure of the quasar 4C39.25 has
previously been described as consisting of two components whose angular
separation remained constant at ~2 marc s, whereas their relative
flux densities varied with time1-3. This behaviour is
in marked contrast to other similar sources whose radio structures
expand superluminally4. Recently, Shaffer5
suggested that 4C39. 25 may have been contracting superluminally in the
period 1979-82. Here, based on our map of this source made from VLBI
observations in 1983 at λ3.6 cm, we conclude that this conjecture is
not correct. We find three distinct components in the structure, two of
which are separated by 2.0 marc s, whereas the third, presumably new
and not previously reported, is situated between the other two. It is
possible either that the third component is stationary and that its
flux density has rapidly increased to render it visible, or that it
has recently been ejected from the westernmost component.
Title: Observations of 63 μm atomic oxygen emission in the earth's
atmosphere from balloon altitudes: astronomical implications.
Authors: Naylor, D. A.; Hoogerdijk, J. M.; Boreiko, R. T.; Clark,
T. A.; Fitton, B.; Kessler, M. F.; Emery, R. J.
Bibcode: 1985InfPh..25..485N
Altcode:
Measurements of 3P1→3P2
63 μm atomic oxygen (O I) emission in the earth's atmosphere
obtained with a balloon-borne telescope and high-resolution
Fourier transform spectrometer are presented. Three results
emerge from analysis of this data: (1) the frequency of the O I
3P1→3P2 transition was
determined to be 158.2693±0.003 cm-1; (2) the integrated
line intensity of the atmospheric O I emission was determined to be
2.4±0.5×10-5Wm-2sr-1; and (3) the
integrated line intensity of the atmospheric O I emission was found to
be constant over a range of zenith angles corresponding to air-mass
values between 1.27 and >20. The implications of these results on
astronomical observations of O I emission are discussed.
Title: The quasars 1038+528 A and B.
Authors: Marcaide, J. M.; Shapiro, I. I.; Corey, B. E.; Cotton, W. D.;
Gorenstein, M. V.; Rogers, A. E. E.; Romney, J. D.; Schild, R. E.;
Baath, L.; Bartel, N.; Cohen, N. L.; Clark, T. A.; Preston, R. A.;
Ratner, M. I.; Whitney, A. R.
Bibcode: 1985A&A...142...71M
Altcode:
The results of VLBI observations of the quasars 1038 + 528 A and B at
2.8, 3.6, 13, and 18 cm at various times between November 1979 and March
1981 are reported. The observations and data calibration are described,
as are the mapping and astrometric techniques applied in the study. Both
quasars are found to have 'core-jet' morphologies. The core of the A
quasar dominates its morphology at centrimetric wavelengths with the
brightness temperature of its 400 pc long jet being about 1/100 that of
the core. By contrast, the 'jet' in the B quasar is very short (about
70 pc); the tail of this jet has the steepest spectral index found to
date in extragalactic compact sources, indicating that high electron
losses are responsible for the shortness of the jet. No evidence for
appreciable morphological change in the B quasar was found over the
time span of the study, whereas a new feature may be emerging from
the A quasar core at superluminal speed.
Title: Downward flux of atmospheric 63-µm emission from atomic
oxygen at balloon altitudes
Authors: Clark, T. A.; Naylor, D. A.; Boreiko, R. T.; Hoogerdijk,
J. M.; Fitton, B.; Kessler, M. F.; Emery, R. J.
Bibcode: 1985Natur.313..206C
Altcode:
The 63-µm emission line from the ground electronic state fine-structure
transition (3P1-3P2) of
atomic oxygen, first suggested as a major source of thermospheric
cooling by Bates1 and subsequently discussed
theoretically2,3, has been measured over a range of
thermospheric altitudes4-6. The rocket measurements showed
that the downward intensity remained essentially constant between 85
and 100 km, as expected for an optically-thick emitting region. As a
result, OI emission is now thought to be less important as a source of
atmospheric cooling than upward radiation from the 5.3 µm band of NO
(ref. 7). Nevertheless, measurements of the intensity distribution
of OI emission in the lower thermosphere should help to discriminate
between theoretical models8 and, in particular, address
the appropriateness of `local thermodynamic equilibrium' at these
altitudes. We report here high spectral resolution measurements of OI
emission at 30 km. The downward OI flux is measured to be (2.4 +/-
0.5) × 10-5 W m-2 sr-1, somewhat
larger than expected on the basis of previous rocket measurements
or theoretical predictions. Furthermore, this value is found to be
independent of zenith angle.
Title: Line strengths and positions of the submillimeter magnetic
dipole transitions of O2.
Authors: Boreiko, R. T.; Smithson, T. L.; Clark, T. A.; Wieser, H.
Bibcode: 1984JQSRT..32..109B
Altcode: 1984JQSRT..32..109S
Strengths and positions of lines between 14 and 160 cm-1
from pure rotational magnetic dipole transitions of the homonuclear
molecule O2 have been measured under carefully controlled
conditions over a range of pressures from 52 to 672 torr in a long-path
cell using a Fourier transform spectrometer. The data show excellent
agreement with the theory of Tinkham and Strandberg over the above
range of measurement. The possible implication of this work to the
calibration of balloon-borne measurements of the cosmologically
significant microwave background is also briefly discussed.
Title: Atmospheric emission in the 20-micron window from Mauna Kea
Authors: Naylor, D. A.; Boreiko, R. T.; Clark, T. A.; Emery, R. J.;
Fitton, B.; Kessler, M. F.
Bibcode: 1984PASP...96..167N
Altcode:
The emission spectrum within the 20-μm window of the atmosphere above
Mauna Kea has been measured to a resolution of 0.01 cm-1
with a Michelson interferometer and compared to a single-layer synthetic
spectrum in order to test the feasibility of observing fine-structure
emission lines from astronomical sources from this site. It is
demonstrated that the observed spectrum can be very closely simulated
by the inclusion of CO2, H2O, and N2O
in the synthetic spectrum, a situation which is presumed to hold for
other high, dry observing sites. The present data indicate that large
telescopes equipped with high-resolution spectrometers can still be
used to advantage in the observation of selected fine-structure lines
against the background emission from these sites, particularly when
careful background subtraction techniques are used.
Title: Transmission of woven scrim polypropylene laminate material
between 2and 500 μm: a low-cost, robust filter for solar FIR studies.
Authors: Clark, T. A.; Kendall, D. J. W.; Boreiko, R. T.
Bibcode: 1983InfPh..23..289C
Altcode:
A polypropylene scrim laminate material, Griffolyn GW24, consisting of
a coarse weave of translucent polypropylene sandwiched between layers
of white and black polypropylene, has been investigated as a filter
for FIR solar studies. This combination has been shown to exhibit good
FIR transmittance while rejecting near i.r. radiation. Filter heating
in solar applications is reduced by the reflection of visible and
near i.r. radiation by the white polypropylene layer. Its physical
properties of durability over a wide temperature range, high tear
resistance and strength and high u.v. tolerance further enhance its
value as a primary filter for the above purpose.
Title: Recent SETI observations at Arecibo
Authors: Tarter, J. C.; Duquet, R. T.; Clark, T. A.; Lesyna, L.
Bibcode: 1983AcAau..10..277T
Altcode:
During 1980 and 1981, the 305-m radio telescope at the Arecibo
Observatory in Puerto Rico was used to conduct a high resolution
search for narrowband signals from the direction of 210 nearby solar
type stars and 5 OH masers. For each star at least 4 MHz of bandwidth
surrounding the 21-cm HI line and/or the 18-cm OH lines was studied
with a spectral resolution of 5.5 Hz in both right and left circular
polarization. The formal limit of sensitivity achieved during the
course of this search varied depending upon the particular receivers
available. In all cases the search could have detected a narrow band
transmitter of power comparable to the Arecibo planetary radar, had
any such been transmitting on the frequencies searched during the time
of observation out to the distance of the farthest target star. As in
previous searches, the number of "false alarms" encountered was far
greater than predicted on the basis of Gaussian noise statistics. A
small number of stars have exhibited signals which cannot immediately
be explained in terms of astrophysical or man-made sources and deserve
re-observation. This is typical of the results of previous non-real-time
searches and does not yet constitute the detection of an ETI.
Title: Airborne Total Eclipse Observation of the Extreme Solar Limb
at 400-MICRON
Authors: Clark, T. A.; Boreiko, R. T.
Bibcode: 1983SoPh...83..187C
Altcode:
No abstract at ADS
Title: Very-Long-Baseline Radio Interferometry: The Mark III System
for Geodesy, Astrometry, and Aperture Synthesis
Authors: Rogers, A. E. E.; Cappallo, R. J.; Hinteregger, H. F.; Levine,
J. I.; Nesman, E. F.; Webber, J. C.; Whitney, A. R.; Clark, T. A.;
Ma, C.; Ryan, J.; Corey, B. E.; Counselman, C. C.; Herring, T. A.;
Shapiro, I. I.; Knight, C. A.; Shaffer, D. B.; Vandenberg, N. R.;
Lacasse, R.; Mauzy, R.; Rayhrer, B.; Schupler, B. R.; Pigg, J. C.
Bibcode: 1983Sci...219...51R
Altcode:
The Mark III very-long-baseline interferometry (VLBI) system allows
recording and later processing of up to 112 megabits per second from
each radio telescope of an interferometer array. For astrometric and
geodetic measurements, signals from two radio-frequency bands (2.2 to
2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at
all antenna sites. From these dual-band recordings the relative group
delays of signals arriving at each pair of sites can be corrected for
the contributions due to the ionosphere. For many radio sources for
which the signals are sufficiently intense, these group delays can be
determined with uncertainties under 50 picoseconds. Relative positions
of widely separated antennas and celestial coordinates of radio sources
have been determined from such measurements with 1 standard deviation
uncertainties of about 5 centimeters and 3 milliseconds of arc,
respectively. Sample results are given for the lengths of baselines
between three antennas in the United States and three in Europe as
well as for the arc lengths between the positions of six extragalactic
radio sources. There is no significant evidence of change in any of
these quantities. For mapping the brightness distribution of such
compact radio sources, signals of a given polarization, or of pairs of
orthogonal polarizations, can be recorded in up to 28 contiguous bands
each nearly 2 megahertz wide. The ability to record large bandwidths
and to link together many large radio telescopes allows detection and
study of compact sources with flux densities under 1 millijansky.
Title: High-resolution observations of atmospheric emission spectra
in the 20-micron window from Mauna Kea: comparison with theoretical
spectra.
Authors: Naylor, D. A.; Boreiko, R. T.; Clark, T. A.; Emery, R.;
Fitton, B.
Bibcode: 1982JRASC..76..323N
Altcode:
No abstract at ADS
Title: Recent SETI observations at Arecibo
Authors: Tarter, J. C.; Duquet, R. T.; Clark, T. A.; Lesyna, L.
Bibcode: 1982pari.iafcQ....T
Altcode:
Preliminary results are presented for a high-resolution search for
narrowband signals from the direction of 210 nearby solar-type stars
and five OH masers. The 305-m Arecibo radio telescope was used to
seek narrowband radio emission at frequencies surrounding the 21-cm H
I line and/or the 18-cm OH lines; the observations were made in right
and left circular polarizations simultaneously. At the 98% level, 291
'birdies' were found, of which six sources at 18 cm and eight at 21
cm are considered potential candidates for reobservation and further
study to identify the nature of the signals. It is noted that: (1)
five of the 21-cm 'birdies' are probably H I clouds along the line of
sight; (2) some of the 18-cm 'birdies' are associated with the extreme
13 frequency bands bordering unprotected bands above and below the
established radio astronomy band; and (3) one of the 21-cm 'birdies'
is distinctly narrowband and has no signal detected in the 'off' source.
Title: Recent SETI Observations at Arecibo
Authors: Tarter, J. C.; Duquet, R. T.; Clark, T. A.; Lesyna, L.
Bibcode: 1982BAAS...14R.885T
Altcode:
No abstract at ADS
Title: Radio interferometric detection of a traveling ionospheric
disturbance excited by the explosion of Mount St. Helens
Authors: Roberts, D. H.; Rogers, A. E. E.; Allen, B. R.; Bennett,
C. L.; Burke, B. F.; Greenfield, P. E.; Lawrence, C. R.; Clark, T. A.
Bibcode: 1982JGR....87.6302R
Altcode:
A large-amplitude traveling ionospheric disturbance (TID) was
detected over Owens Valley, California, on May 18, 1980, by a highly
sensitive very long baseline interferometry (VLBI) radio astronomy
experiment. This TID is interpreted as the response of the ionosphere
to a gravity wave excited in the neutral atmosphere by the explosion
of Mount St. Helens that took place at 1532 UT on that day. A model,
invoking the point-excitation of internal gravity waves in an isothermal
atmosphere, which fits observations of the TID at several other
stations, leads to identification of the features observed in the VLBI
data. Small-amplitude higher-frequency changes in the ionosphere were
detected for several hours after the passage of the large-amplitude
Mount St. Helens TID, but it is not clear whether these were excited
by the passage of the gravity wave or were background fluctuations.
Title: Airborne Total Eclipse Observation of the Extreme Solar Limb
at 400-MICRON
Authors: Clark, T. A.; Boreiko, R. T.
Bibcode: 1982SoPh...76..117C
Altcode:
The total solar eclipse of February 26, 1979 was monitored at far
infrared wavelengths from the NASA Lear Jet Observatory flying
at 12.9 km in the eclipse shadow. The resultant eclipse curve for
radiation within a bandwidth of 20 cm−1 centered upon 25
cm−1 (400 μm) was measured and analysed at an equivalent
angular resolution of 1 arc sec over a 100 arc sec region adjacent
to the limb to provide information on the intensity distribution of
continuum radiation close to this limb. The curve has been compared
to predictions derived from models of the solar atmosphere for the
specific geometry of this eclipse, and is shown to match most closely
that derived from a uniform distribution of radiation across the
disk. This is in distinct contrast to the result obtained in the only
other comparable experiment, carried out over Africa in 1973 from a
supersonic Concorde aircraft, in which an intense but narrow `spike'
of far infrared radiation at the extreme solar limb was inferred
from the data. The absence also in the present observations of the
significant limb brightening predicted by the HSRA model (in which
homogeneity within the source region is assumed) is in substantial
agreement with lower resolution results from mountain altitudes. This
result is interpreted as further evidence for the presence in the
Sun's lower chromosphere of significant inhomogeneity with a scale
size of at least 1000 km at this depth.
Title: Rothney Astrophysical Observatory, The University of Calgary,
Alberta, T2N 1N4, Canada. Report.
Authors: Milone, E. F.; Clark, T. A.
Bibcode: 1982BAAS...14..467M
Altcode:
No abstract at ADS
Title: Optical Observations of the Primary Minimum of the Solar-Type
Binary AI Phe with the IUE Satellite
Authors: Milone, E. F.; Hrivnak, B. J.; Clark, T. A.; Kjeldseth Moe,
O.; Blades, J. C.; Shelton, I.
Bibcode: 1981IBVS.2060....1M
Altcode:
No abstract at ADS
Title: Determination of stratospheric H2O and O3
column densities from balloon altitude far infrared absorption
spectra by a curve of growth method.
Authors: Naylor, D. A.; Clark, T. A.; Boreiko, R. T.
Bibcode: 1981InfPh..21..271N
Altcode:
Pure rotational lines of H 2O, Q branches of O 3
and single lines of O 3 in the far infrared absorption
spectrum of the stratosphere, taken at an altitude of 29.1 km above
Texas on 19 June, 1978 from a balloon-borne solar telescope equipped
with a rapid-scanning Michelson interferometer, have been analyzed by a
curve-of-growth method to yield good values of vertical column densities
for these important minor constituents. In this mid-latitude atmosphere,
vertical column densities of H 2O and O 3
were found to be 1.32(±0.39) × 10 18 and 1.72(±0.55)
× 10 18 molecules cm -2, respectively, the
major contribution to the uncertainty coming from a correction to
the overall spectral envelope necessitated by detector nonlinearity
in this specific flight. The present data demonstrate the promise of
this technique for the measurement of number density profiles of other
important minor constituents, such as HCl, H 2O 2,
NO 2, HO 2 which are expected to contribute to
this spectrum in the stratosphere.
Title: Detection of minor constitutents of the stratosphere by far
infrared emission spectroscopy
Authors: Kendall, D. J. W.; Clark, T. A.
Bibcode: 1981IJIMW...2..783K
Altcode:
The far infrared (30 110 cm-1) emission spectrum of the
lower stratosphere has been measured from balloon altitudes with
a high resolution (0.06 cm-1) rapid-scanning Michelson
interferometer on two flights in 1976. The quality and resolution
of the spectra obtained from two altitudes have permitted a careful
search for emission lines from environmentally important molecules
such as HCl, NO2, OH, H2O2, and CO,
among the more prominent and well-known features due to H2O,
O3 and O2. Column densities have been determined
for H2O and O3 and upper limit estimates
have been made from tentative identifications of several other
constituents. However, the large angular field of view observed by the
instrument prevented the determination of concentration profiles from
atmospheric limb scans to the horizon. The possible future directions
of this technique are outlined on the basis of operating experience
over a 6 year programme. The viability of this method of monitoring the
concentrations of minor constituents in the stratosphere is discussed
with respect to other equivalent techniques.
Title: Observation of the extreme solar limb at 3.9 microns during
the partial solar eclipse of 10 July, 1972
Authors: Clark, T. A.; Clay, R. W.
Bibcode: 1981A&A...100..254C
Altcode:
A simple spatially-chopping near-infrared photometer was used to
monitor the 4th contact of the partial solar eclipse of July 10,
1972 at 3.9 microns. The eclipse curve agrees with that derived from
the data of Lena (1970) and Johnson (1971) to mu = cos theta = 0.15,
but departs rapidly from their curves, showing extreme limb darkening
to mu = 0.10. The results also show tentative evidence for an enhanced
peak of near infrared energy within 4 arcsec of the limb, the reality
of which is discussed with respect to other such observations.
Title: Infrared variability and spectrum of SS 433.
Authors: Clark, T. A.; Milone, E. F.
Bibcode: 1981PASP...93..338C
Altcode:
Infrared monitoring of SS 433 from April 13, 1979 UT to April 17,
1979 UT inclusive at J, H, K, and L wavelengths demonstrated the
variability of this source over time scales of days with tentative
evidence of much shorter period fluctuations. These limited data show
a substantially different pattern of variation to that expected from
the inferred light curve of Giles et al. (1980), casting doubt upon the
validity of this light curve as a representation of infrared variations,
at least over the above time period. Color-index changes appear to be
related to J intensity, the source becoming redder as the intensity
decreases. The spectrum when corrected for interstellar reddening fits
reasonably well to a blackbody curve, with a significant excess at L
(3.5 microns) possibly indicating the existence of thermal emission
from circumstellar material at a temperature below 1000 K.
Title: An Optical Analogue of the Gravitational Lens - a Classroom
Demonstration of the Twin Quasar Phenomenon
Authors: Clark, T. A.
Bibcode: 1981JRASC..75..109C
Altcode:
No abstract at ADS
Title: Balloon-borne stratospheric far-IR spectral absorption
measurements: the design of a solar telescope and high-resolution
Michelson interferometer combination.
Authors: Naylor, D. A.; Clark, T. A.; Boreiko, R. T.
Bibcode: 1981ApOpt..20.1132N
Altcode:
The design, construction, and performance of a combined solar
telescope and Michelson interferometer for balloon-borne stratospheric
far-IR absorption studies are discussed in terms of the relevant
parameters and precautions necessary to obtain high resolution
radiometrically calibrated spectra of the stratosphere between 20
and 100 kaysers. Preliminary data are presented to indicate that the
system performed as designed and provided constituent concentration
values for H2O and O3 from measurements of strong absorption lines in
this spectrum.
Title: Mark III VLBI: Astrometry and Epoch J2000.0
Authors: Ma, C.; Clark, T. A.; Shaffer, D. B.
Bibcode: 1981BAAS...13..899M
Altcode:
No abstract at ADS
Title: Mark III VLBI: UT1, Polar Motion, and Baselines
Authors: Clark, T. A.; Ryan, J. W.; Shaffer, D. B.
Bibcode: 1981BAAS...13..899C
Altcode:
No abstract at ADS
Title: Geodesy by radio interferometry: intercontinental distance
determinations with subdecimeter precision
Authors: Herring, T. A.; Corey, B. E.; Counselman, C. C., III; Shapiro,
I. I.; Ronnang, B. O.; Rydbeck, O. E. H.; Clark, T. A.; Coates, R. J.;
Ma, C.; Ryan, J. W.
Bibcode: 1981JGR....86.1647H
Altcode:
Analysis of very-long-baseline interferometer (VLBI) observations
yielded estimates of the distances between three radio telescopes in
the United States and one in Sweden, with formal standard errors
of a few centimeters: Westford, Massachusetts-Onsala, Sweden:
5,599,712.66+/-0.03m Green Bank, West Virginia-Onsala, Sweden:
6,319,317.75+/-0.03m and Owens Valley, California-Onsala, Sweden:
7,914,131.19+/-0.04m, where the earth-fixed reference points are defined
in each case with respect to the axes of the telescopes. The actual
standard errors are difficult to estimate reliably but are probably
not greater than twice the formal errors.
Title: Infrared Observations of the Solar Atmosphere
Authors: Clark, T. A.
Bibcode: 1981BAAS...13..560C
Altcode:
No abstract at ADS
Title: Mark III VLBI: from 'Light Bulb' to Ap.J. or J. G. R.
Authors: Vandenberg, N. R.; Shaffer, D. B.; Clark, T. A.
Bibcode: 1981BAAS...13..899V
Altcode:
No abstract at ADS
Title: Detection of the 18 May 1980 Explosion of Mt. St. Helens by
Very Long Baseline Interferometry
Authors: Roberts, D. H.; Rogers, A. E. E.; Allen, B. R.; Bennett,
C. L.; Burke, B. F.; Clark, T. A.
Bibcode: 1980BAAS...12..814R
Altcode:
No abstract at ADS
Title: Airborne Infrared Observations of the Annular Solar Eclipse
of August 10th 1980
Authors: Clark, T. A.; Boreiko, R. T.
Bibcode: 1980BAAS...12..817C
Altcode:
No abstract at ADS
Title: Line positions and strengths of magnetic dipole transitions
of molecular oxygen from stratospheric emission spectra.
Authors: Clark, T. A.; Kendall, D. J. W.
Bibcode: 1980JQSRT..24...65C
Altcode:
Submillimeter emission spectra of the low stratosphere (24.5 km)
between 30 and 110 kaysers have been used to determine line positions
and strengths for many of the lines originating in magnetic dipole
transitions of the homonuclear molecule O2. Observed line positions are
shown to be in excellent agreement with recently derived theoretical
values. Line strengths for these lines are found to be significantly
higher than values calculated on the basis of recent theoretical work
and, for those lines for which a comparison is possible, higher than
previously obtained laboratory determinations. This general feature
of the present data is vital not only for the establishment of basic
molecular parameters for O2, but also for the application of recent
methods for H2O and O2 stratospheric concentration determination in
which O2 lines are used as an internal calibration of the balloon-borne
instrumentation.
Title: Submillimeter airborne observations of the total solar eclipse
of February 26th, 1979.
Authors: Clark, T. A.; Boreiko, R. T.
Bibcode: 1980BAAS...12..750C
Altcode:
No abstract at ADS
Title: Time-dependent radio fine structure of the compact sources
NRAO 150 and 4C 39.25.
Authors: Baath, L. B.; Cotton, W. D.; Counselman, C. C.; Shapiro,
I. I.; Wittels, J. J.; Hinteregger, H. F.; Knight, C. A.; Rogers,
E. E.; Whitney, A. R.; Clark, T. A.; Hutton, L. K.; Niell, A. E.
Bibcode: 1980A&A....86..364B
Altcode: 1980AJ.....86..364B
Very long baseline interferometer observations at 7.85 GHz have been
used to probe the milliarcsecond structure of the unidentified, very
compact radio source NRAO 150 and QSO 4 C 39.25. NRAO 150 exhibited
no structural variations from 1972 to the end of 1974. A model with
two circular Gaussian components fits the data well. NRAO 150 had a
flux density of 7.6 plus or minus 0.5 Jy in the compact component;
4 C 39.25 showed a two-component structure, the components having
a separation of (2.02 plus or minus 0.05 arc sec) x 10 to the -3rd
power. The upper bound on the speed of transverse separation is 0.0001
arc sec per year or less than 2.7 c. From the spectrum there are also
indications of a third, larger component.
Title: The very flat radio spectrum of 0735 plus 178 - A cosmic
conspiracy
Authors: Cotton, W. D.; Wittels, J. J.; Shapiro, I. I.; Marcaide,
J.; Owen, F. N.; Spangler, S. R.; Rius, A.; Angulo, C.; Clark, T. A.;
Knight, C. A.
Bibcode: 1980ApJ...238L.123C
Altcode:
Multifrequency interferometric and total flux density measurements of
the radiation from 0735 plus 178 are discussed. It is shown that it
is far more likely that the very flat radio spectrum of this source
results from a superposition of incoherent synchrotron radiation from
four distinct, homogeneous components, each with a peaked spectrum,
than from radiation from a single inhomogeneous component.
Title: Infrared Excesses in Close Binaries
Authors: Milone, E. F.; Clark, T. A.
Bibcode: 1980BAAS...12..437M
Altcode:
No abstract at ADS
Title: Automation of the Mark-Iii Field System
Authors: Vandenberg, N. R.; Clark, T. A.; Foster, L. N.; Whitney,
A. R.; Lampe, G.
Bibcode: 1980ritg.conf..291V
Altcode:
No abstract at ADS
Title: Radio Source Positions and Astronomical Constants
Authors: Clark, T. A.
Bibcode: 1980ritg.conf..163C
Altcode:
No abstract at ADS
Title: Polar Motion and UT1 - Comparison of VLBI Lunar Laser Satellite
Laser Satellite Doppler and Conventional Astrometric Determinations
Authors: Robertson, D. S.; Clark, T. A.; Coates, R. J.; Ma, C.; Ryan,
J. W.; Corey, B. E.; Counselman, C. C.; King, R. W.; Shapiro, I. I.;
Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.; Whitney, A. R.;
Pigg, J. C.; Schupler, B. R.
Bibcode: 1980ritg.conf...33R
Altcode:
No abstract at ADS
Title: Mark-Iii System Overview
Authors: Clark, T. A.
Bibcode: 1980ritg.conf..285C
Altcode:
No abstract at ADS
Title: Submilliarcsecond astrometry via VLBI. I. Relative position
of the radio sources 3C 345 and NRAO 512.
Authors: Shapiro, I. I.; Wittels, J. J.; Counselman, C. C., III;
Robertson, D. S.; Whitney, A. R.; Hinteregger, H. F.; Knight, C. A.;
Rogers, A. E. E.; Clark, T. A.; Hutton, L. K.; Niell, A. E.
Bibcode: 1979AJ.....84.1459S
Altcode:
The relative position and relative proper motion of the radio sources
3C 345 and NRAO 512 are estimated from four sets of VLBI observations
spread out over the period from October 1971 to May 1974. The use
of phase-connection techniques yields the separation, in 1950.0
coordinates, of the centers of brightness of the compact components
of the two sources. An upper bound of 0.0005 arcsec/yr is placed on
the relative proper motion (70% estimated confidence limits). Bounds
that can be placed on the distances to the two sources are considered,
prospects for improvement in the determination of relative position
and proper motion of these sources are discussed, and other possible
applications of the basic technique are described.
Title: Geodetic interferometry submission for the IUGG (International
Union of Geodesy and Geophysics) quadrennial report. Reviews of
geophysics and space physics.
Authors: Clark, T. A.
Bibcode: 1979RvGSP..17.1430C
Altcode: 1979RvGeo..17.1430C
The present paper reviews the activities of two major VLBI (Very Long
Baseline Interferometry) groups, within the United States, which have
been concentrating on geodetic measurements for a number of years. The
activities have resulted in the development of transportable VLBI
terminals for regional surveying applications; development of VLBI
techniques for obtaining station positions; establishment of relative
epochs and rates of the hydrogen maser clocks at the stations; the
acquisition of polar motion and earth rotation data in support of
deep space tracking functions; and the development of VLBI techniques
necessary for tectonic measurements on trans- and intercontinental
baselines and for astrometry, polar-motion and earth-rotation
observations.
Title: Synchronization of clocks by very-long-baseline interferometry
Authors: Clark, T. A.; Ryan, J. W.; Counselman, C. C., III; Ford,
P. G.; Hanson, L. B.; Hinteregger, H. F.; Knight, C. A.; Rogers,
A. E. E.; Klepczynski, W. J.; Robertson, D. S.
Bibcode: 1979ITIM...28..184C
Altcode:
Two hydrogen-maser clocks, one at Haystack Observatory and one at
the National Radio Astronomy Observatory, were synchronized by means
of observations of several extragalactic radio sources on March 28,
and again on September 23, 1977. Observations were made sequentially
in eight 360-kHz bands distributed between about 8.4 and 8.5 GHz
with spacings designed to enable the group-delay difference between
the signals received at the two observatories from a given source to
be estimated unambiguously, within an uncertainty of less than 1 ns
set by receiver noise. The epoch and the rate differences between the
observatories' clocks for each experiment were estimated by analysis of
observations that spanned several hours. The application of corrections
for the contributions to the delays of the antennas, feeds, receiver
systems, and recorders yielded absolute determinations of the clock
epoch differences. During each experiment, portable cesium clocks
were flown from the U.S. Naval Observatory to the observatories and
back. The traveling-clock data, analyzed in each case after the VLBI
synchronization had been completed, confirmed the VLBI results to
within 18 and 14 ns for the first and second experiments, respectively.
Title: The pure rotational atmospheric lines of hydroxyl.
Authors: Kendall, D. J. W.; Clark, T. A.
Bibcode: 1979JQSRT..21..511K
Altcode:
No abstract at ADS
Title: 3C 279: the case for "superluminal" expansion.
Authors: Cotton, W. D.; Counselman, C. C., III; Geller, R. B.;
Shapiro, I. I.; Wittels, J. J.; Hinteregger, H. F.; Knight, C. A.;
Rogers, A. E. E.; Whitney, A. R.; Clark, T. A.
Bibcode: 1979ApJ...229L.115C
Altcode:
The compact extragalactic radio source 3C 279 was observed with the
Haystack-Goldstone interferometer (wavelength approximately 3.8 cm)
during six separate sessions spread between October 1970 and April
1972. The fringe amplitudes from each of these observation sessions were
consistent with a two-component model of the brightness distribution
of the source. The position angle of the line joining the components
remained at 38 + or - 2 deg, while the angular separation between
the components increased nearly linearly at the rate of 0.5 + or 0.1
milliarcsec/yr during this period. The corresponding apparent expansion
speed is (21 + or - 4)c, for H = 50 km/s per Mpc and q = 0.05
Title: SS 433
Authors: Gottlieb, E. W.; Liller, W.; Milone, E. F.; Clark, T. A.
Bibcode: 1979IAUC.3354....1G
Altcode:
E. W. Gottlieb and W. Liller, Center for Astrophysics, report that
the blue magnitudes of SS 433, as derived from plates in the Harvard
archival collection, show a significant tendency to be cyclic with a
period of 161.7 +/- 0.3 days. Prior to 1929 there was little indication
of periodicity; instead the star stayed near its minimum brightness
at B = 17.5 +/- 0.3 with occasional flares to B < 17.0. Since 1929
the lightcurve cycle has repeated with a spread of +/- 0.3 magnitude
with only three of 39 points falling more than 0.5 magnitude below the
mean lightcurve. This preliminary value of the period agrees well with
the 160 +/- 3 days over which spectral-line motions recur (Margon et
al., IAUC 3345). E. F. Milone, University of Calgary, reports that
JHKL observations of SS 433 carried out with the 150-cm Mt. Lemmon
infrared telescope by T. A. Clark and himself indicate variability
on a timescale of days. Compared to theta Lyr and BD +34 4213, SS 433
dimmed by average values of 0.23, 0.21, 0.12 and 0.07 magnitude in J,
H, K and L, respectively, on Apr. 15.5 UT with respect to the situation
on the adjacent nights of Apr. 14 and 17. There is further a suggestion
of smaller variations over a shorter timescale, and the object's J-L
color index is more than 1.2 magnitudes greater than that of theta Lyr.
Title: Balloon-borne far-infrared Michelson interferometer for
atmospheric emission studies
Authors: Kendall, D. J. W.; Clark, T. A.
Bibcode: 1979ApOpt..18..346K
Altcode:
A series of far-IR Michelson interferometers utilizing the
rapid-scanning technique have been designed and built for balloon-borne
measurement of the emission spectrum of the stratosphere. Design
criteria for such instrumentation are presented, and details of the
evolution of these designs are discussed, including liquid helium-cooled
bolometer detector systems, internal blackbody calibration, and
atmospheric limb-scanning. Stratospheric emission spectra between 30
kaysers and 110 kaysers at a resolution of 0.07 kayser are presented
as examples of results taken at balloon altitudes, and the merits of
this type of instrumentation for monitoring stratospheric trace gas
constituent concentrations are discussed.
Title: Recent Results of Radio Interferometric Determinations of a
Transcontinental Baseline, Polar Motion, and Earth Rotation
Authors: Robertson, D. S.; Carter, W. E.; Corey, B. E.; Cotton, W. D.;
Counselman, C. C.; Shapiro, I. I.; Wittels, J. J.; Hinteregger, H. F.;
Knight, C. A.; Rogers, A. E. E.; Whitney, A. R.; Ryan, J. W.; Clark,
T. A.; Coates, R. J.; Ma, C.; Moran, J. M.
Bibcode: 1979IAUS...82..217R
Altcode:
Results are discussed for radio interferometric observations of
extragalactic radio sources with antennas at Haystack Observatory in
Massachusetts and the Owens Valley Radio Observatory in California
(3900-km baseline) during 14 separate experiments distributed between
September 1976 and May 1978. Simultaneous analysis of the data from
several experiments yields estimates of changes in the x component
of pole position and in earth's rotation (UT1). Comparison with the
corresponding results obtained by the Bureau International de l'Heure
(BIH) reveals systematic differences. In particular, the trends in the
radio interferometric determinations of the changes in pole position
are found to agree more closely with those from the International Polar
Motion Service and from Doppler observations of satellites than with
those from the BIH.
Title: University of Calgary, Rothney Astrophysical Observatory,
Calgary, Alberta, Canada. Report.
Authors: Clark, T. A.; Milone, E. F.
Bibcode: 1979BAAS...11...32C
Altcode:
No abstract at ADS
Title: The Mark III VLBI System
Authors: Vandenberg, N. R.; Clark, T. A.; Foster, L. N.; Ma, C.; Ryan,
J. W.; Hinteregger, H. R.; Knight, C. A.; Nesman, E. F.; Rogers,
A. E. E.; Whiteney, A. R.; Rayhrer, B.; Lacasse, R.; Robertson,
D. S.; Pigg, J. C.; Schupler, B. R.; Corey Pigg, B. E.; Schupler,
B. R.; Corey, B. E.
Bibcode: 1978BAAS...10..640V
Altcode:
No abstract at ADS
Title: A high declination search at 8 GHz for compact radio sources.
Authors: Wittels, J. J.; Shapiro, I. I.; Robertson, D. S.; Counselman,
C. C.; Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.; Whitney,
A. R.; Clark, T. A.; Hutton, L. K.; Ma, C.; Niell, A. E.; Resch,
G. M.; Rönnäng, B. O.; Rydbeck, O. E. H.
Bibcode: 1978AJ.....83..560W
Altcode:
With the Haystack-NRAO interferometer (baseline length of 20 million
wavelengths at 3.8 cm) 37 sources were observed whose declinations
were above 50 deg. Seven of these sources have compact cores with
diameters smaller than 5 milliarcsec and with correlated flux
densities greater than about 0.5 Jy; the remaining sources have no
cores with flux densities above about 0.3 Jy, the sensitivity limit
of the interferometer. Two of the sources with detected compact
cores, 4C 67.05 and 3C 418, were also observed with longer-baseline
interferometers; the diameter of the core of 4C 67.05 was estimated
to be smaller than 1 milliarcsec and that of 3C 418 to be smaller
than 0.4 milliarcsec. All diameter estimates were based on an assumed
circular Gaussian distribution of radio brightness and refer to the
contour with brightness density e to the -1/2 power times that of the
center. Positions for the detected sources were also obtained from the
interferometric data, the uncertainty in these coordinate estimates
ranging from 0.04 to 0.6 arcsec. The compact core detected in 3C 390.3
was found to lie near the center of this extended (approximately 4
arcmin in diameter) double radio source and to be coincident to within
1 arcsec with an N galaxy previously identified with 3C 390.3.
Title: Geodesy by radio interferometry: Determination of a 1.24-km
base line vector with ~5-mm repeatability
Authors: Rogers, A. E. E.; Knight, C. A.; Hinteregger, H. F.; Whitney,
A. R.; Counselman, C. C.; Shapiro, I. I.; Gourevitch, S. A.; Clark,
T. A.
Bibcode: 1978JGR....83..325R
Altcode:
The 1.24-km base line vector between the two antennas of the
Haystack Observatory was determined from X band radio interferometric
observations of extragalactic sources via a new method that utilizes
the precision inherent in fringe phase measurements. This method
was employed in 11 separate experiments distributed between October
1974 and January 1976, each being between about 5 and 20 hours in
duration. The rms scatters about the means for the veritcal and the two
horizontal components of the base line obtained from the 11 independent
determinations were 7.5, and 3 mm, respectively. The corresponding
scatter for the base line length was 3 mm; the mean differed from
the result obtained in a conventional survey by 8 mm, well within the
20-mm uncertainty of the survey. (The determination of the direction
from the survey was too crude to be useful.) Another external check
on our data was possible, since the azimuth and elevation axes of
one of the antennas do not intersect but are separated by 318 mm. We
estimated this horizontal offset from the radio interferometry data
and found a difference of 10+/-9 mm from the directly measured value,
the relatively large rms scatter being due to the ~0.96 correlation
between the estimate of this offset and that of the vertical component
of the base lines. Use of a newly completed calibration system in future
experiments should allow the scatter to be reduced to the millimeter
level in all coordinates for short base lines. For long base lines,
such repeatability should be degraded only to about the centimeter
level if calibrated observations with sufficient sensitivity are made
simultaneously at two frequency bands. An assessment of the accuracy of
either our present or future base line results awaits the availability
of an accepted, more accurate, standard for comparison. Nonetheless,
base line changes can be determined reliably at any established level
of repeatability.
Title: Mylar beam-splitter efficiency in far infrared interferometers:
angle of incidence and absorption effects
Authors: Naylor, D. A.; Boreiko, R. T.; Clark, T. A.
Bibcode: 1978ApOpt..17.1055N
Altcode:
Absorption and complete multipath interference have been included in
the calculation of the modulation efficiency of a far IR Michelson
interferometer with 25-micron and 100-micron Mylar beam splitters over
the range of wavenumbers between 20 cm to the -1 and 125 cm to the -1
for angles of incidence between 45 deg and 80 deg. These results show
that optimum performance of an interferometer in terms of highest and
most uniform modulation efficiency for unpolarized radiation will
be obtained by selecting the beam-splitter thickness to cover the
wave-number range of interest within the first interference lobe and by
utilizing higher angles of incidence than the mechanically convenient
45 deg. Practical constraints will usually limit this angle to a value
somewhat less than the optimum of about 75 deg for Mylar beam splitters.
Title: VLBI observations of 3C 345 and NRAO 512 in right and left
circular polarization.
Authors: Menyuk, C. R.; Shapiro, I. I.; Wittels, J. J.; Hinteregger,
H. F.; Knight, C. A.; Rogers, A. E. E.; Whitney, A. R.; Clark, T. A.;
Hutton, L. K.
Bibcode: 1978ApJ...220L..27M
Altcode:
In October 1975, the radio telescopes of the Haystack, National
Radio Astronomy, and Owens Valley Radio Observatories were used as
an interferometer to monitor, at 8 GHz, the right and left circularly
polarized radiation emitted by the quasars 3C 345 and NRAO 512. The data
for each polarization are used separately to estimate several parameters
describing a model of the fine structure of the radio brightness of 3C
345 and, subsequently, the angular separation between 3C 345 and NRAO
512. The results for the two polarizations are in approximate agreement,
indicating that to the limit of resolution about 0.5 milliarcsec), the
fourth Stokes parameter, V, is not significantly different from zero
within the compact components of these radio sources. The corresponding
quantitative limits on the degree of circular polarization are 0.08 +
or - 0.07 for 3C 345 and 0.01 + or - 0.08 for NRAO 512.
Title: The infrared light curve of RW Comae Berenices.
Authors: Milone, E. F.; Clark, T. A.; Naylor, D. A.; Robb, R. M.
Bibcode: 1978JRASC..72Q.285M
Altcode:
No abstract at ADS
Title: Balloon-borne far-infrared atmospheric emission studies.
Authors: Kendall, D. J. W.; Clark, T. A.
Bibcode: 1978InfPh..18..803K
Altcode:
Stratospheric far-infrared emission spectra have been obtained at an
altitude of 32.6 km between 30 and 110 cm -1 and are compared
in detail with a single-layer synthetic spectrum. Excellent agreement
is obtained for strong H 2O and O 3 lines and
magnetic dipole lines of O 2, several of which are resolved
for the first time. Weak lines of ozone dominate most of this spectral
region at this altitude and make identification of lines from other
constituents difficult, although emissions are tentatively identified
from Q-branches of NO 2, from lines of CO and from OH, the
origin of which is most probably the mesosphere. Concentration values
are obtained for H 2O and O 3 which are consistent
with those obtained from other techniques on the same balloon flight.
Title: VLBI clock synchronization.
Authors: Counselman, C. C., III; Shapiro, I. I.; Rogers, A. E. E.;
Hinteregger, H. F.; Knight, C. A.; Whitney, A. R.; Clark, T. A.
Bibcode: 1977IEEEP..65.1622C
Altcode:
The potential accuracy of VLBI (very long baseline interferometry)
for clock epoch and rate comparisons was demonstrated by results
from long- and short-baseline experiments. It was found that atomic
clocks at widely separated sites (several thousand kilometers apart)
can be synchronized to within several nanoseconds from a few minutes
of VLBI observations and to within one nanosecond from several hours
of observations.
Title: Periodic fluctuations in continuum near-IR solar intensity
and CO absorption.
Authors: Clark, T. A.; Burrell, D. A.
Bibcode: 1977JRASC..71..403C
Altcode:
No abstract at ADS
Title: Searching for extraterrestrial intelligence: the ultimate
exploration.
Authors: Black, D.; Tarter, J.; Cuzzi, J. N.; Conners, M.; Clark, T. A.
Bibcode: 1977Mercu...6....3B
Altcode:
A survey highlighting the central issues of the SETI program
(Search for Extraterrestrial Intelligence), including its rationale,
scope, search problems, and goals is presented. Electromagnetic
radiation is suggested as the most likely means via which knowledge
of extraterrestrial intelligence will be obtained, and the variables
governing these signals are discussed, including: signal frequency and
polarization, state, possible coordinates, and signal duration. The
modern history of SETI and NASA's involvement is briefly reviewed,
and the search strategies used by the Jet Propulsion Laboratory and the
Ames Research Center are discussed and compared. Some of the potential
scientific and cultural impacts of the SETI program are mentioned,
noting advancements in technological, biological, and chemical research.
Title: SETI - A preliminary search for narrowband signals at microwave
frequencies
Authors: Cuzzi, J. N.; Clark, T. A.; Tarter, J. C.; Black, D. C.
Bibcode: 1977cosp.meetQ....C
Altcode:
In the search for intelligent signals of extraterrestrial
origin, certain forms of signals merit immediate and special
attention. Extremely narrowband signals of spectral width similar
to our own television transmissions are most favored energetically
and least likely to be confused with natural celestial emission. A
search of selected stars has been initiated using observational
and data processing techniques optimized for the detection of such
signals. These techniques allow simultaneous observation of 10
to the 5th to 10 to the 6th channels within the observed spectral
range. About two hundred nearby (within 80 LY) solar type stars have
been observed at frequencies near the main microwave transitions of
the hydroxyl radical. In addition, several molecular (hydroxyl) masers
and other non-thermal sources have been observed in this way in order
to uncover any possible fine spectral structure of natural origin and
to investigate the potential of such an instrument for radioastronomy.
Title: Universal Time: Lunar Ranging Results and Comparisons with
VLBI and Classical Techniques
Authors: King, R. W.; Clark, T. A.; Counselman, C. C., III; Robertson,
D. S.; Shapiro, I. I.; Knight, C. A.
Bibcode: 1977ASSL...62..219K
Altcode: 1977sall.conf..219K
No abstract at ADS
Title: Time-dependent radio fine structure of the quasar 3C 345.
Authors: Wittels, J. J.; Shapiro, I. I.; Cotton, W. D.; Counselman,
C. C.; Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.; Whitney,
A. R.; Clark, T. A.; Hutton, L. K.; Niell, A. E.; Ronnang, B. O.;
Rydbeck, O. E. H.
Bibcode: 1976AJ.....81..933W
Altcode:
Results are reported for VLBI observations of 3C 345 at a wavelength
of 3.8 cm with left circular polarization. Sixteen sets of correlated
flux densities and three sets of closure phases were obtained from
observations made over a three-year period with six independent
interferometers formed from up to four antennas. The mathematical
models employed to represent the radio brightness distribution of
the source are described, and the data are analyzed on the basis of
a two-component model. The results show that the compact source in 3C
345 consists of two components whose separation increased by about 0.3
milliarcsec over the observational period, that the smaller and weaker
component is to the east and south of the larger and stronger one, and
that the apparent expansion velocity would be about 2.5c for a redshift
of 0.6, a Hubble constant of 60 km/sec per Mpc, and a deceleration
parameter of unity. It is concluded that these findings are difficult
to reconcile with the 'Christmas tree' model for the apparent change
of separation with time over any given series of observations.
Title: A 10 Micron Superheterodyne Receiver For Spectral Line
Observations.
Authors: Abbas, M. M.; Brown, L. W.; Buhl, D.; Clark, T. A.; Hillman,
J.; Kostiuk, T.; Kunde, V.; Mumma, M. J.
Bibcode: 1976BAAS....8..508A
Altcode:
No abstract at ADS
Title: Universal time: lunar ranging results and comparisons with
VLBI and classical techniques.
Authors: King, R. W.; Clark, T. A.; Knight, C. A.; Counselman, C. C.,
III; Robertson, D. S.; Shapiro, I. I.
Bibcode: 1976BGeod..50..261K
Altcode:
No abstract at ADS
Title: Near Infra-Red Observations of "Five-Minute" Oscillations in
the Quiet Solar Atmosphere.
Authors: Clark, T. A.; Burrell, D. A.
Bibcode: 1976BAAS....8..525C
Altcode:
No abstract at ADS
Title: Radio source positions from very-long-baseline interferometry
observations.
Authors: Clark, T. A.; Hutton, L. K.; Marandino, G. E.; Counselman,
C. C.; Robertson, D. S.; Shapiro, I. I.; Wittels, J. J.; Hinteregger,
H. F.; Knight, C. A.; Rogers, A. E. E.; Whitney, A. R.; Niell, A. E.;
Ronnang, B. O.; Rydbeck, O. E. H.
Bibcode: 1976AJ.....81..599C
Altcode:
Accurate positions of compact radio sources have been determined
from very-long-baseline interferometry (VLBI) observations based
on the bandwidth-synthesis technique. The coordinates for 18
extragalactic sources were obtained from sets of observations spread
over the period from April 1972 to January 1975; the scatter among
the independent determinations of the source coordinates from the
separate sets of observations is about 0.05 arcsec, except for the
declinations of near-equatorial sources, where the scatter is about
0.15 arcsec. Comparison of these positions with those determined with
the Cambridge 5-km radio interferometer shows the rms scatter about
the mean difference to be about 0.04 arcsec in each coordinate (no
sources of low declination were in common). A similar comparison of the
present results with those obtained by the Jet Propulsion Laboratory
from separate VLBI observations yields a slightly larger rms scatter,
after exlusion of the declinations of the near-equatorial sources. A
position is also obtained for the galactic object Beta Persei (Algol),
which agrees well with the position given in the FK 4 catalogue.
Title: Meter-wavelength VLBI. III. Pulsars.
Authors: Vandenberg, N. R.; Clark, T. A.; Erickson, W. C.; Resch,
G. M.; Broderick, J. J.
Bibcode: 1976ApJ...207..937V
Altcode:
Observations of pulsars, especially the Crab Nebula pulsar, made in very
long baseline interferometry (VLBI) experiments are discussed. Based
on a crude 144 MHz visibility curve which is consistent with a Gaussian
brightness distribution, the measured visibilities at 196, 111, and 74
MHz were interpreted to yield apparent angular diameters (at half-power)
of about 0.03 sec, 0.07 sec, and 0.18 sec, respectively. These
sizes scale approximately as wavelength-squared, and the 74 MHz size
agrees with recent observations using interplanetary scintillation
techniques. The total flux densities lie on the extrapolation from
higher frequencies of the pulsing flux densities. Variations in the
total flux density up to 25 per cent were observed. A lack of fine
structure other than the pulsar in the nebula is indicated by the
simple visibility curves. The pulse shapes are similar to single-dish
measurements at 196 MHz but reveal a steady, nonpulsing component at
111 MHz. The ratio of pulsing to total power was approximately equal
to one-half but varied with time. It was found that four strong,
low-dispersion pulsars were only slightly resolved.
Title: Apparent "superrelativistic" expansion of the extragalactic
radio source 3C 345.
Authors: Wittels, J. J.; Cotton, W. D.; Counselman, C. C., III;
Shapiro, I. I.; Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.;
Whitney, A. R.; Clark, T. A.; Hutton, L. K.; Rönnäng, B. O.; Rydbeck,
O. E. H.; Niell, A. E.
Bibcode: 1976ApJ...206L..75W
Altcode:
The compact extragalactic radio source 3C 345 was observed by
very-long-baseline interferometry (wavelength about 3.8 cm) at 12
epochs distributed over the nearly four-year period from February 1971
to October 1974. For one of these epochs, the multibaseline data were
sufficient to allow the brightness distribution to be estimated in
a model-independent manner; the resultant distribution was clearly
dominated by two components. The remaining sets of data were also
represented adequately by two-component models. The angular separation
of the two components increased during this period from about 1.00
to 1.30 milliarcsec, corresponding to an apparent average speed of
expansion of approximately 2.5 c at a fixed position angle of 105
(plus or minus 5) deg. These results, coupled with the fact that
contraction has never been observed, seem difficult to reconcile
with the so-called Christmas-tree model of the 'superrelativistic'
expansion of extragalactic radio sources.
Title: An unusual strong radio outburst in Algol: VLBI observations.
Authors: Clark, T. A.; Hutton, L. K.; Ma, C.; Shapiro, I. I.; Wittels,
J. J.; Robertson, D. S.; Hinteregger, H. F.; Knight, C. A.; Rogers,
A. E. E.; Whitney, A. R., Niell, A. E.; Resch, G. M.; Webster,
W. J., Jr.
Bibcode: 1976ApJ...206L.107C
Altcode:
For 8 hours during a strong radio flare on Jan. 15, 16, 1975, the close
binary system Beta Persei (Algol) was observed with a three-station
VLBI array operating at 7850 MHz. The size of the radio source was
estimated to have been about 1.7 milliarcsec (0.05 AU), based on a model
of a uniformly bright disk. The corresponding brightness temperature
was nearly 10 billion K, indicating that the emission was probably
nonthermal. There was no evidence for expansion of the source; the
upper limit on the rate of any expansion was 100 km/s. The position
of the Algol radio source with respect to an extragalactic reference
frame was also determined from these observations with an uncertainty
of about 0.1 arcsec in each coordinate.
Title: A very-long-baseline interferometer system for geodetic
applications.
Authors: Whitney, A. R.; Rogers, A. E. E.; Hinteregger, H. F.; Knight,
C. A.; Levine, J. I.; Lippincott, S.; Clark, T. A.; Shapiro, I. I.;
Robertson, D. S.
Bibcode: 1976RaSc...11..421W
Altcode:
A very-long-baseline interferometer system was designed and built for
geodetic applications. Each interferometer terminal records a 360-kHz
spectral band of noise from a compact extragalactic radio source. The
center frequency of the spectral band can be selected to sample
sequentially bands covering a much wider frequency range to obtain
subnanosecond accuracy in group-delay measurements. A tunnel-diode
pulse generator is used to calibrate the delays in the receiver. The
necessary sets of algorithms and computer programs have been developed
to analyze the data and have allowed the system to be employed to make
accurate determinations of vector baselines, radio-source positions,
polar motion, and universal time.
Title: Proper-Motion Evidence Against a Galactic Origin for Quasars
Authors: Shapiro, I. I.; Wittels, J. J.; Counselman, C. C.; Whitney,
A. R.; Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.; Clark,
T. A.; Hutton, L. K.; Robertson, D. S.; Ronnang, B. O.; Rydbeck,
O. E. H.; Niell, A. E.
Bibcode: 1976BAAS....8..366S
Altcode:
No abstract at ADS
Title: Evolution of the Radio Fine Structure of 3C 273B and 3C 279
Authors: Cotton, W. D.; Geller, R. B.; Shapiro, I. I.; Wittels,
J. J.; Clark, T. A.; Hutton, L. K.; Hinteregger, H. F.; Knight, C. A.;
Rogers, A. E. E.; Whitney, A. R.
Bibcode: 1976BAAS....8R.366C
Altcode:
No abstract at ADS
Title: Apparent 'Superrelativistic' Expansion of the Extragalactic
Radio Source 3C 345
Authors: Wittels, J. J.; Cotton, W. D.; Counselman, C. C., III;
Shapiro, I. I.; Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.;
Whitney, A. R.; Clark, T. A.; Hutton, L. K.; Ronnang, B. O.; Rydbeck,
O. E. H.; Niell, A. E.
Bibcode: 1976BAAS....8..366W
Altcode:
No abstract at ADS
Title: Far infrared emission spectrum of the stratosphere from
balloon altitudes
Authors: Clark, T. A.; Kendall, D. J. W.
Bibcode: 1976Natur.260...31C
Altcode:
WE present here observations of the far infrared emission spectrum
of the stratosphere taken with a balloon-borne interferometer from an
altitude of 22 km above Churchill, Manitoba, Canada (latitude 58.7°N,
longitude 94° W) in July, 1974. The instrument was part of a composite
Atmospheric Environment Service of Canada gondola whose overall aim was
the measurement, by several complementary methods, of the concentrations
of minor constituents of the atmosphere and the monitoring of
their changes with altitude and time during the flight. Many of the
minor constituents of particular interest in the current debate on
stratospheric pollution (O3, H2O, NO2,
N2O, NO, HNO3, HCl, SO2) exhibit pure
rotation spectra in the far infrared and are expected to contribute to
the stratospheric emission spectrum. O2, a well known and
well behaved constituent of the stratosphere emits a series of weak
magnetic dipole lines in this wavelength region, with intensities
matching those of intrinsically stronger ones from less abundant
species, and which can be used for spectral normalisation (see ref. 3).
Title: Meter-wavelength VLBI. II. The observations.
Authors: Clark, T. A.; Erickson, W. C.; Hutton, L. K.; Resch, G. M.;
Vandenberg, N. R.; Broderick, J. J.; Knowles, S. H.; Youmans, A. B.
Bibcode: 1975AJ.....80..923C
Altcode:
Observations made during a series of meter-wavelength very-long-baseline
(VLBI) experiments conducted during 1971-1973 are reported. A
wide variety of objects was observed, including many extragalactic
sources known to have compact components, several strong pulsars
(especially the Crab nebula pulsar), and a selection of supernova
remnants. The experiments are discussed in detail, and tests made
to check the consistency of the results are described. The measured
correlated flux densities are presented for each source as a function of
interferometer baseline and observing frequency. An assessment is made
of the measurement errors and of the possibility of confusion within
the interferometer beam. The results show that all sources except
the pulsars, which are known to have intrinsically small sizes, are
resolved on the longest baseline. We also conclude that no supernova
remnants except the Crab nebula and Cassiopeia A gave evidence of
compact components.
Title: The far-infra-red sun - review of recent results and indication
of future prospects.
Authors: Clark, T. A.
Bibcode: 1975JRASC..69..254C
Altcode:
No abstract at ADS
Title: Comparison between VLBI and IPS Observations of Compact Sources
Authors: Resch, G. M.; Vandenberg, N. R.; Erickson, W. C.; Clark, T. A.
Bibcode: 1975BAAS....7Q.437R
Altcode:
No abstract at ADS
Title: The Intrinsic Sizes of Compact Radio Sources at Meter
Wavelengths
Authors: Resch, G. M.; Erickson, W. C.; Vandenberg, N. R.; Clark, T. A.
Bibcode: 1975BAAS....7R.437R
Altcode:
No abstract at ADS
Title: Results of Closure Phase Analysis of VLBI Data
Authors: Hutton, L. K.; Clark, T. A.; Shapiro, I. I.; Wittels, J. J.;
Hinteregger, H. F.; Knight, C. A.; Rogers, A. E. E.; Whitney, A. R.;
Niell, A. E.; Ronnang, B. O.; Rydbeck, O. E. H.
Bibcode: 1975BAAS....7..413H
Altcode:
No abstract at ADS
Title: Superheterodyne Receiver for Spectroscopy at 10 Microns
Authors: Buhl, D.; Mumma, M.; Kostiuk, T.; Clark, T. A.
Bibcode: 1975BAAS....7..390B
Altcode:
No abstract at ADS
Title: Fine structure of 25 extragalactic radio sources.
Authors: Wittels, J. J.; Knight, C. A.; Shapiro, I. I.; Hinteregger,
H. F.; Rogers, A. E. E.; Whitney, A. R.; Clark, T. A.; Hutton, L. K.;
Marandino, G. E.; Niell, A. E.; Rönnäng, B. O.; Rydbeck, O. E. H.;
Klemperer, W. K.; Warnock, W. W.
Bibcode: 1975ApJ...196...13W
Altcode:
Interferometric observations taken at 7.8 GHz (gamma approximately =
3.8 cm) with five pairings of antennae of 25 extragalactic radio
sources between April, 1972 and May, 1973 are reported. These
sources exhibit a broad variety of fine structure from very simple
to complex. The total flux and the correlated flux of some of the
sources underwent large changes in a few weeks, while the structure
and total power of others remained constant during the entire period
of observation. Some aspects of the data processing and a discussion of
errors are presented. Numerous figures are provided and explained. The
individual radio sources are described in detail.
Title: Solar infra-red limb scans using a simple rapid-scanning
Michelson interferometer.
Authors: Burrell, D. A.; Clark, T. A.
Bibcode: 1975JRASC..69Q.254B
Altcode:
No abstract at ADS
Title: Transcontinental Baselines and the Rotation of the Earth
Measured by Radio Interferometry
Authors: Shapiro, I. I.; Robertson, D. S.; Knight, C. A.; Counselman,
C. C., III; Rogers, A. E. E.; Hinteregger, H. F.; Lippincott, S.;
Whitney, A. R.; Clark, T. A.; Niell, A. E.; Spitzmesser, D. J.
Bibcode: 1974Sci...186..920S
Altcode:
Nine separate very-long-baseline interferometry (VLBI) experiments,
carried out in 1972 and 1973 with radio telescopes 3900 kilometers
apart, yielded values for the baseline length with a root-mean-square
deviation about the mean of less than 20 centimeters. The corresponding
fractional spread is about five parts in 108. Changes in
universal time and in polar motion were also determined accurately
from these data; the root-mean-square scatter of these results with
respect to those based on optical methods were 2.9 milliseconds and
1.3 meters, respectively. Solid-earth tides were apparently detected,
but no useful estimate of their amplitude was extracted.
Title: Solar Gravitational Deflection of Radio Waves Measured by
Very-Long-Baseline Interferometry
Authors: Counselman, C. C., III; Kent, S. M.; Knight, C. A.; Shapiro,
I. I.; Clark, T. A.; Hinteregger, H. F.; Rogers, A. E. E.; Whitney,
A. R.
Bibcode: 1974PhRvL..33.1621C
Altcode:
Utilizing a four-antenna technique, we observed simultaneously, at each
end of an 845-km baseline, the radio sources 3C279 and 3C273B which are
10° apart in the sky. Differences in interferometric phases at 3.7-cm
wavelength monitored near the time of the 1972 occultation of 3C279 by
the sun, yielded a gravitational deflection of 0.99+/-0.03 times the
value predicted by general relativity, corresponding to γ=0.98+/-0.06
(standard error).
Title: Meter-wavelength VLBI. I. Cassiopeia A.
Authors: Hutton, L. K.; Clark, T. A.; Erickson, W. C.; Resch, G. M.;
Vandenberg, N. R.; Knowles, S. H.; Youmans, A. B.
Bibcode: 1974AJ.....79.1248H
Altcode:
Very-long-baseline interferometric observations of the supernova remnant
Cassiopeia A, at 74 MHz with a 12,000-wavelength baseline and at 111 MHz
with a 18,500-wavelength baseline, are reported. The fringe amplitudes
are strongly varying on a time scale of about 15 to 30 minutes, which
is attributed to much the same complex structure as that observed at
higher frequencies, plus one other compact source. Due to the poor
(u, nu)-plane coverage, the location of the extra source can not be
isolated unambiguously, but possibilities are suggested. The source
must lie outside the supernova remnant shell, possibly associated with
a concentration of emission north of the shell, or lying outside the
gap in the northeastern side of the shell. The flux and spectral index
deduced for the compact source depend on the assumed size, with a range
of 100 Jy and 500 Jy at 74 MHz. If the source is associated with the
supernova explosion, it must have been traveling at least 5000 km/sec.
Title: The structure of radio sources 3C 273B and 3C 84 deduced
from the "closure" phases and visibility amplitudes observed with
three-element interferometers.
Authors: Rogers, A. E. E.; Hinteregger, H. F.; Whitney, A. R.;
Counselman, C. C.; Shapiro, I. I.; Wittels, J. J.; Klemperer, W. K.;
Warnock, W. W.; Clark, T. A.; Hutton, L. K.; Marandino, G. E.; Ronnang,
B. O.; Rydbeck, O. E. H.; Niell, A. E.
Bibcode: 1974ApJ...193..293R
Altcode:
The derived 'closure' phase relation for a three-element interferometer
is used in a presented analysis of data obtained from observations
at 7.8 GHz of the radio sources 3C 273B and 3C 84 by antennas in
Massachusetts, California, Alaska, and Sweden (the first two antennas
were used in combination with each of the last two separately to form
two three-element interferometers). The brightness distribution is
found for each source by expansion of both the fringe amplitude and
the fringe phase in separate Fourier series.
Title: Meter-wavelength VLBI Observations of the Crab Nebula Pulsar.
Authors: Vandenberg, N. R.; Clark, T. A.; Erickson, W. C.; Resch,
G. M.; Broderick, J. J.
Bibcode: 1974BAAS....6..454V
Altcode:
No abstract at ADS
Title: Radio Astronomy
Authors: Alexander, J.; Clark, T. A.
Bibcode: 1974hepq.conf..273A
Altcode:
No abstract at ADS
Title: Worldwide time and frequency synchronization by planned
VLBI networks
Authors: Coates, R. J.; Clark, T. A.
Bibcode: 1974ptti.meet..361C
Altcode:
Accurate baseline determinations and clock synchronization results
obtained from the Quasar Patrol observations at X band with the
Goldstone-Haystack baseline are presented. In addition, data from
stations at Greenbank, West Virginia, and Onsala, Sweden were used. It
was estimated that clock accuracy was on the order of 16 cm.
Title: Extragalactic Radio Sources: Accurate Positions from Very-Long
Interferometry Observations
Authors: Rogers, A. E. E.; Counselman, C. C., III; Hinteregger,
H. F.; Knight, C. A.; Robertson, D. S.; Shapiro, I. I.; Whitney,
A. R.; Clark, T. A.
Bibcode: 1973ApJ...186..801R
Altcode:
Relative positions for 12 extragalactic radio sources have been
determined via wide-band verylong-baseline interferometry (A 3.8
cm). The standard error, based on consistency between results from
widely separated periods of observation, appears to be no more than 0'!1
for each coordinate of the seven sources that were well observed during
two or more periods. The uncertainties in the coordinates determined for
the other five sources are larger, but in no case exceed 0'!5. Subject
heading: radio sources
Title: Long wavelength VLBI.
Authors: Clark, T. A.; Erickson, W. C.
Bibcode: 1973IEEEP..61.1230C
Altcode:
No abstract at ADS
Title: Possible observation at Calgary of the occultation of BD +2
2913 by the minor planet 2 Pallas.
Authors: Clark, T. A.; Milone, E. F.
Bibcode: 1973JRASC..67..198C
Altcode:
No abstract at ADS
Title: C 120: Intense Outburst (s) of Radio Radiation Detected with
the Goldstone-Haystack Interferometer
Authors: Shapiro, I. I.; Hinteregger, H. F.; Knight, C. A.; Punsky,
J. J.; Robertson, D. S.; Rogers, A. E. E.; Whitney, A. R.; Clark,
T. A.; Marandino, G. E.; Goldstein, R. M.; Spitsmesser, D. J.
Bibcode: 1973ApJ...183L..47S
Altcode:
Observations of the Seyfert galaxy 3C 120 with the Goldstone-Haystack
interferometer at a radio frequency of 7850 MHz ( - 3.8 cm) show that
the correlated flux increased almost threefold between 1972 June 6
and August 29. The disappearance of virtually all structure in the
fringe-amplitude pattern for the August data is consistent with the
occurrence of an explosive outburst of radio radiation between the
two dates. Further observations with the same interferometer on 1972
November 7 disclose an additional increase in correlated flux with a
reappearance of structure in the fringe-amplitude curve. These findings
are consistent with a single, spherically symmetric source expanding
with an apparent velocity several times the speed of light. The
assumption that multiple, independent outbursts occurred during this
period avoids the implication of relativistic expansion. Subject
headings: image-processing - quasi-stellar sources or objects - radio
radiation - radio sources - Seyfert galaxies
Title: Atmospheric Water Vapour at Mt. Kobau and Calgary and its
Relevance to Infrared Astronomical Measurements
Authors: Clark, T. A.; Irwin, G.
Bibcode: 1973JRASC..67..142C
Altcode:
No abstract at ADS
Title: Upper Limit to the 11.4 m Flux of Saturn using VLBI
Authors: Shawhan, S. D.; Clark, T. A.; Cronyn, W. M.; Basart, J. P.
Bibcode: 1973NPhS..243...65S
Altcode: 1973Natur.243...65S
Searches continue for non-thermal continuum1,2 and noise
storm (ref. 3 and S. Ya. Braude, personal communication) radio emissions
from Saturn which might be analogous to the decimetric and decametric
emissions from Jupiter4,5. From wavelengths of 1 mm to
3.5 cm the measurements of Saturn can be fitted to a 140 K thermal
blackbody curve. From 9 cm to longer wavelengths the equivalent
blackbody temperature rises. Yerbury, Condon and Jauncey1
measure a temperature of 400+/-65 K at 49.5 cm and 540+/-110 K at 94.3
cm using the Arecibo radio telescope. Observations of thermal emission
at longer wavelengths are difficult because of the large collecting
areas required. Gulkis2 fits the existing emission curve with
a deep, hot model atmosphere. Luthey6, however, considers
the possibility of synchrotron radiation as a non-thermal explanation
of the rising temperature curve at larger wavelengths. So far the
observations of decametric noise storm emissions from Saturn seem to
be negative3 although Braude reports possible emissions of
several tens of flux units at 25, 20 and 16.7 MHz.
Title: VLBI Observations of the Crab Nebula Pulsar
Authors: Vandenberg, N. R.; Clark, T. A.; Erickson, W. C.; Resch,
G. M.; Broderick, J. J.; Payne, R. R.; Knowles, S. H.; Youmans, A. B.
Bibcode: 1973ApJ...180L..27V
Altcode:
Observations of the Crab Nebula pulsar at meter wavelengths using VLBi
techniques have been made. At 196.5 MHz we observe no resolution of
the pulsar, all the puise shapes observed with the interferometers
are similar to single-dish profiles, and all the power puisates. At
111.5 MHz besides the puising power there is always a steady component,
presumably due to multipath propagation effects. The puisar is slightly
resolved at 111.5 MHz with an apparent angular diameter of 0"07 t
0'.'01. We observe 50 percent linear polarization of the time-averaged
power at 196.5 MHz; at 111.5 MHz, 20 percent of the total time-averaged
power is polarized, 35 percent of the pulsing power is polarized. The
steady component is unpolarized. The total flux of the steady plus
pulsating component appears to remain constant while the distribution
of power betw&n these components varies. Subject headings:pulsars -
Crab Nebula
Title: The zodiacal light observed from latitude 52 north.
Authors: Clark, T. A.; Babott, F.
Bibcode: 1973S&T....46..130C
Altcode:
No abstract at ADS
Title: An Upper Limit to the 11.2 m-λ Flux of Saturn Using VLBI.
Authors: Shawhan, S. D.; Clark, T. A.; Basart, J. P.; Cronyn, W. M.
Bibcode: 1973BAAS....5...36S
Altcode:
No abstract at ADS
Title: High Resolution Observation of Cas-A at 26.3 MHz.
Authors: Hutton, L. K.; Clark, T. A.; Cronyn, W. M.
Bibcode: 1973BAAS....5...35H
Altcode:
No abstract at ADS
Title: Time, geodesy, and astrometry: Results from radio
interferometry
Authors: Clark, T. A.; Shapiro, I. I.
Bibcode: 1973ptti.meet...33C
Altcode:
The results from a total of a dozen transcontinental and
intercontinental VLBI experiments are discussed. Particular emphasis
is placed on: (1) the inferred behavior of the frequency standards,
usually hydrogen masers, on time scales from 10 to 100,000 seconds;
(2) the estimated celestial positions of the observed radio sources;
(3) the determinations of the vector baselines; and (4) the inferred
values of polar motion and UT.1.
Title: Source Positions from Very Long Baseline Interferometer
Observations.
Authors: Clark, T. A.; Counselman, D. C., III; Hinteregger, H. F.;
Knight, C. A.; Robertson, D. S.; Rogers, A. E. E.; Shapiro, I. I.;
Whitney, A. R.
Bibcode: 1973BAAS....5...30C
Altcode:
No abstract at ADS
Title: Cygnus X-3 Radio Source: Lower Limit on Size and Upper Limit
on Distance
Authors: Hinteregger, H. F.; Catuna, G. W.; Counselman, C. C.; Ergas,
R. A.; King, R. W.; Knight, C. A.; Robertson, D. S.; Rogers, A. E. E.;
Shapiro, I. I.; Whitney, A. R.; Clark, T. A.; Hutton, L. K.; Marandino,
G. E.; Perley, R. A.; Resch, G.; Vandenberg, N. R.
Bibcode: 1972NPhS..240..159H
Altcode: 1972Natur.240..159H
THE sudden increase in radio flux observed1 from the
direction of Cygnus X-3 on September 22-23, 1972, occurred just as we
began a four-antenna very-long-baseline interferometry experiment that
involved a pair of radio telescopes in Green Bank, West Virginia, and
another pair in Massachusetts (Table 1). We were able to take advantage
of this opportunity to observe Cygnus X-3 interferometrically on
September 24 and report here the negative results of these observations.
Title: Precision timing and Very Long Baseline Interferometry (VLBI)
Authors: Clark, T. A.
Bibcode: 1972ptti.meet...74C
Altcode:
The use of very long baseline interferometry (VLBI) for investigating
small angular features in galactic and extragalactic radio sources is
discussed. Mathematical models are developed to describe the operation
of an interferometer and to show the variations in the resultant
fringe frequency. The types of sources to which the interferometer
will respond are identified.
Title: Very Long Baseline Interferometer Observations of Taurus a
and Other Sources at 121.6 MHz
Authors: Erickson, W. C.; Kuiper, T. B. H.; Clark, T. A.; Knowles,
S. H.; Broderick, J. J.
Bibcode: 1972ApJ...177..101E
Altcode:
VLBI observations with an antenna spacing of 92,000 A (2'(2 lobe
separation) were made on a number of small-angular-diameter sources at
a frequency of 121.6 MHz. Through positional and spectral coincidence,
these observations confirm the physical association of the compact
source in Tau A with the pulsar NP 0532; in the east-west direction,
the two objects agree in position to an accuracy of 1011. The fluxes of
the small-angular-diameter components of 3C 48, 3C 84, 3C 144, 3C 147,
3C 273, 3C 274, 3C 298, 3C 405, 3C 459, and 3C 461 are estimated.
Title: Interferometric Observations of an Artificial Satellite
Authors: Preston, R. A.; Ergas, R.; Hinteregger, H. F.; Knight, C. A.;
Robertson, D. S.; Shapiro, I. I.; Whitney, A. R.; Rogers, A. E. E.;
Clark, T. A.
Bibcode: 1972Sci...178..407P
Altcode:
Very-long-baseline interferometric observations of radio signals from
the TACSAT synchronous satellite, even though extending over only 7
hours, have enabled an excellent orbit to be deduced. Precision in
differenced delay and delay-rate measurements reached 0.15 nanosecond
(lesssim 5 centimeters in equivalent differenced distance) and 0.05
picosecond per second (lesssim 0.002 centimeter per second in equivalent
differenced velocity), respectively. The results from this initial
three-station experiment demonstrate the feasibility of using the
method for accurate satellite tracking and for geodesy. Comparisons
are made with other techniques.
Title: Precision Geodesy via Radio Interferometry
Authors: Hinteregger, H. F.; Shapiro, I. I.; Robertson, D. S.; Knight,
C. A.; Ergas, R. A.; Whitney, A. R.; Rogers, A. E. E.; Moran, J. M.;
Clark, T. A.; Burke, B. F.
Bibcode: 1972Sci...178..396H
Altcode:
Very-long-baseline interferometry experiments, involving observations
of extragalactic radio sources, were performed in 1969 to determine
the vector separations between antenna sites in Massachusetts and
West Virginia. The 845.130-kilometer baseline was estimated from two
separate experiments. The results agreed with each other to within
2 meters in all three components and with a special geodetic survey
to within 2 meters in length; the differences in baseline direction
as determined by the survey and by interferometry corresponded to
discrepancies of about 5 meters. The experiments also yielded positions
for nine extragalactic radio sources, most to within 1 arc second, and
allowed the hydrogen maser clocks at the two sites to be synchronized
a posteriori with an uncertainty of only a few nanoseconds.
Title: Further Observations of Brightness Variation In the Small
Scale Structure of 3C273 and 3C279.
Authors: Marandino, G. E.; Resch, G. M.; Vandenberg, N. R.; Clark,
T. A.; Hinteregger, H.; Knight, C. A.; Robertson, D. S.; Rogers,
A. E. E.; Shapiro, I. I.; Whitney, A. R.; Goldstein, R. M.;
Spitzmesser, D.
Bibcode: 1972BAAS....4..315M
Altcode:
No abstract at ADS
Title: VLBI Observations of the Crab Nebula Pulsar.
Authors: Vandenberg, N. R.; Erickson, W. C.; Resch, G. M.; Clark,
T. A.; Broderick, J. J.
Bibcode: 1972BAAS....4..320V
Altcode:
No abstract at ADS
Title: Very Long Baseline Interferometer Observations of NPO532 at
121. 6 MHz.
Authors: Erickson, W. C.; Kuiper, T. B. H.; Clark, T. A.; Knowles,
S. H.; Broderick, J. J.
Bibcode: 1971BAAS....3..463E
Altcode:
No abstract at ADS
Title: Observations with the Haystack-Gold-stone Interferometer of
Phase Scintillations due to the Solar Corona.
Authors: Knight, C. A.; Robertson, D. S.; Shapiro, I. I.; Whitney,
A. R.; Rogers, A. E. E.; Clark, T. A.; Marandino, G. E.; Vandenberg,
N. R.; Goldstein, R. M.
Bibcode: 1971BAAS....3..447K
Altcode:
No abstract at ADS
Title: Measurement of the Gravitational Deflection of Radio Waves.
Authors: Robertson, D. S.; Knight, C. A.; Rogers, A. E. E.; Shapiro,
I. I.; Whitney, A. R.; Clark, T. A.; Marandino, G. E.; Vandenberg,
N. R.; Goldstein, R. M.
Bibcode: 1971BAAS....3..474R
Altcode:
No abstract at ADS
Title: Precision Geodesy Via Radio Interferometry: First Results.
Authors: Hinteregger, H. F.; Ergas, R.; Knight, C. A.; Robertson,
D. S.; Shapiro, I. I.; Whitney, A. R.; Rogers, A. E. E.; Clark, T. A.
Bibcode: 1971BAAS....3..467H
Altcode:
No abstract at ADS
Title: Long Baseline Interferometry at a Decametric Wavelength.
Authors: Cronyn, W. M.; Klemperer, W. K.; Rufenach, C. L.; Shawhan,
S. D.; Basart, J.; Clark, T. A.; Erickson, W. C.
Bibcode: 1971BAAS....3..438C
Altcode:
No abstract at ADS
Title: High-Accuracy Determination of 3C273-3C279 Position Difference
from Long-Baseline Interferometer Fringe Phase Measurements.
Authors: Whitney, A. R.; Shapiro, I. I.; Rogers, A. E. E.; Robertson,
D. S.; Knight, C. A.; Clark, T. A.; Marandino, G. E.; Vandenberg,
N. R.; Goldstein, R. M.
Bibcode: 1971BAAS....3R.465W
Altcode:
No abstract at ADS
Title: Search for Microwave H20 Emission in Comet Bennett (1969i)
Authors: Clark, T. A.; Donn, B.; Jackson, W. M.; Sullivan, W. T.,
III; Vandenberg, N.
Bibcode: 1971AJ.....76..614C
Altcode:
The 85-ft radio telescope of the Naval Research Laboratory was used
in an attempt to detect the 22 235-MHx transition (616 H 523) of
H2O during the recent appearance of Comet Bennett (1969i). No H2O
emission of antenna temperature greater than 2.50K was observed. We
have derived upper limits to the H2O column density ( 2 x 1017
molecules/cm2) for various temperatures of the cometary gas. These
limits have been compared with H2O column densities calculated from
two different cometary models. We find that on one of these models,
our sensitivity was just at the threshold for detection of H2O.
Title: A Measurement of the Brightness Temperature of the Sun in
the Range 65 to 180 cm-1
Authors: Clark, T. A.; Courts, G. R.; Jennings, R. E.
Bibcode: 1971RSPTA.270...55C
Altcode:
No abstract at ADS
Title: Detection of double-source structure in the nucleus of the
quasi-stellar radio sources 3C 279.
Authors: Knight, C. A.; Rogers, A. E. E.; Shapiro, I. I.; Whitney,
A. R.; Clark, T. A.; Goldstein, R. M.; Marandino, G. E.; Vandenberg,
N. R.
Bibcode: 1971BAAS....3..416K
Altcode:
No abstract at ADS
Title: Variations in the Fine Structure of the Quasars 3C279 and
3C273.
Authors: Clark, T. A.; Goldstein, R. M.; Hinteregger, H. F.; Knight,
C. A.; Marandino, G. E.; Robertson, D. S.; Rogers, A. E. E.; Shapiro,
I. I.; Spitzmesser, D. J.; Vandenberg, N. R.; Whitney, A. R.
Bibcode: 1971BAAS....3R.383C
Altcode:
No abstract at ADS
Title: Search for microwave H2O emission in comet Bennett
(1969i).
Authors: Clark, T. A.; Donn, B.; Jackson, W. M.; Sullivan, W. T.,
III; Vanderberg, N.
Bibcode: 1971BAAS....3..281C
Altcode:
No abstract at ADS
Title: Long-baseline interferometry at a decametric wavelength.
Authors: Cronyn, W. M.; Klemperer, W. K.; Rufenach, C. L.; Clark,
T. A.; Erickson, W. C.
Bibcode: 1971BAAS....3Q.438C
Altcode:
No abstract at ADS
Title: Long baseline interferometry at a decametric wavelength.
Authors: Cronyn, W. M.; Klemperer, W. K.; Rufenach, C. L.; Shawhan,
S. D.; Basart, J.; Clark, T. A.; Erickson, W. C.
Bibcode: 1971BAAS....3R.438C
Altcode:
No abstract at ADS
Title: Spectrum of the Extra-galactic Background Radiation at Low
Radio Frequencies
Authors: Clark, T. A.; Brown, L. W.; Alexander, J. K.
Bibcode: 1970Natur.228..847C
Altcode:
THE cosmic noise background radiation observed at metre and
decametre wavelengths is generally considered to result from several
different spatial components. These include synchrotron radiation
from cosmic ray electrons in the galactic disk, similar radiation
from the galactic halo (although the relative importance of this
component is a matter of considerable controversy), and an isotropic
radiation component from the integrated emission of all unresolved
extra-galactic radio sources. Results of recent analyses of metre-wave
measurements1-3 place the brightness I x of the
isotropic component at about one-third the minimum total brightness
observed at a frequency f of 100 MHz. The spectral index α x
of the isotropic radiation is thought to be about equal to the
average spectral index (~0.8) observed for surveys of extra-galactic
discrete sources4 at f ~ 100 MHz where
Title: Long-Baseline Interferometric Measurement of Gravitational
Bending of Radiation from 3C279 in the Solar Gravitational Field.
Authors: Whitney, A. R.; Burke, B. F.; Clark, T. A.; Hinteregger,
H. F.; Knight, C. A.; Robertson, D. S.; Rogers, A. E. E.; Shapiro,
I. I.
Bibcode: 1970BAAS....2S.356W
Altcode:
No abstract at ADS
Title: Low Frequency Cosmic Noise Observa- tions of the Constitution
of the Local System
Authors: Alexander, J. K.; Brown, L. W.; Clark, T. A.; Stone, R. G.
Bibcode: 1970A&A.....6..476A
Altcode:
Based on measurements of the low frequency continuum radiation of the
galaxy, estimates have been obtained for the gross distribution of
thermal electrons, the synchrotron radiation emissivity, and the fiux
and spectrum of low energy cosmic ray electrons for the interstellar
medium in the Local System. The volume emissivity of the synchrotron
radiation at 1 MHz is 10-88 W/(m8 Hz sterad). This value exceeds the
emissivity deduced from measurements at higher frequencies over longer
path lengths and in turn implies a low magnetic field between spiral
arms (S 1 `tG). For a mean interstellar magnetic field of 3 G near the
sun, the radio data indicate a cosmic ray electron intensity at 0.3
GeV of 10 el/(m8 s sterad GeV). That this intensity exceeds the value
obtained from direct measurements by a factor of 100 suggests either
a large residual solar modulation or gradients in the interstellar
distribution of cosmic rays.
Title: The Spectrum of the Continuum Radio Emission from the Local
Spiral Arm
Authors: Alexander, J. K.; Brown, L. W.; Clark, T. A.; Stone, R. G.;
Weber, R. R.
Bibcode: 1970BAAS....2Q.180A
Altcode:
No abstract at ADS
Title: Radio-astronomical observations of high-energy particles.
Authors: Clark, T. A.
Bibcode: 1970NASSP.243..219C
Altcode:
No abstract at ADS
Title: The Spectrum of the Cosmic Radio Background Between 0.4 and
6.5 MHz
Authors: Alexander, J. K.; Brown, L. W.; Clark, T. A.; Stone, R. G.;
Weber, R. R.
Bibcode: 1969ApJ...157L.163A
Altcode:
No abstract at ADS
Title: Spectral and Spatial Distribution of Cosmic Noise Observed
by RAE-I
Authors: Weber, R. R.; Alexander, J. K.; Stone, R. G.; Clark, T. A.
Bibcode: 1969BAAS....1T.265W
Altcode:
No abstract at ADS
Title: Auroral X-rays and their association with rapidly changing
auroral forms
Authors: Pilkington, G. R.; Anger, C. D.; Clark, T. A.
Bibcode: 1968P&SS...16..815P
Altcode:
No abstract at ADS
Title: Morphology of electron precipitation during auroral substorms
Authors: Clark, T. A.; Anger, C. D.
Bibcode: 1967P&SS...15.1287C
Altcode:
A Study of auroral substorms using coordinated measurements of a number
of parameters at Ft. Churchill, Manitoba ( L = 8) in October 1963 has
yielded interesting conclusions on the electron precipitation close to
the northern auroral boundary, the morphology of which appears to follow
closely the working model proposed by Akasofu. Extensions to this model
are suggested that include high energy electron precipitation (>30
keV) as determined from X-ray measurements at balloon altitudes. During
surges and auroral substorms near local midnight, very localized
precipitation of electrons with a wide spectrum of energies produced
a sharp northern optical and radio absorption border which moved
rapidly northwards and contained the auroral electrojet. During the
decay phases of the substorms, a region of high energy precipitation
receded southwards in advance of the northern border of luminous
aurora and appeared to be accompanied by the ionospheric electric
current. In contrast to this, the optical northern border produced no
noticeable auroral absorption or magnetic activity on its southward
overhead passage later in the substorm. Systematic spectral changes
near the border indicated a softening of the electron spectrum above
40 keV with increasing northward position (or increasing L value), in
agreement with satellite observations. Highly structured enhancements
of precipitation of high energy electrons occurred at times when
small scale folds in auroral bands were reported during break-up and
at times of occurrence of Type B aurora.
Title: Absolute position of the Jovian decametric radio source
Authors: Clark, T. A.; Alexander, J. K.
Bibcode: 1967AJ.....72Q.294C
Altcode:
No abstract at ADS
Title: Geomagnetic and ionospheric observations associated with
auroral activity during the total solar eclipse of July 20, 1963
Authors: Clark, T. A.; Anger, C. D.
Bibcode: 1965CaJPh..43..457C
Altcode:
No abstract at ADS