explanation blue bibcodes open ADS page with paths to full text
Author name code: cram
ADS astronomy entries on 2022-09-14
author:"Cram, Lawrence E."
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Title: Commission 12: Solar Radiation and Structure
Authors: Martínez Pillet, Valentin; Kosovichev, Alexander;
Mariska, John T.; Bogdan, Thomas J.; Asplund, Martin; Cauzzi, Gianna;
Christensen-Dalsgaard, Jørgen; Cram, Lawrence E.; Gan, Weiqun; Gizon,
Laurent; Heinzl, Petr; Rovira, Marta G.; Venkatakrishnan, P.
2009IAUTA..27..104M Altcode:
Commission 12 encompasses investigations on the internal structure
and dynamics of the Sun, mostly accessible through the techniques of
local and global helioseismology, the quiet solar atmosphere, solar
radiation and its variability, and the nature of relatively stable
magnetic structures like sunspots, faculae and the magnetic network. A
revision of the progress made in these fields is presented. For some
specific topics, the review has counted with the help of experts
outside the Commission Organizing Committee that are leading and/or
have recently presented relevant works in the respective fields. In
this cases the contributor's name is given in parenthesis.
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Title: The PHOENIX Deep Survey: Extremely Red Galaxies and Cluster
Candidates
Authors: Smith, Anthony G.; Hopkins, Andrew M.; Hunstead, Richard W.;
Schmidt, Samuel J.; Afonso, José; Georgakakis, Antonis E.; Cram,
Lawrence E.; Mobasher, Bahram; Sullivan, Mark
2008AJ....136..358S Altcode: 2008arXiv0804.3866S
We present the results of a study of a sample of 375 extremely red
galaxies (ERGs) in the Phoenix Deep Survey, 273 of which constitute a
subsample which is 80% complete to K<SUB>s</SUB> = 18.5 over an area
of 1160 arcmin<SUP>2</SUP>. The angular correlation function for ERGs
is estimated, and the association of ERGs with faint radio sources
explored. We find tentative evidence that ERGs and faint radio sources
are associated at z gsim 0.5. A new overdensity-mapping algorithm
has been used to characterize the ERG distribution, and identify a
number of cluster candidates, including a likely cluster containing
ERGs at 0.5 < z < 1. Our algorithm is also used in an attempt
to probe the environments in which faint radio sources and ERGs are
associated. We find limited evidence that the I - K<SUB>s</SUB> >
4 criterion is more efficient than R - K<SUB>s</SUB> > 5 at selecting
dusty star-forming galaxies, rather than passively evolving ERGs.
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Title: Deep ATCA and GMRT Observations of the CDFS
Authors: Afonso, J.; Messias, H.; Mobasher, B.; Koekemoer, A.; Norris,
R. P.; Cram, L.; Kanekar, N.; Farrah, D.; Chengalur, J.
2007ASPC..380..243A Altcode:
The Chandra Deep Field South (CDFS) is one of the most extensively
observed regions of the sky, with some of the deepest multiwavelength
coverage ever. The richness of the available data makes this the field
of choice for performing studies of distant, often elusive, galaxy
populations. Deep radio observations of the CDFS have been performed at
1.4 GHz and 327 MHz, with the ATCA and the GMRT, respectively. Using the
data available at other wavelengths, we explore the nature of the faint
radio population in the CDFS, addressing in particular the optically
unidentified microJansky radio sources. Finally, using the 327 MHz
data, we offer a first glimpse of a new project aimed at detecting
the population of Ultra Steep Spectrum sources, known to be efficient
tracers of high redshift radio galaxies, at the very faintest radio
flux levels.
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Title: Commission 12: Solar Radiation & Structure
Authors: Bogdan, Thomas. J.; Martínez Pillet, Valentin; Asplund,
M.; Christensen-Dalsgaard, J.; Cauzzi, G.; Cram, L. E.; Dravins, D.;
Gan, W.; Henzl, P.; Kosovichev, A.; Mariska, J. T.; Rovira, M. G.;
Venkatakrishnan, P.
2007IAUTA..26...89B Altcode:
Commission 12 covers research on the internal structure and dynamics
of the Sun, the "quiet" solar atmosphere, solar radiation and its
variability, and the nature of relatively stable magnetic structures
like sunspots, faculae and the magnetic network. There is considerable
productive overlap with the other Commissions of Division II as
investigations move progressively toward the fertile intellectual
boundaries between traditional research disciplines. In large part,
the solar magnetic field provides the linkage that connects these
diverse themes. The same magnetic field that produces the more subtle
variations of solar structure and radiative output over the 11 yr
activity cycle is also implicated in rapid and often violent phenomena
such as flares, coronal mass ejections, prominence eruptions, and
episodes of sporadic magnetic reconnection.The last three years have
again brought significant progress in nearly all the research endeavors
touched upon by the interests of Commission 12. The underlying causes
for this success remain the same: sustained advances in computing
capabilities coupled with diverse observations with increasing levels
of spatial, temporal and spectral resolution. It is all but impossible
to deal with these many advances here in anything except a cursory and
selective fashion. Thankfully, the Living Reviews in Solar Physics; has
published several extensive reviews over the last two years that deal
explicitly with issues relevant to the purview of Commission 12. The
reader who is eager for a deeper and more complete understanding of
some of these advances is directed to http://www.livingreviews.org
for access to these articles.
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Title: The Phoenix Deep Survey: the star formation rates and the
stellar masses of extremely red objects
Authors: Georgakakis, A.; Hopkins, A. M.; Afonso, J.; Sullivan, M.;
Mobasher, B.; Cram, L. E.
2006MNRAS.367..331G Altcode: 2005astro.ph.12138G; 2006MNRAS.tmp..140G
We estimate the star formation rates and the stellar masses of the
extremely red objects (EROs) detected in a ~180arcmin<SUP>2</SUP>Ks-band
survey (Ks~20 mag). This sample is complemented by sensitive 1.4-GHz
radio observations (12 μJy 1σ rms) and multiwaveband photometric
data (UBVRIJ) as part of the Phoenix Deep Survey. For bright K <
19.5mag EROs in this sample (I-K > 4mag total of 177), we use
photometric methods to discriminate dust-enshrouded active systems
from early-type galaxies and to constrain their redshifts. Radio
stacking is then employed to estimate mean radio flux densities
of ~8.6 (3σ) and 6.4μJy (2.4σ) for the dusty and early-type
sub-samples, respectively. Assuming that dust-enshrouded active
EROs are powered by star formation, the above radio flux density
at the median redshift of z=1 translates to a radio luminosity of
L<SUB>1.4</SUB>=4.5×10<SUP>22</SUP>WHz<SUP>-1</SUP> and a star
formation rate of SFR=25M<SUB>solar</SUB>yr<SUP>-1</SUP>. Combining
this result with photometric redshift estimates, we
find a lower limit to the star formation rate density of
0.02+/-0.01M<SUB>solar</SUB>yr<SUP>-1</SUP>Mpc<SUP>-3</SUP> for
the K<19.5mag dusty EROs in the range z=0.85-1.35. Comparison
with the star formation rate density estimated for previous ERO
samples (with similar selection criteria) using optical emission
lines, suffering dust attenuation, suggests a mean dust reddening
of at least E(B-V)~0.5 for this population. We further use the
Ks-band luminosity as proxy to stellar mass and argue that the
dust-enshrouded starburst EROs in our sample are massive systems,
M>~5 ×10<SUP>10</SUP>M<SUB>solar</SUB>. We also find that EROs
represent a sizable fraction (about 50 per cent) of the number density
of galaxies more massive than M=5×10<SUP>10</SUP>M<SUB>solar</SUB>
at z~1, with almost equal contributions from dusty and early-type
systems. Similarly, we find that EROs contribute about half of the
mass density of the Universe at z~1 (with almost equal contributions
from dusty and early types), after taking into account incompleteness
because of the magnitude limit K=19.5mag.
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Title: Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Durrant, C.; Loughhead, R. E.
2006plsc.book.....B Altcode:
1. Historical introduction; 2. Cool loops: observed properties; 3. Hot
loops: observed properties; 4. Flare loops: observed properties;
5. Structure, dynamics and heating of loops; 6. The plasma loop model
of the coronae of the sun and stars.
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Title: Optical and X-Ray Identification of Faint Radio Sources in
the GOODS CDF-S Advanced Camera for Surveys Field
Authors: Afonso, J.; Mobasher, B.; Koekemoer, A.; Norris, R. P.;
Cram, L.
2006AJ....131.1216A Altcode: 2005astro.ph.10774A
We present optical and X-ray identifications for the 64 radio
sources in the Great Observatories Origins Deep Survey Chandra Deep
Field-South Advanced Camera for Surveys (ACS) field revealed in the
Australia Telescope Compact Array 1.4 GHz survey of the Chandra Deep
Field-South. Optical identifications are made using the ACS images
and catalogs, while the X-ray view is provided by the Chandra X-Ray
Observatory 1 Ms observations. Redshifts for the identified sources are
drawn from publicly available catalogs of spectroscopic observations
and multiband photometric-based estimates. Using this multiwavelength
information we provide a first characterization of the faint radio
source population in this region. The sample contains a mixture of
star-forming galaxies and active galactic nuclei, as identified by
their X-ray properties and optical spectroscopy. A large number of
morphologically disturbed galaxies are found, possibly related to star
formation. In spite of the very deep optical data available in this
field, seven of the 64 radio sources have no optical identification
to z<SUB>850</SUB>~28 mag. Only one of these is identified in the X-ray.
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Title: The Phoenix Deep Survey: Spectroscopic Catalog
Authors: Afonso, J.; Georgakakis, A.; Almeida, C.; Hopkins, A. M.;
Cram, L. E.; Mobasher, B.; Sullivan, M.
2005ApJ...624..135A Altcode: 2004astro.ph.11578A
The Phoenix Deep Survey is a multiwavelength survey based on deep 1.4
GHz radio imaging, reaching well into the sub-100 μJy level. One of
the aims of this survey is to characterize the submillijansky radio
population, exploring its nature and evolution. In this paper we present
the catalog and results of the spectroscopic observations aimed at
characterizing the optically “bright” (R<~21.5 mag) counterparts
of faint radio sources. Of 371 sources with redshift determination,
21% have absorption lines only, 11% show active galactic nucleus
signatures, 32% are star-forming galaxies, 34% show narrow emission
lines that do not allow detailed spectral classification (owing to
poor signal-to-noise ratio and/or lack of diagnostic emission lines),
and the remaining 2% are identified with stars. For the star-forming
galaxies with a Balmer decrement measurement we find a median extinction
of A<SUB>Hα</SUB>=1.9 mag, higher than that of optically selected
samples. This is a result of the radio selection, which is not biased
against dusty systems. Using the available spectroscopic information,
we estimate the radio luminosity function of star-forming galaxies
in two independent redshift bins at z~0.1 and 0.3, respectively. We
find direct evidence for strong luminosity evolution of these systems
consistent with L<SUB>1.4GHz</SUB>~(1+z)<SUP>2.7</SUP>.
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Title: VizieR Online Data Catalog: Phoenix Deep Survey: optical and
NIR catalogs (Sullivan+, 2004)
Authors: Sullivan, M.; Hopkins, A. M.; Afonso, J.; Georgakakis, A.;
Chan, B.; Cram, L. E.; Mobasher, B.; Almeida, C.
2005yCat..21550001S Altcode:
Two pointings (7, 3) were observed in BVRi, and one (pointing 11) in
BVi on the nights of 2001 August 13 and 14, with the WFI camera on the
AAT. The same three pointings were also observed in U with the Mosaic-II
camera on the CTIO 4m Blanco telescope on 2002 September 3. Finally,
four of the PDS fields (2, 3, 6, 7) were observed in U with the WFI on
the ESO 2.2m on the night of 2001 August 18. Our NIR imaging data come
from the Hawaii HgCdTe 1024x1024 pixel array SoFI camera on the 3.6m ESO
New Technology Telescope (NTT). The field of view was 4.9'x4.9' with a
pixel scale of 0.29". Nine contiguous pointings, in a 3x3 pattern, were
observed over the deepest region of the PDS (a subregion of pointing 7;
see Fig. 1), during 2000 October 10 and October 11. <P />(1 data file).
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Title: VizieR Online Data Catalog: Faint 1.4GHz radio sources in
2dFGRS (Chan+, 2004)
Authors: Chan, B. H. P.; Cram, L. E.; Sadler, E. M.; Killeen, N. E. B.;
Jackson, C. A.; Mobasher, B.; Ekers, R. D.
2005yCat..73521245C Altcode:
We have used the Australia Telescope Compact Array (ATCA) to search
for faint radio sources in a ~3deg<SUP>2</SUP> region of sky covered
by the 2dF Galaxy Redshift Survey (2dFGRS, Cat. ). Over the region
surveyed, the 1{sigma} noise level at 1.4GHz ranges from 20Jy to
1mJy. The survey region includes 365 2dFGRS galaxies, of which 316
have good-quality spectra (176 early-type galaxies or active galactic
nuclei, and 140 star-forming galaxies). The fraction of 2dFGRS galaxies
detected as radio sources in our survey rises from ~4% at a 3{sigma}
detection limit of 0.3mJy to 12% at 75{mu}Jy, with roughly equal
numbers of star-forming galaxies and active galactic nuclei (AGNs)
being detected. <P />(2 data files).
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Title: The Phoenix Deep Survey: The Clustering and Environment of
Extremely Red Objects
Authors: Georgakakis, Antonis; Afonso, J.; Hopkins, A. M.; Sullivan,
M.; Mobasher, B.; Cram, L. E.
2005ApJ...620..584G Altcode: 2004astro.ph.11572G
In this paper we explore the clustering properties and environment
of the extremely red objects (EROs; I-K>4 mag) detected in a ~180
arcmin<SUP>2</SUP> deep (K<SUB>s</SUB>~20 mag) K<SUB>s</SUB>-band survey
of a region within the Phoenix Deep Survey, an ongoing multiwavelength
program aiming to investigate the nature and evolution of faint
radio sources. Using our complete sample of 289 EROs brighter than
K<SUB>s</SUB>=20 mag, we estimate a statistically significant
(~3.7 σ) angular correlation function signal with amplitude
A<SUB>w</SUB>=8.7<SUP>+2.1</SUP><SUB>-1.7</SUB>×10<SUP>-3</SUP>
(assuming w(θ)=A<SUB>w</SUB>θ<SUP>-0.8</SUP>, with θ
in degrees), consistent with earlier work based on smaller
samples. This amplitude suggests a clustering length in the range
r<SUB>o</SUB>=12-17h<SUP>-1</SUP> Mpc, implying that EROs trace regions
of enhanced density. Using a novel method, we further explore the
association of EROs with galaxy overdensities by smoothing the K-band
galaxy distribution using the matched filter algorithm of Postman et
al. (1996) and then cross-correlating the resulting density maps with
the ERO positions. Our analysis provides direct evidence that EROs are
associated with overdensities at redshifts z>~1. We also exploit the
available deep radio 1.4 GHz data (limiting flux 60 μJy) to explore
the association of EROs and faint radio sources and whether the two
populations trace similar large-scale structures. Cross-correlation
of the two samples (after excluding 17 EROs with radio counterparts)
gives a 2 σ signal only for the subsample of high-z radio sources
(z>0.6). Although the statistics are poor, this suggests that it is
the high-z radio subsample that traces similar structures with EROs. <P
/>Based on observations collected at the European Southern Observatory,
Chile, ESO 66.A-0193(A).
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Title: The Phoenix Deep Survey: Evolution of Star Forming Galaxies
Authors: Hopkins, A. M.; Afonso, J.; Georgakakis, A.; Sullivan, M.;
Mobasher, B.; Cram, L. E.
2005mmgf.conf...38H Altcode:
The Phoenix Deep Survey (PDS) is a multiwavelength survey based on
deep 1.4 GHz radio observations used to identify a large sample of
star forming galaxies to z=1. Photometric redshifts are estimated for
the optical counterparts to the radio-detected galaxies, and their
uncertainties quantified by comparison with spectroscopic redshift
measurements. The photometric redshift estimates and associated
best-fitting spectral energy distributions are used in a stacking
analysis exploring the mean radio properties of U-band selected
galaxies. Average flux densities of a few μJy are measured.
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Title: Radio Properties of EROs in the Phoenix Deep Survey
Authors: Afonso, J.; Hopkins, A. M.; Sullivan, M.; Mobasher, B.;
Georgakakis, A.; Cram, L. E.
2005mmgf.conf..347A Altcode:
Insensitive to dust obscuration, radio wavelengths are ideal to study
star-forming galaxies free of dust induced biases. Using data from
the Phoenix Deep Survey, we have identified a sample of star-forming
extremely red objects (EROs). Stacking of the radio images of the
radio-undetected star-forming EROs revealed a significant radio
detection. Using the expected median redshift, we estimate an average
star-formation rate of 61 M<SUB>⊙</SUB> yr<SUP>-1</SUP> for these
galaxies.
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Title: The Phoenix Deep Survey: Optical and Near-infrared Imaging
Catalogs
Authors: Sullivan, M.; Hopkins, A. M.; Afonso, J.; Georgakakis, A.;
Chan, B.; Cram, L. E.; Mobasher, B.; Almeida, C.
2004ApJS..155....1S Altcode: 2004astro.ph.11577S
The Phoenix Deep Survey is a multiwavelength galaxy survey based
on deep 1.4 GHz radio imaging. The primary goal of this survey is
to investigate the properties of star formation in galaxies and to
trace the evolution in those properties to a redshift z=1, covering a
significant fraction of the age of the universe. By compiling a sample
of star-forming galaxies based on selection at radio wavelengths we
eliminate possible biases due to dust obscuration, a significant issue
when selecting objects at optical and ultraviolet wavelengths. In
this paper, we present the catalogs and results of deep optical
(UBVRI) and near-infrared (Ks) imaging of the deepest region of
the existing decimetric radio imaging. The observations and data
processing are summarized and the construction of the optical source
catalogs described, together with the details of the identification
of candidate optical counterparts to the radio catalogs. Based on
our UBVRIKs imaging, photometric redshift estimates for the optical
counterparts to the radio detections are explored.
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Title: The Phoenix Deep Survey: the radio properties of the hard
X-ray-selected sample
Authors: Georgakakis, A.; Hopkins, A. M.; Afonso, J.; Sullivan, M.;
Mobasher, B.; Cram, L. E.
2004MNRAS.354..127G Altcode: 2004astro.ph..7078G; 2004MNRAS.tmp..340G
The radio properties of hard (2-8 keV) X-ray-selected sources are
explored by combining a single 50-ks XMM-Newton pointing with the
ultradeep and homogeneous Phoenix radio (1.4-GHz) survey. A total of
43 sources are detected above the X-ray flux limit f<SUB>X</SUB>(2-8
keV) = 7.7 × 10<SUP>-15</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>,
with 14 of them exhibiting radio emission above ~40 μJy (3σ). The
X-ray-radio matched population lies in the borderline between
radio-loud and radio-quiet active galactic nuclei (AGNs) and
comprises sources with both soft and hard X-ray spectral properties,
suggesting both obscured and unobscured systems. The spectroscopically
identified subsample (with a total of six X-ray-radio matches)
comprises narrow emission-line AGNs (four) with hard X-ray spectral
properties and broad line sources (two) with soft X-ray spectra. We
find evidence that the fraction of X-ray-radio matches increases
from ~20 per cent for sources with a rest-frame column density
of N<SUB>H</SUB> < 10<SUP>22</SUP> cm<SUP>-2</SUP> to ~50 per
cent for more absorbed systems. Poor statistics, however, limit
the significance of the above result to the ~2σ level. Also, the
X-ray-radio matched sources have a flatter co-added X-ray spectrum
(Γ= 1.78<SUP>+0.05</SUP><SUB>-0.03</SUB>) compared with sources
without radio emission (Γ= 2.00<SUP>+0.03</SUP><SUB>-0.04</SUB>). A
possible explanation for the higher fraction of absorbed sources with
radio emission at the μJy level is the presence of circumnuclear
starburst activity that both feeds and obscures the central engine. For
a small subsample of z~ 0.4 radio-emitting AGNs with N<SUB>H</SUB>
> 10<SUP>22</SUP> cm<SUP>-2</SUP> their combined spectrum exhibits
a soft X-ray component that may be associated with star formation
activity, although other possibilities cannot be excluded. We also
find that radio-emitting AGNs make up approximately 13-20 per cent of
the hard-band X-ray background depending on the adopted normalization.
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Title: Faint 1.4-GHz radio sources in the 2dF Galaxy Redshift Survey
Authors: Chan, B. H. P.; Cram, L. E.; Sadler, E. M.; Killeen, N. E. B.;
Jackson, C. A.; Mobasher, B.; Ekers, R. D.
2004MNRAS.352.1245C Altcode: 2003astro.ph.10315C; 2004MNRAS.tmp..173C
We have used the Australia Telescope Compact Array (ATCA) to search
for faint radio sources in a ~3deg<SUP>2</SUP> region of sky covered
by the 2dF Galaxy Redshift Survey (2dFGRS). Over the region surveyed,
the 1σ noise level at 1.4GHz ranges from 20μJy to 1mJy. The survey
region includes 365 2dFGRS galaxies, of which 316 have good-quality
spectra (176 early-type galaxies or active galactic nuclei, and 140
star-forming galaxies). The fraction of 2dFGRS galaxies detected as
radio sources in our survey rises from ~4 per cent at a 3σ detection
limit of 0.3mJy to 12 per cent at 75μJy, with roughly equal numbers
of star-forming galaxies and active galactic nuclei (AGNs) being
detected. The radio luminosity function derived from this sample
agrees with earlier determinations, and we find that while the mean
redshift of the radio-detected galaxies increases toward lower flux
densities for star-forming galaxies, it remains roughly constant for
the AGN/early-type radio detections. We discuss possible observing
strategies for a submJy radio survey of a larger 2dFGRS region, and
show that a survey covering 100deg<SUP>2</SUP> could measure the global
evolution of the star formation density to z~ 0.1 in a way which is
less affected by reddening than traditional measurements using optical
emission lines and ultraviolet photometry.
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Title: The Phoenix Deep Survey
Authors: Hopkins, A. M.; Afonso, J.; Georgakakis, A.; Sullivan, M.;
Mobasher, B.; Cram, L. E.
2004ASSL..301..125H Altcode: 2004muco.conf..125H
No abstract at ADS
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Title: The Phoenix Deep Survey: Evolution of Star Forming Galaxies
Authors: Hopkins, A. M.; Afonso, J.; Georgakakis, A.; Sullivan, M.;
Mobasher, B.; Cram, L. E.
2003astro.ph.12035H Altcode:
The Phoenix Deep Survey (PDS) is a multiwavelength survey based on
deep 1.4 GHz radio observations used to identify a large sample of
star forming galaxies to z=1. Photometric redshifts are estimated for
the optical counterparts to the radio-detected galaxies, and their
uncertainties quantified by comparison with spectroscopic redshift
measurements. The photometric redshift estimates and associated
best-fitting spectral energy distributions are used in a stacking
analysis exploring the mean radio properties of U-band selected
galaxies. Average flux densities of a few microJy are measured.
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Title: Radio Properties of EROs in the Phoenix Deep Survey
Authors: Afonso, J.; Hopkins, A. M.; Sullivan, M.; Mobasher, B.;
Georgakakis, A.; Cram, L. E.
2003astro.ph.12117A Altcode:
Insensitive to dust obscuration, radio wavelengths are ideal to study
star-forming galaxies free of dust induced biases. Using data from
the Phoenix Deep Survey, we have identified a sample of star-forming
extremely red objects (EROs). Stacking of the radio images of the
radio-undetected star-forming EROs revealed a significant radio
detection. Using the expected median redshift, we estimate an average
star-formation rate of 61 M_sun/yr for these galaxies.
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Title: The Phoenix Deep Survey: X-ray properties of faint radio
sources
Authors: Georgakakis, A.; Hopkins, A. M.; Sullivan, M.; Afonso, J.;
Georgantopoulos, I.; Mobasher, B.; Cram, L. E.
2003MNRAS.345..939G Altcode: 2003astro.ph..7377G
In this paper, we use a 50-ks XMM-Newton pointing overlapping with
the Phoenix Deep Survey, a homogeneous radio survey reaching μJy
sensitivities, to explore the X-ray properties and the evolution
of star-forming galaxies. Multiwavelength ultraviolet, optical and
near-infrared photometric data are available for this field and
are used to estimate photometric redshifts and spectral types for
all radio sources brighter than R= 21.5 mag (a total of 82). Faint
radio galaxies with R < 21.5 mag and spiral galaxy spectral energy
distributions (a total of 34) are then segregated into two redshift
bins with a median of z= 0.240 (a total of 19) and 0.455 (a total of
15), respectively. A stacking analysis for both the 0.5-2 and 2-8 keV
bands is performed on the two subsamples. A high confidence level signal
(>3.5σ) is detected in the 0.5-2 keV band, corresponding to a mean
flux of ~ 3 × 10<SUP>-16</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>
for both subsamples. This flux translates to mean luminosities of ~
5 × 10<SUP>40</SUP> and ~ 1.5 × 10<SUP>41</SUP> erg s<SUP>-1</SUP>
for the z= 0.240 and 0.455 subsamples, respectively. Only a marginally
significant signal (2.6σ) is detected in the 2-8 keV band for the
z= 0.455 subsample. This may indicate hardening of the mean X-ray
properties of sub-mJy sources at higher redshifts and/or higher
luminosities. Alternatively, this may be due to contamination of the z=
0.455 subsample by a small number of obscured active galactic nuclei
(AGNs). On the basis of the observed optical and X-ray properties
of the faint radio sample, we argue that the stacked signal above
is dominated by star formation, with the AGN contamination being
minimal. The mean X-ray-to-optical flux ratio and the mean X-ray
luminosity of the two subsamples are found to be higher than optically
selected spirals and similar to starbursts. We also find that the mean
X-ray and radio luminosities of the faint radio sources studied here
are consistent with the L<SUB>X</SUB>-L<SUB>1.4</SUB> correlation of
local star-forming galaxies. Moreover, the X-ray emissivity of sub-mJy
sources to z~ 0.3 is estimated and is found to be elevated compared with
local H II galaxies. The observed increase is consistent with X-ray
luminosity evolution of the form ~ (1 +z)<SUP>3</SUP>. Assuming that
our sample is indeed dominated by star-forming galaxies, this is direct
evidence for evolution of such systems at X-ray wavelengths. Using
an empirical X-ray luminosity to star formation rate (SFR) conversion
factor, we estimate a global SFR density at z~ 0.3 of 0.029 +/- 0.007
M<SUB>solar</SUB> yr<SUP>-1</SUP> Mpc<SUP>-3</SUP>. This is found to
be in fair agreement with previous results based on galaxy samples
selected at different wavelengths.
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Title: Extremely red galaxies in the Phoenix Deep Survey
Authors: Hopkins, A. M.; Afonso, J.; Georgakakis, A.; Sullivan, M.;
Mobasher, B.; Cram, L. E.
2003astro.ph..9147H Altcode:
The Phoenix Deep Survey (PDS) is a multiwavelength survey based on
deep 1.4 GHz radio observations used to identify a large sample of
star forming galaxies to z=1. Here we present an exploration of the
evolutionary constraints on the star-forming population imposed by the
1.4 GHz source counts, followed by an analysis of the average properties
of extremely red galaxies in the PDS, by using the "stacking" technique.
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Title: Determination of Galaxy Members in Clusters
Authors: Bukhari, Fadel A.; Cram, Lawrence E.
2003Ap&SS.288..245B Altcode:
A new empirical procedure is introduced to determine the confirmrd
galaxy members of a cluster. The method depends on both the projected
distances of galaxies in the cluster field from the cluster centre and
their radial velocities. Galaxies of the main body of the cluster are
selected first, then the method works iteratively by increasing the
standard values of the relative radial distance and velocity until
all galaxies belong to the cluster are included. The general apparent
shape of the cluster will result from the distribution of the celestial
coordinates of the cluster members.
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Title: The Phoenix Deep Survey: Evolution in the microJansky radio
population
Authors: Hopkins, A. M.; Afonso, J. M.; Chan, B.; Cram, L. E.;
Georgakakis, A.; Mobasher, B.
2003RMxAC..17..252H Altcode:
The era spanning 0 < z ≲ 1 is witness to strong evolution of
star-formation in galaxies, evidenced by a decline of almost an
order of magnitude in the space density of galaxy star-formation
rates. Understanding galaxy evolution over this significant
fraction of the age of the Universe is an extraordinarily complex
undertaking. Investigation of this cosmologically significant era in a
coherent fashion is complicated by the heterogeneous nature of the many
surveys required to probe the full redshift range. The unknown extent of
dust obscuration at different redshifts, extremely important for studies
of star-formation, also adds to the complexity. These difficulties are
being addressed by the Phoenix Deep Survey, an ongoing very sensitive
radio survey. A homogeneous radio-selected catalogue of over 2000
sources reaching flux densities as faint as 50 mu Jy has been compiled.
---------------------------------------------------------
Title: The Phoenix Deep Survey: The 1.4 GHz Microjansky Catalog
Authors: Hopkins, A. M.; Afonso, J.; Chan, B.; Cram, L. E.;
Georgakakis, A.; Mobasher, B.
2003AJ....125..465H Altcode: 2002astro.ph.11068H
The initial Phoenix Deep Survey (PDS) observations with the Australia
Telescope Compact Array have been supplemented by additional 1.4
GHz observations over the past few years. Here we present details
of the construction of a new mosaic image covering an area of 4.56
deg<SUP>2</SUP>, an investigation of the reliability of the source
measurements, and the 1.4 GHz source counts for the compiled radio
catalog. The mosaic achieves a 1σ rms noise of 12 μJy at its
most sensitive, and a homogeneous radio-selected catalog of over
2000 sources reaching flux densities as faint as 60 μJy has been
compiled. The source parameter measurements are found to be consistent
with the expected uncertainties from the image noise levels and the
Gaussian source fitting procedure. A radio-selected sample avoids
the complications of obscuration associated with optically selected
samples, and by utilizing complementary PDS observations, including
multicolor optical, near-infrared, and spectroscopic data, this radio
catalog will be used in a detailed investigation of the evolution in
star formation spanning the redshift range 0<z<1. The homogeneity
of the catalog ensures a consistent picture of galaxy evolution can be
developed over the full cosmologically significant redshift range of
interest. The 1.4 GHz mosaic image and the source catalog are available
on the World Wide Web; or from the authors by request.
---------------------------------------------------------
Title: Orientation of Galaxies in Clusters
Authors: Bukhari, Fadel A.; Cram, Lawrence E.
2003Ap&SS.283..173B Altcode:
A detailed analysis of the geometry of galaxies in clusters has been
undertaken in both two and three dimensional space. The procedure
was applied to the three Abell clusters A1644, A548 E and A548 W. No
significant alignment trend of galaxies in clusters confirmed in
three dimensional space was found. This result is consistent with
the mixed dark matter model MDM of galaxy formation. The result is
also consistent with Peebles suggestion that protogalaxies acquired
angular momentum from tidal torques exerted by their neighbours in
the early universe. The amount of angular momentum predicted by this
mechanism could be described by a single dimensionless papameter λ ~
0.8. N-body experiments have shown that λ has approximately normal
distribution with mean value about 0.07 and with a standard deviation
of about 0.03. From the analyic fit to flat rotation curves it is
found that tidal torque can provide the observed angular momentum if
the mean collapse factor is about 20 and the mean halo-to-disk mass
ratio is of order 10. The MDM model does not predict any systematic
relation between the tidal torques among the halos of galaxies and the
large scale structures such as the clusters, superclusters of galaxies
and giant voids in between. Further work in this area is still required.
---------------------------------------------------------
Title: Geometrical Properties of Galaxy Clusters
Authors: Bukhari, Fadel A.; Cram, Lawrence E.
2003Ap&SS.283..161B Altcode:
Empirical and analytical procedures are developed to determine the
morphological properties of galaxy clusters. The apparent orientations
and shapes are obtainted in two dimensional space while the direction
towards the cluster pole is found in three dimensional space. These
properties were determined for three Abell clusters and found to be
strongly related.
---------------------------------------------------------
Title: Archetypal analysis of galaxy spectra
Authors: Chan, B. H. P.; Mitchell, D. A.; Cram, L. E.
2003MNRAS.338..790C Altcode: 2003astro.ph..1491C
Archetypal analysis represents each individual member of a set of data
vectors as a mixture (a constrained linear combination) of the pure
types or archetypes of the data set. The archetypes are themselves
required to be mixtures of the data vectors. Archetypal analysis may be
particularly useful in analysing data sets comprising galaxy spectra,
since each spectrum is, presumably, a superposition of the emission from
the various stellar populations, nebular emissions and nuclear activity
making up that galaxy, and each of these emission sources corresponds to
a potential archetype of the entire data set. We demonstrate archetypal
analysis using sets of composite synthetic galaxy spectra, showing that
the method promises to be an effective and efficient way to classify
spectra. We show that archetypal analysis is robust in the presence
of various types of noise.
---------------------------------------------------------
Title: Galaxy evolution from a microJansky radio survey
Authors: Afonso, J.; Mobasher, B.; Hopkins, A.; Georgakakis, A.;
Cram, L.; Chan, B.
2003Ap&SS.285..149A Altcode:
A strong evolution of galaxies is observed for 0<z<1, as
evidenced by an increase of almost an order of magnitude in the galaxy
star-formation rate density. However, it is known that dust obscuration
has affected our understanding of galaxy evolution over this significant
fraction of the age of the Universe. In order to study galaxy evolution
free from dust induced biases, an ultra deep radio survey - the Phoenix
Deep Survey - was initiated. With a detection limit of 60μJy, this
homogeneous survey, complemented with multiwavelength (photometric
and spectroscopic) observations, is being used to build a consistent
picture of galaxy evolution. The ultra-deep radio source counts are
presented, and interpreted using luminosity function evolutionary
models. The discovery of extremely dusty galaxies from this survey,
along with the clustering properties of the sub-mJy radio population,
are also discussed.
---------------------------------------------------------
Title: Morphology and Environments of X-Ray/Radio-Loud AGN in the
GOODS Fields
Authors: Koekemoer, A. M.; Mobasher, B.; Afonso, J.; Chan, B.;
Conselice, C.; Cram, L.; Grogin, N. A.; Jackson, C.; Jogee, S.;
Lucas, R. A.; Norris, R. P.; Padovani, P.; Schreier, E. J.; Urry,
C. M.; Fosbury, R.; Ettori, S.; GOODS Team
2002AAS...201.0602K Altcode: 2002BAAS...34.1098K; 2002AAS...201..602K
The advent of ultra-deep X-ray surveys with Chandra, together with deep
HST/ACS imaging and microJy-level radio surveys, allows us to directly
probe the detailed properties of the environments, host galaxies and
central accretion disks of the most distant radio galaxies. Here we
present results from a combined program of our ultra-deep 20cm radio
survey with the Australia Telescope of the Chandra Deep Field South,
together with data from the multi-band GOODS/ACS imaging program with
HST. We describe a sample of radio-loud AGN in this field and present
results on the optical morphological properties of their hosts and
environments, as well as their X-ray properties. We discuss the results
in the context of previous studies on lower-redshift radio galaxies,
and also present a comparison with the properties of radio-quiet AGN to
examine whether radio-loudness represents the high end of a continuum
of properties or is instead a phenomenon that is quite distinct from
radio-quiet sources. We examine the implications of these results
for the properties of black holes in the early universe. Ground-based
imaging data were taken at ESO 2.2m, NTT, VLT, and NOAO 4m telescopes
and made publicly available.
---------------------------------------------------------
Title: A search for young Galactic supernova remnants
Authors: Misanovic, Zdenka; Cram, Lawrence; Green, Anne
2002MNRAS.335..114M Altcode:
A sample of eight small-diameter radio sources has been selected from
the Molonglo Galactic Plane Survey (MGPS) as candidates for young
Galactic supernova remnants. The sources have been identified in the
IRAS and Midcourse Space Experiment infrared data bases and imaged
in the H107α radio recombination line (RRL) using the Australia
Telescope Compact Array (ATCA). Seven of the sources display high
ratios of infrared-to-radio-continuum flux density and/or detectable
RRLs and are almost certainly H II regions. One source (G282.8-1.2)
is identified as a possible new young Galactic supernova remnant,
based on its relatively weak infrared emission, steep radio spectrum,
and possible X-ray emission. The adopted method for distinguishing
thermal and non-thermal Galactic radio sources seems promising and
could be fruitfully applied to more than 100 small-diameter sources
listed in the MGPS.
---------------------------------------------------------
Title: Image Processing for the Sydney University Molonglo Sky Survey
(SUMSS)
Authors: Chan, B. H. P.; Cram, L. E.
2002PASA...19..201C Altcode:
The Sydney University Molonglo Sky Survey (SUMSS) is a deep radio survey
at 843MHz, covering the region south of -30° declination. Designed
to be a southern counterpart of the northern NRAO VLA Sky Survey
(NVSS), SUMSS is over 40% complete, and it is now time to devise
ways to generate the source catalogue for the survey. We describe
here new methods to deal with image artifacts to minimise spurious
fits by automatic source fitting algorithms. With the new techniques,
an automatically generated, objective catalogue can be made to a 10mJy
cutoff. Catalogues can be made to a 5mJy cutoff provided that special
care is taken and certain artifacts are avoided.
---------------------------------------------------------
Title: Implications of Episodic Star Formation in Disk Galaxies
Authors: D'Cruz, N.; Bryant, J.; Cram, L.
2001AAS...19916003D Altcode: 2002BAAS...34Q.570D
There is a large amount of data present on spiral galaxies in the
nearby Universe. Hα data from Kennicutt and collaborators provides
information about recent star formation, while broad band optical
colours contain the star formation histories of galaxies over their
lifetimes. Radio emission at 1.4 GHz is also a tracer of star formation
as the emission is believed to arise from supernova remnants. It is very
likely that galaxies experience multiple episodes of star formation as
they evolve. In order to understand the nearby galaxies, we model their
star formation history as periodic bursts with varying burst shapes,
and use the PEGASE galaxy evolution code (Fioc and Rocca-Volmerange
2000) to compute Hα fluxes and the optical colours. We will present
some of the star formation histories that we use. We find that bursts
which decay exponentially seem to fit the data better than other burst
shapes that we explored. We also compare our models to the observed
radio-to-optical luminosity function.
---------------------------------------------------------
Title: Discovery of an Extremely Red Galaxy at z=0.65 with Dusty
Star Formation and Nuclear Activity
Authors: Afonso, J.; Mobasher, B.; Chan, B.; Cram, L.
2001ApJ...559L.101A Altcode: 2001astro.ph..8361A
In the course of the follow-up multiwavelength study of a deep radio
survey, we have discovered that the millijansky radio source PDF
J011423 is a low-redshift (z=0.65) extremely red galaxy (ERG) with
K=15.3, R-K=5.8, and J-K=3.1. Optical, infrared, and radio photometry,
together with optical and near-infrared spectroscopy, reveal a heavily
obscured galaxy (A<SUB>V</SUB>=5-6, from the observed Balmer decrement)
undergoing vigorous star formation and presenting an active galactic
nucleus. PDF J011423 is a representative member of the dusty ERG
population, providing a local counterpart for studying more distant
ERGs. Based on observations with the Infrared Space Observatory,
Australia Telescope Compact Array, Anglo-Australian Telescope, Cerro
Tololo Inter-American Observatory, and the European Southern Observatory
(program 266.A-5633).
---------------------------------------------------------
Title: A Comparison of Independent Star Formation Diagnostics for
an Ultraviolet-selected Sample of Nearby Galaxies
Authors: Sullivan, Mark; Mobasher, Bahram; Chan, Ben; Cram, Lawrence;
Ellis, Richard; Treyer, Marie; Hopkins, Andrew
2001ApJ...558...72S Altcode: 2001astro.ph..4425S
We present results from a decimetric radio survey undertaken with
the Very Large Array as part of a longer term goal to intercompare
star formation and dust extinction diagnostics on a galaxy-by-galaxy
basis for a representative sample of nearby galaxies. For our survey
field, Selected Area 57, star formation rates derived from 1.4 GHz
luminosities are compared with earlier nebular emission-line and
ultraviolet (UV) continuum diagnostics. We find broad correlations,
over several decades in luminosity, between the Hα, UV continuum,
and 1.4 GHz diagnostics. However, the scatter in these relations is
found to be larger than observational errors, with offsets between the
observed relations and those expected assuming constant star formation
histories and luminosity-independent extinction models. We investigate
the physical origin of the observed relations and conclude that the
discrepancies between different star formation diagnostics can only be
partly explained by simple models of dust extinction in galaxies. These
models cannot by themselves explain all the observed differences,
introducing the need for temporally varying star formation histories
and/or more complex models of extinction to explain the entire data set.
---------------------------------------------------------
Title: Toward a Resolution of the Discrepancy between Different
Estimators of Star Formation Rate
Authors: Hopkins, A. M.; Connolly, A. J.; Haarsma, D. B.; Cram, L. E.
2001AJ....122..288H Altcode: 2001astro.ph..3253H
Different wavelength regimes and methods for estimating the space
density of the star formation rate (SFR) result in discrepant
values. While it is recognized that ultraviolet (UV) and Hα
emission-line data must be corrected for the effects of extinction,
the magnitude of the required correction is uncertain. Even when
these corrections are made there remains a significant discrepancy
between SFRs derived from UV and Hα measurements compared with
those derived from far-infrared (FIR) and radio luminosities. Since
the FIR-radio-derived SFRs are not affected by extinction and simple
corrections to reconcile the UV and Hα measurement with these do not
fully account for the discrepancies, a more sophisticated correction
may be required. Recent results suggest that at least part of the
solution may be a form of extinction that increases with increasing SFR
(or luminosity, given the common assumption that SFR is proportional to
luminosity). We present an analysis of the effects of a dust reddening
dependent on star formation rate applied to estimators of SFR. We show
(1) that the discrepancies between Hα and FIR-radio SFR estimates
may be explained by such an effect and we present an iterative method
for applying the correction and (2) that UV-based estimates of SFR
are harder to reconcile with FIR-radio estimates using this method,
although the extent of the remaining discrepancy is less than for
a non-SFR-dependent correction. Particularly at high redshift, our
understanding of extinction at UV wavelengths may require a still more
complex explanation.
---------------------------------------------------------
Title: A Complete Microjansky Radio Survey
Authors: Afonso, José; Mobasher, Bahram; Hopkins, Andrew; Cram,
Lawrence
2001Ap&SS.276..941A Altcode:
The Phoenix Deep Survey is an ongoing multi-wavelength survey of a 2^°
diameter field aimed at studying the properties of the sub-mJy and μJy
radio population. Here, we present the latest 1.4 GHz observations of
this field. The new data, reaching a 5 σ flux level of 45 μJy at
the centre of a 50' diameter field, comprise more than 700 sources
with flux densities less than 1 mJy (187 of which have S_1.4 <
100 μJy). This provides one of the deepest radio (1.4 GHz) surveys
currently available. The 1.4 GHz source counts are presented and show
a flattening down to the 50 μJy level. At flux densities around 300
μJy there are indications that the sources detected may exhibit higher
clustering than those observed at higher flux levels. This suggests that
deep radio surveys could be useful for studies of large-scale structure
but it also presents a warning for the representativity of sources in
deep pencil-beam radio surveys. The study of the optical counterparts
of the μJy population seems to indicate that the median R magnitude
starts to decrease below 100 μJy. Spectroscopic classification of a
sample of sources in this survey confirms the trend for an increasing
fraction of star-forming galaxies over other systems down to ~ 100 μJy.
---------------------------------------------------------
Title: ISO Observations of Faint Radio Sources
Authors: Afonso, José; Mobasher, Bahram; Georgakakis, Antonis; Cram,
Lawrence; Hopkins, Andrew
2001ApSSS.277..527A Altcode:
Deep radio surveys have revealed, below the millijansky level,
a population of actively starforming galaxies, undergoing strong
luminosity evolution as found from the observed radio source counts. A
random sample of 65 sub-mJy radio sources, selected from the Phoenix
Deep Survey, was observed at mid and far-infrared wavelengths using
the Infrared Space Observatory. Nine sources were detected at both
far-infrared and at least one of the mid-infrared wavelengths. A
preliminary analysis of the infrared properties of these faint radio
sources is carried out by modeling their infrared Spectral Energy
Distribution. The radio vs. far-infrared relation, for these faint
radio objects, is also presented.
---------------------------------------------------------
Title: ISO Observations of Star-Forming Galaxies
Authors: Mobasher, Bahram; Afonso, José; Cram, Lawrence
2001defi.conf..144M Altcode: 2001astro.ph..1403M
The Infrared Space Observatory (ISO) is used to carry out mid-IR
(7 and 15 μm) and far-IR (90 μm) observations of a sample of
star-forming sub-mJy radio sources. By selecting the sample at radio
wavelengths, one avoids biases due to dust obscuration. It is found
that the mid-IR luminosities, covering the PAH features, measure
the star formation rate for galaxies with P <SUB>1.4GHz </SUB> <
10<SUP>23</SUP> W Hz<SUP>-1</SUP>. This is further confirmed using the
Hα luminosities. The far-IR emission is also found to trace the SFR
over the whole range of radio and Hα luminosities. The implication
of the mid-IR measurements in estimating the SFRs from the future
infrared space missions (SIRTF and ASTRO-F) is discussed.
---------------------------------------------------------
Title: Division IV: Stars
Authors: Barbuy, Beatriz; Cram, L.; Dravins, D.; Evans, T. L.; Mathys,
G.; Scarfe, C.; VandenBerg, D.
2001IAUTB..24..157B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: What Will the Next Generation Radio Telescope Detect at
1.4 GHz?
Authors: Hopkins, A.; Windhorst, R.; Cram, L.; Ekers, R.
2000ExA....10..419H Altcode: 1999astro.ph..6469H
An international project is underway to design and build a radio
telescope with an effective collecting area two orders of magnitude
greater than the largest existing instruments. One of the many
scientific goals of this instrument will be the investigation of the
extragalactic radio source population at flux densities two to three
orders of magnitude fainter than the limits of existing observations. We
present simulations of the radio sky at 1.4 GHz down to a flux density
limit of 0.1 μJy using extrapolations of known radio luminosity
functions for two different population scenarios. The resulting
simulations confirm that a resolution of 0^”_.1 is necessary to
avoid formal confusion, but source blending may still dominate if the
intrinsic size of such faint sources is larger than a few kiloparsecs.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Phoenix Deep Survey: 1.4-GHz
source counts (Hopkins+, 1998)
Authors: Hopkins, A. M.; Mobasher, B.; Cram, L.; Rowan-Robinson, M.
2000yCat..72960839H Altcode:
We present the first results from the Phoenix Deep Survey,
a multiwavelength survey of a 2 deg diameter region. Observations
in the radio continuum at 1.4 GHz carried out with the Australia
Telescope Compact Array are described. The catalogue of over 1000 radio
sources compiled from these observations is analyzed, and the source
counts are presented. We model the observational source counts using
a two-population model and published luminosity functions for these
populations. Upon invoking luminosity and density evolution, we find
that a luminosity evolution model best fits the radio observations,
consistent with earlier work. The redshift distribution of the two
galaxy populations investigated is also modeled and discussed. (1
data file).
---------------------------------------------------------
Title: On the Determination of Star Formation Rates in Evolving
Galaxy Populations
Authors: Afonso, J.; Cram, L.; Mobasher, B.
2000ApJ...536...68A Altcode: 2000astro.ph..1369A
The redshift dependence of the luminosity density in certain wave bands
(e.g., UV and Hα) can be used to infer the history of star formation
in the populations of galaxies producing this luminosity. This history
is a useful datum in studies of galaxy evolution. It is therefore
important to understand the errors that attend the inferring of
star formation rate densities from luminosity densities. This paper
explores the self-consistency of star formation rate diagnostics by
reproducing commonly used observational procedures in a model with
known galaxy populations, evolutionary histories, and spectral emission
properties. The study reveals a number of potential sources of error
in the diagnostic processes arising from the differential evolution
of different galaxy types. We argue that multiwavelength observations
can help to reduce these errors.
---------------------------------------------------------
Title: Microjansky Radio Sources in DC 0107-46 (Abell 2877)
Authors: Hopkins, A.; Georgakakis, A.; Cram, L.; Afonso, J.;
Mobasher, B.
2000ApJS..128..469H Altcode: 2000astro.ph..1413H
The cluster DC 0107-46 (Abell 2877) lies within the Phoenix Deep Survey,
made at 1.4 GHz with the Australia Telescope Compact Array. Of 89
known optical cluster members, 70 lie within the radio survey area. Of
these 70 galaxies, 15 (21%) are detected, with luminosities as faint
as 1.0×10<SUP>20</SUP> W Hz<SUP>-1</SUP>. Spectroscopic observations
are available for 14/15 of the radio-detected cluster galaxies. Six
galaxies show only absorption features and are typical low-luminosity
active galactic nucleus (AGN) radio sources. One galaxy hosts a Seyfert
2 nucleus, two are star-forming galaxies, and the remaining five may
be star-forming galaxies, AGNs, or both.
---------------------------------------------------------
Title: VizieR Online Data Catalog: The Phoenix Survey (Georgakakis+,
1999)
Authors: Georgakakis, A.; Mobasher, B.; Cram, L.; Hopkins, A.; Lidman,
C.; Rowan-Robinson, M.
2000yCat..73060708G Altcode:
Using a deep Australia Telescope Compact Array (ATCA) radio survey
covering an area of ~3deg<SUP>2</SUP> to a 4{sigma} sensitivity
of >=100mmJy at 1.4GHz, we study the nature of faint radio
galaxies. About 50 per cent of the detected radio sources are
identified with an optical counterpart revealed by CCD photometry
to m_R=22.5mag. Near-infrared (K-band) data are also available for a
selected sample of the radio sources, while spectroscopic observations
have been carried out for about 40 per cent of the optically identified
sample. These provide redshifts and information on the stellar
content. Emission-line ratios imply that most of the emission-line
sources are star-forming galaxies, with a small contribution (~10 per
cent) from Sy1/Sy2 type objects. We also find a significant number
of absorption-line systems, likely to be ellipticals. These dominate
at high flux densities (>1mJy) but are also found at sub-mJy
levels. Using the Balmer decrement we find a visual extinction
A<SUB>V</SUB>=1.0 for the star-forming faint radio sources. This
moderate reddening is consistent with the V-R and R-K colours of the
optically identified sources. For emission-line galaxies, there is
a correlation between the radio power and the Halpha luminosity, in
agreement with the result of Benn et al. (1993MNRAS.263....9B). This
suggests that the radio emission of starburst radio galaxies is a good
indicator of star formation activity. <P />(1 data file).
---------------------------------------------------------
Title: Hi and radio continuum study of the isolated SBa Seyfert
galaxy NGC 3783
Authors: Blank, D. L.; Cram, L. E.
2000MNRAS.312..247B Altcode:
NGC 3783 is a nearby SBa, type 1 Seyfert galaxy. We present Hi
and radio continuum images of the galaxy made with the Australia
Telescope Compact Array (ATCA). We find that NGC 3783 has an Hi mass of
8.4x10<SUP>9</SUP>M<SUB>solar</SUB>, an Hi diameter of 1.9 D<SUB>0</SUB>
(D<SUB>0</SUB>=37kpc for h=0.5), and a nuclear depression in the Hi
surface density. The Hi rotation curve is dominated by differential
rotation, with little evidence of warping. The rotation curve suggests
a mass-to-light ratio ML<SUB>B</SUB>=7.2 and a bar-pattern speed
of 19+/-7kms<SUP>-1</SUP>kpc<SUP>-1</SUP>. The total mass of gas
in the inner 50arcsec is >~10per cent of the dynamical mass, and
consistent with models that require significant gas content to fuel
the Seyfert nucleus. There is no evidence that the nuclear activity
in NGC 3783 is being stimulated by an interaction or merger: it may
be a self-generated, perhaps bar-driven, process.
---------------------------------------------------------
Title: The Phoenix radio survey: The angular correlation function
Authors: Georgakakis, A.; Mobasher, B.; Cram, L.; Hopkins, A.;
Rowan-Robinson, M.
2000A&AS..141...89G Altcode: 1999astro.ph.10318G
Using the Phoenix radio survey, a homogeneous survey selected at
1.4 GHz and covering an area of ~3 deg<SUP>2</SUP>, we analyse the
clustering of the sub-mJy radio population using angular correlation
function analysis. Extensive simulations are carried out to investigate
the significance of the estimated angular correlation amplitudes. Our
analysis show that for the S<SUB>1.4</SUB>>0.5 mJy sub-samples the
radio source distribution is anisotropic at the 2sigma significance
level. Additionally, we estimate upper limits for the angular
correlation amplitudes that, despite the large uncertainties, are in
good agreement with the amplitude estimates for sources brighter than 1
mJy, detected in the FIRST radio survey (Cress et al. 1997). Adopting
a radio luminosity function and assuming an evolving spatial
correlation function of the form xi (r)=(r/r_0)<SUP>-gamma </SUP>
(1+z)<SUP>-(3+epsilon )</SUP>, with the evolution parametrised by
epsilon , we find an upper limit for the angular correlation length
r_0~9 h<SUP>-1</SUP> Mpc for S<SUB>1.4</SUB>>0.5 mJy and gamma
=2.1. This agrees well with the value r_0~6-8 h<SUP>-1</SUP> Mpc
estimated from the FIRST radio survey for sources brighter than 1
mJy. Additionally, we quantify the characteristics, in terms of areal
coverage and limiting flux density, of future deep radio surveys to
yield a significant correlation amplitude detection and to explore
possible changes of the correlation amplitude with flux density.
---------------------------------------------------------
Title: What Will the Ska See at 1.4 Ghz?
Authors: Hopkins, A.; Windhorst, R.; Cram, L.; Ekers, R.
2000pras.conf..117H Altcode:
One of the many scientific goals of the Square Kilometer Array (SKA)
will be the investigation of the extragalactic radio source population
at flux densities two to three orders of magnitude fainter than the
limits of existing observations. We present simulations of the radio sky
at 1.4GHz down to a flux density limits of 0.1m Jy using extrapolations
of known radio luminosity functions for two different population
scenarios. The resulting simulations confirm that a resolution of 0.1"
is necessary to avoid formal confusion, but source blending may still
dominate if the intrinsic size of such faint sources is larger than
a few kiloparsecs.
---------------------------------------------------------
Title: Microjansky radio sources in DC0107-46 (Abell 2877)
Authors: Hopkins, Andrew; Georgakakis, Antonis; Cram, Lawrence;
Afonso, José; Mobasher, Bahram
2000ASPC..215...55H Altcode: 2000cegf.conf...55H
No abstract at ADS
---------------------------------------------------------
Title: Commission 36: Theory of Stellar Atmospheres: (Theorie des
Atmospheres Stellaires)
Authors: Pallavicini, R.; Dravins, D.; Barbuy, B.; Cram, L.; Hubeny,
I.; Owocki, S.; Saio, H.; Sasselov, D.; Spite, M.; Stepien, K.;
Wehrse, R.
2000IAUTA..24..219P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Division IV: Stars: (Etoiles)
Authors: Cram, Lawrence; Barbuy, Beatriz; Gerbaldi, Michele; Lambert,
David; Pallavicini, Roberto; Zahn, Jean-Paul; Zinnecker, Hans
2000IAUTA..24..173C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The PHOENIX survey: the pairing fraction of faint radio sources
Authors: Georgakakis, A. E.; Mobasher, B.; Cram, L.; Hopkins, A.
1999MNRAS.310L..15G Altcode: 1999astro.ph.10140G
The significance of tidal interactions in the evolution of the faint
radio population (sub-mJy) is studied using a deep and homogeneous radio
survey (1.4GHz), covering an area of 3.14deg<SUP>2</SUP> and complete
to a flux density of 0.4mJy. Optical photometric and spectroscopic
data are also available for this sample. A statistical approach is
employed to identify candidate physical associations between radio
sources and optically selected `field' galaxies. We find an excess of
close pairs around optically identified faint radio sources, albeit
at a low significance level, implying that the pairing fraction of
the sub-mJy radio sources is similar to that of `field' galaxies
(at the same magnitude limit) but higher than that of local galaxies.
---------------------------------------------------------
Title: The 1.4-GHz and Hα luminosity functions and star formation
rates from faint radio galaxies
Authors: Mobasher, B.; Cram, L.; Georgakakis, A.; Hopkins, A.
1999MNRAS.308...45M Altcode: 1999astro.ph..3293M
A sample of over 1000 objects selected from a 1.4-GHz survey made
by the Australia Telescope Compact Array (ATCA) is used to study the
properties of the faint radio source population. The sample, covering an
area of ~3deg^2, is 50per cent complete to 0.2mJy. Over 50per cent of
the radio sources are found to have optical counterparts brighter than
R~21.5. Spectroscopic observations of 249 optically identified radio
sources have been made, using the 2-degree Field (2dF) facility at the
Anglo-Australian Telescope (AAT). Redshifts and equivalent widths of
several spectral features (e.g. Hα and [Oii] lambda3727) sensitive
to star formation have been measured. On the basis of the photometric
and spectroscopic data, the optically identified radio sources are
classified as (i) absorption-line galaxies, (ii) star-forming galaxies
and (iii) Seyfert-like galaxies. The spectroscopic sample is corrected
for incompleteness and used to estimate the 1.4-GHz and Hα luminosity
functions (LFs) and luminosity density distributions. The 1.4-GHz LF of
the star-forming population has a much steeper faint-end slope (1.85)
than the ellipticals (1.35). This implies an increasing preponderance
of star-forming galaxies among the optically identified (i.e. z<~1)
radio sources at fainter flux densities. The Hα LF of the faint radio
population agrees with published Hα LFs derived from local samples
selected by Hα emission. This suggests that the star-forming faint
radio population is coincident with the Hα-selected population. The
1.4-GHz and Hα luminosity densities have been used to estimate the
star formation rates (SFRs). The two SFRs agree, both giving a SFR
density of 0.032M_solaryr^-1Mpc^-3 in the range z<~1. Radio selection
appears to be as effective as Hα selection in finding the galaxies that
dominate star formation at a given epoch. Although the sample contains
many galaxies lying beyond z~0.3, it does not reveal a significant
rise in the global star formation rate with increasing redshift. This
result suggests that the optical counterparts of galaxies undergoing
vigorous star formation at redshifts beyond z~0.3 are generally fainter
than R~21.
---------------------------------------------------------
Title: Summary of the 'Sub-microJansky Radio Sky' Workshop
Authors: Hopkins, Andrew; Ekers, Ron; Jackson, Carole; Cram, Lawrence;
Green, Anne; Manchester, Dick; Staveley-Smith, Lister; Norris, Ray
1999PASA...16..152H Altcode:
The Square Kilometre Array Radio Telescope is the next generation radio
telescope. An international project is currently under way to design
and build an instrument having an effective collecting area two orders
of magnitude greater than that of any existing telescope. A number of
separate studies are presently investigating how to design the Square
Kilometre Array to best carry out the kinds of observations desired
by the astronomical community. We present a summary of one of these
studies, a workshop called The `Sub-microJansky Radio Sky' held at the
ATNF, Sydney, on 17 June 1998. This workshop addressed the nature of
the radio sky at the very faint flux densities likely to be attainable
by the Square Kilometre Array. In particular, each speaker investigated
a separate population of radio sources and how the expected appearance
of that population at such faint flux densities would dictate how to
refine some of the design constraints for the Square Kilometre Array.
---------------------------------------------------------
Title: VizieR Online Data Catalog: ISO ELAIS 1.4GHz survey
(Gruppioni+, 1999)
Authors: Gruppioni, C.; Ciliegi, P.; Rowan-Robinson, M.; Cram, L.;
Hopkins, A.; Cesarsky, C.; Danese, L.; Franceschini, A.; Genzel, R.;
Lawrence, A.; Lemke, D.; McMahon, R. G.; Miley, G.; Oliver, S.; Puget,
J. -L.; Rocca-Volmerange, B.
1999yCat..73050297G Altcode:
A deep survey of the European Large-Area ISO Survey (ELAIS) field in
the southern celestial hemisphere (hereinafter S1) has been carried
out with the Australia Telescope Compact Array (ATCA) at 1.4GHz. The S1
region, covering about 4deg<SUP>2</SUP>, has also been surveyed in the
mid- and far-infrared (5-200mm) with the Infrared Space Observatory
(ISO). The radio survey provides uniform coverage of the entire S1
region, with a sensitivity (5{sigma}) of 0.4mJy over the whole area
and 0.2mJy in the centre. To this sensitivity, virtually all the radio
counterparts of the far-infrared extragalactic ISO sources should be
detected. This paper presents a radio sample -- complete at the 5{sigma}
level -- consisting of 581 sources detected at 1.4GHz. Of these radio
sources, 349 have peak flux density in the range 0.2-1mJy, forming
a new homogeneous sample of sub-mJy radio sources. Due to its size,
depth and multiwaveband coverage, the sample will allow us to study in
greater detail the sub-mJy radio source population. <P />(1 data file).
---------------------------------------------------------
Title: The Phoenix Survey: optical and near-infrared observations
of faint radio sources
Authors: Georgakakis, A.; Mobasher, B.; Cram, L.; Hopkins, A.; Lidman,
C.; Rowan-Robinson, M.
1999MNRAS.306..708G Altcode: 1999astro.ph..3016G
Using a deep Australia Telescope Compact Array (ATCA) radio survey
covering an area of ~3 deg<SUP>2</SUP> to a 4σ sensitivity of >=
100 μJy at 1.4 GHz, we study the nature of faint radio galaxies. About
50 per cent of the detected radio sources are identified with an
optical counterpart revealed by CCD photometry to m<SUB>R</SUB>=22.5
mag. Near-infrared (K-band) data are also available for a selected
sample of the radio sources, while spectroscopic observations have
been carried out for about 40 per cent of the optically identified
sample. These provide redshifts and information on the stellar
content. Emission-line ratios imply that most of the emission-line
sources are star-forming galaxies, with a small contribution (~
10 per cent) from Sy1/Sy2 type objects. We also find a significant
number of absorption-line systems, likely to be ellipticals. These
dominate at high flux densities (>1 mJy) but are also found at
sub-mJy levels. Using the Balmer decrement we find a visual extinction
A<SUB>V</SUB>=1.0 for the star-forming faint radio sources. This
moderate reddening is consistent with the V-R and R-K colours of the
optically identified sources. For emission-line galaxies, there is a
correlation between the radio power and the Hα luminosity, in agreement
with the result of Benn et al. This suggests that the radio emission of
starburst radio galaxies is a good indicator of star formation activity.
---------------------------------------------------------
Title: Microjansky Sources at 1.4 GHZ
Authors: Hopkins, A.; Afonso, J.; Cram, L.; Mobasher, B.
1999ApJ...519L..59H Altcode: 1999astro.ph..5055H
We present a deep 1.4 GHz survey made with the Australia Telescope
Compact Array, having a background rms of 9 μJy near the image
phase center, up to 25 μJy at the edge of a 50' field of view. Over
770 radio sources brighter than 45 μJy have been cataloged in
the field. The differential source counts in the deep field provide
tentative support for the growing evidence that the microjansky radio
population exhibits significantly higher clustering than found at
higher flux density cutoffs. The optical identification rate on CCD
images is approximately 50% to R=22.5, and the optical counterparts of
the faintest radio sources appear to be mainly single galaxies close
to this optical magnitude limit.
---------------------------------------------------------
Title: The Molonglo Galactic Plane Survey. I. Overview and Images
Authors: Green, A. J.; Cram, L. E.; Large, M. I.; Ye, Taisheng
1999ApJS..122..207G Altcode: 1998astro.ph.10385G
The first-epoch Molonglo Galactic Plane Survey is a radio continuum
survey made using the Molonglo Observatory Synthesis Telescope at 843
MHz with a resolution of 43<SUP>”</SUP>×43<SUP>”</SUP>csc|δ|. The
region surveyed is 245<SUP>deg</SUP><=l<=355<SUP>deg</SUP>,
|b|<=1.5<SUP>deg</SUP>. The 13 9<SUP>deg</SUP>×3<SUP>deg</SUP>
mosaic images presented here are the superposition of over 450 complete
synthesis observations, each taking 12 h and covering a field of
70<SUP>'</SUP>×70<SUP>'</SUP>csc|δ|. The root-mean-square sensitivity
over much of the mosaicked survey is 1-2 mJy beam<SUP>-1</SUP> (1 σ),
and the positional accuracy is ~1<SUP>”</SUP>×1<SUP>”</SUP>csc|δ|
for sources brighter than 20 mJy. The dynamic range is no better than
250:1, and this also constrains the sensitivity in some parts of the
images. The survey area of 330 deg<SUP>2</SUP> contains well over
1.2×10<SUP>4</SUP> unresolved or barely resolved objects, almost all
of which are extragalactic sources lying in the zone of avoidance. In
addition, a significant fraction of this area is covered by extended,
diffuse emission associated with thermal complexes, discrete H II
regions, supernova remnants, and other structures in the Galactic
interstellar medium.
---------------------------------------------------------
Title: A 1.4-GHz survey of the southern European Large-Area ISO
Survey region
Authors: Gruppioni, C.; Ciliegi, P.; Rowan-Robinson, M.; Cram, L.;
Hopkins, A.; Cesarsky, C.; Danese, L.; Franceschini, A.; Genzel, R.;
Lawrence, A.; Lemke, D.; McMahon, R. G.; Miley, G.; Oliver, S.; Puget,
J. -L.; Rocca-Volmerange, B.
1999MNRAS.305..297G Altcode:
A deep survey of the European Large-Area ISO Survey (ELAIS) field in
the southern celestial hemisphere (hereinafter S1) has been carried
out with the Australia Telescope Compact Array (ATCA) at 1.4 GHz. The
S1 region, covering about 4 deg^2, has also been surveyed in the mid-
and far-infrared (5-200 μm) with the Infrared Space Observatory
(ISO). The radio survey provides uniform coverage of the entire S1
region, with a sensitivity (5sigma) of 0.4 mJy over the whole area and
0.2 mJy in the centre. To this sensitivity, virtually all the radio
counterparts of the far-infrared extragalactic ISO sources should be
detected. This paper presents a radio sample - complete at the 5sigma
level - consisting of 581 sources detected at 1.4 GHz. Of these radio
sources, 349 have peak flux density in the range 0.2-1 mJy, forming
a new homogeneous sample of sub-mJy radio sources. Due to its size,
depth and multiwaveband coverage, the sample will allow us to study in
greater detail the sub-mJy radio source population. The full catalogue
will be available from http://athena.ph.ic.ac.uk/pubs.html
---------------------------------------------------------
Title: Star-Forming Activity in Arp-Madore Galaxies
Authors: Hopkins, A. M.; Cram, L. E.
1999IAUS..186..277H Altcode:
We have explored the relationship between star-forming activity and
the presence of peculiar morphology in galaxies by comparing the far
infrared (IRAS) flux of the Arp-Madore peculiar galaxies with a control
sample of 'normal' galaxies. Some 12.5% of the peculiar galaxies are
found to have high levels of star-forming activity, compared with
approximately 2% of the normal galaxies. Of the Arp-Madore morphology
categories, the ones with the highest proportion of activity (such
as M51-type systems with a companion located at the end of an arm)
appear to be 'recent' or 'early' interactions. We discuss our results
in the context of a proposed time sequencing of Arp-Madore types,
related to theoretical predictions of the consequences of galaxy
interactions over different time scales.
---------------------------------------------------------
Title: The Phoenix Deep Survey
Authors: Hopkins, Andrew; Cram, Lawrence; Mobasher, Bahram;
Georgakakis, Antonis
1999ldss.work..120H Altcode:
A brief description of the Phoenix Deep Survey project is presented. A
model of the bivariate (radio/optical) luminosity function is
described and used to predict the bivariate source counts and the
redshift distributions for different combinations of limiting flux
densities. Comparisons are drawn with observations and discussed.
---------------------------------------------------------
Title: A 1.4 GHz Survey of the Southern ELAIS Region
Authors: Gruppioni, C.; Ciliegi, P.; Rowan-Robinson, M.; Cram, L.;
Hopkins, A.; Cesarsky, C.; Danese, L.; Franceschini, A.; Genzel, R.;
Lawrence, A.; Lemke, D.; McMahon, R. G.; Miley, G.; Oliver, S.; Puget,
J-L.; Rocca-Volmerange, B.
1998astro.ph.12256G Altcode:
A deep survey of the European Large Area ISO Survey (ELAIS) field in the
southern celestial hemisphere (hereinafter S1) has been carried out with
the Australia Telescope Compact Array (ATCA) at 1.4 GHz. The S1 region,
covering about 4 square degrees, has been also surveyed in the mid-
and far-infrared (5-200 micron) with the Infrared Space Observatory
(ISO). The radio survey provides uniform coverage of the entire
S1 region, with a sensitivity (5 sigma) of 0.4 mJy over the whole
area and 0.2 mJy in the center. To this sensitivity, virtually all
the radio counterparts of the far-infrared extragalactic ISO sources
should be detected. This paper presents a radio sample - complete at
the 5 sigma level - consisting of 581 sources detected at 1.4 GHz. Of
these radio sources, 349 have peak flux density in the range 0.2-1 mJy,
forming a new homogeneous sample of sub-mJy radio sources. Due to its
size, depth and multi-waveband coverage, the sample will allow us to
study in greater detail the sub-mJy radio source population. The full
catalogue will be available from http://athena.ph.ac.uk/
---------------------------------------------------------
Title: Star Formation Rates in Faint Radio Galaxies
Authors: Cram, L.; Hopkins, A.; Mobasher, B.; Rowan-Robinson, M.
1998ApJ...507..155C Altcode: 1998astro.ph..5327C
The decimetric radio continuum luminosity of a star-forming galaxy
appears to be directly proportional to the rate of formation of
supernovae in the galaxy. Since decimetric radiation does not suffer
significant extinction and is not directive, radio luminosities may thus
provide a particularly straightforward way to determine the current
rate of star formation. Using a sample of over 700 local galaxies,
we confirm the utility of the radio luminosity as a measure of star
formation rate by showing concordance with the rates predicted by
U-band, Hα, and far-infrared luminosities. We also show that there are
systematic discrepancies between these various indicators, suggesting
that the Hα luminosity may underestimate the star formation rate by
approximately an order of magnitude when the star formation rate is
>~20 M<SUB>⊙</SUB> yr<SUP>-1</SUP>. We use this calibration and the
measured radio luminosities of sub-mJy radio sources to infer the star
formation rate in approximately 60 star-forming galaxies at moderate
(z >~ 0.1) redshifts, both as the actual rate and as the fraction
of the existing mass of stars in the galaxy. For some of these objects,
the inferred current rate of star formation could increase the stellar
mass in the galaxy by approximately 10% over an interval of ~30 Myr.
---------------------------------------------------------
Title: The Global Star Formation Rate from the 1.4 GHz Luminosity
Function
Authors: Cram, L. E.
1998ApJ...506L..85C Altcode: 1998astro.ph..8228C
The decimetric luminosity of many galaxies appears to be dominated
by synchrotron emission excited by supernova explosions. Simple
models suggest that the luminosity is directly proportional to the
rate of the supernova explosions of massive stars averaged over the
past ~3×10<SUP>7</SUP> yr. The proportionality may be used, together
with models of the evolving 1.4 GHz luminosity function, to estimate
the global star formation rate density in the era z<~1. The local
value is estimated to be 0.026 M<SUB>solar</SUB> yr<SUP>-1</SUP>
Mpc<SUP>-3</SUP>, twice the value inferred from the Hα luminosity
density. The value at z~1 is found to be 0.30 M<SUB>solar</SUB>
yr<SUP>-1</SUP> Mpc<SUP>-3</SUP>. The tenfold increase in the star
formation rate density is consistent with the increase inferred from
millimeter-wave, far-infrared, ultraviolet, and Hα observations.
---------------------------------------------------------
Title: The PHOENIX Deep Survey: 1.4-GHz source counts
Authors: Hopkins, A. M.; Mobasher, B.; Cram, L.; Rowan-Robinson, M.
1998MNRAS.296..839H Altcode:
We present the first results from the Phoenix Deep Survey,
a multiwavelength survey of a 2 deg diameter region. Observations
in the radio continuum at 1.4 GHz carried out with the Australia
Telescope Compact Array are described. The catalogue of over 1000 radio
sources compiled from these observations is analysed, and the source
counts are presented. We model the observational source counts using
a two-population model and published luminosity functions for these
populations. Upon invoking luminosity and density evolution, we find
that a luminosity evolution model best fits the radio observations,
consistent with earlier work. The redshift distribution of the two
galaxy populations investigated is also modelled and discussed.
---------------------------------------------------------
Title: Relationships between Galactic Radio Continuum and Hα Emission
Authors: Cram, L. E.; Green, A. J.; Bock, D. C. -J.
1998PASA...15...64C Altcode:
Radio continuum emission due to thermal bremsstrahlung and optical
Hα spectral line emission arise from processes involving similar
atomic entities and physical conditions. The relationship between
the flux density of the emission from the two processes is mainly
a function of the electron temperature of the emitting region,
modified by other factors such as the mode of radiation transfer in the
hydrogen spectrum. On the other hand, radio continuum radiation due to
non-thermal synchrotron emission is formed by species and processes not
involved in thermal emission. As a consequence, differences between
the observed radio continuum emission and Hα emission from cosmic
sources can provide reliable information on a variety of important
physical aspects of the sources, including the relative importance
of thermal and non-thermal radio emission and the degree of optical
obscuration. This paper reviews the theory of the formation of Hα and
the radio continuum in the interstellar medium (ISM), discusses some
of the factors that must be considered in comparing observations made
in the two frequency regimes, and summarises the properties of some
classes of galactic object that emit both optical and radio radiation.
---------------------------------------------------------
Title: Achievements and prospects.
Authors: Cram, L. E.
1997IAUS..189..451C Altcode: 1998IAUS..189..451C
This Symposium has provided a timely and wide ranging overview of a
branch of science whose birth coincided with the turn of the Century,
and which has witnessed remarkable progress of the past 100 years. Its
prospects for the next few decades took equally intriguing.
---------------------------------------------------------
Title: Report of IAU Commission 36: Theory of stellar atmospheres
(Thé ories des atmosphères stellaires).
Authors: Cram, L.
1997IAUTA..23..303C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radio recombination line (H92alpha) observations of SGR E
Authors: Cram, L. E.; Claussen, M. J.; Beasley, A. J.; Gray, A. D.;
Goss, W. M.
1996MNRAS.280.1110C Altcode:
Observations of radio recombination line (H92alpha) and 8.3-GHz
continuum emission from several probable thermal sources in the
Galactic Centre HII complex Sgr E have been made using the Very Large
Array. Line emission has been detected from seven of these sources,
confirming their thermal nature and also locating them in a single
kinematical entity moving with nu_LSR~=-205 km s^-1. The continuum
sources are well resolved by the 8-arcsec beam, and several have
complex structure including shells, arcs and cores. One source (G
358.6+0.06) has no significant H92alpha flux, despite its relatively
bright continuum and flat spectrum. Further observations will be needed
to determine whether or not this interesting source is actually thermal.
---------------------------------------------------------
Title: Galactic Fine Structure at 843 MHz
Authors: Green, A. J.; Campbell-Wilson, D.; Cram, L. E.; Large, M. I.;
Piestrzynski, B.; Ye, T.
1996IAUS..169..611G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Anglo-Australian Observatory. Report of the Anglo-Australian
Telescope Board 1 July 1995 to 30 June 1996.
Authors: Cram, L. E.; Cannon, R. D.
1996aora.book.....C Altcode:
No. 79 (Oct 1996) Contents: TTF observation of Hα/[N II] emission
at z = 0.23, astrometry with SuperCOSMOS, proper motions of bright
stars - choosing 2dF guide stars, [S III] λ9069 imaging of galaxies,
instrument news.
---------------------------------------------------------
Title: A Search for Global Acoustic Oscillations on ALPHA-1-CENTAURI
and Beta-Hydri
Authors: Edmonds, P. D.; Cram, L. E.
1995MNRAS.276.1295E Altcode:
Time-series observations of the radial velocities of β Hyi (HR 98,
G2 IV) and α<SUP>1</SUP> Cen (HR 5459, G2 V) have been examined
for the periodicities expected from global p-mode oscillations. For
α<SUP>1</SUP> Cen, the upper limit on the amplitude of any coherent
oscillation in the 2 - 4 mHz band is 0.5 - 0.6 m s<SUP>-1</SUP>. There
is evidence of periodicity in the power spectrum, with splitting
δ<SUB>v0</SUB>/2 ≍ 53 - 55 μHz. For β Hyi, an upper limit of 1.5 -
2.0 m s<SUP>-1</SUP> can be placed on the amplitude of any oscillation
in the expected period range. While we do not claim to have detected
unambiguous evidence of p-mode oscillations on α<SUP>1</SUP> Cen or
β Hyi, we have placed significant upper limits on such oscillations
as might exist. We have also demonstrated the feasibility of using
coud6 spectroscopy to detect oscillations with amplitudes comparable
to those on the Sun.
---------------------------------------------------------
Title: VizieR Online Data Catalog: Molonglo Reference Catalogue of
Radio Sources (Large+ 1991)
Authors: Large, M. I.; Cram, L. E.
1995yCat.8016....0L Altcode:
"408-MHz survey observations made with the Molonglo Radio Telescope
have been used to prepare a catalogue of 12 141 discrete sources
of listed flux density >= 0.7 Jy. The survey covers 7.85 sr of
the sky defined by +18.5 (deg) >= dec(1950) >= -85.0 (deg),
mod(b) >= 3 (deg). A few sources beyond the declination limits
are also included. The catalogue comprises celestial coordinates
with standard error typically lying between 3 and 10 arcsec and
408-MHz flux densities with standard error typically lying between
4 and 10 per cent. Galactic coordinates, notes on source morphology
and cross-references to the Parkes Catalogues are included. The
overall source density is 1500/sr, corresponding to 0.001 per beam
area. There are 7347 sources of listed flux density >= 1.00 Jy, at
which level the catalogue is substantially complete. The reliability
is believed to be better than 99.9 per cent." The MRC was re-issued in
1990 with the original B1950 coordinates supplemented by J2000 values,
and an additional cross-reference flag `J' added to denote (extended)
sources imaged at 843-MHz by P.A. Jones. No other alterations were
made to the original release. The MRC is now available on 5.25 inch,
1.2 Mbyte MS-DOS (IBM) floppy disk (0.5 inch magnetic tape is also
available, but is not the preferred medium). In the floppy disk format,
simple software is provided to facilitate use of the catalogue on a
PC computer. <P />(3 data files).
---------------------------------------------------------
Title: Multifrequency Radio Studies of G359.1-00.2
Authors: Gray, Andrew D.; Nicholls, Jennifer; Ekers, Ron D.; Cram,
Lawrence E.
1995ApJ...448..164G Altcode:
The Molonglo Observatory Synthesis Telescope, the Australia Telescope
Compact Array, and the Very Large Array have been used to carry out
imaging and polarimetry experiments on the unusual Galactic center
filamentary object G359. 1-00.2, also known as "the Snake." The
observations were carried out at 843, 1446, 4790, 5840, and 8640 MHz,
with resolutions as fine as 2". The images reveal intricate internal
structure in the object and physical properties similar to previously
recognized filamentary features in the region. Several models of the
source are discussed, with some form of electrodynamic activity being
favored at present. It is not possible, however, to rule out all other
models discussed a jet or ejectum from a supernova event, a star wake
or trail, a shock front, a phenomenon related to a cosmic string or the
nearby "Great Annihilator," 1E1740.7-2942, a morphologically unusual
supernova remnant--conclusively. Several models do predict observable
changes in the source on timescales of years, so further observations
will help clarify this issue. <P />A fractional linear polarization as
high as ∼50% was found for part of the Snake, although some regions
of the source are completely depolarized. The frequency dependence of
the observed polarization properties suggests a model of the source
as a twisted ribbon embedded in a thermal medium giving rise to an
external rotation measure of at least 5500 rad m<SUP>-2</SUP>, with
strong depolarization due to an internal Faraday depth of up to 1400
rad m<SUP>-2</SUP>. The derived properties of the thermal medium in
this model require a thermal electron density of 10 cm<SUP>-3</SUP>
with a line-of-sight magnetic field strength of 7 μG along a path of
length ∼100 pc. These parameters are consistent with material in a
nuclear disk in the Galactic center.
---------------------------------------------------------
Title: Adaptive Optics at the Anglo-Australian Telescope
Authors: O'Byrne, J. W.; Bryant, J. J.; Minard, R. A.; Fekete, P. W.;
Cram, L. E.
1995PASA...12..106O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Adaptive deconvolution of astronomical radio images.
Authors: Cram, Lawrence; Ye, Taisheng
1995AuJPh..48..113C Altcode:
The novel image-forming methods used in the Molonglo Observatory
Synthesis Telescope (MOST) are not amenable to a direct application
of the self-calibration techniques that have been so effective in
improving the performance of many other aperture synthesis radio
telescopes. Specifically, self-calibration of antenna-based errors
and the use of phase closure conditions is not possible because vital
antenna-based information is lost irretrievably as the MOST forms
interferometer beams in real time. However, it is shown in this
paper that suitable models of errors introduced by the atmosphere
and telescope can be adaptively constructed from the properties of
synthesised images. These models can then be used iteratively with
standard deconvolution methods to improve significantly the fidelity of
MOST images. The method would have general application to tomographic
imaging systems in which non-ideal behavior could be represented by
a small number of unknown parameters.
---------------------------------------------------------
Title: Extended thermal radio emission from the Galactic plane.
Authors: Whiteoak, J. B. Z.; Cram, L. E.; Large, M. I.
1994MNRAS.269..294W Altcode:
A six square degree sample of the MOST southern Galactic plane
radio survey at 1=3120, b =00 is presented. In addition to discrete
radio sources such as classical H ii regions, supernova remnants and
extragalactic background sources, the survey has revealed an abundance
of low-surface-brightness extended structure, mostly too faint to have
been recognized in earlier radio observations. Comparison between
our 0.843-GHz data and IRAS observations suggests that these faint
structures are likely to be thermal. The structures may be linked to
the extended H ii envelopes that have been postulated to explain both
low-frequency spectral turnovers of Galactic supernova remnants and
low-frequency radio recombination lines from apparently blank regions
of the Galactic plane. They may also represent an intermediate state
between classical H ii regions and the warm ionized medium. Key words:
ISM: general - H ii regions - ISM: structure - supernova remnants -
infrared: ISM: continuum - radio continuum: ISM.
---------------------------------------------------------
Title: Increasing the field size of the Molonglo Observatory
Synthesis Telescope
Authors: Large, M. I.; Campbell-Wilson, D.; Cram, L. E.; Davison,
R. G.; Robertson, J. G.
1994PASA...11...44L Altcode: 1994PASAu..11...44L
The Molonglo Observatory Synthesis Telescope (MOST) which at present
images a fully synthesized 70 min field in 12 h, is being converted
to enable observing modes which extend the field size to 160 min. The
new observing modes will allow the MOST to survey completely the sky
south of delta = -30 deg to a (5 sigma) sensitivity limit of about 5
mJy. The result will be a catalog of over 400,000 radio sources with
a spatial density of less than 1 source per 100 beam areas, providing
the foundation for a number of novel astronomical and cosmological
investigations. The conversion involves construction of 352 low-noise
High Electron Mobility Transistor (HEMT) preamplifiers, 88 digitally
controlled UHF quad phase shifters, 88 mixers and IF sections, a new
communication and control system, and several other new sub-systems. The
project has been funded and developments are well advanced.
---------------------------------------------------------
Title: A Search for Solar-Like Oscillations in the Stars of M67 With
CCD Ensemble Photometry on a Network of 4m Telescopes
Authors: Gilliland, R. L.; Brown, T. M.; Kjeldsen, H.; McCarthy,
J. K.; Peri, M. L.; Belmonte, J. A.; Vidal, I.; Cram, L. E.; Palmer,
J.; Frandsen, S.; Parthasarathy, M.; Petro, L.; Schneider, H.; Stetson,
P. B.; Weiss, W. W.
1993AJ....106.2441G Altcode:
Results are presented from a large observational project directed
toward the detection of solar-like oscillations in an ensemble of
open cluster stars. Seven groups collaborated in 1992 January to
observe twelve stars in M67 with 4 m class telescopes for a one week
period. High quality time series were collected on 22 telescope nights
for a total of 156 h. The technique of CCD ensemble photometry allowed
precisions of about 250 micro-mag per minute to be reached in the best
cases, and provided robust results in conditions that sometimes were
far from 'photometric.' The longitude-distributed network, coupled
with generally low noise levels, provided a good window function and
yielded detection thresholds of about 20 micro-mag (five times solar)
for solar-like oscillations in the best ensembled stars. Sensitivity
to solar-like oscillations over our twelve ensemble stars ranges
from 30% to a factor of three better than obtained previously by any
group. When our simulations results for 12 stars is taken into account
this project provides a (multiplexed) factor of 20 to 30 gain over
previous experiments. For two stars we derive interesting upper limits
for oscillation amplitudes that are near the lower range predicted by
theory. Over half the stars in the ensemble show suggestive evidence for
oscillations; we develop the evidence for, and the cautions against,
claiming detections in these cases. We argue that a more aggressive
network campaign could provide a factor of two sensitivity gain with
a resulting high probability of attaining unambiguous oscillation
detections on most of the stars in the M67 ensemble.
---------------------------------------------------------
Title: Chromospheric Activity in Galactic Open Clusters
Authors: Beasley, A. J.; Cram, L. E.
1993ApJ...417..157B Altcode:
Ca II observations of post-main-sequence stars in the Galactic
open clusters NGC 2477 and IC 4756 and the Hyades Supercluster are
described. After calibrating the spectra in absolute surface flux units,
an index of chromospheric activity (ΔF<SUB>CaII</SUB>) is derived for
each star. Using the ΔF<SUB>CaII</SUB> indices we examine the decline
of chromospheric activity for ∼2 M<SUB>sun</SUB> stars evolving
off the main sequence, comparing our indices with the theoretical
predictions of Rutten & Pylyser. Our observations indicate that
their predictions overestimate the levels of activity (and therefore the
rotation velocities) of 2 M<SUB>sun</SUB> stars. We conclude that the
assumptions of rigid-body rotation and/or conservation of total angular
momentum should be relaxed to explain the decline in observed rotational
velocities and chromospheric activity for post-main-sequence stars.
---------------------------------------------------------
Title: Coronal activity from AB DOR and RST 137B.
Authors: Beasley, A. J.; Cram, L. E.
1993MNRAS.264..570B Altcode:
Two 12-h synthesis observations of the active star AB Dor (HD36705)
made with the Molonglo Observatory Synthesis Telescope (MOST) as part
of a 1990 international campaign of observations are presented. A weak
variable source was detected near the stellar position during both
sessions. The derived brightness temperatures are consistent with a
gyrosynchrotron emission model. The complete sample of MOST observations
of AB Dor made since 1985 reveals a quiescent level of radio emission
with flare-like increases, and a discrepancy of ∼5 arcsec between the
843-MHz source and the optical position. An analysis of the variations
in position of the radio source with flux density suggests that this
discrepancy may be the result of confusion with the nearby, active dMe
star RST 137B. Recent Australia Telescope observations have resolved
both AB Dor and RST 137B as radio sources at 5 GHz, supporting this
explanation. The unusually high levels of activity seen from both stars
lead us to examine critically the currently accepted pre-main-sequence
model for AB Dor and RST 137B. We propose a post-main-sequence FK Comae
evolutionary model for AB Dor, and conclude by suggesting a number of
observations that could support this conjecture.
---------------------------------------------------------
Title: Radio continuum observations of SGR E.
Authors: Gray, A. D.; Whiteoak, J. B. Z.; Cram, L. E.; Goss, W. M.
1993MNRAS.264..678G Altcode:
The group of compact sources in the direction of the Galactic Centre
(l=358°.7, b=0°) known as Sgr E has been observed with the Molonglo
Observatory Synthesis Telescope at 843 MHz and with the Very Large
Array at 1.45 and 4.86 GHz. There are 70 discrete sources in the
complex having integrated flux densities S<SUB>1/4 GHz</SUB> ≳ 4 mJy,
confined to an area of ∼0.40 deg<SUP>2</SUP>. We determine the radio
spectra of 34 of the sources. Of these, most have spectral indices
(1.45/4.86 GHz) consistent with H II regions. Simple models of the
compact H II regions and the associated molecular cloud suggest that
the complex contains about 20 OB stars, some 2000 M<SUB>sun</SUB>
of ionized gas, about 10<SUP>4</SUP> M<SUB>sun</SUB> of stellar mass,
and about 2 × 10<SUP>6</SUP> M<SUB>sun</SUB> of molecular gas. A small
proportion of the sources with measured indices have steep spectra (α
<-0.5 S ∝ ν<SUP>α</SUP>), and upper limits on S<SUB>4.86</SUB>
for several other sources imply steep spectra. The surface density of
steep-spectrum sources and their distribution of flux densities are
consistent with all of them being extragalactic, and none is an obvious
supernova candidate. Sgr E is coincident with a region exhibiting a
high line-of-sight velocity (-200 km s<SUP>-1</SUP>) and lying close to
the Galactic Centre. It may represent a small burst of star formation
in part of a circumnuclear disc or in matter ejected from the Galactic
nucleus. The absence of supernovae indicates an age less than ∼5 Myr.
---------------------------------------------------------
Title: Magnetic fields in spiral galaxies.
Authors: Spencer, S.; Cram, Lawrence
1993ppcn.conf..383S Altcode:
Observations of polarized radio emission from spiral galaxies imply the
presence of magnetic fields organized with axisymmetric or bisymmetric
structure on the scale of the whole galaxy. Such fields have been
explained previously either as a systematic patterning of primordial
fields by differential rotation or as the result of dynamo generation
of large-scale components from non-mirror-symmetric turbulence
(α-effect). The authors summarize a new model for the phenomenon based
on magnetic field regeneration by the interaction between turbulent
diffusion and axially and radially sheared galactic winds.
---------------------------------------------------------
Title: Coulomb Interactions Between Cosmic-Rays and Charged Dust
Grains
Authors: Byleveld, S. E.; Melrose, D. B.; Cram, L. E.
1993PASA...10..218B Altcode: 1993PASAu..10..218B
No abstract at ADS
---------------------------------------------------------
Title: A search for solar-like oscillations in the stars of M67
Authors: Gilliland, R. L.; Brown, T. M.; Kjeldsen, H.; Belmonte,
J. A.; Cram, L. E.; Frandsen, S.; McCarthy, J. K.; Parthasarathy,
M.; Peri, M. L.; Petro, L.; Schneider, H.; Stetson, P. B.; Vidal,
I.; Weiss, W. W.
1993prph.conf..145G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Field Generation by Galactic Winds
Authors: Spencer, S. J.; Cram, L. E.
1993IAUS..157..357S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Large-scale magnetic fields in spiral galaxies.
Authors: Spencer, S.; Cram, L.
1993AuJPh..46..195S Altcode:
The magnetic field in several spiral galaxies is observed to be
organized on spatial scales as large as the entire galaxy. Although
irregularities in field strength and direction presumably exist
on scales at least as small as about 1 pc, approximately one-half
of the magnetic energy appears to reside in components with simple
(axisymmetric or bisymmetric) structure on the scale of the whole
galaxy. Explanations of such enormous magnets include the systematic
patterning of primordial fields by differential rotation and the
generation of large-scale components from nonmirror-symmetric turbulence
(the so-called alpha-effect). We discuss the observations and theory
of global magnetic fields in spiral galaxies, and review a new model
for the phenomenon based on the regenerative properties of axially
and radially sheared galactic winds.
---------------------------------------------------------
Title: Book-Review - Plasma Loops in the Solar Corona
Authors: Bray, B. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.;
Cheng, C. C.
1993SSRv...65..185B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Amplification of Large-Scale Magnetic Fields in Spiral
Galaxies by Galactic Winds
Authors: Spencer, S. J.; Cram, L. E.
1992ApJ...400..484S Altcode:
A new mechanism is presented for the amplification of nonaxisymmetric
large-scale magnetic fields in the disks of spiral galaxies. Using a
local theory, we show how a galactic wind with components axial and
radial to the disk can drive magnetic field growth. The wind model
postulates a large-scale plasma flow in which the axial component
varies with radial position across the disk, and the radial component
varies with axial position above the disk. The radial dependence of
the axial wind component induces axial magnetic field from the radial
field. The axial dependence of the radial wind component induces
radial magnetic field from the axial field. These two inductive
processes permit regeneration by coupling the evolution of the field
components. Azimuthal field is induced from radial field by differential
rotation, according to the usual mechanism. The shear in the large-scale
wind leads to indefinite field amplification in situ (regenerative)
without introducing a mean helicity of small-scale plasma motions (the
α-effect), as is done in most other theories of galactic magnetic
field generation. The model is nevertheless formulated within the
framework of turbulent magnetohydrodynamics since turbulent diffusion
of magnetic field is an important feature. Results from a kinematic,
local (one-dimensional) numerical model are presented which illustrate
the time evolution and axial spatial structure of large-scale magnetic
field for various wind motions. The physical essence of wind-driven
magnetic field amplification is demonstrated by a "Lotka-Volterra"
spatially integrated model that highlights the means by which coupling
between field components mediates their time evolution.
---------------------------------------------------------
Title: Radio emission from IRAS-selected quasars.
Authors: Cram, L. E.; North, A.; Savage, A.
1992MNRAS.257..602C Altcode:
All six southern quasars discovered in the IRAS point source catalog
have been detected with the Molonglo Observatory Synthesis Telescope at
843 MHz, with flux densities in the range 10-15 mJy. The corresponding
radio luminosities indicate that these are typical radio-quiet
quasars. The ratio of radio to far-infrared (FIR) luminosity for
the six objects places them on the remarkable correlation between
radio and FIR luminosity that exists for low surface brightness and
early-type spiral galaxies and for galaxies having high rates of
star formation. Unless this is a coincidence or a selection effect,
it appears that the physical processes underlying the radio-FIR
correlation, often identified as a being related to star formation,
dominate both the FIR and the radio emission from these IRAS quasars.
---------------------------------------------------------
Title: Evolutionary Models and the p-Mode Oscillation Spectrum of
alpha Centauri A and B
Authors: Edmonds, Peter; Cram, Lawrence; Demarque, Pierre; Guenther,
D. B.; Pinsonneault, Marc H.
1992ApJ...394..313E Altcode:
Spectroscopically observed abundances of Furenlid and Meylan (1990) and
Los Alamos Opacity Library opacities specifically constructed for this
mixture are used to construct the most detailed models to date for Alpha
Cen A and B. Models including the effects of the diffusion of helium in
Alpha Cen A's interior were constructed. Although the effect of helium
diffusion is small in Alpha Cen A, it is slightly larger than in the
sun because of the larger mass and therefore shallower convection zone
of Alpha Cen A. Keeping the heavy-element mixture unchanged but varying
Z within the uncertainties yields limits to the helium abundance of Y
= 0.295 and 0.305, respectively. The derived age of Alpha Cen is 4.6
+/-0.4 Gyr, very similar to the solar age of 4.5 Gyr.
---------------------------------------------------------
Title: Book Review: Plasma loops in the solar corona / Cambridge U
Press, 1991
Authors: Cram, L. E.; Durrent, C. J.; Loughhead, R. E.; Hartquist,
T. W.
1992Ap&SS.192..160B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The radio counterpart of the Great Annihilator (1E
1740.7-2942).
Authors: Gray, A. D.; Cram, L. E.; Ekers, R. D.
1992MNRAS.256..277G Altcode:
Interest in the Galactic Center annihilation-line sources has sparked
several reports of radio counterparts being found. It is not yet
clear which, if any, of the radio sources in the vicinity of the
annihilation-line source, also identified with the X-ray source 1E
1740.7 - 2942, is the correct counterpart. Results of observations of
this intriguing region are reported, including evidence of possible
extreme variability in one of the sources.
---------------------------------------------------------
Title: Book-Review - Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.;
Kleczek, J.
1992SoPh..138..423B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: Plasma loops in the solar corona / Cambridge U
Press, 1991
Authors: Cram, L. E.; Currant, C. J.; Loughhead, R. E.; Zweibel, E.
1992Sci...255..857C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Inhomogeneous structure in the chromospheres of dwarf M stars.
Authors: Turner, N. J.; Cram, L. E.; Robinson, R. D.
1991MNRAS.253..575T Altcode:
Linear combinations of observed spectra of the H-alpha and Ca-II
resonance and IR lines from the chromospheres of a quiet (Gl 1) and
an active (Gl 735) dwarf-M star are compared with the corresponding
spectra from a star of intermediate activity (Gl 887). It is shown that
the intermediate spectra cannot be explained as a simple juxtaposition
of the extreme chromospheric states. It is concluded that the range
of observed strengths of chromospheric activity indicators in dwarf-M
stars is due, at least in part, to changes in the radial structure
of the chromospheric heating function and not to changes in the area
filling factor.
---------------------------------------------------------
Title: Book-Review - Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Currant, C. J.; Loughhead, R. E.
1991JBAA..101R.300B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A filamentary radio source near the Galactic Centre
Authors: Gray, A. D.; Cram, L. E.; Ekers, R. D.; Goss, W. M.
1991Natur.353..237G Altcode:
NEAR the Galactic Centre are several filamentary radio structures
that have become known as 'threads'<SUP>1</SUP> and which are thought
to signify either magnetic loops<SUP>2</SUP> or electric current
paths<SUP>3</SUP> between active regions and the galactic magnetic
field. Using the Molonglo Observatory Synthesis Telescope, we have found
a new elongated radio source, G359.1-0.2, within 1<SUP>°</SUP> of the
Galactic Centre. Observations with the Australia Telescope Compact Array
and the Very Large Array show it to be filamentary in nature, extending
more than 20 arcmin in length but only 10 arcsec wide. This object is
spectrally similar to the previously known threads, but unlike them has
kinks along its length, and does not appear to be obviously connected
with any active region that might be responsible for its generation.
---------------------------------------------------------
Title: The Parkes-MIT-NRAO (PMN) Southern Sky Survey at 4850 MHz
Authors: Griffith, M.; Wright, A. E.; Hunt, A. J.; Troup, E.; Ekers,
R. D.; Buckett, P.; Cooke, D. J.; Freeman, G.; Glowacki, J.; Jennings,
D.; Knop, U.; Lam, B.; McGovern, I.; McDonnell, D.; Norris, R. P.;
Otrupcek, R.; Twardy, R.; Williams, T.; Behrens, G.; Chestnut, C.;
Burke, B. F.; Fletcher, A.; Russell, K. S.; Savage, A.; Lim, J.;
Vaughn, A. E.; Cote, S.; Anderson, M.; Hons, A.; White, G. L.; Amy, S.;
Burgess, A.; Chan, S.; Cram, L.; Gray, A.; Walsh, W.; Campbell-Wilson,
D.; McIntrye, V.; Randall, P.; Suters, M.; Zealey, W. J.
1991BAAS...23.1335G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plasma Loops in the Solar Corona
Authors: Bray, R. J.; Cram, L. E.; Durrant, C.; Loughhead, R. E.
1991plsc.book.....B Altcode: 1991QB529.P57......
A comprehensive account of the properties of plasma loops, the
fundamental structural elements of the solar corona. Plasma loops
cover a wide range of sizes and range in temperature from tens of
thousands to millions of degrees. They not only define the structure of
individual active regions but connect different active regions--even
across the solar equator. Loops also play an integral and decisive
role in the enormous solar explosions called flares. Over recent
years a wealth of space and ground-based observations of loops has
been obtained in various widely-spaced regions of the electromagnetic
spectrum. In this book the authors have selected the best observational
material from the literature on which to base a detailed account of
the properties of flare and non-flare loops. The book also explores
the larger implications of the loop structures for our understanding
of solar and stellar coronae. The text is enhanced by a large number
of illustrations and unique and beautiful photographs obtained from
the ground and from space.
---------------------------------------------------------
Title: A machine-readable release of the Molonglo Reference Catalogue
of Radio Sources
Authors: Large, M. I.; Cram, L. E.; Burgess, A. M.
1991Obs...111...72L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Coude Auxiliary Feed for the AAT - a Focus for International
Cooperation in Optical Astronomy
Authors: Gillingham, P.; Pettini, M.; Bessell, M.; Cram, L.; Ogura, K.
1991PASA....9..160G Altcode: 1991PASAu...9..160G
No abstract at ADS
---------------------------------------------------------
Title: The Parkes-MIT-NRAO southern sky survey at 4850 MHz
Authors: Griffith, M.; Wright, A. E.; Hunt, A. J.; Troup, E.;
Ekers, R. D.; Buckett, P.; Cooke, D. J.; Freeman, G.; Glowacki,
J.; Jennings, D.; Knop, U.; Lam, B.; McGovern, B.; McConnell, D.;
Norris, R. P.; Otrupcek, R.; Twardy, R.; Williams, T.; Behrens, G.;
Chestnut, C.; Burke, B. F.; Fletcher, A.; Russell, K. S.; Savage,
A.; Lim, J.; Vaughan, A. E.; Cote, S.; Anderson, M.; Hons, A.; White,
G. L.; Amy, S.; Burgess, A.; Chan, S.; Cram, L.; Gray, A.; Walsh, W.;
Campbell-Wilson, D.; McIntyre, V.; Randall, P.; Suters, M.; Zealey,
W. J.
1991PASA....9..243G Altcode: 1991PASAu...9..243G
During 1990 we surveyed the southern sky using a multibeam receiver at
frequencies of 4850 and 843 MHz. The half-power beamwidths were 4 and
25 arcmin, respectively. The finished surveys cover the declination
range between +10 and -90 degrees declination, essentially complete
in right ascension, an area of 7.30 steradians. Preliminary analysis
of the 4850 MHz data indicates that we will achieve a five sigma flux
density limit of about 30 mJy. We estimate that we will find between
80,000 and 90,000 new sources above this limit.
---------------------------------------------------------
Title: The MOST Southern Galactic Plane Survey
Authors: Whiteoak, J. B. Z.; Large, M. I.; Cram, L. E.
1991BAAS...23..827W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Plasma loops in the solar corona.
Authors: Bray, R. J.; Cram, L. E.; Durrant, C. J.; Loughhead, R. E.
1991CAS....18.....B Altcode:
This book presents the first comprehensive account of the properties
of plasma loops, the fundamental structural elements of the solar
corona. Plasma loops not only define the structure of individual
active regions but connect different active regions. Loops also play an
integral and decisive role in solar flares. The authors have selected
the best observational material from the literature on which to base a
detailed account of the properties of flare and non-flare loops. The
book also explores the larger implications of the loop structures in
our understanding of solar and stellar coronae. The text is enhanced
by a large number of illustrations and photographs obtained from the
ground and from space.
---------------------------------------------------------
Title: Global Electrodynamic Coupling in Stellar Atmospheres
Authors: Cram, L.
1991mcch.conf..282C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - the Creation of the Anglo-Australian Observatory
Authors: Gascoigne, S. C. B.; Proust, K. M.; Robins, M. O.; Cram, L. E.
1991PASA....9..342G Altcode: 1991PASAu...9..342G
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric H alpha and CA II Lines in Late-Type Stars
Authors: Robinson, Richard D.; Cram, Lawrence E.; Giampapa, Mark S.
1990ApJS...74..891R Altcode:
Observations of H-alpha and Ca II H and K in the chromospheres of 50
main-sequence K and M stars are reported. The photospheric contribution
to the integrated core flux in these lines is found to be more important
than previously thought, and earlier estimates of the basal flux of cool
dwarf stars are revised. The H-alpha data confirm the presence of both
an upper and a lower limit to the H-alpha equivalent width attained
at any given spectral type. The maximum H-alpha absorption strength
decreases gradually toward cooler stars while the maximum 'saturated'
quiescent emission strength increases. The Ca II emission strength
is related to the strength of the emission or absorption feature at
H-alpha, but there is not a one-to-one correlation. The main results may
be explained in terms of photoionization and collisional control of the
non-LTE H-alpha source function. Several aspects of the structure and
heating of the outer atmospheres of dwarf K and M stars are discussed.
---------------------------------------------------------
Title: Radio Emission from the Sun at 843-MHZ - Part One
Authors: Gray, A.; Large, M. I.; Campbell-Wilson, D.; Cram, L.
1990SoPh..125..359G Altcode:
The Molonglo Observatory Synthesis Telescope (MOST) has recently been
modified to permit observations of the Sun. With a collecting area
of 18000 m<SUP>2</SUP>, MOST makes high-sensitivity measurements in
right-hand circular polarisation over a 3 MHz bandwidth at 843 MHz. The
maximum baseline of the multi-element interferometer is 1600 m, so that
one-dimensional spatial resolution as fine as 32 arc sec is available. A
resistor array produces simultaneously a set of 64 beams separated by 22
arc sec, which may be offset electronically to cover the entire Sun in
a few seconds. Observations may be made with a beam shape corresponding
to either a multiplying or an adding interferometer. By exploiting
the technique of Earth-rotation synthesis the telescope may be used
to make two-dimensional maps of the Sun at the time of the austral
solstice with a synthesized beamwidth of 43 × 110 arc sec. This paper
describes the instrument and the procedures used to make various types
of solar observations, and exhibits some of the first data collected.
---------------------------------------------------------
Title: Book-Review - FGK Stars and T-Tauri Stars
Authors: Cram, L. E.; Kuhi, L. V.
1990Sci...248..617C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Progress on Measuring Stellar Oscillations
Authors: Edmonds, P. D.; Cram, L. E.
1990BAAS...22..817E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: MOST Observations of Two Peculiar Galactic Objects
Authors: Cram, L. E.; Gray, A. D.; Whiteoak, J. B. Z.
1990BAAS...22..813C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Analogues of the Solar Cycle and Activity
Authors: Beasley, A. J.; Cram, L. E.
1990SoPh..125..191B Altcode:
The past two decades have seen a rapid increase in our understanding
of the phenomenology of stellar activity. This has happened principally
as a result of new instrumentation which has allowed studies at X-ray,
EUV, visible and radio wavelengths in ways hitherto impossible. From
this work has emerged a tentative description of a connection between
activity, rotation, convection, and stellar structure and evolution,
linked through pervasive electrodynamic processes. Although most
manifestations of stellar activity studied to date occur with far
greater amplitudes than the apparently analogous phenomena on the Sun,
there is clear support for the notion that the `two-way street' between
studies of solar and stellar activity- the so-called solar-stellar
connection - represents a useful path to improving our understanding
of activity in general. In this paper we review the phenomenology of
stellar activity with a special emphasis on those aspects that seem to
be relevant in understanding the origin of activity cycles. We point
out that the labile character of theories of solar activity makes it
hard to synthesise a common account of activity in the Sun and other
stars. Nevertheless, we show how the stellar data suggest that some
aspects of activity (such as the rotation-activity connection and
the non-linear correlations between different activity indicators)
might be incorporated from the start into models of solar activity.
---------------------------------------------------------
Title: The CA II resonance lines in M dwarf stars without H-alpha
emission.
Authors: Giampapa, Mark S.; Cram, Lawrence E.; Wild, Walter J.
1989ApJ...345..536G Altcode:
Spectra of the Ca II H and K lines in a sample of 31 M dwarf stars
without H-alpha emission are used to calculate chromospheric K
line radiative losses, F(k), and to study the joint response of Ca
II K and H-alpha to chromospheric heating in dwarf M stars. It is
suggested that the poor correlation found in the equivalent width
- log F(K) diagram may be due either to radial segregation of the
H-alpha and K line forming regions or to lateral inhomogeneities
in the chromospheres. The results confirm the existence of dM stars
with weak H-alpha absorption and K line emission only slightly weaker
than that of the dMe stars, and show that dM stars with weak H-alpha
but kinematics and metallicities representative of the young disk
population belong to a class characterized by a comparatively high
degree of chromospheric activity.
---------------------------------------------------------
Title: Introduction and Résumé
Authors: Cram, Lawrence E.
1989NASSP.502....1C Altcode: 1989fstt.book....1C
No abstract at ADS
---------------------------------------------------------
Title: T Tauri Stars
Authors: Kuhi, L. V.; Cram, L. E.
1989NASSP.502...99K Altcode: 1989fstt.book...99K
No abstract at ADS
---------------------------------------------------------
Title: Chromospheres of M dwarf stars with incipient H-alpha emission.
Authors: Robinson, R. D.; Cram, L. E.
1989PASA....8..132R Altcode: 1989PASAu...8..132R
Observations are presented of H-alpha and Ca II resonance lines
in 4 stars having H-alpha features which place them intermediately
between the non-(e) and (e) classifications of dK/dM stars. There is
considerable variety in the shape of the H-alpha line, presumably due in
part to differences in rotation rates. As expected, the energy fluxes
in the Ca II emission lines lie between those typical of non-(e) and
(e) stars. There is some evidence (especially from the binary Gl 876A)
that the energy fluxes in the Ca II and H-alpha emission lines do
not vary from star to star according to a simple proportionality. An
intriguing result is the apparent detection of spatially displaced
chromospheric emission in Gl 907.1 and Gl 890.
---------------------------------------------------------
Title: Dynamical Processes and the Origin of Atmospheric Structure
in Cool Stars
Authors: Cram, Lawrence E.
1989NASSP.502..181C Altcode: 1989fstt.book..181C
No abstract at ADS
---------------------------------------------------------
Title: Classical Theory of Stellar Atmospheres
Authors: Cram, Lawrence E.
1989NASSP.502..139C Altcode: 1989fstt.book..139C
No abstract at ADS
---------------------------------------------------------
Title: Optical chromospheric spectral lines in K and M dwarf stars.
Authors: Robinson, R. D.; Cram, L. E.
1989sasf.confP..75R Altcode: 1989IAUCo.104P..75R; 1988sasf.conf...75R
Observations are reported of the Ca II resonance lines and Hα in dK and
dM stars, made with high S/N ratio and high spectral resolution. Ca II
emission is found in all stars observed, and those having weak Ca II
exhibit marked Hα absorption. It is found that the strengths of the
two kinds of chromospheric lines are not tightly correlated, an effect
which can be shown to be independent of the effective temperature
of the stars. The result implies that a one-parameter description
(e.g. heating rate) of the chromospheres is not viable. While lateral
inhomogeneities are likely to be an important second parameter,
the authors also suggest that the Hα line may be formed in a region
considerable higher than that in which the Ca II lines are formed.
---------------------------------------------------------
Title: Theory of Magnetic Fields in Cool Stars
Authors: Zwann, Cornelis; Cram, Lawrence E.
1989NASSP.502..215Z Altcode: 1989fstt.book..215Z
No abstract at ADS
---------------------------------------------------------
Title: FGK stars and T Tauri stars
Authors: Cram, Lawrence E.; Kuhi, Leonard V.; Jordan, Stuart; Thomas,
Richard; Goldberg, Leo; Pecker, Jean-Claude
1989NASSP.502.....C Altcode: 1989QB843.C6C73....; 1989fstt.book.....C
The purpose of this book, FGK Stars and T Tauri Stars, like all other
volumes of this series, is to exhibit and describe the best space
data and ground based data currently available, and also to describe
and critically evaluate the status of current theoretical models
and physical mechanisms that have been proposed to interpret these
data. The method for obtaining this book was to collect manuscripts
from competent volunteer authors, and then to collate and edit these
contributions to form a well structured book, which will be distributed
to an international community of research astronomers by NASA and by
the French CNRS.
---------------------------------------------------------
Title: A search for non-radial oscillations on late-type stars.
Authors: Edmonds, P. D.; Cram, L. E.
1989PASA....8..154E Altcode: 1989PASAu...8..154E
The detection of non-radial oscillations on late-type dwarf
stars may require the measurements of Doppler shifts of order 10
cm/s. Observations using the coude echelle spectrograph of the 3.9
m Anglo-Australian Telescope are reported which reveal a noise
level in a 1 minute integration about a factor of one hundred
greater than this. A method of imposing a set of stable reference
features on stellar spectra to permit Doppler measurements of the
required accuracy is discussed. The method exploits a voltage-tuned
solid Fabry-Perot interferometer whose passbands are fixed by a
servo-control system to the light from a HeNe laser whose frequency
is polarization-stablized. The desired wavelength stability demands
careful control of the voltage, temperature and tilt of the etalon.
---------------------------------------------------------
Title: A southern galactic survey at 843 MHz.
Authors: Whiteoak, J. B. Z.; Large, M. I.; Cram, L. E.; Piestryzynski,
B.
1989PASA....8..176W Altcode: 1989PASAu...8..176W
The Molonglo Observatory Synthesis Telescope, operating at 843 MHz,
is currently surveying the southern Galactic plane. The resulting maps
provide images of the radio continuum with a synthesized beamwidth or
43 x 43 arsec cosec delta and a noise level of about 1 mJy. The survey
involves 12-h synthesis observations of over 400 fields on a predefined
set of field centers. About half the fields have been observed to
date, and the survey is scheduled for completion in 1990. A noteable
feature in many of the fields is the occurrence of widespread diffuse
filamentary structure, in addition to the expected supernova remants
and H II regions.
---------------------------------------------------------
Title: Formation of Chromospheric Lines in Cool Dwarf Stars
Authors: Cram, L. E.; Giampapa, M. S.
1987ApJ...323..316C Altcode:
A simple theory of the formation of H-alpha and Ca II K in dwarf M
stars has been developed which relates the observed variations in the
emission strengths of Ca II K and the equivalent widths of H-alpha to
physical differences in the underlying chromospheric structure of the
stars. The theory implies that Ca II K line emission fluxes increase
monotonically with increasing chromospheric temperature or mass
loading. However, H-alpha equivalent widths may increase or decrease
with increasing chromospheric temperature or mass loading, depending
on the actual values of the chromospheric parameters and the effective
temperature. The theory is used to elucidate aspects of the available
observational data on H-alpha and Ca II K lines in late-type dwarfs.
---------------------------------------------------------
Title: Global oscillations in late-type stars.
Authors: Cram, L. E.
1987PASA....7....2C Altcode: 1987PASAu...7....2C
The advent of new techniques to measure the global oscillation spectrum
of the sun has provided a new and powerful tool to investigate solar
structure. One of the most challenging and potentially rewarding
problems in contemporary astronomy is to devise techniques which will
allow similar studies of other stars. This paper outlines the theory of
global oscillations of late-type main-sequence stars, and summarizes
some of the achievements of global oscillation studies of the sun. It
then reviews the very few successful attempts that have been made to
study stellar oscillations, and briefly discusses several apparently
promising lines for further instrumental development.
---------------------------------------------------------
Title: Heating of Chromospheres and Coronae: Present Status of Theory
(Invited review)
Authors: Cram, Lawrence
1987LNP...291..123C Altcode: 1987csss....5..123C
Three aspects of the theory of the non-radiative heating of
stellar atmospheres are treated in this review. First, the transient
brightenings seen in the inter-network quiet chromosphere are discussed,
and their importance to the basal heating rate of stellar chromospheres
is emphasized. Second, recent investigations of simple models for
magnetostatic flux tubes are described, and the possible importance of
current filamentation as a heating process in such tubes is noted. It is
also pointed out that departures from simple magnetic topology in and
beneath the photosphere can exert a marked effect on the atmospheric
field structure. Third, an account is given of recent work on models
of electrodynamic heating in stellar coronae, including the mechanisms
of topological heating and resonant absorption, and the use of circuit
models to describe the coupling between the generation and dissipation
regions in the star.
---------------------------------------------------------
Title: Interpretation of H alpha Contrast Profiles of Active Region
Loops
Authors: Cram, L. E.
1986ApJ...300..830C Altcode:
It has been shown recently that the observed H-alpha contrast profiles
of an active region loop can be matched by theoretical contrast profiles
based on a 'cloud' model with four free parameters: optical depth,
Doppler width, source function, and line-of-sight velocity. On the other
hand, the non-LTE theory of the formation of H-alpha by noncoherent
scattering implies that one of these parameters, the source function,
can be deduced from the others, provided certain auxiliary quantities
are known. This paper examines the consistency between values of the
source function inferred by an application of the cloud model and
those calculated using non-LTE theory. Of the seven points measured
on the loop, satisfactory agreement is found at five, although there
is clear disagreement at the other two.
---------------------------------------------------------
Title: Formation of the H-alpha absorption line in the chromospheres
of cool stars
Authors: Cram, L. E.; Mullan, D. J.
1985ApJ...294..626C Altcode:
The authors discuss the theory of the formation of the Hα absorption
line in the chromospheres of cool stars and present a number of results
which demonstrate that observations of this line can provide valuable
information on certain properties of stellar chromospheres. It is
shown that the widespread existence of strong Hα absorption in
cool stars indicates the equally widespread existence of stellar
chromospheres. The calculations also reinforce the idea that the great
widths of Hα absorption lines in late-type giant stars are due to
nonthermal chromospheric velocity fields.
---------------------------------------------------------
Title: A search for long-lived velocity fields at the solar poles
Authors: Durney, B. R.; Lytle, D. M.; Cram, L. E.; Guenther, D. B.;
Keil, S. L.
1985ApJ...292..752D Altcode:
A search has been made in the polar regions of the sun for large-scale
(50-200 Mm) velocity fields with lifetimes of the order of the solar
rotation period (approximately equal to or greater than 30 days). The
observations show that any such large-scale, long-lived velocity
patterns in the polar regions must have an amplitude less than 5
m/s. Marginally significant detections (at the 2-3 sigma level) were
made of two kinds of structures with amplitudes of order 3 m/s. One has
a rotation period approximately 38 days (close to the polar rotation
period at the sun's surface), and a scale approximately 150 Mm; the
other has a period approximately 24 days and a scale approximately
100 Mm. Tentatively, the first structure is interpreted as being of
supergranular origin. The second structure is interpreted as the
overshooting of the dominant convective mode of the lower solar
convection zone - the giant granulation.
---------------------------------------------------------
Title: Implications of millimetre and sub-millimetre observations
for modelsof the quiet chromosphere.
Authors: Cram, L. E.
1985cdm..proc..288C Altcode:
Observations of the dependence of millimetre and sub-millimetre (MSM)
brightness temperatures on wavelength and heliocentric position are not
consistent with predictions based on refined semi-empirical models of
the chromosphere. The origin of these inconsistencies apparently lies
in the fact that the models do not account adequately for chromospheric
fine structure. The author reviews relationships between theories and
observations of MSM radiation and discusses various models incorporating
the effects of fine structure. The importance of observations at the
extreme limb is emphasized.
---------------------------------------------------------
Title: Investigations of solar and stellar atmospheric heating:
a historicalperspective.
Authors: Cram, L. E.
1985rbcc.conf...93C Altcode:
Contents: Introduction. Before 1935: The "problem" of chromospheric
extension. 1936 - 1940: Recognition of the problem of coronal
heating. 1941 - 1945: Alfvén waves. 1946 - 1950: Early theories
of non-radiative heating. 1951 - 1955: Refining models of the
chromosphere and corona. 1956 - 1960: Solar and stellar winds. 1961 -
1965: Exploitation of non-LTE theory. 1966 - 1970: Impact of EUV and
X-ray observations. 1971 - 1975: Small-scale magnetic fields. 1976 -
1985: Current research. Prospects.
---------------------------------------------------------
Title: High Resolution Spectroscopy of Active Regions - Part One -
Observing Procedures
Authors: Zwaan, C.; Brants, J. J.; Cram, L. E.
1985SoPh...95....3Z Altcode:
We describe an observing program designed to obtain spectra of sunspots,
pores, and other features in active regions using the Vacuum Tower
Telescope and Echelle Spectrograph at Sacramento Peak Observatory. The
spectral lines used in this study have been especially chosen to allow
pointed studies of fine structure in the intensity distribution,
and in the velocity and magnetic fields in the photospheric levels
of active regions, and to relate this structure to chromospheric
observations made in the CaII H line. We demonstrate the capacities
of the observing program by two examples: umbral fine structure, and
an emerging active region. Although the umbral spectrograms resolve
the brightness structure down to less than one arc sec we do not
find clear-cut relations in the spatial variations of brightness,
magnetic field strength and line-of-sight velocity across the umbral
structure. In the emerging active region several processes are observed
in their relationship: the rising and draining of an arch-filament
system, the convective collapse of flux tubes, and the growth of a
sunspot pore by coalescing fluxtubes.
---------------------------------------------------------
Title: Interpretation of Hα observations of chromospheric fine
structure.
Authors: Cram, L. E.
1985cdm..proc...53C Altcode:
Observations made in H-alpha underpin the empirical description
of the morphology and evolution of many chromospheric structures,
including mottles, spicules, fibrils, prominences and loops. Therefore,
to improve understanding of the physical mechanisms responsible for
these structures, a reliable and refined theory of the formation of
H-alpha in an inhomogeneous chromosphere should be developed. This
review summarizes the available observational material and discusses
relevant aspects of the theory of radiation transfer in H-alpha.
---------------------------------------------------------
Title: Dynamical phenomena in sunspots. I - Observing procedures
and oscillatory phenomena.
Authors: Thomas, J. H.; Cram, L. E.; Nye, A. H.
1984ApJ...285..368T Altcode:
High resolution spectra consisting of at least 1 hr periods were
obtained of the sunpost atmosphere. The Ca II H and K lines were
scanned to characterize umbral oscillations and flashes. The former
displayed peaks lasting 150-197 sec, while penumbral oscillations
peaked in the 197-300 sec range. Quiet sun oscillations exhibited no
peaks under 300 sec. The Ca II K line umbral flashes were ubiquitous
for all observational periods and were associated with light bridges
in the umbra. Magnetic field, vertical velocity, and chromospheric
intensity measurements taken during the 1 hr scans covered moving
magnetic features (MMF), which traversed the moats around sunspots. MMF
areas increased while the magnetic field intensity decreased with MMF
movement away from a sunspot. Bright Ca II K line wings were apparent
in the MMFs, but cores of the lines were not observed, suggesting that
flux loops generating the line are low in the photosphere.
---------------------------------------------------------
Title: Dynamical Phenomena in Sunspots - Part Two - a Moving Magnetic
Feature
Authors: Nye, A. H.; Thomas, J. H.; Cram, L. E.
1984ApJ...285..381N Altcode:
High-resolution observations of the magnetic field, vertical velocity,
and chromospheric intensity in a typical moving magnetic feature (MMF)
are obtained over a period of 1 hr as it moves outward across the
moat surrounding a large sunspot. The area of the MMF increases and
the magnetic field strength decreases as it moves outward. The MMF
contains a strong downdraft with a velocity of 400 m s<SUP>-1</SUP>
in the photosphere. The lifetime assigned to the MMF depends upon the
signature by which it is observed.
---------------------------------------------------------
Title: Interpretation of millimeter and sub-millimeter observations
of the solar chromosphere
Authors: Cram, L. E.
1984IJIMW...5.1165C Altcode:
Measurements of solar radiation in the millimetre and submillimetre
spectral range (100 μm 10 mm) yield the variation of brightness
temperature with wavelength and disk position. Such information
imposes important constraints on models of the structure of the solar
chromosphere. This paper reviews the observational data and discusses
the models derived from them.
---------------------------------------------------------
Title: Oscillatory Phenomena in a Sunspot
Authors: Thomas, J. H.; Cram, L. E.; Nye, A. H.
1984BAAS...16..531T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Relations Between High and Low Resolution Observations of
the Solar Photosphere (Keynote)
Authors: Cram, L. E.
1984ssdp.conf..389C Altcode:
The development of ideas regarding the structure of the solar
photosphere is described, with an emphasis on the interpretation
of connections between observations made with high and low spatial
resolution. Several related aspects of the physics of radiation
transport are discussed, and an overview of some relevant problems in
convection, waves and magnetic fields is presented.
---------------------------------------------------------
Title: The response of chromospheric emission lines to flares on YZ
Canis Minoris.
Authors: Worden, S. P.; Schneeberger, T. J.; Giampapa, M. S.; Deluca,
E. E.; Cram, L. E.
1984ApJ...276..270W Altcode:
Six flares of the dMe star YZ CMi have been observed with simultaneous
photometry and high-dispersion, time-resolved spectroscopy.The spectra
have temporal resolutions of 3 minutes with spectral resolutions
of 0.24 Å. The largest observed flare had a U band amplitude of
1.5 mag. Hα and Hβ line profiles did not broaden during any of the
observed flares, although the line center intensity increased by over a
factor of 2 during some flares. After the initial increase in intensity,
the emission line strength decreases but remains at enhanced levels
for hours following U band flares. The Hα flare luminosity and total
energy are compared to corresponding properties of solar flares.
---------------------------------------------------------
Title: Investigations of Solar and Stellar Atmospheric Heating:
A Historical Perspective
Authors: Cram, L.
1984rcch.conf...93C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: White-light radiation from semi-empirical flare models.
Authors: Dame, L.; Cram, L.
1983SoPh...87..329D Altcode:
We show that some recently published semi-empirical models for solar
flares predict a significant flux of visible continuum radiation,
due to bound-free radiation from hydrogen atoms and H<SUP>−</SUP>
ions in the chromospheric flare. The ratio of the emergent intensity in
one flare model to that in the quiet Sun is more than 100% at the head
of the Balmer continuum for a flare close to the limb, and 8% at disk
centre. The predicted flare spectrum has a relatively strong Balmer
jump. We compare the theoretical flare continuum with observations and
find disagreement in several important respects. The main disagreements
are: (1) the fact that few flares are observed to emit a white-light
continuum, while the models suggest that they should do so; (2)
the prediction of a strong Balmer jump, which is not observed in
most white-light flares; and (3) the absence of a `blue continuum'
in the theoretical prediction. We conclude that observations of flare
continua provide useful constraints on semi-empirical models, and that
at present the models do not satisfy these constraints.
---------------------------------------------------------
Title: High spatial and temporal resolution observations of the
solar CA II H line
Authors: Cram, L. E.; Dame, L.
1983ApJ...272..355C Altcode:
A 24 minute time series of photographic Ca II H line spectra made with
high spatial and spectral resolution has been analyzed to provide data
on the range of line profile variations in the quiet sun. Distribution
functions of the line-core intensity and the ratio of emission peak
intensities are exhibited and are used to classify the associated
line profiles. It is shown that the range of profile variation is
significantly larger than that covered by the models A-F of Vernazza,
Avrett, and Loeser, especially in relation to the darkest profiles
in which no core emission can be detected. Time-resolved spectra are
used to show that the 3-minute chromospheric oscillation involves
upward-propagating excitation which leads to intense heating in the
cell points. It is conjectured that these observations provide a direct
picture of the processes responsible for a significant part of the
nonradiative heating of the quiet chromosphere.
---------------------------------------------------------
Title: Preliminary observations of velocity fields at the solar poles
Authors: Cram, L. E.; Durney, B. R.; Guenther, D. B.
1983ApJ...267..442C Altcode:
Using the 13 m Littrow spectrograph at Sacramento Peak Observatory,
the Doppler shift of Fe I 5863 A in the polar regions of the sun over
a 20 day interval is studied. The daily observations were assembled
into a polar projection of the line-of-sight velocity field. The
projection shows a very clear pattern of supergranulation. When a
low-pass spatial filter is run over the data, a pattern of large-scale
(80-100 Mm) velocity features can be seen. Cross-correlation studies
show that the supergranular pattern rotates with a synodic period of
35 days, while there is evidence that the larger features rotate with a
shorter period of about 30 days. At present, it is not possible to say
whether the large-scale patterns represent a new scale of convection
(possibly related to the dominant convective eddy in the lower solar
convection zone) or to the low-wavenumber tail of a distribution of
supergranular cells.
---------------------------------------------------------
Title: Electrical Conductivity in Sunspots and the Quiet Photosphere
Authors: Kovitya, P.; Cram, L.
1983SoPh...84...45K Altcode:
The electrical conductivity, thermal conductivity and viscosity of
models of the quiet photosphere and the umbra of a sunspot have been
calculated using LTE ionization equilibria and the Chapman-Enskog theory
of transport coefficients. The results are presented in tabular form,
and compared with previous calculations.
---------------------------------------------------------
Title: Observations of Polar Velocity Fields
Authors: Durney, B. R.; Lytle, D. M.; Cram, L. E.; Guenther, D. B.;
Keil, S. L.
1983BAAS...15..716D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: CA II emission from late-type stars.
Authors: Cram, L. E.
1983PASA....5..152C Altcode: 1983PASAu...5..152C
The use of Ca II spectra to investigate dynamical phenomena in stellar
chromospheres is discussed in a review of recent observational and
theoretical studies. Solar and stellar observations are surveyed, and
sample data are shown graphically. Doppler-shift and non-LTE theories of
line formation and semiempirical non-LTE models of atmospheric structure
are explained, and the limitations of the latter are indicated. The
need for more realistic models of atmospheric oscillations, magnetic
effects, mass loss, and for more observations of the fine structure
of the solar Ca II lines, is stressed.
---------------------------------------------------------
Title: Relationships between solar and stellar magnetic fields
Authors: Cram, L. E.
1983IAUS..102..515C Altcode:
An assessment is made of the findings of observational and theoretical
studies of solar and stellar magnetic fields, with attention to
questions that have emerged as to the influence of magnetic fields on
atmospheric structure and the origins of solar and stellar magnetic
fields. Such stellar observations as those of the Mount Wilson H
and K flux program have reawakened interest in the Hale view of
a solar-stellar connection. It is suggested that the problem of
atmospheric heating will be solved only when present approaches to
the problem are revised to provide a much more realistic account of
the atmospheric plasma.
---------------------------------------------------------
Title: Models for stellar flares.
Authors: Cram, L. E.; Woods, D. T.
1982ApJ...257..269C Altcode:
The response of certain spectral signatures of stellar flares, such
as Balmer line profiles and the broad-band continuum, to changes in
atmospheric structure which might result from physical processes akin
to those thought to occur in solar flares, is investigated. While each
physical process does not have a unique signature, it can be shown
that some of the observed properties of stellar flares can be explained
by a model which involves increased pressures and temperatures in the
flaring stellar chromosphere. It is suggested that changes in stellar
flare area, both with time and with depth in the atmosphere, may play
an important role in producing the observed flare spectrum
---------------------------------------------------------
Title: Five-minute oscillations as a subsurface probe of sunspot
structure
Authors: Thomas, J. H.; Cram, L. E.; Nye, A. H.
1982Natur.297..485T Altcode:
Observations are reported here which show that the 5-min oscillations
in a sunspot umbra actually split into several individual modes
of different period. We interpret these modes of oscillation as
the response of the sunspot to forcing by the 5-min p-modes in the
surrounding quiet atmosphere. Also, we show how detailed observations
of the multiple 5-min modes in a sunspot may be used as a probe of
the structure of a sunspot beneath the solar surface.
---------------------------------------------------------
Title: Model chromospheres of RS CVn stars : Balmer line profiles
in lam And.
Authors: Mullan, D. J.; Cram, L. E.
1982A&A...108..251M Altcode:
Two models have been constructed for the chromosphere of the RS CVn
star Gamma And, one with a low-pressure transition zone, and one with
a high pressure transition zone. The high pressure model predicts an
H alpha line profile which agrees fairly well with high resolution
observations of Gamma And, without the need to include nonthermal
line broadening. The low pressure model predicts an H alpha profile
which agrees very well with the observations, after application of
macroturbulent broadening with a gaussian velocity parameter of about 30
km/sec. Methods which could distinguish between the two alternatives
are discussed, and it is suggested that if the low-pressure model
is valid, the large macroturbulence may be associated with unstable
magnetic flux loops in the atmosphere.
---------------------------------------------------------
Title: High Resolution Observations of a Moving Magnetic Feature
Authors: Nye, A. H.; Thomas, J. H.; Cram, L. E.
1982BAAS...14..624N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray heating of the quiescent chromospheres of dMe stars
Authors: Cram, L. E.
1982ApJ...253..768C Altcode:
The Einstein Observatory has found dwarf M stars to be particularly
intense X-ray sources, with an X-ray luminosity that may be as large
as 10% of the stellar visual luminosity. The present paper discusses
the potential contributions of the coronal X-ray flux to the heating
of dMe star chromospheres. The components of quiescent chromospheric
heating by a coronal X-ray source are examined, with attention given
to X-ray source characteristics, X-ray transfer, and the atmospheric
energy balance. A model chromosphere for dMe stars is constructed based
on a radiative equilibrium model photosphere with solar abundances. It
is shown that X-ray heating may account for both the quantity and
distribution of radiative losses from the chromosphere of a quiescent
dMe star, and thus may resolve the problem of the inadequacy of
acoustic-wave chromospheric heating.
---------------------------------------------------------
Title: Five-minute oscillations as a subsurface probe of sunspot
structure.
Authors: Thomas, J. H.; Cram, L. E.; Nye, A. H.
1982ASNYN...2b..25T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The physics of sunspots
Authors: Cram, Lawrence E.; Thomas, John H.
1981Natur.293..101C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rhe sun as a star.
Authors: Rutten, R. J.; Cram, L. E.
1981NASSP.450..473R Altcode: 1981suas.nasa..473R
The ways in which solar astrophysics serves to improve the methodology
for the interpretation of stellar observations and the construction of
stellar atmospheric models are summarized. The astrophysical processes
highlighted are: stellar mass; stellar rotation; stellar magnetism;
stellar composition; stellar companions; and evolutionary history.
---------------------------------------------------------
Title: Dynamical models for microturbulence
Authors: Cram, L. E.
1981ApJ...247..239C Altcode:
Solar and stellar spectral lines are observed to be broadened by
nonthermal motions. To account for this broadening, astronomical
diagnostic spectroscopists introduce 'microturbulence', which is usually
viewed as a statistical distribution of small-scale velocities whose
only effect is to Doppler-broaden the line profile. However, insofar
as microturbulence is a dynamical phenomenon, this usual picture is
incomplete, since it is not based on a realistic description of the
combined effects of small-scale velocity, temperature, and pressure
variations on the detailed processes of spectra line formation. By
using a number of schematic dynamical models for microturbulence, this
paper shows that the temperature and pressure variations associated
with velocity fields can lead to significant effects on the strength,
shifts, and shapes of photospheric spectral lines.
---------------------------------------------------------
Title: High Resolution Spectroscopy of Solar Activity - Part One -
Observing Procedures
Authors: Cram, L. E.; Robinson, R. D.; Mauter, H. A.; Mann, G. R.;
Phillis, G. L.
1981SoPh...71..237C Altcode:
We describe an observing program designed to obtain high spatial
resolution photographic spectra of solar active region phenomena,
with time resolution as short as 6 s. The Vacuum Tower Telescope
and Echelle Spectrograph at Sacramento Peak Observatory are used to
make observations simultaneously in Hα, He D<SUB>3</SUB>, Ca II K, Mg
b<SUB>1</SUB>, the CN bandhead at λ3883, and the magnetically-sensitive
line Fe I λ6302. Images reflected from the slit jaw are exposed
simultaneously in white-light and Hα. Observations of chromospheric
heating, following a high-velocity infall along an Hα superpenumbral
filament, are presented to illustrate the capabilities of the program.
---------------------------------------------------------
Title: Stellar model chromospheres. XII. High-resolution, absolute
flux profiles of the CaII H and K lines in dMe and non-dMe stars.
Authors: Giampapa, M. S.; Worden, S. P.; Schneeberger, T. J.; Cram,
L. E.
1981ApJ...246..502G Altcode:
We present 142 mÅ resolution spectra of the cores and wings of the
Ca II H and K lines in three dMe and four comparison dwarf M stars,
obtained with the KPNO 4 m echelle spectrograph and blue image
tube. The narrow-band photometry of Willstrop and the Barnes and
Evans relations for stellar angular diameters convert the observed
relative flux to absolute surface flux units with an estimated
uncertainty of ± 15 %. We derive chromospheric radiative loss rates
in the H and K lines and discuss trends in these loss rates with
effective temperature. Monochromatic surface fluxes are tabulated for
different features in the H and K lines, and radiation temperatures
are derived from the mean surface fluxes at K<SUB>1</SUB> and
H<SUB>1</SUB>, respectively. We find T<SUB>R</SUB>(H<SUB>1</SUB>) >
T<SUB>R</SUB>(K<SUB>1</SUB>), consistent with partial redistribution
theory. The T<SUB>R</SUB>(K<SUB>1</SUB>)/T<SUB>eff</SUB> ratio
is higher in these M dwarfs than the giants studied in Paper X,
and it is anomalously high for the dMe flare star YZ CMi. If
T<SUB>R</SUB>(K<SUB>1</SUB>)/T<SUB>eff</SUB> is an empirical age
indicator, then the result for YZ CMi implies that flare activity
and youth are directly correlated, as has been suggested by other
investigators. Moreover, the result implies that a high degree of
nonradiative heating is present in the upper photospheres of dMe
stars. Measurements of line widths at H<SUB>1</SUB> and K<SUB>1</SUB>
are presented together with FWHM data for the H and K lines. We find
that the scaling law proposed by Ayres generally agrees with the
observed trend exhibited by the K<SUB>1</SUB> widths. We also discuss
chromospheric radiative loss rates in the Hɛ line compared with loss
rates in the H and K lines, and present corrected FWHM(K) widths and
compare them to the widths predicted by the Wilson-Bappu relation as
calibrated by Lutz.
---------------------------------------------------------
Title: Relationships between CaII H Line Fine Structure and the
Integrated Solar H Line
Authors: Damé, L.; Cram, L.
1981BAAS...13..829D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Large Macroturbulence in the Chromosphere of an RS CVn Star
Authors: Cram, L. E.; Mullan, D. J.
1981BAAS...13..514C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: How Will High Resolution Ground-Based Observations Contribute
to a Better Understanding of the Sun?
Authors: Cram, L.
1981siwn.conf..397C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Five-Minute Oscillations in Sunspots
Authors: Thomas, J. H.; Cram, L. E.; Nye, A. H.
1981BAAS...13..858T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Effect of Subsurface Inhomogeneities on the Solar k-w
Diagram
Authors: Nye, A. H.; Cram, L. E.
1981BAAS...13..859N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Velocity Fields at the Solar Poles
Authors: Guenther, D.; Cram, L.; Durney, B.
1981BAAS...13Q.906G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Radiative Processes in White-Light Flares
Authors: Damé, L.; Cram, L.
1981BAAS...13Q.820D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sacramento Peak Observatory
Authors: Cram, Lawrence E.
1981SoPh...69..411C Altcode:
This article provides a brief summary of instrumental developments
at Sacramento Peak Observatory over the past decade, and describes
highlights of past and present staff research programs.
---------------------------------------------------------
Title: High Resolution Spectroscopy of the Disk Chromosphere -
Part Seven - Oscillations in Plage and Quiet Sun Regions
Authors: Woods, D. T.; Cram, L. E.
1981SoPh...69..233W Altcode:
We compare temporal power spectra of solar atmospheric oscillations
in plage and quiet Sun regions occurring on different parts of a time
series of high-quality spectrograms. For periods shorter than ∼300
s, the oscillation amplitude in the photospheric and low chromospheric
parts of the plage is reduced. There is a significant increase in long
period power in the chromospheric plage. Our results provide no clear
evidence that plages are heated by the dissipation of short-period
waves.
---------------------------------------------------------
Title: The physics of sunspots. Sacramento Peak Observatory
conference, held at Sunspot, New Mexico, 14 - 17 July 1981.
Authors: Cram, L. E.; Thomas, J. H.
1981phss.conf.....C Altcode:
An overview of current observational and theoretical research
into the physics of sunspots is presented. Observations of the
appearance and evolution of sunspots are reviewed, noting possible
connections with solar granulation and a potential larger flow
pattern. Theoretical aspects of a connection between magnetic fields
and convective forces are considered, with particular attention given
to the sunspot energy deficit as reflected in variations in the solar
luminosity. The discussion is extended to similarities between sunspots
and starspots. Details of sunspot characteristics are explored,
including fine-scale, time-dependent changes in morphology and the
origin of waves and oscillation in sunspots. Possible relationships
between the Evershed flow and penumbral filaments, umbral dots and
the umbral magnetic fine structure, and waves in the umbra and the
penumbra are explored. The Sunspot sunspot model is introduced as a
synthesis of various sunspot models and examined for applications to
phenomena common to different sunspots.
---------------------------------------------------------
Title: Observations of dynamical phenomena in sunspots
Authors: Nye, A. H.; Cram, L. E.; Beckers, J. M.; Thomas, J. H.
1981phss.conf..313N Altcode:
A preliminary report of the results of one observing run based on data
from one spectral line, the photospheric magnetic line Fe 6303, is
presented as part of a series of observations of dynamical phenomena
in sunspots using photographic spectra with the SPO vacuum tower
telescope and echelle spectrograph. The ejection of a magnetic feature
from the outer edge of the penumbra was observed. The initial total
field strength of the feature was about 1000 gauss, which appeared to
decrease as the feature moved away from the sunspot. The proper motion
was about 2 km/s, and the velocity field measured in the V profile
showed a downflow of 400 m/s on the spot-ward side of the moving
magnetic feature. Umbral oscillations at the photospheric level with a
herringbone structure characteristic of horizontally propagating waves,
suggesting some overtone mode of membrane oscillation in the umbra,
were seen. The peak amplitude of the oscillation was about 200 m/s,
and the mean power spectrum had several clear peaks.
---------------------------------------------------------
Title: An emerging active region - Some preliminary results
Authors: Brants, J. J.; Zwaan, C.; Cram, L. E.
1981phss.conf...60B Altcode:
Observations of an emerging flux region on July 24, 1979 are
analyzed in terms of six spectral lines, the broadband continuum,
and the Ca II K line core. The process of formation of the umbrae,
including the appearance of protopores leading to fully formed pores,
is described. Results are presented from spectrographic observation of
the 6302 A and 5692 A lines, taken while pores were still forming. Field
strengths of 1900 and 2500 gauss were detected, in line with previous
measurements of pore groups.
---------------------------------------------------------
Title: Conjectures regarding the structure of a sunspot penumbra
Authors: Cram, L. E.; Nye, A. H.; Thomas, J. H.
1981phss.conf..384C Altcode:
A study of simple radiative transfer models for some of the dark
filaments on the outer edge of penumbras, which observations suggest
may lie several hundred km above the base of the quiet photosphere,
has determined that elevated dark filaments probably have higher
temperatures and densities than the surrounding atmosphere. The
possibility of a connection between the dark filaments, the photospheric
Evershed flow, and umbral dots, is discussed. An important observational
test of the present model would involve an attempt to separate
temperature and optical depth effects in the dark filaments. This
could be accomplished by either continuum photometry at a few, widely
separated wavelengths, or by spectroscopic studies.
---------------------------------------------------------
Title: On the formation of Fe II lines in stellar spectra. I. Solar
spatial intensity variation of lambda 3969.4.
Authors: Cram, L. E.; Rutten, R. J.; Lites, B. W.
1980ApJ...241..374C Altcode:
High-spatial-resolution solar observations of the weak Fe II lambda
3969.4 line are employed to study non-local thermodynamic equilibrium
effects in Fe II line formation. This line is superposed on the wing
of the Ca II H line, which raises its height of formation. The line
shows extraordinary spatial intensity variations, including emission
features whose contrast increases toward the limb. Observed profiles
of the Fe II resonance lines in the UV are used to define formation
parameters in a 15-level atomic model computation, which shows that Fe
II subordinate lines are generally formed out of local thermodynamic
equilibrium as a result of pumping by UV line-wing photons from the
deep photosphere. For the lambda 3969.4 line, this pumping results in
large sensitivity to the atmospheric structure in layers deeper than
the layer of formation of the H-wing background intensity. The absence
of intense emission cores in the Fe II resonance lines, the effects
of partially coherent scattering, and the effects of chromospheric and
photospheric inhomogeneities are discussed. It is found that emission
of lambda 3969.4 provides a diagnostic of the inhomogeneous structure
of the deep photosphere, for the sun and for late-type stars.
---------------------------------------------------------
Title: X-Ray Heating of the Quiescent Chromospheres of dMe Stars
Authors: Cram, L. E.
1980BAAS...12..801C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Models for Stellar Flares Based on the Physics of Solar Flares
Authors: Cram, L. E.; Woods, D. T.
1980BAAS...12..914C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Emission measures derived from far ultraviolet spectra of T
Tau stars.
Authors: Cram, L. E.; Giampapa, M. S.; Imhoff, C. L.
1980ApJ...238..905C Altcode:
Spectroscopic diagnostics based on UV emission line observations have
been developed to study the solar chromosphere, transition region,
and corona. The atmospheric properties that can be inferred from
observations of total line intensities include the temperature, by
identifying the ionic species present; the temperature distribution of
the emission measure, from the absolute intensities; and the electron
density of the source, from line intensity ratios sensitive to the
electron density. In the present paper, the temperature distribution of
the emission measure is estimated from observations of far UV emission
line fluxes of the T Tauri stars, RW Aurigae and RU Lupi, made on the
IUE. A crude estimate of the electron density of one star is obtained,
using density-sensitive line ratios.
---------------------------------------------------------
Title: Sacramento-Peak Observatory
Authors: Zirker, J. B.; Cram, L. E.
1980BAAS...12..351Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal structure of stellar atmospheres
Authors: Cram, L. E.
1980ComAp...9...25C Altcode:
Classical models of stellar atmospheres are based on the assumptions of
hydrostatic and radiative equilibrium within a passive gas, however,
observations are providing evidence that stellar atmospheres are rich
in nonthermal phenomena that cannot be explained by these models. The
present paper reviews the situation and proposes an approach to
its resolution. Empirical evidence for the ubiquitous existence
of nonthermal phenomena in stellar atmospheres is summarized, and
the successes and failures of classical theories and semiempirical
modifications in explaining the observed properties of stellar
atmospheres are discussed. It is concluded that classical models
could explain stellar atmospheres only if they are modified to include
nonthermal phenomena. A program for including such phenomena is then
presented in which the global atmospheric structure produced by steady
and fluctuating boundary conditions imposed by subatmospheric dynamical
processes is considered.
---------------------------------------------------------
Title: Diagnostic Use of Feii H and K Wing Emission Lines
Authors: Cram, L. E.; Rutten, R. J.; Lites, B. W.
1980LNP...114..102C Altcode: 1980IAUCo..51..102C; 1980sttu.coll..102C
No abstract at ADS
---------------------------------------------------------
Title: Effects of Acoustic Waves on Spectral Line Profiles
Authors: Cram, L. E.
1980LNP...114..211C Altcode: 1980sttu.coll..211C; 1980IAUCo..51..211C
No abstract at ADS
---------------------------------------------------------
Title: Atmospheres of T Tau stars : the photosphere and low
chromosphere.
Authors: Cram, L. E.
1979ApJ...234..949C Altcode:
A model for the photospheric and low chromospheric regions of
the atmosphere of an advanced T Tauri star has been constructed,
by superposing an ad hoc temperature rise on a theoretical model
photosphere. This model has been used to synthesize several spectral
features, including the continuum from 300 A to 300 microns and the Fe
I and Fe II spectrum in the interval 4475-4500 A. A comparison between
these predictions and observations supports the conclusion that T Tauri
stars possess a chromosphere that begins deep in the atmosphere, with
the beginning depth of the chromosphere principally determining the
degree of advancement of the T Tauri spectrum. There are a number of
spectral features that cannot be explained by this model, including the
near-IR excess, the large H alpha:H beta decrement, and the asymmetry
of emission lines.
---------------------------------------------------------
Title: Model chromospheres of flare stars.I. Balmer-line profiles.
Authors: Cram, L. E.; Mullan, D. J.
1979ApJ...234..579C Altcode:
In preparation for using the Balmer lines in flare stars as
chromospheric diagnostics, we have computed a grid of model
chromospheres by superposing prescribed temperature rises on published
models for M dwarf photospheres. The chromospheric equation of state
is dominated by the non-LTE ionization of hydrogen, which is treated
by using a model hydrogen atom with five bound levels. The radiative
transfer equation is solved explicitly for the Lyman continuum and
the Balmer lines Ha, Hfl, and H)'. In the absence of a chromosphere,
Ha, Hfl, and H)' appear as weak absorption lines. As the amount of
chromospheric material (between temperatures Te = 5500 K and 50,000 K)
increases, these absorption lines first become deeper, then develop
emission peaks on the outer edges of their wings, and finally, when the
chromosphere is sufficiently massive, the Balmer lines become strong
emission lines. The results obtained here will be used to interpret
the profiles and decrements of the Balmer lines in flare stars, in both
quiescent and flaring states. Subject headings: line profiles - stars:
atmospheres - stars: chromospheres - stars: flare - stars: late-type
---------------------------------------------------------
Title: Some effects of acoustic waves on spectral-line profiles.
Authors: Cram, L. E.; Keil, S. L.; Ulmschneider, P.
1979ApJ...234..768C Altcode:
The paper discusses the formation of spectral lines in the presence of
short-period, nonlinear, radiatively damped acoustic waves propagating
through a model of the solar atmosphere. The temperature and pressure
perturbations associated with the wave strongly influence the line
profile. Although their wavelength is less than the depth of the
velocity response function of photospheric spectral lines, the
acoustic waves produce large (greater than 100 m/s), short-period
line shifts. Acoustic waves of sufficient amplitude to account for
chromospheric heating do not significantly increase the equivalent
widths of photospheric lines and therefore are probably not responsible
for photospheric microturbulence.
---------------------------------------------------------
Title: The Ca II H and K Lines in dMe and non-dMe Stars
Authors: Giampapa, M. S.; Worden, S. P.; Schneeberger, T. J.; Cram,
L. E.
1979BAAS...11..625G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Small-scale solar magnetic fields
Authors: Cram, Lawrence E.
1979Natur.282..133C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Use of the solar limb effect to test photon decay and
cosmological redshift theories
Authors: Beckers, Jacques M.; Cram, Lawrence E.
1979Natur.280..255B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ca II emission from stellar chromospheres.
Authors: Cram, L. E.; Krikorian, R.; Jefferies, J. T.
1979A&A....71...14C Altcode:
Measurements are presented of the separations of the K2 peaks and
the K1 dips of the emission core of the Ca II K line observed on
high-dispersion spectra of 33 late-type stars. These separations
(called W1 and W2) are compared with the emission core width W which
satisfies the Wilson-Bappu correlation. With some qualifications, it
is found that W is directly proportional to the 1.3 power of W1 and
the 1.06 power of W2. Some consequences of this result are discussed.
---------------------------------------------------------
Title: High Resolution Spectroscopy of the Disk
Chromosphere. VI. Power, Phase and Coherence Spectra of Atmospheric
Oscillations
Authors: Cram, L. E.
1978A&A....70..345C Altcode:
Summary. Observations of the solar atmosphere have been made
simultaneously in several photo spheric and chromospheric lines. The
time resolution is 18 S and the duration 30 min, the space resolution
is 1 Mm and the extent 250 Mm. Fluctuations in line position and
intensity have been analysed in the two-dimensional (k, co) Fourier
transform plane. Extensive use is made of phase and coherence spectra,
to study the vertical structure of the atmospheric oscillations. Among
the results are (i) the detection of gravity waves extending into the
chromosphere, (ii) additional evidence for a model of the formation of
the emission core of the Ca ii K line, and (iii) the proposal that the
5 min "photo spheric" and 3 min "chromospheric" oscillations both occur
throughout the photosphere and the chromosphere, with their relative
amplitudes determined by the respective scale heights. Key words:
solar atmospheric oscillations - Fourier transforms
---------------------------------------------------------
Title: Dynamical Processes in the Solar Atmosphere: Observational
and theoretical results concerning the nature of "turbulence"
Authors: Keil, S. L.; Cram, L. E.
1978BAAS...10..638K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Inversion problems in radiative transfer theory - The
Backus-Gilbert formalism
Authors: Cram, L. E.
1978JQSRT..20..305C Altcode:
The method introduced by Backus and Gilbert to study geophysical
inversion problems may be readily applied to the inversion problems
of radiation transfer theory. Using the inversion of limb-darkening
data as an example, we show how the method provides a quantitative
estimate of the amount and reliability of the information that can be
extracted from a given set of noisy data.
---------------------------------------------------------
Title: Departures from radiative equilibrium in stellar
atmospheres. Grey absorption.
Authors: Cram, L. E.
1978A&A....67..301C Altcode:
Some of the consequences of departures from radiative equilibrium in
stellar atmospheres are discussed. Using a discrete-ordinate method
the radiative-transfer equation in a grey atmosphere subjected to
a specified distribution of mechanical heating is solved, and the
resulting temperature changes in LTE and non-LTE conditions are
determined. It is shown how radiative transfer leads to temperature
changes in regions that are not directly heated and how non-LTE effects
lead to an amplification of the temperature rise produced by a given
distribution of heating. An attempt is made to resolve a controversy
surrounding the estimation of excess radiative losses in the solar
chromosphere.
---------------------------------------------------------
Title: Some comments on Suemoto's paper "An empirical, statistical
model for the formation of the cores of chromospheric Fraunhofer
lines".
Authors: Cram, L. E.; Durrant, C. J.; Grossmann-Doerth, U.
1978SoPh...58..279C Altcode:
We discuss a recent model for the solar chromosphere proposed by Suemoto
(Solar Phys.54, 3). We conclude that the model is incompatible with the
basic constraints imposed by high resolution observations and by line
formation theory, and that consequently the model does not adequately
describe the solar chromosphere.
---------------------------------------------------------
Title: Resonance line scattering from optically thin structures
located above the solar limb.
Authors: Cram, L. E.; Vardavas, I. M.
1978SoPh...57...27C Altcode:
We discuss the formation of emission lines by resonance scattering
from optically thin structures located above the solar limb. When
the scattered radiation is only partially redistributed in frequency
and angle, the resulting coherency is sufficient to affect the
interpretation of such lines. In particular the apparent Doppler width
of the scattered line may be different from the Doppler width in the
scattering structure.
---------------------------------------------------------
Title: Observational tests of the shock heating theory for late-type
stellar chromospheres.
Authors: Cram, L. E.; Ulmschneider, P.
1978A&A....62..239C Altcode:
Recent predictions of the positions of stellar temperature minima
are combined with a theory of the formation of Ca(+) resonance lines,
and thus present observable tests of the shock wave heating theory of
stellar chromospheres. Although the trend in the predicted line widths
agrees with the trend in the observations, the quantitative agreement
is only satisfactory for a solar-type star with log g 4 and T(eff) 6000
K. The theoretical minima of giant stars are located much deeper and the
minima of cool dwarf stars are located much higher than the observations
suggest. Possible explanations of this disparity are discussed.
---------------------------------------------------------
Title: Analysis of the solar magnesium I spectrum. II. Sensitivity
of lambda 2852 to partial redistribution effects.
Authors: Canfield, R. C.; Cram, L. E.
1977ApJ...216..654C Altcode:
We have computed theoretical profiles of the Mg 1 A2852 resonance
line by using various models for the frequency redistribution of
the scattered radiation. We find that throughout the line core and
inner wings these profiles are highly sensitive to the assumed
extent of redistribution. In the line core the profile computed
allowing partial redistribution has emission peaks at AA + 0.1 A,
while the profile computed for complete redistribution has no peaks
at all. In the inner wings (0.1 < i AAI < 5.0 A) the residual
intensity with partial redistribution falls as much as a factor of 3
below the complete redistribution profiles. We conclude that partial
redistribution effects in the formation of this line must be taken into
account in subsequent calculations. Subject headings: line formation -
line profiles - radiative transfer - Sun: spectra - ultraviolet: spectra
---------------------------------------------------------
Title: Radiative transfer in geometries other than plane-parallel
layers
Authors: Cram, L. E.
1977MmSAI..48..377C Altcode:
Most of our information on the state and structure of stellar
atmospheres derives from studies of the emitted radiation field,
however, radiation transfer in a stellar atmosphere has been
usually studied within the confines of plane-parallel or spherically
symmetric geometry. In the present paper, the importance of studying
multidimensional radiation transport is pointed out, and some
consequences of introducing more complex and more realistic geometries
to the study of astrophysical radiation transfer are discussed.
---------------------------------------------------------
Title: On the heating of the solar chromosphere.
Authors: Cram, L. E.
1977A&A....59..151C Altcode:
The theory of chromospheric heating is reexamined to assess the validity
of recent claims that short-period waves provide a viable explanation
of the heating of the solar chromosphere. It is concluded that there
is no reliable basis for these claims and that the whole question of
the energy balance of the chromosphere is open. Emphasis is placed on
the need for a careful study of the interplay between line blanketing,
non-LTE effects, and mechanical heating.
---------------------------------------------------------
Title: High resolution spectroscopy of the disk
chromosphere. V. Space-time variations observed simultaneously in
seven lines.
Authors: Cram, L. E.; Brown, D. R.; Beckers, J. M.
1977A&A....57..211C Altcode:
Time sequence spectroscopic observations of the quiet solar
chromosphere along a 200 Mm strip near the center of the disk were
reduced to obtain 30 min of data. Oscillations appear in most of the
observations in selected photospheric and chromospheric lines, but
rarely in continuum observations. At a given point, the oscillations may
be prominent or weak, they are never regular in time, and there is no
unique relationship between the amplitudes at different heights. There
are several examples of granules which apparently excite a burst of
short period oscillations. By considering the line shift and intensity
variations of all the lines, a working model is derived for the velocity
field and related temperature variation.
---------------------------------------------------------
Title: Perturbation solutions of the equation of radiative transfer
in a stellar atmosphere.
Authors: Cram, L. E.
1977A&A....56..401C Altcode:
Of prime importance in the study of gasdynamic phenomena in stellar
atmospheres is the ability to solve the radiative transfer equation in
a nonequilibrium inhomogeneous moving plasma. This paper describes a
flexible and efficient method for solving this type of problem. The
method is based on a perturbation-series solution of the transfer
equation. The terms in the perturbation series are obtained by repeated
solution of a very simple transfer equation; the final solution may
be as accurate as the application requires.
---------------------------------------------------------
Title: A multi-component timt-dependent model for the formation of
the Ca II K line.
Authors: Cram, L. E.
1976A&A....50..263C Altcode:
This paper discusses a synthetic, time-dependent multicomponent
model for the formation of the chromospheric Ca II K line. The
equations describing the conservation of mass, momentum and energy
in a compressible fluid are solved to obtain the nonlinear dynamical
response of a model chromosphere excited by sinusoidal oscillations. A
non-LTE radiation transfer problem for a three-level model of the Ca
II ion is solved to obtain the time evolution of the K and 8542 line
profiles emerging from the moving atmosphere. The agreement between the
temporal evolution of the theoretical K-line profile and the observed
time-sequence behavior of a class of chromospheric fine structures known
as K-grains supports recent suggestions that the K-grains are sites
of local heating due to the dissipation of an acoustic energy flux.
---------------------------------------------------------
Title: Determination of the temperature of the solar corona from
the spectrum of the electron-scattering continuum.
Authors: Cram, L. E.
1976SoPh...48....3C Altcode:
When the K-corona is formed by the scattering of photospheric radiation
from free electrons, the Fraunhofer lines are greatly broadened by
the thermal motions of the hot electrons. This paper discusses the
possibility of measuring the coronal electron temperature from the
residual depressions in the K-coronal spectrum. If the ratio of the
intensities at 4100 Å and 3900 Å can be measured to an accuracy of
±1%, the coronal temperature can be inferred to an accuracy of ±0.2
MK. The temperature of a coronal inhomogeneity may also be measured
by this method, provided the position angle is known.
---------------------------------------------------------
Title: A perturbation solution of the radiative transfer equation
in a differentially moving atmosphere.
Authors: Cram, L. E.; Lopert, P. B.
1976JQSRT..16..347C Altcode:
We present a new technique for solving the radiative transfer
equation in a differentially moving atmosphere. The method is based
on a perturbation of the solution of the transfer problem in a static
atmosphere. The perturbation technique may be applied with any method
for solving the static atmosphere problem and leads to significant
reductions in computer time and storage requirements. The method is
flexible and may be used to solve problems involving depth dependence
in any of the parameters of the transfer equation.
---------------------------------------------------------
Title: Perturbation solutions of the equation of radiative transfer
in a stellar atmosphere.
Authors: Cram, L. E.
1976cppa.conf...H4C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interpretation of Hα contrast profiles of chromospheric
fine structures
Authors: Cram, L. E.
1975SoPh...42...53C Altcode:
Recent observations of the Hα contrast profiles of identifiable
chromospheric fine structures are interpreted in terms of an empirical
model. It is shown that the parameters inferred from an application
of Beckers' `cloud' model are unreliable, and the problem of line
asymmetries is re-examined.
---------------------------------------------------------
Title: Hydromagnetic Waves in Structured Magnetic Fields
Authors: Cram, L. E.; Wilson, P. R.
1975SoPh...41..313C Altcode:
Although the inhomogeneous nature of solar magnetic fields is now
well established, most theoretical analyses of hydromagnetic wave
propagation assume infinite homogeneous fields. Here we reformulate
the hydromagnetic wave problem for magnetic fields which vary in one
direction perpendicular to the field. The permitted modes of small
amplitude hydromagnetic oscillations are considered, first in the case
of a single interface between semi-infinite magnetic and non-magnetic
compressible regions, and secondly for a magnetic flux sheath of
given thickness imbedded in a nonmagnetic region. It is shown that,
for small values of R (the ratio of the Alfvén to the sound speed),
an acoustic or p-mode wave front passes through the flux sheath with
only minor deformation. However, for large R, the transmitted acoustic
wave is attenuated and, depending upon the thickness of the flux sheath
and the angle of incidence, a hydromagnetic wave may be effectively
trapped and guided along the flux sheath.
---------------------------------------------------------
Title: Mass, Energy and Momentum Transport in the Solar Atmosphere
Authors: Cram, L. E.
1975cesra...5...13C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mass, energy and momentum transport in the solar atmosphere
Authors: Cram, L. E.
1975esm..meet...13C Altcode:
A theoretical framework is outlined for the discussion of mass,
momentum, and energy transport in the solar atmosphere. Theoretical
aspects of solar atmospheric dynamics are reviewed, models of stellar
atmospheres are described, and the dynamic equations for the solar
atmosphere are derived from the Boltzmann equation. The equation of
radiative transfer is discussed from the viewpoint of its role in
the dynamic behavior of the atmosphere and its central importance
in the diagnostic process. Spherically symmetric models of the solar
atmosphere are examined, and it is shown that a classical model based
on the joint assumptions of radiative and hydrostatic equilibrium
is totally inadequate for the study of dynamic processes. The
inhomogeneous solar atmosphere is investigated with emphasis on the
subatmospheric nonthermal-energy storage modes (rotation, convection,
and pulsation). Observed dynamic phenomena due to the penetration and
leakage of mass, momentum, and kinetic energy from these storage modes
into the atmosphere are discussed, including photospheric granulation,
chromospheric oscillations, supergranulation, and microturbulence.
---------------------------------------------------------
Title: Mass, energy and momentum transport in the solar atmosphere.
Authors: Cram, L. E.; Thomas, R. N.
1975MmArc.105...11C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of the Ca II K-Line in the quiet solar chromosphere
Authors: Cram, Lawrence Edward
1975PhDT.......252C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Partially coherent scattering models for the formation of
the chromospheric Ca ii K line
Authors: Vardavas, I. M.; Cram, L. E.
1974SoPh...38..367V Altcode:
We discuss a model for the formation of the chromospheric Ca
II K line which does not make the usual assumption of complete
redistribution. Using a physically reasonable scattering model,
we find significant departures due to the frequency dependence of
the line source function, particularly in the relative intensity and
centre-to-limb behaviour of the K<SUB>1</SUB> parts of the line and in
the asymmetry produced by differential velocity fields. We conclude
that the frequency dependence of the K line source function must be
considered in quantitative models for the formation of the K line.
---------------------------------------------------------
Title: High Resolution Spectroscopy of the Disk Chromosphere. IV:
Evidence for the Propagation and Dissipation of Mechanical Energy
in the Chromosphere
Authors: Cram, L. E.
1974SoPh...37...75C Altcode:
We describe time-series observations of small-scale Ca II
emission features located outside the network in the quiet
chromosphere. Simultaneous spectra in K and λ 8542 show unambiguously
that the evolutionary behaviour of the K-line profile due to an
outwardly propagating velocity pulse. Assuming that this pulse is a
progressive acoustic wave, as suggested by the inferred flow parameters,
we show that the wave loses mechanical energy in traversing the
chromosphere. This implies that the bright Ca II features (K-grains)
are the manifestation of local heating in the chromosphere, possibly
by shock waves.
---------------------------------------------------------
Title: The velocity-dependent source function in radiative transfer
theory.
Authors: Cannon, C. J.; Cram, L. E.
1974JQSRT..14...93C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Spectroscopy of the Disk Chromosphere. Iii:
Evidence for the Propagation and Dissipation of Mechanical Energy
in the Chromosphere
Authors: Cram, L.
1974IAUS...56...51C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Shock Waves and the Interpretation of the Chromospheric
Calcium K-line
Authors: Cram, L. E.
1972PASA....2..146C Altcode: 1972PASAu...2..146C
Dissipation of shock waves has often been proposed as the energy
source required to sustain the outward temperature rise in the solar
atmosphere. Theoretical models for the heating process have been
developed by equating the mechanical energy input to the radiative
energy loss at each height, but neither of these processes is well
understood, and the lack of data means that the models are necessarily
crude.
---------------------------------------------------------
Title: Multi-Component Models for the Formation of the Chromospheric
Ca II K Line. II: The Effect of Velocity Fields
Authors: Cram, L. E.
1972SoPh...22..375C Altcode:
Recent high resolution observations of the Ca II fine structure are
discussed. An analytic method is applied to examine the effects of
velocity fields on multi-component model atmospheres in which the
central reversal in the bright components is due to self-absorption. It
is shown that the inclusion of quite reasonable velocity fields permits
the reproduction of not only the high resolution profiles of the small
scale emission features but also the qualitative centre-limb behaviour
of the spatially averaged profiles. The method is also used to examine
models suggested by Pasachoff and others in which the double reversal is
a statistical effect of singly peaked velocity shifted profiles. These
models are shown to encounter severe difficulties near the limb.
