Author name code: walton
ADS astronomy entries on 2022-09-14
=author:"Walton, S.R."
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Title: Disclosing the Firing Protocol of Athenian Pottery Production:
A Raman and Colorimetric Study of Replicates and Original Samples
Authors: Cianchetta, I.; Trentelman, K.; Maish, J.; Walton, M.
Bibcode: 2014LPICo1783.5014C
Altcode:
The work presented here examines the technological foundations of
Athenian pottery production through the replication of the firing
technology. Raman spectroscopy and colorimetry were used to investigate
composition and color of ceramics slips.
Title: On the Variability of the Apparent Solar Radius
Authors: Chapman, G. A.; Dobias, J. J.; Walton, S. R.
Bibcode: 2008ApJ...681.1698C
Altcode:
Full-disk photometric solar images at a wavelength of 672.3 nm have
been obtained daily since 1986 using the CFDT1 (Cartesian Full Disk
Telescope No. 1). An analysis of these images from 1986 through the end
of 2004 December has shown a peak-to-peak variation in the geocentric
north-south solar radius of 0.136 +/- 0.01, approximately in phase
with the solar cycle. The multiple correlation coefficient squared is
R2 = 0.0404 (R = 0.2). While this correlation coefficient
is small, due to the large number of data points (N = 4042), the level
of significance is less than 0.02. The radius had a maximum value near
the times of maximum activity for solar cycles 22 and 23.
Title: A Comparison of Feature Classification Methods for Modeling
Solar Irradiance Variation
Authors: Jones, H. P.; Chapman, G. A.; Harvey, K. L.; Pap, J. M.;
Preminger, D. G.; Turmon, M. J.; Walton, S. R.
Bibcode: 2008SoPh..248..323J
Altcode:
Physical understanding of total and spectral solar irradiance variation
depends upon establishing a connection between the temporal variability
of spatially resolved solar structures and spacecraft observations of
irradiance. One difficulty in comparing models derived from different
data sets is that the many ways for identifying solar features such as
faculae, sunspots, quiet Sun, and various types of "network" are not
necessarily consistent. To learn more about classification differences
and how they affect irradiance models, feature "masks" are compared as
derived from five current methods: multidimensional histogram analysis
of NASA/National Solar Observatory/Kitt Peak spectromagnetograph data,
statistical pattern recognition applied to SOHO/Michelson Doppler
Imager photograms and magnetograms, threshold masks allowing for
influence of spatial surroundings applied to NSO magnetograms, and
"one-trigger" and "three-trigger" algorithms applied to California
State University at Northridge Cartesian Full Disk Telescope intensity
observations. In general all of the methods point to the same areas of
the Sun for labeling sunspots and active-region faculae, and available
time series of area measurements from the methods correlate well with
each other and with solar irradiance. However, some methods include
larger label sets, and there are important differences in detail,
with measurements of sunspot area differing by as much as a factor
of two. The methods differ substantially regarding inclusion of fine
spatial scale in the feature definitions. The implications of these
differences for modeling solar irradiance variation are discussed.
Title: The Behavior of Sunspot Contrast during Cycle 23
Authors: Wesolowski, M. J.; Walton, S. R.; Chapman, G. A.
Bibcode: 2008SoPh..248..141W
Altcode: 2008SoPh..tmp...21W
Results are presented from a study of various sunspot contrast
parameters in broadband red (672.3 nm) Cartesian full-disk digital
images taken at the San Fernando Observatory (SFO) over eight years,
1997 - 2004, of the twenty-third sunspot cycle. A subset of over 2700
red sunspots was analyzed and values of average and maximum sunspot
contrast as well as maximum umbral contrast were compared to various
sunspot parameters. Average and maximum sunspot contrasts were found
to be significantly correlated with sunspot area (rs=−
0.623 and rs=− 0.714, respectively). Maximum umbral
contrast was found to be significantly correlated with umbral area
(rs=− 0.535). These results are in agreement with the
works of numerous other authors. No significant dependence was detected
between average contrast, maximum contrast, or maximum umbral contrast
during the rising phase of the solar cycle (rs=0.024,
rs=0.033, and rs=0.064, respectively). During
the decay phase, no significant correlation was found between average
contrast or maximum contrast and time (rs=− 0.057 and
rs=0.009, respectively), with a weak dependence seen between
maximum umbral contrast and cycle (rs=0.102).
Title: Solar Irradiance Variations: Cycles 22 and 23
Authors: Walton, S. R.
Bibcode: 2006AGUFMSH24A..02W
Altcode:
Improvement in our understanding of solar irradiance variations is
extremely important in our understanding of many aspects of the
Sun-Earth connection. We now have spacecraft measurements of TSI
variations for almost 30 years, from 1978 to 2006. In particular, we
have complete coverage with good quality data for both solar cycles 22
and 23. In this review talk, I will discuss how well solar irradiance
models have worked for both cycles, and what we can still learn from
measurements of future cycles. Several interesting new results have
recently appeared, and more should appear in the future.
Title: Penumbral Moving Magnetic Features
Authors: Penn, M. J.; Jaeggli, S. A.; Henney, C. J.; Luszcz, S.;
Walton, S. R.
Bibcode: 2006ASPC..358...31P
Altcode:
Moving magnetic features are observed in the penumbrae of two sunspots
with time sequences of vector magnetic field measurements taken in
the infrared Fe I 1565 nm spectral line (g=3). These features move
with similar radial velocities as previously observed continuum and
G-band features, and confirm a short sequence of penumbral magnetic
observations in the visible. These features move with similar speeds
to the moving magnetic features seen outside sunspot penumbrae, and
in some cases they are seen to cross the penumbral boundary and move
across the sunspot moat. Magnetic and flow parameters are briefly
compared with predictions from the moving flux tube model.
Title: Can Changing Sunspot and Facular Areas Reproduce the Amplitude
of Total Irradiance Variations?(Look,Mom; No Free Parameters!)
Authors: Foukal, P.; Bernasconi, P. N.; Walton, S. R.
Bibcode: 2005AGUSMSH22B..02F
Altcode:
Empirical models of total solar irradiance variation demonstrate a
high correlation between observed irradiance fluctuations and the
changing areas of spots and faculae. However, the contrast of these
structures (especially the faculae) in integrated light is still
uncertain. Consequently, the agreement in amplitude of the measured
and modeled irradiance time series remains poorly known. Recently, the
first measurements of facular contrast in broad - band integrated light
were obtained using the balloon -borne Solar Bolometric Imager (Foukal
et al., Ap.J. Letts 611,57,2004). These measurements, obtained over
approximately the same wavelength range accepted by radiometers such as
VIRGO or ACRIM, enable the first reconstruction of the total irradiance
expected from spots and faculae, with no free parameters. We compare
this reconstruction with the radiometric record to determine whether
other contributions besides the darkness of spots and brightness of
faculae are required to explain solar irradiance variation, at least
over rotational time scales.
Title: A "Toy" Simulation of Total Solar Irradiance Variations
Authors: Walton, S. R.; Preminger, D. G.
Bibcode: 2005AGUSMSP41B..10W
Altcode:
Recently, we have developed a method for deducing the total solar
irradiance S from sunspot area AS using a finite impulse response FIR
which, when convolved with AS, produces S (Preminger & Walton 2005,
JGR, submitted). In an effort to gain physical insight into the meaning
of the FIR, we have produced a simple model of the solar cycle with
the following characteristics: (1) nd sunspots per day are generated,
each with a fixed area AS = 500 millionths of the solar hemisphere;
(2) sunspots decay exponentially with time constant τS = 10 days;
(3) decayed sunspot area becomes faculae, which in turn decay with a
time constant τF = 45 days. These parameters were deduced from various
characteristics of the actual solar cycle. Each sunspot is generated at
a random solar longitude, and the faculae remain at the same longitude
as the sunspots. Latitude variation is not modeled; that is, they are
always zero. We allow nd to vary as a simple cosine bell from 0 up
to nd,max. Simple models of sunspot and facular contrast are used to
compute a pseudo-TSI. When nd,max=1, the resulting model reproduces a
few of the observed characteristics of the solar activity cycle; e.g.,
the projected sunspot and facular area peak at about 1500 and 45,000
parts per million of the solar disk. If we use this simple model to
compute a FIR, it has a very similar shape to the one found empirically
from the actual measured S and AS. The model FIR is also independent
of nd,max over the range 0.1 to 10. It is missing some qualitatively
important characteristics, however, in particular the fact that S
actually begins to rise some time before AS; we are investigating
refinements to our model which might reproduce this property of the
empirical FIR.
Title: On the Facular Area Surrounding Decaying Sunspots
Authors: Chapman, G. A.; Hoffer, A. S.; Walton, S. R.
Bibcode: 2005SoPh..226...37C
Altcode:
The change in facular area around decaying sunspots is investigated. The
data are from full-disk photometric images from CFDT1 (5 arc sec
pixels) obtained at the Ca II K-line λ = 393.4 nm. The 31 active
regions are from a list previously used to study the decay rate of
sunspots. We find a weak, marginally significant relation between spot
decay rate and growth of the surrounding facular region (r2
= 0.1255). We conclude that, for this group of decaying sunspots,
the growth or decay of the surrounding facular region was not clearly
related to the decay rate of an active region's sunspots.
Title: Modeling total solar irradiance: the data, the models,
the questions
Authors: Walton, S. R.
Bibcode: 2005MmSAI..76..819W
Altcode:
A brief review is given of the modeling of total solar irradiance
(TSI) variations as they have been carried out at the San Fernando
Observatory over the last few years. The modeling techniques used are
described, and recent results of the modeling are summarized, with
the goal of showing what may be learned from TSI modeling using ground
based observations. I then discuss some very recent results which are
part of ongoing investigations: historical reconstruction of TSI using
a new technique, and an ab initio model of the irradiance variations.
Title: Implications of Ground Based Photometric Images for Long Term
Solar Irradiance Variations
Authors: Walton, S. R.; Preminger, D. G.; Chapman, G. A.
Bibcode: 2004AGUFMSH53A0303W
Altcode:
The San Fernando Observatory (SFO) has produced photometric full
disk solar images at 5 arc second resolution since 1986, and 2.5 arc
second resolution since 1989. We have previously shown that the best
quantities for solar irradiance modeling are the photometric sums Σ ,
defined as the summed residual intensity on these photometric images. In
particular, a linear regression of total solar irradiance S to the time
series of Σ r and Σ K, the photometric sums in
broadband red and Ca~II~K filters, respectively, does an excellent job
of reproducing S during cycle 22 (Preminger, Walton, and Chapman 2002,
JGR 107, Issue A11, SSH 6-1). We have also shown (Walton, Preminger and
Chapman 2003, Solar Phys. 213, 301) that variations in the chromospheric
network appear to account for no more than 25% of the change in S over
the solar cycle. In this talk, we extend these results to cycle 23 and
discuss their implication for long term changes in S. In particular,
if Σ r = Σ K = 0 can be taken as representing
the complete absence of solar activity, then one would conclude that the
minimum level of S is not much below those currently observed at solar
minimum; quantitatively, about 0.3 W~m2 below that level.
Title: Inferring Total and Spectral Solar Irradiance From Sunspot
Areas Only
Authors: Preminger, D. G.; Walton, S. R.
Bibcode: 2004AGUFMSH53A0304P
Altcode:
We show that daily sunspot area can be used in simple models to
reconstruct daily variations in total or spectral solar irradiance. The
models assume that all solar irradiance fluctuations can be traced back
to the emergence of sunspots on the solar disk. Cotemporal data for
irradiance and sunspot area are analysed to extract a detailed impulse
response function that describes the time evolution of the irradiance
in response to a sunspot that is a delta function. The analysis is
carried out using data for total solar irradiance (the Fröhlich-Lean
TSI composite) and spectral solar data (the Mg~ii core-wing ratio
and the 10.7cm solar radio flux F10.7). The details of the impulse
response functions are different in each case, but overall they clearly
show the evolution of a dark sunspot into a well-defined bright region
which then spreads out and decays over a period of about 500 days. The
impulse response functions can be used to produce a daily record of
spectral or total solar irradiance from the Greenwich daily sunspot
area database, which extends from the late 1800's to the present. The
reconstructions of TSI, Mg~ii core-wing ratio and F10.7 show little
long-term trend in their levels at solar minimum.
Title: Solar Cycle 23: An Anomalous Cycle?
Authors: de Toma, G.; White, O. R.; Chapman, G. A.; Walton, S. R.;
Preminger, D. G.; Cookson, A. M.
Bibcode: 2004AAS...204.3714D
Altcode: 2004BAAS...36..711D
We discuss the importance of solar cycle 23 as a magnetically
simpler cycle and a variant from recent cycles. We see a significant
decrease in sunspot activity in cycle 23 relative to cycle 22, but
the strength of the total solar irradiance (TSI) cycle did not change
significantly. The latest SOHO/VIRGO TSI time series is analyzed using
new solar variability measures obtained from full-disk solar images made
at the San Fernando Observatory and the MgII 280nm index. The TSI record
for the period 1986 to the present is reproduced within about 130ppm
RMS using only two indices representing photospheric and chromospheric
sources of variability due to magnetic regions. This is in spite of the
difference in magnetic activity between the two cycles. Our results
show the continuing improvement in TSI measurements and surrogates
containing information necessary to account for irradiance variability.
Title: The Spots of October 2003: The Largest Irradiance Dip of
Cycle 23
Authors: Chapman, G. A.; Cookson, A. M.; Preminger, D. P.; Walton,
S. R.
Bibcode: 2004AAS...204.0214C
Altcode: 2004BAAS...36..669C
In October 2003, two large active regions rotated onto the solar
disk. During their transit across the disk, a third region emerged
and rapidly grew. These active regions produced the largest decrease
(over 4 W/m2) in the total solar irradiance (TSI) for cycle
23. Irradiance variations derived from ground-based photometry have been
compared with the TSI record from the TIM/SORCE experiment. We find that
ground-based irradiance variations due to sunspots and faculae/network
are correlated with the TIM/SORCE TSI with a multiple correlation
coefficient R2 = 0.9754 for an eight-month interval from
1 June 2003 to 31 January 2004. The residuals between the TIM/SORCE
TSI and the ground-based data had a daily rms of approximately 80
ppm. The value of the quiet Sun irradiance was found to be 1361.3 ±
0.1 W/m2. This work was partially supported by grants from
NASA and NSF.
Title: IR Vector Magnetic Fields II: Atomic and Molecular Line
Polarization in a Sunspot
Authors: Penn, M. J.; Jaeggli, S. A.; Henney, C. J.; Walton, S. R.;
Ceja, J. A.
Bibcode: 2004AAS...204.3705P
Altcode: 2004BAAS...36..709P
Full Stokes I,Q,U and V measurements of the active region NOAA 10008
were taken from 21-27 June 2002 at the NSO Kitt Peak McMath/Pierce
solar telescope using the CSUN/NSO HgCdTe IR camera and polarimeter at
1565nm. The data is corrected for instrumental polarization as discussed
in Paper I. Here the initial analysis of the atomic and molecular
line polarization data is presented. Inversion of the Fe I g=3
1564.8nm line data with a modified Skumanich and Lites Milne-Eddington
technique is used to measure photospheric magnetic field parameters. A
sequence of scans covering several hours of time shows evolution of
the magnetic field. Examination of the linear polarization of the OH
1565.2nm shows curious temporal variation which results in a magnetic
azimuth radically different from that measured using the photospheric
lines. (Similar OH polarization behavior is seen in data from the
CSUN San Fernando Observatory vacuum telescope taken with the CSUN/NSO
camera in active region NOAA 10069 on 12 Aug 2002.) Finally, maps of
the CN 1564.6nm Stokes I line shift show rapid penumbral Evershed
flows and a curious signal in the sunspot umbra. Some of this
work is carried out through the National Solar Observatory Research
Experiences for Undergraduate (REU) site program, which is co-funded
by the Department of Defense in partnership with the National Science
Foundation REU Program.
Title: Solar irradiance variability: progress in measurement and
empirical analysis
Authors: de Toma, G.; White, O. R.; Chapman, G. A.; Walton, S. R.
Bibcode: 2004AdSpR..34..237D
Altcode:
Here we report the progress in both measurements and analysis of
total solar irradiance (TSI) during the last 24 years. Recent TSI
measurements made by ACRIM III and VIRGO in the last two years agree to
within 0.5 W m -2 and show the same pattern of short-term
variability. A 24-year composite record of TSI measurements gives
estimates of its variation for two solar cycles. Such composites give
the first estimates of secular variation of the solar output. Our
analysis of TSI data from solar minimum to maximum for cycles 22 and
23 gives nearly identical regression equations because of improvement
in VIRGO degradation corrections, thus, resolving the empirical issue
raised by de Toma et al. [Astrophys. J. Lett. 549 (2001) L131]. This
agreement occurs despite a decrease in cycle 23 of sunspot number by
≈33% below solar maximum values for cycles 21 and 22.
Title: Photometry of the full solar disk at the San Fernando
Observatory
Authors: Chapman, G. A.; Cookson, A. M.; Dobias, J. J.; Preminger,
D. G.; Walton, S. R.
Bibcode: 2004AdSpR..34..262C
Altcode:
Daily photometry of the full solar disk began at the San Fernando
Observatory in mid-1985. At present, observations with two
photometric telescopes produce images in the red, blue and CaII
K-line. The smaller telescope obtains images that are 512 ×
512 pixels. The larger one obtains images that are 1024 × 1024
pixels. In addition, the larger telescope produces images with a
narrower K-line and an IR filter. Images are processed to determine
a number of photometric quantities including sunspot deficits and
facular/network excesses. These photometric quantities are highly
correlated with fluctuations in the total solar irradiance (TSI)
from spacecraft experiments.
Title: Imaging Spectropolarimetry of Ti I 2231 nm in a Sunspot
Authors: Penn, M. J.; Cao, W. D.; Walton, S. R.; Chapman, G. A.;
Livingston, W.
Bibcode: 2003SoPh..215...87P
Altcode:
Spectro-polarimetric observations at 2231 nm were made of NOAA 10008
near the west solar limb on 29 June 2002 using the National Solar
Observatory McMath-Pierce Telescope at Kitt Peak and the California
State University Northridge - National Solar Observatory infrared
camera. Scans of spectra in both Stokes I and Stokes V were collected;
the intensity spectra were processed to remove strong telluric
absorption lines, and the Stokes V umbral spectra were corrected for
instrumental polarization. The sunspot temperature is computed using
the continuum contrast and umbral temperatures down to about 3700 K are
observed. A strong Ti i line at 2231.0 nm is used to probe the magnetic
and velocity fields in the spot umbra and penumbra. Measurements of the
Ti i equivalent width versus plasma temperature in the sunspot agree
with model predictions. Zeeman splitting measurements of the Stokes I
and Stokes V profiles show magnetic fields up to 3300 G in the umbra,
and a dependence of the magnetic field on the plasma temperature
similar to that which was seen using Fe i 1565 nm observations of the
same spot two days earlier. The umbral Doppler velocity measurements
are averaged in 16 azimuthal bins, and no radial flows are revealed to
a limit of ± 200 m s−1. A Stokes V magnetogram shows a
reversal of the line-of-sight magnetic component between the limb and
disk center sides of the penumbra. Because the Ti i line is weak in
the penumbra, individual spectra are averaged in azimuthal bins over
the entire penumbral radial extent. The averaged Stokes V spectra show
a magnetic reversal as a function of sunspot azimuthal angle. The mean
penumbral magnetic field as measured with the Stokes V Zeeman component
splitting is 1400 G. Several weak spectral lines are observed in the
sunspot and the variation of the equivalent width versus temperature
for four lines is examined. If these lines are from molecules, it is
possible that lines at 2230.67, 2230.77, and 2231.70 nm originate from
OH, while the line at 2232.21 nm may originate from CN.
Title: Weak Infrared Molecular Lines Reveal Rapid Outflow in Cool
Magnetic Sunspot Penumbral Fibrils
Authors: Penn, M. J.; Cao, W. D.; Walton, S. R.; Chapman, G. A.;
Livingston, W.
Bibcode: 2003ApJ...590L.119P
Altcode:
New imaging spectropolarimetric observations of the Evershed flow
in sunspot penumbrae using weak infrared molecular absorption lines
are presented. A plane-polar coordinate system in the sunspot frame
is defined, allowing averaging of many raw spectra. Molecular lines
show Doppler shifts implying typical horizontal outflow speeds of 6
and up to 9 km s-1. The Ti I polarimetric spectra show the
same rapid outflow and suggest an average penumbral magnetic field
strength of 1400 G. While these observations show Doppler shifts of
the entire line profile, the velocities are in better agreement with
previous measurements from spectral line asymmetries.
Title: A Comparison of Summed Continuum and CaII K-line Images
Authors: Chapman, G. A.; Cookson, A. M.; Walton, S. R.; Smith, C.
Bibcode: 2003SPD....34.0707C
Altcode: 2003BAAS...35..821C
Full-disk photometric images are obtained with two telescopes on
a daily basis at the following wavelengths: 393 nm (CaII K-line),
472 nm and 672 nm. In order to explore the characteristics of the
fainter facular/network elements, we obtain, on occasion, up to 10
images as closely spaced in time as possible. For the work reported
on here, we have used red continuum images at 672 nm (bandpass 10 nm)
from the CFDT2 telescope (pixel size 2.5" x 2.5"). These images have
been coaligned and summed to reduce noise from non-magnetic intensity
features. The customary image processing tools have been applied (Walton
et al. 1998). The quiet sun rms intensity fluctuation drops from about
0.58 % on a single image to about 0.21 % on the summed image. On the
summed red image, bright facular/network features as faint as about
0.6 % become visible across the solar disk. These features will be
compared with those found on images obtained in the CaII K-line to
determine their reality in terms of K-line faculae. This work
has been partially supported by grants from NASA (NAG5-7191) and NSF
(ATM-9912132). Reference Walton, S.R., Chapman, G.A., Cookson,
A.M., Dobias, J.J. and Preminger, D.G. 1998, Solar Phys. 179, 31-42.
Title: Reconstruction of Facular Brightening from Sunspot Deficit
Authors: Preminger, D. G.; Walton, S. R.
Bibcode: 2003SPD....34.0705P
Altcode: 2003BAAS...35..820P
It is well established that variations in the total solar irradiance
S can be accurately reproduced using a model based on the competing
influences of the darkening due to sunspots and brightening due to
faculae. In order to reconstruct S before observations of faculae,
measurements of sunspots alone have been used as a proxy for inferring
the facular brightening. In this work, we would like to improve the
inferred facular brightening as well as gain insight into the time
variation of various solar activity indicators. We make use of the
deficit (darkening) due to sunspots D and the brightness variation
attributed to faculae, as measured either by the excess emission in
the CaIIK line EK or the MgII core-wing ratio. The cross
correlation of D with either facular quantity shows well defined peaks
at zero and negative lags (in the sense that facular excess lags D). We
conclude that dark features decay into bright features, to some extent,
but some bright features form coincident with the dark features. From
the cross correlation we create a window function which is convolved
with D to obtain a predicted E. Comparison of the prediction with
the actual value of E shows that E starts rising at the beginning of
cycle 23 before its reconstruction does. It appears that the onset of
solar activity as measured by facular brightening precedes the rise
in our sunspot deficit. Possible causes are under investigation. This research was supported by NSF grant ATM-9912132 and NASA grants
NAG5-7191 and NAG5-7778.
Title: Photospheric Line Equivalent Widths in Calcium K Faculae
Authors: Walton, S. R.; Preminger, D. G.; Chapman, G. A.; Cookson,
A. M.
Bibcode: 2003SPD....34.0706W
Altcode: 2003BAAS...35..821W
We have recently shown (Preminger, Walton, and Chapman 2002) that
the total solar irradiance S can be modeled by a linear combination
of photometric quantities which measure the fractional brightness
change in the continuum and in the Ca II K line. We concluded that
the change in S on solar cycle time scales is caused by variations in
spectral lines, not in the continuum. In order to further test
this conclusion, we have begun comparing our photometric Ca II K images
with line equivalent width maps made in Fe I 6302.5. Bright features
in our K images are well correlated with areas of lower equivalent
width. We are beginning to quantitatively measure this correlation
and will present further results at the meeting. This research
has been supported by NSF grant ATM-9912132.
Title: Weak IR Lines Reveal Rapid Outflow in Cool Magnetic Penumbra
Authors: Penn, M. J.; Cao, W. D.; Walton, S. R.; Chapman, G. A.;
Livingston, W.
Bibcode: 2003SPD....34.1106P
Altcode: 2003BAAS...35..827P
New imaging spectropolarimetric observations of the Evershed flow in
sunspot penumbrae using weak infrared molecular absorption lines are
presented. A plane-polar coordinate system in the sunspot frame is
defined, allowing averaging of many raw spectra. Molecular lines show
Doppler shifts implying typical horizontal outflow speeds of 6 to 9
km/sec. The Ti I polarimetric spectra show the same rapid outflow
and suggest an average penumbral magnetic field strength of 1400
Gauss. While these observations show Doppler shifts of the entire
line profile the velocities are in better agreement with previous
measurements from spectral line asymmetries.
Title: On the decay rate of sunspots
Authors: Chapman, G. A.; Dobias, J. J.; Preminger, D. G.; Walton, S. R.
Bibcode: 2003GeoRL..30.1178C
Altcode: 2003GeoRL..30d..27C
We have analyzed the decay of 32 sunspots observed during the years
1988 through 2001 at the San Fernando Observatory (SFO). The data are
from digital images obtained in the red (672 nm) with the Cartesian
Full Disk Telescope No.1 (CFDT1). We find that the rate of decay is
strongly correlated with the total sunspot area and the umbral to
total area ratio. The multiple correlation coefficient is 0.93. Thus,
the unexplained variance from this simple model is (1-0.87). We find
that for the sunspots of this study, the decay rate is not a constant
and that there is no significant correlation between the decay rate
and the square root of the total spot area.
Title: Modeling the Variations in TSI Using Precision Ground-Based
Photometric Images
Authors: Chapman, G. A.; Walton, S. R.; Cookson, A. M.; Dobias, J. J.;
Preminger, D. G.
Bibcode: 2002AGUFMSH21B..01C
Altcode:
Precision photometric full-disk images of the sun have been obtained
at the San Fernando Observatory (SFO) beginning in mid-1985. Images
in several wavelengths are obtained daily but for modeling the Total
Solar Irradiance (TSI) from spacecraft, the red (672 nm) and the
K-line (393 nm) images have been the most useful. Two telescopes are
in regular operation, Cartesian Full Disk Telescope (CFDT) number
1 and 2. They produce images that have 512 x 512 pixels and 1024 x
1024 pixels, respectively. Multiple linear regressions of sunspot
deficits and facular excesses compared with Nimbus-7 and ACRIM-I
values of TSI give values of R2 of from 0.80 to 0.85,
depending on data intervals and the particular spacecraft. More recent
fits to the composite TSI of Fröhlich and Lean for cycle 22 give
values of R2 of 0.91. These fits are affected by noise in
both ground-based and space-based data. This value of R2
suggests, especially considering the effects of noise, that less than
10% of the TSI variance is unexplained by the effects of sunspots and
faculae/network. We are in the process of determining whether or not
the coefficients from fits to cycle 22 TSI will also provide good fits
to cycle 23 TSI. This research has been partially supported by grants
from NSF (ATM-9912132) and NASA (NAG5-7191 and NAG5-7778).
Title: Photometric quantities for solar irradiance modeling
Authors: Preminger, D. G.; Walton, S. R.; Chapman, G. A.
Bibcode: 2002JGRA..107.1354P
Altcode:
We analyze photometric quantities for the modeling of the total
solar irradiance, S. These quantities are derived from full-disk
solar images taken at the San Fernando Observatory. We introduce a
new quantity, the photometric sum, Σ, which is the sum over an entire
image of each pixel's contribution to the irradiance in that image. Σ
combines both bright and dark features; and because the sum is over
the entire image, it will include low contrast features that cannot
be identified directly. Specifically, we examine Σr,
Σb, and ΣK, the photometric sums over
broadband red, broadband blue, and 1-nm bandpass Ca II K images,
respectively. Σr and Σb measure the effects
of solar features on the variability in S at two different continuum
wavelengths. ΣK measures the variability in spectral lines
due to solar features. We find that Σr and Σb
have no long-term trend. ΣK, however, varies in phase with
the solar cycle. We carry out several multiple linear regressions on
the value of S from cycle 22; the best fit uses Σr and
ΣK and reproduces the observed composite S with a multiple
regression coefficient R = 0.96. We conclude that the long-term change
in S over the solar cycle can be accounted for by the variability in
the spectral lines as measured by ΣK, assuming no change
in the quiet Sun; the contribution of the continuum to the variations
in S is only on active region timescales.
Title: Preliminary Analysis of Stokes Profiles via the
Levenberg-Marquardt Method at the San Fernando Observatory
Authors: Ceja, J. A.; Walton, S. R.
Bibcode: 2002AAS...200.5509C
Altcode: 2002BAAS...34R.733C
A Levenberg-Marquardt fitting technique was developed and applied to
Stokes profiles obtained from the San Fernando Observatory's Video
Spectra-Spectroheliograph (SFO-VSSHG). Fits were the result of a sum of
Gaussians that fitted a given profile through the Marquardt method. The
fits were then used to create maps of the magnetic field properties
in the data. Herein, we present maps of these properties and their
comparison to maps done by the current method of profile analysis
at the observatory, the center of gravity method. Furthermore, the
Marquardt method also provides a new dimension to the SFO-VSSHG data;
it allows further analysis of the profile properties themselves, and
we show some of these preliminary results as well. This research was
supported by NSF grant ATM-0077624.
Title: Solar Irradiance Observations during Solar Cycles 22 and 23
Authors: White, O. R.; de Toma, G.; Chapman, G. A.; Walton, S. R.;
Preminger, D. G.; Cookson, A. M.; Harvey, K. L.; Livingston, W. C.
Bibcode: 2002AAS...200.5707W
Altcode: 2002BAAS...34..737W
We present a study of Total Solar Irradiance (TSI) variations during
solar cycles 22 and 23 from 1986 to the present. We will review the
recent measurements of solar magnetism, solar activity, and radiative
variability from both ground-based and space observatories and compare
TSI observations with empirical models of solar irradiance variability
based on facular and sunspot observations. To estimate facular/plage and
sunspot contribution to TSI we use the photometric indices derived from
the SFO full-disk solar images from 1988 to the present in the CaIIK
line at 393.4nm and in the red continuum at 672.3 nm. In these indices,
each solar structure is included with its measured contrast and area. We
also use the MgII core-to-wing index from space observatories as an
alternative index for plages and network. Comparison of the rising
and maximum phases of the two solar cycles, shows that cycle 23 is
magnetically weaker with sunspot and facular area almost a factor of
two lower than in solar cycle 22. However, analysis of multi-wavelength
observations indicate that different wavelengths respond differently
to the decreased magnetic activity during solar cycle 23.
Title: The Contribution of Faculae and Network to Long Term Changes
in the Total Solar Irradiance
Authors: Walton, S. R.; Preminger, D. G.; Chapman, G. A.
Bibcode: 2002AAS...200.5709W
Altcode: 2002BAAS...34..738W
A new database of individual solar features has been compiled from
the full disk photometric images taken at the San Fernando Observatory
(SFO) since 1989. The distribution of facular region sizes differs at
different phases of the solar cycle; the area coverage of large active
regions is reduced by a factor of about 20 at solar minimum compared
to solar maximum, while the smaller regions cover about half as much
area at minimum as at maximum. We have used this data set to model
the fraction of variation in the total solar irradiance S which is
due to solar features of various sizes. The data show that large-scale
solar features dominate the 0.1% change in S between solar maximum and
solar minimum; the chromospheric network produces about 15% to 25%
of the total change. We have also used new total irradiance models
to evaluate the plausible level of S in the absence of all magnetic
activity on the sun, and conclude that S would be reduced by about
0.3 W/m2 below the level presently observed at activity
minimum. This work was supported by NSF grant ATM-9912132 and NASA
grants NAG5-7191 and NAG5-7778.
Title: Predicting Total Solar Irradiance Using Sunspot Deficit Only
Authors: Preminger, D. G.; Walton, S. R.
Bibcode: 2002AAS...200.5706P
Altcode: 2002BAAS...34..737P
It has been well established that variations in the total solar
irradiance S can be accurately reproduced using a model based on
the competing influences of sunspots and faculae. These models can,
in principle, be used to reconstruct the value of S before accurate
spacecraft measurements began in 1979. However, while sunspots
have been well observed since the early seventeenth century,
information about the faculae is not available for much of the
period of interest. We are experimenting with a new technique to
reconstruct the facular contribution to the total solar irradiance
S from the sunspot signal. The sunspot deficit Dr is well
correlated with short-term variations in the total solar irradiance
S. The total variation in the Ca II K line signal, Σ K, is
correlated with long-term variations in S. Using the cross correlation
of Dr and Σ K, we can obtain a window function
that can be used to model Σ K from Dr. The cross
correlation has five significant peaks at lags of zero to -4 solar
rotations. The main peak is at a negative lag, in the sense that Σ
K lags Dr. The fit to S using Dr and Σ
K reconstructed in this way during cycle 22 yields a multiple
regression coefficient R2 = 0.70. This work was supported
by NSF grant ATM-9912132 and NASA grants NAG5-7191 and NAG5-7778.
Title: Further Studies of the Bolometric Contrast of Sunspots
Authors: Chapman, G. A.; Cookson, A. M.; Dobias, J. J.; Walton, S. R.
Bibcode: 2002AAS...200.3806C
Altcode: 2002BAAS...34..699C
Daily images are obtained at the San Fernando Observatory (SFO)
of the full solar disk with two photometric telescopes, CFDT1 and
CFDT2. CFDT1 produces images with 5" x 5" pixels while CFDT2 produces
images with 2.5" x 2.5" pixels. In a previous paper (Chapman et
al. 1994) we reported on the bolometric contrast of sunspots using
red images from CFDT1. The bolometric contrast, α eff,
is heuristically defined as α eff = Dr/(2 x
PSI), where Dr is the photometric deficit in the red image
and PSI is the usual Photometric Sunspot Index. Here, we will report
on studies of the bolometric contrast from red CFDT2 images. We will
examine the effects of higher spatial resolution and we will look for
differences in the bolometric contrast between cycle 22 and 23. This
research was partially supported by grants from NSF (ATM-9912132) and
NASA (NAG5-7191). Reference: Chapman, G.A., Cookson, A.M. and Dobias,
J.J. 1994, Ap.J. 432, 403.
Title: Growth and Decay of Solar Active Regions
Authors: Dobias, J. J.; Chapman, G. A.; Cookson, A. M.; Preminger,
D. G.; Walton, S. R.
Bibcode: 2002AAS...200.5710D
Altcode: 2002BAAS...34..738D
We report here on a study of growth and decay rates of sunspot and
facular areas of solar active regions. The data used in this project
come from an ongoing program of daily photometric observations of the
sun with the Cartesian Full Disk Telescope No. 1 (CFDT1) at the San
Fernando Observatory (SFO). Sunspot regions are determined from images
taken with a red filter centered at 672.3 nm with a bandpass of 9.7 nm,
while images taken with a Ca II K line filter, centered at 393.4 nm and
with a bandpass of only 1nm, are used to find facular areas. Before
any areas can be found on any observed images, they have to be
calibrated then flattened by removing limb darkening thus producing
contrast images. Sunspot areas are then determined from any pixel with
contrast of -8.5% or less, while any pixel on a K line contrast image
with a contrast of +4.8%/μ or higher, where μ is the cosine of the
heliocentric angle, is considered to be a facular pixel. To identify
the areas as clearly as possible, studied active regions were usually
observed on the sun with relatively low activity; that means that
each region is either alone on the sun's disk or with only very few
other active regions present. Furthermore, to obtain growth and decay
patterns of the areas as reliably as possible, only such active regions
must be chosen for which there is as complete observational coverage as
possible. At the present time studies have been finished for only a few
active regions, but analysis of several others is on going. Obtained
results will be presented at the meeting. This work is supported by
NSF grant ATM-9912132 and NASA grants NAG5-7191 and NAG5-7778.
Title: Linking to On-Line Solar Photometric Data at the San Fernando
Observatory
Authors: Cookson, A. M.; Walton, S. R.; Fulton, D. K.
Bibcode: 2002AAS...200.5510C
Altcode: 2002BAAS...34S.733C
An important function of any observatory is the dissemination of
its accumulated data to the science-minded community, whether it
be professional or amateur. The San Fernando Observatory (SFO) has
full-disk photometric images of the Sun as well as sunspot and faculae
statistical data from these images beginning in 1986. These images
were obtained at wavelengths of 672.3 nm (red), 472.3 nm (blue), and
393.4 nm (CaII K-line). In order to make our data-products accessible,
we present here a newly designed and developing website for the SFO that
includes our location and contact information, history, instrumentation,
staff, published material, daily-updated graphs of various solar cycle
activities and trends, and interactive access to our data. Through
this site, a user can query our database by single or multiple dates,
times, feature types, and/or wavelengths, and we are providing a short
tutorial for those new to our procedures. As with any growing thing,
this is a work in progress. We believe this newly developed website,
with its general content and on-line retrieval of archived visual
and statistical data, will be useful to the solar community. We also
believe it will provide educational and public outreach opportunities
for both SFO and the Physics and Astronomy Department at California
State University, Northridge (CSUN), to which it belongs. This work
was supported by NSF grant ATM-9912132 and NASA grants NAG5-7191
and NAG5-7778.
Title: Comparison of Solar Photometric Data from Two Telescopes
Authors: Chapman, G. A.; Walton, S. R.; deToma, G.; White, O. R.
Bibcode: 2001AAS...199.8804C
Altcode: 2001BAAS...33.1433C
Sunspot areas from two photometric telescopes have been compared. The
two telescopes are the Precision Solar Photometric Telescope (PSPT)
operated on Mauna Loa by the High Altitude Observatory (HAO)
and the Cartesian Full Disk Telescope 2 (CFDT2) operated at the
San Fernando Observatory (SFO). The PSPT images originally 2048 x
2048 have been binned by two to agreee more closely with those from
CFDT2. The binned PSPT pixels are 2" x 2" and the CFDT2 pixels are
2.5" x 2.5". A preliminary analysis shows that sunspot areas from the
two are highly correlated although only seven image pairs have been
correlated. Comparing the red PSPT spot areas with the red CFDT2 spot
areas gives an r2 of 0.9947 and a scale factor of 0.909 +/-
0.03 where the scale factor implies the red areas are slightly too
small. For CFDT2 blue images versus the red PSPT the r2
is 0.9895 with a scale factor of 1.06 +/- 0.05 implying that the blue
areas are slightly too large. Results from other wavelengths and from
an expanded data set will be presented and discussed. This research was
partially supported by grants from NSF, NASA and a visiting scientist
grant from HAO.
Title: An Improved Determination of the Area Ratio of Faculae
to Sunspots
Authors: Chapman, G. A.; Cookson, A. M.; Dobias, J. J.; Walton, S. R.
Bibcode: 2001ApJ...555..462C
Altcode:
We report new results on the ratio of facular area to sunspot area from
a program of continuing photometric observations using the Cartesian
Full Disk Telescope No. 1 (CFDT1) at the San Fernando Observatory
(SFO). The facular areas are determined from images obtained with a
1 nm bandpass Ca II K line filter, and sunspot areas are determined
from red images at 672 nm with a 10 nm bandpass filter. On the K line
images faculae were identified by pixels that had a contrast equal to or
greater than 4.8% divided by μ. Previously, we found that the average
facular-to-spot area ratio was 16.7+/-0.5 during the latter part of
solar cycle 22 and that there was a small but statistically significant
rise in the ratio with time. If we take an average from the beginning
of the K line data (mid-1988) until the middle of 1996, excluding days
of zero sunspot area, the average ratio is 16.4+/-0.4. The average ratio
from mid-1996 to the end of 1999 November is 12.6+/-0.5. Including days
of zero sunspot area for these same intervals we find average ratios of
16.8+/-0.5 and 13.2+/-0.6, respectively. We have recently reprocessed
our K line images, which have been photometrically ``cleaned.'' We
can now reliably identify facular pixels with a contrast criterion of
2.4%, resulting in an increase in the average facular-to-spot ratio
of approximately 3. The average facular and sunspot areas for cycle
23 are significantly lower than for cycle 22.
Title: The Decline of Solar Cycles 22 and 23 Compared
Authors: Chapman, G. A.; Cookson, A. M.; Dobias, J. J.; Walton, S. R.
Bibcode: 2001AGUSM..SP31B07C
Altcode:
During the declining phase of solar cycle 22, a dramatic drop by
a factor of two occured in the corrected area of photospheric
faculae as determined by a 1 nm bandwidth K-line filter. This
filter, in the Cartesian Full Disk Telescope no. 1 (CFDT1) at the
San Fernando Observatory, responds primarily to faculae in the upper
photosphere. Although the sunspot area (determined from red photometric
images) also dropped at this time, it seemed to recover over the
succeeding months. In the year 2000 during the peak or declining
phase of cycle 23, the spot area dropped suddenly by a factor of
two or more. However, at this time the facular area seemed to fall
only slightly. Sunspot area and facular area data will be presented
and discussed for these two cycles. This research has been partially
supported by grants from NSF (ATM-9912132) and NASA (NAG5-7191).
Title: Thousands of Faculae Can't be Wrong
Authors: Walton, S. R.; Preminger, D. G.; Chapman, G. A.
Bibcode: 2001AGUSM..SP21A04W
Altcode:
We present results from a study of facular regions on images taken at
the San Fernando Observatory (SFO) CFDT1 telescope; the images are
512 square full disk photometric images taken through two filters:
672.3~nm center, 10~nm bandpass (``red'') and 393.4~nm center, 1~nm
bandpass (``Ca~II~K''). Faculae were identified using an algorithm
which requires three adjacent pixels above a contrast trigger, allowing
reliable identification of very faint features (contrasts of order a
few tenths of a percent). Over 147,000 red faculae were identified, and
about 800,000 Ca~II~K faculae. In addition, we computed the contrasts
of pixels on the red images cospatial with Ca~II~K faculae. Our
observations were interpreted with reference to flux tube models
of solar faculae. There are continuous but systematic differences
among facular regions. We find that the contrast of Ca~II~K faculae
is relatively insensitive to heliocentric angle, but is a strong
function of facular size, in the sense that larger Ca~II~K faculae
are always brighter. The contrast of red faculae is a function of both
heliocentric angle and size. We conclude that larger regions contain
larger flux tubes, contain deeper flux tubes, and have larger filling
factors than small facular regions. Comparisons of cospatial pixels on
red and Ca~II~K images show a tight correlation between the average
contrast of a region in the continuum and its size and heliocentric
angle in the Ca~II~K images. This relation might allow deduction of
the average continuum facular contrast for time periods when only
areas and locations of Ca~II~K faculae are available, and is thus
important for proxies of the solar irradiance. The largest Ca~II~K
faculae are found in the activity belts, but the smaller regions are
more uniformly distributed, so our smaller Ca~II~K regions are actually
bright network. Graphs of dN/dA, the differential size distribution,
of Ca~II~K faculae, show that network is equally prevalant at all
phases of the solar cycle, and thus cannot account for changes in
solar irradiance from maximum to minimum. This work was supported by
NSF grant ATM-9912132 and NASA grant NAG5-7191.
Title: Rotation of CaII K-line Faculae in Solar Cycles 22 and 23
Authors: Chapman, G. A.; Lawrence, J. K.; Walton, S. R.
Bibcode: 2001AAS...198.7103C
Altcode: 2001BAAS...33Q.893C
We have examined the temporal behavior of CaII K-line faculae for
parts of solar cycles 22 and 23. The data are from photometric images
obtained at the San Fernando Observatory (SFO) using the Cartesian Full
Disk Telescope no. 1 (CFDT1). The images are 512 by 512 pixels, each
pixel being 5.12 arc-sec square. The bandpass of the K-line filter
is 1 nm. For the interval mid-1988 to mid-1996 (most of cycle 22)
we find an autocorrelation very much like that published in Chapman,
Cookson and Dobias (1997). At a lag of 150 to 160 days, the 27-day
rotational modulation disappears, reappearing later but at a different
phase. For the second interval, from mid-1996 to the end of 1999,
the autocorrelation shows the 27-day rotational modulation persisting
out to a lag of nearly one year. Lomb periodograms will be shown for
these data for several intervals and the results will be discussed. This
research has been partially supported by NSF Grant ATM-9912132 and NASA
Grant NAG5-7191. Reference: Chapman, G.A., Cookson, A.M. and Dobias,
J.J. 1997, Ap.J. 482, 541.
Title: Sunspot Areas Compared by Hemisphere
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 2001AGUSM..SP31B03C
Altcode:
Photometric images of the whole solar disk are obtained on a daily
basis at the San Fernando Observatory. Red images obtained at 672 nm
are used to determine total and umbral areas as well as photometric
quantities. New software (Preminger, Walton and Chapman, 2001) permits
a search for features by size and location. We will present results
of separately comparing sunspot areas for the northern and southern
hemisphere for the past two solar cycles using data from the smaller
photometric telescope (CFDT1) which has pixels of approximately 5"
x 5". This research has been partially supported by NSF (ATM-9912132)
and NASA (NAG5-7191). Reference Preminger, D.G., Walton, S.R. and
Chapman, G.A. 2001 submitted to Solar Phys.
Title: Global Solar Variability: Cycle 23 Indicates a Change from
Recent Cycles
Authors: de Toma, G.; White, O. R.; Chapman, G. A.; Walton, S. R.;
Harvey, K. L.
Bibcode: 2000SPD....3102115D
Altcode: 2000BAAS...32..831D
This paper focuses on the rising phase of solar cycle 23 from the
time of solar minimum in 1996 to the present high activity level. A
number of observations indicate that cycle 23 maximum is now close, and
maybe is already in the maximum phase. They include the distribution
of coronal streamers, the presence of long--lived solar coronal holes
at low latitudes, the latitudinal distribution of sunspot regions,
and the unipolar magnetic fields in the polar regions. Most of the
activity indices, i.e. sunspot number, sunspot area, photospheric
magnetic flux, 10.7 cm radio flux, and UV irradiances, indicate this
cycle as a relatively weak cycle as compared to cycles 21 and 22. In
particular, observations at San Fernando Observatory of sunspot and
facular area are a factor of two or more lower than in solar cycle
22. This is consistent with the lower magnetic flux measured at NSO/KP
and UV irradiance measurements, but not with total solar irradiance
measurements. We analyze ground--based and space observations to give
a comprehensive picture of the evolution of the current cycle and
compare it to the solar cycle 22.
Title: Differences in the Sun's Radiative Output in Cycles 22 and 23
Authors: White, O. R.; de Toma, G.; Chapman, G. A.; Walton, S. R.;
Harvey, K. L.; Cookson, A. M.; Preminger, D. G.
Bibcode: 2000SPD....31.0127W
Altcode: 2000BAAS...32..806W
We study total solar irradiance (TSI) observations during the rising
phase of cycle 22 and 23 for the 5--year periods during 1986--1990
and 1996--2000. The increase in TSI in cycle 23 is greater than
expected from the observations of the photospheric magnetic flux, and
by traditional activity indices, like sunspot number, 10.7 cm radio
flux, MgII and HeI indices, all of which indicate that cycle 23 is
a relatively weak cycle. Space observations of TSI from SOHO/VIRGO
and UARS/ACRIMII show an increase in TSI of about 1 W/m2
from 1996 to 2000. This is comparable to the increase observed in
TSI during the previous cycle, from 1986 to 1990 as observed from
Nimbus7/ERB. To resolve the discrepancy between the variability in TSI
observed in the two last cycles, we used the San Fernando Observatory
(SFO) photometric data at 393.4 nm and 672.3 nm to evaluate sunspot
and facular contributions to TSI. The SFO image decomposition technique
has been tested against NSO/KP magnetograms decomposition for selected
days, and they are in good agreement. A 3--parameter fit to Nimbus--7
data for the years 1988--1993 based on SFO data and MgII index gives a
correlation coeff. r2 = 0.9. Extrapolation of the fit in time
largely underestimates the current SOHO/VIRGO TSI measurements. This
suggests there is either a problem in the observations or a change in
nature of radiative sources on the Sun.
Title: Solar Feature Identification Using Contrasts and Contiguity
Authors: Walton, S. R.; Preminger, D. G.
Bibcode: 2000SPD....31.0124W
Altcode: 2000BAAS...32..805W
The automatic identification of solar features, such as faculae and
plages, is becoming increasingly important as the size of solar data
sets increases. These identifications are required for quantitative
study of the solar cycle, including but not limited to: locations,
lifetimes, contrasts, and other characteristics of sunspots and faculae;
modeling of the total solar irradiance (TSI); and variations of sunspot
and facular properties with latitude and/or solar cycle phase. We
have been experimenting with an approach which, while simple, is
more sophisticated than a simple threshold technique. We identify
an isolated feature by scanning the disk and finding a pixel whose
contrast exceeds a given criterion called the trigger. We then `walk'
around the trigger pixel, looking for adjacent pixels which are part of
the same spot. If three contiguous pixels meet the trigger criterion,
then a feature has been found. We continue to add adjacent pixels
to the feature; these must meet a less stringent contrast criterion,
the threshold, in order to be considered part of the feature. We find
that this technique allows the trigger to be chosen at a level which is
barely above the noise level in the image while still not identifying
noise as features. This technique allows the identification of very
faint features on these images. We can, for example, reliably identify
faculae on continuum images and study their maximum contrasts as a
function of μ . These increase with decreasing μ , on average, but
have a good deal of scatter. By comparison, maximum facular contrasts
on the K images show no obvious dependence on μ . The sunspot deficit,
which is the main component of total solar irradiance (TSI) models,
becomes somewhat more negative with this identification when compared
to a simple threshold identification at -8.5% contrast, normally used
for SFO data. Sunspot areas increase substantially, and are roughly
50% larger than those reported in, for example, the Solar Geophysical
Data bulletin, due to the inclusion of more low-contrast pixels. We are
investigating the effects of these new feature identifications on total
solar irradiance models. This research has been partially supported
by NSF Grant ATM95-04374 and NASA Grants NAGW-3017 and NAG5-4973.
Title: Comparisons of Sunspot Contrasts and Deficits on SOHO and
San Fernando Observatory Continuum Images
Authors: Walton, S. R.; Preminger, D. G.; Mohageg, M.
Bibcode: 1999AAS...194.9304W
Altcode: 1999BAAS...31Q.989W
The San Fernando Observatory (SFO) Cartesian Full Disk Telescope (CFDT)
instruments have produced a continuous series of thousands of daily
full disk photometric solar images extending (in the case of CFDT1) to
1986. We have begun a project to compare sunspot properties measured
on CFDT images to those measured by the continuum images produced
by the Michaelson Doppler Interferometer (MDI) instrument on the
SOHO spacecraft. Such a comparison requires an extended time period
during which both CFDT and MDI took good data and during which there
was extensive activity. We have chosen September 1997 as the first
period for this comparison. The SFO CFDT images were processed and
restored according to the procedures described in Walton et al. (1996,
Solar Phys. 179, 31) and Walton and Preminger (1999, Ap.J. 514, in
press). As of this writing, preliminary comparisons have been made
between SFO CFDT1 images (512 square, 5 arc second pixels) and MDI full
disk continuum images (1024 square, 2.4 arc second pixels). Maximum
(single pixel) and integrated sunspot contrast were compared for
the largest sunspot in both images. In all cases, restoration of the
CFDT images brings the two data sets into closer agreement, though
differences remain. We also compared the total photometric sunspot
deficit integrated over all sunspot pixels. The agreement between the
restored images and the SOI images is excellent. Further comparisons are
required, but we tentatively conclude that restored SFO CFDT images can
be reliably used to measure the total photometric sunspot deficit. This
research was partially supported by NASA grants NAGW-3017 and NAGS-4973,
and NSF grant ATM-9504374.
Title: A Search For Variations in the Solar Radius
Authors: Chapman, G. A.; Cookson, A. M.; Dobias, J. J.; Walton, S. R.
Bibcode: 1999AAS...194.9302C
Altcode: 1999BAAS...31..988C
We report on an ongoing analysis of the radius of solar images from two
photometric telescopes at the San Fernando Observatory. Data used from
CFDT1 with 5 arc-sec pixels begins in 1986. Data used from CFDT2 with
2.5 arc-sec pixels begins in the summer of 1992. The solar diameter is
determined along the length of the linear diode array in the geocentric
north-south direction by fitting the entire image as described in
Walton, et al. (1998). Previously, we reported a solar radius variation
in phase with the solar cycle using data from CFDT1. A reanalysis
of those data have resulted in a much smaller radius variation than
that reported in Chapman, et al. (1998). We will report on efforts
to compare the radius found from CFDT1 images with that from CFDT2
images. The two instruments have undergone improvements but each at
different times. We will discuss possible radius variations between
the two instruments. This work was supported by NSF grant ATM-9504374
and NASA grant NAG5-4973. References Chapman, G.A., Cookson, S.R.,
Dobias,J.J. and Walton, S.R. 1998, Spring AGU Meeting. Walton, S.R.,
Chapman, G.A., Cookson, A.M., Dobias, J.J. and Preminger, D.G. 1998,
Solar Phys. 179, 31.
Title: Spatiotemporal Correlations and Turbulent Photospheric Flows
from SOHO/MDI Velocity Data
Authors: Cadavid, A. C.; Lawrence, J. K.; Ruzmaikin, A. A.; Walton,
S. R.; Tarbell, T.
Bibcode: 1998ApJ...509..918C
Altcode:
Time series of high-resolution and full-disk velocity images obtained
with the Michelson Doppler Imager (MDI) instrument on board SOHO
have been used to calculate the spacetime spectrum of photospheric
velocity flow. The effects of different methods for filtering acoustic
oscillations have been carefully studied. It is found that the spectra
show contributions both from organized structures that have their origin
in the convection zone and from the turbulent flow. By considering
time series of different duration and cadence in solar regions with
different line-of-sight projections, it is possible to distinguish the
contributions of the spectra from the two different kinds of flows. The
spectra associated with the turbulent velocity fields obey power laws
characterized by two scaling parameters whose values can be used to
describe the type of diffusion. The first parameter is the spectral
exponent of the spatial correlation function and the second is a
scaling parameter of the time correlation function. Inclusion of the
time parameter is an essential difference between the present work
and other solar studies. Within the confidence limits of the data,
the values of the two parameters indicate that the turbulent part of
the flow in the scale range 16-120 Mm produces superdiffusive transport.
Title: Processing Photometric Full-Disk Solar Images
Authors: Walton, S. R.; Chapman, G. A.; Cookson, A. M.; Dobias, J. J.;
Preminger, D. G.
Bibcode: 1998SoPh..179...31W
Altcode:
Daily, photometric, full-disk digital solar images have been taken at
the San Fernando Observatory (SFO) at two resolutions and in several
wavelengths for more than eleven years. We describe the standard data
processing techniques used for these images, including: calibration,
limb fitting, geometric correction, and production of a solar contrast
map by limb-darkening removal. The resulting contrast maps have a
photometric accuracy which is often a few tenths of a percent. We
show that the geometric accuracy of our images, as measured by the
reproducibility of disk and sunspot areas, is very high as well. The
techniques described in this paper should be applicable to any
instrument producing full-disk photometric images.
Title: Precision Ground-Based Photometry from Full-Disk Images
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1998sers.conf..437C
Altcode:
No abstract at ADS
Title: A New Data System for the San Fernando Observatory Video
Spectra-Spectroheliograph
Authors: Walton, S. R.; Chapman, G. A.
Bibcode: 1997AAS...191.7410W
Altcode: 1997BAAS...29.1325W
The San Fernando Observatory Video Spectra-Spectroheliograph (SFO
VSSHG) has been used for observation of vector magnetic fields on
the Sun for the last several years, and was described in Walton and
Chapman (1996), Solar Phys. 166, 267. The current VSSHG camera is a
commercial video format (512 by 480) CCD camera from which spectra are
recorded on analog 3/4'' professional grade videocasettes. Recently,
commercial off-the-shelf hardware has become available which can
equal the high speed and capacity of this system in a pure digital
mode. We are developing a new data system for the VSSHG consisting
of a 1024 square digital CCD camera capable of 15 frames per second,
an Intel Pentium-II based personal computer with fast-wide SCSI hard
disk, and a DLT-7000 digital linear tape drive. This combination of
off-the-shelf hardware, purchased for about \$30,000, should achieve
the data rate of 7.5 megabytes per second (MB/s) required for recording
5 frames per second from the CCD camera to the hard disk in real time,
which is sufficient for the VSSHG. The DLT tape drive can record 35
gigabytes at a rate of 5 MB/s uncompressed, and a small amount of data
compression should allow it to record spectra in real time as well. As
of this writing, only the computer has been received, but preliminary
tests show that its hard disk performs at speeds well over 10 MB/s
with no special optimizations. We will take delivery on the camera
soon, and hope to have the first images with the new camera early
this winter. A detailed description of the data system and on-line
processing algorithms will be presented.
Title: Processing Photometric Full-Disk Solar Images
Authors: Walton, S. R.; Chapman, G. A.; Cookson, A. M.; Dobias, J. J.;
Preminger, D. G.
Bibcode: 1997SPD....28.0222W
Altcode: 1997BAAS...29..897W
The Cartesian Full Disk Telescopes (CFDTs) at the San Fernando
Observatory (SFO) produce daily full-disk digital solar images using
a linear Reticon diode array scanned by the Earth's rotation. In this
paper, we describe in some detail the data processing techniques used
to extract photometric information from CFDT images. We believe our
experience in this field will be found useful by other workers as more
instruments are built and operated with similar scientific goals to
the CFDT. We describe: 1. our photometric calibration techniques and
accuracy; 2. the method we use to identify the position of the limb;
3. production of a contrast map from the image, including finding a mean
limb darkening curve; 4. identification of solar features. Preprints
of a paper giving all algorithms in detail will be available at the
meeting. This research has been supported by NASA grant NAGW-3017 and
NSF grant ATM-9504374.
Title: Spectral Properties of Solar Convection and Diffusion
Authors: Ruzmaikin, A. A.; Cadavid, A. C.; Chapman, G. A.; Lawrence,
J. K.; Walton, S. R.
Bibcode: 1996ApJ...471.1022R
Altcode:
We present the results of a study of the scaling properties of
solar photo spheric motions. We use time series of Doppler images
obtained in good seeing conditions with the San Fernando Observatory
28 cm vacuum telescope and vacuum spectroheliograph in video
spectra-spectroheliograph mode. Sixty line-of- sight Doppler images of
an area of the quiet Sun near disk center are investigated. They were
taken at 60 s intervals over a 1 hr time span at ∼2" resolution. After filtering to remove 5 minute acoustic oscillations, the
time-spatial spectrum of the velocity is calculated. To study the
turbulence of photospheric flows in the mesogranulation scale range,
we estimate two scaling parameters in the spectrum: the exponent of
the spatial part of the power spectrum and the exponent governing the
scaling of time correlations of each spatial mode. These parameters
characterize the type of diffusion involved and the fractal dimension of
the diffusion front. Our results indicate that the turbulent diffusion
produced by motions in this scale range is not normal diffusion but
superdiffusion.
Title: Downflows in a Large EFR
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1996AAS...188.7904C
Altcode: 1996BAAS...28..955C
We observed an emerging flux region (EFR) on January 3, 1996 with the
Video Spectra-Spectroheliograph (VSSHG) of the San Fernando Observatory
(SFO). The region, BBSO no. 3652, was selected based on a BearAlert
from the Big Bear Solar Observatory. Its position was N11 W11 at
2045 UT. The region grew from 110 microhemispheres (microhem) on the
3rd to 190 microhem on the 4th (W. Marquette, private communication,
1996). The observations, carried out over a 3-1/2 hour period beginning
at 20:07 UT, consist of two-dimensional spectra of the 630.25 nm solar
line analyzed for circular and linear polarization. The spectra are
used to produce maps with 0.5 arc-sec pixels of the vector magnetic
field, line-of-sight velocity and core and continuum intensity. A
complete set of such images were produced every ten minutes during
the observing period. From a preliminary analysis of about one-third
of the data, we find that there is a persistent downflow located near
the central portion of the EFR and very little upflow. Any possible
upflows are either of low amplitude or cover a much smaller area than
the downflow. The net downflow for the entire EFR is approximately
180-190 m/s. The strongest downflow, approximately 900-1000 m/s,
occurs in the area of one of the larger sunspots in the EFR. This
research was supported in part by NSF Grant ATM-9115111.
Title: Spectral Properties of the Solar Background Velocity Field
Authors: Cadavid, A. C.; Chapman, G. A.; Lawrence, J. K.; Ruzmaikin,
A. A.; Walton, S. R.
Bibcode: 1996AAS...188.3506C
Altcode: 1996BAAS...28Q.872C
We study the scaling properties of time series of Doppler images
obtained in good seeing conditions with the San Fernando Observatory
28 cm vacuum telescope and vacuum spectroheliograph in video
spectra-spectroheliograph mode. The images correspond to two areas
of quiet Sun near disk center taken at 60 second intervals from one
hour to six hour spans at ~ 2 arcsec resolution. After removal of 5
min acoustic oscillations the time-spatial spectrum of the velocity is
calculated. To study the turbulence of photospheric flows we estimate
two scaling parameters: the exponent of the spatial part of the power
spectrum and the exponent governing the scaling of time correlations
of each spatial mode. The implied diffusive behavior produced by the
solar convection in the mesogranulation scale range is discussed. This
includes characterization of the type of diffusion involved and the
fractal dimension of the diffusion front.
Title: Photometry of Restored Full-Disk Solar Images
Authors: Walton, S. R.; Preminger, D. G.; Toner, C. G.
Bibcode: 1996AAS...188.3614W
Altcode: 1996BAAS...28Q.875W
The San Fernando Observatory (SFO) Cartesian Full Disk Telescope (CFDT)
has been taking full-disk 512 square photometric images of the Sun
through a 100 Angstroms bandpass red filter since 1985, and through a
10 Angstroms bandpass K-line filter since 1989. We have recently begun
a project to attempt to remove the effects of atmospheric blurring
and scattered light on the photometry of these images. Specifically,
we are fitting the convolution of a limb darkening profile expansion
and a model point spread function (PSF) to the radial profiles of SFO
CFDT images, using a technique similar to that of Toner and Jeffries
(Ap. J. 1996, submitted) to remove the PSF from the images. The
blurring-free limb darkening profile is the sum of an expansion in
orthogonal (Legendre) polynomials, and the PSF model is the sum of
three Gaussian components plus a Lorentzian, normalized so that its
integral over the sky is unity. Tests with artificially generated
images with sunspots show that we can recover the sunspot photometric
quantities with excellent results. Comparison of the original and
restored photometry from eight actual red images taken hourly also
show that correlations between the PSF and the photometry disappear
after the restoration. We have been less successful at recovery
of facular photometry in the K line images, and are continuing to
investigate this. We will present details of our fitting procedure and
results. This project was partly supported by NSF Grant ATM-9115111
and NASA grant NAGW-3017.
Title: Downflows Associated with an Emerging Flux Region
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1995SPD....26..203C
Altcode: 1995BAAS...27..951C
No abstract at ADS
Title: Deconvolution of Full Disk Solar Images
Authors: Walton, S. R.; Preminger, D.; Toner, C. G.
Bibcode: 1995SPD....26..503W
Altcode: 1995BAAS...27..956W
No abstract at ADS
Title: Spectra of Solar Magnetic Fields and Diffusion
Authors: Ruzmaikin, A. A.; Cadavid, A. C.; Chapman, G. A.; Lawrence,
J. K.; Walton, S. R.
Bibcode: 1995ASPC...76..292R
Altcode: 1995gong.conf..292R
No abstract at ADS
Title: Correlations Between Full Disk Magnetograms and Solar Contrast
Authors: Walton, S. R.; Chapman, G. A.; Jayasinha, Y.
Bibcode: 1994AAS...185.4410W
Altcode: 1994BAAS...26.1378W
We have embarked on a pilot project to investigate the photometric
properties of sunspots as a function of cycle phase and the relation
between those properties and the magnetic field. The present study uses
full-disk solar contrast maps from the San Fernando Observatory (SFO)
Cartesian Full Disk Telescope 2 (CFDT2) and full-disk magnetograms
from the National Solar Observatory Spectromagnetograph during the
period 11 August to 23 August 1992; active region NOAA 7260 transited
the disk during this period. The CFDT2 instrument is scanned by the
earth's rotation, so its astrometric quality is very high. We fit an
accurate limb to the CFDT2 intensity map, and used this limb plus the
time difference between the CFDT2 and NSO images to re-interpolate
the CFDT2 image onto the same image scale, orientation, and time of
observation as the NSO images. A contrast map is then produced from the
CFDT2 image. This procedure is entirely automatic and quite accurate,
and is thus potentially suitable for the unattended processing of
much larger amounts of data. From these co-aligned images, we produce
two-dimensional histograms, using CFDT2 images taken in both red
continuum and the core of the K line. These histograms contain quite
a bit of scatter around zero field and zero contrast, which seems to
be real. We do see a difference between small and large spots, in the
sense that smaller sunspots show a slower growth of negative contrast
with increasing flux than large sunspots. In other words, if one chooses
a pixel inside a small and a large sunspot with the same magnetic flux,
the corresponding contrast will be larger in the large spot. There is a
''cutoff'' flux of about 1500G above which the sunspot stays at the same
contrast, roughly 20%, as the field strength increases. This research
was supported in part by grants NSF ATM-9115111 and NASA NAGW-3017,
and by the NSF Young Scholars Program. We are grateful to J. Harvey
and H. Jones of NSO for providing the magnetograms.
Title: Observations of Flows around Sunspot Groups
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1994ASPC...68..283C
Altcode: 1994sare.conf..283C
No abstract at ADS
Title: Flows in active regions: penumbral, superpenumbral and Evershed
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1994smf..conf..216C
Altcode:
No abstract at ADS
Title: Scattered Light in Solar Images using Hankel Transforms
Authors: Walton, S. R.; Chapman, G. A.; Cookson, A. M.; Preminger, D.
Bibcode: 1993AAS...183.5908W
Altcode: 1993BAAS...25.1387W
We have been investigating the scattered light properties of the
San Fernando Observatory (SFO) Cartesian Full Disk Telescope
(CFDT). Recently, Toner and Jeffries (1993, Ap. J. 415, 852)
have published a technique for the accurate determination of the
solar limb position, based on the Hankel transform of a radial solar
profile. They show that the Hankel transform of the observed solar limb
profile yields a seeing-independent determination of the solar limb
position and limb darkening profile. In principle, the ratio of the
transform of the observed profile to that of the model, polynomial,
solar limb darkening would then be the modulation transfer function
(MTF) of the atmosphere and telescope. In practice, as with all such
ratios of an observed power spectrum to an analytic one, the noise at
high spatial frequencies makes the division difficult. We have taken
a different approach. Using observed limb profiles from the SFO CFDT,
we do a non-linear least-squares fit of the observed profile to the
convolution of a model limb darkening profile and a model MTF. The model
limb darkening is an expansion in orthonormal Legendre polynomials in mu
rather than simple powers of mu, as orthonormal polynomials have many
desirable numerical features. The model MTF is a sum of short-range
(typically Gaussian) and long-range (typically Lorentzian) parts
(Lawrence, Chapman, Herzog, and Shelton 1985, Ap. J. 292, 297). We
will present results from these model fits and comment on their
robustness. We gratefully acknowledge Eric Hansen of Dartmouth College,
who supplied us with a copy of his Hankel transform code. This work
has been partially supported by NSF grant ATM-9115111 and NASA grants
NAGW-2770 and NAGW-3017.
Title: Association of a Siphon Flow with the Emergence of New Flux
Authors: Corbin, K. H.; Walton, S. R.; Chapman, G. A.
Bibcode: 1993BAAS...25.1217C
Altcode:
No abstract at ADS
Title: Intercomparison of Seven Magnetographs
Authors: Walton, S. R.; Bogart, R. S.; Chapman, G. A.; Henney, C.;
Jones, H.; Kopp, G.; Lites, B.; Mickey, D.; Montgomery, R.; Pillet,
V.; Rabin, D.
Bibcode: 1993BAAS...25.1205W
Altcode:
No abstract at ADS
Title: A Test of a Moment Technique for Vector Field Calculations
Authors: Walton, S. R.
Bibcode: 1992AAS...181.9404W
Altcode: 1992BAAS...24.1269W
Since last year, we have been using a moments technique to calculate
the solar vector magnetic field from measurements of the Stokes profiles
from the San Fernando Observatory Video Spectra-Spectroheliograph (SFO
VSSHG). As part of our evaluation of the accuracy of this technique,
I have carried out simulations using analytic profiles. Let S_n be
the nth moment of Stokes profile S(lambda ). That is: $ S_n = int
lambda (n) S(lambda )dlambda where \lambda = 0 is taken at line center
and the integral is done over the line profile. We use the following
approximations: {Q_2 / I_0} = {1 / 2} B(2) sin (2gamma cos ) 2 chi {U_2
/ I_0} = {1 / 2} B(2) sin (2gamma sin ) 2 chi {V_1 / I_0} = B cos gamma
where B is the magnitude of the field, \gamma is its inclination to the
line of sight, and \chi is its azimuth angle. These approximations are
exact if the Stokes profiles are given by the Seares formulae. We have
applied them to profiles generated in the Unno-Rachkovsky solution to
the transfer equation, and show that they are a useful approximation
for more realistic line profiles as well. The largest systematic errors
are in the azimuth angle \chi$, with smaller errors in determination
of the longitudinal component of the field and essentially no error
in determining the magnitude of the transverse component. This work
was supported in part by NASA grant NAGW-2453 and NSF grant ATM-9115111.
Title: Precise ground-based solar photometry and variations of
total irradiance
Authors: Chapman, G. A.; Herzog, A. D.; Lawrence, J. K.; Walton,
S. R.; Hudson, H. S.; Fisher, B. M.
Bibcode: 1992JGR....97.8211C
Altcode:
Variations in the total solar irradiance measured by the active cavity
radiometer irradiance monitor (ACRIM) on SMM have been correlated
with measures of magnetic activity on the solar disk. Quantitative
indices of magnetic activity were derived from ground-based, full-disk,
photometric images of the Sun at red (6723 Å) and violet (3934-Å K
line) wavelengths. The red images have been obtained on a daily basis
at the San Fernando Observatory since 1985, and the K line images
since 1988. Sunspot irradiance deficits are calculated directly
from the red images while proxy measures of facular irradiance
excesses are derived from the K line images. The images analyzed
here were made during 21 days between June 20 and July 14, 1988,
a period centered on the disk passage of a large sunspot group. The
best two-parameter multiple correlation coefficient between the
ACRIM data and the photometric data is R2=0.97 (21 data
points, 18 degrees of freedom). The zero point S0=1367.27
W m-2 agrees well with the solar irradiance
measured by ACRIM/SMM during the 1986 activity minimum: the residual
standard deviation was 0.13 W m-2 (about 100
ppm). The multiple correlations were extended to include measures
of the irradiance contribution of ``network'' magnetic fields,
unassociated with active regions. NOAA 9 spacecraft observations of UV
MgII lines at 2800 Å gave R2=0.99 (17 degrees of freedom)
with S0=1366.68+0.08 W m-2. The index of 10.7-cm
microwave flux gave R2=0.98, with S0=1366.43+0.11
W m-2. We can thus model short-term irradiance
changes to within 100 ppm relative precision from ground-based data.
Title: Sunspot Deficits Measured With a New, 3-inch Full Disk
Photometric Telescope
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1992AAS...180.1706C
Altcode: 1992BAAS...24..754C
A new photometric telescope has begun operation which is similar
to the old CFDT (Cartesian Full Disk Telescope). The new one has a
3-inch aperture objective and a 1024 element linear diode array. Each
pixel corresponds to 2.5 arc-sec on the sky. As with the old CFDT
(Chapman, et al./ 1989, Ap. J. 343, 547) this telescope uses the
earth's diurnal motion to scan the array and build up a 1024 x 1024
pixel image of the solar disk and nearby sky. Results will be presented
here comparing sunspot areas and deficits as measured with the new
and old CFDT. Analysis of images obtained under conditions of poor
seeing on 24 December 1991 show that the new CFDT gives sunspot areas
and deficits that are 1.36 and 1.16 times greater, respectively, than
those from the old CFDT. This research has been partially supported
by NSF Grant ATM-8817634 and NASA Grant NAG-5-1219.
Title: Doppler and Magnetic Studies of the Flare-Producing Area of
NOAA 6659
Authors: Walton, S. R.; Chapman, G. A.; David, R. S.
Bibcode: 1992AAS...180.5102W
Altcode: 1992BAAS...24..813W
The San Fernando Observatory Video Spectra-Spectroheliograph (VS(2)
HG) produces simultaneous spectra-spectroheliograms in two orthogonal
polarizations; during four successive scans, all four Stokes vectors
are recorded over a spectral region approximately 1.5 Angstroms wide,
with pixels of 8 m Angstroms in the spectral direction and 0.46 seconds
of arc in the spatial direction. Since each individual scan produces a
continuum, line core, and Doppler map, these are both simultaneous and
co-spatial, essentially by definition. The continuum images from each
scan are used to align the separate scans of Stokes Q, U, and V. From
these aligned scans, maps of the vector magnetic field are produced. A
brief description of the VS(2) HG can be found in Lawrence, Chapman,
and Walton (1991), Ap. J. 375, 771; a detailed description of the data
processing procedure is in preparation. We observed active region
NOAA 6659 using the VS(2) HG on 7 June and 10 through 15 June 1991,
a period from two days before to six days after its central meridian
passage. The Doppler maps from the 7th and the 10th show a blueshifted
area just to the west of the northernmost sunspot of the group. This
area was especially prominent on the 10th, and was co-spatial with
the west ribbon as seen in Hα of an M3.2 flare which occurred at
1654 UT. (This region produced a very large flare (X12.0) at 11 June
0229 UT, but as of this writing, we don't have the precise location
of this flare.) The vector maps show a strong tangential component of
the magnetic field in this area. The direction of the tangential field
changes rapidly across the area of the blueshift. The later observations
(12 and 13 June) show what, given the disk position, appears to be an
area of downflow in the same area: i.e., a redshift on the disk center
side and a blueshift on the limbward side. We will show and discuss
further the maps at the meeting. This research has been partially
supported by NASA grant NAGW-2453 and NSF grant ATM-9115111.
Title: Weak Magnetic Fields and Solar Irradiance Variations
Authors: Lawrence, J. K.; Chapman, G. A.; Walton, S. R.
Bibcode: 1991ApJ...375..771L
Altcode:
NOAA active region 5643 was observed from August 17 to 21, 1989. Sets
of video spectra-spectroheliograms including the Fe I line at 6302.5
A were made at least daily with the San Fernando Observatory 28 cm
vacuum telescope and vacuum spectroheliograph. These give simultaneous,
co-registered digital images representing monochromatic continuum
intensity, line core intensity and line-of-sight magnetic field. Three
different criteria are used to define the pixels representing the
quiet sun and the facular portions of the images. These criteria
are the magnetic field strength, the line core intensity, and the
distribution of continuum intensities. Each of these definition schemes
is used to estimate the irradiance change due to facular emission. The
magnetic field and the continuum intensity distribution definitions
give estimates which agree closely. The line core intensity definition
leads to larger estimates of the facular irradiance contribution. Some
model-dependent investigations of the contrasts and sizes of individual
facular elements also are presented.
Title: Ground-Based Modelling of Solar Irradiance Variations
Authors: Lawrence, J. K.; Chapman, G. A.; Herzog, A. D.; Walton,
S. R.; Hudson, H. S.; Fisher, B. M.
Bibcode: 1991BAAS...23..960L
Altcode:
No abstract at ADS
Title: Continuum Contrast and Center to Limb Variation of Solar
Magnetic Elements Observed in the Photosphere
Authors: Swearingen, D. J.; Walton, S. R.; Chapman, G. A.; Lawrence,
J. K.
Bibcode: 1991BAAS...23..960S
Altcode:
No abstract at ADS
Title: Recent results from the San Fernando Observatory video
spectra-spectroheliograph.
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1991sopo.work...37C
Altcode:
Results are presented from VSSHG observations of an extensive sunspot
group, NOAA 5669, that transited disk center on 4 September 1989. The
data are presently processed to obtain four images: a saturation-free
longitudinal magnetogram, a Dopplergram, a continuum image, and a line
core spectroheliogram. All images are from two-dimensional spectral data
with a spectral window of about 1 Å, centered on the 6302.5 Å line
of neutral iron. The images show the well-known "fringing" of sunspot
fields, the "unsymmetrical" Evershed flow as well as large-scale flow
patterns within the active region.
Title: A program of photometric measurements of solar irradiance
fluctuations from ground-based observations.
Authors: Chapman, G. A.; Herzog, A. D.; Lawrence, J. K.; Walton, S. R.
Bibcode: 1990NASCP3086...16C
Altcode: 1990cisv.nasa...16C
Photometric observations of the sun have been carried out at the
San Fernando Observatory since early 1985. Since 1986, observations
have been obtained at two wavelengths in order to separately measure
the contributions of sunspots and bright facular to solar irradiance
variations. The authors believe that the contributions of sunspots can
be measured to an accuracy of about ±30 ppm. The effect of faculae is
much less certain, with uncertainties in the range of ±300 ppm. The
larger uncertainty for faculae reflects both the greater difficulty
in measuring the facular area, due to their lower contrast compared
to sunspots, and the greater uncertainty in their contrast variation
with viewing angle on the solar disk. Recent results from two separate
photometric telescopes will be compared with bolometric observations
from the ACRIM that was on board the Solar Max satellite.
Title: Solar Variability Measured by SMM/ACRIM Compared with
Ground-Based Photometry
Authors: Chapman, G. A.; Herzog, A. D.; Lawrence, J. K.; Walton,
S. R.; Hudson, H. S.; Fisher, B.
Bibcode: 1990BAAS...22..897C
Altcode:
No abstract at ADS
Title: The Relation Between Irradiance Excess and Magnetic Field
for the Sun
Authors: Wilson, R. J.; Walton, S. R.; Chapman, G. A.
Bibcode: 1990BAAS...22..793W
Altcode:
No abstract at ADS
Title: Continuum Contrast of Photospheric Faculae Compared to their
Magnetic Flux
Authors: Lawrence, J. K.; Chapman, G. A.; Walton, S. R.
Bibcode: 1990BAAS...22..839L
Altcode:
No abstract at ADS
Title: Preliminary Results from the Video Spectra-Spectro-Heliograph
at the San Fernando Observatory
Authors: Chapman, G. A.; Walton, S. R.
Bibcode: 1989BAAS...21.1179C
Altcode:
No abstract at ADS
Title: Comparison of SFO Full-Disk Photometric Images with NSO
Full-Disk Magnetograms
Authors: Walton, S. R.; Wilson, R. J.; Chapman, G. A.
Bibcode: 1989BAAS...21.1179W
Altcode:
No abstract at ADS
Title: Magnetic Fields from Video Spectra-Spectroheliograms: A Test
of the Center of Gravity Method
Authors: Walton, S. R.; Chapman, G. A.
Bibcode: 1989BAAS...21..854W
Altcode:
No abstract at ADS
Title: Magnetic Field Strengths from a Digital Magnetogram compared
with those from Viedo Spectra-Spectroheliograms (VSSHG)
Authors: Chapman, G. A.; Herzog, A. D.; Walton, S. R.
Bibcode: 1989BAAS...21..862C
Altcode:
No abstract at ADS
Title: Full Disk CaII K-line Observations of the Sun with a One-Inch
Telescope (CFDT)
Authors: Chapman, G. A.; Walton, S. R.; Bird, M.; Bulharowski, T.;
Cordero, E.; Gluszczak, M.; Mach, C.; Manes, J.; Parker, D.; Wagner, J.
Bibcode: 1988BAAS...20..910C
Altcode:
No abstract at ADS
Title: Observations of NOAO 4835 Using the SFO RFDP
Authors: Walton, S. R.; Chapman, G. A.; Herzog, A. D.; Gluszczak,
M. R.; Arndt, J.; Sherk, J.
Bibcode: 1988BAAS...20..680W
Altcode:
No abstract at ADS
Title: Analysis of SFO RFDP Observatons of Active Regions
Authors: Walton, S. R.; Chapman, G. A.; Herzog, A. D.; Gluszczak,
M. R.; Klein, M. L.
Bibcode: 1987BAAS...19.1132W
Altcode:
No abstract at ADS
Title: Simultaneous Observations of Active Regions
Authors: Herzog, A. D.; Chapman, G. A.; Walton, S. R.; Gluszczak,
M. R.; Klein, M. L.
Bibcode: 1987BAAS...19.1118H
Altcode:
No abstract at ADS
Title: The sky observer's guide : a handbook for amateur astronomers
Authors: Mayall, Robert Newton; Mayall, Margaret Walton; Wyckoff,
Jerome; Polgreen, John
Bibcode: 1985sogh.book.....M
Altcode: 1985QB64.M3........
No abstract at ADS
Title: Flux Tube Models of Solar Plages
Authors: Walton, S. R.
Bibcode: 1984BAAS...16Q.528W
Altcode:
No abstract at ADS
Title: Analysis of flares observed during the solar maximum year
Authors: Zirin, H.; Martin, S. F.; Walton, S. R.
Bibcode: 1982cait.rept.....Z
Altcode:
This report encompasses three major projects: (1) Qualitative
characterization of the H-alpha profiles of the flare of 5 November
1980 at 2233 UT; (2) Construction of a film projector/digitizer for
the purpose of projecting half-frame 35mm images onto a television
camera detector; (3) Images of solar plages near the limb in broadband
continuum, and analysis thereof. These projects are described in the
respective three sections of this report.
Title: Images of Jupiter from the pioneer 10 and pioneer 11 infrared
radiometers: A comparison with visible and 5-μm images
Authors: Orton, G. S.; Ingersoll, A. P.; Terrile, R. J.; Walton, S. R.
Bibcode: 1981Icar...47..145O
Altcode:
All of the data acquired at Jupiter by the Infrared Radiometers on
board Pioneers 10 and 11 are presented in the form of images with
geometric control. The images are compared with 5-μm and visible
images taken in the same time frame. The association of dark (blue or
brown) and light (white or red) areas with warm and cool areas (at 5,
20, and 45 μm) respectively, extends to nearly all features observed
on the planet. Where the normal association of light and dark visible
markings with the zonal velocity breaks down (e.g., at the latitude of
the South Equatorial Belt during the Pioneer encounters), the infrared
emission seems to follow the visible cloud structure rather than the
zonal velocity structure. Exceptions to the general rule involve 20-μm
radiation, which reflects conditions in the altitude range 0.1-0.3
bar. For example, a comparison between Pioneer 10 and 11 images
suggests that the South Equatorial Belt became brighter at 20 μm,
but remained constant at other wavelengths between the two encounters.
Title: Observations of Photospheric Line Profiles in Plages
Authors: Walton, S. R.
Bibcode: 1981BAAS...13Q.913W
Altcode:
No abstract at ADS
Title: Obituary - Ashbrook, Joseph
Authors: Robinson, L. J.; Bok, B. J.; Chapman, C. R.; Federer, C. A.,
Jr.; Gingerich, O.; Haas, W. H.; Jacchia, L. G.; Marsden, B. G.;
Mayall, M. W.; White, J.
Bibcode: 1980S&T....60..281R
Altcode:
No abstract at ADS
Title: The sky observer's guide : a handbook for amateur astronomers
Authors: Mayall, Robert Newton; Mayall, Margaret Walton; Wyckoff,
Jerome; Polgreen, John
Bibcode: 1977sogh.book.....M
Altcode: 1977QB64.M3........
No abstract at ADS
Title: Annual report of the director, 30 September 1973.
Authors: Mayall, M. W.
Bibcode: 1973JAVSO...2...92M
Altcode:
No abstract at ADS
Title: Sundials, how to know, use, and make them
Authors: Mayall, Robert Newton; Mayall, Margaret Walton
Bibcode: 1973sund.book.....M
Altcode: 1973QB215.M3.......
No abstract at ADS
Title: Observations of miscellaneous types of variables, 22 October
1961_- 21 September 1963, J.D. 2,437,595_- 2,438,294.
Authors: Mayall, M. W.
Bibcode: 1972omtv.book.....M
Altcode:
No abstract at ADS
Title: Annual report of the director, 30 September 1972.
Authors: Mayall, M. W.
Bibcode: 1972JAVSO...1...80M
Altcode:
No abstract at ADS
Title: R CrB variables.
Authors: Matchett, V. L.; Mayall, M.; Isles, J. E.; Pennell, W. E.
Bibcode: 1972IAUC.2460....1M
Altcode:
No abstract at ADS
Title: SU Tauri.
Authors: Gaustad, J. E.; Mayall, M.
Bibcode: 1971IAUC.2318....1G
Altcode:
No abstract at ADS
Title: American Association of Variable Star Observers. Abstracts
of papers presented at Rochester meeting, 1 May 1971.
Authors: Mayall, R. N.; Boss, L. J.; Borzelli, C.; Scovil, C. E.;
Mayall, M. W.; Diedrich, G.; Ford, C. B.; Hossfield, C. H.; Cragg,
T. A.
Bibcode: 1971AAVSO.........M
Altcode:
No abstract at ADS
Title: Nova Serpentis 1970
Authors: Kanda, S.; Honda, M.; Mayall, M.; Ford, C. B.
Bibcode: 1970IAUC.2214....1K
Altcode:
Mr. S. Kanda, Yugawara, reports that according to the discoverer,
M. Honda, Kurashiki, the nova was invisible on Feb. 12.8. Mrs. Margaret
Mayall, AAVSO, reports that the nova was observed (through clouds)
by C. B. Ford, Wilton, Connecticut, on Feb. 18.4, the magnitude being
approximately 4.0 to 4.5.
Title: Nova Serpentis 1970
Authors: Seki, T.; Kosai, H.; Honda, M.; Ichimura, E.; Shimizu, M.;
Watanabe, E.; Nariai, K.; Yamashita, Y.; Kiyokawa, M.; Kikuchi, S.;
Kanno; Sugano, M.; Urata, T.; Peltier, L. C.; Hurless, C.; Sweetsir,
R.; Hodson, R.; Mayer, E.; Simmons, K.; Rosebrugh, D.; Mayall, M.;
Lowder, W. M.; Ashbrook, J.; Pilcher, F.
Bibcode: 1970IAUC.2216....1S
Altcode:
The following position has been measured at the Tokyo Astronomical
Observatory from a 50-cm Schmidt plate (f = 100 cm): R.A. (1950)
Decl. 18 28 16.36 + 2 34 41.5 Comparison of this plate with the
Palomar Sky Survey prints suggested five possible candidates for
identification, their blue magnitudes ranging from 14.3 to 19.4, and
their red magnitudes from 11.2 to 15.9. Mr. T. Seki, Kochi, provides a
position differing from the above by -0.18s, +1.3". Mr. H. Kosai, Tokyo
Observatory, has measured the following magnitudes from panchromatic
plates (without filter) taken by M. Honda with his Fujinar camera (f =
21 cm, f/4.5): 1970 UT Mag. Feb. 12.85347 >10.5 13.86007 6.8 The
following photoelectric observations have been made by E. Ichimura,
M. Shimizu and E. Watanabe at the Okayama station of the Tokyo
Observatory. These results are preliminary ones. 1970 UT V B - V U - B
Note Feb. 16.86 4.88 +0.84 +0.33 17.84 4.56 +0.96 +0.53 18.84 4.6 +1.1
+0.9 through clouds Also at the Okayama station, coude spectrograms
(10 A/mm) of the photographic region were obtained by K. Nariai and
Y. Yamashita. At the Dodaira station, prism spectrograms (60 A/mm
at H-gamma) of the photographic and visual regions were obtained
by M. Kiyokawa and S. Kikuchi. On Feb. 16.8 UT the spectrum had
the general appearance of that of an F-type supergiant, with strong
absorption lines of H, Ca II, Fe II, O I, C I and many other ionized
metals. The radial velocity was approximately -500 km/s. Emission
components were also found for some lines between H-alpha and H-beta
and for the Ca II lines. Spectrograms on the following nights
show the gradual decrease in intensity of the absorption lines,
accompanied by broadening. Emission components are increasing in
intensity. On Feb. 18.8 UT new diffuse absorption components with
larger violet displacements were visible for the Ca II lines (H and
K). The following visual magnitude estimates have been reported: 1970
UT mV Observer 1970 UT mV Observer Feb. 15.8 4.9 Kanno Feb. 20.38 4.4
Sweetsir 15.85 4.9 Sugano 20.44 4.8 Lowder 16.8 <4.5 Honda 20.45
5.0 Pilcher 16.83 4.5 Kosai 20.49 4.7 Hodson 16.87 4.9 Seki 21.38
4.6 Mayer 17.8 4.5 Honda 21.38 4.8 Sweetsir 17.83 4.2 Kosai 21.38
4.6 Simmons 17.87 4.7 Seki 21.4 4.8 Rosebrugh 18.4 5.2 Peltier 21.44
4.9 Lowder 18.46 4.5 Lowder 22.36 5.1 Simmons 18.8 4.5 Honda 22.42
4.5 Sweetsir 18.83 3.9 Kosai 22.5 4.8 Rosebrugh 18.85 4.8 Seki 23.5
4.8 " 19.4 5.0 Hurless Kanno, M. Honda and H. Kosai. Communicated
by Tokyo Observatory. M. Sugano (Akashi, Japan). Communicated
by T. Urata. T. Seki (Kochi Observatory). L. C. Peltier,
C. Hurless, R. Sweetsir, R. Hodson, E. Mayer, K. Simmons and
D. Rosebrugh. Communicated by Margaret Mayall. W. M. Lowder (Scarsdale,
N.Y.). Communicated by J. Ashbrook. F. Pilcher (Jacksonville, Illinois).
Title: omicron Ceti.
Authors: Mayall, M. W.
Bibcode: 1970IAUC.2267....1M
Altcode:
No abstract at ADS
Title: Light curves of long period variables, 22_October_1961_-
21_September_1963, J._D._2,437,595_- 2,438,294.
Authors: Mayall, M. W.; Welther, B. L.
Bibcode: 1970lclp.book.....M
Altcode:
No abstract at ADS
Title: Variable star notes.
Authors: Mayall, M. W.
Bibcode: 1969JRASC..63...45M
Altcode:
No abstract at ADS
Title: Variable star notes.
Authors: Mayall, M. W.
Bibcode: 1969JRASC..62..395M
Altcode:
No abstract at ADS
Title: Eclipses of U Geminorum
Authors: Mayall, M. W.
Bibcode: 1969CoKon..65..377M
Altcode: 1969nppv.conf..377M
No abstract at ADS
Title: Skyshooting; photography for amateur astronomers
Authors: Mayall, Robert Newton; Mayall, Margaret Walton
Bibcode: 1968spaa.book.....M
Altcode: 1968QB121.M39......
No abstract at ADS
Title: The sky observer's guide; a handbook for amateur astronomers
Authors: Mayall, Robert Newton; Mayall, Margaret Walton; Wyckoff,
Jerome
Bibcode: 1965sog..book.....M
Altcode: 1965QB64.M3........
No abstract at ADS
Title: Visual Observations of U Geminorum Stars
Authors: Mayall, M. W.
Bibcode: 1965VeBam..27..241M
Altcode:
No abstract at ADS
Title: Variable Star Programs for Amateur Observers
Authors: Mayall, M. W.
Bibcode: 1962VeBam..34..131M
Altcode:
No abstract at ADS
Title: A beginner's guide to the skies
Authors: Mayall, Robert Newton; Mayall, Margaret Walton
Bibcode: 1960bgts.book.....M
Altcode: 1960QB46.M48.......
No abstract at ADS
Title: The sky observer's guide; a handbook for amateur astronomers
Authors: Mayall, Robert Newton; Mayall, Margaret Walton; Wyckoff,
Jerome; Polgreen, John
Bibcode: 1959sogh.book.....M
Altcode: 1959QB64.M3........
No abstract at ADS
Title: Variable star notes (1955).
Authors: Mayall, M. W.
Bibcode: 1955JRASC..50..219M
Altcode:
No abstract at ADS
Title: New Peculiar Spectra
Authors: Mayall, Margaret Walton
Bibcode: 1951BHarO.920...32M
Altcode:
No abstract at ADS
Title: Recent Variations of RR Telescopii
Authors: Mayall, Margaret Walton
Bibcode: 1949BHarO.919...15M
Altcode:
No abstract at ADS
Title: Book Review: General Catalogue of Variable Stars, by
B. V. Kukarkin and P. P. Parenago
Authors: Mayall, Margaret Walton
Bibcode: 1949PA.....57...47M
Altcode:
No abstract at ADS
Title: Skyshooting; hunting the stars with your camera
Authors: Mayall, Robert Newton; Mayall, Margaret Walton
Bibcode: 1949shsc.book.....M
Altcode: 1949QB121.M39......
No abstract at ADS
Title: Six novae, one with a late-type spectrum.
Authors: Mayall, Margaret Walton
Bibcode: 1949AJ.....54R.191M
Altcode: 1949AJ.....54..191M
As a result of the nova patrol program in the Sagittarius region,
I have found 6 more novae in the last few years. They were all found
on objective prism plates taken with the io-inch Metcalf telescope in
South Africa. They are listed in the table with their 1900 positions
and approximate maximum magnitudes. The spectrum of Nova Sgr 1943 is
the most interesting of the group, but the light curve is the most
poorly observed, for it was seen on only 3 chart plates. On a spectrum
plate taken August 19, it appeared to be of a K type, with strong
absorption H and K, and possibly TiO bands, and N4227. Five days later,
a plate showed a banded nova spectrum, with widened hydrogen emission
and strong absorption H and K and N4227. On August 29th, the spectrum
consisted mostly of wide bright bands. The nova is on the edge of the
globular cluster, NGC 6533. Nova a (1900) 1 mpg SgrI943 18h 2~545 -26
0.4 8 SgrI944 i8 I 8 -33 21.8 8 ScoI9~~ 17 46 27 -35 48.9 7.5 SgrI945
18 12 II -28 19.6 SgrI~46 i8 12 48 -24 8.1 12 SgrI947 i8 19 24 -20
15.1 10 Harvard College Observatory, Cambridge, Mass.
Title: Variables Sequences
Authors: Mayall, Margaret Walton
Bibcode: 1949phae.proj.2582M
Altcode:
No abstract at ADS
Title: The Henry Draper extension. II .
Authors: Cannon, Annie J.; Mayall, Margaret Walton
Bibcode: 1949AnHar.112....1C
Altcode:
No abstract at ADS
Title: Nova Sagittarii 1941 and Nova Scorpii 1941
Authors: Mayall, Margaret Walton
Bibcode: 1946BHarO.918....1M
Altcode:
No abstract at ADS
Title: Nova Sagittarii 1913, 1946
Authors: Mayall, Margaret Walton
Bibcode: 1946BHarO.918....3M
Altcode:
No abstract at ADS
Title: The Variations of Rho Cassiopeiae
Authors: Payne-Gaposchkin, Cecilia; Mayall, Margaret Walton
Bibcode: 1946BHarO.918...11P
Altcode:
No abstract at ADS
Title: The Cannon Memorial Volume of the Harvard Annals
Authors: Mayall, Margaret Walton
Bibcode: 1946PAAS...10..231M
Altcode:
No abstract at ADS
Title: Astronomers Meet at Cambridge
Authors: Mayall, Margaret Walton
Bibcode: 1943S&T.....2Q...3M
Altcode:
No abstract at ADS
Title: Plate Examinations, Nove Measures
Authors: Mayall, Margaret Walton
Bibcode: 1942phae.proj.2578M
Altcode:
No abstract at ADS
Title: Spectral Curves of RU Camelopardalis
Authors: Mayall, Margaret Walton
Bibcode: 1941BHarO.915...14M
Altcode:
No abstract at ADS
Title: New Peculiar Spectra
Authors: Mayall, Margaret Walton; Cannon, Annie J.
Bibcode: 1940BHarO.913....7M
Altcode:
No abstract at ADS
Title: The Longest Long-Period Variable Known, H.V. 10446
Authors: Mayall, Margaret Walton
Bibcode: 1940BHarO.913....8M
Altcode:
No abstract at ADS
Title: Spectral Curves for Thirty Cepheid Variables.
Authors: Mayall, Margaret Walton; Baker, Mary Howe
Bibcode: 1940HarCi.436....1M
Altcode:
No abstract at ADS
Title: Milton Bureau Spectrum
Authors: Mayall, Margaret Walton
Bibcode: 1939phae.proj.2584M
Altcode:
No abstract at ADS
Title: An unusual new eclipsing star
Authors: Mayall, Margaret Walton
Bibcode: 1939PAAS....9Q..13M
Altcode:
No abstract at ADS
Title: New Peculiar Spectra
Authors: Cannon, Annie J.; Mayall, Margaret Walton
Bibcode: 1938BHarO.908...20C
Altcode:
No abstract at ADS
Title: Nova Sagittarii 1936.37
Authors: Mayall, Margaret Walton
Bibcode: 1938BHarO.907...28M
Altcode:
No abstract at ADS
Title: A new eclipsing star of unusual character
Authors: Mayall, Margaret Walton; Shapley, Harlow
Bibcode: 1937AnHar.105..491M
Altcode:
No abstract at ADS
Title: Positions of Variables around LMC
Authors: Mayall, Margaret Walton
Bibcode: 1935phae.proj.2499M
Altcode:
No abstract at ADS
Title: RH Plates PTM
Authors: Mayall, Margaret Walton
Bibcode: 1934phae.proj.1297M
Altcode:
No abstract at ADS
Title: RH Plates PTM
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1934phae.proj.1296M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1934phae.proj.1295M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1933phae.proj.1294M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1933phae.proj.1292M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1933phae.proj.1293M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1933phae.proj.1291M
Altcode:
No abstract at ADS
Title: Measure of Positions, Large Magellanic Cloud
Authors: Mayall, Margaret Walton
Bibcode: 1933phae.proj.2583M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1932phae.proj.1286M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1932phae.proj.1287M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1932phae.proj.1285M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1932phae.proj.1288M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1932phae.proj.1289M
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1932phae.proj.1284M
Altcode:
No abstract at ADS
Title: RH Plates PTM - Schilt
Authors: Mayall, Margaret Walton; H. J., P.
Bibcode: 1932phae.proj.1290M
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1931phae.proj.1281M
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1931phae.proj.1282M
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1931phae.proj.1283M
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1931phae.proj.1280M
Altcode:
No abstract at ADS
Title: Variation in spectral class of Cepheid variables (abstract)
Authors: Walton, Margaret L.; Shapley, Harlow
Bibcode: 1931PAAS....6..133W
Altcode:
No abstract at ADS
Title: The spectra of the international Cepheids
Authors: Walton, Margaret L.; Cannon, Annie J.
Bibcode: 1931PAAS....6Q.352W
Altcode:
No abstract at ADS
Title: Becker's Nova Sagittarii 1927.7
Authors: Walton, Margaret L.
Bibcode: 1930BHarO.878....8W
Altcode:
No abstract at ADS
Title: Spectra, of Cepheids of the International Program
Authors: Cannon, Annie J.; Walton, Margaret L.
Bibcode: 1930BHarO.874...19C
Altcode:
No abstract at ADS
Title: The spectra of the international Cepheids
Authors: Walton, Margaret L.; Cannon, Annie J.
Bibcode: 1930PA.....38Q.479W
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Mayall, Margaret Walton; Campbell, Florence M.; H. J., P.
Bibcode: 1930phae.proj.1279M
Altcode:
No abstract at ADS
Title: RH Plates - Schilt
Authors: Campbell, Florence M.; Mayall, Margaret Walton
Bibcode: 1930phae.proj.1278C
Altcode:
No abstract at ADS
Title: Variable measures
Authors: Mayall, Margaret Walton
Bibcode: 1929phae.proj.2587M
Altcode:
No abstract at ADS
Title: Spectral variation of Cepheids
Authors: Mayall, Margaret Walton
Bibcode: 1929phae.proj.2590M
Altcode:
No abstract at ADS
Title: A New Kind of Stellar Variation
Authors: Gerasimovic, B. P.; Walton, Margaret L.
Bibcode: 1928BHarO.862R..25G
Altcode:
No abstract at ADS
Title: Spectra and Color Indices at the North Galactic Pole
Authors: Shapley, Harlow; Walton, Margaret L.
Bibcode: 1928BHarO.859....2S
Altcode:
No abstract at ADS
Title: Variation in spectral class of Cepheid variables (abstract)
Authors: Walton, Margaret L.; Shapley, Harlow
Bibcode: 1928PA.....36..351W
Altcode:
No abstract at ADS
Title: MF plate remarks
Authors: Mayall, Margaret Walton
Bibcode: 1928phae.proj.2586M
Altcode:
No abstract at ADS
Title: Three new variables in Carina.
Authors: Walton, Margaret L.
Bibcode: 1927BHarO.848...13W
Altcode:
No abstract at ADS
Title: Investigations of Cepheid Variables. IV. Beta Doradus, A New
Fourth Magnitude Cepheid.
Authors: Shapley, Harlow; Walton, Margaret L.
Bibcode: 1927HarCi.316....1S
Altcode:
No abstract at ADS
Title: The Distances of Fifty Cepheid Variables
Authors: Walton, Margaret L.
Bibcode: 1927BHarO.845....6W
Altcode:
No abstract at ADS
Title: Investigations of Cepheid Variables. I. The Period-Spectrum
Relation.
Authors: Shapley, Harlow; Walton, Margaret L.
Bibcode: 1927HarCi.313....1S
Altcode:
No abstract at ADS
Title: A survey of the variable stars in the region 15 degrees square
around Messier 11 (abstract)
Authors: Walton, Margaret L.
Bibcode: 1927PAAS....5..412W
Altcode:
No abstract at ADS
Title: A survey of the variable stars in the region 15 degrees square
around Messier 11 (abstract)
Authors: Walton, Margaret L.
Bibcode: 1927PA.....35...25W
Altcode:
No abstract at ADS
Title: North Galactic Pole Region
Authors: Mayall, Margaret Walton
Bibcode: 1927phae.proj.2585M
Altcode:
No abstract at ADS
Title: The Magellanic Clouds, VIII. Note on the Spectral Composition
of the Foreground.
Authors: Shapley, Harlow; Walton, Margaret L.
Bibcode: 1925HarCi.288....1S
Altcode:
No abstract at ADS
Title: Magnitudes and position of Cepheid variables
Authors: Mayall, Margaret Walton
Bibcode: 1925phae.proj.2589M
Altcode:
No abstract at ADS
Title: Occultations during the lunar eclipse of 1924 August 14
Authors: Comrie, Leslie J.; Walton, Margaret L.
Bibcode: 1924JBAA...34..236C
Altcode:
No abstract at ADS
Title: Magnitudes
Authors: Mayall, Margaret Walton
Bibcode: 1924phae.proj.2588M
Altcode:
No abstract at ADS