Author name code: blackwell
ADS astronomy entries on 2022-09-14
=author:"Blackwell, D.E."
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Title: VizieR Online Data Catalog: Effective temperatures by Infrared
Flux Method (Blackwell+ 1998)
Authors: Blackwell, D. E.; Lynas-Gray, A. E.
Bibcode: 1998yCat..41290505B
Altcode:
Effective temperatures for 420 stars with spectral types between A0
and K3, and luminosity classes between II and V, selected for a flux
calibration of the Infrared Space Observatory, ISO, have been determined
using the Infrared Flux Method (IRFM). The determinations are based
on narrow and wide band photometric data obtained for this purpose,
and take into account previously published narrow-band measures of
temperature. (1 data file).
Title: Determination of the temperatures of selected ISO flux
calibration stars using the Infrared Flux Method
Authors: Blackwell, D. E.; Lynas-Gray, A. E.
Bibcode: 1998A&AS..129..505B
Altcode:
Effective temperatures for 420 stars with spectral types between A0
and K3, and luminosity classes between II and V, selected for a flux
calibration of the Infrared Space Observatory, ISO, have been determined
using the Infrared Flux Method (IRFM). The determinations are based
on narrow and wide band photometric data obtained for this purpose,
and take into account previously published narrow-band measures of
temperature. Regression coefficients are given for relations between
the determined temperatures and the photometric parameters (B2-V1),
(b-y) and (B-V), corrected for interstellar extinction through use of
Hipparcos parallaxes. A correction for the effect of metallicity on
the determination of integrated flux is proposed. The importance of a
knowledge of metallicity in the representation of derived temperatures
for Class V, IV and III stars by empirical functions is discussed
and formulae given. An estimate is given for the probable error of
each temperature determination. Based on data from the ESA Hipparcos
Astrometry Satellite.
Title: Determination of the Temperatures of Selected ISO Flux
Calibration Stars Using the Infrared Flux Method
Authors: Blackwell, D. E.; Lynas-Gray, A. E.
Bibcode: 1997STIN...9869702B
Altcode:
Effective temperatures for 420 stars with spectral types between A0
and K3, and luminosity classes between II and V, selected for a flux
calibration of the Infrared Space Observatory, ISO, have been determined
using the Infrared Flux Method (IRFM). The determinations are based
on narrow and wide band photometric data obtained for this purpose,
and take into account previously published narrow-band measures of
temperature. Regression coefficients are given for relations between
the determined temperatures and the photometric parameters (B2-V1),
(b-y) and (B-V), corrected for interstellar extinction through use of
Hipparcos parallaxes. A correction for the effect of metallicity on
the determination of integrated flux is proposed. The importance of a
knowledge of metallicity in the representation of derived temperatures
for Class V, IV and III stars by empirical functions is discussed and
formulae given. An estimate is given for the probable error of each
temperature determination.
Title: On the determination of the solar iron abundance using Fe I
lines. Comments on a paper by H. Holweger et al.
Authors: Blackwell, D. E.; Smith, G.; Lynas-Gray, A. E.
Bibcode: 1995A&A...303..575B
Altcode:
We comment on a response by Holweger et al. (1995) to a recent
paper concerning the solar abundance of iron as determined using
low-excitation Fe I lines (Blackwell et al. 1995). In particular we
consider in detail the precision of oscillator strengths determined by
emission and absorption methods and present evidence for the superior
accuracy of those measured by the absorption technique. Arguments
are given which suggest that the original analysis of Blackwell et
al. (1984), leading to a `high' solar iron abundance as determined
from low-excitation Fe I lines using the Holweger-Mueller model solar
atmosphere, is substantially correct.
Title: On the determination of the solar iron abundance using Fe
I lines.
Authors: Blackwell, D. E.; Lynas-Gray, A. E.; Smith, G.
Bibcode: 1995A&A...296..217B
Altcode:
There presently exist two main-stream solar iron abundances determined
using Fe I lines; a `high' value of which 7.67+/-0.03 (Blackwell
et al. 1984) is typical, and a `low' value typified by 7.50+/-0.07
(Holweger et al. 1991). The `low' abundance agrees with determinations
using Fe II lines, and with the meteoritic value. The two Fe I values
differ by 48 per cent. An in-depth discussion of the two results,
and possible reasons for their difference, is given in the present
paper. It is concluded that the Fe I lines with excitation energy
less than 2.6eV do indeed show a `high' abundance when interpreted
using the Holweger-Mueller empirical model atmosphere. The adoption
of less accurate oscillator strengths and equivalent widths, and less
suitable damping constants, all account, in our opinion, for the `low'
value found by Holweger et al. (1991). However, analyses identical to
those of Blackwell et al. (1984) which use the Kurucz (ATLAS9) and the
new MARCS model atmospheres instead of the Holweger-Mueller empirical
atmosphere, show a `low' abundance in reasonable agreement with the
results of Fe II analyses and the meteoritic determination. These
numerical models, however, are less successful at reproducing observed
limb-darkening than the Holweger-Mueller empirical model, although the
ATLAS9 model reproduces the ultraviolet continuous flux better than
the Holweger-Mueller atmosphere. Existing numerical and empirical
solar model atmospheres would therefore appear to be inadequate;
they cannot both match the observed limb-darkening and emergent flux,
and give a consistent iron abundance determination based on Fe I and
Fe II lines of all excitations.
Title: VizieR Online Data Catalog: Teff and angular diameters from
IRFM (Blackwell+ 1994)
Authors: Blackwell, D. E.; Lynas-Gray, A. E.
Bibcode: 1994yCat..32820899B
Altcode:
Not Available (14 data files).
Title: Stellar effective temperatures and angular diameters determined
by the infrared flux method (IRFM) : revisions using improved Kurucz
LTE stellar atmospheres.
Authors: Blackwell, D. E.; Lynas-Gray, A. E.
Bibcode: 1994A&A...282..899B
Altcode:
Infrared flux method (IRFM) determinations of stellar effective
temperatures and angular diameters are revised using new Kurucz local
thermodynamic equilibrium (LTE) line-blanketed model atmospheres,
which more accurately predict the emergent stellar radiation flux than
models used previously. An improved method for deriving integrated
stellar fluxes is described, together with polynomial coefficients
for evaluating them from V and V-K. Tables were given for making
small corrections appropiate to changes in log g, metallicity, flux
calibration in J, K and L and interstellar extinction, to avoid the
need for additional tabular material. The determined temperatures are
expressed in terms of V and V-K, giving a mean absolute deviation of
0.53%. A comparison of the derived angular diameters for three stars
with determinations using Michelson interferometer shows an average
agreement to better than 1%.
Title: Standard stars for the Infrared Space Observatory, ISO.
Authors: van der Bliek, N. S.; Bouchet, P.; Habing, H. J.; Jourdain
de Muizon, M.; Blackwell, D. E.; Gustafsson, B.; Hammersley, P. L.;
Kessler, M. F.; Lim, T. L.; Manfroid, J.; Metcalfe, L.; Salama, A.
Bibcode: 1992Msngr..70...28V
Altcode:
No abstract at ADS
Title: Data for Absorption Line Analysis
Authors: Blackwell, D. E.
Bibcode: 1992eatc.conf...28B
Altcode:
No abstract at ADS
Title: Derivation of stellar integrated flux from photometric indexes.
Authors: Blackwell, D. E.; Petford, A. D.
Bibcode: 1991A&A...250..459B
Altcode:
Relationships between stellar integrated fluxes and the photometric
indices B, V, I, K are discussed. Formulas based on a recent database of
measured integrated fluxes are derived; these may be used to determine
integrated fluxes for interstellar extinction A(v) = 0.0 from sets of
values of V and V - K, or V and B - V, or R and R - I. A representation
with an accuracy of the order of 2 percent or better is attainable. A
table of corrections for interstellar extinction is given.
Title: Effect of improved H- opacity on the infrared flux
method temperature scale and derived angular diameters. Use of a
self-consistent calibration.
Authors: Blackwell, D. E.; Lynas-Gray, A. E.; Petford, A. D.
Bibcode: 1991A&A...245..567B
Altcode:
The present study uses the infrared flux method (IRFM) to derive
the stellar temperatures and angular diameters derived by Blackwell
et al. (1990). The more accurate calculations of the H(-) opacity
recommended by John (1988) are applied. A Vega self-consistent infrared
calibration is derived using the IRFM. Relations are given to allow
temperatures to be derived from measurements of V-K and B-V. The
original temperatures are increased by up to 1.3 percent, and the
angular diameters are decreased by up to 2.7 percent. The effect of
uncertainties in the H(-) opacity and convection on determined values
of angular diameter and Te is assessed. The chief remaining uncertainty
arises from the absence of a well-established infrared calibration
for Vega.
Title: Determination of temperatures and angular diameters of 114
F-M stars using the infrared flux method (IRFM).
Authors: Blackwell, D. E.; Petford, A. D.; Arribas, S.; Haddock,
D. J.; Selby, M. J.
Bibcode: 1990A&A...232..396B
Altcode:
Temperatures and angular diameters are derived for 114 F-M stars
using the infrared flux (IRFM) method and initially both the Vega
flux calibrations of Dreiling and Bell (DB), and of Mountain et
al. (1985). The DB calibration gives a significantly smaller variation
of temperature with wavelength (0.10%) than the Mountain one (1.59%),
and we adopt the DB one for the final results. Apart from a few
substantial deviations, the temperatures agree well (standard deviation
0.12%), for overlapping stars with the adopted temperatures of Bell
and Gustafsson using synthetic colours. Plots of temperature against
V-Kn, where Kn is a narrow band filter in the K
region, show a mean standard deviation in temperature of 0.46%. It is
suggested that the temperatures have an order of accuracy of better
than 1 %, but the accuracy is critically dependent on that of the
infrared calibration of Vega, which remains uncertain. The possibility
of using IRFM angular diameters as a method of detecting unresolved
binary stars is discussed.
Title: An appraisal of the accuracy of furnace of measurements;
their extension by use of a hollow cathode source
Authors: Blackwell, D. E.
Bibcode: 1990asos.conf..160B
Altcode:
No abstract at ADS
Title: The Instrumental Profile of a DAO 1.22m Telescope Coude
Spectrograph in First and Second Orders, with Reticon Detector
Authors: Booth, A. J.; Blackwell, D. E.; Fletcher, J. M.
Bibcode: 1990PDAO...18....1B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the period 1 Aug 1987 - 31 Jul 1988.
Authors: Blackwell, D. E.
Bibcode: 1989QJRAS..30..345B
Altcode: 1989QJRAS..30..345.
No abstract at ADS
Title: Determination of the absolute flux from VEGA at 2.250 mu-m.
Authors: Booth, A. J.; Selby, M. J.; Blackwell, D. E.; Petford, A. D.;
Arribas, S.
Bibcode: 1989A&A...218..167B
Altcode:
A measurement of the absolute flux from Vega at wavelength of 2.250
microns by comparison with a standard source is presented. The result
is 3.86 10 to the -10 W/sq m micron, with a probable error of 4 percent,
in fair agreement with other determinations made by this method.
Title: Stellar integrated fluxes in the wavelength range 380 NM -
900 NM derived from Johnson 13-colour photometry.
Authors: Petford, A. D.; Blackwell, D. E.
Bibcode: 1989A&AS...78..511P
Altcode:
Petford et al. (1988) have reported measured integrated fluxes for
216 stars with a wide spread of spectral type and luminosity, and
mentioned that a cubic-spline integration over the relevant Johnson
13-color magnitudes, converted to fluxes using Johnson's calibration,
is in excellent agreement with those measurements. In this paper a list
of the fluxes derived in this way, corrected for a small dependence
on B-V, is given for all the 1215 stars in Johnson's 1975 catalog with
complete entries.
Title: Revision of the absolute scale of the Oxford TI I oscillator
strengths and the solar titanium abundance
Authors: Grevesse, N.; Blackwell, D. E.; Petford, A. D.
Bibcode: 1989A&A...208..157G
Altcode:
The Oxford relative oscillator strengths for Ti I (0.00eV-2.31eV),
previously placed on an absolute scale using data from the Bell
et al. (1975) atomic beam technique and lifetimes obtained by the
beam-foil technique, are placed on a more accurate, absolute scale
using the precise lifetime measurements of Rudolph and Helbig (1982)
obtained by selective pulsed laser excitation in an atomic beam. As
a consequence, it is proposed that all published Oxford oscillator
strengths for Ti I should be increased by 0.056 dex (14 percent). The
corresponding titanium solar abundance found from their use should be
decreased to log A = 4.99.
Title: Measurement of relative oscillator strengths for NI I -
Transitions from levels a3F4-2(0.00-0.27 eV), a3D3-1(0.03-0.21 eV)
and a1D2(0.42 eV)
Authors: Blackwell, D. E.; Booth, A. J.; Petford, A. D.; Laming, J. M.
Bibcode: 1989MNRAS.236..235B
Altcode:
Measurements of relative oscillator strengths, made using the Oxford
spectroscopic furnace, are reported for 75 lines of Ni I covering the
wavelength range 298-397 nm and excitation range 0.00-0.42 eV. The
relative values, which have an uncertainty of about 0.7 per cent, are
placed on an absolute scale using principally the lifetime measurements
of Becker et al. (1974). Comparisons are made with the results of other
experiments, and the accuracy of current measures of branching ratios
and lifetimes assessed.
Title: Stellar integrated fluxes for 216 stars in the wavelength
range 380nm-900nm.
Authors: Petford, A. D.; Blackwell, D. E.; Booth, A. J.; Haddock,
D. J.; Leggett, S. K.; Mountain, C. M.; Selby, M. J.; Arribas, S.
Bibcode: 1988A&A...203..341P
Altcode:
The paper reports measurements of the integrated fluxes over the
wavelength range 380 nm - 900 nm for 216 stars using a Reticon
spectrometer in conjunction with the 1 m Kapteyn telescope of the
Observatorio del Roque de los Muchachos of the Instituto de Astrofisica
de Canarias. Methods are proposed for deriving visible integrated
fluxes from 13-colour photometry, UBVRI and BV photometry. Such fluxes
are useful for deriving stellar effective temperatures and angular
diameters.
Title: Narrow band 1 mu.m-4 mu.m infrared photometry of 176 stars.
Authors: Selby, M. J.; Hepburn, I.; Blackwell, D. E.; Booth, A. J.;
Haddock, D. J.; Arribas, S.; Leggett, S. K.; Mountain, C. M.
Bibcode: 1988A&AS...74..127S
Altcode:
Observations of 176 stars have been obtained by filter photometry
over the 1-4 micron range at the Observatorio del Teide in
Tenerife. Measurements for Jn, Kn, and Ln relative to Vega are
presented, along with the probable errors of those stars observed for
several nights during two of the three observing sessions. Mean quoted
probable errors of 0.018 m for Jn, 0.016 for Kn, and 0.027 for Ln are
found. Transformations between the present narrow band magnitudes and
Johnson magnitudes are presented.
Title: An LTE analysis of the solar photospheric TI I and CR I
Spectra - Evidence for non-LTE in excitation
Authors: Blackwell, D. E.; Booth, A. J.; Menon, S. L. R.; Petford,
A. D.
Bibcode: 1987A&A...180..229B
Altcode:
An analysis is made of the Ti I(0.0eV-2.3 eV) and CrI (0.94 eV-3.5
eV) lines in the solar photospheric spectrum, using Oxford oscillator
strengths and damping constants in conjunction with the Holweger-Mueller
solar model atmosphere and a theoretical model constructed following
Gustafsson et al. (1975). The 1 eV Ti I lines at disk center give a
very narrow minimum dispersion in the (log abundance, microturbulence)
diagram with standard deviation 0.014 dex (3.3 percent), but over
the whole range of excitation log A changes regularly with multiplet
number, reaching a peak at 50 and declining to an apparent constancy
at high number In contrast to this, the Cr I lines how a large almost
random spread in log A at low excitation, standard deviation 0.098 dex
(25 percent), with a tendency to a constant value at high multiplet
numbers. It is suggested that these effects are due to non-LTE rather
than to errors in the Ti I and Cr I oscillator strengths or the solar
equivalent widths. The Cr I lines of multiplet 18 are particularly
anomalous. Evidence for a damping enhancement of order 1.1 for 1 eV
TiI lines is discussed.
Title: The infrared flux method and its use for study of alpha Boo,
MU HER and beta Dra; relation to the VEGA 1.2-5mu.m infrared excess.
Authors: Blackwell, D. E.; Booth, A. J.; Petford, A. D.; Leggett,
S. K.; Mountain, C. M.; Selby, M. J.
Bibcode: 1986MNRAS.221..427B
Altcode:
The effective temperatures of α Boo, μ Her, and β Dra are determined
using the infrared flux method. The determinations are based on the
high-quality spectrophotometric data obtained from an aircraft by
Strecker, Erickson & Witteborn, the new infrared calibration of
Vega obtained from observations made at Tenerife between 1979 and 1983,
the use of a Reticon spectrometer to determine the integrated fluxes
in the region 370-950 nm, and the use of model atmospheres constructed
with the MARCS code developed by Gustafsson et al. Temperatures for α
Boo and β Her are also given using the Dreiling & Bell (DB) Vega
calibration in association with the Hanbury-Brown, Davis & Allen
angular diameter for Vega. The large and uncertain reddening for β Dra
prevents the accurate determination of a reliable temperature for this
star. The Tenerife and Dreiling & Bell infrared calibrations for
Vega are considered in relation to the apparent variation of effective
temperature with wavelength for α Boo and μ Her given by the infrared
flux method, in an effort to distinguish between them. It is concluded
that improved spectrophotometry is needed for this, with particular
attention paid to the proper identification of continuum windows.
Title: Measurement of relative oscillator strengths for CR I
lines. II - Measures for transitions from levels with excitation
energy 2.54-3.46 eV
Authors: Blackwell, D. E.; Booth, A. J.; Menon, S. L. R.; Petford,
A. D.
Bibcode: 1986MNRAS.220..303B
Altcode:
Relative oscillator strengths for 53 lines of Cr I, with excitation
energies between 2.54 and 3.46 eV, have been measured using the
Oxford spectroscopic furnace. The oscillator strengths for lines
in the region of 2.5 eV have been placed on an absolute scale by
comparison with 1 eV Cr I lines through temperatures measured using
photoelectric pyrometry. The lifetime measurements by Kwiatowski et
al. have also been used. The two methods agree to better than 1 per
cent. This absolute scale has been extended to lines of excitation 3.5
eV using photoelectric pyrometry. The accuracy of relative oscillator
strengths within this range of excitation is about 1 per cent, whilst
that of the absolute scale is about 7 per cent. Comparison is made
with the experimental results and calculations of other authors.
Title: Measurement of the oscillator strengths of very weak 1 eV Fe
I lines.
Authors: Blackwell, D. E.; Booth, A. J.; Haddock, D. J.; Petford,
A. D.; Leggett, S. K.
Bibcode: 1986MNRAS.220..549B
Altcode:
Relative oscillator strengths are measured for nine very weak 1-eV
Fe I lines, using the Oxford spectroscopic furnace. These oscillator
strengths are placed on an absolute scale using previous Oxford
measurements of stronger 1-eV Fe I lines. The lines are important for
the interpretation of cool star spectra because they are the weakest
Fe I lines in such spectra whose oscillator strengths are known with
good accuracy. Their accuracy is assessed through an interpretation
of the corresponding lines in the center of disk solar spectrum. It
is suggested that the accuracy is 0.015 dex (3.5 percent).
Title: Measurement of relative oscillator strengths for Ti I -
IV. Transitions from levels of excitation energy between 1.42 and
2.31 eV.
Authors: Blackwell, D. E.; Booth, A. J.; Menon, S. L. R.; Petford,
A. D.
Bibcode: 1986MNRAS.220..289B
Altcode:
Measurements of the relative oscillator strengths of 52 lines of
Ti I with excitation potential between 1.42 eV and 2.31 eV, made
to an accuracy of 1 per cent using the Oxford furnace technique,
are reported. The absolute scale for Ti I derived in a previous
paper in this series for 0 eV lines, is rediscussed using the
additional oscillator strengths for high excitation lines contained
in this paper. No change is suggested, and all the relative oscillator
strengths are placed on this absolute scale. Comparisons are made with
the calculated values of Kurucz and Peytremann, the solar values of
Kostyk, and with other experimental results. This paper ends the present
study of Ti I lines using the 3-pass system with the Oxford furnace,
and comparisons are made between all the 137 Oxford oscillator strengths
so far measured and other data. Empirical conversion formulae are given.
Title: The effective temperatures, diameters and luminosities of 22
bright stars by application of the infrared flux method.
Authors: Leggett, S. K.; Mountain, C. M.; Selby, M. J.; Blackwell,
D. E.; Booth, A. J.; Haddock, D. J.; Petford, A. D.
Bibcode: 1986A&A...159..217L
Altcode:
The infrared flux method is used to determine the effective
temperatures and angular diameters of 22 bright stars of various
spectral types. Their parallaxes are combined with the angular
diameters to give linear radii, and with the observed integrated
fluxes to give luminosities. The ratios of stellar integrated flux
to infrared monochromatic flux required by the method were computed
using published Kurucz (1979) model atmospheres and STARLINK generated
MARCS models. These are compared to the observed values of the ratios,
derived using ultraviolet and infrared data taken from the literature,
and visible data obtained by the authors in Tenerife in 1982. A new
absolute infrared calibration of Vega is used. With the present infrared
data, the accuracy of the derived stellar effective temperatures is
about 2.5 percent and of the angular diameters 6 percent, for spectral
types later than A5. The accuracy rapidly becomes worse for earlier
types because of the uncertainty in the ultraviolet component of the
integrated fluxes. Good agreement is found with other determinations
of effective temperatures and angular diameters, including those using
the intensity interferometer.
Title: Erratum - Measurement of Stellar Integrated Flux in the
Wavelength Range 370-NM to 950-NM
Authors: Petford, A. D.; Leggett, S. K.; Blackwell, D. E.; Booth,
A. J.; Mountain, C. M.; Selby, M. J.
Bibcode: 1985A&A...153..284P
Altcode:
No abstract at ADS
Title: Measurement of the absolute flux from VEGA at 4.92 mu.m.
Authors: Mountain, C. M.; Leggett, S. K.; Selby, M. J.; Blackwell,
D. E.; Petford, A. D.
Bibcode: 1985A&A...151..399M
Altcode:
Observations have been made of the absolute infra-red flux from Vega
at 4.92 microns by comparison with a standard furnace, using the 1.5
m flux collector at the Observatorio del Teide, Tenerife. To avoid
difficulty over the determination of atmospheric extinction in the
water vapor region, observations were made in a narrow wavelength
window which is relatively free of water vapor lines, isolated with
the Imperial College cooled grating spectrometer. The results confirm
previous observations at Tenerife of an infra-red excess from Vega
relative to the model of Dreiling and Bell (1980) over the range 2-5
microns. A summary calibration for the wavelength range 1.24-5 microns
is proposed based on these and previous observations that have been
made as part of a continuing programme at Tenerife.
Title: Measurement of stellar integrated flux in the wavelength
range 370 nm-950 nm.
Authors: Petford, A. D.; Leggett, S. K.; Blackwell, D. E.; Booth,
A. J.; Mountain, C. M.; Selby, M. J.
Bibcode: 1985A&A...146..195P
Altcode:
A technique is described for the measurement of stellar integrated flux
over the range 370 nm to 950 nm using a spectrometer with a Reticon
detector for comparison with a standard star. Data from Johnson
and Mitchell 13-colour photometry are included in the analysis of
observations. Absolute flux measurements are presented for 30 stars,
together with values corrected for interstellar extinction.
Title: Use of the recent Oxford data to calibrate the MN I oscillator
strengths measured by Warner and Bowell
Authors: Booth, A. J.; Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1984Obs...104..265B
Altcode:
A formula is given for calibrating the 610 Mn I oscillator strengths
measured in emission by Warner and Bowell (WB) against the more accurate
Oxford data. The standard deviation for log gf(WB, corrected) - log
gf(Oxford) is 0.10 dex (26 per cent), compared with the standard
deviation of 0.21 dex (62 per cent) for the uncorrected data. The
change in absolute scale, resulting chiefly from the use of recent
lifetime measurements in the Oxford calibration, is 0.72 dex (×5.3).
Title: Analysis of MN I lines in the solar spectrum using accurate
oscillator strengths
Authors: Booth, A. J.; Blackwell, D. E.; Shallis, M. J.
Bibcode: 1984MNRAS.209...77B
Altcode:
An analysis is presented of both weak and strong lines of Mn I with
well-defined profiles in the solar photosphere, using the accurate
oscillator strengths measured at Oxford. In an LTE analysis with the
Holweger and Mueller (1974) model solar atmosphere a manganese abundance
of log A = 5.39 at a microturbulence value of 0.85 km/s is found for the
disk center. Comparison of this result with the Oxford determination
for the solar iron abundance shows an interesting discrepancy with
the Fe/Mn ratio found in type C I meteorites.
Title: Measurement of relative oscillator strengths for MN I
Transitions from levels in the range chi between 0 eV and 3 eV
Authors: Booth, A. J.; Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1984MNRAS.208..147B
Altcode:
The authors present relative oscillator strengths for 58 lines of Mn
I for a range of +0.19 > log (gf) > -3.795 in the excitation
interval 0 eV < χ < ≡3 eV. The measurements have been made to
a relative accuracy of better than 2 per cent using the Oxford furnace
technique, with full allowance for hyperfine structure using the data
of Booth et al. The relative values have been placed on an absolute
scale using published lifetime data, to an accuracy of about 7 per cent
for the ground state lines and 3 per cent for the excited state lines.
Title: Measurement of relative oscillator strengths for CR I lines. I
- Measures for transitions from levels a7S3(0.00eV), a5S2(0.94eV)
and a5D0-4(0.96-1.03eV)
Authors: Blackwell, D. E.; Menon, S. L. R.; Petford, A. D.
Bibcode: 1984MNRAS.207..533B
Altcode:
Relative oscillator strengths of 49 lines of Cr I with excitation
energies of up to 1.03 volts have been measured using the Oxford
spectroscopic furnace to an accuracy of better than 1 percent. Where
direct relative measurements could not be made because of the largeness
of the ratios of oscillator strengths, the values obtained by Huber
and Sandeman (1977) using the hook method were adopted. The relative
measures are placed on an absolute scale using lifetime data, and
comparisons are made with data from other authors.
Title: Is there an abundance anomaly for the 2.2eV Fe I lines in
the solar spectrum?
Authors: Blackwell, D. E.; Booth, A. J.; Petford, A. D.
Bibcode: 1984A&A...132..236B
Altcode:
A recent study of Fe I lines in the solar spectrum using Oxford
oscillator strengths has shown that the mean solar abundance for
the eight 2.2 eV lines is about 16 percent smaller than that for all
lines in the range 0 eV-2.6 eV. To test whether this anomaly is due
to errors in the Oxford oscillator strengths, the previous comparison
of oscillator strengths for the 2.2 eV lines (which are apparently
anomalous) and the 2.4 eV lines (which are apparently normal) has
been repeated. The new measurements are in substantial agreement
(approximately 1.5 percent) with those already reported. A solar anomaly
is also discernable when the oscillator strengths of other authors are
used. Possible errors in the interpretation of the solar spectrum are
discussed and it is concluded that the anomaly is real.
Title: Absolute calibration of the infrared flux from Vega at 1.24,
2.20, 3.76 and 4.6 μm by comparison with a standard furnace.
Authors: Blackwell, D. E.; Leggett, S. K.; Petford, A. D.; Mountain,
C. M.; Selby, M. J.
Bibcode: 1983MNRAS.205..897B
Altcode:
A determination has been made at Tenerife of the absolute monochromatic
flux from Vega at 1.24, 2.20, 3.76 and 4.6 μm with an accuracy of
3 per cent for λ < 4 μm and ≡12 per cent for λ > 4 μm,
using a calibrated furnace as standard. The technique differs in detail
from that used for similar observations in 1980. The results confirm
in general those obtained in 1980, especially at λ ≡ 3.8 μm. Both
the 1980 and the 1981 observations show an excess flux of about 7 per
cent for λ > 2 μm compared to that calculated by Dreiling &
Bell using their model atmosphere for Vega.
Title: Measurement of relative oscillator strengths for Ti
I. III. Weak transitions from levels a3F3,4
(0.02 eV, 0.05 eV), a5F1-5 (0.81 eV - 0.85 eV),
a1D2 (0.90 eV), a3P0-3
(1.05 eV - 1.07 eV) with solar analysis.
Authors: Blackwell, D. E.; Menon, S. L. R.; Petford, A. D.
Bibcode: 1983MNRAS.204..883B
Altcode:
The relative oscillator strengths presently given for 18 weak 1-eV and
two 0-eV lines of Ti I have been measured with a relative accuracy of
5 percent by means of the Oxford furnace technique. Relative values are
placed on the absolute scale previously derived for stronger 0- and 1-eV
lines, and a solar analysis is made for the most suitable lines as a
test of their oscillator strengths. Although this is not regarded as a
definitive solar analysis, because of the weakness of the solar lines,
the value of log A = 5.08, with a microturbulence value of 0.89 km/sec,
both agree well with those already found for stronger 0-eV lines.
Title: The effect of hyperfine structure on stellar abundance analysis
Authors: Booth, A. J.; Blackwell, D. E.
Bibcode: 1983MNRAS.204..777B
Altcode:
The authors present a general but quantitative analysis of the effect
of hyperfine structure on the analysis of stellar spectra in terms
of the elemental abundances deduced. It is shown that the effects
are larger than is sometimes appreciated, even on the linear portion
of the curve of growth where the effect is generally considered to be
"small". It is indicated that the available data on hyperfine structures
are generally of insufficient accuracy for high quality analysis.
Title: Empirical improvement in accuracy of atomic oscillator
strengths calculated by Kurucz and Peytremann
Authors: Blackwell, D. E.; Booth, A. J.; Menon, S. L. R.; Petford,
A. D.; Smith, G.
Bibcode: 1983MNRAS.204..141B
Altcode:
The oscillator strengths for lines of Fe I, Ti I, Ti II, Cr I, Mn I,
Ca I, together with solar Fe II values as calculated by Kurucz and
Peytremann (1975) are compared with the measured values made at Oxford
(Blackwell et al., 1979-1983). It is determined that the deviations
between the two sets of oscillator strength data for individual
multiplets are much smaller than the average deviation for all lines
of each element. It is demonstrated that the oscillator strengths
calculated by the semi-empirical method of Kurucz and Peytremann may
be calibrated in this way to give oscillator strengths of improved
accuracy which would be more useful for the construction of model
stellar atmospheres and for use in spectral synthesis work. Several
methods for implementing this calibration are presented. A test of
the method using 407 lines of these elements is found to give standard
deviations of errors of less than 0.1 dex, with the omission of a few
lines. A theoretical interpretation of the regularities in errors is
also presented.
Title: Measurement of the absolute monochromatic flux from VEGA at
Lambda 2.20 and Lambda 3.80 microns by comparison with a furnace.
Authors: Selby, M. J.; Mountain, C. M.; Blackwell, D. E.; Petford,
A. D.; Leggett, S. K.
Bibcode: 1983MNRAS.203..795S
Altcode:
A determination has been made using the 1 .5-m flux collector at
Tenerife of the absolute monochromatic flux from Vega at 2.20 and
3.80 gm by comparison with the flux from a furnace which has been
calibrated against a standard blackbody at a known temperature. The
technique used is an improvement on one previously used by the authors
at Tenerife in 1979. The fluxes found are 3.92×10-10
Wm-2μm-1 at 2.20μm, and 5.28×10-11
Wm-2 μm-1 at 3.80μm, each with an accuracy
of about 4 per cent. The new determination of the 2.20μm flux is
more reliable than the one obtained at Tenerife in 1979, and it is
recommended that the new determination replaces it. Comparison is made
with other calibrations and with calculated fluxes. The agreement with
other calibrations is good, but comparison with the flux calculations
of Dreiling & Bell for their model shows an observed excess flux
of 8 per cent at 3.80μm. Suggestions are made to account for this
excess. An empirical flux distribution over the wavelength range 1μm
< λ < 4μm is proposed with a likely accuracy of 3 per cent.
Title: Measurements of relative oscillator
strengths for FeI: Transitions from levels
b3F2-4(2.61eV-2.56eV). Use of a miltipass
Authors: Blackwell, D. E.; Petford, A. D.; Simmons, G. J.
Bibcode: 1982MNRAS.201..595B
Altcode:
The design of a three-pass optical system for use with the Oxford
spectroscopic furnace is described. Relative oscillator strengths of
16 lines of Fe I (2.56 eV < χ < 2.61 eV, -0.9 > log gf >
-2.7) measured by its use are presented. The accuracy of the relative
values for the stronger lines is 0.006 dex (1.4 per cent) but some
of the weaker lines have an accuracy of only 0.03 dex (7 per cent)
because of possible blending. The relative values have been placed
on an absolute scale through a comparison with Fe I 371.99 via Fe
I lines of excitation energy 1.5 eV. Comparisons are made with the
data of other experimenters and with theoretical values. A formula
is proposed for adjusting the experimental results of Bridges &
Kornblith to bring them into better agreement with the Oxford results.
Title: Precision measurement of relative oscillator strengths for
TI II. I - Transitions from levels /a-4/-F/3/2-9/2/ /0.00-0.05 eV/,
/b-4/-F/5/2-9/2/ /0.12-0.15 eV/
Authors: Blackwell, D. E.; Menon, S. L. R.; Petford, A. D.
Bibcode: 1982MNRAS.201..603B
Altcode:
Relative oscillator strengths measured with an accuracy of 0.5 per
cent using the Oxford furnace technique are given for 18 lines of Ti
ii having excitation energies of up to 0.15eV. The relative values
have been put on an absolute scale by use of lifetime measurements.
Title: Precision measurement of relative oscillator strengths for Ti
I. II. Transitions from levels a-5 -F 1-4 (0.81-0.84 eV), a-1 -D 2
(0.90 eV) and a-3 -P 0-2 (1.5-1.07 eV)
Authors: Blackwell, D. E.; Menon, S. L. R.; Petford, A. D.; Shallis,
M. J.
Bibcode: 1982MNRAS.201..611B
Altcode:
Relative oscillator strengths are given for 22 lines of Ti I in the
range 0.81 eV < X < l.07 eV, 428nm < λ < 843 nm and +0.50
> log gf > -l.47 measured in absorption using the Oxford furnace
technique with an accuracy of 0.5 per cent. The relative values have
been placed on an absolute scale to an estimated accuracy of 12 per
cent by comparison with 0eV Ti I lines, relative measures of which
have previously been placed on an absolute scale using lifetime and
atomic beam measurements. Comparisons are made with the data of other
experimenters and with theoretical values.
Title: Analysis of Fe I lines /chi between 0.00 eV. and 2.6 eV/
in the solar spectrum using improved damping constants and accurate
oscillator strengths - Test of a solar model atmosphere
Authors: Simmons, G. J.; Blackwell, D. E.
Bibcode: 1982A&A...112..209S
Altcode:
An analysis is made of the equivalent widths of 26 well defined Fe I
lines in the solar spectrum measured at five disk positions and in the
radiation from the integrated disk. Damping constants based on the
measurement of strong solar lines, and on laboratory experiments,
together with oscillator strengths measured at Oxford, are used
in the analysis. Iron abundances and microturbulent velocities are
determined using an LTE analysis with the Holweger and Müller (HM)
solar model atmospheres. For this atmosphere the derived iron abundance
varies significantly with excitation potential, with the 2.2 eV lines
standing out as anomalous. It seems unlikely that this anomaly arises
from an inaccurate temperature structure for the model atmosphere. One
purpose of the study is to test the ability of a model atmosphere to
account for the Fe I spectrum across the disc. The HM model atmosphere
performs well in this respect. It gives a mean abundance with excitation
potential of log A =7.63.
Title: Note on the interpretation of Fe I lines /2.18-2.49 eV/
in the solar spectrum
Authors: Blackwell, D. E.; Shallis, M. J.; Simmons, G. J.
Bibcode: 1982MNRAS.199...33B
Altcode:
Fourteen Fe I lines (2.18 eV < χ < 2.4eV) in the centre of disc
solar spectrum are analysed using Oxford oscillator strengths of 1 per
cent accuracy. The iron abundances and microturbulence velocities given
by these lines are discussed. The five lines with excitation energies
2.40-2.48 eV apparently give a higher abundance than the nine lines
of excitation energy 2.18-2.22eV.
Title: Interpretation of TI I lines of excitation energy 0.0-0.05 eV
in the solar spectrum - Use of new oscillator strengths of accuracy
0.5 per cent
Authors: Blackwell, D. E.; Shallis, M. J.; Simmons, G. J.
Bibcode: 1982MNRAS.199...37B
Altcode:
An analysis is made of the seven most suitable 0 eV Ti I lines in the
spectrum of the centre of the solar disc, using oscillator strengths
of 0.5 per cent relative accuracy, and the solar model atmospheres
of Holweger & Müller, and Vernazza et al. The solar abundance of
titanium is found to be log A = 5.08 and the microturbulence is 1.00
km s-1, using the preferred atmosphere of Holweger &
Müller.
Title: Precison measurements of relative oscillator
strengths. IX. Measures of Fe I transitions for the
levels a5P1-3(2.18-2.28eV),
a3P2(2.28eV),
a3P0,1(2.49-2.42eV), z
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.; Simmons,
G. J.
Bibcode: 1982MNRAS.199...43B
Altcode:
Measurements are presented of the relative oscillator strengths of 52
lines of Fe I, with excitation energies of between 2.18 and 2.49 eV, and
with log gf > -3.23, made using the Oxford furnace technique. These
measures have a relative accuracy of 0.004 dex (1 per cent). Absolute
values are also given with an accuracy of 2.5 per cent, assuming log gf
(371.99) = -0.43 ± 0.01 (2.3 per cent). Comparisons are made with other
experimental data and with the results of theoretical calculations. An
expression is proposed for correcting the measured oscillator strengths
of Corliss & Warner to give data having an rms deviation from the
Oxford values of 0.14 dex, compared with an rms deviation of 0.55 dex
for uncorrected data. Measures previously published for six lines are
regarded as unsafe, chiefly because of uncertain blending, and these
are withdrawn. The previous measurement for λ381.453 is corrected.
Title: Precision measurement of relative oscillator strengths for Ti
I.- I. Transitions from levels a3 F2 (0.00 eV) and a3 F3 (0.02 eV)
and a3 F4 (0.05 eV) measured with an accuracy of 0.5 per cent.
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.; Leggett, S.
Bibcode: 1982MNRAS.199...21B
Altcode:
The paper presents measures of the relative oscillator strengths of
45 ground state lines of Ti I, for the range +0.215 > log gf >
-3.84, made with an accuracy of 0.5 per cent using the Oxford furnace
technique. The relative measurements have been placed provisionally
on an absolute scale using the atomic beam measurements of Bell et
al. and the lifetimes measured by Roberts et al.. This scale has an
accuracy of about 12 per cent. Comparisons are made with the measured
values of other experimenters and with the results of calculations.
Title: Department of Astrophysics University of Oxford
Authors: Blackwell, D. E.
Bibcode: 1982QJRAS..23..388B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the period 1979 August 1 to 1980 July 31.
Authors: Blackwell, D. E.
Bibcode: 1981QJRAS..22..197B
Altcode:
No abstract at ADS
Title: Measurement of the absolute flux from VEGA in the K band
(2.2 MU m).
Authors: Selby, M. J.; Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1980MNRAS.193..111S
Altcode:
A method is described for determining absolute stellar flux in the
infrared, based on a direct comparison between a star and a furnace at
a known temperature. Observations have been made of Vega in the K band
(2.2 microns) using the Tenerife flux collector. The absolute flux
from this star at the earth, reduced to the wavelength 2.20 microns,
is found to be 0.375 x 10 to the -9th W/sq m-micron with an uncertainty
of 8 per cent.
Title: Precision measurement of relative oscillator
strengths. VIII. Measures of Fe I transitions from levels
A3F2-4(1.49-1.61eV) with an accuracy of 1 per cent.
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.; Simmons,
G. J.
Bibcode: 1980MNRAS.191..445B
Altcode:
Measurements of relative oscillator strengths are given for 26 lines of
Fe I with excitation energies between 1.49 and 1.61 eV. The measurements
have been made in absorption using the Oxford technique, and have an
accuracy of 0.004 dex (1 per cent). The decrease in accuracy over
previous measurements in this series (0.5 per cent) arises from a
need to economize in electricity consumption. Absolute values with
an accuracy of 0.012 dex (2.8 per cent) are also given assuming that
log gf(371.994) = -0.43 ± 0.01. The effect of damping on the method
of measurement is discussed. Comparisons are made with the calculated
values of Kurucz & Peytremann, the results of other experimenters
and the compilation of Foy.
Title: H. H. Plaskett
Authors: Blackwell, D. E.
Bibcode: 1980Natur.285...58B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford
Authors: Blackwell, D. E.
Bibcode: 1980QJRAS..21..124B
Altcode:
No abstract at ADS
Title: Use of the infra-red flux method for determining stellar
effective temperatures and angular diameters; the stellar temperature
scale.
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1980A&A....82..249B
Altcode:
An alternative method of using the infra-red flux method for
determining stellar effective temperatures and angular diameters
is presented. Tables are presented giving the ratios of integrated
stellar fluxes to monochromatic fluxes as a function of wavelength,
gravity and effective temperature for two model atmospheres. Measured
values of these ratios for 28 stars are used in conjunction with these
tables to determine values of Te and θ for them. The results
have been applied to the construction of a stellar temperature scale
for luminosity class V stars.
Title: Oscillator strengths of Fe II lines derived from the solar
spectrum - Choice of solar model atmosphere
Authors: Blackwell, D. E.; Shallis, M. J.; Simmons, G. J.
Bibcode: 1980A&A....81..340B
Altcode:
The Fe II solar spectrum is interpreted using oscillator strengths
measured by Baschek et al., and the results used in conjunction with
Fe I analyses to make a choice between the solar model atmospheres
of Holweger and Müller, and of Vernazza et al. It is suggested that
the Holweger and atmosphere describes these two spectra better. Solar
oscillator strengths for 42 lines of Fe II are given with a suggested
accuracy of ±015 dex and comparisons made with the calculated values
of Kurucz and Peytremann, and measured values.
Title: Radii of single main sequence stars (A0V-G2V) : comparison
with radiidetermined using binary systems.
Authors: Shallis, M. J.; Blackwell, D. E.
Bibcode: 1980A&A....81..336S
Altcode:
Radii of 12 apparently single stars are determined using angular
diameters derived using the infra-red flux method and published
parallax values. These radii are combined with others determined using
the intensity interferometer for comparison with radii determined for
eclipsing binary systems, which are independent of distance. The two
sets of data agree well. The photometrically determined radii of Gray
are also compared with the infra-red flux values and found to be in
good agreement. Radii are plotted against spectral type and a best
fit found. It is suggested that the observed spread in radius when
plotted against spectral type is due to evolutionary behavior and that
insufficient knowledge is available to draw more detailed conclusions.
Title: The stars as suns.
Authors: Blackwell, D. E.
Bibcode: 1980stun.book...68B
Altcode:
The properties of stars within a few hundred light-years distance of the
sun are discussed with attention to star formation and evolution. The
effective temperature of stars is examined with consideration of
the speckle technique for the measurement of angular diameter. The
stellar inferometer and the infrared flux method are also discussed. A
comparison of the angular diameters obtained for Betelgeuse and Sirius
is provided. The luminosity of stars is addressed, and new techniques
of ascertaining stellar position and distance are reviewed. It is
noted that solar oscillations may permit the determination of the
inner structure of the sun.
Title: Angular diameters, radii, and effective temperatures of
Ap stars.
Authors: Shallis, M. J.; Blackwell, D. E.
Bibcode: 1979A&A....79...48S
Altcode:
The angular diameters and effective temperatures of five Ap stars are
obtained using the infra-red flux method of Blackwell and Shallis
(1977), described more fully by Blackwell et al. (1979). It is
confirmed that previous estimates of effective temperature for these
are too high and that the new temperatures are generally similar to
those found for main sequence stars of the same spectral type. The
spectral classification of Ap stars is discussed in relation to these
new temperatures. Angular diameters are converted to stellar radii using
measured parallaxes. Despite large uncertainties in the distance scale,
the deduced radii are significantly greater than for main sequence A
type stars.
Title: On the composition of H II regions in southern galaxies -
I. NGC 300 and 1365.
Authors: Pagel, B. E. J.; Edmunds, M. G.; Blackwell, D. E.; Chun,
M. S.; Smith, G.
Bibcode: 1979MNRAS.189...95P
Altcode:
AAT/IPCS spectra were obtained from six H II regions at differing
radial distances from the center of the Scd galaxy NGC 300 and from
three H II regions in the giant barred spiral NGC 1365 which has an
active nucleus. The spectra were analyzed to determine abundances of the
elements represented by observed emission lines from a combination of
electron temperatures based on various weak temperature-sensitive lines
and interpolation between photoionization models, using the sum of (O
II) and (O III) intensities relative to the H beta emission to select
plausible model parameters. The NGC 300 and NGC 1365 abundances are
described, noting that the abundances of the latter are fairly close
to solar. One object in NGC 300 is unusual in having stronger (O II)
than usually found in giant H II regions in Scd galaxies, and neon,
sulphur, and argon abundances relative to oxygen are close to those of
Orion and the Magellanic Clouds, while the He/H ratio appears slightly
lower than in Orion.
Title: Department of Astrophysics, University of Oxford. Report for
the period 1977 August 1 to 1978 July 31.
Authors: Blackwell, D. E.
Bibcode: 1979QJRAS..20..282B
Altcode:
No abstract at ADS
Title: The infrared flux method for determining stellar angular
diameters and effective temperatures.
Authors: Blackwell, D. E.; Shallis, M. J.; Selby, M. J.
Bibcode: 1979MNRAS.188..847B
Altcode:
The infrared flux method for deriving stellar angular
diameters and effective temperatures (Blackwell and Shallis) is
elaborated and assessed in relation to the use of the intensity
interferometer. Infrared magnitudes of 17 stars obtained using the
Tenerife flux collector are presented and angular diameters and
effective temperatures for 13 of these stars are derived using the
method. A discrepancy exists between infrared photometry and the
predictions of model atmosphere theory, which is probably the result
of flux calibration errors. It is suggested that given a good flux
calibration, the infrared flux method is capable of greater accuracy
than the intensity interferometer, besides being more versatile.
Title: Obituary - Kluber, Harald-Von
Authors: Dewhirst, D. W.; Blackwell, D. E.
Bibcode: 1979QJRAS..20..475D
Altcode:
No abstract at ADS
Title: Harald von Klüber, 1901 September 6 - 1978 February 14.
Authors: Dewhirst, D. W.; Blackwell, D. E.
Bibcode: 1979QJRAS..20..472D
Altcode:
No abstract at ADS
Title: Interpretation of the solar spectrum 300 - 900 nm - II. Fe I
lines of excitation potential 0.00 - 1.01 eV: use of new oscillator
strengths of 0.5 per cent accuracy.
Authors: Blackwell, D. E.; Shallis, M. J.
Bibcode: 1979MNRAS.186..673B
Altcode:
The solar spectrum is interpreted using Oxford oscillator
strengths for Fe I lines of excitation potential 0.00-1.01 eV of
0.5 percent accuracy. The analysis is used to test the accuracy of
the oscillator strengths and to derive information about the solar
atmosphere. Abundances and microturbulence values are deduced using
the Vernazza, Arnett, and Loeser (1976) model atmosphere and three
other model atmospheres. Using the Vernazza et al. model atmosphere
at mu = 1.0, for the 0 eV lines the microturbulence is 0.78 km/s and
the abundance log A = 7.440, and for 1 eV lines the values are 0.61
km/s and log A = 7.479, implying an increase in microturbulence with
height. Microturbulence values for the integrated disk spectrum are 1.05
and 0.98 km/s, respectively. Until an acceptable model atmosphere is
available the solar abundance of iron derived from the Fe I spectrum
will remain uncertain by at least 0.2 dex. Damping coefficients are
given for seven strong lines, and a curve of growth for the solar
spectrum at mu = 1.0 is also given.
Title: Precision measurement of relative oscillator strengths -
IV. Attainment of 0.5 per cent accuracy. Fe I transitions from levels
a5 D0-4 (0.00-0.12 eV).
Authors: Blackwell, D. E.; Ibbetson, P. A.; Petford, A. D.; Shallis,
M. J.
Bibcode: 1979MNRAS.186..633B
Altcode:
It is shown that the apparatus used at Oxford to measure oscillator
strengths should be capable of a photometric accuracy of better than 1%
when comparing oscillator strengths. Improvements in the apparatus and
procedures are described which were made in an attempt to reach this
theoretical accuracy. Measures for 60 Fe I transitions from levels
a5 D(0-4) are given, including measurements to an accuracy of 0.5%
for most of 37 lines previously measured to a relative accuracy of
5%. The results are compared with previous laboratory data.
Title: Precision measurement of relative oscillator strengths -
VII. Comparison between measured lifetimes of excited Fe I levels
and values calculated from precise oscillator strengths.
Authors: Blackwell, D. E.; Shallis, M. J.
Bibcode: 1979MNRAS.186..669B
Altcode:
Lifetimes of 12 excited levels of Fe I and branching ratios
for radiative deexcitation of these levels are calculated from
Oxford oscillator strengths and compared with various experimental
measurements. It is found that the differences between the calculated
and measured values, and their standard deviations, are rather poor,
except for the results of Figger et al. (1975), for which the mean
deviation is 0.5% and the standard deviation of the differences is
5.8%. It is concluded that the absorption technique used at Oxford
yields the oscillator strengths of excited lines more accurately than
do lifetime measurements.
Title: Precision measurement of relative oscillator strengths
- VI. Measures of Fe I transitions from levels a5
F1-5 (0.86-1.01 eV) with an accuracy of 0.5 per cent.
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1979MNRAS.186..657B
Altcode:
Measurements of relative oscillator strengths are reported for 68 lines
of Fe I with excitation potentials of 0.86 to 1.01 eV and originating
from the levels a5 F(1-5). Evidence is presented to show that the
accuracy of these measurements is about 0.5%. The relative measures
are placed on an absolute scale (with an accuracy of 2.6%) by relating
them to the absolute oscillator strength of the 371.994-nm line. The
results are compared with previous laboratory data.
Title: Precision measurement of relative oscillator strengths -
V. Comparison of oscillator strengths of Fe I transitions from
levels a5 F1-5 (0.86-1.01 eV) and those from
a5 D0-4 (0.00-0.12 eV).
Authors: Andrews, J. W.; Coates, P. B.; Blackwell, D. E.; Petford,
A. D.; Shallis, M. J.
Bibcode: 1979MNRAS.186..651A
Altcode:
A photoelectric pyrometer has been built and used to measure the
temperature of the Oxford spectroscopic furnace on the International
Practical Temperature Scale 1968 to an accuracy of + or - 1 K (3
sigma). Measurements have been made of the relative oscillator strengths
of Fe I absorption lines originating from energy levels separated by
about 1 eV. These measures have an accuracy of about 0.5 percent and are
intended to link existing measures made at Oxford from levels a5 F(1-5)
(0.86-1.01 eV) to measures made from levels a5 D(0-4) (0.00-0.12 eV).
Title: Parallaxes for the Study of Stellar Structure
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1979esa..conf..223B
Altcode:
No abstract at ADS
Title: An optical beam-splitter of variable ratio
Authors: Blackwell, D. E.; Petford, A. D.; Shallis, M. J.
Bibcode: 1978Obs....98..235B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the period 1976 August 1 - 1977 July 31.
Authors: Blackwell, D. E.
Bibcode: 1978QJRAS..19..208B
Altcode:
No abstract at ADS
Title: Obituary: H. von Klüber
Authors: Blackwell, D. E.; Dewhirst, D. W.
Bibcode: 1978Natur.273..414B
Altcode:
No abstract at ADS
Title: Stellar gravities from metallic line profiles, with application
to Arcturus. The effective temperature of Arcturus.
Authors: Blackwell, D. E.; Willis, R. B.
Bibcode: 1977MNRAS.180..169B
Altcode:
Summary. The damping wings of spectral line proriles of metals
are sensitive to gas pressure and may be used to measure stellar
gravity. It is suggested that the method is made insensitive to
effective temperature by measuring the metal abundance from weak lines
that have the same lower level as the strong damping line. The gravity
of Arcturus is determined from the proffle of the line 5269.5 Fe I,
the damping constant having been determined from the profile of the
corresponding solar line. The measured gravity is log g= 1A8 i 0.15
corresponding to a mass of 0.61 * 0.32M0. for an angular diameter
of 0.0201 arcsec. As part of the analysis, the determination of the
effective temperature of Arcturus from the flux distribution in its
spectrum is rediscussed and a revised value of 4400 %6300 is proposed. A
microturbulence of 2.2 * 0.2 km/s is also proposed.
Title: Stellar angular diameters from infrared photometry. Application
to Arcturus and other stars; with effective temperatures.
Authors: Blackwell, D. E.; Shallis, M. J.
Bibcode: 1977MNRAS.180..177B
Altcode:
A method for determining stellar angular diameters from absolute
infrared photometry is described, and an application made to Arcturus
and 27 other stars. The accuracy of the method in the best conditions
using present observations is about 5 per cent, although higher accuracy
is possible. The diameter deduced for Arcturus is 0.0201 plus or minus
0.0010 arcsec, corresponding to an effective temperature of 4410 plus
or minus 88 K. For earlier type stars there is good agreement with
the results of intensity interferometry. Effective temperatures are
calculated for six other stars.
Title: Department of Astrophysics, University of Oxford. Report for
the period 1975 January 1 to 1976 July 31.
Authors: Blackwell, D. E.
Bibcode: 1977QJRAS..18..111B
Altcode:
No abstract at ADS
Title: Precision measurement of relative oscillator strengths -
III. Fe I transitions from levels a5D2
(0.09 eV), a5D1 (0.11 eV) and
a5D0 (0.12 eV).
Authors: Blackwell, D. E.; Ibbetson, P. A.; Petford, A. D.; Willis,
R. B.
Bibcode: 1976MNRAS.177..219B
Altcode:
New oscillator strengths determined using the absorption technique as
practised at Oxford are given for 20 lines of Fe I having excitation
potentials between and eV, together with a listing of those already
determined at Oxford for excitation potentials 0.00 and 0.05 eV. The
uncertainty of the measures is about 0'02 dex. Comparison is made
with measurements using other methods, and it is shown that systematic
differences exist between absorption and emission measurements.
Title: Interpretation of the solar spectrum 300 nm to 900 nm - I. Fe
I lines of excitation potential 0.00 eV - 0.12 eV, microturbulence,
damping, abundance, tests of oscillator strengths.
Authors: Blackwell, D. E.; Ibbetson, P. A.; Petford, A. D.; Willis,
R. B.
Bibcode: 1976MNRAS.177..227B
Altcode:
An application of new values of oscillator strengths, recently measured
by the total absorption method at Oxford, to the interpretation of the
solar spectrum is described. The solar microturbulence is found to be
km at the centre of the disk and 1 2 km -1 in integrated light. Damping
enhancements for strong and medium-strong lines are derived which are
close to unity and are much smaller than most current values. An iron
abundance of 7. 6o is obtained using the HSRA model after a correction
of + for non-LTE: the range given by four modern solar models is -
. The analysis is also used to examine the accuracy of presently
available oscillator strengths within this range of excitation, and it
is concluded that the Oxford oscillator strengths are probably correct
to dex (4.7 per cent).
Title: The Concept of Limiting Magnitude and the Performance of the
Isaac Newton Telescope for Prime Focus Photography
Authors: Blackwell, D. E.; Ibbetson, P. A.; Murray, C. A.; Pratt, N. M.
Bibcode: 1976Ap&SS..43..469B
Altcode:
A quantitative definition of limiting magnitude for stellar photographs
is proposed, together with a method of measurement employing a Racine
prism. Limiting magnitudes inU, B andV for the Isaac Newton telescope
at Herstmonceux derived from a total of 72 prime focus photographs are
presented and the results correlated with the size of the photographed
image. The limiting magnitude for an extrapolated value of the seeing
of 1″ isB=22m.0, in good agreement with a value obtained
by scaling the limiting magnitudes of the 200 inch telescope.
Title: R. O. Redman, 1905 July 17 - 1975 March 6.
Authors: Blackwell, D. E.; Dewhirst, D. W.
Bibcode: 1976QJRAS..17...80B
Altcode:
No abstract at ADS
Title: Presidential Addresses on the Society's Awards
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16..356B
Altcode:
No abstract at ADS
Title: The Presidential Address: Uncertainty in Astronomy
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16..361B
Altcode:
No abstract at ADS
Title: Optics in Switzerland.
Authors: Golay, M.; Huguenin, D.; Pilloud, F.; Bartholdi, P.; Mayor,
M.; Poncet, J. L.; Lotmar, W.; Blackwell, D. E.; Delbouille, L.;
Roland, G.
Bibcode: 1975ApOpt..14.2355G
Altcode:
No abstract at ADS
Title: The continuum flux distribution for Arcturus.
Authors: Blackwell, D. E.; Ellis, R. S.; Ibbetson, P. A.; Petford,
A. D.; Willis, R. B.
Bibcode: 1975MNRAS.171..425B
Altcode:
A composite of all continuum flux data for Arcturus has been plotted
including additional results obtained recently in Israel. The data are
compared with flux distributions calculated from Carbon & Gingerich,
and Peytremann grids of models. There is not good agreement between
the calculated and observed flux distributions at shorter wavelengths,
but the Peytremann model seems considerably better than the Carbon
& Gingerich model. The origin of the discrepancy is discussed and
a compromise value for the effective temperature of 4500 K (plus 50
or minus 120 K) suggested. The need for accurate spectrophotometry
and an improved model atmosphere is stressed.
Title: Precision measurement of relative oscillator strengths-11. Fe
i transitions from levels a5D4 (o-oo eV) and a5D3 (0-05 eV)
Authors: Blackwell, D. E.; Ibbetson, P. A.; Petford, A. D.
Bibcode: 1975MNRAS.171..195B
Altcode:
The advantages of the absorption method for the measurement of relative
oscillator strengths, as used at Oxford, are discussed and improvements
made recently in the technique are described. Using the method, relative
oscillator strengths have been measured for 16 low excitation potential
lines of Fe I, and a photometric scale covering nearly six decades set
up. The accumulated probable error over these six decades is about
5 per cent. A critical comparison is made with the results of other
methods of measurement and with the results of calculation.
Title: Presidential Addresses on the Society's Awards
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16..355B
Altcode:
No abstract at ADS
Title: S. W. Hawking received the Eddington Medal of the Royal
Astronomical Society.
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16Q.359B
Altcode:
No abstract at ADS
Title: Uncertainty in Astronomy
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16..360B
Altcode:
No abstract at ADS
Title: R. Penrose received the Eddington Medal of the Royal
Astronomical Society.
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16R.359B
Altcode:
No abstract at ADS
Title: E. J. Öpik received the Gold Medal of the Royal Astronomical
Society.
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16..358B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the year 1974 December 31.
Authors: Blackwell, D. E.
Bibcode: 1975QJRAS..16..436B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report 1973.
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..508B
Altcode: 1974QJRAS..15..508.
No abstract at ADS
Title: Presidential Addresses on the Society's Awards
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..219B
Altcode:
No abstract at ADS
Title: Annual general meeting 1974 March 8.
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..199B
Altcode:
No abstract at ADS
Title: Stellar Atmospheres and Laboratory Astrophysics
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..224B
Altcode:
The measurement of stellar abundances is considered, giving particular
attention to questions regarding the reliability of the obtained
data. The various determinations of the abundance of iron in the solar
photosphere are discussed along with coronal measures of abundance,
the construction of a basic solar atmospheric model, and various
difficulties regarding the interpretation of spectral lines. It
is demonstrated that even for the sun for which good spectra and a
reasonably good model atmosphere are available, abundances are very
uncertain. In the case of iron, the spectrum of which has been studied
more intensely than that of any other element, the solar abundance is
not known to better than a factor of at least three.
Title: K. Bullen received the Gold Medal of the Royal Astronomical
Society.
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..220B
Altcode:
No abstract at ADS
Title: G. Perry received the Jackson-Gwilt Medal and Gift of the
Royal Astronomical Society.
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..222B
Altcode:
No abstract at ADS
Title: P. Wild received the Herschel Medal of the Royal Astronomical
Society.
Authors: Blackwell, D. E.
Bibcode: 1974QJRAS..15..221B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the year ending 1972 December 31.
Authors: Blackwell, D. E.
Bibcode: 1973QJRAS..14..444B
Altcode:
No abstract at ADS
Title: Anomalous ionization in the umbrae of sunspots.
Authors: Blackwell, D. E.; Mallia, E. A.
Bibcode: 1973MNRAS.165...61B
Altcode:
New observations are presented of sunspot spectra in regions containing
lines of ionized elements, obtained with the rapid scanning spectrometer
at the Oxford-Gornergrat Observatory. The umbral spectra are corrected
for scattered light from penumbra and photosphere by making use of
scans of the solar limb and sky background. The corrected spectra
show anomalously strong lines of Fe ii and Cr ii. The existence
of the anomaly for Fe ii depends critically on the accuracy of the
scattered light measurement. A numerical experiment shows that the
measured value of 26 per cent for the relevant spot is unlikely to be
greatly in error. These anomalies cannot be explained even in terms
of a non-homogeneous model of an umbra in which there is a state of
L.T.E. in each component, and it seems probable that the lines arise
from a non-equilibrium mechanism. The possible presence of a similar
anomaly in the spectra of magnetic stars is briefly discussed.
Title: Department of Astrophysics, University of Oxford. Report for
the year ending 1971 December 31.
Authors: Blackwell, D. E.
Bibcode: 1972QJRAS..13..567B
Altcode:
No abstract at ADS
Title: The Solar Abundance of Manganese
Authors: Blackwell, D. E.; Collins, B. S.; Petford, A. D.
Bibcode: 1972SoPh...23..292B
Altcode:
No abstract at ADS
Title: The damping of the NaD lines in the solar spectrum by atomic
hydrogen
Authors: Blackwell, D. E.; Kirby, J. H.; Smith, G.
Bibcode: 1972MNRAS.160..189B
Altcode:
The paper gives a brief discussion of the nature of the damping
processes in the atmospheres of cooler stars, followed by a calculation
of the absorption in the wings of the Na D lines in the solar spectrum
using damping constants recently calculated by Lewis, McNamara and
Michels. The agreement between theory and observation is discussed
critically.
Title: Effects of uncertainties indamping and microturbulence on
theoretical deductions from solar equivalentwidths
Authors: Blackwell, D. E.; Calamai, G.; Willis, R. B.
Bibcode: 1972MNRAS.160..121B
Altcode:
The paper presents a quantitative discussion of the effect on
the interpretation of the equivalent widths of solar lines,
of present uncertainties in damping constants and in atmospheric
microturbulence. Graphs are given showing the resultant uncertaintv
in the interpretation of equivalent widths as a function of excitation
potential and wavelength.
Title: Precision measurement of relative oscillator
strengths-1. Fundamental technique: A first application to MN i
Authors: Blackwell, D. E.; Collins, B. S.
Bibcode: 1972MNRAS.157..255B
Altcode:
A discussion of the importance of accurate measurements of atomic
oscillator strengths in astrophysics is followed by an analysis of
the accuracy that is potentially available together with a critical
survey of the most useful techniques. A full discussion is given of
the furnace method used in Oxford, and first results obtained for
a few lines of Mn I are presented. It is shown that the accuracy of
even this straightforward method can in some circumstances suffer from
uncertainties about the state of thermodynamic equilibrium.
Title: Further Study of H2O Lines in the Umbral Spectrum
in the Region of 0.93 μ
Authors: Mallia, E. A.; Blackwell, D. E.; Petford, A. D.
Bibcode: 1971SoPh...20..369M
Altcode:
No abstract at ADS
Title: The Use of Echelle Gratings in Single-Pass Spectrometers
Authors: Petford, A. D.; Blackwell, D. E.; Collins, B. S.; Ibbetson,
P. A.; Mallia, E. A.; Smith, G.; Emerson, D.
Bibcode: 1971SoPh...19..264P
Altcode:
Tests of the performance of replicas of the latest echelle gratings
are reported.
Title: Department of Astrophysics, University of Oxford. Report for
the year ending 1970 December 31.
Authors: Blackwell, D. E.
Bibcode: 1971QJRAS..12..328B
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the year ending 1969 December 31.
Authors: Blackwell, D. E.
Bibcode: 1970QJRAS..11..351B
Altcode:
No abstract at ADS
Title: Water Vapour in Sunspots
Authors: Mallia, E. A.; Blackwell, D. E.; Petford, A. D.
Bibcode: 1970Natur.226..735M
Altcode:
FEATURES attributable to the water vapour molecule have been detected
in the spectra of several late type stars during the previous decade,
particularly by Woolf et al.1, who observed in the 1.13 µm,
1.4 µm, 1.9 µm and 2.7 µm absorption bands using a balloon-borne
spectrometer. Spinrad and Newburn2, Wing et al.3
and Spinrad et al.4 have obtained coudé and Cassegrain
spectra in the neighbourhood of 0.9 µm and demonstrated the great
strengthening of the water vapour absorption in this region in the
spectra of many stars, more especially Mira. Sinton5
has worked in the region 1.9 µm to 2.5 µm using a ground-based
interferometer and has shown that there is water vapour absorption in
the stars R Leo and χ Cyg, and McCammon et al.6 have also
obtained spectra in this region at Mt Wilson and Palomar. Although at
the low temperatures of these stars a detectable concentration of water
vapour would be expected, such measurements are of interest because
they provide evidence for particular atmospheric models. The purpose
of this note is to present evidence for the existence of water vapour
in sunspots.
Title: The Possible Existence of HOH Lines in the Sunspot Spectrum
Authors: Mallia, E. A.; Blackwell, D. E.
Bibcode: 1970SoPh...12..101M
Altcode:
No abstract at ADS
Title: The Sun and the Interplanetary Medium
Authors: Blackwell, D. E.
Bibcode: 1970QJRAS..11..396B
Altcode:
No abstract at ADS
Title: A 0.2-MW furnace of spectroscopic studies.
Authors: Collins, B. S.; Petford, A. D.; Blackwell, D. E.
Bibcode: 1970ApOpt...9.1606C
Altcode:
No abstract at ADS
Title: Department of Astrophysics, University of Oxford. Report for
the year ending 1968 December 31.
Authors: Blackwell, D. E.
Bibcode: 1969QJRAS..10..256B
Altcode:
No abstract at ADS
Title: A rapid scanning low noise spectrometer for study of sunspot
spectra
Authors: Blackwell, D. E.; Mallia, E. A.; Petford, A. D.
Bibcode: 1969MNRAS.146...93B
Altcode:
A rapid high resolution photoelectric spectrometer designed for the
study of sunspot spectra is described. The spectrometer employs an
on4ine computer for signal integration, and to reject scans that are
contaminated by false light due to `seeing'. The apparatus is installed
at the Gornergrat, Switzerland, at a height of 3090 metres. An example
of its performance is given.
Title: Photoelectric observations of the brightness of the solar
disk at Nice Observatory, 1963-66
Authors: Mugnier, G.; Blackwell, D. E.; Petford, A. D.
Bibcode: 1967Obs....87...77M
Altcode:
No abstract at ADS
Title: Low noise and laboratory spectroscopy-I. Technique
Authors: Blackwell, D. E.; Petford, A. D.; Mallia, E. A.
Bibcode: 1967MNRAS.136..365B
Altcode:
A calculation of the theoretical signal to noise ratio for optical solar
spectra formed by grating spectrographs is given, and it is shown that
commonly observed spectra are more noisy than this limit by a factor
of more than one hundred. A form of spectrometer designed to yield a
low noise level is described. Examples of solar spectra obtained with
this instrument are given and it is shown that their noise level is
very close to the theoretical limit.
Title: Toward a Unification of Eclipse and Zodiacal-Light Data
Authors: Blackwell, D. E.; Ingham, M. F.
Bibcode: 1967NASSP.150...17B
Altcode:
No abstract at ADS
Title: The distribution of dust in interplanetary space
Authors: Blackwell, D. E.; Ingham, M. F.; Petford, A. D.
Bibcode: 1967MNRAS.136..313B
Altcode:
The paper presents a model of the distribution of interplanetary dust
based upon brightness and polarization measures of the zodiacal light,
brightness and polarization measures of the F-component of the solar
corona and the distribution flinction of particle radius obtained from
measurements using space vehicles. The model differs from previous ones
in that it shows that the density increases with increasing distance
from the Sun as far as I00 but it does not explain the observed
infra-red excess. It is then shown that agreement with observation is
improved and the calculated infra-red excess is increased if it is
supposed that the albedo of the particles increases with increasing
distance from the Sun.
Title: Observations of the 1963 July 20 solar eclipse. II, The
electron density in the solar corona in the region 5 <R/R<
16 obtained from measurements of Fraunhofer line depth and the
polarization of the F corona
Authors: Blackwell, D. E.; Petford, A. D.
Bibcode: 1966MNRAS.131..399B
Altcode:
Values of F, the polarization of the dust component of the solar
corona, are calculated using the values of K/K + F obtained from
the observations of line depth described in Paper I of this series,
and observed values of the total polarization of the corona. Electron
densities are calculated in the region 5 <RIR0 < i6. A model of
the corona, including electron densities, is given to a distance of
4oR0 from the Sun.
Title: Observations of the 1963 July 20 solar eclipse. I Spectroscopic
separation of the F K components of the solar corona at large
distances from the Sun
Authors: Blackwell, D. E.; Petford, A. D.
Bibcode: 1966MNRAS.131..383B
Altcode:
Photoelectric observations were made of the total solar eclipse of
1963 July 20 from an aircraft at an altitude of 30 000 ft. Data are
presented for the absolute brightness of the solar corona and for the
relative depth of the Ha absorption line in the spectrum of the corona
to a distance of I 6R0 the line depth was measured using interference
fflters. A separation of the F and K components based on tbe line
depth measurements is given to I6 from the Sun.
Title: An image-scrambler for use with a photomultiplier
Authors: Blackwell, D. E.; Petford, A. D.; McCrea, S. H.
Bibcode: 1965Obs....85...21B
Altcode:
No abstract at ADS
Title: Further observations of the zodiacal light from a high altitude
station and investigation of the interplanetary plasma, II.
Authors: Beggs, D. W.; Blackwell, D. E.; Dewhirst, D. W.; Wolstencroft,
R. D.
Bibcode: 1964MNRAS.127..329B
Altcode:
A spectrophotometric method is described for separating the
contributions to the zodiacal light of scattering by dust, and by free
electrons. A suitably designed photoelectric spectrophotometer has been
used to compare the intensities of the two Fraunhofer lines Hfl and
Fe i 4384 in the spectra of the zodiacal light (with correction for
night sky background) and of sunlight. The results are interpreted as
indicating an electron density of i6 +20cm-3 in interplanetary space
at i A.U. from the Sun.
Title: Further observations of the zodiacal light from a high altitude
station and investigation of the interplanetary plasma, I.
Authors: Beggs, D. W.; Blackwell, D. E.; Dewhirst, D. W.; Wolstencroft,
R. D.
Bibcode: 1964MNRAS.127..319B
Altcode:
Observational knowledge of the electron density in interplanetary
space is briefly reviewed, and the methods used during an expedition to
Chacaltaya, Bolivia, outlined. Results of scans of the zodiacal light
with a photoelectric photometer made in the course of tbe investigation
are first presented, and a new method used to separate the zodiacal
light from the night sky background. The isophotes thus obtained are
corrected for the effect of scattering in the Earth's atmosphere to
give the true isophotes.
Title: Further observations of the zodiacal light from a high
altitude station and investigations of the interplanetary plasma,
III. Photoelectric measurements of polarization
Authors: Beggs, D. W.; Blackwell, D. E.; Dewhirst, D. W.; Wolstencroft,
R. D.
Bibcode: 1964MNRAS.128..419B
Altcode:
If, as has been suggested by Huruhata, the degree of polarization of
the night sky at high ecliptic latitudes is low (<0.3 per cent),
its value can place a useful upper limit on the electron density in
regions away from the plane of the ecliptic. The polarization of the
night sky has been measured at the Chacaltaya High Altitude Observatory
using a polarimeter incorporating an electro -optic modulator. The mean
polarization observed in the region of' the North ecliptic pole is per
cent, but the individual values vary significantly from night to night;
this variation is attributed to changes in , 9f the night sky. The true
mean value, corrected for the effect of scattered light, is per cent;
it is too high to set a useful upper limit on the electron density. The
significance' of the observations in scattering by an interplanetary
and a geocentric dust cloud is discussed.
Title: The discovery of Aberration
Authors: Blackwell, D. E.
Bibcode: 1963QJRAS...4...44B
Altcode:
No abstract at ADS
Title: Remarks on the limitations of optical methods for measuring
electron densities in the coronia and interplanetary space
Authors: Blackwell, D. E.
Bibcode: 1963SSRv....1..612B
Altcode:
No abstract at ADS
Title: Future of Optical Astronomy
Authors: Blackwell, D. E.
Bibcode: 1962Natur.195..854B
Altcode:
No abstract at ADS
Title: Book Review: La poussière cosmique: les milieux
interplanetaire, interstellaire et intergalactique. A. DAUVILLIER:
Masson, Paris, 1961. pp. 212, 25 NF
Authors: Blackwell, D. E.
Bibcode: 1962P&SS....9..353B
Altcode:
No abstract at ADS
Title: Interference to Optical Astronomy from Belts of Orbiting
Dipoles (Needles)
Authors: Wilson, R.; Blackwell, D. E.
Bibcode: 1962QJRAS...3..109W
Altcode:
No abstract at ADS
Title: Observations of the zodiacal light from a very high altitude
station: II. Electron densities in interplanetarry space
Authors: Blackwell, D. E.; Ingham, M. F.
Bibcode: 1961MNRAS.122..129B
Altcode:
The evidence for and against the existence of an interplanetary gas
is reviewed. Spectra of the zodiacal light obtained in 1958 at the
high altitude station of Chacaltaya (height 17 100 ft) in Bolivia
with a dispersion of 38 A/mm are described and used to investigate
the concentration of free electrons in the plane of the ecliptic at
I A.U. from the Sun. No electrons could be detected along a line of
sight at elongation 320 and it is deduced that the electron density
at I A.U. is not greater than 120 .
Title: Observations of the zodiacal light from a very high altitude
station: I. The average zodiacal light
Authors: Blackwell, D. E.; Ingham, M. F.
Bibcode: 1961MNRAS.122..113B
Altcode:
The paper presents measurements of the absolute surface brightness
at three wavelengths, the polarization at two wavelengths and the
position of the zodiacal light made from the high altitude station of
Chacaltaya in the Bolivian Andes (height 17 100 ft, geomagnetic latitude
30 S). This site is particularly suited to such observations because
the weather is good and the atmospheric extinction is close to that
expected for a dust-free Rayleigh scattering atmosphere. The brightness
and polarization measures extend to within 190 of the Sun. The colour is
close to that of the Sun, but it is slightly more red; the polarization
measures agree well with those recently obtained by .
Title: Observations of the zodiacal light from a very high altitude
station: III. The disturbed zodiacal light and corpuscular radiation
Authors: Blackwell, D. E.; Ingham, M. F.
Bibcode: 1961MNRAS.122..143B
Altcode:
Photometric observations of the zodiacal light made at Chacaltaya in the
Bolivian Andes during 1958 show that there are changes in brightness
which are correlated with geomagnetic activity. The changes in the
zodiacal light and the surrounding sky during the intense magnetic
storm of 1958 July 8 are described. The increase in sky brightness
that was then observed is tentatively ascribed to scattering by
free electrons in a corpuscular stream, the electron density in the
stream being about 300 cm . There was also a corresponding increase in
zodiacal light brightness; the hypothesis that this may be attributed
to fluorescence of the interplanetary dust on impact with the protons
of this corpuscular stream is examined, but found to be inadequate.
Title: THE NIGHT-SKY SPECTRUM λλ 5000-6500 A.
Authors: Blackwell, D. E.; Ingham, M. F.; Rundle, H. N.
Bibcode: 1960ApJ...131...15B
Altcode:
The paper describes a spectrum of the night sky obtained at the
cosmic-ray station of Chacaltaya (latitude - 16 , height 17100 feet)
at zenith distance 840, using a dispersion of 78 A/mm The spectrum
is unusually intense, and in the region XX 5577-6500 fifty-one OH
emission lines (some of which are multiple) are identified; the spin
doubling of many lines is clearly resolved. A comparison between
observed frequencies and frequencies calculated by means of newly
derived band origins and rotational constants is given Rotational
temperatures are determined, and the absolute intensities of OH lines
and the N I emission at X 5199 have been measured The fine structure
of the OH emission in the region of Ha is calculated
Title: Kellogg and Ney's Model of the Solar Corona
Authors: Blackwell, D. E.; Dewhirst, D. W.
Bibcode: 1959Natur.184.1120B
Altcode:
No abstract at ADS
Title: The observation of solar granulation from a manned
balloon. I. Observational Data and measurement of contrast
Authors: Blackwell, D. E.; Dewhirst, D. W.; Dollfuss, A.
Bibcode: 1959MNRAS.119...98B
Altcode:
There appears to be a practical limit to the resolution attainable
in solar photography from a ground station. In an attempt to obtain
greatly improved resolution, photographs have been made with a 29 cm
refracting telescope mounted underneath the nacelle of a manned balloon
at a height of i8 000 ft. Two flights were mad during the second
flight on 1957 April 1,480 frames were exposed. Although the ground
seeing during the flight was very poor, the photographs taken with the
balloon-borne telescope during this second flight are superior to the
best that have been secured at any ground station. The complex structure
of the photosphere is illustrated bY photographs. Autocorrelation
curves for two scans across the best photograph are given. The contrast
transmission functions for the complete telescope (objective, eyepiece,
photographic emulsion) have been measured using sinusoidal gratings,
and the results used to correct microphotometric measurements of
contrast. The corrected mean contrast between granules and intergranular
regions is 40 per cent at a wave-length of 5300 A.
Title: The Transition from the Ionosphere to Interplanetary Space
Authors: Blackwell, D. E.
Bibcode: 1958Natur.181.1237B
Altcode:
No abstract at ADS
Title: The zodiacal light and the nature of interplanetary gas
Authors: Blackwell, D. E.
Bibcode: 1957Obs....77..187B
Altcode:
No abstract at ADS
Title: Phorography of solar granulation from a manned balloon
Authors: Blackwell, D. E.; Dewhirst, D. W.; Dollfus, A.
Bibcode: 1957Obs....77...20B
Altcode:
No abstract at ADS
Title: A study of the monochromatic polarization of Comet Arend-Roland
(1956 h)
Authors: Blackwell, D. E.; Willstrop, R. V.
Bibcode: 1957MNRAS.117..590B
Altcode:
Measurements of the polarization of the Comet Arend-Roland have
been made using combinations of glass and gelatin filters isolating
respectively the continuum near 4530 A and the (o, o) CN emission band
near 3850 A. Measurements in the continuum extend over a range of phase
angle of 26 and give polarizations between 5 and 20 per cent. There
is reasonable agreement between the polarization curve of the Comet
in the continuum and that for a metallic meteorite. Measurements on
the CN emission band show that the plane of polarization is along the
radius vector from Comet to Sun, and the amount of polarization is
consistent with a fluorescence mechanism.
Title: An examination of the observational evidence for the accretion
theory of the solar corona
Authors: Blackwell, D. E.; Dewhirst, D. W.
Bibcode: 1956MNRAS.116..637B
Altcode:
The predictions and requirements of the accretion theory of the
solar corona are compared with the results of observation, with
special reference to the electron distribution in the neighbourhood
of the Sun and convection in the inner corona. It is concluded that,
even with reasonable modification, the theory is unable to satisfy
the requirements of observation, and that accretion is therefore not
likely to be an important coronal mechanism.
Title: Observations from an aircraft of the zodiacal light at small
elongations
Authors: Blackwell, D. E.
Bibcode: 1956MNRAS.116..365B
Altcode:
The need for polarization data for the zodiacal light between
elongations 20 and 35 is discussed. It is shown that such data can
be obtained by observations from high altitude, and especially from
aircraft, under suitable conditions. Measurements of brightness in
absolute units and of polarization obtained between elongations 21 and
31 along the ecliptic using a Sunder- land aircraft at a height of 9000
ft over the South Pacific Ocean on 1955 May 24 are given. The zodiacal
light axis was then vertical to within 0 3. The average ecliptic
latitude of the axis of symmetry on this occasion was only ) 0 17. The
data are interpreted in terms of electron densities in interplanetary
space, and the effect on the computed electron densities of errors in
the data and their interpretation are discussed. The angle between
the axis of symmetry of the electron component and the ecliptic for
this range of elongation is probably less than I
Title: A study of the outer corona from a high altitude aircraft
at the eclipse of 1954 June 30. II. Electron densities in the outer
corona and zodiacal light regions
Authors: Blackwell, D. E.
Bibcode: 1956MNRAS.116...56B
Altcode:
Data on the brightness and polarization of the solar corona given in
a previous paper are analysed to separate the F and K components and
to give the electron density in the outer corona and inner zodiacal
light regions. The electron density is supposed to be a continuous
function of distance from the Sun with a sharp cut-off at a variable
position corresponding to a sudden decrease of ionization. Let pP0 be
the polarization of the F component at elongation 6. The following
results are demonstrated. (i) If no cut-off is assumed and , then p
o for . But if p is sufficiently large and positive, for all 6. (2)
If a cut-off is imposed just inside the orbit of the earth and pF35
0, then for 6>350. The relation between the zodiacal light and the
corona is discussed. It is shown that there is probably a sharp change'
of electron density gradient near a position 30RO. fromtheSun
Title: The excitation temperature of the solar chromosphere determined
from molecular spectra
Authors: Blackwell, D. E.
Bibcode: 1955VA......1..726B
Altcode:
The excitation temperature of the solar chromosphere is derived from a
study of the rotational structure of the 4216 Å system of CN and the P-
and R-branches of the (0, 0) band of the 2Δ - 2II
system of CH. The temperatures are 5400°, 7400°, and 5100°.
Title: A study of the outer corona from a high altitude aircraft at
the eclipse of 1954 June 30. I. Observational data
Authors: Blackwell, D. E.
Bibcode: 1955MNRAS.115..629B
Altcode:
The eclipse of 19S4 June 30 was successfully observed from
an open aircraft at an altitude of 30 000 ft in excellent sky
conditions. Absolute values of the coronal brightness to a distance
of 13 5 from the Sun and the coronal polarization to a distance of
5 are given, together with the sky brightness and polarization and
their variation with altitude The importance of the sky polarization
is discussed. The data are related to those for the zodiacal light.
Title: A comparison of the intensities of infra-red and violet
radiation from the solar corona at the eclipse of 1952 February 25
Authors: Blackwell, D. E.
Bibcode: 1952MNRAS.112..652B
Altcode:
Measurements made in Khartoum at the total solar eclipse of I95
February z5 show a considerable excess of infra-red radiation in the
solar corona at 2 R from the solar centre. The ratio 1( 2. R0) I(I.9
, I.5R0) J(043M,z5R0) I(0A3 , I.5R0) equals , where I(p, q) is the
intensity of the corona at the wave-length p and distance q from the
Sun. The measurements were made with a 20-in. mirror of 45 in. focal
length, using a lead sulphide cell and a photomultiplier. It is shown
that the infra-red excess supports the current theory of an F-corona
caused by diffraction of sunlight by a cloud of interplanetary dust
particles. Three models with widely differing distributions of dust
are calculated but it is not possible to distinguish between them by
using existing infra-red and visible data alone.
Title: A Solar Halo Phenomenon
Authors: Blackwell, D. E.; de La Bere, J. C. W.
Bibcode: 1944Natur.154..491B
Altcode:
A DISPLAY of mock suns was seen here on the morning of August
9. Descriptions of similar displays seen at Cambridge and Godalming have
been published1 and these notes are supplementary to them.