explanation blue bibcodes open ADS page with paths to full text
Author name code: gray
ADS astronomy entries on 2022-09-14
author:"Gray, David F."
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Title: Characterizing Space Debris Objects Using Simultaneous
Multi-Color Optical Array
Authors: Campbell, T.; Reddy, V.; Furfaro, R.; Tucker, S.; Gray, D.
2019LPICo2109.6117C Altcode:
Using high speed simultaneous multi-color photometry to characterize
RSOs, both debris and active.
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Title: A Recipe for Finding Stellar Radii, Temperatures, Surface
Gravities, Metallicities, and Masses Using Spectral Lines
Authors: Gray, David F.; Kaur, Taranpreet
2019ApJ...882..148G Altcode:
A recipe based on physical principles employs the observed
equivalent widths of 10 spectral lines to model the photosphere of
a target star. Coupled with the visual magnitude and an absolute
flux calibration, the recipe yields the angular radius, effective
temperature, surface gravity, and metallicity. With the addition
of a parallax, a linear radius and a mass estimate are added to the
results. The method is applied to a sample of 26 G and K stars that
span luminosity classes V to IIIa. The recipe-determined angular radii
agree with the interferometer radii and have comparable errors. But
unlike interferometers, the recipe is not limited to sizes ≳1 mas. The
veracity of the other recipe-derived parameters is supported by numerous
comparisons with previously published values.
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Title: A Spectroscopic Analysis of the Hyades Cool Giants
Authors: Gray, David F.; Martinez, A.
2019AJ....157...92G Altcode:
High-resolution spectroscopic observations of the four cool giants
in the Hyades cluster, taken at the Elginfield Observatory, are
analyzed. The velocity of γ Tau between 2002 and 2009 is constant to a
few m s<SUP>-1</SUP> small variations, compatible with the planetary
orbit, are seen for ɛ Tau. The primary-to-secondary mass ratio
of θ <SUP>1</SUP> Tau is found to be 2.33 ± 0.07. Absolute radial
velocities are determined for three of the giants from third-signature
plots that correct for granulation blueshifts: 38,615 ± 50, 38,760
± 100, and 38,570 ± 50 m s<SUP>-1</SUP> for γ Tau, δ Tau, and ɛ
Tau respectively. Line-depth ratios show that γ Tau is 33 ± 5 K, δ
Tau is 53 ± 10 K, and θ <SUP>1</SUP> Tau is 30 ± 6 K hotter than
ɛ Tau. Although the λ6253 line bisectors are similar for all four
giants, there are significant differences in the line profiles. Fourier
analysis of the profile shapes yields projected rotation rates of
2.1, 2.4, 2.8, and 2.8 km s<SUP>-1</SUP> for γ Tau, δ Tau, ɛ Tau,
and θ <SUP>1</SUP> Tau respectively, with an uncertainty of ±0.3 km
s<SUP>-1</SUP>. The corresponding radial-tangential macroturbulence
dispersions are 5.07, 5.66, 5.55, and 4.65 km s<SUP>-1</SUP>,
with a uncertainty of ±0.10 km s<SUP>-1</SUP>. Scale factors for
third-signature plots are close to unity, ±10%, implying that the
granulation velocity gradient through their photospheres is similar to
the Sun's. Bisector mapping returns flux differences between granules
and lanes, with average granule-to-lane temperature differences
∼125 K.
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Title: Spectroscopy of the K0 Binary Giant α UMa
Authors: Gray, David F.
2018ApJ...869...81G Altcode:
High-resolution spectroscopic observations of the K0 II-III star α
UMa were taken at the Elginfield Observatory over 11 years. Radial
velocities were measured for nine of these years. They do not
cover enough of the 44.5 year orbital period to give definitive
elements on their own, but combined with published visual orbits,
the spectroscopic-orbit parameters are well constrained. The spectra
show no evidence of the secondary star, which remains an unsolved
puzzle. Line-depth ratios show that α UMa has temperature variations
∼3 K, possibly periodic, over the 2001-2010 interval. Fourier
analysis of the line broadening gives the projected rotation
velocity of 2.66 ± 0.15 km s<SUP>-1</SUP> and a radial-tangential
macroturbulence dispersion of 4.97 ± 0.08 km s<SUP>-1</SUP>. The
third-granulation signature shows the granulation velocities of α
UMa to be essentially solar, with a scale factor of 0.98 ± 0.10. The
absolute radial velocity of the star, with granulation blueshifts
removed is -10,035 ± 100 m s<SUP>-1</SUP> at the mean time of the
observations, 2005.2544. The line bisector of Fe I λ6253 is normal and
shows the classic “C” shape with the blue-most point commensurate
with its absolute magnitude. Mapping this bisector on to the third
signature gives a flux deficit similar to those of other giants,
with a fractional area of 0.131, suggesting a temperature difference
between granules and lanes of 127 K. The velocity position of the
deficit is slightly higher than that for previously analyzed giants,
extending the correlation with absolute magnitude.
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Title: A Solar-flux Line-broadening Analysis
Authors: Gray, David F.
2018ApJ...857..139G Altcode:
The Fourier technique of extracting rotation rates and
macroturbulence-velocity dispersions from the shapes and broadening of
stellar spectral lines is applied to the solar-flux spectrum. Lines
with equivalent widths less than ∼0.055 Å are shown to have the
advantage over stronger lines by allowing the residual transform to
be followed to higher frequencies. The standard radial-tangential
macroturbulence formulation fits the observations well and yields an
equatorial velocity that is within a few percent of the correct rate.
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Title: The Solar-flux Third Granulation Signature
Authors: Gray, David F.; Oostra, Benjamin
2018ApJ...852...42G Altcode:
The velocity shifts of spectral lines as a function of line strength,
so-called the third signature of granulation, are investigated using
three published solar-flux atlases. We use flux atlases because we
wish to treat the Sun as a star, against which stellar observations
can be compared and judged. The atlases are critiqued and compared to
the lower-resolution observations taken with the Elginfield stellar
spectrograph. Third-signature plots are constructed for the 6020-6340
Å region. No dependence on excitation potential or wavelength is found
over this wavelength span. The shape of the plots from the three solar
atlases is essentially the same, with rms line-core velocity differences
of 30-35 m s<SUP>-1</SUP>. High-resolution atlas data are degraded
to the level of the Elginfield spectrograph and compared to direct
observations taken with that spectrograph. The line-core velocities
show good agreement, with rms differences of 38 m s<SUP>-1</SUP>. A new
standard curve is derived and compared with the previously published
one. Only small differences in shape are found, but a significant
(+97 m s<SUP>-1</SUP>) change in the zero point is indicated. The
bisector of the Fe I 6253 line is mapped onto the third-signature plots
and flux deficits are derived, which measure the granule/lane flux
imbalance. The lower spectral resolution lowers the flux deficit area
slightly and moves the peak of the deficit 0.3-0.5 km s<SUP>-1</SUP>
toward higher velocities. These differences, while significant, are
not large compared to measurement errors for stellar data.
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Title: VizieR Online Data Catalog: Radial velocities of δ Sagittae
(Pugh+, 2015)
Authors: Pugh, T.; Gray, D. F.; Griffin, R. F.
2018yCat..74542344P Altcode:
28 spectra were obtained by Gray and Pugh between 2008 July and 2010
October (MJD 2454674-2455479) with the high-resolution (R~100000)
coude spectrograph of the Elginfield Observatory of Western University
(Gray 2009ApJ...697.1032G). The signal-to-noise ratios in the continuum,
estimated from the photon counts, ranged from 152 to 314 with a mean of
220. The spectrograph has a dispersion of ~0.013 Å/mm and can reach a
radial-velocity precision of 25 m/s by reference to water vapour lines
inside the spectrograph (Gray & Brown 2006PASP..118.1112G). In the
current case our measurement errors (based on exposures taken within
a few nights of one another) range from 27 to 160 m/s, with a mean
value of 90 m/s. The radial velocities were determined by measuring
the positions of the spectral lines at 85 per cent of the line depth
for 15 neutral metal lines in the λ6250-Å region. <P />(1 data file).
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Title: A Spectral-line Analysis of the G8 III Standard ɛ VIR
Authors: Gray, David F.
2017ApJ...845...62G Altcode:
Eleven seasons of spectroscopic data comprised of 107 exposures for
the stable G8 III standard star, ɛ Vir are analyzed for projected
rotation rate and granulation parameters. A Fourier analysis of the
line shapes yield v sin I = 3.06 ± 0.20 km s<SUP>-1</SUP> and a
radial-tangential macroturbulence dispersion ζ <SUB>RT</SUB> = 5.16
± 0.08 km s<SUP>-1</SUP>. The radial velocity over nine seasons is
constant to 18 m s<SUP>-1</SUP>. The absolute radial velocity with
granulation blueshifts (but not gravitational redshift) removed is
-14120 ± 75 m s<SUP>-1</SUP>. Line-depth ratios show the temperature
to be constant to 0.7 K over 11 years, although a small secular rise
or cyclic variation ∼1 K cannot be ruled out. The third-signature
plot shows that the star has granulation velocities 10% larger
than the Sun's. Mapping the Fe I λ6253 line bisector on to the
third-signature plot indicates a normal-for-giants flux deficit area
of 12.8%, indicating ∼134 K temperature difference between granules
and lanes. Deficit velocities of GK giants are seen to shift to higher
values with higher luminosity, ∼0.75 km s<SUP>-1</SUP> over ΔM
<SUB>V</SUB> ∼ 1.5, indicating larger velocity differences between
granules and lanes for giants higher in the HR diagram.
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Title: The Orbit, Rotation, and Granulation of the G7 Giant β Her
Authors: Gray, David F.
2016ApJ...832...68G Altcode:
The G7 IIIa single-lined spectroscopic binary, β Her, is studied with
high-resolution, high-signal-to-noise spectra taken over 10 seasons
from 23MR2000 to 10MY2009. Absolute radial velocities, corrected for
convective blueshifts, are determined and new orbital parameters are
derived. Line-depth ratios are used to measure temperature variation
∼2 K. A Fourier analysis is done for the line broadening, yielding
a projected rotation velocity of 3.27 ± 0.20 km s<SUP>-1</SUP>
and a radial-tangential macroturbulence dispersion of 6.43 ± 0.08
km s<SUP>-1</SUP>. The “C” shaped bisector of Fe I λ6253 has its
blue-most point at a relative flux level of 0.52, consistent with what
is expected from β Her’s absolute magnitude. The third-signature plot
indicates granulation velocities 20% larger than the Sun’s. Mapping
the λ6253 line bisector onto the third-signature curve results in a
flux deficit of 12.6 ± 1.0% that can be interpreted as arising from
a temperature difference between granules and inter-granular lanes
of 132 K. The flux deficit peaks near 5.5 km s<SUP>-1</SUP> from the
line center, suggesting the velocity difference between granules and
lanes is ∼20% larger than that found for recently analyzed K giants.
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Title: Erratum: “A Spectroscopic Analysis of the K0 III Binary ɛ
CYGNI” <A href="/abs/2015ApJ...810..117G">(2015, ApJ, 810, 117)</A>
Authors: Gray, David F.
2016ApJ...825...81G Altcode:
No abstract at ADS
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Title: Rotation and Granulation of the K2 Giant alpha SER
Authors: Gray, David F.
2016ApJ...826...92G Altcode:
The red giant α Ser was observed over 10 seasons, 2001-2010,
at the Elginfield Observatory with the high-resolution coudé
spectrograph. Season-mean radial velocities appear to show a small
secular rise ∼11 ± 3 m s<SUP>-1</SUP> yr<SUP>-1</SUP>. The
absolute spectroscopic radial velocity with convective blueshifts
taken into account is 2730 m s<SUP>-1</SUP>. Ten line-depth ratios
were investigated and show that the star's temperature is constant
with any secular variation below 1.3 ± 1.0 K over the 11 years of
observation. Fourier analysis of the line broadening yields v sin I =
2.0 ± 0.3 km s<SUP>-1</SUP> and a radial-tangential macroturbulence
dispersion ζ <SUB>RT</SUB> = 4.50 ± 0.10 km s<SUP>-1</SUP>. The
third-granulation-signature plot shows that the granulation velocities
of α Ser are only 0.55 ± 0.10 as large as the Sun's. The line bisector
of Fe I λ6253 has the usual “C” shape and when mapped onto the
third-signature plot results in a flux deficit that is slightly broader
than seen in other measured K giants. The deficit fractional area of
12.3 ± 1.5% suggests a temperature difference between granules and
lanes of 105 K as seen averaged over the stellar disk.
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Title: LUMINEU: a search for neutrinoless double beta decay based
on ZnMoO<SUB>4</SUB> scintillating bolometers
Authors: Armengaud, E.; Arnaud, Q.; Augier, C.; Benoît, A.; Benoît,
A.; Boiko, L. Bergé S.; Bergmann, T.; Blümer, J.; Broniatowski,
A.; Brudanin, V.; Camus, P.; Cazes, A.; Chapellier, M.; Charlieux,
F.; Chernyak, D. M.; Coron, N.; Coulter, P.; Danevich, F. A.; de
Boissiére, T.; Decourt, R.; De Jesus, M.; Devoyon, L.; Drillien,
A. -A.; Dumoulin, L.; Eitel, K.; Enss, C.; Filosofov, D.; Fleischmann,
A.; Foerster, N.; Fourches, N.; Gascon, J.; Gastaldo, L.; Gerbier,
G.; Giuliani, A.; Gray, D.; Gros, M.; Hehn, L.; Henry, S.; Hervé, S.;
Heuermann, G.; Humbert, V.; Ivanov, I. M.; Juillard, A.; Kéfélian,
C.; Kleifges, M.; Kluck, H.; Kobychev, V. V.; Koskas, F.; Kozlov,
V.; Kraus, H.; Kudryavtsev, V. A.; Le Sueur, H.; Loidl, M.; Magnier,
P.; Makarov, E. P.; Mancuso, M.; de Marcillac, P.; Marnieros, S.;
Marrache-Kikuchi, C.; Menshikov, A.; Nasonov, S. G.; Navick, X. -F.;
Nones, C.; Olivieri, E.; Pari, P.; Paul, B.; Penichot, Y.; Pessina,
G.; Piro, M. C.; Plantevin, O.; Poda, D. V.; Redon, T.; Robinson,
M.; Rodrigues, M.; Rozov, S.; Sanglard, V.; Schmidt, B.; Scorza, S.;
Shlegel, V. N.; Siebenborn, B.; Strazzer, O.; Tcherniakhovski, D.;
Tenconi, M.; Torres, L.; Tretyak, V. I.; Vagneron, L.; Vasiliev, Ya
V.; Velazquez, M.; Viraphong, O.; Walker, R. J.; Weber, M.; Yakushev,
E.; Zhang, X.; Zhdankov, V. N.
2016JPhCS.718f2008A Altcode: 2016arXiv160104989A
The LUMINEU is designed to investigate the possibility to search for
neutrinoless double beta decay in <SUP>100</SUP> Mo by means of a large
array of scintillating bolometers based on ZnMoO4 crystals enriched in
<SUP>100</SUP> Mo. High energy resolution and relatively fast detectors,
which are able to measure both the light and the heat generated upon
the interaction of a particle in a crystal, are very promising for
the recognition and rejection of background events. We present the
LUMINEU concepts and the experimental results achieved aboveground
and underground with large-mass natural and enriched crystals. The
measured energy resolution, the α/β discrimination power and the
radioactive internal contamination are all within the specifications for
the projected final LUMINEU sensitivity. Simulations and preliminary
results confirm that the LUMINEU technology can reach zero background
in the region of interest (around 3 MeV) with exposures of the order
of hundreds kgxyears, setting the bases for a next generation 0v2β
decay experiment capable to explore the inverted hierarchy region of
the neutrino mass pattern.
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Title: The orbit and variations of δ Sagittae
Authors: Pugh, T.; Gray, David F.; Griffin, R. F.
2015MNRAS.454.2344P Altcode:
Radial-velocity observations spanning more than a century are used to
produce a reliable orbit of the δ Sagittae system. We find an orbital
period of 3703.7 ± 1.5 d and a semi-amplitude of 7.73 ± 0.05 km
s<SUP>-1</SUP>. In addition, we find quasi-periodic variations with
time-scales in the range of 550-750 d and a typical amplitude of 1 km
s<SUP>-1</SUP>. The phase and amplitude are both irregular, sometimes
changing very abruptly. We consider pulsation, rotational modulation
and convection as possible causes of the variations, finally favouring
convection.
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Title: A Spectroscopic Analysis of the K0 III Binary ɛ Cygin
Authors: Gray, David F.
2015ApJ...810..117G Altcode:
Spectroscopic observations of ɛ Cyg (K0 III) taken over 12 seasons
from 1999 to 2010 with a resolving power ∼100,000 are analyzed
for radial velocities, granulation properties, and projected
rotation rate. The new radial velocities, which are on an absolute
velocity scale with convective blueshifts removed, contribute
to the determination of the 55-year orbit parameters, but are
insufficient to be definitive. Line-depth ratios show photospheric
temperature variations amounting to ∼4 K, likely arising from a
magnetic cycle. A small velocity variation, ∼100 m s<SUP>-1</SUP>,
may mimic the temperature variations. Fourier analysis of the line
broadening yields the projected rotation rate v sin i = 1.0 ± 0.2
and macroturbulence dispersion {\zeta }<SUB>{RT</SUB>} = 4.45 ± 0.05
km s<SUP>-1</SUP>. A possible rotation modulation in velocity with a
period of ∼1.5 years is noted. The third signature of granulation,
i.e., greater blueshifts for weaker lines, is measured and indicates a
photospheric velocity gradient in ɛ Cyg that is 1.1 ± 0.1 times the
Sun's, which is consistent with previously measured K giants. Mapping
the line bisector of the Fe i λ6253 line on to the third-signature
plot results in a flux deficit with a maximum 4.9 km s<SUP>-1</SUP>
redward of the line core and an amplitude of 16.5% ± 0.5% of the core
depth, values typical of K giants. A 145 K disk-averaged temperature
difference between granules and lanes is implied.
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Title: The Stable K0 Giant Star β Gem
Authors: Gray, David F.
2014ApJ...796...88G Altcode:
A nine-season spectroscopic study of the photosphere of β Gem (K0
III) shows this low-luminosity giant to be stable, with no effective
temperature variations above ~2 K, and no secular temperature
variations over the 2002-2010 time span above 0.2 K per year. The
radial-velocity variations are consistent with an orbital variation of
~40 m s<SUP>-1</SUP>. The projected rotation rate is found to be 1.70 ±
0.20 km s<SUP>-1</SUP> with a macroturbulence dispersion of 4.53 ± 0.10
km s<SUP>-1</SUP>. The third-signature plot is also invariant and shows
a granulation velocity gradient 20% smaller than the solar gradient. The
absolute shift of the third-signature plot gives a blueshift-corrected
radial velocity of 3385 ± 70 m s<SUP>-1</SUP>. Bisector mapping of the
Fe I λ6253 line yields a flux deficit of 12% ± 1% in area, somewhat
smaller than for other giants, but the shape and the position of the
peak at 4.8 km s<SUP>-1</SUP> is consistent with other giants. All of
the investigated photospheric parameters are consistent with β Gem
being a low-luminosity giant in agreement with its absolute magnitude.
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Title: Precise Rotation Rates for Five Slowly Rotating A Stars
Authors: Gray, David F.
2014AJ....147...81G Altcode:
Projected rotation rates of five early A-type slowly rotating stars are
measured spectroscopically to a precision of 0.2 km s<SUP>-1</SUP>. A
detailed Fourier analysis is done, as well as a comparison of profiles
directly. Macroturbulence is needed in addition to rotation to reproduce
the profile shapes. An upper limit of lsim2 km s<SUP>-1</SUP> is placed
on the microturbulence dispersion. Small unexplained differences between
the models and the observations are seen in the sidelobe structure of
the transforms. The v sin i results are: α Dra, 26.2; θ Leo, 22.5;
α CMa A, 16.7; γ Gem A, 10.7; o Peg, 6.0 km s<SUP>-1</SUP>. These
stars are suitable as standards for measuring rotation using less
fundamental methods.
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Title: Short Timescale Variations in the Atmosphere of Antares A
Authors: Pugh, T.; Gray, David F.
2013ApJ...777...10P Altcode:
We analyze three years of high-resolution spectroscopic data and
find radial velocity variations with a characteristic timescale of
100 ± 6 days that are nearly sinusoidal. Simultaneous variations
in line-depth ratios imply temperature variations of up to 100 K. No
photometric variation is seen on a 100 day timescale. The timescale of
the variation and its resonant nature suggest solar-like oscillations
driven by large-scale convection.
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Title: Rotation of the K3 II-III Giant Star α Hydra
Authors: Gray, David F.
2013AJ....146...29G Altcode:
Fundamental spectroscopic determination of projected rotation rates of
slowly rotating stars is challenging because the rotational broadening
of the spectral lines is often comparable to, or smaller than, the
broadening from other sources, most notably macroturbulence. Fourier
techniques have the advantage over direct profile matching when the
observed profiles are complete, but when the profiles are severely
blended, the Fourier analysis is compromised. A process of modeling
partial profiles for determining the rotation rate for stars having
blended spectral lines is investigated and applied to the evolved star
α Hya (K3 II-III). Projected rotation higher than 5 km s<SUP>-1</SUP>
can be definitively ruled out for this star. Not all lines are equally
good, depending on the amount of blending and also depending on the
strength of the line, as the balance between the thermal and non-thermal
components changes. A modest ambiguity arises between macroturbulence
and rotational broadening, but a careful look at the differences
between the observations and the models allows one to measure the
rotation with acceptable precision. The result for α Hya is v sin i =
2.6 ± 0.3 km s<SUP>-1</SUP>.
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Title: The Spectroscopic Variations of Antares A - Two Timescales
of Variation
Authors: Pugh, T.; Gray, D. F.
2013giec.conf30002P Altcode:
Red supegiants as a group are known to demonstrate variability on
several timescales. Based on spectroscopic monitoring performed
at the Elginfield Observatory we examine the radial velocity
and temperature variations of Antares A. Combining our data with
historic radial velocity data we refine the radial velocity curve
of the six-year variation, finding a period of 2167±5 days. This
curve is remarkably similar to those of Long Secondary Periods
(LSPs) seen in some semiregular variables. We predict a brightness
variation of 0.2 mag based on our radial velocity and line-depth ratio
variations. Such a variation is yet to be detected adding further
weight to the LSP conclusion. In addition, we identify a characteristic
timescale of variation of 100-days, which is also seen in the radial
velocities. We interpret this as arising from convection and conclude
that changes in phase and amplitude of this variation mean that the
previous determinations of periods of 200-300 days are not physically
significant. A comparison of the variations in a single star like
Antares to those seen in zeta Aur systems may help isolate the effects
of the hot companion.
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Title: The Two Regimes of Photospheric Motions in α Hydra
Authors: Gray, David F.
2013ApJ...764..100G Altcode:
High-resolution spectroscopic observations of α Hya were acquired
between 2003 and 2010. Analysis of line shifts, differential shifts,
line widths, and line bisectors points to two regimes of velocity
fields in the photosphere of α Hya: (1) normal granulation embedded
in (2) large convection cells. Variations occur on a wide range of
timescales, from several years on down. Radial velocity variations,
which are irregular and span 786 m s<SUP>-1</SUP>, have a distribution
consistent with a true mean rise velocity of the large cells of
~725 m s<SUP>-1</SUP> and a dispersion of ~220 m s<SUP>-1</SUP>. The
distribution of granulation velocities, as measured from the widths
of spectral lines, shows only small variations, consistent with the
two regime concepts. On the multi-year timescale, radial velocity
changes, small temperature variations (~10 K), and small line-width
variations (lsim0.8%) track each other, possibly with phase shifts. The
granulation velocity gradient for α Hya is about half as large as the
Sun's and no variation with time was seen, implying that any variation
in velocity gradient from one large cell to the next must be less than
a few percent. The asymmetry in the granulation velocity distribution,
as specified in the flux deficit, is smaller than expected for α
Hya's position in the HR diagram and appears to be variable.
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Title: On the Six-year Period in the Radial Velocity of Antares A
Authors: Pugh, T.; Gray, D. F.
2013AJ....145...38P Altcode:
We examine the century-long historical data and compare it with our
new radial-velocity measurements to determine an improved period. We
find a period of 2167 ± 5 days (5.93 ± 0.01 years). Both orbital
motion and pulsation are considered as possible causes of the velocity
variation. Temperature variations we deduce from line-depth ratios
support the pulsation hypothesis. A temperature minimum occurs in
2009, 70 days after the radial-velocity minimum. We deduce a radius
change of 19% ± 4% from an integration of the radial-velocity curve
and predict a visual magnitude variation ~0.2 from the radius and
temperature variation.
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Title: Granulation in the Photosphere of ζ Cygni
Authors: Gray, David F.
2012AJ....143..112G Altcode:
A series of 35 high-resolution spectra are used to measure the
third-signature plot of the G8 III star, ζ Cygni, which shows
convective velocities only 8% larger than the Sun. Bisector mapping
yields a flux deficit, a measure of granulation contrast, typical
of other giants. The observations also give radial velocities with
errors ~30 m s<SUP>-1</SUP> and allow the orbit to be refined. Velocity
excursions relative to the smooth orbital motion, possibly from the
granulation, have values exceeding 200 m s<SUP>-1</SUP>. Temperature
variations were looked for using line-depth ratios, but none were found.
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Title: The Third Signature of Granulation in Bright-giant and
Supergiant Stars
Authors: Gray, David F.; Pugh, Teznie
2012AJ....143...92G Altcode:
We investigated third-signature granulation plots for 18 bright giants
and supergiants and one giant of spectral classes G0 to M3. These plots
reveal the net granulation velocities, averaged over the stellar disk,
as a function of depth. Supergiants show significant differences from
the "standard" shape seen for lower-luminosity stars. Most notable is
a striking reversal of slope seen for three of the nine supergiants,
i.e., stronger lines are more blueshifted than weaker lines, opposite
the solar case. Changes in the third-signature plot of α Sco (M1.5 Iab)
with time imply granulation cells that penetrate only the lower portion
of the photosphere. For those stars showing the standard shape, we
derive scaling factors relative to the Sun that serve as a first-order
measure of the strength of the granulation relative to the Sun. For
G-type stars, the third-signature scale of the bright giants and
supergiants is approximately 1.5 times as strong as in dwarfs, but for
K stars, there in no discernible difference between higher-luminosity
stars and dwarfs. Classical macroturbulence, a measure of the velocity
dispersion of the granulation, increases with the third-signature-plot
scale factors, but at different rates for different luminosity classes.
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Title: Photospheric Variations of the Supergiant γ Cyg
Authors: Gray, David F.
2010AJ....140.1329G Altcode:
New high-resolution spectroscopic observations of the supergiant
γ Cyg (F8 Iab) taken between 2000 and 2008 consistently show
strongly reversed-C-shaped bisectors for all unblended spectral
lines. Small-amplitude variations in radial velocity and line
shapes occur in an irregular manner with time scales ~100 days
and longer. The radial velocities occasionally show changes as
large as 2 km s<SUP>-1</SUP>, but much smaller changes are going on
continuously. Differential line bisectors show shape changes and Doppler
displacement characteristic of radial expansion and contraction. These
might arise from non-periodic radial pulsation-like motions or from the
appearance of giant convection cells that occupy most of the visible
hemisphere of the star. Line-depth ratios are correlated with the line
shifts on a seasonal basis and indicate temperature changes ranging
up to ~15 K, with larger temperature occurring during times of most
rapid contraction.
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Title: High-resolution spectroscopic study of red clump stars in
the Galaxy: iron-group elements
Authors: Puzeras, E.; Tautvaišienė, G.; Cohen, J. G.; Gray, D. F.;
Adelman, S. J.; Ilyin, I.; Chorniy, Y.
2010MNRAS.408.1225P Altcode: 2010MNRAS.tmp.1194P; 2010arXiv1006.3857P
The main atmospheric parameters and abundances of the iron-group
elements (vanadium, chromium, iron, cobalt and nickel) are determined
for 62 red giant `clump' stars revealed in the Galactic field by
the Hipparcos orbiting observatory. The stars form a homogeneous
sample with the mean value of temperature T<SUB>eff</SUB> = 4750 +/-
160K, of surface gravity log g = 2.41 +/- 0.26 and the mean value of
metallicity [Fe/H] = -0.04 +/- 0.15dex. A Gaussian fit to the [Fe/H]
distribution produces the mean <[Fe/H]> = -0.01 and dispersion
σ<SUB>[Fe/H]</SUB> = 0.08. The near-solar metallicity and small
dispersion of σ<SUB>[Fe/H]</SUB> of clump stars of the Galaxy obtained
in this paper confirm the theoretical model of the Hipparcos clump by
Girardi & Salaris. This suggests that nearby clump stars are (in
the mean) relatively young objects, reflecting mainly the near-solar
metallicities developed in the local disc during the last few Gyr of
its history. We find iron-group element to iron-abundance ratios in
clump giants to be close to solar.
---------------------------------------------------------
Title: An Explanation of Reversed Spectral-line Bisectors
Authors: Gray, David F.
2010ApJ...721..670G Altcode:
The long-standing puzzle of reversed-C bisectors of spectral lines
is addressed with the tools of the third-signature plot and bisector
mapping. The F8 supergiant γ Cyg, which shows strongly reversed
bisectors, is analyzed and found to have a monotonic decline
in velocities with height in its photosphere, consistent with a
convective overshoot region similar to what is seen for stars on the
cool side of the granulation boundary. Further, a flux deficit is
derived that is not unlike those for stars on the cool side of the
granulation boundary, although the γ Cyg flux deficit is wider and
peaks at a higher velocity. The reversed-C bisector shape is caused by
a combination of a steep decline in velocities with height, as shown in
the third-signature plot, with a flux deficit spanning only a fraction
of the red wing of the line profiles, in contrast to cooler stars where
the deficit extends over most of the red wing. Apparently no unusual
velocity fields or other bizarre behaviors are needed to explain the
granulation boundary; it stems more simply from the continuous changes
of normal convective overshoot across the HR diagram.
---------------------------------------------------------
Title: Empirical Decoding of the Shapes of Spectral-Line Bisectors
Authors: Gray, David F.
2010ApJ...710.1003G Altcode:
The great variety of shapes found for bisectors of spectral lines seen
across the cool half of the Hertzsprung-Russell diagram are explained
and empirically decoded using a novel method. The velocity gradient
through the photosphere, as delineated by the star's third-signature
plot, sets the basic shape of the bisector, which is then modified by
the asymmetry in the amount of light coming from rising versus falling
material. With this concept in place, one can then derive the apparent
deficit of flux from downward flowing material in the granulation
structure, and this is done for nine stars. The deficits peak between 3
and 4 km s<SUP>-1</SUP> for dwarfs and between 4 and 5 km s<SUP>-1</SUP>
for giants, and they span a range from ~1 to 10 km s<SUP>-1</SUP> for
all stars. The amplitudes of the flux deficits increase with effective
temperature and with luminosity and have values ~7%-10% for dwarfs
and ~15%-20% for giants. Such measurements of the contrast between
granules and dark lanes are independent of models of granulation.
---------------------------------------------------------
Title: The Third Signature of Stellar Granulation
Authors: Gray, David F.
2009ApJ...697.1032G Altcode:
Absolute shifts of spectral-line bisectors (the third signature of
granulation) are shown to follow the solar pattern, i.e., weaker lines
are more blue-shifted than stronger lines, for a selection of stars on
the cool side of the granulation boundary in the H-R diagram. These
patterns scale to the solar case by multiplicative factors ranging
from 0.53 to 2.10, which is a measure of the granulation velocity
gradient through the stellar photosphere. The scale factors increase
with effective temperature and are larger in giants than in dwarfs. A
universal relation is constructed relating line depth to convective
blueshift. The scale factors vary in concert with the first and second
granulation signatures, macroturbulence, and asymmetry of spectral
lines. Matching the stellar to the solar third signature also results
in a determination of the apparent absolute radial velocity of the star
with errors ranging from 80 to 300 m s<SUP>-1</SUP>, but potentially
considerably smaller. The star γ Cyg, which shows reversed-C-shaped
bisectors and lies on the hot side of the granulation boundary, also
shows weak lines more blue-shifted than stronger lines.
---------------------------------------------------------
Title: Agricultural Performance Monitoring with Polarimetric SAR
and Optical Imagery
Authors: Dhar, T.; Gray, D.; Menges, C.
2009ESASP.668E..49D Altcode:
This paper presents the results from an experiment measuring yield using
TerraSAR-X dual-polarimetric mode and precision agriculture machinery
which records harvested amounts every few meters. The experimental
field setup and data collection using TerraSAR-X are discussed and
some preliminary results are shown.
---------------------------------------------------------
Title: Asymmetries in the Spectral Lines of Evolved Halo Stars
Authors: Gray, David F.; Carney, Bruce W.; Yong, David
2008AJ....135.2033G Altcode:
We do an initial reconnaissance of asymmetries of spectral lines in
metal-poor field stars using high-resolution observations of four red
horizontal-branch and 11 red giant branch stars taken with the coude
spectrograph at the Canada-France-Hawaii Telescope. We find that (1)
the shapes of the line bisectors for metal-poor stars hotter than 4100
K mimic the well-known C shape of bisectors for solar-metallicity
stars on the cool side of the granulation boundary while (2)
metal-poor stars cooler than 4100 K, or higher up the red giant
branch than M <SUB>V</SUB> = 1.5, show bisectors with a reversed-C
shape, similar to those for solar-metallicity stars on the hot side
of the granulation boundary and similar to the reversed-C shape
found in a previous study for the M-type supergiant Betelgeuse. The
well-documented radial-velocity jitter of high-luminosity stars and the
line bisector characteristics vary in concert up the red giant branch;
both phenomena are probably signatures of large convection cells. <P
/>Based on observations obtained at the Canada-France-Hawaii Telescope
(CFHT) which is operated by the National Research Council of Canada,
the Institut National des Sciences de l'Univers of the Centre National
de la Recherche Scientifique de France, and the University of Hawaii.
---------------------------------------------------------
Title: Long-Term Spectroscopic Monitoring of Arcturus
Authors: Brown, Kevin I. T.; Gray, David F.; Baliunas, Sallie L.
2008ApJ...679.1531B Altcode:
We evaluate observed spectroscopic activity of Arcturus (HR 5340,
K2 III) from 1984 to 2007 using high-resolution spectroscopy and
Ca II H+K emission. Line-depth ratios of the V I λ6251.83 Å to
Fe I λ6252.56 Å lines and line bisectors from Fe I λ6252.56 Å
are used to evaluate spectroscopic activity. Chromospheric emission
within H+K lines is used as a magnetic activity indicator. We observe
a significant portion of what appears to be a magnetic cycle with a
period of >=14 yr. Line-depth ratios show comparable variation, but
with a time lag of 2.0 +/- 0.5 yr with respect to H+K variations. This
time lag is qualitatively similar to previous observations of G and K
dwarfs. No corresponding variation is observed in line bisectors. H+K
and line bisectors also show variability within seasons. A Fourier
analysis reveals periods of 253 and 207 days during the 1984-1989 H+K
seasons. Line bisectors show excess power over the range of ≈115-200
days from 1992 to 2007. We attribute this intraseason variability
to inferred magnetic activity along active longitudes. The range
of periods observed in H+K and line bisectors (≈115-253 days)
may result from migration of active regions within longitude bands,
implying differential rotation. We compare these observations with the
Sun and other solar-type stars. A 1/f noise component to the Fourier
spectrum of the line bisector variations is also observed.
---------------------------------------------------------
Title: The Observation and Analysis of Stellar Photospheres
Authors: Gray, David F.
2008oasp.book.....G Altcode:
1. Background; 2. Fourier transforms; 3. Spectroscopic tools; 4. Light
detectors; 5. Radiation terms and definitions; 6. The black body
and its radiation; 7. Radiative and convective energy transport;
8. The continuous absorption coefficient; 9. The model photosphere;
10. The measurement of stellar continua; 11. The line absorption
coefficient; 12. The measurement of spectral lines; 13. The behavior of
spectral lines; 14. The measurement of stellar radii and temperatures;
15. The measurement of photospheric pressure; 16. Chemical analysis;
17. Velocity fields in stellar photospheres; 18. Stellar rotation.
---------------------------------------------------------
Title: Mass Motions in the Photosphere of Betelgeuse
Authors: Gray, David F.
2008AJ....135.1450G Altcode:
Spectroscopic observations of Betelgeuse, taken at the Elginfield
Observatory, show velocity and temperature variations delineating
the systematic, but generally chaotic, rise and fall of photospheric
material. The characteristic timescale of the variations is 400 days,
while velocities cover a range of ~9 km s<SUP>-1</SUP>. Macroturbulence
is constant to about 13% and does not result from motions on the largest
scales, but from motions within the large structures. The line bisectors
have predominantly a reversed-C shape. Variations in the shapes of
bisectors occur on the 1 km s<SUP>-1</SUP> level and are not obviously
connected to their shifts in wavelength. A likely explanation of the
observations is granulation and giant convection cells accompanied by
short-lived oscillations they trigger. Random convection events may
account for radial-velocity jitter seen in many highly evolved stars.
---------------------------------------------------------
Title: Rotation and Macroturbulence in Metal-Poor Field Red Giant
and Red Horizontal Branch Stars
Authors: Carney, Bruce W.; Gray, David F.; Yong, David; Latham,
David W.; Manset, Nadine; Zelman, Rachel; Laird, John B.
2008AJ....135..892C Altcode: 2007arXiv0711.4984C
We report the results for rotational velocities, V<SUB>rot</SUB>
sin i, and macroturbulence dispersions, ζ<SUB>RT</SUB>, for 12
metal-poor field red giant branch (RGB) stars and 7 metal-poor field
red horizontal branch (RHB) stars. The results are based on Fourier
transform analyses of absorption line profiles from high-resolution
(R ≈ 120,000), high-S/N (≈215 per pixel; ≈345 per resolution
element) spectra obtained with the Gecko spectrograph at the
Canada-France-Hawaii Telescope (CFHT). The stars were selected from
the authors' previous studies of 20 RHB and 116 RGB stars, based
primarily on larger-than-average line-broadening values. We find
that ζ<SUB>RT</SUB> values for the metal-poor RGB stars are very
similar to those for metal-rich disk giants studied earlier by Gray
and his collaborators. Six of the RGB stars have small rotational
values, less than 2.0 km s<SUP>-1</SUP>, while five show significant
rotation/enhanced line broadening, over 3 km s<SUP>-1</SUP>. We
confirm the rapid rotation rate for RHB star HD 195636, found earlier
by Preston. This star's rotation is comparable to that of the fastest
known rotating blue horizontal branch (BHB) stars, when allowance
is made for differences in radii and moments of inertia. The other
six RHB stars have somewhat lower rotation but show a trend to higher
values at higher temperatures (lower radii). Comparing our results with
those for BHB stars from Kinman et al., we find that the fraction of
rapidly rotating RHB stars is somewhat lower than is found among BHB
stars. The number of rapidly rotating RHB stars is also smaller than
we would have expected from the observed rotation of the RGB stars. We
devise two empirical methods to translate our earlier line-broadening
results into V<SUB>rot</SUB> sin i for all the RGB and RHB stars
they studied. Binning the RGB stars by luminosity, we find that most
metal-poor field RGB stars show no detectable sign, on average, of
rotation, which is not surprising given the stars' large radii. However,
the most luminous stars, with M<SUB>V</SUB> <= -1.5, do show
net rotation, with mean values of 2-4 km s<SUP>-1</SUP>, depending
on the algorithm employed, and also show signs of radial velocity
jitter and mass loss. This "rotation" may in fact prove to be due to
other line-broadening effects, such as shock waves or pulsation. <P
/>Based on observations obtained at the Canada-France-Hawaii Telescope
(CFHT) which is operated by the National Research Council of Canada,
the Institut National des Sciences de l'Univers of the Centre National
de la Recherche Scientifique de France, and the University of Hawaii.
---------------------------------------------------------
Title: Spectroscopic Determination of Radius Changes of Cepheid
Variable Stars
Authors: Gray, David F.; Stevenson, Kevin B.
2007PASP..119..398G Altcode:
We introduce a simple method for determining pulsation velocities
of Cepheid variables; namely, the matching of observed spectral line
profiles in both shape and absolute position with model profiles. This
approach avoids the ambiguous meaning of radial velocity for asymmetric
lines, and it avoids the awkward projection factor (the “p” factor)
used to expand radial velocities to pulsation velocities. In this
investigation, we employ a simple pure-geometry model that reproduces
all the major features in the observations. We illustrate the method
using spectroscopic observations of ζ Gem, η Aql, and δ Cep taken
at the Elginfield Observatory, and derive the absolute radius changes.
---------------------------------------------------------
Title: The Rotation of Arcturus and Active Longitudes on Giant Stars
Authors: Gray, David F.; Brown, Kevin I. T.
2006PASP..118.1112G Altcode:
From two decades of high-resolution spectroscopic measurements of
Arcturus (HR 5340, K2 III), we identify a 2 yr modulation in the
velocity span of the bisector of the Fe I λ6252.57 line. It seems
likely that this is the rotation period, and we deduce the equatorial
rotation rate to be 1.8 +/- 0.3 km s<SUP>-1</SUP>, based on a radius of
25.4 R<SUB>solar</SUB>. From detailed Fourier analysis of the broadening
and shapes of the spectral lines, we derive vsini = 1.5 +/- 0.3 km
s<SUP>-1</SUP> and a radial-tangential macroturbulence dispersion of 5.2
+/- 0.2 km s<SUP>-1</SUP>. The inclination of the rotation axis to the
line of sight is then 58° +/- 25°. Considering the periods found by
H.-J. Choi et al. from variations in the Ca II H and K line emission,
we suggest that giant stars have two or three active longitudes and,
therefore, that periods found from the modulation of magnetic features
will be one-half or one-third of the rotation period.
---------------------------------------------------------
Title: Precise Spectroscopic Radial Velocity Measurements Using
Telluric Lines
Authors: Gray, David F.; Brown, Kevin I. T.
2006PASP..118..399G Altcode:
Telluric absorption inside our coudé spectrograph is used as a
reference spectrum for precise radial velocity measurement. The optical
path for this telluric absorption is stable and is not compromised by
atmospheric disturbances, such as the jet stream. As an added bonus,
the telluric fiducial spectrum is free; i.e., one does not need to
construct, regulate, maintain, or suffer throughput losses from a
captive-gas absorption cell. The telluric and stellar spectra span
the same portion of the detector and are observed sequentially, but in
different diffraction orders. In this way the stellar line profiles are
not contaminated by the telluric spectrum and can therefore be used for
normal astrophysical line profile analyses, as well as radial velocity
studies. However, precise measurements of the temperature and pressure
are needed for differential corrections between orders, because the
index of refraction of the air in the spectrograph is wavelength
dependent. Precision in radial velocity of ~25 m s<SUP>-1</SUP>
is demonstrated.
---------------------------------------------------------
Title: Quiet Sun unaffected by Activity Cycle
Authors: Livingston, W.; Gray, D.; Wallace, L.; White, O. R.
2005ASPC..346..353L Altcode:
The Sun's 11 year sunspot cycle, and all related phenomena, are driven
by magnetism in the form of hot flux tubes which thread through the
surface from below. Full disk chromospheric Ca K intensity observations
track the activity cycle. But center disk Ca K and photospheric
temperature sensitive lines are invariant to cycle magnetism. Recent
high resolution photographs of the photosphere show that the flux
tubes are confined between the granulation cells and do not interact
with them. The result is a constant basal atmosphere without cyclic
consequences for the Earth.
---------------------------------------------------------
Title: The Observation and Analysis of Stellar Photospheres
Authors: Gray, David F.
2005oasp.book.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotational Velocities of Selected F-Type Stars
Authors: Power, Jenny; Gray, David F.
2005JRASC..99T.143P Altcode:
Measurements of rotation velocities of a number of selected
F-type stars were performed based on observations obtained at the
University of Western Ontario Elginfield Observatory high-resolution
spectrograph. Rotation velocities were determined by comparing the
Fourier transform of the Fe i line at 6065.48 Å to the model rotation
profile. Errors of 1 to 2% were found.
---------------------------------------------------------
Title: Simultaneous Radial-Velocity and High-Resolution Spectroscopic
Monitoring of Cool Giant Stars
Authors: Brown, Kevin; Gray, David F.
2005JRASC..99R.135B Altcode:
We present results from the simultaneous radial velocity and line
profile monitoring of cool giant stars. Spectroscopic observations
with resolving power of R = 100,000 were made using the University
of Western Ontario's Elginfield Observatory. The radial-velocity
measurements use telluric lines within the spectrograph as a reference
against which the stellar spectra are compared. Our technique avoids
contamination of the observed stellar spectrum by the reference
spectrum, a commonly encountered problem in precision radialvelocity
measurements. We are then able to measure line-depth ratios and
other spectroscopic parameters of interest in concert with the
radial-velocity measurements. This approach is useful for studies of
pulsation, granulation variations, surface features, magnetic cycles,
non-radial oscillations, and orbital motion arising from extra-solar
planets or binary-star companions.
---------------------------------------------------------
Title: The Blue Bump in Spectral Line Bisectors
Authors: Gray, David
2005JRASC..99R.129G Altcode:
Most spectral lines in stellar spectra are slightly asymmetric. This
asymmetry is conveniently expressed by using the bisector of the
line. Bisectors of solar lines typically have a slightly distorted C
shape, and many cool stars mimic the Sun. But there are very significant
differences from one star to the next depending primarily on the vigor
of the granulation and the structure of the star's atmosphere. The
interesting relation discussed here is the coupling of the height of
the "blue bump" (blue-most point on the bisector) with luminosity:
the more luminous the star, the lower the blue bump. As a luminosity
discriminant, the blue bump is about five times better than a standard
spectral type classification. As a revealer of secrets about stellar
atmospheres, it tells us that the brighter the star, the higher in
the atmospheres the granulation penetrates. These results are based
on observations taken at the Elginfield Observatory at UWO.
---------------------------------------------------------
Title: Shapes of Spectral Line Bisectors for Cool Stars
Authors: Gray, David F.
2005PASP..117..711G Altcode:
The shape of the line bisector for the prototype spectral line Fe
I λ6253 was measured for an array of 54 stars on the cool half of
the HR diagram. These bisectors are given in tables along with their
errors. The classic C shape is shown by only a rather restricted
range in effective temperature and luminosity. The detailed change in
bisector shape with effective temperature and luminosity is documented
more precisely than in previous work. The most blueward point on the
bisector changes its height systematically with luminosity and can be
used as a luminosity or gravity discriminant. The wide range of bisector
shapes contains significant information about the velocity fields in
the atmospheres of these stars, but extracting that information may
require extensive modeling.
---------------------------------------------------------
Title: High resolution spectroscopic study of red clump stars in
the Galaxy: main atmospheric parameters
Authors: Tautvaišiene, G.; Stasiukaitis, E.; Puzeras, E.; Gray,
D. F.; Ilyin, I.
2005ESASP.560..989T Altcode: 2005csss...13..989T
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic line-depth ratios and solar variability
Authors: Gray, David F.
2004AdSpR..34..308G Altcode:
Line-depth ratios, i.e., the ratios of the central depths of
suitably-chosen spectral lines, have proved to be an effective
thermometer for stars on the cool half of the HR diagram. Several
individual stars show line-depth-ratios changing in concert with Ca
II H&K emission over decade time scales; some have amplitudes of
many degrees. The disk-integrated solar spectrum shows variations
in line-depth ratios that are quite weak, amounting to a degree
or so. Although we have observations for only one solar cycle,
there can be little doubt that the variation is part of the cycle
process. The physical cause of the variation is likely the changing
fraction of the surface infused with magnetic field (plage), where the
run of temperature with optical depth differs from the non-magnetic
regions. Line-depth ratios may prove useful in understanding the
variation in photospheric structure with changing magnetic activity,
and for monitoring secular changes over many solar cycles.
---------------------------------------------------------
Title: Amazing Grace
Authors: Talbot, G.; Chopping, A.; Dee, K.; Gray, D.; Jolley, P.
2003INGN....7...19T Altcode:
T he profile of the William Herschel Telescope (WHT) has changed since
the beginning of this year, with the addition of a new facility at one
of the telescope's Nasmyth platforms. For many years the WHT has had the
GHRIL building on the Nasmyth1 platform - now the ING has added GRACE
to the opposite side of the telescope. GRACE (GRound based Adaptive
optics Controlled Environment) is a dedicated structure designed to
facilitate the routine use of adaptive optics (AO) at the WHT, using
ING's AO instrument suite. The design of GRACE allows for the future
use of laser guide stars.
---------------------------------------------------------
Title: Giant Convection Cells, Where Are You?
Authors: Gray, D. F.
2003csss...12..344G Altcode:
High-resolution high S/N observations of photospheric lines in the
spectrum of Betelgeuse are devoid of the structure one would expect
if only a few giant convection cells dominated the surface of the star.
---------------------------------------------------------
Title: Stellar Photospheres: Success, Failure, Ambiguity,
&Ambition
Authors: Gray, D. F.
2003IAUS..210..287G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling of Stellar Atmospheres
Authors: Piskunov, N.; Weiss, W. W.; Gray, D. F.
2003IAUS..210.....P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Chemical Homogeneity of Atmospheres in Clump Stars of the
Galaxy
Authors: Tautvaisiene, G.; Puzeras, E.; Gray, D. F.; Ilyin, I.
2003IAUS..210P..D6T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line Absorption as a Metallicity Index for Giant Stars
Authors: Gray, David F.; Scott, Heather R.; Postma, Joseph E.
2002PASP..114..536G Altcode:
The fraction of light removed from a star's spectrum by the spectral
lines, the line absorption, is shown to be a precise empirical
indicator of metallicity. We measured the line absorption in 89 class
III giant stars in a 42.5 Å window between 6219.0 and 6261.5 Å and
then calibrated these values against published metallicities. We show
that the line absorption can be measured precisely enough to improve
the metallicity precision about fivefold over the original calibration
metallicities, reaching a precision of 0.01 dex in favorable cases.
---------------------------------------------------------
Title: Spetroscopic Line-Depth Ratios and Solar Variability
Authors: Gray, D.
2002cosp...34E.314G Altcode: 2002cosp.meetE.314G
The ratios of the central depths of selected spectral lines has proved
to be a sensitive index of a star's temperature. Line-depth ratios
have been successfully applied to main sequence stars (Gray 1994
P.A.S.P. 106, 1248) as well as giants (Gray &Brown 2001 P.A.S.P.,
113, 723). A stellar calibration and subsequent application to solar
data over a magnetic cycle gave plausible results (Gray &Livingston
1997 Ap.J., 474, 802), indicating a solar temperature variation ~
1.5 K. This result is subject to unresolved criticisms. I will review
these results and focus on possible meanings of the variations in
solar line-depth ratios.
---------------------------------------------------------
Title: Betelgeuse: Giant Convection Cells
Authors: Gray, David F.
2001PASP..113.1378G Altcode:
Spectroscopic observations of the M supergiant star Betelgeuse
were taken at the Elginfield Observatory over 17 months in the
1999-2000 observing seasons in order to search for giant convection
cells. Although the photospheric spectral lines show some temporal
variations, mainly in their depths (consistent with a previously study),
the Doppler shift distribution inferred from them is remarkably
stable. The spectral lines show characteristic macroturbulence
dispersion ~15 km s<SUP>-1</SUP> and cover a full span of +/-50-60
km s<SUP>-1</SUP>. The widths of the lines show occasional as well
as longer term changes of a few percent but no evidence for giant
convection cells. These spectroscopic observations are more consistent
with a classical picture of nonthermal photospheric velocities in
which large numbers of convection cells appear on the stellar disk at
all times.
---------------------------------------------------------
Title: Line-Depth Ratios: Temperature Indices for Giant Stars
Authors: Gray, David F.; Brown, Kevin
2001PASP..113..723G Altcode:
Ratios of the depths of appropriately chosen spectral lines are shown
to be excellent indicators of stellar temperatures for giant stars
in the G3 to K3 spectral type range. We calibrate five line-depth
ratios against B-V and R-I color indices and then translate these
into temperatures. Our goal is to set up line-depth ratios to (1)
accurately monitor any temperature variations of a few degrees or
less that may occur during magnetic cycles or oscillations and (2)
rank giants precisely on a temperature coordinate. This is not an
absolute calibration of stellar temperatures. We show how giant
spectra can be misleading because of the complex dependences of
spectral lines on metallicity and absolute magnitude as well as
temperature, and it is essential to make corrections to accommodate
these complications. The five line-depth ratios we use yield precision
for monitoring, i.e., detecting temperature variations, of 4 K from
a single exposure. Ranking giants by temperature can be done with
errors of ~25 K but could be improved with better determinations of
the metallicity and absolute-magnitude corrections.
---------------------------------------------------------
Title: Spectral-Line Profiles in Daytime Skylight
Authors: Gray, David F.; Tycner, Christopher; Brown, Kevin
2000PASP..112..328G Altcode:
The 1.2 m telescope and coudé spectrograph at our Elginfield
Observatory was used to investigate the suitability of daytime skylight
as a reference spectrum for astrophysical work. We show that with
sufficient care, skylight does give the flux (or disk-integrated)
spectrum of the Sun, allowing direct comparison with other stars. The
line profiles in skylight become shallower with increasing angular
separation from the Sun up to ~100 deg, and then for larger angles they
deepen slightly again. The amplitude of this variation is typically
3%-4% of the depth of the line. If the profiles are normalized to
their central depths, their shapes remain unaltered. This implies
that astrophysical analyses based on the shapes of spectral lines or
ratios of depths of spectral lines in skylight should not be seriously
affected. However, equivalent widths are not conserved; they can be
reduced by up to the same 3%-4% unless care is taken to observe the
sky close to the Sun or unless the angular variation is measured,
as described here, and corrections applied. The skylight variations
can be explained as a combination of aerosol and Rayleigh-Brillouin
scattering. There is no discernible dependence with altitude of the Sun,
ruling out a significant ground-albedo effect.
---------------------------------------------------------
Title: The Half Arcsecond Programme (I)
Authors: Packham, C.; Wilson, R. W.; Azzaro, M.; O'Mahony, N.; Fine,
S.; Gray, D.; Reyes, V.; Martín, C.
2000INGN....2...21P Altcode:
Over the last three years, the Half Arcsecond Program (HAP)
has found some important and surprising results. These
results, recently published in the MNRAS (Wilson et
al., 1999, 309, 379), are summarised on the HAP WWW site
(http://www.ing.iac.es/Astronomy/development/hap/haphomepage.htm)
and a short summary of the key conclusions follows.
---------------------------------------------------------
Title: Betelgeuse and Its Variations
Authors: Gray, David F.
2000ApJ...532..487G Altcode:
Observations of Betelgeuse show that (1) the photospheric spectral
lines are very broad with a 1/e width of 11 km s<SUP>-1</SUP>, but
they have stable shapes with time as the star varies in other ways;
(2) all the spectral lines within the observed wavelength region
change their depths by essentially the same factor and in phase
with the photometric brightness of the star on timescales of months;
(3) small deviations from perfect scaling of the line depths imply
temperature variations that to first order are in phase with the
line depths, i.e., cooler temperatures go with weaker lines; and (4)
to second order, the temperature variations lag behind the changes in
line depths by ~5 days. The hypothesis of changing continuous opacity
is put forward as a coherent explanation of all of these spectroscopic
and photometric effects. In addition, the bright spot observed by others
is explained as a region where the opacity does not change; it is not
a giant convection cell. The physical reason for the opacity change
has yet to be identified. Structure in the cores of spectral lines
varies on the timescale of a day, and this may be the signature of
giant convection cells, but other interpretations are also possible,
including hot spots, prominences, or nonradial oscillations.
---------------------------------------------------------
Title: Commission 29: Stellar Spectra: (Spectres Stellaires)
Authors: Barbuy, B.; Mathys, G.; Bessell, M.; Cottrell, P.; Spite,
F.; Gray, D. F.; Heber, U.; Khokhlova, V. L.; Renzini, A.; Lyubimkov,
L.; Nissen, P. E.; Peterson, R.; Sneden, C.; Wolf, B.
2000IAUTA..24..190B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The magic of Betelgeuse.
Authors: Gray, D. F.
1999JRASC..93..181G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Rotation and Precise Radial Velocities
Authors: Gray, D. F.
1999ASPC..185..243G Altcode: 1999IAUCo.170..243G; 1999psrv.conf..243G
Two aspects will be considered. First, I will view the spectroscopic
measurement of rotation rates as a differential precision radial
velocity: how do we get rotation rates; what are the uncertainties
stemming from differential rotation, time variable profiles
caused by spots, uncertain limb darkening, and the presence of
macroturbulence? What do we even mean by the rotation rate when
there is differential rotation? Second, I will discuss the effects of
rotation on specifying the precise position of spectral lines, i.e.,
the classical radial velocity of a star. I will present some thoughts on
the effects of having our sharp markers of the Doppler effect degraded
by rotation, the meaning of line position when the Doppler effects of
rotation and convection interact, and the altered shapes of composite
spectrum features with increased rotational smearing.
---------------------------------------------------------
Title: Stars and Sun; Treasures and Threats
Authors: Gray, David F.
1998ASPC..154..193G Altcode: 1998csss...10..193G
Magnetic cycles unify a good deal of our thinking concerning cool
stars. Here I review some aspects of how the Sun stands apart from
other cool stars, specifically its low amplitude of variation, its
lack of a time lag of temperature variation behind H&K variation,
and possibly its differential rotation.
---------------------------------------------------------
Title: A planetary companion for 51 Pegasi implied by absence of
pulsations in the stellar spectra
Authors: Gray, David F.
1998Natur.391..153G Altcode:
Systematic variations in the Doppler shifts of absorption lines in
the spectrum of the star 51 Pegasi were interpreted as indicating the
presence of a planet about half the mass of Jupiter, very close to the
star,. But that interpretation was called into question when variations
in the line shapes that tracked the apparent orbital phase were
reported,; this suggested that a planet was an inadequate explanation of
the radial-velocity data. Here I report results from recent monitoring
of 51 Peg; the oscillations I previously published are not evident in
the new data. When combined with two other high-precision observations
of 51 Peg (refs 5-7), that also see no changes in line shape, a planet
may indeed be the best explanation for the radial-velocity results.
---------------------------------------------------------
Title: Evolved Stars: What Happens to Activity Off the Main Sequence
Authors: Strassmeier, K. G.; Fekel, F. C.; Gray, D. F.; Hatzes, A. P.;
Schmitt, J. H. M. M.; Solanki, S. K.
1998ASPC..154..257S Altcode: 1998csss...10..257S
Magnetic activity on the main sequence has been well studied, in
contrast to researches on sub-giants, giants, and supergiant stars. In
this discussion we will address three main topics associated with
activity in evolved stars: (1) rotation regimes for evolved stars;
(2) rotation-activity relations in the H-R diagram; (3) polar spots.
---------------------------------------------------------
Title: Non-Radial Oscillation in the Solar-Temperature Star 51 Pegasi
Authors: Gray, David F.; Hatzes, Artie P.
1997ApJ...490..412G Altcode:
We present results of high-resolution spectroscopic observations of the
solar-temperature star 51 Peg taken between 1989 and 1996. Variations in
the shape of the Fe I λ6252.53 Fe I spectral line are investigated in
detail to establish their reality, nature, and likely cause. Because
our spectroscopic data were gathered for purposes other than the
present one, they are thinly distributed over the 7 years. This
makes it difficult for us to prove beyond doubt that the variations
in the shapes of the profiles are one and the same as the 4.23 day
period of radial velocity variations found by Mayor & Queloz and
Marcy et al. Nevertheless, we show that the probability of our data
matching the periodicity of the radial velocity data the way it does
by pure chance is only one in several hundred. Since the probability
strongly favors the reality of the 4.23 day profile shape variations,
we proceed to model them with nonradial oscillations having low order
and low degree. The shifts and distortions of spectral lines induced
by oscillations having l = -m = 4 fully account for both the radial
velocity observations and the changes in line profiles delineated by our
high-resolution spectroscopy. The planet hypothesis, proposed in the
above mentioned papers, cannot account for implicit variations of the
spectral line profiles. Assuming these variations are real, the planet
hypothesis is no longer viable, and the need to explain the unseen and
puzzling planet in an unusual orbit no longer exists. Instead, the door
may have been opened to the important new area of research: low-order
nonradial pulsation in solar-temperature stars. In the Appendix we
refute various suggestions by which the originally proposed planet
might induce the line-profile variations.
---------------------------------------------------------
Title: The Antics of 51 Peg
Authors: Gray, D. F.
1997BAAS...29.1116G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum: Monitoring the Solar Temperature: Spectroscopic
Temperature Variations of the Sun
Authors: Gray, David F.; Livingston, William C.
1997ApJ...484..511G Altcode:
In the paper “Monitoring the Solar Temperature: Spectroscopic
Temperature Variations of the Sun” by David F. Gray and William
C. Livingston (<A href="/abs/1997ApJ...474..802">ApJ, 474, 802
[1997]</A>), equation (4), giving the variation in observed
line depth, is incorrect. It should read δd<SUB>obs</SUB>=δs
((A<SUB>0</SUB>-1)d<SUB>true</SUB>)/((1-sA<SUB>0</SUB>)<SUP>2</SUP>)
. The remainder of § 5 following equation (4) stems from the incorrect
equation and should be disregarded. These changes do not affect the
results of the paper, except that a possible explanation for the nearly
synchronized variation of the central depths of all three spectral lines
no longer obtains. <P />The authors note that an error in setting the
continuum level is farthest from explaining the scaling behavior of the
line depths shown in Figures 4 and 5 of the original paper. Continuum
errors affect weaker lines proportionately more than stronger lines,
which is just the opposite of what is observed. An error in zero
level, which is close to the effect of scattered light, causes line
depths to scale proportional to their depth. This is closer to what
is observed, but does not go far enough in this direction, since the
percent variation in the weaker C I line (depth 0.13) is only about
half that of the Ti II (depth 0.48) and Fe I (depth 0.52) lines.
---------------------------------------------------------
Title: Absence of a planetary signature in the spectra of the star
51 Pegasi
Authors: Gray, David F.
1997Natur.385..795G Altcode:
51 Pegasi, one of many nearby Sun-like stars, was undistinguished
until the recent detections of apparent variations in its radial
velocity, which have been attributed to reflex motion caused by a
planetary companion<SUP>1,2</SUP>. The velocity variation inferred
from variations in the spectral lines of 51 Peg has an amplitude of
56-59 m s<SUP>-l</SUP> and a period of 4.23 days, implying a planet
of at least half the mass of Jupiter moving in an embarrassingly
small orbit of 0.05 astronomical units. But the techniques currently
used to identify these exceedingly small radial velocity variations
do not allow for the possibility that changes of comparable size
might be occurring in the intrinsic shapes of the spectral lines;
such variations are expected when a star pulsates or has spots on its
surface, and could be mistaken for radial velocity variations. Here
I present high-spectral-resolution observations of 51 Peg that show
that its spectral lines exhibit intrinsic shape variations with a
period of 4.23 days, and an amplitude comparable to that previously
attributed<SUP>1,2</SUP> to radial velocity variations. As the presence
of a planet will not influence the shapes of spectral lines, these
variations are likely to reflect a hitherto unknown mode of stellar
oscillation. The presence of a planet is not required to explain
the data.
---------------------------------------------------------
Title: The Rotation of the G0 Dwarf β Comae
Authors: Gray, David F.; Baliunas, Sallie L.
1997ApJ...475..303G Altcode:
The rotation of β Comae (HR 4983, HD 114710, G0 V) is studied
using the available information from spectral line broadening
and from rotational modulation. The line broadening yields v sin
i = 4.10 +/- 0.06 km s<SUP>-1</SUP>, which agrees with previous
values. Rotational modulation was looked for but not seen in the
photospheric parameters of temperature and granulation, although this
might be a result of data sampling not being well suited for modulation
studies. Rotational modulation is seen in the S index of the Ca II
chromospheric emission. Two period sequences characterize β Comae
between 1981 and 1994. The periods decline monotonically with time,
paralleling the decline in magnetic activity as indicated by the
average strength of the Ca II emission. We interpret the decrease in
period as differential rotation coupled with systematic migration in
latitude of the active regions. It is not possible to separate the
differential rotation profile of β Comae from its rate and sense of
latitude migration. We compare the changes of β Comae with the Sun's
and point out similarities and differences.
---------------------------------------------------------
Title: High resolution spectroscopy.
Authors: Gray, D. F.
1997ilt..book..163G Altcode:
This lecture series discusses the specific instrumental requirements
and observing and reduction techniques required for high resolution
optical spectroscopy. The topics discussed include: (1) what is a
spectrograph? (2) diffraction gratings; (3) the basic spectrograph;
(4) the fundamental reasoning; (5) telescope-spectrograph coupling;
(6) image slicers - another way out; (7) high-order solution: echelle
spectrographs; (8) comments on detectors; (9) some examples of high
resolution spectrographs; (10) using spectrographs, or so that's the way
it works! (11) the instrumental profile; (12) the problem of scattered
light; (13) other system light problems; (14) stability checks;
(15) comments on instrumentally - induced distortions of the data;
(16) spectral lines: an extension of our spectroscopic tool box;
(17) choosing the right equipment.
---------------------------------------------------------
Title: Monitoring the Solar Temperature: Spectroscopic Temperature
Variations of the Sun
Authors: Gray, David F.; Livingston, William C.
1997ApJ...474..802G Altcode:
The C I λ5380 line in the solar flux spectrum was measured over
the 1978-1992 interval. Analysis of the data shows seasonal and
instrumental effects, but after allowance for these, the ratios of
spectral line depths, C I λ5380 to Fe I λ5379 and to Ti II λ5381,
are shown to be robust indicators of effective temperature. These
data show the solar temperature to have varied systematically during
the activity cycle and nearly in phase with other indicators of the
cycle. The amplitude of the variation is 1.5 K +/- 0.2 K, similar to
but slightly less than the range implied by the variations of the
sunspot-corrected irradiance. There is also evidence for a secular
trend amounting to ~+0.014 K per year.
---------------------------------------------------------
Title: Monitoring the Solar Temperature: Empirical Calibration of
the Temperature Sensitivity of C I λ5380
Authors: Gray, David F.; Livingston, William C.
1997ApJ...474..798G Altcode:
We observed a set of six dwarf stars spanning a range in temperatures
around the solar value, and from them we have determined empirically
the temperature sensitivity of C I λ5380.32, a line that has been
monitored in the solar flux spectrum for nearly two decades at Kitt
Peak. When the C I line is compared to the adjacent Fe I λ5379.58 line,
it should be possible to detect apparent temperature differences of
a fraction of 1 K.
---------------------------------------------------------
Title: Variation of the solar temperature 1978 - 92.
Authors: Gray, D. F.
1996JRASC..90..306G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic, Photometric, Temperature, and Granulation Variations
of XI Bootis A 1984--1993
Authors: Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff,
Brian A.
1996ApJ...465..945G Altcode:
The magnetically active G8 dwarf star, ξ Boo A = HR 5544 = HD 13 1156
is studied for magnetic- cycle type variations over the 1984-1993
interval. We present measurements of Ca II H and K emission as an
indirect indicator of magnetic activity, blue and visual magnitudes as
an indication of the power output and temperature, line-depth ratios
of V I λ6251.83 to Fe I λ6252.57 as a measure of temperature, and
line bisectors as a measure of the star's granulation. The season
means of all these parameters show the same pattern of variation with
several irregular rises and falls, rather different from the relatively
smooth variations seen for the Sun. As found for several other stars in
previous studies, the magnetic signal leads the others in time. Time
lags relative to the H and K index variation are 1.4±0.4 yr for
the photometric brightness, 1.5±0.5 yr for the b -y color index,
1.8±0.3 yr for the line-depth ratio, and 2.1±0.4 yr for the line
bisectors. The ≍1.7 year temperature lag for ξ Boo A is close to
the linear relation between lag and effective temperature found for
the other stars that have been measured.
---------------------------------------------------------
Title: In memoriam William "Bill" H. Wehlau (1926 - 1995).
Authors: Wehlau, A.; Gray, D. F.; Rice, J.
1996IAUS..176D..13W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Variations of beta Comae through a Magnetic Minimum
Authors: Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff,
Brian A.
1996ApJ...456..365G Altcode:
The dwarf star β Com = HR 4983 = HD 114710 (GO V, B-V = 0.57) is close
to the Sun in the H-R diagram, being only ≍260 K hotter. We present
measurements done over several years of (1) the line depth ratios
of V I λ6251.83 to Fe I λ6252.57 to establish the temperature,
(2) the line bisectors as a measure of the star's granulation, (3)
Ca II H and K emission as an indirect indicator of magnetic activity,
and (4) the blue and visual magnitudes as an indication of the power
output. All these parameters show a similar variation consisting of a
broad minimum extending over approximately 5 years, but the minima do
not occur at the same epoch. The magnetic signature leads the others
in time. Time lags relative to the magnetic variation are 0.9±0.3
yr for the photometric data, 2.9±0.3 yr for the temperature, and
2.9±0.5 yr for the granulation. A 1% variation in radius during the
5 yr interval is indicated.
---------------------------------------------------------
Title: The determination of temperature from spectral lines
Authors: Gray, D. F.
1996IAUS..176..227G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: The Sun as a Variable Star ; Solar and Stellar
Irradiance Variations (IAU colloquium 143) / Cambridge U Press, 1994
Authors: Gray, D. F.
1995JRASC..89..239G Altcode: 1995JRASC..89..239P
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Activity Variations of epsilon Eridani
Authors: Gray, David F.; Baliunas, Sallie L.
1995ApJ...441..436G Altcode:
The variations in magnetic activity, temperature and granulation of
epsilon Eri (HR 1084, HD 22049, K2 V, B-V = 0.88) in the interval from
1986 to 1992 are discussed in this paper. We monitored the magnetic
activity with the Ca II H and K-line emission, the temperature with
the ratio of depths of two spectral lines, and the granulation with
spectral-line asymmetries. Rotational modulation is seen only in the
H and K emission, and it shows a period of 11.10 +/- 0.03 days, in
agreement with earlier published values. The star has one dominant
activity longitude. The magnetic activity of epsilon Eri is strong
and shows irregular excursions that may be superposed on a cyclic
variation having a period approximately equal to 5 yr. During the
1986-1992 interval the magnetic activity went through a broad relative
minimum. Temperature and granulation changes mimic the variation in
H and K emission, with excursions approximately equal to 15 K and
approximately equal to 35 m/s, repectively. No long-term photometric
observations are available for epsilon Eri, but we calculate a 1.2%
variation in luminosity and 0.014 mag in V to have occurred, assuming
the radius of the star is constant.
---------------------------------------------------------
Title: Comparing the Sun with Other Stars along the Temperature
Coordinate
Authors: Gray, David F.
1995PASP..107..120G Altcode:
The temperature of the sun relative to other stars is determined
using high-precision measurements of the ratios of depth of spectral
lines. In effect, the sun is placed within the stellar grid of relative
temperatures with an estimated uncertainty of +- 10 K. Among others,
16 Cyg A is found to be 5 +- 12 K hotter than the sun, while 16 Cyg
B is found to be 45 +- 12 K cooler than the sun. In a similar manner,
color indices are inferred with the results that R-I = 0.338 +- 0.002
on the Cousins system and B-V = 0.648 +- 0.006. This latter value
supersedes the value of 0.656 published in 1992. (SECTION: Stars)
---------------------------------------------------------
Title: Abundances of Elements in Gamma Draconis
Authors: Sinha, K.; Sanwal, B. B.; Gray, D. F.
1995ASPC...78..407S Altcode: 1995aapn.conf..407S
No abstract at ADS
---------------------------------------------------------
Title: Spectral Line-Depth Ratios as Temperature Indicators for
Cool Stars
Authors: Gray, David F.
1994PASP..106.1248G Altcode:
The use of spectral line-depth ratios as a stellar thermometer in G
and K dwarfs is developed and refined beyond an earlier study (Gray
and Johnson 1991). Ratios incorporating a line with any degree of
saturation, as with the lambda-6252 V I to lambda-6253 Fe I ratio used
in the 1991 work, produce metallicity dependent results. This dependence
is investigated here, and a correction derived. Ten line-depth
ratios using only weak lines are shown to have negligible metallicty
dependence and resolve temperature differences as small as 6 K for
early K dwarfs from a single exposure having a signal-to-noise ratio
of 500. Precision deteriorates badly toward G0 for these particular
spectral lines. Smaller temperature differences can be resolved by
combining exposures. Relative temperatures of 65 dwarfs are given, a
few having errors near 1 K. Inconsistencies ~50 K between temperatures
derived from color indices and from spectral lines are most likely a
result of interstellar reddening affecting the photometry. (SECTION:
Stars)
---------------------------------------------------------
Title: Jupiter
Authors: Billebaud, F.; Merlin, P.; Sibille, F.; Vauglin, I.; Drossart,
P.; Lellouch, E.; Gray, D.; Rogers, J.; Levy, D. H.
1994IAUC.6119....1B Altcode:
F. Billebaud, Space Science Department, ESA-ESTEC, Noordwijk; P. Merlin,
F. Sibille, and I. Vauglin, Equipe Infrarouge, Observatoire de Lyon; and
P. Drossart and E. Lellouch, DESPA, Observatoire de Paris, report: "We
have observed Jupiter on Dec. 18 and 19 with the 10-micron array camera
'C10mu' and its Circular Variable Filter (CVF; spectral resolution
50) at the Canada-France- Hawaii telescope on Mauna Kea. We have
recorded images at several CVF wavelengths, in particular 7.81 and
7.93 microns. The images recorded at those two wavelengths exhibit
a lower flux on a belt at the latitude of the impact sites of comet
1993e, compared to all other latitudes. Although not homogeneous,
the belt seems to cover all longitudes, and the extension in latitude
seems to be on the order of 20o. Preliminary processing of the images
indicates that the flux is about 40 percent lower at 7.81 microns
and 30 percent lower at 7.93 microns, when compared to the flux at
near-equatorial regions. This corresponds roughly to a contrast of 7 K
at 7.81 microns and 5 K at 7.93 microns; these two wavelengths probe the
methane emissions in the mid-stratosphere (>/about 30 mbar at 7.93
microns, and somewhat higher at 7.81 microns). We suggest that this
atmospheric cooling in the impact regions may have two origins: (1)
cooling by efficient infrared radiators (NH3, HCN, H2O, etc.) injected
in the stratosphere during the impact period; (2) thermal cooling of
the haze and reflection of sunlight to space." Visual observations of
Jupiter in poor seeing by D. Gray (Durham, England, 0.4-m telescope;
via J. Rogers) on Dec. 14-16 and by D. H. Levy (Tucson, AZ, 0.20-m
reflector) on Dec. 18.58 UT suggest that the dark impact band is still
very obvious, similar to its appearance in September.
---------------------------------------------------------
Title: Stellar activity cycles: complications.
Authors: Gray, D. F.
1994JRASC..88Q.261G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Telluric line radial velocities of late-type giant stars.
Authors: Holmgren, D. E.; Gray, D. F.
1994JRASC..88Q.263H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Activity Cycle of tau Ceti
Authors: Gray, David F.; Baliunas, Sallie L.
1994ApJ...427.1042G Altcode:
The temperature, granulation, and chromospehric emission of tau Ceti (HR
509, HD 10700, G8 V, B-V = 0.72) in the 1984-1992 interval are studied
for magnetic-cycle type variations. Yearly-mean temperature measurements
are determined to +/- 3-4 K using ratios of spectral line depths, and
show no systematic variations over the 9 yr interval. Granulation
is monitored using the asymmetries of spectral lines. There is
some indication of systematic variation in velocity span, but this
variation is not well established. The Ca II H and K line emission,
although weak by stellar standards, may show two cycles of variability
in the 1970-1992 time span with a period of approximately = 11 yr. No
rotation modulation is seen in any of the parameters, but the very
narrow spectral lines of tau Cet points to a nearly pole-on orientation
so that none would be expected.
---------------------------------------------------------
Title: The Temperature and Granulation Stability of eta Cephei
Authors: Gray, David F.
1994ApJ...428..765G Altcode:
As part of a larger long-term project to measure variations in
photospheric temperature and granulation arising from rotational
modulation and stellar magnetic cycles, the null results for the
subgiant star eta Cep (HR 7957, HD 198149, K0 IV, B-V=0.92) in
the 1989-1992 interval are reported here. Temperature variations on
rotational timescales are less than 5 K, and year-to-year variations,
such as those one might expect during a magnetic cycle, are less
than 1.7 K. No variation is detected in the velocity span of the
spectral-line bisectors above 19m/sec on rotational timescales, and
any year-to-year variations must be less than 5 m/sec.
---------------------------------------------------------
Title: Stellar Magnetic-Cycle Phasing
Authors: Gray, David F.
1994PASP..106..145G Altcode:
During magnetic-cycle type variations in dwarf stars, changes in the
H & K magnetic activity index precede change in temperature by
times ranging from several years at G0 down to near zero at K2. These
results are preliminary however because they are based on observations
of only three stars. (SECTION: Stars)
---------------------------------------------------------
Title: Book-Review - the Observation and Analysis of Stellar
Photospheres
Authors: Gray, D. F.; Trimble, V.
1993ComAp..16..278G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Activity Cycle of sigma Draconis
Authors: Gray, David F.; Baliunas, Sallie L.; Lockwood, G. W.; Skiff,
Brian A.
1992ApJ...400..681G Altcode:
Investigations of the temperature and granulation of Sigma Draconis
(HR 7462, HD 185144, K0 V) are discussed. Temperature is monitored
using a line-depth ratio, and temperature variations of about 5 K are
seen. Intermediate-band photometry and Ca II H and K-line emission mimic
the temperature changes: a monotonic decline from the 1984 season,
a smooth minimum around 1988, followed by a rise back to the 1984
values at the current time. The temperature variations are physically
compatible with the photometric ones, implying a constant radius
over the activity cycle. Granulation is invariant during this portion
of the activity cycle, at least to the level of about +/- 3 m/s, or
about +/- 5 percent. The temperature variations by themselves can also
be interpreted as rotational modulation with a 20.3-d period, but no
evidence of this period is seen in the photometry, the H and K emission,
or the line asymmetries, and it is argued to be a chance occurrence.
---------------------------------------------------------
Title: Activity cycles in dwarfs: σ Draconis.
Authors: Gray, D. F.; Baliunas, S. L.; Lockwood, G. W.; Skiff, B. A.
1992JRASC..86..277G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Inferred Color Index of the Sun
Authors: Gray, David F.
1992PASP..104.1035G Altcode:
The high temperature sensitivity of the line-depth ratio V I
lambda-6251.83 to Fe I lambda-6252.57, measured in the daytime sky,
is used to infer the color indices of the sun: B-V = 0.656 +/- 0.005,
b-y = 0.414 +/- 0.003, and B2-V1 = 0.393 +/- 0.004. (SECTION: Stars)
---------------------------------------------------------
Title: Book Review: Atoms, Stars and Nebulae -- 3rd edition /
Cambridge U Press, 1991
Authors: Gray, D. F.
1992JRASC..86..271G Altcode: 1992JRASC..86..271A
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Observations and Analysis of Stellar Photospheres
- ED.2
Authors: Gray, D. F.
1992Sci...257.1978G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Books-Received - the Observation and Analysis of Stellar
Photospheres - ED.2
Authors: Gray, D. F.
1992JBAA..102..230G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The observation and analysis of stellar photospheres.
Authors: Gray, D. F.
1992oasp.book.....G Altcode: 1992CAS....20.....G
The starlight we see comes from the outer layers of a star, from the
region known as the photosphere. Most of what we know about stars is
learned by studying the light from the photosphere. This book describes
the equipment, observational techniques and analysis used in the
investigation of stellar photospheres. The opening chapters describe
the basic tools, such as spectrographs and light detectors, as well as
the physics of radiative transfer and the construction of models. Next
the author introduces the measurement and modelling of the continuum
spectrum. This is followed by the study of spectral line radiation. The
final chapters explain how these techniques enable astronomers to
deduce valuable information on basic properties of stars. For example,
temperature, radius, surface gravity, chemical composition, rotation
rate, and velocity fields can be derived from stellar spectroscopy.
---------------------------------------------------------
Title: Area^2 Dynamos Performing on Center Stage?
Authors: Gray, David F.
1992ASPC...27..472G Altcode: 1992socy.work..472G
No abstract at ADS
---------------------------------------------------------
Title: Stellar Convection: The Observations (Invited Review)
Authors: Gray, D. F.
1992ASPC...26..127G Altcode: 1992csss....7..127G
No abstract at ADS
---------------------------------------------------------
Title: The Observatories of the University of Western Ontario,
London, Ontario N6A 3K7, Canada. Report for the period 1 Jul 1990 -
1 Jul 1991.
Authors: Gray, D. F.
1992BAAS...24..651G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A technique for precisely measuring stellar temperatures.
Authors: Gray, D. F.; Johanson, H. L.
1991JRASC..85..183G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Precise Measurement of Stellar Temperatures Using Line-Depth
Ratios
Authors: Gray, David F.; Johanson, Heather L.
1991PASP..103..439G Altcode:
The ratio of line depth for two spectral lines is used to determine
stellar temperatures with a precision = 10 K = 0.2 percent. For
stars between late-F and early-K spectral types, the V I 6251 to Fe
I 6253 depth ratio is easy to measure. It is also applicable to other
temperature regimes if suitable lines can be found.
---------------------------------------------------------
Title: Report of IAU Commission 36: Theory of stellar atmospheres
(Théorie des atmosphères stellaires).
Authors: Gray, D. F.
1991IAUTA..21..439G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamo Action in Evolved Stars
Authors: Gray, David F.
1991LNP...380..336G Altcode: 1991IAUCo.130..336G; 1991sacs.coll..336G
Evolved stars tell us a great deal about dynamos. The granulation
boundary shows us where solar-type convection begins. Since activity
indicators also start at this boundary, it is a good bet that
solar-type convection is an integral part of dynamo activity for all
stars. The rotation boundary tells us where the magnetic fields of
dynamos become effective in dissipating angular momentum, and rotation
beyond the boundary tells us the limiting value needed for a dynamo
to function. The observed uniqueness of rotation rates after the
rotation boundary is crossed can be understood through the rotostat
hypothesis. Quite apart from the reason for the unique rotation rate,
its existence can be used to show that magnetic activity of giants
is concentrated to the equatorial latitudes, as it is in the solar
case. The coronal boundary in the H-R diagram is probably nothing more
than a map of where rotation becomes too low to sustain dynamo activity.
---------------------------------------------------------
Title: Book-Review - Lectures on Spectral Line Analysis - F G and
K Stars
Authors: Gray, D. F.; Gussmann, E. A.
1991AN....312...44G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rotation of Evolved Stars
Authors: Gray, D. F.
1991ASIC..340..183G Altcode: 1991amey.conf..183G
No abstract at ADS
---------------------------------------------------------
Title: Interpreting the Coronal Boundary
Authors: Gray, D. F.
1990ASPC....9..155G Altcode: 1990csss....6..155G
No abstract at ADS
---------------------------------------------------------
Title: Rotation of Hot Stars after they Cool off
Authors: Gray, D. F.
1990ASIC..316..283G Altcode: 1990amml.conf..283G
No abstract at ADS
---------------------------------------------------------
Title: High-resolution spectroscopy - Why, how, and what for
Authors: Gray, David F.
1990MmSAI..61..503G Altcode:
Some of the techniques used in high-resolution spectroscopy are
described together with the results that can be obtained using this
technique. It is shown that the information provided by high-resolution
spectrometers on individual (and often narrow) spectral lines can be
used in studies of rotation of stars, photospheric turbulence, and
stellar granulation and for mapping chemical areas and star spots
and patches. It is noted that ESO has a suitable high-resolution
spectrograph for such studies, and the Canada-France-Hawaii telescope
is in the process of building one.
---------------------------------------------------------
Title: Evidence for Equatorial Activity Belts
Authors: Gray, David F.
1989PASP..101.1126G Altcode:
Plots of C II and C IV and of Ca II K-line activity indicators as a
function of orientation of rotation axes show that magnetic activity
in C and early K giants is concentrated to equatorial latitudes.
---------------------------------------------------------
Title: The Rotational Break for G Giants
Authors: Gray, David F.
1989ApJ...347.1021G Altcode:
New high-resolution spectroscopic observations have been obtained
for 73 G giants. Fourier analysis of their spectral lines yields
rotation velocities and macroturbulence dispersions. Combined with
data from an earlier study, total of 86 analyses of luminosity
class III giants is now available. The existence of a rotational
discontinuity for luminosity class III giants is confirmed, but it
is found to be near G0 III rather than G5 III, as indicated in the
earlier work. Evidence for rotation being a single-valued function
of spectral type is strengthened. The observations are interpreted in
terms of a dynamo-generated magnetic brake and a 'rotostat' phenomenon.
---------------------------------------------------------
Title: Stellar activity is equatorial.
Authors: Gray, D. F.
1989JRASC..83..298G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Morphology of Reversed Spectral Line Bisectors
Authors: Gray, David F.
1989PASP..101..832G Altcode:
Spectral-line asymmetries of stars on the hot side of the granulation
boundary in the H-R diagram are contrasted with those on the cool side
by comparing the line bisectors of 41 Cyg to those of Alpha CMi. The
reversed line bisectors for stars on the hot side of the boundary
are interpreted to indicate large upward-stream velocities, about
-10 to -20 km/s, over a small time-averaged fraction of the surface,
equal to about 10 percent. Scaling properties of the bisectors imply
no differential velocities within the up-flow.
---------------------------------------------------------
Title: Rotation Rates of Giant Stars
Authors: Gray, David F.; Pallavicini, R.
1989PASP..101..695G Altcode:
The rotation rates and macroturbulence dispersion of 14 G and K giants
were measured using Fourier reduction of spectral-line profiles. The
high-spectral-resolution, high-signal-to-noise observations were
taken with the Coude Echelle Spectrometer of the European Southern
Observatory. Good agreement was found between the present results and
previous investigations, showing that no large systematic differences
are introduced by using different spectrographs and detectors. The
results generally confirm the low rotation seen for cool giants.
---------------------------------------------------------
Title: The Granulation Boundary in the H-R Diagram
Authors: Gray, David F.; Nagel, Thomas
1989ApJ...341..421G Altcode:
A granulation boundary in the H-R diagram is found. The boundary runs
smoothly from spectral type G1 Ib to near F0 on the main sequence. On
the cool side of the boundary, the spectral line bisectors are of
the classical type associated with granulation. On the hot side the
bisectors show a reversed slope and curvature indicative of some
other type of photospheric velocity field, possibly having velocities
substantially larger than typical granulation velocities.
---------------------------------------------------------
Title: Granulation in the Photospheres of Stars
Authors: Gray, D. F.
1989ASIC..263...71G Altcode: 1989ssg..conf...71G
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal Phenomena in the Photospheres of Cool Starts
Authors: Gray, David F.
1989NASSP.502....7G Altcode: 1989fstt.book....7G
No abstract at ADS
---------------------------------------------------------
Title: The Star Patch on the G8 Dwarf chi Bootis A
Authors: Toner, C. G.; Gray, David F.
1988ApJ...334.1008T Altcode:
The G8 dwarf ξ Boo A has been spectroscopically monitored for
four observing seasons. The authors find systematic variations in
spectral line asymmetries and equivalent widths with a 6.43±0.01
day period. There is no evidence of a change in period or phase
shift over the four seasons. The observations are understandable in
terms of a surface feature carried across the apparent disk of the
star by rotation. The authors have developed a numerical simulation
that reproduces both the asymmetry variations and the line strength
variations. This leads to the gross characteristics of the feature:
temperature 3.7% (≡200K) cooler than the rest of the star, areal
coverage 10%±5% of the visible disk, latitude 55°±8°, and velocity
fields that are enhanced over those for the rest of the surface.
---------------------------------------------------------
Title: The Starpatch on the G8 Dwarf ξ Boo A
Authors: Toner, C. G.; Gray, D. F.
1988BAAS...20..707T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The buying Power of High Signal-To Ratios in Spectroscopy
Authors: Gray, D. F.
1988IAUS..132..185G Altcode:
High S/N is a good first step toward accurate profiles.
---------------------------------------------------------
Title: Lectures on spectral-line analysis: F,G, and K stars
Authors: Gray, David F.
1988lsla.book.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Analysis of the Photospheric Line Profiles in F, G, and
K Supergiants
Authors: Gray, David F.; Toner, C. G.
1987ApJ...322..360G Altcode:
The spectral-line broadening for 30 F, G, and K Ib supergiants has been
measured. Fourier analysis for macroturbulence and rotation shows (1)
macroturbulent velocities larger than but compatible with values found
for lower luminosity stars and (2) rotation results that cannot be
fully explained. Three plausible scenarios are suggested, but the one
in which angular momentum of the surface 'shell' is conserved during the
evolutionary changes experienced by these stars is favored. The unusual
distribution of rotation velocities may result from a preferential
alignment of rotation axes with the galactic poles.
---------------------------------------------------------
Title: Line-shaping phenomena in cool stars
Authors: Gray, David F.
1987sls..conf..605G Altcode:
The central problem formerly encountered in studies of the line
profiles of cool stars, those with surface temperatures lower than
7000 K, was the inability to distinguish rotational broadening from
the broadening caused by the atmospheric motions. The introduction of
Fourier analysis into diagnostics solved this problem, and it is now
possible to measure the rotation rate of cool stars with a precision
of about 10 percent. Attention is presently given to the prospects
for magnetic field measurement and stellar granulation studies.
---------------------------------------------------------
Title: Rotation and Macroturbulence in Bright Giants
Authors: Gray, David F.; Toner, C. G.
1986ApJ...310..277G Altcode:
Spectral line profiles of 35 F, G, and K bright giants were
analyzed to obtain rotation rates, v sin i, and macroturbulence
dispersion. This sample indicates that rotation rates of cool class II
giants is less than 11 km/s, in contrast with some recent periodicity
measurements. Macroturbulence dispersion generally increases with
effective temperature, but the range of values at a given effective
temperature is much larger than seen for lower luminosity classes;
this is interpreted in terms of red-giant and blue-loop evolution. No
evidence is found for angular momentum dissipation on the first crossing
of the H-R diagram.
---------------------------------------------------------
Title: Spectral line asymmetries of F and G Ib-supergiants.
Authors: Toner, C. G.; Gray, D. F.
1986JRASC..80..284T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The remarkable spectral line asymmetries of F and G Ib
supergiant stars.
Authors: Gray, D. F.; Toner, C. G.
1986PASP...98..499G Altcode:
The authors observed a group of supergiants spanning the F5 Ib to K2
Ib interval. The line asymmetries of the F supergiants are found to be
large and opposite in direction from the normal case seen in cooler
and less-luminous stars, and in the Sun. There is a continuous and
monotonic change in the bisector behavior with spectral type, with
the transition from the anomalous to the normal asymmetry occurring
near G1 Ib. The authors reproduce the observations with numerical
simulations based on a simple two-stream model, and from this deduce
velocities of rise of the hot material to be ≡ -25 km s<SUP>-1</SUP>
for the F Ib supergiants.
---------------------------------------------------------
Title: The rotation effect - A mechanism for measuring granulation
velocities in stars.
Authors: Gray, D. F.
1986PASP...98..319G Altcode:
The Doppler effects of stellar granulation, when combined with those of
the star's rotation, have been predicted to enhance the asymmetries in
spectral line profiles, a process referred to as the rotation effect. A
dozen F stars were observed for the rotation effect. The effect is seen
in some, but not all, of them. The asymmetries, as expressed in the
line bisectors, are compared to numerical simulations from which it is
possible to obtain the average velocity of rise of the hot granules on
an absolute velocity scale. Values ≡ -1.5 to -3.0 km s <SUP>-1</SUP>
are deduced.
---------------------------------------------------------
Title: Magnetic activity in evolved stars
Authors: Gray, David F.
1986AdSpR...6h.161G Altcode: 1986AdSpR...6..161G
A rotational boundary, a coronal boundary, and a possible granulation
boundary are discussed. Evidence for the magnetic nature of some of
the observed activity in evolved stars is convincing for subgiants
and giants, but much less so for luminosity classes II and Ib.
---------------------------------------------------------
Title: Convection as a regulator of dynamos
Authors: Gray, D. F.
1986HiA.....7..411G Altcode:
Evidence for a process in which the physical properties of the
convection control the generation of magnetic field, and through it,
the rotation of the star, is presented. The decrease in rotation from
about 5 km/s at G5 III to about 2.5 km/s at K2 III could represent a
boundary line along which the physical conditions for dynamo activity
are at their limiting value. The data suggest that a magnetic brake
may dissipate the entrained angular momentum when it is on, with the
dynamo flickering on and off as the star evolves; on whenever the
rotation builds up sufficiently, off when rotation drops below some
critical value. The possibility of this process functioning in main
sequence stars is also considered.
---------------------------------------------------------
Title: Measurement of Line Profiles
Authors: Gray, David F.
1986IAUS..118..401G Altcode:
Techniques and equipment are described which enhance the accuracy
and usefulness of spectral line profile measurements with small
telescopes. The selection of diffraction grating, i.e., the largest
which can be accommodated, is guided by the grating pattern, the
characteristic width, and the capability of ensuring that no light
losses occur. Factors limiting the attainable signal/noise ratio (SNR)
are discussed, along with methods for setting the exposure time to
attain a desired SNR. Architectural and design details are provided
for the 1.2 telescope and associated facilities for performing coude
spectroscopy at the observatory at the University of Western Ontario.
---------------------------------------------------------
Title: The rotational discontinuity shown by luminosity class
IV stars.
Authors: Gray, D. F.; Nagar, P.
1985ApJ...298..756G Altcode:
Spectroscopic data with high signal-to-noise ratio were analyzed for
rotation and macroturbulence in a sample of 20 F-, G-, and K-class IV
stars. Near GO IV, a sudden drop in rotation is seen with advancing
spectral type, in complete analogy to the drop seen at G5 III in the
giants. Rotation of tens of km/sec is common in the F subgiants, but
all the G and K subgiants in the observed sample rotate more slowly
than 4 km/per sec. The rotation (v sin i) slowly decreases from about
4 km/sec at G0 IV to about 2.5 km/sec at K2 IV. The macroturbulence
values decrease monotonically with advancing spectral type and lie
between similar relations for luminosity classes III and V.
---------------------------------------------------------
Title: Rotation velocities of higher luminosity-class stars.
Authors: Toner, C. G.; Gray, D. F.
1985JRASC..79..244T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic fields in cool stars: a universal magnetic constant.
Authors: Gray, D. F.
1985JRASC..79..234G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An apparent universal magnetic constant for cool stars.
Authors: Gray, D. F.
1985PASP...97..719G Altcode:
Zeeman broadening measurements are examined for G and K dwarfs,
revealing a remarkable relation between B, the magnetic field strength,
and A-sub-zero, the areal coverage factor. The product BA-sub-zero is
a constant independent of physical parameters such as spectral type
and rotational velocity. If this is not an artifact of the measuring
or reduction techniques, the number of magnetic field lines, when
averaged over the star, is a universal magnetic constant for cool stars.
---------------------------------------------------------
Title: Inferred properties of stellar granulation.
Authors: Gray, D. F.; Toner, C. G.
1985PASP...97..543G Altcode:
Apparent characteristics of stellar granulation in F and G main-sequence
stars are inferred directly from observed spectral-line asymmetries and
from comparisons of numerical simulations with the observations: (1)
the apparent granulation velocity increases with increasing effective
temperature, (2) the dispersion of granule velocities about their mean
velocity of rise increases with the apparent granulation velocity,
(3) the mean velocity of rise of granules must be less than the total
line broadening, (4) the apparent velocity difference between granules
and dark lanes corresponds to the "granulation velocity" deduced
from stellar line bisectors, (5) the dark lanes show velocities of
fall approximately twice as large as the granule rise velocities,
(6) the light contributed to the stellar flux by the granules is
four to ten times more than the light from the dark lanes. Stellar
rotation is predicted to produce distortions in the line bisectors
which may give information on the absolute velocity displacements of
the line bisectors.
---------------------------------------------------------
Title: Stellar granulation.
Authors: Gray, D. F.
1984ESASP.220..211G Altcode: 1984ESPM....4..211G
Properties of stellar granulation are inferred from observed line
bisectors.
---------------------------------------------------------
Title: Inferred properties of stellar granulation.
Authors: Gray, D. F.; Toner, C. G.
1984JRASC..78..206G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Is the rotation of the sun normal?
Authors: Gray, D. F.
1984JRASC..78..203G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The synchronous rotation of IOTA Pegasi.
Authors: Gray, D. F.
1984PASP...96..537G Altcode:
Measured rotation rates of the spectroscopic binary stars ι Peg A
(6.5±0.3 km s<SUP>-1</SUP>) and B(5±1 km s<SUP>-1</SUP>) are found
to be equal to the orbital synchronization values. The question of
whether synchronization has actually occurred is discussed and the
evidence is found to favor the hypothesis.
---------------------------------------------------------
Title: Measurements of rotation and turbulence in F, G and K dwarfs.
Authors: Gray, D. F.
1984ApJ...281..719G Altcode:
Spectral line broadening in 18 F, G, and K dwarfs is analyzed for
rotation and macroturbulence. Zeeman broadening is shown to have a
significant effect on the derived parameters in late G and early
K dwarfs. Support is found for the traditional (lower) v sin i
scale. The rotation of the sun is probably normal compared to other
stars. The average macroturbulence velocity decreases rapidly with
advancing spectral type at the rate of 4 km/s per thousand degrees of
effective temperature. The macroturbulence velocity is proportional
to the granulation velocities for F and G stars.
---------------------------------------------------------
Title: On the constancy of spectral-line bisectors, revisited.
Authors: Gray, D. F.
1984PASP...96..382G Altcode:
Even line profiles suffering from line blending can be useful in
comparative studies of line bisectors. The source of the systematic
difference in bisectors for 70 Oph A and δ Dra remains unknown.
---------------------------------------------------------
Title: Measurements of Zeeman broadening in F, G, and K dwarfs.
Authors: Gray, D. F.
1984ApJ...277..640G Altcode:
Zeeman broadening was detected and measured in the spectra of seven
out of a sample of 18 F, G, and K dwarfs. All of the sample from G6
V and cooler show magnetic fields, typically 1.9 kilogauss; almost
none earlier did. The analysis employs the leverage of many spectral
lines used directly in the Fourier transform domain. In the F, G, and
K dwarfs, the Zeeman broadening is often small compared to the Doppler
broadening of rotation and turbulence. In such cases it is difficult
to separate the strength of the field from the fraction of the stellar
disk covered by field; it is impractical to seek a distribution of field
strengths. Several limitations and systematic errors are considered.
---------------------------------------------------------
Title: Zeeman Broadening in Solar Type Stars (Keynote)
Authors: Gray, D. F.
1984ssdp.conf..447G Altcode:
Measurements of Zeeman broadening in solar type stars are
discussed. Techniques, ambiguities, and results are given.
---------------------------------------------------------
Title: Electronic Detector Arrays for Spectral Classification
Authors: Gray, D. F.
1984mpsc.conf..112G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Measurements of magnetic fields in late-type dwarfs.
Authors: Gray, D. F.
1983JRASC..77..256G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the constancy of spectral-line bisectors.
Authors: Gray, D. F.
1983PASP...95..252G Altcode:
Bisectors of spectral line profiles in cool stars indicate the
strength of convection in the photospheres of these objects. The
present investigation is concerned with the feasibility of studying
time variations in line bisectors, the reality of apparent line-to-line
differences within the same stellar spectrum, and bisector differences
between stars of identical spectral types. The differences considered
pertain to the shape of the bisector. The material used in the
investigation was acquired at the McDonald Observatory using a 1728
diode Reticon array at the coudefocus of the 2.1-m telescope. Observed
bisector errors are discussed. It is established that different lines
in the same star show significantly different bisectors. The observed
error bands are shown by the shaded regions. The slope and curvature
are unique for each case.
---------------------------------------------------------
Title: Stellar rotation as a controller of coronae and chromospheres
of giant stars.
Authors: Gray, D. F.
1983PASP...95..181G Altcode:
The flux of X-ray emission from F, G, and K giants drops abruptly
at G5 III. This mimics the drop in rotation rates of giant seen
previously. The X-ray flux, when normalized to the bolometric flux,
varies as the square of the equatorial surface rotatin velocity. Lines
formed in the chromospheric and transition region do not show such
a close relationship with rotation, but are still correlated with
it. Other H-R-diagram boundaries, such as the one for the V/R ratio
for the Ca II K-line emission, appear not to be directly coupled to
the stellar rotation.
---------------------------------------------------------
Title: Book-Review - Stellar Turbulence
Authors: Gray, D. F.; Linsky, J. L.; Elste, G. H.
1983ApL....23..174G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The remarkable rotational braking of G5 giants
Authors: Gray, D. F.
1983IAUS..102..461G Altcode:
The stellar dynamo phenomenon is approched from the viewpoint of the
strong rotational braking seen in the G5 III stage of evolution. It
is noted that the giant spectral sequence indicates the time order of
events, in contrast to the main sequence, which indicates ordering by
mass. The comprehensive calculations of Endal and Sofia (1979) are used
as the basis of the present treatment, in which simple evolutionary
expansion from a main sequence rotation of about 150 km/sec results
in a sixfold increase in the moment of inertia and reproduces the
observed 25 km/sec rotation as a star enters G5 III.
---------------------------------------------------------
Title: The temperature dependence of rotation and turbulence in
giant stars.
Authors: Gray, D. F.
1982ApJ...262..682G Altcode:
Rotation and turbulence velocities of 23 luminosity class III giants are
obtained from their line profiles by Fourier analysis. The rotational
discontinuity at G5 III is clearly delineated. It is shown that a dynamo
brake is the most likely explanation, that the brake turns on and off
before the star evolves more than one- or two-tenths in spectral class,
and that all giants leave the braking stage with the same rotation rate
of 5 km/s. The macroturbulence dispersion is double valued for most
stars in the G8 III to K2 III interval. The larger of the two values,
derived from the weaker lines, shows a linear change with spectral
class from 7.0 km/s at G5 III to 4.6 km/s at K2 III. Expressed as
a function of effective temperature, the macroturbulence dispersion
varies as Teff to the 2.6 power.
---------------------------------------------------------
Title: Discovery and implications of the dramatic rotation brake
at GG5III.
Authors: Gray, D. F.
1982JRASC..76..319G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The rotation of cool main-sequence stars
Authors: Gray, D. F.
1982ApJ...261..259G Altcode:
The monotonic decrease in rotation with advancing spectral type is one
of the interesting characteristics discovered early in the study of
stellar rotation. One of the objectives of the present investigation
is to delineate the run of main sequence rotation with spectral type
for cool stars. A second is to propose a conceptual parallel between
the giant star changes and those seen for main sequence stars, and
to use the parallel as a framework for understanding the run of lower
main sequence rotation with spectral type. It is found that the idea
of main sequence stars evolving through a phase of rapid rotational
braking early in their lives leads immediately to an explanation of
the observed decrease in main sequence rotation rates with advancing
spectral type. There are at least two likely physical causes for the
cessation of the rapid braking.
---------------------------------------------------------
Title: Observational evidence against differential rotation in
F stars.
Authors: Gray, D. F.
1982ApJ...258..201G Altcode:
The interaction of stellar rotation with a convective envelope is
expected to produce a differential effect in the surface rotation. The
sun is the one example of the effect, and for it, the equator rotates
15%-20% faster than do higher latitudes. Such an effect has never been
detected in other stars. An investigation is conducted of F stars,
taking into account careful measurements of spectral line shapes
which, in certain cases, are expected to reflect the characteristics
of differential rotation. It is found that the evidence in the line
profiles of F stars near or on the main sequence is strongly against
the expected differential rotation. In fact, the differential rotation
in these stars is apparently very much less than in the sun.
---------------------------------------------------------
Title: Observations of spectral line asymmetries and convective
velocities in F, G and K stars.
Authors: Gray, D. F.
1982ApJ...255..200G Altcode:
Line asymmetries are found to exist generally in F, G, and K stars. Line
bisectors were measured for 11 relatively unblended lines in each of 27
stars, and an average line bisector was determined for each star. The
average bisectors show systematic changes in velocity span and shape
with spectral type. The bisector characteristics are interpreted in
terms of granulation-type motion. Convective velocities are deduced as
a function of spectral type. Values of approximately 3 times solar are
seen in F5IV and V, in G0 III, and in K4 III stars. Minimum convective
velocities occur near G8 with a value of approximately 0 for luminosity
types IV and V but near the solar value for type III. The height of
penetration of convection is found to be lowest in solar-type stars
with convection essentially dying out before reaching the top of their
photospheres. In nonsolar-type stars, larger convective velocities
produce greater height penetration.
---------------------------------------------------------
Title: The angular momentum history of the Hyades K giants.
Authors: Gray, D. F.; Endal, A. S.
1982ApJ...254..162G Altcode:
Measurements of the rotation velocities and macroturbulence dispersions
in the four Hyades K giants are presented. The observed rotation
is approximately 40% of that expected from evolutionary models in
which convective envelopes are assumed to rotate as rigid bodies. It
is possible to explain this discrepancy either by postulating that a
magnetic braking has occurred or that the coupling is not strong enough
to maintain rigid-body rotation in convective layers. Evolutionary
models having uniform specific angular momentum in the convective layers
are constructed and found to agree with the observed rotation rates.
---------------------------------------------------------
Title: Book Review - Radiation Transfer and Stellar Atmospheres
Authors: Gray, David F.
1982JRASC..76...63G Altcode: 1982JRASC..76...62S
No abstract at ADS
---------------------------------------------------------
Title: Observations of rotation and velocity fields of cool stars
Authors: Gray, D. F.
1982MmSAI..53..931G Altcode:
Adoption of the dynamo hypothesis leads to investigations of the
driving forces: rotation, differential rotation, and convective
velocities and their patterns. Attention must also be given to
the effects of the dynamo: magnetic field strengths, starspots,
the chromosphere and corona,flares and other eruptions, rotational
braking, and the geometrical configuration of the fields insofar as
they affect the granulation. In this review, emphasis is given to the
observational information now available. The general measurements of
nonthermal velocity fields referred to as turbulence are analyzed. Other
photospheric topics are then discussed, among them stellar granulation,
magnetic fields, oscillation, and stellar rotation. A selection of
relevant chromospheric and coronal information is presented.
---------------------------------------------------------
Title: Asymmetries in the spectral lines of Procyon
Authors: Gray, D. F.
1981ApJ...251..583G Altcode:
Asymmetries, including a blueshifted core asymmetry, are measured in
the spectral line profiles of the F5 IV-V star Procyon. Amplitudes of
the asymmetry are proportional to line strengths, and characteristic
widths change modestly with line strength, ranging from 2.5 km/s
to 3.5 km/s. The scaling of asymmetry amplitude with line strength
implies that all lines have approximately the same shape regardless
of their strength.
---------------------------------------------------------
Title: Rotation and turbulence in G giant stars.
Authors: Gray, D. F.
1981ApJ...251..155G Altcode:
Measurements of rotation rates and turbulence parameters are presented
for five G-type giant stars. Fourier transform analysis was applied to
all possible lines in spectra taken between 6122 and 6270 A for the G5
III stars Tau Persei, Beta Leporis, Omicron Ursa Majoris, Beta Corvi
and Epsilon Ursa Minoris. Rotation rates, found by comparison of the
mean residual transforms of all lines of a given star following removal
of instrumental and microturbulence profiles with model transforms,
reveal all but Epsilon UMi to be slow rotators, requiring the presence
of a rotational brake. Epsilon UMi, with a rotation rate of 27 km/sec,
is suggested to be presently undergoing the stage of rapid rotational
braking, which will reduce its rotation to about 5 km/sec, whereas the
other G giants have already passed through that stage. Macroturbulence
is found to be on the order of 7 km/sec in the G giants, which is
markedly higher than in K giants and in agreement with the temperature
dependence of nonradial oscillations.
---------------------------------------------------------
Title: A Fourier analysis of the spectral lines of Procyon.
Authors: Gray, D. F.
1981ApJ...251..152G Altcode:
A Fourier analysis is presented of the line broadening of Procyon,
a bright star of spectral type F5-Iv-V which may be useful as a
reference star of intermediate spectral type. The 34 lines used in
the analysis were observed in spectral regions centered on 6160 and
6250 A, represent eight chemical species and are generally of weak
to intermediate strength. The analysis involved the computation
of the individual line profiles, the removal of instrumental and
thermal microturbulence profiles, and the averaging of the residual
transforms. The microturbulence dispersion of the individual profiles
are observed to increase rapidly with excitation potential above 3.5 eV,
which may be interpreted as a depth effect. The mean residual transform
of the 34 lines is best fit with a radial-tangential macroturbulence
dispersion of 7.0 + or - 0.1 km/sec, and a projected rotation rate of
2.8 + or 0.3 km/sec.
---------------------------------------------------------
Title: An analysis of the spectral line broadening of Arcturus.
Authors: Gray, D. F.
1981ApJ...245..992G Altcode:
Line broadening in 36 spectral lines of Arcturus is analyzed to obtain
information on rotation and turbulence parameters. Spectral regions
of approximately 18 A width with central wavelengths between 6010 and
6250 A were observed and analyzed in terms of a model of rotation,
macroturbulence and microturbulence as the nonthermal sources of the
broadening. The weak and strong lines are found to be compatible with
a rotation rate of 2.4 + or - 0.4 km/sec and a radial-tangential
macroturbulence dispersion of 5.1 + or - 0.2 km/sec, while the
intermediate-intensity lines exhibit unexplained discrepancies. The
microturbulence dispersion is found to vary with line strength,
increasing from zero for the weak lines to 1.75 km/sec for the strong
lines, and implying depth dependence.
---------------------------------------------------------
Title: Book-Review - Stellar Turbulence - I.A.U. Colloquium 51 -
London Ontario, Canada - 1979AUG27-30
Authors: Gray, D. F.; Linsky, J. L.; Hubeny, I.
1981BAICz..32..255G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Stellar Turbulence - I.A.U. Coll. - Ontario,
Canada - 1979AUG27-30
Authors: Gray, D. F.; Linsky, J. L.; Gussmann, E. A.
1981AN....302..208G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review - Stellar Turbulence IAU Colloquium no.
Authors: Gray, D. F.; Linsky, J. L.; de Jager, C.
1981SSRv...28..113G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of rotation velocities in A stars.
Authors: Gray, D. F.
1980PASP...92..771G Altcode:
Projected rotation of 19 early-type stars are documented.
---------------------------------------------------------
Title: Book-Review - Stellar Turbulence / Colloquium / London,
Ontario, Canada
Authors: Gray, D. F.; Linsky, J. L.
1980Sci...210..635G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Depth Dependent Microturbulence in Arcturus
Authors: Gray, D. F.
1980BAAS...12..797G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Variations in the K-line emission of Arcturus
Authors: Gray, D. F.
1980ApJ...240..125G Altcode:
High-resolution photoelectric measurements of the Ca II K line of
Arcturus show the K(2V) emission peak to vary 1.7 times as much
and in the opposite sense as the K(2R) emission. During the span
of observations the ratio of violet to red emission peaks (V/R)
varied from 0.80 to 1.05. The wavelength position of K 3 is found to
change with V/R. The rise from K(1V) to K(2V) is more abrupt than the
corresponding rise on the red side. Solar analog models and mass-loss
models are considered in the light of these data.
---------------------------------------------------------
Title: Book-Review - Stellar Turbulence
Authors: Gray, D. F.; Linsky, J. L.
1980S&T....60...57G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum - Accuracy of Line-Profile Measurements
Authors: Gray, D. F.; Smith, M. A.; Wynne-Jones, I.; Wayte, R. C.;
Griffin, R.; Griffin, R. F.
1980PASP...92..248G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The rotation rate of Vega.
Authors: Gray, D. F.
1980PASP...92..154G Altcode:
The rotation rate of Vega has been determined by comparing the Fourier
transforms of the observed spectra with the transforms of theoretical
rotation profiles. It is found that the projected rotation velocity
is 23.4 km/sec plus or minus 0.4 km/sec. This value agrees reasonably
well with the preliminary value of about 25 km/sec found by Kurucz
(1979) from model fitting to the photoelectric Balmer-line measurements.
---------------------------------------------------------
Title: Erratum - Upper Photospheric Temperature Models of K Giants -
a Comparison of Super Metal-Rich Giants with Normal Giants
Authors: Desikachary, K.; Gray, D. F.
1980ApJ...236.1056D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar turbulence
Authors: Gray, D. F.; Linsky, J. L.
1980LNP...114.....G Altcode: 1980sttu.coll.....G; 1980IAUCo..51.....G
The generation, nature, and implications of stellar turbulence are
discussed, considering both the stellar and solar domains. Attention
is given to the generation of motions by convection, rotation,
oscillations, the measurement and observed characteristics of
turbulence, modeling and theoretical interpretation of turbulence,
and the relation of chromospheres, coronae, and mass loss to the
turbulence. In particular, the Wilson-Bappu effect, non-thermal motions,
observations of velocity fields, and micro-, meso- and macroturbulence
are considered. Topics include the generation of oscillatory motions
in the stellar atmosphere, photospheric macroturbulence in late-type
stars, the effects of acoustic waves on spectral line profiles, and
mechanical energy transport.
---------------------------------------------------------
Title: Measurements of spectral line asymmetries for Arcturus and
the sun
Authors: Gray, D. F.
1980ApJ...235..508G Altcode:
Spectral line asymmetries have been measured in photospheric lines of
Arcturus and the sun. The asymmetries are not detectable in weak lines
but increase with line strength to 3% of the continuum for Arcturus
and 5% of the continuum for the sun. The direction of the asymmetry
for Arcturus is opposite that for the sun, with the line cores shifted
toward shorter wavelengths for Arcturus and longer wavelengths for
the sun. Possible explanations of the asymmetries include granulation
motions and acoustic waves.
---------------------------------------------------------
Title: Analysis of high resolution stellar line profiles
Authors: Gray, D. F.
1980LNP...114...75G Altcode: 1980IAUCo..51...75G; 1980sttu.coll...75G
The paper considers the analysis of spectral line shapes for obtaining
information on line broadening, and on details concerning the physical
mechanisms for turbulence. Analysis in the Fourier domain is discussed,
considering the use of the convolution approximation to combine the
effects of macroturbulence and rotation, and the use of integrations
over the disc. Attention is also given to measuring line asymmetries
in photospheric lines of late-type stars by analysis in the wavelength
domain; examples of asymmetries as seen in Arcturus and the solar flux
spectrum are presented.
---------------------------------------------------------
Title: Changes of Photospheric Line Asymmetries with Effective
Temperature
Authors: Gray, D. F.
1980LNP...114..297G Altcode: 1980sttu.coll..297G; 1980IAUCo..51..297G
No abstract at ADS
---------------------------------------------------------
Title: Observations and analysis of stellar photospheres.
Authors: Gray, D. F.
1980oasp.book.....G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Accuracy of line-profile measurements.
Authors: Gray, D. F.; Smith, M. A.; Wynne-Jones, I.; Wayte, R. C.;
Griffin, R.; Griffin, R.
1979PASP...91..719G Altcode:
Comparisons are made among high-resolution line-profile measurements
of Fe I 6065 and 6253 wavelengths in the spectrum of Arcturus. The
line-profile measurements were made with four entirely different
sets of equipment in order to have a leverage on external errors;
three coude spectrographs and one Fourier transform spectrometer are
used. The results indicate consistency in line shape to about 1%
but zero-level differences of 2-5%. This represents a substantial
improvement over the accuracy attained in the past decades. Reference
profiles are tabulated for comparison by future observers.
---------------------------------------------------------
Title: A comparison of turbulence in normal and super-metal-rich K
giant stars.
Authors: Gray, D. F.; Martin, B. E.
1979ApJ...231..139G Altcode:
The microturbulence, macroturbulence, and rotation in five normal and
three super-metal-rich (SMR) K giant stars have been measured by Fourier
analysis of line profiles. There appears to be no systematic difference
between the two groups of stars. This implies that differences in
mechanical energy dissipation are not likely to be the cause of the
differences in temperature distributions that exists between normal
and SMR stars. Further, it shows that the difference in temperature
contributions in these stars cannot be used to establish a link between
temperature enhancements and turbulence. Values of macroturbulence
dispersion are near 4 km/s, while rotational velocities of 2.5-3 km/s
are found.
---------------------------------------------------------
Title: Book reviews
Authors: Lequeux, J.; Reijnen, G. C. M.; Kleczek, Josip; Gray, D. F.;
Dommanget, J.; Namba, O.; Verbunt, Frank; Savonije, Gertian; de Jager,
Cornelis; van Bueren, H. G.; Hovenier, J. W.; Fokker, A. D.; Hoekstra,
Roel; Hultqvist, Bengt; Kresák, L.
1979SSRv...23..683L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High resolution spectroscopy the touchstone of photometry.
Authors: Gray, D. F.
1979DudOR..14..309G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Upper photospheric temperature models of K giants: a comparison
of super-metal-rich giants with normal giants.
Authors: Desikachary, K.; Gray, D. F.
1978ApJ...226..907D Altcode:
The LTE version of K-line synthesis that takes partial coherency
effects into account is applied to the Ca II K-line wings in the
spectra of four normal K giants (Beta Gem, Nu Cyg, Rho Oph, Alpha Ari)
and two super-metal-rich (SMR) K giants (Alpha Ser, Beta Oph) in order
to derive upper-photospheric temperature models. A model-atmosphere
flux-calibration procedure that precludes the necessity of a measured
angular diameter is used in the analysis of the K-line wing profiles,
on the basis of which the SMR and normal K giants are compared
quantitatively. The results show that temperature enhancements of 200
to 300 K in excess of radiative-equilibrium models are required in the
upper photospheres of all six stars and that the upper photospheres of
the SMR star models are up to 180 K cooler than those of the normal
models. The temperature enhancements are interpreted as departures
from radiative equilibrium, and the differential cooling in the SMR
stars is tentatively attributed to enhanced CN and CO line absorption.
---------------------------------------------------------
Title: Turbulence in stellar atmospheres.
Authors: Gray, D. F.
1978SoPh...59..193G Altcode:
Stellar photospheric turbulence is discussed. Conceptualizations of
turbulence are examined with attention to the micro-macroturbulence
model and to models including mesoturbulence. Techniques are considered
with reference to the curve of growth, line widths and shapes, Fourier
transforms of line profiles, the separation of macroturbulence from
rotation, and line shifts. Discussed topics relating to the behavior
of turbulence across the HR diagram include microturbulence in main
sequence stars, microturbulence in stars above the main sequence,
macroturbulence in stars above the main sequence, the H and K
connection, and turbulence and convection zones. Several physical
aspects of turbulence are described.
---------------------------------------------------------
Title: The effects of rotation and macroturbulence on the empirical
temperature models derived from line-center fluxes in a muliplet.
Authors: Desikachary, K.; Gray, D. F.
1978ApJ...224.1073D Altcode:
The effects of rotation and macroturbulence on the line-center fluxes
are considered. It is pointed out that the presence of either rotation
or macrovelocity in excess of a few kilometers/second introduces
systematic errors in the multiplet method of deriving empirical
temperature models from the line-center fluxes.
---------------------------------------------------------
Title: Methods and Technique for Separating Line Broadening Mechanisms
Authors: Gray, D. F.
1978hrs..conf..268G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: a Comparison of Some Current Observational Capability
Authors: Gray, D. F.
1978hrs..conf..698G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Upper photospheric temperature models of K giants with
emphasis on a comparison of SMR (super metal rich) K giants with
normal K giants.
Authors: Desikachary, K.; Gray, D. F.
1978BASI....6R..54D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The effect of rotation and macroturbulence on empirical
temperature models derived from line centre fluxes in a multiplet.
Authors: Desikachary, K.; Gray, D. F.
1978BASI....6Q..54D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A test of the micro-macroturbulence model on the solar flux
spectrum.
Authors: Gray, D. F.
1977ApJ...218..530G Altcode:
The micro-macroturbulence model of velocity fields is applied
to 20 lines taken from a solar flux spectrum obtained with high
photometric precision and high spectral resolution. The analysis
is performed first by adopting a value of 1.9 km/s for the sun's
rotational velocity and then by treating the rotational velocity as
an unknown. The results obtained are compared with those of previous
intensity profile analyses. It is concluded that if the sun were seen
as a distant (unresolved) star, it would be interpreted as having a
classical microturbulence dispersion of 0.5 + or - 0.1 km/s along with
a radial-tangential macroturbulence characterized by a dispersion of
3.1 + or - 0.1 km/s.
---------------------------------------------------------
Title: A test of the micro-marcoturbulence model of non-thermal
velocities.
Authors: Gray, D. F.
1977JRASC..71..401G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Turbulence in α BOO.
Authors: Gray, D. F.
1977BAAS....9..572G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A quest for differential stellar rotation in A stars.
Authors: Gray, D. F.
1977ApJ...211..198G Altcode:
Photoelectric line-profile measurements of the Mg II line at 4481 A and
the Fe II line at 4352 A in the A stars Alpha Aql, Alpha Peg, Beta Eri,
Alpha Cep, Gamma Boo, and Gamma Her are subjected to Fourier analysis
in order to detect differential rotation. Effects of limb darkening on
a rotationally broadened line profile are considered and compared with
those of differential rotation. In the analysis, a measured rotationally
broadened flux profile is expressed as a convolution of the rotation
profile, and the existence of differential rotation is identified by
finding a line-profile transform having an anomalously small ratio
of first to second sidelobe amplitudes. The results indicate that
differential rotation is apparently absent in A stars
---------------------------------------------------------
Title: The Observation and Analysis of Stellar Photospheres (Book
Review)
Authors: Gray, D. F.
1977ApL....18Q..93G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fourier analysis of spectral line profiles: a new tool for
an old art.
Authors: Smith, M. A.; Gray, D. F.
1976PASP...88..809S Altcode:
The paper discusses some questions about Fourier transforms, how they
enter into quantitative spectrum analysis, and how they can be applied
to learn more about stars. Physical processes that are better analyzed
in terms of Fourier transforms rather than line profiles, and vice
versa, are identified; advantages of Fourier analysis are enumerated;
and the analysis technique is outlined. The use of Fourier transforms is
demonstrated by summarizing typical applications to stellar rotation,
macro- and microturbulence, stellar magnetic fields, and velocity
distributions in globular clusters and galaxies. Observational
techniques that should be employed to obtain the best results from a
Fourier analysis are considered along with some basic limitations of
the Fourier approach.
---------------------------------------------------------
Title: Review of Publications- The Observation and Analysis of
Stellar Photospheres
Authors: Gray, David F.
1976JRASC..70..204G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The observation and analysis of stellar photospheres
Authors: Gray, David F.
1976oasp.book.....G Altcode: 1976QB809.G67......
The present book provides an introduction to techniques and analyses
used in observing stellar photospheres. Fourier transforms are examined,
and instruments employed for photospheric observations are described,
including spectroscopic devices and light detectors. The basic
quantities of radiation measurement are identified, blackbody radiation
theory is reviewed, and the processes of radiative and convective
energy transfer are outlined. Calculation of the continuous absorption
coefficient is explained, the construction of model photospheres
is described in detail, and the measurement of stellar continua is
discussed along with instruments and analytical techniques for such
measurements. Other topics include the measurement and behavior of
spectral lines, chemical analysis of stellar spectra, measurements
of stellar temperatures and radii, spectroscopic measurements of
photospheric pressure and surface gravity, stellar rotation, and
photospheric turbulence.
---------------------------------------------------------
Title: Atmospheric turbulence measured in stars above the main
sequence.
Authors: Gray, D. F.
1975ApJ...202..148G Altcode:
Measurements of broadened line profiles are analyzed to identify,
measure, and separate macroturbulence from rotation. Evidence is
presented for the possibility of more than one macroturbulence velocity
distribution.
---------------------------------------------------------
Title: Turbulence measurements in giants and supergiants.
Authors: Gray, D. F.
1975JRASC..69..245G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The na D Lines as Surface Gravity Indicators
Authors: Gray, David F.
1975mpth.conf..457G Altcode: 1975mpth.proc..457G
No abstract at ADS
---------------------------------------------------------
Title: On Scattered Light Corrections for Stellar Spectrographs
Authors: Gray, David F.
1974PASP...86..526G Altcode:
It is shown how the scattered light correction can easily be
incorporated into the correction for the instrumental profile. Key
words: spectrographs - scattered light - line profiles
---------------------------------------------------------
Title: Scattered Light Corrections in Spectroscopic Observations.
Authors: Gray, D. F.
1974BAAS....6Q.306G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photoelectric Profile Measurements of Halpha and Hbeta in
be Stars
Authors: Gray, David F.; Marlborough, J. M.
1974ApJS...27..121G Altcode:
We present photoelectric measurements of Ha and H in 14 Be stars. We
find from a shape analysis of the wings of Ha that a Gaussian
broadening mechanism is reasonable whereas a damping profile is
not. It is suggested on this basis that the width and shape of Ha
can be reasonably interpreted as a combination of shell rotation and
electron scattering. Subject headings: Be stars - line profiles -
rotation, stellar
---------------------------------------------------------
Title: The Search for Stellar Microturbulence
Authors: Gray, David F.; Evans, John C.
1973JRASC..67..241G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Existence of Classical Microturbulence
Authors: Gray, David F.
1973ApJ...184..461G Altcode:
A Fourier transform technique is developed by which it is possible to
distinguish between microturbulence, macroturbulence, and rotation. The
method is applied to photoelectric observations of the Fe I A6065 line
in six stars. It is found that microturbulence can be used to give a
quantitatively consistent interpretation of the observations. Subject
headings: atmospheres, stellar - rotation, stellar - turbulence
---------------------------------------------------------
Title: A New Method of Line Profile Analysis with Application to
Turbulence in Stellar Atmospheres.
Authors: Gray, D. F.
1973BAAS....5..337G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hydrogen lines in A and Ap stars. Photoelectric observations.
Authors: Gray, D. F.; Evans, J. C.
1973ApJ...182..147G Altcode:
We present photoelectrically measured profiles of Hy and H in twelve
normal A stars and nine peculiar A stars. The average random error
per point is 1.1 percent. Systematic errors appear to be small. We
find the functional relation between hydrogen line strength and color
indices to be the same for these two groups of stars to within a 1
percent uncertainty. Subject headings: line profiles - peculiar A stars
---------------------------------------------------------
Title: A new approach to periodogram analyses.
Authors: Gray, D. F.; Desikachary, K.
1973ApJ...181..523G Altcode:
We present a method for Fourier analyzing quasi-periodic light
and radial velocity variations. The scheme gives a particularly
clear interpretation to the periodogram, reduces the alias problem,
allows detection of very weak components, has potential for greater
precision in frequency measurement, and is a shorter computation than
the usual method. Our development points out the possibility of error
in evaluating the zero-frequency component by the usual method. We
derive, under appropriate assumptions, a rigorous evaluation of the
phase of each component. Subject headings: pulsation - variable stars
---------------------------------------------------------
Title: A Heliostat for Measuring the Solar Flux Spectrum
Authors: Gray, David F.
1972PASP...84..721G Altcode:
In order to use ffie sun as a spectrophotometric reference for other
stars, it is desirable to measure the spectrum of the sun integrated
over the disk. A device to facilitate such measurement is described. Key
words: instrumentation - solar spectrum
---------------------------------------------------------
Title: A New Approach to Periodogram Analyses.
Authors: Gray, D. F.; Desikachary, K.
1972BAAS....4..337G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line Broadening by Macroturbulence.
Authors: Evans, J. C.; Ramsey, L. W.; Gray, D. F.
1972BAAS....4..333E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Determination of the Trace Element Levels in Atmospheric
Pollutants by Instrumental Neutron Activation Analysis
Authors: Gray, D.; McKown, D. M.; Kay, M.; Eichor, M.; Vogt, J. R.
1972ITNS...19..194G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The theoretical behavior of Na I 5890 in a solar type star.
Authors: Gray, D. F.
1972JRASC..66...70G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn Notes
Authors: Murray, J. B.; Foulkes, M.; Veitch, R. G.; Gray, D.;
Gainsford, M. J.
1971Astr....8..144M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn Notes
Authors: Gainsford, M. J.; Gray, D.; Veitch, R. G.
1971Astr....8..124G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coude Spectral Line Scanner.
Authors: Gray, D. F.
1971BAAS....3R.387G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Radial Velocity Variation of Epsilon Cephei
Authors: Gray, David F.
1971PASP...83..103G Altcode:
The radial velocity variation of E Cephei was measured on three nights
and found to have a variable amplitude. A beat phenomenon is a likely
explanation. Key words: Scuti variable radial velocity
---------------------------------------------------------
Title: Saturn notes.
Authors: Foulkes, Michael; Burch, S. F.; Gray, David
1970Astr....7..127F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photometry of beta Cephei.
Authors: Gray, D. F.
1970AJ.....75..958G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Miscellanea.
Authors: Miles, Howard; Gainsford, M. J.; Gray, David
1970Astr....7...46M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Jupiter notes.
Authors: Heath, A. W.; Pinnion, D.; Gainsford, M. J.; Gray, D.; Allen,
D. A.
1970Astr....7...31H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Miscellanea.
Authors: Botley, Cicely; Churchward, Clive; Gray, D.; MacKenzie, R. A.
1970Astr....7...26B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comet Bennett 1969i.
Authors: Gainsford, M. J.; Steer, R.; Sturdy, Keith; Wilson, J. E.;
Comello, G.; Gray, D.; Law, T. J.; Feijth, Henk; Smith, Alan
1970Astr....7...29G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Jupiter.
Authors: Gray, David; Allen, D. A.; Pinnion, D.
1970Astr....7...10G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comet Bennett 1969i.
Authors: Sutherland, P. G.; Feijth, Henk; Pinnion, D.; Ginman, T.;
Comello, G.; Norman, P. C.; Gainsford, M. J.; Sturdy, K. M.; Bus,
E. P.; Wilson, J. E.; Pearce, G. S.; Foulkes, Michael; Forno, Alan;
Murray, J. B.; Osman, P. E.; Hughes, P.; Steer, R.; Burch, S. F.;
Allen, D. A.; Hollis, A. J.; Carter, B. A.; Gray, David; Brown, D. S.;
Lloyd, G. K.
1970Astr....7....3S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Notes on the novae.
Authors: Feijth, Henk; Pennell, W. E.; Carter, B. A.; Hollis, A. J.;
Gray, David; Gainsford, M. J.
1970Astr....7...13F Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Jupiter, February 1970.
Authors: Gray, David; Pinnion, D.; MacKenzie, R. A.
1970Astr....6..246G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Saturn, February 1970.
Authors: Gray, David; MacKenzie, R. A.
1970Astr....6..247G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Jupiter - January 1970.
Authors: Gray, David; MacKenzie, R. A.
1970Astr....6..220G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn Notes.
Authors: Gainsford, M. J.; Gray, David
1970Astr....6..222G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Saturn.
Authors: Gray, D.; Gainsford, M. J.; Heath, A. W.; MacKenzie, R. A.;
Gouldstone, T.
1970Astr....6..186G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Jupiter.
Authors: Heath, A. W.; MacKenzie, R. A.; Gray, D.; Burch, S. F.
1970Astr....6..190H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Jupiter drawing : 1969 Nov 10.
Authors: Gray, D.
1969Astr....6..170G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Jupiter observations.
Authors: Gray, David
1969Astr....6..166G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn observations.
Authors: Gainsford, M. J.; Gray, D.; Murray, J. B.
1969Astr....6..162G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn observations : a new bright spot.
Authors: Gray, David; Mackenize, R. A.; Allen, D. A.; Fisher, N. E.;
Gainsford, M. J.
1969Astr....6..137G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn observations.
Authors: Gray, D.; Appleyard, A.
1969Astr....6...96G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Correction to Saturn report in 1969 Aug issue.
Authors: Gray, D.
1969Astr....6...86G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Saturn observations.
Authors: Gray, D.; Fisher, N. E.
1969Astr....6...72G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Surface Gravities
Authors: Gray, D. F.
1969tons.conf..291G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A list of photometric stellar radii.
Authors: Gray, D. F.
1968AJ.....73..769G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Possible Test for Wavelength-Independent Interstellar
Extinction
Authors: Gray, D. F.
1968ApJ...153L.113G Altcode:
A new method is presented for detection of interstellar extinction
---------------------------------------------------------
Title: Integrated colors and magnitudes of open clusters.
Authors: Gray, D. F.
1967AJ.....72..800G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photometric Determination of Stellar Radii
Authors: Gray, David F.
1967ApJ...149..317G Altcode:
A simple and accurate method is developed to measure stellar
radii. Succinctly stated, one compares the observed absolute
energy distribution with an energy distribution predicted from a
model-atmosphere computation. The radius is given by the square
root of the flux ratio multiplied by the distance to the star. The
radius can be determined with an uncertainty of 10 per cent or less
provided the distance to the star is well known. The method has the
advantages that it uses only the observable region of the spectrum,
it does not depend on bolometric corrections, and it is independent
of any effective temperature scale The energy distributions of
the three visual binary stars 21 Cas A, Boo A, and 70 Oph A were
measured with a grating spectrum scanner attached to the Francis
C. McMath 24-inch telescope. Line absorption was measured on 8.9
A/mm spectrograms taken with the coud spectrograph on the Kitt Peak
84-inch telescope. Model atmospheres were constructed using a scaled
solar temperature distribution. The models include the continuous
absorption of the neutral hydrogen atom, the negative hydrogen ion,
and the H2 molecule as well as a hydrogenic approximation for the
continuous absorption of the heavier elements. The continuous spectra
of the models were combined with the observations to give R = 1.11 Ro
1 7 per cent for21 Cas A, R = 1.01 Ro 1 7 per cent for Boo A, and R =
1.21 Ro 1 7 per cent for 70 Oph A. Using the masses derived from the
orbital elements, it was possible to obtain accurate values of surface
gravity for these stars: g = 2.09 X 10 cm/seci 1 17 per cent for 21 Cas
A, 2.20 X 10 cm/sec2 1 17 per cent for Boo A, and 1.82 X 10 cm/sec2 1 15
per cent for 70 Oph A. Photometric radii determined for Vega, Sirius,
and the Sun showed close agreement with values obtained from other
independent methods. For Sirius g = 1.42 X 10 cm/sec2 1 15 per cent is
derived. Using published energy distributions, photometric radii were
determined for twenty-nine additional stars. Excellent correlations
exist between radius and absolute magnitude, radius and color index,
and radius and spectral type. The subgiant stars are clearly separated
from the main sequence. The subgiant a C Mi is found to have a surface
gravity of 0.99 X 10 cm/sec2 1 14 per cent.
---------------------------------------------------------
Title: Integrated Colors and Magnitudes of Open Clusters.
Authors: Gray, David F.
1967AJ.....72Q.800G Altcode:
Integrated colors and magnitudes may be the only observable
characteristics of some stellar systems. As a convenient standard
of reference we can use the integrated colors and magnitudes of
open clusters in the galaxy which are easily found by summing the
luminosities of the individual stars comprising the cluster. The
integrated colors and magnitudes of open clusters have been shown
to be correlated along a line interpreted as an aging trajectory
(Gray, D. F., Astron. J. 70, 362, 1965). In the present investigation
artificial cluster evolution is investigated numerically to see if in
fact any given cluster moves parallel to the observed correlation. This
psuedoevolution is accomplished by subtracting, sequentially in order
of brightness, the flux of each star from the cluster total. The giant
stage of the star's life is neglected. In the majority of cases the
cluster does follow the expected trajectory. It is also found that
the computed tracks depend only slightly on the cluster's luminosity
function. Each computed track must eventually end up on the stellar
main sequence if the faintest stars left in the cluster are main
sequence objects. After evolving parallel to the observed correlation,
the cluster usually drops steeply onto the stellar main sequence. This
is particularly noticeable in the U-B plane where the characteristic
wiggle of the stellar main sequence holds the color between 0.0 and
0.10 for a three-magnitude range in My.
---------------------------------------------------------
Title: Photometric Determination of Stellar Radii.
Authors: Gray, David Frank
1966PhDT.........4G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Parallax and proper motion of the white dwarf CC 398 from
plates taken with the Sproul 24-inch refractor
Authors: Gray, David F.
1965AJ.....70..414G Altcode:
Measurements of the white dwarf CC 398 yield a parallax of 0'.'056+0.004
(p.e.) and a total proper motion of 0 `.`096/yr.
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Title: Integrated colors and magnitudes of open clusters.
Authors: Gray, D. F.
1965AJ.....70..362G Altcode:
No abstract at ADS
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Title: Parallax and mass ratio of BD +77361 from plates taken with
the Sproul 24-inch refractor
Authors: Gray, David F.
1965AJ.....70..304G Altcode:
Sproul plates ranging from 1937 to 1963 have been measured and reduced
to give a relative parallax of 0'.'042+'.'006 (p.e.), and a value of
Q0'.'0155+'.'0078 for the semi-axis major of the photocentric orbit. The
adopted absolute parallax is Q0'.'045+'.'004 which leads to masses of
0.750 and 0.680 for the two components
---------------------------------------------------------
Title: Parallax and mass ratio of 12173 from photographs taken with
the Sproul 24-inch refractor
Authors: Gray, David F.
1964AJ.....69..406G Altcode:
Plates taken from 1912 to 1963 have been measured and reduced to give
a relative parallax of +0047+007 (p.e.) and a value of +0"0115+'.'0055
for the semimajor axis of the photocentric orbit. The adopted absolute
parallax of 0"051+'.'004 leads to masses of 1.94 0 and 1.83 0 for the
two components.
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Title: Evolutional changes in galactic cluster luminosity functions
Authors: Gray, David F.
1963AJ.....68..572G Altcode:
The bright end of 52 galactic cluster luminosity functions is
investigated statistically, and the slope of the functions is found to
change slowly and smoothly with log time. A fairly adequate explanation
is given by taking into account the brightening of the stars as they
leave the main sequence. Alternative theories are suggested briefly.
