Author name code: gray ADS astronomy entries on 2022-09-14 author:"Gray, David F." ------------------------------------------------------------------------ Title: Characterizing Space Debris Objects Using Simultaneous Multi-Color Optical Array Authors: Campbell, T.; Reddy, V.; Furfaro, R.; Tucker, S.; Gray, D. Bibcode: 2019LPICo2109.6117C Altcode: Using high speed simultaneous multi-color photometry to characterize RSOs, both debris and active. Title: A Recipe for Finding Stellar Radii, Temperatures, Surface Gravities, Metallicities, and Masses Using Spectral Lines Authors: Gray, David F.; Kaur, Taranpreet Bibcode: 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. Title: A Spectroscopic Analysis of the Hyades Cool Giants Authors: Gray, David F.; Martinez, A. Bibcode: 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-1 small variations, compatible with the planetary orbit, are seen for ɛ Tau. The primary-to-secondary mass ratio of θ 1 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-1 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 1 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-1 for γ Tau, δ Tau, ɛ Tau, and θ 1 Tau respectively, with an uncertainty of ±0.3 km s-1. The corresponding radial-tangential macroturbulence dispersions are 5.07, 5.66, 5.55, and 4.65 km s-1, with a uncertainty of ±0.10 km s-1. 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. Title: Spectroscopy of the K0 Binary Giant α UMa Authors: Gray, David F. Bibcode: 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-1 and a radial-tangential macroturbulence dispersion of 4.97 ± 0.08 km s-1. 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-1 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. Title: A Solar-flux Line-broadening Analysis Authors: Gray, David F. Bibcode: 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. Title: The Solar-flux Third Granulation Signature Authors: Gray, David F.; Oostra, Benjamin Bibcode: 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-1. 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-1. 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-1) 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-1 toward higher velocities. These differences, while significant, are not large compared to measurement errors for stellar data. Title: VizieR Online Data Catalog: Radial velocities of δ Sagittae (Pugh+, 2015) Authors: Pugh, T.; Gray, D. F.; Griffin, R. F. Bibcode: 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.

(1 data file). Title: A Spectral-line Analysis of the G8 III Standard ɛ VIR Authors: Gray, David F. Bibcode: 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-1 and a radial-tangential macroturbulence dispersion ζ RT = 5.16 ± 0.08 km s-1. The radial velocity over nine seasons is constant to 18 m s-1. The absolute radial velocity with granulation blueshifts (but not gravitational redshift) removed is -14120 ± 75 m s-1. 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-1 over ΔM V ∼ 1.5, indicating larger velocity differences between granules and lanes for giants higher in the HR diagram. Title: The Orbit, Rotation, and Granulation of the G7 Giant β Her Authors: Gray, David F. Bibcode: 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-1 and a radial-tangential macroturbulence dispersion of 6.43 ± 0.08 km s-1. 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-1 from the line center, suggesting the velocity difference between granules and lanes is ∼20% larger than that found for recently analyzed K giants. Title: Erratum: “A Spectroscopic Analysis of the K0 III Binary ɛ CYGNI” (2015, ApJ, 810, 117) Authors: Gray, David F. Bibcode: 2016ApJ...825...81G Altcode: No abstract at ADS Title: Rotation and Granulation of the K2 Giant alpha SER Authors: Gray, David F. Bibcode: 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-1 yr-1. The absolute spectroscopic radial velocity with convective blueshifts taken into account is 2730 m s-1. 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-1 and a radial-tangential macroturbulence dispersion ζ RT = 4.50 ± 0.10 km s-1. 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. Title: LUMINEU: a search for neutrinoless double beta decay based on ZnMoO4 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. Bibcode: 2016JPhCS.718f2008A Altcode: 2016arXiv160104989A The LUMINEU is designed to investigate the possibility to search for neutrinoless double beta decay in 100 Mo by means of a large array of scintillating bolometers based on ZnMoO4 crystals enriched in 100 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. Title: The orbit and variations of δ Sagittae Authors: Pugh, T.; Gray, David F.; Griffin, R. F. Bibcode: 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-1. 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-1. 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. Title: A Spectroscopic Analysis of the K0 III Binary ɛ Cygin Authors: Gray, David F. Bibcode: 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-1, 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 }{RT} = 4.45 ± 0.05 km s-1. 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-1 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. Title: The Stable K0 Giant Star β Gem Authors: Gray, David F. Bibcode: 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-1. The projected rotation rate is found to be 1.70 ± 0.20 km s-1 with a macroturbulence dispersion of 4.53 ± 0.10 km s-1. 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-1. 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-1 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. Title: Precise Rotation Rates for Five Slowly Rotating A Stars Authors: Gray, David F. Bibcode: 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-1. 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-1 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-1. These stars are suitable as standards for measuring rotation using less fundamental methods. Title: Short Timescale Variations in the Atmosphere of Antares A Authors: Pugh, T.; Gray, David F. Bibcode: 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. Title: Rotation of the K3 II-III Giant Star α Hydra Authors: Gray, David F. Bibcode: 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-1 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-1. Title: The Spectroscopic Variations of Antares A - Two Timescales of Variation Authors: Pugh, T.; Gray, D. F. Bibcode: 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. Title: The Two Regimes of Photospheric Motions in α Hydra Authors: Gray, David F. Bibcode: 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-1, have a distribution consistent with a true mean rise velocity of the large cells of ~725 m s-1 and a dispersion of ~220 m s-1. 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. Title: On the Six-year Period in the Radial Velocity of Antares A Authors: Pugh, T.; Gray, D. F. Bibcode: 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. Title: Granulation in the Photosphere of ζ Cygni Authors: Gray, David F. Bibcode: 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-1 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-1. Temperature variations were looked for using line-depth ratios, but none were found. Title: The Third Signature of Granulation in Bright-giant and Supergiant Stars Authors: Gray, David F.; Pugh, Teznie Bibcode: 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. Title: Photospheric Variations of the Supergiant γ Cyg Authors: Gray, David F. Bibcode: 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-1, 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. 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. Bibcode: 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 Teff = 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[Fe/H] = 0.08. The near-solar metallicity and small dispersion of σ[Fe/H] 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. Bibcode: 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. Bibcode: 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-1 for dwarfs and between 4 and 5 km s-1 for giants, and they span a range from ~1 to 10 km s-1 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. Bibcode: 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-1, 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. Bibcode: 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 Bibcode: 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 V = 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.

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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1. 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-1 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. Bibcode: 2008AJ....135..892C Altcode: 2007arXiv0711.4984C We report the results for rotational velocities, Vrot sin i, and macroturbulence dispersions, ζRT, 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 ζRT 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-1, while five show significant rotation/enhanced line broadening, over 3 km s-1. 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 Vrot 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 MV <= -1.5, do show net rotation, with mean values of 2-4 km s-1, 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.

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. Bibcode: 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. Bibcode: 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-1, based on a radius of 25.4 Rsolar. From detailed Fourier analysis of the broadening and shapes of the spectral lines, we derive vsini = 1.5 +/- 0.3 km s-1 and a radial-tangential macroturbulence dispersion of 5.2 +/- 0.2 km s-1. 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. Bibcode: 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-1 is demonstrated. Title: Quiet Sun unaffected by Activity Cycle Authors: Livingston, W.; Gray, D.; Wallace, L.; White, O. R. Bibcode: 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. Bibcode: 2005oasp.book.....G Altcode: No abstract at ADS Title: Rotational Velocities of Selected F-Type Stars Authors: Power, Jenny; Gray, David F. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2005ESASP.560..989T Altcode: 2005csss...13..989T No abstract at ADS Title: Spectroscopic line-depth ratios and solar variability Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2003IAUS..210..287G Altcode: No abstract at ADS Title: Modelling of Stellar Atmospheres Authors: Piskunov, N.; Weiss, W. W.; Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1 and cover a full span of +/-50-60 km s-1. 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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-1, 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. Bibcode: 2000IAUTA..24..190B Altcode: No abstract at ADS Title: The magic of Betelgeuse. Authors: Gray, D. F. Bibcode: 1999JRASC..93..181G Altcode: No abstract at ADS Title: Stellar Rotation and Precise Radial Velocities Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (ApJ, 474, 802 [1997]), equation (4), giving the variation in observed line depth, is incorrect. It should read δdobs=δs ((A0-1)dtrue)/((1-sA0)2) . 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.

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. Bibcode: 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 companion1,2. The velocity variation inferred from variations in the spectral lines of 51 Peg has an amplitude of 56-59 m s-l 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 attributed1,2 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. Bibcode: 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-1, 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1994JRASC..88Q.263H Altcode: No abstract at ADS Title: The Activity Cycle of tau Ceti Authors: Gray, David F.; Baliunas, Sallie L. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1992JRASC..86..277G Altcode: No abstract at ADS Title: The Inferred Color Index of the Sun Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 1992Sci...257.1978G Altcode: No abstract at ADS Title: Books-Received - the Observation and Analysis of Stellar Photospheres - ED.2 Authors: Gray, D. F. Bibcode: 1992JBAA..102..230G Altcode: No abstract at ADS Title: The observation and analysis of stellar photospheres. Authors: Gray, D. F. Bibcode: 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. Bibcode: 1992ASPC...27..472G Altcode: 1992socy.work..472G No abstract at ADS Title: Stellar Convection: The Observations (Invited Review) Authors: Gray, D. F. Bibcode: 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. Bibcode: 1992BAAS...24..651G Altcode: No abstract at ADS Title: A technique for precisely measuring stellar temperatures. Authors: Gray, D. F.; Johanson, H. L. Bibcode: 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. Bibcode: 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. Bibcode: 1991IAUTA..21..439G Altcode: No abstract at ADS Title: Dynamo Action in Evolved Stars Authors: Gray, David F. Bibcode: 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. Bibcode: 1991AN....312...44G Altcode: No abstract at ADS Title: Rotation of Evolved Stars Authors: Gray, D. F. Bibcode: 1991ASIC..340..183G Altcode: 1991amey.conf..183G No abstract at ADS Title: Interpreting the Coronal Boundary Authors: Gray, D. F. Bibcode: 1990ASPC....9..155G Altcode: 1990csss....6..155G No abstract at ADS Title: Rotation of Hot Stars after they Cool off Authors: Gray, D. F. Bibcode: 1990ASIC..316..283G Altcode: 1990amml.conf..283G No abstract at ADS Title: High-resolution spectroscopy - Why, how, and what for Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1989JRASC..83..298G Altcode: No abstract at ADS Title: The Morphology of Reversed Spectral Line Bisectors Authors: Gray, David F. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1989ASIC..263...71G Altcode: 1989ssg..conf...71G No abstract at ADS Title: Nonthermal Phenomena in the Photospheres of Cool Starts Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 1988BAAS...20..707T Altcode: No abstract at ADS Title: The buying Power of High Signal-To Ratios in Spectroscopy Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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-1 for the F Ib supergiants. Title: The rotation effect - A mechanism for measuring granulation velocities in stars. Authors: Gray, D. F. Bibcode: 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 -1 are deduced. Title: Magnetic activity in evolved stars Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1985JRASC..79..244T Altcode: No abstract at ADS Title: Magnetic fields in cool stars: a universal magnetic constant. Authors: Gray, D. F. Bibcode: 1985JRASC..79..234G Altcode: No abstract at ADS Title: An apparent universal magnetic constant for cool stars. Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1984JRASC..78..206G Altcode: No abstract at ADS Title: Is the rotation of the sun normal? Authors: Gray, D. F. Bibcode: 1984JRASC..78..203G Altcode: No abstract at ADS Title: The synchronous rotation of IOTA Pegasi. Authors: Gray, D. F. Bibcode: 1984PASP...96..537G Altcode: Measured rotation rates of the spectroscopic binary stars ι Peg A (6.5±0.3 km s-1) and B(5±1 km s-1) 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1984mpsc.conf..112G Altcode: No abstract at ADS Title: Measurements of magnetic fields in late-type dwarfs. Authors: Gray, D. F. Bibcode: 1983JRASC..77..256G Altcode: No abstract at ADS Title: On the constancy of spectral-line bisectors. Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 1983ApL....23..174G Altcode: No abstract at ADS Title: The remarkable rotational braking of G5 giants Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 1982JRASC..76..319G Altcode: No abstract at ADS Title: The rotation of cool main-sequence stars Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1981SSRv...28..113G Altcode: No abstract at ADS Title: Observations of rotation velocities in A stars. Authors: Gray, D. F. Bibcode: 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. Bibcode: 1980Sci...210..635G Altcode: No abstract at ADS Title: Depth Dependent Microturbulence in Arcturus Authors: Gray, D. F. Bibcode: 1980BAAS...12..797G Altcode: No abstract at ADS Title: Variations in the K-line emission of Arcturus Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 1980PASP...92..248G Altcode: No abstract at ADS Title: The rotation rate of Vega. Authors: Gray, D. F. Bibcode: 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. Bibcode: 1980ApJ...236.1056D Altcode: No abstract at ADS Title: Stellar turbulence Authors: Gray, D. F.; Linsky, J. L. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1979SSRv...23..683L Altcode: No abstract at ADS Title: High resolution spectroscopy the touchstone of photometry. Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1978hrs..conf..268G Altcode: No abstract at ADS Title: a Comparison of Some Current Observational Capability Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1977JRASC..71..401G Altcode: No abstract at ADS Title: Turbulence in α BOO. Authors: Gray, D. F. Bibcode: 1977BAAS....9..572G Altcode: No abstract at ADS Title: A quest for differential stellar rotation in A stars. Authors: Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1976JRASC..70..204G Altcode: No abstract at ADS Title: The observation and analysis of stellar photospheres Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 1975JRASC..69..245G Altcode: No abstract at ADS Title: The na D Lines as Surface Gravity Indicators Authors: Gray, David F. Bibcode: 1975mpth.conf..457G Altcode: 1975mpth.proc..457G No abstract at ADS Title: On Scattered Light Corrections for Stellar Spectrographs Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1973JRASC..67..241G Altcode: No abstract at ADS Title: On the Existence of Classical Microturbulence Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1972BAAS....4..337G Altcode: No abstract at ADS Title: Line Broadening by Macroturbulence. Authors: Evans, J. C.; Ramsey, L. W.; Gray, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1971Astr....8..144M Altcode: No abstract at ADS Title: Saturn Notes Authors: Gainsford, M. J.; Gray, D.; Veitch, R. G. Bibcode: 1971Astr....8..124G Altcode: No abstract at ADS Title: Coude Spectral Line Scanner. Authors: Gray, D. F. Bibcode: 1971BAAS....3R.387G Altcode: No abstract at ADS Title: The Radial Velocity Variation of Epsilon Cephei Authors: Gray, David F. Bibcode: 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 Bibcode: 1970Astr....7..127F Altcode: No abstract at ADS Title: Photometry of beta Cephei. Authors: Gray, D. F. Bibcode: 1970AJ.....75..958G Altcode: No abstract at ADS Title: Miscellanea. Authors: Miles, Howard; Gainsford, M. J.; Gray, David Bibcode: 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. Bibcode: 1970Astr....7...31H Altcode: No abstract at ADS Title: Miscellanea. Authors: Botley, Cicely; Churchward, Clive; Gray, D.; MacKenzie, R. A. Bibcode: 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 Bibcode: 1970Astr....7...29G Altcode: No abstract at ADS Title: Observations of Jupiter. Authors: Gray, David; Allen, D. A.; Pinnion, D. Bibcode: 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. Bibcode: 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. Bibcode: 1970Astr....7...13F Altcode: No abstract at ADS Title: Observations of Jupiter, February 1970. Authors: Gray, David; Pinnion, D.; MacKenzie, R. A. Bibcode: 1970Astr....6..246G Altcode: No abstract at ADS Title: Observations of Saturn, February 1970. Authors: Gray, David; MacKenzie, R. A. Bibcode: 1970Astr....6..247G Altcode: No abstract at ADS Title: Observations of Jupiter - January 1970. Authors: Gray, David; MacKenzie, R. A. Bibcode: 1970Astr....6..220G Altcode: No abstract at ADS Title: Saturn Notes. Authors: Gainsford, M. J.; Gray, David Bibcode: 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. Bibcode: 1970Astr....6..186G Altcode: No abstract at ADS Title: Observations of Jupiter. Authors: Heath, A. W.; MacKenzie, R. A.; Gray, D.; Burch, S. F. Bibcode: 1970Astr....6..190H Altcode: No abstract at ADS Title: Jupiter drawing : 1969 Nov 10. Authors: Gray, D. Bibcode: 1969Astr....6..170G Altcode: No abstract at ADS Title: Jupiter observations. Authors: Gray, David Bibcode: 1969Astr....6..166G Altcode: No abstract at ADS Title: Saturn observations. Authors: Gainsford, M. J.; Gray, D.; Murray, J. B. Bibcode: 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. Bibcode: 1969Astr....6..137G Altcode: No abstract at ADS Title: Saturn observations. Authors: Gray, D.; Appleyard, A. Bibcode: 1969Astr....6...96G Altcode: No abstract at ADS Title: Correction to Saturn report in 1969 Aug issue. Authors: Gray, D. Bibcode: 1969Astr....6...86G Altcode: No abstract at ADS Title: Saturn observations. Authors: Gray, D.; Fisher, N. E. Bibcode: 1969Astr....6...72G Altcode: No abstract at ADS Title: Stellar Surface Gravities Authors: Gray, D. F. Bibcode: 1969tons.conf..291G Altcode: No abstract at ADS Title: A list of photometric stellar radii. Authors: Gray, D. F. Bibcode: 1968AJ.....73..769G Altcode: No abstract at ADS Title: A Possible Test for Wavelength-Independent Interstellar Extinction Authors: Gray, D. F. Bibcode: 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. Bibcode: 1967AJ.....72..800G Altcode: No abstract at ADS Title: Photometric Determination of Stellar Radii Authors: Gray, David F. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Title: Integrated colors and magnitudes of open clusters. Authors: Gray, D. F. Bibcode: 1965AJ.....70..362G Altcode: No abstract at ADS Title: Parallax and mass ratio of BD +77361 from plates taken with the Sproul 24-inch refractor Authors: Gray, David F. Bibcode: 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. Bibcode: 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. Title: Evolutional changes in galactic cluster luminosity functions Authors: Gray, David F. Bibcode: 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.