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Leckrone, D. S.

Publications and source records attributed to Leckrone, D. S..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

The Goddard High Resolution Spectrograph: Instrument, goals, and science results

The Goddard High Resolution Spectrograph (GHRS), currently in Earth orbit on the Hubble Space Telescope (HST), operates in the wavelength range 1150-3200 A with spectral resolutions (lambda/delta lambda) of approximately 2 x 10(exp 3), 2 x 10(exp 4), and 1 x 10(exp 3). The instrument and its development from inception, its current status, the approach to operations, representative results in the major areas of the scientific goals, and prospects for the future are described.

Brandt, J. C.↗
NASA NTRS1993

Observations of 3C 273 with the Goddard High Resolution Spectrograph on the Hubble Space Telescope

The observations of the quasar 3C 273 taken with the Goddard High Resolution Spectrograph in 1991 February are presented here. We have included both the reduced raw data, and smoothed and deconvolved spectra. Also, a list of observed absorption lines is presented. The data comprise 11 spectra, including one low resolution and 10 medium resolution observations. The wavelength region covered ranged from about 1150 to 2820 A, but was not all inclusive. The procedures used to obtain and reduce the data, including corrections for fixed pattern noise, compensation for the effects of spherical aberration in the HST primary mirror, and objective detection of weak absorption lines, are described. We also have included a short discussion on the detection of galactic Ni II and Virgo cluster metal lines.

Brandt, J. C.↗
NASA NTRS1991

A line identification study of the IUE SWP high dispersion spectrum of the UV-bright star Barnard 29 of Messier 13

A line identification study was performed of the coaddition of three SWP high dispersion IUE exposures of the UV-bright star Barnard 29 of Messier 13. One of these images took two IUE shifts. The previous study by de Boer and Savage (1983) was extended and stellar lines of C I, C II, C III, C IV, N I, N III, O I, O III, O IV,Al III, Si II, Si III, Si IV, P III, S II, and S III and interstellar lines of C I, C II, C IV, N I, N III, N IV, N V, O I, Al II, Al III, Si II, Si IV, S II, and Fe II were found. These lines are the strongest expected lines in a hot Population II star. Apparent intensity minima corresponding to interstellar features are noted, especially those matching a high velocity cloud found by de Boer and Savage.

Adelman, S. J.↗
NASA NTRS1986

The ultraviolet IUE spectrum of the population II horizontal-branch A star HD 109995

Eight SWP and six LWP high dispersion IUE images of the field horizontal-branch A star HD 109995 have been averaged to increase the signal-to-noise ratio. The line density in the UV is greater than that of the optical region, but less than that of comparable population I A stars. Many of the identified lines are those of Fe II. Lines of C I, C II, N I, O I, Mg I, Mg II, Al II, Al III, Si I, Si II, P II, S I, Cl I, Ti II, V II, Cr II, Mn II, Fe I, Co II, Ni II, Zn II, and Ge II are also present. Definite interstellar lines of C II, Mg I, Mg II, Al II, Si II, and Fe II were found.

Adelman, S. J.↗
NASA NTRS1985

The field horizontal-branch star HD 109995: New results with coadded ultraviolet and optical region spectra

A comprehensive ultraviolet and optical region abundance analysis of the field horizontal branch Population 2 A-type star HD 109995 is described. Coaddition of IUE high dispersion images and DAO 6.5 A/mm IIaO spectrograms improved the signal-to-noise ratio of the data. We have identified ultraviolet lines whose analysis will provide more complete and accurate elemental abundances than those obtained from optical region spectra alone. A preliminary elemental abundance analysis of the optical region shows that log Z/Z (solar) approx. = -2. A first attempt to synthesize two Fe 2 ultraviolet resonance lines yields an iron abundance a few tenths of a deg higher than the average obtained from optical region Fe 2 lines.

Adelman, S. J.↗
NASA NTRS1984

The resonance lines of Hg II in IUE spectra of chemically peculiar stars

Twenty IUE images of chemically peculiar (CP) stars are analyzed to demonstrate that the previously detected Hg II overabundances in CP stars is real. Attention was focused on the Hg II resonance lines at 1650 and 1942 A. A total of eight stars were scanned and spectrum synthesis computations were performed to characterize the model atmospheres for each object. The 1942 A line was found to be insensitive to effective temperature, microturbulence and isotopic mixture influences, and therefore well-suited to abundance analyses. A non-LTE process was ruled out as a source of the Hg anomaly. Finally, it is suggested that diffusion-type processes be attributed to Hg enhancements in main sequences B stars.

Leckrone, D. S.↗
NASA NTRS1984

On the need for spectroscopic data in ultraviolet stellar spectral synthesis calculations

A general discussion of the quality of spectroscopic data for ultraviolet (less than 3000 A) spectral synthesis calculations is presented. It is pointed out that progress in the generation of complete and accurate lists of atomic lines, and in the computation and measurement of accurate transition probabilities of the spectra of many elements is lagging behind current and near-term observational capabilities. Theoretical syntheses of the line profiles in the spectra of three middle-to-late B type stars (Pi Cet, 134 Tau, and vCap) are computed. The computations are found to be complicated and ambiguous due to the low accuracy of the oscillator strengths used in the analysis. Some characteristics of star-to-star variations in elemental abundances are discussed.

Adelman, S. J.↗
NASA NTRS1982

Spectroscopic equipment for the Space Telescope

The Space Telescope will provide views of the Universe of remarkable clarity. Central to its capabilities is an f/24 Ritchey-Chretien telescope with 40,000 sq cm unobscured collecting area, which will provide point-source images less than 0.1 sec in radius at wavelengths below 633 nm. It will operate over the range 110 nm to 1 mm. The initial flight instrumentation includes two spectrographs, the Faint Object Spectrograph (F.O.S.) and the High-Resolution Spectrograph (H.R.S.). The F.O.S. is sensitive from 115 to 800 nm. It will provide data at resolving powers 1000-100 on extremely faint sources. The H.R.S. operates at the wavelengths 107-320 nm. It will achieve high photometric accuracy at resolving powers 100,000, in the echelle mode, or 10,000-1000 in first order, on brighter targets. The two cameras on board the Space Telescope will provide ancillary spectroscopic capabilities.

Leckrone, D. S.↗
NASA NTRS1981

The resonance line of B II in IUE spectra of chemically peculiar stars

A description is presented of high-dispersion spectroscopic observations of eight chemically peculiar stars including Kappa Cnc and Mu Lep, and of one normal comparison star, Nu Cap, in the vicinity of 1362 A. The reported data were obtained with the International Ultraviolet Explorer during the first 15 months of its operation. The initial reduction of the data, which were originally described in a qualitative summary by Leckrone (1980), was affected by a serious error in the calibration of the instrument's intensity transfer function. This error has been corrected in the currently presented data. The results of spectrum syntheses of the 1362 A feature are also described for several of the stars.

Leckrone, D. S.↗
NASA NTRS1980

The space telescope scientific instruments

The paper describes the space telescope with a 2.4 m aperture to be launched at 500 km altitude in late 1983. Four axial-bay and one radial-bay scientific instrument, a wide-field and planetary camera, a faint-object camera, a faint-object spectrograph, and a high-speed photometer are to be installed to conduct the initial observations. The axial instruments are constrained to envelopes with dimensions 0.9 x 0.9 x 2.2 m and their masses cannot exceed 317 kg. The observatory will also be equipped with fine-guidance sensors and a microprocessor. The design concepts of the instruments are outlined and some of the astronomical capabilities including studies of distant and local galaxies, physical properties of quasars, interrelations between quasars and active galactic nuclei are mentioned.

Leckrone, D. S.↗
NASA NTRS1979

The ultraviolet flux distribution of Alpha-2 Canum Venaticorum

Intermediate- and narrow-band UV spectrophotometry from Copernicus, OAO 2, the S2-68 experiment on TD 1, and a sounding-rocket experiment are combined with ground-based observations to define the absolute flux distribution of the bright magnetic Ap star Alpha-2 CVn over the wavelength range from 1030 to 7580 A. Two flux distributions are presented which coincide more or less with the rare-earth maximum and minimum in the star's cycle. The results are compared with those for two normal stars, the UV variability of Alpha-2 CVn is characterized as a function of wavelength, and non-LTE effects on the UV continua of C I and Si I are analyzed. Some physical properties of Alpha-2 CVn are estimated, and the evolutionary age of the star is estimated to be between 220 million and 300 million years. It is concluded that Alpha-2 CVn is old enough to have been magnetically braked to its current rotational velocity by either the centrifugal-wind or the accretion mechanism and to have developed its chemical peculiarities by either mechanism.

Leckrone, D. S.↗
NASA NTRS1979

Space telescope scientific instruments

The paper describes the Space Telescope (ST) observatory, the design concepts of the five scientific instruments which will conduct the initial observatory observations, and summarizes their astronomical capabilities. The instruments are the wide-field and planetary camera (WFPC) which will receive the highest quality images, the faint-object camera (FOC) which will penetrate to the faintest limiting magnitudes and achieve the finest angular resolution possible, and the faint-object spectrograph (FOS), which will perform photon noise-limited spectroscopy and spectropolarimetry on objects substantially fainter than those accessible to ground-based spectrographs. In addition, the high resolution spectrograph (HRS) will provide higher spectral resolution with greater photometric accuracy than previously possible in ultraviolet astronomical spectroscopy, and the high-speed photometer will achieve precise time-resolved photometric observations of rapidly varying astronomical sources on short time scales.

Leckrone, D. S.↗
NASA NTRS1976

Properties of Ap stars in the ultraviolet

A review is presented of the current state of knowledge concerning the emitted flux distributions of Ap stars and their ultraviolet photometric variability especially as it relates to photometric and spectrum variability observed in the visible. A table of Ap stars observed in the ultraviolet from space vehicles is presented along with a graph which shows the observed flux distributions, normalized to unity flux at 3320 A, for the Si star theta Aur and for the normal stars 134 Tau and gamma UMa. Attention is given to ultraviolet color indices and ultraviolet light curves for variable Ap stars.

Leckrone, D. S.↗
NASA NTRS1974

Ultraviolet photometry from the orbiting astronomical observatory. XV - The strongly magnetic variable HD 215441

The Wisconsin Experiment Package on OAO-2 was used to obtain light curves of the strongly magnetic, variable Ap star HD 215441 over the wavelength range 1550 to 4250 A. This star is characterized by a lack of outstanding spectrum variability at wavelengths accessible from the ground, while undergoing UBV photometric variations of large amplitude. The observations of HD 215441 demonstrate that an Ap star need not be a striking spectrum variable at blue-visible wavelengths for its photometric variations to be controlled by opacity variations in the ultraviolet.

Leckrone, D. S.↗
NASA NTRS1973

Ultraviolet photometry from the Orbiting Astronomical Observatory. VIII

A comprehensive ultraviolet photometric survey of the blue Ap stars was conducted in order to determine whether the close similarity, deduced from ground observations, between the blue Ap stars and normal B stars with similar UBV colors is maintained at wavelengths shortward of 3000 A. Data are presented for 24 Ap stars and 31 normal comparison standard dwarfs and giants observed by the Wisconsin Experiment Package on OAO 2. Both normal and peculiar stars were chosen, with a few exceptions, for their minimal interstellar reddening and for the absence of known bright companions. The similarity between blue Ap stars and normal B stars of similar UBV colors is not maintained in the ultraviolet. The blue Ap stars emit less ultraviolet flux than normal stars of like UBV colors. They are underluminous and cool in effective temperature for their colors.

Leckrone, D. S.↗
NASA NTRS1973

Ultraviolet photometry from the orbiting astronomical observatory. 8: The blue Ap stars

The filter photometers in the Wisconsin Experiment Package on OAO-2 were used to obtain data for a carefully selected set of 24 blue Ap stars and 31 comparison standard B and A dwarfs and giants for a program of relative photometry. Observations were made in seven bandpasses over the effective wavelength range 1430A-4250A. The Ap stars observed include members of the Si, Hg-Mn and Sr-Cr-Eu peculiarity classes. Most of them are too blue in B-V for their published MK spectral classes. The blue Ap stars are markedly deficient in emitted ultraviolet flux and are underluminous as compared to normal stars with the same UBV colors. The Hg-Mn stars appear less flux deficient in the ultraviolet for their UBV colors than do Si or Sr-cr-Eu stars. Most of the Ap stars observed possess ultraviolet flux distributions, or ultraviolet color temperatures, consistent with their published MK spectral classes to well within the classification uncertainties.

Leckrone, D. S.↗
NASA NTRS1973

Ultraviolet observations of peculiar B and A stars from OAO-2

Plotted photometric data in two far-ultraviolet bandpasses at 1550 and 1430 A for both normal and peculiar stars are compared for flux distribution. It is shown that the ultraviolet flux distribution of an A sub p or B sub p star is consistent with its spectral class and is notably inconsistent with its UBV colors. It is assumed that the helium line strength suppression mechanism is related to an abnormal atmospheric structure in the peculiar stars.

Leckrone, D. S.↗