Engineering topics

Hartig, G. F.

Publications and source records attributed to Hartig, G. F..

10 records

NASA NTRS1996

The Hubble Space Telescope Quasar Absorption Line Key Project: The Unusual Absorption-Line System in the Spectrum of PG 2302+029--Ejected or Intervening?

We report the discovery of a high-ionization broad absorption line system at a redshift of z(sub abs) = 0.695 in the spectrum of the z(sub em) = 1.052 radio-quiet quasar PG 2302+029. Broad absorption with FWHM from 3000 to 5000 km/s is detected from C iv, N v, and O vi in Hubble Space Telescope (HST) Faint Object Spectrograph spectra of the quasar. A narrow-line system (FWHM approx. 250 km/s) at z(sub abs) = 0.7016 is resolved from the broad blend and includes absorption by Ly alpha and the C iv, N v, and O vi doublets. No absorption by low-ionization metal species (e.g., Si II and Mg II) is detected in the HST or ground-based spectra for either the broad or the narrow system. The centroids of the broad system lines are displaced by approx. 56,000 km/s to the blue of the quasar's broad emission lines. The reddest extent of the broad-line absorption is more than 50,000 km/s from the quasar. The properties of this system are unprecedented, whether it is an intervening or an ejected system.

Jannuzi, B. T.↗

NASA NTRS1993

Performance of the FOS Detectors in a Variable External Magnetic Field

We present the results of an investigation of the in-orbit performance of the Digicon detectors in the Faint Object Spectrograph (FOS), conducted as part of the commissioning phase of the Hubble Space Telescope. This paper includes orbital results on detector background noise, sensor image stability, and photometric stability along with several typical FOS observations. New techniques for suppressing cosmic ray induced background and geomagnetic induced image motion in electron tube detectors are also discussed.

Fitch, J. E.↗

NASA NTRS1991

Faint object spectrograph observations of the low-luminosity Seyfert galaxy NGC 1566

FOS observations of the Seyfert galaxy NGC 1566 show it to possess the broad lines characteristic of a typical Seyfert 1 galaxy, even in states of very low luminosity. The continuum, however, is steep with no suggestion of the ultraviolet excess seen in higher luminosity AGNs. The broad emission lines have symmetric profiles, but are redshifted by 200-1000 km/s relative to the systemic velocity. The broad-line ratios indicate a low ionization parameter, and the strength of lines such as Fe II, Mg II, and the Balmer continuum relative to the UV continuum supports models for X-ray heating of the broad-line cloud interiors.

Kriss, G. A.↗

NASA NTRS1988

Cosmic ultraviolet background radiation and zodiacal light

Spectroscopic measurements of the diffuse cosmic UV background in the 1700-2850-A range are presented. In agreement with previous results, the data have resulted in the detection at high Galactic latitude of an intensity of 300 + or - 100 photons/sq cm s sr A at 1800 A without correction for starlight or airglow, a similar intensity over the 1900-2500-A range after correction for measured airglow, and a similar intensity over the 2500-2800-A range after correction for zodiacal light. It is suggested that this radiation may originate partly in line radiation from a Galactic halo and partly from extragalactic sources, perhaps the integrated light of distant galaxies.

Tennyson, P. D.↗

NASA NTRS1986

Near-midnight observations of nitric oxide delta- and gamma-band chemiluminescence

Chemiluminescent nightglow emission of the nitric oxide delta and gamma bands was measured from a sounding rocket launched on April 27, 1981, near local midnight. The integrated band emission rates for this near zenith observation above 205 km were less than 10 Rayleighs. The solar zenith angle was 127 deg. The branching ratio from the C2Pi state to the A2Sigma(+) state of NO was determined from comparison of the total emission rate of the delta band system to that of the gamma band system and found to be 0.30 + or - 0.06. The branching ratios within each of the band systems were found to be consistent with previous theoretical and experimental determinations. The vertical atomic nitrogen distribution, derived with the use of a model atmosphere, was found to have a peak density of 2.0 x 10 to the 7th atoms/cu cm at an altitude of 205 km. The analysis of these data indicate the presence of residual NO emission above 270 km at local midnight on the order of 1 Rayleigh of total band emission.

Tennyson, P. D.↗

NASA NTRS1982

A photon-counting photodiode array detector for far ultraviolet (FUV) astronomy

A compact, stable, single-stage intensified photodiode array detector designed for photon-counting, far ultraviolet astronomy applications employs a saturable, 'C'-type MCP (Galileo S. MCP 25-25) to produce high gain pulses with a narrowly peaked pulse height distribution. The P-20 output phosphor exhibits a very short decay time, due to the high current density of the electron pulses. This intensifier is being coupled to a self-scanning linear photodiode array which has a fiber optic input window which allows direct, rigid mechanical coupling with minimal light loss. The array was scanned at a 250 KHz pixel rate. The detector exhibits more than adequate signal-to-noise ratio for pulse counting and event location.

Hartig, G. F.↗

NASA NTRS1982

Photon counting photodiode array detector for far ultraviolet (FUV) astronomy

Hartig, G. F.↗

NASA NTRS1981

The Johns Hopkins Ultraviolet Telescope for Shuttle astronomy

The Hopkins Ultraviolet Telescope (HUT) is a 90-cm f/2 prime focus telescope and spectrometer with a photon-counting microchannel plate detector designed to obtain moderate resolution (wavelength interval, approximately 4 A) spectrophotometry of faint (visual magnitude, less than approximately 17) objects in the far-ultraviolet spectral region (approximately 900-1700 A). The HUT will be mounted on the Spacelab Instrument Pointing System and will be operated by a Payload Specialist using a field acquisition TV system to assist in locating targets. The initial flight of the HUT, expected in 1984 or 1985, will be devoted primarily to the study of quasars and active galactic nuclei, emphasizing the 900-1200 A spectral region which is inaccessible with other existing or currently planned orbiting instruments.

Davidson, A. F.↗

NASA NTRS1980

Rocket instrument for far-UV spectrophotometry of faint astronomical objects

A sensitive sounding rocket instrument for moderate (about 10-A) resolution far-UV (1160-1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employes a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed.

Hartig, G. F.↗

NASA NTRS1977

Ultraviolet spectrum of quasi-stellar object 3C273

The first direct observation of the ultraviolet spectrum of a quasi-stellar object (QSO) has been made with a rocket-borne telescope. The emission line spectrum of 3C273 is similar to the spectra of high-redshift QSOs, but no absorption is observed. The results provide important new constraints on theoretical models of QSOs, place a severe limit on the density of neutral hydrogen in the intergalactic medium, and suggest a cosmological origin for much of the absorption seen in high-redshift QSOs. Comparison of the ultraviolet spectrophotometry of low- and high-redshift QSOs suggests that the universe is closed, with a deceleration parameter of about 1.

Davidsen, A. F.↗