The Grating Carrousel Mechanism Of The Goddard High Resolution Spectrograph For The Hubble Space Telescope

Ebbets, Dennis; Christon, P. R.; Garner, H.

doi:10.1117/12.977970

Cited by 5 publications

(9 citation statements)

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“…This value is in agreement with the value of ∼1.8% determined by Ebbets (1992), which was calculated from GHRS G160M spectra of interstellar absorption lines at 1670Å.…”

Section: Optical Depths and Covering Factorssupporting

confidence: 92%

“…We reduced the spectra using the IDL procedures written for the GHRS Instrument -6 -Definition Team (Blackwell et al 1993). For each readout, an average background across the diode array was determined and subtracted from the gross spectrum, since the background level (due primarily to Cerenkov radiation) is constant to within a few percent as a function of diode, but generally variable by a factor of two as the geomagnetic latitude of HST changes over time (Ebbets 1992). In the regions of overlap, the average fluxes from the two wavelength settings agree to within 4%, so no scaling was done between them.…”

Section: Observations and Direct Measurementsmentioning

confidence: 99%

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Resolving the Intrinsic CivAbsorption in the Seyfert 1 Galaxy NGC 3516

Crenshaw¹,

Maran²,

Mushotzky³

1998

ApJ

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We observed the Seyfert 1 galaxy NGC 3516 with the Goddard High Resolution Spectrograph on the Hubble Space T elescope, and obtained UV spectra at a resolution of j/*j B 20,000 in the redshifted C IV j1549 region. The intrinsic C IV absorption in the core of the broad emission line is resolved for the Ðrst time into four distinct kinematic components, which are all blueshifted, relative to the systemic radial velocity of the host galaxy. Two components are narrow (D20 and D30 km s~1 FWHM) and at small radial velocities ([90 and [30 km s~1, respectively), and could arise from the interstellar medium or halo of the host galaxy. The two broad components are centered at radial velocities of [380 and [150 km s~1, have widths of 130 and 210 km s~1 FWHM, respectively, and most likely arise in outÑowing gas near the active nucleus. At the times of observation, 1995 April 24 and 1995 October 22, there was no evidence for the variable absorption component at a higher outÑow velocity that disappeared some time after 1989 October.The cores of the broad C IV absorption components are very close to zero intensity, indicating that the absorption regions are extended enough to occult completely the broad C IV emitting region (which is D9 light-days in extent). The total column density of the C IV absorption is substantially larger than that measured by Kriss et al. from contemporaneous Hopkins Ultraviolet Telescope (HUT) spectra, but we agree with their conclusion that the UV absorption is too strong to arise primarily from the X-ray warm absorber region. The GHRS observations, separated by six months, reveal no appreciable changes in the equivalent widths or radial velocities of any of the absorption components, although a change in the column density of either broad component at a level ¹25% cannot be ruled out, because the lines are highly saturated. At present, we know of two Seyfert galaxies, NGC 3516 and NGC 4151, with complex multiple absorption zones, which can remain stable in column density and velocity Ðeld over timescales of months to years.

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“…This value is in agreement with the value of ∼1.8% determined by Ebbets (1992), which was calculated from GHRS G160M spectra of interstellar absorption lines at 1670Å.…”

Section: Optical Depths and Covering Factorssupporting

confidence: 92%

Section: Observations and Direct Measurementsmentioning

confidence: 99%

Resolving the Intrinsic CivAbsorption in the Seyfert 1 Galaxy NGC 3516

Crenshaw¹,

Maran²,

Mushotzky³

1998

ApJ

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“…The intentional displacements in wavelength for different subexposures in the GHRS FP-SPLIT observing routine allowed these variations to be differentiated from real absorption features in the raw spectra. The method used here to derive independently the detector's fixed-pattern signal and the real spectral signal gave a direct solution and thus differed from the iterative technique described by Ebbets (1992), Cardelli & Ebbets (1994) and Fitzpatrick & Spitzer (1994). Details of this more direct method of solution are given in Appendix A.…”

Section: Removal Of Detector Artifactsmentioning

confidence: 99%

“…The extremes of this correction can in principle differ by as much as twice the orbital velocity of approximately 7 km s −1 times the cosine of the angle of the target with respect HST orbital plane at the time of observation. The other effect, a much smaller one, arises from small changes in the influence of the Earth's magnetic field on the trajectories of the electrons traveling from the detector's photocathode to the sensing diodes (Ebbets 1992). Figure 2 illustrates the importance of recognizing these shifts and compensating for them in the analysis that eliminates the fixed-pattern noise.…”

Section: Removal Of Detector Artifactsmentioning

confidence: 99%

Thermal Pressures in Neutral Clouds inside the Local Bubble, as Determined from CiFine‐Structure Excitations

Jenkins

2002

ApJ

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High-resolution spectra covering the absorption features from interstellar C I were recorded for four early-type stars with spectrographs on the Hubble Space Telescope, in a program to measure the fine-structure excitation of this atom within neutral clouds inside or near the edge of the Local Bubble, a volume of hot (T ∼ 10 6 K) gas that emits soft x-rays and extends out to about 100 pc away from the Sun. The excited levels of C I are populated by collisions, and the ratio of excited atoms to those in the ground level give a measure of the local thermal pressure. Absorptions from the two lowest levels of C I were detected toward α Del and δ Cyg, while only marginal indications of excited C I were obtained for γ Ori, and λ Lup. Along with temperature limits derived by other means, the C I fine-structure populations indicate that for the clouds in front of γ Ori, δ Cyg and α Del, 10 3 < p/k < 10 4 cm −3 K at about the ±1σ confidence level in each case. The results for λ Lup are not as well constrained, but still consistent with the other three stars. The results indicate that the thermal pressures are below generally accepted estimates p/k > 10 4 cm −3 K for the Local Bubble, based on the strength of x-ray and EUV emission from the hot gas. This inequality of pressure for these neutral clouds and their surroundings duplicates a condition that exists for the local, partly-ionized cloud that surrounds the Sun. An appendix in the paper describes a direct method for determining and eliminating small spectral artifacts arising from variations of detector sensitivity with position.

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“…' A detailed description of the GHRS optics and the digicon detectors has been presented in Paper I, and readers are referred to it to obtain an understanding of the instrument design and operation. Further information can be found in the GHRS Science Verification Report (Ebbets 1992) and the GHRS Instrument Handbook (Soderblom 1993). An extensive set of engineering reports was generated by the GHRS prime contractor, Ball Aerospace, and the team.…”

Section: Introductionmentioning

confidence: 99%

The Goddard High Resolution Spectrograph: In-Orbit Performance

Heap¹,

Brandt²,

Randall³

et al. 1995

PASP

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ABSTRACT. The in-orbit performance of the Goddard High-Resolution Spectrograph onboard the Hubble Space Telescope (HST) is presented. This report covers the pre-COSTAR period, when instrument performance was limited by the effects of spherical aberration of the telescope's primary mirror. The digicon detectors provide a linear response to count rates spanning over six orders of magnitude, ranging from the normal background flux of 0.01 counts diode -1 s -1 to values larger than 10 4 counts diode -1 s -1 . Scattered light from the first-order gratings is small and can be removed by standard background-subtraction techniques. Scattered light in the echelle mode is more complex in origin, but it also can be accurately removed. Data have been obtained over a wavelength range from below 1100 Â to 3300 Â, at spectral resolutions as high asR = \/A\ = 90,000. The wavelength scale is influenced by spectrograph temperature, outgassing of the optical bench, and interaction of the magnetic field within the detector with the Earth's magnetic field. Models of these effects lead to a default wavelength scale with an accuracy better than 1 diode, corresponding to 3 km s -1 in the echelle mode. With care, the wavelength scale can be determined to an accuracy of 0.2 diodes. Calibration of the instrument sensitivity functions is tied into the HST flux calibration through observations of spectrophotometric standard stars. The measurements of vignetting and the echelle blaze function provide relative photometric precision to about 5% or better. The effects of fixed-pattern noise have been investigated, and techniques have been devised for recognizing and removing it from the data. The ultimate signal-to-noise ratio achievable with the spectrograph is essentially limited only by counting statistics, and values approaching 1000:1 have been obtained.

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The Grating Carrousel Mechanism Of The Goddard High Resolution Spectrograph For The Hubble Space Telescope

Cited by 5 publications

References 0 publications

Resolving the Intrinsic CivAbsorption in the Seyfert 1 Galaxy NGC 3516

Resolving the Intrinsic CivAbsorption in the Seyfert 1 Galaxy NGC 3516

Thermal Pressures in Neutral Clouds inside the Local Bubble, as Determined from CiFine‐Structure Excitations

The Goddard High Resolution Spectrograph: In-Orbit Performance

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