Paul Zucchino

High resolution spectroscopy in the far UV: Observations of the interstellar medium by IMAPS on ORFEUS-SPAS

The Interstellar Medium Absorption Profile Spectrograph (IMAPS) is an objectivegrating, echelle spectrograph built to observe the spectra of bright, hot stars over the spectral region 950–1150Å, below the wavelength coverage of HST. This instrument has a high wavelength resolving power, making it especially well suited for studies of interstellar absorption lines. Following a series of sounding rocket flights in the 1980s, IMAPS flew on its first Shuttle-launched orbital mission in September 1993, as a partner in the ORFEUS-SPAS program sponsored by the US and German Space Agencies, NASA and DARA.On ORFEUS-SPAS, IMAPS spent one day of orbital time observing the spectra of 10 O- and early B-type stars. In addition to outlining how IMAPS works, we document some special problems that had an influence on the data, and we explain the specific steps in data reduction that were employed to overcome them. This discussion serves as a basic source of information for people who may use archival data from this flight, as well as those who are interested in some specific properties of the data that will be presented in forthcoming research papers.IMAPS is scheduled to fly once again on ORFEUS-SPAS in late 1996. On this flight, 50% of the observing time available for IMAPS and two other spectrographs on the mission will be available to guest observers.

The spectrum of the quasi-stellar object PHL 957.

Spectra of the radio-quiet quasar PHL 957 were obtained at a 200-in. telescope with a Cassegrain image tube, a Cassegrain multichannel spectrometer, and an integrating television camera on the spectrograph. The image-tube spectra revealed 64 absorption lines between 3200 and 6800 A. The absolute energy distribution indicates that this quasar is one of the most luminous known. The absorption line redshifts and line profiles observed are discussed.

IMAPS - A high-resolution, echelle spectrograph to record far-ultraviolet spectra of stars from sounding rockets

We have incorporated contemporary grating and detector technologies into the design of a new sounding rocket payload which consists of a slitless, objective grating spectrograph with no transmission elements in the opti-cal train (or detector). Built several years ago, this instrument has an effective collecting area of about 4 cm2 and can record spectra of point-like sources at a wavelength resolution of 0.004Å (profile FWITM) and with a sample interval (pixel width) of 0.002Å. It is designed to give continuous coverage over the wavelength range 950 < X < 1150A, a region of immense importance to our research on the interstellar medium. The instrument, called the Interstellar Medium Absorption Profile Spectrograph (IMAPS), has flown on a Black Brant rocket and obtained a spectrum of superb quality on an early-type star, π Scorpii. Data obtained on this flight also demonstrated the excellent response of our imaging detector, which uses an electron-bombarded CCD to register individual photoevents.

ICCD Development at Princeton

Publisher Summary This chapter discusses the intensified charge coupled devices (ICCD) development at Princeton. ICCDs are promising detectors for both laboratory measurements of high temperature plasmas in Tokamak nuclear fusion machines and in astronomy. There has been an interest for some time in image intensifier configurations that allow the use of opaque substrate photocathodes which exhibit higher quantum efficiency than semi-transparent photocathodes, especially in the ultraviolet and near infrared. Because the purpose of oblique magnetic focusing is to obtain a given lateral displacement of the focal plane from the optical axis, one must consider the trade-off of increased focal distance versus larger tilt angles. For a given accelerating voltage the aberrations increase with focal distance.

Echelle spectroscopy with a charge-coupled device /CCD/

Observations made with an RCA thinned back illuminated CCD on the echelle spectrograph of the Kitt Peak 4-meter Mayall telescope are discussed. With emphasis on interstellar line measurements in bright and faint background sources, the system efficiency, spectrum format, achieved signal-to-noise, interference fringes, and overall performance are discussed. A signal-to-noise of > 100/1 has been achieved at 0.2 Å resolution in two hours on a 13.2 mag star. Projected CCD improvements should yield signal-to-noise ratios of 20/1 for 18th magnitude objects (V) in 2 hours. With appropriate gratings, 1500 Å of continuous spectrum can be obtained.

Intensified Charge-Coupled Device (ICCD) Single Photoelectron Response

Princeton University Observatory has developed an Intensified Charge Coupled Device (ICCD) image tube with a 200 mm diagonal S-20 photocathode and a 100 x 160 pixel Texas Instruments CCD. Measurements of the CCDs response to accelerated photoelectrons have been made with this tube, as well as other configurations. The paper presents the pulse height distribution and point spread function for single photoelectrons of 20 keV energy. These data are discussed in relation to a photon counting image system.

Virtual Phase Charge Coupled Device Imager Operated In Frontside Electron-Bombarded Mode

The Texas Instruments virtual phase CCD imager has been successfully operated in the frontside electron-bombarded mode. The entire active area of the imager was covered with 130 nm of thermally grown gate oxide while only the clocked half of each pixel was additionally covered with a 500 nm polysilicon electrode. No protective overcoat was grown over the imager. A 20 kV electron beam was focused onto the imager to a total dose in excess of 120,000 primary electrons per pixel. Both the parallel and serial clocks were operated between -15 V and +2 V throughout, and no adjustment in any of the operating parameters was required. However, flat band shifts on the order of 2 V were detected. Single primary electron events were clearly detected with a signal-to-noise ratio exceeding 10. In excess of 90% of the secondary charge generated by a primary event was collected in a single pixel. The standard virtual phase imager with only the protective overcoat deleted can be used with a photocathode in the electron-bombarded mode for observing low to moderate light levels and can act as a true photon counter.

Evaluation of RCA thinned buried channel charge-coupled devices /CCDs/ for scientific applications

The RCA 512 x 320 pixel buried channel CCD has been employed in a number of astronomical observations ii the past year and the astronomical results are presented in several companion papers. This paper reports on recent laboratory evaluation of an experimental version of this CCD which has a lower input capacitance on-chip amplifier. The data presented includes readout noise measured in several ways, charge transfer efficiency as a function of signal level, and dark current as a function of temperature. The response of the RCA buried channel CCD to single energetic electrons and soft X-rays is also presented.

Development of a photon-counting capability for the electron-bombarded far-UV image sensor

We have developed a video signal processing system to detect and store photoevents recorded by a magnetically focused, electron-bombarded CCD (EBCCD) image sensor of the type that flew on the Interstellar Medium Absorption Profile Spectrograph (IMAPS). The EBCCD represents a good alternative to detectors that use microchannel plates: the opaque photocathode is on a solid substrate which leads to a very uniform response with a high quantum efficiency. Our experience with sounding rocket missions has demonstrated that this image sensor can perform well in poor vacuum conditions. Previous uses of the EBCCD on IMAPS missions have worked with video signals that were accumulated in an analog fashion. To make the EBCCD more useful for viewing very faint images in the future, we have recently developed new circuitry to detect photoevents in real time and store them discretely. This photon-counting signal processing mode overcomes the CCD readout noise penalty that accumulates when many successive analog frames are added together. The new circuits also provide for an automatic, accurate subtraction of the CCD dark current pattern.