Gabriel L. Epstein

An EUV imaging spectrograph for high-resolution observations of the solar corona

An extreme ultraviolet (EUV) imaging spectrograph for the wavelength range from 235 to 450 Å has been developed and used for high resolution observations of the Sun. The instrument incorporates a glancing incidence Wolter Type II Telescope and a near-normal incidence toroidal grating spectrograph to achieve near-stigmatic performance over this spectral range. The design of the spectrograph entrance aperture enables both stigmatic spectra with spectral resolution adequate to observe emission line profiles and spectroheliograms of restricted portions of the Sun to be obtained concurrently. In this paper we describe the design and performance of the instrument and provide an overview of results obtained during a sounding rocket flight on May 5, 1989.

Spectrum of doubly ionized yttrium (Y iii)

The spectrum of doubly ionized yttrium was observed from 600 to 9700 A by means of plane- and concave-grating spectrographs at NBS. About 100 new lines were observed. From these measurements, 40 new energy levels were derived. The known level system (Rb i isoelectronic sequence, 4p6nl) now includes the series ns (n = 5–9), np (n = 5–9), nd (n = 4–8), nf (n = 4–10), ng (n = 5–8), and nh (n = 6–8). The nf series shows irregular fine-structure splittings, 4f having a negative splitting of about 3 cm−1. The ionization energy of Y iii was determined to be 165 540.5 ± 1.0 cm−1 (20.52457 ± 0.00012 eV). A reexamination of Kiess’s data for Zr iv in the light of the Y iii analysis yielded a revised value for the ionization energy of Zr iv of 277 550 ± 20 cm−1 (34.412 ± 0.003 eV).

Resonance lines of Cs ii, Ba iii, and La iv

The resonance line spectra of ions in the Xe i isoelectronic sequence, consisting of the 5 transitions to the 5p6 1S0 ground state from levels with J = 1 in the 5p5 5d and 6s configurations, have been observed for Cs ii, Ba iii, and La iv. The observations were made with a sliding spark on the 10.7-m normal-incidence vacuum spectrograph at NBS. The resonance transitions from the 5p5 6d and 7s configurations were also observed for these ions, except for that from 5p5 6d3P1 of Ba iii. Several resonance transitions from higher nd and ns levels were also observed. Estimated values for the J = 1 levels of the 5p5 7s configuration of Ce v were obtained by extrapolation. The derived ionization energies in eV are Cs ii 23.17(4), Ba iii 35.79(6), La iv 45.95(6), Ce v 65.55(25).

Spectrum and energy levels of triply ionized yttrium (Y iv)

The spectrum of Y iv was observed in the region from 300 to 5000 A with the 10.7-m normal-incidence vacuum spectrograph and the 10.7-m Eagle spectrograph in air at the National Bureau of Standards. The light source was a sliding spark discharge. About 560 lines were classified as transitions between 129 energy levels. The observed level system (Kr i isoelectronic sequence) includes nearly all levels of the 4s24p6, 4s24p55s, 6s, 7s, 4d, 5d, 6d, 4f, 5f, 5g, 6g, and 4s4p64d configurations. About 190 lines remain unclassified. All observed configurations have been theoretically interpreted. The energy parameters determined by least-squares fits to the observed levels are compared with Hartree–Fock calculations. The ionization energy as derived from the 4p5ng (n = 5, 6) levels is 488 830 ± 20 cm−1 (60.608 ± 0.002 eV).

Resonance lines and energy levels of Cs iii, Ba iv, and La v

The spectra of Cs iii, Ba iv, and La v have been observed in a sliding spark discharge on the 10.7 m normal-incidence vacuum spectrograph at NBS. Analysis of the observations of Cs iii and La v has yielded the energy levels of the 5s25p5 and 5s5p6 configurations and nearly all levels of the 5s25p45d and 5s25p46s configurations that can combine with the 5s25p5 2P° ground term. The observations for Ba iv have yielded the levels of the 5s25p5 and 5s5p6 configurations. The 5s25p45d + 5s25p46s + 5s5p6 levels of Cs iii and La v have been theoretically interpreted, with configuration interaction included. The energy parameters determined from a least-squares fit to the observed level values are compared with Hartree-Fock calculations. The ionization energies are found to be 33.38 ± 0.25 eV for Cs iii, 47.1 ± 0.6 eV for Ba iv, and 61.6 ± 0.6 eV for La v. By extrapolating these values the ionization energy of Ce vi is estimated as 77.6 ± 1.2 eV.

A short-lived chromospheric flare-point with a lifetime of 20 seconds and rise and fall times of 5 seconds

We have observed a chromospheric brightening in the H alpha and Ca II K lines with a diameter of about 1 arc second. The time structure of this event, obtained with a relative resolution of 1 second, shows the rise time to be 4 seconds, the lifetime (FWHM) to be 20 seconds, and the decay time to be 5 seconds. This imposes new constraints on flare-point models. These restrictions can be accommodated easily by either an infall-impact flare model or a model invoking the precipitation of high-energy particles from the corona.

Spectrum and energy levels of triply ionized lanthanum (La iv)

The spectrum of La iv has been observed in a sliding spark discharge with the NBS 10.7-m normal incidence vacuum spectrograph and the NBS 10.7-m Eagle spectrograph in air. A total of 368 lines have been observed in the region from 300 to 5000 A. About 190 lines have been classified as transitions between 49 energy levels. All levels of the 5p6, 5p5 5d, 6s, 6d, and 7s configurations as well as half of the levels of the 5p5 4f configuration have been located. Because of the greatly contracted 4f orbital, the lowest excited configuration is 5p5 4f. All configurations have been theoretically interpreted. The energy parameters determined from least-squares fits to the observed levels are compared with Hartree-Fock calculations. Some new measurements for La iii are presented that confirm the 1967 results of Odasbasi.

Layered Synthetic Microstructures for Solar EUV Telescopes

Due to the recent development of the design and production of layered synthetic microstructures (LSMs) we can entertain concepts for EUV instrument design that use normal incidence components. Thus, LSMs offer the possibility of producing an efficient extreme ultraviolet (EUV) telescope for solar studies that takes advantage of contemporary normal incidence mirror technology. This paper discusses the applica-tion of LSMs to figured mirrors suitable for solar EUV instruments. Initial studies were performed for a single mirror telescope consisting of an f/18, 200cm focal length, off-axis paraboloid. The design trades in terms of peak reflectance and broad bandpass in the 300Å region and deposition considerations will be discussed.

Electronic systems for the new multichannel spectrometer at Sacramento Peak.

A three-day meeting to discuss astronomical instrumentation was held at Lick Observatory, University of California at Santa Cruz, from 31 August to 2 September 1971. The papers presented at the meeting are published here to provide wider dissemination to the scientific community. Two papers, those by William Spicer and Dick Mack, were invited papers, the others were contributed by the participants. In order to expedite the publication of the proceedings, we have not included in the proceedings any of the discussion that accompanied the presentation of the papers. We would like to thank the University administration at Santa Cruz, the employees of Lick Observatory, and George Herbig for their continual support both before and during the meeting. We are particularly grateful to D. H. McNamara, Editor of the Publications of the Astronomical Society of the Pacific for his prompt handling of the manuscripts. The publication costs have been supported, in part, by the National Aeronautics and Space Administration under Grant NGR 05-061-014. Lloyd B. Robinson

Performance comparison of two Wolter type II telescopes in the far ultraviolet

Experimental results for image quality and scatter in far-UV light are used to choose between the conventionally polished Solar Extreme-Ultraviolet Rocket Telescope and Spectrograph (SERTS-A) and computer-controlled polished SERTS-C Wolter type II solar rocket telescopes for an extreme-UV flight instrument. In 124-nm light the SERTS-C telescope image had a 0.67-arcsec full width at half-maximum (FWHM), compared with a 1.25-arcsec FWHM for the SERTS-A telescope. In addition SERTS-C had twice the peak irradiance of SERTS-A and an order of magnitude lower near-angle scatter. The inflight performance of the telescopes is consistent with laboratory findings.