Copernicus Spectra Research Articles

The 0.7–5.3 μm IR spectra of Mercury and the Moon: Evidence for high-Ca clinopyroxene on Mercury

We present infrared spectra of Mercury and the Moon in the wavelength range 0.7–5.3 μm obtained with the SpeX spectrograph at the NASA Infrared Telescope Facility. The spectra were acquired from pole and terminator locations of Mercury's surface and of Mersenius C and the Copernicus central peak on the Moon. Spectra of both bodies were measured in close temporal succession and were reduced in the same manner with identical calibration stars to minimize differences in the reduction process. The Copernicus spectra display the expected absorption features due to mafic minerals in the near infrared and show spectral features in the SiO combination/overtone vibrational band region above 4 μm. The spectra of Mercury from longitude 170° and north and south mid-latitudes display a 1-μm absorption band indicative of high-Ca clinopyroxene, while a spectrum from longitude 260° and northern mid-latitudes does not. The Mercury spectra show a broad feature of low emittance over the full 3–5 μm thermal infrared region, but no narrow features in this spectral range. The longitude 260° spectrum shows excess thermal emission around 5 μm attributable to the existence of a thermal gradient in the insolated dayside regolith. The thermal-IR spectra suggest a significant difference in the compositional and/or structural properties of Mercury and the Moon that may be due to grain size, absorption coefficient, or the magnitude of near-surface thermal gradients. The results indicate that the composition of Mercury's surface is heterogeneous on regional scales, and that the near infrared wavelength range provides more discriminative information on the surface composition than the 2–4 μm region, where the solar reflected and thermally emitted radiation contribute approximately equally to the observed flux of these bodies.

The Abundances of Vega from the Ultraviolet Spectrum

AbstractWe derived preliminary abundances from the ultraviolet spectrum of Vega by comparing high-resolution Copernicus spectra with spectra computed with the ATLAS9 code and with updated line lists. The Teff=9400 K, log g=3.90 model, which fits the visual flux and the Balmer profiles is able to fit the ultraviolet flux either with [M/H]=−l and microturbulent velocity ξ= 2 km s−1 or with [M/H]=−0.5 and ξ=0 km s−1. The line spectrum is fitted by ξ=2 ± 0.5 km s−1 and by an iron abundance log (N(Fe)/Ntot)=−5.2 ±0.1 dex. All the observed elements indicate underabundances ranging from about −0.35 dex (C ) up to about −1 dex (Ni, Zn). The origin of the underabundances is an open question.

The Moon: Mid-infrared (7.5- to 11.4-μm) spectroscopy of selected regions

Groundbased observations of midinfrared (7.5- to 11.4-μm) spectral radiance from five locations on the Moon are reported. We have obtained medium resolution spectra from three locations in Copernicus crater and two locations in mare basalt. Two locations in the crater walls of Copernicus show similar spectra which in turn differ from spectra from the eastermost central peak. Mineralogic interpretation of the features in the central peak spectra is consistent with the composition of the locations as determined by near-infrared reflectance (0.67- to 2.5-μm) spectroscopy. In addition to emission minima, which we attribute to olivine, there are unidentified features in the spectra which may provide additional compositional information. An emissivity maximum at shorter wavelengths than the reststrahlen bands is identified as the Christiansen feature in the Copernicus spectra. The wavelength of maximum emission shifts to longer wavelengths with increasing mafic composition as predicted by laboratory spectroscopy. The mare locations observed are of different albedos and our spectra indicate that the locations are of slightly different composition. We see a broad emission minimum centered at 8.5 μm in the Kepler ejecta spectrum but not in that from the mare east of Euler. Spectra from both mare locations have a triplet of minima at 8.1, 8.4, and 8.75 μm which are not identified. Spectra from both mare locations exhibit local maxima just longward of 9 μm and a sharp drop in emissivity at wavelengths longer than 11 μm.

On the completeness of the analysis of third and fourth spectra of the iron group, and the spectra of early B stars

The spectroscopic analysis of normal, early B stars requires a sound atomic data base, especially for the third and fourth spectra of the iron-group elements. We review the present status of the term analyses of third and fourth spectra of vanadium-nickel as of the Sugar-Corliss compilation. Incompleteness of the analyses of the third spectra is typically evident about halfway to the first ionization limit. The fourth spectra are less well known. For Fe, Co, and Ni IV, only the lowest three configurations have been located. Copernicus spectra described by Rogerson and his coworkers have been studied in detail. We conclude that present atomic data is approaching a sufficient degree of completeness to allow a realistic analysis of the satellite ultraviolet of the “normal” star. Without analytical work of the last decade, the analysis of the UV spectrum of this star would have been hopeless.

Identification of lines in the satellite ultraviolet - The spectrum of Tau Scorpii

The method of wavelength coincidence statistics (WCS) is applied to the ultraviolet spectra of Tau Sco obtained by the IUE. No identifications of elements heavier than Zn were made. With the exception of Zn IV, all identifications had been previously made in an exhaustive study of Copernicus spectra by Rogerson and Ewell (1985). A comparison of the identifications made in the two studies is in very good agreement for those spectra rich in lines, where the WCS parameters indicate the strong presence of the species. Useful information is added by WCS in cases where species are only weakly, or arguably, present. It is shown that WCS is an important tool in the exploration of any complicated stellar spectrum, and even in the case of a spectrum that has been well studied by traditional methods, it adds important information.

About the Photometric Calibration of IUE High Resolution Spectra: Quantification of the Order Overlap for the SWP Camera

In order to quantify the errors in the IUE line profiles caused by the order overlap, we have compared line depths in IUE and Copernicus spectra. The excess line depth in IUE spectra suggests that the amount of order overlap is about 32% at 1150Å and decreases to zero at about 1400Å, for spectra extracted with the recent version of IUESISPS (the IUE standard extraction software). The transfer of a spectral feature from one order to the next is below the 5% level.Based on these results, a correction technique is described.

Variation of Anomalous Stages of Ionization with Spectral Type for Be Stars

One of the interesting results of ultraviolet (UV) astronomy was the discovery of ions from unexpected stages of ionization in spectra of O,B stars. The most common ions concerned are O VI and N V, but also C IV and Si IV in B stars. The presence of these ions is anomalous because generally their abundance is expected to be negligible if they are produced by photoionization by stellar radiation, either in the photosphere or in a cool circumstellar envelope (CE). The same ions are observed in the UV spectra of Be stars. Previous investigations, largely with Copernicus spectra, have reported O VI and N V in late Oe and early Be stars and Si IV in stars as cool as B5 (Marlborough, 1981 and references therein). In this paper we present the results of a preliminary survey of IUE spectra of Be stars covering a wide range of spectral type.

Narrow components in UV line profiles as evidence for a two component stellar wind for 0 and B stars

The UV resonance lines of early type stars show narrow absorption components, with a width of the order of 300 km s-1, superimposed on the wider P Cygni profiles. Such narrow components have been detected in the Copernicus spectra of a few early type stars by Morton (1976) and Snow and Morton (1979). The variability of these components was studied by Snow (1977) who compared two scans of the UV line profiles of 15 stars taken about four years apart. He found that the narrow components do not change in velocity (except for the CIII λ 1175 line in ζ, Pup) but that the strength of the components can change drastically. In some stars the narrow components were present in only one of the two spectra. We studied the characteristics of these narrow components in the Copernicus spectra (Snow and Jenkins, 1977). The stars are listed in Table 1. Examples of these narrow components are shown in Figure 1.

Ultraviolet observations of cool stars. VII - Local interstellar hydrogen and deuterium Lyman-alpha

High-resolution Copernicus spectra of Epsilon Eri and Epsilon Ind containing interstellar hydrogen and deuterium L-alpha absorption lines are presented, reduced, and analyzed. Parameters of the interstellar hydrogen and deuterium toward these two stars are derived independently, without any assumptions concerning the D/H ratio. Copernicus spectra of Alpha Aur and Alpha Cen A are reanalyzed, and limits on the D/H number-density ratio consistent with the data for all four stars are considered. A comparison of the present estimates for the parameters of the local interstellar medium with those obtained by other techniques shows that there is no compelling evidence for significant variations in the hydrogen density and D/H ratio in the local interstellar medium. On this basis the hypothesis of an approaching local interstellar cloud proposed by Vidal-Madjar et al. (1978) is rejected

An interstellar cloud density from Copernicus observations of CO in the spectrum of Zeta Ophiuchi

Interstellar CO absorption bands in Copernicus spectra of Zeta Oph have been studied. Absorption profiles, computed under the assumption that excitation is due to collisions with H2 molecules and interaction with the 3-K background radiation field, were fitted to the reduced data of nine bands. When a gas kinetic temperature of 56 K is assumed, the best-fit condition implies a hydrogen-nucleus density of 120 per cu cm, a CO column density of 1.2 by 10 to the 15th power per sq cm, and a radial-velocity dispersion of 0.9 km/s. The relevance of these results to existing ideas concerning the Zeta Oph interstellar clouds is discussed. It is suggested that the strongest interstellar component is not circumstellar in origin but is instead part of a supernova remnant. Simple calculations are made to establish the plausibility of the supernova-remnant identification. This suggestion is also supported by Heiles's (1976) 21-cm pictures.

Behaviors of B Star Continua and Absorption Features Determined from the TD1 S2/68 “Ultraviolet Bright Star Spectrophotometric Catalogue” and from Copernicus Spectra

Ultraviolet low resolution spectra of most of the B stars observed with the S2/68 experiment onboard the TD1 satellite in the spectral range 1350 A - 2500 A are computer-investigated in order to define a grid of standard behaviors (J.M. Vreux and J.P. Swings, 1976 Astron. Astrophys., in press). The behavior of the relative intensities of the Balmer and Paschen continua is studied as a function of the spectral type and the visible photometric index Q: both relations are shown to be luminosity dependent. A comparison to theoretical predictions and to previous studies is also presented. A measure of the slope of the pseudo-continuum drawn between ~ λ 1660 A and ~ λ 2550 A is studied in the same way: the effect of luminosity is discussed in connection with recently proposed temperature scales for super-giants. The behavior of the depths of the absorption features at λλ 1550 A, 1940 A, 2000 A, 2055 A, 2105 A, 2340 A and 2395 A with respect to the spectral type, the Q index and the luminosity class is also briefly presented. Special emphasis is given to the absorption features at λ 1550 A in connection to the discussion of the Felll lines in the ultraviolet spectra of early B stars by J.P. Swings, M. Klutz, J.M. Vreux and E. Peytremann (1976, Astron. Astrophys. Suppl. 25, 193). Preliminary results of a study of high resolution Copernicus spectra in the A 1550 A region are also presented: it is shown that the role of Felll remains predominant for stars of spectral type as early as about BIII - BIIII (J.P. Swings and J.M. Vreux, to be published).