Engineering topics

Ferlet, R.

Publications and source records attributed to Ferlet, R..

9 records

NASA NTRS2002

Deuterium Abundance Toward WD2211-495: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

We present a deuterium abundance analysis of the line of sight toward the white dwarf WD 2211-495 observed with the Far Ultraviolet Spectroscopic Explorer (FUSE). Numerous interstellar lines are detected on the continuum of the stellar spectrum. A thorough analysis was performed through the simultaneous fit of interstellar absorption lines detected in the four FUSE channels of multiple observations with different slits. We excluded all saturated lines in order to reduce possible systematic errors on the column density measurements. We report the determination of the average interstellar D/O and D/N ratios along this line of sight at the 95% confidence level: D/O = 4.0 (+/-1.2) x 10(exp -2); D/N = 4.4 (+/-1.3) x 10(exp -1). In conjunction with FUSE observations of other nearby sight lines, the results of this study will allow a deeper understanding of the present-day abundance of deuterium in the local interstellar medium and its evolution with time.

Hebrard, G.↗

NASA NTRS2002

Deuterium Abundance Toward G191-B2B: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission

High-resolution spectra of the hot white dwarf G191-B2B covering the wavelength region 905-1187A were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). This data was used in conjunction with existing high-resolution Hubble Space Telescope STIS observations to evaluate the total H(sub I), D(sub I), O(sub I) and N(sub I) column densities along the line of sight. Previous determinations of N(D(sub I)) based upon GHRS (Goddard High Resolution Spectrograph) and STIS (Space Telescope Imaging Spectrograph) observations were controversial due to the saturated strength of the D(sub I) Lyman alpha line. In the present analysis the column density of D(sub I) has been measured using only the unsaturated Lyman beta and Lyman gamma lines observed by FUSE. A careful inspection of possible systematic uncertainties tied to the modeling of the stellar continuum or to the uncertainties in the FUSE instrumental character series has been performed. The column densities derived are: log N(D(sub I)) = 13.40+/-0.07, log N(O(sub I)) = 14.86+/-0.07, and log N(N(sub I)) = 13.87+/-0.07 quoted with 2sigma, uncertainties. The measurement of the H(sub I) column density by profile fitting of the Lyman alpha line has been found to be unsecure. If additional weak hot interstellar components are added to the three detected clouds along the line of sight, the H(sub I)) column density can be reduced quite significantly, even though the signal-to-noise ratio and spectral resolution at Lyman alpha are excellent. The new estimate of N(H(sub I)) toward G191-B2B reads: logN(H (sub I)) = 18.18+/-0.18 (2sigma uncertainty), so that the average (D/H) ratio on the line of sight is: (D/H)= 1.66(+0.9/-0.6) x 10(exp -5) (2sigma uncertainty).

Lemoine, M.↗

NASA NTRS1993

The Beta Pictoris circumstellar disk. XV - Highly ionized species near Beta Pictoris

Temporal variations of the Fe II, Mg II, and Al III circumstellar lines towards Beta Pictoris have been detected and monitored since 1985. However, the unusual presence of Al III ions is still puzzling, since the UV stellar flux from an A5V star such as Beta Pic is insufficient to produce such an ion. In order to better define the origin of such a phenomenon, new observations have been carried out to detect faint signatures of other highly ionized species in the short UV wavelength range, where the stellar continuum flux is low. These observations reveal variations not only near the C IV doublet lines, but also in C I and Al II lines, two weakly ionized species, not clearly detectable until now. In the framework of an infalling body scenario, highly ionized species would be created in the tail, far from the comet head, by collisions with ambient gas surrounding the star, or a weak stellar wind. Spectral changes have also been detected near a CO molecular band location, which, if confirmed, would provide the first molecular signature around Beta Pictoris.

Deleuil, M.↗

NASA NTRS1991

Variable interstellar absorption toward HD 72127A. II - 1981-1988

The present study examines eight new echelle spectra of HD 72127A found between 1981 and 1988 near the Ca II K line, along with four similar spectra near the Na I D lines. In addition to the unrivaled intensity and width of this interstellar K line formed at a distance of not more than 500 pc, which were previously discovered by Thackeray (1974), the spectra show clearly the unique temporal variability of the interstellar absorption along this light path, which was reported in an earlier study by Hobbs et al. (1982). The new results strengthen further the hypothesis that the interstellar absorption toward this star occurs predominantly in the disturbed gas located within the SNR, in which the interstellar grains have been largely destroyed. The variable interstellar lines were found to consist of at least 120 components at the K line and of at least eight generally corresponding components at the D lines. The total column densities summed over all of these interstellar clouds varied irregularly by about 45 percent in five and about 38 percent in ten years, respectively.

Hobbs, L. M.↗

NASA NTRS1988

The location of the Ca II ions in the beta Pictoris disk

Echelle spectra of beta Pictoris have been obtained in the region of the Ca II 8542A line which arises from the metastable 3d 2D5/2 level. A narrow, weak, circumstellar absorption line is seen at the stellar radial velocity. A simple theory is developed of the radiative pumping of the metastable levels of the Ca II ions by the radiation from the star at the H and K lines. The relatively large fractional population, N3(Ca II)/N1(Ca II) of roughly 0.05, observed for the metastable level then requires that the calcium absorbers be largely concentrated within about 1 AU of the star. This result confirms two previous, independent estimates of the location of this gas. A time-variable circumstellar component of the 8542A line also is found at an infall velocity of about 15 km/s.

Hobbs, L. M.↗

NASA NTRS1985

The gaseous component of the disk around Beta Pictoris

Optical spectra of alpha Lyr, alpha PsA, and beta Pic have been obtained at a velocity resolution of 3 km/s. No circumstellar absorption lines of Ca II or Na I are detected toward alpha Lyr or alpha PsA at sensitive limits. In the favorable case of beta Pic, where the circumstellar disk imaged by Smith and Terrile (1984) is seen nearly edge-on, a strong, narrow, circumstellar Ca II K absorption line previously reported by Slettebak (1982) and weaker, still narrower circumstellar Na I D lines are detected. Negative results of high sensitivity also are obtained for the Ca I 4226 A and CH(+) 4232 A lines, along with upper limits on the Zn II 2026, 2062 A doublet from archival IUE spectra. Under assumptions which agree with other well-established observations of the gaseous abundances of calcium and zinc, the total gaseous column density of hydrogen along a radius of the circumstellar disk is between 10 to the 18th and 4 x 10 to the 20th/sq cm. Within the boundaries of the dust disk detected by Smith and Terrile (1984) the total gaseous mass then is less than about 2, or less than 1 percent of the mass of the planetary system. A simplified model of the density distribution in the gaseous disk yields a characteristic total density n(H) of about 100,000/cu cm, which exceeds that of all interplanetary gas at earth's position by a factor of about 10,000.

Hobbs, L. M.↗

NASA NTRS1984

A Type Stars as Probes of the Local Interstellar Medium

With the aim to sample the Local Interstellar Medium (LISM), it was proposed to use A stars as targets. The Mg II UV lines seem to be the best interstellar absorption candidates. Several hundreths of A stars can be reached within 100 pc. First preliminary results (20 lines of sight) are presented, based on previous Copernicus and actual IUE observations.

Ferrero, R. F.↗

NASA NTRS1984

Deuterium Abundance in the Local Interstellar Medium

The present situation of deuterium abundance evaluation in interstellar space is discussed, and it is shown that it should be or = .00001 by studying in more detail lambda the Sco line of sight and by observing two NaI interstellar components toward that star, it can be shown that the D/H evaluation made toward lambda Sco is in fact related to the local interstellar medium (less than 10 pc from the Sun). Because this evaluation is also or = .00001 it is in striking contrast with the one made toward alpha Aur (D/H or = .000018 confirming the fact that the deuterium abundance in the local interstellar medium varies by at least a factor of two over few parsecs.

Ferlet, R.↗

NASA NTRS1980

The interstellar medium on the Gamma Cassiopeiae line of sight

The interstellar medium on the Gamma Cas line of sight is studied through the observations of O I, H2, H I, D I, and Ar I absorption features with the Copernicus satellite. By using the velocity structure of the line of sight previously determined through atomic nitrogen, it is demonstrated that these neutrals are located in the same physical regions and that the O I and Ar I abundances could be solar, on the average, relative to N I in all components. The 1066.660 A Ar I line profile is contaminated by an unidentified line, already detected in the spectrum of Zeta Pup. Furthermore, a peculiar behavior of the Ar I abundance in the different components is reported, possibly associated with high-velocity interstellar gas present on the line of sight. It is concluded that the Gamma Cas line of sight could intercept a dense cloud which has been engulfed and disrupted by a shock.

Ferlet, R.↗