Engineering topics

Benvenuti, P.

Publications and source records attributed to Benvenuti, P..

15 records

NASA NTRS1994

The peculiar behaviour of the 5780 and 5797 DIBs in HD25137

The interstellar environment close to the high latitude molecular cloud Lynds 1569 (L1569, Lynds 1962), also known as MBM 18 (Magnani, Blitz and Mundy, 1985), has been analyzed by Penrase et al. (1990) and Penrase (1993). Their observations of the CH, CH(sup+), and CN molecular features, are consistent with a region having a high molecular and reduced dust content. They also observed the background star HD 24263- located 8 degrees far from the center of L1569 - reporting a CH rich line of sight and the presence of two intervening clouds from a sodium lines spectra. The infrared excess which has been revealed by the IRAS survey at 12 microns might suggest the presence of PAH's molecules, the well know candidate for the Unidentified Infrared Bands and Diffuse Interstellar Bands. This interesting scenario led to the investigation of the behavior of the diffuse interstellar bands toward HD 25137, which is supposed to be a background object for L1569 (Penrase et al., 1990); as well as the field star HD 24263. As part of a wider observational program devoted to study the HLC's special environments, the observations of the diffuse interstellar bands (DIB's) at 5780 and 5797 lambda lambda in the direction of the two above mentioned stars, HD 24263 and HD 25137 are presented here.

Porceddu, Ignazio↗

NASA NTRS1992

HST observations of the inner coma of Comet Levy 1990c

Data reduction procedures which will make it possible to model the nucleus of future targets of cometary space missions were tested on the basis of observations of Comet Levy 1990c by the HST on September 27, 1990. Faint hemispherical shells expanding in the coma, which is structured as a sunward fan deflected by solar radiation pressure, were observed. The Eddington fountain model makes it possible to infer the ejection times of the expanding shells and the initial velocity of the dust. Three shells ejected at time intervals of 11.5 and 12.5 h with an initial velocity of 0.35 km/s were observed for dust grains of 3-micron size. The lag angle of the fan is between 10 and 15 deg, thus suggesting a time delay of the most active sublimation of 1 h after midday. The observed time periodicities suggest a nucleus rotating in 24 h with a surface characterized by two active areas placed almost exactly in opposite hemispheres, even if a longer rotation period and a more complex nucleus topography can be excluded.

Fulle, M.↗

NASA NTRS1984

IUE and ground-based observations of the Hubble-Sandage variables in M31 and M33

Ultraviolet spectra were obtained from the International Ultraviolet Explorer for the brightest Hubble-Sandage (H-S) variables in M31 and M33. The ultraviolet fluxes were then used in combination with ground-based visual and infrared photometry to determine the energy distributions, luminosities, and temperatures of these stars. When corrected for interstellar extinction, the integrated energy distributions yield the total luminosities and blackbody temperatures of the H-S variables. The resulting bolometric magnitudes and temperatures confirm that these peculiar stars are indeed very luminous, hot stars. They occupy the same regions of the bolometric magnitude vs temperature diagram as Eta Car and P Cyg in the Galaxy and S Dor in the LMC.

Blaha, C.↗

NASA NTRS1984

Evolution of the ultraviolet coma of comet Austin (1982g.)

Ultraviolet spectra of comet Austin (1982) obtained in July 1982 at heliocentric distances ranging from 1.10 to 0.81 AU preperihelion with the IUE reveal that the comet is very similar in chemical composition and appearance to comet Bradfield (1979X). In addition, the derived H2O production rate is found to vary with heliocentric distance as r to the -3.6, similar to the r to the -3.7 behavior found for comet Bradfield. It is pointed out, however, that the limited sample rate precludes the observation of the short-term variations which could be produced by a rotating nonuniform cometary nucleus.

Feldman, P. D.↗

NASA NTRS1982

The UV stellar classification program

The UV stellar classification program based on IUE data, its rationale, and its status, are described. The program provides sequences of calibrated spectra covering all spectral types.

Heck, A.↗

NASA NTRS1982

The interstellar spectrum of the supernova 1980k in NGC 6946

Bright supernovae in external galaxies offer a rare opportunity to probe the intervening interstellar media over very extended path-lengths, including the disk and halo of the Galaxy and the parent galaxy of the supernova. SN 1980k was discovered in NGC 6946 on 1980 October 29. In the first month after discovery, high resolution optical and ultraviolet observations were obtained to exploit the supernova as a probe of the intervening interstellar media. The obtained data are discussed. In the spectra, absorption lines were observed of Mg I, Mg II, Fe II, Mn II, Ca II and Na I. The absorption lines are attributed to the intervening interstellar media distributed over the very extended line of sight sampled, of order 7 Mpc. These lines are wider and stronger than any previously measured in the quiescent interstellar gas in the halo and disk of the Milky Way and of external galaxies

Pettini, M.↗

NASA NTRS1982

Four years of IUE research on clumpy irregular galaxies

During the first four years of IUE operations seven shifts were used to observe 4 clumpy irregular galaxies: Markarian 7, 8, 297, and 325. All spectra were obtained at low resolution in both short and long wavelength, with exposure time ranging from half to a full shift. The IUE spectra of clumpy irregular galaxies show that the clumps contain a very large number of early O and B type stars, with a large number of supergiants with respect to the main sequence stars. Possibly Wolf-Rayet stars and massive objects of the type of R 136a could also contribute to the clump luminosity. On the average, each clump radiates in the UV 100 times more than 30 Dor. On the other end the liner dimension of a clump is not much larger than the one of 30 Dor.

Benvenuti, P.↗

NASA NTRS1982

Coordinated observations of Seyfert I galaxies

A program to obtain simultaneous observations from the X-ray to the IR of Seyfert I galaxies is outlines. Of particular interest is the variability of these Seyfert nuclei. The continuum flux distribution in the UV for AkN 120 and ESO 113-IG45 (F-9) is examined.

Wamsteker, W.↗

NASA NTRS1982

Hydrogen two photon emission in the UV spectrum of type 2 supernovae

The continuum emission of Type 2 supernovae demonstrates an ultraviolet (UV) excess when fit by black body emission is attempted. The H two photon emission is advanced as an explanation of the UV excess. A function by which the UV spectra of two Type 2 supernovae (SN 1979c in NGC 4321 and SN 1980k in NGC 6946) are fitted with U,B,V photometric data is presented. The angular velocity of expansion of the supernovae envelope is derived. From this, the linear velocity of expansion and the distances of the parent galaxies are derived. A distance of 17.3 Mpc is obtained for NGC 4321, and a distance of 7.1 Mpc for NGC 6946.

Benvenuti, P.↗

NASA NTRS1981

IUE and ground-based observations of mass-loss in the Magellanic Clouds

Ground based and IUE observations of hot stars in the large and small Magellanic Clouds were carried out to investigate the mass loss process in these objects and to search for differences with galactic hot stars. Preliminary results show that in a large proportion of the stars observed the mass loss process is taking place. A mechanism for acceleration of the wind in OB stars is proposed.

Macchetto, F.↗

NASA NTRS1981

Observations of the nucleus of M100

The galaxy M100 = NGC 4321 is a spiral galaxy in which a bright Type II Supernova was discovered on April 19, 1979. Its spectral evolution was followed with IUE for more than two months (refs. 1,2). At all epochs, the spectrum was dominated by continuous radiation on which emission and absorption features were superimposed. The equivalent width of most of the absorption features appeared not to vary with time suggesting that they originated in the interstellar media of M100 and our own galaxy.

Panagia, N.↗

NASA NTRS1980

IUE observations of the UV spectrum of Comet Bradfield

Comet Bradfield (1979), discovered shortly after perihelion on Christmas day 1979, is characterized by a retrograde orbit of period approximately equal to 250 yr. This orbit was very favorable for observation by the IUE satellite, and the first observations, the preliminary results of which are reported here, were made on 10 and 11 January 1980. Previously, comprehensive vacuum UV cometary spectra were available only for Comet West (1976VI) from rocket observations and Comet Seargent (1978m) with IUE, hence three comets have now been observed in the wavelength region where most of the major constituents are detectable spectroscopically. The UV spectra of these comets are remarkably similar, despite large differences between them in the gas-to-dust ratio and the different heliocentric distances at which the observations were made, and although the statistical basis is still very small, the implication for cosmogony is that nearly all comets have the same primary composition and origin.

Feldman, P. D.↗

NASA NTRS1979

The ultraviolet spectrum of Comet Seargent 1978m

UV spectrograms of Comet Seargent (1978m) have been obtained with the IUE satellite in the low- (1.8-nm) and high- (0.1-nm) dispersion modes. In the long-wavelength region (189-340 nm) emission bands of OH, CS, CO2(+), NH, and CO(+) can be identified, and the rotational structure of OH could clearly be resolved. In the short-wavelength region (119-192 nm) emission lines of H(Lyman-alpha), O I, C I, and S I appear. These observations demonstrate that the IUE observatory can effectively be used to obtain high-quality spectra of comets as faint as ninth magnitude.

Jackson, M. W.↗

NASA NTRS1978

IUE observations of extragalactic objects

During the commissioning phase of IUE several extragalactic objects were observed spectrally at low dispersion in the UV range lambda lambda 1150-3200: the Seyfert galaxies NGC4151 and NGC1068, the QSO 3C273, the BL Lacertae object B2 1101+38, the giant elliptical galaxy M87 and the spiral galaxy M81. The results obtained are presented and a preliminary analysis given for all six objects, discussing the continuous spectrum, extinction, emission line spectrum and absorption line spectrum, where possible for each case. Several new or confirmatory astrophysical results are obtained.

Boksenberg, A.↗

NASA NTRS1976

Spectroscopic observations of comet Kohoutek (1973f), 2

Spectroscopic observations of comet Kohoutek at the Asiago Astrophysical Observatory are described. Spectra cover six nights before perihelion and five nights after perihelion. The spectra of the coma and tail of comet Kohoutek are characterized by fairly strong, asymmetric H2O(+) emissions in the red and the near infrared spectral regions and by the appearance of the 01 forbidden lines at 6300-6364 A, already at heliocentric distance r=1.55 A.U. These peculiarities suggest that some differences in chemical abundances or in physical conditions exist between comet Kohoutek and other comets.

Benvenuti, P.↗