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Rudy, R. J.

Publications and source records attributed to Rudy, R. J..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Locating the Accretion Footprint on a Herbig Ae Star: MWC 480

Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-chromatic data for the Herbig Ae star MWC 480 to address whether similar processes occur in intermediate-mass stars. MWC 480 has X-ray emission typical of actively accreting Herbig Ae stars, but with 5-9 x more photoelectric absorption than expected from optical and FUV data. We consider 3 sources for the absorption: the disk absorption in a wind or jet, and accretion. While we detect the disk in scattered light in are-analysis of archival HST data. the data are consistent with grazing illumination of the dust disk. We find that MWC 480's disk is stratified, geometrically thin, and is not responsible for the observed photoelectric absorption. MWC 480 drives a bipolar jet, but with a mass loss rate which is low compared to other Herbig Ae stars, where the outflow is more favorably oriented and enhanced photoelectric absorption is not seen. This excludes a jet or wind origin for the enhanced photoelectric absorption. We compare MWC 480's 0 VI emission with other Herbig Ae stars. The distribution of the emission in inclination, and lack of a correlation of profile shape and system inclination excludes equatorially-confined accretion for the FUSE Herbig Ae stars. The photoelectric absorption data further suggest that the accretion footprint on MWC 480 and other Herbig Ae stars is located at high temperate, rather than polar, latitudes. These findings support the presence of funneled accretion in MWC 480 and Herbig Ae stars, strengthening the parallel to T Tauri stars.

Grady, C. A.↗
NASA NTRS2009

A New Spectroscopic and Interferometric Study of the Young Stellar Object V645 Cyg

Aims. We present the results of high-resolution optical spectroscopy, low-resolution near-IR spectroscopy and near-infrared speckle interferometry of the massive young stellar object candidate V645 Cyg that were taken in order to refine its fundamental parameters and properties of its circumstellar envelope. Methods. Speckle interferometry in the H- and K-bands and an optical spectrum in the range 5200-6680 A with a spectral resolving power of R = 60000 were obtained at the 6 m telescope of the Russian Academy of Sciences. Another optical spectrum in the range 4300-10500 A with R = 79000 was obtained at the 3.6m CFHT. A low-resolution spectrum in the ranges 0.46-1.4 and 1.4-2.5 microns with a R approx. 800 and approx. 700, respectively, were obtained at the 3m Shain telescope of the Lick Observatory. Results. Using a new kinematic method based on non-linear modeling of the neutral hydrogen density profile in the direction toward the object, we suggest a new a distance D = 4.2+/-0.2 kpc. We also suggest a new estimate for the star's effective temperature, T(sub eff) approx. 25000 K. We have resolved the object in both H- and K-bands. Using a two-component ring fit, we derived a compact component size of 18 mas and 15 mas in the H- and K-band, respectively, which correspond to 37 and 33 AU at the new distance. Analysis of our and previously published data shows a approx. 2 mag drop of the near-infrared brightness of V645 Cyg in the beginning of the 1980 s. At the same time, the cometary nebular condensation N1 seems to fade in this wavelength range with respect to the N0 object, which represent the star with a nearly pole-on optically-thick disk and an optically-thin envelope. Conclusions. We conclude that V645 Cyg is a young massive main-sequence star, which recently emerged from its cocoon. and already passed the protostellar accretion stage. The presence of accretion is not necessary to account for the high observed luminosity of (2.6) x 10(exp 4) Solar Mass/yr. The receding part of a strong, mostly uniform outflow with a terminal velocity of approx.800 km/s is only blocked from view far from the star, where forbidden lines form. The near-infrared size of the source is consistent with the dust sublimation distance near this hot and luminous star and is the largest among young stellar objects observed interferometrically to-date.

Miroshinichenko, A. S.↗
NASA NTRS2007

Time Variability of the Dust Sublimation Zones in Pre-Main Sequence Disk Systems

The dust sublimation zone (DSZ) is the region of pre-main sequence (PMS) disks where dust grains most easily anneal, sublime, and condense out of the gas. Because of this, it is a location where crystalline material may be enhanced and redistributed throughout the rest of the disk. A decade-long program to monitor the thermal emission of the grains located in this region demonstrates that large changes in emitted flux occur in many systems. Changes in the thermal emission between 3 and 13.5 microns were observed in HD 31648 (MWC 480), HD 163296 (MWC 275), and DG Tau. This emission is consistent with it being produced at the DSZ, where the transition from a disk of gas to one of gas+dust occurs. In the case of DG Tau, the outbursts were accompanied by increased emission on the 10 micron silicate band on one occasion, while on another occasion it went into absorption. This requires lofting of the material above the disk into the line of sight. Such changes will affect the determination of the inner disk structure obtained through interferometry measurements, and this has been confirmed in the case of HD 163296. Cyclic variations in the heating of the DSZ will lead to the annealing of large grains, the sublimation of smaller grains, possibly followed by re-condensation as the zone enters a cooling phase. Lofting of dust above the disk plane, and outward acceleration by stellar winds and radiation pressure, can re-distribute the processed material to cooler regions of the disk, where cometesimals form. This processing is consistent with the detection of the preferential concentration of large crystalline grains in the inner few AU of PMS disks using interferometric spectroscopy with the VLTI.

Sitko, Michael L.↗
NASA NTRS1988

Small-aperture infrared photometry of Seyfert 1 galactic nuclei

Multiaperture infrared photometry of the nuclei of five Seyfert 1 galaxies is presented. When apertures approaching the seeing limit were used, it was found that all of the nuclei have observed power law energy distributions with F(nu) proportional to 1/nu sq from 1.25 to 3.45 micron. After correcting for reddening, the spectral indices had a range of alpha = 1.4-1.9. These results are supported through infrared imaging of one of the program galaxies, and they demonstrate the importance of properly isolating the nuclear component from the stellar disk through the use of extremely small apertures. Although the nature of the infrared emissions cannot be determined, results indicate that a common energy source exists among the observed galaxies.

Simons, D. A.↗
NASA NTRS1986

Multiple aperture airborne infrared measurements of Comet Halley

Observations at 10 microns with a 3.5' diameter beam made from the NASA Lear Jet Observatory during April 7.6 to 11.6, 1986 UT are presented. Data show evidence for a dramatic outburst (factor of 3 in 10 micron flux) with a turn-on time of 1 day and turn-off time of 1 to 2 days. Total mass ejected in the outburst is estimated. When combined with 8 and 10 microns data taken by Campins et al the dependence of the dust density on distance from the nucleus can be evaluated. It is shown that the flux within an aperture of diameter D is directly proportional to D well beyond 60" (2 million m at the comet). At 64 million m diameter (210"), the measurements are only 30% below the level expected for a strict F varies as d dependence. This, combined with the time scales of the event, places constraints on processes of grain destruction. The energy of the outburst is derived and compared to solar heating.

Russell, R. W.↗
NASA NTRS1985

IUE observations of the Seyfert 1.9 galaxy Markarian 423

UV observations of the Seyfert 1.9 galaxy Markarian 423 show a moderately strong UV continuum in the 1200-2000 A region, a strong narrow Lyman-alpha conponent, and no detectable broad lines. This absence of broad UV lines, in conjunction with the steep broad line Balmer decrement, indicates that the gas giving rise to the broad emission lines is significantly reddened. An upper limit on the equivalent width of the broad Lyman-alpha component suggests that the reddening of the broad line region is greater than that of the interstellar continuum, which furnishes evidence of local dust concentration.

Rudy, R. J.↗
NASA NTRS1984

Multifrequency observations of the BL Lacertae objects OQ 530 and ON 325

Spectral measurements of the two BL Lac objects OQ 530 and ON 325 are presented. The measurements were taken at frequencies ranging from radio to ultraviolet. Both sources show spectral curvature between the infrared and ultraviolet frequencies. The intensity and spectral shape of OQ 530 vary, but the spectral shape of ON 325 appears to remain constant during intensity variability. A nonthermal theoretical model of jet emission is developed which incorporates both the spectral and time variability data. The model predicts that ON 325 radiates at X-ray frequencies with Compton radiation dominating over synchrotron emission. The angular size of the jet emission is predicted to be less than 0.1 milli-arcsec at high radio frequencies.

Worrall, D. M.↗
NASA NTRS1984

He I 10830 emission in Seyfert galaxies and QSOs

He I line fluxes at 10830 A are reported for eight type-1 Seyfert galaxies, three QSOs and two type-2 Seyfert galaxies. The data are combined with He I line fluxes at 5876 A in order to obtain the ratio 10830/5876. The He I flux values resulting from this ratio are compared to fiducial values measured in gaseous nebulae. It is found that the values for gaseous nebulae are very similar to values observed in type-2 Seyfert galaxies, but are considerably larger than He I line flux values for type-1 Seyfert galaxies and QSOs. The data indicate the presence of high dust reddening and powerful optical depth effects in the type-2 Seyfert galaxies.

Levan, P. D.↗
NASA NTRS1984

Continuum emission from the nucleus of NGC 1275

Submillimeter and multi-aperture near-infrared observations of NGC 1275 are presented. The luminosity of the extended stellar component within the near-infrared apertures has been determined, and consequently also the 1.25-3.5 micron energy distribution of the unresolved nucleus. The 1 micron-30 cm energy distribution is reviewed. It is argued that the most likely origin for the 100 micron-30 cm radiation is synchrotron emission, with this nonthermal component also contributing significant flux at 10 microns. No observations are yet available which make it possible to distinguish unequivocally between a thermal (dust) and synchrotron emission mechanism in the 1-10 micron region, but the evidence marginally favors a nonthermal origin.

Longmore, A. J.↗
NASA NTRS1984

The spatial extent of the 3.3 micron emission feature in the Seyfert galaxy NGC 7469

Observations have been made of the 3.3-micron feature and the infrared continuum in the type 1 Seyfert galaxy NGC 7469 using multiaperture techniques. While as much as 10 to the 7th solar luminosities in 3.3-micron line emission may arise from within the nucleus, the data indicate that the 3.3-micron emission-line region is extended, with a significant fraction of the luminosity of the line originating at distances greater than 240 pc from the nucleus. Possible mechanisms for the heating of the dust associated with the extended emission are discussed together with observational tests which can be used to verify the more promising of these mechanisms.

Cutri, R. M.↗
NASA NTRS1984

Two multifrequency observations of 3C 371

Observations of 3C371 made at frequencies from the radio to the ultraviolet and coordinated during two short time intervals separated by 3 months are presented. Also presented are 1 keV X-ray flux densities measured at a different time. The multifrequency measurements indicate spectral steepening at visual wavelengths, and that an extrapolation of the ultraviolet continuum falls below the X-ray data. The infrared through X-ray data is explained as relativistically beamed synchrotron self-Compton emission, and source parameters are derived for two possible models. The present ultraviolet spectra both show strong Lyman-alpha emission at the same redshift as weak optical emission lines reported previously. Production of these lines by recombination of gas, after its ionization by the ultraviolet to X-ray continuum radiation, is favored as an explanation. C IV and N V absorption lines are tentatively identified in one ultraviolet spectrum, which, if real, suggest the presence of a hot (about 300,000 K) gaseous halo in 3C 371.

Puschell, J. J.↗
NASA NTRS1984

The dusty, luminous broad-line radio galaxy 3C 109

In the present optical polarimetry and IR photometry for the broad line radio galaxy 3C 109, the absence of variability, in conjunction with a polarization in H-alpha that is identical to that of the adjacent continuum, suggests that the strong polarization of this galaxy is due to extinction by aligned dust grains. This is the process which gives rise to interstellar polarization within the Galaxy. The energy output of 3C 109, from the optical to 20 microns, exceeds by a factor of 2-4 that of the Seyfert 1 galaxy Markarian 231. These observations, together with recent polarimetry of other broad line radio galaxies, indicate that their broad line regions are more heavily reddened than those of either the Seyfert 1 galaxies or quasars. Evidence for a gradual decrease in dust content with increasing source luminosity is discussed.

Rudy, R. J.↗
NASA NTRS1984

Spectral components at visual and infrared wavelengths in active galactic nuclei

Aperture-dependent infrared photometry of active galactic nuclei are presented which illustrate the importance of eliminating starlight of the galaxy in order to obtain the intrinsic spectral distribution of the active nuclei. Separate components of emission are required to explain the infrared emission with a spectral index of alpha approx = 2 and the typical visual-ultraviolet continuum with alpha approx = 0.3 (where F(nu) varies as nu(sup-alpha). Present evidence does not allow unique determination of the appropriate mechanisms, but the characteristics of each are discussed.

Stein, W. A.↗
NASA NTRS1982

The heating of dust in the broad-line regions of active galaxies and quasars

The present investigation is concerned with the relevant energy sources which heat (and, in many cases, destroy) the dust grains in the emission-line clouds (ELCs) that give rise to the broad-line emission seen in active extragalactic objects. The heating rates from the external radiation field, trapped line radiation, and the diffuse bound-free continua are compared. The relevant grain parameters are considered, taking into account the composition, size, and emission and absorption cross sections. Three distinct regions of an ELC are identified, including the cloud face, the extended ionized zone, and the neutral zone. The thermal emission of the dust in each of these regions is shown to be different. An upper limit to the heating is provided by an LTE model which is discussed.

Rudy, R. J.↗
NASA NTRS1982

Abundances in five nearby galactic H II regions from infrared forbidden lines

Airborne measurements of the Ar II (6.99 micron) and S II (18.7) micron lines for five compact H II regions in the solar neighborhood are presented, as well as 2-4 micron and 8-13 micron spectroscopy where available. From these data and radio data, lower limits to the elemental abundances of Ar, Ne, and S are deduced. Some of these H II regions suffer substantial nebular extinction, and some are extended. After correcting for beam size effects an extinction, it is found that four of the objects are consistent with standard abundances, within the uncertainties of correcting for unobserved ionization states. A Perseus arm object, S156, is apparently overabundant in sulfur.

Herter, T.↗
NASA NTRS1982

Near-infrared spectrophotometry of four Seyfert 1 galaxies and NGC 1275

Low-resolution spectrophotometry from 2 to 4 microns is reported for the four Seyfert 1 galaxies Mrk 335, 3C 120, Mrk 509, NGC 7469, and the peculiar emission-line galaxy NGC 1275. The spectrum of NGC 7469 exhibits a strong 3.3-micron dust feature, indicating a thermal origin for the bulk of its considerable nonstellar infrared emission. NGC 1275 has a large stellar contribution to its infrared flux at wavelengths shortward of 3 microns. The spectrum from 3 to 4 microns fits a power law which fits the 10-micron and 20-micron broad bands, as well. A thermal model which can explain the spectrum of NGC 1275 is discussed. Mrk 335 displays a complex spectrum suggestive of thermal dust emission. 3C 120 and Mrk 509 have nonstellar infrared emission shortward of 2 microns, but the data are ambiguous as to whether this emission is thermal or nonthermal in origin.

Rudy, R. J.↗
NASA NTRS1982

Observations of Paschen alpha in the broad-line radio galaxy 3C 445

P alpha line flux measurements of the broad-line radio galaxy 3C 445 made at the NASA IR Telescope Facility in September 1981 are discussed. Broad-band measurements were obtained at H of 1.65 micron and K of 2.2 microns. A line flux of P alpha was found at 3.4 times 10 to the -13th ergs/sq cm sec. No discernable variation was detectable regarding measurements made in 1976. Substantial reddening was concluded to exist, although the H gamma lines observed were not due to reddening. The total H alpha luminosity was determined to be 4 x 10 to the 43rd ergs/sec. Steep Balmer line decrements are concluded to be due to interposed dust.

Rudy, R. J.↗