Hopkins Ultraviolet Telescope Research Articles

Two-dimensional intensified photodiode array detector for spaceflight use

A two-dimensional, ultraviolet photon-counting detector suitable for spaceflight use, consisting of a microchannel plate intensifier coupled to a Reticon photodiode array, has been constructed and tested. The design is an extension of the one-dimensional detector flown on the Hopkins Ultraviolet Telescope. Extensive laboratory measurements have determined the operating characteristics of the detector and shown that it can successfully centroid with subdiode resolution. It was flown as part of an ultraviolet spectrometer on two sounding rockets, and successfully obtained long slit spectra of Comet Austin (1990 V) and the Io plasma torus surrounding Jupiter in the wavelength range of 1150–1850 Å. Details of the design, construction, testing, and flight performance of the detector are presented.

Cooling of the white dwarf in U Geminorum between outbursts

view Abstract Citations (51) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cooling of the White Dwarf in U Geminorum between Outbursts Long, Knox S. ; Sion, Edward M. ; Huang, Min ; Szkody, Paula Abstract We have obtained far-ultraviolet (1150-1610 A) spectra of U Gem with the Faint Object Spectrograph on the Hubble Space Telescope approximately 13 and 70 days after the end of a normal dwarf nova outburst of the system. Both spectra appear dominated by the White Dwarf (WD) in U Gem. At 1400 A, the flux from U Gem declined approximately 28% between the two observations. Detailed comparison of the spectra with solar abundance WD models suggest that average surface temperature of the WD surface cooled from approximately 39,400 K to approximately 32,100 K between the two observations. The main features which are not fitted well by WD models are absorption due to N V lambda lambda-1239, 1243 and emission at Lyman-alpha. These observations provide unambiguous confirmation that the WD in U Gem cools during quiescence, as was suggested by analyses of far-ultraviolet spectra obtained with International Ultraviolet Explorer (IUE) and Hopkins Ultraviolet Telescope (HUT). Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/187272 Bibcode: 1994ApJ...424L..49L Keywords: Accretion Disks; Cataclysmic Variables; Data Processing; Ephemerides; H Alpha Line; Novae; White Dwarf Stars; Faint Object Camera; Hubble Space Telescope; Iue; Line Of Sight; Signal To Noise Ratios; Astrophysics; STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: INDIVIDUAL CONSTELLATION NAME: U GEMINORUM; ULTRAVIOLET: STARS; STARS: WHITE DWARFS full text sources ADS | data products MAST (2) SIMBAD (1) ESA (1)

Hopkins Ultraviolet Telescope determination of the Io torus electron temperature

view Abstract Citations (17) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hopkins Ultraviolet Telescope Determination of the Io Torus Electron Temperature Hall, D. T. ; Bednar, C. J. ; Durrance, S. T. ; Feldman, P. D. ; McGrath, M. A. ; Moos, H. W. ; Strobel, D. F. Abstract Sulfur ion emissions from the Io plasma torus observed by the Hopkins Ultraviolet Telescope (HUT) in 1990 December have been analyzed to determine the effective temperature of the exciting electrons. Spectra were obtained with a long slit that extended from 3.1 to 8.7 Jupiter radii RJ on both dawn and dusk torus ansae. The average temperature of electrons exciting S(2+) emissions from the dawn ansa is (4800 +/- 2400) K lower than on the dusk ansa, a dawn-dusk asymmetry comparable in both sign and magnitude to that measured by the Voyager Ultraviolet Spectrograph (UVS) experiment. Emissions from S(2+) ions are generated in a source region with electron temperatures in the range 32,000-56,000 K; S(3+) ion emissions are excited by electrons that average 20,000-40,000 K hotter. This distinct difference suggests that the S(3+) emission source region is spatially separate from the S(2+) source region. Estimated relative aperture filling factors suggest that the S(3+) emissions originate from a region more extended out of the centrifugal plane than the S(2+) emissions. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/187159 Bibcode: 1994ApJ...420L..45H Keywords: Electron Energy; Io; Plasma Temperature; Sulfur; Toruses; Ultraviolet Astronomy; Ultraviolet Spectra; Ultraviolet Spectrometers; Ultraviolet Telescopes; Voyager 1 Spacecraft; Voyager 2 Spacecraft; Astronomy; PLANETS AND SATELLITES: INDIVIDUAL IO; PLANETS AND SATELLITES: INDIVIDUAL JUPITER; ULTRAVIOLET: SOLAR SYSTEM full text sources ADS | data products MAST (1)

Observations of stars with the Hopkins Ultraviolet Telescope

The Hopkins Ultraviolet Telescope (HUT) was flown aboard the space shuttle Columbia as part of the Astro-1 mission during December 1990. During the nine-day flight, HUT carried out 3Åresolution spectrophotometry of a wide variety of astronomical objects, including a number of stellar targets, in the 912–1860Årange of the far ultraviolet. A few nearby stars were observed in the 415–912Årange of the extreme ultraviolet as well. For nearly all of these targets, the spectra obtained by HUT are the first ever obtained in the spectroscopically rich region between Lyman α (1216Å) and the Lyman limit (912Å). Here, we present highlights of the results obtained by HUT in a variety of areas of stellar astronomy.

Sub-Lyman-α observations of supernova remnants

The first map of Ovi λ1035 emission of the Cygnus Loop has now been obtained with Voyager. The first good spectra of the sub-Lyα region in the Cygnus Loop and in the LMC remnant N49 have been obtained with the Hopkins Ultraviolet Telescope. The lines detected below 1200Åinclude Svi λλ933,945, Ciii λ977, Niii λ991, and Ovi λλ1032, 1038. The Ovi luminosities of the Cygnus Loop and of N49 exceed their soft X-ray luminosities. There is Ovi emission at the primary shock front in the Cygnus Loop and from the bright optical filaments. The HUT spectra of the Cygnus Loop can be interpreted in terms of shocks with velocities of 170–190 km s−1; the differences between the two spectra are due to the time since the beginning of the shock-cloud encounter.

The optically thick C III spectrum. 2: Level/term populations and line/multiplet intensities using an improved hybrid model

view Abstract Citations (2) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Optically Thick C III Spectrum. II. Level/Term Populations and Line/Multiplet Intensities Using an Improved Hybrid Model Bhatia, A. K. ; Kastner, S. O. Abstract An improved hybrid level/term calculation is employed to obtain C III level/term populations and line/fractional multiplet intensities over the extended range of electron density 4.0 less than or equal log Ne less than or equal 12.0, for column lengths L ranging from zero (optically thin) to 1020/sq cm (moderately optically thick), at electron temperatures Te approximately 40,000 K(log Te = 4.6), Te approximately 63,000 K (log Te = 4.8), Te approximately 79,500 K (log Te = 4.9), and Te = 100,000 K (log Te = 5.0). The tabulated results are relevant to the interpretation of space observations obtained over extended spectral ranges by new and planned facilities including the Hopkins Ultraviolet Telescope (HUT) and the Far-Ultraviolet Spectrographic Explorer (FUSE). Publication: The Astrophysical Journal Supplement Series Pub Date: November 1993 DOI: 10.1086/191846 Bibcode: 1993ApJS...89..227B Keywords: Atomic Physics; Electron Density (Concentration); Electron Energy; Hybrid Structures; Far Uv Spectroscopic Explorer; Length; Optical Thickness; Telescopes; Astrophysics; ATOMIC PROCESSES full text sources ADS | data products MAST (1)

The Spectrum of EZ Canis Majoris (HD 50896) to the Lyman Limit with the Hopkins Ultraviolet Telescope

A unique flux-calibrated spectrum, extending to the Lyman limit of the Wolf-Rayet star EZ CMa (also known as WR 6, HD 50896, spectral type WN5) has been recorded by the Hopkins Ultraviolet Telescope. We compare the spectrum to a pure He continuum model with the stellar parameters L * =10 5.2 L ○. , R * =4.5 R ○. T eff =57,000 K, V∞=1700 km s −1 , and M˙=10 −4 yr −1 . These parameters are very close to those derived by Hamann et al. (1988) from quantitative spectroscopy of ultraviolet, visual, and infrared He emission lines (although they represent only one solution from a locus of solutions that scale with distance)

Voyager 2 observations of NGC 7023 - Dust scattering shortward of 1600 A

We report the first observational determination of the nebular-to-stellar flux ratio out to wavelengths as short as 1000 A for the reflection nebula NGC 7023, using a combination of spectroscopic data from Voyager 2 and from the Hopkins Ultraviolet Telescope (HUT) on the Astro 1 mission. After accounting for contributions by H2 fluorescence to the nebular flux, the wavelength variation of the ratio of the residual dust scattered flux to that observable from the embedded star is consistent with a reduction of the dust albedo by 25 percent over the wavelength interval 1300-1000 A. This is most easily interpreted, if the particles responsible for the FUV rise in the extinction curve are low-albedo, not necessarily zero-albedo, grains. The direct proportionality between the nebular surface brightness, measured at 22 arcsec offset by HUT, and the nebular flux suggests that the phase function of scattering does not vary in the 2000-1000 A range.

Extreme ultraviolet observations of HZ 43 and the local H/He ratio with the Hopkins Ultraviolet Telescope

We present a spectrum of the hot DA white dwarf HZ 43 in the EUV, near the 504-A ionization edge of neutral helium, obtained with the Hopkins Ultraviolet Telescope (HUT) during the 1990 December Astro-1 mission. The interstellar column densities derived from this spectrum rule out the anomalous interstellar absorption model proposed by Heise et al.(1991), which required a greater column density of neutral helium than neutral hydrogen toward HZ 43 in order to explain the low EUV flux from HZ 43 reported by EXOSAT. Instead, we find the interstellar neutral H/He ratio toward HZ 43 to be consistent with the canonical cosmic abundance ratio of 10 or with the 11.6 +/- 1.0 ratio measured by HUT along the line of sight toward another DA white dwarf, G191-B2B. The HUT observations suggest that either there is a substantial calibration error in the EXOSAT spectroscopy of HZ 43, or otherwise undetected metals in the nominally pure hydrogen HZ 43 atmosphere suppress its flux between 150 and 300 A, or both.

The hot stellar component in elliptical galaxies and spiral bulges. I - The far-ultraviolet spectrum of the bulge of M31

view Abstract Citations (85) References (57) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Hot Stellar Component in Elliptical Galaxies and Spiral Bulges. I. The Far-Ultraviolet Spectrum of the Bulge of M31 Ferguson, Henry C. ; Davidsen, Arthur F. Abstract We present a spectrum of the bulge of M31 from 1850 A to the Lyman limit measured through a 9" X 116" aperture by the Hopkins Ultraviolet Telescope (HUT) during the Astro-1 space shuttle mission in 1990 December. Apart from airglow, no significant emission features are present in the spectrum. A search for stellar absorption features reveals several significant detections, but uncertainties in the interstellar-medium contribution and the temperatures of the stars contributing to the spectrum preclude any definite conclusions about the metallicity of the stellar population. We compare the HUT spectra of the M31 bulge and of NGC 1399, the central giant elliptical in the Fornax Cluster. We find significant differences that are relatively insensitive to the assumptions about extinction. Evidently the stars producing the far-UV upturn in UV-bright galaxies such as NGC 1399 are not just more of the same stars producing the emission in UV-fainter galaxies like M31. We investigate the possibility that the two spectral-energy distributions (SEDs) differ only in the fractional contribution from classical post-asymptotic giant branch (PAGB) stars and in the amount of extinction. We find an acceptable fit to the M31 spectrum for E(B - V) = 0.11 if ~65% of the flux (at ~ 1400A) comes from PAGB stars and the rest comes from stars of the type producing the far-UV emission in NGC 1399. The known PAGB population from optical observations (central stars of planetary nebulae) can account for less than 1% of the total far-UV flux. The pointlike sources recently detected at 1750 A by the HST Faint Object Camera are probably PAGB stars with masses lower than planetary-nebula central stars (thought to be ~0.6 M_sun_). These sources too appear to account for only a small fraction (~15%) of the flux observed by HUT at 1750 A. These results suggest that PAGB stars with still lower masses, which would be fainter than the FOC detection limit for point sources, contribute to the M31 SED. We examine the hypothesis that the UV continuum in both galaxies is dominated by stars in post-horizontal branch (post-HB) phases of evolution, with a distribution of post-HB masses governed by the mean metallicity and metallicity spread of the population. The number of UV photons produced per star increases toward lower mass, while the characteristic temperature of the UV emitting population decreases. In this scenario, the far-UV flux of NGC 1399 is produced mostly by low-mass extreme horizontal branch, post-early-AGB, and/or AGB-Manque stars, while in M31 there is a large contribution from classical PAGB stars as well. We can thus qualitatively explain both the relative fluxes of the UV rising branches in NGC 1399 and M31, and the shapes of their SEDs. This scenario makes a prediction, which we confirm from existing surveys, that the number of planetary nebulae per unit luminosity is anticorrelated with the strength of the UV upturn. It also makes. testable predictions for the far-UV SEDs of low-metallicity ellipticals and the spectral evolution of giant ellipticals. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/172572 Bibcode: 1993ApJ...408...92F Keywords: Elliptical Galaxies; Far Ultraviolet Radiation; Galactic Bulge; Galactic Radiation; Hot Stars; Spiral Galaxies; Ultraviolet Astronomy; Absorption Spectra; Asymptotic Giant Branch Stars; Planetary Nebulae; Spectral Energy Distribution; Ultraviolet Spectra; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M31; GALAXIES: INDIVIDUAL MESSIER NUMBER: M32; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 1399; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (3) NED (3) MAST (2) INES (1)

Hopkins Ultraviolet Telescope observations of far-ultraviolet scattering in NGC 7023 - The dust albedo

view Abstract Citations (17) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Hopkins Ultraviolet Telescope Observations of Far-Ultraviolet Scattering in NGC 7023: The Dust Albedo Murthy, Jayant ; Dring, Andrew ; Henry, Richard C. ; Kruk, Jeffrey W. ; Blair, William P. ; Kimble, Randy A. ; Durrance, Samuel T. Abstract We have obtained the first sub-Ly-alpha spectroscopic observations of the reflection nebula NGC 7023 and its illuminating star, HD 200775, using the Hopkins UV Telescope during the Astro-1 mission in December, 1990. The ratio of the nebular to stellar flux is virtually flat between 1100 and 1860 A, indicating that sigma(a), the cross section for absorption, must rise sharply with decreasing wavelength. Independent of any model, this means that much of the far-UV rise in the extinction curve is due to an increase in absorption rather than scattering. If, in addition, we assume a spherical geometry, we derive an albedo of 0.5 at 1100 A with somewhat higher values at longer wavelengths. If the geometry is not spherical, lower values of the albedo may be obtained. Publication: The Astrophysical Journal Pub Date: May 1993 DOI: 10.1086/186840 Bibcode: 1993ApJ...408L..97M Keywords: Albedo; Interstellar Matter; Light Scattering; Nebulae; Ultraviolet Photography; Ultraviolet Telescopes; Airglow; Interstellar Extinction; Ultraviolet Spectra; Astronomy; ISM: DUST; EXTINCTION; ISM: INDIVIDUAL NGC NUMBER: NGC 7023; ISM: REFLECTION NEBULAE; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (2) MAST (1)

Observations of the white dwarf in the U Geminorum system with the Hopkins Ultraviolet Telescope

view Abstract Citations (60) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the White Dwarf in the U Geminorum System with the Hopkins Ultraviolet Telescope Long, Knox S. ; Blair, William P. ; Bowers, Charles W. ; Davidsen, Arthur F. ; Kriss, Gerard A. ; Sion, Edward M. ; Hubeny, Ivan Abstract The Hopkins Ultraviolet Telescope was used to obtain an FUV spectrum of U Gem about 10 d after the end of an outburst. Most of the FUV emission from U Gem appears to rise from the white dwarf (WD) in the system. Various possibilities to explain the hot component in the present spectrum are explored. It is most likely due to radiation from the boundary-layer region of the WD surface rather than from the accretion disk which exists in U Gem in quiescence. If the standard picture of boundary-layer emission is correct, then the hot component is not due to ongoing accretion onto the WD because the temperature observed is too low. Delayed emission from a viscously heated, differentially rotating atmosphere is argued to be a more valid explanation. Publication: The Astrophysical Journal Pub Date: March 1993 DOI: 10.1086/172365 Bibcode: 1993ApJ...405..327L Keywords: Cataclysmic Variables; Dwarf Novae; Far Ultraviolet Radiation; Ultraviolet Astronomy; Ultraviolet Emission; White Dwarf Stars; Absorption Spectra; Stellar Models; Ultraviolet Spectra; Astrophysics; STARS: INDIVIDUAL CONSTELLATION NAME: U GEMINORUM; STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: WHITE DWARFS; ULTRAVIOLET: STARS full text sources ADS | data products MAST (2) SIMBAD (1) INES (1)

The spectrum of the Jovian dayglow observed at 3 A resolution with the Hopkins ultraviolet telescope

Ultraviolet spectra of the Jovian equatorial dayglow in the spectral range 830-1850 A were obtained at about 3 A resolution. The observed spectrum is dominated by electron impact excitation of the H2 Lyman and Werner band systems. Solar Lyman-beta induced fluorescence in the (6, nu-double prime) Lyman band progression is clearly identified in five distinct P(1) lines, and the contribution of solar fluorescence to the total 2.3 kR slit-averaged H2 emission rate is estimated to be 17-22 percent. The electron excitation spectrum is characterized by a relative weakness of the Werner band system and the absence of cascade contributions to the Lyman system and is very similar to that of the south polar aurora. The integrated H2 emission rate in the 900-1100 A band is a factor of two lower than that measured by the Voyager UVS. Based on model calculations, photoelectron excitation does not appear able to account for the amount of observed electron-excited H2 emission.

Extreme ultraviolet observations of G191-B2B and the local interstellar medium with the Hopkins Ultraviolet Telescope

During the Astro-l mission in 1990 December, the Hopkins Ultraviolet Telescope (HUT) was used to observe the extreme ultraviolet spectrum (415-912 A) of the hot DA white dwarf GI91-B2B. Absorption by neutral helium shortward of the 504 A He I absorption edge is clearly detected in the raw spectrum. Model fits to the observed spectrum require interstellar neutral helium and neutral hydrogen column densities of 1.45 +/- 0.065 x 10 exp 17/sq cm and 1.69 +/- 0.12 x 10 exp 18/sq cm, respectively. Comparison of the neutral columns yields a direct assessment of the ionization state of the local interstellar cloud surrounding the Sun. The neutral hydrogen to helium ratio of 11.6 +/- 1.0 observed by HUT strongly contradicts the widespread view that hydrogen is much more ionized than helium in the local interstellar medium, a view which has motivated some exotic theoretical explanations for the supposed high ionization.

Far-Ultraviolet Astronomy on the Astro-1 Space Shuttle Mission

The Astro-1 mission obtained observations related to a wide variety of current problems in astronomy during a 9-day flight of the space shuttle Columbia. Early results from one of the instruments, the Hopkins Ultraviolet Telescope, are reviewed here. Among these are new insights concerning the origin of the ultraviolet light from the old stellar population in elliptical galaxies, new evidence for a hot, gaseous corona surrounding the Milky Way, improved views of the physical conditions in active galactic nuclei, and a measurement of the ionization state of the local interstellar medium.

Far-ultraviolet observations of the supernova remnant N49 using the Hopkins Ultraviolet Telescope

view Abstract Citations (15) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Ultraviolet Observations of the Supernova Remnant N49 Using the Hopkins Ultraviolet Telescope Vancura, Olaf ; Blair, William P. ; Long, Knox S. ; Davidsen, Arthur F. ; Bowers, Charles W. ; Dixon, W. Van Dyke ; Durrance, Samuel T. ; Feldman, Paul D. ; Ferguson, Henry C. ; Henry, Richard C. ; Kimble, Randy A. ; Kriss, Gerard A. ; Kruk, Jeffrey W. ; Moos, H. Warren Abstract Using the Hopkins Ultraviolet Telescope on the Astro-1 space shuttle mission in 1990 December, we have obtained a far-ultraviolet spectrum (912-1860 A at 3.5 A resolution) of a complex of bright filaments located in the eastern part of the supernova remnant N49 in the Large Magellanic Cloud. This is the first observation of an extragalactic supernova remnant that extends to the Lyman limit. We detect lines of O VI λ1035, O IV] λ1403, C IV λ1550, and He II λ1640. The O VI emission that we observe cannot originate in shocks with velocities <= 140 km s^-1^ which are responsible for the bulk of both the C IV and the optical line emission. Likewise, the main blast wave with a velocity ~730 km s^-1^ is unable to account for the brightness of O VI. Most of the O VI originates in optically faint, 190-270 km s^-1^ shocks, traversing clouds with densities of 20-40 cm^-3^. We expand upon earlier modeling of N49 IUE and optical spectra that assumed a distribution of shock velocities including data from below Lyα, such models still describe the data well. Publication: The Astrophysical Journal Pub Date: December 1992 DOI: 10.1086/172054 Bibcode: 1992ApJ...401..220V Keywords: Astronomical Models; Far Ultraviolet Radiation; Spaceborne Astronomy; Supernova Remnants; Carbon; Helium Ions; Magellanic Clouds; Oxygen Spectra; Astrophysics; ISM: INDIVIDUAL ALPHANUMERIC: N49; GALAXIES: MAGELLANIC CLOUDS; SHOCK WAVES; ISM: SUPERNOVA REMNANTS; ULTRAVIOLET: INTERSTELLAR full text sources ADS | data products NED (2) MAST (2) SIMBAD (1)

Spectroscopy of a Balmer-dominated filament in the Cygnus Loop with the Hopkins Ultraviolet Telescope

A fair UV spectrum of a nonradiative filament in the Cygnus Loop covering the wavelength range 830-1860 A at 3.5-A resolution was obtained using the Hopkins Ultraviolet Telescope (HUT) on the Astro-1 space shuttle mission. Nonradiative shock models which include a more sophisticated treatment of Lyman line transfer are calculated. It is found that the HUT spectrum can be explained in terms of a shock with velocity 175-185 km/s propagating into a low-density medium. This shock velocity can be reconciled with the 135-km/s width of the broad component of H-alpha in this filament if equilibration of the postshock electron and ion temperatures proceeds much more rapidly than Coulomb equilibration time scales. The time required for a 180-km/s shock to develop a partial recombination zone is short, about 200 yr if n is approximately equal to 2/cu cm. This suggests that the shock is decelerating as it encounters denser material. The current analysis patently favors rapid equilibration of electrons and ions behind the shock.

Far-ultraviolet observations of the Crab Nebula using the Hopkins Ultraviolet Telescope

Observations of the FUV spectrum of the central portion of the Crab Nebula SNR using the Hopkins Ultraviolet Telescope (HUT) aboard the Astro-1 space shuttle mission in December 1990 are reported. The C IV 1549-A emission line shows two resolved components representing the front and back sides of the shell expanding at roughly +/- 1100 km/s. The He II 1640-A emission line shows only a blueshifted component corresponding to the near side of the shell. The HUT observation is compared to optical emission-line imagery and to archival IUE observations. This comparison indicates that a distribution emission component, consisting of either a number of individually faint filaments or a diffuse component, produces the bulk of the emission seen by HUT. A grid of photoionization models for the Crab Nebula filaments is calculated to infer the range of limits. The differing UV line ratios observed for these components indicates that varying carbon and/or He abundances are present in the observed material.

Evidence for Shock-heated Gas in the Hopkins Ultraviolet Telescope Spectrum of NGC 1068: Erratum

view Abstract Citations References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for Shock-heated Gas in the Hopkins Ultraviolet Telescope Spectrum of NGC 1068: Erratum Kriss, Gerard A. ; Davidsen, Arthur F. ; Blair, William P. ; Ferguson, Henry C. ; Long, Knox S. Abstract In the Letter "Evidence for Shock-heated Gas in the Hopkins Ultraviolet Telescope Spectrum of NGC 1068" by Gerard A. Kriss, Arthur F. Davidsen, William P. Blair, Henry C. Ferguson, and Knox S. Long (ApJ, 394, L37 C1992]), Figure 1 (Plate L5) was printed as a mirror image due to a printer's error. The figure has been reprinted correctly as Plate L10 of this issue. The Journal regrets the error. We also apologize for the incorrect spelling of Knox S. Long in the author list in the table of contents for the 1992 August 1 issue. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/186561 Bibcode: 1992ApJ...397L.127K Keywords: ERRATA; ADDENDA full text sources ADS | data products NED (1) MAST (1) Related Materials (1) Original Paper: 1992ApJ...394L..37K

Evidence for shock-heated gas in the Hopkins Ultraviolet Telescope spectrum of NGC 1068

We obtained far-UV spectra of the prototypical Seyfert 2 galaxy NGC 1068 with the Hopkins Ultraviolet Telescope during the flight of Astro-1 aboard the space shuttle Columbia in 1990 December. In two separate observations of NGC 1068 lasting 2356 and 2692 s we used circular apertures of 18" and 30" diameter, respectively. The spectra reveal strong emission lines of C III λ977, N III λ991, Lyβ, O VI λλ1032, 1038, and He II λ1085, all seen for the first time in a Seyfert 2 galaxy. Longward of Lyα the spectrum is similar to previous observations obtained with the IUE. Broad-line components are visible for both Lyα and C IV. The relative ratios of broad Lyα, C IV, and Hβ are typical of those seen in Seyfert 1 galaxies and QSOs. A flat, blue continuum is observed down to the Lyman limit imposed by interstellar absorption in our own Galaxy. Excess continuum emission is present through the 30" aperture which can plausibly be attributed to young stars in the starburst ring. The moderately strong C III λ977 and N III λ991 emission is unusual for an AGN, and the line ratios below Lyα are similar to those seen in HUT observations of the Cygnus Loop supernova remnant. The ratios of C III] λ1909 to λ977 and N III] λ1750 to λ991 imply temperatures exceeding 26,700 K and 24,000 K, respectively. Since these temperatures are much higher than those typically encountered in photoionized gas with abundant C^+2^ and N^+2^ populations, shock heating should be reconsidered as an additional source of emission lines in the nucleus of NGC 1068. Shocks could arise from the interaction of an X-ray-heated wind from the nucleus with the surrounding interstellar medium, or from radio jets striking interstellar clouds. Shocks from supernovae in starburst regions near the active nucleus are not a likely explanation.