Search Publications
The Extragalactic Distance Scale Key Project. III. The Discovery of Cepheids and a New Distance to M101 Using the Hubble Space Telescope
Kelson, Daniel D.; Illingworth, Garth D.; Madore, Barry F. +15 more
We report on the discovery of 29 Cepheid variables in the galaxy M101 using the original Wide Field Camera (WFC) and the new Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope. We observed a field in M101 at 17 independent epochs in V (F555W), five epochs in I (F785LP/ F814W), and one epoch in B (F439W), with a time interval b…
Statistical acceleration of interstellar pick-up ions in co-rotating interaction regions
Schwadron, N. A.; Gloeckler, G.; Fisk, L. A.
Observations from the SWICS instrument on Ulysses reveal that there is little evidence for the acceleration of interstellar pick-up ions at the forward and reverse shocks which surround Co-rotating Interactions Regions (CIR's) in the solar wind. Rather, the pick-up ions exhibit strong acceleration in regions within the CIR where there are increase…
Radio Outflows and the Origin of the Narrow-Line Region in Seyfert Galaxies
Boksenberg, A.; Capetti, A.; Sparks, W. B. +2 more
We present the results of Hubble Space Telescope medium-band imaging of four Seyfert 2 galaxies, Mrk 573, Mrk 348, Mrk 3, and Mrk 78, which show extended radio emission, and ground based Johnson A images of Mrk 3 and Mrk 78 obtained with the William Herschel Telescope. Together these two data sets allow us to investigate the relationship between t…
A search for interstellar gas-phase CO_2_. Gas: solid state abundance ratios.
de Graauw, T.; van Dishoeck, E. F.; Salama, A. +15 more
We present searches for gas-phase CO_2_ features in the ISO-SWS infrared spectra of four deeply embedded massive young stars, which all show strong solid CO_2_ absorption. The abundance of gas-phase CO_2_ is at most 2x10^-7^ with respect to H_2_, and is less than 5% of that in the solid phase. This is in strong contrast to CO, which is a factor of…
Long-term spectroscopic monitoring of BA-type supergiants. I. Halpha_ line-profile variability.
Stahl, O.; Wolf, B.; Kaufer, A. +5 more
We have obtained time series of spectra in the wavelength range 4000-6800 A over several months with high S/N and high resolution in wavelength (λ/{DELTA}λ=~20000) and time ({DELTA}t=~1d) of the late-type B and early-type A supergiants HD91619 (B7Ia), βOri (B8Ia), HD96919 (B9Ia), HD92207 (A0Ia), HD100262 (A2Ia) and αCyg (A2Ia). Halpha_ …
Abundance of 3He in the local interstellar cloud
Gloeckler, George; Geiss, Johannes
THE primordial abundances of the light elements and their isotopes provide essential information regarding the nucleosynthetic processes that occurred in the Big Bang1,2. At present the best estimates of the baryon/photon ratio of the Universe, a fundamental cosmological parameter, are extrapolations to primordial times of light-element…
Observations of Saturn's Ring-Plane Crossings in August and November 1995
Nicholson, Philip D.; French, Richard G.; Dones, Luke +7 more
Observations of Saturn's ring system with the Hubble Space Telescope during the 10 August 1995 Earth crossing and the 17 to 21 November 1995 solar crossing indicate that the F ring dominates their apparent edge-on thickness of 1.2 to 1.5 kilometers. The F ring is slightly inclined with respect to the A ring, which may explain the approximately 50-…
Nuclei of Nearby Disk Galaxies.I.A Hubble Space Telescope Imaging Survey
Franx, Marijn; Illingworth, Garth D.; MacKenty, John W. +1 more
We present deconvolved images of the central regions of 20 nearby disk galaxies, obtained with the original Planetary Camera of the Hubble Space Telescope. The galaxies span a range in Hubble type from S0 to Sm. We have measured surface brightness profiles, and inverted these to estimate luminosity-density profiles. Surface brightness profiles in …
Reverberation Mapping and the Disk-Wind Model of the Broad-Line Region
Chiang, J.; Murray, N.
Using the disk-wind model of Murray et al., we calculate line profiles and frequency-resolved response functions for broad-line emission from the surface of an accretion disk in an active galactic nucleus in the presence of a radiatively driven wind. We find that the combined effects of the shears in the wind and in the dIsk itself produce anisotr…
Spectral analyses of late-type WC central stars of planetary nebulae.
Hamann, W. -R.; Jeffery, C. S.; Leuenhagen, U.
The optical spectra of the seven late-type Wolf-Rayet central stars NGC40 ([WC8]), BD+30 3639 ([WC9]), He2-99 ([WC9]), CPD-56 8032, He2-113, M4-18 and K2-16 (all [WC11]) are analyzed by means of spherically expanding model atmospheres. The NLTE simulations account for the elements helium, carbon and oxygen. As main results effective temperature T_…