Search Publications
The Nuclear and Circumnuclear Stellar Population in Seyfert 2 Galaxies: Implications for the Starburst-Active Galactic Nucleus Connection
Heckman, Timothy; Leitherer, Claus; González Delgado, Rosa M.
We report the results of a spectroscopic investigation of a sample of 20 of the brightest type 2 Seyfert nuclei. Our goal is to search for the direct spectroscopic signature of massive stars and thereby probe the role of circumnuclear starbursts in the Seyfert phenomenon. The method used is based on the detection of the higher order Balmer lines a…
Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808
Brown, Thomas M.; Hubeny, Ivan; Sweigart, Allen V. +2 more
We present an ultraviolet color-magnitude diagram (CMD) spanning the hot horizontal branch (HB), blue straggler, and white dwarf populations of the globular cluster NGC 2808. These data were obtained with the far-UV and near-UV cameras on the Space Telescope Imaging Spectrograph (STIS). Although previous optical CMDs of NGC 2808 show a high-temper…
Theory of Extrasolar Giant Planet Transits
Hubbard, W. B.; Fortney, J. J.; Lunine, J. I. +3 more
We present a synthesis of physical effects influencing the observed light curve of an extrasolar giant planet (EGP) transiting its host star. The synthesis includes a treatment of Rayleigh scattering, cloud scattering, refraction, and molecular absorption of starlight in the EGP atmosphere. Of these effects, molecular absorption dominates in deter…
Order and chaos in the local disc stellar kinematics induced by the Galactic bar
Fux, R.
The Galactic bar causes a characteristic splitting of the disc phase space into regular and chaotic orbit regions which is shown to play an important role in shaping the stellar velocity distribution in the Solar neighbourhood. A detailed orbital analysis within an analytical 2D rotating barred potential reveals that this splitting is mainly dicta…
M82-F: a doomed super star cluster?
Smith, Linda J.; Gallagher, John S.
We present high-dispersion echelle spectroscopy of the very luminous, young super star cluster (SSC) `F' in M82, obtained with the 4.2-m William Herschel Telescope, for the purpose of deriving its dynamical mass and assessing whether it will survive to become an old globular cluster. In addition to the stellar lines, the spectrum contains complex …
The Expansion Center and Dynamical Age of the Galactic Supernova Remnant Cassiopeia A
Thorstensen, John R.; van den Bergh, Sidney; Fesen, Robert A.
We present proper motions for 21 bright main shell and 17 faint, higher velocity, outer ejecta knots in the Cas A supernova remnant and use them to derive new estimates for the remnant's expansion center and age. Our study included 1951-1976 Palomar 5 m prime focus plates, 1988-1999 CCD images from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 H…
High-Resolution X-Ray Spectroscopy and Modeling of the Absorbing and Emitting Outflow in NGC 3783
Brandt, W. N.; Kaspi, Shai; Garmire, Gordon P. +6 more
The high-resolution X-ray spectrum of NGC 3783 shows several dozen absorption lines and a few emission lines from the H-like and He-like ions of O, Ne, Mg, Si, and S, as well as from Fe XVII-Fe XXIII L-shell transitions. We have reanalyzed the Chandra HETGS spectrum using better flux and wavelength calibrations, along with more robust methods. Com…
High-Mass, OB Star Formation in M51: Hubble Space Telescope Hα and Paα Imaging
Scoville, N. Z.; Polletta, M.; Thompson, R. +3 more
We have obtained Hα and Paα emission-line images covering the central 3'-4' of M51 using the WFPC2 and NICMOS instruments on the Hubble Space Telescope to study the high-mass stellar population. The 0.1"-0.2" pixels provide 4.6-9 pc resolution in M51, and the Hα/Paα line ratios are used to obtain extinction estimates. A sample of 1373 Hα emission …
Three-dimensional numerical simulation of MHD waves observed by the Extreme Ultraviolet Imaging Telescope
Plunkett, S. P.; Thompson, B. J.; Wu, S. T. +4 more
We investigate the global large amplitude waves propagating across the solar disk as observed by the SOHO/Extreme Ultraviolet Imaging Telescope (EIT). These waves appear to be similar to those observed in Hα in the chromosphere and which are known as ``Moreton waves,'' associated with large solar flares [Moreton, 1960, 1964]. Uchida [19…
The X-Ray Globular Cluster Population in NGC 1399
Angelini, Lorella; Loewenstein, Michael; Mushotzky, Richard F.
We report on the Chandra observations of the elliptical galaxy NGC 1399, concentrating on the X-ray sources identified with globular clusters (GCs). A large fraction of the 2-10 keV X-ray emission in the 8'×8' Chandra image is resolved into point sources with luminosities >=5×1037 ergs s-1. These sour…