Search Publications
Subarcsecond Mid-Infrared Structure of the Dust Shell around IRAS 22272+5435
Ueta, Toshiya; Fazio, Giovanni G.; Meixner, Margaret +6 more
We report subarcsecond imaging of extended mid-IR emission from a proto-planetary nebula (PPN), IRAS 22272+5435, performed at the MMT observatory with its newly upgraded 6.5 m aperture telescope and at the Keck observatory. The mid-IR emission structure is resolved into two emission peaks separated by 0.5"-0.6" in the MMT 11.7 µm image and i…
The Relative Star Formation Histories of Spiral Bulges and Elliptical Galaxies in the Hubble Deep Fields
Dickinson, Mark; Ellis, Richard S.; Abraham, Roberto G.
Hierarchical galaxy formation models make specific predictions concerning the relative assembly rates and star formation histories of spiral bulges and field ellipticals. Independently of the cosmological model and initial power spectrum of fluctuations, at all epochs the stellar populations in spiral bulges should be older and redder than those i…
The Solar Helium Abundance in the Outer Corona Determined from Observations with SUMER/SOHO
Feldman, U.; Laming, J. M.
At altitudes of about 1.05 Rsolar or more, the corona above quiet solar regions becomes essentially isothermal. This obviates many of the difficulties associated with the inverse problem of determining emission measure distributions and allows for fairly straightforward relative element abundance measurements. We present new values for …
Preliminary Astrometric Masses for Proposed Extrasolar Planetary Companions
Han, Inwoo; Gatewood, George; Black, David C.
As a first step in the implementation of an astrometric survey, we have reduced the Hipparcos intermediate astrometric data (IAD) for 30 stars that currently exhibit small-amplitude periodic radial velocity variations. We consider only systems with periods longer than 10 days, where the motion is attributed to the presence of an ``extrasolar plane…
Quasi-periodic Oscillation in Seyfert Galaxies: Significance Levels. The Case of Markarian 766
Yaqoob, Tahir; Staubert, Rüdiger; Wilms, Jörn +2 more
We discuss methods to compute significance levels for the existence of quasi-periodic oscillations (QPOs) in active galactic nuclei (AGNs) that take the red-noise character of the X-ray light curves of these objects into account. Applying epoch folding and periodogram analysis to the XMM-Newton observation of the Seyfert galaxy Mrk 766, a possible…
Chromospheric Heating in the Late Phase of Two-Ribbon Flares
De Pontieu, B.; Czaykowska, A.; Alexander, D.
Fast upflows observed in the late gradual phase of an M6.8 two-ribbon flare by the Solar and Heliospheric Observatory/Coronal Diagnostic Spectrometer have provided evidence for the presence of chromospheric evaporation more than an hour after the impulsive phase of the flare. The chromospheric heating necessary to generate these upflows requires t…
Ultraluminous Infrared Galaxies: Mergers of Sub-L* Galaxies?
Lucas, Ray A.; Colina, Luis; Bushouse, Howard +6 more
A sample of 27 low-redshift, mostly cool, ultraluminous infrared galaxies (ULIRGs) has been imaged at 1.6 µm with the Hubble Space Telescope (HST) Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). The majority (67%) of the sample's galaxies are multiple-nucleus galaxies with projected separations of up to 17 kpc, and the rest of t…
Analysis of the Hipparcos Observations of the Extrasolar Planets and the Brown Dwarf Candidates
Mazeh, Tsevi; Zucker, Shay
We analyzed the Hipparcos astrometric observations of 47 stars that were discovered to harbor giant planets and 14 stars with brown dwarf secondary candidates. The Hipparcos measurements were used together with the corresponding stellar radial velocity data to derive an astrometric orbit for each system. To find out the significance of the derived…
High Temporal Resolution XMM-Newton Monitoring of PKS 2155-304
Markowitz, Alex; Edelson, Rick; Sembay, Steve +3 more
The bright, strongly variable BL Lacertae object PKS 2155-304 was observed by XMM-Newton for two essentially uninterrupted periods of ~11 and 16 hr on 2000 May 30-31. The strongest variations occurred in the highest energy bands. After scaling for this effect, the three softest bands (0.1-1.7 keV) showed strong correlation with no measurable lag t…
Far-Ultraviolet Observations of Flares on the dM0e Star AU Microscopii
Robinson, Richard D.; Woodgate, Bruce E.; Linsky, Jeffrey L. +1 more
We report on far-ultraviolet (FUV) observations of flares on the dM0e star AU Microscopii obtained on 1998 September 6 with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The data consist of medium-resolution echelle spectra covering the wavelength region from 1170 to 1730 Å with a spectral resolution of λ/Δλ=45,800. …