Search Publications
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. …
The Accuracy of the Born and Ray Approximations in Time-Distance Helioseismology
Kosovichev, A. G.; Birch, A. C.; Price, G. H. +1 more
Time-distance helioseismology measures the time for acoustic wave packets to travel, through the solar interior, from one location on the solar surface to another. Interpretation of travel times requires an understanding of their dependence on subsurface inhomogeneities. Traditionally, time-distance measurements have been modeled in the ray approx…
Microwave Detection of Umbral Oscillation in NOAA Active Region 8156: Diagnostics of Temperature Minimum in Sunspot
Shibasaki, Kiyoto
A radio brightness oscillation of 3 minutes at 17 GHz was detected in a compact radio source associated with a sunspot umbra in the NOAA active region 8156. We interpret the radio brightness oscillation by the density and temperature fluctuations due to upward-traveling acoustic waves through the third harmonic gyroresonance layer (2000 G). SOHO/S…
Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud
Redfield, Seth; Linsky, Jeffrey L.
We analyze high-resolution UV spectra of the Mg II h and k lines for 18 members of the Hyades to study inhomogeneity along these proximate lines of sight. The observations were taken by the Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope (HST). Three distinct velocity components are observed. All 18 lines…
Constraints on Galaxy Formation from Stars in the Far Outer Disk of M31
Ferguson, Annette M. N.; Johnson, Rachel A.
Numerical simulations of galaxy formation within the cold dark matter (CDM) hierarchical clustering framework are unable to produce large disk galaxies without invoking some form of feedback to suppress gas cooling and collapse until a redshift of unity or below. An important observational consequence of delaying the epoch of disk formation until …
Star Counts across the Red Giant Branch Bump and Below
Zoccali, M.; Bono, G.; Piotto, G. +1 more
We present a new observable-Rbump-which is the ratio between the star counts across the red giant branch (RGB) bump and fainter RGB stars to investigate the occurrence of a deep-mixing phenomenon during these evolutionary phases. The comparison between predicted and empirical Rbump-values, based on a large and homogeneous set…