Search Publications
Hubble Space Telescope WFPC2 Study of the Trapezium Cluster: The Influence of Circumstellar Disks on the Initial Mass Function
Panagia, N.; Robberto, M.; Song, J. +3 more
We have performed the first measures of mass accretion rates in the core of the Orion Nebula Cluster. Four adjacent fields centered on the Trapezium stars have been imaged in the U and B bands using the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope. We obtained photometry for 91 stars in the U band (F336W) and 71 stars …
Discovery of a Dwarf Poststarburst Galaxy near a High Column Density Local Lyα Absorber
Stocke, John T.; Keeney, Brian A.; Giroux, Mark L. +3 more
We report the discovery of a dwarf (MB=-13.9) poststarburst galaxy coincident in recession velocity (within uncertainties) with the highest column density absorber (NHI=1015.85 cm-2 at cz=1586 km s- 1) in the 3C 273 sight line. This galaxy is by far the closest galaxy to this absorber, project…
A Study of a Tiny Two-Ribbon Flare Driven by Emerging Flux
Shibata, Kazunari; Akiyama, Sachiko; Brooks, David H. +6 more
We present observations of the eruption of a miniature filament that occurred near NOAA Active Region 9537 on 2001 July 14. The eruption was observed by the Hida Observatory Domeless Solar Telescope, in the Hα line center and +/-0.4 Å wings, the Solar and Heliospheric Observatory EUV Imaging Telescope (EIT) and Michelson Doppler Imager, and the Yo…
The Effective Temperatures of Hot Stars. II. The Early-O Types
Bianchi, Luciana; Garcia, Miriam
We derived the stellar parameters of a sample of Galactic early-O type stars by analyzing their UV and far-UV spectra from the Far Ultraviolet Spectroscopic Explorer (905-1187 Å), the International Ultraviolet Explorer, the Hubble Space Telescope STIS, and the Orbiting and Retrievable Far and Extreme Ultraviolet Spectrometer (1200-2000 Å). The dat…
Ultralow Iron Abundances in the Distant Hot Gas in Galaxy Groups
Buote, David A.; Brighenti, Fabrizio; Mathews, William G.
A new XMM observation of the outer regions of the galaxy group NGC 5044 indicates hot gas iron abundances of only ZFe/Zsolar~0.15 between r=0.2rvir and 0.4rvir. While the total baryon mass within the virial radius may be close to the cosmic mean value observed in rich clusters, the ratio of total iron ma…
Does Solar Structure Vary with Solar Magnetic Activity?
Basu, Sarbani; Mandel, Anna
We present evidence that solar structure changes with changes in solar activity. We find that the adiabatic index, Γ1, changes near the second helium ionization, i.e., at a depth of about 0.98 Rsolar. We believe that this change is a result of the change in the effective equation of state caused by magnetic fields. Inversions…
Coronal Loop Oscillations and Flare Shock Waves
Hudson, H. S.; Warmuth, A.
A statistical analysis of coronal loop oscillations observed by the Transition Region and Coronal Explorer (TRACE) shows that 12 of 28 cases were associated with metric type II bursts. The timing is consistent with the idea that in many cases the loop oscillations result from the passage of a large-scale wave disturbance originating in a flare in …
Chromospheric Waves Observed in the He I Spectral Line (λ = 10830 Å): A Closer Look
Gilbert, Holly R.; Holzer, Thomas E.
Although ``Moreton'' waves have historically been observed in Hα data, more recently waves have also been observed in chromospheric He I (λ=10830 Å) images. In a previous study, we found that chromospheric waves observed in He I data (from the Mauna Loa Solar Observatory) in two events (occurring on 2000 November 25 and 2001 January 20) are cospat…
The Absorption Signatures of Dwarf Galaxies: The z=1.04 Multicloud Weak Mg II Absorber toward PG 1634+706
Charlton, Jane C.; Churchill, Christopher W.; Zonak, Stephanie G. +1 more
We analyze high-resolution spectra of a multicloud weak [defined as Wr(MgII)<0.3 Å] absorbing system along the line of sight to PG 1634+706. This system gives rise to a partial Lyman limit break and absorption in Mg II, Si II, C II, Si III, Si IV, C IV, and O VI. The lower ionization transitions arise in two kinematic subsystems with…
Radiative Cooling and Heating and Thermal Conduction in M87
Molendi, Silvano; Ghizzardi, Simona; De Grandi, Sabrina +1 more
The crisis of the standard cooling flow model brought about by Chandra and XMM-Newton observations of galaxy clusters has led to the development of several models that explore different heating processes in order to assess whether they can quench the cooling flow. Among the most appealing mechanisms are thermal conduction and heating through buoya…