Search Publications
Holmberg IX: The Nearest Young Galaxy
Sabbi, E.; Gallagher, J. S.; Smith, L. J. +2 more
We present a study of the M81 companion dwarf irregular galaxy Holmberg IX using deep images taken with the Wide Field Channel of the Advanced Camera for Surveys on board the Hubble Space Telescope. Based on color-magnitude diagrams the resolved stellar population toward Holmberg IX contains numerous stars with ages of lesssim200 Myr as well as ol…
Rise of a Dark Bubble through a Quiescent Prominence
de Toma, G.; Burkepile, J. T.; Low, B. C. +1 more
We report on a dynamical event observed in a quiescent prominence on 2007 November 8: a well-formed dark "bubble" with a bright core rose vertically through the prominence without causing it to erupt. This event was observed in Hα and He I 1083 nm with the instruments of the Mauna Loa Solar Observatory. The dark bubble had a size of over 40'' and …
Biases on Initial Mass Function Determinations. II. Real Multiple Systems and Chance Superpositions
Maíz Apellániz, J.
When calculating stellar initial mass functions (IMFs) for young clusters, one has to take into account that (1) most massive stars are born in multiple systems, (2) most IMFs are derived from data that cannot resolve such systems, and (3) multiple chance superpositions between members are expected to happen if the cluster is too distant. In this …
Forward Modeling of Active Region Coronal Emissions. II. Implications for Coronal Heating
Leka, K. D.; Lundquist, L. L.; Fisher, G. H. +2 more
In Paper I, we introduced and tested a method for predicting solar active region coronal emissions using magnetic field measurements and a chosen heating relationship. Here, we apply this forward-modeling technique to 10 active regions observed with the Mees Solar Observatory Imaging Vector Magnetograph and the Yohkoh Soft X-ray Telescope. We prod…
Isolated OB Associations in Stripped H I Gas Clouds
Freeman, K. C.; Ryan-Weber, E. V.; Oey, M. S. +4 more
HST ACS HRC images in UV (F250W), V (F555W), and I (F814W) resolve three isolated OB associations that lie up to 30 kpc from the stellar disk of the S0 galaxy NGC 1533. Previous narrowband Hα imaging and optical spectroscopy showed these objects as unresolved intergalactic H II regions having Hα luminosities consistent with single early-type O sta…
Observations of Doppler Shift Oscillations with the EUV Imaging Spectrometer on Hinode
Warren, Harry P.; Watanabe, Tetsuya; Mariska, John T. +1 more
Damped Doppler shift oscillations have been observed in emission lines from ions formed at flare temperatures with the Solar Ultraviolet Measurements of Emitted Radiation spectrometer on the Solar and Heliospheric Observatory and with the Bragg Crystal Spectrometer on Yohkoh. This Letter reports the detection of low-amplitude damped oscillations i…
Damping of Slow MHD Coronal Loop Oscillations by Shocks
Verwichte, E.; Haynes, M.; Arber, T. D. +1 more
The damping of slow magnetoacoustic coronal loop oscillations by shock dissipation is investigated. Observations of large-amplitude slow-mode observations made by SUMER show a clear dependency of the damping rate on the oscillation amplitude. Fully nonlinear MHD simulations of slow-mode oscillations in the presence of thermal conduction are perfor…
GALEX Spectroscopy of SN 2005ay Suggests Ultraviolet Spectral Uniformity among Type II-P Supernovae
Smith, G. P.; Gal-Yam, A.; Kirshner, R. P. +24 more
We present the initial results from our GALEX program designed to obtain ultraviolet (UV) spectra of nearby core-collapse supernovae (SNe). Our first target, SN 2005ay in the nearby galaxy NGC 3938, is a typical member of the SN II-P subclass. Our spectra show remarkable similarity to those of the prototypical Type II-P SN 1999em, and resemble als…
Analysis of Interplanetary Coronal Mass Ejection Parameters as a Function of Energetics, Source Location, and Magnetic Structure
Reinard, A. A.
We describe a study of how ICME parameters vary as function of source location, associated flare magnitude, and magnetic structure. The strongest compositional enhancements are found to occur in events originating in central longitudes of the Sun, those with large associated flares, and those that are identified as magnetic clouds. In situ velocit…
Millisecond Microwave Spikes: Statistical Study and Application for Plasma Diagnostics
Rozhansky, I. V.; Fleishman, G. D.; Huang, G. -L.
We analyze a dense cluster of solar radio spikes registered at 4.5-6 GHz by the Purple Mountain Observatory spectrometer (Nanjing, China), operating in the 4.5-7.5 GHz range with 5 ms temporal resolution. To handle the data from the spectrometer, we developed a new technique that uses a nonlinear multi-Gaussian spectral fit based on χ2 …