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Comparison of Empirical Models for Polar and Equatorial Coronal Holes
Romoli, M.; Cranmer, S. R.; Kohl, J. L. +2 more
We present a self-consistent empirical model for several plasma parameters of a large equatorial coronal hole observed on 1999 November 12 near solar maximum. The model was derived from observations with the Ultraviolet Coronagraph Spectrometer on the Solar and Heliospheric Observatory. In this Letter, we compare the observations of O VI λλ1032, 1…
WFPC2 Observations of Massive and Compact Young Star Clusters in M31
Williams, Benjamin F.; Hodge, Paul W.
We present color-magnitude diagrams of four blue massive and compact star clusters in M31: G38, G44, G94, and G293. The diagrams of the four clusters reveal a well-populated upper main sequence and various numbers of supergiants. The U-B and B-V colors of the upper main sequence stars are used to determine reddening estimates of the different line…
Photoevaporating Flows from the Cometary Knots in the Helix Nebula (NGC 7293)
Henney, W. J.; Raga, A. C.; López-Martín, L. +2 more
We explain the Hα emission of the cometary knots in the Helix Nebula (NGC 7293) with an analytical model that describes the emission of the head of the globules as a photoevaporated flow produced by the incident ionizing radiation of the central star. We compare these models with the Hα emission obtained from the Hubble Space Telescope (HST) archi…
Infrared Space Observatory Spectra of R Coronae Borealis Stars. I. Emission Features in the Interval 3-25 Microns
Rao, N. Kameswara; Lambert, David L.; Pandey, Gajendra +1 more
Infrared Space Observatory 3-25 µm spectra of the R Coronae Borealis stars V854 Cen, R CrB, and RY Sgr are presented and discussed. Sharp emission features coincident in wavelength with the well-known unidentified emission features are present in the spectrum of V854 Cen but not in the spectra of R CrB and RY Sgr. Since V854 Cen is not parti…
Coronal Inflows and Sector Magnetism
Sheeley, N. R., Jr.; Wang, Y. -M.
We have remeasured the rate of coronal inflows during 1996-2001, taking into account multiple occurrences per day, and have displayed the results in Carrington stack plots to study their long-term behavior. The stack plots show long-lived recurrence patterns related to the sectorial component of the Sun's large-scale field. In particular, most inf…
A 2000 Kilometer per Second ``Pristine'' Post-asymptotic Giant Branch Wind in the Proto-planetary Nebula He 3-1475
Sahai, R.; Sánchez Contreras, C.
We analyze (archival) Space Telescope Imaging Spectrograph long-slit Hα spectra of the proto-planetary nebula He 3-1475. We find two remarkable blueshifted absorption features arising from the inner ~5×1016 cm of the nebula, revealing the presence of two different winds outflowing at high velocity from the central star. The kinematic ag…
MACHO 96-LMC-2: Lensing of a Binary Source in the Large Magellanic Cloud and Constraints on the Lensing Object
Alcock, C.; Allsman, R. A.; Alves, D. R. +21 more
We present photometry and analysis of the microlensing alert MACHO 96-LMC-2 (event LMC-14 in an earlier paper). This event was initially detected by the MACHO Alert System and subsequently monitored by the Global Microlensing Alert Network (GMAN). The ~3% photometry provided by the GMAN follow-up effort reveals a periodic modulation in the light c…
Spatial Structure of Simple Spiky Bursts at Microwave/Millimeter Wavelengths
Kundu, M. R.; White, S. M.; Shibasaki, K. +2 more
We present the results of a study of spatial structure of sources of microwave and millimeter bursts with simple spiky time profiles at 17 and 34 GHz, similar to those found to be common at 3 mm wavelength. These bursts are of short duration, with fast 2-4 s rise time to peak, followed by a rapid exponential decay. When mapped at high spatial reso…
Molecular Gas in Optically Selected Mergers
Yun, Min S.; Hibbard, J. E.
We have mapped the 2.6 mm CO J=1-->0 emission in three optically selected ``Toomre sequence'' mergers (NGC 520, NGC 3921, NGC 4676). The molecular gas distribution is well resolved by the observations. For NGC 520 and NGC 4676A, the nuclear gas concentrations form a disklike or a ringlike structure, and the gas kinematics are regular and consis…
Supernova 1991T and the Value of the Hubble Constant
Gibson, Brad K.; Stetson, Peter B.
Based on multiepoch Hubble Space Telescope observations, we present the discovery of 16 high-quality Cepheid candidates in NGC 4527. Corrected for metallicity effects in the Cepheid period-luminosity relation, we derive a distance, including both random (r) and systematic (s) uncertainties, of 13.0+/-0.5(r)+/-1.2(s) Mpc. Our result is then used to…