Search Publications
Helioseismic Analysis of the Hydrogen Partition Function in the Solar Interior
Basu, Sarbani; Däppen, Werner; Nayfonov, Alan
The difference in the adiabatic gradient γ1 between inverted solar data and solar models is analyzed. To obtain deeper insight into the issues of plasma physics, the so-called intrinsic difference in γ1 is extracted, that is, the difference due to the change in the equation of state alone. Our method uses reference models bas…
A Multiwavelength Campaign on γ Cassiopeiae. III. The Case for Magnetically Controlled Circumstellar Kinematics
Smith, Myron A.; Robinson, Richard D.
In two previous papers, we have discussed simultaneous Rossi X-Ray Timing Explorer (RXTE) and Hubble Space Telescope GHRS observations made of γ Cas (B0.5e) over a full day on 1996 March 14-15. The light curves generated from these data show features that anticorrelate and led us to conclude that the star has multiple surface activity centers that…
A Variable Asymmetry in the Circumstellar Disk of HH 30
Ballester, Gilda E.; Krist, John E.; Crisp, David +13 more
We report Hubble Space Telescope observations of variability within the reflection nebulosity of HH 30, a compact bipolar nebula that is a nearly edge-on accretion disk system. A dramatic lateral asymmetry appeared in the upper reflection nebula in the spring of 1998, but was largely absent in 1994 and 1995 images. The variability timescale is muc…
Hubble Space TelescopeStudies of the WLM Galaxy. I. The Age and Metallicity of the Globular Cluster
Dolphin, Andrew E.; Mateo, Mario; Hodge, Paul W. +1 more
We have obtained V and I images of the lone globular cluster that belongs to the dwarf Local Group irregular galaxy known as WLM. The color-magnitude diagram of the cluster shows that it is a normal old globular cluster with a well-defined giant branch reaching to MV=-2.5, a horizontal branch at MV=+0.5, and a subgiant branch…
Infrared Space Observatory Observations toward the Reflection Nebula NGC 7023: A Nonequilibrium Ortho-to-Para-H2 Ratio
Rodríguez-Fernández, N. J.; Martín-Pintado, J.; Fuente, A. +3 more
We have observed the S(0), S(1), S(2), S(3), S(4), and S(5) rotational lines of molecular hydrogen (H2) toward the peak of the photodissociation region (PDR) associated with the reflection nebula NGC 7023. The observed H2 line ratios show that they arise in warm gas with kinetic temperatures ~300-700 K. However, the data cann…
Evolution of the Light Echo of SN 1991T
Panagia, N.; Della Valle, M.; Sparks, W. B. +4 more
Schmidt et al. presented strong evidence (photometry and spectroscopy) that the late time optical emission of SN 1991T in the Virgo spiral NGC 4527 is caused by a light echo. Here, we present photometry with the Wide Field and Planetary Camera 2 and high-resolution imaging polarimetry and photometry with the Faint Object Camera on board the Hubble…
Does the Sun Have a Full-Time Chromosphere?
Kalkofen, Wolfgang; Ulmschneider, Peter; Avrett, Eugene H.
The successful modeling of the dynamics of H2v bright points in the nonmagnetic chromosphere by Carlsson & Stein gave as a by-product a part-time chromosphere lacking the persistent outward temperature increase of time-average empirical models, which is needed to explain observations of UV emission lines and continua. We discuss the…
Fractal Analysis of Michelson Doppler Imager Magnetograms: A Contribution to the Study of the Formation of Solar Active Regions
Meunier, N.
In this paper a fractal analysis of active regions observed by the Michelson Doppler Imager (MDI) instrument on the SOHO spacecraft is performed. The purpose of such an analysis is to study the shape of these magnetic regions via their fractal dimension, which characterizes their complexity, and to deduce some information on the processes that led…
Infrared Space Observatory Observations of IRAS 16594-4656: A New Proto-Planetary Nebula with a Strong 21 Micron Dust Feature
Manteiga, Minia; García-Lario, Pedro; Manchado, Arturo +1 more
Based on ISO short-wavelength spectrograph (SWS) + long-wavelength spectrograph (LWS) observations, IRAS 16594-4656 is identified as a new member of the rare class of C-rich proto-planetary nebulae with the 21 µm dust feature in emission. In addition, the major polycyclic aromatic hydrocarbon (PAH) emission bands at 3.3, 6.2, 7.7, 8.6, and 1…
Hubble Space Telescope Observations of the Dusty Small Magellanic Cloud H II Region N88A
Garnett, D. R.; Skillman, E. D.; Dufour, R. J. +5 more
We present results from the analysis of Hubble Space Telescope Faint Object Spectrograph (FOS), WFPC1, IUE, and Cerro Tololo Inter-American Observatory 4 m observations of the morphology, physical conditions, and chemical abundances in the anomalous H II region N88A in the Small Magellanic Cloud. Not only is N88A unusual among SMC H II regions bec…