Search Publications
Rapid Submillimeter Brightenings Associated with a Large Solar Flare
Rovira, M.; Costa, J. E. R.; Levato, H. +8 more
We present high time resolution observations of Active Region 8910 obtained simultaneously at 212 and 405 GHz during a large Hα flare, which produced a soft X-ray class X1.1 event. Data were obtained with the new solar submillimeter telescope recently installed at the El Leoncito Observatory to explore this poorly known part of the solar emission …
Scattered Light Models of Protostellar Envelopes: Multiple Outflow Cavities and Misaligned Circumstellar Disks
Wood, Kenneth; Wolff, Michael J.; Bjorkman, Karen S. +4 more
Ground-based imaging, imaging polarimetry, and recent Hubble Space Telescope WFPC2 and NICMOS images of protostars have revealed very complex scattered light patterns that cannot be entirely explained by two-dimensional radiation transfer models. We present here for the first time radiation transfer models of T Tau and IRAS 04016+2610 that are ful…
The Planetary Nebula A39: An Observational Benchmark for Numerical Modeling of Photoionized Plasmas
Korista, Kirk T.; Jacoby, George. H.; Ferland, Gary. J.
Galactic nebulae are the main probes for the chemical evolution of the interstellar medium. Yet, recent observations have shown that chemical abundances determined from recombination and collisionally excited emission lines can differ by as much as an order of magnitude in some planetary nebulae (PNs). Many PNs have complex geometries and morpholo…
A Spectroscopic Study of Component C and the Extended Emission around I Zw 18
Green, Richard F.; Chaffee, Frederic H.; Thuan, Trinh X. +5 more
Long-slit Keck II,1 4 m Kitt Peak,2 and 4.5 m MMT3 spectrophotometric data are used to investigate the stellar population and the evolutionary status of I Zw 18C, the faint C component of the nearby blue compact dwarf galaxy I Zw 18. Hydrogen Hα and Hβ emission lines are detected in the spectra of I Zw 18C, which implies that ionizing massive star…
Reconciling Extreme-Ultraviolet and Radio Observations of the Sun's Corona
Zhang, J.; Kundu, M. R.; White, S. M. +2 more
The Sun's corona, which is composed of plasma at a temperature of a few millions of degrees, can be best viewed in two electromagnetic domains, one from wavelengths of a few angstroms to hundreds of angstroms (in the soft X-ray and EUV domain), the other from wavelengths of a few centimeters to several tens of centimeters (in the radio domain). In…
Identification and Analysis of Young Star Cluster Candidates in M31
Williams, Benjamin F.; Hodge, Paul W.
We present a method for finding clusters of young stars in M31 using broadband WFPC2 data from the HST data archive. Applying our identification method to 13 WFPC2 fields, covering an area of ~60 arcmin2, has revealed 79 new candidate young star clusters in these portions of the M31 disk. Most of these clusters are small (<~5 pc), yo…
Circumnuclear Spiral Arms and Starburst Rings in Magnetized Barred Spiral Galaxies
Fan, Zuhui; Lou, Yu-Qing; Yuan, Chi +1 more
The Seyfert galaxy NGC 1097 has a prominent bar and a luminous circumnuclear starburst ``ring.'' Magnetic fields as revealed by nonthermal radio continuum emissions correlate well with the optical barred spiral structure on large scales, have a gross enhancement overlapping with the optical/infrared ``ring,'' and show a trailing swirl around and w…
Gas-Phase Polycyclic Aromatic Hydrocarbons in Absorption toward Protostellar Sources?
Bregman, Jesse D.; Temi, Pasquale
One of the major criticisms of identifying the infrared emission bands with polycyclic aromatic hydrocarbon (PAH) molecules has been the lack of a match between laboratory spectra of individual PAHs and the emission features. Part of the difficulty arises from the complexity of modeling the emission mechanism with an a priori unknown mixture of io…
Evidence for Expanding Superbubbles in a Galaxy at z=0.7443
Vogt, Steven S.; Charlton, Jane C.; Churchill, Christopher W. +1 more
The intervening z=0.7443 Mg II absorption system in the spectrum of MC 1331+170 shows an unusual series of line pairs, each with Δv~30 km s-1. These lines could be explained as the shells of expanding superbubbles residing in the outer regions of an edge-on spiral galaxy visible in the optical image of the MC 1331+170 field. The color a…
The Bismuth Abundance in the HGMN Stars χ Lupi and HR 7775 and Improved Atomic Data for Selected Transitions of BI I, BI II, and BI III
Leckrone, D. S.; Wahlgren, G. M.; Johansson, S. +6 more
High-resolution spectra of the chemically peculiar HgMn stars χ Lupi and HR 7775, obtained with the Hubble Space Telescope/Goddard High Resolution Spectrograph, are investigated for their abundance of bismuth by comparison with LTE synthetic spectrum modeling. HR 7775, previously known from International Ultraviolet Explorer spectra to display str…