Search Publications
HST/COS Observations of the Warm Ionized Gaseous Halo of NGC 891
Bregman, Joel N.; Qu, Zhijie; Hodges-Kluck, Edmund J.
The metallicity of galactic gaseous halos provides insights into accretion and feedback of galaxies. The nearby edge-on galaxy NGC 891 has a multicomponent gaseous halo and a background active galactic nucleus (AGN; LQAC 035+042 003) projected 5 kpc above the disk near the minor axis. Against the UV continuum of this AGN, we detect lines from 13 i…
Onset and Evolution of the Oblique, Resonant Electron Firehose Instability in the Expanding Solar Wind Plasma
Velli, Marco; Innocenti, Maria Elena; Tenerani, Anna +1 more
A double adiabatically expanding solar wind would quickly develop large parallel to perpendicular temperature anisotropies in electrons and ions that are not observed. One reason is that firehose instabilities would be triggered, leading to an ongoing driving/saturation evolution mechanism. We verify this assumption here for the first time for the…
The Variability of Solar Coronal Abundances in Active Regions and the Quiet Sun
Doschek, G. A.; Warren, H. P.
Measurements of elemental abundances hold important clues to how mass and energy flow through the solar atmosphere. Variations in abundances are organized by an element’s first ionization potential (FIP), and many previous studies have assumed that low FIP (less than 10 eV) elements are enriched by a factor of 3-4 in the corona. In this paper, we …
Optical Counterparts of ULXs and Their Host Environments in NGC 4490/4485
Balman, Şölen; Fabrika, Sergei; Akyuz, Aysun +6 more
We report the identification of the possible optical counterparts of five out of seven ultraluminous X-ray sources (ULXs) in the galaxy pair NGC 4490/4485. Using archival Hubble Space Telescope (HST) imaging data, we identified a single optical candidate for two ULXs (X-4 and X-7) and multiple optical candidates for the other three (X-2, X-3, and …
S and VV Corona Australis: Spectroscopic Variability in Two Young Binary Star Systems
Edwards, Suzan; Schaefer, Gail H.; Prato, L. +2 more
We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, taken over multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis and VV Corona Australis. The stars in these 1″-2″ separation systems have optically thick circumstellar disks and high extincti…
On the Possible Mechanism of GLE Initiation
Gan, W. Q.; Rodríguez-Pacheco, J.; Li, Y. P. +2 more
With the goal of understanding the initiations of solar energetic particle (SEP) (MeV) and ground-level enhancement (GLE) (GeV) particles, we have studied relative timings at approximately the Sun between temporal evolutions of the particles and some electromagnetic radiation components representing flares and shocks. Results show that GLE onsets …
An Efficient Spectral Selection of M Giants Using XGBoost
Luo, A. -Li; Yi, Zhenping; Chen, Zesheng +4 more
In optical bands, the spectra of M giants often overlap with those of M dwarfs due to their similarities, especially for low or moderate resolution spectra. Traditionally, several feature indices, such as Na I, CaH, TiO5, and K I, are used to distinguish between M giants and M dwarfs. However, these features are selected by experience based on a s…
Comparison of the Asteroseismic Mass Scale of Red Clump Giants with Photometric Mass Estimates
Pinsonneault, Marc H.; Terndrup, Donald M.; Chung, Chul +1 more
Asteroseismology can provide joint constraints on masses and radii of individual stars. While this approach has been extensively tested for red giant branch (RGB) stars, it has been more difficult to test for helium core-burning red clump (RC) giants because of the lack of fundamental calibrators. To provide independent mass estimates, we utilize …
SOFIA/FORCAST Observations of the Sgr A-H H II Regions: Using Dust Emission to Elucidate the Heating Sources
Morris, M. R.; Mills, E. A. C.; Lau, R. M. +2 more
The Sgr A-H H II regions are a collection of sources that may represent one of the most recent sites of star formation in the Galactic center (GC). Examining these H II regions provides important information on the prevalence and distribution of massive stars in the region and may provide clues on the origin of other massive field stars throughout…
Modeling the Spatial Distribution and Origin of CO Gas in Debris Disks
Gorti, Uma; Carpenter, John M.; Hales, A. S. +2 more
The detection of gas in debris disks raises the question of whether this gas is a remnant from the primordial protoplanetary phase, or released by the collision of secondary bodies. In this paper we analyze ALMA observations at 1″-1.″5 resolution of three debris disks where the 12CO(2-1) rotational line was detected: HD 131835, HD 13881…