Search Publications
Testing Metal-Poor Stellar Models and Isochrones with HST Parallaxes of Metal-Poor Stars
McArthur, B. E.; Benedict, G. F.; Sarajedini, A. +7 more
Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H] < -1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes rangi…
DDO 216-A1: A Central Globular Cluster in a Low-luminosity Transition-type Galaxy
Dolphin, Andrew E.; Skillman, Evan D.; Williams, Benjamin F. +11 more
We confirm that the object DDO 216-A1 is a substantial globular cluster at the center of Local Group galaxy DDO 216 (the Pegasus dwarf irregular), using Hubble Space Telescope ACS imaging. By fitting isochrones, we find the cluster metallicity [M/H] = -1.6 ± 0.2, for reddening E(B-V) = 0.16 ± 0.02 the best-fit age is 12.3 ± 0.8 Gyr. There are ≈ 30…
Shocks and Tides Quantified in the “Sausage” Cluster, CIZA J2242.8+5301 Using N-body/Hydrodynamical Simulations
Broadhurst, T.; Molnar, S. M.
The colliding cluster, CIZA J2242.8+5301, displays a spectacular, almost 2 Mpc long shock front with a radio based Mach number M≃ 5, that is puzzlingly large compared to the X-ray estimate of M≃ 2.5. The extent to which the X-ray temperature jump is diluted by cooler unshocked gas projected through the cluster currently lacks quantification. Here …
On the Origin of the Flare Emission in IRIS’ SJI 2832 Filter:Balmer Continuum or Spectral Lines?
Krucker, Säm; Heinzel, Petr; Kleint, Lucia
Continuum (“white-light,” WL) emission dominates the energetics of flares. Filter-based observations, such as the IRIS SJI 2832 filter, show WL-like brightenings during flares, but it is unclear whether the emission arises from real continuum emission or enhanced spectral lines, possibly turning into emission. The difficulty in filter-based observ…
No Sign of Strong Molecular Gas Outflow in an Infrared-bright Dust-obscured Galaxy with Strong Ionized-gas Outflow
Imanishi, Masatoshi; Toba, Yoshiki; Nagao, Tohru +4 more
We report the discovery of an infrared (IR)-bright dust-obscured galaxy (DOG) that shows a strong ionized-gas outflow but no significant molecular gas outflow. Based on detailed analysis of their optical spectra, we found some peculiar IR-bright DOGs that show strong ionized-gas outflow ([O III] λ5007) from the central active galactic nucleus (AGN…
Evidence for Relativistic Disk Reflection in the Seyfert 1h Galaxy/ULIRG IRAS 05189-2524 Observed by NuSTAR and XMM-Newton
Walton, Dominic J.; García, Javier A.; Harrison, Fiona A. +3 more
We present a spectral analysis of the NuSTAR and XMM-Newton observations of the Seyfert 1h galaxy/ULIRG IRAS 05189-2524 taken in 2013. We find evidence for relativistic disk reflection in the broadband X-ray spectrum: a highly asymmetric broad Fe Kα emission line extending down to 3 keV and a Compton scattering component above 10 keV. Physical mod…
Simultaneous Observations of p-mode Light Walls and Magnetic Reconnection Ejections above Sunspot Light Bridges
Hou, Yijun; Li, Ting; Yang, Shuhong +2 more
Recent high-resolution observations from the Interface Region Imaging Spectrograph reveal bright wall-shaped structures in active regions (ARs), especially above sunspot light bridges. Their most prominent feature is the bright oscillating front in the 1400/1330 Å channel. These structures are named light walls and are often interpreted to be driv…
The Three-part Structure of a Filament-unrelated Solar Coronal Mass Ejection
Chen, Y.; Li, B.; Song, H. Q. +6 more
Coronal mass ejections (CMEs) often exhibit the typical three-part structure in the corona when observed with white-light coronagraphs, I.e., the bright leading front, dark cavity, and bright core, corresponding to a high-low-high density sequence. As CMEs result from eruptions of magnetic flux ropes (MFRs), which can possess either lower (e.g., c…
NGC 741—Mergers and AGN Feedback on a Galaxy-group Scale
Giacintucci, S.; O'Sullivan, E.; David, L. +5 more
Low-mass galaxy cluster systems and groups will play an essential role in upcoming cosmological studies, such as those to be carried out with eROSITA. Though the effects of active galactic nuclei (AGNs) and merging processes are of special importance to quantify biases like selection effects or deviations from hydrostatic equilibrium, they are poo…
A Nonthermal Radio Filament Connected to the Galactic Black Hole?
Morris, Mark R.; Goss, W. M.; Zhao, Jun-Hui
Using the Very Large Array, we have investigated a nonthermal radio filament (NTF) recently found very near the Galactic black hole and its radio counterpart, Sgr A*. While this NTF—the Sgr A West Filament (SgrAWF)—shares many characteristics with the population of NTFs occupying the central few hundred parsecs of the Galaxy, the SgrAWF has the di…