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Three-dimensional modeling of chromospheric spectral lines in a simulated active region
Cheung, Mark C. M.; Rempel, Matthias; Danilovic, Sanja +4 more
Context. Because of the complex physics that governs the formation of chromospheric lines, interpretation of solar chromospheric observations is difficult. The origin and characteristics of many chromospheric features are, because of this, unresolved.
Aims: We focus on studying two prominent features: long fibrils and flare ribbons. To model …
Distant Comet C/2017 K2 and the Cohesion Bottleneck
Mutchler, Max; Jewitt, David; Agarwal, Jessica +3 more
The distant long-period comet C/2017 K2 (PANSTARRS) has been outside the planetary region of the solar system for ∼3 Myr, negating the possibility that heat retained from the previous perihelion could be responsible for its activity. This inbound comet is also too cold for water ice to sublimate and too cold for amorphous water ice, if present, to…
Buried Black Hole Growth in IR-selected Mergers: New Results from Chandra
Ellison, Sara L.; Ricci, Claudio; Blecha, Laura +8 more
Observations and theoretical simulations suggest that a significant fraction of merger-triggered accretion onto supermassive black holes is highly obscured, particularly in late-stage galaxy mergers, when the black hole is expected to grow most rapidly. Starting with the Wide-Field Infrared Survey Explorer all-sky survey, we identified a populatio…
Comparing the Quenching Times of Faint M31 and Milky Way Satellite Galaxies
Lewis, Geraint F.; Dolphin, Andrew E.; Skillman, Evan D. +8 more
We present the star formation histories (SFHs) of 20 faint M31 satellites (-12 ≲ M V ≲ -6) that were measured by modeling sub-horizontal branch depth color-magnitude diagrams constructed from Hubble Space Telescope (HST) imaging. Reinforcing previous results, we find that virtually all galaxies quenched between 3 and 9 Gyr ago, indepe…
The EREBOS project: Investigating the effect of substellar and low-mass stellar companions on late stellar evolution. Survey, target selection, and atmospheric parameters
Geier, S.; Dreizler, S.; Heber, U. +14 more
Eclipsing post-common-envelope binaries are highly important for resolving the poorly understood, very short-lived common-envelope phase of stellar evolution. Most hot subdwarfs (sdO/Bs) are the bare helium-burning cores of red giants that have lost almost all of their hydrogen envelope. This mass loss is often triggered by common-envelope interac…
In Situ Data and Effect Correlation During September 2017 Solar Particle Event
Müller, D.; Vainio, R.; Sánchez-Cano, B. +28 more
Solar energetic particles are one of the main sources of particle radiation seen in space. In the first part of September 2017 the most active solar period of cycle 24 produced four large X-class flares and a series of (interplanetary) coronal mass ejections, which gave rise to radiation storms seen over all energies and at the ground by neutron m…
Titan as Revealed by the Cassini Radar
Rodriguez, S.; Barnes, J. W.; Soderblom, J. M. +45 more
Titan was a mostly unknown world prior to the Cassini spacecraft's arrival in July 2004. We review the major scientific advances made by Cassini's Titan Radar Mapper (RADAR) during 13 years of Cassini's exploration of Saturn and its moons. RADAR measurements revealed Titan's surface geology, observed lakes and seas of mostly liquid methane in the …
Subpercent Photometry: Faint DA White Dwarf Spectrophotometric Standards for Astrophysical Observatories
Rest, Armin; Matheson, Thomas; Points, Sean +18 more
We have established a network of 19 faint (16.5 mag < V < 19 mag) northern and equatorial DA white dwarfs (WDs) as spectrophotometric standards for present and future wide-field observatories. Our analysis infers spectral energy distribution (SED) models for the stars that are tied to the three CALSPEC primary standards. Our SED models are c…
A deep view of a fossil relic in the Galactic bulge: the Globular Cluster HP 1
Bica, E.; Nardiello, D.; Barbuy, B. +7 more
HP 1 is an α-enhanced and moderately metal-poor bulge globular cluster with a blue horizontal branch. These combined characteristics make it a probable relic of the early star formation in the innermost Galactic regions. Here, we present a detailed analysis of a deep near-infrared (NIR) photometry of HP 1 obtained with the NIR GSAOI + GeMS camera …
What the Sudden Death of Solar Cycles Can Tell Us About the Nature of the Solar Interior
Rempel, Matthias; McIntosh, Scott W.; Leamon, Robert J. +3 more
We observe the abrupt end of solar-activity cycles at the Sun's Equator by combining almost 140 years of observations from ground and space. These "terminator" events appear to be very closely related to the onset of magnetic activity belonging to the next solar cycle at mid-latitudes and the polar-reversal process at high latitudes. Using multi-s…