Search Publications
Ultralow-amplitude RR Lyrae Stars in M4
Wallace, Joshua J.; Hartman, Joel D.; Bakos, Gáspár Á. +1 more
We report evidence for a new class of variable star, which we dub millimagnitude RR Lyrae (mmRR). From K2 observations of the globular cluster M4, we find that out of 24 horizontal branch stars not previously known to be RR Lyrae variables, two show photometric variability with periods and shapes consistent with those of first-overtone RR Lyrae va…
Dependence of Galactic Halo Kinematics on the Adopted Galactic Potential
Beers, Timothy C.; Lee, Young Sun; Kim, Young Kwang
We explore differences in Galactic halo kinematic properties derived from two commonly employed Galactic potentials: the Stäckel potential and the default Milky Way-like potential used in the “Galpy” package (MWPotential2014), making use of stars with available metallicities, radial velocities, and proper motions from Sloan Digital Sky Survey Data…
The Two Most Recent Thermonuclear Supernovae in the Local Group: Radio Constraints on their Progenitors and Evolution
Chomiuk, Laura; Badenes, Carles; Tremou, Evangelia +3 more
Young supernova remnants (SNRs) provide a unique perspective on supernova (SN) progenitors and connect the late evolution of SNe with the onset of the SNR phase. Here we study SN 1885A and G1.9+0.3, the most recent thermonuclear SNe in the Local Group (with ages ∼100 yr) with radio data, which provide a sensitive probe of the SN environment and en…
New Spatially Resolved Imaging of the SR 21 Transition Disk and Constraints on the Small-grain Disk Geometry
van der Marel, N.; Ireland, M. J.; Puglisi, A. +9 more
We present new 0.6-4 µm imaging of the SR 21 transition disk from Keck/NIRC2 and Magellan/MagAO. The protoplanetary disk around SR 21 has a large (∼30-40 au) clearing first inferred from its spectral energy distribution and later detected in submillimeter imaging. Both the gas and small dust grains are known to have a different morphology, w…
Four Metal-poor Stars in the Sagittarius Dwarf Spheroidal Galaxy
Frebel, Anna; Chiti, Anirudh
We present the metallicities and carbon abundances of four newly discovered metal-poor stars with -2.2 < [Fe/H] < -1.6 in the Sagittarius dwarf spheroidal galaxy. These stars were selected as metal-poor member candidates using a combination of public photometry from the SkyMapper Southern Sky Survey and proper-motion data from the second dat…
Modeling the Protoplanetary Disks of Two Brown Dwarfs in the Taurus Molecular Cloud
Espaillat, Catherine C.; Macías, Enrique; Rilinger, Anneliese M.
Measuring the properties of protoplanetary disks around brown dwarfs (BDs) is central to understanding the formation of BDs and their planetary companions. We present modeling of CFHT Tau 4 and 2M0444, two BDs with protoplanetary disks in the Taurus Molecular Cloud. By combining modeling of the spectral energy distributions and Atacama Large Milli…
Photometry and Spectroscopy of Faint Candidate Spectrophotometric Standard DA White Dwarfs
Rest, Armin; Matheson, Thomas; Points, Sean +14 more
We present precise photometry and spectroscopy for 23 candidate spectrophotometric standard white dwarfs. The selected stars are distributed in the Northern hemisphere and around the celestial equator, and are all fainter than r ∼ 16.5 mag. This network of stars, when established as standards and together with the three Hubble Space Telescope prim…
MCMC Inversion of Stokes Profiles
Sun, Leilei; Xu, Zhi; Li, Hao +1 more
Stokes inversion techniques, based on the analysis of the polarization in spectral lines, are the most powerful tools to obtain the information about the magnetic and thermodynamic quantities in the solar atmosphere. In this paper, we present a Milne-Eddington inversion code based on Bayesian inference, which is implemented with the Markov chain M…
Formation and Eruption of Sigmoidal Structure from a Weak Field Region of NOAA 11942
Ravindra, B.; Doddamani, V. H.; Vemareddy, P. +1 more
Using observations from the Solar Dynamics Observatory, we studied an interesting example of a sigmoid formation and eruption from small-scale flux-canceling regions of active region (AR) 11942. Through an analysis of Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly observations we infer that initially the AR is compact and bipola…
Observations of the Ultra-compact X-Ray Binary 4U 1543-624 in Outburst with NICER, INTEGRAL, Swift, and ATCA
Altamirano, D.; Fabian, A. C.; Miller, J. M. +17 more
We report on X-ray and radio observations of the ultra-compact X-ray binary 4U 1543-624 taken in August 2017 during an enhanced accretion episode. We obtained Neutron Star Interior Composition Explorer (NICER) monitoring of the source over a ∼10 day period during which target-of-opportunity observations were also conducted with Swift, INTErnationa…