Search Publications
Measuring Star Formation Histories, Distances, and Metallicities with Pixel Color-Magnitude Diagrams. II. Applications to Nearby Elliptical Galaxies
van Dokkum, Pieter; Conroy, Charlie; Cook, B. A.
We present spatially resolved measurements of star formation histories (SFHs), metallicities, and distances in three nearby elliptical galaxies and the bulge of M31 derived using the pixel color-magnitude diagram (pCMD) technique. We compute pCMDs from archival Hubble Space Telescope photometry of M87, M49, NGC 3377, and M31, and we fit the data u…
On the Origin of Metal-poor Stars in the Solar Neighborhood
Bilir, Selçuk; Şahin, Timur
We determined the ages, kinematic parameters, and Galactic orbital parameters of six metal-poor (-2.4 < [Fe/H] < -1.0 dex), F-type, high-proper-motion (HPM) stars to investigate their HPM nature and origin. For the kinematical procedure, the astrometric data from the Gaia DR2 were used. High-resolution ELODIE spectra of the six dwarfs were a…
Chromospheric Magnetic Field: A Comparison of He I 10830 Å Observations with Nonlinear Force-free Field Extrapolation
Shimizu, Toshifumi; Asensio Ramos, Andrés; Inoue, Satoshi +1 more
The nonlinear force-free field (NLFFF) modeling has been extensively used to infer the three-dimensional magnetic field in the solar corona. One of the assumptions in the NLFFF extrapolation is that the plasma beta is low, but this condition is considered to be incorrect in the photosphere. We examine direct measurements of the chromospheric magne…
On the Nature of the T Tauri Triple System
Chapillon, E.; Schaefer, G. H.; Guilloteau, S. +4 more
We present a multiwavelength analysis to reveal the nature of the enigmatic T Tauri triple star system. New optical and infrared measurements are coupled with archival X-ray, UV, and millimeter data sets to show the morphologies of disk material and outflow kinematics. A dark lane of obscuring material is seen in silhouette in several emission lin…
Physical Conditions of Gas Components in Debris Disks of 49 Ceti and HD 21997
Moór, Attila; Kóspál, Ágnes; Nomura, Hideko +2 more
Characterization of the gas component in debris disks is of fundamental importance for understanding their origin. To address this goal, we have conducted non-LTE (local thermodynamic equilibrium) analyses of the rotational spectral lines of CO including those of rare isotopologues (13CO and C18O) that have been observed towa…
Geometry of the Draco C1 Symbiotic Binary
Sarazin, Craig L.; Cunha, Katia; Smith, Verne V. +14 more
Draco C1 is a known symbiotic binary star system composed of a carbon red giant and a hot, compact companion—likely a white dwarf—belonging to the Draco dwarf spheroidal galaxy. From near-infrared spectroscopic observations taken by the Apache Point Observatory Galactic Evolution Experiment (APOGEE-2), part of Sloan Digital Sky Survey IV, we provi…
EVR-CB-004: An Inflated Hot Subdwarf O Star + Unseen WD Companion in a Compact Binary Discovered with the Evryscope
Law, Nicholas M.; Kupfer, Thomas; Glazier, Amy +10 more
We present the discovery of EVR-CB-004, a close binary with a remnant stellar core and an unseen white dwarf (WD) companion. The analysis in this work reveals that the primary is potentially an inflated hot subdwarf (sdO) and more likely is a rarer post-blue horizontal branch (post-BHB) star. Post-BHBs are the short-lived shell-burning final stage…
Solar Filaments and Interplanetary Magnetic Field Bz
Martens, Petrus C.; Aparna, V.
The direction of the axis of an interplanetary coronal mass ejection (ICME) plays an important role in determining if it will cause a geomagnetic disturbance in the Earth's magnetosphere upon impact. Long period southward-pointing ICME fields are known to cause significant space weather impacts and thus geomagnetic storms. We present an extensive …
A New Transition Wolf-Rayet WN/C Star in the Milky Way
Shi, Jianrong; Zhang, Tianmeng; Todt, Helge +7 more
We report the discovery of a new transition type Wolf-Rayet (W-R) WN/C star in the Galaxy. According to its coordinates (R.A., decl.)J2000 = ${18}^{{\rm{h}}}{51}^{{\rm{m}}}39\buildrel{\rm{s}}\over{.} 7$ , -05°34'51"1, and the distance (7.11 ${}_{-1.22}^{+1.56}\,$ kpc away from Earth) inferred from the second Gaia data release, it is fou…
Quantifying the Toroidal Flux of Preexisting Flux Ropes of Coronal Mass Ejections
Qiu, Jiong; Cheng, X.; Ding, M. D. +3 more
In past decades, much progress has been achieved in understanding the origin and evolution of coronal mass ejections (CMEs). In situ observations of the counterparts of CMEs, especially magnetic clouds (MCs) near the Earth, have provided measurements of the structure and total flux of CME flux ropes. However, it has been difficult to measure these…