Search Publications
Revisiting the Spectral and Timing Properties of NGC 4151
Miller, J. M.; Zoghbi, A.; Cackett, E.
NGC 4151 is the brightest Seyfert 1 nucleus in X-rays. It was the first object to show short time delays in the Fe K band, which were attributed to relativistic reverberation, providing a new tool for probing regions at the black hole scale. Here we report the results of a large XMM-Newton campaign in 2015 to study these short delays further. Anal…
WOBBLE: A Data-driven Analysis Technique for Time-series Stellar Spectra
Hogg, David W.; Foreman-Mackey, Daniel; Bedell, Megan +2 more
In recent years, dedicated extreme precision radial velocity (RV) spectrographs have produced vast quantities of high-resolution, high-signal-to-noise (S/N) time-series spectra for bright stars. These data contain valuable information for the dual purposes of planet detection via the measured RVs and stellar characterization via the coadded spectr…
A massive white-dwarf merger product before final collapse
Langer, Norbert; Kniazev, Alexei Y.; Gvaramadze, Vasilii V. +4 more
Gravitational-wave emission can lead to the coalescence of close pairs of compact objects orbiting each other1,2. In the case of neutron stars, such mergers may yield masses above the Tolman-Oppenheimer-Volkoff limit (2 to 2.7 solar masses)3, leading to the formation of black holes4. For white dwarfs, the mass of t…
Self-lensing Discovery of a 0.2 M ⊙ White Dwarf in an Unusually Wide Orbit around a Sun-like Star
Bieryla, Allyson; Latham, David W.; Aoki, Wako +4 more
We report the discovery of the fifth self-lensing binary in which a low-mass white dwarf (WD) gravitationally magnifies its 15th magnitude G-star companion, KIC 8145411, during eclipses. The system was identified from a pair of such self-lensing events in the Kepler photometry, and was followed up with the Tillinghast Reflector Echelle Spectrograp…
A method for global inversion of multi-resolution solar data
de la Cruz Rodríguez, J.
Understanding the complex dynamics and structure of the upper solar atmosphere strongly benefits from the use of a combination of several diagnostics. Frequently, such diverse diagnostics can only be obtained from telescopes and/or instrumentation operating at widely different spatial resolution. To optimize the utilization of such data, we propos…
Spectral Analysis of the September 2017 Solar Energetic Particle Events
de Nolfo, G. A.; Christian, E. R.; Ryan, J. M. +2 more
An interval of exceptional solar activity was registered in early September 2017, late in the decay phase of solar cycle 24, involving the complex Active Region 12673 as it rotated across the western hemisphere with respect to Earth. A large number of eruptions occurred between 4 and 10 September, including four associated with X-class flares. The…
Comparison of Gaia DR2 Parallaxes of Stars with VLBI Astrometry
Reid, Mark J.; Zhang, Bo; Xu, Shuangjing +2 more
We compare the parallaxes of stars from VLBI astrometry in the literature to those in the Gaia DR2 catalog. Our full sample contains young stellar objects, evolved AGB stars, pulsars, and other radio stars. Excluding AGB stars, which show significant discrepancies between Gaia and VLBI parallaxes, and stars in binary systems, we obtain an average,…
On the Use of Field RR Lyrae as Galactic Probes. I. The Oosterhoff Dichotomy Based on Fundamental Variables
Valenti, E.; Marinoni, S.; Thévenin, F. +21 more
We collected a large data set of field RR Lyrae stars (RRLs) by using catalogs already available in the literature and Gaia DR2. We estimated the iron abundances for a subsample of 2382 fundamental RRLs (ΔS method: Ca II K, Hβ, Hγ, and Hδ lines) for which there are publicly available medium-resolution SDSS-SEGUE spectra. We also included similar e…
Stellar ages, masses, and radii from asteroseismic modeling are robust to systematic errors in spectroscopy
Hekker, S.; Basu, S.; Stokholm, A. +2 more
Context. The search for twins of the Sun and Earth relies on accurate characterization of stellar and the exoplanetary parameters age, mass, and radius. In the modern era of asteroseismology, parameters of solar-like stars are derived by fitting theoretical models to observational data, which include measurements of their oscillation frequencies, …
The missing light of the Hubble Ultra Deep Field
Borlaff, Alejandro; Eliche-Moral, M. Carmen; Beckman, John E. +11 more
Context. The Hubble Ultra Deep field (HUDF) is the deepest region ever observed with the Hubble Space Telescope. With the main objective of unveiling the nature of galaxies up to z ∼ 7 - 8, the observing and reduction strategy have focused on the properties of small and unresolved objects, rather than the outskirts of the largest objects, which ar…