Search Publications
Constraining the Konoplya-Rezzolla-Zhidenko deformation parameters: Limits from supermassive black hole x-ray data
Tripathi, Ashutosh; Abdikamalov, Askar B.; Ayzenberg, Dimitry +2 more
X-ray reflection spectroscopy is a powerful technique for probing the nature of gravity around black holes in the so-called strong-field regime. One popular approach is to look at theory-agnostic deviations away from the Kerr solution, which is the only astrophysically relevant black hole solution within classical general relativity, in order to v…
Internal Structure of the 2019 April 2 CME
Vourlidas, Angelos; Wood, Brian E.; Braga, Carlos R.
We present the first analysis of internal coronal mass ejection (CME) structure observed very close to the Sun by the Wide-field Imager for Solar PRobe (WISPR) instrument on board the Parker Solar Probe (PSP). The transient studied here is a CME observed during PSP's second perihelion passage on 2019 April 2, when PSP was only 40 R ⊙ fr…
Understanding X-ray and optical selection of galaxy clusters: a comparison of the XXL and CAMIRA cluster catalogues obtained in the common XXL-HSC SSP area
Okabe, N.; Chiappetti, L.; Altieri, B. +31 more
Large samples of galaxy clusters provide knowledge of both astrophysics in the most massive virialized environments and the properties of the cosmological model that defines our Universe. However, an important issue that affects the interpretation of galaxy cluster samples is the role played by the selection waveband and the potential for this to …
Detection of Al II in the Ultraviolet Spectra of Metal-poor Stars: An Empirical LTE Test of NLTE Aluminum Abundance Calculations
Roederer, Ian U.; Lawler, James E.
We report the detection of an Al II line at 2669.155 Å in 11 metal-poor stars, using ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We derive Al abundances from this line using a standard abundance analysis, assuming local thermodynamic equilibrium (LTE). The mean [Al/Fe] ratio is -0…
Multiwavelength Evidence for a New Flare-mode Transitional Millisecond Pulsar
Strader, Jay; Bahramian, Arash; Chomiuk, Laura +7 more
We report the discovery of a new low-mass X-ray binary near the center of the unassociated Fermi GeV γ-ray source 4FGL J0540.0-7552. The source shows the persistent presence of an optical accretion disk and exhibits extreme X-ray and optical variability. It also has an X-ray spectrum well-fit by a hard power law with Γ = 1.8 and a high ratio of X-…
Long Term Evolution of Surface Features on the Red Supergiant AZ Cyg
Gies, Douglas R.; Monnier, John D.; Schaefer, Gail H. +23 more
We present H-band interferometric observations of the red supergiant (RSG) AZ Cyg that were made with the Michigan Infra-Red Combiner (MIRC) at the six-telescope Center for High Angular Resolution Astronomy (CHARA) Array. The observations span 5 yr (2011-2016), which offers insight into the short and long-term evolution of surface features on RSGs…
A fully-spectroscopic triple-source-plane lens: the Jackpot completed
Collett, Thomas E.; Smith, Russell J.
We present a spectroscopic determination of the redshift of the second source in the Jackpot gravitational lens system J0946 + 1006, for which only a photometric estimate of zphot = 2.41$^{+0.04}_{-0.21}$ has previously been available. By visually inspecting an archival Very Large Telescope (VLT) X-Shooter observation, we located a sing…
WIYN Open Cluster Study. LXXXV. Li in NGC 2243: Implications for Stellar and Galactic Evolution
Twarog, Bruce A.; Anthony-Twarog, Barbara J.; Deliyannis, Constantine P.
High-dispersion spectra in the Li λ6708 region have been obtained and analyzed in the old, metal-deficient cluster NGC 2243. From Hydra spectra for 29 astrometric and radial velocity members, we derive rotational velocities, as well as [Fe/H], [Ca/H], [Si/H], and [Ni/H] based on 17, 1, 1, and 3 lines, respectively. Using ROBOSPECT, an automatic eq…
Runaway blue main-sequence stars at high Galactic latitudes. Target selection with Gaia and spectroscopic identification
Raddi, Roberto; Irrgang, Andreas; Heber, Ulrich +2 more
Context. The ESA Gaia mission is a remarkable tool for stellar population analysis through its accurate Hertzsprung-Russell diagram. Its precise astrometry has propelled detailed kinematic studies of the Milky Way and the identification of high-velocity outliers.
Aims: Motivated by the historical identification of runaway main-sequence (MS) s…
A new transient ultraluminous X-ray source in NGC 7090
Salvaterra, R.; Harrison, F. A.; Stern, D. +17 more
We report on the discovery of a new, transient ultraluminous X-ray source (ULX) in the galaxy NGC 7090. This new ULX, which we refer to as NGC 7090 ULX3, was discovered via monitoring with Swift during 2019-2020, and to date has exhibited a peak luminosity of LX ~ 6 × 1039 erg s-1. Archival searches show that, prio…