Search Publications

Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness

Harrison, F. A.; Stern, D.; Zhang, W. W. +19 more

We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ≈2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a p…

Hubble Space Telescope CALSPEC Flux Standards: Sirius (and Vega)

Bohlin, R. C.

The Space Telescope Imaging Spectrograph (STIS) has measured the flux for Sirius from 0.17 to 1.01 µm on the Hubble Space Telescope (HST) White Dwarf scale. Because of the cool debris disk around Vega, Sirius is commonly recommended as the primary IR flux standard. The measured STIS flux agrees well with predictions of a special Kurucz model…

The Dynamical Fingerprint of Core Scouring in Massive Elliptical Galaxies

Saglia, R. P.; Thomas, J.; Bender, R. +2 more

The most massive elliptical galaxies have low-density centers or cores that differ dramatically from the high-density centers of less massive ellipticals and bulges of disk galaxies. These cores have been interpreted as the result of mergers of supermassive black hole binaries, which depopulate galaxy centers by gravitationally slingshotting centr…

The climate history of early Mars: insights from the Antarctic McMurdo Dry Valleys hydrologic system

Head, James W.; Marchant, David R.

Fingerprints of Galactic Loop I on the Cosmic Microwave Background

Liu, Hao; Mertsch, Philipp; Sarkar, Subir

We investigate possible imprints of galactic foreground structures such as the "radio loops" in the derived maps of the cosmic microwave background. Surprisingly, there is evidence for these not only at radio frequencies through their synchrotron radiation, but also at microwave frequencies where emission by dust dominates. This suggests the mecha…

Highly accreting quasars: sample definition and possible cosmological implications

Marziani, P.; Sulentic, J. W.

We propose a method to identify quasars radiating closest to the Eddington limit, defining primary and secondary selection criteria in the optical, UV and X-ray spectral range based on the 4D eigenvector 1 formalism. We then show that it is possible to derive a redshift-independent estimate of luminosity for extreme Eddington ratio sources. Using …

Constraints on the Progenitor System of the Type Ia Supernova 2014J from Pre-explosion Hubble Space Telescope Imaging

Filippenko, Alexei V.; Cenko, S. Bradley; Kelly, Patrick L. +7 more

We constrain the properties of the progenitor system of the highly reddened Type Ia supernova (SN Ia) 2014J in Messier 82 (M82; d ≈ 3.5 Mpc). We determine the supernova (SN) location using Keck-II K-band adaptive optics images, and we find no evidence for flux from a progenitor system in pre-explosion near-ultraviolet through near-infrared Hubble …

Chasing the phantom: A closer look at type Ia supernovae and the dark energy equation of state

Shafer, Daniel L.; Huterer, Dragan

Some recent observations provide >2σ evidence for phantom dark energy—a value of the dark energy equation of state less than the cosmological-constant value of -1. We focus on constraining the equation of state by combining current data from the most mature geometrical probes of dark energy: type Ia supernovae (SNe Ia) from the Supernova Legacy…

Field-aligned currents in Saturn's southern nightside magnetosphere: Subcorotation and planetary period oscillation components

Coates, A. J.; Dougherty, M. K.; Alexeev, I. I. +6 more

We investigate magnetic data showing the presence of field-aligned magnetosphere-ionosphere coupling currents on 31 Cassini passes across Saturn's southern postmidnight auroral region. The currents are strongly modulated in magnitude, form, and position by the phase of the southern planetary period oscillations (PPOs). PPO-independent currents are…

Wide Cool and Ultracool Companions to Nearby Stars from Pan-STARRS 1

Chambers, Kenneth C.; Magnier, Eugene A.; Wainscoat, Richard J. +18 more

We present the discovery of 57 wide (>5'') separation, low-mass (stellar and substellar) companions to stars in the solar neighborhood identified from Pan-STARRS 1 (PS1) data and the spectral classification of 31 previously known companions. Our companions represent a selective subsample of promising candidates and span a range in spectral type…