Search Publications
Galaxy Inclination and the IRX-β Relation: Effects on UV Star Formation Rate Measurements at Intermediate to High Redshifts
Barro, Guillermo; Pérez-González, Pablo G.; Ferguson, Henry C. +11 more
At intermediate and high redshifts, measurements of galaxy star formation rates are usually based on rest-frame ultraviolet (UV) data. A correction for dust attenuation, A UV, is needed for these measurements. This correction is typically inferred from UV spectral slopes (β) using an equation known as “Meurer's Relation.” In this paper,…
Stellar Population Diagnostics of the Massive Star Binary Fraction
Dorn-Wallenstein, Trevor Z.; Levesque, Emily M.
Populations of massive stars are directly reflective of the physics of stellar evolution. Counts of subtypes of massive stars and ratios of massive stars in different evolutionary states have been used ubiquitously as diagnostics of age and metallicity effects. While the binary fraction of massive stars is significant, inferences are often based u…
Two Solar Tornadoes Observed with the Interface Region Imaging Spectrograph
Chen, Yajie; Tian, Hui; Zhang, Jingwen +4 more
The barbs or legs of some prominences show an apparent motion of rotation, which are often termed solar tornadoes. It is under debate whether the apparent motion is a real rotating motion, or caused by oscillations or counter-streaming flows. We present analysis results from spectroscopic observations of two tornadoes by the Interface Region Imagi…
Localized Quasi-periodic Fluctuations in C II, Si IV, and Fe XXI Emission during Chromospheric Evaporation in a Flare Ribbon Observed by IRIS on 2017 September 9
Brosius, Jeffrey W.; Inglis, Andrew R.
We investigate the onset of a GOES M3.7 flare on 2017 September 9 with rapid-cadence (9.4 s) UV stare spectra obtained with IRIS in five 1″ slit segments. Our analysis is based primarily on integrated intensities and Doppler velocities of C II λ1334.5 (T ≈ 2.5 × 104 K), Si IV λ1402.7 (7.9 × 104 K), and Fe XXI λ1354.1 (1.1 × 1…
Statistical Analysis on XMM-Newton X-Ray Flares of Mrk 421: Distributions of Peak Flux and Flaring Time Duration
Wang, Jiancheng; Zhang, Pengfei; Zhang, Li +3 more
The energy dissipation mechanism in blazar jet is unknown. Blazar flares could provide insights into this problem. Here we report statistical results of XMM-Newton observations of X-ray flares in Mrk 421. We analyze all public XMM-Newton X-ray observations for Mrk 421, and construct the light curves. Through fitting the light curves, we obtain the…
Where Is the Flux Going? The Long-term Photometric Variability of Boyajian’s Star
Kochanek, C. S.; van Saders, Jennifer; Shappee, Benjamin J. +5 more
We present ∼800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ∼4000 days of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star has steadily decreased at a rate of 6.3 ± 1.4 mmag yr-1,…
The High-velocity Stars in the Local Stellar Halo from Gaia and LAMOST
Du, Cuihua; Li, Hefan; Liu, Shuai +2 more
Based on the first Gaia data release and spectroscopy from the LAMOST Data Release 4, we study the kinematics and chemistry of the local halo stars. The halo stars are identified kinematically with a relative speed of at least 220 km s-1 with respect to the local standard of rest. In total, 436 halo stars are identified. From this halo …
A Long Hard-X-Ray Look at the Dual Active Galactic Nuclei of M51 with NuSTAR
Harrison, F. A.; Hornschemeier, A. E.; Ptak, A. +14 more
We present a broadband X-ray spectral analysis of the M51 system, including the dual active galactic nuclei (AGNs) and several off-nuclear point sources. Using a deep observation by NuSTAR, new high-resolution coverage of M51b by Chandra, and the latest X-ray torus models, we measure the intrinsic X-ray luminosities of the AGNs in these galaxies. …
Steep Hard-X-Ray Spectra Indicate Extremely High Accretion Rates in Weak Emission-line Quasars
Brandt, W. N.; Luo, B.; Fan, X. +8 more
We present XMM-Newton imaging spectroscopy of 10 weak emission-line quasars (WLQs) at 0.928≤slant z≤slant 3.767, six of which are radio-quiet, and four that are radio-intermediate. The new X-ray data enabled us to measure the power-law photon index, at rest-frame energies >2 keV, in each source with relatively high accuracy. These measurements …
Asymmetry in Solar Torsional Oscillation and the Sunspot Cycle
Antia, H. M.; Nandy, Dibyendu; Lekshmi, B.
Solar torsional oscillations are migrating bands of slower- and faster-than-average rotation, which are strongly related to the Sun’s magnetic cycle. We perform a long-term study (16 yr) of hemispherical asymmetry in solar torsional oscillation velocity using helioseismic data for the first time. We study the north-south asymmetry in the velocity …