Search Publications
Elongation of Flare Ribbons
Qiu, Jiong; Longcope, Dana W.; Cassak, Paul A. +1 more
We present an analysis of the apparent elongation motion of flare ribbons along the polarity inversion line (PIL), as well as the shear of flare loops in several two-ribbon flares. Flare ribbons and loops spread along the PIL at a speed ranging from a few to a hundred km s-1. The shear measured from conjugate footpoints is consistent wi…
Luminous and Variable Stars in M31 and M33. IV. Luminous Blue Variables, Candidate LBVs, B[e] Supergiants, and the Warm Hypergiants: How to Tell Them Apart
Humphreys, Roberta M.; Gordon, Michael S.; Martin, John C. +2 more
In this series of papers we have presented the results of a spectroscopic survey of luminous stars in the nearby spirals M31 and M33. Here, we present spectroscopy of 132 additional stars. Most have emission-line spectra, including luminous blue variables (LBVs) and candidate LBVs, Fe II emission line stars, the B[e] supergiants, and the warm hype…
Absolute Ages and Distances of 22 GCs Using Monte Carlo Main-sequence Fitting
Chaboyer, Brian; O'Malley, Erin M.; Gilligan, Christina
The recent Gaia Data Release 1 of stellar parallaxes provides ample opportunity to find metal-poor main-sequence stars with precise parallaxes. We select 21 such stars with parallax uncertainties better than σ π /π ≤ 0.10 and accurate abundance determinations suitable for testing metal-poor stellar evolution models and determining the …
The Sirius System and Its Astrophysical Puzzles: Hubble Space Telescope and Ground-based Astrometry
Schaefer, Gail H.; Bond, Howard E.; Burleigh, Matthew R. +11 more
Sirius, the seventh-nearest stellar system, is a visual binary containing the metallic-line A1 V star Sirius A, the brightest star in the sky, orbited in a 50.13 year period by Sirius B, the brightest and nearest white dwarf (WD). Using images obtained over nearly two decades with the Hubble Space Telescope (HST), along with photographic observati…
The PdBI Arcsecond Whirlpool Survey (PAWS): The Role of Spiral Arms in Cloud and Star Formation
Leroy, Adam K.; Meidt, Sharon E.; Hughes, Annie +9 more
The process that leads to the formation of the bright star-forming sites observed along prominent spiral arms remains elusive. We present results of a multi-wavelength study of a spiral arm segment in the nearby grand-design spiral galaxy M51 that belongs to a spiral density wave and exhibits nine gas spurs. The combined observations of the (ioniz…
Evidence for a Time Lag in Solar Modulation of Galactic Cosmic Rays
Tomassetti, Nicola; Orcinha, Miguel; Barão, Fernando +1 more
The solar modulation effect of cosmic rays in the heliosphere is an energy-, time-, and particle-dependent phenomenon that arises from a combination of basic particle transport processes such as diffusion, convection, adiabatic cooling, and drift motion. Making use of a large collection of time-resolved cosmic-ray data from recent space missions, …
Mass-loss Rates from Coronal Mass Ejections: A Predictive Theoretical Model for Solar-type Stars
Cranmer, Steven R.
Coronal mass ejections (CMEs) are eruptive events that cause a solar-type star to shed mass and magnetic flux. CMEs tend to occur together with flares, radio storms, and bursts of energetic particles. On the Sun, CME-related mass loss is roughly an order of magnitude less intense than that of the background solar wind. However, on other types of s…
Chandra and JVLA Observations of HST Frontier Fields Cluster MACS J0717.5+3745
Churazov, E.; Zitrin, A.; Rosati, P. +24 more
To investigate the relationship between thermal and non-thermal components in merger galaxy clusters, we present deep JVLA and Chandra observations of the HST Frontier Fields cluster MACS J0717.5+3745. The Chandra image shows a complex merger event, with at least four components belonging to different merging subclusters. Northwest of the cluster,…
Signatures of Nitrogen Chemistry in Hot Jupiter Atmospheres
Madhusudhan, Nikku; MacDonald, Ryan J.
Inferences of molecular compositions of exoplanetary atmospheres have generally focused on carbon, hydrogen, and oxygen-bearing molecules. Recently, additional absorption in Hubble Space Telescope Wide Field Camera 3 (WFC3) transmission spectra around 1.55 µm has been attributed to nitrogen-bearing chemical species: NH3 or HCN. Th…
Surface Gravities for 228 M, L, and T Dwarfs in the NIRSPEC Brown Dwarf Spectroscopic Survey
Kirkpatrick, J. Davy; Burgasser, Adam J.; Logsdon, Sarah E. +6 more
We combine 131 new medium-resolution (R ∼ 2000) J-band spectra of M, L, and T dwarfs from the Keck NIRSPEC Brown Dwarf Spectroscopic Survey (BDSS) with 97 previously published BDSS spectra to study surface-gravity-sensitive indices for 228 low-mass stars and brown dwarfs spanning spectral types M5-T9. Specifically, we use an established set of spe…