Search Publications
Low-mass X-Ray Binaries Indicate a Top-heavy Stellar Initial Mass Function in Ultracompact Dwarf Galaxies
Mieske, Steffen; Kroupa, Pavel; Pflamm-Altenburg, Jan +1 more
It has been shown before that the high mass-to-light ratios of ultracompact dwarf galaxies (UCDs) can be explained if their stellar initial mass function (IMF) was top-heavy, i.e., that the IMF was skewed toward high-mass stars. In this case, neutron stars (NSs) and black holes would provide unseen mass in the UCDs. In order to test this scenario …
The Pair Fraction of Massive Galaxies at 0 <= z <= 3
van der Wel, Arjen; Zirm, Andrew W.; Wuyts, Stijn +2 more
Using a mass-selected (M sstarf >= 1011 M ⊙) sample of 198 galaxies at 0 <= z <= 3.0 with Hubble Space Telescope/NICMOS H 160-band images from the COSMOS survey, we find evidence for the evolution of the pair fraction above z ~ 2, an epoch in which massive galaxies are believed to undergo signif…
The Contribution of TP-AGB and RHeB Stars to the Near-IR Luminosity of Local Galaxies: Implications for Stellar Mass Measurements of High-redshift Galaxies
Williams, Benjamin F.; Boyer, Martha L.; Girardi, Léo +9 more
Using high spatial resolution Hubble Space Telescope WFC3 and Advanced Camera for Surveys imaging of resolved stellar populations, we constrain the contribution of thermally pulsing asymptotic giant branch (TP-AGB) stars and red helium burning (RHeB) stars to the 1.6 µm near-infrared (NIR) luminosities of 23 nearby galaxies, including dwarfs…
A Study of the Dark Core in A520 with the Hubble Space Telescope: The Mystery Deepens
Dalcanton, J. J.; Capak, P.; Hoekstra, H. +4 more
We present a Hubble Space Telescope/Wide Field Planetary Camera 2 weak-lensing study of A520, where a previous analysis of ground-based data suggested the presence of a dark mass concentration. We map the complex mass structure in much greater detail, leveraging more than a factor of three increase in the number density of source galaxies availabl…
Hubble Space Telescope Measures of Mass Accretion Rates in the Orion Nebula Cluster
Lodato, G.; Robberto, M.; Da Rio, N. +4 more
The present observational understanding of the evolution of the mass accretion rates (\dot{M}_acc) in pre-main-sequence stars is limited by the lack of accurate measurements of \dot{M}_acc over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk e…
Rapid Changes of Photospheric Magnetic Field after Tether-cutting Reconnection and Magnetic Implosion
Xu, Yan; Liu, Chang; Jing, Ju +6 more
The rapid, irreversible change of the photospheric magnetic field has been recognized as an important element of the solar flare process. This Letter reports such a rapid change of magnetic fields during the 2011 February 13 M6.6 flare in NOAA AR 11158 that we found from the vector magnetograms of the Helioseismic and Magnetic Imager (HMI) with 12…
Late-time Optical Emission from Core-collapse Supernovae
Chevalier, Roger A.; Kirshner, Robert P.; Challis, Peter +3 more
Ground-based optical spectra and Hubble Space Telescope images of 10 core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted l…
On the Migration of Jupiter and Saturn: Constraints from Linear Models of Secular Resonant Coupling with the Terrestrial Planets
Lin, D. N. C.; Agnor, Craig B.
We examine how the late divergent migration of Jupiter and Saturn may have perturbed the terrestrial planets. Using a modified secular model we have identified six secular resonances between the ν5 frequency of Jupiter and Saturn and the four apsidal eigenfrequencies of the terrestrial planets (g 1-4). We derive analytic uppe…
Galaxy-scale Star Formation on the Red Sequence: The Continued Growth of S0s and the Quiescence of Ellipticals
Faber, S. M.; Salim, Samir; Rich, R. Michael +2 more
This paper examines star formation (SF) in relatively massive, primarily early-type galaxies (ETGs) at z ~ 0.1. A sample is drawn from bulge-dominated Galaxy Evolution Explorer/Sloan Digital Sky Survey (GALEX/SDSS) galaxies on the optical red sequence with strong UV excess and yet quiescent SDSS spectra. High-resolution far-UV imaging of 27 such E…
Photospheric Flux Cancellation and the Build-up of Sigmoidal Flux Ropes on the Sun
van Ballegooijen, A. A.; Green, L. M.; DeLuca, E. E. +1 more
In this study we explore the scenario of photospheric flux cancellation being the primary formation mechanism of sigmoidal flux ropes in decaying active regions. We analyze magnetogram and X-ray observations together with data-driven non-linear force-free field (NLFFF) models of observed sigmoidal regions to test this idea. We measure the total an…