570 research outputs found
Elucidating the Molecular Mechanisms Behind the Progression from Hepatic Steatosis to Hepatocellular Carcinoma
Implications for the Formation of Blue Straggler Stars from HST Ultraviolet Observations of NGC 188
We present results of a Hubble Space Telescope far-ultraviolet (FUV) survey
searching for white dwarf (WD) companions to blue straggler stars (BSSs) in
open cluster NGC 188. The majority of NGC 188 BSSs (15 of 21) are single-lined
binaries with properties suggestive of mass-transfer formation via Roche lobe
overflow, specifically through an asymptotic giant branch star transferring
mass to a main sequence secondary, yielding a BSS binary with a WD companion.
In NGC 188, a BSS formed by this mechanism within the past 400 Myr will have a
WD companion hot and luminous enough to be directly detected as a FUV
photometric excess with HST. Comparing expected BSS FUV emission to observed
photometry reveals four BSSs with WD companions above 12,000 K (younger than
250 Myr) and three WD companions with temperatures between 11,000-12,000 K.
These BSS+WD binaries all formed through recent mass transfer. The location of
the young BSSs in an optical color-magnitude diagram (CMD) indicates that
distance from the zero-age main sequence does not necessarily correlate with
BSS age. There is no clear CMD separation between mass transfer-formed BSSs and
those likely formed through other mechanisms, such as collisions. The seven
detected WD companions place a lower limit on the mass-transfer formation
frequency of 33%. We consider other possible formation mechanisms by comparing
properties of the BSS population to theoretical predictions. We conclude that
14 BSS binaries likely formed from mass transfer, resulting in an inferred
mass-transfer formation frequency of approximately 67%.Comment: 13 pages, 6 figures, accepted to the Astrophysical Journa
Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
Several possible formation pathways for blue straggler stars have been
developed recently, but no one pathway has yet been observationally confirmed
for a specific blue straggler. Here we report the first findings from a Hubble
Space Telescope ACS/SBC far-UV photometric program to search for white dwarf
companions to blue straggler stars. We find three hot and young white dwarf
companions to blue straggler stars in the 7-Gyr open cluster NGC 188,
indicating that mass transfer in these systems ended less than 300 Myr ago.
These companions are direct and secure observational evidence that these blue
straggler stars were formed through mass transfer in binary stars. Their
existence in a well-studied cluster environment allows for observational
constraints of both the current binary system and the progenitor binary system,
mapping the entire mass transfer history.Comment: 5 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Effect of body tilt on the constancy of the stereo vertical
Effect of body tilt on the constancy of the stereo vertica
The magnetic-resonance force microscope: a new tool for high-resolution, 3-D, subsurface scanned probe imaging
The magnetic-resonance force microscope (MRFM) is a novel scanned probe instrument which combines the three-dimensional (3-D) imaging capabilities of magnetic-resonance imaging with the high sensitivity and resolution of atomic-force microscopy. It will enable nondestructive, chemical-specific, high-resolution microscopic studies and imaging of subsurface properties of a broad range of materials. The MRFM has demonstrated its utility for study of microscopic ferromagnets, and it will enable microscopic understanding of the nonequilibrium spin polarization resulting from spin injection. Microscopic MRFM studies will provide unprecedented insight into the physics of magnetic and spin-based materials. We will describe the principles and the state-of-the-art in magnetic-resonance force microscopy, discuss existing cryogenic MRFM instruments incorporating high-Q, single-crystal microresonators with integral submicrometer probe magnets, and indicate future directions for enhancing MRFM instrument capabilities
Lipidomic Profiling of Neoplastic, Pre-Neoplastic, and Healthy Tissues Using Electrocautery Paired with Mass Spectroscopic Equipment
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