100 research outputs found
Ariel - Volume 11 Number 5
Executive Editors
Ellen Feldman
Leonardo S. Nasca, Jr.
Business Managers
Alex Macones
Martin B. Getzow
News Editor
Hugh A. Gelabert
Features Editor
Aaron D. Bleznak
CAHS Editor
Joan M. Greco
Editorial Page Editor
Samuel Markind
Photography Editor
Todd L. Demmy
Sports Editor
Paul F. Mansfield
Commons Editor
Saul I. Helfin
Colloidal Electrostatic Interactions Near a Conducting Surface
Charge-stabilized colloidal spheres dispersed in deionized water are supposed
to repel each other. Instead, artifact-corrected video microscopy measurements
reveal an anomalous long-ranged like-charge attraction in the interparticle
pair potential when the spheres are confined to a layer by even a single
charged glass surface. These attractions can be masked by electrostatic
repulsions at low ionic strengths. Coating the bounding surfaces with a
conducting gold layer suppresses the attraction. These observations suggest a
possible mechanism for confinement-induced attractions.Comment: 4 pages, 2 figure
Ariel - Volume 12 Number 1
Executive Editors
David G. Polin
Larry H. Pastor
Business Manager
Alex Macones
Jean Lien
Editorial Page Editor
Sam Markind
Photography Editors
Ken Yonemura
Lois Leach
Sports Editor
Todd Hoove
Observation of Flux Reversal in a Symmetric Optical Thermal Ratchet
We demonstrate that a cycle of three holographic optical trapping patterns
can implement a thermal ratchet for diffusing colloidal spheres, and that the
ratchet-driven transport displays flux reversal as a function of the cycle
frequency and the inter-trap separation. Unlike previously described ratchet
models, the approach we describe involves three equivalent states, each of
which is locally and globally spatially symmetric, with spatiotemporal symmetry
being broken by the sequence of states.Comment: 4 pages, 2 figures, submitted for publication in Physical Review
Letter
ZTF 18aaqeasu (SN 2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar Mass White Dwarf
The detonation of a helium shell on a white dwarf has been proposed as a
possible explosion triggering mechanism for Type Ia supernovae. Here, we report
ZTF 18aaqeasu (SN 2018byg/ATLAS 18pqq), a peculiar Type I supernova, consistent
with being a helium-shell double-detonation. With a rise time of
days from explosion, the transient reached a peak absolute magnitude of mag, exhibiting a light curve akin to sub-luminous SN
1991bg-like Type Ia supernovae, albeit with an unusually steep increase in
brightness within a week from explosion. Spectra taken near peak light exhibit
prominent Si absorption features together with an unusually red color ( mag) arising from nearly complete line blanketing of flux blue-wards
of 5000 \AA. This behavior is unlike any previously observed thermonuclear
transient. Nebular phase spectra taken at and after days from peak
light reveal evidence of a thermonuclear detonation event dominated by Fe-group
nucleosynthesis. We show that the peculiar properties of ZTF 18aaqeasu are
consistent with the detonation of a massive ( M) helium
shell on a sub-Chandrasekhar mass ( M) white dwarf after
including mixing of M of material in the outer ejecta.
These observations provide evidence of a likely rare class of thermonuclear
supernovae arising from detonations of massive helium shells.Comment: 10 pages, 6 figures. Submitted to ApJ
Pili allow dominant marine cyanobacteria to avoid sinking and evade predation
How oligotrophic marine cyanobacteria position themselves in the water column is currently unknown. The current paradigm is that these organisms avoid sinking due to their reduced size and passive drift within currents. Here, we show that one in four picocyanobacteria encode a type IV pilus which allows these organisms to increase drag and remain suspended at optimal positions in the water column, as well as evade predation by grazers. The evolution of this sophisticated floatation mechanism in these purely planktonic streamlined microorganisms has important implications for our current understanding of microbial distribution in the oceans and predator–prey interactions which ultimately will need incorporating into future models of marine carbon flux dynamics
ZTF Early Observations of Type Ia Supernovae. III. Early-time Colors As a Test for Explosion Models and Multiple Populations
Colors of Type Ia supernovae (SNe Ia) in the first few days after explosion provide a potential discriminant between different models. In this paper, we present g-r colors of 65 SNe Ia discovered within 5 days from first light by the Zwicky Transient Facility in 2018, a sample that is about three times larger than that in the literature. We find that g-r colors are intrinsically rather homogeneous at early phases, with about half of the dispersion attributable to photometric uncertainties (σnoise ∼ σ int ∼ 0.18 mag). Colors are nearly constant starting from 6 days after first light (g-r ∼-0.15 mag), while the time evolution at earlier epochs is characterized by a continuous range of slopes, from events rapidly transitioning from redder to bluer colors (slope of ∼-0.25 mag day-1) to events with a flatter evolution. The continuum in the slope distribution is in good agreement both with models requiring some amount of 56Ni mixed in the outermost regions of the ejecta and with "double-detonation"models having thin helium layers MHe=0.01 M⊙) and varying carbon-oxygen core masses. At the same time, six events show evidence for a distinctive "red bump"signature predicted by double-detonation models with larger helium masses. We finally identify a significant correlation between the early-time g-r slopes and supernova brightness, with brighter events associated to flatter color evolution (p-value = 0.006). The distribution of slopes, however, is consistent with being drawn from a single population, with no evidence for two components as claimed in the literature based on B-V colors
ZTF Early Observations of Type Ia Supernovae. III. Early-time Colors As a Test for Explosion Models and Multiple Populations
Colors of Type Ia supernovae (SNe Ia) in the first few days after explosion provide a potential discriminant between different models. In this paper, we present g − r colors of 65 SNe Ia discovered within 5 days from first light by the Zwicky Transient Facility in 2018, a sample that is about three times larger than that in the literature. We find that g − r colors are intrinsically rather homogeneous at early phases, with about half of the dispersion attributable to photometric uncertainties (σ_(noise)∼σ_(int) ~ 0.18 mag). Colors are nearly constant starting from 6 days after first light (g − r ~ −0.15 mag), while the time evolution at earlier epochs is characterized by a continuous range of slopes, from events rapidly transitioning from redder to bluer colors (slope of ~−0.25 mag day⁻¹) to events with a flatter evolution. The continuum in the slope distribution is in good agreement both with models requiring some amount of ⁵⁶Ni mixed in the outermost regions of the ejecta and with "double-detonation" models having thin helium layers (M_(He) = 0.01 M_⊙) and varying carbon–oxygen core masses. At the same time, six events show evidence for a distinctive "red bump" signature predicted by double-detonation models with larger helium masses. We finally identify a significant correlation between the early-time g − r slopes and supernova brightness, with brighter events associated to flatter color evolution (p-value = 0.006). The distribution of slopes, however, is consistent with being drawn from a single population, with no evidence for two components as claimed in the literature based on B − V colors
SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Massive Helium-Shell Detonation in a Star-Forming Galaxy
The detonation of a thin () helium shell
(He-shell) atop a white dwarf (WD) is a promising
mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker
He-shells and less massive WDs may explain some recently observed peculiar SNe
Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the
Zwicky Transient Facility (ZTF). Near maximum light, SN 2020jgb is slightly
subluminous (ZTF -band absolute magnitude between and
mag depending on the amount of host galaxy extinction) and shows an unusually
red color ( between 0.4 and 0.2 mag) due to
strong line-blanketing blueward of 5000 . These properties
resemble those of SN 2018byg, a peculiar SN Ia consistent with a thick He-shell
double detonation (DDet) SN. Using detailed radiative transfer models, we show
that the optical spectroscopic and photometric evolution of SN 2020jgb are
broadly consistent with a (C/O core + He-shell;
up to depending on the total host extinction)
progenitor ignited by a thick () He-shell. We
detect a prominent absorption feature at 1 in the
near-infrared (NIR) spectrum of SN 2020jgb, which could originate from unburnt
helium in the outermost ejecta. While the sample size is limited, similar 1
features have been detected in all the thick He-shell DDet
candidates with NIR spectra obtained to date. SN 2020jgb is also the first
subluminous, thick He-shell DDet SN discovered in a star-forming galaxy,
indisputably showing that He-shell DDet objects occur in both star-forming and
passive galaxies, consistent with the normal SN Ia population.Comment: 23 pages, 10 figures. Updated to accepted version (ApJ
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