63 research outputs found
Multiplicity at the Stellar/Substellar Boundary in Upper Scorpius
We present the results of a high-resolution imaging survey of 12 brown dwarfs
and very low mass stars in the closest (~145 pc) young (~5 Myr) OB association,
Upper Scorpius. We obtained images with the Advanced Camera for Surveys/High
Resolution Camera on HST through the F555W (V), F775W (i'), and F850LP (z')
filters. This survey discovered three new binary systems, including one
marginally resolved pair with a projected separation of only 4.9 AU, resulting
in an observed binary fraction of 25+/-14% at separations >4 AU. After
correcting for detection biases assuming a uniform distribution of mass ratios
for q>0.6, the estimated binary fraction is 33+/-17%. The binary fraction is
consistent with that inferred for higher-mass stars in Upper Sco, but the
separation and mass ratio distributions appear to be different. All three
low-mass binary systems in Upper Sco are tight (<18 AU) and of similar mass
(q>0.6), consistent with expectations based on previous multiplicity studies of
brown dwarfs and very low mass stars in the field and in open clusters. The
implication is that the distinct separation and mass ratio distributions of
low-mass systems are set in the formation process or at very young ages, rather
than by dynamical disruption of wide systems at ages >5 Myr. Finally, we
combine the survey detection limits with the models of Burrows et al. (1997) to
show that there are no planets or very low-mass brown dwarfs with masses >10
M_J at projected separations >20 AU, or masses >5 M_J at projected separations
>40 AU orbiting any of the low-mass (0.04-0.10 M_sun) objects in our sample.Comment: Accepted for publication in ApJ; 10 pages, 4 figures in emulateapj
forma
Multiplicity and Optical Excess Across the Substellar Boundary in Taurus
We present the results of a high-resolution imaging survey of 22 brown dwarfs
and very low mass stars in the nearby (~145 pc) young (~1-2 Myr) low-density
star-forming region Taurus-Auriga. We obtained images with the Advanced Camera
for Surveys/High Resolution Channel on HST through the F555W (V), F775W (i'),
and F850LP (z') filters. This survey confirmed the binarity of MHO-Tau-8 and
discovered a new candidate binary system, V410-Xray3, resulting in a binary
fraction of 9+/-5% at separations >4 AU. Both binary systems are tight (<10 AU)
and they possess mass ratios of 0.75 and 0.46, respectively. The binary
frequency and separations are consistent with low-mass binary properties in the
field, but the mass ratio of V410-Xray3 is among the lowest known. We find that
the binary frequency is higher for very low mass stars and high-mass brown
dwarfs than for lower-mass brown dwarfs, implying either a decline in frequency
or a shift to smaller separations for the lowest mass binaries. Combining these
results with multiplicity statistics for higher-mass Taurus members suggests a
gradual decline in binary frequency and separation toward low masses. The
implication is that the distinct binary properties of very low-mass systems are
set during formation and that the formation process is similar to the process
which creates higher-mass stellar binaries, but occurs on a smaller scale. We
show that there are no planets or very low-mass brown dwarfs with mass >3 M_J
at projected separation >40 AU orbiting any of the Taurus members in our
sample. We identify several BDs with significant (>1 mag) V-band excesses. The
excesses appear to be correlated with signatures of accretion, and if
attributed to accretion luminosity, may imply mass accretion rates several
orders of magnitude above those inferred from line-profile analyses. (abridged)Comment: Accepted for publication in ApJ; 15 pages, 8 figures in emulateapj
forma
The Role of Mass and Environment in Multiple Star Formation: A 2MASS Survey of Wide Multiplicity in Three Young Associations
We present the results of a search for wide binary systems among 783 members
of three nearby young associations: Taurus-Auriga, Chamaeleon I, and two
subgroups of Upper Scorpius. Near-infrared (JHK) imagery from 2MASS was
analyzed to search for wide (1-30"; ~150-4500 AU) companions to known
association members, using color-magnitude cuts to reject likely background
stars. We identify a total of 131 candidate binary companions with colors
consistent with physical association, of which 39 have not been identified
previously in the literature. Our results suggest that the wide binary
frequency is a function of both mass and environment, with significantly higher
frequencies among high-mass stars than lower-mass stars and in the T
associations than in the OB association. We discuss the implications for wide
binary formation and conclude that the environmental dependence is not a direct
result of stellar density or total association mass, but instead might depend
on another environmental parameter like the gas temperature. We also analyze
the mass ratio distribution as a function of mass and find that it agrees with
the distribution for field stars to within the statistical uncertainties. The
binary populations in these associations generally follow the empirical
mass-maximum separation relation observed for field binaries, but we have found
one candidate low-mass system (USco-160611.9-193532; Mtot~0.4 Msun) which has a
projected separation (10.8"; 1550 AU) much larger than the suggested limit for
its mass. (Abridged)Comment: Accepted to ApJ; 27 pages in emulateapj format. The full version of
table 2 can be downloaded via http://www.astro.caltech.edu/~alk/tab2.pdf
(PDF) or http://www.astro.caltech.edu/~alk/tab2.txt (text
The Lantern Vol. 49, No. 1, Fall 1982
• The Dormant Tree • Les Maitres des mots... • The Bartender • Time • Small Silent Creatures • Appreciation de la vie • Mon Seigneur, Mon Ami • In Gratitude • Cathedral • Child • Grow Old With Me • To Keep The Land • Lesetta • No Answer • The Hunt • You Came to Me • A Day in the Life of a Thought • Revenge • The Dance • Unclaimed • Where e\u27er There Be a Reason • Pour le coin • Thinking of You • You Were The Onehttps://digitalcommons.ursinus.edu/lantern/1121/thumbnail.jp
The proteasome cap RPT5/Rpt5p subunit prevents aggregation of unfolded ricin A chain
The plant cytotoxin ricin enters mammalian cells by receptor-mediated endocytosis, undergoing retrograde transport to the endoplasmic reticulum (ER) where its catalytic A chain (RTA) is reductively separated from the holotoxin to enter the cytosol and inactivate ribosomes. The currently accepted model is that the bulk of ER-dislocated RTA is degraded by proteasomes. We show here that the proteasome has a more complex role in ricin intoxication than previously recognised, that the previously reported increase in sensitivity of mammalian cells to ricin in the presence of proteasome inhibitors simply reflects toxicity of the inhibitors themselves, and that RTA is a very poor substrate for proteasomal degradation. Denatured RTA and casein compete for a binding site on the regulatory particle of the 26S proteasome, but their fates differ. Casein is degraded, but the mammalian 26S proteasome AAA-ATPase subunit RPT5 acts as a chaperone that prevents aggregation of denatured RTA and stimulates recovery of catalytic RTA activity in vitro. Furthermore, in vivo, the ATPase activity of Rpt5p is required for maximal toxicity of RTA dislocated from the Saccharomyces cerevisiae ER. Our results implicate RPT5/Rpt5p in the triage of substrates in which either activation (folding) or inactivation (degradation) pathways may be initiated
The Palomar/Keck Adaptive Optics Survey of Young Solar Analogs: Evidence for a Universal Companion Mass Function
We present results from an adaptive optics survey for substellar and stellar
companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3Myr
to 3Gyr age range with distances of 10-190pc. Results from the survey include
the discovery of two brown dwarf companions (HD49197B and HD203030B), 24 new
stellar binaries, and a triple system. We infer that the frequency of
0.012-0.072Msun brown dwarfs in 28-1590AU orbits around young solar analogs is
3.2% (+3.1%,-2.7%; 2sigma limits). The result demonstrates that the deficiency
of substellar companions at wide orbital separations from Sun-like stars is
less pronounced than in the radial velocity "brown dwarf desert." We infer that
the mass distribution of companions in 28-1590AU orbits around solar-mass stars
follows a continuous dN/dM_2 ~ M_2^(-0.4) relation over the 0.01-1.0Msun
secondary mass range. While this functional form is similar to that for
<0.1Msun isolated objects, over the entire 0.01-1.0Msun range the mass
functions of companions and of isolated objects differ significantly. Based on
this conclusion and on similar results from other direct imaging and radial
velocity companion surveys in the literature, we argue that the companion mass
function follows the same universal form over the entire range between 0-1590AU
in orbital semi-major axis and 0.01-20Msun in companion mass. In this context,
the relative dearth of substellar versus stellar secondaries at all orbital
separations arises naturally from the inferred form of the companion mass
function.Comment: Final version accepted by ApJ Supplements. 50 pages, including 12
tables + 16 figures. Version with full tables available at
http://www.astro.sunysb.edu/metchev/PUBLICATIONS/cmf.pd
Neighbourhood deprivation and small-for-gestational-age term births in the United States
Residential context has received increased attention as a possible contributing factor to race/ethnic and socioeconomic disparities in birth outcomes in the United States. Utilizing vital statistics birth record data, this study examined the association between neighbourhood deprivation and the risk of a term small-for-gestational-age (SGA) birth among non-Hispanic whites and non-Hispanic blacks in eight geographic areas: Baltimore City, Baltimore County, Montgomery County and Prince Georges County in Maryland, 16 pooled cities in Michigan, Durham County and Wake County in North Carolina, and Philadelphia, Pennsylvania. Multilevel random intercept logistic regression models were employed and statistical tests were performed to examine if the association between neighbourhood deprivation and SGA varied by race/ethnicity and study site. The risk of term SGA was higher among non-Hispanic blacks (range: 10.8%–17.5%) than non-Hispanic whites (range: 5.1%–9.2%) in all areas and it was higher in cities than in suburban locations. In all areas, non-Hispanic blacks lived in more deprived neighbourhoods than non-Hispanic whites. However, the adjusted associations between neighbourhood deprivation and term SGA did not vary significantly by race/ethnicity or study site. The summary fully-adjusted pooled odds ratios, indicating the effect of one standard deviation increase in the deprivation score, were 1.15 [95% CI: 1.08–1.22] for non-Hispanic whites and 1.09 [95% CI: 1.05–1.14] for non-Hispanic blacks. Thus, neighbourhood deprivation was weakly associated with term SGA among both non-Hispanic whites and non-Hispanic blacks
The state of the Martian climate
60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes
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