2,693 research outputs found
Discovery of low mass objects in Taurus
In infrared (2.2 micron, K-band) search of small regions (25 in square) near 26 members of the Taurus star-forming association has revealed 20 dim (K = 13-16 mag) stellar objects near 13 of them. Of these 20 objects, 9 are exceptionally red. It is argued that these 9 are probably also Taurus members. From the luminosities (0.4 to 4 times 10 the -3 power luminosity) and ages (estimated at 10(exp 6) years), masses can be determined by reference to theoretical low-mass cooling curves. The masses are in the range 0.005 to 0.015 solar mass, i.e., low-mass brown dwarfs. Proper motion studies of 7 of the objects visible on the POSS plates conducted by Burton Jones establish that 4 are highly probable Taurus members while 1 is a possible member
Starbursts and Star Clusters in the Ultraviolet
Hubble Space Telescope ultraviolet (UV) images of nine starburst galaxies
reveal them to be highly irregular, even after excluding compact sources
(clusters and resolved stars). Most (7/9) are found to have a similar intrinsic
effective surface brightnesses, suggesting that a negative feedback mechanism
is setting an upper limit to the star formation rate per unit area. All
starbursts in our sample contain UV bright star clusters indicating that
cluster formation is an important mode of star formation in starbursts. On
average about 20% of the UV luminosity comes from these clusters. The brightest
clusters, or super star clusters (SSC), are preferentially found at the very
heart of starbursts. The size of the nearest SSCs are consistent with those of
Galactic globular clusters. The luminosity function of SSCs is well represented
by a power law with a slope alpha ~ -2. There is a strong correlation between
the far infrared excess and the UV spectral slope. The correlation is well
modeled by a geometry where much of their dust is in a foreground screen near
to the starburst, but not by a geometry of well mixed stars and dust.Comment: 47 pages, text only, LaTeX with aaspp.sty (version 3.0), compressed
postscript figures available at
ftp://eta.pha.jhu.edu/RecentPublications/meurer
High Carbon in I Zwicky 18: New Results from Hubble Space Telescope Spectroscopy
We present new measurements of the gas-phase C/O abundance ratio in both the
NW and SE components of the extremely metal-poor dwarf irregular galaxy I Zw
18, based on ultraviolet spectroscopy of the two H II regions using the Faint
Object Spectrograph on the Hubble Space Telescope. We determine values of log
C/O = -0.63 +/- 0.10 for the NW component and log C/O = -0.56 +/- 0.09 for the
SE component. In comparison, log C/O = -0.37 in the sun, while log C/O = -0.85
+/- 0.07 in the three most metal-poor irregular galaxies measured by Garnett et
al. (1995a). Our measurements show that C/O in I Zw 18 is significantly higher
than in other comparably metal-poor irregular galaxies, and above predictions
for the expected C/O from massive star nucleosynthesis. These results suggest
that carbon in I Zw 18 has been enhanced by an earlier population of lower-mass
carbon producing stars; this idea is supported by stellar photometry of I Zw 18
and its companion, which demonstrate that the current bursts of massive stars
were not the first. Despite its very low metallicity, it is likely that I Zw 18
is not a ``primeval'' galaxy.Comment: 14 pages including 4 figures; uses aaspp4.sty. Accepted for
publication in ApJ. Postscript version also available by e-mail request to
author at [email protected]
Radiocarbon dating of methane and carbon dioxide evaded from a temperate peatland stream
Streams draining peatlands export large quantities of carbon in different chemical forms and
are an important part of the carbon cycle. Radiocarbon (14C) analysis/dating provides unique
information on the source and rate that carbon is cycled through ecosystems, as has recently
been demonstrated at the air-water interface through analysis of carbon dioxide (CO2) lost
from peatland streams by evasion (degassing). Peatland streams also have the potential to
release large amounts of methane (CH4) and, though 14C analysis of CH4 emitted by ebullition
(bubbling) has been previously reported, diffusive emissions have not. We describe methods
that enable the 14C analysis of CH4 evaded from peatland streams. Using these methods, we
investigated the 14C age and stable carbon isotope composition of both CH4 and CO2 evaded
from a small peatland stream draining a temperate raised mire. Methane was aged between
1617-1987 years BP, and was much older than CO2 which had an age range of 303-521 years
BP. Isotope mass balance modelling of the results indicated that the CO2 and CH4 evaded
from the stream were derived from different source areas, with most evaded CO2 originating
from younger layers located nearer the peat surface compared to CH4. The study demonstrates
the insight that can be gained into peatland carbon cycling from a methodological
development which enables dual isotope (14C and 13C) analysis of both CH4 and CO2 collected
at the same time and in the same way
Factors associated with drinking behaviour during COVID-19 social distancing and lockdown among adults in the UK
Aim: To assess what factors were associated with reported changes to usual alcohol drinking behaviour during the start of lockdown in the UK. /
Design: Online cross-sectional survey from 21st March to 4th April 2020. /
Setting: UK. /
Participants: 30,375 adults aged ≥ 18y. /
Measurements: Changes in drinking over the past week, sociodemographic characteristics, diagnosed or suspected COVID-19, adherence to COVID-19 protective behaviours, stress about COVID-19, finances or boredom, recent drop in household income, key worker status, and health conditions. /
Findings: Of 22,113 drinkers (65.7% of analytic sample), 48.1% (95% CI=47.0-49.1%) reported drinking about the same as usual, 25.7% (24.8-26.6%) reported drinking less than usual, and 26.2% (25.4-27.1%) reported drinking more than usual over the past week. Drinking less than usual was independently associated with being younger (OR=0.88 [95% CI=0.83-0.93]), male (OR=0.76 [0.68-0.84]), of an ethnic minority (OR=0.76 [0.61-0.97]), low annual household income (OR=0.74 [0.66-0.83]), having diagnosed or suspected COVID-19 (OR=2.04 [1.72-2.41]), adhering to COVID-19 protective behaviours (OR=1.58 [1.08-2.32]), being significantly stressed about becoming seriously ill from COVID-19 (OR=1.26 [1.08-1.48]) and not being a key worker (OR=0.87 [0.76-0.99]). Drinking more than usual was independently associated with being younger (OR=0.73 [0.69-0.78]), female (OR=1.36 [1.22-1.51]), post-16 qualifications (OR=1.21 [1.04-1.40]), high annual household income (OR=1.43 [1.27-1.61]), being significantly stressed about catching (OR=1.22 [1.03-1.45]) or becoming seriously ill from COVID-19 (OR=1.28 [1.10-1.48]), being significantly stressed about finances (OR=1.43 [1.24-1.66]), and having a diagnosed anxiety disorder (OR=1.24 [1.05-1.46]). /
Conclusions: In a representative sample of adults in the UK, about half of drinkers reported drinking the same amount of alcohol as usual during the start of the COVID-19 related lockdown, with a quarter drinking more and a quarter drinking less than usual. Drinking more than usual was associated with being younger, female, high socioeconomic position, having an anxiety disorder, and being stressed about finances or COVID-19. These groups may benefit targeted alcohol reduction support if there are further periods of lockdown. /
Registration: The analysis plan was pre-registered on Open Science Framework (https://osf.io/pnrhq/)
Cortisol relates to executive functioning for children attending Head Start preschool
Background: Approximately 15 million children in the United States grow up in poverty circumstances (National Center for Children in Poverty, 2018), as 24% of all children under the age of 6 live in households with income levels classified as below the federal poverty guideline (Jiang et al., 2016). Recent research has highlighted the impact of early childhood poverty circumstances on physiological systems that respond to stress (Lupien et al., 2001), with implications for typical development in the prefrontal cortex (Hair et al., 2015) and related executive functioning (Blair & Raver, 2016). Method: The present study investigated relations among various components of teacher-reported executive functioning (BRIEF; Gioia et al., 2000) and total cortisol output of 318 young children (ages 3-5 years) across a preschool day. Salivary cortisol was sampled in duplicate at 4 times across 2 days in the beginning of the school year, resulting in a total of 16 samples per child. Results and Implications: We hypothesized that higher cortisol levels, likely attributable to poverty-stress (Blair et al., 2011) across the preschool day would relate to greater difficulties in teacher-reported EF, controlling for child age, sex, and family income. A multiple regression model that aligned with this hypothesis predicted BRIEF, General Composite Score with statistical significance. Moreover, child salivary cortisol across the preschool day predicted teacher-reported executive functioning for each domain score of the BRIEF. Implications concern understanding the impact of stress on executive functioning in the preschool classroom and promoting positive outcomes for children facing poverty risk
Effective electronic response of a system of metallic cylinders
The electronic response of a composite consisting of aligned metallic
cylinders in vacuum is investigated, on the basis of photonic band structure
calculations. The effective long-wavelength dielectric response function is
computed, as a function of the filling fraction. A spectral representation of
the effective response is considered, and the surface mode strengths and
positions are analyzed. The range of validity of a Maxwell-Garnett-like
approach is discussed, and the impact of our results on absorption spectra and
electron energy-loss phenomena is addressed.Comment: 15 pages, 6 figures, to appear in Phys. Rev.
A Weighted Estimate for the Square Function on the Unit Ball in \C^n
We show that the Lusin area integral or the square function on the unit ball
of \C^n, regarded as an operator in weighted space has a linear
bound in terms of the invariant characteristic of the weight. We show a
dimension-free estimate for the ``area-integral'' associated to the weighted
norm of the square function. We prove the equivalence of the classical
and the invariant classes.Comment: 11 pages, to appear in Arkiv for Matemati
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