5,200 research outputs found
A Search for Intrinsic Polarization in O Stars with Variable Winds
New observations of 9 of the brightest northern O stars have been made with
the Breger polarimeter on the 0.9~m telescope at McDonald Observatory and the
AnyPol polarimeter on the 0.4~m telescope at Limber Observatory, using the
Johnson-Cousins UBVRI broadband filter system. Comparison with earlier
measurements shows no clearly defined long-term polarization variability. For
all 9 stars the wavelength dependence of the degree of polarization in the
optical range can be fit by a normal interstellar polarization law. The
polarization position angles are practically constant with wavelength and are
consistent with those of neighboring stars. Thus the simplest conclusion is
that the polarization of all the program stars is primarily interstellar.
The O stars chosen for this study are generally known from ultraviolet and
optical spectroscopy to have substantial mass loss rates and variable winds, as
well as occasional circumstellar emission. Their lack of intrinsic polarization
in comparison with the similar Be stars may be explained by the dominance of
radiation as a wind driving force due to higher luminosity, which results in
lower density and less rotational flattening in the electron scattering inner
envelopes where the polarization is produced. However, time series of
polarization measurements taken simultaneously with H-alpha and UV spectroscopy
during several coordinated multiwavelength campaigns suggest two cases of
possible small-amplitude, periodic short-term polarization variability, and
therefore intrinsic polarization, which may be correlated with the more widely
recognized spectroscopic variations.Comment: LaTeX2e, 22 pages including 11 tables; 12 separate gif figures; uses
aastex.cls preprint package; accepted by The Astronomical Journa
Enhancing Environmental Health Literacy about the Asthma- Air Pollution Connection at Childcare Centers in Asthma Prevalent Philadelphia Neighborhoods
Objective: To determine environmental health literacy of childcare providers about outdoor air quality alert resources, the connection between air pollution and asthma and determine if childcare providers would use the resource to benefit children in their care. Methods: We designed a free outreach program about asthma prevalence, dangers of poor air quality, and air quality alert resources for staff at childcare centers in Philadelphia, Pennsylvania during summer and fall of 2015-2017. Pre-surveys were administered to evaluate baseline understanding. Post-surveys were administered at 4 weeks and returned within 4-12 weeks. Summary statistics were calculated, and pre/post knowledge compared using a paired t-test. Results: 258 staffers at 45 childcare centers attended the presentations. 214 completed both pre/post surveys. 74% reported never/rarely using air quality alerts before the program. Post-survey, 40% reported signing up for alerts. Post-survey there was an 8% mean increase in knowledge score (95% CI: 6.3-9.5%, Conclusions: This easily administered program using freely available information was useful to childcare providers and increased their environmental health literacy to benefit children in their care.
Keywords: Environmental Health Literacy; Air Pollution; Asthma; Community Engagement; Public Health
Objective: To determine environmental health literacy of childcare providers about outdoor air quality alert resources, the connection between air pollution and asthma and determine if childcare providers would use the resource to benefit children in their care. Methods: We designed a free outreach program about asthma prevalence, dangers of poor air quality, and air quality alert resources for staff at childcare centers in Philadelphia, Pennsylvania during summer and fall of 2015-2017. Pre-surveys were administered to evaluate baseline understanding. Post-surveys were administered at 4 weeks and returned within 4-12 weeks. Summary statistics were calculated, and pre/post knowledge compared using a paired t-test. Results: 258 staffers at 45 childcare centers attended the presentations. 214 completed both pre/post surveys. 74% reported never/rarely using air quality alerts before the program. Post-survey, 40% reported signing up for alerts. Post-survey there was an 8% mean increase in knowledge score (95% CI: 6.3-9.5%, pConclusions: This easily administered program using freely available information was useful to childcare providers and increased their environmental health literacy to benefit children in their care
The rotation of alpha Oph investigated using polarimetry
Recently we have demonstrated that high-precision polarization observations
can detect the polarization resulting from the rotational distortion of a
rapidly rotating B-type star. Here we investigate the extension of this
approach to an A-type star. Linear-polarization observations of Oph
(A5IV) have been obtained over wavelengths from 400 to 750 nm. They show the
wavelength dependence expected for a rapidly-rotating star combined with a
contribution from interstellar polarization. We model the observations by
fitting rotating-star polarization models and adding additional constraints
including a measured . However, we cannot fully separate the
effects of rotation rate and inclination, leaving a range of possible
solutions. We determine a rotation rate between
0.83 and 0.98 and an axial inclination i > 60 deg. The rotation-axis position
angle is found to be 142 4 deg, differing by 16 deg from a value obtained
by interferometry. This might be due to precession of the rotation axis due to
interaction with the binary companion. Other parameters resulting from the
analysis include a polar temperature Tp = 8725 175 K, polar gravity
(dex cgs), and polar radius Rsun. Comparison with rotating-star evolutionary models indicates that
Oph is in the later half of its main-sequence evolution and must have
had an initial of 0.8 or greater. The interstellar polarization has a
maximum value at a wavelength () of nm,
consistent with values found for other nearby stars.Comment: 14 pages, 11 figures, 5 tables, Accepted in MNRA
Large-scale wind structures in OB supergiants: a search for rotationally modulated H\alpha variability
We present the results of a long-term monitoring campaign of the H\alpha line
in a sample of bright OB-supergiants (O7.5-B9) that aims at detecting
rotationally modulated changes potentially related to the existence of
large-scale wind structures. A total of 22 objects were monitor ed during 36
nights spread over 6 months in 2001-2002. Coordinated broad-band photometric
observations were also obtained for some targets. Conspicuous evidence for
variability in H\alpha is found for the stars displaying a feature contaminated
by wind emission. Most changes take place on a daily time-scale, although
hourly variations are also occasionally detected. Convincing evidence for a
cyclical pattern of variability in H\alpha has been found in 2 stars: HD 14134
and HD 42087 (periodic signals are also detected in other stars, but
independent confirmation is required). Rotational modulation is suggested from
the similarity between the observed recurrence time-scales (in the range 13-25
days) and estimated periods of stellar rotation. We call attention to the
atypical case of HD 14134 which exhibits a clear 12.8-d periodicity both in the
photometric and in the spectroscopic data sets. This places this object among a
handful of early-type stars where one may observe a clear link between extended
wind structures and photospheric disturbances. Further modelling may test the
hypothesis that azimuthally-extended wind streams are responsible for the
patterns of spectral variability in our target stars.Comment: 18 pages, accepted for publication in MNRA
A Stellar Rotation Census of B Stars: from ZAMS to TAMS
Two recent observing campaigns provide us with moderate dispersion spectra of
more than 230 cluster and 370 field B stars. Combining them and the spectra of
the B stars from our previous investigations (430 cluster and 100
field B stars) yields a large, homogeneous sample for studying the rotational
properties of B stars. We derive the projected rotational velocity ,
effective temperature, gravity, mass, and critical rotation speed for each star. We find that the average is significantly lower
among field stars because they are systematically more evolved and spun down
than their cluster counterparts. The rotational distribution functions of
for the least evolved B stars show that lower mass B
stars are born with a larger proportion of rapid rotators than higher mass B
stars. However, the upper limit of that may separate
normal B stars from emission line Be stars (where rotation promotes mass loss
into a circumstellar disk) is smaller among the higher mass B stars. We compare
the evolutionary trends of rotation (measured according to the polar gravity of
the star) with recent models that treat internal mixing. The spin-down rates
observed in the high mass subset () agree with predictions, but
the rates are larger for the low mass group (). The faster spin
down in the low mass B stars matches well with the predictions based on
conservation of angular momentum in individual spherical shells. Our results
suggest the fastest rotators (that probably correspond to the emission line Be
stars) are probably formed by evolutionary spin up (for the more massive stars)
and by mass transfer in binaries (for the full range of B star masses).Comment: 44 pages, 10 figures, accepted for publication in Ap
Engineered membranes for residual cell trapping on microfluidic blood plasma separation systems. A comparison between porous and nanofibrous membranes
Blood-based clinical diagnostics require challenging limit-of-detection for low abundance, circulating molecules in plasma. Micro-scale blood plasma separation (BPS) has achieved remarka-ble results in terms of plasma yield or purity, but rarely achieving both at the same time. Here, we proposed the first use of electrospun polylactic-acid (PLA) membranes as filters to remove residual cell population from continuous hydrodynamic-BPS devices. The membranes hydrophilicity was improved by adopting a wet chemistry approach via surface aminolysis as demonstrated through Fourier Transform Infrared Spectroscopy and Water Contact Angle analysis. The usability of PLA-membranes was assessed through degradation measurements at extreme pH values. Plasma purity and hemolysis were evaluated on plasma samples with residual red blood cell content (1, 3, 5% hematocrit) corresponding to output from existing hydrodynamic BPS systems. Commercially available membranes for BPS were used as benchmark. Results highlighted that the electrospun membranes are suitable for downstream residual cell removal from blood, permitting the collection of up to 2 mL of pure and low-hemolyzed plasma. Fluorometric DNA quantification revealed that electrospun membranes did not significantly affect the concentration of circulating DNA. PLA-based electrospun membranes can be combined with hydrodynamic BPS in order to achieve high volume plasma separation at over 99% plasma purity
Young peoples’ reflections on what teachers think about family obligations that conflict with school: A focus on the non-normative roles of young caring and language brokering
In “Western” contexts school attendance is central for an ‘ideal’ childhood. However, many young people engage with home roles that conflict with school expectations. This paper explores perceptions of that process in relation two home activities - language brokering and young caring. We interviewed 46 young people and asked them to reflect on what the teacher would think when a child had to miss school to help a family member. This paper discusses the young people’s overall need to keep their out-of-school lives private from their teachers
The spectral variability and magnetic field characteristics of the Of?p star HD 148937
We report magnetic and spectroscopic observations and modeling of the Of?p
star HD 148937 within the context of the MiMeS LP at the CFHT. Thirty-two high
signal-to-noise ratio circularly polarised (Stokes V) spectra and 13
unpolarised (Stokes I) spectra of HD 148937 were acquired in 2009 and 2010. A
definite detection of a Stokes V Zeeman signature is obtained in the grand mean
of all observations (in both LSD mean profiles and individual spectral lines).
The longitudinal magnetic field inferred from the Stokes V LSD profiles is
consistently negative, in contrast to the essentially zero field strength
measured from the diagnostic null profiles. A period search of equivalent width
measurements confirms the previously-reported 7.03 d variability period. The
variation of equivalent widths is not strictly periodic: we present evidence
for evolution of the amount or distribution of circumstellar plasma.
Interpreting the 7.03 d period as the stellar rotational period within the
context of the ORM, we have phased the equivalent widths and longitudinal field
measurements. The longitudinal field measurements show a weak sinusoidal
variation of constant sign, with extrema out of phase with the H{\alpha}
variation by about 0.25 cycles. The inferred magnetic configuration confirms
the suggestion of Naz\'e et al (2010), who proposed that the weaker variability
of HD 148937 as compared to other members of this class is a consequence of the
stellar geometry. Based on the derived magnetic properties and published wind
characteristics, we find a wind magnetic confinement parameter \eta\ast \simeq
20 and rotation parameter W = 0.12, supporting a picture in which the Halpha
emission and other line variability have their origin in an oblique, rigidly
rotating magnetospheric structure resulting from a magnetically channeled wind.
(Abridged.)Comment: 13 pages, MNRAS. Version 2, small change to Fig. 1
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