124 research outputs found
Solar ultraviolet protection provided by human head hair
The solar erythemal UV irradiances through human hair and the protection from UV provided by human head hair have been investigated for a solar zenith angle (SZA) range of 17 to 51 degrees for the conditions of a head upright in full sun, a head upright in shade and a head in full sun tilted towards the sun. The two hair lengths investigated were 49.1+-7.1 mm for the short type and 109.5+-5.5 mm for the long type. For the head upright in full sun, the irradiances through the hair ranged from 0.75 to 1.4 SED/h for SZA less than 25 degrees and less than 0.6 SED/h in shade. The ultraviolet protection factor (UPF) ranged from approximately 5 to 17 in full sun, with the UPF increasing with higher SZA. The longer hair provided a lower UPF than the shorter hair and for the head oriented towards the sun, there was a marginally lower UPF than for the upright head. This research shows that the UV exposure limits to the scalp through hair can be exceeded within short timeframes and provides important information to assist employers to comply with Workplace Health and Safety legislation
Young stars at large distances from the galactic plane: mechanisms of formation
We have collected from the literature a list of early-type stars, situated at
large distances from the galactic plane, for which evidence of youth seems
convincing. We discuss two possible formation mechanisms for these stars:
ejection from the plane by dynamical interactions within small clusters, and
formation away from the plane, via induced shocks created by spiral density
waves. We identify the stars that could be explained by each mechanism. We
conclude that the ejection mechanism can account for about two thirds of the
stars, while a combination of star formation at z = 500-800 pc from the plane
and ejection, can account for 90 percent of these stars. Neither mechanism, nor
both together, can explain the most extreme examples.Comment: 6 pages, No figures. Sixth Pacific Rim Conference on Stellar
Astrophysics - A tribute to Helmut Abt, (Kluwer
A Third Hot White Dwarf Companion Detected by Kepler
We have found a system listed in the Kepler Binary Catalog (3.273 day period;
Prsa et al. 2010) that we have determined is comprised of a low-mass,
thermally-bloated, hot white dwarf orbiting an A star of about 2.3 solar
masses. In this work we designate the object, KIC 10657664, simply as KHWD3. We
use the transit depth of ~0.66%, the eclipse depth of ~1.9%, and regular smooth
periodic variations at the orbital frequency and twice the orbital frequency to
analyze the system parameters. The smooth periodic variations are identified
with the classical ellipsoidal light variation and illumination effects, and
the newly utilized Doppler boosting effect. Given the measured values of R/a
and inclination angle of the binary, both the ELV and DB effects are mostly
sensitive to the mass ratio, q = M_2/M_1, of the binary. The two effects yield
values of q which are somewhat inconsistent - presumably due to unidentified
systematic effects - but which nonetheless provide a quite useful set of
possibilities for the mass of the white dwarf (either 0.18 +/- 0.03 M_Sun or
0.37 +/- 0.08 M_Sun). All of the other system parameters are determined fairly
robustly. In particular, we show that the white dwarf has a radius of 0.15 +/-
0.01 R_Sun which is extremely bloated over the radius it would have as a fully
degenerate object, and an effective temperature T_eff = 14,100 +/- 350 K.
Binary evolution scenarios and models for this system are discussed. We suggest
that the progenitor binary was comprised of a primary of mass ~2.2 M_Sun (the
progenitor of the current hot white dwarf) and a secondary of mass ~1.4 M_Sun
(the progenitor of the current A star in the system). We compare this new
system with three other white dwarfs in binaries that likely were formed via
stable Roche-lobe overflow (KOI-74, KOI-81, and Regulus).Comment: Accepted for publication in Ap
Circulating Exosomal microRNAs as Predictive Biomarkers of Neoadjuvant Chemotherapy Response in Breast Cancer
Background: Neoadjuvant chemotherapy (NACT) is an increasingly used approach for treatment of breast cancer. The pathological complete response (pCR) is considered a good predictor of disease-specific survival. This study investigated whether circulating exosomal microRNAs could predict pCR in breast cancer patients treated with NACT. Method: Plasma samples of 20 breast cancer patients treated with NACT were collected prior to and after the first cycle. RNA sequencing was used to determine microRNA profiling. The Cancer Genome Atlas (TCGA) was used to explore the expression patterns and survivability of the candidate miRNAs, and their potential targets based on the expression levels and copy number variation (CNV) data. Results: Three miRNAs before that NACT (miR-30b, miR-328 and miR-423) predicted pCR in all of the analyzed samples. Upregulation of miR-127 correlated with pCR in triple-negative breast cancer (TNBC). After the first NACT dose, pCR was predicted by exo-miR-141, while miR-34a, exo-miR182, and exo-miR-183 predicted non-pCR. A significant correlation between the candidate miRNAs and the overall survival, subtype, and metastasis in breast cancer, suggesting their potential role as predictive biomarkers of pCR. Conclusions: If the miRNAs identified in this study are validated in a large cohort of patients, they might serve as predictive non-invasive liquid biopsy biomarkers for monitoring pCR to NACT in breast cancer
The Origin of Massive O-type Field Stars. Part II: Field O stars as runaways
In two papers we try to confirm that all Galactic high-mass stars are formed
in a cluster environment, by excluding that O-type stars found in the Galactic
field actually formed there. In de Wit et al. (2004) we presented deep K-band
imaging of 5 arcmin fields centred on 43 massive O-type field stars that
revealed that the large majority of these objects are single objects. In this
contribution we explore the possibility that the field O stars are dynamically
ejected from young clusters, by investigating their peculiar space velocity
distribution, their distance from the Galactic plane, and their spatial
vicinity to known young stellar clusters. We (re-)identify 22 field O-type
stars as candidate runaway OB-stars. The statistics show that ~4% of all O-type
stars with V < 8 can be considered as formed outside a cluster environment.
Most are spectroscopically single objects, some are visual binaries. The
derived percentage for O-type stars that form isolated in the field based on
our statistical analyses is in agreement with what is expected from
calculations adopting a universal cluster richness distribution with power
index of beta = 1.7, assuming that the cluster richness distribution is
continuous down to the smallest clusters containing one single star.Comment: 9 pages, 4 figures. Accepted for publication in A&
HD 69686: A Mysterious High Velocity B Star
We report on the discovery of a high velocity B star, HD 69686. We estimate
its space velocity, distance, surface temperature, gravity, and age. With these
data, we are able to reconstruct the trajectory of the star and to trace it
back to its birthplace. We use evolutionary tracks for single stars to estimate
that HD 69686 was born 73 Myr ago in the outer part of our Galaxy (
kpc) at a position well below the Galactic plane ( kpc), a very
unusual birthplace for a B star. Along the star's projected path in the sky, we
also find about 12 other stars having similar proper motions, and their
photometry data suggest that they are located at the same distance as HD 69686
and probably have the same age. We speculate on the origin of this group by
star formation in a high velocity cloud or as a Galactic merger fragment.Comment: 28 pages, 6 figures, accepted for publication in Ap
A Spectroscopic Study of Field and Runaway OB Stars
Identifying binaries among runaway O- and B-type stars offers valuable
insight into the evolution of open clusters and close binary stars. Here we
present a spectroscopic investigation of 12 known or suspected binaries among
field and runaway OB stars. We find new orbital solutions for five single-lined
spectroscopic binaries (HD 1976, HD 14633, HD 15137, HD 37737, and HD 52533),
and we classify two stars thought to be binaries (HD 30614 and HD 188001) as
single stars. In addition, we reinvestigate their runaway status using our new
radial velocity data with the UCAC2 proper motion catalogs. Seven stars in our
study appear to have been ejected from their birthplaces, and at least three of
these runaways are spectroscopic binaries and are of great interest for future
study.Comment: 21 pages, 1 figure, 7 tables; Accepted to Ap
Now you see it, now you don't - the circumstellar disk in the GRO J1008--57 system
Multiwavelength observations are reported here of the Be/X-ray binary pulsar
system GRO J1008-57. Over ten years worth of data are gathered together to show
that the periodic X-ray outbursts are dependant on both the binary motion and
the size of the circumstellar disk. In the first instance an accurate orbital
solution is determined from pulse periods, and in the second case the strength
and shape of the Halpha emission line is shown to be a valuable indicator of
disk size and its behaviour. Furthermore, the shape of the emission line
permits a direct determination of the disk size which is in good agreement with
theoretical estimates. A detailed study of the pulse period variations during
outbursts determined the binary period to be 247.8, in good agreement with the
period determined from the recurrence of the outbursts.Comment: Accepted for publication in MNRA
Nitrogen Enrichment in Atmospheres of A- and F- Type Supergiants
Using new accurate fundamental parameters of 30 Galactic A and F supergiants,
namely their effective temperatures Teff and surface gravities log g, we
implemented a non-LTE analysis of the nitrogen abundance in their atmospheres.
It is shown that the non-LTE corrections to the N abundances increase with
Teff. The nitrogen overabundance as a general feature of this type of stars is
confirmed. A majority of the stars has a nitrogen excess [N/Fe] between 0.2 and
0.9 dex with the maximum position of the star's distribution on [N/Fe] between
0.4 and 0.7 dex. The N excesses are discussed in light of predictions for
B-type main sequence (MS) stars with rotationally induced mixing and for their
next evolutionary phase, i.e. A- and F-type supergiants that have experienced
the first dredge-up. Rotationally induced mixing in the MS progenitors of the
supergiants may be a significant cause of the nitrogen excesses. When comparing
our results with predictions of the theory developed for stars with the mixing,
we find that the bulk of the supergiants (28 of 30) show the N enrichment that
can be expected (i) either after the MS phase for stars with the initial
rotational velocities v0 = 200-400 km s-1, (ii) or after the first dredge-up
for stars with v0 = 50-400 km s-1. The latter possibility is preferred on
account of the longer lifetime for stars on red-blue loops following the first
dredge-up. Two supergiants without a discernible N enrichment, namely HR 825
and HR 7876, may be post-MS objects with the relatively low initial rotational
velocity of about 100 km s-1. The suggested range for v0 is approximately
consistent with inferences from the observed projected rotational velocities of
B-type MS stars, progenitors of A and F supergiants.Comment: 14 pages, 13 figure
Early type stars at high galactic latitudes I. Ten young massive B-type stars
We present the results of quantitative spectral analyses of ten apparently
normal B-type stars. These stars were found to be young massive B-type stars at
distances of z=2.6 to 7.6 kpc from the galactic plane based on their positions
in the (Teff, log g) diagram, normal abundance patterns and/or large projected
rotational velocities. We discuss formation scenarios (runaway star scenarios
versus a scenario for star formation in the halo) by comparing times-of-flight
and evolutionary time scales. For all stars (except SB 357 and HS 1914+7139)
both the scales are similar, indicating that the stars could have formed in the
galactic disk and been ejected from there soon aftertheir birth. Derived
ejection velocities range from 130 km/s to 440 km/s and may be used to
constrain models for ejection mechanisms. Using new proper motion measurements
we show that PHL 346, which was considered the most likely candidate for a
young B-type star born in the halo, can be explained as a runaway star from the
galactic plane.Comment: 11 pages, 5 eps-files, accepted for publication in Astronomy and
Astrophysic
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