1,000 research outputs found
On-Line Diffusion Profile of a Lipophilic Model Dye in Different Depths of a Hair Follicle in Human Scalp Skin
In skin and hair research, drug targeting to the hair follicle is of great interest in the treatment of skin diseases. The aim of this study is to visualize on-line the diffusion processes of a model fluorophore into the hair follicle at different depths using fresh human scalp skin and confocal laser scanning microscopy. Up to a depth of 500 ÎŒm in the skin, a fast increase of fluorescence is observed in the gap followed by accumulation of the dye in the hair cuticle. Penetration was also observed via the stratum corneum and the epidermis. Little label reached depths greater than 2000 ÎŒm. Fat cells accumulated the label fastest, followed by the cuticular area and the outer root sheath of the hair follicle. Sweat glands revealed very low staining, whereas the bulb at a depth of 4000 ÎŒm was visualized only by autofluorescence. From this study, we conclude that on-line visualization is a promising technique to access diffusion processes in deep skin layers even on a cellular level. Furthermore, we conclude that the gap and the cuticle play an important role in the initial diffusion period with the label in the cuticle originating from the gap
The Missing Luminous Blue Variables and the Bistability Jump
We discuss an interesting feature of the distribution of luminous blue
variables on the H-R diagram, and we propose a connection with the bistability
jump in the winds of early-type supergiants. There appears to be a deficiency
of quiescent LBVs on the S Dor instability strip at luminosities between log
L/Lsun = 5.6 and 5.8. The upper boundary, is also where the
temperature-dependent S Dor instability strip intersects the bistability jump
at about 21,000 K. Due to increased opacity, winds of early-type supergiants
are slower and denser on the cool side of the bistability jump, and we
postulate that this may trigger optically-thick winds that inhibit quiescent
LBVs from residing there. We conduct numerical simulations of radiation-driven
winds for a range of temperatures, masses, and velocity laws at log L/Lsun=5.7
to see what effect the bistability jump should have. We find that for
relatively low stellar masses the increase in wind density at the bistability
jump leads to the formation of a modest to strong pseudo photosphere -- enough
to make an early B-type star appear as a yellow hypergiant. Thus, the proposed
mechanism will be most relevant for LBVs that are post-red supergiants. Yellow
hypergiants like IRC+10420 and rho Cas occupy the same luminosity range as the
``missing'' LBVs, and show apparent temperature variations at constant
luminosity. If these yellow hypergiants do eventually become Wolf-Rayet stars,
we speculate that they may skip the normal LBV phase, at least as far as their
apparent positions on the HR diagram are concerned.Comment: 20 pages, 4 figs, accepted by Ap
The Infrared Continuum Sizes of Be Star Disks
We present an analysis of the near-infrared continuum emission from the
circumstellar gas disks of Be stars using a radiative transfer code for a
parametrized version of the viscous decretion disk model. This isothermal gas
model creates predicted images that we use to estimate the HWHM emission radius
along the major axis of the projected disk and the spatially integrated flux
excess at wavelengths of 1.7, 2.1, 4.8, 9, and 18 ?m. We discuss in detail the
effect of the disk base density, inclination angle, stellar effective
temperature, and other physical parameters on the derived disk sizes and color
excesses. We calculate color excess estimates relative to the stellar V -band
flux for a sample of 130 Be stars using photometry from 2MASS and the AKARI
infrared camera all-sky survey. The color excess relations from our models make
a good match of the observed color excesses of Be stars. We also present our
results on the projected size of the disk as a function of wavelength for the
classical Be star ? Tauri, and we show that the model predictions are
consistent with interferometric observations in the H, K', and 12 \mu m bands
Critical Micronutrients in Pregnancy, Lactation, and Infancy: Considerations on Vitamin D, Folic Acid, and Iron, and Priorities for Future Research
The Early Nutrition Academy and the European Commission-funded EURRECA Network of Excellence jointly sponsored a scientific workshop on critical micronutrients in pregnancy, lactation, and infancy. Current knowledge and unresolved questions on the supply of vitamin D, folic acid, and iron for pregnant women, lactating women, and infants, and their health effects were discussed. The question was addressed of whether, and under which circumstances, supplementation with these micronutrients in addition to usual dietary intakes is advisable. The workshop participants concluded that public health strategies for improving supplementation with these micronutrients in pregnancy, lactation, and infancy are required. Further research priorities should focus on adequately powered human intervention trials to obtain a stronger evidence base for the amounts of vitamin D, folic acid, and iron that have optimal effects on health. The conclusions of the workshop should help to inform the scientific community as well as public health policy strategies. Copyright (C) 2011 S. Karger AG, Base
The first X-ray survey of Galactic Luminous Blue Variables
Aims: The X-ray emission of massive stars has been studied when these objects
are in their main-sequence phase, as well as in their Wolf-Rayet phase.
However, the X-ray properties of the transitional Luminous Blue Variable (LBV)
phase remain unknown. Methods: Using a dedicated but limited XMM survey as well
as archival XMM and Chandra observations, we performed the first X-ray survey
of LBVs: about half of the known LBVs or candidate LBVs are studied. Results:
Apart from the well known X-ray sources eta Car and Cyg OB2 #12, four
additional LBVs are detected in this survey, though some doubt remains on the
association with the X-ray source for two of these. For the other LBVs, upper
limits on the flux were derived, down to for
PCyg. This variety in the strength of the X-ray emission is discussed, with
particular emphasis on the potential influence of binarity.Comment: 13 pages, 2 figures, accepted by A&
Fundamental parameters of Be stars located in the seismology fields of COROT
In preparation for the COROT space mission, we determined the fundamental
parameters (spectral type, temperature, gravity, vsini) of the Be stars
observable by COROT in its seismology fields (64 Be stars). We applied a
careful and detailed modeling of the stellar spectra, taking into account the
veiling caused by the envelope, as well as the gravitational darkening and
stellar flattening due to rapid rotation. Evolutionary tracks for fast rotators
were used to derive stellar masses and ages. The derived parameters will be
used to select Be stars as secondary targets (i.e. observed for 5 consecutive
months) and short-run targets of the COROT mission. Furthermore, we note that
the main part of our stellar sample is falling in the second half of the main
sequence life time, and that in most cases the luminosity class of Be stars is
inaccurate in characterizing their evolutionary status.Comment: 25 pages, 9 figures, Accepted for publication in A&
Hard X-ray emission in the star-forming region ON2: discovery with XMM-Newton
We obtained X-ray XMM-Newton observations of the open cluster Berkeley 87 and
the massive star-forming region (SFR) ON 2. In addition, archival infrared
Spitzer Space Telescope observations were used. It is likely that the SFR ON 2
and Berkeley 87 are at the same distance, 1.23 kpc, and hence are associated.
The XMM-Newton observations detected X-rays from massive stars in Berkeley 87
as well as diffuse emission from the SFR ON 2. The two patches of diffuse X-ray
emission are encompassed in the shell-like H II region GAL 75.84+0.40 in the
northern part of ON 2 and in the ON 2S region in the southern part of ON 2. The
diffuse emission from GAL 75.84+0.40 suffers an absorption column equivalent to
A_V approx. 28 mag. Its spectrum can be fitted either with a thermal plasma
model at T < 30 MK or by an absorbed power-law model with gamma; approx. -2.6.
The X-ray luminosity of GAL 75.84+0.40 is L_X approx. 6 10^31 erg/s. The
diffuse emission from ON 2S is adjacent to the ultra-compact H II (UCHII)
region Cygnus 2N, but does not coincide with it or with any other known UCHII
region. It has a luminosity of L_X approx. 4 10^31 erg/s. The spectrum can be
fitted with an absorbed power-law model with gamma; approx.-1.4. We adopt the
view of Turner and Forbes (1982) that the SFR ON 2 is physically associated
with the massive star cluster Berkeley 87 hosting the WO type star WR 142. We
discuss different explanations for the apparently diffuse X-ray emission in
these SFRs. These include synchrotron radiation, invoked by the co-existence of
strongly shocked stellar winds and turbulent magnetic fields in the
star-forming complex, cluster wind emission, or an unresolved population of
discrete sources.Comment: ApJ 2010, 712, 763. Reduced fig. resolution. Full resolution version
is at
http://www.astro.physik.uni-potsdam.de/research/abstracts/oskinova-ber87.htm
MN112: a new Galactic candidate Luminous Blue Variable
We report the discovery of a new Galactic candidate Luminous Blue Variable
(cLBV) via detection of an infrared circular nebula and follow-up spectroscopy
of its central star. The nebula, MN112, is one of many dozens of circular
nebulae detected at m in the {\it Spitzer Space Telescope} archival
data, whose morphology is similar to that of nebulae associated with known
(c)LBVs and related evolved massive stars. Specifically, the core-halo
morphology of MN112 bears a striking resemblance to the circumstellar nebula
associated with the Galactic cLBV GAL 079.29+00.46, which suggests that both
nebulae might have a similar origin and that the central star of MN112 is a
LBV. The spectroscopy of the central star showed that its spectrum is almost
identical to that of the bona fide LBV P Cygni, which also supports the LBV
classification of the object. To further constrain the nature of MN112, we
searched for signatures of possible high-amplitude (\ga 1 mag) photometric
variability of the central star using archival and newly obtained photometric
data covering a 45 year period. We found that the B magnitude of the star was
constant ( 17.10.3 mag) over this period, while in the I band the
star brightened by mag during the last 17 years. Although the
non-detection of large photometric variability leads us to use the prefix
`candidate' in the classification of MN112, we remind that the long-term
photometric stability is not unusual for genuine LBVs and that the brightness
of P Cygni remains relatively stable during the last three centuries.Comment: 6 pages, 3 figures, accepted to MNRA
Discovery of a detached HI gas shell surrounding alpha Orionis
We report the detection of the HI line at 21 cm in the direction of alpha Ori
with the Nancay Radiotelescope and with the Very Large Array. The observations
confirm the previous detection of HI emission centered on alpha Ori, but
additionally reveal for the first time a quasi-stationary detached shell of
neutral atomic hydrogen ~4 arcmin. in diameter (0.24 pc at a distance of 200
pc). The detached shell appears elongated in a direction opposite to the star's
space motion. A simple model shows that this detached atomic gas shell can
result from the collision of the stellar wind from alpha Ori with the local
interstellar medium (ISM). It implies that alpha Ori has been losing matter at
a rate of ~ 1.2x10^-6 solar masses per year for the past 8x10^4 years. In
addition, we report the detection of atomic hydrogen associated with the
far-infrared arc located 6 arcmin. north-east of alpha Ori, that has been
suggested to trace the bow shock resulting from the motion of the star through
the ISM. We report also the detection by the Galaxy Evolution Explorer (GALEX)
of a far-UV counterpart to this arc.Comment: Accepted for publication in the Monthly Notices; version with full
resolution figures available at
http://aramis.obspm.fr/~lebertre/paper-alphaOri_MNRAS.pd
Spectral Energy Distributions of Be and Other Massive Stars
We present spectrophotometric data from 0.4 to 4.2 microns for bright,
northern sky, Be stars and several other types of massive stars. Our goal is to
use these data with ongoing, high angular resolution, interferometric
observations to model the density structure and sky orientation of the gas
surrounding these stars. We also present a montage of the H-alpha and
near-infrared emission lines that form in Be star disks. We find that a
simplified measurement of the IR excess flux appears to be correlated with the
strength of emission lines from high level transitions of hydrogen. This
suggests that the near-IR continuum and upper level line fluxes both form in
the inner part of the disk, close to the star.Comment: 2010, PASP, 122, 37
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