514 research outputs found
High-resolution Spectroscopy of [Ne II] Emission from TW Hya
We present high-resolution echelle spectra of [Ne II] 12.81 micron emission
from the classical T Tauri star (CTTS) TW Hya obtained with MICHELLE on Gemini
North. The line is centered at the stellar radial velocity and has an intrinsic
FWHM of 21\pm 4 km/s. The line width is broader than other narrow emission
lines typically associated with the disk around TW Hya. If formed in a disk,
the line broadening could result from turbulence in a warm disk atmosphere,
Keplerian rotation at an average distance of 0.1 AU from the star, or a
photoevaporative flow from the optically-thin region of the disk. We place
upper limits on the [Ne II] emission flux from the CTTSs DP Tau and BP Tau.Comment: Accepted by ApJ. 18 pages, including 2 figures and 2 table
Far infrared CO and HO emission in intermediate-mass protostars
Intermediate-mass young stellar objects (YSOs) provide a link to understand
how feedback from shocks and UV radiation scales from low to high-mass star
forming regions. Aims: Our aim is to analyze excitation of CO and HO in
deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass
YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with
bolometric luminosities of . The maps
cover spatial scales of AU in several CO and HO lines located
in the m range. Results: Rotational diagrams of CO show two
temperature components at K and
K, comparable to low- and high-mass protostars
probed at similar spatial scales. The diagrams for HO show a single
component at K, as seen in low-mass protostars, and
about K lower than in high-mass protostars. Since the uncertainties in
are of the same order as the difference between the
intermediate and high-mass protostars, we cannot conclude whether the change in
rotational temperature occurs at a specific luminosity, or whether the change
is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation
in intermediate-mass protostars is comparable to the central AU of
low-mass protostars and consistent within the uncertainties with the high-mass
protostars probed at AU scales, suggesting similar shock
conditions in all those sources.Comment: Accepted to Astronomy & Astrophysics. 4 pages, 5 figures, 3 table
Testing particle trapping in transition disks with ALMA
We present new Atacama Large Millimeter/submillimeter Array (ALMA) continuum
observations at 336GHz of two transition disks, SR21 and HD135344B. In
combination with previous ALMA observations from Cycle 0 at 689GHz, we compare
the visibility profiles at the two frequencies and calculate the spectral index
(). The observations of SR21 show a clear shift in the
visibility nulls, indicating radial variations of the inner edge of the cavity
at the two wavelengths. Notable radial variations of the spectral index are
also detected for SR21 with values of in the
inner region ( AU) and outside. An
axisymmetric ring (which we call the ring model) or a ring with the addition of
an azimuthal Gaussian profile, for mimicking a vortex structure (which we call
the vortex model), is assumed for fitting the disk morphology. For SR21, the
ring model better fits the emission at 336GHz, conversely the vortex model
better fits the 689GHz emission. For HD135344B, neither a significant shift in
the null of the visibilities nor radial variations of are
detected. Furthermore, for HD135344B, the vortex model fits both frequencies
better than the ring model. However, the azimuthal extent of the vortex
increases with wavelength, contrary to model predictions for particle trapping
by anticyclonic vortices. For both disks, the azimuthal variations of
remain uncertain to confirm azimuthal trapping. The
comparison of the current data with a generic model of dust evolution that
includes planet-disk interaction suggests that particles in the outer disk of
SR21 have grown to millimetre sizes and have accumulated in a radial pressure
bump, whereas with the current resolution there is not clear evidence of radial
trapping in HD135344B, although it cannot be excluded either.Comment: Minor changes after language edition. Accepted for publication in A&A
(abstract slightly shortened for arXiv
The Effects of UV Continuum and Lyman alpha Radiation on the Chemical Equilibrium of T Tauri Disks
We show in this Letter that the spectral details of the FUV radiation fields
have a large impact on the chemistry of protoplanetary disks surrounding T
Tauri stars. We show that the strength of a realistic stellar FUV field is
significantly lower than typically assumed in chemical calculations and that
the radiation field is dominated by strong line emission, most notably Lyman
alpha radiation. The effects of the strong Lyman alpha emission on the chemical
equilibrium in protoplanetary disks has previously been unrecognized. We
discuss the impact of this radiation on molecular observations in the context
of a radiative transfer model that includes both direct attenuation and
scattering. In particular, Lyman alpha radiation will directly dissociate water
vapor and may contribute to the observed enhancements of CN/HCN in disks.Comment: 14 pages, 4 figures, accepted by ApJ Letter
Herschel PACS observations of shocked gas associated with the jets of L1448 and L1157
In the framework of the WISH key program, several H2O (E_u>190 K), high-J CO,
[OI], and OH transitions are mapped with PACS in two shock positions along the
two prototypical low-luminosity outflows L1448 and L1157. Previous HIFI H2O
observations (E_u=53-249 K) and complementary Spitzer mid-IR H2 data are also
used, with the aim of deriving a complete picture of the excitation conditions.
At all selected spots a close spatial association between H2O, mid-IR H2, and
high-J CO emission is found, whereas the low-J CO emission traces either
entrained ambient gas or a remnant of an older shock. The excitation analysis
at L1448-B2 suggests that a two-component model is needed to reproduce the H2O,
CO, and mid-IR H2 lines: an extended warm component (T~450 K) is traced by the
H2O emission with E_u =53-137 K and by the CO lines up to J=22-21, and a
compact hot component (T=1100 K) is traced by the H2O emission with E_u>190 K
and by the higher-J CO lines. At L1448-B2 we obtain an H2O abundance
(3-4)x10^{-6} for the warm component and (0.3-1.3)x10^{-5} for the hot
component; we also detect OH and blue-shifted [OI] emission, spatially
coincident with the other molecular lines and with [FeII] emission. This
suggests a dissociative shock for these species, related to the embedded atomic
jet. On the other hand, a non-dissociative shock at the point of impact of the
jet on the cloud is responsible for the H2O and CO emission. The other examined
shock positions show an H2O excitation similar to L1448-B2, but a slightly
higher H2O abundance (a factor of 4). The two gas components may represent a
gas stratification in the post-shock region. The extended and low-abundance
warm component traces the post-shocked gas that has already cooled down to a
few hundred Kelvin, whereas the compact and possibly higher-abundance hot
component is associated with the gas that is currently undergoing a shock
episode.Comment: Accepted for publication in Astronomy and Astrophysic
Differential effects of caffeine on hair shaft elongation, matrix and outer root sheath keratinocyte proliferation, and TGF-beta2-/IGF-1-mediated regulation of hair cycle in male and female human hair follicles in vitro.
BACKGROUND: Caffeine reportedly counteracts the suppression of hair shaft production by testosterone in organ-cultured male human hair follicles (HFs). OBJECTIVES: We aimed at investigating the impact of caffeine a) on additional key hair growth parameters, b) on major hair growth-regulatory growth factors and c) on male versus female HFs in the presence of testosterone. METHODS: Microdissected male and female human scalp HFs were treated in serum-free organ culture for 120 h with testosterone alone (0,5 mug/ml) or in combination with caffeine (0.005-0.0005%), and effects on hair shaft elongation, HF cycling (i.e. anagen-catagen transition), hair matrix keratinocyte proliferation and expression of a key catagen inducer, transforming growth factor beta2 (TGF-beta2), and anagen-prolonging insulin-like growth factor 1 (IGF-1) were evaluated by quantitative (immuno-) histomorphometry. Caffeine effects were further investigated in human outer root sheath keratinocytes (ORSK). RESULTS: Caffeine enhanced hair shaft elongation, prolonged anagen duration and stimulated hair matrix keratinocyte proliferation. Female HFs showed higher sensitivity to caffeine compared to male HFs. Caffeine counteracted testosterone-enhanced TGF-beta2 protein expression in male HFs. In female HFs, testosterone failed to induce TGF-beta2 expression, while caffeine reduced it. In male and female HFs, caffeine enhanced IGF-1 protein expression. In ORSK, caffeine stimulated cell proliferation, inhibited apoptosis/necrosis, up-regulated IGF-1 gene expression and protein secretion, while TGF-beta2 protein secretion was down-regulated. CONCLUSIONS: This study reveals new growth-promoting effects of caffeine on human hair follicles of both genders at different (molecular, cellular and organ) levels. This article is protected by copyright. All rights reserved
X-Shooter study of accretion in Chamaeleon I: II. A steeper increase of accretion with stellar mass for very low mass stars?
The dependence of the mass accretion rate on the stellar properties is a key
constraint for star formation and disk evolution studies. Here we present a
study of a sample of stars in the Chamaeleon I star forming region carried out
using the VLT/X-Shooter spectrograph. The sample is nearly complete down to
M~0.1Msun for the young stars still harboring a disk in this region. We derive
the stellar and accretion parameters using a self-consistent method to fit the
broad-band flux-calibrated medium resolution spectrum. The correlation between
the accretion luminosity to the stellar luminosity, and of the mass accretion
rate to the stellar mass in the logarithmic plane yields slopes of 1.9 and 2.3,
respectively. These slopes and the accretion rates are consistent with previous
results in various star forming regions and with different theoretical
frameworks. However, we find that a broken power-law fit, with a steeper slope
for stellar luminosity smaller than ~0.45 Lsun and for stellar masses smaller
than ~ 0.3 Msun, is slightly preferred according to different statistical
tests, but the single power-law model is not excluded. The steeper relation for
lower mass stars can be interpreted as a faster evolution in the past for
accretion in disks around these objects, or as different accretion regimes in
different stellar mass ranges. Finally, we find two regions on the mass
accretion versus stellar mass plane empty of objects. One at high mass
accretion rates and low stellar masses, which is related to the steeper
dependence of the two parameters we derived. The second one is just above the
observational limits imposed by chromospheric emission. This empty region is
located at M~0.3-0.4Msun, typical masses where photoevaporation is known to be
effective, and at mass accretion rates ~10^-10 Msun/yr, a value compatible with
the one expected for photoevaporation to rapidly dissipate the inner disk.Comment: Accepted for publication on Astronomy & Astrophysics. Abstract
shortened for arxiv constraints. Revised version after language editin
[OI]63micron jets in class 0 sources detected by Herschel
We present Herschel PACS mapping observations of the [OI]63 micron line
towards protostellar outflows in the L1448, NGC1333-IRAS4, HH46, BHR71 and
VLA1623 star forming regions. We detect emission spatially resolved along the
outflow direction, which can be associated with a low excitation atomic jet. In
the L1448-C, HH46 IRS and BHR71 IRS1 outflows this emission is kinematically
resolved into blue- and red-shifted jet lobes, having radial velocities up to
200 km/s. In the L1448-C atomic jet the velocity increases with the distance
from the protostar, similarly to what observed in the SiO jet associated with
this source. This suggests that [OI] and molecular gas are kinematically
connected and that this latter could represent the colder cocoon of a jet at
higher excitation. Mass flux rates (\.M(OI)) have been measured from
the [OI]63micron luminosity adopting two independent methods. We find values in
the range 1-4 10 Mo/yr for all sources but HH46, for which an order of
magnitude higher value is estimated. \.M(OI) are compared with mass
accretion rates (\.M) onto the protostar and with \.M derived
from ground-based CO observations. \.M(OI)/\.M ratios are in
the range 0.05-0.5, similar to the values for more evolved sources.
\.M(OI) in HH46 IRS and IRAS4A are comparable to \.M(CO), while
those of the remaining sources are significantly lower than the corresponding
\.M(CO). We speculate that for these three sources most of the mass
flux is carried out by a molecular jet, while the warm atomic gas does not
significantly contribute to the dynamics of the system.Comment: 37 pages and 12 figures, accepted for publication on Astrophysical
Journa
Morphological evidence for enhanced kisspeptin and neurokinin B signaling in the infundibular nucleus of the aging man.
Peptidergic neurons synthesizing kisspeptin (KP) and neurokinin B (NKB) in the hypothalamic infundibular nucleus have been implicated in negative sex steroid feedback to GnRH neurons. In laboratory rodents, testosterone decreases KP and NKB expression in this region. In the present study, we addressed the hypothesis that the weakening of this inhibitory testosterone feedback in elderly men coincides with enhanced KP and NKB signaling in the infundibular nucleus. This central hypothesis was tested in a series of immunohistochemical studies on hypothalamic sections of male human individuals that were divided into arbitrary "young" (21-49 yr, n = 11) and "aged" (50-67 yr, n = 9) groups. Quantitative immunohistochemical experiments established that the regional densities of NKB-immunoreactive (IR) perikarya and fibers, and the incidence of afferent contacts they formed onto GnRH neurons, exceeded several times those of the KP-IR elements. Robust aging-dependent enhancements were identified in the regional densities of KP-IR perikarya and fibers and the incidence of afferent contacts they established onto GnRH neurons. The abundance of NKB-IR perikarya, fibers, and axonal appositions to GnRH neurons also increased with age, albeit to lower extents. In dual-immunofluorescent studies, the incidence of KP-IR NKB perikarya increased from 36% in young to 68% in aged men. Collectively, these immunohistochemical data suggest an aging-related robust enhancement in central KP signaling and a moderate enhancement in central NKB signaling. These changes are compatible with a reduced testosterone negative feedback to KP and NKB neurons. The heavier KP and NKB inputs to GnRH neurons in aged, compared with young, men may play a role in the enhanced central stimulation of the reproductive axis. It requires clarification to what extent the enhanced KP and NKB signaling upstream from GnRH neurons is an adaptive response to hypogonadism or, alternatively, a consequence of a decline in the androgen sensitivity of KP and NKB neurons
The formation of planetary disks and winds: an ultraviolet view
Planetary systems are angular momentum reservoirs generated during star
formation. This accretion process produces very powerful engines able to drive
the optical jets and the molecular outflows. A fraction of the engine energy is
released into heating thus the temperature of the engine ranges from the 3000K
of the inner disk material to the 10MK in the areas where magnetic reconnection
occurs. There are important unsolved problems concerning the nature of the
engine, its evolution and the impact of the engine in the chemical evolution of
the inner disk. Of special relevance is the understanding of the shear layer
between the stellar photosphere and the disk; this layer controls a significant
fraction of the magnetic field building up and the subsequent dissipative
processes ougth to be studied in the UV.
This contribution focus on describing the connections between 1 Myr old suns
and the Sun and the requirements for new UV instrumentation to address their
evolution during this period. Two types of observations are shown to be needed:
monitoring programmes and high resolution imaging down to, at least,
milliarsecond scales.Comment: Accepted for publication in Astrophysics and Space Science 9 figure
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