4,365 research outputs found
Jets from young stars and brown dwarfs
The protostellar outflow mechanism operates for a significant fraction of the
pre-main sequence phase of a solar mass star and is thought to have a key role
in star and perhaps even planet formation. This energetic mechanism manifests
itself in several different forms and on many scales. Thus outflow activity can
be probed in numerous different regimes from radio to X-ray wavelengths. Recent
discoveries have shown that it is not only solar mass stars that launch
outflows during their formation but also the sub-stellar brown dwarfs. In this
article what is currently known about jets from young stars is summarised,
including an outline of why it is important to study jets. The second part of
this article is dedicated to jets from young brown dwarfs. While only a small
number of brown dwarf outflows have been investigated to date, interesting
properties have been observed. Here observations of brown dwarf outflows are
described and what is currently known of their properties compared to low mass
protostellar outflows.Comment: Astronomische Nachrichten, Special Issue: Reviews in Modern
Astrononm
HH 1158: The lowest luminosity externally irradiated Herbig-Haro jet
We have identified a new externally irradiated Herbig-Haro (HH) jet, HH 1158,
within ~2 pc of the massive OB type stars in the sigma Orionis cluster. At an
Lbol ~ 0.1 Lsun, HH 1158 is the lowest luminosity irradiated HH jet identified
to date in any cluster. Results from the analysis of high-resolution optical
spectra indicate asymmetries in the brightness, morphology, electron density,
velocity, and the mass outflow rates for the blue and red-shifted lobes. We
constrain the position angle of the HH 1158 jet at 102+/-5 degree. The mass
outflow rate and the mean accretion rate for HH 1158 using multiple diagnostics
are estimated to be (5.2 +/- 2.6) x 10^(-10) Msun/yr and (3.0 +/- 1.0) x
10^(-10) Msun/yr, respectively. The properties for HH 1158 are notably similar
to the externally irradiated HH 444 -- HH 447 jets previously identified in
sigma Orionis. In particular, the morphology is such that the weaker jet beam
is tilted towards the massive stars, indicating a higher extent of
photo-evaporation. The high value for the Halpha/[SII] ratio is also consistent
with the ratios measured in other irradiated jets, including HH 444 -- HH 447.
The presence of an extended collimated jet that is bipolar and the evidence of
shocked emission knots make HH 1158 the first unique case of irradiated HH jets
at the very low-luminosity end, and provides an opportunity to learn the
physical properties of very faint HH jet sources.Comment: Accepted in ApJ Letter
Classical T Tauri-like Outflow Activity in the Brown Dwarf Mass Regime
Over the last number of years spectroscopic studies have strongly supported
the assertion that protostellar accretion and outflow activity persists to the
lowest masses. In this paper we present the results of our latest investigation
of brown dwarf (BD) outflow activity and report on the discovery of two new
outflows. Here ISO-Oph 32 is shown to drive a blue-shifted outflow with a
radial velocity of 10-20 km/s and spectro-astrometric analysis constrains the
position angle of this outflow to 240 +/- 7 degrees. The BD candidate ISO-Cha1
217 is found to have a bipolar outflow bright in several key forbidden lines
(radial velocity = -20 km/s, +40 km/s) and with a PA of 190-210 degrees. A
striking feature of the ISO-Cha1 217 outflow is the strong asymmetry between
the red and blue-shifted lobes. This asymmetry is revealed in the relative
brightness of the two lobes (red-shifted lobe is brighter), the factor of two
difference in radial velocity (the red-shifted lobe is faster) and the
difference in the electron density (again higher in the red lobe). Such
asymmetries are common in jets from low mass protostars and the observation of
a marked asymmetry at such a low mass supports the idea that BD outflow
activity is scaled down from low mass protostellar activity.
In addition to presenting these new results, a comprehensive comparison is
made between BD outflow activity and jets launched by CTTSs. In particular, the
application of current methods for investigating the excitation conditions and
mass loss rates in CTT jets to BD spectra is explored.Comment: Accepted by Astrophysical Journa
Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217
As the number of observed brown dwarf outflows is growing it is important to
investigate how these outflows compare to the well studied jets from young
stellar objects. A key point of comparison is the relationship between outflow
and accretion activity and in particular the ratio between the mass outflow and
accretion rates (/). The brown dwarf candidate
ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric
study of brown dwarfs, to be driving an asymmetric outflow with the
blue-shifted lobe having a position angle of 20. The aim here
is to further investigate the properties of ISO-ChaI 217, the morphology and
kinematics of its outflow, and to better constrain
(/). The outflow is spatially resolved in the
lines and is detected out to 1\farcs6
in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry
between the two lobes is confirmed although the velocity asymmetry is less
pronounced with respect to our previous study. Using thirteen different
accretion tracers we measure log() [M/yr]= -10.6
0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI
217 outflow was derived for a range of values of A, up to
a value of A = 2.5 mag estimated for the source extinction. The logarithm
of the mass outflow () was estimated in the range -11.7 to -11.1
for both jets combined. Thus / [\Msun/yr] lies
below the maximum value predicted by magneto-centrifugal jet launching models.
Finally, both model fitting of the Balmer decrements and spectro-astrometric
analysis of the H line show that the bulk of the H I emission comes
from the accretion flow.Comment: accepted by Astronomy & Astrophysic
Effect of Photobiomodulation on Vinblastine-Poisoned Murine HERS Cells
Objective: The aim of this study was to investigate the effect of near-infrared (NIR) photobiomodulation on the proliferation and glutathione levels in murine Hertwig\u27s epithelial root sheath (HERS) cells after poisoning with vinblastine. Background: Photobiomodulation has been shown to improve wound healing in a number of animal models. There have been no studies on the effect of photobiomodulation on cancer-related chemotherapy injury to the cells that initiate tooth root growth. Materials and Methods: Control groups consisted of murine HERS cells without vinblastine (VB−) and cells with vinblastine at 10, 20, and 30 ng/mL (VB10, VB20, and VB30). Experimental groups consisted of these same groups with light therapy (VB-L, VB10L, VB20L, and VB30L). The cells were exposed to vinblastine for 1 h. Photobiomodulation consisted of a 75-cm2 gallium-aluminum-arsenide light-emitting diode (LED) array at an energy density of 12.8 J/cm2, delivered with 50 mW/cm2 power over 256 s. Results: Vinblastine alone significantly decreased HERS cell proliferation and glutathione levels at all concentrations (VB10 [−55%, p \u3c 1.0 × 10−8]; VB20 [−72%, p \u3c 1.0 × 10−9]; VB30 [−80%, p \u3c 1.0 × 10−10]; and VB10 [−36%, p \u3c 0.0001]; VB20 [−49%, p \u3c 1.0 × 10−6]; VB30 [−53%, p \u3c 1.0 × 10−7] respectively). Photobiomodulation significantly increased cell proliferation at all levels of vinblastine exposure (VB10L [+50%, p \u3c 0.0001]; VB20L [+45%, p \u3c 0.05]; VB30 [+39%, p \u3c 0.05]) but not of the control (+22%, p  = 0.063). The photobiomodulation significantly increased glutathione production in all concentrations of vinblastine except 20 ng/mL (VB10L [+39%, p = 0.007]; VB20L [+19%, p = 0.087]; VB30 [+14%, p = 0.025]) and the control (+12%, p = 0.13). Conclusions: Photobiomodulation demonstrated an improvement in proliferation and glutathione levels in vinblastine-poisoned murine HERS cells
XMM-Newton observation of SNR J0533-7202 in the Large Magellanic Cloud
Aims. We present an X-ray study of the supernova remnant SNR J0533-7202 in
the Large Magellanic Cloud (LMC) and determine its physical characteristics
based on its X-ray emission. Methods. We observed SNR J0533-7202 with
XMM-Newton (flare-filtered exposure times of 18 ks EPIC-pn and 31 ks
EPIC-MOS1/MOS2). We produced X-ray images of the SNR, performed an X-ray
spectral analysis, and compared the results to multi-wavelength studies.
Results. The distribution of X-ray emission is highly non-uniform, with the
south-west region brighter than the north-east. The X-ray emission is
correlated with the radio emission from the remnant. We determine that this
morphology is likely due to the SNR expanding into a non-uniform ambient medium
and not an absorption effect. We estimate the size to be 53.9 (\pm 3.4) x 43.6
(\pm 3.4) pc, with the major axis rotated ~64 degrees east of north. We find no
spectral signatures of ejecta and infer that the X-ray plasma is dominated by
swept-up interstellar medium. Using the spectral fit results and the Sedov
self-similar solution, we estimate an age of ~17-27 kyr, with an initial
explosion energy of (0.09-0.83) x 10^51 erg. We detected an X-ray source
located near the centre of the remnant, namely XMMU J053348.2-720233. The
source type could not be conclusively determined due to the lack of a
multi-wavelength counterpart and low X-ray counts. We find that it is likely
either a background active galactic nucleus or a low-mass X-ray binary in the
LMC. Conclusions. We detected bright thermal X-ray emission from SNR J0533-7202
and determined that the remnant is in the Sedov phase of its evolution. The
lack of ejecta emission prohibits us from typing the remnant with the X-ray
data. Therefore, the likely Type Ia classification based on the local stellar
population and star formation history reported in the literature cannot be
improved upon.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Treatment of calibration uncertainty in multi-baseline cross-correlation searches for gravitational waves
Uncertainty in the calibration of gravitational wave (GW) detector data leads to systematic errors, which must be accounted for in setting limits on the strength of GW signals. When cross-correlation measurements are made using data from a pair of instruments, as in searches for a stochastic GW background, the calibration uncertainties of the individual instruments can be combined into an uncertainty associated with the pair. With the advent of multi-baseline GW observation (e.g., networks consisting of multiple detectors such as the LIGO observatories and Virgo), a more sophisticated treatment is called for. We have described how the correlations between calibration factors associated with different pairs can be taken into account by marginalizing over the uncertainty associated with each instrument
Stochastic Background Search Correlating ALLEGRO with LIGO Engineering Data
We describe the role of correlation measurements between the LIGO
interferometer in Livingston, LA, and the ALLEGRO resonant bar detector in
Baton Rouge, LA, in searches for a stochastic background of gravitational
waves. Such measurements provide a valuable complement to correlations between
interferometers at the two LIGO sites, since they are sensitive in a different,
higher, frequency band. Additionally, the variable orientation of the ALLEGRO
detector provides a means to distinguish gravitational wave correlations from
correlated environmental noise. We describe the analysis underway to set a
limit on the strength of a stochastic background at frequencies near 900 Hz
using ALLEGRO data and data from LIGO's E7 Engineering Run.Comment: 8 pages, 2 encapsulated PostScript figures, uses IOP class files,
submitted to the proceedings of the 7th Gravitational Wave Data Analysis
Workshop (which will be published in Classical and Quantum Gravity
Uncovering the Outflow Driven by the Brown Dwarf LS-RCr A1: H-alpha as a Tracer of Outflow Activity in Brown Dwarfs
It is now apparent that classical T Tauri-like outflows commonly accompany
the formation of young brown dwarfs. To date two optical outflows have been
discovered and results presented in this paper increase this number to three.
Using spectro-astrometry the origin of the LS-RCrA 1 forbidden emission lines
in a blue-shifted outflow is confirmed. The non-detection of the red-shifted
component of the outflow in forbidden lines, along with evidence for some
separation between low and high velocity outflow components, do not support the
hypothesis that LS-RCrA 1 has an edge-on accretion disk. The key result of this
analysis is the discovery of an outflow component to the H-alpha line. The
H-alpha line profile has blue and red-shifted features in the wings which
spectro-astrometry reveals to also originate in the outflow. The discovery that
H-alpha emission in BDs can have a significant contribution from an outflow
suggests the use of H-alpha line widths as a proxy of mass accretion in BDs is
not clear-cut. This method assumes that any contribution to the H-alpha line
flux from a possible outflow is negligible. Finally the fact that the H-alpha
line traces both lobes of the outflow while only the blue-shifted lobe is seen
in forbidden emission points to the presence of a dust hole in the accretion
disk of LS-RCrA 1. This is commonly seen in CTTSs and is assumed to signal the
onset of planet formation.Comment: 13 pages, 2 figure
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