5,677 research outputs found
Gamma-rays from massive protostars
Massive protostars have associated bipolar outflows with velocities of
hundreds of km/s. Such outflows produce strong shocks when interact with the
ambient medium leading to regions of non-thermal radio emission. Under certain
conditions, the population of relativistic particles accelerated at the
terminal shocks of the protostellar jets can produce significant gamma-ray
emission. We estimate the conditions necessary for high-energy emission in the
non-thermal hot spots of jets associated with massive protostars embedded in
dense molecular clouds. Our results show that particle-matter interactions can
lead to the detection of molecular clouds hosting massive young stellar objects
by the Fermi satellite at MeV-GeV energies and even by Cherenkov telescope
arrays in the GeV-TeV range. Astronomy at gamma-rays can be used to probe the
physical conditions in star forming regions and particle acceleration processes
in the complex environment of massive molecular clouds.Comment: Proceeding of the conference "High Energy Phenomena in Massive
Stars". Jaen (Spain), 2-5 February 200
Theory of phonon-assisted "forbidden" optical transitions in spin-gapped systems
We consider the absorption of light with emission of one S(tot)=1 magnetic
excitation in systems with a spin gap induced by quantum fluctuations. We argue
that an electric dipole transition is allowed on the condition that a virtual
phonon instantaneously breaks the inversion symmetry. We derive an effective
operator for the transition and argue that the proposed theory explains the
polarized experiments in CuGeO(3) and SrCu(2)[BO(3)](2).Comment: 9 pages, 4 figure
Comparative investigation of the coupled-tetrahedra quantum spin systems Cu2Te2O5X2, X=Cl, Br and Cu4Te5O12Cl4
We present a comparative study of the coupled-tetrahedra quantum spin systems
Cu2Te2O5X2, X=Cl, Br (Cu-2252(X)) and the newly synthesized Cu4Te5O12Cl4
(Cu-45124(Cl)) based on ab initio Density Functional Theory calculations. The
magnetic behavior of Cu-45124(Cl) with a phase transition to an ordered state
at a lower critical temperature T=13.6K than in Cu-2252(Cl) (T=18K) can
be well understood in terms of the modified interaction paths. We identify the
relevant structural changes between the two systems and discuss the
hypothetical behavior of the not yet synthesized Cu-45124(Br) with an ab initio
relaxed structure using Car-Parrinello Molecular Dynamics.Comment: 2 pages, 1 figure; submitted to Proceedings of M2S-HTSC VIII, Dresden
200
Exercise training attenuates acute hyperalgesia in streptozotocin-induced diabetic female rats
OBJECTIVES: We investigated the effects of chronic (eight weeks) low-to moderate-intensity swimming training on thermal pain sensitivity in streptozotocin-induced diabetic female rats. METHODS: Female Wistar rats (n = 51) were divided into the following groups: trained streptozotocin-induced diabetic rats [hyperglycemic trained (HT)], sedentary streptozotocin-induced diabetic rats [hyperglycemic sedentary (HS)], normoglycemic trained rats (NT) and normoglycemic sedentary rats (NS). Diabetes was induced by a single injection of streptozotocin (50 mg/kg, i.p.). One day after the last exercise protocol (60 min/day, five days/week for eight weeks) in the trained groups or after water stress exposure (ten min/twice a week) in the sedentary groups, the rats were subjected to a hot plate test. RESULTS: After eight weeks of swimming training, streptozotocin-induced diabetic rats presented a significantly lower body mass (trained: 219.5±29 g, sedentary: 217.8±23 g) compared with the normoglycemic groups (trained: 271±24 g, sedentary: 275.7±32 g). Interestingly, we did not find differences in blood glucose levels (mg/dl) between the trained and sedentary groups of the hyperglycemic or normoglycemic rats (HT: 360.2±6.6, HS: 391.7±6.7, NT: 83.8±14.0, NS: 77.5±10.1). In the hot plate test, the rats from the HT group presented a significantly lower latency than the other rats (HT: 11.7±7.38 s, HS: 7.02±7.38 s, NT: 21.21±7.64 s, NS: 22.82±7.82 s). CONCLUSION: Low-to-moderate swimming training for a long duration reduces thermal hyperalgesia during a hot plate test in streptozotocin-induced diabetic female rats
The Giraffe Inner Bulge Survey (GIBS) II. Metallicity distributions and alpha element abundances at fixed Galactic latitude
High resolution (R22,500) spectra for 400 red clump giants, in four
fields within and , were obtained within the GIRAFFE
Inner Bulge Survey (GIBS) project. To this sample we added another 400
stars in Baade's Window, observed with the identical instrumental
configuration. We constructed the metallicity distributions for the entire
sample, as well as for each field individually, in order to investigate the
presence of gradients or field-to-field variations in the shape of the
distributions. The metallicity distributions in the five fields are consistent
with being drawn from a single parent population, indicating the absence of a
gradient along the major axis of the Galactic bar. The global metallicity
distribution is well fitted by two Gaussians. The metal poor component is
rather broad, with a mean at dex and dex.
The metal-rich one is narrower, with mean and
dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with
respect to solar in the metal-poor regime, similar to the one observed for
giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend,
but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is
observed at dex. This \textit{knee} is in agreement with our
previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in
metallicity than the one reported for the Bulge micro lensed dwarf and
sub-giant stars. We found no variation in -element abundance
distributions between different fields.Comment: Accepted for publication in A&
Explosion of a massive, He-rich star at z=0.16
We present spectroscopic and photometric data of the peculiar SN 2001gh,
discovered by the 'Southern inTermediate Redshift ESO Supernova Search'
(STRESS) at a redshift z=0.16. SN 2001gh has relatively high luminosity at
maximum (M_B = -18.55 mag), while the light curve shows a broad peak. An
early-time spectrum shows an almost featureless, blue continuum with a few weak
and shallow P-Cygni lines that we attribute to HeI. HeI lines remain the only
spectral features visible in a subsequent spectrum, obtained one month later. A
remarkable property of SN 2001gh is the lack of significant spectral evolution
over the temporal window of nearly one month separating the two spectra. In
order to explain the properties of SN 2001gh, three powering mechanism are
explored, including radioactive decays of a moderately large amount of 56Ni,
magnetar spin-down, and interaction of SN ejecta with circumstellar medium. We
favour the latter scenario, with a SN Ib wrapped in a dense, circumstellar
shell. The fact that no models provide an excellent fit with observations,
confirms the troublesome interpretation of the nature of SN 2001gh. A rate
estimate for SN 2001gh-like event is also provided, confirming the intrinsic
rarity of these objects.Comment: 11 pages, 8 figures, 3 tables. Accepted by MNRA
The Type IIP SN 2007od in UGC 12846: from a bright maximum to dust formation in the nebular phase
Ultraviolet (UV), optical and near infrared (NIR) observations of the type
IIP supernova (SN) 2007od are presented, covering from the maximum light to the
late phase, allowing to investigate in detail different physical phenomena in
the expanding ejecta. These data turn this object into one of the most peculiar
IIP ever studied. The early light curve of SN 2007od is similar to that of a
bright IIPs with a short plateau, a bright peak (MV = -18 mag), but a very
faint optical light curve at late time. However, with the inclusion of mid
infrared (MIR) observations during the radioactive decay we have estimate a
M(56Ni) ~ 2\times10^-2 M\odot. Modeling the bolometric light curve, ejecta
expansion velocities and black-body temperature, we estimate a total ejected
mass was 5 - 7.5 M\odot with a kinetic energy of at least 0.5 \times 10^51 erg.
The early spectra reveal a boxy H{\alpha} profile and high velocities features
of the Balmer series that suggest interaction between the ejecta and a close
circum-stellar matter (CSM). SN 2007od may be, therefore, an intermediate case
between a Type IIn SN and a typical Type IIP SN. Also late spectra show a clear
evidence of CSM and the presence of dust formed inside the ejecta. The episodes
of mass loss short before explosion, the bright plateau, along with the
relatively small amount of 56Ni and the faint [O I] observed in the nebular
spectra are consistent with a super-asympthotic giant branch (super-AGB)
progenitor (M~9.7 - 11 M\odot).Comment: V2, some test added and three figures changed from the first version.
21 pages, 18 figures, accepted for publication in MNRAS on May 24, 201
A Panchromatic Study of the Globular Cluster NGC 1904. I: The Blue Straggler Population
By combining high-resolution (HST-WFPC2) and wide-field ground based (2.2m
ESO-WFI) and space (GALEX) observations, we have collected a multi-wavelength
photometric data base (ranging from the far UV to the near infrared) of the
galactic globular cluster NGC1904 (M79). The sample covers the entire cluster
extension, from the very central regions up to the tidal radius. In the present
paper such a data set is used to study the BSS population and its radial
distribution. A total number of 39 bright () BSS has been
detected, and they have been found to be highly segregated in the cluster core.
No significant upturn in the BSS frequency has been observed in the outskirts
of NGC 1904, in contrast to other clusters (M 3, 47 Tuc, NGC 6752, M 5) studied
with the same technique. Such evidences, coupled with the large radius of
avoidance estimated for NGC 1904 ( core radii), indicate that
the vast majority of the cluster heavy stars (binaries) has already sunk to the
core. Accordingly, extensive dynamical simulations suggest that BSS formed by
mass transfer activity in primordial binaries evolving in isolation in the
cluster outskirts represent only a negligible (0--10%) fraction of the overall
population.Comment: ApJ accepte
Characteristic velocities of stripped-envelope core-collapse supernova cores
The velocity of the inner ejecta of stripped-envelope core-collapse
supernovae (CC-SNe) is studied by means of an analysis of their nebular
spectra. Stripped-envelope CC-SNe are the result of the explosion of bare cores
of massive stars ( M), and their late-time spectra are
typically dominated by a strong [O {\sc i}] 6300, 6363 emission
line produced by the innermost, slow-moving ejecta which are not visible at
earlier times as they are located below the photosphere. A characteristic
velocity of the inner ejecta is obtained for a sample of 56 stripped-envelope
CC-SNe of different spectral types (IIb, Ib, Ic) using direct measurements of
the line width as well as spectral fitting. For most SNe, this value shows a
small scatter around 4500 km s. Observations ( days) of
stripped-envelope CC-SNe have revealed a subclass of very energetic SNe, termed
broad-lined SNe (BL-SNe) or hypernovae, which are characterised by broad
absorption lines in the early-time spectra, indicative of outer ejecta moving
at very high velocity (). SNe identified as BL in the early phase
show large variations of core velocities at late phases, with some having much
higher and some having similar velocities with respect to regular CC-SNe. This
might indicate asphericity of the inner ejecta of BL-SNe, a possibility we
investigate using synthetic three-dimensional nebular spectra.Comment: 14 pages, 10 figures, MNRAS accepte
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