500 research outputs found
Merging of globular clusters within inner galactic regions. II. The Nuclear Star Cluster formation
In this paper we present the results of two detailed N-body simulations of
the interaction of a sample of four massive globular clusters in the inner
region of a triaxial galaxy. A full merging of the clusters takes place,
leading to a slowly evolving cluster which is quite similar to observed Nuclear
Clusters. Actually, both the density and the velocity dispersion profiles match
qualitatively, and quantitatively after scaling, with observed features of many
nucleated galaxies. In the case of dense initial clusters, the merger remnant
shows a density profile more concentrated than that of the progenitors, with a
central density higher than the sum of the central progenitors central
densities. These findings support the idea that a massive Nuclear Cluster may
have formed in early phases of the mother galaxy evolution and lead to the
formation of a nucleus, which, in many galaxies, has indeed a luminosity
profile similar to that of an extended King model. A correlation with galactic
nuclear activity is suggested.Comment: 18 pages, 10 figures, 3 tables. Submitted to ApJ, main journa
Near-IR spectroscopic ages of massive star clusters in M82
Like other starburst galaxies, M82 hosts compact, massive young star clusters
that are interesting both in their own right and as benchmarks for population
synthesis models. Can spectral synthesis models at resolutions around 1000
adequately reproduce the near-IR spectral features and the energy distribution
of these clusters between 0.8 and 2.4 microns? How do the derived cluster
properties compare with previous results from optical studies?
We analyse the spectra of 5 massive clusters in M82, using data acquired with
the spectrograph SpeX on the InfraRed Telescope Facility (NASA/IRTF) and a new
population synthesis tool with a highly improved near-IR extension, based on a
recent collection of empirical and theoretical spectra of red supergiant stars.
We obtain excellent fits across the near-IR with models at quasi-solar
metallicity and a solar neighbourhood extinction law. Spectroscopy breaks a
strong degeneracy between age and extinction in the near-IR colours in the red
supergiant-dominated phase of evolution. The estimated near-IR ages cluster
between 9 and 30 Myr, i.e. the ages at which the molecular bands due to
luminous red supergiants are strongest in the current models. They do not
always agree with optical spectroscopic ages. Adding optical data sometimes
leads to the rejection of the solar neighbourhood extinction law. This is not
surprising considering small-scale structure around the clusters, but it has no
significant effect on the near-IR based spectroscopic ages. [abridged]Comment: 14 pages, 20 figures, uses aa.cl
Super stellar clusters with a bimodal hydrodynamic solution: an Approximate Analytic Approach
We look for a simple analytic model to distinguish between stellar clusters
undergoing a bimodal hydrodynamic solution from those able to drive only a
stationary wind. Clusters in the bimodal regime undergo strong radiative
cooling within their densest inner regions, which results in the accumulation
of the matter injected by supernovae and stellar winds and eventually in the
formation of further stellar generations, while their outer regions sustain a
stationary wind. The analytic formulae are derived from the basic hydrodynamic
equations. Our main assumption, that the density at the star cluster surface
scales almost linearly with that at the stagnation radius, is based on results
from semi-analytic and full numerical calculations. The analytic formulation
allows for the determination of the threshold mechanical luminosity that
separates clusters evolving in either of the two solutions. It is possible to
fix the stagnation radius by simple analytic expressions and thus to determine
the fractions of the deposited matter that clusters evolving in the bimodal
regime blow out as a wind or recycle into further stellar generations.Comment: 5 pages, 4 figures, accepted by A&
BEAM POSITION AND PHASE MONITORS FOR THE LANSCE LINAC*
Abstract New beam-position and phase monitors are under development for the linac at the Los Alamos Neutron Science Center (LANSCE.) Transducers have been designed and are being installed. We are considering many options for the electronic instrumentation to process the signals and provide position and phase data with the necessary precision and flexibility to serve the various required functions. We'll present the various options under consideration for instrumentation along with the advantages and shortcomings of these options
A Giant Outburst at Millimeter Wavelengths in the Orion Nebula
BIMA observations of the Orion nebula discovered a giant flare from a young
star previously undetected at millimeter wavelengths. The star briefly became
the brightest compact object in the nebula at 86 GHz. Its flux density
increased by more than a factor of 5 on a timescale of hours, to a peak of 160
mJy. This is one of the most luminous stellar radio flares ever observed.
Remarkably, the Chandra X-ray observatory was in the midst of a deep
integration of the Orion nebula at the time of the BIMA discovery; the source's
X-ray flux increased by a factor of 10 approximately 2 days before the radio
detection. Follow-up radio observations with the VLA and BIMA showed that the
source decayed on a timescale of days, then flared again several times over the
next 70 days, although never as brightly as during the discovery. Circular
polarization was detected at 15, 22, and 43 GHz, indicating that the emission
mechanism was cyclotron. VLBA observations 9 days after the initial flare yield
a brightness temperature Tb > 5 x 10^7 K at 15 GHz. Infrared spectroscopy
indicates the source is a K5V star with faint Br gamma emission, suggesting
that it is a weak-line T Tauri object. Zeeman splitting measurements in the
infrared spectrum find B ~ 2.6 +/- 1.0 kG. The flare is an extreme example of
magnetic activity associated with a young stellar object. These data suggest
that short observations obtained with ALMA will uncover hundreds of flaring
young stellar objects in the Orion region.Comment: 29 pages, 7 figures, accepted for publication in Ap
Gas Accretion by Star Clusters and the Formation of Ultraluminous X-ray Sources from Cusps of Compact Remnants
Here we show that the overabundance of ultra-luminous, compact X-ray sources
(ULXs) associated with moderately young clusters in interacting galaxies such
as the Antennae and Cartwheel can be given an alternative explanation that does
not involve the presence of intermediate mass black holes (IMBHs). We argue
that gas density within these systems is enhanced by the collective potential
of the cluster prior to being accreted onto the individual cluster members and,
as a result, the aggregate X-ray luminosity arising from the neutron star
cluster members can exceed . Various observational
tests to distinguish between IMBHs and accreting neutron star cusps are
discussed.Comment: 4 pages, 3 figures, accepted to ApJ
Supernovae and radio transients in M 82
We present optical and near-infrared (IR) photometry and near-IR spectroscopy
of SN 2004am, the only optically detected supernova (SN) in M 82. These
demonstrate that SN 2004am was a highly reddened type II-P SN similar to the
low luminosity type II-P events such as SNe 1997D and 2005cs. We show that SN
2004am was located coincident with the obscured super star cluster M 82-L, and
from the cluster age infer a progenitor mass of 12 +7/-3 Msun. In addition to
this, we present a high spatial resolution Gemini-N K-band adaptive optics
image of the site of SN 2008iz and a second transient of uncertain nature, both
detected so far only at radio wavelengths. Using image subtraction techniques
together with archival data from the Hubble Space Telescope, we are able to
recover a near-IR transient source co-incident with both objects. We find the
likely extinction towards SN 2008iz to be not more than Av ~ 10. The nature of
the second transient remains elusive and we regard an extremely bright
microquasar in M 82 as the most plausible scenario.Comment: 14 pages, 8 figures, accepted for publication in MNRA
Effect of Acute High-intensity Interval Exercise on Whole-body Fat Oxidation and Subcutaneous Adipose Tissue Cell Signaling in Overweight Women
International Journal of Exercise Science 13(2): 554-566, 2020. Exercise-induced alterations in adipose tissue insulin and/or β-adrenergic signaling may contribute to increases in whole-body fat oxidation following acute exercise. Thus, we examined changes in insulin (Akt, AS160) and β-adrenergic (PKA) signaling proteins in subcutaneous adipose tissue and whole-body fat oxidation in overweight women following acute high-intensity interval exercise (HIIE). Overweight females completed two experimental sessions in a randomized order: 1) control (bed rest) and 2) HIIE (10 x 4 min running intervals at 90% HRmax, 2-min recovery). Subcutaneous abdominal adipose tissue biopsies were obtained from 10 participants before (pre-), immediately (0hr) after (post-), 2hr post-, and 4hr post-exercise. Plasma glucose and insulin levels were assessed in venous blood samples obtained at each biopsy time-point from a different group of 5 participants (BMI-matched to biopsy group). Fat oxidation rates were estimated using the respiratory exchange ratio (RER) in all participants using indirect calorimetry pre-, 2hr post-, and 4hr post-exercise. RER was decreased (p \u3c 0.05) at 2hr post-exercise after HIIE (0.77 ± 0.04) compared to control (0.84 ± 0.04). Despite higher plasma glucose (p \u3c 0.01) and insulin (p \u3c 0.05) levels at 0hr post-exercise versus control, no significant interaction effects were observed for Akt or AS160 phosphorylation (p \u3e 0.05). Phosphorylation of PKA substrates was unaltered in both conditions (p \u3e 0.05). Collectively, altered β-adrenergic and insulin signaling in subcutaneous adnominal adipose tissue does not appear to explain increased whole-body fat oxidation following acute HIIE
The mass-to-light ratio of rich star clusters
We point out a strong time-evolution of the mass-to-light conversion factor
eta commonly used to estimate masses of unresolved star clusters from observed
cluster spectro-photometric measures. We present a series of gas-dynamical
models coupled with the Cambridge stellar evolution tracks to compute
line-of-sight velocity dispersions and half-light radii weighted by the
luminosity. We explore a range of initial conditions, varying in turn the
cluster mass and/or density, and the stellar population's IMF. We find that
eta, and hence the estimated cluster mass, may increase by factors as large as
3 over time-scales of 50 million years. We apply these results to an hypothetic
cluster mass distribution function (d.f.) and show that the d.f. shape may be
strongly affected at the low-mass end by this effect. Fitting truncated
isothermal (Michie-King) models to the projected light profile leads to
over-estimates of the concentration parameter c of delta c ~ 0.3 compared to
the same functional fit applied to the projected mass density.Comment: 6 pages, 2 figures, to appear in the proceedings of the "Young
massive star clusters", Granada, Spain, September 200
KELT-20b: A Giant Planet With A Period Of P ~ 3.5 Days Transiting The V ~ 7.6 Early A Star HD 185603
We report the discovery of KELT-20b, a hot Jupiter transiting a early A star, HD 185603, with an orbital period of days. Archival and follow-up photometry, Gaia parallax, radial velocities, Doppler tomography, and AO imaging were used to confirm the planetary nature of KELT-20b and characterize the system. From global modeling we infer that KELT-20 is a rapidly rotating ( ) A2V star with an effective temperature of K, mass of , radius of , surface gravity of , and age of . The planetary companion has a radius of , a semimajor axis of au, and a linear ephemeris of . We place a upper limit of on the mass of the planet. Doppler tomographic measurements indicate that the planetary orbit normal is well aligned with the projected spin axis of the star ( ). The inclination of the star is constrained to , implying a three-dimensional spin–orbit alignment of . KELT-20b receives an insolation flux of , implying an equilibrium temperature of of ∼2250 K, assuming zero albedo and complete heat redistribution. Due to the high stellar , KELT-20b also receives an ultraviolet (wavelength nm) insolation flux of , possibly indicating significant atmospheric ablation. Together with WASP-33, Kepler-13 A, HAT-P-57, KELT-17, and KELT-9, KELT-20 is the sixth A star host of a transiting giant planet, and the third-brightest host (in V ) of a transiting planet
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