573 research outputs found
Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198478
Blue supergiant stars are known to display photometric and spectroscopic
variability that is suggested to be linked to stellar pulsations. Pulsational
activity in massive stars strongly depends on the star's evolutionary stage and
is assumed to be connected with mass-loss episodes, the appearance of
macroturbulent line broadening, and the formation of clumps in the wind. To
investigate a possible interplay between pulsations and mass-loss, we carried
out an observational campaign of the supergiant 55 Cyg over a period of five
years to search for photospheric activity and cyclic mass-loss variability in
the stellar wind. We modeled the H, He I, Si II and Si III lines using the
nonlocal thermal equilibrium atmosphere code FASTWIND and derived the
photospheric and wind parameters. In addition, we searched for variability in
the intensity and radial velocity of photospheric lines and performed a moment
analysis of the line profiles to derive frequencies and amplitudes of the
variations. The Halpha line varies with time in both intensity and shape,
displaying various types of profiles: P Cygni, pure emission, almost complete
absence, and double or multiple peaked. The star undergoes episodes of variable
mass-loss rates that change by a factor of 1.7-2 on different timescales. We
also observe changes in the ionization rate of Si II and determine a
multiperiodic oscillation in the He I absorption lines, with periods ranging
from a few hours to 22.5 days. We interpret the photospheric line variations in
terms of oscillations in p-, g-, and strange modes. We suggest that these
pulsations can lead to phases of enhanced mass loss. Furthermore, they can
mislead the determination of the stellar rotation. We classify the star as a
post-red supergiant, belonging to the group of alpha Cyg variables.Comment: 20 pages, 18 figures, 3 tables, accepted to Astronomy & Astrophysic
Restoration of Hypoglycemia Awareness After Islet Transplantation
OBJECTIVE—To determine the impact of islet transplantation (ITx) on hypoglycemia awareness in patients with unstable type 1 diabetes and its relation to islet function
Analytical solutions for radiation-driven winds in massive stars - II: The δ-slow regime
Accurate mass-loss rates and terminal velocities from massive stars winds are essential to obtain synthetic spectra from radiative transfer calculations and to determine the evolutionary path of massive stars. From a theoretical point of view, analytical expressions for the wind parameters and velocity profile would have many advantages over numerical calculations that solve the complex non-linear set of hydrodynamic equations. In a previous work, we obtained an analytical description for the fast wind regime. Now, we propose an approximate expression for the line-force in terms of new parameters and obtain a velocity profile closed-form solution (in terms of the Lambert W function) for the δ-slow regime. Using this analytical velocity profile, we were able to obtain the mass-loss rates based on the m-CAK theory. Moreover, we established a relation between this new set of line-force parameters with the known stellar and m-CAK line-force parameters. To this purpose, we calculated a grid of numerical hydrodynamical models and performed a multivariate multiple regression. The numerical and our descriptions lead to good agreement between their values.Fil: Araya, I.. Universidad Mayor; ChileFil: Christen, A.. Universidad de Valparaíso; ChileFil: Cure, M.. Universidad de Valparaíso; ChileFil: Cidale, Lydia Sonia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Venero, Roberto Oscar José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Arcos, C.. Universidad de Valparaíso; ChileFil: Gormaz Matamala, A.. Universidad de Valparaíso; Chile. Universidad Adolfo Ibañez; ChileFil: Haucke, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Escarate, P.. Universidad Austral de Chile; ChileFil: Clavería, H.. Pontificia Universidad Católica de Valparaíso; Chil
Differences in the gas and dust distribution in the transitional disk of a sun-like young star, PDS 70
We present ALMA 0.87 mm continuum, HCO+ J=4--3 emission line, and CO J=3--2
emission line data of the disk of material around the young, Sun-like star PDS
70. These data reveal the existence of a possible two component transitional
disk system with a radial dust gap of 0."2 +/- 0."05, an azimuthal gap in the
HCO+ J=4--3 moment zero map, as well as two bridge-like features in the gas
data. Interestingly these features in the gas disk have no analogue in the dust
disk making them of particular interest. We modeled the dust disk using the
Monte Carlo radiative transfer code HOCHUNK3D (Whitney et al. 2013) using a two
disk components. We find that there is a radial gap that extends from 15-60 au
in all grain sizes which differs from previous work
High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A
We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on
the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk
object, with a gap structure separating its inner and outer disks. Our imagery
taken with the 0.15 (21 AU) radius coronagraphic mask has revealed a strongly
polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a
spatial resolution of 0.1 (14 AU). It is inclined by 46 \pm 2 degree as the
west side is nearest. Although SED modeling and sub-millimeter imagery
suggested the presence of a gap in the disk, with the inner edge of the outer
disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at
the limit of our inner working angle (23 AU) at the near-infrared wavelength.
We attribute the observed strong polarization (up to 66 %) to light scattering
by dust grains in the disk. However, neither polarization models of the
circumstellar disk based on Rayleigh scattering nor Mie scattering
approximations were consistent with the observed azimuthal profile of the
polarization degrees of the disk. Instead, a geometric optics model of the disk
with nonspherical grains with the radii of 30 micron meter is consistent with
the observed profile. We suggest that the dust grains have experienced frequent
collisional coagulations and have grown in the circumstellar disk of UX Tau A.Comment: 20 pages, 8 figures, and 1 table. accepted to PAS
Discovery of Small-Scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory
We present high-resolution, H-band, imaging observations, collected with
Subaru/HiCIAO, of the scattered light from the transitional disk around SAO
206462 (HD 135344B). Although previous sub-mm imagery suggested the existence
of the dust-depleted cavity at r~46AU, our observations reveal the presence of
scattered light components as close as 0.2" (~28AU) from the star. Moreover, we
have discovered two small-scale spiral structures lying within 0.5" (~70AU). We
present models for the spiral structures using the spiral density wave theory,
and derive a disk aspect ratio of h~0.1, which is consistent with previous
sub-mm observations. This model can potentially give estimates of the
temperature and rotation profiles of the disk based on dynamical processes,
independently from sub-mm observations. It also predicts the evolution of the
spiral structures, which can be observable on timescales of 10-20 years,
providing conclusive tests of the model. While we cannot uniquely identify the
origin of these spirals, planets embedded in the disk may be capable of
exciting the observed morphology. Assuming that this is the case, we can make
predictions on the locations and, possibly, the masses of the unseen planets.
Such planets may be detected by future multi-wavelengths observations.Comment: 8 pages, 5 figures, ApJL in press, typo correcte
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