53 research outputs found
An independent distance estimate to the AGB star R Sculptoris
For the carbon AGB star R Sculptoris, the uncertain distance significantly
affects the interpretation of observations regarding the evolution of the
stellar mass loss during and after the most recent thermal pulse. We aim to
provide a new, independent measurement of the distance to R Sculptoris,
reducing the absolute uncertainty of the distance estimate to this source. R
Scl is a semi-regular pulsating star, surrounded by a thin shell of dust and
gas created during a thermal pulse approximately 2000 years ago. The stellar
light is scattered by the dust particles in the shell at a radius of 19 arcsec.
The variation in the stellar light affects the amount of dust-scattered light
with the same period and amplitude ratio, but with a phase lag that depends on
the absolute size of the shell. We measured this phase lag by observing the
star R Scl and the dust-scattered stellar light from the shell at five epochs
between June - December 2017. By observing in polarised light, we imaged the
shell in the plane of the sky, removing any uncertainty due to geometrical
effects. The phase lag gives the absolute size of the shell, and together with
the angular size of the shell directly gives the absolute distance to R
Sculptoris. We measured a phase lag between the stellar variations and the
variation in the shell of 40.0 +/- 4.0 days. The angular size of the shell is
measured to be 19.1 arcsec +/- 0.7 arcsec. Combined, this gives an absolute
distance to R Sculptoris of 361 +/- 44 pc. We independently determined the
absolute distance to R Scl with an uncertainty of 12%. The estimated distance
is consistent with previous estimates, but is one of the most accurate
distances to the source to date. In the future, using the variations in
polarised, dust-scattered stellar light, may offer an independent possibility
to measure reliable distances to AGB stars.Comment: accepted by A&A, 8 pages, 8 figure
Properties of dust in the detached shells around U Ant, DR Ser, and V644 Sco
Understanding the properties of dust produced during the asymptotic giant
branch phase of stellar evolution is important for understanding the evolution
of stars and galaxies. Recent observations of the carbon AGB star R Scl have
shown that observations at far-infrared and submillimetre wavelengths can
effectively constrain the grain sizes in the shell, while the total mass
depends on the structure of the grains (solid vs. hollow or fluffy). We aim to
constrain the properties of the dust observed in the submillimetre in the
detached shells around the three carbon AGB stars U Ant, DR Ser, and V644 Sco,
and to investigate the constraints on the dust masses and grain sizes provided
by far-infrared and submm observations. We observed the carbon AGB stars U Ant,
DR Ser, and V644 Sco at 870 micron using LABOCA on APEX. Combined with
observations from the optical to far-infrared, we produced dust radiative
transfer models of the spectral energy distributions (SEDs) with contributions
from the stars, present-day mass-loss and detached shells. We tested the effect
of different total dust masses and grain sizes on the SED, and attempted to
consistently reproduce the SEDs from the optical to the submm. We derive dust
masses in the shells of a few 10e-5 Msun, assuming spherical, solid grains. The
best-fit grain radii are comparatively large, and indicate the presence of
grains between 0.1 micron-2 micron. The LABOCA observations suffer from
contamination from 12CO(3-2), and hence gives fluxes that are higher than the
predicted dust emission at submm wavelengths. We investigate the effect on the
best-fitting models by assuming different degrees of contamination and show
that far-infrared and submillimetre observations are important to constrain the
dust mass and grain sizes in the shells.Comment: Accepted by A&
Dusty shells surrounding the carbon variables S Scuti and RT Capricorni
For the Mass-loss of Evolved StarS (MESS) programme, the unprecedented
spatial resolution of the PACS photometer on board the Herschel space
observatory was employed to map the dusty environments of asymptotic giant
branch (AGB) and red supergiant (RSG) stars. Among the morphologically
heterogeneous sample, a small fraction of targets is enclosed by spherically
symmetric detached envelopes. Based on observations in the 70 {\mu}m and 160
{\mu}m wavelength bands, we investigated the surroundings of the two carbon
semiregular variables S Sct and RT Cap, which both show evidence for a history
of highly variable mass-loss. S Sct exhibits a bright, spherically symmetric
detached shell, 138" in diameter and co-spatial with an already known CO
structure. Moreover, weak emission is detected at the outskirts, where the
morphology seems indicative of a mild shaping by interaction of the wind with
the interstellar medium, which is also supported by the stellar space motion.
Two shells are found around RT Cap that were not known so far in either dust
emission or from molecular line observations. The inner shell with a diameter
of 188" shows an almost immaculate spherical symmetry, while the outer ~5'
structure is more irregularly shaped. MoD, a modification of the DUSTY
radiative transfer code, was used to model the detached shells. Dust
temperatures, shell dust masses, and mass-loss rates are derived for both
targets
Modelling the carbon AGB star R Sculptoris: Constraining the dust properties in the detached shell based on far-infrared and sub-millimeter observations
Context. On the asymptotic giant branch (AGB), Sun-like stars lose a large portion of their mass in an intensive wind and enrich the surrounding interstellar medium with nuclear processed stellar material in the form of molecular gas and dust. For a number of carbon-rich AGB stars, thin detached shells of gas and dust have been observed. These shells are formed during brief periods of increased mass loss and expansion velocity during a thermal pulse, and open up the possibility to study the mass-loss history of thermally pulsing AGB stars. Aims. We study the properties of dust grains in the detached shell around the carbon AGB star R Scl and aim to quantify the influence of the dust grain properties on the shape of the spectral energy distribution (SED) and the derived dust shell mass. Methods. We modelled the SED of the circumstellar dust emission and compared the models to observations, including new observations of Herschel/PACS and SPIRE (infrared) and APEX/LABOCA (sub-millimeter). We derived present-day mass-loss rates and detached shell masses for a variation of dust grain properties (opacities, chemical composition, grain size, and grain geometry) to quantify the influence of changing dust properties to the derived shell mass. Results. The best-fitting mass-loss parameters are a present-day dust mass-loss rate of 2
7 10-10M⊙yr-1and a detached shell dust mass of (2.9 \ub1 0.3)
7 10-5M⊙. Compared to similar studies, the uncertainty on the dust mass is reduced by a factor of 4. We find that the size of the grains dominates the shape of the SED, while the estimated dust shell mass is most strongly affected by the geometry of the dust grains. Additionally, we find a significant sub-millimeter excess that cannot be reproduced by any of the models, but is most likely not of thermal origin
Probing the Mass Loss History of AGB Stars with Herschel
An overview is given of AGB stars imaged with the PACS and SPIRE instruments on-board the Herschel Space Observatory in the framework of the MESS Guaranteed Time Key Programme. The objects AQ And, U Ant, W Aql, U Cam, RT Cap, Y CVn, TT Cyg, UX Dra, W Ori, AQ Sgr, and X TrA all show detached or extended circumstellar emission
The detached dust shells of AQ And, U Ant, and TT Cyg
Detached circumstellar dust shells are detected around three carbon variables
using Herschel-PACS. Two of them are already known on the basis of their
thermal CO emission and two are visible as extensions in IRAS imaging data. By
model fits to the new data sets, physical sizes, expansion timescales, dust
temperatures, and more are deduced. A comparison with existing molecular CO
material shows a high degree of correlation for TT Cyg and U Ant but a few
distinct differences with other observables are also found.Comment: Letter accepted for publication on the A&A Herschel Special Issu
Transit timing variations of AU Microscopii b and c
Funding: A.C.C. and T.W. acknowledge support from STFC consolidated grant number ST/M001296/1.Here we report large-amplitude transit timing variations (TTVs) for AU Microcopii b and c as detected in combined TESS (2018, 2020) and CHEOPS (2020, 2021) transit observations. AU Mic is a young planetary system with a debris disk and two transiting warm Neptunes. A TTV on the order of several minutes was previously reported for AU Mic b, which was suggested to be an outcome of mutual perturbations between the planets in the system. In 2021, we observed AU Mic b (five transits) and c (three transits) with the CHEOPS space telescope to follow-up the TTV of AU Mic b and possibly detect a TTV for AU Mic c. When analyzing TESS and CHEOPS 2020-2021 measurements together, we find that a prominent TTV emerges with a full span of >= 23 min between the two TTV extrema. Assuming that the period change results from a periodic process -such as mutual perturbations- we demonstrate that the times of transits in the summer of 2022 are expected to be 30-85 min later than predicted by the available linear ephemeris.Publisher PDFPeer reviewe
The tidal deformation and atmosphere of WASP-12b from its phase curve
Ultra-hot Jupiters present a unique opportunity to understand the physics and
chemistry of planets at extreme conditions. WASP-12b stands out as an archetype
of this class of exoplanets. We performed comprehensive analyses of the
transits, occultations, and phase curves of WASP-12b by combining new CHEOPS
observations with previous TESS and Spitzer data to measure the planet's tidal
deformation, atmospheric properties, and orbital decay rate. The planet was
modeled as a triaxial ellipsoid parameterized by the second-order fluid Love
number, , which quantifies its radial deformation and provides insight
into the interior structure. We measured the tidal deformation of WASP-12b and
estimated a Love number of (at 3.2) from its
phase curve. We measured occultation depths of ppm and ppm
in the CHEOPS and TESS bands, respectively, while the dayside emission spectrum
indicates that CHEOPS and TESS probe similar pressure levels in the atmosphere
at a temperature of 2900K. We also estimated low geometric albedos of
and in the CHEOPS and TESS passbands,
respectively, suggesting the absence of reflective clouds in the dayside of the
WASP-12b. The CHEOPS occultations do not show strong evidence for variability
in the dayside atmosphere of the planet. Finally, we refine the orbital decay
rate by 12% to a value of -30.230.82 ms/yr.
WASP-12b becomes the second exoplanet, after WASP-103b, for which the Love
number has been measured (at 3) from the effect of tidal deformation in
the light curve. However, constraining the core mass fraction of the planet
requires measuring with a higher precision. This can be achieved with
high signal-to-noise observations with JWST since the phase curve amplitude,
and consequently the induced tidal deformation effect, is higher in the
infrared.Comment: accepted for publication in A&
Effects on short term outcome of non-invasive ventilation use in the emergency department to treat patients with acute heart failure: A propensity score-based analysis of the EAHFE Registry
Objective: To assess the effects of non-invasive ventilation (NIV) in emergency department (ED) patients with acute heart failure (AHF) on short term outcomes.
Methods: Patients from the EAHFE Registry (a multicenter, observational, multipurpose, cohort-designed database including consecutive AHF patients in 41 Spanish EDs) were grouped based on NIV treatment (NIV+ and NIV–groups). Using propensity score (PS) methodology, we identified two subgroups of patients matched by 38 covariates and compared regarding 30-day survival (primary outcome). Interaction was investigated for age, sex, ischemic cardiomyopathy, chronic obstructive pulmonary disease, AHF precipitated by an acute coronary syndrome (ACS), AHF classified as hypertensive or acute pulmonary edema (APE), and systolic blood pressure (SBP). Secondary outcomes were intensive care unit (ICU) admission; mechanical ventilation; in-hospital, 3-day and 7-day mortality; and prolonged hospitalization (>7 days).
Results: Of 11, 152 patients from the EAHFE (age (SD): 80 (10) years; 55.5% women), 718 (6.4%) were NIV+ and had a higher 30-day mortality (HR = 2.229; 95%CI = 1.861–2.670) (p 85 years, p < 0.001), AHF associated with ACS (p = 0.045), and SBP < 100 mmHg (p < 0.001). No significant differences were found in the secondary endpoints except for more prolonged hospitalizations in NIV+ patients (OR = 1.445; 95%CI = 1.122–1.862) (p = 0.004).
Conclusion: The use of NIV to treat AHF in ED is not associated with improved mortality outcomes and should be cautious in old patients and those with ACS and hypotension
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