698 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&
Embedded Stellar Populations towards Young Massive Star Formation Regions I. G305.2+0.2
We present deep, wide-field J, H and Ks images taken with IRIS2 on the Anglo
Australian Telescope, towards the massive star formation region G305.2+0.2.
Combined with 3.6, 4.5, 5.8 and 8.0 micron data from the GLIMPSE survey on the
Spitzer Space Telescope, we investigate the properties of the embedded stellar
populations. After removing contamination from foreground stars we separate the
sources based on their IR colour. Strong extended emission in the GLIMPSE
images hampers investigation of the most embedded sources towards the known
sites of massive star formation. However, we find a sizeable population of IR
excess sources in the surrounding region free from these completeness effects.
Investigation reveals the recent star formation activity in the region is more
widespread than previously known.
Stellar density plots show the embedded cluster in the region, G305.24+0.204,
is offset from the dust emission. We discuss the effect of this cluster on the
surrounding area and argue it may have played a role in triggering sites of
star formation within the region. Finally, we investigate the distribution of
IR excess sources towards the cluster, in particular their apparent lack
towards the centre compared with its immediate environs.Comment: 16 pages, 16 figures (significantly size reduced), 2 tables, accepted
MNRA
The detached dust shells around the carbon AGB stars R Scl and V644 Sco
Detached shells are believed to be created during a thermal pulse, and
constrain the time scales and physical properties of one of the main drivers of
late stellar evolution. We aim at determining the morphology of the detached
dust shells around the carbon AGB stars R Scl and V644 Sco, and compare this to
observations of the detached gas shells. We observe the polarised,
dust-scattered stellar light around these stars using the PolCor instrument
mounted on the ESO 3.6m telescope. Observations were done with a coronographic
mask to block out the direct stellar light. The polarised images clearly show
the detached shells. Using a dust radiative transfer code to model the
dust-scattered polarised light, we constrain the radii and widths of the shells
to 19.5 arcsec and 9.4 arcsec for the detached dust shells around R Scl and
V644 Sco, respectively. Both shells have an overall spherical symmetry and
widths of approx. 2 arcsec. For R Scl we can compare the observed dust emission
directly with high spatial-resolution maps of CO(3-2) emission from the shell
observed with ALMA. We find that the dust and gas coincide almost exactly,
indicating a common evolution. The data presented here for R Scl are the most
detailed observations of the entire dusty detached shell to date. For V644 Sco
these are the first direct measurements of the detached shell. Also here we
find that the dust most likely coincides with the gas shell. The observations
are consistent with a scenario where the detached shells are created during a
thermal pulse. The determined radii and widths will constrain hydrodynamical
models describing the pre-pulse mass loss, the thermal pulse, and post-pulse
evolution of the star
ALMA view of the circumstellar environment of the post-common-envelope-evolution binary system HD101584
We study the circumstellar evolution of the binary HD101584, consisting of a
post-AGB star and a low-mass companion, which is most likely a
post-common-envelope-evolution system. We used ALMA observations of the 12CO,
13CO, and C18O J=2-1 lines and the 1.3mm continuum to determine the morphology,
kinematics, masses, and energetics of the circumstellar environment. The
circumstellar medium has a bipolar hour-glass structure, seen almost pole-on,
formed by an energetic jet, about 150 km/s. We conjecture that the
circumstellar morphology is related to an event that took place about 500 year
ago, possibly a capture event where the companion spiraled in towards the AGB
star. However, the kinetic energy of the accelerated gas exceeds the released
orbital energy, and, taking into account the expected energy transfer
efficiency of the process, the observed phenomenon does not match current
common-envelope scenarios. This suggests that another process must augment, or
even dominate, the ejection process. A significant amount of material resides
in an unresolved region, presumably in the equatorial plane of the binary
system.Comment: A&A Letter, accepte
An Infrared Study of the Circumstellar Material Associated with the Carbon Star R Sculptoris
The asymptotic giant branch (AGB) star R Sculptoris (R Scl) is one of the
most extensively studied stars on the AGB. R Scl is a carbon star with a
massive circumstellar shell () which
is thought to have been produced during a thermal pulse event years
ago. To study the thermal dust emission associated with its circumstellar
material, observations were taken with the Faint Object InfraRed CAMera for the
SOFIA Telescope (FORCAST) at 19.7, 25.2, 31.5, 34.8, and 37.1 m. Maps of
the infrared emission at these wavelengths were used to study the morphology
and temperature structure of the spatially extended dust emission. Using the
radiative transfer code DUSTY and fitting the spatial profile of the emission,
we find that a geometrically thin dust shell cannot reproduce the observed
spatially resolved emission. Instead, a second dust component in addition to
the shell is needed to reproduce the observed emission. This component, which
lies interior to the dust shell, traces the circumstellar envelope of R Scl. It
is best fit by a density profile with where
and dust mass of
. The strong departure from an
law indicates that the mass-loss rate of R Scl has not been constant.
This result is consistent with a slow decline in the post-pulse mass-loss which
has been inferred from observations of the molecular gas.Comment: 10 pages, 10 figures, accepted to Ap
ALMA observations of the vibrationally-excited rotational CO transition towards five AGB stars
We report the serendipitous detection with ALMA of the vibrationally-excited
pure-rotational CO transition towards five asymptotic giant branch
(AGB) stars, Cet, R Aqr, R Scl, W Aql, and Gru. The observed lines
are formed in the poorly-understood region located between the stellar surface
and the region where the wind starts, the so-called warm molecular layer. We
successfully reproduce the observed lines profiles using a simple model. We
constrain the extents, densities, and kinematics of the region where the lines
are produced. R Aqr and R Scl show inverse P-Cygni line profiles which indicate
infall of material onto the stars. The line profiles of Cet and R Scl show
variability. The serendipitous detection towards these five sources shows that
vibrationally-excited rotational lines can be observed towards a large number
of nearby AGB stars using ALMA. This opens a new possibility for the study of
the innermost regions of AGB circumstellar envelopes.Comment: 6 pages, 2 figures, 2 tables, 2016MNRAS.463L..74
VerlÀufe von Traumafolgen bei ehemaligen politisch Inhaftierten der DDR: Ein 15-Jahres-Follow-up
Zusammenfassung: Hintergrund: In einer Mitte der 1990er Jahre untersuchten Stichprobe ehemaliger politisch Inhaftierter der DDR wurden im 15-Jahres-Follow-up die VerĂ€nderungen der Diagnose- und SymptomprĂ€valenzen der posttraumatischen Belastungsstörung (PTBS) sowie anderer psychischer Störungen untersucht. Zudem wurden die durch Kliniker erhobenen DiagnosenverlĂ€ufe mit den retrospektiven subjektiven EinschĂ€tzungen der Studienteilnehmer verglichen. Methode: Dreiundneunzig ehemals politisch inhaftierte Personen nahmen an der Folgestudie teil (85% Wiederteilnahme), ihr mittleres Alter betrug 64Jahre. Diagnosen und Symptome wurden mittels strukturierter klinischer Interviews sowie Fragebögen erfasst. Die retrospektiven subjektiven VerlaufseinschĂ€tzungen der Teilnehmer wurden mittels eines PTBS-Symptomindex basierend auf 4Symptomgruppen (Intrusionen, Vermeidung, Numbing, Hyperarousal) errechnet. Ergebnisse: Eine aktuelle PTBS lag bei 33% vor (1997: 29%). Nur ca. in der HĂ€lfte der FĂ€lle lag diese schon 1994 vor, bei der anderen HĂ€lfte handelt es sich um neu-inzidente bzw. remittierte FĂ€lle. NĂ€chsthĂ€ufige Diagnosen waren Major-Depression, Episode (26%), Panik (mit oder ohne Agoraphobie: 24%) sowie somatoforme Störungen (19%). Im PTBS-Symptomprofil nahmen Intrusionen, Flashbacks bzw. EntfremdungsgefĂŒhl im Zeitverlauf ab, Reizbarkeit und Schreckreaktionen hingegen zu. Die subjektive SelbsteinschĂ€tzung der PTBS-SymptomverlĂ€ufe durch die Studienteilnehmer ergab im Vergleich mit den Diagnostikern hĂ€ufiger ein resilientes ("nie PTBS") oder verzögertes und seltener ein remittiertes Verlaufsmuster. Schlussfolgerung: Die Ergebnisse sprechen fĂŒr eine traumabezogene LangzeitmorbiditĂ€t, die allerdings instabiler ist als bisher angenomme
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