699 research outputs found

    An independent distance estimate to the AGB star R Sculptoris

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    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

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    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

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    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

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    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

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    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

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    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 (Mshell∌7.3×10−3 M⊙M_{shell}\sim 7.3\times10^{-3}~M_{\odot}) which is thought to have been produced during a thermal pulse event ∌2200\sim2200 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 ÎŒ\mum. 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 n∝rαn \propto r^{\alpha} where α=0.75−0.25+0.45\alpha=0.75^{+0.45}_{-0.25} and dust mass of Md=9.0−4.1+2.3×10−6 M⊙M_d=9.0^{+2.3}_{-4.1}\times10^{-6}~M_{\odot}. The strong departure from an r−2r^{-2} 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 v=1,J=3−2v=1, J=3-2 towards five AGB stars

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    We report the serendipitous detection with ALMA of the vibrationally-excited pure-rotational CO transition v=1,J=3−2v=1, J=3-2 towards five asymptotic giant branch (AGB) stars, oo Cet, R Aqr, R Scl, W Aql, and π1\pi^1 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 oo 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

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    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