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Publications (10 of 35) Show all publications
Saberi, M., Vlemmings, W. H., De Beck, E., Montez, R. & Ramstedt, S. (2018). Detection of CI line emission towards the oxygen-rich AGB star omi Ceti. Astronomy and Astrophysics, 612, Article ID L11.
Open this publication in new window or tab >>Detection of CI line emission towards the oxygen-rich AGB star omi Ceti
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 612, article id L11Article in journal (Refereed) Published
Abstract [en]

We present the detection of neutral atomic carbon CI(3P13P0) line emission towards omi Cet. This is the first time that CI is detected in the envelope around an oxygen-rich M-type asymptotic giant branch (AGB) star. We also confirm the previously tentative CI detection around V Hya, a carbon-rich AGB star. As one of the main photodissociation products of parent species in the circumstellar envelope (CSE) around evolved stars, CI can be used to trace sources of ultraviolet (UV) radiation in CSEs. The observed flux density towards omi Cet can be reproduced by a shell with a peak atomic fractional abundance of 2.4 × 10−5 predicted based on a simple chemical model where CO is dissociated by the interstellar radiation field. However, the CI emission is shifted by ~4 km s−1 from the stellar velocity. Based on this velocity shift, we suggest that the detected CI emission towards omi Cet potentially arises from a compact region near its hot binary companion. The velocity shift could, therefore, be the result of the orbital velocity of the binary companion around omi Cet. In this case, the CI column density is estimated to be 1.1 × 1019 cm−2. This would imply that strong UV radiation from the companion and/or accretion of matter between two stars is most likely the origin of the CI enhancement. However, this hypothesis can be confirmed by high-angular resolution observations.

Keywords
astrochemistry, stars: individual: omi Cet, V Hya, circumstellar matter, atomic processes, stars: abundances, stars: AGB and post-AGB
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-356493 (URN)10.1051/0004-6361/201833080 (DOI)000431823900002 ()
Funder
EU, European Research Council, 614264Swedish National Space Board
Available from: 2018-07-30 Created: 2018-07-30 Last updated: 2018-07-30Bibliographically approved
Paladini, C., Baron, F., Jorissen, A., Le Bouquin, J.-B. -., Freytag, B., Van Eck, S., . . . Ramstedt, S. (2018). Large granulation cells on the surface of the giant star π1 Gruis. Nature, 553(7688), 310-+
Open this publication in new window or tab >>Large granulation cells on the surface of the giant star π1 Gruis
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2018 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 553, no 7688, p. 310-+Article in journal (Refereed) Published
Abstract [en]

Convection plays a major part in many astrophysical processes, including energy transport, pulsation, dynamos and winds on evolved stars, in dust clouds and on brown dwarfs1,2. Most of our knowledge about stellar convection has come from studying the Sun: about two million convective cells with typical sizes of around 2,000 kilometres across are present on the surface of the Sun3—a phenomenon known as granulation. But on the surfaces of giant and supergiant stars there should be only a few large (several tens of thousands of times larger than those on the Sun) convective cells3, owing to low surface gravity. Deriving the characteristic properties of convection (such as granule size and contrast) for the most evolved giant and supergiant stars is challenging because their photospheres are obscured by dust, which partially masks the convective patterns4. These properties can be inferred from geometric model fitting5,6,7, but this indirect method does not provide information about the physical origin of the convective cells5,6,7. Here we report interferometric images of the surface of the evolved giant star π1 Gruis, of spectral type8,9 S5,7. Our images show a nearly circular, dust-free atmosphere, which is very compact and only weakly affected by molecular opacity. We find that the stellar surface has a complex convective pattern with an average intensity contrast of 12 per cent, which increases towards shorter wavelengths. We derive a characteristic horizontal granule size of about 1.2 × 1011 metres, which corresponds to 27 per cent of the diameter of the star. Our measurements fall along the scaling relations between granule size, effective temperature and surface gravity that are predicted by simulations of stellar surface convection10,11,12.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-343860 (URN)10.1038/nature25001 (DOI)000423475100045 ()29258298 (PubMedID)
Funder
EU, Horizon 2020, 730890
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
Vlemmings, W. H., Khouri, T., De Beck, E., Olofsson, H., Garcia-Segura, G., Villaver, E., . . . Ramstedt, S. (2018). Rotation of the asymptotic giant branch star R Doradus [Letter to the editor]. Astronomy and Astrophysics, 613, Article ID L4.
Open this publication in new window or tab >>Rotation of the asymptotic giant branch star R Doradus
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, article id L4Article in journal, Letter (Refereed) Published
Abstract [en]

High-resolution observations of the extended atmospheres of asymptotic giant branch (AGB) stars can now directly be compared to the theories that describe stellar mass loss. Using Atacama Large Millimeter/submillimeter Array (ALMA) high angular resolution (30 x 42 mas) observations, we have for the first time resolved stellar rotation of an AGB star, R Dor. We measure an angular rotation velocity of omega(R) sin i = (3.5 +/- 0.3) x 10(-9) rad s(-1), which indicates a rotational velocity of vertical bar nu(rot) sin i vertical bar = 1.0 +/- 0.1 km s(-1) at the stellar surface (R-* = 31.2 mas at 214 GHz). The rotation axis projected on the plane of the sky has a position angle Phi = 7 +/- 6 degrees. We find that the rotation of R Dor is two orders of magnitude faster than expected for a solitary AGB star that will have lost most of its angular momentum. Its rotational velocity is consistent with angular momentum transfer from a close companion. As a companion has not been directly detected, we suggest R Dor has a low-mass, close-in companion. The rotational velocity approaches the critical velocity, set by the local sound speed in the extended envelope, and is thus expected to affect the mass-loss characteristics of R Dor.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2018
Keywords
stars: AGB and post-AGB, stars: rotation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357271 (URN)10.1051/0004-6361/201832929 (DOI)000432980000002 ()
Funder
EU, European Research Council, 614264Swedish Research Council
Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2018-08-20
Montez, R. J., Ramstedt, S., Kastner, J. H., Vlemmings, W. & Sanchez, E. (2017). A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars. Astrophysical Journal, 841(1), Article ID 33.
Open this publication in new window or tab >>A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars
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2017 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 841, no 1, article id 33Article in journal (Refereed) Published
Abstract [en]

We have performed a comprehensive study of the UV emission detected from asymptotic giant branch (AGB) stars by the Galaxy Evolution Explorer (GALEX). Of the 468 AGB stars in our sample, 316 were observed by GALEX. In the near-UV (NUV) bandpass (lambda(eff) similar to 2310 angstrom), 179 AGB stars were detected and 137 were not detected. Only 38 AGB stars were detected in the far-UV (FUV) bandpass (lambda(eff) similar to 1528 angstrom). We find that NUV emission is correlated with optical to near-infrared emission, leading to higher detection fractions among the brightest, and hence closest, AGB stars. Comparing the AGB time-variable visible phased light curves to corresponding GALEX NUV phased light curves, we find evidence that for some AGB stars the NUV emission varies in phase with the visible light curves. We also find evidence that the NUV emission and possibly the FUV emission are anticorrelated with the circumstellar envelope density. These results suggest that the origin of the GALEX-detected UV emission is an inherent characteristic of the AGB stars that can most likely be traced to a combination of photospheric and chromospheric emission. In most cases, UV detections of AGB stars are not likely to be indicative of the presence of binary companions.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2017
Keywords
general, stars: AGB and post-AGB, stars: chromospheres, ultraviolet: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-326239 (URN)10.3847/1538-4357/aa704d (DOI)000402310500019 ()
Funder
EU, European Research Council, 614264
Available from: 2017-07-06 Created: 2017-07-06 Last updated: 2017-07-06Bibliographically approved
Wittkowski, M., Hofmann, K.-H. -., Höfner, S., Le Bouquin, J. B., Nowotny, W., Paladini, C., . . . Weigelt, G. (2017). Aperture synthesis imaging of the carbon AGB star R Sculptoris Detection of a complex structure and a dominating spot on the stellar disk. Astronomy and Astrophysics, 601, Article ID A3.
Open this publication in new window or tab >>Aperture synthesis imaging of the carbon AGB star R Sculptoris Detection of a complex structure and a dominating spot on the stellar disk
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 601, article id A3Article in journal (Refereed) Published
Abstract [en]

Aims. We present near-infrared interferometry of the carbon-rich asymptotic giant branch (AGB) star R Sculptoris (R Scl). Methods. We employ medium spectral resolution K-band interferometry obtained with the instrument AMBER at the Very Large Telescope Interferometer (VLTI) and H-band low spectral resolution interferometric imaging observations obtained with the VLTI instrument PIONIER. We compare our data to a recent grid of dynamic atmosphere and wind models. We compare derived fundamental parameters to stellar evolution models. Results. The visibility data indicate a broadly circular resolved stellar disk with a complex substructure. The observed AMBER squared visibility values show drops at the positions of CO and CN bands, indicating that these lines form in extended layers above the photosphere. The AMBER visibility values are best fit by a model without a wind. The PIONIER data are consistent with the same model. We obtain a Rosseland angular diameter of 8.9 +/- 0.3 mas, corresponding to a Rosseland radius of 355 +/- 55 R-Theta, an effective temperature of 2640 +/- 80 K, and a luminosity of log L/L-Theta = 3.74 +/- 0.18. These parameters match evolutionary tracks of initial mass 1.5 +/- 0.5 M-Theta and current mass 1.3 +/- 0.7 M-Theta. The reconstructed PIONIER images exhibit a complex structure within the stellar disk including a dominant bright spot located at the western part of the stellar disk. The spot has an H- band peak intensity of 40% to 60% above the average intensity of the limb-darkening-corrected stellar disk. The contrast between the minimum and maximum intensity on the stellar disk is about 1:2.5. Conclusions. Our observations are broadly consistent with predictions by dynamic atmosphere and wind models, although models with wind appear to have a circumstellar envelope that is too extended compared to our observations. The detected complex structure within the stellar disk is most likely caused by giant convection cells, resulting in large-scale shock fronts, and their effects on clumpy molecule and dust formation seen against the photosphere at distances of 2-3 stellar radii.

Place, publisher, year, edition, pages
EDP Sciences, 2017
Keywords
techniques: interferometric, stars: AGB and post-AGB, stars: atmospheres, stars: fundamental parameters, stars: mass-loss, stars: individual: R Scl
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-327053 (URN)10.1051/0004-6361/201630214 (DOI)000402313500003 ()
Available from: 2017-08-03 Created: 2017-08-03 Last updated: 2017-08-03Bibliographically approved
De Nutte, R., Decin, L., Olofsson, H., Lombaert, R., de Koter, A., Karakas, A., . . . Van de Sande, M. (2017). Nucleosynthesis in AGB stars traced by oxygen isotopic ratios I. Determining the stellar initial mass by means of the O-17/O-18 ratio. Astronomy and Astrophysics, 600, Article ID A71.
Open this publication in new window or tab >>Nucleosynthesis in AGB stars traced by oxygen isotopic ratios I. Determining the stellar initial mass by means of the O-17/O-18 ratio
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 600, article id A71Article in journal (Refereed) Published
Abstract [en]

Aims. We seek to investigate the O-17/O-18 ratio for a sample of AGB stars containing M-, S-, and C-type stars. These ratios are evaluated in relation to fundamental stellar evolution parameters: the stellar initial mass and pulsation period.

Methods. Circumstellar (CO)-C-13-O-16, (CO)-C-12-O-17, and (CO)-C-12-O-18 line observations were obtained for a sample of nine stars with various single-dish long-wavelength facilities. Line intensity ratios are shown to relate directly to the surface O-17/O-18 abundance ratio.

Results. Stellar evolution models predict the O-17/O-18 ratio to be a sensitive function of initial mass and to remain constant throughout the entire TP-AGB phase for stars initially less massive than 5 M-circle dot. This makes the measured ratio a probe of the initial stellar mass.

Conclusions. Observed O-17/O-18 ratios are found to be well in the range predicted by stellar evolution models that do not consider convective overshooting. From this, accurate initial mass estimates are calculated for seven sources. For the remaining two sources, there are two mass solutions, although there is a larger probability that the low-mass solution is correct. Finally, we present hints at a possible separation between M/S- and C-type stars when comparing the O-17/O-18 ratio to the stellar pulsation period.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2017
Keywords
stars: AGB and post-AGB, stars: evolution, stars: fundamental parameters, circumstellar matter
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-324337 (URN)10.1051/0004-6361/201629195 (DOI)000400754000041 ()
Funder
EU, FP7, Seventh Framework ProgrammeEU, European Research Council, 646758 AEROSOLSwedish Research Council
Available from: 2017-06-15 Created: 2017-06-15 Last updated: 2017-06-15Bibliographically approved
Kerschbaum, F., Maercker, M., Brunner, M., Lindqvist, M., Olofsson, H., Mecina, M., . . . Wittkowski, M. (2017). Rings and filaments: The remarkable detached CO shell of U Antliae. Astronomy and Astrophysics, 605, Article ID A116.
Open this publication in new window or tab >>Rings and filaments: The remarkable detached CO shell of U Antliae
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A116Article in journal (Refereed) Published
Abstract [en]

Aims. Our goal is to characterize the intermediate age, detached shell carbon star U Antliae morphologically and physically in order to study the mass-loss evolution after a possible thermal pulse.

Methods. High spatial resolution ALMA observations of unprecedented quality in thermal CO lines allow us to derive first critical spatial and temporal scales and constrain modeling efforts to estimate mass-loss rates for both the present day as well as the ejection period of the detached shell.

Results. The detached shell is remarkably thin, overall spherically symmetric, and shows a barely resolved filamentary substructure possibly caused by instabilities in the interaction zone of winds with different outflow velocities. The expansion age of the detached shell is of the order of 2700 yr and its overall width indicates a high expansion-velocity and high mass-loss period of only a few hundred years at an average mass-loss rate of approximate to 10(-5) M-circle dot yr(-1). The post-high-mass-loss-rate-epoch evolution of U Ant shows a significant decline to a substantially lower gas expansion velocity and a mass-loss rate amounting to 4 x 10(-8) M-circle dot yr(-1), at present being consistent with evolutionary changes as predicted for the period between thermal pulses.

Keywords
stars: AGB and post-AGB, stars: carbon, stars: evolution, stars: mass-loss
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-337756 (URN)10.1051/0004-6361/201730665 (DOI)000412231200087 ()
Funder
Swedish Research Council
Note

Acknowledgements: F.K. and M.B. acknowledge funding by the Austrian Science Fund FWF under project number P23586. M.B. further acknowledges funding through the uni: docs fellowship of the University of Vienna. M.M., H.O., and W.V. acknowledge financial support from the Swedish Research Council. C.P. is supported by the Belgian Fund for Scientific Research F.R.S.-FNRS.

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-12Bibliographically approved
De Beck, E., Decin, L., Ramstedt, S., Olofsson, H., Menten, K. M., Patel, N. A. & Vlemmings, W. H. (2017). Search for aluminium monoxide in the winds of oxygen-rich AGB stars. Astronomy and Astrophysics, 598, Article ID A53.
Open this publication in new window or tab >>Search for aluminium monoxide in the winds of oxygen-rich AGB stars
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 598, article id A53Article in journal (Refereed) Published
Abstract [en]

Context. Aluminium monoxide (AlO) is likely efficiently depleted from the gas around oxygen-rich evolved stars to form alumina (Al2O3) clusters and dust seeds. The presence of AlO gas in the extended atmospheres of evolved stars has been derived from optical spectroscopy. More recently, AlO gas was also detected at long wavelengths around the supergiant VY CMa and the oxygenrich asymptotic giant branch star o Cet (Mira A). The central role aluminium might play in dust formation and wind driving, in combination with these first detections of AlO at long wavelengths, shows the need for a wider search for this molecule in the winds of evolved stars. Aims. The detection at long wavelengths of emission in rotational transitions of AlO towards asymptotic giant branch stars can help constrain the presence and location of AlO gas in the outflows and ultimately also the efficiency of the depletion process. Methods. In search of AlO, we mined data obtained with APEX, the IRAM 30m telescope, Herschel / HIFI, SMA, and ALMA, which were primarily aimed at studying other species around asymptotic giant branch stars. We report here on observations of AlO towards a sample of eight oxygen-rich asymptotic giant branch stars in different rotational transitions, up to seven for some stars. Results. We present definite detections of one rotational transition of AlO for o Cet and R Aqr, and tentative detections of one transition for R Dor and o Cet and two transitions for IK Tau and W Hya. The presented spectra of WX Psc, R Cas, and TX Cam show no signature of AlO. For o Cet, R Aqr, and IK Tau, we find that the AlO (N = 9 8) emission likely traces the inner parts of the wind, out to only a few tens of AU, where the gas has not yet been accelerated to its terminal velocity. This is in agreement with recently published results from a detailed study on o Cet. Conclusions. The conclusive detections of AlO emission in the case of o Cet and R Aqr confirm the presence of AlO in the gas phase in outflows of asymptotic giant branch stars. The tentative detections further support this. Since most of the observations presented in this study were obtained with stronger emission from other species than AlO in mind, observations with higher sensitivity in combination with high angular resolution will improve our understanding of the presence and behaviour of AlO. From the current data sets we cannot firmly conclude whether there is a direct correlation between the wind properties and the detection rate of AlO emission. We hope that this study can serve as a stimulus to perform sample studies in search of AlO in oxygen-rich outflows.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2017
Keywords
stars: AGB and post-AGB, stars: mass-loss, circumstellar matter, astrochemistry, submillimeter: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-320501 (URN)10.1051/0004-6361/201628928 (DOI)000394465000053 ()
Funder
EU, European Research Council, 614264 646758 AEROSOLSwedish Research Council
Available from: 2017-04-20 Created: 2017-04-20 Last updated: 2017-04-20Bibliographically approved
Danilovich, T., Van de Sande, M., De Beck, E., Decin, L., Olofsson, H., Ramstedt, S. & Millar, T. J. (2017). Sulphur-bearing molecules in AGB stars. Astronomy and Astrophysics, 606, Article ID A124.
Open this publication in new window or tab >>Sulphur-bearing molecules in AGB stars
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 606, article id A124Article in journal (Refereed) Published
Abstract [en]

Context. Sulphur is a relatively abundant element in the local Galaxy that is known to form a variety of molecules in the circumstellar envelopes of AGB stars. The abundances of these molecules vary based on the chemical types and mass-loss rates of AGB stars. Aims. Through a survey of (sub-) millimetre emission lines of various sulphur-bearing molecules, we aim to determine which molecules are the primary carriers of sulphur in different types of AGB stars. In this paper, the first in a series, we investigate the occurrence of H2S in AGB circumstellar envelopes and determine its abundance, where possible. Methods. We surveyed 20 AGB stars with a range of mass-loss rates and different chemical types using the Atacama Pathfinder Experiment (APEX) telescope to search for rotational transition lines of five key sulphur-bearing molecules: CS, SiS, SO, SO2, and H2S. Here we present our results for H2S, including detections, non-detections, and detailed radiative transfer modelling of the detected lines. We compared results based on various descriptions of the molecular excitation of H2S and different abundance distributions, including Gaussian abundances, where possible, and two different abundance distributions derived from chemical modelling results. Results. We detected H2S towards five AGB stars, all of which have high mass-loss rates of. M >= 5 x 10(-6) M-circle dot yr(-1) and are oxygen rich. H2S was not detected towards the carbon or S-type stars that fall in a similar mass-loss range. For the stars in our sample with detections, we find peak o-H2S abundances relative to H-2 between 4 x 10(-7) and 2.5 x 10(-5). Conclusions. Overall, we conclude that H2S can play a significant role in oxygen-rich AGB stars with higher mass-loss rates, but is unlikely to play a key role in stars of other chemical types or in lower mass-loss rate oxygen-rich stars. For two sources, V1300 Aql and GX Mon, H2S is most likely the dominant sulphur-bearing molecule in the circumstellar envelope.

Place, publisher, year, edition, pages
EDP SCIENCES S A, 2017
Keywords
stars: AGB and post-AGB, circumstellar matter, stars: evolution, stars: mass-loss
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-340749 (URN)10.1051/0004-6361/201731203 (DOI)000413564700004 ()
Available from: 2018-02-08 Created: 2018-02-08 Last updated: 2018-02-08
Ramstedt, S., Mohamed, S., Vlemmings, W. H., Danilovich, T., Brunner, M., De Beck, E., . . . Quintana-Lacaci, G. (2017). The circumstellar envelope around the S-type AGB star W Aql Effects of an eccentric binary orbit. Astronomy and Astrophysics, 605, Article ID A126.
Open this publication in new window or tab >>The circumstellar envelope around the S-type AGB star W Aql Effects of an eccentric binary orbit
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2017 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 605, article id A126Article in journal (Refereed) Published
Abstract [en]

Context. Recent observations at subarcsecond resolution, now possible also at submillimeter wavelengths, have shown intricate circumstellar structures around asymptotic giant branch (AGB) stars, mostly attributed to binary interaction. The results presented here are part of a larger project aimed at investigating the effects of a binary companion on the morphology of circumstellar envelopes (CSEs) of AGB stars.

Aims. AGB stars are characterized by intense stellar winds that build CSEs around the stars. Here, the CO(J = 3 -> 2) emission from the CSE of the binary S-type AGB star W Aql has been observed at subarcsecond resolution using ALMA. The aim of this paper is to investigate the wind properties of the AGB star and to analyse how the known companion has shaped the CSE.

Methods. The average mass-loss rate during the creation of the detected CSE is estimated through modelling, using the ALMA brightness distribution and previously published single-dish measurements as observational constraints. The ALMA observations are presented and compared to the results from a 3D smoothed particle hydrodynamics (SPH) binary interaction model with the same properties as the W Aql system and with two different orbital eccentricities. Three-dimensional radiative transfer modelling is performed and the response of the interferometer is modelled and discussed.

Results. The estimated average mass-loss rate of W Aql is (M) over dot = 3.0 x 10(-6) M-circle dot yr(-1) and agrees with previous results based on single-dish CO line emission observations. The size of the emitting region is consistent with photodissociation models. The inner 10 0 0 of the CSE is asymmetric with arc-like structures at separations of 23" scattered across the denser sections. Further out, weaker spiral structures at greater separations are found, but this is at the limit of the sensitivity and field of view of the ALMA observations.

Conclusions. The CO(J = 3 -> 2) emission is dominated by a smooth component overlayed with two weak arc patterns with different separations. The larger pattern is predicted by the binary interaction model with separations of similar to 10" and therefore likely due to the known companion. It is consistent with a binary orbit with low eccentricity. The smaller separation pattern is asymmetric and coincides with the dust distribution, but the separation timescale (200 yr) is not consistent with any known process of the system. The separation of the known companions of the system is large enough to not have a very strong effect on the circumstellar morphology. The density contrast across the envelope of a binary with an even larger separation will not be easily detectable, even with ALMA, unless the orbit is strongly asymmetric or the AGB star has a much larger mass-loss rate.

Keywords
stars: AGB and post-AGB, circumstellar matter, binaries: general, submillimeter: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-337758 (URN)10.1051/0004-6361/201730934 (DOI)000412231200088 ()
Funder
EU, European Research Council, 614264; 646758EU, FP7, Seventh Framework Programme, 610256 (NANOCOSMOS)
Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-12Bibliographically approved
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