77 research outputs found
Investigating the nature of the Fried Egg nebula: CO mm-line and optical spectroscopy of IRAS 17163-3907
Through CO mm-line and optical spectroscopy, we investigate the properties of
the Fried Egg nebula IRAS 17163-3907, which has recently been proposed to be
one of the rare members of the yellow hypergiant class. The CO J=2-1 and J=3-2
emission arises from a region within 20" of the star and is clearly associated
with the circumstellar material. The CO lines show a multi-component
asymmetrical profile, and an unexpected velocity gradient is resolved in the
east-west direction, suggesting a bipolar outflow. This is in contrast with the
apparent symmetry of the dust envelope as observed in the infrared. The optical
spectrum of IRAS 17163-3907 between 5100 and 9000 {\AA} was compared with that
of the archetypal yellow hypergiant IRC+10420 and was found to be very similar.
These results build on previous evidence that IRAS 17163-3907 is a yellow
hypergiant.Comment: 14 pages including appendix, accepted for publication in A&
ALMA Compact Array observations of the Fried Egg nebula: Evidence for large-scale asymmetric mass-loss from the yellow hypergiant IRAS 17163-3907
Yellow hypergiants are rare and represent a fast evolutionary stage of massive evolved stars. That evolutionary phase is characterised by a very intense mass loss, the understanding of which is still very limited. Here we report ALMA Compact Array observations of a 50-mosaic toward the Fried Egg nebula, around one of the few Galactic yellow hypergiants IRAS 17163-3907. The emission from the CO J=2-1 line, H30 recombination line, and continuum is imaged at a resolution of 8, revealing the morphology of the molecular environment around the star. The continuum emission is unresolved and peaks at the position of the star. The radio recombination line H30 shows unresolved emission at the star, with an approximately gaussian spectrum centered on a velocity of 213~km/s with a width of 576~km/s. In contrast, the CO 2-1 emission is complex and decomposes into several components beyond the contamination from interstellar gas in the line of sight. The CO spectrum toward the star is a broad plateau, centered at the systemic velocity of +18 km/s and with an expansion velocity of 10010 km/s. Assuming isotropic and constant mass-loss, we estimate a mass-loss rate of 81.5 ~M yr. At a radius of 25 from the star, we detect CO emission associated with the dust ring previously imaged by {\it Herschel}. The kinematics of this ring, however, is not consistent with an expanding shell, but show a velocity gradient of 20 km/s. In addition, we find a puzzling bright feature radially connecting the star to the CO ring, at a velocity of +40 km/s relative to the star. This spur feature may trace a unidirectional ejection event from the star. Our ACA observations reveal the complex morphology around IRAS 17163 and illustrate the breakthroughs that ALMA will bring to the field of massive stellar evolution
Optical and near-infrared observations of the Fried Egg Nebula
Context. The fate of a massive star during the latest stages of its evolution is highly dependent on its mass-loss rate and geometry and therefore knowing the geometry of the circumstellar material close to the star and its surroundings is crucial.
Aims. We aim to provide insight into the nature (i.e. geometry, rates) of mass-loss episodes, and in particular, the connection between the observed asymmetries due to the mass lost in a fast wind or during a previous, prodigious mass-losing phase. In this context, yellow hypergiants offer a good opportunity to study mass-loss events.
Methods. We analysed a large set of optical and near-infrared data in spectroscopic and photometric, spectropolarimetric, and interferometric (GRAVITY/VLTI) modes, towards the yellow hypergiant IRAS 17163â3907. We used X-shooter optical observations to determine the spectral type of this yellow hypergiant and we present the first model-independent, reconstructed images of IRAS 17163â3907 at these wavelengths tracing milli-arcsecond scales. Lastly, we applied a 2D radiative transfer model to fit the dereddened photometry and the radial profiles of published diffraction-limited VISIR images at 8.59 ÎŒm, 11.85 ÎŒm, and 12.81 ÎŒm simultaneously, adopting a revised distance determination using Gaia Data Release 2 measurements.
Results. We constrain the spectral type of IRAS 17163â3907 to be slightly earlier than A6Ia (TeffââŒâ8500 K). The interferometric observables around the 2 ÎŒm window towards IRAS 17163â3907 show that the BrÎł emission appears to be more extended and asymmetric than the NaâŻI and the continuum emission. Interestingly, the spectrum of IRAS 17163â3907 around 2 ÎŒm shows MgâŻII emission that is not previously seen in other objects of its class. In addition, BrÎł shows variability in a time interval of four months that is not seen towards NaâŻI. Lastly, in addition to the two known shells surrounding IRAS 17163â3907, we report on the existence of a third hot inner shell with a maximum dynamical age of only 30 yr.
Conclusions. The 2 ÎŒm continuum originates directly from the star and not from hot dust surrounding the stellar object. The observed spectroscopic variability of BrÎł could be a result of variability in the mass-loss rate. The interpretation of the presence of NaâŻI emission at closer distances to the star compared to BrÎł has been a challenge in various studies. To address this, we examine several scenarios. We argue that the presence of a pseudo-photosphere, which was traditionally considered to be the prominent explanation, is not needed and that it is rather an optical depth effect. The three observed distinct mass-loss episodes are characterised by different mass-loss rates and can inform theories of mass-loss mechanisms, which is a topic still under debate both in theory and observations. We discuss these in the context of photospheric pulsations and wind bi-stability mechanisms
A prospective Swedish study on body size, body composition, diabetes, and prostate cancer risk
Obesity may be associated with increased risk of prostate cancer (PCa). According to one hypothesis, obesity could lower the risk of non-aggressive tumours, while simultaneously increasing the risk of aggressive cancer. Furthermore, central adiposity may be independently associated with PCa risk; it is also associated with diabetes, which itself may influence risk of PCa. We studied the associations between height, body composition, and fat distribution, diabetes prevalence and risk of total, aggressive, and non-aggressive PCa in 10â564 initially cancer-free men (aged 45â73 years) of the population-based Malmö Diet and Cancer cohort. Anthropometric and body composition measurements, including bioelectrical impedance for estimation of fat mass, were performed by study nurses. Diabetes prevalence was self-reported. Cancer cases and clinical characteristics were ascertained through national and regional registry data. Dietary and other background data were obtained through a modified diet history method and an extensive questionnaire. During a mean follow-up of 11.0 years, 817 incidental PCa cases were diagnosed. Of these, 281 were classified as aggressive. There were 202 cases occurring before 65 years of age. Height was positively associated with total and non-aggressive PCa risk. Waistâhip ratio (WHR), a measure of central adiposity, was positively associated with PCa before age 65, and less strongly, with total PCa. This association was independent of body mass index (BMI) and other potential confounders. General adiposity, expressed as BMI or body fat percentage, and prevalent diabetes were not associated with PCa risk. In this study, WHR and body height were stronger PCa predictors than general adiposity
The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview:Sample characterization through polarization analysis
Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to
present a consistent view of a sample of 17 nearby cool evolved stars
(Aymptotic Giant Branch and red supergiant stars).
Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the
visible of 14 out of the 17 ATOMIUM sources. They were obtained
contemporaneously with the ALMA high spatial resolution data. To help interpret
the polarized signal, we produced synthetic maps of light scattering by dust,
through 3D radiative transfer simulations with the RADMC3D code.
Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads
across several optical filters. We infer that it primarily probes dust located
just outside of the point spread function, and in or near the plane of the sky,
with a total optical depth close to unity in the line of sight, representing
only a fraction of the total circumstellar dust. The maximum DoLP ranges from
0.03-0.38 depending on the source, fractions that can be reproduced by our 3D
pilot models for grains composed of common dust species. The spatial structure
of the DoLP shows a diverse set of shapes. Only for three sources do we note a
correlation between the ALMA CO and SiO lines, which trace the gas density, and
the DoLP, which traces the dust.
Conclusion. The clumpiness of the DoLP and the lack of a consistent
correlation between the gas and the dust location show that, in the inner
circumstellar environment (CSE), dust formation occurs at very specific sites.
This has potential consequences for the derived mass-loss rates and dust-to-gas
ratio in the inner region of the CSE. Except for ~Gru and perhaps GY
Aql, we do not detect interactions between the circumstellar wind and the
hypothesized companions that shape the wind at larger scales. This suggests
that the orbits of any other companions are tilted out of the plane of the sky.Comment: Accepted for publication in Astronomy & Astrophysics. 22 pages, 15
figures, 5 table
(Sub)stellar companions shape the winds of evolved stars
Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe
The VLT/SPHERE view of the ATOMIUM cool evolved star sample. I. Overview: Sample characterization through polarization analysis
Aims. Through the ATOMIUM project, based on an ALMA large program, we aim to
present a consistent view of a sample of 17 nearby cool evolved stars
(Aymptotic Giant Branch and red supergiant stars).
Methods. Here we present VLT/SPHERE-ZIMPOL polarimetric maps obtained in the
visible of 14 out of the 17 ATOMIUM sources. They were obtained
contemporaneously with the ALMA high spatial resolution data. To help interpret
the polarized signal, we produced synthetic maps of light scattering by dust,
through 3D radiative transfer simulations with the RADMC3D code.
Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads
across several optical filters. We infer that it primarily probes dust located
just outside of the point spread function, and in or near the plane of the sky,
with a total optical depth close to unity in the line of sight, representing
only a fraction of the total circumstellar dust. The maximum DoLP ranges from
0.03-0.38 depending on the source, fractions that can be reproduced by our 3D
pilot models for grains composed of common dust species. The spatial structure
of the DoLP shows a diverse set of shapes. Only for three sources do we note a
correlation between the ALMA CO and SiO lines, which trace the gas density, and
the DoLP, which traces the dust.
Conclusion. The clumpiness of the DoLP and the lack of a consistent
correlation between the gas and the dust location show that, in the inner
circumstellar environment (CSE), dust formation occurs at very specific sites.
This has potential consequences for the derived mass-loss rates and dust-to-gas
ratio in the inner region of the CSE. Except for ~Gru and perhaps GY
Aql, we do not detect interactions between the circumstellar wind and the
hypothesized companions that shape the wind at larger scales. This suggests
that the orbits of any other companions are tilted out of the plane of the sky.Comment: Accepted for publication in Astronomy & Astrophysics. 22 pages, 15
figures, 5 table
CHIMPS2: Survey description and <sup>12</sup>CO emission in the Galactic Centre
Abstract The latest generation of Galactic-plane surveys is enhancing our ability to study the effects of galactic environment upon the process of star formation. We present the first data from CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). CHIMPS2 is a survey that will observe the Inner Galaxy, the Central Molecular Zone (CMZ), and a section of the Outer Galaxy in 12CO, 13CO, and C18O (J = 3 â 2) emission with the Heterodyne Array Receiver Program on the James Clerk Maxwell Telescope (JCMT). The first CHIMPS2 data presented here are a first look towards the CMZ in 12CO J = 3â2 and cover â3⠆⠆5â and âŁâŁ †05 with angular resolution of 15 arcsec, velocity resolution of 1 km sâ1, and rms 0.58 K at these resolutions. Such high-resolution observations of the CMZ will be a valuable data set for future studies, whilst complementing the existing Galactic Plane surveys, such as SEDIGISM, the infrared Galactic Plane Survey, and ATLASGAL. In this paper, we discuss the survey plan, the current observations and data, as well as presenting position-position maps of the region. The position-velocity maps detect foreground spiral arms in both absorption and emission
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The VLT/SPHERE view of the ATOMIUM cool evolved star sample
Context. Low- and intermediate-mass asymptotic giant stars and massive red supergiant stars are important contributors to the chemical enrichment of the Universe. They are among the most efficient dust factories of the Galaxy, harboring chemically rich circumstellar environments. Yet, the processes that lead to dust formation or the large-scale shaping of the mass loss still escape attempts at modeling.
Aims. Through the ATOMIUM project, we aim to present a consistent view of a sample of 17 nearby cool evolved stars. Our goals are to unveil the dust-nucleation sites and morphologies of the circumstellar envelope of such stars and to probe ambient environments with various conditions. This will further enhance our understanding of the roles of stellar convection and pulsations, and that of companions in shaping the dusty circumstellar medium.
Methods. Here we present and analyze VLT/SPHERE-ZIMPOL polarimetric maps obtained in the visible (645â820 nm) of 14 out of the 17 ATOMIUM sources. They were obtained contemporaneously with the ALMA high spatial resolution data. To help interpret the polarized signal, we produced synthetic maps of light scattering by dust, through 3D radiative transfer simulations with the RADMC3D code.
Results. The degree of linear polarization (DoLP) observed by ZIMPOL spreads across several optical filters. We infer that it primarily probes dust located just outside of the point spread function of the central source, and in or near the plane of the sky. The polarized signal is mainly produced by structures with a total optical depth close to unity in the line of sight, and it represents only a fraction of the total circumstellar dust. The maximum DoLP ranges from 0.03â0.38 depending on the source, fractions that can be reproduced by our 3D pilot models for grains composed of olivine, melilite, corundum, enstatite, or forsterite. The spatial structure of the DoLP shows a diverse set of shapes, including clumps, arcs, and full envelopes. Only for three sources do we note a correlation between the ALMA CO Ï
= 0, J = 2â1 and SiO Ï
= 0, J = 5â4 lines, which trace the gas density, and the DoLP, which traces the dust.
Conclusions. The clumpiness of the DoLP and the lack of a consistent correlation between the gas and the dust location show that, in the inner environment, dust formation occurs at very specific sites. This has potential consequences for the derived mass-loss rates and dust-to-gas ratio in the inner region of the circumstellar environment. Except for Ï1 Gru and perhaps GY Aql, we do not detect interactions between the circumstellar wind and the hypothesized companions that shape the wind at larger scales. This suggests that the orbits of any other companions are tilted out of the plane of the sky
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