Post-asymptotic giant branch (post-AGB) stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the AGB towards the ...planetary nebula stage. There is growing evidence that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VLT spectrometer and imager for the mid-infrared (VISIR)/VLT, T-Recs/Gemini-South and Michelle/Gemini-North. We found that all the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non-resolved. The resolved targets can be divided into two categories. (i) The nebulae with a dense central core, that are either bipolar and multipolar and (ii) the nebulae with no central core, with an elliptical morphology. The dense central torus observed likely hosts binary systems which triggered fast outflows that shaped the nebulae.
SMC-Last Extracted Photometry Kuchar, T. A.; Sloan, G. C.; Mizuno, D. R. ...
The Astronomical journal,
04/2024, Volume:
167, Issue:
4
Journal Article
Peer reviewed
Open access
Abstract We present point-source photometry from the Spitzer Space Telescope's final survey of the Small Magellanic Cloud (SMC). We mapped nearly 30 deg 2 in two epochs in 2017, with the second ...extending to early 2018 at 3.6 and 4.5 μ m using the Infrared Array Camera. This survey duplicates the footprint from the SAGE-SMC program in 2008. Together, these surveys cover a nearly 10 yr temporal baseline in the SMC. We performed aperture photometry on the mosaicked maps produced from the new data. We did not use any prior catalogs as inputs for the extractor in order to be sensitive to any moving objects (e.g., foreground brown dwarfs) and other transient phenomena (e.g., cataclysmic variables or FU Ori–type eruptions). We produced a point-source catalog with high-confidence sources for each epoch as well as a combined-epoch catalog. For each epoch and the combined-epoch data, we also produced a more complete archive with lower-confidence sources. All of these data products will be made available to the community at the Infrared Science Archive.
ABSTRACT We have identified a new class of Asymptotic Giant Branch (AGB) stars in the Small and Large Magellanic Clouds (SMC/LMC) using optical to infrared photometry, light curves, and optical ...spectroscopy. The strong dust production and long-period pulsations of these stars indicate that they are at the very end of their AGB evolution. Period-mass-radius relations for the fundamental-mode pulsators give median current stellar masses of in the LMC and in the SMC (with dispersions of 0.21 and 0.18 , respectively), and models suggest initial masses of <1.5 and <1.25 , respectively. This new class of stars includes both O-rich and C-rich chemistries, placing the limit where dredge-up allows carbon star production below these masses. A high fraction of the brightest among them should show S star characteristics indicative of atmospheric C/O 1, and many will form O-rich dust prior to their C-rich phase. These stars can be separated from their less-evolved counterparts by their characteristically red colors.
Radio Stars of the SKA Yu, Bin; Zijlstra, Albert; Jiang, Biwei
Universe,
2021, Volume:
7, Issue:
5
Journal Article
Peer reviewed
Open access
Radio emission from stars can be used, for example, to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array ...(SKA) brings a survey ability to the topic of radio stars. In this paper we investigate what the SKA can detect, and what sensitivity will be required for deep surveys of the stellar Milky Way. We focus on the radio emission from OB stars, Be stars, flares from M dwarfs, and Ultra Compact HII regions. The stellar distribution in the Milky Way is simulated using the Besançon model, and various relations are used to predict their radio flux. We find that the full SKA will easily detect all UltraCompact HII regions. At the limit of 10 nJy at 5 GHz, the SKA can detect 1500 Be stars and 50 OB stars per square degree, out to several kpc. It can also detect flares from 4500 M dwarfs per square degree. At 100 nJy, the numbers become about 8 times smaller. SKA surveys of the Galactic plane should be designed for high sensitivity. Deep imaging should consider the significant number of faint flares in the field, even outside the plane of the Milky Way.
Abstract
Iron suffers from high levels of depletion in the highly ionized environments of planetary nebulae, making the direct determination of undepleted elemental iron abundances difficult. Zinc, ...which does not suffer from the same depletion effects as iron, may be used as a surrogate element to measure iron abundances as there is an approximately constant zinc-to-iron ratio across a wide range of metallicities. In this paper, we report zinc abundances of six Galactic bulge planetary nebulae determined from new observations taken with Infrared Spectrometer And Array Camera (ISAAC) on the Very Large Telescope, Chile, prior to the instrument's decommissioning as well as a further three based upon literature observations. Ultraviolet and Visual Echelle Spectrograph (UVES) data of the sample planetary nebulae are presented and have been used to derive abundances, temperatures and densities of a variety of elements and ions. The abundances derived from the UVES data agree well with results from the literature. Zn/H, determined from the ISAAC observations, is found to be generally subsolar and O/Zn is found to be either consistent or enriched with respect to solar.
Interaction with the interstellar medium (ISM) cannot be ignored in understanding planetary nebula (PN) evolution and shaping. In an effort to understand the range of shapes observed in the outer ...envelopes of PNe, we have run a comprehensive set of three-dimensional hydrodynamic simulations, from the beginning of the asymptotic giant branch (AGB) superwind phase until the end of the post-AGB/PN phase. A ‘triple-wind’ model is used, including a slow AGB wind, fast post-AGB wind and third wind reflecting the linear movement through the ISM. A wide range of stellar velocities, mass-loss rates and ISM densities have been considered. We find that ISM interaction strongly affects outer PN structures, with the dominant shaping occurring during the AGB phase. The simulations predict four stages of PN–ISM interaction whereby (i) the PN is initially unaffected, (ii) then limb-brightened in the direction of motion, (iii) then distorted with the star moving away from the geometric centre, and (iv) finally so distorted that the object is no longer recognizable as a PN and may not be classed as such. Parsec-size shells around PNe are predicted to be common. The structure and brightness of ancient PNe are largely determined by the ISM interaction, caused by rebrightening during the second stage; this effect may address the current discrepancies in Galactic PN abundance. The majority of PNe will have tail structures. Evidence for strong interaction is found for all known PNe in globular clusters.
ABSTRACT
We present the highest resolution single-dish submillimetre observations of the detached shell source U Antliae to date. The observations were obtained at $450$ and $850\,{\mu}{\rm m}$ with ...SCUBA-2 instrument on the James Clerk Maxwell Telescope as part of the Nearby Evolved Stars Survey. The emission at $850\,{\mu}{\rm m}$ peaks at 40 arcsec with hints of a second peak seen at ∼20 arcsec. The emission can be traced out to a radius of 56 arcsec at a 3σ level. The outer peak observed at $850\,{\mu}{\rm m}$ aligns well with the peak observed at Herschel/PACS wavelengths. With the help of spectral energy distribution fitting and radiative transfer calculations of multiple-shell models for the circumstellar envelope, we explore the various shell structures and the variation of grain sizes along the in the circumstellar envelope. We determine a total shell dust mass of (2.0 ± 0.3) × 10−5 M⊙ and established that the thermal pulse that gave rise to the detached shell occurred 3500 ± 500 yr ago.
It is important to understand the interplay between nuclear star formation and nuclear activity when studying the evolution of gas-rich galaxy mergers. We present here new spatially resolved L-band ...integral field unit observations of the inner kpc of the luminous infrared galaxy NGC 1614. A broad ring of 3.3-μm polycyclic aromatic hydrocarbon (PAH) emission is found at a distance of approximately 200 pc from the core. This ring overlaps with a previously established star-forming ring detected with Paα and radio continuum observations, but peaks outside it, especially if determined using the PAH equivalent width. Using the characteristics of the PAH emission and the ionized gas emission, we argue that NGC 1614 features an outward propagating ring of star formation, where the equivalent width of the PAH emission localizes the regions where the current star formation is just expanding into the molecular gas outward of the nucleus. The core itself shows a highly luminous, slightly resolved (at ∼80 pc) L-band continuum source. We find no evidence of active galactic nucleus (AGN) activity and rule out the presence of an obscured AGN using L-band diagnostics. Furthermore, we detect the likely companion galaxy from archival Hubble Space Telescope/Advanced Camera for Surveys (ACS) imaging. The star formation and dynamical characteristics of the system are consistent with a relatively major merger just after its second passage. An outstanding question is how a gas-rich advanced merger such as this one, with strong luminous infrared galaxies level nuclear starburst and major-merger-like tidal features, has not yet developed an active nucleus.
Abstract Stellar atmosphere modelling predicts the luminosity and temperature of a star, together with parameters such as the effective gravity and the metallicity, by reproducing the observed ...spectral energy distribution. Most observational data come from photometric surveys, using a variety of passbands. We herein present the Python Stellar Spectral Energy Distribution (PySSED) routine, designed to combine photometry from disparate catalogues, fit the luminosity and temperature of stars, and determine departures from stellar atmosphere models such as infrared or ultraviolet excess. We detail the routine’s operation, and present use-cases on both individual stars, stellar populations, and wider regions of the sky. PySSED benefits from fully automated processing, allowing fitting of arbitrarily large data sets at the rate of a few seconds per star.
Planetary Nebulae (PNe) that are physical members of Galactic open clusters are powerful probes that allow precise determination of their distance and crucially their initial mass on the main ...sequence. Here, we revisit the physical association of the PN BMP J1613–5406 with the open cluster NGC 6067 and present our preliminary results based on our new ESO/VLT FORS2 data. Our PN spectral data permit the calculation of a precise radial velocity and reddening to the PN that shows a tight consistency with the literature corresponding cluster parameters including importantly the radial velocity. Our measurements, combined with the agreement between the distances of the two objects and the fact that the PN is located well within the cluster boundaries, confirm that the PN is physically associated with the cluster. The cluster has a turn-off mass of around 5 solar masses that indicates a PN initial mass of around 5.6 solar masses. This is closer to the theoretical lower limit of core-collapse supernova formation than has ever been previously observed, providing a unique opportunity for further stellar and Galactic chemical evolution studies using this system.
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