| 1. |
- Quintana-Lacaci, Guillermo, et al.
(author)
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Hints of the Existence of C-rich Massive Evolved Stars
- 2019
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In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 876:2
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Journal article (peer-reviewed)abstract
- We aim to study the properties of a particular type of evolved stars, C-rich evolved stars with high expansion velocities. For this purpose we have focused on the two best studied objects within this group, IRC+10401 and AFGL 2233. We focused on determining their luminosity by studying their spectral energy distribution. Also, we have obtained single-dish line profiles and interferometric maps of the CO J - 1-0 and J = 2-1. emission lines for both objects. We have modeled this emission using a LVG radiative transfer code to determine the kinetic temperature and density profiles of the gas ejected by these stars. We have found that the luminosities obtained for these objects (log(L/L-circle dot). =. 4.1 and 5.4) locate them in the domain of the massive asymptotic giant branch stars (AGBs) and the red supergiant stars (RSGs). In addition, the mass-loss rates obtained (1.5. x. 10(-5)-6. x 10(-3)M(circle dot) yr(-1)) suggest that while IRC+ 10401 might be an AGB star, AFGL 2233 could be an RSG star. All these results, together with those from previous works, suggest that both objects are massive objects, IRC+10401 a massive evolved star with M-init similar to 5-9M(circle dot). which could correspond to an AGB or an RSG and AFGL 2233 an RSG with M-init similar to 20M(circle dot), which would confirm the existence of massive C-rich evolved stars. Two scenarios are proposed to form these types of objects. The first one is capable of producing high-mass AGB stars up to similar to 8M(circle dot). and the second one is capable of forming C-rich RSGs like AFGL 2233.
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| 2. |
- Velilla Prieto, Luis, 1981, et al.
(author)
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Circumstellar chemistry of Si-C bearing molecules in the C-rich AGB star IRC+10216
- 2018
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In: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 14, s. 535-537
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Conference paper (peer-reviewed)abstract
- Silicon carbide together with amorphous carbon are the main components of dust grains in the atmospheres of C-rich AGB stars. Small gaseous Si-C bearing molecules (such as SiC, SiCSi, and SiC2) are efficiently formed close to the stellar photosphere. They likely condense onto dust seeds owing to their highly refractory nature at the lower temperatures (i.e., below about 2500 K) in the dust growth zone which extends a few stellar radii from the photosphere. Beyond this region, the abundances of Si-C bearing molecules are expected to decrease until they are eventually reformed in the outer shells of the circumstellar envelope, owing to the interaction between the gas and the interstellar UV radiation field. Our goal is to understand the time-dependent chemical evolution of Si-C bond carriers probed by molecular spectral line emission in the circumstellar envelope of IRC+10216 at millimeter wavelengths.
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| 3. |
- Berné, O., et al.
(author)
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Formation of the methyl cation by photochemistry in a protoplanetary disk
- 2023
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In: Nature. - 0028-0836 .- 1476-4687. ; 621:7977, s. 56-59
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Journal article (peer-reviewed)abstract
- Forty years ago, it was proposed that gas-phase organic chemistry in the interstellar medium can be initiated by the methyl cation CH3+ (refs. 1–3), but so far it has not been observed outside the Solar System 4,5. Alternative routes involving processes on grain surfaces have been invoked 6,7. Here we report James Webb Space Telescope observations of CH3+ in a protoplanetary disk in the Orion star-forming region. We find that gas-phase organic chemistry is activated by ultraviolet irradiation.
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| 4. |
- Berne, Olivier, et al.
(author)
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PDRs4All : A JWST Early Release Science Program on Radiative Feedback from Massive Stars
- 2022
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In: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 134:1035
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Journal article (peer-reviewed)abstract
- Massive stars disrupt their natal molecular cloud material through radiative and mechanical feedback processes. These processes have profound effects on the evolution of interstellar matter in our Galaxy and throughout the universe, from the era of vigorous star formation at redshifts of 1-3 to the present day. The dominant feedback processes can be probed by observations of the Photo-Dissociation Regions (PDRs) where the far-ultraviolet photons of massive stars create warm regions of gas and dust in the neutral atomic and molecular gas. PDR emission provides a unique tool to study in detail the physical and chemical processes that are relevant for most of the mass in inter- and circumstellar media including diffuse clouds, proto-planetary disks, and molecular cloud surfaces, globules, planetary nebulae, and star-forming regions. PDR emission dominates the infrared (IR) spectra of star-forming galaxies. Most of the Galactic and extragalactic observations obtained with the James Webb Space Telescope (JWST) will therefore arise in PDR emission. In this paper we present an Early Release Science program using the MIRI, NIRSpec, and NIRCam instruments dedicated to the observations of an emblematic and nearby PDR: the Orion Bar. These early JWST observations will provide template data sets designed to identify key PDR characteristics in JWST observations. These data will serve to benchmark PDR models and extend them into the JWST era. We also present the Science-Enabling products that we will provide to the community. These template data sets and Science-Enabling products will guide the preparation of future proposals on star-forming regions in our Galaxy and beyond and will facilitate data analysis and interpretation of forthcoming JWST observations.
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| 5. |
- Chown, Ryan, et al.
(author)
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PDRs4All: IV. An embarrassment of riches: Aromatic infrared bands in the Orion Bar
- 2024
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In: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 685
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Journal article (peer-reviewed)abstract
- Context. Mid-infrared observations of photodissociation regions (PDRs) are dominated by strong emission features called aromatic infrared bands (AIBs). The most prominent AIBs are found at 3.3, 6.2, 7.7, 8.6, and 11.2 µm. The most sensitive, highest-resolution infrared spectral imaging data ever taken of the prototypical PDR, the Orion Bar, have been captured by JWST. These high-quality data allow for an unprecedentedly detailed view of AIBs. Aims. We provide an inventory of the AIBs found in the Orion Bar, along with mid-IR template spectra from five distinct regions in the Bar: the molecular PDR (i.e. the three H2 dissociation fronts), the atomic PDR, and the H II region. Methods. We used JWST NIRSpec IFU and MIRI MRS observations of the Orion Bar from the JWST Early Release Science Program, PDRs4All (ID: 1288). We extracted five template spectra to represent the morphology and environment of the Orion Bar PDR. We investigated and characterised the AIBs in these template spectra. We describe the variations among them here. Results. The superb sensitivity and the spectral and spatial resolution of these JWST observations reveal many details of the AIB emission and enable an improved characterization of their detailed profile shapes and sub-components. The Orion Bar spectra are dominated by the well-known AIBs at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 µm with well-defined profiles. In addition, the spectra display a wealth of weaker features and sub-components. The widths of many AIBs show clear and systematic variations, being narrowest in the atomic PDR template, but showing a clear broadening in the H II region template while the broadest bands are found in the three dissociation front templates. In addition, the relative strengths of AIB (sub-)components vary among the template spectra as well. All AIB profiles are characteristic of class A sources as designated by Peeters (2022, A&A, 390, 1089), except for the 11.2 µm AIB profile deep in the molecular zone, which belongs to class B11.2. Furthermore, the observations show that the sub-components that contribute to the 5.75, 7.7, and 11.2 µm AIBs become much weaker in the PDR surface layers. We attribute this to the presence of small, more labile carriers in the deeper PDR layers that are photolysed away in the harsh radiation field near the surface. The 3.3/11.2 AIB intensity ratio decreases by about 40% between the dissociation fronts and the H II region, indicating a shift in the polycyclic aromatic hydrocarbon (PAH) size distribution to larger PAHs in the PDR surface layers, also likely due to the effects of photochemistry. The observed broadening of the bands in the molecular PDR is consistent with an enhanced importance of smaller PAHs since smaller PAHs attain a higher internal excitation energy at a fixed photon energy. Conclusions. Spectral-imaging observations of the Orion Bar using JWST yield key insights into the photochemical evolution of PAHs, such as the evolution responsible for the shift of 11.2 µm AIB emission from class B11.2 in the molecular PDR to class A11.2 in the PDR surface layers. This photochemical evolution is driven by the increased importance of FUV processing in the PDR surface layers, resulting in a “weeding out” of the weakest links of the PAH family in these layers. For now, these JWST observations are consistent with a model in which the underlying PAH family is composed of a few species: the so-called ‘grandPAHs’.
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| 6. |
- Dunér, David, et al.
(author)
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Copernican Principle
- 2021
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In: Encyclopedia of Astrobiology. - Berlin/Heidelberg : Springer Berlin/Heidelberg. ; 1:1, s. 1-3
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Journal article (peer-reviewed)abstract
- The Copernican principle states that Earth has not any privileged position in the universe. In astrobiological terms, it means that terrestrial life, including the human beings, has not any particularly privileged, special, or unique position in the universe, which leads to the assumption that, given the presence of life on Earth, life will exist also in other places in the universe.
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| 7. |
- Dunér, David, et al.
(author)
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Great Chain of Being
- 2021
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In: Encyclopedia of Astrobiology. - Berlin/Heidelberg : Springer Berlin/Heidelberg. ; 1:1, s. 1-2
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Journal article (peer-reviewed)abstract
- A prevailing idea through the ages is that of the Great Chain of Being, understanding the universe as a hierarchy of beings, an unbroken chain of existence, from the simplest forms to the most complex ones, from non-living matter to the most rational creatures (Lovejoy 1936). In his History of Animals from the fourth century BCE, Aristotle arranged all beings in a ladder of nature, a scala naturae, a gradation of natural things from minerals, through plants and animals, to the human being. The chain of being got biological significance with, among others, Gottfried Wilhelm Leibniz, Carl Linnaeus, Georges-Louis Leclerc de Buffon, and Charles Bonnet. Nature does not make jumps, Natura non-facit saltus, as Carl Linnaeus formulated it in Philosophia Botanica (1751). There is continuity in nature. In that respect, the Great Chain of Being is connected to the Principle of Plenitude, the fullness of being. The principle suggests that every possible form of creature exists. This could also be understood in a temporal sense that every possible form of creature, even though not existing right now, might have existed before or could be realized at some stage in the future. Continuity is an idea implicit in that of plenitude. In the early nineteenth century, this continuity of nature became understood in temporal meaning. Jean-Baptiste de Lamarck went from a static concept of the series of life-forms to a theory of species transformation that life had developed over time from simpler to more complex forms. During the nineteenth century, the Great Chain of Being was replaced by another metaphor, the Tree of Life, which also stressed on the continuity of nature, but took into account the genealogy and evolution of life-forms, as in Lamarck’s Philosophie zoologique (1809) and Darwin’s Origin of Species (1859).
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| 8. |
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| 9. |
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| 10. |
- Dunér, David, et al.
(author)
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Principle of Plenitude
- 2022
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In: Encyclopedia of Astrobiology. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783642278334 ; 1:1, s. 1-3
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Book chapter (other academic/artistic)
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