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Herschel/HIFI observations of ionised carbon in the beta Pictoris debris disk
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
Vise andre og tillknytning
2014 (engelsk)Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 563, artikkel-id A66Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Context. The dusty debris disk around the similar to 20 Myr old main-sequence A-star beta Pictoris is known to contain gas. Evidence points towards a secondary origin of the gas as opposed to being a direct remnant from the initial protoplanetary disk, although the dominant gas production mechanism is so far not identified. The origin of the observed overabundance of C and O compared with solar abundances of metallic elements such as Na and Fe is also unclear. Aims. Our goal is to constrain the spatial distribution of C in the disk, and thereby the gas origin and its abundance pattern. Methods. We used the HIFI instrument on board the Herschel Space Observatory to observe and spectrally resolve C II emission at 158 mu m from the beta Pic debris disk. Assuming a disk in Keplerian rotation and a model for the line emission from the disk, we used the spectrally resolved line profile to constrain the spatial distribution of the gas. Results. We detect the C II 158 mu m emission. Modelling the shape of the emission line shows that most of the gas is located at about similar to 100 AU or beyond. We estimate a total C gas mass of 1.3(-0.5)(+1.3) x 10(2) M-circle plus (central 90% confidence interval). The data suggest that more gas is located on the south-west side of the disk than on the north-east side. The shape of the emission line is consistent with the hypothesis of a well mixed gas (constant C/Fe ratio throughout the disk). Assuming instead a spatial profile expected from a simplified accretion disk model, we found it to give a significantly poorer fit to the observations. Conclusions. Since the bulk of the gas is found outside 30 AU, we argue that the cometary objects known as falling evaporating bodies are probably not the dominant source of gas; production from grain-grain collisions or photodesorption seems more likely. The incompatibility of the observations with a simplified accretion disk model might favour a preferential depletion explanation for the overabundance of C and O, although it is unclear how much this conclusion is affected by the simplifications made. More stringent constraints on the spatial distribution will be available from ALMA observations of C I emission at 609 mu m.

sted, utgiver, år, opplag, sider
2014. Vol. 563, artikkel-id A66
Emneord [en]
protoplanetary disks, stars: individual: beta Pictoris, planetary systems, methods: observational, circumstellar matter, infrared: general
HSV kategori
Forskningsprogram
astronomi
Identifikatorer
URN: urn:nbn:se:su:diva-103302DOI: 10.1051/0004-6361/201323126ISI: 000333798000066OAI: oai:DiVA.org:su-103302DiVA, id: diva2:717660
Merknad

AuthorCount:12;

Tilgjengelig fra: 2014-05-16 Laget: 2014-05-12 Sist oppdatert: 2022-02-23bibliografisk kontrollert
Inngår i avhandling
1. Debris disks and the search for life in the universe
Åpne denne publikasjonen i ny fane eller vindu >>Debris disks and the search for life in the universe
2016 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Circumstellar debris disks are the extrasolar analogues of the asteroid belt and the Kuiper belt. These disks consist of comets and leftover planetesimals that continuously collide to produce copious amounts of circumstellar dust that can be observed as infrared excess or in resolved imaging. As an obvious outcome of the planet formation process, debris disks can help us constrain planet formation theories and learn about the history of our own solar system. Structures in the disks such as gaps or warps can hint at the presence of planets. Thus, the study of debris disks is an important branch of exoplanetary science. In this thesis, some aspects of debris disks are considered in detail.

A handful of debris disks show observable amounts of gas besides the dust. One such case is the edge-on debris disk around the young A-type star β Pictoris, where the gas is thought to be of secondary origin, i.e. derived from the dust itself. By observing this gas, we can thus learn something about the dust, and therefore about the building blocks of planets. In paper I, spectrally resolved observations of C II emission with Herschel/HIFI are presented. The line profile is used to constrain the spatial distribution of carbon gas in the disk, which helps understanding the gas producing mechanism. In paper II, we analyse C II and O I emission detected with Herschel/PACS and find that the oxygen must be located in a relatively dense region, possibly similar to the CO clump seen by ALMA. An upcoming analysis of our ALMA C I observations will give us a clearer picture of the system.

Another famous debris disk is found around the nearby, 440 Myr old A-star Fomalhaut. Its morphology is that of an eccentric debris belt with sharp edges, suggesting shaping by a planet. However, gas-dust interactions may result in a similar morphology without the need to invoke planets. We test this possibility in paper III by analysing non-detections of C II and O I emission by Herschel/PACS. We find that there is not enough gas present to efficiently sustain gas-dust interactions, implying that the morphology of the Fomalhaut belt is due to a yet unseen planet or alternatively stellar encounters.

One of the biggest challenges in exoplanetary research is to answer the question whether there are inhabited worlds other than the Earth. With the number of known rocky exoplanets in the habitable zone increasing rapidly, we might actually be able to answer this question in the coming decades. Different approaches exist to detect the presence of life remotely, for example by studying exoplanetary atmospheres or by analysing light reflected off the surface of an exoplanet. In paper IV, we study whether biosignatures (for example, certain minerals or microorganisms) ejected into a circumstellar debris disk by an impact event could be detected. We consider an impact similar to the Chicxulub event and model the collisional evolution of the ejected debris. Dust from such an event can potentially be detected by current telescopes, but analysis of the debris composition has to wait for future, advanced instruments.

sted, utgiver, år, opplag, sider
Stockholm: Department of Astronomy, Stockholm University, 2016. s. 73
Emneord
debris disks, astrobiology
HSV kategori
Forskningsprogram
astronomi
Identifikatorer
urn:nbn:se:su:diva-127263 (URN)978-91-7649-366-3 (ISBN)
Disputas
2016-04-15, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (engelsk)
Opponent
Veileder
Merknad

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Submitted.

Tilgjengelig fra: 2016-03-21 Laget: 2016-02-29 Sist oppdatert: 2022-02-23bibliografisk kontrollert

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