Exocomets: A spectroscopic survey

Rebollido, Isabel; Eiroa, C.; Montesinos, B.; Maldonado, J.; Villaver, E.; Absil, Olivier; Bayo, A.; Cánovas, H.; Chen, Ch.; Henning, Th.; Iglesias, Daniela; Launhardt, R.; Liseau, R.; Meeus, G.; Moór, A.; Mora, A.; Olofsson, Johan; Rauw, Grégor; Riviére-Marichalar, P.

doi:10.1051/0004-6361/201936071

Cited by 35 publications

(33 citation statements)

References 155 publications

(166 reference statements)

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“…Several systems of similar age as HD 152384 such as β Pic also display variable absorption features in their spectrum which are interpreted as due to infalling evaporating comets (e.g. Ferlet et al 1987;Beust et al 1991;Kiefer et al 2014;Vidal-Madjar et al 2017;Rebollido et al 2020), demonstrating the dynamic nature of newly formed planetary systems. Collisions are also believed to have played an important role in shaping our own solar system, and may have led to the formation of our Earth's moon (e.g.…”

Section: Discussionmentioning

confidence: 99%

First detection of a disk free of volatile elements around a young A-type star: A possible sign of collisions between rocky planets

Ancker

Fusillo

Haworth

et al. 2021

A&A

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Aims. We present the first detailed analysis of the astrophysical parameters of the poorly studied Sco-Cen member HD 152384 and its circumstellar environment. Methods. We analyse newly obtained optical-near-IR X-shooter spectra, as well as archival TESS data, of HD 152384. In addition, we use literature photometric data to construct a detailed spectral energy distribution (SED) of the star. Results. The photospheric absorption lines in the spectrum of HD 152384 are characteristic of an A0 V star, for which we derive a stellar mass of 2.1 ± 0.1 M⊙ and a stellar age > 4.5 Myr. Superimposed on the photospheric absorption, the optical spectrum also displays double-peaked emission lines of Ca II, Fe I, Mg I, and Si I, typical of circumstellar disks. Notably, all hydrogen and helium lines appear strictly in absorption. A toy model shows that the observed emission line profiles can be reproduced by emission from a compact (radius < 0.3 au) disk seen at an inclination of ∼24°. Further evidence for the presence of circumstellar material comes from the detection of a moderate IR excess in the SED, similar to those found in extreme debris disk systems. Conclusions. We conclude that HD 152384 is surrounded by a tenuous circumstellar disk that, although rich in refractory elements, is highly depleted of volatile elements. To the best of our knowledge, such a disk is unique among young stars. However, it is reminiscent of the disks seen in some white dwarfs, which have been attributed to the disruption of rocky planets. We suggest that the disk around HD 152384 may have a similar origin and may be due to collisions in a newly formed planetary system.

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Section: Discussionmentioning

confidence: 99%

First detection of a disk free of volatile elements around a young A-type star: A possible sign of collisions between rocky planets

Ancker

Fusillo

Haworth

et al. 2021

A&A

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“…Whilst it may be possible to trap hot dust in the gas released by comets, it is unclear whether the gas would form a stable disc that could trap dust for long periods. We therefore argue that variable hot gas detections of Rebollido et al (2018Rebollido et al ( , 2020 with FEBs, and that if the trapping mechanism occurs in those systems, it operates with distinct, undetected gas. The gas trap model is not incompatible with FEBs, and could benefit from them.…”

Section: Observability Of the Gasmentioning

confidence: 90%

“…Dust released by FEBs near the star takes less time to reach the sublimation region than dust from the habitable zone, so trapped grains could have shorter lifetimes without a significantly decreased NIR-to-MIR flux ratio. Rebollido et al (2020) suggest a tentative trend for variable gas detections in systems with NIR excesses, so FEBs could help supply dust to the inner system. Additionally, whilst the large and variable quantities of gas released by comets may struggle to trap bound grains, they may significantly slow the escape of unbound grains released close to the star (Section 3.3).…”

Section: Observability Of the Gasmentioning

confidence: 93%

“…We therefore conclude that gas trapping may operate with sub-detection levels of gas, and that non-detections of gas emission around stars with NIR excesses would not invalidate the model. Rebollido et al (2018Rebollido et al ( , 2020 detected hot CaII and NaI gas in absorption around some stars with NIR excesses. The absorption is variable, and is probably produced close to stars by Falling Evaporating Bodies (FEBs).…”

Section: Observability Of the Gasmentioning

confidence: 99%

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Gas trapping of hot dust around main-sequence stars

Pearce,

Krivov,

Booth

2020

Preprint

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In 2006 Vega was discovered to display excess near-infrared emission. Surveys now detect this phenomenon for one fifth of main-sequence stars, across various spectral types and ages. The excesses are interpreted as populations of small, hot dust grains very close to their stars, which must originate from comets or asteroids. However, the presence of such grains in copious amounts is mysterious, since they should rapidly sublimate or be blown out of the system. Here we investigate a potential mechanism to generate excesses: dust migrating inwards under radiation forces sublimates near the star, releasing modest quantities of gas which then traps subsequent grains. This mechanism requires neither specialised system architectures nor high dust supply rates, and could operate across diverse stellar types and ages. The model naturally reproduces many features of inferred dust populations, in particular their location, preference for small grains, steep size distribution, and dust location scaling with stellar luminosity. For Sun-like stars the mechanism can produce 2.2 µm excesses that are an order of magnitude larger than those at 8.5 µm, as required by observations. However, for A-type stars the simulated near-infrared excesses were only twice those in the mid infrared; grains would have to be 5 − 10 times smaller than those trapped in our model to be able to explain observed near-infrared excesses around A stars. Further progress with any hot dust explanation for A stars requires a means for grains to become very hot without either rapidly sublimating or being blown out of the system.

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“…Exocomets were first found orbiting β Pic through their absorption in the Ca II H&K lines [16]. A recent survey of 117 main sequence stars [43] found signatures of absorption from gas possibly attributable to exocomets in about 25 % of the sample. The sample was biased to maximise such detections so this should not be interpreted as an occurrence rate.…”

Section: Exocometsmentioning

confidence: 99%