Fe I in the <i>β</i> Pictoris circumstellar gas disk

Vidal‐Madjar, A.; Kiefer, F.; Étangs, A. Lecavelier des; Bourrier, V.; Ehrenreich, D.; Ferlet, R.; Hébrard, G.; Wilson, Paul

doi:10.1051/0004-6361/201630040

Cited by 9 publications

(1 citation statement)

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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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The co-existence of hot and cold gas in debris discs

Rebollido

Eiroa

Montesinos

et al. 2018

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Context. Debris discs have often been described as gas-poor discs as the gas-to-dust ratio is expected to be considerably lower than in primordial, protoplanetary discs. However, recent observations have confirmed the presence of a non-negligible amount of cold gas in the circumstellar (CS) debris discs around young main-sequence stars. This cold gas has been suggested to be related to the outgassing of planetesimals and cometary-like objects. Aims. The goal of this paper is to investigate the presence of hot gas in the immediate surroundings of the cold-gas-bearing debris-disc central stars.Methods. High-resolution optical spectra of all currently known cold-gas-bearing debris-disc systems, with the exception of β Pic and Fomalhaut, have been obtained from La Palma (Spain), La Silla (Chile), and La Luz (Mexico) observatories. To verify the presence of hot gas around the sample of stars, we have analysed the Ca ii H&K and the Na i D lines searching for non-photospheric absorptions of CS origin, usually attributed to cometary-like activity. Results. Narrow, stable Ca ii and/or Na i absorption features have been detected superimposed to the photospheric lines in 10 out of the 15 observed cold-gas-bearing debris-disc stars. Features are found at the radial velocity of the stars, or slightly blue-or red-shifted, and/or at the velocity of the local interstellar medium (ISM). Some stars also present transient variable events or absorptions extended towards red wavelengths (red wings). These are the first detections of such Ca ii features in 7 out of the 15 observed stars. Although an ISM origin cannot categorically be excluded, the results suggest that the stable and variable absorptions arise from relatively hot gas located in the CS close-in environment of the stars. This hot gas is detected in at least ∼ 80%, of edge-on cold-gas-bearing debris discs, while in only ∼ 10% of the discs seen close to face-on. We interpret this result as a geometrical effect, and suggest that the non-detection of hot gas absorptions in some face-on systems is due to the disc inclination and likely not to the absence of the hot-gas component. This gas is likely released in physical processes related in some way to the evaporation of exocomets, evaporation of dust grains, or grain-grain collisions close to the central star.

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Fe I in the β Pictoris circumstellar gas disk

Kiefer

Vidal‐Madjar

Étangs

et al. 2019

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The young planetary system β Pictoris is surrounded by a debris disk of dust and gas. The gas source of this disk could be exocomets (or “falling and evaporating bodies”, FEBs), which produce refractory elements (Mg, Ca, Fe) through sublimation of dust grains at several tens of stellar radii. Nearly 1700 high resolution spectra of β Pictoris were obtained between 2003 and 2017 using the HARPS spectrograph. In Paper I, we showed that a high signal to noise ratio allows the detection of many weak Fe I lines in more than ten excited levels, and we derived the physical characteristics of the iron gas in the disk. The measured temperature of the gas (~1300 K) suggests that it is produced by evaporation of grains at about 0.3 au (38 R⋆) from the star. Here, we describe the yearly variations of the column densities of all Fe I components (from both ground and excited levels). The drop in the Fe I ground level column density after 2011 coincides with a drop in Fe I excited levels column density, as well as in the Ca II doublet and a ground level Ca I line at the same epoch. All drops are compatible with photoionisation-recombination equilibrium and β Pic like relative abundances, in a medium at 1300 K and at 0.3 au from β Pictoris. Interestingly, this warm medium does not correlate with the numerous exocomets in the circumstellar environnement of this young star.

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Fe I in the β Pictoris circumstellar gas disk

Cited by 9 publications

References 50 publications

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

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

The co-existence of hot and cold gas in debris discs

Fe I in the β Pictoris circumstellar gas disk

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