The Appearance and Disappearance of Exocomet Gas Absorption

Welsh, Barry Y.; Montgomery, Sharon L.

doi:10.1155/2015/980323

Cited by 21 publications

(19 citation statements)

References 74 publications

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“…Details of the continuum fit process and the measurement of the absorption EWs can be found elsewhere (Welsh & Montgomery 2015). In Table 1 we list the date and (UT) time of each spectral observation together with the (EW FEB ) of any HV absorption component in the Ca II K-line profile presumable caused by an FEB event and the velocity range over which the EW of this absorption feature was measured.…”

Section: Discussionmentioning

confidence: 99%

“…During the following 30 years over a dozen more A-type stars with surrounding debris disks of ages <100 Myr have been shown to exhibit similar circumstellar Ca II K-line absorption variability on timescales of hours to a few days (Montgomery & Welsh 2012;Kiefer et al 2014;Welsh & Montgomery 2015). The study of these star-grazing exocomets allows us the opportunity to investigate the elemental composition of the potential building blocks of planet formation.…”

Section: Introductionmentioning

confidence: 99%

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Exocomet Circumstellar Fe I Absorption in the Beta Pictoris Gas Disk

Welsh¹,

Montgomery

2016

PASP

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We present an archival study of 27 circumstellar Fe I (λ3860 Å) and Ca II (λ3933 Å) absorption spectra of the β Pictoris system recorded over the 2003-2014 timeframe. We have detected several transient absorption events at velocities red-shifted by >+20 km s −1 from the main central absorption line profiles of both Fe I and Ca II. Such events can be attributed to the presence of kilometer-sized infalling evaporating bodies (i.e., exocomets) on their grazing approach to the central star. The majority of the transient absorption events detected in the Fe I profiles occur at velocities in the +35 to +50 km s −1 range. This is consistent with that found for Ca II gas that has been sublimated from the "D" family of β Pictoris exocomets recently found by Kiefer et al. These spectra also reveal that the strength of the main component of the Fe I absorption line at V helio ∼+21 km s −1 has weakened by ∼30% since 2011. Since neutrals, when ionized, are the main source of the ion-braking mechanism of Brandeker for circumstellar gas in the β Pictoris system, then this may have some measurable effect on the size and/or location of the main circumstellar gas disk. Finally we note that we have failed to detect any circumstellar Fe I absorption in our previously reported spectra of similar gas disks surrounding 28 young A-type stars. Thus, it would appear that the β Pictoris is anomalous with regards to circumstellar Fe I absorption.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Exocomet Circumstellar Fe I Absorption in the Beta Pictoris Gas Disk

Welsh¹,

Montgomery

2016

PASP

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“…These features have been interpreted to be the result of the gas released by the evaporation of exocomets grazing or falling onto the star (Ferlet et al 1987;Kiefer et al 2014b, and references therein) that are driven into the vicinity of the star by the perturbing action of a larger body, that is, by a planet (Beust et al 1991). Variable absorptions like this have also been observed toward several A-type stars (e.g., Redfield et al 2007;Roberge & Weinberger 2008;Welsh & Montgomery 2015).…”

Section: Introductionmentioning

confidence: 91%

Exocomet signatures around the A-shell starφLeonis?

Eiroa

Rebollido

Montesinos³

et al. 2016

A&A

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We present an intensive monitoring of high-resolution spectra of the Ca ii K line in the A7IV shell star φ Leo at very short (minutes, hours), short (night to night), and medium (weeks, months) timescales. The spectra show remarkable variable absorptions on timescales of hours, days, and months. The characteristics of these sporadic events are very similar to most that are observed toward the debris disk host star β Pic, which are commonly interpreted as signs of the evaporation of solid, comet-like bodies grazing or falling onto the star. Therefore, our results suggest the presence of solid bodies around φ Leo. To our knowledge, with the exception of β Pic, our monitoring has the best time resolution at the mentioned timescales for a star with events attributed to exocomets. Assuming the cometary scenario and considering the timescales of our monitoring, our results indicate that φ Leo presents the richest environment with comet-like events known to date, second only to β Pic.

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“…We found that the line profiles obtained using this process were identical to the profile obtained using a simple coaddition process, showing that the pollution by FEB signatures is negligible. A few FEBs were observed in Fe I (Welsh & Montgomery 2015; there is, however, a very low number of detections, and all of them are found to be at high radial velocity, away from the stable gas absorption signature, which remains at the stellar radial velocity. The pollution of the Fe I profile by transiting exocomets is therefore negligible.…”

Section: Observationsmentioning

confidence: 99%

Fe I in the β Pictoris circumstellar gas disk

Vidal‐Madjar

Kiefer

Étangs

et al. 2017

A&A

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The young planetary system β Pictoris is surrounded by a circumstellar disk of dust and gas. Because both dust and gas have a lifetime shorter than the system age, they need to be replenished continuously. The gas composition is partly known, but its location and its origin are still a puzzle. The gas source could be the exocomets (or so-called falling and evaporating bodies, FEBs), which are observed as transient features in absorption lines of refractory elements (Mg, Ca, and Fe) when they transit in front of the star at several tens of stellar radii. Nearly 1700 high-resolution spectra of β Pictoris have been obtained from 2003 to 2015 using the HARPS spectrograph. In these spectra, the circumstellar disk is always detected as a stable component among the numerous variable absorption signatures of transiting exocomets. Summing all the 1700 spectra allowed us to reach a signal-to-noise ratio higher than 1000, which is an unprecedentedly high number for a β Pictoris spectrum. It revealed many weak Fe I absorption lines of the circumstellar gas in more than ten excited states. These weak lines bring new information on the physical properties of the neutral iron gas in the circumstellar disk. The population of the first excited levels follows a Boltzmann distribution with a slope consistent with a gas temperature of about 1300 K; this temperature corresponds to a distance to the star of ~38 RStar and implies a turbulence of ξ ~ 0.8 km s-1.

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The Appearance and Disappearance of Exocomet Gas Absorption

Cited by 21 publications

References 74 publications

Exocomet Circumstellar Fe I Absorption in the Beta Pictoris Gas Disk

Exocomet Circumstellar Fe I Absorption in the Beta Pictoris Gas Disk

Exocomet signatures around the A-shell starφLeonis?

Fe I in the β Pictoris circumstellar gas disk

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