Detection of Nitrogen gas in the $beta$ Pictoris circumstellar disk. (arXiv:1811.04927v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wilson_P/0/1/0/all/0/1">P. A. Wilson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kerr_R/0/1/0/all/0/1">R. Kerr</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Etangs_A/0/1/0/all/0/1">A. Lecavelier des Etangs</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bourrier_V/0/1/0/all/0/1">V. Bourrier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vidal_Madjar_A/0/1/0/all/0/1">A. Vidal-Madjar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kiefer_F/0/1/0/all/0/1">F. Kiefer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Snellen_I/0/1/0/all/0/1">I. A. G. Snellen</a>
The debris disk surrounding $beta$ Pictoris has a gas composition rich in
carbon and oxygen, relative to solar abundances. Two possible scenarios have
been proposed to explain this enrichment. The preferential production scenario
suggests that the gas produced may be naturally rich in C and O, while the
alternative preferential depletion scenario states that the enrichment has
evolved to the current state from a gas with solar-like abundances. In the
latter case, the radiation pressure from the star expels the gas outwards,
leaving behind species less sensitive to stellar radiation such as C and O.
Nitrogen is also not sensitive to radiation pressure due to its low oscillator
strength, which would make it also overabundant under the preferential
depletion scenario. As such, the abundance of N in the disk may provide clues
to why C and O are overabundant. We aim to measure the N column density in the
direction of $beta$ Pic, and use this information to disentangle these
different scenarios explaining the C and O overabundance. Using far-UV
spectroscopic data collected by the HST’s Cosmic Origins Spectrograph (COS)
instrument, we analyse the spectrum and characterise the NI triplet by
modelling the absorption lines. We measure the N column density in the
direction of $beta$ Pic for the first time, and find it to be
$log(N_{mathrm{NI}}/1,mathrm{cm}^2) = 14.9pm0.7$. The N gas is found to be
consistent with solar abundances and Halley dust. The solar N abundance
supports the preferential production hypothesis, in which the composition of
gas in $beta$,Pic is the result of photodesorption from icy grains rich in C
and O or collisional vaporisation of C and O rich dust in the disk. It does not
support the hypothesis that C and O are overabundant due to the insensitivity
of C and O to radiation pressure thereby leaving them to accumulate in the
disk.
The debris disk surrounding $beta$ Pictoris has a gas composition rich in
carbon and oxygen, relative to solar abundances. Two possible scenarios have
been proposed to explain this enrichment. The preferential production scenario
suggests that the gas produced may be naturally rich in C and O, while the
alternative preferential depletion scenario states that the enrichment has
evolved to the current state from a gas with solar-like abundances. In the
latter case, the radiation pressure from the star expels the gas outwards,
leaving behind species less sensitive to stellar radiation such as C and O.
Nitrogen is also not sensitive to radiation pressure due to its low oscillator
strength, which would make it also overabundant under the preferential
depletion scenario. As such, the abundance of N in the disk may provide clues
to why C and O are overabundant. We aim to measure the N column density in the
direction of $beta$ Pic, and use this information to disentangle these
different scenarios explaining the C and O overabundance. Using far-UV
spectroscopic data collected by the HST’s Cosmic Origins Spectrograph (COS)
instrument, we analyse the spectrum and characterise the NI triplet by
modelling the absorption lines. We measure the N column density in the
direction of $beta$ Pic for the first time, and find it to be
$log(N_{mathrm{NI}}/1,mathrm{cm}^2) = 14.9pm0.7$. The N gas is found to be
consistent with solar abundances and Halley dust. The solar N abundance
supports the preferential production hypothesis, in which the composition of
gas in $beta$,Pic is the result of photodesorption from icy grains rich in C
and O or collisional vaporisation of C and O rich dust in the disk. It does not
support the hypothesis that C and O are overabundant due to the insensitivity
of C and O to radiation pressure thereby leaving them to accumulate in the
disk.
http://arxiv.org/icons/sfx.gif
