ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) II: Vertical stratification of CO, CS, CN, H2CO, and CH3OH in a Class I disk. (arXiv:2008.12648v1 [astro-ph.SR])

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT) II: Vertical stratification of CO, CS, CN, H2CO, and CH3OH in a Class I disk. (arXiv:2008.12648v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Podio_L/0/1/0/all/0/1">L. Podio</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garufi_A/0/1/0/all/0/1">A. Garufi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Codella_C/0/1/0/all/0/1">C. Codella</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fedele_D/0/1/0/all/0/1">D. Fedele</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bianchi_E/0/1/0/all/0/1">E. Bianchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bacciotti_F/0/1/0/all/0/1">F. Bacciotti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ceccarelli_C/0/1/0/all/0/1">C. Ceccarelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Favre_C/0/1/0/all/0/1">C. Favre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mercimek_S/0/1/0/all/0/1">S. Mercimek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rygl_K/0/1/0/all/0/1">K. Rygl</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Testi_L/0/1/0/all/0/1">L. Testi</a>

The chemical composition of planets is inherited from the one of
protoplanetary disks at the time of their formation. Increasing observational
evidence suggests that planet formation occurs in less than $1-2$ Myr. This
motivates the need for spatially resolved spectral observations of young Class
I disks, as carried out by the ALMA-DOT campaign in Taurus. In the context of
ALMA-DOT, we observe the edge-on disk around the Class I source IRAS 04302+2247
(the butterfly star) in the 1.3 mm continuum and five molecular lines. We
report the first tentative detection of methanol (CH$_3$OH) in a Class I disk
and resolve for the first time the vertical structure of a disk with multiple
molecular tracers. The bulk of the emission in the CO $2-1$, CS $5-4$, and
o-H$_2$CO $3_{1,2}-2_{1,1}$ lines originates from the warm molecular layer,
with the line intensity peaking at increasing disk heights, $z$, for increasing
radial distances, $r$. Molecular emission is vertically stratified, with CO
observed at larger disk heights (aperture $z/r sim 0.41 – 0.45$) compared to
both CS and H$_2$CO, which are nearly co-spatial ($z/r sim 0.21-0.28$). In the
outer midplane, the line emission decreases due to molecular freeze-out onto
dust grains (freeze-out layer) by a factor of $> 100$ (CO) and 15 (CS). H$_2$CO
decreases by a factor of only about 2, possibly due to H$_2$CO formation on icy
grains, followed by non-thermal release into gas-phase. The inferred
[CH$_3$OH]/[H$_2$CO] abundance ratio is $0.5-0.6$, which is $1-2$ orders of
magnitude lower than for Class 0 hot-corinos, a factor $sim 2.5$ lower than
the only other value inferred for a protoplanetary disk (in TW Hya, $1.3-1.7$),
and at the lower edge but still consistent with the values in comets. This may
indicate that some chemical reprocessing occurs in disks before the formation
of planets and comets.

The chemical composition of planets is inherited from the one of
protoplanetary disks at the time of their formation. Increasing observational
evidence suggests that planet formation occurs in less than $1-2$ Myr. This
motivates the need for spatially resolved spectral observations of young Class
I disks, as carried out by the ALMA-DOT campaign in Taurus. In the context of
ALMA-DOT, we observe the edge-on disk around the Class I source IRAS 04302+2247
(the butterfly star) in the 1.3 mm continuum and five molecular lines. We
report the first tentative detection of methanol (CH$_3$OH) in a Class I disk
and resolve for the first time the vertical structure of a disk with multiple
molecular tracers. The bulk of the emission in the CO $2-1$, CS $5-4$, and
o-H$_2$CO $3_{1,2}-2_{1,1}$ lines originates from the warm molecular layer,
with the line intensity peaking at increasing disk heights, $z$, for increasing
radial distances, $r$. Molecular emission is vertically stratified, with CO
observed at larger disk heights (aperture $z/r sim 0.41 – 0.45$) compared to
both CS and H$_2$CO, which are nearly co-spatial ($z/r sim 0.21-0.28$). In the
outer midplane, the line emission decreases due to molecular freeze-out onto
dust grains (freeze-out layer) by a factor of $> 100$ (CO) and 15 (CS). H$_2$CO
decreases by a factor of only about 2, possibly due to H$_2$CO formation on icy
grains, followed by non-thermal release into gas-phase. The inferred
[CH$_3$OH]/[H$_2$CO] abundance ratio is $0.5-0.6$, which is $1-2$ orders of
magnitude lower than for Class 0 hot-corinos, a factor $sim 2.5$ lower than
the only other value inferred for a protoplanetary disk (in TW Hya, $1.3-1.7$),
and at the lower edge but still consistent with the values in comets. This may
indicate that some chemical reprocessing occurs in disks before the formation
of planets and comets.

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