3 research outputs found
Tracing snowlines and C/O ratio in a planet-hosting disk: ALMA molecular line observations towards the HD169142 disk
The composition of a forming planet is set by the material it accretes from
its parent protoplanetary disk. Therefore, it is crucial to map the chemical
make-up of the gas in disks to understand the chemical environment of planet
formation. This paper presents molecular line observations taken with the
Atacama Large Millimeter/submillimeter Array of the planet-hosting disk around
the young star HD 169142. We detect N2H+, CH3OH, [CI], DCN, CS, C34S, 13CS,
H2CS, H2CO, HC3N and c-C3H2 in this system for the first time. Combining these
data with the recent detection of SO and previously published DCO+ data, we
estimate the location of H2O and CO snowlines and investigate radial variations
in the gas phase C/O ratio. We find that the HD 169142 disk has a relatively
low N2H+ flux compared to the disks around Herbig stars HD 163296 and MWC 480
indicating less CO freeze-out and place the CO snowline beyond the millimetre
disk at ~150 au. The detection of CH3OH from the inner disk is consistent with
the H2O snowline being located at the edge of the central dust cavity at ~20
au. The radially varying CS/SO ratio across the proposed H2O snowline location
is consistent with this interpretation. Additionally, the detection of CH3OH in
such a warm disk adds to the growing evidence supporting the inheritance of
complex ices in disks from the earlier, colder stages of star formation.
Finally, we propose that the giant HD 169142 b located at 37 au is forming
between the CO2 and H2O snowlines where the local elemental make of the gas is
expected to have C/O=1.0.Comment: Accepted A&A 13th August 202
The young embedded disk L1527 IRS: constraints on the water snowline and cosmic ray ionization rate from HCO+ observations
The water snowline in circumstellar disks is a crucial component in planet
formation, but direct observational constraints on its location remain sparse
due to the difficulty of observing water in both young embedded and mature
protoplanetary disks. Chemical imaging provides an alternative route to locate
the snowline, and HCO isotopologues have been shown to be good tracers in
protostellar envelopes and Herbig disks. Here we present
0.5 resolution (35 au radius) Atacama Large
Millimeter/submillimeter Array (ALMA) observations of HCO and
HCO toward the young (Class 0/I) disk L1527 IRS. Using a
source-specific physical model with the midplane snowline at 3.4 au and a small
chemical network, we are able to reproduce the HCO and HCO
emission, but for HCO only when the cosmic ray ionization rate is lowered
to s. Even though the observations are not sensitive to the
expected HCO abundance drop across the snowline, the reduction in HCO
above the snow surface and the global temperature structure allow us to
constrain a snowline location between 1.8 and 4.1 au. Deep observations are
required to eliminate the envelope contribution to the emission and to derive
more stringent constraints on the snowline location. Locating the snowline in
young disks directly with observations of HO isotopologues may therefore
still be an alternative option. With a direct snowline measurement, HCO
will be able to provide constraints on the ionization rate.Comment: Accepted for publication in ApJ, 15 pages, 6 figures and appendi
Deuterium-enriched water ties planet-forming disks to comets and protostars
Water is a fundamental molecule in the star and planet formation process, essential for catalysing the growth of solid material and the formation of planetesimals within disks1,2. However, the water snowline and the HDO:H2O ratio within proto-planetary disks have not been well\ua0characterized because water only sublimates at roughly 160 K (ref. 3), meaning that most water is frozen out onto dust grains and\ua0that the water snowline radii are less than 10 AU (astronomical units)4,5. The sun-like protostar V883 Ori (M* = 1.3 M⊙)6 is undergoing an accretion burst7, increasing its luminosity to roughly 200 L⊙ (ref. 8), and previous observations suggested that its water snowline is 40-120 AU in radius6,9,10. Here we report the direct detection of gas phase water (HDO and [Formula: see text]) from the disk of V883 Ori. We measure a midplane water snowline radius of approximately 80 AU, comparable to the scale of the Kuiper Belt, and detect\ua0water out to a radius of roughly 160 AU. We then measure the HDO:H2O ratio of the disk to be (2.26 \ub1 0.63) 
7 10-3. This ratio is comparable to those\ua0of\ua0protostellar envelopes and comets, and exceeds that of Earth\u27s oceans by 3.1σ. We conclude that disks directly inherit water from the star-forming cloud and this water becomes incorporated into large icy bodies, such as comets, without substantial chemical alteration