11 research outputs found
Infrared Spectroscopy of U Equulei's Warm Circumstellar Gas
Medium and high resolution spectroscopy of U Equulei from 1 to 4 microns
during 1997-2003 has revealed information about its unusual circumstellar
envelope, observed previously at optical and radio wavelengths. Strong
absorption bands of H2O and of CO dominate the 1-4um spectrum. The gas has a
mean temperature of 600 K and 12C/13C =< 10. The CO 2-0 line profiles and
velocities imply no net ejection or infall and indicate either rapid radial gas
motions being seen along a narrow continuum beam, or absorption by orbiting gas
that is nearly coincident with a highly extended continuum source. The gas
could be located in a disk-like structure. The observed high column densities
of warm CO and H2 normally would be associated with sufficient dust to
completely obscure the star at optical wavelengths. The observations thus
indicate either a highly abnormal gas-to-dust ratio, consistent with the
earlier optical observation of abundant refractory metal oxides in the
circumstellar gas, or peculiar geometry and/or illumination.Comment: 21 pages incl. 8 postscript figures and 1 table; typos correcte
JWST Observations of Young protoStars (JOYS+): Detection of icy complex organic molecules and ions. I. CH, SO, HCOO, OCN, HCO, HCOOH, CHCHOH, CHCHO, CHOCHO, CHCOOH
Complex organic molecules (COMs) detected in the gas phase are thought to be
mostly formed on icy grains, but no unambiguous detection of icy COMs larger
than CH3OH has been reported so far. Exploring this matter in more detail has
become possible with the JWST the critical 5-10 m range. In the JOYS+
program, more than 30 protostars are being observed with the MIRI/MRS. This
study explores the COMs ice signatures in the low and high-mass protostar, IRAS
2A and IRAS 23385, respectively. We fit continuum and silicate subtracted
observational data with IR laboratory ice spectra. We use the ENIIGMA fitting
tool to find the best fit between the lab data and the observations and to
performs statistical analysis of the solutions. We report the best fits for the
spectral ranges between 6.8 and 8.6 m in IRAS 2A and IRAS 23385,
originating from simple molecules, COMs, and negative ions. The strongest
feature in this range (7.7 m) is dominated by CH4 and has contributions of
SO2 and OCN-. Our results indicate that the 7.2 and 7.4 m bands are mostly
dominated by HCOO-. We find statistically robust detections of COMs based on
multiple bands, most notably CH3CHO, CH3CH2OH, and CH3OCHO. The likely
detection of CH3COOH is also reported. The ice column density ratios between
CH3CH2OH and CH3CHO of IRAS 2A and IRAS 23385, suggests that these COMs are
formed on icy grains. Finally, the derived ice abundances for IRAS 2A correlate
well with those in comet 67P/GC within a factor of 5. Based on the MIRI/MRS
data, we conclude that COMs are present in interstellar ices, thus providing
additional proof for a solid-state origin of these species in star-forming
regions. The good correlation between the ice abundances in comet 67P and IRAS
2A is in line with the idea that cometary COMs can be inherited from the early
protostellar phases.Comment: Accepted for publication in A&
Water in the terrestrial planet-forming zone of the PDS 70 disk
Terrestrial and sub-Neptune planets are expected to form in the inner
(AU) regions of protoplanetary disks. Water plays a key role in their
formation, although it is yet unclear whether water molecules are formed
in-situ or transported from the outer disk. So far Spitzer Space Telescope
observations have only provided water luminosity upper limits for dust-depleted
inner disks, similar to PDS 70, the first system with direct confirmation of
protoplanet presence. Here we report JWST observations of PDS 70, a benchmark
target to search for water in a disk hosting a large (AU)
planet-carved gap separating an inner and outer disk. Our findings show water
in the inner disk of PDS 70. This implies that potential terrestrial planets
forming therein have access to a water reservoir. The column densities of water
vapour suggest in-situ formation via a reaction sequence involving O, H,
and/or OH, and survival through water self-shielding. This is also supported by
the presence of CO emission, another molecule sensitive to UV
photodissociation. Dust shielding, and replenishment of both gas and small dust
from the outer disk, may also play a role in sustaining the water reservoir.
Our observations also reveal a strong variability of the mid-infrared spectral
energy distribution, pointing to a change of inner disk geometry.Comment: To appear in Nature on 24 July 2023. 21 pages, 10 figures; includes
extended data. Part of the JWST MINDS Guaranteed Time Observations program's
science enabling products. Spectra downloadable on Zenodo at
https://zenodo.org/record/799102
Water in the terrestrial planet-forming zone of the PDS 70 disk
Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 AU) regions of protoplanetary disks1. Water plays a key role in their formation2-4, although it is yet unclear whether water molecules are formed in situ or transported from the outer disk5,6. So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks7, similar to PDS 70, the first system with direct confirmation of protoplanet presence8,9. Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large (approximately 54 AU) planet-carved gap separating an inner and outer disk10,11. Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H2 and/or OH, and survival through water self-shielding5. This is also supported by the presence of CO2 emission, another molecule sensitive to ultraviolet photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir12. Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry.status: Published onlin
Water in the terrestrial planet-forming zone of the PDS 70 disk
Terrestrial and sub-Neptune planets are expected to form in the inner (less than 10 au) regions of protoplanetary disks 1. Water plays a key role in their formation 2–4, although it is yet unclear whether water molecules are formed in situ or transported from the outer disk 5,6. So far Spitzer Space Telescope observations have only provided water luminosity upper limits for dust-depleted inner disks 7, similar to PDS 70, the first system with direct confirmation of protoplanet presence 8,9. Here we report JWST observations of PDS 70, a benchmark target to search for water in a disk hosting a large (approximately 54 au) planet-carved gap separating an inner and outer disk 10,11. Our findings show water in the inner disk of PDS 70. This implies that potential terrestrial planets forming therein have access to a water reservoir. The column densities of water vapour suggest in-situ formation via a reaction sequence involving O, H2 and/or OH, and survival through water self-shielding 5. This is also supported by the presence of CO2 emission, another molecule sensitive to ultraviolet photodissociation. Dust shielding, and replenishment of both gas and small dust from the outer disk, may also play a role in sustaining the water reservoir 12. Our observations also reveal a strong variability of the mid-infrared spectral energy distribution, pointing to a change of inner disk geometry.</p
A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star
status: publishe
MINDS. The Detection of (CO2)-C-13 with JWST-MIRI Indicates Abundant CO2 in a Protoplanetary Disk
status: publishe
A rich hydrocarbon chemistry and high C to O ratio in the inner disk around a very low-mass star
International audienceCarbon is an essential element for life but how much can be delivered to young planets is still an open question. The chemical characterization of planet-forming disks is a crucial step in our understanding of the diversity and habitability of exoplanets. Very low-mass stars (less than 0.2 M⊙) are interesting targets because they host a rich population of terrestrial planets. Here we present the James Webb Space Telescope detection of abundant hydrocarbons in the disk of a very low-mass star obtained as part of the Mid-InfraRed Instrument mid-INfrared Disk Survey (MINDS). In addition to very strong and broad emission from C2H2 and its 13C12CH2 isotopologue, C4H2, benzene and possibly CH4 are identified, but water, polycyclic aromatic hydrocarbons and silicate features are weak or absent. The lack of small silicate grains indicates that we can look deep down into this disk. These detections testify to an active warm hydrocarbon chemistry with a high C/O ratio larger than unity in the inner 0.1 astronomical units (AU) of this disk, perhaps due to destruction of carbonaceous grains. The exceptionally high C2H2/CO2 and C2H2/H2O column density ratios indicate that oxygen is locked up in icy pebbles and planetesimals outside the water iceline. This, in turn, will have important consequences for the composition of forming exoplanets