Context . The inner few AU of disks around young stars, where terrestrial planets are thought to form, are best probed in the infrared. The James Webb Space Telescope is now starting to characterize ...the chemistry of these regions in unprecedented detail, building on earlier results of the Spitzer Space Telescope that the planet-forming zone of disks contain a rich chemistry. One peculiar subset of sources characterized by Spitzer are the so-called CO 2 -only sources, in which only a strong 15 μm CO 2 feature was detected in the spectrum. Aims . One scenario that could explain the weak or even non-detections of molecular emission from H 2 O is the presence of a small, inner cavity in the disk. If this cavity were to extend past the H 2 O snowline, but not past the CO 2 snowline, this could strongly suppress the H 2 O line flux with respect to that of CO 2 . For this work, we aimed to test the validity of this statement. Methods . Using the thermo-chemical code Dust And LInes (DALI), we created a grid of T Tauri disk models with an inner cavity, meaning we fully depleted the inner region of the disk in gas and dust starting from the dust sublimation radius and ranging until a certain cavity radius. Cavity radii varying in size from 0.1 to 10 AU were explored for this work. We extended this analysis to test the influence of cooling through H 2 O ro-vibrational lines and the luminosity of the central star on the CO 2 /H 2 O flux ratio. Results . We present the evolution of the CO 2 and H 2 O spectra of a disk with inner cavity size. The line fluxes show an initial increase as a result of an increasing emitting area, followed by a sharp decrease. As such, when a large-enough cavity is introduced, a spectrum that was initially dominated by H 2 O lines can become CO 2 -dominated instead. However, the cavity size needed for this is around 4–5 AU, exceeding the nominal position of the CO 2 snowline in a full disk, which is located at 2 AU in our fiducial, L * = 1.4 L ⊙ model. The cause of this is most likely the alteration of the thermal structure by the cavity, which pushes the snowlines outward. In contrast, our models show that global temperature fluctuations, for example due to changes in stellar luminosity, impact the fluxes of H 2 O and CO 2 roughly equally, thus not impacting their ratio much. Alternative explanations for bright CO 2 emission are also briefly discussed. Conclusions . Our modeling work shows that it is possible for the presence of a small inner cavity to explain strong CO 2 emission in a spectrum. However, the cavity needed to do so is larger than what was initially expected. As such, this scenario will be easier to test with sufficiently high angular resolution (millimeter) observations.
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Context. The inner few AU of disks around young stars, where terrestrial planets are thought to form, are best probed in the infrared. The James Webb Space Telescope is now starting to characterize ...the chemistry of these regions in unprecedented detail, building on earlier results of the Spitzer Space Telescope that the planet-forming zone of disks contain a rich chemistry. One peculiar subset of sources characterized by Spitzer are the so-called CO2-only sources, in which only a strong 15 μm CO2 feature was detected in the spectrum. Aims. One scenario that could explain the weak or even non-detections of molecular emission from H2O is the presence of a small, inner cavity in the disk. If this cavity were to extend past the H2O snowline, but not past the CO2 snowline, this could strongly suppress the H2O line flux with respect to that of CO2. For this work, we aimed to test the validity of this statement. Methods. Using the thermo-chemical code Dust And LInes (DALI), we created a grid of T Tauri disk models with an inner cavity, meaning we fully depleted the inner region of the disk in gas and dust starting from the dust sublimation radius and ranging until a certain cavity radius. Cavity radii varying in size from 0.1 to 10 AU were explored for this work. We extended this analysis to test the influence of cooling through H2O ro-vibrational lines and the luminosity of the central star on the CO2 /H2O flux ratio. Results. We present the evolution of the CO2 and H2O spectra of a disk with inner cavity size. The line fluxes show an initial increase as a result of an increasing emitting area, followed by a sharp decrease. As such, when a large-enough cavity is introduced, a spectrum that was initially dominated by H2O lines can become CO2-dominated instead. However, the cavity size needed for this is around 4–5 AU, exceeding the nominal position of the CO2 snowline in a full disk, which is located at 2 AU in our fiducial, L* = 1.4 L⊙ model. The cause of this is most likely the alteration of the thermal structure by the cavity, which pushes the snowlines outward. In contrast, our models show that global temperature fluctuations, for example due to changes in stellar luminosity, impact the fluxes of H2O and CO2 roughly equally, thus not impacting their ratio much. Alternative explanations for bright CO2 emission are also briefly discussed. Conclusions. Our modeling work shows that it is possible for the presence of a small inner cavity to explain strong CO2 emission in a spectrum. However, the cavity needed to do so is larger than what was initially expected. As such, this scenario will be easier to test with sufficiently high angular resolution (millimeter) observations.
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The Medium Resolution Spectrometer (MRS) of the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) gives insights into the chemical richness and complexity of the inner regions ...of planet-forming disks. Several disks that are compact in the millimetre dust emission have been found by Spitzer to be particularly bright in H_2O which is thought to be caused by the inward drift of icy pebbles. Here, we analyse the H_2O -rich spectrum of the compact disk DR Tau using high-quality JWST-MIRI observations. We infer the H_2O column densities (in cm$^ $) using methods presented in previous works, as well as introducing a new method to fully characterise the pure rotational spectrum. We aim to further characterise the abundances of H_2O in the inner regions of this disk and its abundance relative to CO . We also search for emission of other molecular species, such as CH_4 NH_3 CS H_2 SO_2 and larger hydrocarbons; commonly detected species, such as CO CO_2 HCN and C_2H_2 have been investigated in our previous paper. We first use 0D local thermodynamic equilibrium (LTE) slab models to investigate the excitation properties observed in different wavelength regions across the entire spectrum, probing both the ro-vibrational and rotational transitions. To further analyse the pure rotational spectrum (geq 10 $ mu $m), we use the spectrum of a large, structured disk (CI Tau) as a template to search for differences with our compact disk. Finally, we fit multiple components to characterise the radial (and vertical) temperature gradient(s) present in the spectrum of DR Tau. The 0D slab models indicate a radial gradient in the disk, as the excitation temperature (emitting radius) decreases (increases) with increasing wavelength, which is confirmed by the analysis involving the large disk template. To explain the derived emitting radii, we need a larger inclination for the inner disk ($i agreeing with our previous analysis on CO . From our multi-component fit, we find that at least three temperature components ($T_1 K, $T_2 K, and $T_3 K) are required to reproduce the observed rotational spectrum of H_2O arising from the inner $R_ em au. By comparing line ratios, we derived an upper limit on the column densities (in $) for the first two components of $ (N) within sim 1.2 au. We note that the models with a pure temperature gradient provide as robust results as the more complex models, which include spatial line shielding. No robust detection of the isotopologue H_2 ^ O can be made and upper limits are provided for other molecular species. Our analysis confirms the presence of a pure radial temperature gradient present in the inner disk of DR Tau, which can be described by at least three components. This gradient scales roughly as $ R_ em $ in the emitting layers, in the inner 2 au. As the observed H_2O is mainly optically thick, a lower limit on the abundance ratio of H_2O CO sim 0.17 is derived, suggesting a potential depletion of H_2O . Similarly to previous work, we detect a cold H_2O component ($T K) originating from near the snowline, now with a multi-component analysis. Yet, we cannot conclude whether an enhancement of the H_2O reservoir is observed following radial drift. A consistent analysis of a larger sample is necessary to study the importance of drift in enhancing the H_2O abundances.
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The majority of young stars form in multiple systems, the properties of which can significantly impact the evolution of any circumstellar disks. We investigate the physical and chemical properties of ...the equal-mass, small-separation (sim 66 milliarcsecond, sim 9 au) binary system DF Tau. Previous spatially resolved observations indicate that only DF Tau A has a circumstellar disk, while DF Tau B does not, as concluded by a lack of accretion signatures and a near-infrared excess. We present JWST-MIRI MRS observations of DF Tau. The MIRI spectrum shows emission from a forest of H$_2$O lines and emission from CO, C$_2$H$_2$, HCN, CO$_2$, and OH. Local thermodynamic equilibrium slab models were used to determine the properties of the gas. The binary system is not spatially or spectrally resolved in the MIRI observations; therefore, we analyzed high spatial and spectral resolution observations from ALMA, VLTI-GRAVITY, and IRTF-iSHELL to aid in the interpretation of the molecular emission observed with JWST. The 1.3 mm ALMA observations show two equal-brightness sources of compact ($R au) continuum emission that are detected at high significance, with separations consistent with astrometry from VLTI-GRAVITY and movement consistent with the known orbital parameters of the system. We interpret this as a robust detection of the disk around DF Tau B, which we suggest may host a small (sim 1 au) cavity; such a cavity would reconcile all of the observations of this source. In contrast, the disk around DF Tau A is expected to be a full disk, and spatially and spectrally resolved dust and gas emission traced by ground-based infrared observations point to hot, close-in ($ au) material around this star. High-temperature emission (sim 500-1000 K) from H$_2$O, HCN, and potentially C$_2$H$_2$ in the MIRI data likely originates in the disk around DF Tau A, while a cold H$_2$O component (lesssim 200 K) with an extended emitting area is consistent with an origin from both disks. Given the unique characteristics of this binary pair, complementary observations are critical for constraining the properties of these disks. Despite the very compact outer disk properties, the inner disk composition and the conditions of the DF Tau disks are remarkably similar to those of isolated systems, suggesting that neither the outer disk evolution nor the close binary nature are driving factors in setting the inner disk chemistry in this system. However, constraining the geometry of the disk around DF Tau B, via higher angular resolution ALMA observations for instance, would provide additional insight into the properties of the mid-infrared gas emission observed with MIRI. JWST observations of spatially resolved binaries, at a range of separations, will be important for understanding the impact of binarity on inner disk chemistry more generally.
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5.
MINDS Gasman, Danny; van Dishoeck, Ewine F.; Grant, Sierra L. ...
Astronomy and astrophysics (Berlin),
11/2023, Volume:
679
Journal Article, Web Resource
Peer reviewed
Open access
Context.
The Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) on board the
James Webb
Space Telescope (JWST) allows us to probe the inner regions of protoplanetary disks, where the ...elevated temperatures result in an active chemistry and where the gas composition may dictate the composition of planets forming in this region. The disk around the classical T Tauri star Sz 98, which has an unusually large dust disk in the millimetre with a compact core, was observed with the MRS, and we examine its spectrum here.
Aims.
We aim to explain the observations and put the disk of Sz 98 in context with other disks, with a focus on the H
2
O emission through both its ro-vibrational and pure rotational emission. Furthermore, we compare our chemical findings with those obtained for the outer disk from Atacama Large Millimeter/submillimeter Array (ALMA) observations.
Methods.
In order to model the molecular features in the spectrum, the continuum was subtracted and local thermodynamic equilibrium (LTE) slab models were fitted. The spectrum was divided into different wavelength regions corresponding to H
2
O lines of different excitation conditions, and the slab model fits were performed individually per region.
Results.
We confidently detect CO, H
2
O, OH, CO
2
, and HCN in the emitting layers. Despite the plethora of H
2
O lines, the isotopo-logue H
2
18
O is not detected. Additionally, no other organics, including C
2
H
2
, are detected. This indicates that the C/O ratio could be substantially below unity, in contrast with the outer disk. The H
2
O emission traces a large radial disk surface region, as evidenced by the gradually changing excitation temperatures and emitting radii. Additionally, the OH and CO
2
emission is relatively weak. It is likely that H
2
O is not significantly photodissociated, either due to self-shielding against the stellar irradiation, or UV shielding from small dust particles. While H
2
O is prominent and OH is relatively weak, the line fluxes in the inner disk of Sz 98 are not outliers compared to other disks.
Conclusions.
The relative emitting strength of the different identified molecular features points towards UV shielding of H
2
O in the inner disk of Sz 98, with a thin layer of OH on top. The majority of the organic molecules are either hidden below the dust continuum, or not present. In general, the inferred composition points to a sub-solar C/O ratio (<0.5) in the inner disk, in contrast with the larger than unity C/O ratio in the gas in the outer disk found with ALMA.
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The understanding of planet formation has changed recently, embracing the new idea of pebble accretion. This means that the influx of pebbles from the outer regions of planet-forming disks to their ...inner zones could determine the composition of planets and their atmospheres. The solid and molecular components delivered to the planet-forming region can be best characterized by mid-infrared spectroscopy. With Spitzer low-resolution (
R
= 100, 600) spectroscopy, this approach was limited to the detection of abundant molecules, such as H
2
O, C
2
H
2
, HCN and CO
2
. This contribution will present the first results of the MINDS (MIRI mid-INfrared Disk Survey, PI:Th Henning) project. Due do the sensitivity and spectral resolution provided by the James Webb Space Telescope (JWST), we now have a unique tool to obtain the full inventory of chemistry in the inner disks of solar-type stars and brown dwarfs, including also less-abundant hydrocarbons and isotopologues. The Integral Field Unit (IFU) capabilities will enable at the same time spatial studies of the continuum and line emission in extended sources such as debris disks, the flying saucer and also the search for mid-IR signatures of forming planets in systems such as PDS 70. These JWST observations are complementary to ALMA and NOEMA observations of outer-disk chemistry; together these datasets will provide an integral view of the processes occurring during the planet-formation phase.
The Mid-InfraRed Instrument/Medium-Resolution Spectrometer (MIRI/MRS) on board the James Webb Space Telescope reveals the rich and diverse chemistry in the planet forming regions around Sun-like and low-mass stars.
MINDS: The JWST MIRI Mid-INfrared Disk Survey Henning, Thomas; Kamp, Inga; Samland, Matthias ...
Publications of the Astronomical Society of the Pacific,
05/2024, Volume:
136, Issue:
5
Journal Article
Peer reviewed
Open access
Abstract The study of protoplanetary disks has become increasingly important with the Kepler satellite finding that exoplanets are ubiquitous around stars in our galaxy and the discovery of enormous ...diversity in planetary system architectures and planet properties. High-resolution near-IR and ALMA images show strong evidence for ongoing planet formation in young disks. The JWST MIRI mid-INfrared Disk Survey (MINDS) aims to (1) investigate the chemical inventory in the terrestrial planet-forming zone across stellar spectral type, (2) follow the gas evolution into the disk dispersal stage, and (3) study the structure of protoplanetary and debris disks in the thermal mid-IR. The MINDS survey will thus build a bridge between the chemical inventory of disks and the properties of exoplanets. The survey comprises 52 targets (Herbig Ae stars, T Tauri stars, very low-mass stars and young debris disks). We primarily obtain MIRI/MRS spectra with high signal-to-noise ratio (∼100–500) covering the complete wavelength range from 4.9 to 27.9 μ m. For a handful of selected targets we also obtain NIRSpec IFU high resolution spectroscopy (2.87–5.27 μ m). We will search for signposts of planet formation in thermal emission of micron-sized dust—information complementary to near-IR scattered light emission from small dust grains and emission from large dust in the submillimeter wavelength domain. We will also study the spatial structure of disks in three key systems that have shown signposts for planet formation, TW Hya and HD 169142 using the MIRI coronagraph at 15.5 μ m and 10.65 μ m respectively and PDS 70 using NIRCam imaging in the 1.87 μ m narrow and the 4.8 μ m medium band filter. We provide here an overview of the MINDS survey and showcase the power of the new JWST mid-IR molecular spectroscopy with the TW Hya disk spectrum where we report the detection of the molecular ion CH 3 + and the robust confirmation of HCO + earlier detected with Spitzer.
We present JWST-MIRI Medium Resolution Spectrometer (MRS) spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey Guaranteed Time ...Observations program. Emission from 12CO2, 13CO2, H2O, HCN, C2H2, and OH is identified with 13CO2 being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few astronomical units of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The Q branches of these molecules, including those of hot bands, are particularly sensitive to temperature and column density. We find that the 12CO2 emission in the GW Lup disk is coming from optically thick emission at a temperature of ∼400 K. 13CO2 is optically thinner and based on a lower temperature of ∼325 K, and thus may be tracing deeper into the disk and/or a larger emitting radius than 12CO2. The derived NCO2/NH2O ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on Spitzer-InfraRed-Spectrograph data. This high column density ratio may be due to an inner cavity with a radius in between the H2O and CO2 snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.
Abstract
We present JWST-MIRI Medium Resolution Spectrometer (MRS) spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey Guaranteed Time ...Observations program. Emission from
12
CO
2
,
13
CO
2
, H
2
O, HCN, C
2
H
2
, and OH is identified with
13
CO
2
being detected for the first time in a protoplanetary disk. We characterize the chemical and physical conditions in the inner few astronomical units of the GW Lup disk using these molecules as probes. The spectral resolution of JWST-MIRI MRS paired with high signal-to-noise data is essential to identify these species and determine their column densities and temperatures. The
Q
branches of these molecules, including those of hot bands, are particularly sensitive to temperature and column density. We find that the
12
CO
2
emission in the GW Lup disk is coming from optically thick emission at a temperature of ∼400 K.
13
CO
2
is optically thinner and based on a lower temperature of ∼325 K, and thus may be tracing deeper into the disk and/or a larger emitting radius than
12
CO
2
. The derived
N
CO
2
/
N
H
2
O
ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on Spitzer-InfraRed-Spectrograph data. This high column density ratio may be due to an inner cavity with a radius in between the H
2
O and CO
2
snowlines and/or an overall lower disk temperature. This paper demonstrates the unique ability of JWST to probe inner disk structures and chemistry through weak, previously unseen molecular features.
We studied the properties of the young stellar populations in the NGC 299 cluster in the Small Magellanic Cloud using observations obtained with the Hubble Space Telescope in the \(V, I\), and ...\(H\alpha\) bands. We identified 250 stars with H\(\alpha\) excess exceeding 5 \(\sigma\) and an equivalent width of the H\(\alpha\) emission line of at least 20 Å, indicating that these stars are still undergoing accretion and therefore represent bona fide pre-main-sequence (PMS) objects. For 240 of these stars, we derived the mass, age, and mass accretion rate by comparing the observed photometry with theoretical models. We find evidence for the existence of two populations of PMS stars, with median ages of 25 and 50 Myr respectively. The average mass accretion rate for these PMS stars is \(\sim 5 \times 10^{-9}\) M\(_\odot\) yr\(^{-1}\), which is comparable to the values found in other low-metallicity, low-density clusters in the Magellanic Clouds, but is about a factor of three lower than those measured for stars of similar mass and age in denser Magellanic Cloud stellar regions. Our findings support the hypothesis that both the metallicity and density of the forming environment can affect the mass accretion rate and thus the star formation process in a region. A study of the spatial distribution of both massive stars and (low-mass) PMS objects reveals that the former are clustered near the nominal centre of NGC 299, whereas the PMS stars are rather uniformly distributed over the field. To explore whether the stars formed in an initially more diffuse or compact structure, we studied the cluster's stellar density profile. We find a core radius \(r_c\simeq 0.6\) pc and a tidal radius \(r_t\simeq 5.5\) pc, with an implied concentration parameter \(c \simeq 1\), suggesting that the cluster could be dispersing into the field.