arXiv subjects

Donna Rodgers-Lee

Publications and source records attributed to Donna Rodgers-Lee.

15 recordsLinked to original sources

arXiv2025

The role of magnetic fields in shaping $\gamma$-ray emission from the Fermi bubbles

Despite their discovery fifteen years ago, the nature and origin of the Fermi bubbles remain unclear. We here investigate the effect a magnetic field can have on a subsonic breeze outflow emanating from the Galactic centre region. The presence of this magnetic field allows anisotropic diffusion of cosmic rays within the outflow, shaping the resultant cosmic ray distribution obtained out at large distances within the Galactic halo. We show that our magnetohydrodynamic Galactic breeze model, in combination with an opening angle for the injection of cosmic rays, leads to $\gamma$-ray emission from the Fermi bubble region with relatively sharp edges.

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arXiv2025

High-resolution Ultraviolet-to-nearinfrared Characterization of Exoplanet Atmospheres

The Habitable Worlds Observatory (HWO) offers a unique opportunity to revolutionize our understanding of planetary formation and evolution. The goal of this Science Case Development Document (SCDD) is to investigate the physical and chemical processes that shape the composition and atmospheric mass loss in exoplanets. We review the key observables currently known as diagnostics of mass loss via transit observations, i.e., absorption lines of escaping hydrogen (Lyman-alpha), helium, and metals (Fe, Mg, C, O). We also explore the challenges to infer planetary formation processes based on atmospheric composition characterization. HWO could enable a broad, continuous coverage from far-ultraviolet to near-infrared spectroscopy (~100--1600 nm) at high resolution (R > 60, 000), which is essential to make these measurements, disentangle their planetary origin from stellar activity, and ultimately, contextualize the escape rates by simultaneously characterizing the composition, cloud predominance, and thermal structure of exoplanet atmospheres.

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arXiv2024

MINDS: Mid-infrared atomic and molecular hydrogen lines in the inner disk around a low-mass star

This work aims to measure the mass accretion rate, the accretion luminosity, and more generally the physical conditions of the warm emitting gas in the inner disk of the very low-mass star 2MASS-J16053215-1933159. We investigate the source mid-infrared spectrum for atomic and molecular hydrogen line emission. We present the full James Webb Space Telescope (JWST) Mid-InfraRed Instrument (MIRI) Medium Resolution Spectrometer (MRS) spectrum of the protoplanetary disk around the very low-mass star 2MASS-J16053215-1933159 from the MINDS GTO program, previously shown to be abundant in hydrocarbon molecules. We analyzed the atomic and molecular hydrogen lines in this source by fitting one or multiple Gaussian profiles. We then built a rotational diagram for the H2 lines to constrain the rotational temperature and column density of the gas. Finally, we compared the observed atomic line fluxes to predictions from two standard emission models. We identify five molecular hydrogen pure rotational lines and 16 atomic hydrogen recombination lines. The spectrum indicates optically thin emission for both species. We use the molecular hydrogen lines to constrain the mass and temperature of the warm emitting gas. The HI (7-6) recombination line is used to measure the mass accretion rate and luminosity onto the central source. HI recombination lines can also be used to derive the physical properties of the gas using atomic recombination models. The JWST-MIRI MRS observations for the very low-mass star 2MASS-J16053215-1933159 reveal a large number of emission lines, many originating from atomic and molecular hydrogen because we are able to look into the disk warm molecular layer. Their analysis constrains the physical properties of the emitting gas and showcases the potential of JWST to deepen our understanding of the physical and chemical structure of protoplanetary disks

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arXiv2024

MINDS. The DR Tau disk I: combining JWST-MIRI data with high-resolution CO spectra to characterise the hot gas

The MRS mode of the JWST-MIRI instrument has been shown to be a powerful tool to characterise the molecular gas emission of the inner region of planet-forming disks. Here, we analyse the spectrum of the compact T-Tauri disk DR Tau, which is complemented by high spectral resolution (R~60000-90000) CO ro-vibrational observations. Various molecular species, including CO, CO$_2$, HCN, and C$_2$H$_2$ are detected in the JWST-MIRI spectrum, for which excitation temperatures of T~325-900 K are retrieved using LTE slab models. The high-resolution CO observations allow for a full treatment of the line profiles, which show evidence for two components of the main isotopologue, $^{12}$CO: a broad component tracing the Keplerian disk and a narrow component tracing a slow disk wind. Rotational diagrams yield excitation temperatures of T>725 K for CO, with consistently lower temperatures found for the narrow components, suggesting that the disk wind is launched from a larger distance. The inferred excitation temperatures for all molecules suggest that CO originates from the highest atmospheric layers close to the host star, followed by HCN and C$_2$H$_2$, which emit, together with $^{13}$CO, from slightly deeper layers, whereas the CO$_2$ originates from even deeper inside or further out in the disk. Additional analysis of the $^{12}$CO line wings hint at a misalignment between the inner (i~20 degrees) and outer disk (i~5 degrees). Finally, we emphasise the need for complementary high-resolution CO observations, as in combination with the JWST-MIRI observations they can be used to characterise the CO kinematics and the physical and chemical conditions of the other observed molecules with respect to CO.

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arXiv2024

MINDS: The JWST MIRI Mid-INfrared Disk Survey

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 S/N (~100-500) covering the complete wavelength range from 4.9 to 27.9 μm. For a handful of selected targets we also obtain NIRSpec IFU high resolution spectroscopy (2.87-5.27 μm). 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 μm and 10.65 μm respectively and PDS70 using NIRCam imaging in the 1.87 μm narrow and the 4.8 μm medium band filter. ...

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arXiv2024

MINDS. JWST-MIRI Reveals a Dynamic Gas-Rich Inner Disk Inside the Cavity of SY Cha

SY Cha is a T Tauri star surrounded by a protoplanetary disk with a large cavity seen in the millimeter continuum but has the spectral energy distribution (SED) of a full disk. Here we report the first results from JWST-MIRI Medium Resolution Spectrometer (MRS) observations taken as part of the MIRI mid-INfrared Disk Survey (MINDS) GTO Program. The much improved resolution and sensitivity of MIRI-MRS compared to Spitzer enables a robust analysis of the previously detected H2O, CO, HCN, and CO2 emission as well as a marginal detection of C2H2. We also report the first robust detection of mid-infrared OH and ro-vibrational CO emission in this source. The derived molecular column densities reveal the inner disk of SY Cha to be rich in both oxygen and carbon bearing molecules. This is in contrast to PDS 70, another protoplanetary disk with a large cavity observed with JWST, which displays much weaker line emission. In the SY Cha disk, the continuum, and potentially the line, flux varies substantially between the new JWST observations and archival Spitzer observations, indicative of a highly dynamic inner disk.

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arXiv2023

MINDS. Abundant water and varying C/O across the disk of Sz 98 as seen by JWST/MIRI

MIRI/MRS on board the JWST allows us to probe the inner regions of protoplanetary disks. Here we examine the disk around the classical T Tauri star Sz 98, which has an unusually large dust disk in the millimetre with a compact core. We 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. In order to model the molecular features in the spectrum, the continuum was subtracted and 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. We confidently detect CO, H$_2$O, OH, CO$_2$, and HCN in the emitting layers. The isotopologue H$^{18}_2$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. The OH and CO$_2$ emission are 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. The relative emitting strength of the different identified molecular features point 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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arXiv2023

The Chemical Inventory of the Inner Regions of Planet-forming Disks -- The JWST/MINDS Program

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 H2O, C2H2, HCN and CO2. This contribution will present first results of the MINDS (MIRI mid-IR Disk Survey, PI: Th. Henning) project. Due do the sensitivity and spectral resolution (R~1500-3500) provided by JWST we now have a unique tool to obtain the full inventory of chemistry in the inner disks of solar-types stars and brown dwarfs, including also less abundant hydrocarbons and isotopologues. The Integral Field Unit (IFU) capabilities 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 PDS70. These JWST observations are complementary to ALMA and NOEMA observations of the outer disk chemistry; together these datasets provide an integral view of the processes occurring during the planet formation phase.

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arXiv2023

MINDS. The detection of $^{13}$CO$_{2}$ with JWST-MIRI indicates abundant CO$_{2}$ in a protoplanetary disk

We present JWST-MIRI MRS spectra of the protoplanetary disk around the low-mass T Tauri star GW Lup from the MIRI mid-INfrared Disk Survey (MINDS) GTO 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 au 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 $\sim$400 K. $^{13}$CO$_{2}$ is optically thinner and based on a lower temperature of $\sim$325 K, may be tracing deeper into the disk and/or a larger emitting radius than $^{12}$CO$_{2}$. The derived $N_{\rm{CO_{2}}}$/$N_{\rm{H_{2}O}}$ ratio is orders of magnitude higher than previously derived for GW Lup and other targets based on \textit{Spitzer}-IRS 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.

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arXiv2022

Galactic breeze origin for the Fermi bubbles emission

The origin of the Fermi bubbles, which constitute two gamma-ray emitting lobes above and below the Galactic plane, remains unclear. The possibility that this Fermi bubbles gamma-ray emission originates from hadronic cosmic rays advected by a subsonic Galactic outflow, or breeze, is here explored. The simulation of a breeze solution and subsequent cosmic ray transport is carried out using the hydrodynamical code, PLUTO, in combination with a cosmic ray transport code. The Galactic outflow model obtained is found to be compatible with both inferences of the decelerating outflow velocity profile of the gas in the Fermi bubbles region, and evidence for the presence of a large amount of hot ionised gas out in the Galactic halo region. Although simple, this model is found to be able to reproduce the observed Fermi-LAT energy flux at high Galactic latitudes. Following these results a prediction concerning the gamma-ray emission for 1-3~TeV photons is made for future comparison with CTA/SWGO measurements.

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arXiv2020

Galactic 26Al traces metal loss through hot chimneys

Radioactive 26Al is an excellent tracer for metal ejection in the Milky Way, and can provide a direct constraint on the modelling of supernova feedback in galaxy evolution. Gamma-ray observations of the 26Al decay line have found high velocities and hence require a significant fraction of the Galactic 26Al in the hot component. At the same time, meteoritic data combined with simulation results suggest that a significant amount of 26Al makes its way into stars before decay. We investigated the distribution into hot and cold channels with a simulation of a Milky-Way-like galaxy with massive-star feedback in superbubbles and with ejecta traced by 26Al. About 30-40 per cent of the ejecta remain hot, with typical cooling times of the order Gyr. 26Al traces the footpoints of a chimney-fed outflow that mixes metals turbulently into the halo of the model galaxy on a scale of at least 50 kpc. The rest diffuses into cold gas with temperatures less than about 10,000 K, and may therefore be quickly available for star formation. We discuss the robustness of the result by comparison to a simulation with a different global flow pattern. The branching ratio into hot and cold components is comparable to that of longer term average results from chemical evolution modelling of galaxies, clusters and the intracluster medium.

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arXiv2020

Impact of low-energy cosmic rays on star formation

In recent years, exciting developments have taken place in the identification of the role of cosmic rays in star-forming environments. Observations from radio to infrared wavelengths and theoretical modelling have shown that low-energy cosmic rays (<1 TeV) play a fundamental role in shaping the chemical richness of the interstellar medium, determining the dynamical evolution of molecular clouds. In this review we summarise in a coherent picture the main results obtained by observations and by theoretical models of propagation and generation of cosmic rays, from the smallest scales of protostars and circumstellar discs, to young stellar clusters, up to Galactic and extragalactic scales. We also discuss the new fields that will be explored in the near future thanks to new generation instruments, such as: CTA, for the $γ$-ray emission from high-mass protostars; SKA and precursors, for the synchrotron emission at different scales; and ELT/HIRES, JWST, and ARIEL, for the impact of cosmic rays on exoplanetary atmospheres and habitability.

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arXiv2017

The ionising effect of low energy cosmic rays from a class II object on its protoplanetary disk

We investigate the ionising effect of low energy cosmic rays (CRs) from a young star on its protoplanetary disk (PPD). We consider specifically the effect of $\sim3\,$GeV protons injected at the inner edge of the PPD. An increase in the ionisation fraction as a result of these CRs could allow the magnetorotational instability to operate in otherwise magnetically dead regions of the disk. For the typical values assumed we find an ionisation rate of $ζ_\mathrm{CR} \sim 10^{-17}\mathrm{s^{-1}}$ at $1\,$au. The transport equation is solved by treating the propagation of the CRs as diffusive. We find for increasing diffusion coefficients the CRs penetrate further in the PPD, while varying the mass density profile of the disk is found to have little effect. We investigate the effect of an energy spectrum of CRs. The influence of a disk wind is examined by including an advective term. For advective wind speeds between $1-100\mathrm{km\,s^{-1}}$ diffusion dominates at all radii considered here (out to 10$\,$au) for reasonable diffusion coefficients. Overall, we find that low energy CRs can significantly ionise the midplane of PPDs out to $\sim\,1\,$au. By increasing the luminosity or energy of the CRs, within plausible limits, their radial influence could increase to $\sim2\,$au at the midplane but it remains challenging to significantly ionise the midplane further out.

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arXiv2016

Global multifluid simulations of the magnetorotational instability in radially stratified protoplanetary disks

The redistribution of angular momentum is a long standing problem in our understanding of protoplanetary disk (PPD) evolution. The magnetorotational instability (MRI) is considered a likely mechanism. We present the results of a study involving multifluid global simulations including Ohmic dissipation, ambipolar diffusion and the Hall effect in a dynamic, self-consistent way. We focus on the turbulence resulting from the non-linear development of the MRI in radially stratified PPDs and compare with ideal MHD simulations. In the multifluid simulations the disk is initially set up to transition from a weak Hall dominated regime, where the Hall effect is the dominant non-ideal effect but approximately the same as or weaker than the inductive term, to a strong Hall dominated regime, where the Hall effect dominates the inductive term. As the simulations progress a substantial portion of the disk develops into a weak Hall dominated disk. We find a transition from turbulent to laminar flow in the inner regions of the disk, but without any corresponding overall density feature. We introduce a dimensionless parameter, $α_\mathrm{RM}$, to characterise accretion with $α_\mathrm{RM} \gtrsim 0.1$ corresponding to turbulent transport. We calculate the eddy turnover time, $t_\mathrm{eddy}$, and compared this with an effective recombination timescale, $t_\mathrm{rcb}$, to determine whether the presence of turbulence necessitates non-equilibrium ionisation calculations. We find that $t_\mathrm{rcb}$ is typically around three orders of magnitude smaller than $t_\mathrm{eddy}$. Also, the ionisation fraction does not vary appreciably. These two results suggest that these multifluid simulations should be comparable to single fluid non-ideal simulations.

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arXiv2014

The Herschel view of circumstellar discs: a multi-wavelength study of Chamaeleon I

We present the results of a multi-wavelength study of circumstellar discs around 44 young stellar objects in the 3 Myr old nearby Chamaeleon I star-forming region. In particular, we explore the far-infrared/submm regime using Herschel fluxes. We show that Herschel fluxes at 160-500$\,μ$m can be used to derive robust estimates of the disc mass. The median disc mass is 0.005$M_{\odot}$ for a sample of 28 Class IIs and 0.006$M_{\odot}$ for 6 transition disks (TDs). The fraction of objects in Chamaeleon-I with at least the `minimum mass solar nebula' is 2-7%. This is consistent with previously published results for Taurus, IC348, $ρ$ Oph. Diagrams of spectral slopes show the effect of specific evolutionary processes in circumstellar discs. Class II objects show a wide scatter that can be explained by dust settling. We identify a continuous trend from Class II to TDs. Including Herschel fluxes in this type of analysis highlights the diversity of TDs. We find that TDs are not significantly different to Class II discs in terms of far-infrared luminosity, disc mass or degree of dust settling. This indicates that inner dust clearing occurs independently from other evolutionary processes in the discs.

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