Atomic Gas in Debris Discs

We have conducted a search for optical circumstellar absorption lines in the spectra of 16 debris disc host stars. None of the stars in our sample showed signs of emission line activity in either H$_{\alpha}$, Ca II or Na I, confirming their more evolved nature. Four stars were found to exhibit narrow absorption features near the cores of the photospheric Ca II and Na I D lines (when Na I D data were available). We analyse the characteristics of these spectral features to determine whether they are of circumstellar or interstellar origins. The strongest evidence for circumstellar gas is seen in the spectrum of HD110058, which is known to host a debris disc observed close to edge-on. This is consistent with a recent ALMA detection of molecular gas in this debris disc, which shows many similarities to the $\beta$ Pictoris system.Comment: Accepted 13/12/2016. Received 2/12/2016; Deposited on 22/11/2016. - 13 Pages, 9 Figures - MNRAS Advance Access published December 15, 201

Diagnosing 0.1–10 au Scale Morphology of the FU Ori Disk Using ALMA and VLTI/GRAVITY

We report new Atacama Large Millimeter/submillimeter Array Band 3 (86–100 GHz; ~80 mas angular resolution) and Band 4 (146–160 GHz; ~50 mas angular resolution) observations of the dust continuum emission toward the archetypal and ongoing accretion burst young stellar object FU Ori, which simultaneously covered its companion, FU Ori S. In addition, we present near-infrared (2–2.45 μm) observations of FU Ori taken with the General Relativity Analysis via VLT InTerferometrY (GRAVITY; ~1 mas angular resolution) instrument on the Very Large Telescope Interferometer (VLTI). We find that the emission in both FU Ori and FU Ori S at (sub)millimeter and near-infrared bands is dominated by structures inward of ~10 au radii. We detected closure phases close to zero from FU Ori with VLTI/GRAVITY, which indicate the source is approximately centrally symmetric and therefore is likely viewed nearly face-on. Our simple model to fit the GRAVITY data shows that the inner 0.4 au radii of the FU Ori disk has a triangular spectral shape at 2–2.45 μm, which is consistent with the H2O and CO absorption features in a 10−4 M ⊙ yr−1, viscously heated accretion disk. At larger (~0.4–10 au) radii, our analysis shows that viscous heating may also explain the observed (sub)millimeter and centimeter spectral energy distribution when we assume a constant, ~10−4 M ⊙ yr−1 mass inflow rate in this region. This explains how the inner 0.4 au disk is replenished with mass at a modest rate, such that it neither depletes nor accumulates significant masses over its short dynamic timescale. Finally, we tentatively detect evidence of vertical dust settling in the inner 10 au of the FU Ori disk, but confirmation requires more complete spectral sampling in the centimeter bands

ALMA 1.3 Millimeter Map of the HD 95086 System

Planets and minor bodies such as asteroids, Kuiper-belt objects and comets are integral components of a planetary system. Interactions among them leave clues about the formation process of a planetary system. The signature of such interactions is most prominent through observations of its debris disk at millimeter wavelengths where emission is dominated by the population of large grains that stay close to their parent bodies. Here we present ALMA 1.3 mm observations of HD 95086, a young early-type star that hosts a directly imaged giant planet b and a massive debris disk with both asteroid- and Kuiper-belt analogs. The location of the Kuiper-belt analog is resolved for the first time. The system can be depicted as a broad ($\Delta R/R \sim$0.84), inclined (30\arcdeg$\pm$3\arcdeg) ring with millimeter emission peaked at 200$\pm$6 au from the star. The 1.3 mm disk emission is consistent with a broad disk with sharp boundaries from 106$\pm$6 to 320$\pm$20 au with a surface density distribution described by a power law with an index of --0.5$\pm$0.2. Our deep ALMA map also reveals a bright source located near the edge of the ring, whose brightness at 1.3 mm and potential spectral energy distribution are consistent with it being a luminous star-forming galaxy at high redshift. We set constraints on the orbital properties of planet b assuming co-planarity with the observed disk.Comment: accepted for publication in A

Diagnosing 0.1─10 au Scale Morphology of the FU Ori Disk Using ALMA and VLTI/GRAVITY

We report new Atacama Large Millimeter/submillimeter Array Band 3 (86─100 GHz; ∼80 mas angular resolution) and Band 4 (146─160 GHz; ∼5 mas angular resolution) observations of the dust continuum emissio toward the archetypal and ongoing accretion burst young stellar objec FU Ori, which simultaneously covered its companion, FU Ori S. I addition, we present near-infrared (2─2.45 μm) observations of FU Or taken with the General Relativity Analysis via VLT InTerferometr (GRAVITY; ∼1 mas angular resolution) instrument on the Very Larg Telescope Interferometer (VLTI). We find that the emission in both F Ori and FU Ori S at (sub)millimeter and near-infrared bands is dominate by structures inward of ∼10 au radii. We detected closure phases clos to zero from FU Ori with VLTI/GRAVITY, which indicate the source i approximately centrally symmetric and therefore is likely viewed nearl face-on. Our simple model to fit the GRAVITY data shows that the inne 0.4 au radii of the FU Ori disk has a triangular spectral shape a 2─2.45 μm, which is consistent with the H2O and CO absorptio features in a \\dot{M} ∼ 10−4 M ☉ yr−1 viscously heated accretion disk. At larger (∼0.4─10 au) radii, ou analysis shows that viscous heating may also explain the observe (sub)millimeter and centimeter spectral energy distribution when w assume a constant, ∼10−4 M ☉ yr−1 mas inflow rate in this region. This explains how the inner 0.4 au disk i replenished with mass at a modest rate, such that it neither deplete nor accumulates significant masses over its short dynamic timescale Finally, we tentatively detect evidence of vertical dust settling in th inner 10 au of the FU Ori disk, but confirmation requires more complet spectral sampling in the centimeter band

Solar polar brightening and radius at 100 and 230 GHz observed by ALMA

Polar brightening of the Sun at radio frequencies has been studied for almost fifty years and yet a disagreement persists between solar atmospheric models and observations. Some observations reported brightening values much smaller than the expected values obtained from the models, with discrepancies being particularly large at millimeter wavelengths. New clues to calibrate the atmospheric models can be obtained with the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) radio interferometer. In this work, we analyzed the lower limit of the polar brightening observed at 100 and 230 GHz by ALMA, during its Science Verification period, 2015 December 16-20. We find that the average polar intensity is higher than the disk intensity at 100 and 230 GHz, with larger brightness intensities at the South pole in eight of the nine maps analyzed. The observational results were compared with calculations of the millimetric limb brightnening emission for two semi-empirical atmospheric models, FAL- C (Fontenla et al. 1993) and SSC (Selhorst et al. 2005a). Both models presented larger limb intensities than the averaged observed values. The intensities obtained with the SSC model were closer to the observations, with polar brightenings of 10.5% and 17.8% at 100 and 230 GHz, respectively. This discrepancy may be due to the presence of chromospheric features (like spicules) at regions close to the limb

ALMA High-frequency Long Baseline Campaign in 2021: Highest Angular Resolution Submillimeter Wave Images for the Carbon-rich Star R Lep

The Atacama Large Millimeter/submillimeter Array (ALMA) was used in 2021 to image the carbon-rich evolved star R Lep in Bands 8-10 (397-908 GHz) with baselines up to 16 km. The goal was to validate the calibration, using band-to-band (B2B) phase referencing with a close phase calibrator J0504-1512, 1.2 deg from R Lep in this case, and the imaging procedures required to obtain the maximum angular resolution achievable with ALMA. Images of the continuum emission and the hydrogen cyanide (HCN) maser line at 890.8 GHz, from the J=10-9 transition between the (1110) and (0400) vibrationally excited states, achieved angular resolutions of 13, 6, and 5 mas in Bands 8-10, respectively. Self-calibration (self-cal) was used to produce ideal images as to compare with the B2B phase referencing technique. The continuum emission was resolved in Bands 9 and 10, leaving too little flux for self-cal of the longest baselines, so these comparisons are made at coarser resolution. Comparisons showed that B2B phase referencing provided phase corrections sufficient to recover 92%, 83%, and 77% of the ideal image continuum flux densities. The HCN maser was sufficiently compact to obtain self-cal solutions in Band 10 for all baselines (up to 16 km). In Band 10, B2B phase referencing as compared to the ideal images recovered 61% and 70% of the flux density for the HCN maser and continuum, respectively.Comment: 37 pages, 12 figures, 9 tables, accepted by ApJ (Aug 30, 2023

The clumpy structure of ϵ\epsilon Eridani's debris disc revisited by ALMA

$\epsilon$ Eridani is the closest star to our Sun known to host a debris disc. Prior observations in the (sub-)millimetre regime have potentially detected clumpy structure in the disc and attributed this to interactions with an (as yet) undetected planet. However, the prior observations were unable to distinguish between structure in the disc and background confusion. Here we present the first ALMA image of the entire disc, which has a resolution of 1.6"$\times$1.2". We clearly detect the star, the main belt and two point sources. The resolution and sensitivity of this data allow us to clearly distinguish background galaxies (that show up as point sources) from the disc emission. We show that the two point sources are consistent with background galaxies. After taking account of these, we find that resolved residuals are still present in the main belt, including two clumps with a $>3\sigma$ significance -- one to the east of the star and the other to the northwest. We perform $n$-body simulations to demonstrate that a migrating planet can form structures similar to those observed by trapping planetesimals in resonances. We find that the observed features can be reproduced by a migrating planet trapping planetesimals in the 2:1 mean motion resonance and the symmetry of the most prominent clumps means that the planet should have a position angle of either ${\sim10^\circ}$ or ${\sim190^\circ}$. Observations over multiple epochs are necessary to test whether the observed features rotate around the star.Comment: 16 pages, 10 figures, accepted for publication in MNRA