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Title: A Complete ALMA Map of the Fomalhaut Debris Disk

Abstract

We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 μ Jy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt an MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3 ± 0.9 au and width of 13.5 ± 1.8 au. We determine a best-fit eccentricity of 0.12 ± 0.01. Assuming a size distribution power-law index of q = 3.46 ± 0.09, we constrain the dust absorptivity power-law index β to be 0.9 < β < 1.5. The geometry of the disk is robustly constrained with inclination 65.°6 ± 0.°3, position angle 337.°9 ± 0.°3, and argument of periastron 22.°5 ± 4.°3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with Hubble Space Telescope , SCUBA, and ALMA. However, we cannot rule out structures ≤10 au in size or that only affect smaller grains. The central star ismore » clearly detected with a flux density of 0.75 ± 0.02 mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.« less

Authors:
;  [1]; ; ; ;  [2]; ; ;  [3];  [4];  [5]; ;  [6];  [7];  [8];  [9];  [10];  [11]
  1. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  3. Astronomy Department, University of California, Berkeley CA 94720-3411 (United States)
  4. MIT Department of Earth, Atmospheric, and Planetary Sciences, Cambridge, MA 02139 (United States)
  5. Department of Astronomy, Van Vleck Observatory, Wesleyan University, Middletown, CT 06459 (United States)
  6. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
  7. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  8. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095 (United States)
  9. UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom)
  10. (United Kingdom)
  11. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
Publication Date:
OSTI Identifier:
22663249
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 842; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTIVITY; BEAMS; DETECTION; DISTRIBUTION; DUSTS; EMISSION; FLUX DENSITY; GHZ RANGE; INCLINATION; SENSITIVITY; SIMULATION; SPACE; STARS; TELESCOPES; WAVELENGTHS

Citation Formats

MacGregor, Meredith A., Wilner, David J., Matrà, Luca, Kennedy, Grant M., Wyatt, Mark C., Shannon, Andrew, Kalas, Paul, Duchene, Gaspard, Graham, James R., Pan, Margaret, Hughes, A. Meredith, Rieke, George H., Su, Kate, Clampin, Mark, Fitzgerald, Michael P., Holland, Wayne S., Institute for Astronomy, Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, and Panić, Olja. A Complete ALMA Map of the Fomalhaut Debris Disk. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA71AE.
MacGregor, Meredith A., Wilner, David J., Matrà, Luca, Kennedy, Grant M., Wyatt, Mark C., Shannon, Andrew, Kalas, Paul, Duchene, Gaspard, Graham, James R., Pan, Margaret, Hughes, A. Meredith, Rieke, George H., Su, Kate, Clampin, Mark, Fitzgerald, Michael P., Holland, Wayne S., Institute for Astronomy, Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, & Panić, Olja. A Complete ALMA Map of the Fomalhaut Debris Disk. United States. doi:10.3847/1538-4357/AA71AE.
MacGregor, Meredith A., Wilner, David J., Matrà, Luca, Kennedy, Grant M., Wyatt, Mark C., Shannon, Andrew, Kalas, Paul, Duchene, Gaspard, Graham, James R., Pan, Margaret, Hughes, A. Meredith, Rieke, George H., Su, Kate, Clampin, Mark, Fitzgerald, Michael P., Holland, Wayne S., Institute for Astronomy, Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, and Panić, Olja. Sat . "A Complete ALMA Map of the Fomalhaut Debris Disk". United States. doi:10.3847/1538-4357/AA71AE.
@article{osti_22663249,
title = {A Complete ALMA Map of the Fomalhaut Debris Disk},
author = {MacGregor, Meredith A. and Wilner, David J. and Matrà, Luca and Kennedy, Grant M. and Wyatt, Mark C. and Shannon, Andrew and Kalas, Paul and Duchene, Gaspard and Graham, James R. and Pan, Margaret and Hughes, A. Meredith and Rieke, George H. and Su, Kate and Clampin, Mark and Fitzgerald, Michael P. and Holland, Wayne S. and Institute for Astronomy, Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH9 3HJ and Panić, Olja},
abstractNote = {We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 μ Jy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt an MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of 136.3 ± 0.9 au and width of 13.5 ± 1.8 au. We determine a best-fit eccentricity of 0.12 ± 0.01. Assuming a size distribution power-law index of q = 3.46 ± 0.09, we constrain the dust absorptivity power-law index β to be 0.9 < β < 1.5. The geometry of the disk is robustly constrained with inclination 65.°6 ± 0.°3, position angle 337.°9 ± 0.°3, and argument of periastron 22.°5 ± 4.°3. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with Hubble Space Telescope , SCUBA, and ALMA. However, we cannot rule out structures ≤10 au in size or that only affect smaller grains. The central star is clearly detected with a flux density of 0.75 ± 0.02 mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.},
doi = {10.3847/1538-4357/AA71AE},
journal = {Astrophysical Journal},
number = 1,
volume = 842,
place = {United States},
year = {Sat Jun 10 00:00:00 EDT 2017},
month = {Sat Jun 10 00:00:00 EDT 2017}
}
  • The innermost parts of dusty debris disks around main-sequence stars are currently poorly known due to the high contrast and small angular separation with their parent stars. Using near-infrared interferometry, we aim to detect the signature of hot dust around the nearby A4 V star Fomalhaut, which has already been suggested to harbor a warm dust population in addition to a cold dust ring located at about 140 AU. Archival data obtained with the VINCI instrument at the VLTI are used to study the fringe visibility of the Fomalhaut system at projected baseline lengths ranging from 4 m to 140more » m in the K band. A significant visibility deficit is observed at short baselines with respect to the expected visibility of the sole stellar photosphere. This is interpreted as the signature of resolved circumstellar emission, producing a relative flux of 0.88% +- 0.12% with respect to the stellar photosphere. While our interferometric data cannot directly constrain the morphology of the excess emission source, complementary data from the literature allow us to discard an off-axis point-like object as the source of circumstellar emission. We argue that the thermal emission from hot dusty grains located within 6 AU from Fomalhaut is the most plausible explanation for the detected excess. Our study also provides a revised limb-darkened diameter for Fomalhaut (theta{sub LD} = 2.223 +- 0.022 mas), taking into account the effect of the resolved circumstellar emission.« less
  • Vega and Fomalhaut are similar in terms of mass, ages, and global debris disk properties; therefore, they are often referred to as 'debris disk twins'. We present Spitzer 10-35 {mu}m spectroscopic data centered at both stars and identify warm, unresolved excess emission in the close vicinity of Vega for the first time. The properties of the warm excess in Vega are further characterized with ancillary photometry in the mid-infrared and resolved images in the far-infrared and submillimeter wavelengths. The Vega warm excess shares many similar properties with the one found around Fomalhaut. The emission shortward of {approx}30 {mu}m from bothmore » warm components is well described as a blackbody emission of {approx}170 K. Interestingly, two other systems, {epsilon} Eri and HR 8799, also show such an unresolved warm dust using the same approach. These warm components may be analogous to the solar system's zodiacal dust cloud, but of far greater mass (fractional luminosity of {approx}10{sup -5} to 10{sup -6} compared to 10{sup -8} to 10{sup -7}). The dust temperature and tentative detections in the submillimeter suggest that the warm excess arises from dust associated with a planetesimal ring located near the water-frost line and presumably created by processes occurring at similar locations in other debris systems as well. We also review the properties of the 2 {mu}m hot excess around Vega and Fomalhaut, showing that the dust responsible for the hot excess is not spatially associated with the dust we detected in the warm belt. We suggest it may arise from hot nano grains trapped in the magnetic field of the star. Finally, the separation between the warm and cold belt is rather large with an orbital ratio {approx}>10 in all four systems. In light of the current upper limits on the masses of planetary objects and the large gap, we discuss the possible implications for their underlying planetary architecture and suggest that multiple, low-mass planets likely reside between the two belts in Vega and Fomalhaut.« less
  • We report on high-contrast mid-infrared observations of Fomalhaut obtained with the Keck Interferometer Nuller (KIN) showing a small resolved excess over the level expected from the stellar photosphere. The measured null excess has a mean value of 0.35% {+-} 0.10% between 8 and 11 {mu}m and increases from 8 to 13 {mu}m. Given the small field of view of the instrument, the source of this marginal excess must be contained within 2 AU of Fomalhaut. This result is reminiscent of previous VLTI K-band ({approx_equal}2{mu}m) observations, which implied the presence of a {approx}0.88% excess, and argued that thermal emission from hotmore » dusty grains located within 6 AU from Fomalhaut was the most plausible explanation. Using a parametric two-dimensional radiative transfer code and a Bayesian analysis, we examine different dust disk structures to reproduce both the near- and mid-infrared data simultaneously. While not a definitive explanation of the hot excess of Fomalhaut, our model suggests that the most likely inner few AU disk geometry consists of a two-component structure, with two different and spatially distinct grain populations. The 2-11 {mu}m data are consistent with an inner hot ring of very small ({approx_equal}10-300 nm) carbon-rich grains concentrating around 0.1 AU. The second dust population-inferred from the KIN data at longer mid-infrared wavelengths-consists of larger grains (size of a few microns to a few tens of microns) located further out in a colder region where regular astronomical silicates could survive, with an inner edge around 0.4 AU-1 AU. From a dynamical point of view, the presence of the inner concentration of submicron-sized grains is surprising, as such grains should be expelled from the inner planetary system by radiation pressure within only a few years. This could either point to some inordinate replenishment rates (e.g., many grazing comets coming from an outer reservoir) or to the existence of some braking mechanism preventing the grains from moving out.« less
  • We present 1.3 mm ALMA Cycle 0 observations of the edge-on debris disk around the nearby, {approx}10 Myr old, M-type star AU Mic. These observations obtain 0.''6 (6 AU) resolution and reveal two distinct emission components: (1) the previously known dust belt that extends to a radius of 40 AU and (2) a newly recognized central peak that remains unresolved. The cold dust belt of mass {approx}1 M{sub Moon} is resolved in the radial direction with a rising emission profile that peaks sharply at the location of the outer edge of the 'birth ring' of planetesimals hypothesized to explain themore » midplane scattered light gradients. No significant asymmetries are discerned in the structure or position of this dust belt. The central peak identified in the ALMA image is {approx}6 times brighter than the stellar photosphere, which indicates an additional emission process in the inner regions of the system. Emission from a stellar corona or activity may contribute, but the observations show no signs of temporal variations characteristic of radio-wave flares. We suggest that this central component may be dominated by dust emission from an inner planetesimal belt of mass {approx}0.01 M{sub Moon}, consistent with a lack of emission shortward of 25 {mu}m and a location {approx}<3 AU from the star. Future millimeter observations can test this assertion, as an inner dust belt should be readily separated from the central star at higher angular resolution.« less
  • Circumstellar disks around stars older than 10 Myr are expected to be gas-poor. There are, however, two examples of old (30-40 Myr) debris-like disks containing a detectable amount of cold CO gas. Here we present Atacama Large Millimeter/Submillimeter Array (ALMA) and Herschel Space Observatory observations of one of these disks, around HD 21997, and study the distribution and origin of the dust and its connection to the gas. Our ALMA continuum images at 886 μm clearly resolve a broad ring of emission within a diameter of ∼4.''5, adding HD 21997 to the dozen debris disks resolved at (sub)millimeter wavelengths. Modelingmore » the morphology of the ALMA image with a radiative transfer code suggests inner and outer radii of ∼55 and ∼150 AU, and a dust mass of 0.09 M {sub ⊕}. Our data and modeling hints at an extended cold outskirt of the ring. Comparison with the morphology of the CO gas in the disk reveals an inner dust-free hole where gas nevertheless can be detected. Based on dust grain lifetimes, we propose that the dust content of this gaseous disk is of secondary origin and is produced by planetesimals. Since the gas component is probably primordial, HD 21997 is one of the first known examples of a hybrid circumstellar disk, a thus-far little studied late phase of circumstellar disk evolution.« less