arXiv subjects

Antonio S. Hales

Publications and source records attributed to Antonio S. Hales.

23 records · Page 2Linked to original sources

arXiv2017

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 ($ΔR/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.

astro-ph.EP↗

arXiv2017

The Northern Arc of $ε$ Eridani's Debris Ring as Seen by ALMA

We present the first ALMA observations of the closest known extrasolar debris disc. This disc orbits the star $ε$ Eridani, a K-type star just 3.2pc away. Due to the proximity of the star, the entire disc cannot fit within the ALMA field of view. Therefore, the observations have been centred 18" North of the star, providing us with a clear detection of the northern arc of the ring, at a wavelength of 1.3mm. The observed disc emission is found to be narrow with a width of just 11-13AU. The fractional disc width we find is comparable to that of the Solar System's Kuiper Belt and makes this one of the narrowest debris discs known. If the inner and outer edges are due to resonances with a planet then this planet likely has a semi-major axis of 48AU. We find tentative evidence for clumps in the ring, although there is a strong chance that at least one is a background galaxy. We confirm, at much higher significance, the previous detection of an unresolved emission at the star that is above the level of the photosphere and attribute this excess to stellar chromospheric emission.

astro-ph.EP↗

arXiv2016

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$_α$, 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 $β$ Pictoris system.

astro-ph.EP↗

arXiv2016

Resolving the Planetesimal Belt of HR 8799 with ALMA

The star HR 8799 hosts one of the largest known debris discs and at least four giant planets. Previous observations have found evidence for a warm belt within the orbits of the planets, a cold planetesimal belt beyond their orbits and a halo of small grains. With the infrared data, it is hard to distinguish the planetesimal belt emission from that of the grains in the halo. With this in mind, the system has been observed with ALMA in band 6 (1.34 mm) using a compact array format. These observations allow the inner edge of the planetesimal belt to be resolved for the first time. A radial distribution of dust grains is fitted to the data using an MCMC method. The disc is best fit by a broad ring between $145^{+12}_{-12}$ AU and $429^{+37}_{-32}$ AU at an inclination of $40^{+5}_{-6}$° and a position angle of $51^{+8}_{-8}$°. A disc edge at ~145 AU is too far out to be explained simply by interactions with planet b, requiring either a more complicated dynamical history or an extra planet beyond the orbit of planet b.

astro-ph.EP↗

arXiv2009

IPHAS A-type Stars with Mid-IR Excesses in Spitzer Surveys

We have identified 17 A-type stars in the Galactic Plane that have mid-IR excesses at 8 micron. From the observed colors in the (r'-H_alpha)-(r'-i') plane, we first identified 23050 early A-type main sequence (MS) star candidates in the Isaac Newton Photometric H-Alpha Survey (IPHAS) point source database that are located in Spitzer GLIMPSE Galactic Plane fields. Imposing the requirement that they be detected in all seven 2MASS and IRAC bands led to a sample of 2692 candidate A-type stars with fully sampled 0.6 to 8 micron SEDs. Optical classification spectra of 18 of the IPHAS candidate A-type MS stars showed that all but one could be well fitted using main sequence A-type templates, with the other being an A-type supergiant. Out of the 2692 A-type candidates 17 (0.6%) were found to have 8-micron excesses above the expected photospheric values. Taking into account non-A-Type contamination estimates, the 8-micron excess fraction is adjusted to ~0.7%. The distances to these sources range from 0.7-2.5 kpc. Only 10 out of the 17 excess stars had been covered by Spitzer MIPSGAL survey fields, of which 5 had detectable excesses at 24 micron. For sources with excesses detected in at least two mid-IR wavelength bands, blackbody fits to the excess SEDs yielded temperatures ranging from 270 to 650 K, and bolometric luminosity ratios L_IR/L* from 2.2x10^{-3}-1.9x10^{-2}, with a mean value of 7.9x10^{-3} (these bolometric luminosities are lower limits as cold dust is not detectable by this survey). Both the presence of mid-IR excesses and the derived bolometric luminosity ratios are consistent with many of these systems being in the planet-building transition phase between the early protoplanetary disk phase and the later debris disk phase.

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