Discovery of an Extremely Red Object in the Field of HD 155826

Monthly Notices of the Royal Astronomical Society

2004

121

We present new submillimetre observations of Vega‐excess stars, and consistent modelling for all known Vega‐excess stars with submillimetre data. Our analysis uses dust grain models with realistic optical properties, with the aim of determining physical parameters of the unresolved discs from just their spectral energy distributions (SEDs). For the resolved targets, we find that different objects require very different dust grain properties in order to fit the image data and SED simultaneously. Fomalhaut and Vega require solid dust grains, while HR 4796 and HD 141569 can only be fitted using porous grains. The older stars tend to have grains which are less porous than the younger stars, which may indicate that collisions in the discs have reprocessed the initially fluffy grains into a more solid form. ε Eri appears to be deficient in small dust grains compared with our best‐fitting model. This may show that it is important to include all the factors that cause the size distribution to depart from a simple power law for grains close to the radiation pressure blow‐out limit. Alternatively, this discrepancy may be due to some external influence on the disc (e.g. a planet). When the model is applied to the unresolved targets, an estimate of the disc size can be made. However, the large diversity in dust composition for the resolved discs means that we cannot make a reliable assumption as to the composition of the grains in an unresolved disc, and there is corresponding uncertainty in the disc size. In addition, the poor fit for ε Eri shows that the model cannot always account for the SED even if the disc size is known. These two factors mean that it may not be possible to determine the size of a disc without actually resolving it.

Section: Resultsmentioning

confidence: 99%

Submillimetre observations and modelling of Vega-type stars

Sheret

Dent

Monthly Notices of the Royal Astronomical Society

2004

121

“…All concluded that only 2 ± 2% of these stars have hot dust with infrared luminosities f = L ir /L ⋆ > 10 −4 , finding a total of 3 candidates. Other hot dust candidates exist in the literature, however some IRAS excess fluxes have turned out to arise from chance alignments with background objects (e.g., Lisse et al 2002), including the candidate HD128400 from the hot dust survey of Gaidos (1999) (Zuckerman, priv. comm.).…”

Section: Application To Rare Systems With Hot Dustmentioning

confidence: 99%

Transience of Hot Dust around Sun‐like Stars

Smith

Greaves

et al. 2007

ApJ

349

584

There is currently debate over whether the dust content of planetary systems is stochastically regenerated or originates in planetesimal belts evolving in quasi-steady state. In this paper a simple model for the steady state evolution of debris disks due to collisions is developed and confronted with the properties of the emerging population of 7 sun-like stars that have hot dust at < 10 AU. The model shows that there is a maximum possible disk mass at a given age, since more massive primordial disks process their mass faster. The corresponding maximum dust luminosity is f max = 0.16 × 10 −3 r 7/3 t −1age , where r is disk radius in AU and t age is system age in Myr. The majority (4/7) of the hot disks exceed this limit by a factor ≫ 1000 and so cannot be the products of massive asteroid belts, rather the following systems must be undergoing transient events characterized by an unusually high dust content near the star: η Corvi, HD69830, HD72905 and BD+20307. It is also shown that the hot dust cannot originate in a recent collision in an asteroid belt, since there is also a maximum rate at which collisions of sufficient magnitude to reproduce a given dust luminosity can occur in a disk of a given age. For the 4 transient disks, there is at best a 1:10 5 chance of witnessing such an event compared with 2% of stars showing this phenomenon. Further it is shown that the planetesimal belt feeding the dust in these systems must be located further from the star than the dust, typically at ≫ 2 AU. Other notable properties of the 4 hot dust systems are: two also have a planetesimal belt at > 10 AU (η Corvi and HD72905); one has 3 Neptune mass planets at < 1 AU (HD69830); all exhibit strong silicate features in the mid-IR. We consider the most likely origin for the dust in these systems to be a dynamical instability which scattered planetesimals inwards from a more distant planetesimal belt in an event akin to the Late Heavy Bombardment in our own system, the dust being released from such planetesimals in collisions and possibly also sublimation. Further detailed study of the planet, planetesimal and dust populations in these rare objects has the potential to uncover the chaotic evolutionary history of these systems and to shed light on the history of the solar system.

“…In this study HD 53246 and HD 128400 are in and near the galactic plane respectively, and have been found to have been erroneously identified as hosts of debris. HD 155826, identified by Lisse et al (2002) as being a bogus disk due to source confusion also lies in the galactic plane at b = −0.1. Removal of bogus disks is important when attempting to perform a statistical analysis on disk populations.…”

Section: Background Exclusion and The Importance Of Confirmationmentioning

confidence: 99%

The nature of mid-infrared excesses from hot dust around Sun-like stars

Smith

Dent

2008

A&A

Aims. Studies of the debris disk phenomenon have shown that most systems are analogous to the Edgeworth-Kuiper Belt (EKB). However a rare subset of sun-like stars possess dust which lies, in contrast, in the terrestrial planet region. In this study we aim to determine how many sources with apparent mid-infrared excess are truly hosts of warm dust, and investigate where the dust in these systems must lie. Methods. We observed using ground-based mid-infrared imaging with TIMMI2, VISIR and MICHELLE a sample of FGK main sequence stars previously reported to have hot dust. A new modelling approach was developed to determine the constraints that can be set on the radial extent of excess emission in such observations by demonstrating how the detectability of a disk of a given flux as a fraction of the total flux from the system (F disk /F total ) depends primarily on the ratio of disk radius to PSF width and on the uncertainty on that PSF width. Results. We confirm the presence of warm dust around three of the candidates; η Corvi, HD 145263 and HD 202406. For η Corvi modelling constrains the dust to lie in regions smaller than ∼3.5 AU. The modelling constrains the dust to regions smaller than 80−100 AU for HD 145263 and HD 202406, with SED fitting suggesting the dust lies at a few tens of AU. Of two alternative models for the η Corvi excess emission, we find that a model with one hot dust component at less than 0. 164 (<3 AU) (combined with the known submm dust population at ∼150 AU) fits all the data better at the 2.6σ level than an alternative model with two populations of dust emitting in the mid-infrared: hot dust at less than 0. 19 (<3.5 AU) and a mid-temperature component at ∼0. 66 (12 AU). We identify several systems which have a companion (HD 65277 and HD 79873) or background object (HD 53246, HD 123356 and HD 128400) responsible for their mid-infrared excess, and for three other systems we were able to rule out a point-like mid-infrared source near the star at the level of excess observed in lower resolution observations (HD 12039, HD 69830 and HD 191089). Conclusions. Hot dust sources are either young and possibly primordial or transitional in their emission, or have relatively small radius steady-state planetesimal belts, or they are old and luminous with transient emission. High resolution imaging can be used to constrain the location of the disk and help to discriminate between different models of disk emission. For some small disks, interferometry is needed to resolve the disk location.