scholarly journals The Origin and Evolution of Transition Discs: Successes, Problems, and Open Questions

2016 ◽  
Vol 33 ◽  
Author(s):  
James E. Owen
Keyword(s):  
Spectral Energy Distribution ◽  
Theoretical Work ◽  
Spectral Energy ◽  
Theoretical Understanding ◽  
Origin And Evolution ◽  
Hidden Population ◽  
Open Questions ◽  
Accretion Rates ◽  
Show Evidence ◽  
Dust Component

AbstractTransition discs are protoplanetary discs that show evidence for large holes or wide gaps (with widths comparable to their radii) in their dust component. These discs could be giving us clues about the disc destruction mechanism or hints about the location and time-scales for the formation of planets. However, at the moment there remain key gaps in our theoretical understanding. The vast majority of transition discs are accreting onto their central stars, indicating that—at least close to the star—dust has been depleted from the gas by a very large amount. In this review, we discuss evidence for two distinct populations of transition discs: mm-faint—those with low mm-fluxes, small holes (≲ 10 AU), and low accretion rates (~ 10−10 − 10−9 M⊙ yr−1) and mm-bright—discs with large mm-fluxes, large holes (≳ 20 AU), and high accretion rates ~ 10−8 M⊙ yr−1. MM-faint transition discs are consistent with what would naively be expected from a disc undergoing dispersal; however, mm-bright discs are not, and are likely to be rare and long-lived objects. We discuss the two commonly proposed mechanisms for creating transition discs: photoevaporation and planet–disc interactions, with a particular emphasis on how they would evolve in these models, comparing these predictions to the observed population. More theoretical work on explaining the lack of optically thick, non-accreting transition discs is required in both the photoevaporation and planetary hypothesis, before we can start to use transition discs to constrain models of planet formation. Finally, we suggest that the few discs with primordial looking spectral energy distribution, but serendipitously imaged showing large cavities in the mm (e.g. MWC758 and WSB 60) may represent a hidden population of associated objects. Characterising and understanding how these objects fit into the overall paradigm may allow us to unravel the mystery of transition discs.

scholarly journals Sporadic and intense accretion in a 1 Myr-old brown dwarf candidate

2020 ◽  
Vol 634 ◽  
pp. A128
Author(s):  
D. Nguyen-Thanh ◽  
N. Phan-Bao ◽  
S. J. Murphy ◽  
M. S. Bessell
Keyword(s):  
Spectral Energy Distribution ◽  
Brown Dwarfs ◽  
Photometric Data ◽  
Spectral Energy ◽  
Brown Dwarf ◽  
M Dwarfs ◽  
Trigonometric Parallax ◽  
Accretion Process ◽  
Accretion Rates ◽  
Low Mass

Context. Studying the accretion process in very low-mass objects has important implications for understanding their formation mechanism. Many nearby late-M dwarfs that have previously been identified in the field are in fact young brown dwarf members of nearby young associations. Some of them are still accreting. They are therefore excellent targets for further studies of the accretion process in the very low-mass regime at different stages. Aims. We aim to search for accreting young brown dwarf candidates in a sample of 85 nearby late-M dwarfs. Methods. Using photometric data from DENIS, 2MASS, and WISE, we constructed the spectral energy distribution of the late- M dwarfs based on BT-Settl models to detect infrared excesses. We then searched for lithium and Hα emission in candidates that exhibit infrared excesses to confirm their youth and the presence of accretion. Results. Among the 85 late-M dwarfs, only DENIS-P J1538317−103850 (M5.5) shows strong infrared excesses in WISE bands. The detection of lithium absorption in the M5.5 dwarf and its Gaia trigonometric parallax indicate an age of ~1 Myr and a mass of 47 MJ. The Hα emission line in the brown dwarf shows significant variability that indicates sporadic accretion. This 1 Myr-old brown dwarf also exhibits intense accretion bursts with accretion rates of up to 10−7.9 M⊙ yr−1. Conclusions. Our detection of sporadic accretion in one of the youngest brown dwarfs might imply that sporadic accretion at early stages could play an important role in the formation of brown dwarfs. Very low-mass cores would not be able to accrete enough material to become stars, and thus they end up as brown dwarfs.

scholarly journals Modelling Kepler eclipsing binaries: homogeneous inference of orbital and stellar properties

2019 ◽  
Vol 489 (2) ◽  
pp. 1644-1666 ◽  
Author(s):  
D Windemuth ◽  
E Agol ◽  
A Ali ◽  
F Kiefer
Keyword(s):  
Main Sequence ◽  
Spectral Energy Distribution ◽  
Eclipsing Binaries ◽  
Spectral Energy ◽  
Parameter Estimates ◽  
Kepler Mission ◽  
Short Period ◽  
Show Evidence ◽  
Stellar Properties ◽  
Stellar Masses

Abstract We report on the properties of eclipsing binaries (EBs) from the Kepler mission with a newly developed photometric modelling code, which uses the light curve, spectral energy distribution of each binary, and stellar evolution models to infer stellar masses without the need for radial velocity (RV) measurements. We present solutions and posteriors to orbital and stellar parameters for 728 systems, forming the largest homogeneous catalogue of full Kepler binary parameter estimates to date. Using comparisons to published RV measurements, we demonstrate that the inferred properties (e.g. masses) are reliable for well-detached main-sequence (MS) binaries, which make up the majority of our sample. The fidelity of our inferred parameters degrades for a subset of systems not well described by input isochrones, such as short-period binaries that have undergone interactions, or binaries with post-MS components. Additionally, we identify 35 new systems which show evidence of eclipse timing variations, perhaps from apsidal motion due to binary tides or tertiary companions. We plan to subsequently use these models to search for and constrain the presence of circumbinary planets in Kepler EB systems.

scholarly journals Modelling the Dust Emission of the L1551 IRS5 Binary System

2004 ◽  
Vol 191 ◽  
pp. 200-201
Author(s):  
M. Osorio ◽  
P. D’Alessio ◽  
J. Muzerolle ◽  
N. Calvet ◽  
L. Hartmann
Keyword(s):  
Binary System ◽  
Energy Distribution ◽  
Spectral Energy Distribution ◽  
Dust Emission ◽  
Composite Model ◽  
Spectral Energy ◽  
Circumstellar Disk ◽  
Physical Parameters ◽  
Collapse Models ◽  
Accretion Rates

AbstractWe model the L1551 IRS5 source as a system containing two protostars, each surrounded by a circumstellar disk, both encircled by a circumbinary disk, and all disks surrounded by an extended infalling flattened envelope With this composite model, we can calculate self-consistently the spectral energy distribution of the source the shape of the ice and silicate features, and the spatial intensity distributions of the envelope and disks. We compare our model results with the observations, determining the physical parameters of the disks and the envelope. We find that flattened envelope collapse models are required in order to explain the observations and that the infall rate of the envelope is much larger than the accretion rates of the binary disks.

scholarly journals Modelling the spectral energy distribution of super-Eddington quasars

2019 ◽  
Vol 489 (1) ◽  
pp. 524-533 ◽  
Author(s):  
Aya Kubota ◽  
Chris Done
Keyword(s):  
Black Hole ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Spectral Energy ◽  
Band Spectrum ◽  
Physical Constraints ◽  
Black Hole Accretion ◽  
Accretion Rates ◽  
Eddington Limit ◽  
Standard Disc

ABSTRACT We develop a broad-band spectral model, agnslim, to describe super-Eddington black hole accretion disc spectra. This is based on the slim disc emissivity, where radial advection keeps the surface luminosity at the local Eddington limit, resulting in L(r) ∝ r−2 rather than the r−3 expected from the Novikov-Thorne (standard, sub-Eddington) disc emissivity. Wind losses should also be important but these are expected to produce a similar radiative emissivity. We assume that the flow is radially stratified, with an outer standard disc, an inner hot Comptonizing region and an intermediate warm Comptonizing region to produce the soft X-ray excess. This gives the model enough flexibility to fit the observed data, but with the additional requirement of energy conservation to give physical constraints. We use this to fit the broad-band spectrum of one of the most extreme Active Galactic Nuclei, the Narrow Line Seyfert 1 RX J0439.6−5311, which has a black hole mass of $(6\sim 9)\times 10^6\, \mathrm{M}_\odot$ as derived from the H β line width. This cannot be fit with the standard disc emissivity at this mass, as even zero spin models overproduce the observed luminosity. Instead, we show that the spectrum is well reproduced by the slim disc model, giving mass accretion rates around (5 ∼ 10) × Eddington limit. There is no constraint on black hole spin as the efficiency is reduced by advection. Such extreme accretion rates should be characteristic of the first Quasars, and we demonstrate this by fitting to the spectrum of a recently discovered super-Eddington Quasar, PSO J006 + 39, at z = 6.6.

scholarly journals What makes a galaxy radio-loud?

2011 ◽  
Vol 7 (S284) ◽  
pp. 221-223
Author(s):  
R. A. Ortega-Minakata ◽  
J. P. Torres-Papaqui ◽  
H. Andernach ◽  
R. Coziol ◽  
J. M. Islas-Islas ◽  
...  
Keyword(s):  
Black Holes ◽  
Energy Distribution ◽  
Spectral Energy Distribution ◽  
Spectral Characteristics ◽  
Spectral Energy ◽  
Isolated Galaxies ◽  
Accretion Rates ◽  
The Masses ◽  
Lower Luminosity ◽  
Eddington Limit

AbstractWe compare the Spectral Energy Distribution (SED) of radio-loud and radio-quiet AGNs in three different samples observed with SDSS: radio-loud AGNs (RLAGNs), Low Luminosity AGNs (LLAGNs) and AGNs in isolated galaxies (IG-AGNs). All these galaxies have similar optical spectral characteristics. The median SED of the RLAGNs is consistent with the characteristic SED of quasars, while that of the LLAGNs and IG-AGNs are consistent with the SED of LINERs, with a lower luminosity in the IG-AGNs than in the LLAGNs. We infer the masses of the black holes (BHs) from the bulge masses. These increase from the IG-AGNs to the LLAGNs and are highest for the RLAGNs. All these AGNs show accretion rates near or slightly below 10% of the Eddington limit, the differences in luminosity being solely due to different BH masses. Our results suggests there are two types of AGNs, radio quiet and radio loud, differing only by the mass of their bulges or BHs.

scholarly journals Spectral Line Surveys of Evolved Stars

2011 ◽  
Vol 7 (S280) ◽  
pp. 237-248 ◽  
Author(s):  
J. Cernicharo ◽  
M. Agúndez ◽  
M. Guélin
Keyword(s):  
Chemical Composition ◽  
Spectral Line ◽  
Physical Properties ◽  
Spectral Energy Distribution ◽  
Spectral Band ◽  
Spectral Energy ◽  
Circumstellar Envelopes ◽  
Chemical Complexity ◽  
Evolved Stars ◽  
Dust Component

AbstractThe observation of evolved stars in selected evolutionary stages allow us to track the evolution of the physical properties and chemical composition of the matter that is being returned to the interstellar medium during these last stages of the life of stars. While the dust component can be characterized through the observation of the spectral energy distribution in the infrared part of the spectrum, spectral line surveys carried out in a wide spectral band provide the best probe of the physical properties and chemical composition of the gas phase. In this lecture we review the different line surveys carried out toward these objects and their impact in our understanding of the chemical complexity evolution in the circumstellar envelopes around evolved stars.

scholarly journals Extreme submillimetre starburst galaxies

2018 ◽  
Vol 619 ◽  
pp. A169 ◽  
Author(s):  
M. Rowan-Robinson ◽  
Lingyu Wang ◽  
Duncan Farrah ◽  
Dimitra Rigopoulou ◽  
Carlotta Gruppioni ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Optical Emission ◽  
Spectral Energy ◽  
Black Hole Growth ◽  
Show Evidence ◽  
Universal Ratio

We have used two catalogues, a Herschel catalogue selected at 500 μm (HerMES) and an IRAS catalogue selected at 60 μm (RIFSCz), to contrast the sky at these two wavelengths. Both surveys demonstrate the existence of “extreme” starbursts, with star-formation rates (SFRs) > 5000 M⊙ yr−1. The maximum intrinsic star-formation rate appears to be ~30 000 M⊙ yr−1. The sources with apparent SFR estimates higher than this are in all cases either lensed systems, blazars, or erroneous photometric redshifts. At redshifts between three and five, the time-scale for the Herschel galaxies to make their current mass of stars at their present rate of star formation is ~108 yr, so these galaxies are making a significant fraction of their stars in the current star-formation episode. Using dust mass as a proxy for gas mass, the Herschel galaxies at redshift three to five have gas masses comparable to their mass in stars. Of the 38 extreme starbursts in our Herschel survey for which we have more complete spectral energy distribution (SED) information, 50% show evidence for QSO-like optical emission, or exhibit AGN dust tori in the mid-infrared SEDs. In all cases however the infrared luminosity is dominated by a starburst component. We derive a mean covering factor for AGN dust as a function of redshift and derive black hole masses and black hole accretion rates. There is a universal ratio of black-hole mass to stellar mass in these high redshift systems of ~10−3, driven by the strong period of star-formation and black-hole growth at z = 1−5.

scholarly journals A study of accretion and disk diagnostics in the NGC 2264 cluster

2019 ◽  
Vol 629 ◽  
pp. A67
Author(s):  
Alana P. Sousa ◽  
Silvia H. P. Alencar ◽  
Luisa M. Rebull ◽  
Catherine C. Espaillat ◽  
Nuria Calvet ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Spectral Energy ◽  
Infrared Observations ◽  
T Tauri ◽  
Stellar Radiation ◽  
Accretion Rates ◽  
Uv Excess ◽  
Stellar Properties ◽  
Full Disk ◽  
Transition Disks

Context. Understanding disk dissipation is essential for studying how planets form. Disk gaps and holes, which almost correspond to dust-free regions, are inferred from infrared observations of T Tauri stars (TTS), indicating the existence of a transitional phase between thick accreting disks and debris disks. Transition disks are usually referred to as candidates for newly formed planets. Aims. We searched for transition disk candidates belonging to NGC 2264. Using stellar and disk parameters obtained in the observational multiwavelength campaign CSI 2264, we characterized accretion, disk, and stellar properties of transition disk candidates and compared them to systems with a full disk and diskless stars. Methods. We modeled the spectral energy distribution (SED) of a sample of 401 TTS, observed with both CFHT equipped with MegaCam and IRAC instrument on the Spitzer, with Hyperion SED fitting code using photometric data from the U band (0.3 μm) to the Spitzer/MIPS 24 μm band. We used the SED modeling to distinguish transition disk candidates, full disk systems, and diskless stars. Results. We classified ∼52% of the sample as full disk systems, ∼41% as diskless stars, and ∼7% of the systems as transition disk candidates, among which seven systems are new transition disk candidates belonging to the NGC 2264 cluster. The sample of transition disk candidates present dust in the inner disk similar to anemic disks, according to the αIRAC classification, which shows that anemic disk systems can be candidate transition disks. We show that the presence of a dust hole in the inner disk does not stop the accretion process since 82% of transition disk candidates accrete and show Hα, UV excess, and mass accretion rates at the same level as full disk systems. We estimate the inner hole sizes, ranging from 0.1 to 78 AU, for the sample of transition disk candidates. In only ∼18% of the transition disk candidates, the hole size could be explained by X-ray photoevaporation from stellar radiation.

Comprehensive Panchromatic Data Analyses and Photoionization Modeling of NGC 6781

2018 ◽  
Vol 14 (S343) ◽  
pp. 514-515
Author(s):  
Toshiya Ueta ◽  
Masaaki Otsuka ◽  
Keyword(s):  
Planetary Nebula ◽  
Milky Way ◽  
Spectral Energy Distribution ◽  
Central Star ◽  
Spectral Energy ◽  
Molecular Gas ◽  
Material Recycling ◽  
Data Analyses ◽  
Dust Component ◽  
Data Points

AbstractWe characterized the dusty circumstellar nebula and central star of the C-rich bipolar planetary nebula (PN) NGC 6781 using our own Herschel data augmented with the archival data from UV to radio and constructed one of the most comprehensive photoionization PN models ever produced consisting of the ionized, atomic and molecular gas components as well as the dust component. We reproduced the observed spectral energy distribution (SED), constrained by 136 observational data points. The total nebula mass was estimated to be 0.41 M⊙, with a significant fraction (about 70 %) of it existing in the photo-dissociation region (PDR) surrounding the ionized nebula. This finding demonstrates the critical importance of the PDR in PNe, which are typically recognized as the hallmark of ionized/H+ region. It is therefore essential to characterize the PDR of the circumstellar nebula to understand material recycling in the Milky Way and other galaxies.

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