Diversity in the outcome of dust radial drift in protoplanetary discs

The growth of dust particles into planet embryos needs to circumvent the radial-drift barrier, i.e. the accretion of dust particles onto the central star by radial migration. The outcome of the dust radial migration is governed by simple criteria between the dust-to-gas ratio and the exponents p and q of the surface density and temperature power laws. The transfer of radiation provides an additional constraint between these quantities because the disc thermal structure is fixed by the dust spatial distribution. To assess which discs are primarily affected by the radial-drift barrier, we used the radiative transfer code MCFOST to compute the temperature structure of a wide range of disc models, stressing the particular effects of grain size distributions and vertical settling. We find that the outcome of the dust migration process is very sensitive to the physical conditions within the disc. For high dust-to-gas ratios (> 0.01) or flattened disc structures (H/R < 0.05), growing dust grains can efficiently decouple from the gas, leading to a high concentration of grains at a critical radius of a few AU. Decoupling of grains can occur at a large fraction (> 0.1) of the initial radius, for a dust-to-gas ratio greater than ~ 0.05. The exact value of the required dust-to-gas ratio for dust to stop its migration is strongly dependent on the disc temperature structure. Non growing dust grains are accreted for discs with flat surface density profiles (p<0.7) while they always remain in the disc if the surface density is steep enough (p>1.2). Both the presence of large grains and vertical settling tend to favour the accretion of non growing dust grains onto the central object, but it slows down the migration of growing dust grains. All the disc configurations are found to have favourable temperature profiles over most of the disc to retain their planetesimals.Comment: 9 pages, 8 figures, accepted for publications in A&A, corrected typo

Super-Earths in the TW Hya disc

We test the hypothesis that the sub-millimetre thermal emission and scattered light gaps seen in recent observations of TW Hya are caused by planet-disc interactions. We perform global three-dimensional dusty smoothed particle hydrodynamics simulations, comparing synthetic observations of our models with dust thermal emission, CO emission and scattered light observations. We find that the dust gaps observed at 24 au and 41 au can be explained by two super-Earths ($\sim 4 \mathrm{M}_{\oplus}$). A planet of approximately Saturn-mass can explain the CO emission and the depth and width of the gap seen in scattered light at 94 au. Our model produces a prominent spiral arm while there are only hints of this in the data. To avoid runaway growth and migration of the planets we require a disc mass of $\lesssim 10^{-2}\,\mathrm{M}_{\odot}$ in agreement with CO observations but 10$-$100 times lower than the estimate from HD line emission.Comment: 6 pages, 5 figures, accepted for publication in MNRA

EFEKTIFITAS GABUNGAN TES SUBJEKTIF DAN TES OBJEKTIF DALAM MENGEVALUSI HASIL BELAJAR FISIKA SISWA SMP NEGERI 11 BANDA ACEH

Kata kunci : efektivitas, tes subjektif, tes objektif, gabungan tes subjektif dan tes objektif , evaluasi, hasil belajarPenelitian yang berjudul Efektivitas Gabungan Tes Subjektif dan Tes Objektif dalam Mengevaluasi Hasil Belajar Fisika Siswa SMP Negeri 11 Banda Aceh.Masalahnya adalah rendahnya hasil belajar fisika siswa yang diduga akibat belum sempurnanya sistem evaluasi yang digunakan guru,baik yang subjektif maupunobjektif. Penelitian ini bertujuan untuk mengetahui efektifitas gabungan tes subjektif dan tes objektif dalam mengevaluasi hasil belajar fisika siswa. Populasi penelitian ini adalah siswa kelas VIII SMP Negeri 11 Banda Aceh tahun pelajaran 2015/2016 yang berjumlah 46 siswa. Dan jumlah populasi tersebut dijadikan sampel berjumlah 20 siswa. Penentuan sampel dilakukan secara random (random sampling). Metode yang digunakan metode kualitatifdengan pendekatan deskriftif. Pengumpulan data dilakukan dengan teknik tes dan pengolahan data menggunakan persentase (hasil yang dicapai setiap siswa dihitung dari persentase jawaban yang benar). Hasil analisis data menunggunakan persentase menunjukkan bahwa terdapat efektivitas gabungan tes subjektif dan tes objektif dalam mengevaluasi hasil belajar fisika siswa SMP Negeri 11 Banda Aceh. Berdasarkan kategori nilai yang menjadi acuan penelitian ini, nilai rata-rata diatas 60% berada pada katagori baik. Dengan demikian, kemampuan rata-rata siswa kelas VIII SMP Negeri 11 Banda Aceh tahun pelajaran 2015/2016 dalam gabungan tes subjektif dan objektif berdasarkan hasil penelitian ini tergolong baik

The Herschel view of GAS in Protoplanetary Systems (GASPS): First comparisons with a large grid of models

The Herschel GASPS key program is a survey of the gas phase of protoplanetary discs, targeting 240 objects which cover a large range of ages, spectral types, and disc properties. To interpret this large quantity of data and initiate self-consistent analyses of the gas and dust properties of protoplanetary discs, we have combined the capabilities of the radiative transfer code MCFOST with the gas thermal balance and chemistry code ProDiMo to compute a grid of ≈300  000 disc models (DENT). We present a comparison of the first Herschel/GASPS line and continuum data with the predictions from the DENT grid of models. Our objective is to test some of the main trends already identified in the DENT grid, as well as to define better empirical diagnostics to estimate the total gas mass of protoplanetary discs. Photospheric UV radiation appears to be the dominant gas-heating mechanism for Herbig stars, whereas UV excess and/or X-rays emission dominates for T Tauri stars. The DENT grid reveals the complexity in the analysis of far-IR lines and the difficulty to invert these observations into physical quantities. The combination of Herschel line observations with continuum data and/or with rotational lines in the (sub-)millimetre regime, in particular CO lines, is required for a detailed characterisation of the physical and chemical properties of circumstellar discs

Benchmark problems for continuum radiative transfer. High optical depths, anisotropic scattering, and polarisation

Solving the continuum radiative transfer equation in high opacity media requires sophisticated numerical tools. In order to test the reliability of such tools, we present a benchmark of radiative transfer codes in a 2D disc configuration. We test the accuracy of seven independently developed radiative transfer codes by comparing the temperature structures, spectral energy distributions, scattered light images, and linear polarisation maps that each model predicts for a variety of disc opacities and viewing angles. The test cases have been chosen to be numerically challenging, with midplane optical depths up 10^6, a sharp density transition at the inner edge and complex scattering matrices. We also review recent progress in the implementation of the Monte Carlo method that allow an efficient solution to these kinds of problems and discuss the advantages and limitations of Monte Carlo codes compared to those of discrete ordinate codes. For each of the test cases, the predicted results from the radiative transfer codes are within good agreement. The results indicate that these codes can be confidently used to interpret present and future observations of protoplanetary discs.Comment: 15 pages, 10 figures, accepted for publication in A&

Planet gaps in the dust layer of 3D proto-planetary disks: Observability with ALMA

Among the numerous known extrasolar planets, only a handful have been imaged directly so far, at large orbital radii and in rather evolved systems. The Atacama Large Millimeter/submillimeter Array (ALMA) will have the capacity to observe these wide planetary systems at a younger age, thus bringing a better understanding of the planet formation process. Here we explore the ability of ALMA to detect the gaps carved by planets on wide orbits.Comment: 2 pages, 2 figures, to appear in the Proceedings of IAU Symp. 299: Exploring the Formation and Evolution of Planetary Systems (Victoria, Canada

The Foggy Disks Surrounding Herbig Ae Stars: a Theoretical Study of the H2O Line Spectra

Water is a key species in many astrophysical environments, but it is particularly important in proto-planetary disks. So far,observations of water in these objects have been scarce, but the situation should soon change thanks to the Herschel satellite. We report here a theoretical study of the water line spectrum of a proto-planetary disk surrounding Ae stars. We show that several lines will be observable with the HIFI instrument onboard the Herschel Space Observatory. We predict that some maser lines could also be observable with ground telescopes and we discuss how the predictions depend not only on the adopted physical and chemical model but also on the set of collisional coefficients used and on the H2 ortho to para ratio through its effect on collisional excitation. This makes the water lines observations a powerful, but dangerous -if misused- diagnostic tool.Comment: Accepted for publication in ApJ Letter

PENERAPAN MODEL PEMBELAJARAN MENGGUNAKAN PENDEKATAN SAINTIFIK DENGAN MODEL INQUIRY BERBANTUAN MEDIA PREZI UNTUK MENINGKATKAN HASIL BELAJAR GEOGRAFISISWA KELAS XI SMA NEGERI 8 BANDA ACEH

ABSTRAKKata Kunci : Inquiry, Media Prezi, Hasil Belajar, Geografi Penerapan pendekatan Saintifik dalam pembelajaran melibatkan keterampilan proses seperti mengamati, menanya, mengumpulkan informasi, mengasosiasi, dan menyimpulkan. Model pembelajaran Inquiry merupakan pembelajaran yang berupaya menanamkan dasar-dasar berfikir ilmiah pada diri siswa, sehingga dalam proses pembelajaran ini siswa lebih banyak belajar sendiri. Penelitian ini bertujuan untuk mengetahui (1) Peningkatan hasil belajar siswa; (2) Aktivitas guru dan siswa; (3) Keterampilan guru dalam mengelola pembelajaran; dan (4) Respon siswa terhadap Penerapan pendekatan Saintifik dengan model Inquiry berbantuan media Prezi. Pengumpulan data dilakukan dengan menggunakan (1) Lembar soal; (2) Lembar pengamatan aktivitas guru dan siswa; (3) Lembar pengamatan keterampilan guru; dan (4) lembar respon siswa. Analisis data menggunakan statistic deskriptif. Hasil penelitian menunjukkan bahwa (1) Persentase ketuntasan secara individual meningkat dari 22 siswa menjadi 27 siswa yang tuntas belajar, sedangkan persentase ketuntasan klasikal pun meningkat dari 60% menjadi 90%; (2) Aktivitas guru dan siswa antara siklus I sampai siklus II telah mencerminkan penerapan Pendekatan Saintifik dengan model Inquiry berbantuan media Prezi, terjadi peningkatan pada aktivitas guru dan siswa secara keseluruhan sudah mengalami peningkatan (3) Keterampilan guru dalam mengelola pembelajaran dengan menggunakan penerapan Pendekatan Saintifik dengan model Inquiry berbantuan media Prezi meningkat dari perolehan skor rata-rata 2,6 dengan kategori baik menjadi 3,4 dengan kategori baik; dan (4) Respon siswa, terhadap penerapan Pendekatan Saintifik dengan model Inquiry berbantuan media Prezi dapat dikatakan baik. 93 persen dari 29 siswa berpendapat bahwa dengan belajar melalui pembelajaran penerapan Pendekatan Saintifik dengan model Inquiry berbantuan media Prezi siswa dapat memahami materi pelajaran yang telah mereka ikuti