20 research outputs found
Planetary formation seen with ALMA : gas and dust properties in protoplanetary disks around young low-mass stars
No full textCette thèse porte sur l’étude des propriétés du gaz et de la poussière dans le disque protoplanétaire entourant l’étoile jeune triple de faible masse (∼ 1.2 M⊙) GG Tau A. Comprendre les propriétés dynamiques, physiques et chimiques des systèmes stellaires multiples est nécessaire pour comprendre comment une planète peut se former et survivre dans ces environnements complexes. Les interactions gravitationnelles, dues à la multiplicité stellaire, créent une cavité centrale dans le disque protoplanétaire, la matière (gaz et poussières) se répartissant alors près des étoiles (disques internes) et en un anneau situé au delà de la cavité. Dans la cavité, le gaz et la poussière transitent sous la forme de filaments ("streamers") qui nourrissent les disques internes permettant aux étoiles centrales (puis aux planètes) de se former. Ce travail consiste en l’analyse de l’émission de CO (12CO, 13CO et C18O) et de CS observées dans le domaine millimétrique/sub-millimétrique ainsi que des cartes de l’émission thermique de la poussière. L’ émission de 12CO fournit des informations sur la couche moléculaire proche de l’atmosphère du disque, 13CO et C18O, qui sont moins abondants, apportent des informations sur des couches plus profondes, tandis que l’émission de CS devrait être plus proche du plan médian. L’ émission de la poussière permet de caractériser les propriétés du disque de poussières autour de ce même plan.Après avoir introduit le sujet, je présente l’analyse de la morphologie du disque de poussières et de gaz et de sa cinématique qui est dérivée de l’émission de CO.Je présente également un modèle de transfert radiatif de la partie dense du disque (l’anneau) réalisé à partir des donnés CO et CS. La soustraction de ce modèle d’anneau aux données originales révèle l’émission ténue du gaz moléculaire située dans la cavité. Ainsi, je suis en mesure d’évaluer les propriétés des filaments de gaz à l’intérieur de cette cavité, telles que: la dynamique et les conditions d’excitation du gaz en- tourant les trois étoiles et la quantité de masse dans la cavité. Le disque externe est en rotation keplerienne jusqu’au bord interne de l’anneau dense à ∼ 160au. Le disque est relativement froid avec une température pour le gaz (CO) de 25 K et une température pour les poussières de 14 K à 200 ua environ des étoiles centrales. Les températures du gaz et de la poussière chutent très rapidement (∝ r−1). La dynamique du gaz à l’intérieur de la cavité est dominée par la rotation Keplerienne,la contribution de mouvement de chute ("infall") étant évaluée à ∼ 10 − 15% de la vitesse Keplerienne. La température du gaz est de l’ordre de 40 to 80 K. La densité de colonne pour CO et la densité de H2 le long des “streamers”, proches des étoiles (environ 0.3′′ − 0.5′′), sont de l’ordre de quelques 1017 cm−2 et 107 cm−3, respective- ment. La masse totale de gaz à l’intérieur de la cavité est de ∼ 1.6 × 10−4 M⊙ et le taux d’accrétion est de l’ordre de 6.4 × 10−8 M⊙ yr−1. Ces résultats permettent de dresser la première vision un tant soit peu complète de la physique d’un système multiple jeune capable de former des planètes.La chimie dans l’anneau est aussi discutée. Je présente ainsi la première détec- tion de H2S dans un disque protoplanétaire et les détections de DCO+, HCO+ et H13CO+ dans le disque de GG Tau A. Mon analyse des observations et la modélisa- tion chimique associée suggèrent que notre compréhension de la chimie du Soufre est encore incomplète . Dans GG Tau A, la détection de H2S a probablement été possible car le disque est plus massif (facteur ∼ 3 − 5) que les autres disques sur lesquels H2S a été recherché. Une telle masse rend le système adapté à la détection de molécules rares, faisant de lui un bon candidat pour étudier la chimie dans les disques protoplanétaires.This thesis presents the analysis of the gas and dust properties of the protoplanetary disk surrounding the young low-mass (∼ 1.2 M⊙) triple star GG Tau A. Studying such young multiple stars is mandatory to understand how planets can form and survive in such systems shaped by gravitational disturbances. Gravitational interactions linked to the stellar multiplicity create a large cavity around the stars, the matter (gas and dust) being either orbiting around the stars (inner disks) or beyond the cavity (outer disk). In between, the matter is streaming from the outer disk onto the inner disks to feed up the central stars (and possible planets).This work makes use of millimeter/sub-millimeter observations of rotational lines of CO (12CO, 13CO and C18O) together with dust continuum maps. While the 12CO emission gives information on the molecular layer close to the disk atmosphere, its less abundant isotopologues (13CO and C18O) bring information much deeper in the molecular layer. The dust mm emission samples the dust disk around the mid-plane.After introducing the subject, I present the analysis of the morphology of the dust and gas disk. The disk kinematics is derived from the CO analysis. I also present a radiative transfer model of the ring in CO. The subtraction of this model from the original data reveals the weak emission of the molecular gas lying inside the cavity. Thus, I am able to evaluate the properties of the gas inside the cavity, such as the gas dynamics and excitation conditions and the amount of mass in the cavity. The outer disk is in Keplerian rotation until the inner edge of the dense ring at ∼ 160 au. The disk is relatively cold with a CO gas temperature of 25 K and a dust temperature of ∼14 K at 200 au from the central stars. Both CO gas and dust temperatures drop very fast (∝ r−1). The gas dynamics inside the cavity is dominated by Keplerian rotation motion. The contribution of infall motion is evaluated at ∼ 10 − 15% of the Keplerian velocity. The gas temperature inside the cav- ity is of the order of 40 − 80 K. The CO column density and H2 density along the “streamers”, which are close to the binary components (around 0.3′′ − 0.5′′) are of the order of a few 1017 cm−2 and 107 cm−3, respectively. The total mass of gas inside the cavity is ∼ 1.6 × 10−4 M⊙ and the accretion rate is estimated at the level of 6.4 × 10−8 M⊙ yr−1. These new results provide the first quantitative global picture of the physical properties of a protoplanetary disk orbiting around a young low-mass multiple star able to create planets.I also discuss some chemical properties of the GG Tau A disk. I report the first detection of H2S in a protoplanetary disk, and the detections of DCO+, HCO+ and H13CO+ in the disk of GG Tau A. Our analysis of the observations and its chemical modeling suggest that our understanding of the S chemistry is still incomplete. In GG Tau A, the detection of H2S has been likely possible because the disk is more massive (a factor ∼ 3 − 5) than other disks where H2S was searched. Such a large disk mass makes the system suitable to detect rare molecules and to study cold- chemistry in protoplanetary disks
Planetary formation seen with ALMA : gas and dust properties in protoplanetary disks around young low-mass stars
No full textCette thèse porte sur l’étude des propriétés du gaz et de la poussière dans le disque protoplanétaire entourant l’étoile jeune triple de faible masse (∼ 1.2 M⊙) GG Tau A. Comprendre les propriétés dynamiques, physiques et chimiques des systèmes stellaires multiples est nécessaire pour comprendre comment une planète peut se former et survivre dans ces environnements complexes. Les interactions gravitationnelles, dues à la multiplicité stellaire, créent une cavité centrale dans le disque protoplanétaire, la matière (gaz et poussières) se répartissant alors près des étoiles (disques internes) et en un anneau situé au delà de la cavité. Dans la cavité, le gaz et la poussière transitent sous la forme de filaments ("streamers") qui nourrissent les disques internes permettant aux étoiles centrales (puis aux planètes) de se former. Ce travail consiste en l’analyse de l’émission de CO (12CO, 13CO et C18O) et de CS observées dans le domaine millimétrique/sub-millimétrique ainsi que des cartes de l’émission thermique de la poussière. L’ émission de 12CO fournit des informations sur la couche moléculaire proche de l’atmosphère du disque, 13CO et C18O, qui sont moins abondants, apportent des informations sur des couches plus profondes, tandis que l’émission de CS devrait être plus proche du plan médian. L’ émission de la poussière permet de caractériser les propriétés du disque de poussières autour de ce même plan.Après avoir introduit le sujet, je présente l’analyse de la morphologie du disque de poussières et de gaz et de sa cinématique qui est dérivée de l’émission de CO.Je présente également un modèle de transfert radiatif de la partie dense du disque (l’anneau) réalisé à partir des donnés CO et CS. La soustraction de ce modèle d’anneau aux données originales révèle l’émission ténue du gaz moléculaire située dans la cavité. Ainsi, je suis en mesure d’évaluer les propriétés des filaments de gaz à l’intérieur de cette cavité, telles que: la dynamique et les conditions d’excitation du gaz en- tourant les trois étoiles et la quantité de masse dans la cavité. Le disque externe est en rotation keplerienne jusqu’au bord interne de l’anneau dense à ∼ 160au. Le disque est relativement froid avec une température pour le gaz (CO) de 25 K et une température pour les poussières de 14 K à 200 ua environ des étoiles centrales. Les températures du gaz et de la poussière chutent très rapidement (∝ r−1). La dynamique du gaz à l’intérieur de la cavité est dominée par la rotation Keplerienne,la contribution de mouvement de chute ("infall") étant évaluée à ∼ 10 − 15% de la vitesse Keplerienne. La température du gaz est de l’ordre de 40 to 80 K. La densité de colonne pour CO et la densité de H2 le long des “streamers”, proches des étoiles (environ 0.3′′ − 0.5′′), sont de l’ordre de quelques 1017 cm−2 et 107 cm−3, respective- ment. La masse totale de gaz à l’intérieur de la cavité est de ∼ 1.6 × 10−4 M⊙ et le taux d’accrétion est de l’ordre de 6.4 × 10−8 M⊙ yr−1. Ces résultats permettent de dresser la première vision un tant soit peu complète de la physique d’un système multiple jeune capable de former des planètes.La chimie dans l’anneau est aussi discutée. Je présente ainsi la première détec- tion de H2S dans un disque protoplanétaire et les détections de DCO+, HCO+ et H13CO+ dans le disque de GG Tau A. Mon analyse des observations et la modélisa- tion chimique associée suggèrent que notre compréhension de la chimie du Soufre est encore incomplète . Dans GG Tau A, la détection de H2S a probablement été possible car le disque est plus massif (facteur ∼ 3 − 5) que les autres disques sur lesquels H2S a été recherché. Une telle masse rend le système adapté à la détection de molécules rares, faisant de lui un bon candidat pour étudier la chimie dans les disques protoplanétaires.This thesis presents the analysis of the gas and dust properties of the protoplanetary disk surrounding the young low-mass (∼ 1.2 M⊙) triple star GG Tau A. Studying such young multiple stars is mandatory to understand how planets can form and survive in such systems shaped by gravitational disturbances. Gravitational interactions linked to the stellar multiplicity create a large cavity around the stars, the matter (gas and dust) being either orbiting around the stars (inner disks) or beyond the cavity (outer disk). In between, the matter is streaming from the outer disk onto the inner disks to feed up the central stars (and possible planets).This work makes use of millimeter/sub-millimeter observations of rotational lines of CO (12CO, 13CO and C18O) together with dust continuum maps. While the 12CO emission gives information on the molecular layer close to the disk atmosphere, its less abundant isotopologues (13CO and C18O) bring information much deeper in the molecular layer. The dust mm emission samples the dust disk around the mid-plane.After introducing the subject, I present the analysis of the morphology of the dust and gas disk. The disk kinematics is derived from the CO analysis. I also present a radiative transfer model of the ring in CO. The subtraction of this model from the original data reveals the weak emission of the molecular gas lying inside the cavity. Thus, I am able to evaluate the properties of the gas inside the cavity, such as the gas dynamics and excitation conditions and the amount of mass in the cavity. The outer disk is in Keplerian rotation until the inner edge of the dense ring at ∼ 160 au. The disk is relatively cold with a CO gas temperature of 25 K and a dust temperature of ∼14 K at 200 au from the central stars. Both CO gas and dust temperatures drop very fast (∝ r−1). The gas dynamics inside the cavity is dominated by Keplerian rotation motion. The contribution of infall motion is evaluated at ∼ 10 − 15% of the Keplerian velocity. The gas temperature inside the cav- ity is of the order of 40 − 80 K. The CO column density and H2 density along the “streamers”, which are close to the binary components (around 0.3′′ − 0.5′′) are of the order of a few 1017 cm−2 and 107 cm−3, respectively. The total mass of gas inside the cavity is ∼ 1.6 × 10−4 M⊙ and the accretion rate is estimated at the level of 6.4 × 10−8 M⊙ yr−1. These new results provide the first quantitative global picture of the physical properties of a protoplanetary disk orbiting around a young low-mass multiple star able to create planets.I also discuss some chemical properties of the GG Tau A disk. I report the first detection of H2S in a protoplanetary disk, and the detections of DCO+, HCO+ and H13CO+ in the disk of GG Tau A. Our analysis of the observations and its chemical modeling suggest that our understanding of the S chemistry is still incomplete. In GG Tau A, the detection of H2S has been likely possible because the disk is more massive (a factor ∼ 3 − 5) than other disks where H2S was searched. Such a large disk mass makes the system suitable to detect rare molecules and to study cold- chemistry in protoplanetary disks.Chủ đề nghiên cứu của luận án là về tính chất của khí và bụi trên đĩa tiền hành tinhquanh một hệ đa sao có khối lượng ∼1.2 Msun, GG Tau A. Nghiên cứu các hệ đa saotrẻ là cần thiết để hiểu về sự hình thành và tồn tại của hệ hành tinh trong môi trườngnhiễu loạn hấp dẫn. Tương tác hấp dẫn của hệ đa sao tạo nên một khoang rỗng lớnxung quanh các sao thành phần, vật chất (khí và bụi) của hệ có thể quay quanh từngsao đơn ("đĩa trong") và bên ngoài khoang rỗng, xung quanh cả hệ sao ("đĩa ngoài").Ở giữa hai phần này của hệ, vật chất được truyền từ đĩa ngoài vào đĩa trong để nuôidưỡng các sao ở trung tâm (hoặc có thể cả hành tinh).Nghiên cứu của luận án sử dụng các quan sát thiên văn vô tuyến ở bướcsóng millimet/dưới-millimet phát ra bởi các phân tử CO (12CO, 13CO và C18O) và bụi.Phát xạ từ 12CO cung cấp thông tin về lớp phân tử gần với khí quyển của đĩa, cácđồng phân kém phổ biến hơn (13CO và C18O) cung cấp thông tin nằm sâu hơn tronglớp phân tử của đĩa. Phát xạ mm của bụi giúp nghiên cứu các tính chất trên mặtphẳng giữa của đĩa.Sau khi giới thiệu về chủ đề và đối tượng nghiên cứu, tôi trình bày về hình tháivà động học của đĩa khí và bụi của hệ sao. Tôi cũng trình bày mô hình truyền bức xạcủa đĩa ngoài sử dụng các đồng phân của CO. Đĩa ngoài của hệ tuân theo chuyểnđộng Kepler cho đến gần khoang rỗng, ∼160 au từ tâm sao, và tương đối lạnh. Nhiệtđộ khí CO và bụi lần lượt là 25K và 14K tại khoảng cách 200au, và giảm nhanh khikhoảng cách tới tâm tăng, T ∝ r−1. Việc trừ mô hình đĩa ngoài từ số liệu ban đầu biểulộ rõ ràng hơn phát xạ yếu của các phân tử khí trong khoang rỗng. Do đó, động họcvà điều kiện phát xạ của khí trong khoang rỗng có thể được đánh giá. Các phân tửkhí bên trong khoang rỗng bị chi phối bởi chuyển động quay, với sự đóng góp nhỏcủa chuyển động rơi được đánh giá vào cỡ 10–15% chuyển động Kepler. Nhiệt độkhí bên trong khoang rỗng trong khoảng 40–80 K, mật độ dài của khí CO và mật độkhối của H2 lần lượt là 1017cm−2 và 107cm−3. Tổng khối lượng khí trong khoang rỗnglà ∼1.6×10−4 Msun, tốc độ truyền vật chất từ đĩa ngoài vào đĩa trong được tính vàokhoảng ∼ 6.4×10−8 Msun yr−1. Các kết quả nghiên cứu này góp phần cung cấp mộtbức tranh tổng quát định lượng đầu tiên về tính chất vật lý của đĩa tiền hành tinhquay xung quanh một hệ đa sao trẻ có khối lượng thấp, nơi có khả năng hình thànhhành tinh.Một vài tính chất hóa học của đĩa tiền hành tinh GG Tau A cũng được nghiêncứu trong luận án này. Tôi trình bày về sự phát hiện lần đầu tiên H2S trong đĩa tiềnhành tinh, cũng như sự phát hiện lần đầu tiên DCO+, HCO+ và H13CO+ trong đĩa GGTau A. Kết quả phân tích số liệu thực nghiệm và mô hình hóa học cho thấy sự hiểubiết của chúng ta về hóa học các phân tử có chứa sulfur trong đĩa là chưa hoànthiện. Trong đĩa tiền hành tinh GG Tau A, khả năng phát hiện được phân tử hiếmnhư H2S có thể là nhờ vào khối lượng lớn của đĩa (lớn hơn khoảng 3–5 lần so vớicác đĩa tiền hành tinh nơi H2S đã từng được tìm kiếm). GG Tau A với đĩa tiền hànhtinh có khối lượng lớn là thích hợp để tìm kiếm các phân tử hiếm và nghiên cứu vềthành phần hóa học của đĩa có nhiệt độ thấp
Large Myr-old Disks Are Not Severely Depleted of Gas-phase CO or Carbon
No full textWe present an ACA search for [C i] 1-0 emission at 492 GHz toward large T Tauri disks (gas radii ≳ 200 au) in the ∼1-3 Myr-old Lupus star-forming region. Combined with Atacama Large Millimeter/submillimeter Array 12 m archival data for IM Lup, we report [C i] 1-0 detections in six out of 10 sources, thus doubling the known detections toward T Tauri disks. We also identify four Keplerian double-peaked profiles and demonstrate that the [C i] 1-0 fluxes correlate with 13CO, C18O, and 12CO(2-1) fluxes, as well as with the gas disk outer radius measured from the latter transition. These findings are in line with the expectation that atomic carbon traces the disk surface. In addition, we compare the carbon and carbon monoxide (CO) line luminosities of a Lupus and literature sample with [C i] 1-0 detections with predictions from the self-consistent disk thermo-chemical models of Ruaud et al. These models adopt interstellar medium carbon and oxygen elemental abundances as input parameters. With the exception of the disk around Sz 98, we find that these models reproduce all the available line luminosities and upper limits, with gas masses comparable to or higher than the minimum-mass solar nebula and gas-to-dust mass ratios ≥10. Thus, we conclude that the majority of large Myr-old disks conform to the simple expectation that they are not significantly depleted in gas, CO, or carbon. © 2023. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
High-speed molecular cloudlets around the Galactic center’s supermassive black hole
No full textInternational audienc
Revised spectroscopic parameters of SH +from ALMA and IRAM 30 m observations
No full textHydrides represent the first steps of interstellar chemistry. Sulfanylium (SH+), in particular, is a key tracer of energetic processes. We used ALMA and the IRAM 30 m telescope to search for the lowest frequency rotational lines of SH+toward the Orion Bar, the prototypical photo-dissociation region illuminated by a strong UV radiation field. On the basis of previous Herschel/HIFI observations of SH+, we expected to detect emission of the two SH+hyperfine structure (HFS) components of the NJ= 10-01fine structure (FS) component near 346 GHz. While we did not observe any lines at the frequencies predicted from laboratory data, we detected two emission lines, each ~15 MHz above the SH+predictions and with relative intensities and HFS splitting expected for SH+. The rest frequencies of the two newly detected lines are more compatible with the remainder of the SH+laboratory data than the single line measured in the laboratory near 346 GHz and previously attributed to SH+. Therefore, we assign these new features to the two SH+HFS components of the NJ= 10-01FS component and re-determine its spectroscopic parameters, which will be useful for future observations of SH+, in particular if its lowest frequency FS components are studied. Our observations demonstrate the suitability of these lines for SH+searches at frequencies easily accessible from the ground.We thank the Spanish MINECO for funding support under grants CSD2009-00038, AYA2009-07304, and AYA2012-32032. We thank the European Research Council for funding support under ERC-2013-Syg 610256-NANOCOSMOS. H.S.P.M. is supported by the German Bundesministerium für Bildung und Forschung (BMBF) via the ALMA Regional Center (ARC) Node project 5A11PK3 for maintanance and upgrade of the CDMS. S.C. was supported by a FPI-INTA grant
Compression and ablation of the photo-irradiated molecular cloud the Orion Bar
No full textInternational audienceThe Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Our relative closeness to the Orion nebula (about 1,350 light years away from Earth) means that we can study the effects of stellar feedback on the parental cloud in detail. Visible-light observations of the Orion Bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the Earth-Sun distance). Static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the Orion Bar (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. Here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. In contrast to stationary model predictions, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO[+] emission. This implies that the H/H2 and C[+]/C/CO transition zones are very close. We find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. The results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution
Spatially resolved images of reactive ions in the Orion Bar
No full textInternational audienceWe report high angular resolution (4.9" x 3.0") images of reactive ions SH+, HOC+, and SO+ toward the Orion Bar photodissociation region (PDR). We used ALMA-ACA to map several rotational lines at 0.8 mm, complemented with multi-line observations obtained with the IRAM 30m telescope. The SH+ and HOC+ emission is restricted to a narrow layer of 2"- to 10"-width (~800 to 4000 AU depending on the assumed PDR geometry) that follows the vibrationally excited H2^* emission. Both ions efficiently form very close to the H/H2 transition zone, at a depth of A_V < 1 mag into the neutral cloud, where abundant C+, S+, and H2^* coexist. SO+ peaks slightly deeper into the cloud. The observed ions have low rotational temperatures (T_rot~10-30 K << T_k) and narrow line-widths (~2-3 km/s), a factor of ~2 narrower that those of the lighter reactive ion CH+. This is consistent with the higher reactivity and faster radiative pumping rates of CH+ compared to the heavier ions, which are driven relatively faster toward smaller velocity dispersion by elastic collisions and toward lower T_rot by inelastic collisions. We estimate column densities and average physical conditions from a non-LTE excitation model (n(H2)~10^5-10^6 cm^-3, n(e^-)~10 cm^-3, and T_k~200 K). Regardless of the excitation details, SH+ and HOC+ clearly trace the most exposed layers of the UV-irradiated molecular cloud surface, whereas SO+ arises from slightly more shielded layers
An unbiased NOEMA 2.6 to 4 mm survey of the GG Tau ring: First detection of CCS in a protoplanetary disk
No full textContext. Molecular line surveys are among the main tools to probe the structure and physical conditions in protoplanetary disks (PPDs), the birthplace of planets. The large radial and vertical temperature as well as density gradients in these PPDs lead to a complex chemical composition, making chemistry an important step to understand the variety of planetary systems. Aims. We aimed to study the chemical content of the protoplanetary disk surrounding GG Tau A, a well-known triple T Tauri system. Methods. We used NOEMA with the new correlator PolyFix to observe rotational lines at ∼2.6 to 4 mm from a few dozen molecules. We analysed the data with a radiative transfer code to derive molecular densities and the abundance relative to 13CO, which we compare to those of the TMC1 cloud and LkCa 15 disk. Results. We report the first detection of CCS in PPDs. We also marginally detect OCS and find 16 other molecules in the GG Tauri outer disk. Ten of them had been found previously, while seven others (13CN, N2H+, HNC, DNC, HC3N, CCS, and C34S) are new detections in this disk. Conclusions. The analysis confirms that sulphur chemistry is not yet properly understood. The D/H ratio, derived from DCO+/HCO+, DCN/HCN, and DNC/HNC ratios, points towards a low temperature chemistry. The detection of the rare species CCS confirms that GG Tau is a good laboratory to study the protoplanetary disk chemistry, thanks to its large disk size and mass.Universidad Autónoma de Chil
SL9 Species Imaging in Jupiter's Auroral Regions with ALMA
No full textInternational audienceComet Shoemaker-Levy 9 (SL9) impacted Jupiter in 1994 at mid-southern latitudes. The impacts resulted in the delivery of new species to Jupiter's stratosphere, like CO, HCN, CS, H2O and CO2. These species have been used ever since to assess stratospheric chemistry and the magnitude of meridional transport. In March 2017, and thus more than 20 years after the impacts, we successfully mapped HCN and CO with ALMA. Our observations provide us with a latitudinal resolution of 3 at the equator and 7 at 70S. While most of the material is confined to the mbar level from the low to the mid latitudes, in agreement with predictions, we find unexpected emissions at high altitudes in the south polar region. These emissions are very well correlated with the position of the auroral oval. At the observation central meridian longitude, the northern auroral oval was not very visible from Earth, regardless of any SL9-related hemispheric differences in HCN and CO abundances. We will present our observations and discuss the implications on stratospheric chemistry, temperature and advective transport
Possible planet formation in the young, low-mass, multiple stellar system GG Tau A
No full textInternational audienceThe formation of planets around binary stars may be more difficult than around single stars1, 2, 3. In a close binary star(with a separation of less than a hundred astronomical units), theory predicts the presence of circumstellar disks aroundeach star, and an outer circumbinary disk surrounding a gravitationally cleared inner cavity around the stars4, 5. Given thatthe inner disks are depleted by accretion onto the stars on timescales of a few thousand years, any replenishing materialmust be transferred from the outer reservoir to fuel planet formation (which occurs on timescales of about one millionyears). Gas flowing through disk cavities has been detected in single star systems6. A circumbinary disk was discoveredaround the young low-mass binary system GG Tau A (ref. 7), which has recently been shown to be a hierarchical triplesystem8. It has one large inner disk9 around the single star, GG Tau Aa, and shows small amounts of shocked hydrogengas residing within the central cavity10, but other than a single weak detection11, the distribution of cold gas in this cavityor in any other binary or multiple star system has not hitherto been determined. Here we report imaging of gas fragmentsemitting radiation characteristic of carbon monoxide within the GG Tau A cavity. From the kinematics we conclude that theflow appears capable of sustaining the inner disk (around GG Tau Aa) beyond the accretion lifetime, leaving time for planetformation to occur there. These results show the complexity of planet formation around multiple stars and confirm thegeneral picture predicted by numerical simulations
