The shaping effect of collimated fast outflows in the Egg nebula

We present high angular resolution observations of the HC$_3$N J=5--4 line from the Egg nebula, which is the archetype of protoplanetary nebulae. We find that the HC$_{\rm 3}$N emission in the approaching and receding portion of the envelope traces a clumpy hollow shell, similar to that seen in normal carbon rich envelopes. Near the systemic velocity, the hollow shell is fragmented into several large blobs or arcs with missing portions correspond spatially to locations of previously reported high--velocity outlows in the Egg nebula. This provides direct evidence for the disruption of the slowly--expanding envelope ejected during the AGB phase by the collimated fast outflows initiated during the transition to the protoplanetary nebula phase. We also find that the intersection of fast molecular outflows previously suggested as the location of the central post-AGB star is significantly offset from the center of the hollow shell. From modelling the HC$_3$N distribution we could reproduce qualitatively the spatial kinematics of the HC$_3$N J=5--4 emission using a HC$_3$N shell with two pairs of cavities cleared by the collimated high velocity outflows along the polar direction and in the equatorial plane. We infer a relatively high abundance of HC$_3$N/H$_2$ $\sim$3x10$^{-6}$ for an estimated mass--loss rate of 3x10$^{-5}$ M$_\odot$ yr$^{-1}$ in the HC$_3$N shell. The high abundance of HC$_3$N and the presence of some weaker J=5--4 emission in the vicinity of the central post-AGB star suggest an unusually efficient formation of this molecule in the Egg nebula.Comment: 22 pages, 6 figures, submitted to the Astrophysical Journa

Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind

Context: The presence of water in the wind of the extreme carbon star IRC+10216 has been confirmed by the Herschel telescope. The regions where the high-J H2O lines have been detected are close to the star at radii r \geq 15 R\ast. Aims: We investigate the formation of water and related molecules in the periodically-shocked inner layers of IRC+10216 where dust also forms and accelerates the wind. Methods: We describe the molecular formation by a chemical kinetic network involving carbon-and oxygen-based molecules. We then apply this network to the physical conditions pertaining to the dust-formation zone which experiences the passage of pulsation- driven shocks between 1 and 5 R\ast. We solve for a system of stiff, coupled, ordinary, and differential equations. Results: Non-equilibrium chemistry prevails in the dust-formation zone. H2O forms quickly above the photosphere from the synthesis of hydroxyl OH induced by the thermal fragmentation of CO in the hot post-shock gas. The derived abundance with respect to H2 at 5 R\ast is 1.4\times10-7, which excellently agrees the values derived from Herschel observations. The non-equilibrium formation process of water will be active whatever the stellar C/O ratio, and H2O should then be present in the wind acceleration zone of all stars on the Asymptotic Giant Branch.Comment: 5 pages, 2 figures. Accepted for publication in A&A Letter

Rotational Excitation of HC_3N by H_2 and He at low temperatures

Rates for rotational excitation of HC3N by collisions with He atoms and H2 molecules are computed for kinetic temperatures in the range 5-20K and 5-100K, respectively. These rates are obtained from extensive quantum and quasi-classical calculations using new accurate potential energy surfaces (PES)

Tracing the asymmetry in the envelope around the carbon star CIT 6

We present high angular resolution observations of HC$_3$N J=5--4 line and 7 mm continumm emission from the extreme carbon star CIT 6. We find that the 7 mm continuum emission is unresolved and has a flux consistent with black-body thermal radiation from the central star. The HC$_3$N J=5--4 line emission originates from an asymmetric and clumpy expanding envelope comprising two separate shells of HC$_3$N J=5--4 emission: (i) a faint outer shell that is nearly spherical which has a radius of 8\arcsec; and (ii) a thick and incomplete inner shell that resembles a one-arm spiral starting at or close to the central star and extending out to a radius of about 5\arcsec. Our observations therefore suggest that the mass loss from CIT 6 is strongly modulated with time and highly anisotropic. Furthermore, a comparison between the data and our excitation modelling results suggests an unusually high abundance of HC$_3$N in its envelope. We discuss the possibility that the envelope might be shaped by the presence of a previously suggested possible binary companion. The abundance of HC$_3$N may be enhanced in spiral shocks produced by the interaction between the circumstellar envelope of CIT 6 and its companion star.Comment: 23 pages, 5 figures, submitted to the Astrophysical Journa

Re-evaluation of l(+)-tartaric acid (E 334), sodium tartrates (E 335), potassium tartrates (E 336), potassium sodium tartrate (E 337) and calcium tartrate (E 354) as food additives

Acknowledgements: The FAF Panel wishes to thank Claude Lambre and Lieve Herman for the support provided to this scientific output. The FAF Panel wishes to acknowledge all European competent institutions, Member State bodies and other organisations that provided data for this scientific output.Publisher PD

Détermination de l'enthalpie d'ionisation du peroxyde d'azote à partir des mesures de conductivité et de permittivité

La conductivité et la permittivité du peroxyde d'azote liquide ont été mesurées entre . 10 °C et + 25 °C sous une pression égale à la tension de vapeur. Le calcul de l'enthalpie accompagnant la dismutation hétérolytique montre que l'ionisation du peroxyde est un phénomène très endothermique (ΔHi = 49 772 cal.mole-1)

Détermination de la composition des deux phases liquides des mélanges N

La composition en HNO3, N2O4, [math], NO+, HNO3N2O4, des mélanges d’acide nitrique aqueux (90, 95 et 100 % masse) et de peroxyde d’azote, à la démixtion, a été déterminée à partir des valeurs relatives des intensités des raies de diffusion Raman. Pour cela, une relation a été établie entre le pourcentage molaire et les rapports des intensités des raies Raman diffusées par le mélange étudié, l’intensité de l’une de ces raies étant prise comme référence. Cette relation n’a été utilisée que pour les mélanges ayant une composition globale correspondant à l’une ou l’autre des phases liquides existant au moment de la démixtion à 20 °C

N° 143. — Propriétés physico-chimiques déduites de l’étude de la démixtion des solutions d’acide nitrique anhydre et de peroxyde d’azote

Les valeurs expérimentales obtenues dans l’étude de la solubilité du peroxyde d’azote dans l’acide nitrique anhydre permettent de calculer certaines fonctions thermodynamiques et de suivre leurs variations. Les activités des deux constituants sont déterminées à partir de l’équation de Van der WAALS relative aux liquides. Les valeurs obtenues conduisent à calculer les volumes molaires partiels et les principales fonctions d’excès : entropie, enthalpie, enthalpie libre. Elles permettent de donner une expression de la densité. Elles indiquent la présence d’une association HNO3, N2O4

Détermination de l’enthalpie de démixtion des mélanges de peroxyde d’azote, d’acide nitrique et d’eau a partir des mesures de tensions de vapeur

Lorsque les deux phases liquides coexistent dans le système ternaire N2O4 — HNO3 — H2O, il est possible de calculer l’cnthalpie de démixtion ΔHD à partir des enthalpies de vaporisation ΔHv des mélanges. La relation obtenue est [math]. Pour les trois acides nitriques aqueux étudiés, 90 %, 95 % et 100 % masse, ΔHD vaut — 1 235 cal/mole et correspond à la formation du complexe HNO3, N2O4