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Mookerjea B.,Tata Institute of Fundamental Research | Ossenkopf V.,University of Cologne | Ricken O.,University of Cologne | Gusten R.,Max Planck Institute for Radio Astronomy | And 5 more authors.
Astronomy and Astrophysics | Year: 2012

By observing radiation-affected gas in the Cepheus B molecular cloud, we probe whether the sequential star formation in this source is triggered by the radiation from newly formed stars. We used the dual band receiver GREAT onboard SOFIA to map [C II] and CO 13-12 and 11-10 in Cep B and compared the spatial distribution and the spectral profiles with complementary ground-based data of low-J transitions of CO isotopes, atomic carbon, and the radio continuum. The interaction of the radiation from the neighboring OB association creates a large photon-dominated region (PDR) at the surface of the molecular cloud traced through the photoevaporation of C +. Bright internal PDRs of hot gas are created around the embedded young stars, where we detect evidence of the compression of material and local velocity changes; however, on the global scale we find no indications that the dense molecular material is dynamically affected. © 2012 ESO.

Cernicharo J.,CSIC - National Institute of Aerospace Technology | Cernicharo J.,CSIC - Institute of Materials Science | Bailleux S.,CNRS Atomic and Molecular Physics Laboratory | Alekseev E.,Ukrainian Academy of Sciences | And 10 more authors.
Astrophysical Journal | Year: 2014

We report the tentative detection in space of the nitrosylium ion, NO+. The observations were performed toward the cold dense core Barnard 1-b. The identification of the NO+ J = 2-1 line is supported by new laboratory measurements of NO+ rotational lines up to the J = 8-7 transition (953207.189 MHz), which leads to an improved set of molecular constants: B 0 = 59597.1379(62) MHz, D 0 = 169.428(65) kHz, and eQq 0(N) = -6.72(15) MHz. The profile of the feature assigned to NO+ exhibits two velocity components at 6.5 and 7.5 km s-1, with column densities of 1.5 × 1012 and 6.5 × 1011 cm-2, respectively. New observations of NO and HNO, also reported here, allow us to estimate the following abundance ratios: X(NO)/X(NO+) ≃ 511, and X(HNO)/X(NO+) ≃ 1. This latter value provides important constraints on the formation and destruction processes of HNO. The chemistry of NO+ and other related nitrogen-bearing species is investigated by the means of a time-dependent gas phase model which includes an updated chemical network according to recent experimental studies. The predicted abundance for NO+ and NO is found to be consistent with the observations. However, that of HNO relative to NO is too high. No satisfactory chemical paths have been found to explain the observed low abundance of HNO. HSCN and HNCS are also reported here with an abundance ratio of ≃ 1. Finally, we have searched for NNO, NO2, HNNO+, and NNOH+, but only upper limits have been obtained for their column density, except for the latter for which we report a tentative 3σ detection. © 2014. The American Astronomical Society. All rights reserved..

Baez-Rubio A.,CSIC - National Institute of Aerospace Technology | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | Thum C.,Institute Radio Astronomia Milimetrica IRAM | Planesas P.,Observatorio Astronomico Nacional IGN | Torres-Redondo J.,CSIC - National Institute of Aerospace Technology
Astronomy and Astrophysics | Year: 2014

The UC-HII region of MWC 349A is the prototype of an ionized wind driven by a massive star surrounded by a disk. Recent high angular resolution observations of the millimeter recombination lines have shown that the disk rotates with a Keplerian law in its outer parts. However, the kinematics of innermost regions in the UC-HII region of MWC 349A is still unknown, in particular, the radius where the wind is launched from the disk. We performed hydrogen recombination line observations with the Heterodyne Instrument for the Far Infrared (HIFI) onboard the Herschel Space Observatory to study the kinematics of its innermost regions by studying their spectral features. In addition to the two laser peaks, we report the first detection of two new components that are blueshifted with respect to the laser peaks for all the recombination lines with principal quantum number inline-formula specific-use=simple-mathitalic = 21. These new spectral features originate from the region where the wind is ejected from the disk. We used our 3D non-LTE radiative transfer model for recombination lines MORELI to show that these features are consistent with the wind being ejected at a radius of 24 AU from the star, which supports magnetohydrodynamic wind models.

Quintana-Lacaci G.,CSIC - National Institute of Aerospace Technology | Quintana-Lacaci G.,Institute Radio Astronomia Milimetrica IRAM | Agundez M.,University of Bordeaux 1 | Agundez M.,French National Center for Scientific Research | And 5 more authors.
Astronomy and Astrophysics | Year: 2013

Aims. During a full line survey towards IRC +10420 in the 3 and 1 mm bands, we detected the emission of circumstellar nitric oxide for the first time. We aim to study the formation of NO and to confirm the enrichment of nitrogen expected for the most massive, evolved stars predicted by the hot bottom burning process. Methods. We counted on a detailed model of the structure and kinematics of the molecular gas around IRC+̇10420. In addition, we used a chemical model to derive the NO abundance profile. We modified the initial nitrogen abundance in order to fit the observed NO profiles. These synthetic profiles were obtained using an LVG radiative transfer code. Results. We have detected NO in a circumstellar envelope for the first time, along with a variety of N-rich molecules, which in turn shows that IRC +10420 presents a N-rich chemistry. Furthermore, we have found that to reproduce the observed NO line profiles, the initial abundance of nitrogen in the chemical model has to be increased by a factor 20 with respect to the values of the standard O-rich stars. © ESO, 2013.

Baez-Rubio A.,CSIC - National Institute of Aerospace Technology | Martin-Pintado J.,CSIC - National Institute of Aerospace Technology | Thum C.,Institute Radio Astronomia Milimetrica IRAM | Planesas P.,Observatorio Astronomico Nacional IGN
Astronomy and Astrophysics | Year: 2013

Context. The best example of a massive star with an ionized outflow launched from its photoevaporating disk is MWC349A. The large amount of reported radio-continuum and radio-recombination line (RRL) observations toward this galactic UC-HII region offers a unique possibility to build a model of the ionized envelope of this source. Aims. To understand the physical conditions and kinematics of the ionized region of the circumstellar disk and also of the outflow of MWC349A. Methods. We compared the bulk of radio-continuum maps, RRL profiles, and the H30α centroid map published to date with the predictions of our non-LTE 3D radiative transfer model, MOdel for REcombination LInes (MORELI), which we describe here in detail. Results. Our non-LTE 3D radiative transfer model provides new evidence that the UC-HII region of MWC349A is composed of an ionized circumstellar disk rotating in Keplerian fashion around a star of 38 M™, and an ionized outflow expanding with a terminal velocity of 60 km s-1 and rotating in the same sense as the disk. The model shows that while maser amplification is the dominant process involved for Hnα RRL emission with quantum numbers n < 41, stimulated emission is relevant for the emission of RRLs with n > 41 up at least the H76α line. Conclusions. For the first time, we present a model of MWC349A which satisfactorily explains the vast amount of reported observational data for a very wide range of frequencies and angular resolutions. © 2013 ESO.

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