Observatorio Astronomico Nacional OAN IGN

Alcalá de Henares, Spain

Observatorio Astronomico Nacional OAN IGN

Alcalá de Henares, Spain
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Fuente A.,Observatorio Astronomico Nacional OAN IGN | Cernicharo J.,CSIC - National Institute of Aerospace Technology | Agundez M.,CSIC - National Institute of Aerospace Technology | Agundez M.,University of Bordeaux 1 | Agundez M.,French National Center for Scientific Research
Astrophysical Journal Letters | Year: 2012

The Plateau de Bure Interferometer has been used to map the continuum emission at 3.4 mm and 1.1 mm together with the J = 1→0 and J = 3→2 lines of HCN and HCO+ toward the binary star GV Tau. The 3.4 mm observations did not resolve the binary components, and the HCN J = 1→0 and HCO+ J = 1→0 line emissions trace the circumbinary disk and the flattened envelope. However, the 1.1 mm observations resolved the individual disks of GV Tau N and GV Tau S and allowed us to study their chemistry. We detected the HCN 3→2 line only toward the individual disk of GV Tau N, and the emission of the HCO+ 3→2 line toward GV Tau S. Simple calculations indicate that the 3→2 line of HCN is formed in the inner R < 12 AU of the disk around GV Tau N where the HCN/HCO+ abundance ratio is >300. On the contrary, this ratio is <1.6 in the disk around GV Tau S. The high HCN abundance measured in GV Tau N is well explained by photochemical processes in the warm (>400 K) and dense (n > 107 cm-3) disk surface. © 2012. The American Astronomical Society. All rights reserved.


Fuente A.,Observatorio Astronomico Nacional OAN IGN | Cernicharo J.,CSIC - Institute of Materials Science | Caselli P.,Max Planck Institute for Extraterrestrial Physics | McCoey C.,University of Waterloo | And 9 more authors.
Astronomy and Astrophysics | Year: 2014

Context. This paper is dedicated to the study of the chemistry of the intermediate-mass (IM) hot core NGC 7129 FIRS 2, probably the most compact warm core found in the 2-8 M⊙ stellar mass range. Aims. Our aim is to determine the chemical composition of the IM hot core NGC 7129 FIRS 2, and to provide new insights on the chemistry of hot cores in a more general context. Methods. NGC 7129 FIRS 2 (hereafter, FIRS 2) is located at a distance of 1250 pc and high spatial resolution observations are required to resolve the hot core at its center. We present a molecular survey from 218 200 MHz to 221 800 MHz carried out with the IRAM Plateau de Bure Interferometer (PdBI). These observations were complemented with a long integration single-dish spectrum taken with the IRAM 30 m telescope in Pico de Veleta (Spain). We used a local thermodynamic equilibrium (LTE) single temperature code to model the whole dataset. Results. The interferometric spectrum is crowded with a total of 300 lines from which a few dozen remain unidentified. The spectrum has been modeled with a total of 20 species and their isomers, isotopologues, and deuterated compounds. Complex molecules like methyl formate (CH3OCHO), ethanol (CH3CH2OH), glycolaldehyde (CH2OHCHO), acetone (CH3COCH3), dimethyl ether (CH3OCH 3), ethyl cyanide (CH3CH2CN), and the aGg' conformer of ethylene glycol (aGg'-(CH2OH)2) are among the detected species. The detection of vibrationally excited lines of CH 3CN, CH3OCHO, CH3OH, OCS, HC3N, and CH3CHO proves the existence of gas and dust at high temperatures. The gas kinetic temperature estimated from the vibrational lines of CH 3CN, ∼405-67 +100 K, is similar to that measured in massive hot cores. Our data allow an extensive comparison of the chemistry in FIRS 2 and the Orion hot core. Conclusions. We find a quite similar chemistry in FIRS 2 and Orion. Most of the studied fractional molecular abundances agree within a factor of 5. Larger differences are only found for the deuterated compounds D2CO and CH2DOH and a few molecules (CH3CH2CN, SO2, HNCO and CH3CHO). Since the physical conditions are similar in both hot cores, only different initial conditions (warmer pre-collapse and collapse phase in the case of Orion) and/or different crossing times of the gas in the hot core can explain this behavior. We discuss these two scenarios. © ESO, 2014.


Bujarrabal V.,Observatorio Astronomico Nacional OAN IGN | Alcolea J.,Observatorio Astronomico Nacional OAN IGN
Astronomy and Astrophysics | Year: 2013

Aims. We aim to study the excitation conditions of the molecular gas in the rotating disk of the Red Rectangle, the only post-asymptotic-giant-branch object in which the existence of an equatorial rotating disk has been demonstrated. For this purpose, we developed a complex numerical code that accurately treats radiative transfer in 2D, adapted to the study of molecular lines from rotating disks. Methods. We present far-infrared Herschel/HIFI observations of the 12CO and 13CO J = 6-5, J = 10-9, and J = 16-15 transitions in the Red Rectangle. We also present our code in detail and discuss the accuracy of its predictions, from comparison with well-tested codes. Theoretical line profiles are compared with the empirical data to deduce the physical conditions in the disk by means of model fitting. Results. We conclude that our code is very efficient and produces reliable results. The comparison of the theoretical predictions with our observations reveals that the temperature of the Red Rectangle disk is typically ~100-150 K, about twice as high as previously deduced from mm-wave observations of lower-J lines. We discuss the relevance of these new temperature estimates for understanding the thermodynamics and dynamics of this prototype object, as well as for interpreting observations of other rarely studied post-AGB disks. Despite our sophisticated treatment of the line formation, our model cannot explain the relatively strong line-wing emission for intermediate-J transitions. We argue that a model including a rotating disk only cannot reproduce these data and suggest that there is an additional extended (probably bipolar) structure expanding at about 7-15 km s-1. © 2013 ESO.


Hacar A.,University of Vienna | Kainulainen J.,Max Planck Institute for Astronomy | Tafalla M.,Observatorio Astronomico Nacional OAN IGN | Beuther H.,Max Planck Institute for Astronomy | Alves J.,University of Vienna
Astronomy and Astrophysics | Year: 2016

Filaments play a central role in the molecular clouds' evolution, but their internal dynamical properties remain poorly characterized. To further explore the physical state of these structures, we have investigated the kinematic properties of the Musca cloud. We have sampled the main axis of this filamentary cloud in 13CO and C18O (2-1) lines using APEX observations. The different line profiles in Musca shows that this cloud presents a continuous and quiescent velocity field along its ∼6.5 pc of length. With an internal gas kinematics dominated by thermal motions (i.e. σNT/cs ≲ 1) and large-scale velocity gradients, these results reveal Musca as the longest velocity-coherent, sonic-like object identified so far in the interstellar medium. The transonic properties of Musca present a clear departure from the predicted supersonic velocity dispersions expected in the Larson's velocity dispersion-size relationship, and constitute the first observational evidence of a filament fully decoupled from the turbulent regime over multi-parsec scales. © ESO, 2016.


Bujarrabal V.,Observatorio Astronomico Nacional OAN IGN | Alcolea J.,Observatorio Astronomico Nacional OAN IGN | Van Winckel H.,Catholic University of Leuven | Santander-Garcia M.,Observatorio Astronomico Nacional OAN IGN | And 2 more authors.
Astronomy and Astrophysics | Year: 2013

Context. There is a group of binary post-AGB stars that show conspicuous near-infrared (NIR) excess, which is usually assumed to arise from hot dust in very compact possibly rotating disks. These stars are surrounded by significantly fainter nebulae than the standard, well studied protoplanetary and planetary nebulae (PPNe, PNe). Aims. We aim to identify and study extended rotating disks around these stars and shed light on the role of disks in the formation and shaping of planetary nebulae. Methods. We present high-sensitivity mm-wave observations of CO lines in 24 objects of this type. The resulting CO lines are compared with profiles expected to arise from rotating disks from both theoretical and observational grounds. We derive simple formulae that allow us to determine the mass of the CO-emitting gas and estimate its extent. The reliability and uncertainty of the methods are also widely discussed. Results. CO emission is detected in most observed sources, and the line profiles show that the emissions very probably come from disks in rotation. We derive typical values of the disk mass between 10-3 and 10-2 M ⊙ about two orders of magnitude lower than the (total) masses of standard PPNe. The high-detection rate (upper limits being not very significant) clearly confirm that the NIR excess of these stars arises from compact disks in rotation, which are likely the inner parts of those found here. Low-velocity outflows are also found in about eight objects with moderate expansion velocities of ~10 km s-1 to be compared with the velocities of about 100 km s-1 often found in standard PPNe. Except for two sources with complex profiles, the outflowing gas in our objects represents a minor nebular component. Our simple estimates of the typical disk sizes yields values ̃0.5-1 arcsec, which is between 5 × 1015 and 3 × 1016 cm. Estimates of the linear momenta carried by the outflows, which can only be performed in a few well studied objects, also yield moderate values when compared to the linear momenta that can be released by the stellar radiation pressure (contrary, again, to the case of the very massive and fast bipolar outflows in standard PPNe that are strongly overluminous). The mass and dynamics of nebulae around various classes of post-AGB stars differ very significantly, and we can expect the formation of PNe with very different properties. © 2013 ESO.


Bujarrabal V.,Observatorio Astronomico Nacional OAN IGN | Castro-Carrizo A.,Institute Of Radioastronomie Millimetrique | Alcolea J.,Observatorio Astronomico Nacional OAN IGN | Van Winckel H.,Catholic University of Leuven
Astronomy and Astrophysics | Year: 2015

Aims. So far, only one rotating disk has been clearly identified and studied in AGB or post-AGB objects (in the Red Rectangle), by means of observations with high spectral and spatial resolution. However, disks are thought to play a key role in the late stellar evolution and are suspected to surround many evolved stars. We aim to extend our knowledge on these structures. Methods. We present interferometric observations of 12CO J = 2-1 emission from the nebula surrounding the post-AGB star AC Her, a source belonging to a class of objects that share properties with the Red Rectangle and show hints of Keplerian disks. Results. We clearly detect the Keplerian dynamics of a second disk orbiting an evolved star. Its main properties (size, temperature, central mass) are derived from direct interpretation of the data and model fitting. With this we confirm that there are disks orbiting the stars of this relatively wide class of post-AGB objects. © ESO, 2015


Bujarrabal V.,Observatorio Astronomico Nacional OAN IGN | Castro-Carrizo A.,Institute Of Radioastronomie Millimetrique | Alcolea J.,Observatorio Astronomico Nacional OAN IGN | Santander-Garcia M.,Observatorio Astronomico Nacional OAN IGN | And 3 more authors.
Astronomy and Astrophysics | Year: 2016

Aims. We aim to study the rotating and expanding gas in the Red Rectangle, which is a well known bipolar nebula surrounding a double stellar system whose primary is a post-asymptotic giant branch (post-AGB) star. We analyze the properties of both components and the relation between them. Rotating disks have been very elusive in post-AGB nebulae, in which gas is almost always found to be in expansion. Methods. We present new high-quality ALMA observations of this source in C17O J = 6-5 and H13CN J = 4-3 line emission and results from a new reduction of already published 13CO J = 3-2 data. A detailed model fitting of all the molecular line data, also discussing previous maps and single-dish observations of lines of CO, CII, and CI, was performed using a sophisticated code that includes an accurate nonlocal treatment of radiative transfer in 2D (assuming axial symmetry). These observations (of low- and high-opacity lines requiring various degrees of excitation) and the corresponding modeling allowed us to deepen the analysis of the nebular properties. We also stress the uncertainties, particularly in the determination of the boundaries of the CO-rich gas and some properties of the outflow. Results. We confirm the presence of a rotating equatorial disk and an outflow, which is mainly formed of gas leaving the disk. The mass of the disk is ~0.01 M, and that of the CO-rich outflow is around ten times smaller. High temperatures of 100 K are derived for most components. From comparison of the mass values, we roughly estimate the lifetime of the rotating disk, which is found to be of about 10 000 yr. Taking data of a few other post-AGB composite nebulae into account, we find that the lifetimes of disks around post-AGB stars typically range between about 5000 and more than 20 000 yr. The angular momentum of the disk is found to be high, ~9 MAU km s-1, which is comparable to that of the stellar system at present. Our observations of H13CN show a particularly wide velocity dispersion and indicate that this molecule is only abundant in the inner Keplerian disk, at 60 AU from the stellar system. We suggest that HCN is formed in a dense photodissociation region (PDR) due to the UV excess known to be produced by the stellar system, following chemical mechanisms that are well established for interstellar medium PDRs and disks orbiting young stars. We further suggest that this UV excess could lead to an efficient formation and excitation of PAHs and other C-bearing macromolecules, whose emission is very intense in the optical counterpart. © ESO, 2016.


Planesas P.,Observatorio Astronomico Nacional OAN IGN | Alcolea J.,Observatorio Astronomico Nacional OAN IGN | Bachiller R.,Observatorio Astronomico Nacional OAN IGN
Astronomy and Astrophysics | Year: 2016

Aims. We present new measurements of the flux densities at submillimeter wavelengths based on ALMA band 7 (338 GHz, λ0.89 mm) and band 9 (679 GHz, λ0.44 mm) observations to better constrain the origin of the continuum emission of the Mira AB binary system and to check its orbit. Methods. We have measured the Mira A and Mira B continuum in ALMA band 7, with a resolution of ~0.? 31, and for the first time in ALMA band 9, with a resolution of ~0.? 18. We have resolved the binary system at both bands, and derived the continuum spectral index of the stars and their relative position. We also analyzed ALMA Science Verification data obtained in bands 6 and 3. Measurements at centimeter wavelengths obtained by other authors have been included in our study of the spectral energy distribution of the Mira components. Results. The Mira A continuum emission has a spectral index of 1.98 ± 0.04 extending from submillimeter down to centimeter wavelengths. The spectral index of the Mira B continuum emission is 1.93 ± 0.06 at wavelengths ranging from submillimeter to ~3.1 mm, and a shallower spectral index of 1.22 ± 0.09 at longer wavelengths. The high precision relative positions of the A and B components are shown to significantly depart from the current (preliminary) orbit by ~14 mas. Conclusions. The Mira A continuum emission up to submillimeter wavelengths is consistent with that of a radio photosphere surrounding the evolved star for which models predict a spectral index close to 2. The Mira B continuum emission cannot be described with a single ionized component. An extremely compact and dense region around the star can produce the nearly thermal continuum measured in the range λ0.4-3.1 mm, and an inhomogeneous, less dense, and slightly larger ionized envelope could be responsible for the emission at longer wavelengths. Our results illustrate the potential of ALMA for high precision astrometry of binary systems. We have found a significant discrepancy between the ALMA measurements and the predicted orbit positions. © ESO, 2016.


PubMed | CSIC - Institute of Materials Science, University of Michigan, Rutherford Appleton Laboratory, Harvard - Smithsonian Center for Astrophysics and 11 more.
Type: Journal Article | Journal: The Astrophysical journal | Year: 2015

We present the first ~7.511.5 velocity-resolved (~0.2 km s


PubMed | CSIC - Institute of Materials Science, Catholic University of Leuven, Institute Of Radioastronomie Millimetrique, CSIC - National Institute of Aerospace Technology and Observatorio Astronomico Nacional OAN IGN
Type: | Journal: Astronomy and astrophysics | Year: 2016

We aim to study the rotating and expanding gas in the Red Rectangle, which is a well known object that recently left the asymptotic giant branch (AGB) phase. We analyze the properties of both components and the relation between them. Rotating disks have been very elusive in post-AGB nebulae, in which gas is almost always found to be in expansion.We present new high-quality ALMA observations of CWe confirm the presence of a rotating equatorial disk and an outflow, which is mainly formed of gas leaving the disk. The mass of the disk is ~ 0.01

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