arXiv subjects

Jose Cernicharo

Publications and source records attributed to Jose Cernicharo.

At least 37 records · Page 2Linked to original sources

arXiv2014

The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations

We present low spectral resolution molecular interferometric observations at 1.2 mm obtained with the Combined Array for Research in Millimetre-wave Astronomy (CARMA) towards the C-rich AGB star IRC+10216. We have mapped the emission of several lines of SiS, H13CN, SiO, and SiC2 in the ground and first excited vibrational states with a high angular resolution of 0.25 arcsec. These observations have allowed us to partially resolve the emission of the envelope at distances from the star <50 stellar radii (R*), where the stellar wind is mainly accelerated. The structure of the molecular emission has been modelled with a 3D radiation transfer code. The emission of line SiS(v=0,J=14-13) is best reproduced with a set of maser emitting arcs arranged between 5 and 20 R*. The abundance of H13CN with respect to H2 decreases from 8e-7 at 1-5 R* to 3e-7 at 20 R*. The SiO observations are explained with an abundance <2e-8 in the shell-like region between 1 and 5 R*. At this point, the SiO abundance sharply increases up to (2-3)e-7. The vibrational temperature of SiO increases by a factor of 2 due North-East between 20 and 50 R*. SiC2 is formed at the stellar surface with an abundance of 8e-7 decreasing down to 8e-8 at 20 R* probably due to depletion on to dust grains. Several asymmetries are found in the abundance distributions of H13CN, SiO, and SiC2 which define three remarkable directions (North-East, South-Southwest, and South-East) in the explored region of the envelope. There are some differences between the red- and blue-shifted emissions of these molecules suggesting the existence of additional asymmetries in their abundance distributions along the line-of-sight.

astro-ph.SR↗

arXiv2014

IRAM-30m large scale survey of $^{12}$CO(2-1) and $^{13}$CO(2-1) emission in the Orion molecular cloud

Using the IRAM 30m telescope we have surveyed a $1\times0.8^{\circ}$ part of the Orion molecular cloud in the $^{12}$CO and $^{13}$CO (2-1) lines with a maximal spatial resolution of $\sim$11" and spectral resolution of $\sim$ 0.4 km~s$^{-1}$. The cloud appears filamentary, clumpy and with a complex kinematical structure. We derive an estimated mass of the cloud of 7700 M$_{\text{Sun}}$ (half of which is found in regions with visual extinctions $A_V$ below $\sim$10) and a dynamical age for the nebula of the order of 0.2 Myrs. The energy balance suggests that magnetic fields play an important role in supporting the cloud, at large and small scales. According to our analysis, the turbulent kinetic energy in the molecular gas due to outflows is comparable to turbulent kinetic energy resulting from the interaction of the cloud with the HII region. This latter feedback appears negative, i.e. the triggering of star formation by the HII region is inefficient in Orion. The reduced data as well as additional products such as the column density map are made available online at http://userpages.irap.omp.eu/~oberne/Olivier_Berne/Data.

astro-ph.GA↗

arXiv2014

Formation of Hydrocarbons from Hydrogenated Graphene in Circumstellar Clouds

We describe a mechanism that explains the formation of hydrocarbons and hydrocarbyls from hydrogenated graphene/graphite; hard C-C bonds are weakened and broken by the synergistic effect of chemisorbed hydrogen and high temperature vibrations. Total energies, optimized structures, and transition states are obtained from Density Functional Theory simulations. These values have been used to determine the Boltzman probability for a thermal fluctuation to overcome the kinetic barriers, yielding the time scale for an event to occur. This mechanism can be used to rationalize the possible routes for the creation of small hydrocarbons and hydrocarbyls from etched graphene/graphite in stellar regions.

cond-mat.mes-hall↗

arXiv2014

Herschel/PACS spectroscopy of trace gases of the stratosphere of Titan

Aims: We investigate the composition of Titan's stratosphere from new medium-resolution far-infrared observations performed with the full range of Herschel's Photodetector Array Camera and Spectrometer (PACS) (51-220 $μ$m at a resolution $λ$/$Δλ$ ranging from 950 to 5500 depending on wavelength and grating order). Methods: Using PACS, we obtained the spectral emission of several features of the Titan's stratosphere. We used a line-by-line radiative transfer code and the least-squares fitting technique to infer the abundances of the trace constituents. Results: Numerous spectral features attributable to CH$_4$, CO, HCN, and H$_2$O are present. From the flux density spectrum measured and by a detailed comparison with synthetic spectra, we constrain the stratospheric abundance of CH4, which is assumed to be constant with altitude, to be 1.29 $\pm$ 0.03%. Similarly, we constrain the abundance of CO to be 50 $\pm$ 2 ppm, and the HCN vertical distribution consistent with an increase from 40 ppb at $\sim$100 km to 4 ppm at $\sim$200 km, which is an altitude region where the HCN signatures are sensitive. Measurements of three H$_2$O rotational lines confirm the H$_2$O distribution profile recently obtained with Herschel. Furthermore, we determine the isotopic ratios $^{12}$C/$^{13}$C in CO and HCN to be 124 $\pm$ 58, and 66 $\pm$ 35, respectively. Comparisons between our results and the values derived with other instruments show that our results are consistent with the vertical distributions and isotopic ratios in previous studies, except for the HCN distribution obtained with Cassini/CIRS, which does not agree with the PACS lines at the 1-sigma confidence interval.

astro-ph.EP↗

arXiv2013

Laboratory and Astronomical Discovery of HydroMagnesium Isocyanide

We report on the detection of hydromagnesium isocyanide, HMgNC, in the laboratory and in the carbon rich evolved star IRC+10216. The J=1-0 and J=2-1 lines were observed in our microwave laboratory equipment in Valladolid with a spectral accuracy of 3\,KHz. The hyperfine structure produced by the Nitrogen atom was resolved for both transitions. The derived rotational constants from the laboratory data are $B_0$=5481.4333(6)\,MHz, $D_0$=2.90(8)\,KHz, and $eQq(N)$=-2.200(2)\,MHz. The predicted frequencies for the rotational transitions of HMgNC in the millimeter domain have an accuracy of 0.2-0.7\,MHz. Four rotational lines of this species, J=8-7, J=10-9, J=12-11 and J=13-12, have been detected towards IRC+10216. The differences between observed and calculated frequencies are $<$0.5\,MHz. The rotational constants derived from space frequencies are $B_0$=5481.49(3)\,MHz and $D_0$=3.2(1)\,KHz, i.e., identical to the laboratory ones. A merged fit to the laboratory and space frequencies provides $B_0$=5481.4336(4)\,MHz and $D_0$=2.94(5)\,KHz. We have derived a column density for HMgNC of (6$\pm$2)$\times10^{11}$\,cm$^{-2}$. From the observed line profiles the molecule have to be produced produced in the layer where other metal-isocyanides have been already found in this source. The abundance ratio between MgNC and its hydrogenated variety, HMgNC, is $\simeq$20.

astro-ph.GA↗

arXiv2012

The CHESS survey of the L1157-B1 shock: the dissociative jet shock as revealed by Herschel--PACS

Outflows generated by protostars heavily affect the kinematics and chemistry of the hosting molecular cloud through strong shocks that enhance the abundance of some molecules. L1157 is the prototype of chemically active outflows, and a strong shock, called B1, is taking place in its blue lobe between the precessing jet and the hosting cloud. We present the Herschel-PACS 55--210 micron spectra of the L1157-B1 shock, showing emission lines from CO, H2O, OH, and [OI]. The spatial resolution of the PACS spectrometer allows us to map the warm gas traced by far-infrared (FIR) lines with unprecedented detail. The rotational diagram of the high-Jup CO lines indicates high-excitation conditions (Tex ~ 210 +/- 10 K). We used a radiative transfer code to model the hot CO gas emission observed with PACS and in the CO (13-12) and (10-9) lines measured by Herschel-HIFI. We derive 200 10^5 cm-3. The CO emission comes from a region of about 7 arcsec located at the rear of the bow shock where the [OI] and OH emission also originate. Comparison with shock models shows that the bright [OI] and OH emissions trace a dissociative J-type shock, which is also supported by a previous detection of [FeII] at the same position. The inferred mass-flux is consistent with the "reverse" shock where the jet is impacting on the L1157-B1 bow shock. The same shock may contribute significantly to the high-Jup CO emission.

astro-ph.GA↗

arXiv2010

An Interferometric Spectral-line Survey of IRC+10216 in the 345 GHz Band

We report a spectral-line survey of the extreme carbon star IRC+10216 carried out between 293.9 and 354.8 GHz with the Submillimeter Array. A total of 442 lines were detected, more than 200 for the first time; 149 are unassigned. Maps at an angular resolution of ~3" were obtained for each line. A substantial new population of narrow lines with an expansion velocity of ~4 km/s (i.e. ~ 30% of the terminal velocity) was detected. Most of these are attributed to rotational transitions within vibrationally excited states, emitted from energy levels above the v=0, J=0 ground state with excitation energy of 1000-3000 K. Emission from these lines appears to be centered on the star with an angular extent of <1". We use multiple transitions detected in several molecules to derive physical conditions in this inner envelope of IRC+10216.

astro-ph.SR↗

arXiv2010

Photochemistry in the inner layers of clumpy circumstellar envelopes: formation of water in C-rich objects and of C-bearing molecules in O-rich objects

A mechanism based on the penetration of interstellar ultraviolet photons into the inner layers of clumpy circumstellar envelopes around AGB stars is proposed to explain the non-equilibrium chemistry observed in such objects. We show through a simple modelling approach that in circumstellar envelopes with a certain degree of clumpiness or with moderately low mass loss rates (a few 10^(-7) solar masses per year) a photochemistry can take place in the warm and dense inner layers inducing important changes in the chemical composition. In carbon-rich objects water vapor and ammonia would be formed with abundances of 10^(-8) - 10(^-6) relative to H2, while in oxygen-rich envelopes ammonia and carbon-bearing molecules such as HCN and CS would form with abundances of 10^(-9) - 10^(-7) relative to H2. The proposed mechanism would explain the recent observation of warm water vapor in the carbon-rich envelope IRC +10216 with the Herschel Space Observatory, and predict that H2O should be detectable in other carbon-rich objects.

astro-ph.GA↗

arXiv2009

The interstellar gas seen in the mid- and far-infrared: The promise of SPICA Space Telescope

The mid- and far-IR spectral ranges are critical windows to characterize the physical and chemical processes that transform the interstellar gas and dust into stars and planets. Sources in the earliest phases of star formation and in the latest stages of stellar evolution release most of their energy at these wavelengths. Besides, the mid- and far-IR ranges provide key spectral diagnostics of the gas chemistry (water, light hydrides, organic species ...), of the prevailing physical conditions (H2, atomic fine structure lines...), and of the dust mineral and ice composition that can not be observed from ground-based telescopes. With the launch of JAXA's SPICA telescope, uninterrupted studies in the mid- and far-IR will be possible since ESA's Infrared Space Observatory (1995). In particular, SAFARI will provide full access to the 34-210um waveband through several detector arrays and flexible observing modes (from broadband photometry to medium resolution spectroscopy with R~3,000 at 63um), and reaching very high line sensitivities (~10^-19 Wm^-2, 5sigma-1hr) within a large FOV (~2'x2'). Compared to previous far-IR instruments (ISO/LWS, Akari/FIS, Spitzer/MIPS and Herschel/PACS), SAFARI will provide a superior way to obtain fully-sampled spectro-images and continuous SEDs of very faint and extended ISM sources in a wavelength domain not accessible to JWST or ALMA. The much increased sensitivity of SPICA will allow us to step forward and reveal not only the chemical complexity in the local ISM, but also in the extragalactic ISM routinely.

astro-ph.GA↗

arXiv2008

Rotational spectrum of deuterated and 15N ethyl cyanides: CH3CHDCN and CH2DCH2CN and of CH3CH2C15N

Ethyl cyanide is an abundant molecule in hot molecular clouds. Lines from 13C isotopically substituted ethyl cyanide were identified in Orion. To enable the search and the possible detection of other isotopologues of ethyl cyanide in interstellar objects, we have studied the rotational spectrum of deuterated ethyl cyanide: CH2DCH2CN (in-plane and out-of-plane) and CH3CHDCN and the spectrum of15N substituted ethyl cyanide CH3CH2C15N. The rotational spectrum of each species in the ground state was measured in the microwave and millimeter-submillimeter wavelength range using a waveguide Fourier transform spectrometer (8 - 17 GHz) and a source-modulated spectrometer employing backward-wave oscillators (BWOs) (150 - 260 and 580 - 660 GHz). From the fitting procedure, accurate spectroscopic constants were derived for each of the species. These new sets of spectroscopic constants enable us to predict reliably the rotational spectrum (lines frequencies and intensities) in the 4-1000 GHz frequency range and for J and Ka up to 80 and 31, respectively. Combined with IRAM 30 m antenna observations of Orion, this experimental study allowed us to detect 15N substituted ethyl cyanide for the first time in Orion. The derived column density and rotational temperature are 10^13 cm-2 and 150 K for the plateau and 3 10^14 cm-2 and 300 K for the hot core. The deuterated species were searched for but were not detected. The upper limit to the column density of each deuterated isotopologues was 10^14 cm-2.

astro-ph↗

arXiv2008

Formation of simple organic molecules in inner T Tauri disks

We present time dependent chemical models for a dense and warm O-rich gas exposed to a strong far ultraviolet field aiming at exploring the formation of simple organic molecules in the inner regions of protoplanetary disks around T Tauri stars. An up-to-date chemical network is used to compute the evolution of molecular abundances. Reactions of H2 with small organic radicals such as C2 and C2H, which are not included in current astrochemical databases, overcome their moderate activation energies at warm temperatures and become very important for the gas phase synthesis of C-bearing molecules. The photodissociation of CO and release of C triggers the formation of simple organic species such as C2H2, HCN, and CH4. In timescales between 1 and 10,000 years, depending on the density and FUV field, a steady state is reached in the model in which molecules are continuously photodissociated but also formed, mainly through gas phase chemical reactions involving H2. The application of the model to the upper layers of inner protoplanetary disks predicts large gas phase abundances of C2H2 and HCN. The implied vertical column densities are as large as several 10^(16) cm^(-2) in the very inner disk (< 1 AU), in good agreement with the recent infrared observations of warm C2H2 and HCN in the inner regions of IRS 46 and GV Tau disks. We also compare our results with previous chemical models studying the photoprocessing in the outer disk regions, and find that the gas phase chemical composition in the upper layers of the inner terrestrial zone (a few AU) is predicted to be substantially different from that in the upper layers of the outer disk (> 50 AU).

astro-ph↗

arXiv2006

Oxygen Chemistry in the Circumstellar Envelope of the Carbon-Rich Star IRC+10216

In this paper we study the oxygen chemistry in the C-rich circumstellar shells of IRC+10216. The recent discoveries of oxygen bearing species (water, hydroxyl radical and formaldehyde) toward this source challenge our current understanding of the chemistry in C-rich circumstellar envelopes. The presence of icy comets surrounding the star or catalysis on iron grain surfaces have been invoked to explain the presence of such unexpected species. This detailed study aims at evaluating the chances of producing O-bearing species in the C-rich circumstellar envelope only by gas phase chemical reactions. For the inner hot envelope, it is shown that although most of the oxygen is locked in CO near the photosphere (as expected for a C/O ratio greater than 1), some stellar radii far away species such as H2O and CO2 have large abundances under the assumption of thermochemical equilibrium. It is also shown how non-LTE chemistry makes very difficult the CO-->H2O,CO2 transformation predicted in LTE. Concerning the chemistry in the outer and colder envelope, we show that formaldehyde can be formed through gas phase reactions. However, in order to form water vapor it is necessary to include a radiative association between atomic oxygen and molecular hydrogen with a quite high rate constant. The chemical models explain the presence of HCO+ and predict the existence of SO and H2CS (which has been detected in a 3 mm line survey to be published). We have modeled the line profiles of H2CO, H2O, HCO+, SO and H2CS using a non-local radiative transfer model and the abundance profiles predicted by our chemical model. The results have been compared to the observations and discussed.

astro-ph↗

arXiv2006

Far-IR Excited OH Lines from Orion KL Outflows

As part of the first far-IR line survey towards Orion KL, we present the detection of seven new rotationally excited OH Lambda-doublets (at 48, 65, 71, 79, 98 and 115 um). Observations were performed with the Long Wavelength Spectrometer (LWS) Fabry-Perots on board the Infrared Space Observatory (ISO). In total, more than 20 resolved OH rotational lines, with upper energy levels up to 620 K, have been detected at an angular and velocity resolutions of 80$'' and 33 km s^-1 respectively. OH line profiles show a complex behavior evolving from pure absorption, P-Cygni type to pure emission. We also present a large scale 6' declination raster in the OH ^2Π_3/2 J=5/2^+-3/2^- and ^2Π_3/2 J=7/2^-5/2^+ lines (at 119.441 and 84.597 um) revealing the decrease of excitation outside the core of the cloud. From the observed profiles, mean intrinsic line widths and velocity offsets between emission and absorption line peaks we conclude that most of the excited OH arises from Orion outflow(s), i.e. the ``plateau'' component. We determine an averaged OH abundance relative to H_2 of X(OH)=(0.5-1.0)x10^-6, a kinetic temperature of 100 K and a density of n(H_2)=5x10^5 cm^-3. Even with these conditions, the OH excitation is heavily coupled with the strong dust continuum emission from the inner hot core regions and from the expanding flow itself.

astro-ph↗

arXiv2005

Trends in Space Astronomy and Cosmic Vision 2015-2025

As a short introduction to the astronomy session, the response of the community to the Call for Themes issued by ESA and the specific themes selected by the Astronomy Working Group are briefly presented in connection with the four grand themes finally selected for the ESA Science Programme. They are placed in the context of the main discoveries of the past decade and the astronomy projects currently in their development or definition phase. Finally, possible strategies for their implementation are summarised.

astro-ph↗

arXiv2004

OH rotational lines as a diagnostic of the warm neutral gas in galaxies

We present Infrared Space Observatory (ISO) observations of several OH, CH and H2O rotational lines toward the bright infrared galaxies NGC253 and NGC1068. As found in the Galactic clouds in SgrB2 and Orion, the extragalactic far-IR OH lines change from absorption to emission depending on the physical conditions and distribution of gas and dust along the line of sight. As a result, most of the OH rotational lines that appear in absorption toward NGC253 are observed in emission toward NGC1068. We show that the far-IR spectrum of OH can be used as a powerful diagnostic to derive the physical conditions of extragalactic neutral gas. In particular, we find that a warm (Tk~150 K, n(H2)< 5 10^4 cm^-3) component of molecular gas with an OH abundance of 10^{-7} from the inner <15'' can qualitatively reproduce the OH lines toward NGC253. Similar temperatures but higher densities (5 10^5 cm^-3) are required to explain the OH emission in NGC1068.

astro-ph↗

arXiv2004

A new Unidentified Far Infrared Band in NGC7027

We report on the detection of a molecular band centered at ~98 um (~102 cm^-1), observed with the Infrared Space Observatory in the young Planetary Nebula NGC7027. The band structure and intensity can not be reproduced by atomic fine structure lines, recombination lines or by the rotational emission of abundant molecules. We discuss the possible contribution of the low-energy bending modes of pure carbon chains to the unidentified far-IR bands (UfIBs) observed in C-rich evolved objects. In particular, we speculate that the band emission could arise from the nu_9 and nu_7 bending modes of C_6 and C_5, for which wavenumbers of 90+/-50 and 107+/-5 cm^-1 have been estimated from photoelectron spectroscopy.

astro-ph↗

arXiv2004

Far-IR spectroscopy towards Sagittarius B2

The far-IR is a unique wavelength range for Astrophysical studies, however, it can only be fully sampled from space platforms. The fundamental rotational transitions of light molecules, the high-J transitions of polyatomic species, the bending modes of non-polar molecules, several atomic fine structure lines and many frequencies blocked by the earth atmosphere can only be observed between 50 and 200 um (6.0 and 1.5 THz). In this contribution we present the far-IR spectrum of Sgr B2 at a resolution of ~35 km s^{-1}, the ``Rosetta stone'' of ISO's far-IR spectra. We also discuss the perspectives of the far-IR Astronomy in the context of the future telescopes under development.

astro-ph↗

arXiv2000

Molecular Carbon Chains and Rings in TMC-1

We present mapping results in several rotational transitions of HC3N, C6H, both cyclic and linear C3H2 and C3H, towards the cyanopolyyne peak of the filamentary dense cloud TMC-1 using the IRAM 30m and MPIfR 100m telescopes. The spatial distribution of the cumulene carbon chain propadienylidene H2C3 (hereafter l-C3H2) is found to deviate significantly from the distributions of the cyclic isomer c-C3H2, HC3N, and C6H which in turn look very similar. The cyclic over linear abundance ratio of C3H2 increases by a factor of 3 across the filament, with a value of 28 at the cyanopolyyne peak. This abundance ratio is an order of magnitude larger than the range (3 to 5) we observed in the diffuse interstellar medium. The cyclic over linear abundance ratio of C3H also varies by ~2.5 in TMC-1, reaching a maximum value (13) close to the cyanopolyyne peak. These behaviors might be related to competitive processes between ion-neutral and neutral-neutral reactions for cyclic and linear species.

astro-ph↗