P. de Vicente

Warm H

We present ISO observations of several H2 pure-rotational lines (from S(0) to S(5)) towards a sample of 16 molecular clouds distributed along the central ~ 500 pc of the Galaxy. We also present C18O and 13CO J=1->0 and J=2->1 observations of these sources made with the IRAM-30m telescope. With the CO data we derive H2 densities of 10e(3.5-4.0) cm-3 and H2 column densities of a few 10e22 cm-2. We have corrected the H2 data for ~ 30 magnitudes of visual extinction using a self-consistent method. In every source, we find that the H2 emission exhibits a large temperature gradient. The S(0) and S(1) lines trace temperatures (T) of ~150 K while the S(4) and S(5) lines indicate temperatures of ~ 600K. The warm H2 column density is typically ~1-2 x 10e22 cm-2, and is predominantly gas with T=150 K. This is the first direct estimate of the total column density of the warm molecular gas in the Galactic center region. These warm H2 column densities represent a fraction of ~ 30 % of the gas traced by the CO isotopes emission. The cooling by H2 in the warm component is comparable to that by CO. Comparing our H2 and CO data with available ammonia NH3 observations from literature one obtains relatively high NH3 abundances of a few 10e(-7) in both the warm and the cold gas. A single shock or Photo-Dissociation Region (PDR) cannot explain all the observed H2 lines. Alternatives for the heating mechanisms are discussed.

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This paper presents and discusses the final data set of a long-term and short-spaced monitoring of 21 SiO maser sources, mostly evolved stars, carried out in two SiO maser lines at 43 GHz with the Observatorio Astronomico Nacional 13.7 m telescope at the Centro Astronomico de Yebes (Guadalajara, Spain). In most objects, more than 80 spectra per transition over a period of 11 years have been recorded. The new data presented here, previously unpublished, represent nearly 50% of the total SiO data collected in the project. In addition, the availability of optical light curves from the AAVSO for most of the objects during the whole period of the SiO monitoring, ground-based near-IR data for four sources overlapping with 3 to 5 observed SiO periods, and DIRBE near-IR data covering a significant portion of an SiO period in 10 sources, make this data set a unique reference for comparing optical, NIR and SiO variability in order to elucidate the physical mechanisms that pump SiO masers in evolved stars. The basis for the conclusions obtained in this work comes from a numerical time series analysis of the suitable SiO, optical and NIR light curves in regular variables to obtain precise values of the periods and phase lags between the different curves. This analysis shows evidence that in regular variable evolved stars the three types of emission have the same period and that the SiO maxima happen in phase with NIR maxima and with a phase lag typically between 0.05 and 0.20 with respect to optical maxima. We conclude that in these objects the observational evidence presented in this work favors the radiative pumping of SiO masers against the collisional pumping.

in the Galactic center region

The nucleus of M82 has been mapped in several 3 and 1 mm lines of CN, HCN, C2H, c-C3H2, CH3C2H, HC3N, and HOC+ using the IRAM 30 m telescope. These species have been purposely selected as good tracers of photon-dominated chemistry. We have measured [CN]/[HCN] ~ 5 in the inner 650 pc galaxy disk. Furthermore, we have detected the HOC+ 1 → 0 line with an intensity similar to that of the H13CO+ 1 → 0 line. This implies an [HCO+]/[HOC+] ratio of ~40. These results corroborate the existence of a giant photodissociation region (PDR) in the nucleus of M82. In fact, the low [HCO+]/[HOC+] ratio can only be explained if the nucleus of M82 is formed by small (r < 0.02-0.2 pc) and dense (n ~ a few times 104-105 cm-3) clouds immersed in an intense UV field (G0 ~ 104 in units of the Habing field). The detection of the hydrocarbons c-C3H2 and CH3C2H in the nucleus of M82 suggests that a complex carbon chemistry is developing in this giant PDR.

28 SiO v =1 and v =2 , J = 1-0 maser variability in evolved stars. Eleven years of short spaced monitoring

We present observations of C2H5OH toward molecular clouds in Sgr A and Sgr B2 and associated with thermal and nonthermal features in the Galactic center (GC). C2H5OH emission in Sgr A and Sgr B2 is widespread but not uniform. C2H5OH emission is much weaker, or it is not detected in some molecular clouds in both complexes, in particular those with radial velocities between 70 and 120 km s-1. While most of the clouds associated with the thermal features do not show C2H5OH emission, that associated with the nonthermal radio arc shows emission. The fractional abundance of C2H5OH in most of the clouds with radial velocities between 0 and 70 km s-1 in Sgr A and Sgr B2 is relatively high, of a few times 10-8. The C2H5OH abundance decreases by more than a factor of 10 (10-9) in the clouds associated with the thermal features. The large abundance of C2H5OH in the gas phase indicates that C2H5OH has formed in grains and released to gas phase by shocks in the last ~105 yr. The implications of this finding in the origin of the shocks in the GC is briefly discussed.

Photon-dominated chemistry in the nucleus of M82: Widespread HOC + emission in the inner 650 parsec disk

We present an analysis of selected ne structure lines (Neii 12.8 m, Neiii 15.6 m, Siii 18.7 and 33.5 m, Oiii 52 and 88 m, Nii 122 ma nd Niii 57 m) observed with the Infrared Space Observatory (ISO) toward the Radio Arc in the Galactic center region (GCR). Most of the data were retrieved from the ISO Data Archive. We study the density of the ionized gas and the large scale ionization structure in a region of 30 30 pc 2 by means of the Oiii 52 m/88 m, Siii 18.7 m/33.5 m, Neiii 15.6 m/Neii12.8 ma nd Niii 57 m/Nii 122 m line ratios. The electron densities (ne) derived from the Oiii lines ratio indicate the presence of di use ionized material withne of 10 1:8 2:6 cm 3 .T he Neiii 15.6 m/Neii 12.8 ma nd Niii 57 m/Nii 122 m line ratios vary from source to source from 0.05 to 0.30 and from 0.3 to 2.5, respec- tively. The Niii 57/Nii 122 m ratio show two clear gradients, one pointing toward the Quintuplet cluster and the other pointing toward the Arches cluster. We have used a simple model to explain the ionization structure observed in the Niii/Nii and Neiii/Neii lines ratios. The model shows that the large scale ionization of the whole region can be accounted for by the UV radiation produced by the Quintuplet and the Arches cluster. Any other ionization mechanism should play a minor role. We also investigate the influence of the clusters on the bubble of warm dust (hereafter Radio Arc Bubble, RAB) seen in the Midcourse Space Experiment (MSX) infrared images. We nd that the warm dust is well correlated with the ionized gas indicating that the dust is also heated by the radiation from both clusters. Furthermore, the elliptical rather than circular symmetry of some structures like the Thermal Filaments can also be explained when one considers the combined eects of both the Arches and the Quintuplet clusters. We have also found that the RAB is lled with continuum emission of hard X-rays and with emission from the 6.4 keV line of neutral or low ionized Fe. We briefly discuss the implications of these ndings on the structure and morphology of the GCR interstellar medium and the possible origin of the RAB.

Large-Scale Grain Mantle Disruption in the Galactic Center

Cyanogen (NCCN) is the simplest member of the series of dicyanopolyynes. It has been hypothesized that this family of molecules can be important constituents of interstellar and circumstellar media, although the lack of a permanent electric dipole moment prevents its detection through radioastronomical techniques. Here we present the first solid evidence of the presence of cyanogen in interstellar clouds through the detection of its protonated form toward the cold dark clouds TMC-1 and L483. Protonated cyanogen (NCCNH+) has been identified through the J = 5 - 4 and J = 10 - 9 rotational transitions using the 40m radiotelescope of Yebes and the IRAM 30m telescope. We derive beam averaged column densities for NCCNH+ of (8.6 ± 4.4) × 1010 cm-2 in TMC-1 and (3.9 ± 1.8) × 1010 cm-2 in L483, which translate to fairly low fractional abundances relative to H2, in the range (1-10) × 10-12. The chemistry of protonated molecules in dark clouds is discussed, and it is found that, in general terms, the abundance ratio between the protonated and non protonated forms of a molecule increases with increasing proton affinity. Our chemical model predicts an abundance ratio NCCNH+/NCCN of ~ 10-4, which implies that the abundance of cyanogen in dark clouds could be as high as (1-10) × 10-8 relative to H2, i.e., comparable to that of other abundant nitriles such as HCN, HNC, and HC3N.

Large scale ionization of the Radio Arc region by the Quintuplet and the Arches clusters

Context. The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency’s Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet–satellite systems. Aims. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. Methods. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. Results. We achieved, on average, mHz precision (30 μm/s at a 10 s integration time) for radial three-way Doppler estimates and sub-nanoradian precision for lateral position measurements, which in a linear measure (at a distance of 1.4 AU) corresponds to ~50 m.

Probing non-polar interstellar molecules through their protonated form: Detection of protonated cyanogen (NCCNH+)

Aims. The phase scintillation of the European Space Agencys Venus Express (VEX) spacecraft telemetry signal was observed at X-band (lambda = 3.6 cm) with a number of radio telescopes of the European Very Long Baseline Interferometry (VLBI) Network in the period 2009-2013. Methods. We found a phase fluctuation spectrum along the Venus orbit with a nearly constant spectral index of -2.42 +/- 0.25 over the full range of solar elongation angles from 0 degrees to 45 degrees, which is consistent with Kolmogorov turbulence. Radio astronomical observations of spacecraft signals within the solar system give a unique opportunity to study the temporal behaviour of the signals phase fluctuations caused by its propagation through the interplanetary plasma and the Earths ionosphere. This gives complementary data to the classical interplanetary scintillation (IPS) study based on observations of the flux variability of distant natural radio sources. Results. We present here our technique and the results on IPS. We compare these with the total electron content for the line of sight through the solar wind. Finally, we evaluate the applicability of the presented technique to phase-referencing VLBI and Doppler observations of currently operational and prospective space missions.

Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos fly-by

In September 2016, the microquasar Cygnus X-3 underwent a giant radio flare, which was monitored for 6 days with the Medicina Radio Astronomical Station and the Sardinia Radio Telescope. Long observations were performed in order to follow the evolution of the flare on a hourly scale, covering six frequency ranges from 1.5 GHz to 25.6 GHz. The radio emission reached a maximum of 13.2 ± 0.7 Jy at 7.2 GHz and 10 ± 1 Jy at 18.6 GHz. Rapid flux variations were observed at high radio frequencies at the peak of the flare, together with rapid evolution of the spectral index: α steepened from 0.3 to 0.6 (with S

Observations and analysis of phase scintillation of spacecraft signal on the interplanetary plasma

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