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Register a new userFirst astronomical detection of the CF+ ion
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D. A. Neufeld
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We report the first astronomical detection of the CF+ (fluoromethylidynium) ion obtained by recent observations of its J = 1 - 0 (102.6 GHz), J = 2 - 1 (205.2 GHz), and J = 3 - 2 (307.7 GHz) pure rotational emissions toward the Orion Bar. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few x E-10 in UV-irradiated molecular regions where C+ is present. The measurements confirm the predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds.
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We report the first detection of the J = 1 - 0 (102.6 GHz) rotational lines of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive protostar of the Cygnus X region. This detection occurred as part of an unbiased spectral survey of this object in the 0.8-3 mm range, performed with the IRAM 30m telescope. The data were analyzed using a local thermodynamical equilibrium model (LTE model) and a population diagram in order to derive the column density. The line velocity (-4 km s-1) and line width (1.6 km s-1) indicate an origin from the collapsing envelope of the protostar. We obtain a CF+ column density of 4.10e11 cm-2. The CF+ ion is thought to be a good tracer for C+ and assuming a ratio of 10e-6 for CF+/C+, we derive a total number of C+ of 1.2x10e53 within the beam. There is no evidence of carbon ionization caused by an exterior source of UV photons suggesting that the protostar itself is the source of ionization. Ionization from the protostellar photosphere is not efficient enough. In contrast, X-ray ionization from the accretion shock(s) and UV ionization from outflow shocks could provide a large enough ionizing power to explain our CF+ detection. Surprisingly, CF+ has been detected towards a cold, massive protostar with no sign of an external photon dissociation region (PDR), which means that the only possibility is the existence of a significant inner source of C+. This is an important result that opens interesting perspectives to study the early development of ionized regions and to approach the issue of the evolution of the inner regions of collapsing envelopes of massive protostars. The existence of high energy radiations early in the evolution of massive protostars also has important implications for chemical evolution of dense collapsing gas and could trigger peculiar chemistry and early formation of a hot core.
The transition between atomic and molecular hydrogen is associated with important changes in the structure of interstellar clouds, and marks the beginning of interstellar chemistry. Because of the relatively simple networks controlling their abundances, molecular ions are usually good probes of the underlying physical conditions including for instance the fraction of gas in molecular form or the fractional ionization. In this paper we focus on three possible probes of the molecular hydrogen column density, HCO+, HOC+, and CF+. We presented high sensitivity ALMA absorption data toward a sample of compact HII regions and bright QSOs with prominent foreground absorption, in the ground state transitions of the molecular ions HCO+, HOC+, and CF+ and the neutral species HCN and HNC, and from the excited state transitions of C3H+(4-3) and 13CS(2-1). These data are compared with Herschel absorption spectra of the ground state transition of HF and p-H2O. We show that the HCO+, HOC+, and CF+ column densities are well correlated with each other. HCO+ and HOC+ are tightly correlated with p-H2O, while they exhibit a different correlation pattern with HF depending on whether the absorbing matter is located in the Galactic disk or in the central molecular zone. We report new detections of C3H+ confirming that this ion is ubiquitous in the diffuse matter, with an abundance relative to H2 of ~7E-11. We confirm that the CF+ abundance is lower than predicted by simple chemical models and propose that the rate of the main formation reaction is lower by a factor of about 3 than usually assumed. In the absence of CH or HF data, we recommend to use the ground state transitions of HCO+, CCH, and HOC+ to trace diffuse molecular hydrogen, with mean abundances relative to H2 of 3E-9, 4E-8 and 4E-11.
Young and close multiple systems are unique laboratories to probe the initial dynamical interactions between forming stellar systems and their dust and gas environment. Their study is a key building block to understanding the high frequency of main-sequence multiple systems. However, the number of detected spectroscopic young multiple systems that allow dynamical studies is limited. GW Orionis is one such system. It is one of the brightest young T Tauri stars and is surrounded by a massive disk. Our goal is to probe the GW Orionis multiplicity at angular scales at which we can spatially resolve the orbit. We used the IOTA/IONIC3 interferometer to probe the environment of GW Orionis with an astronomical unit resolution in 2003, 2004, and 2005. By measuring squared visibilities and closure phases with a good UV coverage we carry out the first image reconstruction of GW Ori from infrared long-baseline interferometry. We obtain the first infrared image of a T Tauri multiple system with astronomical unit resolution. We show that GW Orionis is a triple system, resolve for the first time the previously known inner pair (separation $rhosim$1.4 AU) and reveal a new more distant component (GW Ori C) with a projected separation of $sim$8 AU with direct evidence of motion. Furthermore, the nearly equal (2:1) H-band flux ratio of the inner components suggests that either GW Ori B is undergoing a preferential accretion event that increases its disk luminosity or that the estimate of the masses has to be revisited in favour of a more equal mass-ratio system that is seen at lower inclination. Accretion disk models of GW Ori will need to be completely reconsidered because of this outer companion C and the unexpected brightness of companion B.
We report the first extragalactic detection of CF+, the fluoromethylidynium ion, in the z=0.89 absorber toward PKS1830-211. We estimate an abundance of ~3E-10 relative to H2 and that ~1% of fluorine is captured in CF+. The absorption line profile of CF+ is found to be markedly different from that of other species observed within the same tuning, and is notably anti-correlated with CH3OH. On the other hand, the CF+ profile resembles that of [C I]. Our results are consistent with expected fluorine chemistry and point to chemical differentiation in the column of absorbing gas.
We discuss the first astronomical detection of the CF+ (fluoromethylidynium) ion, obtained by observations of the J=1-0 (102.6 GHz), J=2-1 (205.2 GHz) and J=3-2 (307.7 GHz) rotational transitions toward the Orion Bar region. Our search for CF+, carried out using the IRAM 30m and APEX 12m telescopes, was motivated by recent theoretical models that predict CF+ abundances of a few times 1.E-10 in UV-irradiated molecular regions where C+ is present. The CF+ ion is produced by exothermic reactions of C+ with HF. Because fluorine atoms can react exothermically with H2, HF is predicted to be the dominant reservoir of fluorine, not only in well-shielded regions but also in the surface layers of molecular clouds where the C+ abundance is large. The observed CF+ line intensities imply the presence of CF+ column densities of at least 1.E+12 cm-2 over a region of size at least ~ 1 arcmin, in good agreement with theoretical predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds and widely detectable in absorption by future satellite and airborne observatories.
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