Molecular ions in the O-rich evolved star OH231.8+4.2: HCO$^+$,H$^{13}$CO$^+$ and first detection of SO$^+$, N$_2$H$^+$, and H$_3$O$^+$
C. Sánchez Contreras, L. Velilla Prieto, M. Agúndez, J. Cernicharo, G. Quintana-Lacaci, V. Bujarrabal, J. Alcolea, J. R. Goicoechea, F. Herpin, K. M. Menten, F. Wyrowski
OH 231.8+4.2, a bipolar outflow around a Mira-type variable star, displays a unique molecular richness amongst circumstellar envelopes (CSEs) around O-rich AGB and post-AGB stars. We report line observations of the HCO+ and H13CO+ molecular ions and the first detection of SO+, N2H+, and (tentatively) H3O+ in this source. SO+ and H3O+ have not been detected before in CSEs around evolved stars. These data have been obtained as part of a full mm-wave and far-IR spectral line survey carried out with the IRAM 30 m radio telescope and with Herschel/HIFI. Except for H3O+, all the molecular ions detected in this work display emission lines with broad profiles (FWHM 50-90 km/s), which indicates that these ions are abundant in the fast bipolar outflow of OH 231.8. The narrow profile (FWHM 14 km/s) and high critical densities (>1e6cm-3 ) of the H3O+ transitions observed are consistent with this ion arising from denser, inner (and presumably warmer) layers of the fossil remnant of the slow AGB CSE at the core of the nebula. From rotational diagram analysis, we deduce excitation temperatures of Tex 10-20 K for all ions except for H3O+, which is most consistent with Tex 100 K. Although uncertain, the higher excitation temperature suspected for H3O+ is similar to that recently found for H2O and a few other molecules, which selectively trace a previously unidentified, warm nebular component.The column densities of the molecular ions reported here are in the range Ntot [1-8]x1e13 cm-2, leading to beam-averaged fractional abundances relative to H2 of X(HCO+) 1e-8, X(H13CO+) 2e-9, X(SO+) 4e-9, X(N2H+) 2e-9, and X(H3O+) 7e-9 cm-2. We have performed chemical kinetics models to investigate the formation of these ions in OH 231.8 as the result of standard gas phase reactions initiated by cosmic-ray and UV-photon ionization. (abridged).
Context. The deuterium fraction in low-mass prestellar cores is a good diagnostic indicator of the initial phases of star formations, and it is also a fundamental quantity to infer the ionisation degree in these objects. Aims. With the analysis of multiple transitions of $\rm N_2H^+$, $\rm N_2D^+$, $\rm HC^{18}O^+$ and $\rm DCO^+$ we are able to determine the molecular column density maps and the deuterium fraction in $\rm N_2H^+$ and $\rm HCO^+$ toward the prototypical prestellar core L1544. This is the preliminary step to derive the ionisation degree in the source. Methods. We use a non-loca…
JWST Observations of Young protoStars (JOYS+): Detection of icy complex organic molecules and ions. I. CH$_4$, SO$_2$, HCOO$^-$, OCN$^-$, H$_2$CO, HCOOH, CH$_3$CH$_2$OH, CH$_3$CHO, CH$_3$OCHO, CH$_3$COOH
Ions and electrons play an important role in various stages of the star formation process. By following the magnetic field of their environment and interacting with neutral species, they slow down the gravitational collapse of the proto-star envelope. This process (known as ambipolar diffusion) depends on the ionisation degree, which can be derived from the \hco abundance. We present a study of \hco and its isotopologues (H$^{13}$CO$^+$, HC$^{18}$O$^+$, DCO$^+$, and H$^{13}$CO$^+$) in the low-mass proto-star IRAS16293$-$2422. The structure of this object is complex, and the HCO$^+$ emission ar…
The first stable object to develop in the low-mass star formation process has long been predicted to be the first hydrostatic core (FHSC). Despite much effort, it has still yet to be definitively observed in nature. More specific observational signatures are required to enable observers to distinguish the FHSC from young, faint, but more evolved protostars. Here we present synthetic spectral line observations for CO, SO, CS and HCO$^+$ that were calculated from radiation (magneto)hydrodynamical models, chemical modelling and Monte Carlo radiative transfer. HCO$^+$ $(1-0)$ and SO $(8_7 - 7_6)$ …
Magnetic fields play a role in the dynamics of many astrophysical processes, but they are hard to detect. In a partially ionized plasma, a magnetic field works directly on the ionized medium but not on the neutral medium, which gives rise to a velocity drift between them: ambipolar diffusion. This process is suggested to be important in the process of star formation, but has never been directly observed. We introduce a method that could be used to detect ambipolar diffusion and the magnetic field that gives rise to it, where we exploit the velocity drift between the charged and neutral medium.…
HyGAL: Characterizing the Galactic ISM with observations of hydrides and other small molecules. III. The absorption lines of [O I], CH, and OH
I. Physikalisches Institut, Universität zu Köln（科隆大学第一物理研究所）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）；William H. Miller III Department of Physics & Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学威廉·H·米勒三世物理与天文学系）；Department of Physics & Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文学系）；LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités（巴黎天文台LERMA实验室（隶属PSL研究大学、CNRS、索邦大学））；Department of Astronomy, University of Maryland（马里兰大学天文学系）；Liant（利安特研究所）；Department of Physics, Graduate School of Science, Nagoya University（名古屋大学理学研究科物理学系）
The nature of the gas in CO-rich debris discs remains poorly understood, as it could either be a remnant from the earlier Class II phase or of secondary origin, driven by the destruction of icy planetesimals. The aim of this paper was to elucidate the origin of the gas content in the debris discs via various simple molecules that are often detected in the less-evolved Class II discs. We present millimetre molecular line observations of nine circumstellar discs around A-type stars: four CO-rich debris discs (HD 21997, HD 121617, HD 131488, HD 131835) and five old Herbig Ae protoplanetary discs …
{CircumStellar Envelopes (CSEs) of stars are complex chemical objects for which theoretical models encounter difficulties in elaborating a comprehensive overview of the occurring chemical processes. Along with photodissociation, ion-neutral reactions and dissociative recombination might play an important role in controlling molecular growth in outer CSEs. The aim of this work is to provide experimental insights into pathways of photochemistry-driven molecular growth within outer CSEs to draw a more complete picture of the chemical processes occurring within these molecule-rich environments. A …
Gas accretion is a key process in star formation. However, the gas infall detections in high-mass star forming regions with high-spatial resolution observations are rare. Here we report the detection of gas infall towards a cometary ultracompact H{\sc ii} region "C" in G34.26+0.15 complex. The hot core associated with "C" has a mass of $\sim$76 M$_{\sun}$ and a volume density of 1.1$\times10^{8}$ cm$^{-3}$. The HCN (3--2), HCO$^{+}$ (1--0) lines observed by single-dishes and the CN (2--1) lines observed by the SMA show redshifted absorption features, indicating gas infall. We found a linear re…
Anomalies in the abundance measurements of short lived radionuclides in meteorites indicate that the protosolar nebulae was irradiated by a high amount of energetic particles (E$\gtrsim$10 MeV). The particle flux of the contemporary Sun cannot explain these anomalies. However, similar to T Tauri stars the young Sun was more active and probably produced enough high energy particles to explain those anomalies. We want to study the interaction of stellar energetic particles with the gas component of the disk and identify possible observational tracers of this interaction. We use a 2D radiation th…
We present the results of a spectral-line survey of the W51e1/e2 star-forming region at 68-88 GHz. 79 molecules and their isotopologues were detected, from simple diatomic or triatomic molecules, such as SO, SiO, and CCH, to complex organic compounds, such as CH$_3$OCH$_3$ or CH$_3$COCH$_3$. A number of lines that are absent from the Lovas list of molecular lines observed in space were detected, and most of these were identified. A significant number of the detected molecules are typical for hot cores. These include the neutral molecules HCOOCH$_3$, CH$_3$CH$_2$OH, CH$_3$COCH$_3$ etc, which ar…
Infrared dark clouds (IRDCs) are cold, dense regions of the interstellar medium (ISM) that are likely to represent the initial conditions for massive star formation. It is thus important to study the physical and chemical conditions of IRDCs to provide constraints and inputs for theoretical models of these processes. We aim to determine the astrochemical conditions, especially cosmic ray ionisation rate (CRIR) and chemical age, in different regions of the massive IRDC G28.37+00.07 by comparing observed abundances of multiple molecules and molecular ions with the predictions of astrochemical mo…
