- ID:
- ivo://CDS.VizieR/J/A+A/612/A48
- Title:
- 4 oxygen-rich evolved stars NH3 spectra
- Short Name:
- J/A+A/612/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The circumstellar ammonia (NH_3_) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH_3_ abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry. We would like to characterise the spatial distribution and excitation of NH_3_ in the oxygen-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420. We observed NH_3_ emission from the ground state in the inversion transitions near 1.3cm with the Very Large Array (VLA) and submillimetre rotational transitions with the Heterodyne Instrument for the Far-Infrared (HIFI) aboard Herschel Space Observatory from all four targets. For IK Tau and VY CMa, we observed NH_3_ rovibrational absorption lines in 2 band near 10.5um with the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF).We also attempted to search for the rotational transition within the excited vibrational state (v_2_=1) near 2mm with the IRAM 30m Telescope. Non-LTE radiative transfer modelling, including radiative pumping to the vibrational state, was carried out to derive the radial distribution of NH_3_ in the CSEs of these targets. We detected NH_3_ inversion and rotational emission in all four targets. IK Tau and VY CMa show blueshifted absorption in the rovibrational spectra. We did not detect vibrationally excited rotational transition from IK Tau. Spatially resolved VLA images of IK Tau and IRC +10420 show clumpy emission structures; unresolved images of VY CMa and OH 231.8+4.2 indicate that the spatial-kinematic distribution of NH_3_ is similar to that of assorted molecules, such as SO and SO2, that exhibit localised and clumpy emission. Our modelling shows that the NH_3_ abundance relative to molecular hydrogen is generally of the order of 10^-7^, which is a few times lower than previous estimates that were made without considering radiative pumping and is at least ten times higher than that in the carbon-rich CSE of IRC +10216. NH_3_ in OH 231.8+4.2 and IRC +10420 is found to emit in gas denser than the ambient medium. Incidentally, we also derived a new period of IK Tau from its V-band light curve. NH_3_ is again detected in very high abundance in evolved stars, especially the oxygen-rich ones. Its emission mainly arises from localised spatial-kinematic structures that are probably denser than the ambient gas. Circumstellar shocks in the accelerated wind may contribute to the production of NH_3_. Future mid-infrared spectroscopy and radio imaging studies are necessary to constrain the radii and physical conditions of the formation regions of NH_3_.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/899/15
- Title:
- Parameters for the 58 {tau}HI(v) sightlines
- Short Name:
- J/ApJ/899/15
- Date:
- 14 Mar 2022 07:09:23
- Publisher:
- CDS
- Description:
- Resolving the phase structure of neutral hydrogen (HI) is crucial for understanding the life cycle of the interstellar medium (ISM). However, accurate measurements of HI temperature and density are limited by the availability of background continuum sources for measuring HI absorption. Here we test the use of deep learning for extracting HI properties over large areas without optical depth information. We train a 1D convolutional neural network using synthetic observations of 3D numerical simulations of the ISM to predict the fraction (f_CNM_) of cold neutral medium (CNM) and the correction to the optically thin HI column density for optical depth (R_H_I__) from 21cm emission alone. We restrict our analysis to high Galactic latitudes (|b|>30{deg}), where the complexity of spectral line profiles is minimized. We verify that the network accurately predicts f_CNM_ and R_H_I__ by comparing the results with direct constraints from 21cm absorption. By applying the network to the GALFA-HI survey, we generate large-area maps of f_CNM_ and R_H_I__. Although the overall contribution to the total HI column of CNM-rich structures is small (~5%), we find that these structures are ubiquitous. Our results are consistent with the picture that small-scale structures observed in 21cm emission aligned with the magnetic field are dominated by CNM. Finally, we demonstrate that the observed correlation between HI column density and dust reddening (E(B-V)) declines with increasing R_H_I__, indicating that future efforts to quantify foreground Galactic E(B-V) using HI, even at high latitudes, should increase fidelity by accounting for HI phase structure.
- ID:
- ivo://CDS.VizieR/J/ApJ/796/36
- Title:
- PH_2_CN/CH_3_PH_2_ rotational transition frequency
- Short Name:
- J/ApJ/796/36
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Millimeter/submillimeter spectra of PH_2_CN(~{X} ^1^A') and CH_3_PH_2_(~{X} ^1^A') have been recorded for the first time using direct absorption techniques. This work extends previous measurements of both molecules beyond the 10-50 GHz range. Both species were created in the presence of an AC discharge by the reaction of phosphorus vapor and either cyanogen and hydrogen (PH_2_CN) or methane (CH_3_PH_2_). Twelve rotational transitions of PH_2_CN were recorded over the region 305-422 GHz for asymmetry components K_a_=0 through 8. For CH_3_PH_2_, eight rotational transitions were measured from 210-470 GHz with K_a_=0 through 16; these spectra exhibited greater complexity due to the presence of internal rotation, which splits the K_a_=1, 2, and 3 asymmetry components into A and E states. Combined analyses of the millimeter/submillimeter and previous microwave data were performed for both molecules. For PH_2_CN, the spectra were fit with a Watson S-reduced asymmetric top Hamiltonian, resulting in more accurate rotational and centrifugal distortion constants. In the case of CH_3_PH_2_, an asymmetric top internal-rotation Hamiltonian was employed in the analysis, significantly improving the rotational and torsional parameters over previous microwave estimates. Searches for both molecules were subsequently conducted toward Sgr B2(N), using the 12 m telescope of the Arizona Radio Observatory (ARO). Neither species was identified, with abundance upper limits, relative to H_2_, of f(PH_2_CN/H_2_)<7.0x10^-12^ and f(CH_3_PH_2_/H_2_)<8.4x10^-12^. The nitrogen analogs NH_2_CN and CH_3_NH_2_ are therefore more abundant in Sgr B2(N) by factors of >2 and >200, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A86
- Title:
- PILS-Cygnus. observations of CygX-N30
- Short Name:
- J/A+A/655/A86
- Date:
- 10 Mar 2022 07:33:06
- Publisher:
- CDS
- Description:
- Complex organic molecules (COMs) are commonly detected in and near star-forming regions. However, the dominant process in the release of these COMs from the icy grains -- where they predominately form -- to the gas phase is still an open question. We investigate the origin of COM emission in a high-mass protostellar source, CygX-N30 MM1, through high-angular-resolution interferometric observations over a continuous broad frequency range. We used 32 GHz Submillimeter Array (SMA) observations with continuous frequency coverage from 329 to 361GHz at an angular resolution of ~1'' to do a line survey and obtain a chemical inventory of the source. The line emission in the frequency range was used to determine column densities and excitation temperatures for the COMs. We also mapped out the intensity distribution of the different species. We identified approximately 400 lines that can be attributed to 29 different molecular species and their isotopologues. We find that the molecular peak emission is along a linear gradient, and coincides with the axis of red- and blue- shifted H_2_CO and CS emission. Chemical differentiation is detected along this gradient, with the O-bearing molecular species peaking towards one component of the system and the N- and S-bearing species peaking towards the other. The chemical gradient is offset from but parallel to the axis through the two continuum sources. The inferred column densities and excitation temperatures are compared to other sources where COMs are abundant. Only one deuterated molecule is detected, HDO, while an upper limit for CH_2_DOH is derived, leading to a D/H ratio of <0.1%. We conclude that the origin of the observed COM emission is probably a combination of the young stellar sources along with accretion of infalling material onto a disc-like structure surrounding a young protostar and located close to one of the continuum sources. This disc and protostar are associated with the O-bearing molecular species, while the S- and N- bearing species on the other hand are associated with the other continuum core, which is probably a protostar that is slightly more evolved than the other component of the system. The low D/H ratio likely reflects a pre- stellar phase where the COMs formed on the ices at warm temperatures (~30K), where the deuterium fractionation would have been inefficient. The observations and results presented here demonstrate the importance of good frequency coverage and high angular resolution when disentangling the origin of COM emission.
- ID:
- ivo://CDS.VizieR/J/A+A/637/A7
- Title:
- PKS1830-211 HDO, ND and NH_2_D spectra
- Short Name:
- J/A+A/637/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Deuterium and lithium are light elements of high cosmological and astrophysical importance. In this work we report the first detection of deuterated molecules and a search for lithium hydride, ^7^LiH, at redshift z=0.89 in the spiral galaxy intercepting the line of sight to the quasar PKS 1830-211. We used ALMA to observe several submillimeter lines of ND, NH_2_D, and HDO, and their related isotopomers NH_2_, NH_3_, and H^18^_2_O, in absorption against the southwest image of the quasar, allowing us to derive XD/XH abundance ratios. The absorption spectra mainly consist of two distinct narrow velocity components for which we find remarkable differences. One velocity component shows XD/XH abundances that is about 10 times larger than the primordial elemental D/H ratio, and no variability of the absorption profile during the time span of our observations. In contrast, the other component shows a stronger deuterium fractionation. Compared to the first component, this second component has XD/XH abundances that are 100 times larger than the primordial D/H ratio, a deepening of the absorption by a factor of two within a few months, and a rich chemical composition, with relative enhancements of N_2_H^+^, CH_3_OH, SO_2_ and complex organic molecules. We therefore speculate that this component is associated with the analog of a Galactic dark cloud, while the first component is likely more diffuse. Our search for the ^7^LiH (1-0) line was unsuccessful and we derive an upper limit ^7^LiH/H_2_=4x10^-13^ (3{sigma}) in the z=0.89 absorber toward PKS 1830.211. Besides, with ALMA archival data, we could not confirm the previous tentative detections of this line in the z=0.68 absorber toward B0218+357; we derive an upper limit ^7^LiH/H_2_=5x10^-11^ (3{sigma}), although this is less constraining than our limit toward PKS 1830.211. We conclude that, as in the Milky Way, only a tiny fraction of lithium nuclei are possibly bound in LiH in these absorbers at intermediate redshift.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A174
- Title:
- PKS J1209-2032 & CGRaBS J1549+5038 radio spectra
- Short Name:
- J/A+A/643/A174
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detection of HI 21-cm absorption in a member of the rare and recently discovered class of compact radio sources, "Extremely Inverted Spectrum Extragalactic Radio Sources (EISERS)" . EISERS conceivably form a special sub-class of the inverted spectrum radio galaxies since the spectral index of the optically thick part of the spectrum for these sources crosses the synchrotron self absorption limit of {alpha}=+2.5 (S({nu}) {prop.to} {nu}^{alpha}^). We have searched for HI absorption in two EISERS using the recently upgraded Giant Metrewave Radio Telescope (uGMRT) and detected an absorption feature in one of them. The strong associated HI absorption detected against the source J1209-2032 (z=0.4040) implies an optical depth of 0.178+/-0.02 corresponding to an HI column density of 34.8+/-2.9x10^20^cm^-2^, for an assumed HI spin temperature of 100K and covering factor of 1. This is among the highest known optical depth and HI column densities found for compact radio sources of peaked spectrum type and supports the free-free absorption model for the steeply inverted radio spectrum of this source. For the other source, J1549+5038 (z=2.171), no HI absorption was detected in our observations.
- ID:
- ivo://CDS.VizieR/J/A+A/648/A116
- Title:
- PKS 1830-211 OH and HI spectra
- Short Name:
- J/A+A/648/A116
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The Large Survey Project (LSP) "MeerKAT Absorption Line Survey" (MALS) is a blind HI 21-cm and OH 18-cm absorption line survey in the L- and UHF-bands, with the primary goal to better determine the occurrence of atomic and molecular gas in the circumgalactic and inter-galactic medium, and its redshift evolution. Here we present the first results using the UHF-band, obtained towards the strongly lensed radio source PKS 1830-211, detecting absorption produced by the lensing galaxy. With merely 90 mins of data acquired on-source for science verification and processed using the Automated Radio Telescope Imaging Pipeline (ARTIP), we detect in absorption the known HI 21-cm and OH 18-cm main lines at z=0.89 at an unprecedented signal-to-noise ratio (4000 in the continuum, in each 6km/s wide channel). For the first time we report the detection at z=0.89 of OH satellite lines, so far not detected at z>0.25. We decompose the OH lines into a thermal and a stimulated contribution, where the 1612 and 1720MHz lines are conjugate. The total OH 1720MHz emission line luminosity is 6100L_{sun}_. This is the most luminous known 1720MHz maser line. It is also among the highest luminosities for the OH-main lines megamasers. The absorption components of the different images of the background source sample different light paths in the lensing galaxy, and their weights in the total absorption spectrum are expected to vary in time, on daily and monthly time scales. We compare our normalized spectra with those obtained more than 20yrs ago, and find no variation, in spite of the high signal-to-noise ratios. We interpret the absorption spectra with the help of a lens galaxy model, derived from an N-body hydro-dynamical simulation, with a morphology similar to its optical HST image. The resulting absorption lines depend mainly on the background continuum, and the radial distribution of the gas surface density, for each atomic /molecular species.We show that it is possible to reproduce the observations assuming a realistic spiral galaxy disk, without invoking any central gas outflows. There are, however, distinct and faint high-velocity features in the ALMA millimeter absorption spectra, that most likely originate from high-velocity clouds or tidal features. These clouds may contribute to broaden the Hi and OH spectra.
- ID:
- ivo://CDS.VizieR/J/ApJS/218/30
- Title:
- Propenal (CH_2_CHCHO) transition frequencies
- Short Name:
- J/ApJS/218/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Since interstellar detection of propenal is only based on two rotational transitions in the centimeter wave region, its high resolution rotational spectrum has been measured up to 660GHz and fully characterized by assignment of more than 12000 transitions to provide direct laboratory data to the astronomical community. Spectral assignments and analysis include transitions from the ground state of the trans and cis isomers, three trans-^13^C isotopologues, and ten excited vibrational states of the trans form. Combining new millimeter and submillimeter data with those from the far-infrared region has yielded the most precise set of spectroscopic constants of trans-propenal obtained to date. Newly determined rotational constants, centrifugal distortion constants, vibrational energies, and Coriolis and Fermi interaction constants are given with high accuracy and were used to predict transition frequencies and intensities over a wide frequency range. Results of this work should facilitate astronomers further observation of propenal in the interstellar medium.
- ID:
- ivo://CDS.VizieR/J/AJ/157/144
- Title:
- Protoplanetary disk masses in Taurus
- Short Name:
- J/AJ/157/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Measuring the masses of protoplanetary disks is crucial for understanding their planet-forming potential. Typically, dust masses are derived from (sub-)millimeter flux density measurements plus assumptions for the opacity, temperature, and optical depth of the dust. Here we use radiative transfer models to quantify the validity of these assumptions with the aim of improving the accuracy of disk dust mass measurements. We first carry out a controlled exploration of disk parameter space. We find that the disk temperature is a strong function of disk size, while the optical depth depends on both disk size and dust mass. The millimeter-wavelength spectral index can be significantly shallower than the naive expectation due to a combination of optical depth and deviations from the Rayleigh-Jeans regime. We fit radiative transfer models to the spectral energy distributions (SEDs) of 132 disks in the Taurus-Auriga region using a Markov chain Monte Carlo approach. We used all available data to produce the most complete SEDs used in any extant modeling study. We perform the fitting twice: first with unconstrained disk sizes and again imposing the disk size-brightness relation inferred for sources in Taurus. This constraint generally forces the disks to be smaller, warmer, and more optically thick. From both sets of fits, we find disks to be ~1-5 times more massive than when derived using (sub-)millimeter measurements and common assumptions. With the uncertainties derived from our model fitting, the previously measured dust mass-stellar mass correlation is present in our study but only significant at the 2{sigma} level.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A164
- Title:
- Protoplanetary nebulae and young PN CO spectra
- Short Name:
- J/A+A/649/A164
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fast outflows and their interaction with slow shells (generally known as the fossil circumstellar envelope of asymptotic giant branch stars) play an important role in the structure and kinematics of protoplanetary and planetary nebulae (pPNe, PNe). To properly study their effects within these objects, we also need to observe the intermediate-temperature gas, which is only detectable in the far-infrared (FIR) and submillimetre (submm) transitions. We study the physical conditions of the outflows presented in a number of pPNe and PNe, with a focus on their temperature and excitation states. We carried out Herschel/HIFI observations in the submm lines of 12CO in nine pPNe and nine PNe and complemented them with low-J CO spectra obtained with the IRAM 30m telescope and taken from the literature. The spectral resolution of HIFI allows us to identify and measure the different nebular components in the line profiles. The comparison with large velocity gradient (LVG) model predictions was used to estimate the physical conditions of the warm gas in the nebulae, such as excitation conditions, temperature, and density. We found high kinetic temperatures for the fast winds of pPNe, typically reaching between 75K and 200K. In contrast, the high-velocity gas in the sampled PNe is colder, with characteristic temperatures between 25K and 75K, and it is found in a lower excitation state. We interpret this correlation of the kinetic temperature and excitation state of fast outflows with the amount of time elapsed since their acceleration (probably driven by shocks) as a consequence of the cooling that occurred during the pPN phase.
