- ID:
- ivo://CDS.VizieR/J/AJ/156/68
- Title:
- Comet C/2017 E4 composition with iSHELL at NASA/IRTF
- Short Name:
- J/AJ/156/68
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In 2017 April, we acquired comprehensive high-resolution spectra of newly discovered comet C/2017 E4 (Lovejoy) as it approached perihelion, and before its disintegration. We detected many cometary emission lines in the range (2.8-5.3) {mu}m, in four customized instrument settings (L1-c, L3, Lp1-c, and M1) of iSHELL - the new near-IR high-resolution immersion echelle spectrograph at NASA/IRTF (Maunakea, Hawaii). We identified 12 molecular species: nine primary volatiles (H_2_O, HCN, NH_3_, CO, C_2_H_2_, C_2_H_6_, CH_4_, CH_3_OH, H_2_CO) and three product species (CN, NH_2_, OH). We detected 85 H_2_O emission lines from 12 water vibrational bands across L1-c and M1 settings. The many detected water emission lines enabled retrieval of accurate measures for ortho- and para-H_2_O independently, thereby reducing systematic uncertainty in the derived ortho-para ratio and nuclear spin temperature. Excitation analyses and emission profile analyses were performed for all species, and molecular abundance ratios relative to water are compared with values found for other Oort Cloud comets in our infrared database. Abundance ratios are consistent for most species, with the exception of underabundant methanol and overabundant ammonia in E4.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/867/165
- Title:
- CO molecular clumps in Henize 2-10 dwarf galaxy
- Short Name:
- J/ApJ/867/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Atacama Large Millimeter/Submillimeter Array CO(3-2) observations at 0.3" resolution of He 2-10, a starburst dwarf galaxy and possible high-z galaxy analog. The warm dense gas traced by CO(3-2) is found in clumpy filaments that are kinematically and spatially distinct. The filaments have no preferred orientation or direction; this may indicate that the galaxy is not evolving into a disk galaxy. Filaments appear to be feeding the active starburst; the velocity field in one filament suggests acceleration onto an embedded star cluster. The relative strengths of CO(3-2) and radio continuum vary strongly on decaparsec scales in the starburst. There is no CO(3-2) clump coincident with the nonthermal radio source that has been suggested to be an AGN, nor unusual kinematics. The kinematics of the molecular gas show significant activity that is apparently unrelated to the current starburst. The longest filament, east of the starburst, has a pronounced shear of FWHM ~40km/s across its ~50pc width over its entire ~0.5kpc length. The cause of the shear is not clear. This filament is close in projection to a "dynamically distinct" CO feature previously seen in CO(1-0). The most complex region and the most highly disturbed gas velocities are in a region 200pc south of the starburst. The CO(3-2) emission there reveals a molecular outflow, of line width FWZI~120-140km/s, requiring an energy >~10^53^erg/s. There is at present no candidate for the driving source of this outflow.
- ID:
- ivo://CDS.VizieR/J/ApJ/883/158
- Title:
- Dark molecular gas in the Galaxy II. Perseus arm
- Short Name:
- J/ApJ/883/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results from a new, highly sensitive ({Delta}T_mb_~3mK) survey for thermal OH emission at 1665 and 1667MHz over a dense, 9x9pix grid covering a 1{deg}x1{deg} patch of sky in the direction of l=105.00{deg}, b=+2.50{deg} toward the Perseus spiral arm of our Galaxy. We compare our Green Bank Telescope 1667MHz OH results with archival ^12^CO(1-0) observations from the Five College Radio Astronomy Observatory Outer Galaxy Survey within the velocity range of the Perseus Arm at these galactic coordinates. Out of the 81 statistically independent pointings in our survey area, 86% show detectable OH emission at 1667MHz, and 19% of them show detectable CO emission. We explore the possible physical conditions of the observed features using a set of diffuse molecular cloud models. In the context of these models, both OH and CO disappear at current sensitivity limits below an A_v_ of 0.2, but the CO emission does not appear until the volume density exceeds 100-200cm^-3^. These results demonstrate that a combination of low column density A_v_ and low volume density n_H_ can explain the lack of CO emission along sight lines exhibiting OH emission. The 18cm OH main lines, with their low critical density of n*~1cm^-3^, are collisionally excited over a large fraction of the quiescent galactic environment and, for observations of sufficient sensitivity, provide an optically thin radio tracer for diffuse H_2_.
- ID:
- ivo://CDS.VizieR/J/ApJ/880/127
- Title:
- EMPIRE: IRAM 30m dense gas survey
- Short Name:
- J/ApJ/880/127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present EMPIRE, an IRAM 30m large program that mapped {lambda}=3-4mm dense gas tracers at ~1-2kpc resolution across the whole star-forming disk of nine nearby massive spiral galaxies. We describe the EMPIRE observing and reduction strategies and show new whole-galaxy maps of HCN(1-0), HCO^+^(1-0), HNC(1-0), and CO(1-0). We explore how the HCN-to-CO and IR-to-HCN ratios, observational proxies for the dense gas fraction and dense gas star formation efficiency, depend on host galaxy and local environment. We find that the fraction of dense gas correlates with stellar surface density, gas surface density, molecular-to-atomic gas ratio, and dynamical equilibrium pressure. In EMPIRE, the star formation rate per unit dense gas is anticorrelated with these same environmental parameters. Thus, although dense gas appears abundant in the central regions of many spiral galaxies, this gas appears relatively inefficient at forming stars. These results qualitatively agree with previous work on nearby galaxies and the Milky Way's Central Molecular Zone. To first order, EMPIRE demonstrates that the conditions in a galaxy disk set the gas density distribution and that the dense gas traced by HCN shows an environment-dependent relation to star formation. However, our results also show significant (+/-0.2dex) galaxy-to-galaxy variations. We suggest that gas structure below the scale of our observations and dynamical effects likely also play an important role.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/L2
- Title:
- First detection of HCOOH in TW Hya disk with ALMA
- Short Name:
- J/ApJ/862/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of asteroids, comets, and planets occurs in the interior of protoplanetary disks during the early phase of star formation. Consequently, the chemical composition of the disk might shape the properties of the emerging planetary system. In this context, it is crucial to understand whether and what organic molecules are synthesized in the disk. In this Letter, we report the first detection of formic acid (HCOOH) toward the TW Hydrae protoplanetary disk. The observations of the trans-HCOOH 6_(1,6)-5(1,5)_ transition were carried out at 129GHz with Atacama Large Millimeter/Submillimeter Array (ALMA). We measured a disk-averaged gas-phase t-HCOOH column density of ~(2-4)x10^12^cm^-2^, namely as large as that of methanol. HCOOH is the first organic molecule containing two oxygen atoms detected in a protoplanetary disk, a proof that organic chemistry is very active, albeit difficult to observe, in these objects. Specifically, this simplest acid stands as the basis for synthesis of more complex carboxylic acids used by life on Earth.
- ID:
- ivo://CDS.VizieR/J/A+A/656/A146
- Title:
- HCN and CN emission in Serpens Main region
- Short Name:
- J/A+A/656/A146
- Date:
- 21 Mar 2022 09:00:12
- Publisher:
- CDS
- Description:
- Ultraviolet radiation (UV) influences the physics and chemistry of star-forming regions, but its properties and significance in the immediate surroundings of low-mass protostars are still poorly understood. We aim to extend the use of the CN/HCN ratio, already established for high-mass protostars, to the low-mass regime to trace and characterize the UV field around low-mass protostars on ~0.6x0.6pc scales. The spatial distribution of HCN and CS are well-correlated with CO 6-5 emission that traces outflows. The CN emission is extended from the central protostars to their immediate surroundings also tracing outflows, likely as a product of HCN photodissociation. The ratio of CN to HCN total column densities ranges from ~1 to 12 corresponding to G_0_~10^1^-10^3^ for gas densities and temperatures typical for outflows of low-mass protostars. UV radiation associated with protostars and their outflows is indirectly identified in a significant part of the Serpens Main low-mass star-forming region. Its strength is consistent with the values obtained from the OH and H_2_O ratios observed with Herschel and compared with models of UV-illuminated shocks. From a chemical viewpoint, the CN to HCN ratio is an excellent tracer of UV fields around low- and intermediate-mass star-forming regions.
- ID:
- ivo://CDS.VizieR/J/other/ApSS/361.191
- Title:
- High-mass star forming clumps from MALT90
- Short Name:
- J/other/ApSS/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A total of 197 relatively isolated high-mass star-forming clumps were selected from the Millimeter Astronomy Legacy Team 90GHz (MALT90) survey data and their global chemical evolution investigated using four molecular lines, N_2_H^+^(1-0), HCO^+^(1-0), HCN(1-0), and HNC(1-0). The results suggest that the global averaged integrated intensity ratios I(HCO^+^)/I(HNC), I(HCN)/I(HNC), I(N_2_H^+^)/I(HCO^+^), and I(N_2_H^+^)/ I(HCN) are promising tracers for evolution of high-mass star-forming clumps. The global averaged column densities and abundances of N_2_H^+^, HCO^+^, HCN, and HNC increase as clumps evolve. The global averaged abundance ratios X(HCN)/X(HNC) could be used to trace evolution of high-mass star forming clumps, X(HCO^+^)/X(HNC) is more suitable for distinguishing high-mass star-forming clumps in prestellar (stage A) from those in protostellar (stage B) and HII/PDR region (stage C). These results suggest that the global averaged integrated intensity ratios between HCN(1-0), HNC(1-0), HCO^+^(1-0) and N_2_H^+^(1-0) are more suitable for tracing the evolution of high-mass star forming clumps. We also studied the chemical properties of the target high-mass star-forming clumps in each spiral arm of the Galaxy, and got results very different from those above. This is probably due to the relatively small sample in each spiral arm. For high-mass star-forming clumps in Sagittarius arm and Norma-Outer arm, comparing two groups located on one arm with different Galactocentric distances, the clumps near the Galactic Center appear to be younger than those far from the Galactic center, which may be due to more dense gas concentrated near the Galactic Center, and hence more massive stars being formed there.
- ID:
- ivo://CDS.VizieR/J/ApJ/847/67
- Title:
- High-resolution FIR spectrum of anti-vinyl alcohol
- Short Name:
- J/ApJ/847/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a detailed analysis of the high-resolution far-infrared spectrum of anti-vinyl alcohol, which has been previously identified toward Sagittarius B2(N). The {nu}_15_ OH torsional fundamental investigated here is more than 200cm^-1^ removed from the next nearest vibration, making it practically unperturbed and ideal to help refine the ground state rotational constants that were previously determined from 25 microwave lines. We assigned 1335 lines within the {nu}_15_ fundamental centered at 261.5512cm^-1^, with J and K_a_ ranges of 1-59 and 0-16, respectively. The microwave and far-infrared line positions were fit with Watson-type A- and S-reduced Hamiltonians, with the inclusion of quartic and select sextic distortion terms. This resulted in a significant refinement of the ground state constants, in addition to the determination of the {nu}_15_=1 state constants for the first time. The spectroscopic parameters are in good agreement with the results from anharmonic coupled-cluster calculations, and should be useful in searches for rotationally and/or vibrationally warm anti-vinyl alcohol in interstellar molecular clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A103
- Title:
- History independent tracers
- Short Name:
- J/A+A/658/A103
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Molecular line emission is a powerful probe of the physical conditions of astrophysical objects but can be complex to model and it is often unclear which transitions would be the best targets for observers who wish to constrain a given parameter. We produce a list of molecular species for which the gas history can be ignored, removing a major modelling complexity. We then determine the best of these species to observe in order to constrain various physical parameters. We use a large set of chemical models with different chemical histories to determine which species have abundances at 1 MYr which are insensitive to the initial conditions. We then use radiative transfer modelling to produce the intensity of every transition of these molecules. We finally compute the mutual information between the physical parameters and all transitions and transition ratios in order to rank their usefulness in determining the value of a given parameter. We find 48 species which are insensitive to the chemical history of the gas, 23 of which have collisional data available. We produce a ranked list of all transitions and ratios of these species by their mutual information with various gas properties. We show mutual information is an adequate measure of how well a transition can constrain a physical parameter by recovering known probes and demonstrating random forest regression models become more accurate predictors when high scoring features are included. Therefore, this list can be used to select target transitions for observations in order to maximise knowledge about those physical parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/658/A104
- Title:
- HL Tau SO2 14(0-14)-13(1,13) datacube
- Short Name:
- J/A+A/658/A104
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Planet-forming disks are not isolated systems. Their interaction with the surrounding medium affects their mass budget and chemical content. In the context of the ALMA-DOT program, we obtained high-resolution maps of assorted lines from six disks that are still partly embedded in their natal envelope. In this work, we examine the SO and SO_2_ emission that is detected from four sources: DG Tau, HL Tau, IRAS 04302+2247, and T Tau. The comparison with CO, HCO^+^, and CS maps reveals that the SO and SO_2_ emission originates at the intersection between extended streamers and the planet-forming disk. Two targets, DG Tau and HL Tau, offers clear cases of inflowing material inducing an accretion shock on the disk material. The measured rotational temperatures and radial velocities are consistent with this view. In contrast to younger Class 0 sources, these shocks are confined to the specific disk region impacted by the streamer. In HL Tau, the known accreting streamer induces a shock in the disk outskirt, and the released SO and SO_2_ molecules spiral toward the star in a few hundreds years. These results suggest that shocks induced by late accreting material may be common in the disks of young star-forming regions with possible consequences on the chemical composition and mass content of the disk. They also highlight the importance of SO and SO_2_ line observations to probe accretion shocks from a larger sample.
