IRAS 16293-2422: Evidence for Infall onto a Counter-Rotating Protostellar Accretion Disk

We report high spatial resolution VLA observations of the low-mass star-forming region IRAS 16293-2422 using four molecular probes: ethyl cyanide (CH$_3$CH$_2$CN), methyl formate (CH$_3$OCHO), formic acid (HCOOH), and the ground vibrational state of silicon monoxide (SiO). Ethyl cyanide emiss ion has a spatial scale of $\sim20''$ and encompasses binary cores A and B as determined by continuum emission peaks. Surrounded by formic acid emission, methyl formate emission has a spatial scale of $\sim6''$and is confined to core B. SiO emission shows two velocity components with spatial scales less than 2$''$ that map $\sim2''$ northeast of the A and B symmetry axis. The redshifted SiO is $\sim2''$ northwest of blueshifted SiO along a position angle of $\sim135^o$ which is approximately parallel to the A and B symmetry axis. We interpret the spatial position offset in red and blueshifted SiO emission as due to rotation of a protostellar accretion disk and we derive $\sim$1.4 M$_{\odot}$ interior to the SiO emission. In the same vicinity, Mundy et al. (1986) also concluded rotation of a nearly edge-on disk from OVRO observations of much stronger and ubiquitous $^{13}$CO emission but the direction of rotation is opposite to the SiO emission findings. Taken together, SiO and $^{13}$CO data suggest evidence for a counter-rotating disk. Moreover, archival BIMA array $^{12}$CO data show an inverse P Cygni profile with the strongest absorption in close proximity to the SiO emission, indicating unambiguous material infall toward the counter-rotating protostellar disk at a new source location within the IRAS 16293-2422 complex. The details of these observations and our interpretations are discussed.Comment: 18 pages, 5 figures, accepted for publication in the Astrophysical Journa

A Search for Hydroxylamine (NH2OH) toward Select Astronomical Sources

Observations of 14 rotational transitions of hydroxylamine (NH2OH) using the NRAO 12 m Telescope on Kitt Peak are reported towards IRC+10216, Orion KL, Orion S, Sgr B2(N), Sgr B2(OH), W3IRS5, and W51M. Although recent models suggest the presence of NH2OH in high abundance, these observations resulted in non-detection. Upper limits are calculated to be as much as six orders of magnitude lower than predicted by models. Possible explanations for the lower than expected abundance are explored.Comment: 18 pages, 3 figures, 3 table

A Search for Hydroxylamine (NH_2OH) toward Select Astronomical Sources

Observations of 14 rotational transitions of hydroxylamine (NH_2OH) using the NRAO 12 m telescope on Kitt Peak are reported toward IRC+10216, Orion KL, Orion S, Sgr B2(N), Sgr B2(OH), W3IRS5, and W51M. Although recent models suggest the presence of NH_2OH in high abundance, these observations resulted in non-detection. Upper limits are calculated to be as much as six orders of magnitude lower than those predicted by models. Possible explanations for the lower-than-expected abundance are explored

Weak maser emission of methyl formate toward Sagittarius B2(N) in the Green Bank Telescope PRIMOS Survey

A non-LTE radiative transfer treatment of cis-methyl formate (HCOOCH3) rotational lines is presented for the first time using a set of theoretical collisional rate coefficients. These coefficients have been computed in the temperature range 5-30 K by combining coupled-channel scattering calculations with a high accuracy potential energy surface for HCOOCH3-He. The results are compared to observations toward the Sagittarius B2(N) molecular cloud using the publicly available PRIMOS survey from the Green Bank Telescope. A total of 49 low-lying transitions of methyl formate, with upper levels below 25 K, are identified. These lines are found to probe a presumably cold (~30 K), moderately dense (~1e4 cm-3) and extended region surrounding Sgr B2(N). The derived column density of ~4e14 cm-2 is only a factor of ~10 larger than the column density of the trans conformer in the same source. Provided that the two conformers have the same spatial distribution, this result suggests that strongly non-equilibrium processes must be involved in their synthesis. Finally, our calculations show that all detected emission lines with a frequency below 30 GHz are (collisionally pumped) weak masers amplifying the continuum of Sgr B2(N). This result demonstrates the importance and generality of non-LTE effects in the rotational spectra of complex organic molecules at centimetre wavelengths.Comment: 33 pages, 9 figures, accepted in The Astrophysical Journal (january 4 2014

First Acetic Acid Survey with CARMA in Hot Molecular Cores

Acetic acid (CH$_3$COOH) has been detected mainly in hot molecular cores where the distribution between oxygen (O) and nitrogen (N) containing molecular species is co-spatial within the telescope beam. Previous work has presumed that similar cores with co-spatial O and N species may be an indicator for detecting acetic acid. However, does this presumption hold as higher spatial resolution observations become available of large O and N-containing molecules? As the number of detected acetic acid sources is still low, more observations are needed to support this postulate. In this paper, we report the first acetic acid survey conducted with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at 3 mm wavelengths towards G19.61-0.23, G29.96-0.02 and IRAS 16293-2422. We have successfully detected CH$_3$COOH via two transitions toward G19.61-0.23 and tentatively confirmed the detection toward IRAS 16293-2422 A. The determined column density of CH$_3$COOH is 2.0(1.0)$\times 10^{16}$ cm$^{-2}$ and the abundance ratio of CH$_3$COOH to methyl formate (HCOOCH$_3$) is 2.2(0.1)$\times 10^{-1}$ toward G19.61-0.23. Toward IRAS 16293 A, the determined column density of CH$_3$COOH is $\sim$ 1.6 $\times 10^{15}$ cm$^{-2}$ and the abundance ratio of CH$_3$COOH to methyl formate (HCOOCH$_3$) is $\sim$ 1.0 $\times 10^{-1}$ both of which are consistent with abundance ratios determined toward other hot cores. Finally, we model all known line emission in our passband to determine physical conditions in the regions and introduce a new metric to better reveal weak spectral features that are blended with stronger lines or that may be near the 1-2$\sigma$ detection limit.Comment: 28 pages, 8 figures, accepted for publication in the ApJ; Revised citation in session 2, references remove

Cyclopropenone (c-H2C3O): A New Interstellar Ring Molecule

The three-carbon keto ring cyclopropenone (c-H2C 3O) has been detected largely in absorption with the 100 m Green Bank Telescope (GBT) toward the star-forming region Sagittarius B2(N) by means of a number of rotational transitions between energy levels that have energies less than 10 K. Previous negative results from searches for interstellar c-H2C3O by other investigators attempting to detect rotational transitions that have energy levels ~10 K or greater indicate no significant hot core component. Thus, we conclude that only the low-energy levels of c-H2C3O are populated because the molecule state temperature is low, suggesting that c-H2C3O resides in a star-forming core halo region that has a widespread arcminute spatial scale. Toward Sagittarius B2(N), the GBT was also used to observe the previously reported, spatially ubiquitous, three-carbon ring cyclopropenylidene (c-C3H2 ), which has a divalent carbon that makes it highly reactive in the laboratory. The presence of both c-C3H2 and c-H2C3O toward Sagittarius B2(N) suggests that gas-phase oxygen addition may account for the synthesis of c-H 2C3O from c-C3H2. We also searched for but did not detect the three-carbon sugar glyceraldehyde (CH2OHCHOHCHO)

INTERSTELLAR FORMALDEHYDE - A RETROSPECTIVE

On 31 March 1969, the era of modern radio astrochemistry started with the detection of interstellar formaldehyde (H$_2$CO). It was the first detection at radio wavelengths of a molecule with more than one heavy atom (previous detections up until this discovery were limited to hydrogen atoms attached to a single heavy atom, e.g. CH, OH or NH$_3$) and, with the improvements in radio frequency receivers and new astronomical facilities coming online, heralded an era of discovery that has lasted for now more than 50 years. During this time, the number of new molecule detections has remained nearly constant at 3.7 molecules/year with a vast majority of these discoveries taking place in the radio regime (McGuire, B. 2018, APJS, 239, 17). This presentation will take us back to the time of this first detection, a quick synopsis of how observations of formaldehyde has led to a better understanding of the physical and chemical environments of astronomical sources and finally a look to the future with recent Green Bank Telescope (GBT) and Karl G. Jansky Very Large Array (VLA) observations of the 4830 MHz transition and high frequency searches with the Atacama Large Millimeter/submillimeter Array (ALMA)

THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY - FROM EARLY SCIENCE TO FULL OPERATIONS.

The Atacama Large Millimeter/Submillimeter Array (ALMA) is now entering its 8th cycle of scientific observations - starting with Cycle 0 in 2011. Cycle 7 should be one the last cycles that is considered "Steady State" Operations. With the commissioning of new capabilities over the next several years including wide field polarization, continuum single dish, new receiver bands and high frequency observations at long baselines, ALMA will begin "Full Science" operations. In addition, ALMA is approaching completion of its initially envisaged capabilities and, within the first five years of operations, the original fundamental science goals of ALMA have been essentially achieved. As such, a new ALMA Development Roadmap has been published that highlights the new fundamental science drivers for ALMA as we start the second decade of ALMA operations (https://www.almaobservatory.org/wp-content/uploads/2018/07/20180712-alma-development-roadmap.pdf). In this talk, I will detail the upcoming ALMA Cycle 7 observing capabilities, describe the process of selecting new observing modes for upcoming cycles and provide an update on the status of the ALMA Full Science capabilities including a brief description of the new fundamental science drivers for ALMA