WiSe 2015/2016

Oberseminar

Lecture All Professors, I.Physikalisches Institut (contact schilke[at]ph1.uni-koeln.de)
KLIPS no. 53405
Course Presentations
Talk Mo. 14:00 - 15:30 Seminarraum I. Physik

'Advanced Seminar of Astrophysics and Laboratory Astrophysics'

Talk topics

  • Grain-surface reactions in molecular clouds: the effect of cosmic rays and quantum tunnelling - Schilke
    • Stefan Pols
    • http://cdsads.u-strasbg.fr/abs/2014MNRAS.440.3557R

    • Abstract: Grain-surface reactions play an essential role in interstellar chemistry, since dust grain catalyzes reactions at its surface allowing for the formation of molecules. We used a chemical model in which both gas-phase and grain-surface reactions occur and studied particularly the diffusion mechanisms on the surface of the grains. Surface reactions can occur via thermal hopping when species cross over a potential barrier or via quantum tunnelling when species cross through this barrier. We show that the thermal diffusion (hopping) can be much more efficient after a cosmic ray particle collides with a dust grain, heating it to a peak temperature of 70 K. We present here the results of numerical simulations after including the quantum tunnelling mechanism for species H, H2, and O and considering the effect of cosmic ray particle collision on the surface reactions. As a consequence, the gas-phase and grain-surface abundances are affected and we show that more complex molecules can be formed in molecular clouds.

  • The energy and momentum input of supernova explosions in molecular clouds - Walch-Gassner
    • Dirk Schaefer - 14.12.2015 (tbc)
    • http://adsabs.harvard.edu/abs/2015MNRAS.451.2757W
    • Supernova explosions are amongst the most energetic events in the Universe. However, there particular role in regulating star formation and driving gaseous outflows from disk galaxies is not
      yet fully understood. Here we investigate the early impact of single and binary supernova (SN) explosions on dense gas clouds with three-dimensional, high-resolution, hydrodynamic simulations. The effect of cloud structure, radiative cooling and ionizing radiation from the progenitor stars on the net input of kinetic energy,  thermal energy, and gas momentum to the interstellar medium (ISM) is tested. 
    • Ion dynamics in a trapped ion mobility spectrometer  - Asvany
    • Dominik Strixner - 18.01.2016
    • http://dx.doi.org/10.1039/c3an02174b
    • http://www.faz.net/aktuell/wissen/physik-chemie/chemie-der-kohlenhydrate-die-entschluesselung-der-zuckersphaere-13840873.html
    • Large molecules come in a large variety of geometrical arrangements (conformers) which carry different functionalities. In order to obtain information on the individual conformers it is necessary to separate them. This is done in ion mobility analysers. Recently this method has been extended to trapped ions: In the present paper, theoretical simulations and experimental observations are used to describe the ion dynamics in a trapped ion mobility spectrometer. In particular, the ion motion, iontransmission and mobility separation are discussed as a function of the bath gas velocity, radial confinement, analysis time and speed. Mobility analysis and calibration procedure are reported forthe case of sphere-like molecules for positive and negative ion modes. Results showed that a maximal mobility resolution can be achieved by optimizing the gas velocity, radial confinement (RF amplitude) and ramp speed (voltage range and ramp time). The mobility resolution scales with the electric field and gas velocity and R = 100–250 can be routinely obtained at room temperature.

Open topics

  • ALMA high resolution observations toward the HL Tau Region - Schilke
    • http://cdsads.u-strasbg.fr/abs/2015ApJ...808L...3A and followup papers
    • The first very high resolution images from ALMA have yielded astonishing results, and showing unprecedented detail in a protoplanetary disk. The data were very unlike the theoretical expectations, and the result have spawned many papers trying to interpret them.
    • HL Tau protoplanetary disk.jpg
    • Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) observations from the 2014 Long Baseline Campaign in dust continuum and spectral line emission from the HL Tau region. The continuum images at wavelengths of 2.9, 1.3, and 0.87 mm have unprecedented angular resolutions of 0.″ 075 (10 AU) to 0.″ 025 (3.5 AU), revealing an astonishing level of detail in the circumstellar disk surrounding the young solar analog HL Tau, with a pattern of bright and dark rings observed at all wavelengths. By fitting ellipses to the most distinct rings, we measure precise values for the disk inclination (46\buildrel{\circ}\over{.} 72+/- 0\buildrel{\circ}\over{.} 05) and position angle (+138\buildrel{\circ}\over{.} 02+/- 0\buildrel{\circ}\over{.} 07). We obtain a high-fidelity image of the 1.0 mm spectral index (α), which ranges from α ∼ 2.0 in the optically thick central peak and two brightest rings, increasing to 2.3–3.0 in the dark rings. The dark rings are not devoid of emission, and we estimate a grain emissivity index of 0.8 for the innermost dark ring and lower for subsequent dark rings, consistent with some degree of grain growth and evolution. Additional clues that the rings arise from planet formation include an increase in their central offsets with radius and the presence of numerous orbital resonances. At a resolution of 35 AU, we resolve the molecular component of the disk in HCO+ (1-0) which exhibits a pattern over LSR velocities from 2–12 km s‑1 consistent with Keplerian motion around a ∼1.3 {M}ȯ star, although complicated by absorption at low blueshifted velocities. We also serendipitously detect and resolve the nearby protostars XZ Tau (A/B) and LkHα358 at 2.9 mm.
  • Accretion disks in luminous young stellar objects - Sanchez-Monge
    • Abstract: An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and therefore predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.
  • Gravity or turbulence? - III. Evidence of pure thermal Jeans fragmentation at 0.1 pc scale - Sanchez-Monge
    • http://adsabs.harvard.edu/abs/2015MNRAS.453.3785P
    • Abstract: We combine previously published interferometric and single-dish data of relatively nearby massive dense cores that are actively forming stars to test whether their `fragmentation level' is controlled by turbulent or thermal support. We find no clear correlation between the fragmentation level and velocity dispersion, nor between the observed number of fragments and the number of fragments expected when the gravitationally unstable mass is calculated including various prescriptions for `turbulent support'. On the other hand, the best correlation is found for the case of pure thermal Jeans fragmentation, for which we infer a core formation efficiency around 13 per cent, consistent with previous works. We conclude that the dominant factor determining the fragmentation level of star-forming massive dense cores at 0.1 pc scale seems to be thermal Jeans fragmentation.
  • The value of probability distribution functions to characterize star-formation in molecular clouds - Ossenkopf
    • Schneider et al. (2015) http://esoads.eso.org/abs/2015A%26A...578A..29S Background: Kritsuk et al. (2011) http://esoads.eso.org/abs/2011ApJ...727L..20K
    • The most simple statistics to characterize the structure seen in maps of interstellar clouds is given by counting the observed intensity or column density values. The resulting probability distribution functions have a characteristic shape determined by interstellar turbulence and gravitational collapse. Actually measuring these functions is, however, not trivial due to observational limitations.
  • Young stars in the Galactic Center - Eckart, Zajacek
  • Disk evolution and planet formation in young stellar objects - Labadie/Grellmann
  • The importance of massive stars in astrophysics: study at high-angular resolution - Labadie/Grellmann
  • High-Precision Terahertz Frequency Comb - Schlemmer
    • http://dx.doi.org/10.1103/PhysRevLett.114.163902
    • HIgh potential is seen from the Nobel Prize winning frequency combs (Haensch 2005) which are now commercially available.
      Building a THz spectrometer is a big challenge. This presentation will deal with a recent promising first development based on non-linear optics:
      The generation and detection of a decade-spanning terahertz (THz) frequency comb is reported using
      two Ti:sapphire femtosecond laser oscillators and asynchronous optical sampling THz time-domain
      spectroscopy. The comb extends from 0.15 to 2.4 THz, with a tooth spacing of 80 MHz, a linewidth of
      3.7 kHz, and a fractional precision of 1.8 × 10−9. With time-domain detection of the comb, we measure
      three transitions of water vapor at 10 mTorr between 1–2 THz with an average Doppler-limited fractional
      accuracy of 6.1 × 10−8. Significant improvements in bandwidth, resolution, and sensitivity are possible
      with existing technologies.
  • Buffer Gas Cooling - Schlemmer
    • http://dx.doi.org/10.1080/00268976.2012.679632
    • Most molecules in space are observed at rather low temperatures and very low densities (pressures).
      It is a challenge to prepare these conditions in the laboratory.
      Buffer gas cooling is an obvious way to do so. Recent work along these lines will be discussed in this presentation.
      Abstract:
      Gas phase benzonitrile, acetone, 1-2 propanediol, fluorobenzene, and anisole molecules are produced in a cell at a temperature of 8K, and detected via Fourier transform microwave spectroscopy (FTMW). Helium buffer gas is used to cool the molecules originating from a high flux room temperature beam. This general, continuous source of cold molecules offers comparable spectral resolution to existing seeded pulsed supersonic beam/FTMW spectroscopy experiments but with higher number sensitivity. It is also an attractive tool for quantitative studies of cold molecule–helium and molecule–molecule elastic and inelastic collisions. Preliminary data on helium–molecule low temperature rotational and vibrational relaxation cross-sections are presented. Applications of the technique as a sensitive broad spectrum mixture analyser and a high resolution slow-beam spectrometer are discussed.
  • Laboratory confirmation of C60+ as the carrier of two diffuse interstellar bands - Brünken
    • http://dx.doi.org/10.1038/nature14566
    • The identification of the carriers of the so-called diffuse interstellar bands, around 400 distinct absorption features seen in the UV, optical, and NIR spectra of astronomical sources in our and other galaxies, has been one of the big challenges of astrophysics every since their detection almost 100 years ago. For the first time several of these bands have now been matched to the spectrum of the Buckminsterfullerene ion C60+, which was measured for the first time in the gas phase in a sophisticated ion trap experiment.

      Abstract:
      The diffuse interstellar bands are absorption lines seen towards reddened stars. None of the molecules responsible for these bands have been conclusively identified. Two bands at 9,632 ångströms and 9,577 ångströms were reported in 1994, and were suggested to arise from C60+ molecules, on the basis of the proximity of these wavelengths to the absorption bands of C60+ measured in a neon matrix. Confirmation of this assignment requires the gas-phase spectrum of C60+. Here we report laboratory spectroscopy of C60+ in the gas phase, cooled to 5.8 kelvin. The absorption spectrum has maxima at 9,632.7 ± 0.1 ångströms and 9,577.5 ± 0.1 ångströms, and the full widths at half-maximum of these bands are 2.2 ± 0.2 ångströms and 2.5 ± 0.2 ångströms, respectively. We conclude that we have positively identified the diffuse interstellar bands at 9,632 ångströms and 9,577 ångströms as arising from C60+ in the interstellar medium.