3 research outputs found
First Detection of Near-Infrared Line Emission from Organics in Young Circumstellar Disks
We present an analysis of high-resolution spectroscopy of several bright T
Tauri stars using the VLT/CRIRES and Keck/NIRSPEC spectrographs, revealing the
first detections of emission from HCN and C2H2 in circumstellar disks at
near-infrared wavelengths. Using advanced data reduction techniques we achieve
a dynamic range with respect to the disk continuum of ~500 at 3 microns,
revealing multiple emission features of H2O, OH, HCN, and C2H2. We also present
stringent upper limits for two other molecules thought to be abundant in the
inner disk, CH4 and NH3. Line profiles for the different detected molecules are
broad but centrally peaked in most cases, even for disks with previously
determined inclinations of greater than 20 degrees, suggesting that the
emission has both a Keplerian and non-Keplerian component as observed
previously for CO emission. We apply two different modeling strategies to
constrain the molecular abundances and temperatures: we use a simplified
single-temperature LTE slab model with a Gaussian line profile to make line
identifications and determine a best-fit temperature and initial abundance
ratios, and we compare these values with constraints derived from a detailed
disk radiative transfer model assuming LTE excitation but utilizing a realistic
temperature and density structure. Abundance ratios from both sets of models
are consistent with each other and consistent with expected values from
theoretical chemical models, and analysis of the line shapes suggests the
molecular emission originates from within a narrow region in the inner disk (R
< 1 AU).Comment: Accepted to the Astrophysical Journa
The low frequency receivers for SKA 1-low: Design and verification
The initial phase of the Square Kilometre Array (SKA) [1] is represented by a ~10% instrument and construction should start in 2018. SKA 1-Low, a sparse Aperture Array (AA) covering the frequency range 50 to 350 MHz, will be part of this. This instrument will consist of 512 stations, each hosting 256 antennas creating a total of 131,072 antennas. A first verification system towards SKA 1-Low, Aperture Array Verification System 1 (AAVSl), is being deployed and validated in 2017
The Apertif Radio Transient System (ARTS): Design, commissioning, data release, and detection of the first five fast radio bursts
Fast radio bursts (FRBs) must be powered by uniquely energetic emission mechanisms. This requirement has eliminated a number of possible source types, but several remain. Identifying the physical nature of FRB emitters arguably requires good localisation of more detections, as well as broad-band studies enabled by real-time alerting. In this paper, we present the Apertif Radio Transient System (ARTS), a supercomputing radio-telescope instrument that performs real-time FRB detection and localisation on the Westerbork Synthesis Radio Telescope (WSRT) interferometer. It reaches coherent-addition sensitivity over the entire field of the view of the primary-dish beam. After commissioning results verified that the system performed as planned, we initiated the Apertif FRB survey (ALERT). Over the first 5 weeks we observed at design sensitivity in 2019, we detected five new FRBs, and interferometrically localised each of them to 0.4–10 sq. arcmin. All detections are broad band, very narrow, of the order of 1 ms in duration, and unscattered. Dispersion measures are generally high. Only through the very high time and frequency resolution of ARTS are these hard-to-find FRBs detected, producing an unbiased view of the intrinsic population properties. Most localisation regions are small enough to rule out the presence of associated persistent radio sources. Three FRBs cut through the halos of M31 and M33. We demonstrate that Apertif can localise one-off FRBs with an accuracy that maps magneto-ionic material along well-defined lines of sight. The rate of one every ~7 days ensures a considerable number of new sources are detected for such a study. The combination of the detection rate and localisation accuracy exemplified by the first five ARTS FRBs thus marks a new phase in which a growing number of bursts can be used to probe our Universe