Search results for "MILLIMETER"
showing 10 items of 44 documents
Germanium Dicarbide: Evidence for a T-Shaped Ground State Structure
2017
The equilibrium structure of germanium dicarbide GeC2 has been an open question since the late 1950s. Although most high-level quantum calculations predict an L-shaped geometry, a T-shaped or even a linear geometry cannot be ruled out because of the very flat potential energy surface. By recording the rotational spectrum of this dicarbide using sensitive microwave and millimeter techniques, we unambiguously establish that GeC2 adopts a vibrationally averaged T-shaped structure in its ground state. From analysis of 14 isotopologues, a precise r0 structure has been derived, yielding a Ge–C bond length of 1.952(1) A and an apex angle of 38.7(2)°.
Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D
2017
Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outwards through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud (LMC) is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Ataca…
THEMIS: A Parameter Estimation Framework for the Event Horizon Telescope
2020
This is an open access article.-- Full list of authors: Broderick, Avery E.; Gold, Roman; Karami, Mansour; Preciado-López, Jorge A.; Tiede, Paul; Pu, Hung-Yi; Akiyama, Kazunori; Alberdi, Antxon; Alef, Walter; Asada, Keiichi; Azulay, Rebecca; Baczko, Anne-Kathrin; Baloković, Mislav; Barrett, John; Bintley, Dan; Blackburn, Lindy; Boland, Wilfred; Bouman, Katherine L.; Bower, Geoffrey C.; Bremer, Michael; Brinkerink, Christiaan D.; Brissenden, Roger; Britzen, Silke; Broguiere, Dominique; Bronzwaer, Thomas; Byun, Do-Young; Carlstrom, John E.; Chael, Andrew; Chatterjee, Shami; Chatterjee, Koushik; Chen, Ming-Tang; Chen, Yongjun; Cho, Ilje; Conway, John E.; Cordes, James M.; Crew, Geoffrey B.; Cu…
First M87 Event Horizon Telescope Results. III. Data Processing and Calibration
2019
We present the calibration and reduction of Event Horizon Telescope (EHT) 1.3 mm radio wavelength observations of the supermassive black hole candidate at the center of the radio galaxy M87 and the quasar 3C 279, taken during the 2017 April 5–11 observing campaign. These global very long baseline interferometric observations include for the first time the highly sensitive Atacama Large Millimeter/submillimeter Array (ALMA); reaching an angular resolution of 25 μas, with characteristic sensitivity limits of ~1 mJy on baselines to ALMA and ~10 mJy on other baselines. The observations present challenges for existing data processing tools, arising from the rapid atmospheric phase fluctuations, …
First M87 Event Horizon Telescope Results. II. Array and Instrumentation
2019
The Event Horizon Telescope (EHT) is a very long baseline interferometry (VLBI) array that comprises millimeter- and submillimeter-wavelength telescopes separated by distances comparable to the diameter of the Earth. At a nominal operating wavelength of ~1.3 mm, EHT angular resolution (λ/D) is ~25 μas, which is sufficient to resolve nearby supermassive black hole candidates on spatial and temporal scales that correspond to their event horizons. With this capability, the EHT scientific goals are to probe general relativistic effects in the strong-field regime and to study accretion and relativistic jet formation near the black hole boundary. In this Letter we describe the system design of th…
Event Horizon Telescope imaging of the archetypal blazar 3C 279 at an extreme 20 microarcsecond resolution
2020
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society.--All authors: Kim, Jae-Young; Krichbaum, Thomas P.; Broderick, Avery E.; Wielgus, Maciek; Blackburn, Lindy; Gómez, José L.; Johnson, Michael D.; Bouman, Katherine L.; Chael, Andrew; Akiyama, Kazunori; Jorstad, Svetlana; Marscher, Alan P.; Issaoun, Sara; Janssen, Michael; Chan, Chi-kwan; Savolainen, Tuomas; Pesce, Dominic W.; Özel, Feryal; Alberdi, Antxon; Alef, Walt…
The cryogenic anticoincidence detector for ATHENA-XMS: preliminary results from the new prototype
2012
ATHENA has been the re-scoped IXO mission, and one of the foreseen focal plane instrument was the X-ray Microcalorimeter Spectrometer (XMS) working in the energy range 0.3-10 keV, which was a kilo-pixel array based on TES (Transition Edge Sensor) detectors. The need of an anticoincidence (AC) detector is legitimated by the results performed with GEANT4 simulations about the impact of the non x-ray background onto XMS at L2 orbit (REQ. < 0.02 cts/cm2/s/keV). Our consortium has both developed and tested several samples, with increasing area, in order to match the large area of the XMS (64 mm2). Here we show the preliminary results from the last prototype. The results achieved in this work off…
Discovery of off-axis jet structure of TeV blazar Mrk 501 with mm-VLBI
2016
Context. High-resolution millimeter wave very-long-baseline interferometry (mm-VLBI) is an ideal tool for probing the structure at the base of extragalactic jets in detail. The TeV blazar Mrk 501 is one of the best targets among BL Lac objects for studying the nature of off-axis jet structures because it shows different jet position angles at different scales. Aims. The aim of this study is to investigate the properties of the off-axis jet structure through high-resolution mm-VLBI images at the jet base and physical parameters such as kinematics, flux densities, and spectral indices. Methods. We performed Very Long Baseline Array (VLBA) observations over six epochs from 2012 February to 201…
Stars associated to Eagle Nebula (M16=NGC6611)
2011
Massive star-forming regions are characterized by intense ionizing fluxes, strong stellar winds and, occasionally, supernovae explosions, all of which have important effects on the surrounding media, on the star-formation process and on the evolution of young stars and their circumstellar disks. We present a multiband study of the massive young cluster NGC 6611 and its parental cloud (the Eagle Nebula) with the aim of studying how OB stars affect the early stellar evolution and the formation of other stars. We search for evidence of triggering of star formation by the massive stars inside NGC 6611 on a large spatial scale (~10 parsec) and ongoing disk photoevaporation in NGC 6611 and how it…
Blue stars with disk photometry in NGC 6611
2010
NGC 6611 and its parental cloud, the Eagle Nebula (M 16), are well-studied star-forming regions, thanks to their large content of both OB stars and stars with disks and the observed ongoing star formation. In our previous studies of the Eagle Nebula, we identified 834 disk-bearing stars associated with the cloud, after detecting their excesses in NIR bands from J band to 8.0um. In this paper, we study in detail the nature of a subsample of disk-bearing stars that show peculiar characteristics. They appear older than the other members in the V vs. V-I diagram, and/or they have one or more IRAC colors at pure photospheric values, despite showing NIR excesses, when optical and infrared colors …