| 1. |
- Fomalont, E. B., et al.
(författare)
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THE 2014 ALMA LONG BASELINE CAMPAIGN: AN OVERVIEW
- 2015
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 808:1
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Tidskriftsartikel (refereegranskat)abstract
- A major goal of the Atacama Large Millimeter/submillimeter Array (ALMA) is to make accurate images with resolutions of tens of milliarcseconds, which at submillimeter (submm) wavelengths requires baselines up to similar to 15 km. To develop and test this capability, a Long Baseline Campaign (LBC) was carried out from 2014 September to late November, culminating in end-to-end observations, calibrations, and imaging of selected Science Verification (SV) targets. This paper presents an overview of the campaign and its main results, including an investigation of the short-term coherence properties and systematic phase errors over the long baselines at the ALMA site, a summary of the SV targets and observations, and recommendations for science observing strategies at long baselines. Deep ALMA images of the quasar 3C 138 at 97 and 241 GHz are also compared to VLA 43 GHz results, demonstrating an agreement at a level of a few percent. As a result of the extensive program of LBC testing, the highly successful SV imaging at long baselines achieved angular resolutions as fine as 19 mas at similar to 350 GHz. Observing with ALMA on baselines of up to 15 km is now possible, and opens up new parameter space for submm astronomy.
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| 2. |
- Wells, M., et al.
(författare)
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The Mid-Infrared Instrument for the James Webb Space Telescope, VI: The Medium Resolution Spectrometer
- 2015
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Ingår i: Publications of the Astronomical Society of the Pacific. - : IOP Publishing. - 0004-6280 .- 1538-3873. ; 127:953, s. 646-664
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Tidskriftsartikel (refereegranskat)abstract
- We describe the design and performance of the Medium Resolution Spectrometer (MRS) for the JWST-MIRI instrument. The MRS incorporates four coaxial spectral channels in a compact opto-mechanical layout that generates spectral images over fields of view up to 7.7 x 7.7 '' in extent and at spectral resolving powers ranging from 1300 to 3700. Each channel includes an all-reflective integral field unit (IFU): an "image slicer" that reformats the input field for presentation to a grating spectrometer. Two 1024 x 1024 focal plane detector arrays record the output spectral images with an instantaneous spectral coverage of approximately one third of the full wavelength range of each channel. The full 5-28.5 mu m spectrum is then obtained by making three exposures using gratings and pass-band-determining filters that are selected using just two three-position mechanisms. The expected on-orbit optical performance is presented, based on testing of the MIRI Flight Model and including spectral and spatial coverage and resolution. The point spread function of the reconstructed images is shown to be diffraction limited and the optical transmission is shown to be consistent with the design expectations.
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| 3. |
- Hlozek, R., et al.
(författare)
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Results of the Photometric LSST Astronomical Time-series Classification Challenge (PLAsTiCC)
- 2023
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Ingår i: Astrophysical Journal Supplement Series. - 0067-0049 .- 1538-4365. ; 267:2
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Tidskriftsartikel (refereegranskat)abstract
- Next-generation surveys like the Legacy Survey of Space and Time (LSST) on the Vera C. Rubin Observatory (Rubin) will generate orders of magnitude more discoveries of transients and variable stars than previous surveys. To prepare for this data deluge, we developed the Photometric LSST Astronomical Time-series Classification Challenge (PLAsTiCC), a competition that aimed to catalyze the development of robust classifiers under LSST-like conditions of a nonrepresentative training set for a large photometric test set of imbalanced classes. Over 1000 teams participated in PLAsTiCC, which was hosted in the Kaggle data science competition platform between 2018 September 28 and 2018 December 17, ultimately identifying three winners in 2019 February. Participants produced classifiers employing a diverse set of machine-learning techniques including hybrid combinations and ensemble averages of a range of approaches, among them boosted decision trees, neural networks, and multilayer perceptrons. The strong performance of the top three classifiers on Type Ia supernovae and kilonovae represent a major improvement over the current state of the art within astronomy. This paper summarizes the most promising methods and evaluates their results in detail, highlighting future directions both for classifier development and simulation needs for a next-generation PLAsTiCC data set.
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| 4. |
- Labiano, A., et al.
(författare)
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Wavelength calibration and resolving power of the JWST MIRI Medium Resolution Spectrometer
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 656
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Tidskriftsartikel (refereegranskat)abstract
- Context. The Mid-Infrared Instrument (MIRI) onboard the James Webb Space Telescope (JWST) will provide imaging, coronagraphy, low-resolution spectroscopy, and medium-resolution spectroscopy at unprecedented sensitivity levels in the mid-infrared wavelength range. The Medium Resolution Spectrometer (MRS) of MIRI is an integral field spectrograph that provides diffraction-limited spectroscopy between 4.9 and 28.3 μm, within a field of view (FOV) varying from ∼13 to ∼56 arcsec square. The design for MIRI MRS conforms with the goals of the JWST mission to observe high redshift galaxies and to study cosmology as well as observations of galactic objects, and stellar and planetary systems. Aims. From ground testing, we calculate the physical parameters essential for general observers and calibrating the wavelength solution and resolving power of the MRS which is critical for maximizing the scientific performance of the instrument. Methods. We have used ground-based observations of discrete spectral features in combination with Fabry-Perot etalon spectra to characterize the wavelength solution and spectral resolving power of the MRS. We present the methodology used to derive the MRS spectral characterization, which includes the precise wavelength coverage of each MRS sub-band, computation of the resolving power as a function of wavelength, and measuring slice-dependent spectral distortions. Results. The ground calibration of the MRS shows that it will cover the wavelength ranges from 4.9 to 28.3 μm, divided in 12 overlapping spectral sub-bands. The resolving power is R 3500 in channel 1, R 3000 in channel 2, R 2500 in channel 3, and R 1500 in channel 4. The MRS spectral resolution optimizes the sensitivity for detection of spectral features with a velocity width of ∼100 km s-1 which is characteristic of most astronomical phenomena JWST aims to study in the mid-infrared. Based on the ground test data, the wavelength calibration accuracy is estimated to be below one-tenth of a pixel (0.1 nm at 5 μm and 0.4 at 28 μm), with small systematic shifts due to the target position within a slice for unresolved sources that have a maximum amplitude of about 0.25 spectral resolution elements. The absolute wavelength calibration is presently uncertain at the level of 0.35 nm at 5 μm and 46 nm at 28 μm, and it will be refined using in-flight commissioning observations. Conclusions. Based on ground test data, the MRS complies with the spectral requirements for both the R and wavelength accuracy for which it was designed. We also present the commissioning strategies and targets that will be followed to update the spectral characterization of the MRS.
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| 5. |
- Teleman, Johan, et al.
(författare)
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Numerical compression schemes for proteomics mass spectrometry data.
- 2014
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Ingår i: Molecular & Cellular Proteomics. - 1535-9484. ; 13:6, s. 1537-1542
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Tidskriftsartikel (refereegranskat)abstract
- The open XML format mzML, used for representation of mass spectrometry (MS) data, is pivotal for the development of platform-independent MS analysis software. Although conversion from vendor formats to mzML must take place on a platform on which the vendor libraries are available (i.e. Windows), once mzML files have been generated, they can be used on any platform. However, the mzML format has turned out to be less efficient than vendor formats. In many cases, the naive mzML representation is 4-fold or even up to 18-fold larger compared to the original vendor file. In disk I/O limited setups, a larger data file also leads to longer processing times, which is a problem given the data production rates of modern mass spectrometers. In an attempt to reduce this problem, we here present a family of numerical compression algorithms called MS-Numpress, intended for efficient compression of MS data. To facilitate ease of adoption, the algorithms target the binary data in the mzML standard, and support in main proteomics tools is already available. Using a test set of 10 representative MS data files we demonstrate typical file size decreases of 90% when combined with traditional compression, as well as read time decreases of up to 50%. It is envisaged that these improvements will be beneficial for data handling within the MS community.
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