Allam was an active researcher in multiple and varied fields of observational astronomy, including dust and star formation in galaxies, strongly lensed galaxies, photometric calibration, and the optical follow-up of gravitational wave events.

We present cosmological constraints from the sample of Type Ia supernovae (SN Ia) discovered during the full five years of the Dark Energy Survey (DES) Supernova Program. In contrast to most previous cosmological samples, in which SN are classified based on their spectra, we classify the DES SNe using a machine learning algorithm applied to their light curves in four photometric bands. Spectroscopic redshifts are acquired from a dedicated follow-up survey of the host galaxies. After accounting for the likelihood of each SN being a SN Ia, we find 1635 DES SNe in the redshift range $0.100.5$ SNe compared to the previous leading compilation of Pantheon+, and results in the tightest cosmological constraints achieved by any SN data set to date. To derive cosmological constraints we combine the DES supernova data with a high-quality external low-redshift sample consisting of 194 SNe Ia spanning $0.025

We present a detailed chemical abundance analysis of the brightest star in the ultra-faint dwarf (UFD) galaxy candidate Cetus II from high-resolution Magellan/MIKE spectra. For this star, DES J011740.53-173053, abundances or upper limits of 18 elements from Carbon to Europium are derived. Its chemical abundances generally follow those of other UFD galaxy stars, with a slight enhancement of the alpha-elements (Mg, Si, and Ca) and low neutron-capture element (Sr, Ba, Eu) abundances supporting the classification of Cetus II as a likely UFD. The star exhibits lower Sc, Ti, and V abundances than Milky Way (MW) halo stars with similar metallicity. This signature is consistent with yields from a supernova (SN) originating from a star with a mass of ~11.2 solar masses. In addition, the star has a Potassium abundance of [K/Fe] = 0.81 which is somewhat higher than the K abundances of MW halo stars with similar metallicity, a signature which is also present in a number of UFD galaxies. A comparison including globular clusters (GC) and stellar stream stars suggests that high K is a specific characteristic for some UFD galaxy stars and can thus be used to help classify objects as UFD galaxies.

This Technical Note presents a catalog of calibrated reference stars that was generated by the Forward Calibration Method (FGCM) pipeline (arXiv:1706.01542) as part of the FGCM photometric calibration of the full Dark Energy Survey (DES) 6-Year data set (Y6). This catalog provides DES grizY magnitudes for 17 million stars with i-band magnitudes mostly in the range 16 < i < 21 spread over the full DES footprint covering 5000 square degrees over the Southern Galactic Cap at galactic latitudes b < -20 degrees (plus a few outlying fields disconnected from the main survey footprint). These stars are calibrated to a uniformity of better than 1.8 milli-mag (0.18%) RMS over the survey area. The absolute calibration of the catalog is computed with reference to the STISNIC.007 spectrum of the Hubble Space Telescope CalSpec standard star C26202; including systematic errors, the absolute flux system is known at the approximately 1% level. As such, these stars provide a useful reference catalog for calibrating grizY-band or grizY-like band photometry in the Southern Hemisphere, particularly for observations within the DES footprint.

On 2019 August 14 at 21:10:39 UTC, the LIGO/Virgo Collaboration (LVC) detected a possible neutron star–black hole merger (NSBH), the first ever identified. An extensive search for an optical counterpart of this event, designated GW190814, was undertaken using the Dark Energy Camera on the 4 m Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Target of Opportunity interrupts were issued on eight separate nights to observe 11 candidates using the 4.1 m Southern Astrophysical Research (SOAR) telescope’s Goodman High Throughput Spectrograph in order to assess whether any of these transients was likely to be an optical counterpart of the possible NSBH merger. Here, we describe the process of observing with SOAR, the analysis of our spectra, our spectroscopic typing methodology, and our resultant conclusion that none of the candidates corresponded to the gravitational wave merger event but were all instead other transients. Finally, we describe the lessons learned from this effort. Application of these lessons will be critical for a successful community spectroscopic follow-up program for LVC observing run 4 (O4) and beyond.

Supersaturated solid solutions of Al and corrosion-resistant alloying elements (M: V, Mo, Cr, Ti, Nb), produced by non-equilibrium processing techniques, have been reported to exhibit high corrosion resistance and strength. The corrosion mechanism for such improved corrosion performance has not been well understood. We present a fundamental understanding of the role of V in corrosion of an Al-V alloy, which will provide a theoretical background for developing corrosion-resistant Al alloys. High-energy ball milling of the elemental powder of Al and V produced an in situ consolidated Al-V alloy, which exhibited high solid solubility of V. The corrosion resistance of Al-V alloy was significantly higher than that of pure Al, which was attributed to the (1) enrichment of V at the passive film/substrate interface, (2) incorporation of V into the passive film, and (3) deposition of V on the iron-containing cathodic particles and therefore, retardation of cathodic reaction.

We present optical follow-up imaging obtained with the Katzman Automatic Imaging Telescope, Las Cumbres Observatory Global Telescope Network, Nickel Telescope, Swope Telescope, and Thacher Telescope of the LIGO/Virgo gravitational wave (GW) signal from the neutron star–black hole (NSBH) merger GW190814. We searched the GW190814 localization region (19 deg2 for the 90th percentile best localization), covering a total of 51 deg2 and 94.6% of the two-dimensional localization region. Analyzing the properties of 189 transients that we consider as candidate counterparts to the NSBH merger, including their localizations, discovery times from merger, optical spectra, likely host galaxy redshifts, and photometric evolution, we conclude that none of these objects are likely to be associated with GW190814. Based on this finding, we consider the likely optical properties of an electromagnetic counterpart to GW190814, including possible kilonovae and short gamma-ray burst afterglows. Using the joint limits from our follow-up imaging, we conclude that a counterpart with an r-band decline rate of 0.68 mag day−1, similar to the kilonova AT 2017gfo, could peak at an absolute magnitude of at most −17.8 mag (50% confidence). Our data are not constraining for “red” kilonovae and rule out “blue” kilonovae with M > 0.5 M ⊙ (30% confidence). We strongly rule out all known types of short gamma-ray burst afterglows with viewing angles <17° assuming an initial jet opening angle of ∼5.°2 and explosion energies and circumburst densities similar to afterglows explored in the literature. Finally, we explore the possibility that GW190814 merged in the disk of an active galactic nucleus, of which we find four in the localization region, but we do not find any candidate counterparts among these sources.

ABSTRACT We extend the SDSS Stripe 82 Standard Stars catalogue with post-2007 SDSS imaging data. This improved version lists averaged SDSS ugriz photometry for nearly a million stars brighter than r ∼ 22 mag. With 2–3 times more measurements per star, random errors are 1.4–1.7 times smaller than in the original catalogue, and about three times smaller than for individual SDSS runs. Random errors in the new catalogue are $\lesssim$0.01 mag for stars brighter than 20.0, 21.0, 21.0, 20.5, and 19.0 mag in u, g, r, i, and z-bands, respectively. We achieve this error threshold by using the Gaia Early Data Release 3 (EDR3) Gmag photometry to derive grey photometric zeropoint corrections, as functions of RA and Declination, for the SDSS catalogue, and use the Gaia BP–RP colour to derive corrections in the ugiz bands, relative to the r-band. The quality of the recalibrated photometry, tested against Pan-STARRS1, DES, CFIS, and GALEX surveys, indicates spatial variations of photometric zeropoints ≦ 0.01 mag (rms), with typical values of 3–7 millimag in the RA, and 1–2 millimag in the Declination directions, except for $\lesssim$6 millimag scatter in the u-band. We also report a few minor photometric problems with other surveys considered here, including a magnitude-dependent ∼0.01 mag bias between 16 ≤ GGaia ≤ 20 in the Gaia EDR3. Our new, publicly available catalogue offers robust calibration of ugriz photometry below 1 per cent level, and will be helpful during the commissioning of the Vera C. Rubin Observatory Legacy Survey of Space and Time.

We describe the Dark Energy Survey (DES) photometric data set assembled from the first three years of science operations to support DES Year 3 cosmologic analyses, and provide usage notes aimed at the broad astrophysics community. Y3 GOLD improves on previous releases from DES, Y1 GOLD, and Data Release 1 (DES DR1), presenting an expanded and curated data set that incorporates algorithmic developments in image detrending and processing, photometric calibration, and object classification. Y3 GOLD comprises nearly 5000 deg2 of grizY imaging in the south Galactic cap, including nearly 390 million objects, with depth reaching a signal-to-noise ratio ∼10 for extended objects up to i AB ∼ 23.0, and top-of-the-atmosphere photometric uniformity <3 mmag. Compared to DR1, photometric residuals with respect to Gaia are reduced by 50%, and per-object chromatic corrections are introduced. Y3 GOLD augments DES DR1 with simultaneous fits to multi-epoch photometry for more robust galactic color measurements and corresponding photometric redshift estimates. Y3 GOLD features improved morphological star–galaxy classification with efficiency >98% and purity >99% for galaxies with 19 < i AB < 22.5. Additionally, it includes per-object quality information, and accompanying maps of the footprint coverage, masked regions, imaging depth, survey conditions, and astrophysical foregrounds that are used to select the cosmologic analysis samples.

Objectives: Subjects in a Phase 2b study of MK-7264, a P2X3 antagonist, were evaluated to characterize the baseline profile and potential cough triggers of patients with refractory chronic cough (1). Methods: In a double-blind, parallel group study (NCT02612610) conducted in the US and UK, subjects with refractory or unexplained chronic cough (duration ≥1 year) were randomized to placebo or MK-7264. Randomized subjects completed a medical history questionnaire at baseline in which they reported their frequency of triggers eliciting cough (i.e., ‘Always,’ ‘Most of the Time,’ ‘A Lot of the Time,’ ‘Some of the Time,’ ‘Little of the Time,’ or ‘Never’). Results: In the 253 subjects who were randomized, mean age was 60 years, 76% of subjects were female, mean BMI was 27.7 kg/m2, and median duration of cough was 11 years. Of 252 subjects who completed the questionnaire, items/triggers eliciting ‘Always’ to ‘A Lot of the Time’ responses included: ‘My cough is unpredictable’ (79%), ‘A tickle in my throat’ (73%), and ‘An irritation in my throat’ (73%), followed by external triggers of ‘Poor air quality’ (50%) and ‘A change in air temperature’ (43%). Only 4-5% of subjects reported ‘Never’ for throat tickle or irritation. Conclusions: Refractory chronic cough subjects in this trial were mostly female, on average middle/older age, and slightly overweight. Overall, cough triggers were characterized as unpredictable, although a high proportion of patients reported triggers consistent with a neuronal hypersensitivity. Reference: (1) Smith JA et al. American Thoracic Society 2017.

INTRODUCTION:The API AutosomalDominant AD (ADAD) Colombia Trial is a placebo-controlled clinical trial of crenezumab in 252 cognitively unimpaired 30 to 60-year-old Presenilin 1 (PSEN1) E280A kindred members, including mutation carriers randomized to active treatment or placebo and non-carriers who receive placebo.METHODS:Of the 252 enrolled, we present data on a total of 242 mutation carriers and non-carriers matched by age range, excluding data on 10 participants to protect participant confidentiality, genetic status, and trial integrity.RESULTS:We summarize demographic, clinical, cognitive, and behavioral data from 167 mutation carriers and 75 non-carriers, 30 to 53 years of age. Carriers were significantly younger than non-carriers ((mean age ± SD) 37 ± 5 vs 42 ± 6), had significantly lower Mini Mental Status Exam (MMSE) scores (28.8 ± 1.4 vs 29.2 ± 1.0), and had consistently lower memory scores.DISCUSSION:Although PSEN1 E280A mutation carriers in the Trial are cognitively unimpaired, they have slightly lower MMSE and memory scores than non-carriers. Their demographic characteristics are representative of the local population.

We present a measurement of the Hubble constant H-0 using the gravitational wave (GW) event GW190814, which resulted from the coalescence of a 23M(circle dot) black hole with a 2.6M(circle dot) compact object, as a standard siren. No compelling electromagnetic counterpart has been identified for this event; thus our analysis accounts for thousands of potential host galaxies within a statistical framework. The redshift information is obtained from the photometric redshift (photo-z) catalog from the Dark Energy Survey. The luminosity distance is provided by the LIGO/Virgo gravitational wave sky map. Since this GW event has the second-smallest localization volume after GW170817, GW190814 is likely to provide the best constraint on cosmology from a single standard siren without identifying an electromagnetic counterpart. Our analysis uses photo-z probability distribution functions and corrects for photoz biases. We also reanalyze the binary black hole GW170814 within this updated framework. We explore how our findings impact the H-0 constraints from GW170817, the only GW merger associated with a unique host galaxy. From a combination of GW190814, GW170814, and GW170817, our analysis yields H-0 = 72.0(-8.2)(+12) km s(-1) Mpc(-1) (68% highest-density interval, HDI) for a prior in H-0 uniform between [20and140] km s(-1)Mpc(-1). The addition of GW190814 and GW170814 to GW170817 improves the 68% HDI from GW170817 alone by similar to 18%, showing how well-localized mergers without counterparts can provide a significant contribution to standard siren measurements, provided that a complete galaxy catalog is available at the location of the event.

BackgroundGefapixant is an oral P2X3 receptor antagonist that has previously shown efficacy and safety in refractory chronic cough and unexplained chronic cough. We therefore aim to confirm the efficacy and safety of gefapixant in participants with refractory chronic cough and unexplained chronic cough.MethodsCOUGH-1 and COUGH-2 were both double-blind, randomised, parallel-group, placebo-controlled, phase 3 trials. COUGH-1 was done in 156 sites in 17 countries and COUGH-2 in 175 sites in 20 countries. We enrolled participants who were 18 years or older with a diagnosis of refractory chronic cough or unexplained chronic cough of 1 year duration or more. Participants were also required to have a cough severity visual analogue scale score of 40 mm or more at screening and baseline. Eligible participants were randomly allocated (1:1:1), using a computer-generated allocation schedule, to one of three treatment groups: placebo, gefapixant 15 mg twice per day, or gefapixant 45 mg twice per day. All study treatments were given orally. Participants were treated over a 12-week main study period in COUGH-1 and a 24-week main study period in COUGH-2; followed by extension periods for a total of up to 52 weeks of treatment in both trials. The primary outcome was placebo-adjusted mean change in 24-h cough frequency at 12 weeks in COUGH-1 and 24 weeks in COUGH-2. Both studies were registered with ClinicalTrials.gov, NCT03449134 (COUGH-1) and NCT03449147 (COUGH-2).FindingsFrom March 14, 2018, (first participant screened) to July 26, 2019, (last participant screened) 732 patients were recruited in COUGH-1 and 1317 in COUGH-2. COUGH-1 randomly assigned and treated 730 participants (243 [33×3%] with placebo, 244 [33×4%] with gefapixant 15 mg twice per day, and 243 [33×3%] with gefapixant 45 mg twice per day); COUGH-2 randomly assigned and treated 1314 participants (435 [33×1%] with placebo, 440 [33×5%] with gefapixant 15 mg twice per day, and 439 [33×4%] with gefapixant 45 mg twice per day). Participants were mostly female (542 [74×2%] of 730 in COUGH-1 and 984 [74×9%] of 1314 in COUGH-2). The mean age was 59×0 years (SD 12×6) in COUGH-1 and 58×1 years (12×1) in COUGH-2, and the mean cough duration was 11·6 years (SD 9·5) in COUGH-1 and 11·2 years (9·8) in COUGH-2. Gefapixant 45 mg twice per day showed significant reductions in 24-h cough frequency compared with placebo at week 12 in COUGH-1 (18·5% [95% CI 32·9–0·9]; p=0·041) and at week 24 in COUGH-2 (14·6% [26·1–1·4]; p=0·031). Gefapixant 15 mg twice per day did not show a significant reduction in cough frequency versus placebo in both studies. The most common adverse events were related to taste disturbance: ageusia (36 [4·9%] of 730 in COUGH-1 and 86 [6·5%] of 1314 in COUGH-2), dysgeusia (118 [16·2%] in COUGH-1 and 277 [21·1%] in COUGH-2), hypergeusia (3 [0·4%] in COUGH-1 and 6 [0×5%] in COUGH-2), hypogeusia (19 [2·6%] in COUGH-1 and 80 [6·1%] in COUGH-2), and taste disorder (28 [3·8%] in COUGH-1 and 46 [3·5%] in COUGH-2).InterpretationGefapixant 45 mg twice per day is the first treatment to show efficacy with an acceptable safety profile in phase 3 clinical trials for refractory chronic cough or unexplained chronic cough.FundingMerck Sharp & Dohme.

SESSION TITLE: Wednesday Electronic Posters 5 SESSION TYPE: Original Inv Poster Discussion PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM PURPOSE: The negative impact of chronic cough on patients' daily lives is multi-faceted; therefore, the evaluation of chronic cough treatment requires an approach including both objective and subjective measures. The efficacy of gefapixant, a P2X3 receptor antagonist, on patient-reported outcomes included as secondary endpoints in a phase 2b clinical trial was assessed. METHODS: This Phase 2b, 12-week, randomized controlled trial included subjects with severe refractory or unexplained chronic cough (duration >1 year; baseline VAS≥40 mm). Treatments included placebo or gefapixant (7.5, 20, or 50 mg BID) in a 1:1:1:1 ratio. Awake Objective Cough Frequency at 12 weeks was the primary endpoint; several PROs were included as secondary endpoints including Patient Global Impression of Change (PGIC), Cough Severity Diary (CSD), and the Leicester Cough Questionnaire (LCQ). PGIC is a patient rating of improvement (from very much, much, or minimally improved to no change or minimally, much, and very much worse). CSD was scored daily and summarized weekly and is comprised of 7 items (0-10 [best-worst] scale) including subscales capturing subjects' impression of frequency, disruption, and intensity. LCQ is a 19-item questionnaire (0-7 [worst-best] scale) including domains quantifying patients' impression of physical, psychological and social effects of cough. RESULTS: 253 subjects were randomized with subjects on gefapixant 50 mg demonstrating significant reduction (p<0.01) of Awake Cough Frequency at 12 weeks vs. placebo (Smith et al, Am J Respir Crit Care Med 2017: 195:A7608). For PGIC, 65% vs. 30% of subjects reported much or very much improved for gefapixant 50 mg vs. placebo at Week 12 (p<0.0001). LS mean (95% CI) change from baseline in CSD total score at 12 weeks was -1.9 (-2.4, -1.4) vs. -1.2 (-1.6, -0.7) for gefapixant 50 mg vs. placebo at Week 12 (p=0.02); Mean (SD) change from baseline in subscales showed -2.0 (1.70) vs. -1.3 (1.75) (p=0.06; Frequency), -2.1 (1.86) vs. -1.2 (1.73) (p=0.02; Intensity), and -1.6 (1.24) vs. -0.8 (1.43) (p=0.0003; Disruption) for gefapixant 50 mg vs. placebo at Week 12. Mean (SD) change from baseline in total LCQ score at Week 12 for 50 mg vs. placebo was 4.2 (4.13) vs. 2.1 (3.38) (p=0.0028). Mean (SD) change from baseline in domain scores at Week 12 for 50 mg vs. placebo were: 1.6 (1.71) vs. 0.8 (1.41) (p=0.0123) for Social; 1.5 (1.53) vs. 0.8 (1.38) (p=0.0082) for Psychological; 1.2 (1.15) vs. 0.5 (0.99) (p=0.0009) for Physical. CONCLUSIONS: Improvements in PROs in this trial are consistent with data on objective cough frequency reductions and indicate benefits related to quality of life, particularly with regard to disruption and psychological impact from cough. CLINICAL IMPLICATIONS: Improvements with gefapixant in patients with chronic cough were demonstrated in subjective, patient-reported measures, which is consistent with previously-reported results using objective measures. DISCLOSURES: Advisory Committee Member relationship with Merck Please note: $1001 - $5000 Added 03/14/2019 by Surinder Birring, source=Web Response, value=Consulting fee No relevant relationships by Lorcan McGarvey, source=Web Response Employee Advisory Committee Member relationship with Merck Please note: $5001 - $20000 Added 03/15/2019 by Alyn Morice, source=Web Response, value=Consulting fee Advisory Committee Member relationship with Bellus Please note: $5001 - $20000 Added 03/15/2019 by Alyn Morice, source=Web Response, value=Consulting fee Advisory Committee Member relationship with Bayer Please note: $5001 - $20000 Added 03/15/2019 by Alyn Morice, source=Web Response, value=Consulting fee Advisory Committee Member relationship with Sanofi Please note: $5001 - $20000 Added 03/15/2019 by Alyn Morice, source=Web Response, value=Consulting fee No relevant relationships by David Muccino, source=Web Response Employee relationship with Merck & Co., Inc. Please note: >$100000 Added 03/16/2019 by Jonathan Schelfhout, source=Web Response, value=Salary Consultant relationship with NeRRe Please note: $5001 - $20000 Added 03/14/2019 by Mandel Sher, source=Web Response, value=Consulting fee Consultant relationship with Bayer Please note: $1001 - $5000 Added 03/14/2019 by Mandel Sher, source=Web Response, value=Consulting fee Advisory Committee Member relationship with Merck Please note: $1001 - $5000 Added 03/14/2019 by Mandel Sher, source=Web Response, value=Consulting fee Consultant relationship with Bellus Please note: $1001 - $5000 Added 03/14/2019 by Mandel Sher, source=Web Response, value=Consulting fee Advisory relationship with Optinose Please note: $1001 - $5000 Added 03/14/2019 by Mandel Sher, source=Web Response, value=Honoraria Scientific Medical Advisor relationship with Merck Please note: $1001 - $5000 Added 03/15/2019 by Jacky Smith, source=Web Response, value=Consulting fee Scientific Medical Advisor relationship with Vitalograph Ltd Please note: $5001 - $20000 Added 03/15/2019 by Jacky Smith, source=Web Response, value=Grant/Research Support

Open-access telescopes of all apertures are needed to operate a competitive and efficient national science program. While larger facilities contribute light-gathering power and angular resolution, smaller ones dominate for field of view, time-resolution, and especially, total available observing time, thereby enabling our entire, diversely-expert community. Smaller aperture telescopes therefore play a critical and indispensable role in advancing science. Thus, the divestment of NSF support for modest-aperture (1 - 4 m) public telescopes poses a serious threat to U.S. scientific leadership, which is compounded by the unknown consequences of the shift from observations driven by individual investigators to survey-driven science. Given the much higher cost efficiency and dramatic science returns for investments in modest aperture telescopes, it is hard to justify funding only the most expensive facilities. We therefore urge the Astro2020 panel to explicitly make the case for modest aperture facilities, and to recommend enhancing this funding stream to support and grow this critical component of the OIR System. Further study is urgently needed to prioritize the numerous exciting potential capabilities of smaller facilities,and to establish sustainable, long-term planning for the System.

Austin Peay State University (APSU) was well -placed for viewing the 2017 total solar eclipse with the campus being totally within the path of totality. This location made us the 4-year university closest to the point of "Greatest Eclipse" in Hopkinsville, Kentucky. These circumstances meant we would have several visitors from around the country, and possibly the world, in town for the day. We discuss the APSU preparation for the event, the activities we hosted or supported concentrating in two areas, and the lessons learned for use by others at future events.

The citizen Continental-America Telescopic Eclipse (CATE) Experiment was a new type of citizen science experiment designed to capture a time sequence of white-light coronal observations during totality from 17:16 to 18:48 UT on 2017 August 21. Using identical instruments the CATE group imaged the inner corona from 1 to 2.1 RSun with 1.″43 pixels at a cadence of 2.1 s. A slow coronal mass ejection (CME) started on the SW limb of the Sun before the total eclipse began. An analysis of CATE data from 17:22 to 17:39 UT maps the spatial distribution of coronal flow velocities from about 1.2 to 2.1 RSun, and shows the CME material accelerates from about 0 to 200 km s−1 across this part of the corona. This CME is observed by LASCO C2 at 3.1–13 RSun with a constant speed of 254 km s−1. The CATE and LASCO observations are not fit by either constant acceleration nor spatially uniform velocity change, and so the CME acceleration mechanism must produce variable acceleration in this region of the corona.

We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the solar system, exploring the transient optical sky, and mapping the Milky Way. LSST will be a large, wide-field ground-based system designed to obtain repeated images covering the sky visible from Cerro Pachón in northern Chile. The telescope will have an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg 2 field of view, a 3.2-gigapixel camera, and six filters ( ugrizy ) covering the wavelength range 320–1050 nm. The project is in the construction phase and will begin regular survey operations by 2022. About 90% of the observing time will be devoted to a deep-wide-fast survey mode that will uniformly observe a 18,000 deg 2 region about 800 times (summed over all six bands) during the anticipated 10 yr of operations and will yield a co-added map to r ∼ 27.5. These data will result in databases including about 32 trillion observations of 20 billion galaxies and a similar number of stars, and they will serve the majority of the primary science programs. The remaining 10% of the observing time will be allocated to special projects such as Very Deep and Very Fast time domain surveys, whose details are currently under discussion. We illustrate how the LSST science drivers led to these choices of system parameters, and we describe the expected data products and their characteristics.