Real time wavefront control system for the Large Synoptic Survey Telescope (LSST)

The LSST is an integrated, ground based survey system designed to conduct a decade-long time domain survey of the optical sky. It consists of an 8-meter class wide-field telescope, a 3.2 Gpixel camera, and an automated data processing system. In order to realize the scientific potential of the LSST, its optical system has to provide excellent and consistent image quality across the entire 3.5 degree Field of View. The purpose of the Active Optics System (AOS) is to optimize the image quality by controlling the surface figures of the telescope mirrors and maintaining the relative positions of the optical elements. The basic challenge of the wavefront sensor feedback loop for an LSST type 3-mirror telescope is the near degeneracy of the influence function linking optical degrees of freedom to the measured wavefront errors. Our approach to mitigate this problem is modal control, where a limited number of modes (combinations of optical degrees of freedom) are operated at the sampling rate of the wavefront sensing, while the control bandwidth for the barely observable modes is significantly lower. The paper presents a control strategy based on linear approximations to the system, and the verification of this strategy against system requirements by simulations using more complete, non-linear models for LSST optics and the curvature wavefront sensors

LSST Active Optics System Software Architecture

The Large Synoptic Survey Telescope (LSST) is an 8-meter class wide-field telescope now under construction on Cerro Pachon, near La Serena, Chile. This ground-based telescope is designed to conduct a decade-long time domain survey of the optical sky. In order to achieve the LSST scientific goals, the telescope requires delivering seeing limited image quality over the 3.5 degree field-of-view. Like many telescopes, LSST will use an Active Optics System (AOS) to correct in near real-time the system aberrations primarily introduced by gravity and temperature gradients. The LSST AOS uses a combination of 4 curvature wavefront sensors (CWS) located on the outside of the LSST field-of-view. The information coming from the 4 CWS is combined to calculate the appropriate corrections to be sent to the 3 different mirrors composing LSST. The AOS software incorporates a wavefront sensor estimation pipeline (WEP) and an active optics control system (AOCS). The WEP estimates the wavefront residual error from the CWS images. The AOCS determines the correction to be sent to the different degrees of freedom every 30 seconds. In this paper, we describe the design and implementation of the AOS. More particularly, we will focus on the software architecture as well as the AOS interactions with the various subsystems within LSST

Confirmation of SBS 1150+599A As An Extremely Metal-Poor Planetary Nebula

SBS 1150+599A is a blue stellar object at high galactic latitude discovered in the Second Byurakan Survey. New high-resolution images of SBS 1150+599A are presented, demonstrating that it is very likely to be an old planetary nebula in the galactic halo, as suggested by Tovmassian et al (2001). An H-alpha image taken with the WIYN 3.5-m telescope and its "tip/tilt" module reveals the diameter of the nebula to be 9.2", comparable to that estimated from spectra by Tovmassian et al. Lower limits to the central star temperature were derived using the Zanstra hydrogen and helium methods to determine that the star's effective temperature must be > 68,000K and that the nebula is optically thin. New spectra from the MMT and FLWO telescopes are presented, revealing the presence of strong [Ne V] lambda 3425, indicating that the central star temperature must be > 100,000K. With the revised diameter, new central star temperature, and an improved central star luminosity, we can constrain photoionization models for the nebula significantly better than before. Because the emission-line data set is sparse, the models are still not conclusive. Nevertheless, we confirm that this nebula is an extremely metal-poor planetary nebula, having a value for O/H that is less than 1/100 solar, and possibly as low as 1/500 solar.Comment: 19 pages, 6 figures. Accepted for publication in the Astronomical Journa

Real time wavefront control system for the Large Synoptic Survey Telescope (LSST)

The LSST is an integrated, ground based survey system designed to conduct a decade-long time domain survey of the optical sky. It consists of an 8-meter class wide-field telescope, a 3.2 Gpixel camera, and an automated data processing system. In order to realize the scientific potential of the LSST, its optical system has to provide excellent and consistent image quality across the entire 3.5 degree Field of View. The purpose of the Active Optics System (AOS) is to optimize the image quality by controlling the surface figures of the telescope mirrors and maintaining the relative positions of the optical elements. The basic challenge of the wavefront sensor feedback loop for an LSST type 3-mirror telescope is the near degeneracy of the influence function linking optical degrees of freedom to the measured wavefront errors. Our approach to mitigate this problem is modal control, where a limited number of modes (combinations of optical degrees of freedom) are operated at the sampling rate of the wavefront sensing, while the control bandwidth for the barely observable modes is significantly lower. The paper presents a control strategy based on linear approximations to the system, and the verification of this strategy against system requirements by simulations using more complete, non-linear models for LSST optics and the curvature wavefront sensors

LSST Active Optics System Software Architecture

The Large Synoptic Survey Telescope (LSST) is an 8-meter class wide-field telescope now under construction on Cerro Pachon, near La Serena, Chile. This ground-based telescope is designed to conduct a decade-long time domain survey of the optical sky. In order to achieve the LSST scientific goals, the telescope requires delivering seeing limited image quality over the 3.5 degree field-of-view. Like many telescopes, LSST will use an Active Optics System (AOS) to correct in near real-time the system aberrations primarily introduced by gravity and temperature gradients. The LSST AOS uses a combination of 4 curvature wavefront sensors (CWS) located on the outside of the LSST field-of-view. The information coming from the 4 CWS is combined to calculate the appropriate corrections to be sent to the 3 different mirrors composing LSST. The AOS software incorporates a wavefront sensor estimation pipeline (WEP) and an active optics control system (AOCS). The WEP estimates the wavefront residual error from the CWS images. The AOCS determines the correction to be sent to the different degrees of freedom every 30 seconds. In this paper, we describe the design and implementation of the AOS. More particularly, we will focus on the software architecture as well as the AOS interactions with the various subsystems within LSST

Whole Earth Telescope Observations of the Helium Interacting Binary PG 1346+082 (CR Bootis)

We present our analysis of 240 hr of white-light, high-speed photometry of the dwarf nova-like helium variable PG 1346+082 (CR Boo). We identify two frequencies in the low-state power spectrum, at 679.670 ± 0.004 μHz and 669.887 ± 0.008 μHz. The 679.670 μHz variation is coherent over at least a 2 week time span, the first demonstration of a phase-coherent photometric variation in any dwarf nova-like interacting binary white dwarf system. The high-state power spectrum contains a complex fundamental with a frequency similar, but not identical, to the low-state spectrum, and a series of harmonics not detected in low state. We also uncover an unexpected dependence of the high-frequency power\u27s amplitude and frequency structure on overall system magnitude. We discuss these findings in light of the general AM CVn system model, particularly the implications of the high-order harmonics on future studies of disk structure, mass transfer, and disk viscosity

LSST Science Book, Version 2.0

A survey that can cover the sky in optical bands over wide fields to faint magnitudes with a fast cadence will enable many of the exciting science opportunities of the next decade. The Large Synoptic Survey Telescope (LSST) will have an effective aperture of 6.7 meters and an imaging camera with field of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over 20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a total point-source depth of r~27.5. The LSST Science Book describes the basic parameters of the LSST hardware, software, and observing plans. The book discusses educational and outreach opportunities, then goes on to describe a broad range of science that LSST will revolutionize: mapping the inner and outer Solar System, stellar populations in the Milky Way and nearby galaxies, the structure of the Milky Way disk and halo and other objects in the Local Volume, transient and variable objects both at low and high redshift, and the properties of normal and active galaxies at low and high redshift. It then turns to far-field cosmological topics, exploring properties of supernovae to z~1, strong and weak lensing, the large-scale distribution of galaxies and baryon oscillations, and how these different probes may be combined to constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at http://www.lsst.org/lsst/sciboo

LSST: from Science Drivers to Reference Design and Anticipated Data Products

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. 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 wide-field ground-based system sited at Cerro Pach\'{o}n 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, and a 3.2 Gigapixel camera. The standard observing sequence will consist of pairs of 15-second exposures in a given field, with two such visits in each pointing in a given night. With these repeats, the LSST system is capable of imaging about 10,000 square degrees of sky in a single filter in three nights. The typical 5$\sigma$ point-source depth in a single visit in $r$ will be $\sim 24.5$ (AB). The project is in the construction phase and will begin regular survey operations by 2022. The survey area will be contained within 30,000 deg$^2$ with $\delta<+34.5^\circ$, and will be imaged multiple times in six bands, $ugrizy$, covering the wavelength range 320--1050 nm. About 90\% of the observing time will be devoted to a deep-wide-fast survey mode which will uniformly observe a 18,000 deg$^2$ region about 800 times (summed over all six bands) during the anticipated 10 years of operations, and yield a coadded map to $r\sim27.5$. The remaining 10\% of the observing time will be allocated to projects such as a Very Deep and Fast time domain survey. The goal is to make LSST data products, including a relational database of about 32 trillion observations of 40 billion objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures available from https://www.lsst.org/overvie

The significance of Ruzizi Delta: Rusizi Burundian Delta and Ruzizi Congolese Delta, in the Great Lakes Region, for the Conservation of Birds

ABSTRACT The significance of the Ruzizi Delta: Rusizi Burundian Delta (RBD) and Ruzizi Congolese Delta (RCD), in the Great Lakes Region for bird conservation was investigated from April 2019 to November 2021 in five sites of the RBD and five sites of the RCD. The investigation was conducted by direct observation on transects counts, counting points and on bird species recognition routes using binoculars and two telescopes. Travels were facilitated by the motorized fiberglass boat and the double cabin field vehicle of the Centre for Research in Hydrobiology (CRH) in Uvira, Democratic Republic of Congo (DRC). At the end of our investigations, we drew up the list of 490 species divided into 84 families and 18 orders. The following groups were listed: (i) 359 species of resident birds, of which 74 (21%) were recorded in the RCD, 148 (41%) in the RBD and 137 species (38%) were recorded both in the RCD and the RBD; (ii) 131 migrant bird species, of which 24 (18%) were recorded only in the RCD, 44 (34%) in the RBD and 63 species (48%) were recorded both in the RCD and the RBD; (iii) 176 water bird species, of which 26 (15%) were only recorded in the RCD, 49 (28%) in the RBD and 101 (57%) were recorded both in the RCD and the RBD; (iv) 238 (49%) Ramsar bird species for the criteria A1, A2, A3, A4i, A4ii and A4iv, among them, 29 (12%) species were only recorded in the RCD, 107 ( 45%) in the RBD and 102 species (43%) recorded in both the RCD and the RBD; (v) 21 species (4%) of birds with IUCN (International Union for Nature Conservation) status, of which only one species (Limosa limosa, Black-tailed Godwit) was recorded only in the RCD, 13 (62%) were only recorded in the RBD and 7 species (33%) were recorded both in the RCD and the RBD; Finally, the research pinpointed 60 newly recorded bird species in the Ruzizi Delta, of which four 4 (7%) were recorded only in the RCD, 37 (61%) in the RBD and 19 species (32%) were recorded in both the RCD and the RBD. The sustainability of all these species and their groups in the Ruzizi Delta requires the protection of the wetlands of the Ruzizi Congolese Delta as a community reserve and potential Ramsar site which will be submitted by the Congolese Institute for Nature Conservation (ICCN) to the Ramsar Secretariat for designation as a Ruzizi Congolese Delta Ramsar site. Keywords: Significance of the Ruzizi Delta; Ruzizi Congolese Delta; Rusizi Burundian Delta; Bird conservation; Great Lakes region. References Bashonga, A. B., Sande, E., Kahindo, C., & Ntakimazi, G. (2023). Checklist of the Bird Species from the Ruzizi Delta, Northern End of lake Tanganyika, in Burundi and the Democratic Republic of Congo. Biolife 11 (2);115-129. Chimatiro, S., & al, e. (2021). The African Great Lakes Regional Food System; the contribution of fisheries- the case of small pelagic fishes. A Discussion Paper. . Penang Malaysia: World Fish & Natural Resources Institute (NRI), 43 pages. www.fish.cgiar.org 23/8/2023. Cousin, P. H., Sinclair, L., Alain, J. F., & Love, C. E. (1993). Larousse & Collins Pratique; Dictionnaire Francais-Anglais/Anglais-Francais Voyages-Correspondance, 70000 mots et expressions. Londrs-Glasgow: Harper Collins Publishers, No 9 782850 36 140 1, 358 pages. Demey, R., & Louette, M. (2001). Democratic Republic of Congo. In Fishpool L.D.C.& Evans M.I eds Important Bird Areas in Africa:Priority Sites for Conservation. Pisces Publications and BirdLife International, 199-218. Dowset, & Dowset-Lemaire. (1993). A contribution to the Distribution and Taxonomy of Afrotropical and Malagasy birds Tauraco Research Report . Liège, Belgium.: Tauraco Press, Jupille No. 5 pp195-204. Fishpool, L., & Evans, M. (2001). Important Bird Areas in Africa and Associated Islands, Priority Sites for Conservation. Newbury and Cambridge, UK: BirdLife International, 1144 pages. www.birdlife.net. Gaugris, Y. (1979). Les oiseaux aquatiques de la plaine de la basse Rusizi (Burundi) (1973-1978). Belgium: l’Oiseau et la Revue française d’ornithologie, volume 49 n° 21:33-153. Guggisberg, C. (1986). Birds of East Africa. Supra Safari Guide No 6 Volume II. Nairobi: Mount Kenya Sundries, 196 pages. Guggisberg, C. (1988). Birds of East Africa. Supra Safari Guide No 6 Volum I. Nairobi: Mount Kenya Sundries, 198 pages . MEEATU, Ramsar, C., & WWF. (2014). Atlas of Burundi's four Ramsar sites: Location and Resources. Bujumbura, Burundi: Ministry of Water, Environment, Land Use Planning and Town Planning (MEEATU), 44p. Nkezabahizi, L., & Bizimana, D. (2008). Burundi’s Important Bird Areas, Status and Trends. Bujumbura-Burundi: Association Burundaise pour la protection des Oiseaux, 58 pages. Nkezabahizi, L., & Manirambona, A. (2011). Burundi’s Important Bird Areas Status and Trend 2010. London: BirdLife International & RSPB (Royal Society for the Protection of Birds (UK), 36 pages