Abstract
Vera C. Rubin Observatory is a ground-based astronomical facility under construction, a joint project of the National Science Foundation and the U.S. Department of Energy, designed to ...conduct a multipurpose 10 yr optical survey of the Southern Hemisphere sky: the Legacy Survey of Space and Time. Significant flexibility in survey strategy remains within the constraints imposed by the core science goals of probing dark energy and dark matter, cataloging the solar system, exploring the transient optical sky, and mapping the Milky Way. The survey’s massive data throughput will be transformational for many other astrophysics domains and Rubin’s data access policy sets the stage for a huge community of potential users. To ensure that the survey science potential is maximized while serving as broad a community as possible, Rubin Observatory has involved the scientific community at large in the process of setting and refining the details of the observing strategy. The motivation, history, and decision-making process of this strategy optimization are detailed in this paper, giving context to the science-driven proposals and recommendations for the survey strategy included in this Focus Issue.
We present an algorithm to photometrically calibrate wide-field optical imaging surveys, which simultaneously solves for the calibration parameters and relative stellar fluxes using overlapping ...observations. The algorithm decouples the problem of "relative" calibrations from that of "absolute" calibrations; the absolute calibration is reduced to determining a few numbers for the entire survey. We pay special attention to the spatial structure of the calibration errors, allowing one to isolate particular error modes in downstream analyses. Applying this to the SDSS imaging data, we achieve similar to 1% relative calibration errors across 8500 deg super(2) in griz; the errors are similar to 2% for the u band. These errors are dominated by unmodeled atmospheric variations at Apache Point Observatory. These calibrations, dubbed "ubercalibration," are now public with SDSS Data Release 6 and will be a part of subsequent SDSS data releases.
Using the photometric parallax method we estimate the distances to similar to 48 million stars detected by the Sloan Digital Sky Survey (SDSS) and map their three-dimensional number density ...distribution in the Galaxy. The currently available data sample the distance range from 100 pc to 20 kpc and cover 6500 deg super(2) of sky, mostly at high Galactic latitudes ( degree 'b degree ' > 25). These stellar number density maps allow an investigation of the Galactic structure with no a priori assumptions about the functional form of its components. The data show strong evidence for a Galaxy consisting of an oblate halo, a disk component, and a number of localized overdensities. The number density distribution of stars as traced by M dwarfs in the solar neighborhood (D < 2 kpc) is well fit by two exponential disks (the thin and thick disk) with scale heights and lengths, bias corrected for an assumed 35% binary fraction, of H sub(1) = 300 pc and L sub(1) = 2600 pc, and H sub(2) = 900 pc and L sub(2) = 3600 pc, and local thick-to-thin disk density normalization P sub(thick) (R unk)/ unk (R unk) = 12%. we use the stars near main-sequence turnoff to measure the shape of the Galactic halo. We find a strong preference for oblate halo models, with best-fit axis ratio c/a = 0.64, PH proportional to r super(-2.8) power-law profile, and the local halo-to-thin disk normalization of 0.5%. Based on a series of Monte Carlo simulations, we estimate the errors of derived model parameters not to be larger than similar to 20% for the disk scales and similar to 10% for the density normalization, with largest contributions to error coming from the uncertainty in calibration of the photometric parallax relation and poorly constrained binary fraction. While generally consistent with the above model, the measured density distribution shows a number of statistically significant localized deviations. In addition to known features, such as the Monoceros stream, we detect two overdensities in the thick disk region at cylindrical galactocentric radii and heights (R, Z) similar to (6.5, 1.5) kpc and (R, Z) similar to (9.5, 0.8) kpc and a remarkable density enhancement in the halo covering over 1000 deg super(2) of sky toward the constellation of Virgo, at distances of similar to 6-20 kpc. Compared to counts in a region symmetric with respect to the l = 0 degree line and with the same Galactic latitude, the Virgo overdensity is responsible for a factor of 2 number density excess and may be a nearby tidal stream or a low-surface brightness dwarf galaxy merging with the Milky Way. The u-g color distribution of stars associated with it implies metallicity lower than that of thick disk stars and consistent with the halo metallicity distribution. After removal of the resolved overdensities, the remaining data are consistent with a smooth density distribution; we detect no evidence of further unresolved clumpy substructure at scales ranging from similar to 50 pc in the disk to similar to 1-2 kpc in the halo.
A New Milky Way Dwarf Galaxy in Ursa Major Willman, Beth; Dalcanton, Julianne J; Martinez-Delgado, David ...
Astrophysical journal/The Astrophysical journal,
06/2005, Letnik:
626, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In this Letter, we report the discovery of a new dwarf satellite to the Milky Way, located at ( alpha sub(2000), delta sub(2000)) = (158 degree .72, 51 degree .92) in the constellation of Ursa Major. ...This object was detected as an overdensity of red, resolved stars in Sloan Digital Sky Survey data. The color-magnitude diagram of the Ursa Major dwarf looks remarkably similar to that of Sextans, the lowest surface brightness Milky Way companion known, but with approximately an order of magnitude fewer stars. Deeper follow-up imaging confirms that this object has an old and metal-poor stellar population and is similar to 100 kpc away. We roughly estimate M sub(V) = -6.75 and r sub(1/2) = 250 pc for this dwarf. Its luminosity is several times fainter than the faintest known Milky Way dwarf. However, its physical size is typical for dwarf spheroidal galaxies. Even though its absolute magnitude and size are presently quite uncertain, Ursa Major is likely the lowest luminosity and lowest surface brightness galaxy yet known.
We present a catalog of 9316 spectroscopically confirmed white dwarfs from the Sloan Digital Sky Survey Data Release 4. We have selected the stars through photometric cuts and spectroscopic modeling, ...backed up by a set of visual inspections. About 6000 of the stars are new discoveries, roughly doubling the number of spectroscopically confirmed white dwarfs. We analyze the stars by performing temperature and surface gravity fits to grids of pure hydrogen and helium atmospheres. Among the rare outliers are a set of presumed helium-core DA white dwarfs with estimated masses below 0.3 M sub( ), including two candidates that may be the lowest-mass yet found. We also present a list of 928 hot subdwarfs.
We describe the design, construction, and performance of the Sloan Digital Sky Survey telescope located at Apache Point Observatory. The telescope is a modified two-corrector Ritchey-Chretien design ...with a 2.5 m, f/2.25 primary, a 1.08 m secondary, a Gascoigne astigmatism corrector, and one of a pair of interchangeable highly aspheric correctors near the focal plane, one for imaging and the other for spectroscopy. The final focal ratio is f/5. The telescope is instrumented by a wide-area, multiband CCD camera and a pair of fiber-fed double spectrographs. Novel features of the telescope include the following: (1) A 3° diameter (0.65 m) focal plane that has excellent image quality and small geometric distortions over a wide wavelength range (3000-10,600 A) in the imaging mode, and good image quality combined with very small lateral and longitudinal color errors in the spectroscopic mode. The unusual requirement of very low distortion is set by the demands of time-delay-and-integrate (TDI) imaging. (2) Very high precision motion to support open-loop TDI observations. (3) A unique wind baffle/enclosure construction to maximize image quality and minimize construction costs. The telescope had first light in 1998 May and began regular survey operations in 2000.
We present the discovery of seven quasars at z > 5.7, selected from ~2000 deg2 of multicolor imaging data of the Sloan Digital Sky Survey. The new quasars have redshifts z from 5.79 to 6.13. Five are ...selected as part of a complete flux-limited sample in the SDSS northern Galactic cap; two have larger photometric errors and are not part of the complete sample. One of the new quasars, SDSS J1335+3533 (z = 5.93), exhibits no emission lines; the 3 s limit on the rest-frame equivalent width of the Lya+N V line is 5 A. It is the highest redshift lineless quasar known and could be a gravitational lensed galaxy, a BL Lac object, or a new type of quasar. Two new z > 6 quasars, SDSS 1250+3130 (z = 6.13) and SDSS J1137+3549 (z = 6.01), show deep Gunn-Peterson absorption gaps in Lya. These gaps are narrower than the complete Gunn-Peterson absorption troughs observed among quasars at z > 6.2 and do not have complete Lyb absorption.
We report the discovery of Andromeda X, a new dwarf spheroidal satellite of M31, based on stellar photometry from the Sloan Digital Sky Survey. Using follow-up imaging data we have estimated its ...distance and other physical properties. We find that Andromeda X has a dereddened central surface brightness of k sub(v,0) 6 26.7 mag arcsec super(-2) and a total apparent magnitude of V sub(tot) 6 16.1, which at the derived distance modulus, (m - M) sub(0) 6 24.12-24.34, yields an absolute magnitude of M sub(v) 6 -8.1 c 0.5; these values are quite comparable to those of Andromeda IX, a previously discovered low-luminosity M31 satellite. The discoveries of Andromeda X and of numerous other extremely faint satellites around M31 and the Milky Way in the past few years suggest that such objects may be plentiful in the Local Group.
Discoveries of two new white dwarf plus M star binaries with striking optical cyclotron emission features from the Sloan Digital Sky Survey (SDSS) brings to six the total number of X-ray-faint, ...magnetic accretion binaries that accrete at rates M 10 super(-13) M sub( )yr super(-1), or <1% of the values normally encountered in cataclysmic variables. This fact, coupled with donor stars that underfill their Roche lobes and very cool white dwarfs, brand the binaries as post-common-envelope systems whose orbits have not yet decayed to the point of Roche Iobe contact. They are premagnetic cataclysmic variables, or pre-Polars. The systems exhibit spin-orbit synchronism and apparently accrete by efficient capture of the stellar wind from the secondary star, a process that has been dubbed a "magnetic siphon." Because of this, period evolution of the binaries will occur solely by gravitational radiation, which is very slow for periods >3 hr. Optical surveys for the cyclotron harmonics appear to be the only means of discovery, so the space density of pre-Polars could rival that of Polars, and the binaries provide an important channel of progenitors (in addition to the asynchronous intermediate Polars). Both physical and SDSS observational selection effects are identified that may help to explain the clumping of all six systems in a narrow range of magnetic field strength around 60 MG.
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