This paper identifies the cataclysmic variables that appear in spectra obtained in 2004 as part of the Sloan Digital Sky Survey. Spectra of 41 objects, including seven systems that were previously ...known (CC Cnc, DW Cnc, PQ Gem, AR UMa, AN UMa, RX J1131.3+4322, and UMa 6) and 34 new cataclysmic variables are presented. The positions and ugriz photometry of all 41 systems are given, as well as additional follow-up spectroscopic, photometric, and/or polarimetric observations of eight of the new systems. The new objects include three eclipsing systems, six with prominent He II emission, and six systems that show the underlying white dwarf.
We announce the discovery of a new dwarf galaxy, Leo T, in the Local Group. It was found as a stellar overdensity in the Sloan Digital Sky Survey Data Release 5 (SDSS DR5). The color-magnitude ...diagram of Leo T shows two well-defined features, which we interpret as a red giant branch and a sequence of young, massive stars. As judged from fits to the color-magnitude diagram, it lies at a distance of 420 kpc and has an intermediate-age stellar population with a metallicity of Fe/H = -1.6, together with a young population of blue stars of age 200 Myr. There is a compact cloud of neutral hydrogen with mass 10 super(5) M sub( )and radial velocity +35 km s super(-1) coincident with the object visible in the HIPASS channel maps. Leo T is the smallest, lowest luminosity galaxy found to date with recent star formation. It appears to be a transition object similar to, but much lower luminosity than, the Phoenix dwarf.
A Curious Milky Way Satellite in Ursa Major Zucker, D. B; Belokurov, V; Evans, N. W ...
Astrophysical journal/The Astrophysical journal,
10/2006, Letnik:
650, Številka:
1
Journal Article
Recenzirano
Odprti dostop
In this Letter, we study a localized stellar overdensity in the constellation of Ursa Major, first identified in Sloan Digital Sky Survey (SDSS) data and subsequently followed up with Subaru imaging. ...Its color-magnitude diagram (CMD) shows a well-defined subgiant branch, main sequence, and turnoff, from which we estimate a distance of 630 kpc and a projected size of 6250 x 125 pc super(2). The CMD suggests a composite population with some range in metallicity and/or age. Based on its extent and stellar population, we argue that this is a previously unknown satellite galaxy of the Milky Way, hereby named Ursa Major II (UMa II) after its constellation. Using SDSS data, we find an absolute magnitude of Mv6-3.8, which would make it the faintest known satellite galaxy. UMall's isophotes are irregular and distorted with evidence for multiple concentrations; this suggests that the satellite is in the process of disruption.
We report a detection of the baryon acoustic oscillation (BAO) feature in the three-dimensional correlation function of the transmitted flux fraction in the Lyα forest of high-redshift quasars. The ...study uses 48 640 quasars in the redshift range 2.1 ≤ z ≤ 3.5 from the Baryon Oscillation Spectroscopic Survey (BOSS) of the third generation of the Sloan Digital Sky Survey (SDSS-III). At a mean redshift z = 2.3, we measure the monopole and quadrupole components of the correlation function for separations in the range 20 h-1 Mpc < r < 200 h-1 Mpc. A peak in the correlation function is seen at a separation equal to (1.01 ± 0.03) times the distance expected for the BAO peak within a concordance ΛCDM cosmology. This first detection of the BAO peak at high redshift, when the universe was strongly matter dominated, results in constraints on the angular diameter distance DA and the expansion rate H at z = 2.3 that, combined with priors on H0 and the baryon density, require the existence of dark energy. Combined with constraints derived from cosmic microwave background observations, this result implies H(z = 2.3) = (224 ± 8) km s-1 Mpc-1, indicating that the time derivative of the cosmological scale parameter ȧ = H(z = 2.3)/(1 + z) is significantly greater than that measured with BAO at z ~ 0.5. This demonstrates that the expansion was decelerating in the range 0.7 < z < 2.3, as expected from the matter domination during this epoch. Combined with measurements of H0, one sees the pattern of deceleration followed by acceleration characteristic of a dark-energy dominated universe.
The Hercules-Aquila Cloud Belokurov, V; Evans, N. W; Bell, E. F ...
Astrophysical journal/The Astrophysical journal,
03/2007, Letnik:
657, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present evidence for a substantial overdensity of stars in the direction of the constellations of Hercules and Aquila. The cloud is centered at a Galactic longitude of l - 40 and extends above and ...below the Galactic plane by at least 50. Given its off-centeredness and height, it is unlikely that the Hercules-Aquila cloud is related to the bulge or thick disk. More likely, this is a new structural component of the Galaxy that passes through the disk. The cloud stretches 680 in longitude. Its heliocentric distance lies between 10 and 20 kpc so that the extent of the cloud in projection is 620 kpc by 615 kpc. It has an absolute magnitude of Mu = -13, and its stellar population appears to be comparable to, but somewhat more metal-rich than, M92.
We present a spectroscopic sample of 747 detached close binary systems from the Sloan Digital Sky Survey (SDSS) Fourth Data Release. The majority of these binaries consist of a white dwarf primary ...and a low-mass secondary (typically M dwarf) companion. We have determined the temperature and gravity for 496 of the white dwarf primaries and the spectral type and magnetic activity properties for 661 of the low-mass secondaries. We have estimated the distances for each of the white dwarf-main-sequence star binaries and use white dwarf evolutionary grids to establish the age of each binary system from the white dwarf cooling times. With respect to a spectroscopically identified sample of ~8000 isolated M dwarf stars in the SDSS, the M dwarf secondaries show enhanced activity with a higher active fraction at a given spectral type. The white dwarf temperatures and gravities are similar to the distribution of ~1900 DA white dwarfs from the SDSS. The ages of the binaries in this study range from ~0.5 Myr to nearly 3 Gyr (average age ~0.20 Gyr).
Abstract
We obtain constraints on cosmological parameters from the spherically averaged redshift-space correlation function of the CMASS Data Release 9 (DR9) sample of the Baryonic Oscillation ...Spectroscopic Survey (BOSS). We combine this information with additional data from recent cosmic microwave background (CMB), supernova and baryon acoustic oscillation measurements. Our results show no significant evidence of deviations from the standard flat Λ cold dark matter model, whose basic parameters can be specified by Ωm = 0.285 ± 0.009, 100 Ωb = 4.59 ± 0.09, n
s = 0.961 ± 0.009, H
0 = 69.4 ± 0.8 km s−1 Mpc−1 and σ8 = 0.80 ± 0.02. The CMB+CMASS combination sets tight constraints on the curvature of the Universe, with Ω
k
= −0.0043 ± 0.0049, and the tensor-to-scalar amplitude ratio, for which we find r < 0.16 at the 95 per cent confidence level (CL). These data show a clear signature of a deviation from scale invariance also in the presence of tensor modes, with n
s < 1 at the 99.7 per cent CL. We derive constraints on the fraction of massive neutrinos of f
ν < 0.049 (95 per cent CL), implying a limit of ∑m
ν < 0.51 eV. We find no signature of a deviation from a cosmological constant from the combination of all data sets, with a constraint of w
DE = −1.033 ± 0.073 when this parameter is assumed time-independent, and no evidence of a departure from this value when it is allowed to evolve as w
DE(a) = w
0 + w
a
(1 − a). The achieved accuracy on our cosmological constraints is a clear demonstration of the constraining power of current cosmological observations.
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