We report a photometric and spectroscopic study of the peculiar cataclysmic variable SDSS 1507+52. The star shows very deep eclipses on the 67 minute orbital period, and those eclipses are easily separable into white-dwarf and hot-spot components. This leads to tight constraints on binary parameters, with M_1=0.83(8) solar masses, M_2=0.057(8) solar masses, R_1=0.0097(9) solar radii, R_2=0.097(4) solar radii, q=0.069(2), and i=83.18(13) degrees. Such numbers suggest possible membership among the WZ Sge stars, a common type of dwarf nova. The spectroscopic behavior (strong and broad H emission, double-peaked and showing a classic rotational disturbance during eclipse) is also typical. But the star's orbital period is shockingly below the "period minimum" of approximately 77 min which is characteristic of hydrogen-rich CVs; producing such a strange binary will require some tinkering with the theory of cataclysmic-variable evolution. The proper motion is also remarkably high for a star of its distance, which we estimate from photometry and trigonometric parallax as 230 +- 40 pc. This suggests a transverse velocity of 164 +- 30 km/s - uncomfortably high if the star belongs to a Galactic-disk population. These difficulties with understanding its evolution and space velocity can be solved if the star belongs to a Galactic-halo population.
We use FUSE, HST, and SDSS spectra of the cataclysmic variable SDSSJ0809 to illustrate procedures for calculating and testing system models. Our final model has an accretion disk temperature profile similar to the SW Sextantis profile determined from tomographic reconstruction.
Our observations of the first reported outburst of SDSS J081321.91+452809.4 during 2008 April show that this cataclysmic variable is a dwarf nova. The outburst amplitude was at least 3.1 magnitudes and the outburst appears to have been rather short-lived at around 3 days with a rapid decline to quiescence of 0.73 mag/day.
The Sloan Digital Sky Survey has identified a total of 212 cataclysmic variables, most of which are fainter than 18th magnitude. This is the deepest and most populous homogeneous sample of cataclysmic variables to date, and we are undertaking a project to characterise this population. We have found that the SDSS sample is dominated by a great ``silent majority'' of old and faint CVs. We detect, for the first time, a population spike at the minimum period of 80 minutes which has been predicted by theoretical studies for over a decade.
The orbital period of the eclipsing cataclysmic variable SDSS J170213.26+322954.1 has been measured as 0.10008215+/-0.00000001d using observations of eclipses during the first recorded superoutburst in October 2005 together with eclipses observed in quiescence in July 2003. This period puts the system in the centre of the period gap. Observation of superhumps during the October 2005 outburst with a period of 0.10496+/-0.00015d confirms this to be a UGSU-type system with a period excess of 4.9%.
We find from high speed photometry of the Sloan Digital Survey cataclysmic variable candidate SDSS J161033.64-010223.3 that it has a double humped modulation, which is probably orbital, with a period of 80.52 minutes, and shows strong ZZ Cet type pulsations. The largest amplitude oscillations have periods near 607, 345, 304 and 221 s. The amplitudes of some of the oscillations are seen to vary on time scales of hours, indicating modes with unresolved multiplets in which the splittings are ~1 d^-1. This is only the second dwarf nova found to have non-radial pulsations of its white dwarf primary…
This paper continues the series that identifies new cataclysmic variables found in the Sloan Digital Sky Survey. We present 36 cataclysmic variables and one possible symbiotic star from Sloan spectra obtained during 2002, of which 34 are new discoveries, 2 are known dwarf novae (BC UMa, KS UMa) and one is a known CV identified from the 2dF survey. The positions, colors and spectra of all 37 systems are presented, along with follow-up spectroscopic/photometric observations of 10 systems. As in the past 2 years of data, the new SDSS systems show a large variety of characteristics based on their …
We present time resolved CCD photometry of 15 cataclysmic variables (CVs) identified by the Sloan Digital Sky Survey (SDSS). The data were obtained as part of the 2004/05 International Time Programme on La Palma. We discuss the morphology of the light curves and the CV subtypes and give accurate orbital periods for 11 systems. Nine systems are found below the 2-3h orbital period gap, of which five have periods within a few minutes of the ~80min minimum orbital period. One system each is found within and above the gap. This confirms the previously noted trend for a large fraction of short-perio…
We present the results obtained from unfiltered photometric CCD observations of the newly discovered cataclysmic variable SDSS J040714.78-064425.1 made during 7 nights in November 2003. We establish the dwarf nova nature of the object as it was in outburst during our observations. We also confirm the presence of deep eclipses with a period of 0.17017d+/-0.00003 in the optical light curve of the star. In addition, we found periods of 0.166d+/-0.001 and possibly also 5.3d+/-0.7 in the data. The 0.17017d periodicity is consistent within the errors with the proposed orbital period of 0.165d (Szkod…
We present time-series VLT spectroscopy and NTT photometry of the cataclysmic variable SDSS J220553.98+115553.7, which contains a pulsating white dwarf. We determine a spectroscopic orbital period of 82.825 +/- 0.089 min from velocity measurements of the Halpha emission line. A period analysis of the light curves reveals a dominant periodicity at 44.779 +/- 0.038 min which is not related to the spectroscopic period. However, the light curves do not exhibit a variation at any frequency which is attributable to GW Lib type pulsations, to a detection limit of 5 mmag. This non-detection is in cont…
The first full year of operation following the commissioning year of the Sloan Digital Sky Survey has revealed a wide variety of newly discovered cataclysmic variables. We show the SDSS spectra of forty-two cataclysmic variables observed in 2002, of which thirty-five are new classifications, four are known dwarf novae (CT Hya, RZ Leo, T Leo and BZ UMa), one is a known CV identified from a previous quasar survey (Aqr1) and two are known ROSAT or FIRST discovered CVs (RX J09445+0357, FIRST J102347.6+003841). The SDSS positions, colors and spectra of all forty-two systems are presented. In additi…
Ultraviolet observations using the Solar Blind Channel on the Hubble Space Telescope provide light curves and low resolution spectra of three pulsating white dwarfs in the cataclysmic variables SDSS013132.39-090122.3, SDSSJ161033.64-010223.3 and SDSSJ220553.98+115553.7. The UV light curves show enhanced pulsation amplitudes over those from simultaneous and previous optical photometry, while the UV-optical spectra are fit with white dwarf temperatures near 15,000K. These temperatures place the accreting white dwarfs outside the instability zone for non-interacting DAV white dwarfs and show that…
We present results from high speed photometry of a further thirteen faint cataclysmic variables. V356 Aql (Nova Aql 1936) shows flare-like outbursts with recurrence time scales ~ 3000 s, but no coherent periodicities. Aqr1 is an intermediate polar with a spin period of 6.7284 min and a probable orbital period P(orb) = 3.226 h derived from orbital sidebands. Its orbital sideband frequencies show very variable amplitudes. The published spectroscopic period of 2.0 h suggests that Aqr1 is similar to GW Lib and FS Aur in having an additional periodicity of unknown origin. FIRST J1023+0038 has P(orb…
We present medium-resolution VLT/FORS2 spectroscopy of six cataclysmic variables discovered by the Sloan Digital Sky Survey. We determine orbital periods for SDSS J023322.61+005059.5 (96.08 +/- 0.09 min), SDSS J091127.36+084140.7 (295.74 +/- 0.22 min), SDSS J103533.02+055158.3 (82.10 +/- 0.09 min), and SDSS J121607.03+052013.9 (most likely 98.82 +/- 0.16 min, but the one-day aliases at 92 min and 107 min are also possible) using radial velocities measured from their H_alpha and H_beta emission lines. Three of the four orbital periods measured here are close to the observed 75--80 min minimum p…
We present high-speed, three-colour photometry of the eclipsing cataclysmic variable SDSS J170213.26+322954.1 (hereafter SDSS J1702+3229). This system has an orbital period of 2.4 hours, placing it within the ``period gap'' for cataclysmic variables. We determine the system parameters via a parameterized model of the eclipse fitted to the observed light curve by chi-squared minimization. We obtain a mass ratio of q = 0.215 +/- 0.015 and an orbital inclination i = 82.4 +- 0.4 degrees. The primary mass is M_w = 0.94 +/- 0.01 Msun. The secondary mass and radius are found to be Mr = 0.20 +/- 0.01 …
The commissioning year of the Sloan Digital Sky Survey has demonstrated that many cataclysmic variables have been missed in previous surveys with brighter limits. We report the identification of 22 cataclysmic variables, of which 19 are new discoveries and 3 are known systems (SW UMa, BH Lyn and Vir4). A compendium of positions, colors and characteristics of these systems obtained from the SDSS photometry and spectroscopy is presented along with data obtained during follow-up studies with the Apache Point Observatory (APO) and Manastash Ridge Observatory (MRO) telescopes. We have determined or…
The number of discovered non-radially pulsating white dwarfs (WDs) in cataclysmic variables (CVs) is increasing rapidly by the aid of the Sloan Digital Sky Survey (SDSS). We performed photometric observations of two additional objects, SDSS J133941.11+484727.5 (SDSS 1339), independently discovered as a pulsator by Gansicke et al., and SDSS J151413.72+454911.9, which we identified as a CV/ZZ Ceti hybrid. In this Letter we present the results of the remote observations of these targets performed with the Nordic Optical Telescope (NOT) during the Nordic-Baltic Research School at Moletai Observato…
Two newly identified magnetic cataclysmic variables discovered in the Sloan Digital Sky Survey (SDSS), SDSSJ155331.12+551614.5 and SDSSJ132411.57+032050.5, have spectra showing highly prominent, narrow, strongly polarized cyclotron humps with amplitudes that vary on orbital periods of 4.39 and 2.6 hrs, respectively. In the former, the spacing of the humps indicates the 3rd and 4th harmonics in a magnetic field of ~60 MG. The narrowness of the cyclotron features and the lack of strong emission lines imply very low temperature plasmas and very low accretion rates, so that the accreting area is h…
We have observed a new cataclysmic variable (CV) SDSS J080434.20+510349.2 and study the origin of a long-term variability found in its light curve. Multi-longitude time-resolved photometric observations were carried out to analyze the uncommon behavior also found recently in two newly discovered CVs. This study of SDSS J080434.20+510349.2 mainly concerns the understanding of the nature of the observed double-humped light curve and its relation to a cyclic brightening occurring during quiescence. The observations were obtained early in 2007, when the object was at about V~17.1, 0.4 mag brighter…
We present VLT and Magellan spectroscopy and NTT photometry of nine faint cataclysmic variables (CVs) which were spectroscopically identified by the SDSS. We measure orbital periods for five of these from the velocity variations of the cores and wings of their Halpha emission lines. Four of the five have orbital periods shorter than the 2-3 hour period gap observed in the known population of CVs. SDSS J004335.14-003729.8 has an orbital period of Porb = 82.325 +/- 0.088 min; Doppler maps show emission from the accretion disc, bright spot and the irradiated inner face of the secondary star. In i…
We present the latest catalog of more than 1200 spectroscopically-selected close binary systems observed with the Sloan Digital Sky Survey through Data Release Five. We use the catalog to search for magnetic white dwarfs in cataclysmic variable progenitor systems. Given that approximately 25% of cataclysmic variables contain a magnetic white dwarf, and that our large sample of close binary systems should contain many progenitors of cataclysmic variables, it is quite surprising that we find only two potential magnetic white dwarfs in this sample. The candidate magnetic white dwarfs, if confirme…
Continuing our work from Paper I (Southworth et al., 2006) we present medium-resolution spectroscopy and broad-band photometry of seven cataclysmic variables (CVs) discovered by the SDSS. For six of these objects we derive accurate orbital periods, all which are measured for the first time. For SDSS J013132.39+090122.2, which contains a non-radially pulsating white dwarf, we find an orbital period of 81.54 +/- 0.13 min and a low radial velocity variation amplitude indicative of an extreme mass ratio. For SDSS J205914.87+061220.4, we find a period of 107.52 +/- 0.14 min. This object is a dwarf …
We present high-speed, three-colour photometry of the eclipsing cataclysmic variable SDSS J150722.30+523039.8 (hereafter SDSS J1507). This system has an orbital period of 66.61 minutes, placing it below the observed ``period minimum'' for cataclysmic variables. We determine the system parameters via a parameterised model of the eclipse fitted to the observed lightcurve by chi^2 minimisation. We obtain a mass ratio of q = 0.0623 +/- 0.0007 and an orbital inclination i = 83.63 +/- 0.05 degrees. The primary mass is M_w = 0.90 +/- 0.01 M_sun. The secondary mass and radius are found to be M_r =0.05…
We present spectroscopy of four cataclysmic variables. Using radial velocity measurements, we find orbital periods for the first time. The stars and their periods are GY Hya, 0.347230(9) d; SDSS J204448-045929, 1.68(1) d; V392 Hya, 0.324952(5) d; and RX J1951.7+3716, 0.492(1) d. We also detect the spectra of the secondary stars, estimate their spectral types, and derive distances based on surface brightness and Roche lobe constraints.
We report follow-up observations of the Sloan Digital Sky Survey Cataclysmic Variable SDSS J210014.12+004446.0 (hereafter SDSS J2100). We obtained photometry and spectroscopy in both outburst and quiescent states, providing the first quiescent spectrum of this source. In both states, non-sinusoidal photometric modulations are apparent, suggestive of superhumps, placing SDSS J2100 in the SU UMa subclass of dwarf novae. However, the periods during outburst and quiescence differ significantly, being 2.099 plus or minus 0.002 hr and 1.96 plus or minus 0.02 hr respectively. Our phase-resolved spect…
We report the discovery of two new accreting pulsating white dwarf stars amongst the cataclysmic variables of the Sloan Digital Sky Survey: SDSSJ074531.91+453829.5 and SDSSJ091945.10+085710.0. We observe high amplitude non-sinusoidal variations of 4.5-7% at a period close to 1230s in the optical light curves of SDSSJ074531.91+453829.5 and a low amplitude variation of 0.7-1.6% near 260s in the light curves of SDSSJ091945.10+085710.0. We infer that these optical variations are a consequence of nonradial g-mode pulsations in the accreting primary white dwarfs of these cataclysmic variables. Howev…
Photometric and spectroscopic observations reveal the Sloan Digital Sky Survey cataclysmic variable SDSS J132723.39+652854.2 to be a likely SW Sex star with an orbital period of P = 3.28 hours. The Sloan Digital Sky Survey spectrum shows strong HeI, HeII and Balmer emission lines. Time resolved spectra acquired at Apache Point Observatory reveal absorption-line structure within the emission lines near phase 0.5. Photometric data obtained at Manastash Ridge Observatory using Harris V and B filters reveal a high inclination system (i = 80 degrees) with deep (~ 2 mag.) eclipses. The orbital perio…
The halo structure at high Galactic latitudes near both the north and south poles is studied using SDSS and SuperCOSMOS data. For the south cap halo, the archive of the SuperCOSMOS photographic photometry sky survey is used. The coincident source rate between SuperCOSMOS data in $B_J$ band from $16^m.5$ to $20^m.5$ and SDSS data is about 92%, in a common sky area in the south. While that in the $R_F$ band is about 85% from $16^m.5$ to $19^m.5$. Transformed to the SuperCOSMOS system and downgraded to the limiting magnitudes of SuperCOSMOS, the star counts in the northern Galactic cap from SDSS …
We present halo model predictions for the expected angular clustering and associated errors from the completed Sloan Digital Sky Survey (SDSS) photometric galaxy sample. These results are used to constrain halo model parameters under the assumption of a fixed LCDM cosmology using standard Fisher matrix techniques. Given the ability of the five-color SDSS photometry to separate galaxies into sub-populations by intrinsic color, we also use extensions of the standard halo model formalism to calculate the expected clustering of red and blue galaxy sub-populations as a further test of the galaxy ev…
We present high speed photometry of the Sloan Digital Sky Survey cataclysmic variable SDSS J013701.06-091234.9 in quiescence and during its 2003 December superoutburst. The orbital modulation at 79.71\pm0.01 min is double humped; the superhump period is 81.702\pm0.007 min. Towards the end of the outburst late superhumps with a period of 81.29\pm0.01 min were observed. We argue that this is a system of very low mass transfer rate, and that it probably has a long outburst interval.
We present a statistical analysis of halo emission for a sample of 1047 edge-on disk galaxies imaged in five bands by the Sloan Digital Sky Survey (SDSS). Stacking the homogeneously rescaled images of the galaxies, we can measure surface brightnesses as deep as mu_r~31 mag/arcsec^2. The results strongly support the almost ubiquitous presence of stellar halos around disk galaxies, whose spatial distribution is well described by a power-law $ρ\propto r^{-3}$, in a moderately flattened spheroid (c/a~0.6). The colour estimates in g-r and r-i, although uncertain, give a clear indication for extreme…
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 < 10^{-13} Msun/yr, 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-lobe contact. They are pre-magnetic CVs, or pre-Polars. The syst…
We discuss the density and radial velocity distributions of over 3000 candidate RR Lyrae stars selected by various methods using Sloan Digital Sky Survey data for about 1000 deg^2 of sky. This is more than 20 times larger sample than previously reported by SDSS (Ivezic et al. 2000), and includes candidate RR Lyrae stars out to the sample limit of 100 kpc. A cutoff in the radial distribution of halo RR Lyrae at ~50-60 kpc that was suggested by the early SDSS data appears to be a statistical anomaly confined to a small region (~100 deg^2). Despite the large increase in observed area, the most pr…
We discuss a sample of over 3000 candidate RR Lyrae stars selected by various methods using Sloan Digital Sky Survey data for about 1000 deg^2 of sky. These stars probe the halo structure out to ~100 kpc from the Galactic center. Their spatial and radial velocity distributions are very inhomogeneous, with the most prominent features tracing the Sgr dwarf tidal stream. Outside the Sgr dwarf tidal stream, the spatial distribution in the 5-60 kpc range of Galactocentric radius R is well described by an R^{-3} power law.
We measure the ellipticity of isolated clusters of galaxies in the Sloan Digital Sky Survey (SDSS) using gravitational lensing. We stack the clusters, rotating so that the major axes of the ellipses determined by the positions of cluster member galaxies are aligned. We exclude the signal from the central 0.5 h^-1 Mpc to avoid problems with stacking alignment and cluster member contamination. We fit an elliptical NFW profile and find an axis ratio for the dark matter of f = b/a = 0.48+0.14-0.09 (1 sigma), and rule out f=1 at 99.6 per cent confidence thus ruling out a spherical halo. We find tha…
We report parallax and distance estimates for twelve more cataclysmic binaries and related objects observed with the 2.4m Hiltner telescope at MDM Observatory. The final parallax accuracy is typically about 1 mas. For only one of the twelve objects, IR Gem, do we fail to detect a significant parallax. Notable results include distances for V396 Hya (CE 315), a helium double degenerate with a relatively long orbital period, and for MQ Dra (SDSSJ155331+551615), a magnetic system with a very low accretion rate. We find that the Z Cam star KT Persei is physically paired with a K main-sequence star …
We combine the measurements of luminosity dependence of bias with the luminosity dependent weak lensing analysis of dark matter around galaxies to derive the galaxy bias and constrain nonlinear mass and cosmological parameters. We take advantage of theoretical and simulation predictions that predict that while halo bias is rapidly increasing with mass for high masses, it is nearly constant in low mass halos. We use a new weak lensing analysis around the same SDSS galaxies to determine their halo mass probability distribution. These halo mass probability distributions are used to predict the bi…
Current analytic and semi-analytic dark matter halo models distinguish between the central galaxy in a halo and the satellite galaxies in halo substructures. Using a recent halo-model description of the color dependence of galaxy clustering (Skibba & Sheth 2008), we investigate the colors of central and satellite galaxies predicted by the model and compare them to those of two galaxy group catalogs constructed from the Sloan Digital Sky Survey (Yang et al. 2007, Berlind et al. 2006a). In the model, the environmental dependence of galaxy color is determined by that of halo mass, and the predict…
We model the luminosity-dependent projected two-point correlation function of DEEP2 (z~1) and SDSS (z~0) galaxies within the Halo Occupation Distribution (HOD) framework. At both epochs, there is a tight correlation between central galaxy luminosity and halo mass, with the slope and scatter decreasing for larger halo masses, and the fraction of satellite galaxies decreasing at higher luminosity. Central L* galaxies reside in halos a few times more massive at z~1 than at z~0. We find little evolution in the relation between mass scales of host halos for central galaxies and satellite galaxies a…
Using a large galaxy group catalogue constructed from the SDSS, we investigate the correlation between various galaxy properties and halo mass. We split the population of galaxies in early types, late types, and intermediate types, based on their colour and specific star formation rate. At fixed luminosity, the early type fraction increases with increasing halo mass. Most importantly, this mass dependence is smooth and persists over the entire mass range probed, without any break or feature at any mass scale. We argue that the previous claim of a characteristic feature on galaxy group scales i…
Successful halo-model descriptions of the luminosity dependence of clustering distinguish between the central galaxy in a halo and all the others (satellites). To include colors, we provide a prescription for how the color-magnitude relation of centrals and satellites depends on halo mass. This follows from two assumptions: (i) the bimodality of the color distribution at fixed luminosity is independent of halo mass, and (ii) the fraction of satellite galaxies which populate the red sequence increases with luminosity. We show that these two assumptions allow one to build a model of how galaxy c…
We use measurements of luminosity-dependent galaxy bias at several different redshifts, SDSS at $z=0.05$, DEEP2 at $z=1$ and LBGs at $z=3.8$, combined with WMAP five-year cosmic microwave background anisotropy data and SDSS Red Luminous Galaxy survey three-dimensional clustering power spectrum to put constraints on cosmological parameters. Fitting this combined dataset, we show that the luminosity-dependent bias data that probe the relation between halo bias and halo mass and its redshift evolution are very sensitive to sum of the neutrino masses: in particular we obtain the upper limit of $\s…
The relationship between galaxies and dark matter can be characterized by the halo mass of the central galaxy and the fraction of galaxies that are satellites. Here we present observational constraints from the SDSS on these quantities as a function of r-band luminosity and stellar mass using galaxy-galaxy weak lensing, with a total of 351,507 lenses. We use stellar masses derived from spectroscopy and virial halo masses derived from weak gravitational lensing to determine the efficiency with which baryons in the halo of the central galaxy have been converted into stars. We find that an L* gal…
The kinematics of satellite galaxies reflect the masses of the extended dark matter haloes in which they orbit, and thus shed light on the mass-luminosity relation (MLR) of their corresponding central galaxies. In this paper we select a large sample of centrals and satellites from the Sloan Digital Sky Survey (SDSS) and measure the kinematics (velocity dispersions) of the satellite galaxies as a function of the $r$-band luminosity of the central galaxies. Using the analytical framework presented in Paper I, we use these data to infer {\it both} the mean and the scatter of the MLR of central ga…
We study the alignments between the angular momentum of individual objects and the large-scale structure in cosmological numerical simulations and real data from the Sloan Digital Sky Survey, Data Release 6. To this end we measure anisotropies in the two point cross-correlation function around simulated halos and observed galaxies, studying separately the 1- and 2-halo regimes. The alignment of the angular momentum of dark-matter haloes in LCDM simulations is found to be dependent on scale and halo mass. At large distances (2-halo regime), the spins of high mass haloes are preferentially orien…
We investigate various halo occupation statistics using a large galaxy group catalogue constructed from the SDSS DR4 with an adaptive halo-based group finder. The conditional luminosity function (CLF) is measured separately for all, red and blue galaxies, as well as in terms of central and satellite galaxies. The CLFs for central and satellite galaxies can be well modelled with a log-normal distribution and a modified Schechter form, respectively. About 85% of the central galaxies and about 80% of the satellite galaxies in halos with masses $M_h\ga 10^{14}\msunh$ are red galaxies. These number…
We present spectroscopy of seven cataclysmic variable stars with orbital periods P(orb) greater than 5 hours, all but one of which are known to be dwarf novae. Using radial velocity measurements we improve on previous orbital period determinations, or derive periods for the first time. The stars and their periods are TT Crt, 0.2683522(5) d; EZ Del, 0.2234(5) d; LL Lyr, 0.249069(4) d; UY Pup, 0.479269(7) d; RY Ser, 0.3009(4) d; CH UMa, 0.3431843(6) d; and SDSS J081321+452809, 0.2890(4) d. For each of the systems we detect the spectrum of the secondary star, estimate its spectral type, and deriv…
We derive new constraints on the mass of the Milky Way's dark matter halo, based on a set of halo stars from SDSS as kinematic tracers. Our sample comprises 2401 rigorously selected Blue Horizontal-Branch (BHB) halo stars drawn from SDSS DR-6. To interpret these distributions, we compare them to matched mock observations drawn from two different cosmological galaxy formation simulations designed to resemble the Milky Way, which we presume to have an appropriate orbital distribution of halo stars. We then determine which value of $\rm V_{cir}(r)$ brings the observed distribution into agreement …
A 2.5 x 100 degree region along the celestial equator (Stripe 82) has been imaged repeatedly from 1998 to 2005 by the Sloan Digital Sky Survey. A new catalogue of ~4 million light-motion curves, together with over 200 derived statistical quantities, for objects in Stripe 82 brighter than r~21.5 has been constructed by combining these data by Bramich et al. (2007). This catalogue is at present the deepest catalogue of its kind. Extracting the ~130000 objects with highest signal-to-noise ratio proper motions, we build a reduced proper motion diagram to illustrate the scientific promise of the ca…
We have undertaken deep optical imaging observations of three 6.2<z<6.5 quasar fields in the i' and z' filters. These data are used to search for foreground galaxies which are gravitationally lensing the quasars and distant galaxies physically associated with the quasars. Foreground galaxies are found closer than 5 arcsec from the lines-of-sight of two of the three quasars. However, the faintness of these galaxies suggests they have fairly low masses and provide only weak magnifications (mu<1.1). No convincing galaxies physically associated with the quasars are found and the number of i'-band …
We present the results of a search for pulsations in six of the recently discovered carbon-atmosphere white dwarf ("hot DQ") stars. Based on our theoretical calculations, the star SDSS J142625.71+575218.3 is the only object expected to pulsate. We observe this star to be variable, with significant power at 417.7 s and 208.8 s (first harmonic), making it a strong candidate as the first member of a new class of pulsating white dwarf stars, the DQVs. Its folded pulse shape, however, is quite different from that of other white dwarf variables, and shows similarities with that of the cataclysmic va…
We identify galaxy groups and clusters in volume-limited samples of the SDSS redshift survey, using a redshift-space friends-of-friends algorithm. We optimize the friends-of-friends linking lengths to recover galaxy systems that occupy the same dark matter halos, using a set of mock catalogs created by populating halos of N-body simulations with galaxies. Extensive tests with these mock catalogs show that no combination of perpendicular and line-of-sight linking lengths is able to yield groups and clusters that simultaneously recover the true halo multiplicity function, projected size distribu…
We investigate the orientation correlation of giant elliptical galaxies by measuring the intrinsic ellipticity correlation function of 83,773 luminous red galaxies (LRGs) at redshifts 0.16 -- 0.47 from the Sloan Digital Sky Survey. We have accurately determined the correlation up to 30 $h^{-1}$Mpc. Luminosity dependence of the ellipticity correlation is also detected although the error bars are large, while no evidence is found for its redshift evolution between $z=0.2$ and $z=0.4$. Then we use a cosmological $N$-body simulation to examine misalignment between the central LRGs and their parent…
Two studies have recently reported the discovery of pronounced Halo substructure in the Sloan Digital Sky Survey (SDSS) commissioning data. Here we show that this Halo substructure is almost in its entirety due to the expected tidal stream torn off the Sagittarius dwarf galaxy during the course of its many close encounters with the Milky Way. This interpretation makes strong predictions on the kinematics and distances of these stream stars. Comparison of the structure in old horizontal branch stars, detected by the SDSS team, with the carbon star structure discovered in our own survey, indicat…
SDSS J162718.39+120435.0 was suspected of being a dwarf nova from spectroscopic observations made available by the Sloan Digital Sky Survey. Photometry conducted during the 2008 outburst, the first ever outburst of this object detected and followed up in real time, shows that the outburst reached magnitude 14.6 at maximum, had an amplitude of 4.6 magnitudes and lasted for at least 18 days. Common superhumps were detected with an amplitude of up to 0.4 magnitudes, confirming it to be a member of the SU UMa family. Initially the superhump period, Psh, was 0.10993(7) days (2.638 hours), but it su…
We analyze the small-scale clustering in "MegaZ-LRG", a large photometric-redshift catalogue of Luminous Red Galaxies extracted from the imaging dataset of the Sloan Digital Sky Survey. MegaZ-LRG, presented in a companion paper, spans the redshift range 0.4 < z < 0.7 with an r.m.s. redshift error dz ~ 0.03(1+z), covering 5,914 deg^2 to map out a total cosmic volume 2.5 h^-3 Gpc^3. In this study we use 380,000 photometric redshifts to measure significant deviations from the canonical power-law fit to the angular correlation function in a series of narrow redshift slices, in which we construct v…
