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Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H0by measuring the time delays between the quasar images. Here we report the measurement of two independent time delays in the quadruply imaged quasar WFI J2033-4723  (z= 1.66). Our data consist of R-band images obtained with the Swiss 1.2 m EULER telescope located at La Silla and with the 1.3 m SMARTS telescope located at Cerro Tololo. The light curves have 218 independent epochs spanning 3 full years of monitoring between March 2004 and May 2007, with a mean temporal sampling of one observation every 4th day. We measure the time delays using three different techniques, and we obtain $\Delta t_{B-A}$= 35.5 ±1.4 days (3.8%) and $\Delta t_{B-C} = 62.6^{+\,4.1}_{-\,2.3}~{\rm days} ~\ (^{+\,6.5\%}_{-\,3.7\%})$, where Ais a composite of the close, merging image pair. After correcting for the time delays, we find R-band flux ratios of $F_{A}/F_{B} = 2.88$±0.04, $F_{A}/F_{C} = 3.38$±0.06, and $F_{A1}/F_{A2} = 1.37$±0.05 with no evidence for microlensing variability over a time scale of three years. However, these flux ratios do not agree with those measured in the quasar emission lines, suggesting that longer term microlensing is present. Our estimate of H0agrees with the concordance value: non-parametric modeling of the lensing galaxy predicts H0= 67$^{+13}_{-10}$km s-1Mpc-1, while the Single Isothermal Sphere model yields H0= 63$^{+7}_{-3}$km s-1Mpc-1(68% confidence level). More complex lens models using a composite de Vaucouleurs plus NFW galaxy mass profile show twisting of the mass isocontours in the lensing galaxy, as do the non-parametric models. As all models also require a significant external shear, this suggests that the lens is a member of the group of galaxies seen in field of view of WFI J2033-4723.

We present the first results from Citizen ASAS-SN, a citizen science project for the All-Sky Automated Survey for Supernovae (ASAS-SN) hosted on the Zooniverse platform. Citizen ASAS-SN utilizes the newer, deeper, higher cadence ASAS-SN g-band data and tasks volunteers to classify periodic variable star candidates based on their phased light curves. We started from 40,640 new variable candidates from an input list of ∼7.4 million stars with δ< −60° and the volunteers identified 10,420 new discoveries which they classified as 4234 pulsating variables, 3132 rotational variables, 2923 eclipsing binaries, and 131 variables flagged as Unknown. They classified known variable stars with an accuracy of 89% for pulsating variables, 81% for eclipsing binaries, and 49% for rotational variables. We examine user performance, agreement between users, and compare the citizen science classifications with our machine learning classifier updated for the g-band light curves. In general, user activity correlates with higher classification accuracy and higher user agreement. We used the user’s “Junk” classifications to develop an effective machine learning classifier to separate real from false variables, and there is a clear path for using this “Junk” training set to significantly improve our primary machine learning classifier. We also illustrate the value of Citizen ASAS-SN for identifying unusual variables with several examples.

We performed an automated comparison of the FIRST radio survey with the Automatic Plate Measuring (APM) optical catalog to find radio lobes with optical counterparts. Based on an initial survey covering ~3000 deg2, we selected a sample of 33 lens candidates for VLA confirmation. VLA and optical observations of these candidates yielded two lens systems, one a new discovery (J0816+5003) and one that was previously known (J1549+3047). Two other candidates have radio lobes with galaxies superposed but lack evidence of multiple imaging. One of our targets (J0958+2947) is a projected close pair of quasars (8'' separation at redshifts 2.064 and 2.744). Our search method is highly efficient, with greater than 5% of our observing targets being lensed, compared to the usual success rate of less than 1%. Using the whole FIRST survey, we expect to find five to 10 lenses in short order using this approach, and the sample could increase to hundreds of lensed lobes in the northern sky, using deeper optical surveys and planned upgrades to the VLA. Such a sample would be a powerful probe of galaxy structure and evolution.

We develop a theory of Einstein rings and demonstrate it using the infrared Einstein ring images of the quasar host galaxies observed in PG 1115+080, B1608+656, and B1938+666. The shape of an Einstein ring accurately and independently determines the shape of the lens potential and the shape of the lensed host galaxy. We find that the host galaxies of PG 1115+080, B1608+656, and B1938+666 have axis ratios of 0.58 ± 0.02, 0.69 ± 0.02, and 0.62 ± 0.14, respectively, including the uncertainties in the lens models. The Einstein rings break the degeneracies in the mass distributions or Hubble constants inferred from observations of gravitational lenses. In particular, the Einstein ring in PG 1115+080 rules out the centrally concentrated mass distributions that lead to a high Hubble constant (H0> 60 km s-1Mpc-1) given the measured time delays. Deep, detailed observations of Einstein rings will be revolutionary for constraining mass models and determining the Hubble constant from time-delay measurements.

We report on a program to obtain Hubble Space Telescope(HST) observations of galaxy-mass gravitational lens systems at optical and infrared wavelengths. Here we discuss the properties of 10 two-image gravitational lens systems (Q0142-100 = UM 673, B0218+357, SBS 0909+532, BRI 0952-0115, LBQS 1009-0252, Q1017-207 = J03.13, B1030+074, HE 1104-1805, Q1208+1011, and PKS 1830-211). We grouped these 10 systems because they have limited lens model constraints and often show poor contrast between the images and the lens galaxy. Of the 10 lens galaxies, seven are probably early-type galaxies, two are probably late-type galaxies (B0218+357 and PKS 1830-211), and one was not detected (Q1208+1011). We detect the host galaxies of the zs= 4.50 lensed quasar in BRI 0952-0115, the zs= 2.32 lensed quasar in HE 1104-1805, and the unlensed z= 1.63 quasar near LBQS 1009-0252. We fit a set of four standard lens models to each lens that had sufficient constraints to compare isothermal dark matter and constant mass-to-light lens models, and to explore the effects of local tidal shears.

We study gravitational lensing by spiral galaxies, using realistic models consisting of halo, disk, and bulge components combined to produce a flat rotation curve. Proper dynamical normalization of the models is critical because a disk has less (projected) mass than does a spherical halo with the same rotation curve-a face-on Mestel disk has a lensing cross section only 41% as large as that of a comparable singular isothermal sphere. Lensing cross sections are sensitive to inclination and are dominated by edge-on galaxies that, if very flattened, produce a large number of lenses with an unobserved image geometry consisting of 2 or 3 images off to one side of the galaxy center and straddling the projected disk. The absence of this "disk" image geometry among known lenses suggests that lens galaxies cannot be highly flattened. When averaged over inclination, disk+halo models predict 10% more lenses than do pure halo models, except in cases in which the disk is unreasonably massive, so including a disk does not significantly increase the expected number of spiral galaxy lenses. Models with an exponential disk and a central bulge are sensitive to the properties of the bulge. In particular, an exponential disk model normalized to our Galaxy but without a bulge cannot produce multiple images, and including a bulge reduces the net flattening of edge-on galaxies. The dependence of the lensing properties on the masses and shapes of the halo, disk, and bulge means that a sample of spiral galaxy lenses would provide useful constraints on galactic structure.

We are conducting a redshift survey of 177 flat-spectrum radio sources in three samples covering the 5 GHz flux ranges 50-100, 100-200, and 200-250 mJy. So far, we have measured 124 redshifts with completenesses of 80%, 68%, and 58% for the bright, intermediate, and faint flux ranges. Using the newly determined redshift distribution, we can derive cosmological limits from the statistics of the six gravitational lenses in the Jodrell Bank-VLA Astrometric Survey sample of 2500 flat-spectrum radio sources brighter than 200 mJy at 5 GHz. For flat cosmological models with a cosmological constant, the limit using only radio data is ?0> 0.27 at 2 ? (0.47 < ?0< 1.38 at 1 ?). The limits are statistically consistent with those for lensed quasars, and the combined radio + optical sample requires ?0> 0.38 at 2 ? (0.64 < ?0< 1.66 at 1 ?) for our most conservative redshift completeness model, assuming that there are no quasar lenses produced by spiral galaxies. Our best-fit model improves by approximately 1 ? if extinction in the early-type galaxies makes the lensed quasars fainter by ?m= 0.58 ± 0.45 mag, but we still find a limit of ?0> 0.26 at 2 ? in flat cosmologies. The increasing fraction of radio galaxies as compared to quasars at fainter radio fluxes (rising from ~10% at 1 Jy to ~50% at 0.1 Jy) explains why lensed optical emission is common for radio lenses and partly explains the red color of radio-selected lenses.

We develop a statistical method for using multicolor photometry to determine distances using Cepheid variables, including the effects of temperature, extinction, and metallicity, and apply it to UBVRIJHKphotometry of 694 Cepheids in 17 galaxies. We derive homogeneous distance, extinction, and uncertainty estimates for four models, starting from the standard extragalactic method and then adding the physical effects of temperature distributions and extinction distributions, requiring positive definite extinctions and metallicity. While we find general agreement with published distances when we make similar systematic assumptions, there is a clear problem in the standard distances because they require Cepheids with negative extinctions, particularly in low-metallicity galaxies, unless the mean LMC extinction exceeds E(B- V) 0.20. The problem can be explained by the physically expected metallicity dependence of the Cepheid distance scale, where metal-poor Cepheids are hotter and possibly fainter at Vand Ithan metal-rich Cepheids, or by large systematic errors in Cepheid photometry. For Vand Iwe found that the mean magnitude change is -0.14 ± 0.14 mag dex-1and the mean color change is 0.13 ± 0.04 mag dex-1, with the change in color dominating the change in distance. The effect on Type Ia supernova estimates of the Hubble constant is dramatic because most were found in the metal-poor galaxies with the bluest Cepheids. The Type Ia multicolor light-curve shape method estimate for H0formally rises from 69 ± 8 to 80 ± 6 km s-1Mpc-1with the metallicity correction.

We describe the goals of the CASTLES (CfA-Arizona-Space-Telescope-LEns-Survey) project including a sample of NICMOS images of gravitational lenses and a brief list of the preliminary findings.

The All-Sky Automated Survey for Supernovae (ASAS-SN) is working toward imaging the entire visible sky every night to a depth of mag. The present data covers the sky and spans ?2-5 years with ?100-400 epochs of observation. The data should contain some ?1 million variable sources, and the ultimate goal is to have a database of these observations publicly accessible. We describe here a first step, a simple but unprecedented web interface https://asas-sn.osu.edu/that provides an up to date aperture photometry light curve for any user-selected sky coordinate. The Vband photometry is obtained using a two-pixel (16.?0) radius aperture and is calibrated against the APASS catalog. Because the light curves are produced in real time, this web tool is relatively slow and can only be used for small samples of objects. However, it also imposes no selection bias on the part of the ASAS-SN team, allowing the user to obtain a light curve for any point on the celestial sphere. We present the tool, describe its capabilities, limitations, and known issues, and provide a few illustrative examples.

In this paper, we present for the first time a proper-motion-selected white dwarf (WD) sample of the old Galactic open cluster M 67, down to the bottom of the WD cooling sequence (CS). The color-magnitude diagram is based on data collected with the LBC-Blue camera at the prime-focus of LBT. As first epoch data, we used CFHT-archive images collected 10 years before LBC data. We measured proper motions of all the identified sources. Proper motions are then used to separate foreground and background objects from the cluster stars, including WDs. Finally, the field-object cleaned WD CS in the Vvs. B–Icolor-magnitude diagram is compared with the models. We confirm that the age derived from the location of the bottom of the WD CS is consistent with the turn off age.

In this paper, we present for the first time a proper-motion-selected white dwarf (WD) sample of the old Galactic open cluster M 67, down to the bottom of the WD cooling sequence (CS). The color-magnitude diagram is based on data collected with the LBC-Blue camera at the prime-focus of LBT. As first epoch data, we used CFHT-archive images collected 10 years before LBC data. We measured proper motions of all the identified sources. Proper motions are then used to separate foreground and background objects from the cluster stars, including WDs. Finally, the field-object cleaned WD CS in the Vvs. B–Icolor-magnitude diagram is compared with the models. We confirm that the age derived from the location of the bottom of the WD CS is consistent with the turn off age.