Search

In Smith et al. we published estimates of the volumetric rate of supernovae within 100 Mpc. These were incorrect and we present the correct values in this corrigendum.

We report the results of the Mount Stromlo Abell cluster supernova search, a three-year project to find supernovae (SNe) in a well-defined sample of high-density, southern Abell clusters with redshifts 0.02 ≥ z ≥ 0.08. The search discovered 48 SNe, 23 of which were consistent with SNe of type Ia (SNIa). Of these, 15 were spectroscopically classified SNIa, with the remaining 8 SNe tentatively classified as SNIa via the goodness of fit of the template light curves. This paper describes the methods employed to produce the light curves for the SNe discovered during the Mount Stromlo Abell cluster supernova search. We derive the redshift-independent distances to the SNIa from the search, as well as a large sample of other well-observed SNIa taken from the literature via a modified Δm15 template light curve fitting technique. This technique and the problems encountered in using it are described in detail. We construct a Hubble diagram for SNIa and show that our data with z < 0.2 are consistent with an accelerating universe. Using current Cepheid HST calibrations, we estimate that the value of the Hubble constant lies between 53 < H0 < 83 km-1 s-1 Mpc-1, with the large spread almost entirely due to possible systematic errors in the Cepheid calibration.

We report on a search for long duration microlensing events towards the Large Magellanic Cloud. We find none, and therefore put limits on the contribution of high mass objects to the Galactic dark matter. At 95% confidence level we exclude objects in the mass range 0.3 solar masses to 30.0 solar masses from contributing more than 4 times 10^11 solar masses to the Galactic halo. Combined with earlier results, this means that objects with masses under 30 solar masses cannot make up the entire dark matter halo if the halo is of typical size. For a typical dark halo, objects with masses under 10 solar masses contribute less than 40% of the dark matter.

We present observations of SN1997cy, a supernova discovered as part of the Mount Stromlo Abell Cluster SN Search, which does not easily fit into the traditional classification scheme for supernovae. This object's extraordinary optical properties and coincidence with GRB970514, a short duration gamma ray burst, suggest a second case, after SN1998bw/GRB980425, for a SN-GRB association. SN1997cy is among the most luminous SNe yet discovered and has a peculiar spectrum. We present evidence that SN1997cy ejected approximately 2 solar masses of 56Ni, supported by its late-time light curve, and FeII/[FeIII] lines in its spectrum, although it is possible that both these observations can be explained via circumstellar interaction. While SN1998bw and SN1997cy appear to be very different objects with respect to both their gamma ray and optical properties, SN1997cy and the optical transient associated with GRB970508 have roughly similar late-time optical behavior. This similarity may indicate that the late-time optical output of these two intrinsically bright transient events have a common physical process. Although the connection between GRB970514 and SN1997cy is suggestive, it is not conclusive. However, if this association is real, followup of short duration GRBs detected with BATSE or HETE2 should reveal objects similar to SN1997cy.

We have initiated a three-year project to find supernovae (SNe) in a well-defined sample of high-density southern Abell clusters with redshifts $z\leq0.08$. These observations will provide a volume-limited sample of SNe Ia to more than a magnitude below their peak brightness, and will enable us to: (1) measure the luminosity function of SNe, (2) further explore the correlation of light curve shape with the absolute luminosity of SNe Ia to better understand SNe Ia as distance indicators, (3) measure SN rates, (4) measure the bulk motion of the Local Group using SNe Ia, and (5) directly compare SN Ia distances to brightest cluster galaxy distances. We use the MaCHO wide-field 2-color imager on the 1.3m telescope at Mount Stromlo to routinely monitor $\sim 12$ clusters per week. We describe our technique for target selection and scheduling search observations, and for finding and identifying SN candidates. We also describe the results from the first year of our program, including the detection of 19 SNe, several RR-Lyrae variables, and hundreds of asteroids., Comment: 20 pages, 10 figures, 3 tables. Accepted for publication in AJ, Jan. 1998 issue

We use measurements from the South Pole Telescope (SPT) Sunyaev-Zel'dovich (SZ) cluster survey in combination with X-ray measurements to constrain cosmological parameters. We present a statistical method that fits for the scaling relations of the SZ and X-ray cluster observables with mass while jointly fitting for cosmology. The method is generalizable to multiple cluster observables, and self-consistently accounts for the effects of the cluster selection and uncertainties in cluster mass calibration on the derived cosmological constraints. We apply this method to a data set consisting of an SZ-selected catalog of 18 galaxy clusters at z > 0.3 from the first 178 deg^2 of the 2500 deg^2 SPT-SZ survey, with 14 clusters having X-ray observations from either Chandra or XMM-Newton. Assuming a spatially flat ΛCDM cosmological model, we find the SPT cluster sample constrains σ_8(Ω_m /0.25)^(0.30) = 0.785 ± 0.037. In combination with measurements of the cosmic microwave background (CMB) power spectrum from the SPT and the seven-year Wilkinson Microwave Anisotropy Probe data, the SPT cluster sample constrains σ_8 = 0.795 ± 0.016 and Ω_m = 0.255 ± 0.016, a factor of 1.5 improvement on each parameter over the CMB data alone. We consider several extensions beyond the ΛCDM model by including the following as free parameters: the dark energy equation of state (w), the sum of the neutrino masses (Σm ν), the effective number of relativistic species (N_(eff)), and a primordial non-Gaussianity (f_(NL)). We find that adding the SPT cluster data significantly improves the constraints on w and Σm_ν beyond those found when using measurements of the CMB, supernovae, baryon acoustic oscillations, and the Hubble constant. Considering each extension independently, we best constrain w = –0.973 ± 0.063 and the sum of neutrino masses Σm_ν < 0.28 eV at 95% confidence, a factor of 1.25 and 1.4 improvement, respectively, over the constraints without clusters. Assuming a ΛCDM model with a free N_(eff) and Σm_ν, we measure N_(eff) = 3.91 ± 0.42 and constrain Σm_ν < 0.63 eV at 95% confidence. We also use the SPT cluster sample to constrain f_(NL) = –220 ± 317, consistent with zero primordial non-Gaussianity. Finally, we discuss the current systematic limitations due to the cluster mass calibration, and future improvements for the recently completed 2500 deg^2 SPT-SZ survey. The survey has detected ~500 clusters with a median redshift of ~0.5 and a median mass of ~2.3 × 10^(14) M_☉ h^(–1) and, when combined with an improved cluster mass calibration and existing external cosmological data sets will significantly improve constraints on w.

We present results of X-ray observations of a sample of 15 clusters selected via their imprint on the cosmic microwave background from the thermal Sunyaev-Zel'dovich (SZ) effect. These clusters are a subset of the first SZ-selected cluster catalog, obtained from observations of 178 deg^2 of sky surveyed by the South Pole Telescope (SPT). Using X-ray observations with Chandra and XMM-Newton, we estimate the temperature, T_X, and mass, M_g, of the intracluster medium within r_500 for each cluster. From these, we calculate Y_X = M_(g)T_X and estimate the total cluster mass using an M_(500)-Y_X scaling relation measured from previous X-ray studies. The integrated Comptonization, Y SZ, is derived from the SZ measurements, using additional information from the X-ray-measured gas density profiles and a universal temperature profile. We calculate scaling relations between the X-ray and SZ observables and find results generally consistent with other measurements and the expectations from simple self-similar behavior. Specifically, we fit a Y_(SZ)-Y_X relation and find a normalization of 0.82 ± 0.07, marginally consistent with the predicted ratio of Y_(SZ)/Y_X = 0.91 ± 0.01 that would be expected from the density and temperature models used in this work. Using the Y_X-derived mass estimates, we fit a Y_(SZ)-M_500 relation and find a slope consistent with the self-similar expectation of Y_(SZ) ∝ M^(5/3) with a normalization consistent with predictions from other X-ray studies. We find that the SZ mass estimates, derived from cosmological simulations of the SPT survey, are lower by a factor of 0.78 ± 0.06 relative to the X-ray mass estimates. This offset is at a level of 1.3σ when considering the ~15% systematic uncertainty for the simulation-based SZ masses. Overall, the X-ray measurements confirm that the scaling relations of the SZ-selected clusters are consistent with the properties of other X-ray-selected samples of massive clusters, even allowing for the broad redshift range (0.29 < z < 1.08) of the sample.

The Large Synoptic Survey Telescope (LSST) will be a large, wide-field ground-based system designed to obtain, starting in 2015, multiple images of the sky that is visible from Cerro Pachon in Northern Chile. About 90% of the observing time will be devoted to a deep-wide-fast survey mode which will observe a 20,000 deg$^2$ region about 1000 times during the anticipated 10 years of operations (distributed over six bands, $ugrizy$). Each 30-second long visit will deliver 5$\sigma$ depth for point sources of $r\sim24.5$ on average. The co-added map will be about 3 magnitudes deeper, and will include 10 billion galaxies and a similar number of stars. We discuss various measurements that will be automatically performed for these 20 billion sources, and how they can be used for classification and determination of source physical and other properties. We provide a few classification examples based on SDSS data, such as color classification of stars, color-spatial proximity search for wide-angle binary stars, orbital-color classification of asteroid families, and the recognition of main Galaxy components based on the distribution of stars in the position-metallicity-kinematics space. Guided by these examples, we anticipate that two grand classification challenges for LSST will be 1) rapid and robust classification of sources detected in difference images, and 2) {\it simultaneous} treatment of diverse astrometric and photometric time series measurements for an unprecedentedly large number of objects., Comment: Presented at the "Classification and Discovery in Large Astronomical Surveys" meeting, Ringberg Castle, 14-17 October, 2008

We present the first constraints on pure-gravity sector Standard-Model Extension (SME) parameters using Lunar Laser Ranging (LLR). LLR measures the round trip travel time of light between the Earth and the Moon. With 34+ years of LLR data, we have constrained six independent linear combinations of SME parameters at the level of $10^{-6}$ to $10^{-11}$. There is no evidence for Lorentz violation in the LLR dataset., 7 pages, presented at the Fourth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, August 2007

The MACHO Project is a microlensing survey that monitors the brightnesses of 60 million stars in the Large Magellanic Cloud (LMC), Small Magellanic Cloud, and Galactic bulge. Our database presently contains about 80 billion photometric measurements, a significant fraction of all astronomical photometry. We describe the calibration of MACHO two-color photometry and transformation to the standard Kron-Cousins V and R system. Calibrated MACHO photometry may be properly compared with all other observations on the Kron-Cousins standard system, enhancing the astrophysical value of these data. For 9 million stars in the LMC bar, independent photometric measurements of 20,000 stars with V < 18 mag in field-overlap regions demonstrate an internal precision sigV = 0.021, sigR = 0.019, and sig(V-R) = 0.028 mag. The accuracy of the zero-point in this calibration is estimated to be +-0.035 mag for stars with colors in the range -0.1 < (V-R) < 1.2 mag. A comparison of calibrated MACHO photometry with published photometric sequences and new Hubble Space Telescope observations shows agreement. The current calibration zero-point uncertainty for the remainder of the MACHO photometry database is estimated to be +- 0.10 mag in V or R and +-0.04 mag in (V-R). We describe the first application of calibrated MACHO photometry data: the construction of a color-magnitude diagram used to calculate our experimental sensitivity to detect microlensing in the LMC., to appear in PASP, 11pt aaspp4.sty, 47 pages, includes 21 figures (4 are bitmapped)

The MACHO project carries out regular photometric monitoring of millions of stars in the Magellanic Clouds and Galactic Bulge, to search for very rare gravitational microlensing events due to compact objects in the galactic halo and disk. A preliminary analysis of one field in the Galactic Bulge, containing {$\sim430,000$} stars observed for 190 days, reveals four stars which show clear evidence for brightenings which are time-symmetric, achromatic in our two passbands, and have shapes consistent with gravitational microlensing. This is significantly higher than the $\sim 1$ event expected from microlensing by known stars in the disk. If all four events are due to microlensing, a 95\% confidence lower limit on the optical depth towards our bulge field is $1.3 \times 10^{-6}$, and a ``best fit" value is $\tau \approx 1.6 \times 10^{-6}/\epsilon$,where $\epsilon$ is the detection efficiency of the experiment, and $\epsilon < 0.4$. If the true optical depth is close to the ``best fit" value, possible explanations include a ``maximal" disk which accounts for most of the galactic circular velocity at the solar radius, a halo which is centrally concentrated, or bulge-bulge microlensing., Comment: submitted to Astrophysical Journal Letters, 10 pages text as uuencoded compressed PostScript, 5 figures and paper also available via anonymous ftp from merlin.anu.edu.au in /pub/kcf/macho

We have developed an astronomical imaging system tailored to our search for gravitational microlensing by compact objects in the halo and disk of the Galaxy. The challenge of detecting rare microlensing events is to monitor ∼10 million stars per night and distinguish genuine events from other sources of variability. The Large Magellanic Cloud and the Galactic bulge provide the high surface density of resolvable stars necessary for this task. A dedicated 50 inch telescope at Mt. Stromlo Observatory has been producing science data since the fall of 1992. Our system incorporates eight 2048 x 2048 CCDs into two focal planes for simultaneous imaging in two passbands (4500-6300 and 6300-8100 A). Each focal plane consists of four ‘edge-buttable’ CCDs in a custom mounted 2 x 2 array. The 0.62 arcsecond pixel scale (15 μ) yields a 40 x 40 arcminute square field of view in each frame. A sophisticated point spread fitting photometry package extracts up to 600,000 useful magnitudes per color per frame. The data collection rate we need is obtained by simultaneously reading out all sixteen CCD outputs (two per chip) at 34 KHz with 16 bit digitization. With exposure times of 150-300 seconds and a 70 second readout time we can collect up to 100 fields per night. These rates are designed to allow us to detect or rule out massive compact halo objects (MACHOs) in the 10-6 - 10 1 M⊙range.

SN2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SNIa), and a member of the distinct SN2002cx-like class of SNeIa. Its light curves are similar to the prototypical SN2002cx, but are slightly broader and have a later rise to maximum in g. SN2009ku is brighter (~0.6 mag) than other SN2002cx-like objects, peaking at M_V = -18.4 mag - which is still significantly fainter than typical SNeIa. SN2009ku, which had an ejecta velocity of ~2000 kms^-1 at 18 days after maximum brightness is spectroscopically most similar to SN2008ha, which also had extremely low-velocity ejecta. However, SN2008ha had an exceedingly low luminosity, peaking at M_V = -14.2 mag, ~4 mag fainter than SN2009ku. The contrast of high luminosity and low ejecta velocity for SN2009ku is contrary to an emerging trend seen for the SN2002cx class. SN2009ku is a counter-example of a previously held belief that the class was more homogeneous than typical SNeIa, indicating that the class has a diverse progenitor population and/or complicated explosion physics. As the first example of a member of this class of objects from the new generation of transient surveys, SN2009ku is an indication of the potential for these surveys to find rare and interesting objects., Comment: 7 pages, 3 figures