Distance to the Sagittarius Dwarf Galaxy using MACHO Project RR Lyrae stars

We derive the distance to the northern extension of the Sagittarius (Sgr) dwarf spheroidal galaxy from 203 Sgr RR0 Lyrae stars found in the MACHO database. Their distances are determined differentially with respect to 288 Galactic Bulge RR0 Lyrae stars also found in the MACHO data. We find a distance modulus difference of 2.41 mags at $l$ = 5$^{\circ}$ and $b$ = -8$^{\circ}$ and that the extension of the Sgr galaxy towards the galactic plane is inclined toward us. Assuming $\rm R_{GC}$ = 8 kpc, this implies the distance to these stars is $(m-M)_0$ = 16.97 $\pm$ 0.07 mags, which corresponds to D = 24.8 $\pm$ 0.8 kpc. Although this estimate is smaller than previous determinations for this galaxy and agrees with previous suggestions that Sgr's body is truly closer to us, this estimate is larger than studies at comparable galactic latitudes.Comment: accepted in A

An Oosterhoff Analysis of the Galactic Bulge Field RR Lyrae stars: Implications On Their Absolute Magnitudes

We present an analysis of the period-$V$-amplitude plane for RR0 Lyrae stars (fundamental mode pulsators) with "normal" light curves in the bulge using the MACHO bulge fields. Although bulge globular clusters have RR Lyraes that divide into two reasonable distinct groups according to the average period of the RR0 Lyraes (Oosterhoff 1939), there is no evidence of a gap between Oosterhoff I and II stars in the bulge field star sample. The majority of the bulge RR0 Lyrae field star population have a difference in period compared to the Oosterhoff I cluster M3 (Delta log P) that is shifted by about 0.02 days with regard to the Milky Way Oosterhoff I population, and the sample includes stars with Delta log P > 0.06 days, a characteristic hardly seen in Milky Way globular clusters. The metal-rich RR0 Lyrae stars in the Galactic bulge sample have Delta log P values on the other side of the spectrum as those in the metal-rich globular clusters NGC 6388 and NGC 6441. We find that the $V$-amplitude for a given period is a function of Delta log P, and not of metal abundance, similar to the result found by Clement & Shelton (1999) for RR Lyrae stars in Milky Way globular clusters. A comparative study of the bulge field stars with similar metallicities but different Oosterhoff types is carried out. Bulge field RR0 Lyrae variables with Delta log P values similar to Oosterhoff II clusters are about 0.2 mag brighter than RR0 Lyrae variables with Delta log P similar to Oosterhoff I clusters. Reliance upon a single absolute magnitude-[Fe/H] relation may be inappropriate when considering populations with different Delta log P.Comment: accepted to AJ, 9 figure

Identification of the Microlens in Event MACHO-LMC-20

We report on the identification of the lens responsible for microlensing event MACHO-LMC-20. As part of a \textit{Spitzer}/IRAC program conducting mid-infrared follow-up of the MACHO Large Magellanic Cloud microlensing fields, we discovered a significant flux excess at the position of the source star for this event. These data, in combination with high resolution near-infrared \textit{Magellan}/PANIC data has allowed us to classify the lens as an early M dwarf in the thick disk of the Milky Way, at a distance of $\sim 2$ kpc. This is only the second microlens to have been identified, the first also being a M dwarf star in the disk. Together, these two events are still consistent with the expected frequency of nearby stars in the Milky Way thin and thick disks acting as lenses.Comment: 6 pages, 4 figures, submitted to ApJ Letter

The Determination Of Reddening From Intrinsic VR Colors Of RR Lyrae Stars

New R-band observations of 21 local field RR Lyrae variable stars are used to explore the reliability of minimum light (V-R) colors as a tool for measuring interstellar reddening. For each star, R-band intensity mean magnitudes and light amplitudes are presented. Corresponding V-band light curves from the literature are supplemented with the new photometry, and (V-R) colors at minimum light are determined for a subset of these stars as well as for other stars in the literature. Two different definitions of minimum light color are examined, one which uses a Fourier decomposition to the V and R light curves to find (V-R) at minimum V-band light, (V-R)_{min}^F, and the other which uses the average color between the phase interval 0.5-0.8, (V-R)_{min}^{\phi(0.5-0.8)}. From 31 stars with a wide range of metallicities and pulsation periods, the mean dereddened RR Lyrae color at minimum light is (V-R)_{min,0}^F = 0.28 pm 0.02 mag and (V-R)_{min,0}^{\phi(0.5-0.8)} = 0.27 pm 0.02 mag. As was found by Guldenschuh et al. (2005) using (V-I) colors, any dependence of the star's minimum light color on metallicity or pulsation amplitude is too weak to be formally detected. We find that the intrinsic (V-R) of Galactic bulge RR Lyrae stars are similar to those found by their local counterparts and hence that Bulge RR0 Lyrae stars do not have anomalous colors as compared to the local RR Lyrae stars.Comment: accepted by A

Library 2.0: balancing the risks and benefits to maximise the dividends

Purpose \u2013 The purpose of this paper is to provide a number of examples of how Web 2.0 technologies and approaches (Library 2.0) are being used within the library sector. The paper acknowledges that there are a variety of risks associated with such approaches. The paper describes the different types of risks and outlines a risk assessment and risk management approach which is being developed to minimise the dangers while allowing the benefits of Library 2.0 to be realised. Design/methodology/approach \u2013 The paper outlines various risks and barriers which have been identified at a series of workshops run by UKOLN (a national centre of expertise in digital information management based in the UK) for the cultural heritage sector. A risk assessment and risk management approach, which was initially developed to support use of Web 2.0 technologies at events organised by UKOLN, is described and its potential for use within the wider library community, in conjunction with related approaches for addressing areas such as accessibility and protection of young people, is described. Findings \u2013 Use of Library 2.0 approaches is becoming embedded across many libraries which seek to exploit the benefits which such technologies can provide. The need to ensure that the associated risks are identified and appropriate mechanisms implemented to minimise such risks is beginning to be appreciated. Practical implications \u2013 The areas described here should be of relevance to many library organisations which are making use of Library 2.0 services.Peer reviewed: YesNRC publication: Ye

Difference Imaging of Lensed Quasar Candidates in the SDSS Supernova Survey Region

Difference imaging provides a new way to discover gravitationally lensed quasars because few non-lensed sources will show spatially extended, time variable flux. We test the method on lens candidates in the Sloan Digital Sky Survey (SDSS) Supernova Survey region from the SDSS Quasar Lens Search (SQLS) and their surrounding fields. Starting from 20768 sources, including 49 SDSS quasars and 36 candidate lenses/lensed images, we find that 21 sources including 15 SDSS QSOs and 7 candidate lenses/lensed images are non-periodic variable sources. We can measure the spatial structure of the variable flux for 18 of these sources and identify only one as a non-point source. This source does not display the compelling spatial structure of the variable flux of known lensed quasars, so we reject it as a lens candidate. None of the lens candidates from the SQLS survive our cuts. Given our effective survey area of order 0.71 square degrees, this indicates a false positive rate of order one per square degree for themethod. The fraction of quasars not found to be variable and the false positive rate should both fall if we analyze the full, later data releases for the SDSS fields. While application of the method to the SDSS is limited by the resolution, depth, and sampling of the survey, several future surveys such as Pan-STARRS, LSST, and SNAP will avoid these limitations.Comment: Submitted to ApJ, 24 pages, 5 figure

Can policy be risk-based? The cultural theory of risk and the case of livestock disease containment

This article explores the nature of calls for risk-based policy present in expert discourse from a cultural theory perspective. Semi-structured interviews with professionals engaged in the research and management of livestock disease control provide the data for a reading proposing that the real basis of policy relating to socio-technical hazards is deeply political and cannot be purified through ‘escape routes’ to objectivity. Scientists and risk managers are shown calling, on the one hand, for risk-based policy approaches while on the other acknowledging a range of policy drivers outside the scope of conventional quantitative risk analysis including group interests, eventualities such as outbreaks, historical antecedents, emergent scientific advances and other contingencies. Calls for risk-based policy are presented, following cultural theory, as ideals connected to a reductionist epistemology and serving particular professional interests over others rather than as realistic proposals for a paradigm shift