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A New Reddening Law for M4
Benjamin Hendricks,Peter B. Stetson,Don A. VandenBerg,Massimo Dall'Ora
Physics , 2012, DOI: 10.1088/0004-6256/144/1/25
Abstract: We have used a combination of broad-band near-infrared and optical Johnson-Cousins photometry to study the dust properties in the line of sight to the Galactic globular cluster M4. We have investigated the reddening effects in terms of absolute strength and variation across the cluster field, as well as the form of the reddening law defined by the type of dust. Here, we determine the ratio of absolute to selective extinction (R_V) in the line of sight towards M4, which is known to be a useful indicator for the type of dust and therefore characterizes the applicable reddening law. Our method is independent of age assumptions and appears to be significantly more precise and accurate than previous approaches. We obtain A_V/E(B-V)=3.76\pm0.07 (random error) for the dust in the line of sight to M4 for our set of filters. With this value, the distance to M4 is found to be 1.80\pm0.05 kpc (random error). A reddening map for M4 has been created, which reveals a spatial differential reddening of delta E(B-V)>0.2 mag across a field within 10' around the cluster centre and a total mean reddening of E(B-V)=0.37\pm0.01. In order to provide accurate zero points for the extinction coefficients of our photometric filters, we investigated the impact of stellar parameters such as temperature, surface gravity and metallicity on the extinction properties in different bandpasses. Using both synthetic ATLAS9 spectra and observed spectral energy distributions, we found similar sized effects for the range of temperature, surface gravity, and metallicity typical of globular cluster stars: each causes a change of about 3% in the necessary correction factor for each filter combination. From our calculations, we provide extinction zero points for Johnson-Cousins and 2MASS filters, spanning a wide range of stellar parameters and dust types, suited for accurate, object-specific extinction corrections.
Fiducial Stellar Population Sequences for the VJKs Photometric System
Crystal Brasseur,Peter B. Stetson,Don A. VandenBerg,Luca Casagrande,Giuseppe Bono,Massimo Dall'Ora
Physics , 2010, DOI: 10.1088/0004-6256/140/6/1672
Abstract: We have obtained broad-band near-infrared photometry for seven Galactic star clusters (M92, M15, M13, M5, NGC1851, M71 and NGC6791) using the WIRCam wide-field imager on the Canada-France-Hawaii Telescope, supplemented by images of NGC1851 taken with HAWK-I on the VLT. In addition, 2MASS observations of the [Fe/H] ~ 0.0 open cluster M67 were added to the cluster database. From the resultant (V-J)-V and (V-Ks)-V colour-magnitude diagrams (CMDs), fiducial sequences spanning the range in metallicity, -2.4 < [Fe/H] < +0.3, have been defined which extend (for most clusters) from the tip of the red-giant branch (RGB) to ~ 2.5 magnitudes below the main-sequence turnoff. These fiducials provide a valuable set of empirical isochrones for the interpretation of stellar population data in the 2MASS system. We also compare our newly derived CMDs to Victoria isochrones that have been transformed to the observed plane using recent empirical and theoretical colour-Teff relations. The models are able to reproduce the entire CMDs of clusters more metal rich than [Fe/H] ~ -1.4 quite well, on the assumption of the same reddenings and distance moduli that yield good fits of the same isochrones to Johnson-Cousins BV(RI)C photometry. However, the predicted giant branches become systematically redder than the observed RGBs as the cluster metallicity decreases. Possible explanations for these discrepancies are discussed.
RR Lyrae the Stellar Beacons of the Galactic Structure
Giuseppe Bono,Massimo Dall'Ora,Filippina Caputo,Giuseppina Coppola,Katia Genovali,Marcella Marconi,Anna Marina Piersimoni,Robert F. Stellingwerf
Physics , 2011,
Abstract: We present some recent findings concerning the use of RR Lyrae as distance indicators and stellar tracers. We outline pros and cons of field and cluster RR Lyrae stars and discuss recent theoretical findings concerning the use of the Bailey (amplitude vs pulsation period) diagram to constrain the possible occurrence of Helium enhanced RR Lyrae stars. Nonlinear, convective RR Lyrae models indicate that the pulsation properties of RR Lyrae stars are minimally affected by the helium content. The main difference between canonical and He enhanced models is due to the increase in luminosity predicted by evolutionary models. Moreover, we focus our attention on the near-infrared Period-Luminosity (PL) relation of RR Lyrae and summarize observational evidence concerning the slope of the K-band PL relation in a few globulars (M92, Reticulum, M5, Omega Cen) covering a range in metallicity of ~1 dex. Current findings suggest that the slope has a mild dependence on the metal content when moving from the metal-poor to the metal-intermediate regime. Finally, we also discuss the use of RR Lyrae stars either to estimate (helium indicator: A-parameter) or to measure (absorption and emission lines) the helium content.
Variable stars in the ultra-faint dwarf spheroidal galaxy Ursa Major I
Alessia Garofalo,Felice Cusano,Gisella Clementini,Vincenzo Ripepi,Massimo Dall'Ora,Maria Ida Moretti,Giuseppina Coppola,Ilaria Musella,Marcella Marconi
Physics , 2013, DOI: 10.1088/0004-637X/767/1/62
Abstract: We have performed the first study of the variable star population of Ursa Major I (UMa I), an ultra-faint dwarf satellite recently discovered around the Milky Way by the Sloan Digital Sky Survey. Combining time series observations in the B and V bands from four different telescopes, we have identified seven RR Lyrae stars in UMa I, of which five are fundamental-mode (RRab) and two are first-overtone pulsators (RRc). Our V, B-V color-magnitude diagram of UMa I reaches V~23 mag (at a signal-to-noise ratio of ~ 6) and shows features typical of a single old stellar population. The mean pulsation period of the RRab stars = 0.628, {\sigma} = 0.071 days (or = 0.599, {\sigma} = 0.032 days, if V4, the longest period and brightest variable, is discarded) and the position on the period-amplitude diagram suggest an Oosterhoff-intermediate classification for the galaxy. The RR Lyrae stars trace the galaxy horizontal branch at an average apparent magnitude of = 20.43 +/- 0.02 mag (average on 6 stars and discarding V4), giving in turn a distance modulus for UMa I of (m-M)0 = 19.94 +/- 0.13 mag, distance d= 97.3 +6.0/-5.7 kpc, in the scale where the distance modulus of the Large Magellanic Cloud is 18.5 +/- 0.1 mag. Isodensity contours of UMa I red giants and horizontal branch stars (including the RR Lyrae stars identified in this study) show that the galaxy has an S-shaped structure, which is likely caused by the tidal interaction with the Milky Way. Photometric metallicities were derived for six of the UMa I RR Lyrae stars from the parameters of the Fourier decomposition of the V-band light curves, leading to an average metal abundance of [Fe/H] = -2.29 dex ({\sigma} = 0.06 dex, average on 6 stars) on the Carretta et al. metallicity scale.
Stellar Archaeology in the Galactic halo with Ultra-Faint Dwarfs: VII. Hercules
Ilaria Musella,Vincenzo Ripepi,Marcella Marconi,Gisella Clementini,Massimo Dall'Ora,Victoria Scowcroft,Maria Ida Moretti,Luca Di Fabrizio,Claudia Greco,Giuseppina Coppola,David Bersier,Márcio Catelan,Aniello Grado,Luca Limatola,Horace A. Smith,Karen Kinemuchi
Physics , 2012, DOI: 10.1088/0004-637X/756/2/121
Abstract: We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes 6 fundamental-mode (ab-type) and 3 first overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, < Pab >= 0.68 d (sigma = 0.03 d), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening and distance to Hercules, for which we find: [Fe/H] = -2.30+-0.15 dex, E(B -V) = 0.09+-0.02 mag, and (m-M)o = 20.6+-0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V ~ 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' {\times} 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular clusters M68.
Period Change Similarities among the RR Lyrae Variables in Oosterhoff I and Oosterhoff II Globular Systems
Andrea Kunder,Alistair Walker,Peter B. Stetson,Giuseppe Bono,James M. Nemec,Roberto de Propris,Matteo Monelli,Santi Cassisi,Gloria Andreuzzi,Massimo Dall'Ora,Alessandra Di Cecco,Manuela Zoccali
Physics , 2010, DOI: 10.1088/0004-6256/141/1/15
Abstract: We present period change rates (dP/dt) for 42 RR Lyrae variables in the globular cluster IC$\,$4499. Despite clear evidence of these period increases or decreases, the observed period change rates are an order of magnitude larger than predicted from theoretical models of this cluster. We find there is a preference for increasing periods, a phenomenon observed in most RR Lyrae stars in Milky Way globular clusters. The period-change rates as a function of position in the period-amplitude plane are used to examine possible evolutionary effects in OoI clusters, OoII clusters, field RR Lyrae stars and the mixed-population cluster $\omega$~ Centauri. It is found that there is no correlation between the period change rate and the typical definition of Oosterhoff groups. If the RR Lyrae period changes correspond with evolutionary effects, this would be in contrast to the hypothesis that RR Lyrae variables in OoII systems are evolved HB stars that spent their ZAHB phase on the blue side of the instability strip. This may suggest that age may not be the primary explanation for the Oosterhoff types.
The Long-Lived UV "Plateau" of SN 2012aw
Amanda J. Bayless,Tyler Pritchard,Peter W. A. Roming,Paul Kuin,Peter J. Brown,Maria Teresa Botticella,Massimo Dall'Ora,Lucille H. Frey,Wesley Even,Chris L. Fryer,Justyn R. Maund,Morgan Fraser
Physics , 2012, DOI: 10.1088/2041-8205/764/1/L13
Abstract: Observations with the Swift UVOT have unambiguously uncovered for the first time a long-lived, UV "plateau" in a Type II-P supernova (SN). Although this flattening in slope is hinted at in a few other SNe, due to its proximity and minimal line-of-sight extinction, SN 2012aw has afforded the first opportunity to clearly observe this UV plateau. The observations of SN 2012aw revealed all Swift UV and u-band lightcurves initially declined rapidly, but 27 days after explosion the light curves flattened. Some possible sources of the UV plateau are: the same thermal process that cause the optical plateau, heating from radioactive decay, or a combination of both processes.
Supersolar Ni/Fe production in the Type IIP SN 2012ec
Anders Jerkstrand,Stephen J. Smartt,Jesper Sollerman,Cosimo Inserra,Morgan Fraser,Jason Spyromilio,Claes Fransson,Ting-Wan Chen,Cristina Barbarino,Massimo Dall'Ora,Maria Teresa Botticella,Massimo Della Valle,Avishay Gal-Yam,Stefano Valenti,Kate Maguire,Paolo Mazzali,Lina Tomasella
Physics , 2014, DOI: 10.1093/mnras/stv087
Abstract: SN 2012ec is a Type IIP supernova (SN) with a progenitor detection and comprehensive photospheric-phase observational coverage. Here, we present Very Large Telescope and PESSTO observations of this SN in the nebular phase. We model the nebular [O I] 6300, 6364 lines and find their strength to suggest a progenitor main-sequence mass of 13-15 Msun. SN 2012ec is unique among hydrogen-rich SNe in showing a distinct and unblended line of stable nickel [Ni II] 7378. This line is produced by 58Ni, a nuclear burning ash whose abundance is a sensitive tracer of explosive burning conditions. Using spectral synthesis modelling, we use the relative strengths of [Ni II] 7378 and [Fe II] 7155 (the progenitor of which is 56Ni) to derive a Ni/Fe production ratio of 0.20pm0.07 (by mass), which is a factor 3.4pm1.2 times the solar value. High production of stable nickel is confirmed by a strong [Ni II] 1.939 micron line. This is the third reported case of a core-collapse supernova producing a Ni/Fe ratio far above the solar value, which has implications for core-collapse explosion theory and galactic chemical evolution models.
EXOTIME: searching for planets around pulsating subdwarf B stars
Sonja Schuh,Roberto Silvotti,Ronny Lutz,Bjoern Loeptien,Elizabeth M. Green,Roy H. Ostensen,Silvio Leccia,Seung-Lee Kim,Gilles Fontaine,Stephane Charpinet,Myriam Francoeur,Suzanna Randall,Cristina Rodriguez-Lopez,Valerie van Grootel,Andrew P. Odell,Margit Paparo,Zsofia Bognar,Peter Papics,Thorsten Nagel,Benjamin Beeck,Markus Hundertmark,Thorsten Stahn,Stefan Dreizler,Frederic V. Hessman,Massimo Dall'Ora,Dario Mancini,Fausto Cortecchia,Serena Benatti,Riccardo Claudi,Rimvydas Janulis
Physics , 2010, DOI: 10.1007/s10509-010-0356-4
Abstract: In 2007, a companion with planetary mass was found around the pulsating subdwarf B star V391 Pegasi with the timing method, indicating that a previously undiscovered population of substellar companions to apparently single subdwarf B stars might exist. Following this serendipitous discovery, the EXOTIME (http://www.na.astro.it/~silvotti/exotime/) monitoring program has been set up to follow the pulsations of a number of selected rapidly pulsating subdwarf B stars on time-scales of several years with two immediate observational goals: 1) determine Pdot of the pulsational periods P 2) search for signatures of substellar companions in O-C residuals due to periodic light travel time variations, which would be tracking the central star's companion-induced wobble around the center of mass. These sets of data should therefore at the same time: on the one hand be useful to provide extra constraints for classical asteroseismological exercises from the Pdot (comparison with "local" evolutionary models), and on the other hand allow to investigate the preceding evolution of a target in terms of possible "binary" evolution by extending the otherwise unsuccessful search for companions to potentially very low masses. While timing pulsations may be an observationally expensive method to search for companions, it samples a different range of orbital parameters, inaccessible through orbital photometric effects or the radial velocity method: the latter favours massive close-in companions, whereas the timing method becomes increasingly more sensitive towards wider separations. In this paper we report on the status of the on-going observations and coherence analysis for two of the currently five targets, revealing very well-behaved pulsational characteristics in HS 0444+0458, while showing HS 0702+6043 to be more complex than previously thought.
The first and second data releases of the Kilo-Degree Survey
Jelte T. A. de Jong,Gijs A. Verdoes Kleijn,Danny R. Boxhoorn,Hugo Buddelmeijer,Massimo Capaccioli,Fedor Getman,Aniello Grado,Ewout Helmich,Zhuoyi Huang,Nancy Irisarri,Konrad Kuijken,Francesco La Barbera,John P. McFarland,Nicola R. Napolitano,Mario Radovich,Gert Sikkema,Edwin A. Valentijn,Kor G. Begeman,Massimo Brescia,Stefano Cavuoti,Ami Choi,Oliver-Mark Cordes,Giovanni Covone,Massimo Dall'Ora,Hendrik Hildebrandt,Giuseppe Longo,Reiko Nakajima,Maurizio Paolillo,Emanuella Puddu,Agatino Rifatto,Crescenzo Tortora,Edo van Uitert,Axel Buddendiek,Joachim Harnois-Déraps,Thomas Erben,Martin B. Eriksen,Catherine Heymans,Henk Hoekstra,Benjamin Joachimi,Thomas D. Kitching,Dominik Klaes,Léon V. E. Koopmans,Fabian K?hlinger,Nivya Roy,Cristóbal Sifon,Peter Schneider,Will J. Sutherland,Massimo Viola,Willem-Jan Vriend
Physics , 2015, DOI: 10.1051/0004-6361/201526601
Abstract: The Kilo-Degree Survey (KiDS) is an optical wide-field imaging survey carried out with the VLT Survey Telescope and the OmegaCAM camera. KiDS will image 1500 square degrees in four filters (ugri), and together with its near-infrared counterpart VIKING will produce deep photometry in nine bands. Designed for weak lensing shape and photometric redshift measurements, the core science driver of the survey is mapping the large-scale matter distribution in the Universe back to a redshift of ~0.5. Secondary science cases are manifold, covering topics such as galaxy evolution, Milky Way structure, and the detection of high-redshift clusters and quasars. KiDS is an ESO Public Survey and dedicated to serving the astronomical community with high-quality data products derived from the survey data, as well as with calibration data. Public data releases will be made on a yearly basis, the first two of which are presented here. For a total of 148 survey tiles (~160 sq.deg.) astrometrically and photometrically calibrated, coadded ugri images have been released, accompanied by weight maps, masks, source lists, and a multi-band source catalog. A dedicated pipeline and data management system based on the Astro-WISE software system, combined with newly developed masking and source classification software, is used for the data production of the data products described here. The achieved data quality and early science projects based on the data products in the first two data releases are reviewed in order to validate the survey data. Early scientific results include the detection of nine high-z QSOs, fifteen candidate strong gravitational lenses, high-quality photometric redshifts and galaxy structural parameters for hundreds of thousands of galaxies. (Abridged)
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