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M. Maio

Publications and source records attributed to M. Maio.

At least 19 recordsLinked to original sources
arXiv2012

Superembedding methods for 4d N-extended SCFTs

We consider the embedding method of the superconformal group in four dimensions in the case of extended supersymmetry, hence generalizing the recent work of Goldberger, Skiba and Son which was restricted at N=1. Moreover, we work out explicitly the case of N=2 chiral superfields in four dimensions, putting the component fields in correspondence with Pascal's pyramid at layer N. This correspondence is a generic property of the N-extended chiral sector.

hep-th↗
arXiv2011

Simple current extensions and permutation orbifolds in string theory

We review extensions by integer spin simple currents in two-dimensional conformal field theories and their applications in string theory. In particular, we study the problem of resolving the fixed points of a simple current and apply the formalism to the permutation orbifold. In terms of string compactifications, we construct permutations of N=2 minimal models and use them as building blocks in heterotic Gepner models.

hep-th↗
arXiv2011

Permutation orbifolds of heterotic Gepner models

We study orbifolds by permutations of two identical N=2 minimal models within the Gepner construction of four dimensional heterotic strings. This is done using the new N=2 supersymmetric permutation orbifold building blocks we have recently developed. We compare our results with the old method of modding out the full string partition function. The overlap between these two approaches is surprisingly small, but whenever a comparison can be made we find complete agreement. The use of permutation building blocks allows us to use the complete arsenal of simple current techniques that is available for standard Gepner models, vastly extending what could previously be done for permutation orbifolds. In particular, we consider (0,2) models, breaking of SO(10) to subgroups, weight-lifting for the minimal models and B-L lifting. Some previously observed phenomena, for example concerning family number quantization, extend to this new class as well, and in the lifted models three family models occur with abundance comparable to two or four.

hep-th↗
arXiv2010

Permutation Orbifold of N=2 Supersymmetric Minimal Models

In this paper we apply the previously derived formalism of permutation orbifold conformal field theories to N=2 supersymmetric minimal models. By interchanging extensions and permutations of the factors we find a very interesting structure relating various conformal field theories that seems not to be known in literature. Moreover, unexpected exceptional simple currents arise in the extended permuted models, coming from off-diagonal fields. In a few situations they admit fixed points that must be resolved. We determine the complete CFT data with all fixed point resolution matrices for all simple currents of all Z_2-permutations orbifolds of all minimal N=2 models with k\neq 2 mod 4.

hep-th↗
arXiv2009

Complete Analysis of Extensions of $D(n)_1$ Permutation Orbifolds

We give the full set of $S$ matrices for extensions of $D(n)_1$ permutation orbifolds, extending our previous work to the yet unknown case of integer spin spinor currents. The main tool is triality of SO(8). We also provide fixed point resolution matrices for spinor currents of $D(n)_1$ permutation orbifolds with $n$ even and not multiple of four, where the spinor currents have half-integer spin.

hep-th↗
arXiv2009

Fixed Point Resolution in Extensions of Permutation Orbifolds

We determine the simple currents and fixed points of the orbifold theory $CFT\otimes CFT/\mathbb{Z}_2$, given the simple currents and fixed point of the original $CFT$. We see in detail how this works for the $SU(2)_k$ WZW model, focusing on the field content (i.e. $h$-spectrum of the primary fields) of the theory. We also look at the fixed point resolution of the simple current extended orbifold theory and determine the $S^J$ matrices associated to each simple current for $SU(2)_2$ and for the $B(n)_1$ and $D(n)_1$ series.

hep-th↗
arXiv2007

NGC 2419: an "intergalactic wanderer" or a simple Galactic Globular Cluster?

We have carried out a new photometric study of the remote Galactic globular cluster NGC 2419, using proprietary and archive B,V,I time-series CCD photometry of the cluster, that allowed us to discover a large number of new variable stars and to obtain a new colour magnitude diagram that reaches V ~26 mag over a field of 50X43 square arcmin centered on NGC 2419. The new variables include 39 RR Lyrae and 11 SX Phoenicis stars. The pulsation properties of the new RR Lyrae stars confirm and strengthen the classification of NGC 2419 as an Oosterhoff type II cluster.

astro-ph↗
arXiv2007

On the remote Galactic globular cluster NGC 2419

We present a new, deep (V ~ 26) study of the Galactic globular cluster NGC 2419 based on B,V,I time-series CCD photometry over about 10 years and extending beyond the cluster published tidal radius. We have identified 101 variable stars of which 60 are new discoveries, doubling the known RR Lyrae stars and including 12 SX Phoenicis stars. The average period of the RR Lyrae stars ( =0.662 d, and =0.366 d, for fundamental-mode -RRab- and first-overtone pulsators, respectively), and the position in the period-amplitude diagram both confirm that NGC 2419 is an Oosterhoff II cluster. The average apparent magnitude of the RR Lyrae stars is =20.31 +/- 0.01 (sigma=0.06, 67 stars) and leads to the distance modulus (m-M)o=19.60 +/- 0.05. The Color-Magnitude Diagram, reaching about 2.6 mag below the cluster turn-off, does not show clear evidence of multiple stellar populations. Cluster stars are found until r~ 10.5', and possibly as far as r~15', suggesting that the literature tidal radius might be underestimated. No extra-tidal structures are clearly detected in the data. NGC 2419 has many blue stragglers and a well populated horizontal branch extending from the RR Lyrae stars down to an extremely blue tail ending with the "blue-hook", for the first time recognized in this cluster. The red giant branch is narrow ruling out significant metallicity spreads. Our results seem to disfavor the interpretation of NGC 2419 as either having an extragalactic origin or being the relict of a dwarf galaxy tidally disrupted by the Milky Way.

astro-ph↗
arXiv2007

Variable stars in the Fornax dSph Galaxy. I. The Globular Cluster Fornax 4

Variable stars have been identified for the first time in Fornax 4, the globular cluster located near the center of the Fornax dwarf spheroidal galaxy. By applying the image subtraction technique to B,V time series photometry obtained with the MagIC camera of the 6.5-m Magellan/Clay telescope and with the wide field imager of the 4-m Blanco/CTIO telescope, we detected 27 RR Lyrae stars (22 fundamental mode, 3 first overtone, and 2 double-mode pulsators) in a 2.4'x2.4' area centered on Fornax 4. The average and minimum periods of the ab-type RR Lyrae stars, = 0.594 d and P(ab,min)=0.5191 d, respectively, as well as the revised position of the cluster in the horizontal branch type--metallicity plane, all consistently point to an Oosterhoff-intermediate status for the cluster, unlike what is seen for the vast majority of Galactic globular clusters, but in agreement with previous indications for the other globular clusters in Fornax. The average apparent magnitude of the RR Lyrae stars located within 30 arcsec from the cluster center is =21.43 +/- 0.03 mag (sigma=0.10 mag, average on 12 stars), leading to a true distance modulus of (m-M)o=20.64 +/- 0.09 mag or (m-M)o=20.53 +/- 0.09 mag, depending on whether a low ([Fe/H]=-2.0) or a moderately high ([Fe/H]=-1.5) metallicity is adopted.

astro-ph↗
arXiv2006

IZw18, or the picture of Dorian Gray: the more you watch it, the older it gets

IZw18 has been recurrently claimed to be a young galaxy, but stars of increasingly older ages are found every time deeper magnitude levels are reached with high-resolution photometry: from the original few Myrs to, possibly, several Gyrs. We summarize the history of IZw18's age and an HST project which will allow us to derive both its distance and age.

astro-ph↗
arXiv2005

Variable stars in the globular cluster NGC 2419

We have used DOLORES at the TNG to obtain B,V time series photometry of NGC 2419, one of the most distant and bright clusters in the Galactic halo. These data will be used to study its variable star population in order to check whether the cluster could be the relic of an extragalactic system accreted by the Milky Way. Using the Image Subtraction technique (Alard 2000) we have identified about 300 candidate variables, many of which are in the cluster central regions. Several of the variables appear to be RR Lyrae stars, but we detected variability also around the tip of the red giant branch, and in other regions of the colour-magnitude diagram. To improve the light curve sampling and to resolve variables in the cluster inner regions, the TNG data were combined with HST archive data. Preliminary results are presented on the light curves from the combined data set.

astro-ph↗
arXiv2005

Variable stars in Fornax dwarf spheroidal galaxy

We present the first results of a variable star search in the field and in the globular clusters of the Fornax dwarf spheroidal galaxy. Variable stars were identified using the Image Subtraction Technique (Alard 2000) on time-series data obtained with the ESO 2.2 m and the Magellan 6.5 m telescopes. The variable star sample includes RR Lyrae stars, Dwarf Cepheids and Anomalous Cepheids. The pulsation properties (namely: periods, light curves, period-amplitude relations and classification in Oosterhoff types) of Fornax variables from the present study are discussed in some detail.

astro-ph↗
arXiv2004

Variable stars in the bar of the Large Magellanic Cloud: the photometric catalogue

The catalogue of the Johnson-Cousins B,V and I light curves obtained for 162 variable stars (135 RR Lyrae, 4 candidate Anomalous Cepheids, 11 Classical Cepheids, 11 eclipsing binaries and 1 delta Scuti star) in two areas close to the bar of the Large Magellanic Cloud is presented along with coordinates, finding charts, periods, epochs, amplitudes, and mean quantities (intensity- and magnitude-averaged luminosities) of the variables with full coverage of the light variations. A star by star comparison is made with MACHO and OGLE II photometries based on both variable and constant stars in common, and the transformation relationships to our photometry are provided. The pulsation properties of the RR Lyrae stars in the sample are discussed in detail. Parameters of the Fourier decomposition of the light curves are derived for the fundamental mode RR Lyrae stars with complete and regular curves (29 stars). They are used to estimate metallicities, absolute magnitudes, intrinsic (B-V)o colours, and temperatures of the variable stars, according to Jurcsik and Kovacs (1996), and Kovacs and Walker (2001) method. Quantities derived from the Fourier parameters are compared with the corresponding observed quantities. In particular, the "photometric" metallicities are compared with the spectroscopic metal abundances derived by Gratton et al. (2004) from low resolution spectra obtained with FORS at the Very Large Telescope.

astro-ph↗
arXiv2004

Metal abundances of RR Lyrae stars in the bar of the Large Magellanic Cloud

Metallicities ([Fe/H]) from low resolution spectroscopy obtained with the Very Large Telescope (VLT) are presented for 98 RR Lyrae and 3 short period Cepheids in the bar of the Large Magellanic Cloud. Our metal abundances have typical errors of +/-0.17 dex. The average metallicity of the RR Lyrae stars is [Fe/H]=-1.48 +/- 0.03 +/- 0.06 on the scale of Harris (1996). The star-to-star scatter (0.29 dex) is larger than the observational errors, indicating a real spread in metal abundances. The derived metallicities cover the range -2.12 < [Fe/H] <-0.27, but there are only a few stars having [Fe/H] > -1. For the ab-type variables we compared our spectroscopic abundances with those obtained from the Fourier decomposition of the light curves. We find good agreement between the two techniques, once the systematic offset of 0.2 dex between the metallicity scales used in the two methods is taken into account. The spectroscopic metallicities were combined with the dereddened apparent magnitudes of the variables to derive the slope of the luminosity-metallicity relation for the LMC RR Lyrae stars: the resulting value is 0.214 +/- 0.047 mag/dex. Finally, the 3 short period Cepheids have [Fe/H] values in the range -2.0 < [Fe/H] <-1.5 . They are more metal-poor than typical LMC RR Lyrae stars, thus they are more likely to be Anomalous Cepheids rather than the short period Classical Cepheids that are being found in a number of dwarf Irregular galaxies.

astro-ph↗
arXiv2003

Distance scale and variable stars in Local Group Galaxies: LMC and Fornax

We briefly review our photometric and spectroscopic study of RR Lyrae variable stars in the bar of the Large Magellanic Cloud (LMC), that allowed us to reconcile the so-called "short" and "long" distance moduli of the LMC on the value mod_LMC=18.51 +/- 0.085 mag. Then we present preliminary results from the photometric study of a 33' x 34' area in the Fornax dwarf spheroidal galaxy containing the stellar clusters Fornax 3 (NGC 1049) and 6. We identified about 1000 candidate variables in this field of Fornax, and report the first detection and measure of about 60 RR Lyrae variable stars in the globular cluster Fornax 3.

astro-ph↗
arXiv2003

Variable Stars in the LMC: the Photometric Catalogue

New B, V, I photometry was obtained for a sample of 152 variables (125 RR Lyrae's, 4 anomalous Cepheids, 11 classical Cepheids, 11 eclipsing binaries and a delta Scuti star) in two regions near the bar of the Large Magellanic Cloud (LMC). We derived complete and well sampled B and V light curves, very accurate periods, epochs of maximum light, amplitudes, intensity- and magnitude-averaged apparent luminosities for about 95% of the RR Lyrae stars. All these informations are contained in the photometric catalogue. Metallicities from the Fourier decomposition of the V light curves were derived for 29 of the ab type RR Lyrae's and are compared with the DeltaS metal abundances from low resolution spectra obtained with the Very Large Telescope (VLT).

astro-ph↗