Publications

This is my publication list. I try to keep it updated as much as possible… but that’s not that difficult 😉 For each paper you will find both the ADS and ArXiv links. Papers are listed in reverse chronological order and, whenever relevant, a short comment may be attached.

For the non-astronomers: refereed papers are published on peer-reviewed journals, meaning that the paper, before being published, is reviewed by another astronomer who is supposed to assess the overall quality of the contribution and decide if it is worth publishing and if it needs any editing before doing so. Most of the time the referee is very helpuful and provides useful feedback that helps the authors to improve their paper, when it is already sound enough, or make them step a little back and better investigate the overlooked aspects of their research. Unfortunately, sometimes it happens that the referee is not really helpful and, on the contrary, tries to slow you down, because he is from a competing group or just because he/she does not have enough time to properly review the paper. Yes, I know it is sad but it definitively happen! Concerning the links: ADS will point you to the published version for which you will need the adequate journal subscription. The ArXiv access is free but it could happen that the finally published version differs somewhat from the pre-print one… but, let me tell you again, it’s free.
Conference proceeding are papers that were presented to a conference as a talk or a poster and are usually not refereed.

Supernova rates from the Southern inTermediate Redshift ESO Supernova Search (STRESS)

Authors: Botticella, M. T.; Riello, M.; Cappellaro, E.; Benetti, S.; Altavilla, G.; Pastorello, A.; Turatto, M.;Greggio, L.; Patat, F.; Valenti, S.;Zampieri, L.; Harutyunyan, A.; Pignata, G.; Taubenberger, S.

Abstract: Aims.To measure the supernova (SN) rates at intermediate redshift we performed a search, the Southern inTermediate Redshift ESO Supernova Search (STRESS). Unlike most of the current high redshift SN searches, this survey was specifically designed to estimate the rate for both type Ia and core collapse (CC) SNe. Methods: We counted the SNe discovered in a selected galaxy sample measuring SN rate per unit blue band luminosity. Our analysis is based on a sample of 43 000 galaxies and on 25 spectroscopically confirmed SNe plus 64 selected SN candidates. Our approach is aimed at obtaining a direct comparison of the high redshift and local rates and at investigating the dependence of the rates on specific galaxy properties, most notably their colour. Results: The type Ia SN rate, at mean redshift $z=0.3$, is $0.22^{+0.10+0.16}_{-0.08 -0.14} h_{70}^2$ SNu, while the CC SN rate, at $z=0.21$, is $0.82^{+0.31+0.30}_{-0.24 -0.26} h_{70}^2$ SNu. The quoted errors are the statistical and systematic uncertainties. Conclusions: With respect to the local value, the CC SN rate at z=0.2 is higher by a factor of 2, whereas the type Ia SN rate remains almost constant. This implies that a significant fraction of SN Ia progenitors has a lifetime longer than 2{-}3 Gyr. We also measured the SN rates in the red and blue galaxies and found that the SN Ia rate seems to be constant in galaxies of different colour, whereas the CC SN rate seems to peak in blue galaxies, as in the local Universe. SN rates per unit volume were found to be consistent with other measurements showing a steeper evolution with redshift for CC SNe than SNe Ia. We have exploited the link between SFH and SN rates to predict the evolutionary behaviour of the SN rates and compare it with the path indicated by observations. We conclude that in order to constrain the mass range of CC SN progenitors and SN Ia progenitor models it is necessary to reduce the uncertainties in the cosmic SFH. In addition it is important to apply a consistent dust extinction correction both to SF and to CC SN rate and to measure the SN Ia rate in star forming and in passively evolving galaxies over a wide redshift range.

The United Kingdom Infrared Telescope Infrared Deep Sky Survey First Data Release

Authors: Warren, S. J.; Hambly, N. C.; Dye, S.; Almaini, O.; Cross, N. J. G.; Edge, A. C.; Foucaud, S.; Hewett, P. C.; Hodgkin, S. T.; Irwin, M. J.; Jameson, R. F.; Lawrence, A.; Lucas, P. W.; Adamson, A. J.; Bandyopadhyay, R. M.; Bryant, J.; Collins, R. S.; Davis, C. J.; Dunlop, J. S.; Emerson, J. P.; Evans, D. W.; Gonzales-Solares, E. A.; Hirst, P.; Jarvis, M. J.; Kendall, T. R.; Kerr, T. H.; Leggett, S. K.; Lewis, J. R.; Mann, R. G.; McLure, R. J.; McMahon, R. G.; Mortlock, D. J.; Rawlings, M. G.; Read, M. A.; Riello, M.; Simpson, C.; Smith, D. J. B.; Sutorius, E. T. W.; Targett, T. A.; Varricatt, W. P.

Abstract: The First Data Release (DR1) of the United Kingdom Infrared Telescope Infrared Deep Sky Survey (UKIDSS) took place on 2006 July 21. The UKIDSS is a set of five large near-infrared surveys, covering a complementary range of areas, depths and Galactic latitudes. The DR1 is the first large release of survey-quality data from the UKIDSS and includes 320 deg2 of multicolour data to (Vega) K = 18, complete (depending on the survey) in three to five bands from the set ZYJHK, together with 4 deg2 of deep JK data to an average depth K = 21. In addition, the release includes a similar quantity of data with incomplete filter coverage. In JHK, in regions of low extinction, the photometric uniformity of the calibration is better than 0.02mag in each band. The accuracy of the calibration in ZY remains to be quantified, and the same is true of JHK in regions of high extinction. The median image full width at half-maximum across the data set is 0.82arcsec. We describe changes since the Early Data Release in the implementation, pipeline and calibration, quality control, and archive procedures. We provide maps of the areas surveyed, and summarize the contents of each of the five surveys in terms of filters, areas and depths. The DR1 marks completion of 7 per cent of the UKIDSS seven-year goals.

2007 MNRAS 375, 213 [ADS] [ARXIV]

The UKIRT Infrared Deep Sky Survey Early Data Release

Authors: Dye, S.; Warren, S. J.; Hambly, N. C.; Cross, N. J. G.; Hodgkin, S. T.; Irwin, M. J.; Lawrence, A.; Adamson, A. J.; Almaini, O.; Edge, A. C.; Hirst, P.; Jameson, R. F.; Lucas, P. W.; van Breukelen, C.; Bryant, J.; Casali, M.; Collins, R. S.; Dalton, G. B.; Davies, J. I.; Davis, C. J.; Emerson, J. P.; Evans, D. W.; Foucaud, S.; Gonzales-Solares, E. A.; Hewett, P. C.; Kendall, T. R.; Kerr, T. H.; Leggett, S. K.; Lodieu, N.; Loveday, J.; Lewis, J. R.; Mann, R. G.; McMahon, R. G.; Mortlock, D. J.; Nakajima, Y.; Pinfield, D. J.; Rawlings, M. G.; Read, M. A.; Riello, M.; Sekiguchi, K.; Smith, A. J.; Sutorius, E. T. W.; Varricatt, W.; Walton, N. A.; Weatherley, S. J.

Abstract: This paper defines the UKIRT Infrared Deep Sky Survey (UKIDSS) Early Data Release (EDR). UKIDSS is a set of five large near-infrared surveys being undertaken with the United Kingdom Infrared Telescope Wide Field Camera (WFCAM). The programme began in 2005 May and has an expected duration of 7yr. Each survey uses some or all of the broad-band filter complement ZYJHK. The EDR is the first public release of data to the European Southern Observatory (ESO) community. All worldwide releases occur after a delay of 18 months from the ESO release. The EDR provides a small sample data set, ~50deg2 (about 1 per cent of the whole of UKIDSS), that is a lower limit to the expected quality of future survey data releases. In addition, an EDR+ data set contains all EDR data plus extra data of similar quality, but for areas not observed in all of the required filters (amounting to ~220deg2). The first large data release, DR1, will occur in mid-2006. We provide details of the observational implementation, the data reduction, the astrometric and photometric calibration and the quality control procedures. We summarize the data coverage and quality (seeing, ellipticity, photometricity, depth) for each survey and give a brief guide to accessing the images and catalogues from the WFCAM Science Archive.

2006 MNRAS 372, 1227 [ADS] [ARXIV]

Extinction correction for Type Ia supernova rates – I. The model

Authors: Riello, M.; Patat, F.

Abstract: In this paper, we present and discuss a new Monte Carlo approach aimed at correcting the observed supernova (SN) rates for the effects of host galaxy dust extinction. The problem is addressed in a general way and the model includes SN position distributions, SN light-curve and spectral library and dust properties and distribution as input ingredients. Even though the recipe we propose is in principle applicable to all SN types, in this paper, we illustrate the use of our model only for Type Ia. These represent, in fact, the simplest test case, basically due to their spectroscopic homogeneity, which to a first approximation allows one to treat them all in the same way. This test case shows that the final results do not depend critically on the spiral arm dust geometry, while the total amount of dust, its properties and the size of the Galactic bulge do have a strong effect. With the availability of more complete spectral libraries and a more accurate knowledge of SN spatial distribution, the method we propose here can be easily extended to core collapse events.

2005 MNRAS 362, 671 [ADS] [ARXIV]

A homogeneous set of globular cluster relative distances and reddenings

Authos: Recio-Blanco, A.; Piotto, G.; de Angeli, F.; Cassisi, S.; Riello, M.; Salaris, M.; Pietrinferni, A.; Zoccali, M.; Aparicio, A.

Abstract: We present distance modulus and reddening determinations for 72 Galactic globular clusters from the homogeneous photometric database of Piotto et al. ([CITE]), calibrated to the HST flight F439W and F555W bands. The distances have been determined by comparison with theoretical absolute magnitudes of the ZAHB. For low and intermediate metallicity clusters, we have estimated the apparent Zero Age Horizontal Branch (ZAHB) magnitude from the RR Lyrae level. For metal rich clusters, the ZAHB magnitude was obtained from the fainter envelope of the red HB. Reddenings have been estimated by comparison of the HST colour-magnitude diagrams (CMD) with ground CMDs of template clusters with low reddening. The homogeneity of both the photometric data and the adopted methodological approach allowed us to obtain highly accurate relative cluster distances and reddenings. Our results are also compared with recent compilations in the literature.

2005 A&A 432, 851 [ADS] [ARXIV]

Death rate of massive stars at redshift $\latex \sim0.3$

Authors: Cappellaro, E.; Riello, M.; Altavilla, G.; Botticella, M. T.; Benetti, S.; Clocchiatti, A.; Danziger, J. I.; Mazzali, P.; Pastorello, A.; Patat, F.; Salvo, M.; Turatto, M.; Valenti, S.

Abstract: We report the first result of a supernova search program designed to measure the evolution of the supernova rate with redshift. To make the comparison with local rates more significant we copied, as much as possible, the same computation recipes as for the measurements of local rates. Moreover, we exploited the multicolor images and the photometric redshift technique to characterize the galaxy sample and accurately estimate the detection efficiency. Combining our data with the recently published measurements of the SN Ia rate at different redshifts, we derived the first, direct measurement of the core collapse supernova rate at z = 0.26 as $r_{cc} = 1.45^{+0.55}_{-0.45} h^2 SNu$ [h=H0/75]. This is a factor of three (±50%) larger than the local estimate. The increase for a look back time of 2.8 Gyr is more rapid than predicted by most of the published models of SN rate evolution. Core-collapse SN rates measure the death rate of massive stars and, because of the short time scale of evolution, can be translated into a measurement of the ongoing SFR. Assuming a Salpeter IMF and the standard scenario for core-collapse progenitors we derived an estimate of the star formation rate at redshift $3.1^{+1.1}_{-1.0} \times 10^{-2} h^3 M_{\odot} yr^{-1} Mpc^{-3}$ which compares very well with a recent estimate based on the measurement of the Hα luminosity density at the same redshift.

2005 A&A 430, 83 [ADS] [ARXIV]

The initial helium abundance of the Galactic globular cluster system

Authors: Salaris, M.; Riello, M.; Cassisi, S.; Piotto, G.

Abstract: In this paper we estimate the initial He content in about 30% of the Galactic globular clusters (GGCs) from new star counts we have performed on the recently published HST snapshot database of Colour Magnitude Diagrams (Piotto et al. \cite{Piotto02}). More specifically, we use the so-called R-parameter and estimate the He content from a theoretical calibration based on a recently updated set of stellar evolution models. We performed an accurate statistical analysis in order to assess whether GGCs show a statistically significant spread in their initial He abundances, and whether there is a correlation with the cluster metallicity. As in previous works on the subject, we do not find any significant dependence of the He abundance on the cluster metallicity; this provides an important constraint for models of Galaxy formation and evolution. Apart from GGCs with the bluest Horizontal Branch morphology, the observed spread in the individual helium abundances is statistically compatible with the individual errors. This means that either there is no intrinsic abundance spread among the GGCs, or that this is masked by the errors. In the latter case we have estimated a firm $1\sigma$ upper limit of 0.019 to the possible intrinsic spread. In case of the GGCs with the bluest Horizontal Branch morphology we detect a significant spread towards higher abundances inconsistent with the individual errors; this can be fully explained by additional effects not accounted for in our theoretical calibrations, which do not affect the abundances estimated for the clusters with redder Horizontal Branch morphology. In the hypothesis that the intrinsic dispersion on the individual He abundances is zero, taking into account the errors on the individual R-parameter estimates, as well as the uncertainties on the cluster metallicity scale and theoretical calibration, we have determined an initial He abundance mass fraction YGGC=$0.250\pm0.006$. This value is in perfect agreement with current estimates based on Cosmic Microwave Background radiation analyses and cosmological nucleosynthesis computations.

2004 A&A 420, 911 [ADS] [ARXIV]

Cepheid calibration of Type Ia supernovae and the Hubble constant

Authors: Altavilla, G.; Fiorentino, G.; Marconi, M.; Musella, I.; Cappellaro, E.; Barbon, R.; Benetti, S.; Pastorello, A.; Riello, M.; Turatto, M.; Zampieri, L.

Abstract: We investigate how a different calibration of the Cepheid period-luminosity (PL) relation, taking into account metallicity corrections, affects the absolute magnitude calibration of Type Ia supernovae (SNe Ia) and, in turn, the determination of the Hubble constant H0. We use SN Ia light curves from the literature and previously unpublished data to establish the $M_B-\Delta m_{15}(B)$ relation, and calibrate the zero point by means of nine SNe Ia with Cepheid-measured distances. This relation is then used to establish the Hubble diagram, and in turn to derive H0. In the attempt to correct for the host-galaxy extinction, we find that the data suggest a value for the total to selective absorption ratio of RB= 3.5, which is smaller than the standard value for our own Galaxy of RB= 4.315. Depending on the metallicity correction for the Cepheid PL relation, the value of RB, and SN sample selection criteria, the value of the Hubble constant H0 takes a value in the range 68-74 km s-1 Mpc-1, with associated uncertainties of the order of 10 per cent.

2004 MNRAS 349, 1344 [ADS] [ARXIV]

Supernova 2002bo: inadequacy of the single parameter description

Authors: Benetti, S.; Meikle, P.; Stehle, M.; Altavilla, G.; Desidera, S.; Folatelli, G.; Goobar, A.; Mattila, S.; Mendez, J.; Navasardyan, H.; Pastorello, A.; Patat, F.; Riello, M.; Ruiz-Lapuente, P.; Tsvetkov, D.; Turatto, M.; Mazzali, P.; Hillebrandt, W.

Abstract: We present optical/near-infrared photometry and spectra of the type Ia SN 2002bo spanning epochs from -13 d before maximum B-band light to +102 d after. The pre-maximum optical coverage is particularly complete. The extinction deduced from the observed colour evolution and from interstellar Na I D absorption is quite high, namely $E(B-V) = 0.43\pm0.10$. On the other hand, model matches to the observed spectra point to a lower reddening [$E(B-V) \sim 0.30$]. In some respects, SN 2002bo behaves as a typical `Branch normal’ type Ia supernova (SN Ia) at optical and infrared wavelengths. We find a B-band risetime of 17.9 +/- 0.5 d, a $\Delta m_{15}(B)$ of $1.13\pm 0.05$, and a dereddened $M_B=-19.41\pm 0.42$. However, comparison with other type Ia supernovae having similar $\Delta m_{15}(B)$ values indicates that in other respects SN 2002bo is unusual. While the optical spectra of SN 2002bo are very similar to those of SN 1984A [$\Delta m_{15}(B) = 1.19$], lower velocities and a generally more structured appearance are found in SNe 1990N, 1994D and 1998bu. For supernovae having $\Delta m_{15}(B) > 1.2$, we confirm the variation of with $\Delta m_{15}(B)$. However, for supernovae such as SN 2002bo, with lower values of $\Delta m_{15}(B)$ the relation breaks down. Moreover, the evolution of for SN 2002bo is strikingly different from that shown by other type Ia supernovae. The velocities of SN 2002bo and 1984A derived from S II 5640 Å, Si II 6355 Å and Ca II H and K lines are either much higher and/or evolve differently from those seen in other normal SNe Ia events. Thus, while SN 2002bo and SN 1984A appear to be highly similar, they exhibit behaviour which is distinctly different from other SNe Ia having similar $\Delta m_{15}(B)$ values. We suggest that the unusually low temperature, the presence of high-velocity intermediate-mass elements and the low abundance of carbon at early times indicates that burning to Si penetrated to much higher layers than in more normal type Ia supernovae. This may be indicative of a delayed detonation explosion.

2004 MNRAS 348, 261 [ADS] [ARXIV]

Low-luminosity Type II supernovae: spectroscopic and photometric evolution

Authors: Pastorello, A.; Zampieri, L.; Turatto, M.; Cappellaro, E.; Meikle, W. P. S.; Benetti, S.; Branch, D.; Baron, E.; Patat, F.; Armstrong, M.; Altavilla, G.; Salvo, M.; Riello, M.

Abstract: In this paper we present spectroscopic and photometric observations for four core-collapsed supernovae (SNe), namely SNe 1994N, 1999br, 1999eu and 2001dc. Together with SN 1997D, we show that they form a group of exceptionally low-luminosity events. These SNe have narrow spectral lines (indicating low expansion velocities) and low luminosities at every phase (significantly lower than those of typical core-collapsed supernovae). The very-low luminosity during the 56Co radioactive decay tail indicates that the mass of 56Ni ejected during the explosion is much smaller ($M_{Ni}\sim 2-8 \times 10^{-3} M_{\odot}$) than the average ($M_{Ni}\sim 6-10\times 10^{-2} M_{\odot}$). Two supernovae of this group (SN 1999br and SN 2001dc) were discovered very close to the explosion epoch, allowing us to determine the lengths of their plateaux (~100 d) as well as establishing the explosion epochs of the other, less completely observed SNe. It is likely that this group of SNe represent the extreme low-luminosity tail of a single continuous distribution of Type II plateau supernovae events. Their kinetic energy is also exceptionally low. Although an origin from low-mass progenitors has also been proposed for low-luminosity core-collapsed SNe, recent work provides evidence in favour of the high-mass progenitor scenario. The incidence of these low-luminosity SNe could be as high as 4-5 per cent of all Type II SNe.

2004 MNRAS 347, 74 [ADS] [ARXIV]

The Red Giant Branch luminosity function bump

Authors: Riello, M.; Cassisi, S.; Piotto, G.; Recio-Blanco, A.; De Angeli, F.; Salaris, M.; Pietrinferni, A.; Bono, G.; Zoccali, M.

Abstract: We present observational estimates of the magnitude difference between the luminosity function red giant branch bump and the horizontal branch ($\Delta F555W^{bump}_{HB}$), and of star counts in the bump region (Rbump), for a sample of 54 Galactic globular clusters observed by the HST. The large sample of stars resolved in each cluster, and the high photometric accuracy of the data allowed us to detect the bump also in a number of metal poor clusters. To reduce the photometric uncertainties, empirical values are compared with theoretical predictions obtained from a set of updated canonical stellar evolution models which have been transformed directly into the HST flight system. We found an overall qualitative agreement between theory and observations. Quantitative estimates of the confidence level are hampered by current uncertainties on the globular cluster metallicity scale, and by the strong dependence of $\Delta F555W^{bump}_{HB}$ on the cluster metallicity. In case of the Rbump parameter, which is only weakly affected by the metallicity, we find a very good quantitative agreement between theoretical canonical models and observations. For our full cluster sample the average difference between predicted and observed Rbump values is practically negligible, and ranges from -0.002 to -0.028, depending on the employed metallicity scale. The observed dispersion around these values is entirely consistent with the observational errors on Rbump. As a comparison, the value of Rbump predicted by theory in case of spurious bump detections due to Poisson noise in the stellar counts would be $\sim0.10$ smaller than the observed ones. We have also tested the influence on the predicted $\Delta F555W^{bump}_{HB}$ and Rbump values of an He-enriched component in the cluster stellar population, as recently suggested by D’Antona et al. (2002). We find that, under reasonable assumptions concerning the size of this He-enriched population and the degree of enrichment, the predicted $\Delta F555W^{bump}_{HB}$ and Rbump values are only marginally affected.

2003 A&A 410, 553 [ADS] [ARXIV]

HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands

Authors: Piotto, G.; King, I. R.; Djorgovski, S. G.; Sosin, C.; Zoccali, M.; Saviane, I.; De Angeli, F.; Riello, M.; Recio-Blanco, A.; Rich, R. M.; Meylan, G.; Renzini, A.

Abstract: We present the complete photometric database and the color-magnitude diagrams for 74 Galactic globular clusters observed with the HST/WFPC2 camera in the F439W and F555W bands. A detailed discussion of the various reduction steps is also presented, and of the procedures to transform instrumental magnitudes into both the HST F439W and F555W flight system and the standard Johnson ( B ) and ( V ) systems. We also describe the artificial star experiments which have been performed to derive the star count completeness in all the relevant branches of the color magnitude diagram. The entire photometric database and the completeness function will be made available on the Web immediately after the publication of the present paper.

2002 A&A 391, 945 [ADS] [ARXIV]

Observations of a Sample of 22 Supernovae at Redshift 0.1
Authors: Valenti, S.; Altavilla, G.; Benetti, S.; Botticella, M.; Cappellaro, E.; Pastorello, A.; Patat, F.; Riello, M.; Turatto, M.; Zampieri, L.

Measuring Supernova Rates with the VLT Survey Telescope
Authors: Botticella, M. T.; Cappellaro, E.; Riello, M.; Benetti, S.; Patat, F.; Turatto, M.; Valenti, S.; Zampieri, L.

Variable sources and data mining: an example
Authors: Riello, Marco

An Intermediate Redshift Supernova Search at ESO: Reduction Tools and Efficiency Tests
Authors: Riello, Marco; Altavilla, Giuseppe; Cappellaro, Enrico; Benetti, Stefano; Pastorello, Andrea; Patat, Ferdinando; Prevedello, Marco; Turatto, Massimo; Zampieri, Luca

An Intermediate Redshift Supernova Search at ESO: Preliminary Results
Authors: Altavilla, Giuseppe; Riello, Marco; Cappellaro, Enrico; Benetti, Stefano; Pastorello, Andrea; Patat, Ferdinando; Prevedello, Marco; Turatto, Massimo; Zampieri, Luca

The Red Giant Branch Bump
Authors: Riello, M.; Piotto, G.; Recio-Blanco, A.; Cassisi, S.; Salaris, M.

HST Color-Magnitude Diagrams of 74 Galactic Globular Clusters: the Snapshot Database
Authors: Piotto, G.; de Angeli, F.; Riello, M.; Recio-Blanco, A.; King, I. R.; Djorgovski, S. G.; Zoccali, M.; Renzini, A.; Saviane, I.; Sosin, C.; Rich, R. M.; Meylan, G.