Giuseppe Altavilla

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

Aims. To measure the supernova (SN) rates at intermediate redshift we performed 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∼ 43000 galaxies and on 25 spectroscopically confirmed SNe plu s 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 rat es on specific galaxy properties, most notably their colour. Results. The type Ia SN rate, at mean redshift z = 0.3, amounts to 0.22 +0.10+0.16 −0.08−0.14 h 2 70 SNu, while the CC SN rate, at z = 0.21, is 0.82 +0.31+0.30 −0.24−0.26 h 2 70 SNu. The quoted errors are the statistical and systematic un certainties. Conclusions. With respect to local value, the CC SN rate at z = 0.2 is higher by a factor of∼ 2 already at redshift , whereas the type Ia SN rate remains almost constant. This implies that a significant fraction of SN Ia progenitors has a lifetime longer tha n 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 with respect to SNe Ia. Finally 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 uncertainti es 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 SN Ia rate in star forming and in passive evolving galaxies in a wide redshift range.

Cepheid calibration of Type Ia supernovae and the Hubble constant

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 H 0 . We use SN Ia light curves from the literature and previously unpublished data to establish the M B -Δm 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 H 0 . 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 R B = 3.5, which is smaller than the standard value for our own Galaxy of R B = 4.315. Depending on the metallicity correction for the Cepheid PL relation, the value of R B , and SN sample selection criteria, the value of the Hubble constant H 0 takes a value in the range 68-74 km s -1 Mpc -1 , with associated uncertainties of the order of 10 per cent. Unpublished photometry is also presented for 18 SNe of our sample (1991S, 1991T, 1992A, 1992K, 1993H, 1993L, 1994D, 1994M, 1994ae, 1995D, 1995ac, 1995bd, 1996bo, 1997bp, 1997br, 1999aa, 1999dk, 2000cx). These data are the results of a long-standing effort in supernova monitoring at ESO - La Silla and Asiago observatories.

Gaia Data Release 1 - The photometric data

Context. This paper presents an overview of the photometric data that are part of the first Gaia data release. Aims. The principles of the processing and the main characteristics of the Gaia photometric data are presented. Methods. The calibration strategy is outlined briefly and the main properties of the resulting photometry are presented. Results. Relations with other broadband photometric systems are provided. The overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases.

Gaia Data Release 1 - Principles of the photometric calibration of the G band

Context. Gaia is an ESA cornerstone mission launched on 19 December 2013 aiming to obtain the most complete and precise 3D map of our Galaxy by observing more than one billion sources. This paper is part of a series of documents explaining the data processing and its results for Gaia Data Release 1, focussing on the G band photometry. Aims. This paper describes the calibration model of the Gaia photometric passband for Gaia Data Release 1. Methods. The overall principle of splitting the process into internal and external calibrations is outlined. In the internal calibration, a self-consistent photometric system is generated. Then, the external calibration provides the link to the absolute photometric flux scales. Results. The Gaia photometric calibration pipeline explained here was applied to the first data release with good results. Details are given of the various calibration elements including the mathematical formulation of the models used and of the extraction and preparation of the required input parameters (e.g. colour terms). The external calibration in this first release provides the absolute zero point and photometric transformations from the Gaia G passband to other common photometric systems. Conclusions. This paper describes the photometric calibration implemented for the first Gaia data release and the instrumental effects taken into account. For this first release no aperture losses, radiation damage, and other second-order effects have not yet been implemented in the calibration.

Gaia Data Release 2. Photometric content and validation

This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). The Gaia mission website is https://www.cosmos.esa.int/gaia. The Gaia Archive website is http://gea.esac.esa.int/archive/. This work has been supported by the United Kingdom Rutherford Appleton Laboratory, the United Kingdom Science and Technology Facilities Council (STFC) through grant ST/L006553/1, and the United Kingdom Space Agency (UKSA) through grant ST/N000641/1. This work was supported by the MINECO (Spanish Ministry of Economy) through grant ESP2016-80079-C2-1-R (MINECO/FEDER, UE) and ESP2014-55996-C2-1-R (MINECO/FEDER, UE) and MDM-2014-0369 of ICCUB (Unidad de Excelencia “Maria de Maeztu”). This work was supported by the Italian funding agencies Agenzia Spaziale Italiana (ASI) through grants I/037/08/0, I/058/10/0, 2014-025- R.0, and 2014- 025-R.1.2015 to INAF and contracts I/008/10/0 and 2013/030/I.0 to ALTEC S.p.A and Istituto Nazionale di Astrofisica (INAF). This research has made use of the APASS database, located at the AAVSO web site. Funding for APASS has been provided by the Robert Martin Ayers Sciences Fund. We thank A. Vallenari for supplying us with spectra for the validation of the external flux calibration and passband determination

The gaia -ESO survey: Calibration strategy

The Gaia -ESO survey (GES) is now in its fifth and last year of observations and has produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and chemical abundance ratios will be both internally consistent and easily comparable with other literature results, especially from other large spectroscopic surveys and from Gaia . The calibration of GES is particularly delicate because of (i) the large space of parameters covered by its targets, ranging from dwarfs to giants, from O to M stars; these targets have a large wide of metallicities and also include fast rotators, emission line objects, and stars affected by veiling; (ii) the variety of observing setups, with different wavelength ranges and resolution; and (iii) the choice of analyzing the data with many different state-of-the-art methods, each stronger in a different region of the parameter space, which ensures a better understanding of systematic uncertainties. An overview of the GES calibration and homogenization strategy is also given, along with some examples of the usage and results of calibrators in GES iDR4, which is the fourth internal GES data release and will form the basis of the next GES public data release. The agreement between GES iDR4 recommended values and reference values for the calibrating objects are very satisfactory. The average offsets and spreads are generally compatible with the GES measurement errors, which in iDR4 data already meet the requirements set by the main GES scientific goals.

Supernovae and Gaia

Despite decades of dedicated efforts there are still basic questions to answer with regard to Supernova progenitor systems and explosion mechanisms. In particular, in the last years a number of exceptionally bright objects and extremely faint events have demonstrated an unexpected large Supernova variety.The large number of Supernovae candidates at different redshifts provided by the next generation surveys, from ground and space, will allow to reach a better insight of the Supernova events in all their flavours. In particular it will be the possible to assess the systematics of type Ia Supernovae as distance indicator at any redshift.The Gaia astrometric mission is expected to discover a huge number of transient events, including Supernovae, which will be immediately disseminated to the astronomical community by a transients alert system for a suitable follow up.

The Gaia spectrophotometric standard stars survey — III. Short-term variability monitoring

We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 hour - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725.

SN 1999ga: a low-luminosity linear type II supernova?

Context. Type II-linear supernovae are thought to arise from progenitors that have lost most of their H envelope by the time of the explosion, and they are poorly understood because they are only occasionally discovered. It is possible that they are intrinsically rare, but selection effects due to their rapid luminosity evolution may also play an important role in limiting the number of detections. In this context, the discovery of a subluminous type II-linear event is even more interesting. Aims. We investigate the physical properties and characterise the explosion site of the type II SN 1999ga, which exploded in the nearby spiral galaxy NGC 2442. Methods. Spectroscopic and photometric observations of SN 1999ga allow us to constrain the energetics of the explosion and to estimate the mass of the ejected material, shedding light on the nature of the progenitor star in the final stages of its life. The study of the environment in the vicinity of the explosion site provides information on a possible relation between these unusual supernovae and the properties of the galaxies hosting them. Results. Despite the lack of early-time observations, we provide reasonable evidence that SN 1999ga was probably a type II-linear supernova that ejected a few solar masses of material, with a very small amount of radioactive elements of the order of 0.01 M� .

The Puzzling Case of the Deep-Space Debris WT1190F: A Test Bed for Advanced SSA Techniques

We report on somewhat unique photometric and spectroscopic observations of the deep-space debris WT1190F, which entered Earth atmosphere off the Sri Lanka coast, last 2015 November 13. This striking case has been imposing to the worldwide SSA community as an outstanding opportunity to effectively assess origin and physical nature of such extemporary impactors and appraise their potential threat for Earth. Our observations indicate for WT1190F an absolute magnitude R = 32.45 ± 0.31, with a flat dependence on the phase angle, and slope 0.007 ± 0.002 mag deg−1. The detected short-timescale variability suggests a “four-facet” geometry, with the body likely spinning with a period P = 2.9114 ± 0.0009 s. In the BVRI color domain, WT1190F closely resembled the Planck deep-space probe, a feature that points to an anthropic origin of the object. This match, together with a depressed reflectance around 4000 and 8500 A may be suggestive of a “grey” (aluminized) surface texture. An analysis is in progress to assess the two prevailing candidates to WT1190F’s identity, namely the Athena II upper stage of the Lunar Prospector mission, and the ascent stage of the Apollo 10 lunar module (LEM LM-4) “Snoopy”, by comparing observations with the synthetic photometry from accurate mock-up modeling and reflectance rendering.