arXiv subjects

E. Cappellaro

Publications and source records attributed to E. Cappellaro.

At least 199 records · Page 11Linked to original sources

arXiv2004

Death rate of massive stars at redshift ~0.3

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 recepies 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 meaurements 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=H_0/75]. This is a factor three {+/- 50%)} larger than the local estimate. The increase for a look back time of "only" 2.8 Gyr is more rapid than predicted by most of the published models of the SN rate evolution. Core-collapse SN rates measure the death rate of massive star and, because of the short time scale of evolution, can be translated in a measurement of the ongoing SFR. Assuming a Salpeter IMF and the standard scenario for core-collapse progenitors we derived to an estimate of the star formation rate at redshift 3.1^{+1.1}{-1.0} 10^-2 h^3 M_sun yr^-1 Mpc^{-3} which compare very well with a recent estimate based on the measurement of the Halpha luminosity density at the same redshift.

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arXiv2004

SN Ib 1990I: Clumping and Dust in the Ejecta?

Photometry and spectra of the type Ib SN 1990I are presented and analysed, covering about 400 days of evolution. The presence of optical helium lines is shown. SN 1990I seems to show higher velocities compared to a sample of type Ib events. The nebular emission lines display a high degree of asymmetry and the presence of fine structures. Using the [O I] 6300,64A flux, we estimate a lower limit on the oxygen mass to fall in the range (0.7-1.35) M_solar. The oxygen mass requires a filling factor as small as 10^{-2} on day 254, indicating a highly clumpy distribution of the oxygen material. A blueshift of the order 600 km/s is reported in the [O I] 6300,64A after day 254. The [Ca II] 7307.5A emission profile appears blueshifted as well at late epochs . We recover the quasi-bolometric "BVRI" light curve of SN 1990I. The constructed bolometric light curve shows a change of slope at late phases, with an e-folding time of 60 +/-2 d in the [50:200] d time interval, considerably faster than the one of {56}Co decay (i.e. 111.3 d), suggesting the gamma-rays escape with lower deposition, owing to the low mass nature of the ejecta. After day 200, an $e$-folding time ~47 +/-2.8 d is measured. A simplified gamma-ray deposition model is applied after adding a contribution of about 35% to the computed pseudo-bolometric light curves to account for near-IR luminosities to estimate the ejecta and {56}Ni masses (M({56}Ni)=0.11 M_solar and M_{ej}=3.7 M_solar). The deficit in luminosity is estimated to be about 50% around day 308. The observed spectral blueshift combined with the dramatic and sudden drop in the pseudo-bolometric light curve and (B-V) colour is interpreted to be a consequence of dust condensation in the ejecta of SN 1990I around day 250.

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arXiv2004

The Rates of Hypernovae and Gamma-Ray Bursts: Implications for their Progenitors

A critical comparison of estimates for the rates of hypernovae (HNe) and gamma-ray bursts (GRBs) is presented. Within the substantial uncertainties, the estimates are shown to be quite comparable and give a Galactic rate of $10^{-6}$ -- $10^{-5} $yr$^{-1}$ for both events. These rates are several orders of magnitude lower than the rate of core-collapse supernovae, suggesting that the evolution leading to a HN/GRB requires special circumstances, very likely due to binary interactions. Various possible binary channels are discussed, and it is shown that these are generally compatible with the inferred rates.

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arXiv2004

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 the metallicity corrections, affects the absolute magnitude calibration of Supernovae (SNe) Ia and, in turn, the determination of the Hubble constant H_0. We exploit SN Ia light curves from literature and previously unpublished data, to build the M_B -- Delta m_{15}(B) relation and we calibrate the zero point by means of 9 type Ia SNe with Cepheid measured distances. This relation was then used to build the Hubble diagram and in turn to derive H_0. In the attempt to correct for the host galaxy extinction, we found that the data seems to suggest a value for the total to selective absorption ratio, R_B=3.5, which is smaller than the standard value for our own Galaxy R_B=4.315. Depending on different metallicity corrections for the Cepheids P-L relation, values of R_B and SN sample selection criteria, we found that the values of the Hubble constant H_0 is in the range 68--74 km s^{-1} Mpc^{-1}, with associated uncertainties of the order of 10%. 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), which are the results of a long standing effort for supernova monitoring at ESO - La Silla and Asiago Observatories.

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arXiv2003

The 3-D ionization structure and evolution of NGC 7009 (Saturn Nebula)

Tomographic and 3-D analyses for extended, emission-line objects are applied to long-slit ESO NTT + EMMI high-resolution spectra of the intriguing planetary nebula NGC 7009, covered at twelve position angles. We derive the gas expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model and the spatial recovery of the plasma structure and evolution. The Saturn Nebula (distance~1.4 kpc, age~6000 yr, ionized mass~0.18 Mo) consists of several interconnected components, characterized by different morphology, physical conditions, excitation and kinematics. The internal shell, the main shell, the streams and the ansae expand at V(exp)~4.0xR" km/s, the outer shell, the caps and the equatorial pseudo-ring at V(exp)~3.15xR" km/s, and the halo at V(exp)~10 km/s. We compare the radial distribution of the physical conditions and the line fluxes observed in the eight sub-systems with the theoretical profiles coming from the photo-ionization code CLOUDY, inferring that all the spectral characteristics of NGC 7009 are explainable in terms of photo-ionization by the central star, a hot (logT*~4.95) and luminous (log L*/Lo~3.70) 0.60--0.61 Mo post--AGB star in the hydrogen-shell nuclear burning phase. The 3--D shaping of the Saturn Nebula is discussed within an evolutionary scenario dominated by photo-ionization and supported by the fast stellar wind: it begins with the superwind ejection, passes through the neutral, transition phase (lasting ~ 3000 yr), the ionization start (occurred ~2000 yr ago), and the full ionization of the main shell (~1000 yr ago), at last reaching the present days: the whole nebula is optically thin to the UV stellar flux, except the caps and the ansae.

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arXiv2003

Low Luminosity Type II Supernovae: Spectroscopic and Photometric Evolution

In this paper we present spectroscopic and photometric observations for four core collapse 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-collapse supernovae). The very low luminosity during the ^{56}Co radioactive decay tail indicates that the mass of ^{56}Ni ejected during the explosion is much smaller (M(Ni) ~ 2-8 x 10^{-3} Mo) than the average (M(Ni) ~ 6-10 x 10^{-2} Mo). 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 days) as well as establishiing 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 SN II-P events. Their kinetic energy is also exceptionally low. Although an origin from low mass progenitors has also been proposed for low-luminosity core-collapse 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$ $ of all type II SNe.

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arXiv2003

Optical and near-infrared photometry of the Type Ia Supernova 2000E in NGC 6951

We present optical and near-infrared photometry, along with optical spectra, of the Type Ia supernova SN 2000E in the spiral galaxy NGC 6951. It was discovered by the staff of the Teramo Observatory during the monitoring of the SN 1999el. The observations span a time interval of 234 days in the optical and 134 days in the near-infrared (starting 16 days and 7 days before maximum B light, respectively). Optical spectra are available from 6 days before maximum B light to 122 days after it. SN 2000E exhibits a Dm15(B) = 0.94, thus being classifiable as a slow-declining Type Ia SN and showing the distinctive features of such a class of objects. Spectroscopically, SN 2000E appears as a normal Type Ia SN, like SN 1990N. We could constrain reddening [E(B-V) ~0.5 mag] and distance (mu0 ~32.14 mag) using a number of different methods. The bolometric luminosity curve of SN 2000E, allows a determination of the Ni56 mass amounting to 0.9Msun.

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arXiv2002

Determination of Primordial Metallicity and Mixing in the Type IIP Supernova 1993W

We present the results of a large grid of synthetic spectra and compare them to early spectroscopic observations of SN 1993W. This supernova was discovered close to its explosion date and at a recession velocity of 5400 km/s is located in the Hubble flow. We focus here on two early spectra that were obtained approximately 5 and 9 days after explosion. We parameterize the outer supernova envelope as a power-law density profile in homologous expansion. In order to extract information on the value of the parameters a large number of models was required. We show that very early spectra combined with detailed models can provide constraints on the value of the power law index, the ratio of hydrogen to helium in the surface of the progenitor, the progenitor metallicity and the amount of radioactive nickel mixed into the outer envelope of the supernova. The spectral fits reproduce the observed spectra exceedingly well. The spectral results combined with the early photometry predict that the explosion date was 4.7 \pm 0.7 days before the first spectrum was obtained. The ability to obtain the metallicity from early spectra make SN IIP attractive probes of chemical evolution in the universe and by showing that we have the ability to pin down the parameters of the progenitor and mixing during the supernova explosion, it is likely to make SN IIP useful cosmological distance indicators which are at the same time complementary to SNe Ia.

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arXiv2002

The 3--D ionization structure of NGC 6818: a Planetary Nebula threatened by recombination

Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally spaced position angles, reduced according to the 3-D methodology introduced by Sabbadin et al. (2000a,b), allowed us to derive: the expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model, the 3-D reconstruction in He II, [O III] and [N II], the multicolor projection and a series of movies. The Little Gem results to be a young (3500 years), optically thin (quasi-thin in some directions) double shell (Mion~0.13 Msun) at a distance of 1.7 kpc, seen almost equatorial on: a tenuous and patchy spherical envelope (r~0.090 pc) encircles a dense and inhomogeneous tri-axial ellipsoid (a/2~0.077 pc, a/b~1.25, b/c~1.15) characterized by a hole along the major axis and a pair of equatorial, thick moustaches. NGC 6818 is at the start of the recombination phase following the luminosity decline of the 0.625 Msun central star, which has recently exhausted the hydrogen shell nuclear burning and is rapidly moving toward the white dwarf domain (log T*~5.22 K; log(L*/Lsun)~3.1). The nebula is destined to become thicker and thicker, with an increasing fraction of neutral, dusty gas in the outermost layers. Only over some hundreds of years the plasma rarefaction due to the expansion will prevail against the slower and slower stellar decline, leading to a gradual re-growing of the ionization front. The exciting star of NGC 6818 (mV~17.06) is a visual binary: a faint, red companion (mV~17.73) appears at 0.09 arcsec in PA=190deg, corresponding to a separation >=150 AU and to an orbital period >=1500 years

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arXiv2002

SN1999E: Another piece in the SN-GRB connection puzzle

Detailed optical and near-IR observations of SN 1999E have confirmed early suggestions that this supernova was indeed a twin of the peculiar type II SN 1997cy: it was exceptionally luminous and had evolved slowly, and the line profiles had narrow peaks and broad wings, indicating interaction with the circumstellar material. Nevertheless, the most intriguing characteristic was that, in analogy to SN 1997cy, it exploded at a position consistent in time and location with a BATSE event (GRB980910). The "a posteriori" probability that the only two SNe with such an optical appearance are associated with two different BATSE GRB is only 0.2%. This raises the possibility that some GRB are associated with H--rich SNe.

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arXiv2002

Variety in Supernovae

Detailed observations of a growing number of supernovae have determined a bloom of new peculiar events. In this paper we take a short tour through the SN diversity and discuss some important, physical issues related to it. Because of the role of SN Ia in determining the cosmological parameters, it is crucial to understand the physical origin of even subtle, observed differences. An important issue is also the reddening correction. We belive that the measure of interstellar lines on medium resolution spectra of SNe can be used to derive lower limits on the interstellar extinction. A few physical parameters of the progenitor, namely radius, mass, density structure and angular momentum, may explain most of the diversity of core-collapse events. In addition, if the ejecta expand into a dense circumstellar medium the ejecta-CSM interaction may dominate the observed outcome and provide a mean to probe the mass loss history of the SN progenitor in the last stages of its evolution.

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arXiv2002

An Intermediate Redshift Supernova Search at ESO: Reduction Tools and Efficiency Tests

We present the reduction and archiving tools developed for our search for supernovae at intermediate redshifts at ESO as well as the efficiency tests performed. The data reduction recipes developed for the SN candidates selection are described. All the variable sources detected are stored using a MySQL database which enables the identification of previously detected variable sources during past observational runs. Finally, experiments performed with artificial stars have shown that seeing plays a crucial role for the limiting magnitude of detection. Crucial is also the detection threshold used by Sextractor.

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arXiv2002

Peculiar, Low Luminosity Type II Supernovae: Low Energy Explosions in Massive Progenitors?

A number of supernovae, classified as Type II, show remarkably peculiar properties such as an extremely low expansion velocity and an extraordinarily small amount of $^{56}$Ni in the ejecta. We present a joint analysis of the available observations for two of these peculiar Type II supernovae, SN 1997D and SN 1999br, using a comprehensive semi-analytic method that can reproduce the light curve and the evolution of the line velocity and continuum temperature. We find that these events are under-energetic with respect to a typical Type II supernova and that the inferred mass of the ejecta is relatively large. We discuss the possibility that these supernovae originate from the explosion of a massive progenitor in which the rate of early infall of stellar material on the collapsed core is large. Events of this type could form a black hole remnant, giving rise to significant fallback and late-time accretion.

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arXiv2002

Photometry and Spectroscopy of the Type IIP SN 1999em from Outburst to Dust Formation

We present photometry and spectra of the type IIP SN1999em in NGC 1637 from several days after the outburst till day 642. An amount of $\approx 0.02 M_{\odot}$ of ejected $^{56}$Ni is inferred using the recovered bolometric light curve . The H$α$ and He I 10830 Ålines at the nebular epoch show that the distribution of the bulk of $^{56}$Ni can be represented approximately by a sphere of $^{56}$Ni with a velocity of 1500 km s$^{-1}$, which is shifted towards the far hemisphere by about 400 km s$^{-1}$. The fine structure of the H$α$ at the photospheric epoch reminiscent of the "Bochum event" in SN 1987A is analysed . The late time spectra show a dramatic transformation of the [O I] 6300 Åline profile between days 465 and 510, which we interpret as an effect of dust condensation during this period. Late time photometry supports the dust formation scenario after day 465. The [O I] line profile suggests that the dust occupies a sphere with velocity $\approx 800$ km s$^{-1}$ and optical depth $\gg10$. The plateau brightness and duration combined with the expansion velocity suggest a presupernova radius of $120-150 R_{\odot}$, ejecta mass of $10-11 M_{\odot}$ and explosion energy of $(0.5-1)\times10^{51}$ erg. The ejecta mass combined with the neutron star and a conservative assumption about mass loss implies the main sequence progenitor of $M_{\rm ms}\approx 12-14 M_{\odot}$. From the [O I] 6300,6364 Ådoublet luminosity we infer the oxygen mass to be a factor four lower than in SN 1987A which is consistent with the estimated SN 1999em progenitor mass . We note a "second-plateau" behaviour of the light curve after the main plateau at the beginning of the radioactive tail. This feature seems to be common to SNe IIP with low $^{56}$Ni mass.

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arXiv2002

Exceptionally Bright Type Ib Supernova 1991D

Photometric and spectroscopic observations of the peculiar Type Ib Supernova 1991D are presented. SN 1991D was exceptionally bright for a Type Ib supernova. The He I lines were rather weak and the velocity at the photosphere as a function of time was unusually low. Comparison of the observed and synthetic spectra indicates that either hydrogen was ejected with a minimum velocity of 12,000 km/s or the spectrum contained features caused by lines of Ne I. Light curve modelling suggests that the progenitor probably had a very large radius (~10^14 cm) and that a considerable amount of 56Ni was synthesized during the explosion (~0.7 Msolar). We suggest a progenitor model of SN 1991D that involves a binary system.

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arXiv2002

Optical and infrared observations of the supernova SN 1999el

Optical and near-infrared light curves of the Type IIn supernova 1999el in NGC 6951 are presented. A period of 220 days (416 days in the near-infrared) is covered from the first observation obtained a few days before maximum light. Spectroscopic observations are also discussed. Using as a distance calibrator the Type Ia SN 2000E, which occurred some months later in the same galaxy, and fitting a blackbody law to the photometric data we obtain a maximum bolometric luminosity for SN 1999el of $\sim 10^{44}$ erg s$^{-1}$. In general, the photometric properties of SN 1999el are very similar to those of SN 1998S, a bright and well studied Type IIn SN, showing a fast decline in all observed bands similar to those of Type II-L SNe. The differences with SN 1998S are analyzed and ascribed to the differences in a pre-existing circumstellar envelope in which dust was already present at the moment of the SN outburst. We infer that light echoes may play a possibly significant role in affecting the observed properties of the light curves, although improved theoretical models are needed to account for the data. We conclude that mass loss in the progenitor RG stars is episodic and occurs in an asymmetric way. This implies that collapsing massive stars appear as normal Type II SN if this occurs far from major mass loss episodes, whereas they appear as Type IIn SNe if a large mass loss episode is in progress.

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arXiv2002

The Type IIn SN 1995G: Interaction with the CSM

We present the photometric and spectroscopic evolution of the type IIn SN 1995G in NGC 1643, on the basis of 4 years of optical and infrared observations. This supernova shows very flat optical light curves similar to SN 1988Z, with a slow decline rate at all times. The spectra are characterized by strong Balmer lines with multiple components in emission and with a P-Cygni absorption component blueshifted by only 700 km/s. This feature indicates the presence of a slowly expanding shell above the SN ejecta as in the case of SNe 1994aj and 1996L. As in other SNe IIn the slow luminosity decline cannot be explained only with a radioactive energy input and an additional source of energy is required, most likely that produced by the interaction between supernova ejecta and a pre--existent circumstellar medium. It was estimated that the shell material has a density n(H) >> 10^8 cm^-3, consistent with the absence of forbidden lines in the spectra. About 2 years after the burst the low velocity shell is largely overtaken by the SN ejecta and the luminosity drops at a faster rate.

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arXiv2002

The 3-D ionization structure of the planetary nebula NGC6565

A detailed study of the planetary nebula NGC6565 has been carried out on long-slit echellograms at six, equally spaced position angles. The expansion velocity field, the c(Hbeta) distribution and the radial profile of the physical conditions (electron temperature and density) are obtained. The distance, radius, mass and filling factor of the nebula and the temperature and luminosity of the central star are derived. The radial ionization structure is analyzed using both the classical method and the photo-ionization code CLOUDY. Moreover, we present the spatial structure in a series of images from different directions. NGC6565 is a young (2000--2500 years), patchy, optically thick triaxial ellipsoid projected almost pole-on. The matter close to major axis was swept-up by some accelerating agent forming two faint and asymmetric polar cups. A large cocoon of almost neutral gas completely embeds the ionized nebula. NGC6565 is in a recombination phase. The stellar decline started about 1000 years ago, but the main nebula remained optically thin for other 600 years before the recombination phase occurred. In the near future the ionization front will re-grow, since the dilution factor due to the expansion will prevail on the slower and slower stellar decline. NGC6565 is at a distance of 2.0(+-0.5) Kpc and can be divided into three radial zones: the ``fully ionized'' one, extending up to 0.029--0.035 pc at the equator (0.050 pc at the poles), the ``transition'' one, up to 0.048--0.054 pc (0.080 pc), the ``halo'', detectable up to 0.110 pc. The ionized mass (~0.03 Modot) is only a fraction of the total mass (> 0.15 Modot), which has been ejected by an equatorial enhanced superwind of 4(+-2)x10^(-5) Modot/yr lasted for 4(+-2)x10^3 years.

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