arXiv subjects

I. J. Danziger

Publications and source records attributed to I. J. Danziger.

At least 19 recordsLinked to original sources

arXiv2011

The Yellow Supergiant Progenitor of the Type II Supernova 2011dh in M51

We present the detection of the progenitor of the Type II SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the SN in the pre-explosion images was determined to within 23mas. The progenitor object was found to be consistent with a F8 supergiant star (log L/L_{\odot}=4.92+/-0.20 and T_{eff}=6000+/-280K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M_{ZAMS}=13+/-3M_{\odot}. The possibility of the progenitor source being a cluster is rejected, on the basis of: 1) the source is not spatially extended; 2) the absence of excess Hα\, emission; and 3) the poor fit to synthetic cluster SEDs. It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax, and suggest that a large amount of the progenitor's hydrogen envelope was removed before explosion.

astro-ph.SR↗

arXiv2011

Photometric Evolution of SNe Ib/c 2004ao, 2004gk and 2006gi

Photometric observations of three core collapse supernovae (SNe 2004ao, 2004gk and 2006gi), covering about 200 days of evolution are presented and analyzed. The photometric behaviour of the three objects is consistent with their membership of the envelope-stripped type Ib/c class. Pseudo-bolometric light curves are constructed. The corresponding measured $e$-folding times are found to be faster compared to the $^{56}$Co decay (i.e. 111.3 d), suggesting that a proportion of $γ$-rays increasing with time have escaped without thermalization, owing to the low mass nature of the ejecta. SN 2006gi has almost identical post maximum decline phase luminosities as SN 1999ex, and found to be similar to both SNe 1999dn and 1999ex in terms of the quasi-bolometric shape, placing it among the fast decliner Ib objects. SN 2004ao appears to fit within the slow decliner Ib SNe. SNe 2004ao and 2004gk display almost identical luminosities in the [50-100] days time interval, similar to SN 1993J. A preliminary simplified $γ-$ray deposition model is described and applied to the computed pseudo-bolometric light curves, allowing one to find a range in the ejecta and $^{56}$Ni masses. The optical and quasi-bolometric light curves, and the $B-V$ colour evolution of SN 2004gk are found to show a sudden drop after day 150. Correlating this fact to dust formation is premature and requires further observational evidence.

astro-ph.CO↗

arXiv2011

An empirical calibration of Lick indices using Milky Way Globular Clusters

To provide an empirical calibration relation in order to convert Lick indices into abundances for the integrated light of old, simple stellar populations for a large range in the observed [Fe/H] and [alpha/Fe]. This calibration supersedes the previously adopted ones because it is be based on the real abundance pattern of the stars instead of the commonly adopted metallicity scale derived from the colours. We carried out a long-slit spectroscopic study of 23 Galactic globular cluster for which detailed chemical abundances in stars have been recently measured. The line-strength indices, as coded by the Lick system and by Serven et al. (2005), were measured in low-resolution integrated spectra of the GC light. The results were compared to average abundances and abundance ratios in stars taken from the compilation by Pritzl et al. (2005) as well as to synthetic models. Fe-related indices grow linearly as a function of [Fe/H] for [Fe/H]>-2. Mg-related indices respond in a similar way to [Mg/H] variations, however Mgb turns out to be a less reliable metallicity indicator for [Z/H]<-1.5 . Despite the known Mg overabundance with respect to Fe in GC stars, it proved impossible to infer a mean [Mg/Fe] for integrated spectra that correlates with the resolved stars properties, because the sensitivity of the indices to [Mg/Fe] is smaller at lower metallicities. We present empirical calibrations for Ca, TiO, Ba and Eu indices as well as the measurements of H_alpha and NaD.

astro-ph.GA↗

arXiv2009

On the progenitor and early evolution of the type II supernova 2009kr

We report the identification of a source coincident with SN 2009kr in HST pre-explosion images. The object appears to be a single point source with an intrinsic colour V-I = 1.1 and M_V = -7.6. If this is a single star it would be a yellow supergiant of log L/L_{sol} \sim 5.1 and a mass of 15 (+5/-4) M_{sol}. The spatial resolution does not allow us yet to definitively determine if the progenitor object is a single star, a binary system, or a compact cluster. We show that the early lightcurve is flat, similar to IIP SNe, but that the the spectra are somewhat peculiar, displaying unusual P-Cygni profiles. The evolution of the expanding ejecta will play an important role in understanding the progenitor object.

astro-ph.CO↗

arXiv2008

VLT detection of a red supergiant progenitor of the type IIP supernova 2008bk

We report the identification of a source coincident with the position of the nearby type II-P supernova (SN) 2008bk in high quality optical and near-infrared pre-explosion images from the ESO Very Large Telescope (VLT). The SN position in the optical and near-infrared pre-explosion images is identified to within about +-70 and +-40 mas, respectively, using post-explosion Ks-band images obtained with the NAOS CONICA adaptive optics system on the VLT. The pre-explosion source detected in four different bands is precisely coincident with SN 2008bk and is consistent with being dominated by a single point source. We determine the nature of the point source using the STARS stellar evolutionary models and find that its colours and luminosity are consistent with the source being a red supergiant progenitor of SN 2008bk with an initial mass of 8.5 +- 1.0 Msun.

astro-ph↗

arXiv2008

The type IIb SN 2008ax: the nature of the progenitor

A source coincident with the position of the type IIb supernova (SN) 2008ax is identified in pre-explosion Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observations in three optical filters. We identify and constrain two possible progenitor systems: (i) a single massive star that lost most of its hydrogen envelope through radiatively driven mass loss processes, prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen envelope, and (ii) an interacting binary in a low mass cluster producing a stripped progenitor. Late time, high resolution observations along with detailed modelling of the SN will be required to reveal the true nature of this progenitor star.

astro-ph↗

arXiv2008

Integral field spectroscopy of planetary nebulae: mapping the line diagnostics and hydrogen-poor zones with VLT FLAMES

(Abridged) Results from the first dedicated study of Galactic PNe by means of optical integral field spectroscopy with the VLT FLAMES Argus IFU are presented. Three typical Galactic-disk PNe have been mapped with the 11.5''x7.2'' Argus array: two dimensional spectral maps of NGC 5882, 6153 and 7009 with 297 spatial pixels per target were obtained at sub-arcsec resolutions and 297 spectra per target were obtained in the 396.4-507.8 nm range. Spatially resolved maps of emission lines and of nebular physical properties were produced. The abundances of helium and of doubly ionized carbon and oxygen were derived from optical recombination lines (ORLs), while those of O^2+ were also derived from the collisionally excited lines (CELs). The abundance discrepancy problem was investigated by mapping the ratio of ORL/CEL abundances for O^2+ (the abundance discrepancy factor; ADF) across the face of the PNe. The ADF varies between targets and also with position within the targets attaining values of ~40 in the case of NGC 6153. Correlations of the ADF with geometric distance from the nucleus, as well as with [O III] electron temperature, plasma ionization state and other physical properties are established. Very small values of the temperature fluctuation parameter in the plane of the sky are found in all cases. It is argued that these results provide further evidence for the existence in typical PNe of a distinct nebular component consisting of hydrogen-deficient plasma. The zones containing this posited component appear as undulations in the C II and C II ORL abundance diagnostics of about 2 spatial pixels across; any associated structures should have physical sizes of less than ~1000 astronomical units. We propose that circumstellar disks, Abell 30-type knots, or Helix-type cometary globules may be involved.

astro-ph↗

arXiv2007

Infrared and X-Ray Evidence for Circumstellar Grain Destruction by the Blast Wave of Supernova 1987A

Multiwavelength observations of supernova remnant (SNR) 1987A show that its morphology and luminosity are rapidly changing at X-ray, optical, infrared, and radio wavelengths as the blast wave from the explosion expands into the circumstellar equatorial ring, produced by mass loss from the progenitor star. The observed infrared (IR) radiation arises from the interaction of dust grains that formed in mass outflow with the soft X-ray emitting plasma component of the shocked gas. Spitzer IRS spectra at 5 - 30 microns taken on day 6190 since the explosion show that the emission arises from ~ 1.1E-6 Msun of silicate grains radiating at a temperature of ~180+20-15 K. Subsequent observations on day 7137 show that the IR flux had increased by a factor of 2 while maintaining an almost identical spectral shape. The observed IR-to-X-ray flux ratio (IRX) is consistent with that of a dusty plasma with standard Large Magellanic Cloud dust abundances. IRX has decreased by a factor of ~ 2 between days 6190 and 7137, providing the first direct observation of the ongoing destruction of dust in an expanding SN blast wave on dynamic time scales. Detailed models consistent with the observed dust temperature, the ionization timescale of the soft X-ray emission component, and the evolution of IRX suggest that the radiating silicate grains are immersed in a 3.5E6 K plasma with a density of (0.3-1)E4 cm^{-3}, and have a size distribution that is confined to a narrow range of radii between 0.023 and 0.22 microns. Smaller grains may have been evaporated by the initial UV flash from the supernova.

astro-ph↗

arXiv2007

Goodness-of-Fit Tests DIFF1 and DIFF2 for Locally-Normalized Supernova Spectra

Two quantitative tests DIFF1 and DIFF2 for measuring goodness-of-fit between two locally-normalized supernova spectra are presented. Locally-normalized spectra are obtained by dividing a spectrum by the same spectrum smoothed over a wavelength interval relatively large compared to line features, but relatively small compared to continuum features. DIFF1 essentially measures the mean relative difference between the line patterns of locally-normalized spectra and DIFF2 is DIFF1 minimized by a relative logarithmic wavelength shift between the spectra: the shift is effectively an artificial relative Doppler shift. Both DIFF1 and DIFF2 measure the physical similarity of line formation, and thus of supernovae. DIFF1 puts more weight on overall physical similarity of the supernovae than DIFF2 because the DIFF2 shift compensates somewhat for some physical distinction in the supernovae. Both tests are useful in ordering supernovae into empirical groupings for further analysis. We present some examples of locally-normalized spectra for Type IIb supernova SN 1993J with some analysis of these spectra. The UV parts of two of the SN 1993J spectra are HST spectra that have not been published before. We also give an example of fitted locally-normalized spectra and, as an example of the utility of DIFF1 and DIFF2, some preliminary statistical results for hydrogen-deficient core-collapse (HDCC) supernova spectra. This paper makes use of and refers to material to found at the first author's online supernova spectrum database SUSPEND (SUpernovae Spectra PENDing further analysis: see http://www.nhn.ou.edu/~jeffery/astro/sne/spectra/spectra.html)

astro-ph↗

arXiv2006

Observations and analysis of two type IIP supernovae: the intrinsically faint object SN 2005cs and the ambiguous object SN 2005ay

Aims: To derive observational properties and physical parameters of the progenitor stars of type IIP supernovae SN 2005ay and SN 2005cs from their U,B,V,R,I CCD photometry, and to define their velocity behaviour. Methods: Light curves are analysed, and the velocities and spectral characteristics of SN 2005cs are obtained using synthetic spectra modeling. Results: Both supernovae are found to be fainter than the average SN IIP, with SN 2005cs being more subluminous and showing slight brightening in the second half of plateau stage in the V,R,I bands and a low expansion velocity. The effects of two different plausible distance moduli on the derived physical parameters of SN 2005ay are considered. Two approaches are used to recover the amounts of the ejected 56Ni, indicating masses of the order of 0.02 Msun, although late luminosities might indicate a higher amount for SN 2005ay, especially for the large distance case. Constraints on the progenitor properties are also presented, based on empirical analytical models. Two approaches are used to estimate the expansion velocities at the middle of the plateau phase. SN 2005cs represents an example of where all 3 physical parameters, velocity, energy and 56Ni mass are lower than average, a correlation not always observed in SNe IIP. SN 2005ay may belong to the same class if the shorter distance possibility is adopted. Furthermore, the estimated mass range for SN 2005cs is in agreement with limits established by using pre-supernova imaging.

astro-ph↗

arXiv2006

SNe 2005ay and 2005cs: Two interesting II-Plateau events

The "U,B,V,R,I" light curves of the type IIP supernovae (SNe IIP) SN 2005ay and SN 2005cs, and one spectrum for SN 2005cs, are presented and analyzed. We found both events to be fainter than the average SN IIP, with SN 2005cs showing slight brightening in the second half of plateau stage in the $V,R,I$ bands and a low expansion velocity. The effects of two different plausible distance moduli on the derived physical parameters of SN 2005ay are considered. Two approaches are used to estimate the expansion velocities at the middle of the plateau phase. Based on empirical analytical models we derived constraints on the progenitor properties. The amounts of the ejected $^{56}$Ni are also recovered.

astro-ph↗

arXiv2006

Hydrogen issue in Core Collapse Supernovae

We discuss results of analyzing a time series of selected photospheric-optical spectra of core collapse supernovae (CCSNe). This is accomplished by means of the parameterized supernovae synthetic spectrum (SSp) code ``SYNOW''. Special attention is addressed to traces of hydrogen at early phases, especially for the stripped-envelope SNe (i.e. SNe Ib-c). A thin low mass hydrogen layer extending to very high ejection velocities above the helium shell, is found to be the most likely scenario for Type Ib SNe.

astro-ph↗

arXiv2006

Unravelling the chemical inhomogeneity of PNe with VLT FLAMES integral-field unit spectroscopy

Recent weak emission-line long-slit surveys and modelling studies of PNe have convincingly argued in favour of the existence of an unknown component in the planetary nebula plasma consisting of cold, hydrogen-deficient gas, as an explanation for the long-standing recombination-line versus forbidden-line temperature and abundance discrepancy problems. Here we describe the rationale and initial results from a detailed spectroscopic study of three Galactic PNe undertaken with the VLT FLAMES integral-field unit spectrograph, which advances our knowledge about the small-scale physical properties, chemical abundances and velocity structure of these objects across a two-dimensional field of view, and opens up for exploration an uncharted territory in the study and modelling of PNe and photoionized nebulae in general.

astro-ph↗

arXiv2006

Hydrogen and helium traces in type Ib-c supernovae

The spectroscopic properties of a selected optical photospheric spectra of core collapse supernovae (CCSNe) are investigated.Special attention is devoted to traces of hydrogen at early phases. The generated spectra are found to match the observed ones reasonably well, including a list of only 23 candidate ions. Guided by SN Ib 1990I, the observed trough near 6300Åis attributed to H$α$ in almost all Type Ib events, although in some objects it becomes too weak to be discernible, especially at later phases. Alternative line identifications are discussed. Differences in the way hydrogen manifests its presence within CCSNe are highlighted. In Type Ib SNe, the H$α$ contrast velocity (i.e. line velocity minus the photospheric velocity) seems to increase with time at early epochs, reaching values as high as 8000 km s$^{-1}$ around 15-20 days after maximum and then remains almost constant. The derived photospheric velocities, indicate a lower velocity for Type II SNe 1987A and 1999em as compared to SN Ic 1994I and SN IIb 1993J, while Type Ib events display a somewhat larger variation. The scatter, around day 20, is measured to be $\sim$5000 km s$^{-1}$. Following two simple approaches, rough estimates of ejecta and hydrogen masses are given. A mass of hydrogen of approximately 0.02 $M_\odot$ is obtained for SN 1990I, while SNe 1983N and 2000H ejected $\sim$0.008 $M_\odot$ and $\sim$0.08 $M_\odot$ of hydrogen, respectively. SN 1993J has a higher hydrogen mass, $\sim 0.7$ $M_\odot$ with a large uncertainty. A low mass and thin hydrogen layer with very high ejection velocities above the helium shell, is thus the most likely scenario for Type Ib SNe. Some interesting and curious issues relating to oxygen lines suggest future investigations.

astro-ph↗

arXiv2005

The Progenitor of SN 2005cs in the Whirlpool Galaxy

The progenitor of SN 2005cs, in the galaxy M51, is identified in pre-explosion HST ACS WFC imaging. Differential astrometry, with post-explosion ACS HRC F555W images, permitted the identification of the progenitor with an accuracy of 0.006". The progenitor was detected in the F814W pre-explosion image with I=23.3+/-0.2, but was below the detection thresholds of the F435W and F555W images, with B<24.8 and V<25 at 5-sigma. Limits were also placed on the U and R band fluxes of the progenitor from pre-explosion HST WFPC2 F336W and F675W images. Deep images in the infra-red from NIRI on the Gemini-North telescope were taken 2 months prior to explosion, but the progenitor is not clearly detected on these. The upper limits for the JHK magnitudes of the progenitor were J<21.9,H<21.1 and K<20.7. Despite having a detection in only one band, a restrictive spectral energy distribution of the progenitor star can be constructed and a robust case is made that the progenitor was a red supergiant with spectral type between mid-K to late-M. The spectral energy distribution allows a region in the theoretical HR diagram to be determined which must contain the progenitor star. The initial mass of the star is constrained to be M(ZAMS)=9+3/-2 M_solar, which is very similar to the identified progenitor of the type II-P SN 2003gd, and also consistent with upper mass limits placed on five other similar SNe. The upper limit in the deep K-band image is significant in that it allows us to rule out the possibility that the progenitor was a significantly higher mass object enshrouded in a dust cocoon before core-collapse. This is further evidence that the trend for type II-P SNe to arise in low to moderate mass red supergiants is real.

astro-ph↗

arXiv2005

Dark matter in early-type galaxies: dynamical modelling of IC1459, IC3370, NGC3379 and NGC4105

We analyse long-slit spectra of four early-type galaxies which extend from ~1 to ~3 effective radii: IC1459, IC3370, NGC3379 and NGC4105. We have extracted the full line-of-sight velocity distribution (in the case of NGC3379 we also used data from the literature) which we model using the two-integral approach. Using two-integral modelling we find no strong evidence for dark haloes, but the fits suggest that three-integral modelling is necessary. We also find that the inferred constant mass-to-light ratio in all four cases is typical for early-type galaxies. Finally, we also discuss the constraints on the mass-to-light ratio which can be obtained using X-ray haloes in the case of IC1459, NGC3379 and NGC4105 and compare the estimated values with the predictions from the dynamical modelling.

astro-ph↗

arXiv2005

Self-enrichment in globular clusters. I. An analytic approach

By means of analytical calculations, we explore the self-enrichment scenario for Globular Cluster formation. According to this scenario, an initial burst of star formation occurs inside the core radius of the initial gaseous distribution. The outward-propagating shock wave sweeps up a shell in which gravitational instabilities may arise, leading to the formation of a second, metal-enriched, population of stars. We find a minimum mass of the proto-globular cluster of the order of 10^6 solar masses. We also find that the observed spread in the Magnitude-Metallicity relation can be explained assuming cluster-to-cluster variations of some parameters like the thermalization efficiency, the mixing efficiency and the Initial Mass Function, as well as variations of the external pressure.

astro-ph↗

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.

astro-ph↗