D. Balam - Academia.edu (original) (raw)

Papers by D. Balam

Research paper thumbnail of Supernova 2010au in Pgc 82347

CBET 2217 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of Comet C/2010 j4 (wise)

Research paper thumbnail of Comet C/2007 k1 (lemmon)

... Authors: Tichy, M.; Ticha, J.; Read, MT; McMillan, RS; Bressi, TH; Donato, L.; Gonano, V.; Gu... more ... Authors: Tichy, M.; Ticha, J.; Read, MT; McMillan, RS; Bressi, TH; Donato, L.; Gonano, V.; Guido, E.; Lepardo, A.; Santini, V.; Sostero, G.; Gonano, M.; Pettarin, E.; Fabris, F.; Lombardi, G.; Piani, F.; Fredrick, R.; Trentman, R.; Robb, RM; Balam, DD; Young, J.; Gibbs, AR; Beshore ...

Research paper thumbnail of Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Geminorum

The Astrophysical Journal, 2012

New and existing CORAVEL, UBVJHK s , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that t... more New and existing CORAVEL, UBVJHK s , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator ζ Gem is a cluster member. The following parameters were inferred for ζ Gem from cluster membership and are tied to new spectral classifications (DAO) established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV): E B−V = 0.02 ± 0.02, log τ = 7.85 ± 0.15, and d = 355 ± 15 pc. The mean distance to ζ Gem from cluster membership and six recent estimates (e.g., IRSB) is d = 363 ± 9(σx) ± 26(σ) pc. The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. Forthcoming precise proper motions (DASCH) and Chandra/XMM-Newton observations of the broader field may be employed to identify cluster members, bolster the cluster's existence, and provide stronger constraints on the Cepheid's fundamental parameters.

Research paper thumbnail of Comet P/2002 T4 (NEAT)

IAUC 7991 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of Anchors for the Cosmic Distance Scale: the Cepheids U Sgr, CF Cas and CEab Cas

New and existing X-ray, U BV JHK s W (1−4) , and spectroscopic observations were analyzed to cons... more New and existing X-ray, U BV JHK s W (1−4) , and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance given they host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids' period evolution (dP/dt) from ∼140 years of observations, helped resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, distances derived for members of M25 and NGC 7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively.

Research paper thumbnail of Supernova 2008gl in UGC 881

CBET 1547 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of The supernova type ia rate evolution with SNLS

AIP Conference Proceedings, 2007

We present a progress report on a project to derive the evolution of the volumetric supernova Typ... more We present a progress report on a project to derive the evolution of the volumetric supernova Type Ia rate from the Supernova Legacy Survey. Our preliminary estimate of the rate evolution divides the sample from Neill et al. [1] into two redshift bins: 0.2 < z < 0.4, and 0.4 < z < 0.6. We extend this by adding a bin from the sample analyzed in Sullivan et al. [2] in the range 0.6 < z < 0.75 from the same time period. We compare the derived trend with previously published rates and a supernova Type Ia production model having two components: one component associated closely with star formation and an additional component associated with host galaxy mass. Our observed trend is consistent with this model, which predicts a rising SN Ia rate out to at least z = 2.

Research paper thumbnail of 1991 Aq

IAUC 5171 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra

The Astrophysical Journal, 2008

We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its disp... more We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. The mean UV spectrum of our z 0.5 SNe Ia and its dispersion is tabulated for use in future applications. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although

Research paper thumbnail of SUBLUMINOUS TYPE Ia SUPERNOVAE AT HIGH REDSHIFT FROM THE SUPERNOVA LEGACY SURVEY

The Astrophysical Journal, 2011

The rate evolution of subluminous Type Ia Supernovae is presented using data from the Supernova L... more The rate evolution of subluminous Type Ia Supernovae is presented using data from the Supernova Legacy Survey. This sub-sample represents the faint and rapidly-declining light-curves of the observed supernova Ia (SN Ia) population here defined by low stretch values (s ≤ 0.8). Up to redshift z = 0.6, we find 18 photometrically-identified subluminous SNe Ia, of which six have spectroscopic redshift (and three are spectroscopically-confirmed SNe Ia). The evolution of the subluminous volumetric rate is constant or slightly decreasing with redshift, in contrast to the increasing SN Ia rate found for the normal stretch population, although a rising behaviour is not conclusively ruled out. The subluminous sample is mainly found in early-type galaxies with little or no star formation, so that the rate evolution is consistent with a galactic mass dependent behavior: r(z) = A × M g , with A = (1.

Research paper thumbnail of THE RISE TIME OF NORMAL AND SUBLUMINOUS TYPE Ia SUPERNOVAE

The Astrophysical Journal, 2012

We calculate the average stretch-corrected rise-time of type Ia supernovae (SNe Ia) in the Supern... more We calculate the average stretch-corrected rise-time of type Ia supernovae (SNe Ia) in the Supernova Legacy Survey. We use the aggregate lightcurves of spectroscopic and photometrically identified SNe Ia to fit the rising part of the lightcurve with a simple quadratic model. We obtain a lightcurve shape corrected, i .e. stretch-corrected, fiducial rise-time of 17.02 +0.18 −0.28 (stat) days. The measured rise-time differs from an earlier finding by the SNLS (Conley et al. 2006) due to the use of different SN Ia templates. We compare it to nearby samples using the same methods and find no evolution in the early part of the lightcurve of SNe Ia up to z = 1. We search for variations among different populations, particularly subluminous objects, by dividing the sample in stretch. Bright and slow decliners (s > 1.0) have consistent stretch-corrected rise-times compared to fainter and faster decliners (0.8 < s ≤ 1.0); they are shorter by 0.57 +0.47 −0.50 (stat). Subluminous SNe Ia (here defined as objects with s ≤ 0.8), although less constrained, are also consistent, with a rise-time of 18.03 +0.81 −1.37 (stat). We study several systematic biases and find that the use of different fiducial templates may affect the average rise-time but not the intrinsic differences between populations. Based on our results, we estimate that subluminous SNe Ia are powered by 0.05 − 0.35M ⊙ of 56 Ni synthesized in the explosion. Our conclusions are the same for the single-stretch and two-stretch parameterizations of the lightcurve.

Research paper thumbnail of THE EFFECT OF PROGENITOR AGE AND METALLICITY ON LUMINOSITY AND 56 Ni YIELD IN TYPE Ia SUPERNOVAE

The Astrophysical Journal, 2009

Timmes et al. found that metallicity variations could theoretically account for a 25% variation i... more Timmes et al. found that metallicity variations could theoretically account for a 25% variation in the mass of 56 Ni synthesized in Type Ia supernovae (SNe Ia), and thus account for a large fraction of the scatter in observed SN Ia luminosities. Higher-metallicity progenitors are more neutron rich, producing more stable burning products relative to radioactive 56 Ni. We develop a new method for estimating bolometric luminosity and 56 Ni yield in SNe Ia and use it to test the theory with data from the Supernova Legacy Survey. We find that the average 56 Ni yield does drop in SNe Ia from high-metallicity environments, but the theory can only account for 7%-10% of the dispersion in SN Ia 56 Ni mass, and thus luminosity. This is because the effect is dominant at metallicities significantly above solar, whereas we find that SN hosts have predominantly subsolar or only moderately above-solar metallicities. We also show that allowing for changes in O/Fe with the metallicity [Fe/H] does not have a major effect on the theoretical prediction of Timmes et al., so long as one is using the O/H as the independent variable. Age may have a greater effect than metallicity-we find that the luminosity-weighted age of the host galaxy is correlated with 56 Ni yield, and thus more massive progenitors give rise to more luminous explosions. This is hard to understand if most SNe Ia explode when the primaries reach the Chandrasekhar mass. Finally, we test the findings of Gallagher et al. that the residuals of SNe Ia from the Hubble diagram are correlated with host galaxy metallicity, and we find no such correlation.

Research paper thumbnail of Gemini Spectroscopy of Supernovae from the Supernova Legacy Survey: Improving High‐Redshift Supernova Selection and Classification

The Astrophysical Journal, 2005

We present new techiques for improving the efficiency of supernova (SN) classification at high re... more We present new techiques for improving the efficiency of supernova (SN) classification at high redshift using 64 candidates observed at Gemini North and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS is an ongoing five year project with the goal of measuring the equation of state of Dark Energy by discovering and following over 700

Research paper thumbnail of SiFTO: An Empirical Method for Fitting SN Ia Light Curves

The Astrophysical Journal, 2008

We present SiFTO, a new empirical method for modeling Type Ia supernovae (SNe Ia) light curves by... more We present SiFTO, a new empirical method for modeling Type Ia supernovae (SNe Ia) light curves by manipulating a spectral template. We make use of high-redshift SN data when training the model, allowing us to extend it bluer than rest frame U. This increases the utility of our high-redshift SN observations by allowing us to use more of the available data. We find that when the shape of the light curve is described using a stretch prescription, applying the same stretch at all wavelengths is not an adequate description. SiFTO therefore uses a generalization of stretch which applies different stretch factors as a function of both the wavelength of the observed filter and the stretch in the rest-frame B band. We compare SiFTO to other published light-curve models by applying them to the same set of SN photometry, and demonstrate that SiFTO and SALT2 perform better than the alternatives when judged by the scatter around the best fit luminosity distance relationship. We further demonstrate that when SiFTO and SALT2 are trained on the same data set the cosmological results agree.

Research paper thumbnail of Rates and Properties of Type Ia Supernovae as a Function of Mass and Star Formation in Their Host Galaxies

The Astrophysical Journal, 2006

We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar popula... more We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar populations, with observed rates that depend on the stellar mass and mean star-formation rates (SFRs) of their host galaxies. Models where the SN Ia rate depends solely on host galaxy stellar mass are ruled out with >99% confidence. Our analysis is based on 100 spectroscopically-confirmed SNe Ia, plus 24 photometrically-classified events, all from the Supernova Legacy Survey (SNLS) and distributed over 0.2<z<0.75. Using multi-band photometry, we estimate stellar masses and SFRs for the SN Ia host galaxies by fitting their broad-band spectral energy distributions with the galaxy spectral synthesis code, PEGASE.2. We show that the SN Ia rate per unit mass is proportional to the specific SFR of the parent galaxies-more vigorously star-forming galaxies host more SNe Ia per unit stellar mass, broadly equivalent to the trend of increasing SN Ia rate in later-type galaxies seen in the local universe. Following earlier suggestions for a simple "two-component" model approximating the SN Ia rate, we find bivariate linear dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of the host systems. We find that the SN Ia rate can be well represented as the sum of 5.3 ± 1.1 × 10 −14 SNe per year per unit stellar mass, and 3.9 ± 0.7 × 10 −4 SNe per year per M ⊙ yr −1 of star formation. We also demonstrate a dependence of distant SN Ia light-curve shapes on star-formation in the host galaxy, similar to trends observed locally. Passive galaxies, with no star-formation, preferentially host faster-declining/dimmer SNe Ia, while slower-declining/brighter events are only found in systems with ongoing star-formation. We model the light-curve width distribution in star-forming galaxies as the sum of a young component, and an old component taken from the distribution in non-star-forming galaxies. Empirically understanding these relationships between SNe Ia and their environments will lead to future improvements in their use as cosmological candles.

Research paper thumbnail of ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas

The Astrophysical Journal, 2012

New X-ray (XMM-Newton) and JHK s (Observatoire du Mont-Mégantic) observations for members of the ... more New X-ray (XMM-Newton) and JHK s (Observatoire du Mont-Mégantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J − H) = 0.08 ± 0.02 and d = 405 ± 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d = 414 ± 5(σx) ± 10(σ) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (δ Cep, ζ Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H 0 .

Research paper thumbnail of EVOLUTION IN THE VOLUMETRIC TYPE Ia SUPERNOVA RATE FROM THE SUPERNOVA LEGACY SURVEY

The Astronomical Journal, 2012

We present a measurement of the volumetric Type Ia supernova (SN Ia) rate (SNR Ia) as a function ... more We present a measurement of the volumetric Type Ia supernova (SN Ia) rate (SNR Ia) as a function of redshift for the first four years of data from the Canada-France-Hawaii Telescope (CFHT) Supernova Legacy Survey (SNLS). This analysis includes 286 spectroscopically confirmed and more than 400 additional photometrically identified SNe Ia within the redshift range 0.1 ≤ z ≤ 1.1. The volumetric SNR Ia evolution is consistent with a rise to z ∼ 1.0 that follows a power-law of the form (1+z) α , with α = 2.11 ± 0.28. This evolutionary trend in the SNLS rates is slightly shallower than that of the cosmic star-formation history over the same redshift range. We combine the SNLS rate measurements with those from other surveys that complement the SNLS redshift range, and fit various simple SN Ia delay-time distribution (DTD) models to the combined data. A simple power-law model for the DTD (i.e., ∝ t −β) yields values from β = 0.98 ± 0.05 to β = 1.15 ± 0.08 depending on the parameterization of the cosmic star formation history. A two-component model, where SNR Ia is dependent on stellar mass (M stellar) and star formation rate (SFR) as SNR Ia (z) = A× M stellar (z)+ B × SFR(z), yields the coefficients A = (1.9 ± 0.1) × 10 −14 SNe yr −1 M −1 ⊙ and B = (3.3 ± 0.2) × 10 −4 SNe yr −1 (M ⊙ yr −1) −1. More general two-component models also fit the data well, but single Gaussian or exponential DTDs provide significantly poorer matches. Finally, we split the SNLS sample into two populations by the light curve width (stretch), and show that the general behavior in the rates of faster-declining SNe Ia (0.8 ≤ s < 1.0) is similar, within our measurement errors, to that of the slower objects (1.0 ≤ s < 1.3) out to z ∼ 0.8.

Research paper thumbnail of Real-Time Analysis and Selection Biases in the Supernova Legacy Survey

The Astronomical Journal, 2010

Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at... more Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada,

Research paper thumbnail of THE TYPE Ia SUPERNOVA RATE IN RADIO AND INFRARED GALAXIES FROM THE CANADA-FRANCE-HAWAII TELESCOPE SUPERNOVA LEGACY SURVEY

The Astronomical Journal, 2010

We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy ... more We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy Survey and catalogs of galaxies with photometric redshifts, Very Large Array 1.4 GHz radio sources, and Spitzer infrared sources. We present eight SNe Ia in early-type host galaxies which have counterparts in the radio and infrared source catalogs. We find the SN Ia rate in subsets of radio and infrared early-type galaxies is ∼1-5 times the rate in all early-type galaxies, and that any enhancement is always 2σ. Rates in these subsets are consistent with predictions of the two-component "A+B" SN Ia rate model. Since infrared properties of radio SN Ia hosts indicate dust-obscured star formation, we incorporate infrared star formation rates into the "A+B" model. We also show the properties of SNe Ia in radio and infrared galaxies suggest the hosts contain dust and support a continuum of delay time distributions (DTDs) for SNe Ia, although other DTDs cannot be ruled out based on our data.

Research paper thumbnail of Supernova 2010au in Pgc 82347

CBET 2217 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of Comet C/2010 j4 (wise)

Research paper thumbnail of Comet C/2007 k1 (lemmon)

... Authors: Tichy, M.; Ticha, J.; Read, MT; McMillan, RS; Bressi, TH; Donato, L.; Gonano, V.; Gu... more ... Authors: Tichy, M.; Ticha, J.; Read, MT; McMillan, RS; Bressi, TH; Donato, L.; Gonano, V.; Guido, E.; Lepardo, A.; Santini, V.; Sostero, G.; Gonano, M.; Pettarin, E.; Fabris, F.; Lombardi, G.; Piani, F.; Fredrick, R.; Trentman, R.; Robb, RM; Balam, DD; Young, J.; Gibbs, AR; Beshore ...

Research paper thumbnail of Discovery of the Host Cluster for the Fundamental Cepheid Calibrator Zeta Geminorum

The Astrophysical Journal, 2012

New and existing CORAVEL, UBVJHK s , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that t... more New and existing CORAVEL, UBVJHK s , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator ζ Gem is a cluster member. The following parameters were inferred for ζ Gem from cluster membership and are tied to new spectral classifications (DAO) established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV): E B−V = 0.02 ± 0.02, log τ = 7.85 ± 0.15, and d = 355 ± 15 pc. The mean distance to ζ Gem from cluster membership and six recent estimates (e.g., IRSB) is d = 363 ± 9(σx) ± 26(σ) pc. The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. Forthcoming precise proper motions (DASCH) and Chandra/XMM-Newton observations of the broader field may be employed to identify cluster members, bolster the cluster's existence, and provide stronger constraints on the Cepheid's fundamental parameters.

Research paper thumbnail of Comet P/2002 T4 (NEAT)

IAUC 7991 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of Anchors for the Cosmic Distance Scale: the Cepheids U Sgr, CF Cas and CEab Cas

New and existing X-ray, U BV JHK s W (1−4) , and spectroscopic observations were analyzed to cons... more New and existing X-ray, U BV JHK s W (1−4) , and spectroscopic observations were analyzed to constrain fundamental parameters for M25, NGC 7790, and dust along their sight-lines. The star clusters are of particular importance given they host the classical Cepheids U Sgr, CF Cas, and the visual binary Cepheids CEa and CEb Cas. Precise results from the multiband analysis, in tandem with a comprehensive determination of the Cepheids' period evolution (dP/dt) from ∼140 years of observations, helped resolve concerns raised regarding the clusters and their key Cepheid constituents. Specifically, distances derived for members of M25 and NGC 7790 are 630 ± 25 pc and 3.40 ± 0.15 kpc, respectively.

Research paper thumbnail of Supernova 2008gl in UGC 881

CBET 1547 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of The supernova type ia rate evolution with SNLS

AIP Conference Proceedings, 2007

We present a progress report on a project to derive the evolution of the volumetric supernova Typ... more We present a progress report on a project to derive the evolution of the volumetric supernova Type Ia rate from the Supernova Legacy Survey. Our preliminary estimate of the rate evolution divides the sample from Neill et al. [1] into two redshift bins: 0.2 < z < 0.4, and 0.4 < z < 0.6. We extend this by adding a bin from the sample analyzed in Sullivan et al. [2] in the range 0.6 < z < 0.75 from the same time period. We compare the derived trend with previously published rates and a supernova Type Ia production model having two components: one component associated closely with star formation and an additional component associated with host galaxy mass. Our observed trend is consistent with this model, which predicts a rising SN Ia rate out to at least z = 2.

Research paper thumbnail of 1991 Aq

IAUC 5171 available at Central Bureau for Astronomical Telegrams.

Research paper thumbnail of Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra

The Astrophysical Journal, 2008

We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its disp... more We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its dispersion using high signal-to-noise Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40% of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high quality local spectra. The mean UV spectrum of our z 0.5 SNe Ia and its dispersion is tabulated for use in future applications. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although

Research paper thumbnail of SUBLUMINOUS TYPE Ia SUPERNOVAE AT HIGH REDSHIFT FROM THE SUPERNOVA LEGACY SURVEY

The Astrophysical Journal, 2011

The rate evolution of subluminous Type Ia Supernovae is presented using data from the Supernova L... more The rate evolution of subluminous Type Ia Supernovae is presented using data from the Supernova Legacy Survey. This sub-sample represents the faint and rapidly-declining light-curves of the observed supernova Ia (SN Ia) population here defined by low stretch values (s ≤ 0.8). Up to redshift z = 0.6, we find 18 photometrically-identified subluminous SNe Ia, of which six have spectroscopic redshift (and three are spectroscopically-confirmed SNe Ia). The evolution of the subluminous volumetric rate is constant or slightly decreasing with redshift, in contrast to the increasing SN Ia rate found for the normal stretch population, although a rising behaviour is not conclusively ruled out. The subluminous sample is mainly found in early-type galaxies with little or no star formation, so that the rate evolution is consistent with a galactic mass dependent behavior: r(z) = A × M g , with A = (1.

Research paper thumbnail of THE RISE TIME OF NORMAL AND SUBLUMINOUS TYPE Ia SUPERNOVAE

The Astrophysical Journal, 2012

We calculate the average stretch-corrected rise-time of type Ia supernovae (SNe Ia) in the Supern... more We calculate the average stretch-corrected rise-time of type Ia supernovae (SNe Ia) in the Supernova Legacy Survey. We use the aggregate lightcurves of spectroscopic and photometrically identified SNe Ia to fit the rising part of the lightcurve with a simple quadratic model. We obtain a lightcurve shape corrected, i .e. stretch-corrected, fiducial rise-time of 17.02 +0.18 −0.28 (stat) days. The measured rise-time differs from an earlier finding by the SNLS (Conley et al. 2006) due to the use of different SN Ia templates. We compare it to nearby samples using the same methods and find no evolution in the early part of the lightcurve of SNe Ia up to z = 1. We search for variations among different populations, particularly subluminous objects, by dividing the sample in stretch. Bright and slow decliners (s > 1.0) have consistent stretch-corrected rise-times compared to fainter and faster decliners (0.8 < s ≤ 1.0); they are shorter by 0.57 +0.47 −0.50 (stat). Subluminous SNe Ia (here defined as objects with s ≤ 0.8), although less constrained, are also consistent, with a rise-time of 18.03 +0.81 −1.37 (stat). We study several systematic biases and find that the use of different fiducial templates may affect the average rise-time but not the intrinsic differences between populations. Based on our results, we estimate that subluminous SNe Ia are powered by 0.05 − 0.35M ⊙ of 56 Ni synthesized in the explosion. Our conclusions are the same for the single-stretch and two-stretch parameterizations of the lightcurve.

Research paper thumbnail of THE EFFECT OF PROGENITOR AGE AND METALLICITY ON LUMINOSITY AND 56 Ni YIELD IN TYPE Ia SUPERNOVAE

The Astrophysical Journal, 2009

Timmes et al. found that metallicity variations could theoretically account for a 25% variation i... more Timmes et al. found that metallicity variations could theoretically account for a 25% variation in the mass of 56 Ni synthesized in Type Ia supernovae (SNe Ia), and thus account for a large fraction of the scatter in observed SN Ia luminosities. Higher-metallicity progenitors are more neutron rich, producing more stable burning products relative to radioactive 56 Ni. We develop a new method for estimating bolometric luminosity and 56 Ni yield in SNe Ia and use it to test the theory with data from the Supernova Legacy Survey. We find that the average 56 Ni yield does drop in SNe Ia from high-metallicity environments, but the theory can only account for 7%-10% of the dispersion in SN Ia 56 Ni mass, and thus luminosity. This is because the effect is dominant at metallicities significantly above solar, whereas we find that SN hosts have predominantly subsolar or only moderately above-solar metallicities. We also show that allowing for changes in O/Fe with the metallicity [Fe/H] does not have a major effect on the theoretical prediction of Timmes et al., so long as one is using the O/H as the independent variable. Age may have a greater effect than metallicity-we find that the luminosity-weighted age of the host galaxy is correlated with 56 Ni yield, and thus more massive progenitors give rise to more luminous explosions. This is hard to understand if most SNe Ia explode when the primaries reach the Chandrasekhar mass. Finally, we test the findings of Gallagher et al. that the residuals of SNe Ia from the Hubble diagram are correlated with host galaxy metallicity, and we find no such correlation.

Research paper thumbnail of Gemini Spectroscopy of Supernovae from the Supernova Legacy Survey: Improving High‐Redshift Supernova Selection and Classification

The Astrophysical Journal, 2005

We present new techiques for improving the efficiency of supernova (SN) classification at high re... more We present new techiques for improving the efficiency of supernova (SN) classification at high redshift using 64 candidates observed at Gemini North and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS is an ongoing five year project with the goal of measuring the equation of state of Dark Energy by discovering and following over 700

Research paper thumbnail of SiFTO: An Empirical Method for Fitting SN Ia Light Curves

The Astrophysical Journal, 2008

We present SiFTO, a new empirical method for modeling Type Ia supernovae (SNe Ia) light curves by... more We present SiFTO, a new empirical method for modeling Type Ia supernovae (SNe Ia) light curves by manipulating a spectral template. We make use of high-redshift SN data when training the model, allowing us to extend it bluer than rest frame U. This increases the utility of our high-redshift SN observations by allowing us to use more of the available data. We find that when the shape of the light curve is described using a stretch prescription, applying the same stretch at all wavelengths is not an adequate description. SiFTO therefore uses a generalization of stretch which applies different stretch factors as a function of both the wavelength of the observed filter and the stretch in the rest-frame B band. We compare SiFTO to other published light-curve models by applying them to the same set of SN photometry, and demonstrate that SiFTO and SALT2 perform better than the alternatives when judged by the scatter around the best fit luminosity distance relationship. We further demonstrate that when SiFTO and SALT2 are trained on the same data set the cosmological results agree.

Research paper thumbnail of Rates and Properties of Type Ia Supernovae as a Function of Mass and Star Formation in Their Host Galaxies

The Astrophysical Journal, 2006

We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar popula... more We show that Type Ia supernovae (SNe Ia) are formed within both very young and old stellar populations, with observed rates that depend on the stellar mass and mean star-formation rates (SFRs) of their host galaxies. Models where the SN Ia rate depends solely on host galaxy stellar mass are ruled out with >99% confidence. Our analysis is based on 100 spectroscopically-confirmed SNe Ia, plus 24 photometrically-classified events, all from the Supernova Legacy Survey (SNLS) and distributed over 0.2<z<0.75. Using multi-band photometry, we estimate stellar masses and SFRs for the SN Ia host galaxies by fitting their broad-band spectral energy distributions with the galaxy spectral synthesis code, PEGASE.2. We show that the SN Ia rate per unit mass is proportional to the specific SFR of the parent galaxies-more vigorously star-forming galaxies host more SNe Ia per unit stellar mass, broadly equivalent to the trend of increasing SN Ia rate in later-type galaxies seen in the local universe. Following earlier suggestions for a simple "two-component" model approximating the SN Ia rate, we find bivariate linear dependencies of the SN Ia rate on both the stellar masses and the mean SFRs of the host systems. We find that the SN Ia rate can be well represented as the sum of 5.3 ± 1.1 × 10 −14 SNe per year per unit stellar mass, and 3.9 ± 0.7 × 10 −4 SNe per year per M ⊙ yr −1 of star formation. We also demonstrate a dependence of distant SN Ia light-curve shapes on star-formation in the host galaxy, similar to trends observed locally. Passive galaxies, with no star-formation, preferentially host faster-declining/dimmer SNe Ia, while slower-declining/brighter events are only found in systems with ongoing star-formation. We model the light-curve width distribution in star-forming galaxies as the sum of a young component, and an old component taken from the distribution in non-star-forming galaxies. Empirically understanding these relationships between SNe Ia and their environments will lead to future improvements in their use as cosmological candles.

Research paper thumbnail of ANCHORING THE DISTANCE SCALE VIA X-RAY/INFRARED DATA FOR CEPHEID CLUSTERS: SU Cas

The Astrophysical Journal, 2012

New X-ray (XMM-Newton) and JHK s (Observatoire du Mont-Mégantic) observations for members of the ... more New X-ray (XMM-Newton) and JHK s (Observatoire du Mont-Mégantic) observations for members of the star cluster Alessi 95, which Turner et al. discovered hosts the classical Cepheid SU Cas, were used in tandem with UCAC3 (proper motion) and Two Micron All Sky Survey observations to determine precise cluster parameters: E(J − H) = 0.08 ± 0.02 and d = 405 ± 15 pc. The ensuing consensus among cluster, pulsation, and trigonometric distances (d = 414 ± 5(σx) ± 10(σ) pc) places SU Cas in a select group of nearby fundamental Cepheid calibrators (δ Cep, ζ Gem). High-resolution X-ray observations may be employed to expand that sample as the data proved pertinent for identifying numerous stars associated with SU Cas. Acquiring X-ray observations of additional fields may foster efforts to refine Cepheid calibrations used to constrain H 0 .

Research paper thumbnail of EVOLUTION IN THE VOLUMETRIC TYPE Ia SUPERNOVA RATE FROM THE SUPERNOVA LEGACY SURVEY

The Astronomical Journal, 2012

We present a measurement of the volumetric Type Ia supernova (SN Ia) rate (SNR Ia) as a function ... more We present a measurement of the volumetric Type Ia supernova (SN Ia) rate (SNR Ia) as a function of redshift for the first four years of data from the Canada-France-Hawaii Telescope (CFHT) Supernova Legacy Survey (SNLS). This analysis includes 286 spectroscopically confirmed and more than 400 additional photometrically identified SNe Ia within the redshift range 0.1 ≤ z ≤ 1.1. The volumetric SNR Ia evolution is consistent with a rise to z ∼ 1.0 that follows a power-law of the form (1+z) α , with α = 2.11 ± 0.28. This evolutionary trend in the SNLS rates is slightly shallower than that of the cosmic star-formation history over the same redshift range. We combine the SNLS rate measurements with those from other surveys that complement the SNLS redshift range, and fit various simple SN Ia delay-time distribution (DTD) models to the combined data. A simple power-law model for the DTD (i.e., ∝ t −β) yields values from β = 0.98 ± 0.05 to β = 1.15 ± 0.08 depending on the parameterization of the cosmic star formation history. A two-component model, where SNR Ia is dependent on stellar mass (M stellar) and star formation rate (SFR) as SNR Ia (z) = A× M stellar (z)+ B × SFR(z), yields the coefficients A = (1.9 ± 0.1) × 10 −14 SNe yr −1 M −1 ⊙ and B = (3.3 ± 0.2) × 10 −4 SNe yr −1 (M ⊙ yr −1) −1. More general two-component models also fit the data well, but single Gaussian or exponential DTDs provide significantly poorer matches. Finally, we split the SNLS sample into two populations by the light curve width (stretch), and show that the general behavior in the rates of faster-declining SNe Ia (0.8 ≤ s < 1.0) is similar, within our measurement errors, to that of the slower objects (1.0 ≤ s < 1.3) out to z ∼ 0.8.

Research paper thumbnail of Real-Time Analysis and Selection Biases in the Supernova Legacy Survey

The Astronomical Journal, 2010

Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at... more Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada,

Research paper thumbnail of THE TYPE Ia SUPERNOVA RATE IN RADIO AND INFRARED GALAXIES FROM THE CANADA-FRANCE-HAWAII TELESCOPE SUPERNOVA LEGACY SURVEY

The Astronomical Journal, 2010

We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy ... more We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy Survey and catalogs of galaxies with photometric redshifts, Very Large Array 1.4 GHz radio sources, and Spitzer infrared sources. We present eight SNe Ia in early-type host galaxies which have counterparts in the radio and infrared source catalogs. We find the SN Ia rate in subsets of radio and infrared early-type galaxies is ∼1-5 times the rate in all early-type galaxies, and that any enhancement is always 2σ. Rates in these subsets are consistent with predictions of the two-component "A+B" SN Ia rate model. Since infrared properties of radio SN Ia hosts indicate dust-obscured star formation, we incorporate infrared star formation rates into the "A+B" model. We also show the properties of SNe Ia in radio and infrared galaxies suggest the hosts contain dust and support a continuum of delay time distributions (DTDs) for SNe Ia, although other DTDs cannot be ruled out based on our data.