arXiv subjects

Nicholas B. Suntzeff

Publications and source records attributed to Nicholas B. Suntzeff.

At least 109 records · Page 6Linked to original sources

arXiv2000

A Search for Environmental Effects on Type Ia Supernovae

We use integrated colors and B and V absolute magnitudes of Type Ia supernova (SN) host galaxies in order to search for environmental effects on the SN optical properties. With the new sample of 44 SNe we confirm the conclusion by Hamuy et al. (1996a) that bright events occur preferentially in young stellar environments. We find also that the brightest SNe occur in the least luminous galaxies, a possible indication that metal-poorer neighbourhoods produce the more luminous events. The interpretation of these results is made difficult, however, due to the fact that galaxies with younger stellar populations are also lower in luminosity. In an attempt to remove this ambiguity we use models for the line strengths in the absorption spectrum of five early-type galaxies, in order to estimate metallicities and ages of the SN host galaxies. With the addition of abundance estimates from nebular analysis of the emission spectra of three spiral galaxies, we find possible further evidence that luminous SNe are produced in metal-poor neighborhoods. Further spectroscopic observations of the SN host galaxies will be necessary to test these results and assist in disentangling the age/metallicity effects on Type Ia SNe.

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arXiv2000

Tests of the Accelerating Universe with Near-Infrared Observations of a High-Redshift Type Ia Supernova

We have measured the rest-frame B,V, and I-band light curves of a high-redshift type Ia supernova (SN Ia), SN 1999Q (z=0.46), using HST and ground-based near-infrared detectors. A goal of this study is the measurement of the color excess, E_{B-I}, which is a sensitive indicator of interstellar or intergalactic dust which could affect recent cosmological measurements from high-redshift SNe Ia. Our observations disfavor a 30% opacity of SN Ia visual light by dust as an alternative to an accelerating Universe. This statement applies to both Galactic-type dust (rejected at the 3.4 sigma confidence level) and greyer dust (grain size > 0.1 microns; rejected at the 2.3 to 2.6 sigma confidence level) as proposed by Aguirre (1999). The rest-frame $I$-band light cur ve shows the secondary maximum a month after B maximum typical of nearby SNe Ia of normal luminosi ty, providing no indication of evolution as a function of redshift out to z~0.5. A n expanded set of similar observations could improve the constraints on any contribution of extragalactic dust to the dimming of high-redshift SNe Ia.

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arXiv2000

The Observations of Type Ia Supernovae

The past ten years have seen a tremendous increase in the number of Type Ia supernovae discovered and in the quality of the basic data presented. The cosmological results based on distances to Type Ia events have been spectacular, leading to statistically accurate values of the Hubble constant, Omega_M, and Omega_Lambda. However, in spite of the recent advances, a number of mysteries continue to remain in our understanding of these events. In this short review, I will concentrate on unresolved problems and curious correlations in the data on Type Ia SNe, whose resolution may lead to a deeper understanding of the physical mechanism of the Type Ia supernova explosions.

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arXiv1999

The Luminous Type Ic SN 1992ar at z=0.145

We present spectroscopic and photometric observations of SN1992ar, the more distant SN in the Calan/Tololo Survey. We compare its spectrum with those of nearby Type Ia and Ic SNe and conclude that the latter type is a better match to SN 1992ar. Using K-corrections based on the spectra of well observed Type Ic and Ia SNe we compute different possible rest frame light curves of SN 1992ar and compare them with those of representative SNe of each type observed in the nearby universe. From the photometry and the spectra, we are able to conclude that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even though the data set collected is fairly complete (one spectrum and 10 photometric points), it is not possible to decide whether SN 1992ar was a fast Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V magnitudes at maximum implied by each of these possibilities are -19.2 and -20.2, respectively. The latter would make SN 1992ar one of the brightest SNe on record. SN 1992ar, hence, illustrates the problem of contamination faced by the high z Type Ia SNe samples whose luminosity distances are used to determine the cosmological parameters of the Universe. We present observational criteria to distinguish the two SN types when the SiII 6355 line is redshifted out of the sensitivity range of typical CCD detectors, and discuss the effect that these luminous Type Ic SNe would have on the measured cosmological parameters, if not removed from the High-z Type Ia SN samples.

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arXiv1999

Star-to-Star Abundance Variations among Bright Giants in the Mildly Metal-Poor Globular Cluster M4

We present a chemical composition analysis of 36 giants in the nearby mildy metal-poor (<[Fe/H]> = -1.18) "CN-bimodal" globular cluster M4. Confronted with a cluster that has large and variable interstellar extinction across the cluster face, we combined traditional spectroscopic abundance methods with modifications to line-depth ratio techniques to determine the atmospheric parameters of our stars. We derive a total-to-selective extinction ratio of 3.4 and an average reddening of 0.33 which is significantly lower than that estimated by using the dust maps made by Schlegel et al. (1998). Abundance ratios for Sc, Ti, V, Ni, & Eu are typical of halo field and cluster stars. However, Si, Al, Ba, & La are overabundant with respect to what is seen in other globular clusters of similar metallicity. Superimposed on the primordial abundance distribution is evidence for the existence of proton-capture synthesis. We recover some of the C, N, O, Na, Mg, & Al abundance swings and correlations found in other more metal-poor globular clusters but the range of variation is muted. The Al enhancements appear to be from the destruction of 25,26Mg, not 24Mg. The C+N+O abundance sum is constant to within the observational errors, and agrees with the C+N+O total that might be expected for M4 stars at birth. The M4 AGB stars have C,N,O abundances that show less evidence for proton- capture nucleosynthesis than is found in the less-evolved stars of the RGB. Deeply-mixed stars of the RGB, subsequent to the helium core flash, might take up residence on the blue end of the HB, and thus fail to evolve back to the AGB but reasons for skepticism concerning this scenario are noted.

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arXiv1998

Optical Light Curve of the Type Ia Supernova 1998bu in M96 and the Supernova Calibration of the Hubble Constant

We present the UBVRI light curves of the Type Ia supernova SN 1998bu which appeared in the nearby galaxy M96 (NGC 3368). M96 is a spiral galaxy in the Leo I group which has a Cepheid-based distance. Our photometry allows us to calculate the absolute magnitude and reddening of this supernova. These data, when combined with measurements of the four other well-observed supernovae with Cepheid based distances, allow us to calculate the Hubble constant with respect to the Hubble flow defined by the distant Calan/Tololo Type Ia sample. We find a Hubble constant of 64.0 +/- 2.2(internal) +/- 3.5(external) km/s/Mpc, consistent with most previous estimates based on Type Ia supernovae. We note that the two well-observed Type Ia supernovae in Fornax, if placed at the Cepheid distance to the possible Fornax spiral NGC 1365, are apparently too faint with respect to the Calan/Tololo sample calibrated with the five Type Ia supernovae with Cepheid distances to the host galaxies.

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arXiv1998

Properties of a Proper-Motion Selected Sample of Giants in the Small Magellanic Cloud near NGC 121

We present both low and high-dispersion abundance analyses of giants drawn from the zero proper motion sample near NGC 121. For the sample of 35 stars, the mean metallicity of the SMC field near NGC 121 is [Fe/H]=-1.3 with a real dispersion of 0.4 dex. The most metal-rich stars are at -0.5 dex and the most metal-poor stars at -2.1 dex. The velocity dispersion of the sample is 25 km/s. The dispersion of various kinematic samples in the SMC is independent of age. The RGB colors are consistent with Galactic globular clusters of similar metallicity. The field population, however, does not have an extended blue horizontal branch, and the main sequence turnoff extends 1 magnitude brighter than the turnoff in M5. Evidently active star formation in this region started roughly at the age of the Galactic globular cluster M5 and extended for about 6 Gyrs, and then stopped.

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arXiv1998

Observational Evidence from Supernovae for an Accelerating Universe and a Cosmological Constant

We present observations of 10 type Ia supernovae (SNe Ia) between 0.16 < z < 0.62. With previous data from our High-Z Supernova Search Team, this expanded set of 16 high-redshift supernovae and 34 nearby supernovae are used to place constraints on the Hubble constant (H_0), the mass density (Omega_M), the cosmological constant (Omega_Lambda), the deceleration parameter (q_0), and the dynamical age of the Universe (t_0). The distances of the high-redshift SNe Ia are, on average, 10% to 15% farther than expected in a low mass density (Omega_M=0.2) Universe without a cosmological constant. Different light curve fitting methods, SN Ia subsamples, and prior constraints unanimously favor eternally expanding models with positive cosmological constant (i.e., Omega_Lambda > 0) and a current acceleration of the expansion (i.e., q_0 < 0). With no prior constraint on mass density other than Omega_M > 0, the spectroscopically confirmed SNe Ia are consistent with q_0 <0 at the 2.8 sigma and 3.9 sigma confidence levels, and with Omega_Lambda >0 at the 3.0 sigma and 4.0 sigma confidence levels, for two fitting methods respectively. Fixing a ``minimal'' mass density, Omega_M=0.2, results in the weakest detection, Omega_Lambda>0 at the 3.0 sigma confidence level. For a flat-Universe prior (Omega_M+Omega_Lambda=1), the spectroscopically confirmed SNe Ia require Omega_Lambda >0 at 7 sigma and 9 sigma level for the two fitting methods. A Universe closed by ordinary matter (i.e., Omega_M=1) is ruled out at the 7 sigma to 8 sigma level. We estimate the size of systematic errors, including evolution, extinction, sample selection bias, local flows, gravitational lensing, and sample contamination. Presently, none of these effects reconciles the data with Omega_Lambda=0 and q_0 > 0.

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arXiv1998

The High-Z Supernova Search: Measuring Cosmic Deceleration and Global Cur vature of the Universe Using Type Ia Supernovae

The High-Z Supernova Search is an international collaboration to discover and monitor type Ia supernovae (SN Ia) at $z > 0.2$ with the aim of measuring cosmic deceleration and global curvature. Our collaboration has pursued a basic understanding of supernovae in the nearby Universe, discovering and observing a large sample of objects, and developing methods to measure accurate distances with SN Ia. This paper describes the extension of this program to $z \geq 0.2$, outlining our search techniques and follow-up program. We have devised high-throughput filters which provide accurate two-color restframe $B$ and $V$ light curves of SN Ia, enabling us to produce precise, extinction-corrected luminosity distances in the range $0.25 < z < 0.55$. Sources of systematic error from K-corrections, extinction, selection effects, and evolution are investigated, and their effects estimated. We present photometric and spectral observations of SN 1995K, our program's first supernova, and use the data to obtain a precise measurement of the luminosity distance to the $z=0.479$ host galaxy. This object, when combined with a nearby sample of SN, yields an estimate for the matter density of the Universe of $Ω_M = -0.2^{+1.0}_{-0.8}$ if $Ω_Λ= 0$. For a spatially flat universe composed of normal matter and a cosmological constant, we find $Ω_M = 0.4^{+0.5}_{-0.4}$, $Ω_Λ= 0.6^{+0.4}_{-0.5}$. We demonstrate that with a sample of $\sim 30$ objects, we should be able to determine relative luminosity distances over the range $0 < z< 0.5$ with sufficient precision to measure $Ω_M$ with an uncertainty of $\pm 0.2$.

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arXiv1997

Optical Light Curves of the Type Ia Supernovae 1990N and 1991T

We present UBVRI light curves for the bright Type Ia supernovae SN 1990N in NGC 4639 and SN 1991T in NGC 4527 based on photometry gathered in the course of the Calan/Tololo supernova program. Both objects have well-sampled light curves starting several days before maximum light and spanning well through the exponential tail. These data supercede the preliminary photometry published by Leibundgut et al (1991) and Phillips et al (1992). The host galaxies for these supernovae have (or will have) accurate distances based on the Cepheid period-luminosity relationship. The photometric data in this paper provide template curves for the study of general population of Type Ia supernova and accurate photometric indices needed for the Cepheid-supernova distance scale.

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arXiv1997

The Ten-Year Photometric Evolution of SN 1987A

Ten years of photometric observations of SN 1987A are reviewed. The optical and near-infrared colors are now declining at less than 1 magnitude per 1000 days, which is consistent with both the infrared ``freeze-out'' and the possible energy sources powering the nebula. The ``uvoir'' bolometric luminosity at ten years is estimated to be log10(L) 36.1-36.4 ergs/s. The most recent photometric measurements are given in Table 1. A deep color-magnitude diagram shows that the young stars are concentrated within a projected distance of 25" (6pc) in a field out to 3' from the supernova. It is likely that Stars 2 and 3 which project to within 0.7pc of the supernova are associated with Sk -69 202.

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arXiv1997

The Hubble Diagram of the Calan/Tololo Type Ia Supernovae and the value of Ho

The Calan/Tololo supernova survey has discovered ~30 Type Ia supernovae out to z~0.1. Using BVI data for these objects and nearby SNe Ia, we have shown that there exists a significant dispersion in the intrinsic luminosities of these objects. We have devised a robust chisquare minimization technique simultaneously fitting the BVI light curves to parametrize the SN event as a function of (tb,m, m15(B)) where tb is the time of B maximum, m is the peak BVI magnitude corrected for luminosity variations, and m15(B) is a single parameter describing the whole light curve morphology. When properly corrected for m15(B), SNe Ia prove to be high precision distance indicators,yielding relative distances with errors 7-10%. The corrected peak magnitudes are used to construct BVI Hubble diagrams (HD), and with Cepheid distances recently measured with the HST to four nearby SNe Ia (37C, 72E, 81B, 90N) we derive a value of the Hubble constant of 63.1+/-3.4 (internal) km/s/Mpc. This value is ~10-15% larger than the value obtained by assuming that SNe Ia are perfect standard candles. As we have shown in Paper V, there is now strong evidence that galaxies with younger stellar population appear to host the slowest-declining, and therefore most luminous SNe Ia. Hence, the use of Pop I objects such as Cepheids to calibrate the zero point of the SNe Ia HD can easily bias the results toward luminous SNe Ia, unless the absolute magnitude-decline relation is taken into account.

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arXiv1996

The Absolute Luminosities of the Calan/Tololo Type Ia Supernovae

We examine the absolute luminosities of 29 SNe Ia in the Calan/Tololo survey. We confirm a relation between the peak luminosity of the SNe and the decline rate as measured by the light curve, as suggested by Phillips (1993). We derive linear slopes to this magnitude-decline rate relation in BV(I)kc colors, using a sample with Bmax-Vmax < 0.2 mag. The scatter around this linear relation (and thus the ability to measure SNe Ia distances) ranges from 0.13 mag (in the I band) to 0.17 mag (in the B band). We also find evidence for significant correlations between the absolute magnitudes or the decline rate of the light curve, and the morphological type of the host galaxy.

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arXiv1996

BVRI Light Curves for 29 Type Ia Supernovae

BVRI light curves are presented for 27 Type Ia supernovae discovered during the course of the Calan/Tololo Survey and for two other SNe Ia observed during the same period. Estimates of the maximum light magnitudes in the B, V, and I bands and the initial decline rate parameter m15(B) are also given.

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arXiv1996

The Morphology of Type Ia Supernovae Light Curves

We present a family of six BVI template light curves for SNe Ia for days -5 and +80, based on high-quality data gathered at CTIO. These templates display a wide range of light curve morphologies, with initial decline rates of their B light curves between m15(B)=0.87 mag and 1.93 mag. We use these templates to study the general morphology of SNe Ia light curves. We find that several of the main features of the BVI templates correlate tightly with m15(B). In particular, the V light curves, which are probably a reasonably good approximation of the bolometric light curves, display an orderly progression in shapes between the most-luminous, slowest-declining events and the least-luminous, fastest-declining SNe. This supports the idea that the observed spectroscopic and photometric sequences of SNe Ia are due primarily to one parameter. Nevertheless, SNe with very similar initial decline rates do show significant differences in their light curve properties when examined in detail, suggesting the influence of one or more secondary parameters.

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arXiv1996

A Preliminary Discussion of the Kinematics of BHB and RR Lyrae Stars near the North Galactic Pole

The radial velocity dispersion of 67 RR Lyrae variable and blue horizontal branch (BHB) stars that are more than 4 kpc above the galactic plane at the North Galactic Pole is 110 km/sec and shows no trend with Z (the height above the galactic plane). Nine stars with Z < 4 kpc show a smaller velocity dispersion (40 +/-9 km/sec) as is to be expected if they mostly belong to a population with a flatter distribution. Both RR Lyrae stars and BHB stars show evidence of stream motion; the most significant is in fields RR2 and RR3 where 24 stars in the range 4.0 < Z < 11.0 kpc have a mean radial velocity of -59 +/- 16 km/sec. Three halo stars in field RR 2 appear to be part of a moving group with a common radial velocity of -90 km/sec. The streaming phenomenon therefore occurs over a range of spatial scales. The BHB and RR Lyrae stars in our sample both have a similar range of metallicity (-1.2 < [Fe/H] < -2.2). Proper motions of BHB stars in fields SA 57 (NGP) and the Anticenter field (RR 7) (both of which lie close to the meridional plane of the Galaxy) show that the stars that have Z < 4 kpc as well as those with Z > 4 kpc have a Galactic V motion that is < -200 km/sec and which is characteristic of the halo. Thus the stars that have a flatter distribution are really halo stars and not members of the metal-weak thick-disk.

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arXiv1996

The Abundance Spread Among Giants and Subgiants in the Globular Cluster Omega Centauri

We present spectroscopic abundances and radial velocities for giant stars in the Galactic globular cluster omega Centauri based on the CaII infrared triplet. Two samples of stars were observed: 234 stars at M_V = 1.25 on the lower giant branch at radial distances between 8 and 23arcmin, and 145 stars at M_V = -1.3 at radial distances between 3 and 22arcmin. Previous metallicity studies found a non-gaussian metallicity distribution containing a tail of metal-rich stars. We confirm these results except our unbiased cluster metallicity distributions are significantly narrower. They contain the following key features: (1) No very metal-poor stars, (2) a sudden rise in the metal-poor distribution to a modal [Fe/H] value of --1.70 consistent with an homogeneous metallicity unresolved at the 0.07 dex level, (3) a tail to higher metallicities with more stars than predicted by simple chemical evolution models, and (4) a weak correlation between metallicity and radius such that the most metal-rich stars are concentrated to the cluster core. The unresolved metal-weak tail implies that the gas out of which omega Cen formed was well-mixed up to the modal metallicity of the cluster. Therefore, omega Cen like other Galactic globular clusters, seems to have formed in a pre-enriched and homogenized (up to the modal metallicity) environment. The existence of a weak metallicity gradient supports the idea that omega Cen self-enriched, with the enriched gas sinking to the cluster center due to gas dissipation processes. We also note, however, that the metal-rich stars are more massive than the bulk of the stars in the cluster, and may have sunk to the center by dynamical mass segregation over the lifetime of the cluster.

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arXiv1996

The CTIO Prime Focus CCD: System Characteristics from 1982-1988

The CTIO Prime Focus CCD instrument with an RCA CCD was in operation at the CTIO 4-m telescope for six years between 1982-1988. A large body of literature has been published based on CCD images taken with this instrument. We review the general properties of the now-retired PFCCD system to aid astronomers in the interpretation of the photometric data in the literature.

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