-
D. Rubin,
R. A. Knop,
E. Rykoff,
G. Aldering,
R. Amanullah,
K. Barbary, M. S. Burns,
A. Conley,
N. Connolly,
S. Deustua, [......],
M. Kowalski,
C. Lidman,
J. Meyers,
J. Nordin,
S. Perlmutter,
C. Saunders,
A. L. Spadafora,
V. Stanishev,
N. Suzuki,
L. Wang
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a redshift 1.71 supernova in the GOODS North
field. The Hubble Space Telescope (HST) ACS spectrum has almost negligible
contamination from the host or neighboring galaxies. Although the rest frame
sampled range is too blue to include any Si ii line, a principal component
analysis allows us to confirm it as a Type Ia supernova with 92% confidence. A
recent serendipitous archival HST WFC3 grism spectrum contributed a key element
of the confirmation by giving a host-galaxy redshift of 1.713 +/- 0.007. In
addition to being the most distant SN Ia with spectroscopic confirmation, this
is the most distant Ia with a precision color measurement. We present the ACS
WFC and NICMOS 2 photometry and ACS and WFC3 spectroscopy. Our derived
supernova distance is in agreement with the prediction of LambdaCDM.
05/2012;
-
R. Amanullah,
C. Lidman,
D. Rubin,
G. Aldering,
P. Astier,
K. Barbary, M. S. Burns,
A. Conley,
K. S. Dawson,
S. E. Deustua, [......],
N. Panagia,
S. Perlmutter,
J. Raux,
P. Ruiz-Lapuente,
A. L. Spadafora,
M. Strovink,
N. Suzuki,
L. Wang,
W. M. Wood-Vasey,
N. Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z > 1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation. The flat concordance ΛCDM model remains an excellent fit to the Union2 data with the best-fit constant equation-of-state parameter w = –0.997+0.050 –0.054(stat)+0.077 –0.082(stat + sys together) for a flat universe, or w = –1.038+0.056 –0.059(stat)+0.093 –0.097(stat + sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depends strongly on redshift. In particular, at z 1, the existence and nature of dark energy are only weakly constrained by the data.
The Astrophysical Journal 05/2010; 716(1):712. · 6.02 Impact Factor
-
R. Amanullah,
C. Lidman,
D. Rubin,
G. Aldering,
P. Astier,
K. Barbary, M. S. Burns,
A. Conley,
K. S. Dawson,
S. E. Deustua, [......],
N. Panagia,
S. Perlmutter,
J. Raux,
P. Ruiz-Lapuente,
A. L. Spadafora,
M Strovink,
N Suzuki,
L Wang,
W. M. Wood-Vasey,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We report on work to increase the number of well-measured Type Ia supernovae
(SNe Ia) at high redshifts. Light curves, including high signal-to-noise HST
data, and spectra of six SNe Ia that were discovered during 2001 are presented.
Additionally, for the two SNe with z>1, we present ground-based J-band
photometry from Gemini and the VLT. These are among the most distant SNe Ia for
which ground based near-IR observations have been obtained. We add these six
SNe Ia together with other data sets that have recently become available in the
literature to the Union compilation (Kowalski et al. 2008). We have made a
number of refinements to the Union analysis chain, the most important ones
being the refitting of all light curves with the SALT2 fitter and an improved
handling of systematic errors. We call this new compilation, consisting of 557
supernovae, the Union2 compilation. The flat concordance LambdaCDM model
remains an excellent fit to the Union2 data with the best fit constant equation
of state parameter w=-0.997^{+0.050}_{-0.054} (stat) ^{+0.077}_{-0.082}
(stat+sys\ together) for a flat universe, or w=-1.035^{+0.055}_{-0.059}
(stat)^{+0.093}_{-0.097} (stat+sys together) with curvature. We also present
improved constraints on w(z). While no significant change in w with redshift is
detected, there is still considerable room for evolution in w. The strength of
the constraints depend strongly on redshift. In particular, at z > 1, the
existence and nature of dark energy are only weakly constrained by the data.
04/2010;
-
S. Nobili,
V. Fadeyev,
G. Aldering,
R. Amanullah,
K. Barbary, M. S. Burns,
K. S. Dawson,
S. E. Deustua,
L. Faccioli,
A. S. Fruchter, [......],
C. Lidman,
J. Meyers,
P. E. Nugent,
R. Pain,
N. Panagia,
S. Perlmutter,
D. Rubin,
A. L. Spadafora,
M. Strovink,
N. Suzuki
[show abstract]
[hide abstract]
ABSTRACT: We present data from the Supernova Cosmology Project for five high redshift Type Ia supernovae (SNe Ia) that were obtained using the NICMOS infrared camera on the Hubble Space Telescope. We add two SNe from this sample to a rest-frame I-band Hubble diagram, doubling the number of high redshift supernovae on this diagram. This I-band Hubble diagram is consistent with a flat universe (ΩM, ΩΛ) = (0.29, 0.71). A homogeneous distribution of large grain dust in the intergalactic medium (replenishing dust) is incompatible with the data and is excluded at the 5σ confidence level, if the SN host galaxy reddening is corrected assuming RV = 1.75. We use both optical and infrared observations to compare photometric properties of distant SNe Ia with those of nearby objects. We find generally good agreement with the expected color evolution for all SNe except the highest redshift SN in our sample (SN 1997ek at z = 0.863) which shows a peculiar color behavior. We also present spectra obtained from ground-based telescopes for type identification and determination of redshift.
The Astrophysical Journal 07/2009; 700(2):1415. · 6.02 Impact Factor
-
R. A. Knop,
G. Aldering,
R. Amanullah,
P. Astier,
G. Blanc, M. S. Burns,
A. Conley,
S. E. Deustua,
M. Doi,
R. Ellis, [......],
K. Schahmaneche,
E. Smith,
A. L. Spadafora,
V. Stanishev,
M. Sullivan,
N. A. Walton,
L. Wang,
W. M. Wood-Vasey,
N. Yasuda,
and (The Supernova Cosmology Project
[show abstract]
[hide abstract]
ABSTRACT: We report measurements of ΩM, ΩΛ, and w from 11 supernovae (SNe) at z = 0.36-0.86 with high-quality light curves measured using WFPC2 on the Hubble Space Telescope (HST). This is an independent set of high-redshift SNe that confirms previous SN evidence for an accelerating universe. The high-quality light curves available from photometry on WFPC2 make it possible for these 11 SNe alone to provide measurements of the cosmological parameters comparable in statistical weight to the previous results. Combined with earlier Supernova Cosmology Project data, the new SNe yield a measurement of the mass density ΩM = 0.25 (statistical) ± 0.04 (identified systematics), or equivalently, a cosmological constant of ΩΛ = 0.75 (statistical) ± 0.04 (identified systematics), under the assumptions of a flat universe and that the dark energy equation-of-state parameter has a constant value w = -1. When the SN results are combined with independent flat-universe measurements of ΩM from cosmic microwave background and galaxy redshift distortion data, they provide a measurement of w = -1.05 (statistical) ± 0.09 (identified systematic), if w is assumed to be constant in time. In addition to high-precision light-curve measurements, the new data offer greatly improved color measurements of the high-redshift SNe and hence improved host galaxy extinction estimates. These extinction measurements show no anomalous negative E(B-V) at high redshift. The precision of the measurements is such that it is possible to perform a host galaxy extinction correction directly for individual SNe without any assumptions or priors on the parent E(B-V) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with P(ΩΛ > 0) > 0.99, a result consistent with previous and current SN analyses that rely on the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution.
The Astrophysical Journal 12/2008; 598(1):102. · 6.02 Impact Factor
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I. M. Hook,
D. A. Howell,
G. Aldering,
R. Amanullah, M. S. Burns,
A. Conley,
S. E. Deustua,
R. Ellis,
S. Fabbro,
V. Fadeyev, [......],
P. Ruiz-Lapuente,
G. Sainton,
B. E. Schaefer,
E. Smith,
A. L. Spadafora,
V. Stanishev,
R. C. Thomas,
N. A. Walton,
L. Wang,
and W. M. Wood-Vasey
[show abstract]
[hide abstract]
ABSTRACT: We present spectra for 14 high-redshift (0.17 < z < 0.83) supernovae, which were discovered by the Supernova Cosmology Project as part of a campaign to measure cosmological parameters. The spectra are used to determine the redshift and classify the supernova type, essential information if the supernovae are to be used for cosmological studies. Redshifts were derived either from the spectrum of the host galaxy or from the spectrum of the supernova itself. We present evidence that these supernovae are of Type Ia (SNe Ia) by matching to spectra of nearby supernovae. We find that the dates of the spectra relative to maximum light determined from this fitting process are consistent with the dates determined from the photometric light curves, and, moreover, the spectral time sequences for SNe Ia at low and high redshift are indistinguishable. We also show that the expansion velocities measured from blueshifted Ca H and K are consistent with those measured for low-redshift SNe Ia. From these first-level quantitative comparisons we find no evidence for evolution in SN Ia properties between these low- and high-redshift samples. Thus, even though our samples may not be complete, we conclude that there is a population of SNe Ia at high redshift whose spectral properties match those at low redshift.
The Astronomical Journal 12/2007; 130(6):2788. · 4.03 Impact Factor
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The Supernova Cosmology Project (G. Garavini,
G. Folatelli,
A. Goobar,
S. Nobili,
G. Aldering,
A. Amadon,
R. Amanullah,
P. Astier,
C. Balland,
G. Blanc, [......],
P. Ruiz-Lapuente,
G. Sainton,
B. E. Schaefer,
K. Schahmaneche,
E. Smith,
A. L. Spadafora,
V. Stanishev,
N. A. Walton,
L. Wang,
W. M. Wood-Vasey
[show abstract]
[hide abstract]
ABSTRACT: We present an extensive new time series of spectroscopic data of the peculiar SN 1999aa in NGC 2595. Our data set includes 25 optical spectra between -11 and +58 days with respect to B-band maximum light, providing an unusually complete time history. The early spectra resemble those of an SN 1991T–like object but with a relatively strong Ca H and K absorption feature. The first clear sign of Si II λ6355, characteristic of Type Ia supernovae, is found at day -7, and its velocity remains constant up to at least the first month after B-band maximum light. The transition to normal-looking spectra is found to occur earlier than in SN 1991T, suggesting SN 1999aa as a possible link between SN 1991T–like and Branch-normal supernovae. Comparing the observations with synthetic spectra, doubly ionized Fe, Si, and Ni are identified at early epochs. These are characteristic of SN 1991T–like objects. Furthermore, in the day -11 spectrum, evidence is found for an absorption feature that could be identified as high velocity C II λ6580 or Hα. At the same epoch C III λ4648.8 at photospheric velocity is probably responsible for the absorption feature at 4500 Å. High-velocity Ca is found around maximum light together with Si II and Fe II confined in a narrow velocity window. Implied constraints on supernovae progenitor systems and explosion hydrodynamic models are briefly discussed.
The Astronomical Journal 12/2007; 128(1):387. · 4.03 Impact Factor
-
G. Garavini,
G. Folatelli,
S. Nobili,
G. Aldering,
R. Amanullah,
P Antilogus,
P. Astier,
G. Blanc,
J. Bronder, M. S. Burns, [......],
G. Sainton,
K. Schahmaneche,
E Smith,
A. L. Spadafora,
V. Stanishev,
R. C. Thomas,
N. A. Walton,
L Wang,
W. M. Wood-Vasey,
N. Yasuda. The Supernova Cosmology Project
[show abstract]
[hide abstract]
ABSTRACT: We develop a method to measure the strength of the absorption features in Type Ia supernova (SN Ia) spectra and use it to make a quantitative comparison between the spectra of Type Ia supernovae at low and high redshifts. In this case study, we apply the method to 12 high-redshift (0.212 < z < 0.912) SNe Ia observed by the Supernova Cosmology Project . Through measurements of the strengths of these features and of the blueshift of the absorption minimum in Ca II H&K, we show that the spectra of the high-redshift SNe Ia are quantitatively similar to spectra of nearby SNe Ia (z < 0.15). One supernova in our high redshift sample, SN 2002fd at z=0.279, is found to have spectral characteristics that are associated with peculiar SN 1991T/SN 1999aa-like supernovae. Comment: accepted for publication on A&A
03/2007;
-
The Supernova Cosmology Project: S. Nobili,
R. Amanullah,
G. Garavini,
A Goobar,
C. Lidman,
V. Stanishev,
G. Aldering,
P Antilogus,
P. Astier, M. S. Burns, [......],
R. Quimby,
J. Raux,
N. Regnault,
P. Ruiz-Lapuente,
G. Sainton,
K. Schahmaneche,
E Smith,
A. L. Spadafora,
R. C. Thomas,
L Wang
[show abstract]
[hide abstract]
ABSTRACT: We present a novel technique for fitting restframe I-band light curves on a data set of 42 Type Ia supernovae (SNe Ia). Using the result of the fit, we construct a Hubble diagram with 26 SNe from the subset at 0.01< z<0.1. Adding two SNe at z~0.5 yields results consistent with a flat Lambda-dominated``concordance universe'' ($\Omega_M,\Omega_\Lambda$)=(0.25,0.75). For one of these, SN 2000fr, new near infrared data are presented. The high redshift supernova NIR data are also used to test for systematic effects in the use of SNe Ia as distance estimators. A flat, Lambda=0, universe where the faintness of supernovae at z~0.5 is due to grey dust homogeneously distributed in the intergalactic medium is disfavoured based on the high-z Hubble diagram using this small data-set. However, the uncertainties are large and no firm conclusion may be drawn. We explore the possibility of setting limits on intergalactic dust based on B-I and B-V colour measurements, and conclude that about 20 well measured SNe are needed to give statistically significant results. We also show that the high redshift restframe I-band data points are better fit by light curve templates that show a prominent second peak, suggesting that they are not intrinsically underluminous. Comment: Accepted for publication in A&A (01/04/2005)
04/2005;
-
M. Kowalski,
G. Aldering,
A. Conley,
B. Farris,
V. Fadeyev,
B. Frye,
R. Gibbons,
G. Goldhaber,
D. E. Groom,
D. A. Howell, [......],
E. Smith,
C. Lidman,
J. Mendez,
G. J. Miller,
H. Newberg,
J. Rich,
G. T. Richards,
B. E. Schaefer,
P. Ruiz-Lapuente,
N. A. Walton
[show abstract]
[hide abstract]
ABSTRACT: Type Ia SNe represent the best distance indicators for cosmology, having
established the presence of dark energy through measurement of the
expansion history of the universe. While high-z SNe are used to study
the change in the expansion rate, low-z SNe establish a baseline for
brightness comparisons and provide the important calibration used for
standardization. Besides the statistical gain in precision from a large
number of SNe, a good understanding of their systematic variations is
essential. We present the B, V, R, I lightcurves for a new sample of
nearby supernova, obtained by the Supernova Cosmology Project in
collaboration with several other supernova groups. A unique challenge of
this dataset is that seventeen different instruments were used to obtain
the follow-up photometry. Therefore, we focus in particular on the
analysis procedure developed for handling and cross-calibrating the data
from various instruments.
This work was supported in part by the U.S. Department of Energy under
Contract No. DE-AC03-76SF00098.
11/2004; 36:1466.
-
C. Lidman,
D. A. Howell,
G. Folatelli,
G. Garavini,
S. Nobili,
G. Aldering,
R. Amanullah,
P Antilogus,
P. Astier,
G. Blanc, [......],
G. Sainton,
B. E. Schaefer,
K. Schahmaneche,
E Smith,
A. L. Spadafora,
V. Stanishev,
N. A. Walton,
L Wang,
W. M. Wood-Vasey,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We present VLT FORS1 and FORS2 spectra of 39 candidate high-redshift supernovae that were discovered as part of a cosmological study using Type Ia supernovae (SNe Ia) over a wide range of redshifts. From the spectra alone, 20 candidates are spectrally classified as SNe Ia with redshifts ranging from z=0.212 to z=1.181. Of the remaining 19 candidates, 1 might be a Type II supernova and 11 exhibit broad supernova-like spectral features and/or have supernova-like light curves. The candidates were discovered in 8 separate ground-based searches. In those searches in which SNe Ia at z ~ 0.5 were targeted, over 80% of the observed candidates were spectrally classified as SNe Ia. In those searches in which SNe Ia with z > 1 were targeted, 4 candidates with z > 1 were spectrally classified as SNe Ia and later followed with ground and space based observatories. We present the spectra of all candidates, including those that could not be spectrally classified as supernova. Comment: 30 pages, 43 figures. Accepted by A&A. A version with higher resolution finding charts is available at http://supernova.lbl.gov/
10/2004;
-
E. Smith,
G. Aldering,
R. Amanullah,
P. Antilogus,
P. Astier,
G. Blanc, M. S. Burns,
A. Conley,
S. E. Deustua,
M. Doi, [......],
B. Schaefer,
K. Schahmaneche,
A. L. Spadafora,
V. Stanishev,
M. Sullivan,
N. Walton,
L. Wang,
W. M. Wood-Vasey,
N. Yasuda,
Supernova Cosmology Project Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We present the spectra of eleven supernovae with redshifts in the range
of 0.35 < z < 0.86. These spectra were obtained at the Keck
observatory and the European Southern Observatory between December 1997
and May 2000. These supernovae were discovered by the Supernova
Cosmology Project; lightcurves and cosmological results appear in ``New
Constraints on Ω M, Ω Λ , and w
from an Independent Set of Eleven High-Redshift Supernovae Observed with
HST" (Knop, et. al, 2003.). Redshifts were obtained through the use of
both galaxy lines and supernovae lines, and supernova type was
determined through spectrum matching.
11/2003; 35:1277.
-
R. A. Knop,
G. Aldering,
R. Amanullah,
P. Astier,
G. Blanc, M. S. Burns,
A. Conley,
S. E. Deustua,
M Doi,
R Ellis, [......],
B. Schaefer,
K. Schahmaneche,
E Smith,
A. L. Spadafora,
V. Stanishev,
M Sullivan,
N. A. Walton,
L Wang,
W. M. Wood-Vasey,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: We report measurements of $\Omega_M$, $\Omega_\Lambda$, and w from eleven supernovae at z=0.36-0.86 with high-quality lightcurves measured using WFPC-2 on the HST. This is an independent set of high-redshift supernovae that confirms previous supernova evidence for an accelerating Universe. Combined with earlier Supernova Cosmology Project data, the new supernovae yield a flat-universe measurement of the mass density $\Omega_M=0.25^{+0.07}_{-0.06}$ (statistical) $\pm0.04$ (identified systematics), or equivalently, a cosmological constant of $\Omega_\Lambda=0.75^{+0.06}_{-0.07}$ (statistical) $\pm0.04$ (identified systematics). When the supernova results are combined with independent flat-universe measurements of $\Omega_M$ from CMB and galaxy redshift distortion data, they provide a measurement of $w=-1.05^{+0.15}_{-0.20}$ (statistical) $\pm0.09$ (identified systematic), if w is assumed to be constant in time. The new data offer greatly improved color measurements of the high-redshift supernovae, and hence improved host-galaxy extinction estimates. These extinction measurements show no anomalous negative E(B-V) at high redshift. The precision of the measurements is such that it is possible to perform a host-galaxy extinction correction directly for individual supernovae without any assumptions or priors on the parent E(B-V) distribution. Our cosmological fits using full extinction corrections confirm that dark energy is required with $P(\Omega_\Lambda>0)>0.99$, a result consistent with previous and current supernova analyses which rely upon the identification of a low-extinction subset or prior assumptions concerning the intrinsic extinction distribution.
10/2003;
-
R. Quimby,
G. Aldering,
P. Nugent,
R. Amanullah,
P. Astier,
G. Blanc, M. S. Burns,
A. Conley,
S. Deustua,
M. Doi, [......],
N. Regnault,
P. Ruiz-Lapuente,
B. Schaefer,
K. Schahmaneche,
A. L. Spadafora,
N. Walton,
L. Wang,
W. M. Wood-Vasey,
N. Yasuda,
Supernova Cosmology Project Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We use the luminosities and B-V colors from the host galaxies of 74
high-redshift (0.17 < z < 0.86) Type Ia supernovae (SNe Ia)
discovered by the Supernova Cosmology Project (SCP) to search for
environmental effects on supernovae peak luminosities. Using the galaxy
luminosity-metallicity relation and the radial metallicity gradient of
galaxies as indicators of the progenitor metallicity, we find no
significant correlation between peak SNe Ia luminosity and host galaxy
metallicity. The projected radial distribution of supernovae tracks the
galaxy light and shows no deficit of SNe Ia near the galaxy cores (Shaw
effect). The host galaxy luminosity function is calculated, and shown to
be consistent with the subset of the Caltech Faint Galaxy Redshift
Survey (Cohen et al. 2000) in the same redshift range, as well as the
luminosity function of nearby galaxies measured by the Sloan Digital Sky
Survey (Blanton et al. 2001).
11/2002; 34:1143.
-
M Sullivan,
R. S. Ellis,
G. Aldering,
R. Amanullah,
P. Astier,
G. Blanc, M. S. Burns,
A. Conley,
S. E. Deustua,
M Doi, [......],
J. Raux,
N. Regnault,
P. Ruiz-Lapuente,
B. Schaefer,
K. Schahmaneche,
A. L. Spadafora,
N. A. Walton,
L Wang,
W. M. Wood-Vasey,
N Yasuda
[show abstract]
[hide abstract]
ABSTRACT: (Abridged) We present new results on the Hubble diagram of distant type Ia supernovae (SNe Ia) segregated according to the type of host galaxy. This makes it possible to check earlier evidence for a cosmological constant by explicitly comparing SNe residing in galaxies likely to contain negligible dust with the larger sample. The cosmological parameters derived from these SNe Ia hosted by presumed dust-free early-type galaxies supports earlier claims for a cosmological constant, which we demonstrate at 5 sigma significance, and the internal extinction implied is small even for late-type systems (A_B<0.2). Thus, our data demonstrate that host galaxy extinction is unlikely to systematically dim distant SNe Ia in a manner that would produce a spurious cosmological constant. We classify the host galaxies of 39 distant SNe discovered by the Supernova Cosmology Project (SCP) using the combination of HST STIS imaging, Keck ESI spectroscopy and ground-based broad-band photometry. We compare with a low-redshift sample of 25 SNe Ia. The scatter observed in the SNe Ia Hubble diagrams correlates closely with host galaxy morphology. We find the scatter in the SNe Ia Hubble diagram is smallest for SNe occurring in early-type hosts and largest for those occurring in late-type galaxies. Moreover, SNe residing in early-type hosts appear only ~0.14+/-0.09 mag brighter in their light-curve-width-corrected luminosity than those in late-type hosts, implying only a modest amount of dust extinction even in the late-type systems. Comment: MNRAS; post-referee version. 21 pages, 10 figures including 4 colour figures. Preprint also available at http://supernova.lbl.gov/
11/2002;
-
R. S. Ellis,
M. Sullivan,
G. Aldering,
R. Amanullah,
P. Antilogus,
P. Astier,
C. Balland,
G. Blanc, M. S. Burns,
A. Conley, [......],
J. Raux,
N. Regnault,
P. Ruiz-Lapuente,
B. Schaefer,
K. Schahmaneche,
A. L. Spadafora,
N. Walton,
L. Wang,
W. M. Wood-Vasey,
Supernova Cosmology Project Collaboration
[show abstract]
[hide abstract]
ABSTRACT: We review the results of an extensive survey which aims to characterize
those galaxies which hosted Type Ia supernovae found by the Supernova
Cosmology Project (SCP). Using Hubble Space Telescope images and
intermediate dispersion Keck spectroscopy, we have classified each host
galaxy into three morphological/spectral types in order to investigate
the dependence of distant supernova properties with respect to the host
galaxy class. Of particular interest is the subset of Type Ia supernovae
hosted by spheroidal galaxies, which are expected to be dust-free and
more tightly scattered about the Hubble diagram. The best-fit cosmology
for this ``clean" subset agrees well with that previously measured by
the SCP. The SN Ia subset in late-type irregulars also yields consistent
results, with the expected larger scatter. Further spectroscopic
programs at the Keck observatory will characterize the progenitor
metallicity of selected high redshift supernovae for comparison with
local data. This work was supported in part by the NASA Space Telescope
Science Institute.
11/2001; 33:1347.
-
08/1990; 22:1215.
-
[show abstract]
[hide abstract]
ABSTRACT: The 50-ms LMC pulsar, PSR 0540-69, is similar to the Crab pulsar in its
negative (U-B)0 color of -0.83(0.37) mag (error), but is marginally
redder than the Crab from B through R, (B-R)0 = 0.57(0.30). The optical
pulse of PSR 0540-69 averages less than 15 percent linear polarization
when resolved at 0.05 cycles (= 2.5 ms). An epoch and frequency for PSR
0540-69 are derived over a four-night span. When combined with
frequencies derived from past optical and X-ray observations, these
frequencies imply a braking index of 3.6(0.8), where 3.0 corresponds to
braking by pure magnetic dipole radiation, provided frequency glitches
of order one part in 10 million or larger are unlikely to occur during a
6-month interval. The secular decrease of optical luminosity of the Crab
pulsar as measured by Kristian (1978) is confirmed.
The Astrophysical Journal 03/1987; 315:142-148. · 6.02 Impact Factor
-
08/1986; 18:1049.
-
[show abstract]
[hide abstract]
ABSTRACT: The spectrum of the pulsed optical and infrared flux from HZ Her has
been measured to be flat by simultaneous observations with the NASA IRTF
3.0-m and the Lick Crossley 91-cm telescopes. The pulsed fluxes in the
3200-7500-A bandpass and the 1.0-2.5-micron bandpass were both measured
to be consistent with 27 micro-Jy and indicate that the reprocessed
pulsation spectrum may be optically thin thermal-bremsstrahlung
radiation, modulated in intensity. However, the temperature required for
a good fit is greater than or equal to 30,000 K. The results of a search
for periodic infrared pulsations from other X-ray and radio pulsars,
supernova remnants, and the galactic center source IRS 16 are also
reported. The possible detection of 3.5-s infrared pulsations from the
X-ray binary pulsar 1E 2259 + 586 is reported. The 285-7-mHz infrared
pulsation frequency from 1E 2259 + 586 is consistent with the 286.6-mHz
second-harmonic X-ray pulsations reprocessed from a companion star in
the close binary orbit whose period has been tentatively established to
be about 2300 s.
The Astrophysical Journal 10/1983; 274:313-326. · 6.02 Impact Factor
