arXiv subjects

Peter Challis

Publications and source records attributed to Peter Challis.

58 records · Page 4Linked to original sources

arXiv1998

BVRI Light Curves for 22 Type Ia Supernovae

We present 1210 Johnson/Cousins B,V,R, and I photometric observations of 22 recent type Ia supernovae (SNe Ia): SN 1993ac, SN 1993ae, SN 1994M, SN 1994S, SN 1994T, SN 1994Q, SN 1994ae, SN 1995D, SN 1995E, SN 1995al, SN 1995ac, SN 1995ak, SN 1995bd, SN 1996C, SN 1996X, SN 1996Z, SN 1996ab, SN 1996ai, SN 1996bk, SN 1996bl, SN 1996bo, and SN 1996bv. Most of the photometry was obtained at the Fred Lawrence Whipple Observatory (FLWO) of the Harvard-Smithsonian Center for Astrophysics in a cooperative observing plan aimed at improving the data base for SN Ia. The redshifts of the sample range from $cz$=1200 to 37000 km s$^{-1}$ with a mean of $cz$=7000 km s$^{-1}$.

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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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arXiv1994

SN~1991T: Reflections of Past Glory

We have obtained photometry and spectra of SN~1991T which extend more than 1000 days past maximum light, by far the longest a SN~Ia has been followed. Although SN~1991T exhibited nearly normal photometric behavior in the first 400 days following maximum, by 600 days its decline had slowed, and by 950~days the supernova brightness was consistent with a constant apparent magnitude of $m_B=21.30$. Spectra near maximum showed minor variations on the SN~Ia theme which grew less conspicuous during the exponential decline. At 270 days the nebular spectrum was composed of Fe and Co lines common to SNe~Ia. However, by 750 days past maximum light, these lines had shifted in wavelength, and were superimposed on a strong blue continuum. The luminosity of SN~1991T at 950 days is more than $9.0\times10^{38}(D/13~{\rm Mpc})^2$~ergs~s$^{-1}$ with a rate of decline of less than $0.04$ mags/100~days. We show that this emission is likely to be light that was emitted by SN~1991T near maximum light which has reflected from foreground dust, much like the light echos observed around SN~1987A.

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